br Acknowledgments This work was supported by

Acknowledgments This work was supported by Grant-in-aid for Scientific Research (S) (20229008) (to T.K.), Targeted Proteins Research Program (to T.K.), the Global COE Research Program (to T.K.) and Translational Systems Biology and Medicine Initiative (to T.K.) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Funding Program for Next Generation World-Leading Researchers (NEXT Program) (to T.Y.) from Cabinet Office, Government of Japan.
Introduction Polycystic ovary syndrome (PCOS) is a major cause of infertility. Despite its high prevalence, the pathophysiological mechanism is incompletely explicated. PCOS is currently recognized as an important metabolic and reproductive disorder [1]. The key etiological characteristics of PCOS include hyperandrogenism (increased androgen synthesis), presence of cystic follicle, anovulation, obesity, hyperinsulinemia, insulin resistance (decreased insulin sensitivity or insulin receptor), dislipidemia and glucose intolerance [2]. About 85% of women with PCOS suffer from insulin resistance [3]. Both insulin resistance and hyperandrogenism are considered to play major role in the pathophysiology of PCOS [4], [5]. Metabolic changes also have a significant impact on various reproductive activities [6]. Adiponectin, the most abundant adipokine, has important role in metabolic activities through modulation of insulin receptor/insulin resistance and may be involved in the underlying mechanism connecting metabolic changes with reproductive disorders. Adiponectin is produced in large quantities by adipocytes [7] and have significant role in preventing development of insulin resistance [8], [9]. Adiponectin, 30 kDa glycoprotein hormone, is mainly produce by adipose tissue [10]. Adiponectin exerts its effect mainly through two distinct receptors, AdipoR1 and AdipoR2 which are expressed in female reproductive tissues, such as ovary, placenta, Alda 1 and oviduct [11]. The circulating adiponectin levels were correlated negatively with obesity, insulin resistance and metabolic syndrome [12], [9]. Recent studies suggest strong correlation between reduced synthesis of adiponectin (hypoadiponectinemia) with the occurrence of PCOS. Serum adiponectin levels of PCOS were significantly lower than control suggesting the role played by adiponectin in the pathogenesis of the syndrome [13], [14], [15], [16]. It was further suggested that hypoadiponectinemia in PCOS may be a consequence of increased androgen associated with obesity [14]. Reduced circulating adiponectin levels along with decreased adiponectin receptors correlates to increased androgen production in women with PCOS [17]. Recently reduced level of circulating adiponectin level as compared with the control was shown in rat model of PCOS [18].
Materials and methods
Results
Discussion The present study showed the direct action of adiponectin in regulating increased androgen synthesis and improving altered steroidogenesis in PCOS-mice. The results showed the expression of adiponectin receptor, AdipoR1, mainly in thecal cells of large antral follicles in the ovary of control mice. Presence of AdipoR1 and AdipoR2 in the ovaries of several species including rat, bat, bovine and chicken has been previously demonstrated [23], [25], [26], [27]. This study further showed a significant decline in AdipoR1 immunostaining in the ovary of PCOS-mice compared to control. This finding substantiates the earlier postulation that the ovarian adiponectin level decline in women with PCOS [28], [29]. The results of this study showed significant increase in levels of testosterone in PCOS-mice group compared to normal control mice. Increased androgen synthesis is one of the major markers of PCOS and strongly implicates the pathogenesis of this disorder [30]. The ovaries of PCOS-mice when treated in vitro with two different doses of adiponectin, showed significant decline in the synthesis of T as compared with the untreated PCOS-ovary. Thus, it explains that low adiponectin level correlates with high androgen synthesis, whereas exogenous adiponectin treatment may suppress androgen synthesis by PCOS-ovary. This finding corroborates the earlier studies showing low adiponectin levels (hypoadiponectinemia) in women with PCOS [31], [32]. Further the increased T synthesis in vitro is correlated significantly with increased expression of LH-R, STAR and 3β-HSD proteins in the ovary of PCOS-mice. The adiponectin-induced decline in T synthesis correlated with decreased expression of LH-R, STAR and 3β-HSD proteins. These findings propose that adiponectin treatment to PCOS-mice significantly suppressed the androgen synthesis by down-regulating ovarian steroidogenic markers (LH-R, STAR and 3β-HSD). Based on these findings it is possible that treatment of adiponectin may inhibit androgen synthesis directly inhibiting the expression of steroidogenic markers in the PCOS-ovary.