The Role Of Fstl1 In Ovary Follicle Development

Folliculogenesis is a highly organized process,any defect in the regulation of which will eventually affect the development and function of the ovary and therefore,impact fertility.Members of TGF-? superfamily are indicated to play important role in ovary development.Abnormalities associated with BMP/TGF-?/Smad signaling could result in female infertility.Fstl1,an inducible extracellular glycoprotein by TGF-?1,can regulate organ development in mouse through modulating BMP/TGF-?/Smad signaling.However,the role of Fstll in folliculogenesis is not clear.In this study,we first examined the expression of Fstll in mouse ovary by realtime PCR and immunohistochemistry(IHC).Expression of Fstl1 was in all stages of ovarian follicle development and decreased gradually after the initiation of primordial follicle.Meanwhile,Fstl1 was expressed in the granulosa cells and oocyte in the mouse ovary at postnatal day 7(P7).The expression of Fstl1 in ovary is spatio-temporal specificity,which suggested that Fstl1 may play a role in regulating folliculogenesis.While Fstl1-/-mice died shortly after birth due to respiratory failure,study using ovary from E18.5 Fstl1-/-mice for the renal capsule transplantation revealed that Fstll deficiency resulted in abnormal follicle development,suggesting the role of Fstll in follicle development.Furthermore,we constructed ovarian granuloma cells and oocyte-specific conditional Fstll knockout mice(Cyp9a1-Cre;Fstl1oxp/loxp and Gdf9-Cre;Fstl1loxp/loxp mice)to examine the role of Fstl1 in folliculogenesis in vivo.Fertility test,ovulated follicles after superovulation,serum levels of hormone and histology of every stages of follicles showed that deletion of Fstll in oocyte did not affect development of ovary.Deletion of Fstl1 in granuloma cell did not affect early fertility,expression level of follicle-stimulating hormone(FSH)and follicle counts of mouse ovary at P23,2M and 6M.However,Fstl1 conditional knockout mice with loss of Fstl1 gene in granulosa cells showed significant reduced fertility in late stage.Further study revealed that deletion of Fstll in granulosa cells significantly reduced the expression level of luteinizing hormone(LH),estrogen and progesterone in serum,which resulted in a decreased number of ovulated oocytes and follicles in mouse ovary at 8M.IHC and TUNEL experiments showed that deletion of Fstll in granulosa cells promoted proliferation of granulosa cells in mouse ovary at P23,which accompanied with the increased apoptosis of granulosa cells in mouse ovary at 2M.LH,produced by the pituitary gland,drives progesterone production,which promoted the ovulation.Deletion of Fstl1 in granulosa cells reduced ovulation through affecting LH expression level and subsequential expressions of estrogen and progesterone.While progesterone regulated formation of corpus luteum,deletion of Fstll in granulosa cells reduced follicle numbers and fertility at late stage through affecting expression level of progesterone.In summary,Fstl1 regulate mouse folliculogenesis and fertility at late stage through modulating proliferation and apoptosis of granulosa cells and subsequentially affecting level of hormone.