Insulin signalling in granulosa cells

Abstract

Polycystic ovary syndrome (PCOS) is characterised by hyperandrogenism and insulin resistance. Granulosa cells in PCOS demonstrate impaired insulin-induced glucose uptake and lactate accumulation, suggesting a post receptor, signalling pathway-specific impairment of insulin action. Gonadotrophins are also important in the regulation of glucose metabolism by of granulosa cells. The first objective of this project was to use KK1 cells an immortalised mouse granulosa cell line, to characterise insulin, androgen and FSH signalling as well as glucose metabolism. Cell lysates were subjected to western immunoblotting for key proteins in the insulin signalling pathways. Glucose metabolism of KK1 cells was also measured. Surprisingly, androgen alone stimulated glucose uptake and lactate production and augmented insulin-induced glucose metabolism. This suggests that the insulin resistance observed in granulosa cells from women with PCOS is not a direct effect of exposure to androgen. The main part of the thesis was examination of insulin action on human primary ovarian granulosa-lutein (GL) cells to investigate the mechanism of insulin resistance in PCOS. Insulin and FSH signalling in GL cells from women with anovulatory PCOS (anovPCO, n=11) was compared to that in GL cells from ovulatory women with (ovPCO, n=8) and without polycystic ovaries (controls n=12). Primary GL cells were incubated with insulin or FSH and analysed for glucose metabolism and progesterone production. Cell lysates were prepared for identification of signalling pathways, using western immunoblotting. The results confirmed selective impairment of glucose metabolism in cells from anovulatory PCOS. No significant impairment of insulin stimulated PI3K signalling was observed. However there was a reduction of p42/44ERK phosphorylation in the ovulatory PCOS group compared to controls. The significance of this finding with respect to impaired glucose metabolism in granulosa cells remains to be determined. We also showed FSH induced glucose metabolism, but without clear evidence of activation of the PI3-kinase pathway.