Effects Of Bmal1 On Estrogen Synthesis In Human Ovarian Granulosa Cells:An Implicative Role Of BMAL1 In PCOS

Background:Polycystic ovary syndrome(PCOS)is one of the most common endocrine and metabolic disorders in women of reproductive age,which has been reported to have blocked estrogen production pathway with unclear mechanism.Brain and muscle ARNT-like protein 1(BMAL1)is necessary for fertility and has been found to be essential to follicle growth and steroidogenesis.Sirtuin1(SIRT1)has been reported to interact with BMAL1 and function in a circadian manner.Evidence has shown that it regulates aromatase expression in estrogen-producing cells.We aimed to ascertain if there is a relationship between polycystic ovary syndrome(PCOS)and BMAL1,and whether and how BMAL1 takes part in estrogen synthesis in human granulosa cells(hGCs).Methods and Results:Twenty-four women diagnosed with PCOS and 24 healthy individuals undergoing assisted reproduction were studied.BMAL1 expression in their granulosa cells(GCs)was observed by using quantitative real-time polymerase chain reaction(qRT-PCR).Our results have shown that the level of expression in the PCOS group was lower than that of the group without PCOS(p < 0.05).Then we utilized human granulosa cells including KGN cell line and hGCs to have analysis further.Estrogen synthesis and aromatase expression were downregulated after both BMAL1 and SIRT1 knock-down and,conversely,upregulated after overexpression treatments of these two genes in KGN cells.Both BMAL1 and SIRT1 had a mutually positive regulation,as did the phosphorylation of JNK.Furthermore,JNK overexpression increased estrogen synthesis activity and the expression levels of aromatase,BMAL1,and SIRT1.In KGN and hGCs,estrogen synthesis and aromatase expression were down-regulated after the treatment with JNK and SIRT1 inhibitors.In addition,BMAL1,SIRT1,and JNK expression levels were all downregulated.Conclusion:Our results demonstrated the effects of BMAL1 on estrogen synthesis in hGCs and suggested a BMAL1-SIRT1 positive feedback cycle in this process,which indicates an important role of BMAL1 in the development of PCOS.