Why do women get lupus?

Clinical Immunology (2012) 144, 53–56

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Clinical Immunology www.elsevier.com/locate/yclim

EDITORIAL

Why do women get lupus? Systemic lupus erythematosus (SLE) is a chronic autoimmune disease which affects predominantly women, causing significant morbidity and mortality. A multi-system disease, SLE is characterized by the production and deposition of autoantibodies, and inflammatory cell infiltration leading to damage of target organs such as the skin, kidneys and brain. Both innate and adaptive arms of the immune system are dysregulated and contribute to disease pathogenesis. Nine out of ten patients afflicted with SLE are women, thus gender plays an important role in disease development. The gender bias in SLE reflects the role of sex chromosomes as well as sex hormones. The importance of the X chromosome was shown in a pristane-induced model of lupus — the XX sex chromosome complement conferred increased susceptibility to disease over the XY − mice [1]. The preponderance of disease is seen in the reproductive years such that before puberty, the female to male prevalence is 3:1 — which increases to 9:1 after the onset of puberty, strongly suggesting the role of hormones in disease pathogenesis. Numerous studies have implicated hormones especially estrogen in lupus pathogenesis. While estrogen levels per se are not found to be altered in the serum from lupus patients, the metabolism of this hormone is abnormally high in patients. There is increased oxidation of dehydroepiandrosterone (DHEA) to 16-hydroxyestrone and estriol resulting in increased levels of these metabolites in patients with SLE. Lower levels of androgens specifically DHEA are found in lupus patients [2]. Early studies in animal models of lupus (both NZB/NZW and MRL/lpr) have shown that lupusprone female mice succumbed to disease sooner than male mice. Studies from castrated mice both male and female have shown the important role of hormones in disease pathogenesis. Oopherectomized female mice have prolonged survival whereas castrated male mice that lost their androgen source die earlier. When either female or male castrated mice were given androgen supplements, disease improved; whereas estrogen administration worsened disease [2,3]. SLE is characterized by a Th2 cytokine environment, and high doses of estrogen are shown to promote a Th2 cytokine (IL4, IL5, IL6, IL10, TGFβ) profile. On the other hand, studies allude to the suppression of the Th1 (IL2, TNFα, IFNγ) cytokines by estrogen [4,5]. Mice treated with synthetic estrogen were susceptible to Listeria monocytogenes infection and their 1521-6616/$ - see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.clim.2012.04.003

splenocytes produced less IL-2 [6]. Estrogen increases IL-17 production in splenocytes from estrogen treated mice [7]. These reports clearly indicate that hormones and especially estrogen are important players in the expression of the disease; yet we know very little about their molecular role and mechanism of action. Studies from the Diamond lab have provided some of the first direct molecular evidence into the role of estrogen in autoimmunity. They showed in nonautoimmune mice (transgenic for the heavy chain of a pathogenic anti-DNA antibody), that estrogen administration upregulates expression of the Bcl-2 anti-apoptotic molecule and promotes survival of autoreactive B cells, allowing their escape from tolerance induction [8]. Estrogen was also shown to suppress activation induced cell death of SLE T cells by downregulating FasL suggesting that it may allow persistence of autoreactive T cells [9]. Studies by Rider et al. showed in human peripheral blood T cells, that estrogen increases the expression of calcineurin mRNA and PP2B phosphatase activity in an estrogen receptor dependent manner [10]. They also showed that estrogen increases the expression of CD40L in T cells from lupus patients but not healthy individuals [11]. We recently showed the molecular effects of estrogen on gene regulation and cytokine suppression. Exposure of human T cells to estradiol led to estrogen receptor (ER)dependent increase in the cyclic AMP response element modulator (CREM) alpha, a transcriptional repressor, and suppression of interleukin-2 (IL-2) production. Interestingly, there was a trend towards greater increase in CREMα expression in T cells from peripheral blood collected in the ovulatory phase of the menstrual cycle, when estrogen levels are the highest. This may allude to a higher sensitivity of the T cells to the estrogen possibly through higher ER expression in this phase, especially since estrogen is known to enhance receptor expression [12]. While estrogen is clearly important, it is by no means the only determinant in the hormone component of disease pathophysiology. For example, pregnancy is characterized by a steady rise in serum hormone levels, and pregnancy in SLE is associated with increased disease activity and flares, however it is not clear if the rising levels of hormones play a role because these hormones were found to be at lower

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EDITORIAL

levels in pregnant women with SLE as compared to healthy pregnant women [13]. The role of estrogen receptors (ERs) and their potentially critical contributions in disease are emerging. ERs alpha (α) and beta (β) are intracellular receptors expressed in most immune cells including T cells, B cells, monocytes and dendritic cells. Estradiol diffuses through the cell membrane and binds to the ERs (Fig. 1). Upon ligand binding, the ERs homo- or hetero-dimerize, then bind consensus estrogen response element (ERE) sites within target genes and act as transcription factors to regulate gene expression. Several studies have highlighted the role of the ERs in lupus [14]. In murine lupus studies, the ERα appears to be critical in disease pathogenesis; deficiency of ERα alone led to autoantibody production [15]; and reduced renal disease and prolonged survival in lupus prone mice [16]. Using estrogen receptors α and β deficient animals it was shown that while both receptors regulate B cell maturation, ERα engagement is responsible for the estrogen induced dampening of the BCR signaling and B-cell selection and thus an important trigger for autoimmunity [17]. Other modes of action of the ER include a transcriptional co-activator role whereby the ER does not directly bind DNA, but complexes with transcription factors such as Specific protein 1 (Sp1), Activator protein (AP)-1 or nuclear factor kappa-light-chain enhancer of activated B cells (NFkB) in gene regulation [18]. Besides these traditional roles, other mechanisms include membrane bound G protein coupled receptors (GPR30) and also cytoplasmic receptors which are involved in certain kinase signaling pathways. Interestingly, the ER can

Figure 1

also act in gene regulation in a ligand independent manner — for example, extracellular stimuli such as insulin, IGF1, EGF and TGFβ can lead to ER phosphorylation by MAP kinases and result in gene transactivation [19,20]. Dendritic cells (DCs) express Toll like receptors (TLRs) abundantly and are at the forefront of the innate immune response. DCs are abnormal in SLE in both patients and in lupus-prone mice such that they exhibit increased amounts of major histocompatibility complexes (MHC) as well as costimulatory molecules CD80/86 [21]. TLRs are shown to be important in lupus pathogenesis such that TLR7 and TLR9 deficient lupus prone mice have reduced disease [22]. Estrogen is required for the activation and differentiation of DCs, specifically those bearing features of a Langerhan cell like DC [23,24]. In this issue of Clinical Immunology, Cunningham et. al. demonstrate the estradiol independent role of the ERα in the innate immune response in lupus [25]. The authors had previously shown that the ERα deficiency mediated protection from renal disease and prolonged survival in lupus prone mice [16]. Using ERα deficient mice in the wild-type and lupus-prone backgrounds, they now show that in the absence of ERα, there is decreased TLR9 mediated inflammatory cytokine (IL-6, MCP-1, IL1β and IL23) production by DCs [25]. IL23R expression is upregulated upon TLR7 and TLR9 stimulation in DCs from the wild-type but not the ERα deficient mice suggesting that the ERα modulates the TLR activation of the IL23/IL17 pathway. Furthermore, they show decreased percentages of IL17 + RORγt + spleen cells

Schematic depicting select roles of estrogen and estrogen receptors in the innate and adaptive immune responses in SLE.

EDITORIAL isolated ex vivo from the ERα deficient NZM mice. They show that the ERα knockout mice have reduced numbers of plasmacytoid dendritic cells with impaired ability to produce IFNα and IL6. Thus, this study provides some insights into the protective effect of the ERα deficiency in lupus renal disease. This is the first report of the requirement of the ERα in the TLR signaling pathway. Although the authors show that these modulations of the TLR signaling by ERα are independent of estradiol, this will need to be rigorously confirmed; since the derivation of the dendritic cells occurs in estrogen replete conditions. While these findings are extremely interesting and important, more studies are needed to understand the exact molecular mechanisms of the ERα involvement in the TLR signaling pathway. Which binding partners are involved, if DNA binding of the ER is required and how phosphorylation of the ER may be important — these mechanistic aspects need to be addressed. While estrogen and estrogen receptors are potential culprits in SLE, estrogen has many beneficial effects especially in bone metabolism and is vital in osteoporosis management in post-menopausal women. The Safety of Estrogens in Lupus Erythematosus National Assessment (SELENA) studies gave hormone replacement therapy to postmenopausal women and showed benefits in osteoporosis [26]. Many clinical trials have studied the utility of administering DHEA and have shown some clinical benefits in terms of tapered doses of prednisone, or improved disease activity and fewer flares [27–29]. Hormone replacement therapy in postmenopausal women with SLE was associated with a small risk of mild to moderate flares [30]. The use of combined estrogen–progesterone oral contraceptives in premenopausal women did not significantly increase the risk of flares in women with SLE with stable disease [31]. Abdou et al. showed some therapeutic benefit of Fulvestrant a selective estrogen receptor downregulator in pre-menopausal women with SLE. The Fulvestrant group had improved SLE disease activity index (SLEDAI) scores and needed reduced medications for lupus therapy. Furthermore, their peripheral blood T cells had lower median values for CD40L and calcineurin expression. However serologic tests, routine lab tests and bone density did not improve in the treated subjects over the placebo group [32]. While we are only beginning to understand the role of hormones and their receptors in autoimmunity and lupus disease pathogenesis, further molecular mechanistic studies will guide us to intelligently modulate these important contributors of disease.

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Vaishali R. Moulton⁎ George C. Tsokos Department of Medicine, Division of Rheumatology Beth Israel Deaconess Medical Center Harvard Medical School, Boston, MA, USA ⁎Corresponding author at: 3, Blackfan Circle, CLS-928, Boston, MA, 02115, USA. Fax: + 1 617 735 4170. E-mail address: [email protected].