Ovarian Hormones

C H A P T E R

25 Ovarian Hormones Elie Hobeika, Marah Armouti, Hamsini Sudheer Kala, Carlos Stocco Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, Chicago, Illinois, USA

1. INTRODUCTION The ovaries form part of the female reproductive system. In humans, the ovaries are oval structures measuring 3e5 cm in length that lie on either side of the uterus against the wall of the pelvis in a region called the ovarian fossa. The ovaries are connected to the pelvic wall by the infundibulopelvic ligament, and to the uterus by the utero-ovarian ligament. This puts them in proximity to the opening of the fallopian tubes. In addition to being the storage and maturation site of oocytes (eggs), the ovaries serve an endocrine role by producing reproductive hormones: estrogen and progesterone. Ovarian function is controlled by gonadotropin-releasing hormone secreted from the hypothalamus, which activates the pituitary gland to produce luteinizing hormone (LH) and follicle-stimulating hormone (FSH), both essential in this regulation.

1.1 Age-Related Changes in Ovarian Hormones A unique characteristic of the hormones produced by the ovary is that secretion and serum levels are influenced by age and by the stage of the menstrual cycle (Fig. 25.1). The main stages of ovarian function in women can be described as childhood, puberty, menarche, reproductive age, and menopause. In developing girls, the hormones that regulate ovarian function are suppressed until puberty. Therefore estradiol and progesterone are present in minute concentrations (Lee, 2003). At puberty, there is an increase in the secretion of gonadotropins and the consequent stimulation of gonadal steroids (Sehested et al., 2000). During the reproductive age, the production of ovarian steroids is cyclically controlled in response to the interactions of hormones produced by the hypothalamus, pituitary, and ovaries. The menstrual cycle, from an ovarian

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standpoint, is divided into two phases: the follicular and the luteal phase. This corresponds to the proliferative and secretory phases, respectively, at the level of the uterine endometrium. During the follicular phase, serum estradiol levels rise in parallel to the growth of follicle size as well as to the increasing number of granulosa cells. Later, under the influence of FSH, the preantral follicle develops a cavity and becomes an antral follicle. Due to continued FSH stimulation, the antral cavity enlarges and transforms the follicle into a preovulatory follicle. Preovulatory follicles secrete large quantities of estrogen, primarily estradiol, due to high levels of CYP19a1 (aromatase), which is also stimulated by FSH. This increase in estradiol causes a shift in the feedback of estradiol from negative to positive on the secretion of gonadotropins, resulting in an increase on the secretion of FSH and mainly LH, which is known as the LH surge. The release of the oocyte from the preovulatory follicle, otherwise known as ovulation, occurs approximately 36 h after the LH surge. The latter also triggers luteinization of the granulosa cells, a process that transforms the remnant of the ovulated follicle into the corpus luteum. The corpus luteum is a very active endocrine organ that secretes high levels of progesterone. Progesterone prepares the estrogen-primed endometrium for implantation. If pregnancy does not occur, the corpus luteum undergoes luteolysis and regresses by the end of the luteal phase, causing the consequent decrease in progesterone levels, and a new cycle begins. This cyclicity continues until menopause. Menopause is defined as the last menstrual period. The postmenopausal period is characterized by a drastic decrease in ovarian function, the result of which is a precipitous loss of estrogens in circulation (Fig. 25.1). This chapter will describe the physiology of estradiol and progesterone, the two primary hormones of the ovary.

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FIGURE 25.1 Average estradiol (E2) and FSH levels across the female lifespan. Estradiol levels fluctuate often during puberty and the premenopausal phase, leading to many physical and emotional changes before levels stabilize. During the reproductive years, there are cyclical changes in the production of estradiol and progesterone. These changes are controlled by the similarly cyclical fluctuation of circulating gonadotropins in response to the variations in serum ovarian hormone levels.

2. ESTRADIOL Estrogens are potent sex hormones that are indispensable for female and male fertility, as proven by reproductive defects of various severity observed when their synthesis (Simpson, 2004) or actions (Schomberg et al., 1999) are blocked. In the ovary, locally produced estradiol acts in concert with the gonadotropins secreted from the anterior pituitary to stimulate folliculogenesis and steroid production. As a secreted hormone, estradiol modulates the structure and function of female reproductive tissues such as the uterus and oviduct. Estradiol is also one of the principal determinants of pituitary neuron function and is critical in enabling these cells to exhibit fluctuating patterns of biosynthetic and secretory activity and to generate the preovulatory surge of LH. Estradiol also contributes to cyclical variations in female sexual behavior.

2.1 Structure As is the characteristic of all steroids, the pillar structure of estrogens is an array of 17 carbon atoms in four fused rings: three of them are hexanes, the other a pentane. This arrangement of rings is known as cyclopentane perhydro phenanthrene (Fig. 25.2). All estrogens have only one other carbon protruding in an angular position at position 13. As the cyclopentane perhydro phenanthrene has no elements of symmetry, each position is distinguishable from each of the others. Thus,

for any given position in the rings, a hydrogen substituent can be attached in the “a”-configuration, projecting toward the rear, or in the “b”-configuration, projecting toward the front of the molecule. More importantly, in all steroids, these alternatives will be chemically and biologically distinct from one another. A radical difference between estrogens and all other steroids is the aromatization of the A ring leading to the formation of a planar structure in which all carbons are in the same plane (Fig. 25.2). In addition to the characteristic aromatic A-ring, all estrogens have hydroxyl groups at the 3, 15, and 16 positions (Fig. 25.2). Combination of hydroxyl groups yields three different estrogens: estrone, estradiol, and estriol. Estradiol is the 17b-isomer of estradiol. 17b-estradiol is the most potent estrogenic steroid and the predominant form in both females and males. Estrone is mostly found in women during menopause (Moon et al., 2011; Segawa et al., 2015). In contrast, estriol is primarily produced during pregnancy by the placenta from 16-hydroxy dehydroepiandrosterone sulfate of fetal origin. During folliculogenesis, however, estrone secretion is more abundant in the early follicular phase than in the preovulatory phase in which estradiol is the predominant form (Segawa et al., 2015).

2.2 Synthesis Estrogens are synthesized from androgen precursors by a unique enzyme called aromatase or cytochrome

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stage is accompanied by the differentiation of granulosa cells and the induction of aromatase; both processes are stimulated by FSH. In antral follicles, the expression of the aromatase gene is controlled in a cell-specific, temporal, and spatial manner, which limits estradiol production only to mural granulosa cells of healthy large antral follicles. This coordinated and cell-specific expression of the aromatase gene in the ovary plays a vital role in the normal progress of the menstrual/estrous cycle. After ovulation, however, aromatase is rapidly downregulated as granulosa cells differentiate again, this time into luteal cells. This decrease in aromatase is responsible for the decrease in estradiol levels that follows ovulation. Luteal cells regain aromatase expression during the luteal phase in several species, including primates and rodents (Stocco, 2008). 2.2.2 Estradiol Is Produced in Incomplete Synthesis Pathways

FIGURE 25.2

Estrogen structures and synthesis.

P450 aromatase (CYP19a1). Aromatase uses the androgenic substrates androstenedione, testosterone, and 16hydroxytestosterone with high specificity, and converts them to their respective estrogens: estrone, estradiol, or estriol (Fig. 25.2). Because both the substrates and the products of this enzyme are potent hormones, alterations in its activity have profound effects on estrogen and androgen physiology. 2.2.1 Aromatase In the ovary, the enzymatic capacity to produce ovarian estradiol is acquired during embryonic life (George and Wilson, 1978). Aromatase expression in fetal ovaries is extremely low, although it can be increased by treatment with a cAMP analog, but not by FSH (George and Ojeda, 1987). Whether aromatase expression in fetal ovaries plays any role in the regulation of ovarian development is not clear since estradiol does not appear to be critical for the normal development of the ovary during fetal life (Fisher et al., 1998). Aromatase activity and mRNA can also be found after birth in the granulosa cell layer of growing follicles (Guigon et al., 2003), which progressively increases in both preantral and small antral follicles in infantile ovaries. However, in the ovaries of sexually mature animals, aromatase is confined to healthy large antral follicles (Guigon et al., 2003) and to the corpus luteum. Thus, undifferentiated granulosa cells of preantral follicles do not express aromatase. The growth and maturation of preantral follicles to the preovulatory

Despite the expression of aromatase in ovarian granulosa cells, estrogens are synthesized in incomplete biosynthetic pathways in the ovary (Fig. 25.3). The main reason for this is that granulosa cells cannot produce androstenedione nor testosterone, the obligate substrate of aromatase. Thus, in the ovary, these androgens are provided by the theca cells of follicles. Theca cells produced androgens diffuse to the granulosa cell layer of the follicle, where they are converted into estrogens by aromatase. The production of androgens and estrogens from two different cells, i.e., by theca and granulosa cells, respectively, under the influence of two different gonadotropins LH and FSH is termed “two-cell/twogonadotropin mechanism.” In this mechanism, LH

FIGURE 25.3 Ovarian estrogens are synthesized by the collaboration of two cells.

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stimulates theca production of androgens, and FSH stimulates granulosa cell aromatization in follicles reviewed in Stocco (2008). Estradiol production reaches its maximum in preovulatory follicles. Thus, circulating estradiol is used to monitor patients undergoing controlled ovarian hyperstimulation and has been incorporated in the criteria used for defining the optimal time for triggering final oocyte maturation (Albano et al., 2000). 2.2.3 Regulation of Estradiol Synthesis As estrogen production depends exclusively on the expression of aromatase, the regulation of estradiol secretion reflexes the regulation of aromatase expression. In preovulatory follicles, aromatase expression follows a gradient of expression where aromatase is high in mural cells at the outer edge of healthy follicles but absent in cumulus cells (Turner et al., 2002; Guigon et al., 2003). The physiologic implication of this differential expression is not yet clear. In cumulus granulosa, aromatase is silenced by oocyte-derived compounds such as bone morphogenetic protein 15 (BMP-15) (Otsuka et al., 2001) and growth differentiation factor-9 (GDF9) (Spicer et al., 2006; Vitt et al., 2000). Supporting an inhibitory role of the oocyte, GDF9-deficient mice show premature induction of aromatase in preantral follicles (Elvin et al., 1999). Therefore, the negative effects of oocyte-derived factors and the stimulatory effect of FSH establish the gradient of expression along the granulosa cell layer of preovulatory follicles (Stocco, 2008). FSH is the primary inducer of aromatase activity and therefore estradiol production in granulosa cells. However, the stimulatory effect of FSH is subject to modulation by numerous factors. Moreover, estradiol itself is necessary for aromatase expression. In the rat, one of the effects of estradiol is to enhance FSH-induced aromatase activity (Fitzpatrick and Richards, 1991; Adashi and Hsueh, 1982). Estradiol actions in rodent granulosa cells are mediated by the activation of estrogen receptor b (ERb) (Wang et al., 2000). Accordingly, in immature ERb knockout mice, the stimulation of aromatase expression by FSH is impaired (Couse et al., 2005). Since estradiol alone does not affect aromatase expression (Fitzpatrick and Richards, 1991) and no estrogen receptors (ER) response elements are present in the aromatase promoter, it is not known if ERb is able to affect the activity of the aromatase promoter directly. Theca cell-derived androgens are also directly involved in the regulation of aromatase. Thus, testosterone stimulates aromatase expression in the absence of FSH, an effect that does not depend on aromatization (Wu et al., 2011). Whereas, the nonaromatizable androgen, dihydrotestosterone, is as effective as estradiol in aromatase regulation (Fitzpatrick and Richards, 1991;

Tetsuka and Hillier, 1997). This evidence indicates that theca cell androgens act not only as a substrate of estrogen synthesis but also modulate FSH action via activation of androgen receptors (Fitzpatrick and Richards, 1991; Tetsuka and Hillier, 1997). In vitro studies suggest that androgens enhance FSH-stimulated steroidogenesis by increasing cAMP synthesis (Hillier and de Zwart, 1982; El-Hefnawy and Zeleznik, 2001). In the rat, androgen receptor expression is highest in preantral/early antral follicles and gradually decreases as follicles mature at the time that aromatase expression increases (Tetsuka and Hillier, 1996). These findings suggest that androgens enhance FSH action at an early stage of follicular development, but during the final stages, they mainly serve as a substrate for estrogen synthesis (Tetsuka and Hillier, 1997). Aromatase expression and estradiol levels are normal in the ovaries of androgen receptor knockout mice (Shiina et al., 2006), suggesting that androgens are not crucial for aromatase expression in vivo. FSH-induced stimulation of aromatase activity is potentiated by insulin-like growth factor-1 (IGF-1) (Davoren et al., 1985; Dorrington et al., 1987; Steinkampf et al., 1988), which also amplifies the synergism between FSH and testosterone on aromatase expression (ElHefnawy and Zeleznik, 2001). In mice, aromatase mRNA is found only in IGF-I and FSH receptorpositive follicles (Zhou et al., 1997). Further evidence of a functional link between the IGF system and stimulation of aromatase by FSH is provided by the fact that IGF-binding protein (IGFBP-4) is a potent inhibitor of FSH-induced estradiol production by murine (Liu et al., 1993) and human (Mason et al., 1998) granulosa cells. Recent findings demonstrated that the expression of the IGF1 receptor in granulosa cells is necessary for the induction of aromatase by FSH in vivo (Baumgarten et al., 2017). In human granulosa cells, however, IGF-2 alone increases estradiol production to levels comparable to those induced by FSH, although FSH and IGFs also have synergistic effects on aromatase expression (Baumgarten et al., 2014, 2015). The timely expression of aromatase in the ovarian follicle is responsible for the cyclic changes in serum estradiol levels. These changes modulate the structure and function of the female reproductive tract, including the oviducts, the uterus, and the vagina. These endocrine actions are essential for oocyte survival, fertilization, and implantation (Korach et al., 2003). Fluctuations in circulating estradiol also establish the characteristic female pattern of gonadotropin secretion from the pituitary gland. More importantly, the strong expression of aromatase in preovulatory follicles leads to the generation of the surge of LH, which triggers ovulation (Naftolin et al., 2007). Therefore, the well-timed and cell-specific expression of aromatase in the ovary is indispensable

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for the autocrine regulation of folliculogenesis, the endocrine control of the female reproductive tract, and the coordination of gonadotropin secretion.

2.3 Estradiol Receptor and Signaling Estradiol regulates target cell function via diffusion through the plasma membrane and activation of intracellular hormone-specific ERs (Fig. 25.4). In this genomic pathway, estradiol binds to ERs in the nucleus, causing conformational changes that lead to the dissociation of chaperone proteins, dimerization, and activation of the receptor transcriptional domain, which in turn stimulates gene expression. In this canonical model, ER-mediated estradiol regulation of gene expression involves the direct binding of dimeric ERs to DNA sequences known as estrogen response elements (EREs). In addition to the genomic pathway, a nongenomic signaling pathway can be activated via plasma membrane-associated ERs leading to both cytoplasmic alterations and to the regulation of gene expression (Marino et al., 2006). The genomic effects of estrogen are mediated by two isoforms of ER, ERa (NR3A1) and ERb (NR3A2), which are encoded by two different genes. The ERa and ERb receptors display distinct tissue distributions and signaling responses. ERa and ERb can also form

heterodimers. As nuclear hormone receptor family members, ERs are composed of functional domains that serve specific roles (Fig. 25.5). Starting from Nterminus, the principal domains are the N-terminal domain (NTD); DNA-binding domain (DBD); and ligand-binding domain (LBD). Two activation function (AF) domains, AF1 and AF2, are located within the NTD and LBD, respectively. The AFs are responsible for regulating the transcriptional activity of ER (Kumar et al., 2011). There is more than 95% amino acid identity on the DBD or ERa and ERb; whereas only a 55% of homology has been described in the LBD. The DBD associates with response elements found in the proximal promoter regions or distant enhancer regions of target genes (Nunez et al., 1987). DNA binding domain of both ERa and ERb recognizes a palindromic hexanucleotide 50 -GGTCAnnnTGACC-30 (Wood et al., 2001). ER regulation of gene expression requires several coregulatory proteins. Within these proteins, the TATA box-binding protein (TBP) has a central role in the basal transcription machinery and directly binds to the NTD of the ERa but not to ERb NTD (Enmark et al., 1997), suggesting that differential TBP binding could lead to the recruitment of different cofactors by ERa and ERb. The AF-1 and AF-2 regions interact with several transcription coactivators, and each one can activate transcription independently, but most synergize with one

OH

ERβ

HO

ERα α

ERα

ERβ

ERβ

ERα

Tethered Pathway

Classical Pathway GRP30 MAPK PI3K/Akt Src

AP1/SP1 RE

AGGT CAnnnT GAC CT EREs

Gene Transcription

FIGURE 25.4 Estradiol activated signaling. In the “classical” signaling pathway, estradiol binds to ERs in the cytosol, inducing conformational changes and receptor dimerization, homodimers or heterodimers, which translocate to the nucleus and bind to specific EREs in the regulatory regions of estrogen-responsive genes. In the “tethered” signaling pathway, ligand-activated ERs interact with other transcription factors that in turn bind to a non-ERE response element to regulate gene expression. In the “nongenomic” pathway, the ligands interact with plasma membrane-bound ERs, which results in activation of cytoplasmic signaling pathways.

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and Korach, 1999), whereas females lacking ERb exhibit decreased fertility (Dupont et al., 2000). 2.4.1 Ovarian Effects

FIGURE 25.5 Organization of the two isoforms of human estrogen receptors, ERa (595 aa) and ERb (530 aa). Different domains are highlighted in different colors: DBD, DNA binding domain in orange; hinge region in gray; LBD, ligand-binding domain in green; NTD, amino-terminal domain in blue. Amino acid sequence position is given for each domain. Two AF domains, AF1 and AF2, located within the NTD and LBD, respectively, are responsible for regulating the transcriptional activity of ERs. The homologies between ERb and ERa are NTD approximately 15%, DBD more than 97%, and w55% for the LBD.

another in a promoter- and cell context-specific manner to stimulate gene expression. Several recent reviews have described in detail the structure and function of the ERs (Kumar et al., 2011; Helsen and Claessens, 2014). Estradiol can also regulate genes that do not contain EREs in the promoter region. Estradiol regulation of genes lacking any ERE-like sequences is mediated by a second DNA-binding transcription factor (Marino et al., 2006). Examples of transcription factors that facilitate the recruitment of ERs in the absence of ERE are stimulating protein-1 (SP1) and activating transcription factor (AP-1) (Marino et al., 2006). 2.3.1 Membrane Estrogen Receptors Even before the identification of ERb in 1996, there was clear evidence that not all effects of estradiol, particularly rapid and membrane-associated signaling, could be attributed to the genomic actions of ERs (Wehling, 1995). These observations led to the idea that alternative membrane-bound ERs could mediate some of the effects of estradiol. In fact, a myriad of evidence has demonstrated that estradiol-mediated rapid signaling events are associated with a G proteinecoupled estrogen receptor (GPER). GPER mediates nongenomic rapid signaling of estradiol, including activation of MAPK, PI3K, PKC, Ca2þ, and cAMP (Prossnitz and Barton, 2011). However, Gper knockout mice show no developmental or functional defects in their reproductive organs (Otto et al., 2009).

2.4 Physiological Effects of Ovarian Estrogens Ovarian estradiol is responsible for the development of primary reproductive characteristics including growth and maturation of reproductive organs and breasts at puberty and maintaining their adult size and function. Estradiol is also a principal modulator of normal mammalian reproductive functions. Thus, female mice lacking ERa or ERa and b are infertile (Couse

Both ERa and ERb are present in mouse ovaries where ERb is found predominantly in the granulosa cells of the follicles, and ERa is located in the thecal and luteal cells and the interstitial region (Couse and Korach, 1999; Sharma et al., 1999). However, findings from ERa, ERb, and aromatase knockout mice indicate that early folliculogenesis occurs in the absence of either estrogenic action in the ovary (Rosenfeld et al., 2001). In the granulosa cells, estradiol stimulates granulosa cell proliferation and facilitates FSH and LH actions in a paracrine/autocrine manner (Richards et al., 2002). One of the main effects of estradiol is to enhance FSHinduced aromatase expression (Fitzpatrick and Richards, 1991; Adashi and Hsueh, 1982). This effect of estradiol was clearly demonstrated in aromatase and ERb knockout mice. In the aromatase knockout (ArKO), follicle development is arrested at a stage before ovulation and no corpora lutea are formed (Fisher et al., 1998). Moreover, although ArKO mice contain follicles at all stages of development, antral follicles are abnormal, presenting blood-filled antra and high numbers of apoptotic granulosa cells (Britt et al., 2000). On the other hand, antral follicles in ERb knockout mice are normal, but aromatase expression is significantly decreased (Couse et al., 2005). Granulosa cells isolated from FSH-treated ERb knockout mice also exhibit less than maximal induction of LH receptor expression. ERb is also required for optimal accumulation of cAMP in FSH-stimulated mouse granulosa cells (Deroo et al., 2009). Therefore, ERb is involved in the expression of several genes required for granulosa cell differentiation and ultimately for the ovulation of a competent oocyte. 2.4.2 Estradiol Guards the Embryo in the Oviduct Estradiol is required for immunoprotection of the vagina and uterus in females (Haddad and Wira, 2014). Another critical function of estradiol is the protection of the embryo in the oviduct. Estradiol, via activation of the ERa in the oviductal epithelial cells, protects embryos from the maternal immune system. Loss of ERa in the oviductal epithelial cells in mice results in excess protease activity that disrupts the zona pellucida and compromises oocyte plasma membrane integrity, causing protease-mediated embryo lysis (Winuthayanon et al., 2015). This suggests that estradiol via ERa suppresses protease-mediated aspects of innate immunity in the oviduct. The transport of the oocyte and the embryo in the oviduct is facilitated by the ciliary beating of the tubal

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epithelial cells and contraction of the oviductal smooth muscle (Croxatto, 2002). Estradiol, via a nongenomic pathway, promotes the transport of the eggs. It causes the phosphorylation of PKC and PKA and induces the production of cAMP, which increases ciliary beat frequency (CBF) (Orihuela and Croxatto, 2001; Orihuela et al., 2001). Finally, fluid secretion from tubal secretory epithelial cells is increased by estradiol, but the fluid production is attenuated when progesterone is coadministered with estradiol, suggesting that progesterone inhibits estradiol-induced fluid secretion (Li and Winuthayanon, 2017). In conclusion, estradiol increases the embryo transport rate by stimulating muscle contraction, inducing fluid production and flow, and increasing the CBF, whereas progesterone reduces embryo transport rate (see later). 2.4.3 Estradiol Effects on the Uterus The uterus plays a central role in reproduction. It responds to estradiol and progesterone with a massive differentiation of stromal components in preparation for embryo implantation. Estradiol-induced uterine growth is a classic estrogenic effect required for initiation and maintenance of pregnancy. In fact, for the most part of the last century, the ability to stimulate proliferation and induce expression of the progesterone receptor in the uterus was enough to determine the estrogenic activity of a compound. In the follicular phase, increasing estradiol levels are needed to cause proliferation of the uterine endometrium. Also, high levels of estrogen are important for the efficacy of oral contraceptives and cyclical hormone treatments for the control of uterine bleeding. On the other hand, estrogen-induced uterine growth is a critical issue during postmenopausal hormonal therapy, where it needs to be counteracted by progestins (Turgeon et al., 2004). The initiation and maintenance of pregnancy depend on the action of ovarian hormones in the uterus. The preovulatory secretion of estradiol is essential for proliferation of the uterine epithelium in preparation for implantation. The uterus expresses significant levels of ERa throughout all the major uterine compartments including the luminal and glandular epithelium, the stroma, and the myometrium (Wang et al., 2000). In the mouse, the expression level of ERa varies during the estrous cycle and peaks during proestrus in accordance with the elevation of circulating estradiol. This increase in estradiol elicits proliferative and antiapoptotic responses in the uterine epithelium (Winuthayanon et al., 2010). These effects of estradiol appear to be mediated mainly by ERa because the uteri of ERa knockout mice do not exhibit sensitivity to estradiol treatment (Couse et al., 1995), whereas the uteri of ERb knockout mice appear comparable to that of a wild type, and normally respond to estradiol (Krege et al., 1998).

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Several studies demonstrated that the uterine expression of growth factors is induced under the influence of estradiol (Robertshaw et al., 2016). IGF-1 is a key growth factor that stimulates the growth of the nearby epithelial cells because of their estrogen-dependent expression in the uterus (Zhu and Pollard, 2007). In addition to the stimulation of growth factors, a crucial effect of estradiol via activation of ERa is the induction of the progesterone receptor, which is essential in modulating the decidual transformation of the stromal component (see later). 2.4.4 Estradiol Regulation of the Mammary Gland Ovaries are required for the functional development of the mammary gland, which, like in the case of the uterus, is also mediated by estradiol and progesterone. In humans and mice, postnatal mammary gland development consists of two distinct growth stages. The first stage occurs at the onset of puberty, whereas the second manifests in response to pregnancy. At puberty, ovarian estradiol and locally acting growth factors stimulate cap cells of terminal end buds to undergo mitosis, driving ductal elongation and dichotomous branching to the limits of the fat pad. Estrogen stimulates the primary ductal system, whereas progesterone controls alveolar budding and development during puberty and pregnancy. The effects of estradiol in the mammary gland are mediated by the ERa, which is expressed both in the mammary epithelium and the mammary stroma. Thus, in ERa knockout mice, there is very little growth of mammary ducts (Wang et al., 2000). 2.4.5 Effects of Estradiol on LH Secretion Estradiol secretion by ovarian granulosa cells plays a key role in the cyclic and biphasic regulation of gonadotropin levels in females (Christian and Moenter, 2010). The pituitary gland and hypothalamus are responsible for sensing the levels of ovarian steroids to release gonadotropins in an adequately regulated manner that guarantees successful follicle development, oocyte maturation, and ovulation. Estradiol is involved in the negative feedback mechanisms in the hypothalamuse hypophysiseovarian axis, by reducing gonadotropinreleasing hormone (GnRH) secretion (Krege et al., 1998). Accordingly, aromatase-deficient mice exhibit elevated levels of gonadotropins (Fisher et al., 1998). Also, in ERa knockout mice, there is an increase in the pituitary gland (mRNA) and serum (protein) levels of LH (Couse and Korach, 1999). However, concentrations of LH and FSH in the ERb knockout female mice are normal, suggesting ERa mediates the negative feedback regulation of LH. A negative feedback effect at the level of the hypothalamicehypophyseal axis leading to a selective decrease in FSH levels is provided by an increase in inhibin expression by the granulosa cells of antral follicles (Weck and Mayo, 2006; Makanji et al., 2014).

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During the follicular phase, estradiol decreases the activity of GnRH neurons in the hypothalamus via negative feedback. Estradiol also has a negative feedback effect directly on pituitary gonadotrophs, where it differentially regulates FSH and LH secretion, with a stronger inhibition on FSH than on LH (Shaw et al., 2010). Because GnRH neurons do not express ERs, the mechanism involved in estradiol regulation of LH secretion has long been unclear and indicates that a separate population of neurons relays the negative effect of estradiol on GnRH. The discovery of kisspeptin (Kiss), a peptide hormone, and kisspeptin neurons as central regulators of GnRH secretion led to a complete understanding of the neuroendocrine regulation of reproduction (de Roux et al., 2003; Seminara et al., 2003). Loss of function of the kisspeptin receptor (KISS1R) leads to hypogonadotropic hypogonadism in humans and rodents (Seminara et al., 2003). The findings demonstrate that the secretion of GnRH is tightly regulated by a collection of Kiss and KNDy (kisspeptin/neurokinin B/dynorphin) neurons within the infundibular region of the hypothalamus in humans (Skorupskaite et al., 2014). The evidence suggests that KISS produced in the neuron of the infundibular nucleus mediates the negative feedback of estradiol. Kiss1 neurons possess ERa (Skorupskaite et al., 2014). Thus, estradiol suppresses kisspeptin (and neurokinin B) release from KNDy neurons, causing a reduction in the stimulatory input to GnRH neurons (Fig. 25.6). In the late follicular phase, the negative feedback switches from negative to positive to induce the GnRH/LH surge required for the induction of ovulation. The “surge” release of LH is preceded by a surge of GnRH secretion from the hypothalamus (Moenter et al., 1992). For the positive feedback effect of LH release to occur in humans, estradiol levels must be greater than 200 pg/mL for approximately 50 h in duration (Young and Jaffe, 1976). Recent evidence suggests that KNDy neurons also mediate the positive feedback of estradiol. However, the neurons that convey estradiol positive feedback differ in rodents and humans. In rodents, the anteroventral periventricular (AVPV) nucleus is the location of estrogen positive feedback, whereas in primates and sheep the neurons in the infundibular appear to be involved (Skorupskaite et al., 2014). Thus, KISS expression increases in the AVPV nucleus in mice and in the arcuate nucleus in sheep at the time of the LH surge. In rodents, Kiss1 neurons exhibit robust circadian patterns of activation that depend on the levels of estradiol in circulation, which allows Kiss1 neurons to serve as integrators of both circadian and ovarian signals needed to trigger ovulation (Khan and Kauffman, 2012; Skorupskaite et al., 2014). Thus, the preovulatory LH surge that occurs in female rodents is due to the

FIGURE 25.6 A simplified diagram showing the kisspeptin-GnRH pathway in humans and rodents. The hypothalamus secretes GnRH that stimulates gonadotrophs to synthesize and secrete FSH and LH. Kisspeptin (KISS1), secreted from neurons located in the anteroventral periventricular (AVPV) and arcuate (ARC) nuclei of the hypothalamus (in rodents) or in the infundibulum (in humans), signals through its receptor (KISSR1) to regulate pulsatile secretion of GnRH. FSH and LH stimulate the ovaries to produce estradiol or progesterone. The feedback of estradiol could be negative or positive depending on additional inputs from the circadian clock and the levels of estradiol in circulation. Estrogen and progesterone receptors are present in Kiss neurons.

interactions between circadian inputs and estrogenic signals. Kisspeptin is also able to stimulate the ovulatory LH surge in humans (Abbara et al., 2013). However, in humans, KNDy neurons in the infundibular nucleus appear to relay both negative and positive feedback signals of estradiol (Skorupskaite et al., 2014). 2.4.6 Nonreproductive Effects of Estradiol In addition to reproductive tissues, ovarian estradiol is required for normal physiologic processes in the heart, muscle, bone, brain, and liver. Therefore, it is not unexpected that estradiol is also involved in the development of the pathology of these systems. It is now evident that the drop in estrogen levels in menopause is associated with an increase in heart disease risk in women. When estrogen levels decline, levels of LDL cholesterol increase, and levels of HDL cholesterol decrease, leading to plaque buildup in the arteries that contribute to both heart attacks and strokes. Thus, before menopause, women have a lower risk of heart

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disease than men, but the risk of heart disease increases after menopause (Yang and Reckelhoff, 2011). Muscle weakness increases with age, most notably in postmenopausal women when the production of estrogens and progesterone declines. This is assumed to be linked to the loss of sex hormones because hormone replacement helps preserve strength (Greising et al., 2009). Similar findings have been observed in mice, in which leg muscles from ovariectomized mice are up to 20% weaker than corresponding muscles from estradioltreated mice (Lowe et al., 2010; Baltgalvis et al., 2010). In the liver, estrogens stimulate lipid and lipoprotein metabolism, which may contribute to beneficial metabolic effects of estrogens (Blum and Cannon, 1998). Estrogen upregulation of some serum proteins, such as thrombin and fibrinogen, is suspected to contribute to an increased risk of venous thromboembolism with estrogen treatment (Battaglioli and Martinelli, 2007). Estradiol also plays an important role in bone growth and maturation as well as in the regulation of bone turnover. In addition to circulating serum estrogen, estrogens are produced locally in bone due to the expression of aromatase (Nawata et al., 1995). In bone, estrogens are needed for proper closure of epiphyseal growth plates both in females and males. Thus, skeletal abnormalities including tall stature and unfused epiphysis are usually the first symptoms observed in estrogen deficiency (Belgorosky et al., 2009). Estrogen deficiency leads to increased osteoclast formation and enhanced bone resorption (Brennan et al., 2014). In menopause, estrogen deficiency induces cancellous as well as cortical bone loss (Miyauchi et al., 2013; Wright and Guise, 2014). ERa is the main receptor expressed in osteoblasts, osteocytes, osteoclasts, and bone marrow stromal cells (Borjesson et al., 2013). Consequently, female mice lacking ERa in osteoblasts have compromised bone mass and strength (Melville et al., 2014). The dominant acute effect of estrogen is the blockade of new osteoclasts, which are involved in bone resorption (Streicher et al., 2017). Thus, postmenopausal osteoporosis is a common problem that can be treated by the administration of estrogens. Estradiol modulates cognitive function in animals and humans (Luine, 2014). ERa and ERb are expressed in the hippocampus, claustrum, cerebral cortex, amygdala, hypothalamus, subthalamic nucleus, and the thalamus (Syan et al., 2017). Recent findings suggest that changes in the level of estradiol during the menstrual cycle influence the communication between the amygdala, an area dense in ERs, and the somatosensory cortex, an area that has been implicated in human perception of emotional empathy (Syan et al., 2017). Reports using learning and memory tasks show that estradiol enhances cognition (Torres-Reveron et al., 2009; Luine, 2008). Consistent with this idea, the cessation of

menstrual cycles affects emotions and cognitive processes (McCarrey and Resnick, 2015). Sleep difficulties are also common in women transitioning to menopause, with some having poor nights of sleep, which severely impact their quality of life (Baker et al., 2018).

3. PROGESTERONE Progesterone is essential for the establishment and maintenance of pregnancy and in the regulation of the menstrual cycle. In nonpregnant females, circulating progesterone levels result from adrenal and ovarian secretion. Thus, in the preovulatory phase of women in the reproductive age as well as prepubertal females, progesterone levels are usually not more than 1 ng/ mL. However, during the luteal phase of women in reproductive age, progesterone levels range from 10 to 20 ng/mL. Progesterone’s most important function is to ensure endometrial maturation in preparation for the implantation of a fertilized egg. Progesterone stimulates the transition of the uterus from a proliferative to a secretory stage, allowing embryo implantation along with maintenance and progression of the pregnancy. If no implantation occurs, then progesterone levels fall, and the endometrium breaks down (Filicori et al., 1984). Thus, progesterone levels play a primary role in the initiation of the menses. The occurrence of pregnancy rescues the corpus luteum until the end of the first trimester, when the placenta takes the leading role in progesterone production (Csapo et al., 1972). Corpus luteum deficiency is reported to be a cause of recurrent miscarriages (Daya, 2009). If pregnancy does not occur, the corpus luteum regresses rapidly. Finally, as with estrogens, the role of progesterone is not limited to fertility, and it is also involved in bone health, mammary gland development, cardiovascular physiology, and central nervous system function.

3.1 Structure and Synthesis Progesterone is a 21-carbon molecule synthesized in large quantities mainly in luteal cells during the luteal or secretory phase of the ovarian cycle, or the placenta during pregnancy. It is also synthesized in smaller amounts during the follicular or proliferative phase by granulosa and theca cells. Like all steroids, progesterone is synthesized from cholesterol. Therefore, the regulation of the uptake and storage of cholesterol plays an integral part in luteal progesterone synthesis (Fig. 25.8). Thus, during luteinization, luteal cells acquire the capacity to uptake and store cholesterol and express several proteins associated with the mobilization of intracellular cholesterol.

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There are different mechanisms of obtaining cholesterol, and this process is regulated in steroidogenic cells. Cholesterol is either internalized from the circulation or synthesized de novo. It can be stored in lipid droplets as sterol esters as well. Circulating cholesterol is in the form of high-density or low-density lipoproteins (HDL or LDL) and is internalized through scavenger receptors (SR-B1) or LDL receptors, respectively. In addition to its uptake, luteal and theca cells synthesize cholesterol de novo in the smooth endoplasmic reticulum, which is abundantly present in all steroidogenic cells (Stocco et al., 2007). Despite their capacity to synthesize cholesterol, the primary method of obtaining this precursor for progesterone production is through lipoprotein uptake from circulation. Therefore, individuals with very low circulating amounts of LDL or defects in the LDL receptor pathway had impaired steroidogenesis and decreased progesterone production (Laue et al., 1987). The synthesis of progesterone is the simplest of all the steroidogenic pathways involving only two enzymes (Fig. 25.7). The mitochondria are the site of the first step in progesterone synthesis. In this organelle, the shuttling of cholesterol through the aqueous intermembrane between the outer to the inner membrane of the mitochondria space is the rate-limiting step of progesterone synthesis. This crucial step is facilitated by steroidogenic acute regulatory protein (StAR). StAR is highly expressed in luteal cells (Stocco et al., 2007). Inside the mitochondria, cholesterol side chain cleavage (P450scc or CYP11a1) is the enzyme that catalyzes the first step of progesterone production, which is cleaving the cholesterol side chain to produce pregnenolone (Fig. 25.8). The conversion of pregnenolone into progesterone occurs in the plasma reticulum catalyzed by the 3b-hydroxysteroid dehydrogenase/D5D4 isomerase (3bHSD) enzyme. 3bHSD catalyzes the dehydrogenation of the pregnenolone 3b-hydroxyl group and subsequent isomerization of carbon 4 to form a ketone, therefore yielding progesterone. There are two 3bHSD genes: type 1, which is expressed mainly in the placenta, liver, breast, and brain, and type 2 in the adrenal cortex and gonads. The expression of StAR and both enzymes P450scc and 3bHSD (Hedin et al., 1987; Oonk et al., 1989) and

FIGURE 25.7 Progesterone synthesis.

the number organelles that house them (Enders, 1973) increases during luteinization, allowing luteal cells to synthesize large amounts of progesterone (Stocco et al., 2007). Both enzymes remain highly expressed in the corpus luteum (Goldring et al., 1987). In rodents, the level of progesterone secreted by the corpus luteum does not depend only on the synthesis but also on the expression of the enzyme 20aHSD that catabolizes progesterone into the inactive progestin, 20a-dihydroprogesterone (20a-DHP). Due to the detrimental effect of 20aHSD on luteal progesterone secretion, little or no 20aHSD activity is found in the rat corpus luteum throughout pregnancy; however, elevated activity is found just before parturition concomitant with the rapid decrease in the concentration of progesterone in serum (Mao et al., 1994, 1997). In rodents, this decrease in serum progesterone is essential for parturition to occur. Accordingly, mice deficient in 20aHSD sustain high progesterone levels and display a delay of several days in parturition (Piekorz et al., 2005). Whereas 20aHSD is one of the most important players in the regulation of luteal progesterone secretion in rodents, the role of this enzyme in the control of progesterone production and/or action in humans needs further investigation. 3.1.1 Hormonal Regulation CL function is controlled by the interaction of tropic hormones secreted by the pituitary, the CL itself, the decidua, and the placenta; however, the kind of hormones secreted by these tissues and their combination differ between species. In humans and nonhuman primates, LH is essential and sufficient for the stimulation and maintenance of luteal function (Stouffer, 2003). LH-R activation in the preovulatory follicle results in the induction of a broad range of genes that are important for ovulation and differentiation of the granulosa cells. In primates, the steroidogenic actions of LH are directed primarily at the delivery of cholesterol to the mitochondria by increasing the expression of StAR (Devoto et al., 2002) and by stimulating the expression of SR-BI (Xu et al., 2005). LH also stimulates the expression of 3bHSD, aromatase, estrogen receptor b (Duffy et al., 2000), and genes involved in tissue remodeling

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575

FIGURE 25.8 Progesterone synthesis in luteal cells.

(Young and Stouffer, 2004) and in the maintenance of luteal vasculature (Ravindranath et al., 1992). In rodents, LH has been shown to increase SR-BI and HDL uptake (Chen and Menon, 1994; McLean and Sandhoff, 1998). Because LH is essential for follicular maturation and ovulation (Lei et al., 2001), knockout animals for LH or the LH receptor have not provided information regarding the role of LH in corpus luteum function. In monkeys, however, treatment with a gonadotropinreleasing hormone (GnRH) antagonist (which blocks pituitary LH secretion) causes a rapid and sustained fall in serum progesterone production (Hutchison and Zeleznik, 1984). In nonpregnant primates, progesterone is produced by the corpus luteum for about 2 weeks, which corresponds to the luteal phase of the cycle. At the end of this period, the corpus luteum regresses, causing a drastic decrease in serum progesterone levels. This process is known as luteolysis. Because progesterone prevents LH and FSH secretion from the pituitary, the regression of the corpus luteum allows a new cycle to begin. In primates, if conception and implantation take place, luteolysis must be prevented to provide adequate levels of progesterone to maintain pregnancy. In humans, progesterone from the corpus luteum is required only during early pregnancy until placental production of progesterone begins, which occurs between the fifth and seventh weeks of gestation. The extension of the lifespan of the corpus luteum during pregnancy in primates is caused by the implanting embryo (Goodman and Hodgen, 1979). At implantation, the syncytiotrophoblast secrete chorionic gonadotrophin (CG), which binds to the same receptors as LH, thus extending luteotrophic signals beyond the normal menstrual cycle. In monkeys, administration of human CG mimics the patterns of circulating levels of progesterone found in early pregnancy (Zeleznik, 1998; Fig. 25.8).

3.2 Progesterone Receptor and Signaling The progesterone receptor (PR) is expressed in two major isoforms, PR-A and PR-B. PR-A is a truncated protein lacking the first 164 amino acids from the NTD; otherwise, the two PRs have an identical amino acid sequence (Fig. 25.9). Both PR proteins arise from the same gene by utilization of two distinct promoters. A third isoform, PR-C, has been found in myometrial tissue (Condon et al., 2006). In common with ERs, PRA and PRB are modular proteins composed of a C-terminal LBD, a central DBD, and an amino-terminal domain (NTD). The two transcriptional activation domains (AFs) in both PRs provide interaction surfaces for cofactors. Of this, AF1 is located within the NTD and AF2 is in the LBD. The DBD of the PR recognizes a common consensus GGT/ AACAnnnTGTTCT response element (Lieberman et al., 1993). Remarkably, this response element is also recognized by the androgen receptor, the mineralocorticoid receptor, and the glucocorticoid receptor. Because these receptors share consensus binding sites, significant crosstalk regulation between these hormones exists. For instance, progesterone acts via GR to repress IL1b-induced gene expression (Lei et al., 2012).

FIGURE 25.9 Structural organization of the human PR-A and PR-B isoforms. Numbers denote the amino acid position of each protein. Ligand-binding domain (LBD), DNA-binding domain (DBD), aminoterminal domain (NTD), transcriptional activation or functional domains (AF1, AF2).

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3.2.1 Membrane Progesterone Receptors Several studies have reported actions of progestins in cells and tissues that are devoid of classical PRs. These actions are mediated by membrane-localized progestin receptors, which are unrelated to classical PRs. These receptors activate rapid nongenomic signals. Two types of membrane PRs have been described: the progesterone membrane component (PGRMC1 and 2) and the membrane progestin receptors (mPs) (Kowalik et al., 2013). These receptors rapidly activate several intracellular signal pathways and can initiate specific cell responses or modulate genomic responses to progesterone (Garg et al., 2017).

3.3 Physiological Effects of Progesterone 3.3.1 Autoregulation of Ovarian Function by Progesterone PR expression is rapidly induced by the LH surge in preovulatory follicles and in cultured granulosa cells of several species (Hild-Petito et al., 1988; Park and Mayo, 1991). In mice and rats, PR expression decreases rapidly after ovulation, and the receptor is not expressed in luteal cells throughout pregnancy (Park and Mayo, 1991; Natraj and Richards, 1993; Park-Sarge et al., 1995). In contrast, in primates, both PR-A and PR-B remain expressed in the CL, where PR-B is the predominant isoform (Duffy et al., 1997). During the periovulatory window, along with the increase in PR expression, there is also a marked increase in progesterone synthesis in preovulatory granulosa cells. Progesterone synthesis increases enormously and is the primary hormone secreted by the luteal cells. Thus, progesterone concentrations during the follicular phase are lower than 1 ng/mL but increase in the luteal phase reaching up to 35 ng/mL. Specifically, levels peak during the midluteal phase and decline in the late luteal phase (Filicori et al., 1984). Progesterone has been shown to play four major roles in the ovary: oocyte meiosis, ovulation, luteinization, and corpus luteum maintenance (Stocco et al., 2007). Progesterone appears to contribute to the reinitiation of meiosis in oocytes by disrupting gap junctions between cumulus cells (Shimada and Terada, 2002). The crucial role of progesterone on ovulation was demonstrated in PR knockout mice, which show impaired follicle rupture but are able to form CL-containing trapped oocytes (Lydon et al., 1996). Similarly, in monkeys, steroid ablation studies demonstrated that only progestins restored follicle rupture (Hibbert et al., 1996). The role of progesterone on the formation and maintenance of corpus luteum function has been clearly established (Stocco et al., 2007). Progesterone also appears to play a role before ovulation during follicle development. Thus, progesterone produced by the preovulatory follicle acts

directly on granulosa cells promoting follicular growth and inhibiting apoptotic genes (Peluso, 2013). 3.3.2 The Fallopian Tube Ovarian steroid hormones, including progesterone, affect the morphology and function of the fallopian tube luminal epithelium, regulating muscular and nerve function and regulating the volume and composition of fluids in the lumen (Hunter, 2012). These effects optimize transport of the ovulated oocyte and nourish the embryo in the early developmental stages (Schneider et al., 1993; Li and Winuthayanon, 2017). However, progesterone roles and mode of action in the fallopian tube have not been definitively defined. It is known that progesterone and estradiol are key players in regulating CBF. Progesterone reduces CBF via classical PRs found on the ciliated oviductal epithelial cells in humans and mice (Mahmood et al., 1998; Bylander et al., 2010). Progesterone also relaxes muscle contraction in mice and reduces both amplitude and frequency of tubal muscle contraction in humans (Wanggren et al., 2008). The evidence indicates that the transport of gametes and embryos in the oviduct involves the action of progesterone on muscular contractility. 3.3.3 Progesterone Effects in the Uterus Progesterone is called “the pregnancy hormone.” Thus, progesterone is extensively used in the treatment of different gynecological pathologies and in assisted reproductive technologies to aid in the maintenance of pregnancy. Progesterone’s indispensable role in pregnancy is mediated in part by the regulation of several aspects of uterine physiology including endometrial maturation, modulation of maternal immune response, suppression of inflammatory response, reduction of uterine contractility, and improvement of uteroplacental circulation. The major function of progesterone is endometrial maturation. This involves the mutual regulation of estrogens and PRs expression in the endometrium. During the preovulatory phase, estradiol increases the expression of PR. Subsequently, progesterone suppresses the expression of endometrial ERs during the luteal phase (Lessey et al., 1988), leading to the cessation of mitosis and organization of the glands stimulated by estradiol (Noyes et al., 1975; Pan et al., 2006; Wang et al., 2007b). Progesterone plays a critical role in the decidualization of the uterus. Decidualization involves the transformation of endometrial stromal fibroblasts into specialized secretory decidual cells that provide a nutritive and immunocompetent matrix indispensable for embryo implantation and placental development (Gellersen and Brosens, 2014). These changes can be detected on ultrasonography by following the transformation of the “triple stripe” image that is usually present in the proliferative phase to a uniformly bright endometrium

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577

FIGURE 25.10 Uterine changes induced by estradiol and progesterone as detected by ultrasound. The arrows indicate the uterus.

(Fig. 25.10). The increase in brightness during the luteal phase appears to be related to increasing length and tortuosity of endometrial glands with mucin and glycogen storage within the functional layer of the uterus. In rodents, the role of progesterone in the uterus was clearly demonstrated in the PR knockout mice, which lack both A and B isoforms. These mice, in addition to anovulation, exhibit hyperplastic uteri, impaired decidualization, and a hypertrophied epithelium, which contains numerous leukocytes and therefore is nonreceptive to embryo implantation (Lydon et al., 1995). Thus, progesterone activated pathways in the uterus are critical to preparing both epithelial and stromal cells to establish the environment required for implantation and the establishment of pregnancy. In nonpregnant females, progesterone deficiency in the presence of excess estrogen causes hyperplasia of the glandular epithelial tissue, with the potential to progress to adenocarcinoma (Kim et al., 2013). Progression usually occurs from a low-grade to a high-grade lesion with loss of stromal tissue and presence of myometrial invasion. Progesterone has the ability to antagonize proliferation and promote atrophy of the endometrium (Charles, 1964). This observation made progesterone a therapeutic option in the treatment of patients with endometrial hyperplasia or adenocarcinoma (Ushijima et al., 2007). 3.3.4 Progesterone Regulation of the Mammary Gland The breast undergoes major changes in the lifespan of a female. Breast development is a progressive process that is initiated during embryonic life with the formation of a rudimentary ductal structure. At puberty, estradiol, growth hormone, and insulin-like growth factors initiate the branching of this structure creating a ductal tree that fills the fat pad (Inman et al., 2015). During pregnancy, progesterone and prolactin stimulate epithelial proliferation, leading to the formation of alveoli, which will

secrete milk during lactation (Inman et al., 2015). Thus, although puberty marks the beginning of glandular maturation, full breast differentiation is attained only during pregnancy and lactation. Like ERa, PR is expressed in both epithelial and stromal compartments in the mammary gland (Russo et al., 1999). As in the uterus, estrogens have been shown to act through ERa to increase expression of PR in human breast cells (Schultz et al., 2003). Mice lacking both PR isoforms demonstrated that progesterone is required for pregnancy-associated ductal proliferation and lobuloalveolar differentiation. Thus, the mammary glands of PR knockout mice failed to develop the side-branching of the ductal epithelium with the associated lobular alveolar differentiation despite postpubertal mammary gland morphogenesis (Lydon et al., 1995). As described previously, progesterone counteracts the proliferative effects of estradiol in the endometrium (Pan et al., 2006). In marked contrast, progesterone via activation of PR-B is a major proliferative hormone in the mouse mammary gland and the normal human breast epithelium (Fernandez-Valdivia et al., 2005; Mulac-Jericevic et al., 2000). The proliferative action of progesterone occurs indirectly through stimulation of paracrine mediators in PR-positive cells that regulate proliferative genes in adjacent cells that do not express PR (Arendt and Kuperwasser, 2015). Progesterone stimulation of proliferation led to the proposal that progesterone increases the risk of breast cancer (Brisken, 2013). 3.3.5 Effects of Progesterone on LH Secretion A main physiologic function of progesterone is the modulation of LH and FSH secretion through a feedback mechanism. In the hypothalamicepituitaryeovarian axis, ovarian progesterone provides negative feedback on GnRH and gonadotropin secretion. Evidence suggests that the hypothalamus has an intrinsic rate of hourly pulsatile GnRH secretion that is fine-tuned by

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the negative feedback provided by the steroid hormones, primarily progesterone (Filicori et al., 1986). Progesterone slows the frequency of LH pulse production by the pituitary gland in the early luteal phase. Estrogen is required for progesterone to slow GnRH pulse frequency, which suggests that estrogen also increases the expression of the PR in the hypothalamus (Romano et al., 1989). Recent evidence demonstrated a role for PR in the hypothalamic AVPV and ARC nuclei in mediating the inhibitory effects of progesterone on the surge and pulsatile release of LH in rats (He et al., 2017). Increased LH pulse frequency and increased LH to FSH ratio are common in women with PCOS, which often have elevated levels of androgen in circulation. The increased LH pulse frequency suggests a hyperactive hypothalamicepituitaryegonadal axis due to impaired negative steroid feedback. In fact, evidence suggests that the inappropriately high levels of androgens found in PCOS impair the negative feedback of estradiol and progesterone. For instance, administration of an antagonist of the androgen receptor reestablish the ability of progesterone (and estradiol) to suppress LH (Eagleson et al., 2000). Supporting this finding, it has been shown that exogenous progesterone is unable to lower LH pulse frequency in patients with hyperandrogenism (Chhabra et al., 2005). Thus, elevated androgen levels antagonize the negative feedback effect of progesterone on the hypothalamus (Pastor et al., 1998). 3.3.6 Nonreproductive Effects of Progesterone in the Brain There is growing evidence that progesterone, and perhaps its metabolite allopregnanolone, exert neuroprotective effects on the injured central nervous system by reducing edema and restoring the function of the blood barrier (Sayeed and Stein, 2009; Andrabi et al., 2017). Allopregnanolone has also been suggested as a neuro-regenerative agent that slows Alzheimer disease progression (Wang et al., 2007a). Despite the many studies, effects of progesterone on memory have been contradictory. Some of the studies supported deleterious effects of this hormone, while others showed beneficial properties (Barros et al., 2015). Progesterone is also suggested to play a role in premenstrual syndrome and premenstrual dysphoric disorder. This is because premenstrual syndrome correlates with a reduction in the plasma progesterone levels. Consequently, exogenous progesterone has beneficial effects on women with premenstrual syndrome (Monteleone et al., 2000).

4. CONCLUSIONS The cyclicity of ovarian hormones represents a unique system. This delicate and complex system of

hormonal checks and balances coordinate the timely and cyclic maturation of the female reproductive tract, the ovaries, and central autonomic and cognitive functions with the ultimate purpose of ensuring oocyte fertilization and embryo development. Several aspects of this system remain still poorly understood. Notably, the effects of aging, the molecular and genetic defects in PCOS, and the significant decrease in fertility of women undergoing cancer treatments are currently being studied extensively. Finally, women undergoing cancer treatment have their fertility significantly decreased if not obliterated. Thus, a better understanding of the role of ovarian hormones will contribute to extending fertility in aging women, effectively treating PCOS, and preserving ovarian function in cancer patients.

Acknowledgments Our apologies to the authors of the numerous publications that contribute to our understanding of the physiology of ovarian hormones that were not cited because of space limitations. This work was supported by NIH grants number R56HD086054 and R01HD057110 (CS). Disclosure summary: The authors have nothing to disclose.

References Abbara, A., Ratnasabapathy, R., Jayasena, C.N., Dhillo, W.S., 2013. The effects of kisspeptin on gonadotropin release in non-human mammals. Adv. Exp. Med. Biol. 784, 63e87. Adashi, E.Y., Hsueh, A.J., 1982. Estrogens augment the stimulation of ovarian aromatase activity by follicle-stimulating hormone in cultured rat granulosa cells. J. Biol. Chem. 257, 6077e6083. Albano, C., Felberbaum, R.E., Smitz, J., Riethmuller-Winzen, H., Engel, J., Diedrich, K., Devroey, P., 2000. Ovarian stimulation with HMG: results of a prospective randomized phase III European study comparing the luteinizing hormone-releasing hormone (LHRH)-antagonist cetrorelix and the LHRH-agonist buserelin. European Cetrorelix Study Group. Hum. Reprod. 15, 526e531. Andrabi, S.S., Parvez, S., Tabassum, H., 2017. Neurosteroids and ischemic stroke: progesterone a promising agent in reducing the brain injury in ischemic stroke. J. Environ. Pathol. Toxicol. Oncol. 36, 191e205. Arendt, L.M., Kuperwasser, C., 2015. Form and function: how estrogen and progesterone regulate the mammary epithelial hierarchy. J. Mammary Gland Biol. Neoplasia 20, 9e25. Baker, F.C., De Zambotti, M., Colrain, I.M., Bei, B., 2018. Sleep problems during the menopausal transition: prevalence, impact, and management challenges. Nat. Sci. Sleep 10, 73e95. Baltgalvis, K.A., Greising, S.M., Warren, G.L., Lowe, D.A., 2010. Estrogen regulates estrogen receptors and antioxidant gene expression in mouse skeletal muscle. PLoS One 5, e10164. Barros, L.A., Tufik, S., Andersen, M.L., 2015. The role of progesterone in memory: an overview of three decades. Neurosci. Biobehav. Rev. 49, 193e204. Battaglioli, T., Martinelli, I., 2007. Hormone therapy and thromboembolic disease. Curr. Opin. Hematol. 14, 488e493. Baumgarten, S.C., Armouti, M., Ko, C., Stocco, C., 2017. IGF1R expression in ovarian granulosa cells is essential for steroidogenesis, follicle survival, and fertility in female mice. Endocrinology 158, 2309e2318.

REFERENCES

Baumgarten, S.C., Convissar, S.M., Fierro, M.A., Winston, N.J., Scoccia, B., Stocco, C., 2014. Follicle stimulating hormone regulates insulin-like growth factor 2 expression in human granulosa cells in an AKT-dependent manner. In: Annual Meeting Society for the Study of Reproduction 2014, Grant Rapids, MI. Baumgarten, S.C., Convissar, S.M., Zamah, A.M., Fierro, M.A., Winston, N.J., Scoccia, B., Stocco, C., 2015. FSH regulates IGF-2 expression in human granulosa cells in an AKT-dependent manner. J. Clin. Endocrinol. Metab. 100, E1046eE1055. Belgorosky, A., Guercio, G., Pepe, C., Saraco, N., Rivarola, M.A., 2009. Genetic and clinical spectrum of aromatase deficiency in infancy, childhood and adolescence. Horm. Res. 72, 321e330. Blum, A., Cannon III, R.O., 1998. Effects of oestrogens and selective oestrogen receptor modulators on serum lipoproteins and vascular function. Curr. Opin. Lipidol. 9, 575e586. Borjesson, A.E., Lagerquist, M.K., Windahl, S.H., Ohlsson, C., 2013. The role of estrogen receptor alpha in the regulation of bone and growth plate cartilage. Cell. Mol. Life Sci. 70, 4023e4037. Brennan, M.A., Haugh, M.G., O’brien, F.J., Mcnamara, L.M., 2014. Estrogen withdrawal from osteoblasts and osteocytes causes increased mineralization and apoptosis. Horm. Metab. Res. 46, 537e545. Brisken, C., 2013. Progesterone signalling in breast cancer: a neglected hormone coming into the limelight. Nat. Rev. Cancer 13, 385e396. Britt, K.L., Drummond, A.E., Cox, V.A., Dyson, M., Wreford, N.G., Jones, M.E., Simpson, E.R., Findlay, J.K., 2000. An age-related ovarian phenotype in mice with targeted disruption of the Cyp 19 (aromatase) gene. Endocrinology 141, 2614e2623. Bylander, A., Nutu, M., Wellander, R., Goksor, M., Billig, H., Larsson, D.G., 2010. Rapid effects of progesterone on ciliary beat frequency in the mouse fallopian tube. Reprod. Biol. Endocrinol. 8, 48. Charles, D., 1964. Iatrogenic endometrial patterns. J. Clin. Pathol. 17, 205e212. Chen, Z., Menon, K.M., 1994. Expression of high density lipoproteinbinding protein messenger ribonucleic acid in the rat ovary and its regulation by gonadotropin. Endocrinology 134, 2360e2366. Chhabra, S., Mccartney, C.R., Yoo, R.Y., Eagleson, C.A., Chang, R.J., Marshall, J.C., 2005. Progesterone inhibition of the hypothalamic gonadotropin-releasing hormone pulse generator: evidence for varied effects in hyperandrogenemic adolescent girls. J. Clin. Endocrinol. Metab. 90, 2810e2815. Christian, C.A., Moenter, S.M., 2010. The neurobiology of preovulatory and estradiol-induced gonadotropin-releasing hormone surges. Endocr. Rev. 31, 544e577. Condon, J.C., Hardy, D.B., Kovaric, K., Mendelson, C.R., 2006. Upregulation of the progesterone receptor (PR)-C isoform in laboring myometrium by activation of nuclear factor-kappaB may contribute to the onset of labor through inhibition of PR function. Mol. Endocrinol. 20, 764e775. Couse, J.F., Curtis, S.W., Washburn, T.F., Eddy, E.M., Schomberg, D.W., Korach, K.S., 1995. Disruption of the mouse oestrogen receptor gene: resulting phenotypes and experimental findings. Biochem. Soc. Trans. 23, 929e935. Couse, J.F., Korach, K.S., 1999. Estrogen receptor null mice: what have we learned and where will they lead us? Endocr. Rev. 20, 358e417. Couse, J.F., Yates, M.M., Deroo, B.J., Korach, K.S., 2005. Estrogen receptor-beta is critical to granulosa cell differentiation and the ovulatory response to gonadotropins. Endocrinology 146, 3247e3262. Croxatto, H.B., 2002. Physiology of gamete and embryo transport through the fallopian tube. Reprod. Biomed. Online 4, 160e169. Csapo, A.I., Pulkkinen, M.O., Ruttner, B., Sauvage, J.P., Wiest, W.G., 1972. The significance of the human corpus luteum in pregnancy

579

maintenance. I. Preliminary studies. Am. J. Obstet. Gynecol. 112, 1061e1067. Davoren, J.B., Hsueh, J.W., Li, C.H., 1985. Somatomedin C augments FSH-induced differentiation of cultured rat granulosa cells. Am. J. Physiol. 249, E26eE33. Daya, S., 2009. Luteal support: progestogens for pregnancy protection. Maturitas 65 (Suppl. 1), S29eS34. de Roux, N., Genin, E., Carel, J.C., Matsuda, F., Chaussain, J.L., Milgrom, E., 2003. Hypogonadotropic hypogonadism due to loss of function of the KiSS1-derived peptide receptor GPR54. Proc. Natl. Acad. Sci. U. S. A. 100, 10972e10976. Deroo, B.J., Rodriguez, K.F., Couse, J.F., Hamilton, K.J., Collins, J.B., Grissom, S.F., Korach, K.S., 2009. Estrogen receptor beta is required for optimal cAMP production in mouse granulosa cells. Mol. Endocrinol. 23, 955e965. Devoto, L., Vega, M., Kohen, P., Castro, O., Carvallo, P., Palomino, A., 2002. Molecular regulation of progesterone secretion by the human corpus luteum throughout the menstrual cycle. J. Reprod. Immunol. 55, 11e20. Dorrington, J.H., Bendell, J.J., Chuma, A., Lobb, D.K., 1987. Actions of growth factors in the follicle. J. Steroid Biochem. 27, 405e411. Duffy, D.M., Chaffin, C.L., Stouffer, R.L., 2000. Expression of estrogen receptor alpha and beta in the rhesus monkey corpus luteum during the menstrual cycle: regulation by luteinizing hormone and progesterone. Endocrinology 141, 1711e1717. Duffy, D.M., Wells, T.R., Haluska, G.J., Stouffer, R.L., 1997. The ratio of progesterone receptor isoforms changes in the monkey corpus luteum during the luteal phase of the menstrual cycle. Biol. Reprod. 57, 693e699. Dupont, S., Krust, A., Gansmuller, A., Dierich, A., Chambon, P., Mark, M., 2000. Effect of single and compound knockouts of estrogen receptors alpha (ERalpha) and beta (ERbeta) on mouse reproductive phenotypes. Development 127, 4277e4291. Eagleson, C.A., Gingrich, M.B., Pastor, C.L., Arora, T.K., Burt, C.M., Evans, W.S., Marshall, J.C., 2000. Polycystic ovarian syndrome: evidence that flutamide restores sensitivity of the gonadotropinreleasing hormone pulse generator to inhibition by estradiol and progesterone. J. Clin. Endocrinol. Metab. 85, 4047e4052. EL-Hefnawy, T., Zeleznik, A.J., 2001. Synergism between FSH and activin in the regulation of proliferating cell nuclear antigen (PCNA) and cyclin D2 expression in rat granulosa cells. Endocrinology 142, 4357e4362. Elvin, J.A., Yan, C., Wang, P., Nishimori, K., Matzuk, M.M., 1999. Molecular characterization of the follicle defects in the growth differentiation factor 9-deficient ovary. Mol. Endocrinol. 13, 1018e1034. Enders, A.C., 1973. Cytology of the corpus luteum. Biol. Reprod. 8, 158e182. Enmark, E., Pelto-Huikko, M., Grandien, K., Lagercrantz, S., Lagercrantz, J., Fried, G., Nordenskjold, M., Gustafsson, J.A., 1997. Human estrogen receptor beta-genew structure, chromosomal localization, and expression pattern. J. Clin. Endocrinol. Metab. 82, 4258e4265. Fernandez-Valdivia, R., Mukherjee, A., Mulac-Jericevic, B., Conneely, O.M., Demayo, F.J., Amato, P., Lydon, J.P., 2005. Revealing progesterone’s role in uterine and mammary gland biology: insights from the mouse. Semin. Reprod. Med. 23, 22e37. Filicori, M., Butler, J.P., Crowley Jr., W.F.,, 1984. Neuroendocrine regulation of the corpus luteum in the human. Evidence for pulsatile progesterone secretion. J. Clin. Investig. 73, 1638e1647. Filicori, M., Santoro, N., Merriam, G.R., Crowley Jr., W.F., 1986. Characterization of the physiological pattern of episodic gonadotropin secretion throughout the human menstrual cycle. J. Clin. Endocrinol. Metab. 62, 1136e1144. Fisher, C.R., Graves, K.H., Parlow, A.F., Simpson, E.R., 1998. Characterization of mice deficient in aromatase (ArKO) because of targeted

580

25. OVARIAN HORMONES

disruption of the Cyp19 gene. Proc. Natl. Acad. Sci. U. S. A. 95, 6965e6970. Fitzpatrick, S.L., Richards, J.S., 1991. Regulation of cytochrome P450 aromatase messenger ribonucleic acid and activity by steroids and gonadotropins in rat granulosa cells. Endocrinology 129, 1452e1462. Garg, D., Ng, S.S.M., Baig, K.M., Driggers, P., Segars, J., 2017. Progesterone-mediated non-classical signaling. Trends Endocrinol. Metabol. 28, 656e668. Gellersen, B., Brosens, J.J., 2014. Cyclic decidualization of the human endometrium in reproductive health and failure. Endocr. Rev. 35, 851e905. George, F.W., Ojeda, S.R., 1987. Vasoactive intestinal peptide enhances aromatase activity in the neonatal rat ovary before development of primary follicles or responsiveness to follicle-stimulating hormone. Proc. Natl. Acad. Sci. U. S. A. 84, 5803e5807. George, F.W., Wilson, J.D., 1978. Conversion of androgen to estrogen by the human fetal ovary. J. Clin. Endocrinol. Metab. 47, 550e555. Goldring, N.B., Durica, J.M., Lifka, J., Hedin, L., Ratoosh, S.L., Miller, W.L., Orly, J., Richards, J.S., 1987. Cholesterol side-chain cleavage P450 messenger ribonucleic acid: evidence for hormonal regulation in rat ovarian follicles and constitutive expression in corpora lutea. Endocrinology 120, 1942e1950. Goodman, A.L., Hodgen, G.D., 1979. Corpus luteum e conceptus e follicle relationships during the fertile cycle in rhesus monkeys: pregnancy maintenance despite early luteal removal. J. Clin. Endocrinol. Metab. 49, 469e471. Greising, S.M., Baltgalvis, K.A., Lowe, D.A., Warren, G.L., 2009. Hormone therapy and skeletal muscle strength: a meta-analysis. J. Gerontol. A Biol. Sci. Med. Sci. 64, 1071e1081. Guigon, C.J., Mazaud, S., Forest, M.G., Brailly-Tabard, S., Coudouel, N., Magre, S., 2003. Unaltered development of the initial follicular waves and normal pubertal onset in female rats after neonatal deletion of the follicular reserve. Endocrinology 144, 3651e3662. Haddad, S.N., Wira, C.R., 2014. Estradiol regulation of constitutive and keratinocyte growth factor-induced CCL20 and CXCL1 secretion by mouse uterine epithelial cells. Am. J. Reprod. Immunol. 72, 34e44. He, W., Li, X., Adekunbi, D., Liu, Y., Long, H., Wang, L., Lyu, Q., Kuang, Y., O’byrne, K.T., 2017. Hypothalamic effects of progesterone on regulation of the pulsatile and surge release of luteinising hormone in female rats. Sci. Rep. 7, 8096. Hedin, L., Rodgers, R.J., Simpson, E.R., Richards, J.S., 1987. Changes in content of cytochrome P450(17)alpha, cytochrome P450scc, and 3-hydroxy-3-methylglutaryl CoA reductase in developing rat ovarian follicles and corpora lutea: correlation with theca cell steroidogenesis. Biol. Reprod. 37, 211e223. Helsen, C., Claessens, F., 2014. Looking at nuclear receptors from a new angle. Mol. Cell. Endocrinol. 382, 97e106. Hibbert, M.L., Stouffer, R.L., Wolf, D.P., Zelinski-Wooten, M.B., 1996. Midcycle administration of a progesterone synthesis inhibitor prevents ovulation in primates. Proc. Natl. Acad. Sci. U. S. A. 93, 1897e1901. Hild-Petito, S., Stouffer, R.L., Brenner, R.M., 1988. Immunocytochemical localization of estradiol and progesterone receptors in the monkey ovary throughout the menstrual cycle. Endocrinology 123, 2896e2905. Hillier, S.G., de Zwart, F.A., 1982. Androgen/antiandrogen modulation of cyclic AMP-induced steroidogenesis during granulosa cell differentiation in tissue culture. Mol. Cell. Endocrinol. 28, 347e361. Hunter, R.H., 2012. Components of oviduct physiology in eutherian mammals. Biol. Rev. Camb. Philos. Soc. 87, 244e255.

Hutchison, J.S., Zeleznik, A.J., 1984. The rhesus monkey corpus luteum is dependent on pituitary gonadotropin secretion throughout the luteal phase of the menstrual cycle. Endocrinology 115, 1780e1786. Inman, J.L., Robertson, C., Mott, J.D., Bissell, M.J., 2015. Mammary gland development: cell fate specification, stem cells and the microenvironment. Development 142, 1028e1042. Khan, A.R., Kauffman, A.S., 2012. The role of kisspeptin and RFamiderelated peptide-3 neurones in the circadian-timed preovulatory luteinising hormone surge. J. Neuroendocrinol. 24, 131e143. Kim, J.J., Kurita, T., Bulun, S.E., 2013. Progesterone action in endometrial cancer, endometriosis, uterine fibroids, and breast cancer. Endocr. Rev. 34, 130e162. Korach, K.S., Emmen, J.M., Walker, V.R., Hewitt, S.C., Yates, M., Hall, J.M., Swope, D.L., Harrell, J.C., Couse, J.F., 2003. Update on animal models developed for analyses of estrogen receptor biological activity. J. Steroid Biochem. Mol. Biol. 86, 387e391. Kowalik, M.K., Rekawiecki, R., Kotwica, J., 2013. The putative roles of nuclear and membrane-bound progesterone receptors in the female reproductive tract. Reprod. Biol. 13, 279e289. Krege, J.H., Hodgin, J.B., Couse, J.F., Enmark, E., Warner, M., Mahler, J.F., Sar, M., Korach, K.S., Gustafsson, J.A., Smithies, O., 1998. Generation and reproductive phenotypes of mice lacking estrogen receptor beta. Proc. Natl. Acad. Sci. U. S. A. 95, 15677e15682. Kumar, R., Zakharov, M.N., Khan, S.H., Miki, R., Jang, H., Toraldo, G., Singh, R., Bhasin, S., Jasuja, R., 2011. The dynamic structure of the estrogen receptor. J. Amino Acids 2011, 812540. Laue, L., Hoeg, J.M., Barnes, K., Loriaux, D.L., Chrousos, G.P., 1987. The effect of mevinolin on steroidogenesis in patients with defects in the low density lipoprotein receptor pathway. J. Clin. Endocrinol. Metab. 64, 531e535. Lee, M.M., 2003. Reproductive hormones in infant girls e a harbinger of adult reproductive function? J. Clin. Endocrinol. Metab. 88, 3513e3514. Lei, K., Chen, L., Georgiou, E.X., Sooranna, S.R., Khanjani, S., Brosens, J.J., Bennett, P.R., Johnson, M.R., 2012. Progesterone acts via the nuclear glucocorticoid receptor to suppress IL-1betainduced COX-2 expression in human term myometrial cells. PLoS One 7, e50167. Lei, Z.M., Mishra, S., Zou, W., Xu, B., Foltz, M., Li, X., Rao, C.V., 2001. Targeted disruption of luteinizing hormone/human chorionic gonadotropin receptor gene. Mol. Endocrinol. 15, 184e200. Lessey, B.A., Killam, A.P., Metzger, D.A., Haney, A.F., Greene, G.L., Mccarty JR., K.S., 1988. Immunohistochemical analysis of human uterine estrogen and progesterone receptors throughout the menstrual cycle. J. Clin. Endocrinol. Metab. 67, 334e340. Li, S., Winuthayanon, W., 2017. Oviduct: roles in fertilization and early embryo development. J. Endocrinol. 232, R1eR26. Lieberman, B.A., Bona, B.J., Edwards, D.P., Nordeen, S.K., 1993. The constitution of a progesterone response element. Mol. Endocrinol. 7, 515e527. Liu, X.J., Malkowski, M., Guo, Y., Erickson, G.F., Shimasaki, S., Ling, N., 1993. Development of specific antibodies to rat insulinlike growth factor-binding proteins (IGFBP-2 to -6): analysis of IGFBP production by rat granulosa cells. Endocrinology 132, 1176e1183. Lowe, D.A., Baltgalvis, K.A., Greising, S.M., 2010. Mechanisms behind estrogen’s beneficial effect on muscle strength in females. Exerc. Sport Sci. Rev. 38, 61e67. Luine, V.N., 2008. Sex steroids and cognitive function. J. Neuroendocrinol. 20, 866e872. Luine, V.N., 2014. Estradiol and cognitive function: past, present and future. Horm. Behav. 66, 602e618. Lydon, J.P., Demayo, F.J., Conneely, O.M., O’malley, B.W., 1996. Reproductive phenotpes of the progesterone receptor null mutant mouse. J. Steroid Biochem. Mol. Biol. 56, 67e77.

REFERENCES

Lydon, J.P., Demayo, F.J., Funk, C.R., Mani, S.K., Hughes, A.R., Montgomery Jr., C.A., Shyamala, G., Conneely, O.M., O’malley, B.W., 1995. Mice lacking progesterone receptor exhibit pleiotropic reproductive abnormalities. Genes Dev. 9, 2266e2278. Mahmood, T., Saridogan, E., Smutna, S., Habib, A.M., Djahanbakhch, O., 1998. The effect of ovarian steroids on epithelial ciliary beat frequency in the human Fallopian tube. Hum. Reprod. 13, 2991e2994. Makanji, Y., Zhu, J., Mishra, R., Holmquist, C., Wong, W.P., Schwartz, N.B., Mayo, K.E., Woodruff, T.K., 2014. Inhibin at 90: from discovery to clinical application, a historical review. Endocr. Rev. 35, 747e794. Mao, J., Duan, R.W., Zhong, L., Gibori, G., Azhar, S., 1997. Expression, purification and characterization of the rat luteal 20 alphahydroxysteroid dehydrogenase. Endocrinology 138, 182e190. Mao, J., Duan, W.R., Albarracin, C.T., Parmer, T.G., Gibori, G., 1994. Isolation and characterization of a rat luteal cDNA encoding 20 alpha- hydroxysteroid dehydrogenase. Biochem. Biophys. Res. Commun. 201, 1289e1295. Marino, M., Galluzzo, P., Ascenzi, P., 2006. Estrogen signaling multiple pathways to impact gene transcription. Curr. Genom. 7, 497e508. Mason, H.D., Cwyfan-Hughes, S., Holly, J.M., Franks, S., 1998. Potent inhibition of human ovarian steroidogenesis by insulin-like growth factor binding protein-4 (IGFBP-4). J. Clin. Endocrinol. Metab. 83, 284e287. Mccarrey, A.C., Resnick, S.M., 2015. Postmenopausal hormone therapy and cognition. Horm. Behav. 74, 167e172. Mclean, M.P., Sandhoff, T.W., 1998. Expression and hormonal regulation of the high-density lipoprotein (HDL) receptor scavenger receptor class B type I messenger ribonucleic acid in the rat ovary. Endocrine 9, 243e252. Melville, K.M., Kelly, N.H., Khan, S.A., Schimenti, J.C., Ross, F.P., Main, R.P., van der Meulen, M.C., 2014. Female mice lacking estrogen receptor-alpha in osteoblasts have compromised bone mass and strength. J. Bone Miner. Res. 29, 370e379. Miyauchi, Y., Sato, Y., Kobayashi, T., Yoshida, S., Mori, T., Kanagawa, H., Katsuyama, E., Fujie, A., Hao, W., Miyamoto, K., Tando, T., Morioka, H., Matsumoto, M., Chambon, P., Johnson, R.S., Kato, S., Toyama, Y., Miyamoto, T., 2013. HIF1alpha is required for osteoclast activation by estrogen deficiency in postmenopausal osteoporosis. Proc. Natl. Acad. Sci. U. S. A. 110, 16568e16573. Moenter, S.M., Brand, R.C., Karsch, F.J., 1992. Dynamics of gonadotropin-releasing hormone (GnRH) secretion during the GnRH surge: insights into the mechanism of GnRH surge induction. Endocrinology 130, 2978e2984. Monteleone, P., Luisi, S., Tonetti, A., Bernardi, F., Genazzani, A.D., Luisi, M., Petraglia, F., Genazzani, A.R., 2000. Allopregnanolone concentrations and premenstrual syndrome. Eur. J. Endocrinol. 142, 269e273. Moon, J.Y., Kim, K.J., Moon, M.H., Chung, B.C., Choi, M.H., 2011. A novel GC-MS method in urinary estrogen analysis from postmenopausal women with osteoporosis. J. Lipid Res. 52, 1595e1603. Mulac-Jericevic, B., Mullinax, R.A., Demayo, F.J., Lydon, J.P., Conneely, O.M., 2000. Subgroup of reproductive functions of progesterone mediated by progesterone receptor-B isoform. Science 289, 1751e1754. Naftolin, F., Garcia-Segura, L.M., Horvath, T.L., Zsarnovszky, A., Demir, N., Fadiel, A., Leranth, C., Vondracek-Klepper, S., Lewis, C., Chang, A., Parducz, A., 2007. Estrogen-induced hypothalamic synaptic plasticity and pituitary sensitization in the control of the estrogen-induced gonadotrophin surge. Reprod. Sci. 14, 101e116. Natraj, U., Richards, J.S., 1993. Hormonal regulation, localization, and functional activity of the progesterone receptor in granulosa cells of rat preovulatory follicles. Endocrinology 133, 761e769.

581

Nawata, H., Tanaka, S., Tanaka, S., Takayanagi, R., Sakai, Y., Yanase, T., Ikuyama, S., Haji, M., 1995. Aromatase in bone cell: association with osteoporosis in postmenopausal women. J. Steroid Biochem. Mol. Biol. 53, 165e174. Noyes, R.W., Hertig, A.T., Rock, J., 1975. Dating the endometrial biopsy. Am. J. Obstet. Gynecol. 122, 262e263. Nunez, A.M., Jakowlev, S., Briand, J.P., Gaire, M., Krust, A., Rio, M.C., Chambon, P., 1987. Characterization of the estrogen-induced pS2 protein secreted by the human breast cancer cell line MCF-7. Endocrinology 121, 1759e1765. Oonk, R.B., Krasnow, J.S., Beattie, W.G., Richards, J.S., 1989. Cyclic AMP-dependent and -independent regulation of cholesterol side chain cleavage cytochrome P-450 (P-450scc) in rat ovarian granulosa cells and corpora lutea. cDNA and deduced amino acid sequence of rat P-450scc. J. Biol. Chem. 264, 21934e21942. Orihuela, P.A., Croxatto, H.B., 2001. Acceleration of oviductal transport of oocytes induced by estradiol in cycling rats is mediated by nongenomic stimulation of protein phosphorylation in the oviduct. Biol. Reprod. 65, 1238e1245. Orihuela, P.A., Rios, M., Croxatto, H.B., 2001. Disparate effects of estradiol on egg transport and oviductal protein synthesis in mated and cyclic rats. Biol. Reprod. 65, 1232e1237. Otsuka, F., Yamamoto, S., Erickson, G.F., Shimasaki, S., 2001. Bone morphogenetic protein-15 inhibits follicle-stimulating hormone (FSH) action by suppressing FSH receptor expression. J. Biol. Chem. 276, 11387e11392. Otto, C., Fuchs, I., Kauselmann, G., Kern, H., Zevnik, B., Andreasen, P., Schwarz, G., Altmann, H., Klewer, M., Schoor, M., Vonk, R., Fritzemeier, K.H., 2009. GPR30 does not mediate estrogenic responses in reproductive organs in mice. Biol. Reprod. 80, 34e41. Pan, H., Deng, Y., Pollard, J.W., 2006. Progesterone blocks estrogeninduced DNA synthesis through the inhibition of replication licensing. Proc. Natl. Acad. Sci. U. S. A. 103, 14021e14026. Park-Sarge, O.K., Parmer, T.G., Gu, Y., Gibori, G., 1995. Does the rat corpus luteum express the progesterone receptor gene? Endocrinology 136, 1537e1543. Park, O.K., Mayo, K.E., 1991. Transient expression of progesterone receptor messenger RNA in ovarian granulosa cells after the preovulatory luteinizing hormone surge. Mol. Endocrinol. 5, 967e978. Pastor, C.L., Griffin-Korf, M.L., Aloi, J.A., Evans, W.S., Marshall, J.C., 1998. Polycystic ovary syndrome: evidence for reduced sensitivity of the gonadotropin-releasing hormone pulse generator to inhibition by estradiol and progesterone. J. Clin. Endocrinol. Metab. 83, 582e590. Peluso, J.J., 2013. Progesterone receptor membrane component 1 and its role in ovarian follicle growth. Front. Neurosci. 7, 99. Piekorz, R.P., Gingras, S., Hoffmeyer, A., Ihle, J.N., Weinstein, Y., 2005. Regulation of progesterone levels during pregnancy and parturition by signal transducer and activator of transcription 5 and 20alpha-hydroxysteroid dehydrogenase. Mol. Endocrinol. 19, 431e440. Prossnitz, E.R., Barton, M., 2011. The G-protein-coupled estrogen receptor GPER in health and disease. Nat. Rev. Endocrinol. 7, 715e726. Ravindranath, N., Little-Ihrig, L., Phillips, H.S., Ferrara, N., Zeleznik, A.J., 1992. Vascular endothelial growth factor messenger ribonucleic acid expression in the primate ovary. Endocrinology 131, 254e260. Richards, J.S., Russell, D.L., Ochsner, S., Hsieh, M., Doyle, K.H., Falender, A.E., Lo, Y.K., Sharma, S.C., 2002. Novel signaling pathways that control ovarian follicular development, ovulation, and luteinization. Recent Prog. Horm. Res. 57, 195e220. Robertshaw, I., Bian, F., Das, S.K., 2016. Mechanisms of uterine estrogen signaling during early pregnancy in mice: an update. J. Mol. Endocrinol. 56, R127eR138.

582

25. OVARIAN HORMONES

Romano, G.J., Krust, A., Pfaff, D.W., 1989. Expression and estrogen regulation of progesterone receptor mRNA in neurons of the mediobasal hypothalamus: an in situ hybridization study. Mol. Endocrinol. 3, 1295e1300. Rosenfeld, C.S., Wagner, J.S., Roberts, R.M., Lubahn, D.B., 2001. Intraovarian actions of oestrogen. Reproduction 122, 215e226. Russo, J., Ao, X., Grill, C., Russo, I.H., 1999. Pattern of distribution of cells positive for estrogen receptor alpha and progesterone receptor in relation to proliferating cells in the mammary gland. Breast Cancer Res. Treat. 53, 217e227. Sayeed, I., Stein, D.G., 2009. Progesterone as a neuroprotective factor in traumatic and ischemic brain injury. Prog. Brain Res. 175, 219e237. Schneider, M.A., Davies, M.C., Honour, J.W., 1993. The timing of placental competence in pregnancy after oocyte donation. Fertil. Steril. 59, 1059e1064. Schomberg, D.W., Couse, J.F., Mukherjee, A., Lubahn, D.B., Sar, M., Mayo, K.E., Korach, K.S., 1999. Targeted disruption of the estrogen receptor-alpha gene in female mice: characterization of ovarian responses and phenotype in the adult. Endocrinology 140, 2733e2744. Schultz, J.R., Petz, L.N., Nardulli, A.M., 2003. Estrogen receptor alpha and Sp1 regulate progesterone receptor gene expression. Mol. Cell. Endocrinol. 201, 165e175. Segawa, T., Teramoto, S., Omi, K., Miyauchi, O., Watanabe, Y., Osada, H., 2015. Changes in estrone and estradiol levels during follicle development: a retrospective large-scale study. Reprod. Biol. Endocrinol. 13, 54. Sehested, A., Juul, A.A., Andersson, A.M., Petersen, J.H., Jensen, T.K., Muller, J., Skakkebaek, N.E., 2000. Serum inhibin A and inhibin B in healthy prepubertal, pubertal, and adolescent girls and adult women: relation to age, stage of puberty, menstrual cycle, folliclestimulating hormone, luteinizing hormone, and estradiol levels. J. Clin. Endocrinol. Metab. 85, 1634e1640. Seminara, S.B., Messager, S., Chatzidaki, E.E., Thresher, R.R., Acierno Jr., J.S., Shagoury, J.K., BO-Abbas, Y., Kuohung, W., Schwinof, K.M., Hendrick, A.G., Zahn, D., Dixon, J., Kaiser, U.B., Slaugenhaupt, S.A., Gusella, J.F., O’rahilly, S., Carlton, M.B., Crowley Jr., W.F., Aparicio, S.A., Colledge, W.H., 2003. The GPR54 gene as a regulator of puberty. N. Engl. J. Med. 349, 1614e1627. Sharma, S.C., Clemens, J.W., Pisarska, M.D., Richards, J.S., 1999. Expression and function of estrogen receptor subtypes in granulosa cells: regulation by estradiol and forskolin. Endocrinology 140, 4320e4334. Shaw, N.D., Histed, S.N., Srouji, S.S., Yang, J., Lee, H., Hall, J.E., 2010. Estrogen negative feedback on gonadotropin secretion: evidence for a direct pituitary effect in women. J. Clin. Endocrinol. Metab. 95, 1955e1961. Shiina, H., Matsumoto, T., Sato, T., Igarashi, K., Miyamoto, J., Takemasa, S., Sakari, M., Takada, I., Nakamura, T., Metzger, D., Chambon, P., Kanno, J., Yoshikawa, H., Kato, S., 2006. Premature ovarian failure in androgen receptor-deficient mice. Proc. Natl. Acad. Sci. U. S. A. 103, 224e229. Shimada, M., Terada, T., 2002. FSH and LH induce progesterone production and progesterone receptor synthesis in cumulus cells: a requirement for meiotic resumption in porcine oocytes. Mol. Hum. Reprod. 8, 612e618. Simpson, E.R., 2004. Models of aromatase insufficiency. Semin. Reprod. Med. 22, 25e30. Skorupskaite, K., George, J.T., Anderson, R.A., 2014. The kisspeptinGnRH pathway in human reproductive health and disease. Hum. Reprod. Update 20, 485e500. Spicer, L.J., Aad, P.Y., Allen, D., Mazerbourg, S., Hsueh, A.J., 2006. Growth differentiation factor-9 has divergent effects on proliferation and steroidogenesis of bovine granulosa cells. J. Endocrinol. 189, 329e339.

Steinkampf, M.P., Mendelson, C.R., Simpson, E.R., 1988. Effects of epidermal growth factor and insulin-like growth factor I on the levels of mRNA encoding aromatase cytochrome P-450 of human ovarian granulosa cells. Mol. Cell. Endocrinol. 59, 93e99. Stocco, C., 2008. Aromatase expression in the ovary: hormonal and molecular regulation. Steroids 73, 473e487. Stocco, C., Telleria, C., Gibori, G., 2007. The molecular control of corpus luteum formation, function, and regression. Endocr. Rev. 28, 117e149. Stouffer, R.L., 2003. Progesterone as a mediator of gonadotrophin action in the corpus luteum: beyond steroidogenesis. Hum. Reprod. Update 9, 99e117. Streicher, C., Heyny, A., Andrukhova, O., Haigl, B., Slavic, S., Schuler, C., Kollmann, K., Kantner, I., Sexl, V., Kleiter, M., Hofbauer, L.C., Kostenuik, P.J., Erben, R.G., 2017. Estrogen regulates bone turnover by targeting RANKL expression in bone lining cells. Sci. Rep. 7, 6460. Syan, S.K., Minuzzi, L., Costescu, D., Smith, M., Allega, O.R., Coote, M., Hall, G.B.C., Frey, B.N., 2017. Influence of endogenous estradiol, progesterone, allopregnanolone, and dehydroepiandrosterone sulfate on brain resting state functional connectivity across the menstrual cycle. Fertil. Steril. 107, 1246e1255 e4. Tetsuka, M., Hillier, S.G., 1996. Androgen receptor gene expression in rat granulosa cells: the role of follicle-stimulating hormone and steroid hormones. Endocrinology 137, 4392e4397. Tetsuka, M., Hillier, S.G., 1997. Differential regulation of aromatase and androgen receptor in granulosa cells. J. Steroid Biochem. Mol. Biol. 61, 233e239. Torres-Reveron, A., Khalid, S., Williams, T.J., Waters, E.M., Jacome, L., Luine, V.N., Drake, C.T., Mcewen, B.S., Milner, T.A., 2009. Hippocampal dynorphin immunoreactivity increases in response to gonadal steroids and is positioned for direct modulation by ovarian steroid receptors. Neuroscience 159, 204e216. Turgeon, J.L., Mcdonnell, D.P., Martin, K.A., Wise, P.M., 2004. Hormone therapy: physiological complexity belies therapeutic simplicity. Science 304, 1269e1273. Turner, K.J., Macpherson, S., Millar, M.R., Mcneilly, A.S., Williams, K., Cranfield, M., Groome, N.P., Sharpe, R.M., Fraser, H.M., Saunders, P.T., 2002. Development and validation of a new monoclonal antibody to mammalian aromatase. J. Endocrinol. 172, 21e30. Ushijima, K., Yahata, H., Yoshikawa, H., Konishi, I., Yasugi, T., Saito, T., Nakanishi, T., Sasaki, H., Saji, F., Iwasaka, T., Hatae, M., Kodama, S., Saito, T., Terakawa, N., Yaegashi, N., Hiura, M., Sakamoto, A., Tsuda, H., Fukunaga, M., Kamura, T., 2007. Multicenter phase II study of fertility-sparing treatment with medroxyprogesterone acetate for endometrial carcinoma and atypical hyperplasia in young women. J. Clin. Oncol. 25, 2798e2803. Vitt, U.A., Hayashi, M., Klein, C., Hsueh, A.J., 2000. Growth differentiation factor-9 stimulates proliferation but suppresses the folliclestimulating hormone-induced differentiation of cultured granulosa cells from small antral and preovulatory rat follicles. Biol. Reprod. 62, 370e377. Wang, H., Eriksson, H., Sahlin, L., 2000. Estrogen receptors alpha and beta in the female reproductive tract of the rat during the estrous cycle. Biol. Reprod. 63, 1331e1340. Wang, J.M., Irwin, R.W., Liu, L., Chen, S., Brinton, R.D., 2007a. Regeneration in a degenerating brain: potential of allopregnanolone as a neuroregenerative agent. Curr. Alzheimer Res. 4, 510e517. Wang, Y., Feng, H., Bi, C., Zhu, L., Pollard, J.W., Chen, B., 2007b. GSK3beta mediates in the progesterone inhibition of estrogen induced cyclin D2 nuclear localization and cell proliferation in cyclin D1-/- mouse uterine epithelium. FEBS Lett. 581, 3069e3075. Wanggren, K., Stavreus-Evers, A., Olsson, C., Andersson, E., GemzellDanielsson, K., 2008. Regulation of muscular contractions in the human Fallopian tube through prostaglandins and progestagens. Hum. Reprod. 23, 2359e2368.

REFERENCES

Weck, J., Mayo, K.E., 2006. Switching of NR5A proteins associated with the inhibin alpha-subunit gene promoter after activation of the gene in granulosa cells. Mol. Endocrinol. 20, 1090e1103. Wehling, M., 1995. Looking beyond the dogma of genomic steroid action: insights and facts of the 1990s. J. Mol. Med. (Berl.) 73, 439e447. Winuthayanon, W., Bernhardt, M.L., Padilla-Banks, E., Myers, P.H., Edin, M.L., Lih, F.B., Hewitt, S.C., Korach, K.S., Williams, C.J., 2015. Oviductal estrogen receptor alpha signaling prevents protease-mediated embryo death. Elife 4, e10453. Winuthayanon, W., Hewitt, S.C., Orvis, G.D., Behringer, R.R., Korach, K.S., 2010. Uterine epithelial estrogen receptor alpha is dispensable for proliferation but essential for complete biological and biochemical responses. Proc. Natl. Acad. Sci. U. S. A. 107, 19272e19277. Wood, J.R., Likhite, V.S., Loven, M.A., Nardulli, A.M., 2001. Allosteric modulation of estrogen receptor conformation by different estrogen response elements. Mol. Endocrinol. 15, 1114e1126. Wright, L.E., Guise, T.A., 2014. The microenvironment matters: estrogen deficiency fuels cancer bone metastases. Clin. Cancer Res. 20, 2817e2819. Wu, Y.G., Bennett, J., Talla, D., Stocco, C., 2011. Testosterone, not 5alpha-dihydrotestosterone, stimulates LRH-1 leading to FSHindependent expression of Cyp19 and P450scc in granulosa cells. Mol. Endocrinol. 25, 656e668.

583

Xu, J., Stouffer, R.L., Searles, R.P., Hennebold, J.D., 2005. Discovery of LH-regulated genes in the primate corpus luteum. Mol. Hum. Reprod. 11, 151e159. Yang, X.P., Reckelhoff, J.F., 2011. Estrogen, hormonal replacement therapy and cardiovascular disease. Curr. Opin. Nephrol. Hypertens. 20, 133e138. Young, J.R., Jaffe, R.B., 1976. Strength-duration characteristics of estrogen effects on gonadotropin response to gonadotropin-releasing hormone in women. II. Effects of varying concentrations of estradiol. J. Clin. Endocrinol. Metab. 42, 432e442. Young, K.A., Stouffer, R.L., 2004. Gonadotropin and steroid regulation of matrix metalloproteinases and their endogenous tissue inhibitors in the developed corpus luteum of the rhesus monkey during the menstrual cycle. Biol. Reprod. 70, 244e252. Zeleznik, A.J., 1998. In vivo responses of the primate corpus luteum to luteinizing hormone and chorionic gonadotropin. Proc. Natl. Acad. Sci. U. S. A. 95, 11002e11007. Zhou, J., Kumar, T.R., Matzuk, M.M., Bondy, C., 1997. Insulin-like growth factor I regulates gonadotropin responsiveness in the murine ovary. Mol. Endocrinol. 11, 1924e1933. Zhu, L., Pollard, J.W., 2007. Estradiol-17beta regulates mouse uterine epithelial cell proliferation through insulin-like growth factor 1 signaling. Proc. Natl. Acad. Sci. U. S. A. 104, 15847e15851.