406. Regulation of insulin receptor and its substrates by follicle stimulating hormone in granulosa cells

Abstract

Insulin receptor signalling receptor regulates the process of follicular development and maturation, however the regulation of insulin receptor (IR) and its signalling component during folliculogenesis is not well understood. This study demonstrates FSH mediated regulation of insulin receptor isoforms specially IR-B, its substrates and some of the insulin related responses like glycogen synthesis and cell proliferation. There was significant increase in mRNAs expression for insulin receptor (IR) isoforms, IR-A and IR-B in ovary in response to PMSG and in granulosa cells (GCs) in response to FSH. IR protein increased in GCs in response to FSH in a dose and time dependent manner. Interestingly, the expression of mRNAs and proteins for IRS-1 and IRS-2 increased significantly in GCs by FSH. Serine phosphorylation (Ser 636/639) of IRS-1 was decreased by FSH, thus facilitating IRS-1 activation. FSH stimulated glycogen synthesis in a dose dependent manner both by PI 3 kinase dependent and independent pathways. Insulin regulated the amount of FSH stimulated glycogen synthesis by granulosa cells. In contrast, FSH and insulin synergistically stimulated glycogen synthesis GC proliferation which was completely inhibited by LY294002. Knockdown of IRS-1 mRNA by siRNA inhibited FSH stimulated GC proliferation indicating an important role of IRS-1 downstream of FSH. Further research is required to delineate the signalling components involving IRS-1 and IRS-2 in response to FSH and thus involved in the cross-talk between FSH and insulin in GCs. Results thus demonstrate that pituitary FSH regulates insulin receptor and its substrates in rat GCs which might be important for follicular growth and oocyte development.