Mechanism Of C-type Natriuretic Peptide In Anovulation Mediated By Hyperandrogen In Polycystic Ovary Syndrome

Polycystic ovary syndrome(PCOS),characterized by hyperandrogenism,polycystic ovary,anovulation and metabolic disorders,caused by the interaction of environment and genetic factors.Of all symptoms in PCOS,hyperandrogenism is the key mediator of pathogenesis.Because of ovulatory dysfunction,the proportion of PCOS in anovulatory infertile patients is up to 50%-70%.In mammals,meiosis begins during fetal life but then is arrested at the diplotene stage of meiosis I for prolonged periods.Oocytes resume meiosis in response to the preovulatory LH surge stimulation,and then ovulate mature oocytes for fertilization.Abnormalities of the first meiotic arresting and resumption progression,and the defects in LH action and secretion may lead to the declined female reproduction rate and infertility.Recently,studies indicate that natriuretic peptide C and its receptor natriuretic peptide receptor 2(CNP/NPR2)play a critical role in maintaining oocyte first meiotic arrest in mice,porcine,bovine and human.Therefore,understanding the regulatory relationship and molecular mechanism of CNP/NPR2 in the formation of PCOS have the important theoretical and clinical significance for the further study of the etiology and clinical treatment of PCOS.At the beginning of the study,we induced prepubertal mouse by dehydroepiandrosterone(DHEA)successfully got the PCOS-like mice model.Firstly,Persistant high levels of CNP/NPR2 were detected in PCOS mice ovaries compared with control mice.The LH peak caused by exogenous hCG-treatment reduced CNP/NPR2 levels and resumed meiosis,and then resumed ovulation.These suggested that CNP/NPR2 played an important role in the oocyte maturation and ovulation of PCOS mice.Secondly,the change of expression of testosterone and estradiol in serum and their receptors in ovary is synchronous with CNP/NPR2.Testosterone promoted the expression of CNP/NPR2 through AR and estradiol-ERs and maintained CNP-mediated the first meiosis arrest in vitro.These results indicated that both androgen and estradiol regulated the expression of CNP/NPR2 system in follicular.Thirdly,coimmunoprecipitation(Co-IP)assay suggested that AR and ERs didn't have the physical interaction in mice ovary.And then the chromatin immunoprecipitation(ChIP)assay showed that AR binded to the specific promoter sequences of Nppc and Npr2 and directly promoted gene transcriptions of Nppc and Npr2.It followed that androgen through AR and ERs in maintaining oocyte meiotic arrest and impacting ovulation by directly promoted Nppc/Npr2 gene transcription to improve their expressions.Additionaly,the anovulation and meiotic arrest in PCOS mice can be resumed by reduced the levels of CNP/NPR2 through treatment with either AR or ERs inhibitor,Flutamide and ICI 182780,respectively.This further demonstrated our previous inference.Finally,clinical test showed that LH induced the the expression of testosterone and estradiol and their receptors,also the CNP/NPR2 levels in PCOS patients.Moreover,overexpression experiments also showed that AN-AR regulated the expression of Nppc/Npr2 in human granulosa cell lines.These were similar to the results in PCOS mice model,suggested that the same regulatory mechanism may exist in PCOS patients.To summarize,our study highlighted the important role of over activated function of CNP/NPR2 system in prevention of oocyte maturation and ovulation in PCOS mice.Hyperandrogen through its receptor AR and aromatized to estradiol through its receptors ERs directly promoted Nppc/Npr2 gene transcription to maintain the high level of CNP/NPR2.Passive interference of the CNP/NPR2 system may reduced the risk of persistent syndromes and thereafter induced ovulation.These findings may provide new insights into potential mechanisms responsible for anovulation induced by hyperandrogen in PCOS patients and opens new window for understanding the underline causes of PCOS.It also provides possible new strategies for the treatment of anovulation of PCOS in clinical.Moreover,the internal regulation mechanism of the first meiosis of oocyte has further improved.