Study On The Role Of Bmi1 In Maintaining Female Reproductive Function

Bmi1(B cell-specific MLV integration site-1),a member of the Polycomb group family,plays a key role in the self-renewal of multiple adult stem cells.Bmi1 deficient mice exhibited growth retardation and premature aging.However,the involvement of Bmi1 in female reproduction remains unclear.To clarify whether Bmi1 deficiency can lead to female infertility by increasing oxidative stress,activating DNA damage response,inhibiting folliculogenesis and inducing ovarian follicle atresia,Bmi1-/-female mice were supplemented of anti-oxidant NAC(N-acetyl-cysteine),and reproductive phenotypes,including body weight,ovarian size and weight,the number of follicle at all stages,the proliferation and apoptosis of granulosa cells,oxidative stress and DNA damage in ovarian tissue and the expression of proteins involved in the regulation of cell cycle and apoptosis,were analyzed using histopathology,cellular and molecular biology.These results showed that Bmi1 was located in follicular granulosa cells and theca cells,and was also highly expressed in stromal cells.Bmil deficient female mice was totally infertile,displayed an ovulatory failure and an irregular estrus cycle with a decreased proestrus and estrus periods,and a prolonged diestrus and metestrus periods.1-week-old Bmi1-/-mice displayed a decline in the number of primordial follicles.4-week-old Bmi1-/-mice exhibited a decreased number of primordial follicles,primary follicles and secondary follicles.7-week-old Bmi1-/-mice showed a significant reduction of ovarian size,ovarian weight,and follicles at all stages with the absence of corpus luteum,and a marked decline in the number of follicular atresia.Bmi1-/-mice showed decreased granulosa cell proliferation and increased apoptosis.The ovary tissue of Bmi1-/-mice exhibited a significantly higher expression of p16,p19 and p53,and a lower level of Bcl2 compared with controls.Bmi1-/-mice displayed mitochondrial injury and malfunction,including a reduced number of mitochondria,mitochondrial swelling,cristae vague and vacuolation.Moreover,compared with controls,the levels of intracellular ROS was significantly higher in Bmi1-/-mice with remarkably lower transcript levels of anti-oxidant genes,including glutathione peroxidase(Gpxl),glutathione reductase(GSR),CAT,SOD1,SOD2 and thioredoxin reductase 1(Txnrdl),and decreased protein levels of SOD2 and SOD2.Additionally,the percentage of y-H2A.X and 8-hydroxydeoxyguanosine(8-OHdG)positive cells was significantly elevated,suggesting the increased DNA damage induced by Bmil deficiency.All phenotypic alterations exhibited in Bmil deficient female mice were largely ameliorated at 3 weeks following NAC treatment.Bmi1-/-mice treated with NAC showed markedly decreased ROS levels and DNA damage with a significant elevation in the expression of SOD2 and SOD2 compared with Bmi1-/-mice.The ovarian size and weight were partly rescued,the number of secondary and mature follicles increased,and the number of atresia follicles dramatically reduced in Bmi1-/-mice treated with NAC compared with Bmi1-/-mice.Meanwhile,treatment with NAC resulted in a rescue of granulosa cell proliferation and apoptosis in Bmi1-/-mice.Our findings demonstrate that Bmil deficiency can result in female infertility by increasing oxidative stress and DNA damage,activating p16/pl9 signaling,inhibiting granulosa cell proliferation,promoting granulosa cell apoptosis,restraining follicular growth and inducing follicular atresia.Our study reveals the role of Bmil in maintaining healthy female reproduction and its relevant mechanism,and provides novel targets and experimental basis for the clinical treatment of female infertility.