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Importance of angiogenesis in reproductive physiology
Importance of Angiogenesis in Reproductive Physiology Robert B. Jaffe
The cyclic angiogenesis that occurs uniquely within the female reproductive tract is critical for normal reproduction. Two families of endothelial cell-specific growth factors and their receptors have been identified in the ovary, uterus, and placenta: vascular endothelial growth factor/vascular permeability factor and the angiopoietins. These appear to have complementary actions on the vasculature and to be involved during intrauterine development as well as in the adult. Within the ovary, a complex cascade of events required for angiogenesis may play a role in follicular maturation and selection as well as in normal corpus luteum function. Aberrant expression of angiogenlc factors plays a role in a wide variety of abnormalities in the ovary. In the uterus, angiogenesis is required for endometrial growth and remodeling. Peptide growth factors such as vascular endothelial growth factor may serve as local mediators of the effects of reproductive hormones on the endometrial vasculamre. Disease states such as dysfunctional uterine bleeding, endometriosis, and endometrial hyperplasia or cancer may be associated with aberrant uterine angiogenesis. Copyright 9 2000 by W.B. Saunders
Company
xcept for wound healing, in the normal
E adult human significant alteration of the
vasculature occurs uniquely in women, specifically in the ovary and uterus, as well as in the placenta during p r e g n a n c y / T h e cyclic development of a new vasculature, cyclic angiogenesis, plays a pivotal role in normal reproductive processes. There is a tightly regulated angiogenic cascade, which involves endothelial cell proliferation, basement membrane and extracellular matrix remodeling, organization of vascular endothelial cells into tubular structures, and initiation of blood flow into newly formed capillary sprouts. A variety of peptides can induce angiogenesis, including basic fibroblast growth factor, transforming growth factor beta, platelet-derived endothelial cell growth factor, and 2 vascular-endothelial cell-specific families of peptides: vascular endothelial growth factor (VEGF) also known as vascular permeability factor (VPF),2 and the more recently described angiopoietins (angiopoietin-1 and angiopoietin-2). The VEGF and angiopoietin families and their receptors have been identified in the ovary, uterus, and placenta. They appear to have complementary actions on the vasculature and appear to be involved in early embryonic and fetal development3-5 as well as in the adult. In this article, the author focuses on processes of angiogenesis in the ovary and uterus in normal and pathophysiologic states.
Ovary Physiology The precise control of angiogenesis in the developing ovarian follicle and corpus luteum (CL) is critical for normal reproductive function. During follicular growth, the dominant follicle develops a complex vascular network within the thecat cell layer. At ovulation, the basement membrane separating the thecal and granulosa cell layers degenerates and a dramatic increase in angiogenesis occurs centripetally from the theca toward the center of the ruptured follicle. In vivo and in vitro studies suggest that the thecal cell layer and luteinized granulosa cell layer are the predominant sites of angiogenic activity within the follicle. This differential localization of angiogenic activity is consistent with the vascular architecture of the ovary as the thecal cell layer is richly vascularized, in contrast to the relatively avascular-preluteinized granulosa cell layer. Similarly, explants from the CL of several From the Department of Obstetrics, Gynecology and Reproductive Sciences, Centerfor ~'oductive Sciences, University of California, San Francisco, CA. Address reprint requests to Robert B. Jaffe, MD, Centerfor Reproductive Sciences, University of California, San Francisco, 505 Parnassus Ave, HSW 1656, San Francisco, CA 94143-0556; e-mail: jaffer@obgyn,ucsf edu Copyright 9 2000 by W.B. Saunders Company 0146-0005/00/2401-0019510. 00/0
Seminars in Perinatology, Vol 24, No 1 (February), 2000: pp 79-81
79
80
Robert B. Jaffe
species induce angiogenesis in a variety of bioassays, indicating that the CL is also a site of angiogenic activity, and the necessity for VEGF in CL angiogenesis has been shown. 6 Two families of vascular endothelial cell-specific peptides, VEGF and angiopoietins (Angl and Ang2), appear to play key roles in ovarian angiogenesis. Hypoxia upregulates VEGF/VPF expression and Ang2 but not Angl facets of the transcriptional regulation of both the VEGF/ VPF and angiopoietin families currently are being explored. In localization studies that use immunocytochemistry in the human ovary, intense immunostaining for VEGF was detected in the thecal cell layer with minimal staining in the granulosa cell layer in healthy follicles. After the mid-cycle surge of gonadotropins and ovulation, strong and specific VEGF immunostaining was detected within the highly vascularized CL. 7 Staining for VEGF also was detected within the myocytes of tile ovarian hilar vessels, but was absent from atretic follicles and from an isolated degenerating CL. Although there have not been extensive studies of angiopoietin localization and function in the h u m a n ovary, studies of Angl, which is widely and abundantly expressed in many adult h u m a n tissues, also have shown its presence in the ovary (but not the heart and liver).8 In contrast, Ang2 expression only is readily detected in ovary, uterus, and placenta; the 3 major sites of vascular remodeling in the adult. In the rat ovary, VEGF mRNA is abundant within the center of the developing CL, including regions where vessels have not yet formed. In contrast, Angl transcripts are associated with blood vessels and appear to follow or coincide with, rather than precede, vessel ingrowth into the early CL, which is consistent with the hypothesis that Angl has a later role in angiogenesis than VEGF, perhaps involving vessel maturation a n d / o r stabilization, s Ang2, which binds to the same receptor (Tie2) as Angl, appears to be a natural antagonist for Tie2 that disrupts angiogenesis. The pattern of Ang2 expression, in contrast to Angl, suggests that Ang2 plays an early role at the sites of vessel invasion. Initially, Ang2 transcripts are clustered in close association with blood vessels in the theca interna of the late preovulatory follicle and then are abundant at the front of vessels invading the developing CL. These observations suggest that Ang2 works in a
coordinated fashion with VEGF at the front of vascular sprouts by blocking a constitutive or stabilizing function of Angl, permitting vessels to be in a plastic state in which they may be m o r e responsive to a sprouting signal provided by VEGF. s In atretic follicles, VEGF is not detectable, whereas Ang2 mRNA is present in large amounts within the granulosum. Aged CLs, in which vessels degenerate, also have small amounts of VEGF mRNA but large amounts of Ang2 mRNA. Thus, it is conceivable that, in the presence of a b u n d a n t VEGF, Ang2 can p r o m o t e vessel sprouting by blocking the stabilizing influence of the Angl signal. Although in the absence of VEGF, Ang2 inhibition of the Angl signal could contribute to vessel regression, s Thus, Ang2 could be participating in both follicular atresia and CL regression.
Pathophysiology VEGF also is a VPF. VEGF/VPF has b e e n strongly linked to the ovarian hyperstimulation syndrome in women who undergo ovulation induction. 9 Ovarian cancer frequently is associated with massive ascites. Most neoplasms require the development o f a new vasculature to grow beyond 2 to 3 ram. VEGF/VPF can cause ovarian cancer growth and ascites formation, and ascites formation can be inhibited by immunoneutralization of VEGF/VPF in an athymic mouse model of h u m a n ovarian cancer with ascites. 1~
Uterus Physiology As in the ovary, the h u m a n e n d o m e t r i u m undergoes a complex process of vascular and glandular proliferation, differentiation, and regeneration with each menstrual cycle in preparation for implantation. In h u m a n endometrium, VEGF mRNA increases relative to early proliferative phase expression by 1.6-, 2-, and 3.6-fold in mid-proliferative, late proliferative, and secretory e n d o m e t r i u m , respectively. 11 In histological sections, VEGF mRNA and protein are localized focally in glandular epithelial ceils and m o r e diffusely in surrounding stroma, with greatest VEGF expression in secretory endometrium. Consistent with these in vivo results, treatment of isolated h u m a n endometrial cells with estra-
Angiogenesis in Reproductive Medicine and Biology
diol ( E 2 ) , m e d r o x y p r o g e s t e r o n e acetate (MPA), or E2+MPA significantly increased VEGF m R N A expression over control by 3.1-, 2.8-, and 4.7fold, respectively. T h e VEGF response t o E 2 was rapid, with steady-state levels of VEGF m R N A reaching 85% m a x i m u m 1 h o u r after the addition o f steroid. Estradiol also caused a 46% increase in secreted VEGF protein and the combination o f E 2 + MPA an 18% increase. Pathophysiology VEGF expression in endometriosis, an angiogenesis-dependent, estrogen-sensitive disease is similar to that seen in eutopic endometrium, n Peritoneal fluid concentrations of VEGF are significantly higher in w o m e n with moderate to severe endometriosis compared with w o m e n with minimal to mild endometriosis or no disease. Therefore, VEGF may be important in both physiological and pathological angiogenesis of human endometrium as it is an estrogen responsive angiogenic factor that varies throughout the menstrual cycle and is elevated in w o m e n with endometriosis. In addition, aberrant angiogenesis likely plays a role in dysfunctional uterine bleeding, often associated with anovulation and altered sex steroid levels and, as with carcinoma of the ovary and many other neoplasms, in the growth and metastasis of endometrial carcinoma.
References 1. Gordon JD, ShifrenJL, Foulk RA, et al: Angiogenesis in the h u m a n female reproductive tract. Obstet Gynecol Surv 50:688-697, 1995
81
2. Ferrara N, Jakeman L, Houck K, et al: Molecular and biological properties of the vascular endothelial growth factor family of proteins. Endocr Rev 13:18-32, 1992 3. Suri C, Jones PF, Patan S, et al: Requisite role of angiopoietin-1, a ligand for the Tie2 receptor, during embryonic angiogenesis. Cell 87:1171-1180, 1996 4. ShifrenjL, Doldi N, Ferrara N, et al: In the h u m a n fetus, vascular endothelial growth factor is expressed in epithelial cells and myocytes, but not vascular endothelium: implications for mode of action. J Clin Endocrinol Metab 79:316-322, 1994 5. Shifren J, Mesiano S, Lee JY, et al: Adrenocorticotropic hormone increases vascular endothelial growth factor in the human fetal adrenal. J Clin Endocrinol Metab 83: 1342-1347, 1998 6. Ferrara N, Chen H, Davis-Smyth T, et al: Vascular endothelial growth factor is essential for corpus luteum angiogenesis. Nat Med 4:336-340, 1998 7. Gordon JD, Mesiano S, Zaloudek cJ, et al: Vascular endothelial growth factor localization in h u m a n ovary and fallopian tubes: Possible role in reproductive function and ovarian cyst formation.J Clin Endocrinol Metab 81:353-359, 1996 8. Maisonpierre PC, Suri C,Jones PF, et al: Angiopoietim2, a natural antagonist for Tie2 that disrupts in vivo angiogenesis. Science 277:55-60, 1997 9. Levin ER, Rosen GF, Cassidenti DL, et al: Role of vascular endothelial cell growth factor in ovarian hyperstimulation syndrome. J Clin Invest 102:1978-1985, 1998 10. Mesiano S, Ferrara N, Jaffe RB: Role of vascular endothelial growth factor in ovarian cancer: Inhibition of ascites formation by immunoneutralization. Am J Pathol 153:1249-1255, 1999 11. Shifi'en JL, TsengJF, Zaloudek cJ, et al: Ovarian steroid regulation of vascular endothelial growth factor in the human endometrium: Implications for angiogenesis during the menstrual cycle and in the pathogenesis of endometriosis. J Clin Endocrinol Metab 81:3112-3118, 1996
The cyclic angiogenesis that occurs uniquely within the female reproductive tract is critical for normal reproduction. Two families of endothelial cell-specific growth factors and their receptors have been identified in the ovary, uterus, and placenta: vascular endothelial growth factor/vascular permeability factor and the angiopoietins. These appear to have complementary actions on the vasculature and to be involved during intrauterine development as well as in the adult. Within the ovary, a complex cascade of events required for angiogenesis may play a role in follicular maturation and selection as well as in normal corpus luteum function. Aberrant expression of angiogenlc factors plays a role in a wide variety of abnormalities in the ovary. In the uterus, angiogenesis is required for endometrial growth and remodeling. Peptide growth factors such as vascular endothelial growth factor may serve as local mediators of the effects of reproductive hormones on the endometrial vasculamre. Disease states such as dysfunctional uterine bleeding, endometriosis, and endometrial hyperplasia or cancer may be associated with aberrant uterine angiogenesis. Copyright 9 2000 by W.B. Saunders
Company
xcept for wound healing, in the normal
E adult human significant alteration of the
vasculature occurs uniquely in women, specifically in the ovary and uterus, as well as in the placenta during p r e g n a n c y / T h e cyclic development of a new vasculature, cyclic angiogenesis, plays a pivotal role in normal reproductive processes. There is a tightly regulated angiogenic cascade, which involves endothelial cell proliferation, basement membrane and extracellular matrix remodeling, organization of vascular endothelial cells into tubular structures, and initiation of blood flow into newly formed capillary sprouts. A variety of peptides can induce angiogenesis, including basic fibroblast growth factor, transforming growth factor beta, platelet-derived endothelial cell growth factor, and 2 vascular-endothelial cell-specific families of peptides: vascular endothelial growth factor (VEGF) also known as vascular permeability factor (VPF),2 and the more recently described angiopoietins (angiopoietin-1 and angiopoietin-2). The VEGF and angiopoietin families and their receptors have been identified in the ovary, uterus, and placenta. They appear to have complementary actions on the vasculature and appear to be involved in early embryonic and fetal development3-5 as well as in the adult. In this article, the author focuses on processes of angiogenesis in the ovary and uterus in normal and pathophysiologic states.
Ovary Physiology The precise control of angiogenesis in the developing ovarian follicle and corpus luteum (CL) is critical for normal reproductive function. During follicular growth, the dominant follicle develops a complex vascular network within the thecat cell layer. At ovulation, the basement membrane separating the thecal and granulosa cell layers degenerates and a dramatic increase in angiogenesis occurs centripetally from the theca toward the center of the ruptured follicle. In vivo and in vitro studies suggest that the thecal cell layer and luteinized granulosa cell layer are the predominant sites of angiogenic activity within the follicle. This differential localization of angiogenic activity is consistent with the vascular architecture of the ovary as the thecal cell layer is richly vascularized, in contrast to the relatively avascular-preluteinized granulosa cell layer. Similarly, explants from the CL of several From the Department of Obstetrics, Gynecology and Reproductive Sciences, Centerfor ~'oductive Sciences, University of California, San Francisco, CA. Address reprint requests to Robert B. Jaffe, MD, Centerfor Reproductive Sciences, University of California, San Francisco, 505 Parnassus Ave, HSW 1656, San Francisco, CA 94143-0556; e-mail: jaffer@obgyn,ucsf edu Copyright 9 2000 by W.B. Saunders Company 0146-0005/00/2401-0019510. 00/0
Seminars in Perinatology, Vol 24, No 1 (February), 2000: pp 79-81
79
80
Robert B. Jaffe
species induce angiogenesis in a variety of bioassays, indicating that the CL is also a site of angiogenic activity, and the necessity for VEGF in CL angiogenesis has been shown. 6 Two families of vascular endothelial cell-specific peptides, VEGF and angiopoietins (Angl and Ang2), appear to play key roles in ovarian angiogenesis. Hypoxia upregulates VEGF/VPF expression and Ang2 but not Angl facets of the transcriptional regulation of both the VEGF/ VPF and angiopoietin families currently are being explored. In localization studies that use immunocytochemistry in the human ovary, intense immunostaining for VEGF was detected in the thecal cell layer with minimal staining in the granulosa cell layer in healthy follicles. After the mid-cycle surge of gonadotropins and ovulation, strong and specific VEGF immunostaining was detected within the highly vascularized CL. 7 Staining for VEGF also was detected within the myocytes of tile ovarian hilar vessels, but was absent from atretic follicles and from an isolated degenerating CL. Although there have not been extensive studies of angiopoietin localization and function in the h u m a n ovary, studies of Angl, which is widely and abundantly expressed in many adult h u m a n tissues, also have shown its presence in the ovary (but not the heart and liver).8 In contrast, Ang2 expression only is readily detected in ovary, uterus, and placenta; the 3 major sites of vascular remodeling in the adult. In the rat ovary, VEGF mRNA is abundant within the center of the developing CL, including regions where vessels have not yet formed. In contrast, Angl transcripts are associated with blood vessels and appear to follow or coincide with, rather than precede, vessel ingrowth into the early CL, which is consistent with the hypothesis that Angl has a later role in angiogenesis than VEGF, perhaps involving vessel maturation a n d / o r stabilization, s Ang2, which binds to the same receptor (Tie2) as Angl, appears to be a natural antagonist for Tie2 that disrupts angiogenesis. The pattern of Ang2 expression, in contrast to Angl, suggests that Ang2 plays an early role at the sites of vessel invasion. Initially, Ang2 transcripts are clustered in close association with blood vessels in the theca interna of the late preovulatory follicle and then are abundant at the front of vessels invading the developing CL. These observations suggest that Ang2 works in a
coordinated fashion with VEGF at the front of vascular sprouts by blocking a constitutive or stabilizing function of Angl, permitting vessels to be in a plastic state in which they may be m o r e responsive to a sprouting signal provided by VEGF. s In atretic follicles, VEGF is not detectable, whereas Ang2 mRNA is present in large amounts within the granulosum. Aged CLs, in which vessels degenerate, also have small amounts of VEGF mRNA but large amounts of Ang2 mRNA. Thus, it is conceivable that, in the presence of a b u n d a n t VEGF, Ang2 can p r o m o t e vessel sprouting by blocking the stabilizing influence of the Angl signal. Although in the absence of VEGF, Ang2 inhibition of the Angl signal could contribute to vessel regression, s Thus, Ang2 could be participating in both follicular atresia and CL regression.
Pathophysiology VEGF also is a VPF. VEGF/VPF has b e e n strongly linked to the ovarian hyperstimulation syndrome in women who undergo ovulation induction. 9 Ovarian cancer frequently is associated with massive ascites. Most neoplasms require the development o f a new vasculature to grow beyond 2 to 3 ram. VEGF/VPF can cause ovarian cancer growth and ascites formation, and ascites formation can be inhibited by immunoneutralization of VEGF/VPF in an athymic mouse model of h u m a n ovarian cancer with ascites. 1~
Uterus Physiology As in the ovary, the h u m a n e n d o m e t r i u m undergoes a complex process of vascular and glandular proliferation, differentiation, and regeneration with each menstrual cycle in preparation for implantation. In h u m a n endometrium, VEGF mRNA increases relative to early proliferative phase expression by 1.6-, 2-, and 3.6-fold in mid-proliferative, late proliferative, and secretory e n d o m e t r i u m , respectively. 11 In histological sections, VEGF mRNA and protein are localized focally in glandular epithelial ceils and m o r e diffusely in surrounding stroma, with greatest VEGF expression in secretory endometrium. Consistent with these in vivo results, treatment of isolated h u m a n endometrial cells with estra-
Angiogenesis in Reproductive Medicine and Biology
diol ( E 2 ) , m e d r o x y p r o g e s t e r o n e acetate (MPA), or E2+MPA significantly increased VEGF m R N A expression over control by 3.1-, 2.8-, and 4.7fold, respectively. T h e VEGF response t o E 2 was rapid, with steady-state levels of VEGF m R N A reaching 85% m a x i m u m 1 h o u r after the addition o f steroid. Estradiol also caused a 46% increase in secreted VEGF protein and the combination o f E 2 + MPA an 18% increase. Pathophysiology VEGF expression in endometriosis, an angiogenesis-dependent, estrogen-sensitive disease is similar to that seen in eutopic endometrium, n Peritoneal fluid concentrations of VEGF are significantly higher in w o m e n with moderate to severe endometriosis compared with w o m e n with minimal to mild endometriosis or no disease. Therefore, VEGF may be important in both physiological and pathological angiogenesis of human endometrium as it is an estrogen responsive angiogenic factor that varies throughout the menstrual cycle and is elevated in w o m e n with endometriosis. In addition, aberrant angiogenesis likely plays a role in dysfunctional uterine bleeding, often associated with anovulation and altered sex steroid levels and, as with carcinoma of the ovary and many other neoplasms, in the growth and metastasis of endometrial carcinoma.
References 1. Gordon JD, ShifrenJL, Foulk RA, et al: Angiogenesis in the h u m a n female reproductive tract. Obstet Gynecol Surv 50:688-697, 1995
81
2. Ferrara N, Jakeman L, Houck K, et al: Molecular and biological properties of the vascular endothelial growth factor family of proteins. Endocr Rev 13:18-32, 1992 3. Suri C, Jones PF, Patan S, et al: Requisite role of angiopoietin-1, a ligand for the Tie2 receptor, during embryonic angiogenesis. Cell 87:1171-1180, 1996 4. ShifrenjL, Doldi N, Ferrara N, et al: In the h u m a n fetus, vascular endothelial growth factor is expressed in epithelial cells and myocytes, but not vascular endothelium: implications for mode of action. J Clin Endocrinol Metab 79:316-322, 1994 5. Shifren J, Mesiano S, Lee JY, et al: Adrenocorticotropic hormone increases vascular endothelial growth factor in the human fetal adrenal. J Clin Endocrinol Metab 83: 1342-1347, 1998 6. Ferrara N, Chen H, Davis-Smyth T, et al: Vascular endothelial growth factor is essential for corpus luteum angiogenesis. Nat Med 4:336-340, 1998 7. Gordon JD, Mesiano S, Zaloudek cJ, et al: Vascular endothelial growth factor localization in h u m a n ovary and fallopian tubes: Possible role in reproductive function and ovarian cyst formation.J Clin Endocrinol Metab 81:353-359, 1996 8. Maisonpierre PC, Suri C,Jones PF, et al: Angiopoietim2, a natural antagonist for Tie2 that disrupts in vivo angiogenesis. Science 277:55-60, 1997 9. Levin ER, Rosen GF, Cassidenti DL, et al: Role of vascular endothelial cell growth factor in ovarian hyperstimulation syndrome. J Clin Invest 102:1978-1985, 1998 10. Mesiano S, Ferrara N, Jaffe RB: Role of vascular endothelial growth factor in ovarian cancer: Inhibition of ascites formation by immunoneutralization. Am J Pathol 153:1249-1255, 1999 11. Shifi'en JL, TsengJF, Zaloudek cJ, et al: Ovarian steroid regulation of vascular endothelial growth factor in the human endometrium: Implications for angiogenesis during the menstrual cycle and in the pathogenesis of endometriosis. J Clin Endocrinol Metab 81:3112-3118, 1996