Insulin attenuates IGF-1-induced luteinized granulosa cell proliferation with an increase in PTEN

Abstract

OBJECTIVE: The influence of insulin on folliculogenesis in women with polycystic ovary syndrome (PCOS), which ofthen shows insulin resistance, has not been fully investigated. To assess the induction of PTEN expression with insulin treatment and effects of PTEN on IGF-1-induced granulosa cell proliferation as well as the correlation of PTEN levels with the concentration of insulin in follicular fluid in PCOS and non-PCOS patients. DESIGN: Assay and in-vitro experiments using human granulosa cells and follicular fluids, and analysis of the correlation with clinical data. MATERIALS AND METHODS: A cell proliferation assay, real-time RT-PCR and Western blotting for PTEN, Akt and ERK1/2 were conducted in primary cultured granulosa cells under IGF-1 stimulation with or without insulin pretreatment. Phosphorylation of Akt and ERK1/2 was also determined by Western blotting. We also measured the insulin concentration in follicular fluid and the levels of PTEN expression in granulosa cells collected at the time of oocyte retrieval of IVF in PCOS and non-PCOS patients. RESULTS: PTEN expression was induced by insulin. Pretreatment with insulin attenuated the IGF-1-induced Akt phosphorylation and cell proliferation, but not ERK1/2 phosphorylation. Suppression of insulin-induced PTEN expression using siRNA recovered IGF-1-induced Akt phosphorylation. PTEN levels in granulosa cells, which tended to be higher in PCOS patients, were correlated with the insulin concentration in follicular fluid. CONCLUSIONS: PTEN may influence the proliferation of human granulosa cells as well as disturbance of follicular growth in PCOS patients.