Increased ovarian follicle atresia in obese Zucker rats is associated with enhanced expression of the forkhead transcription factor FOXO1

It is well established that hyperinsulinemia, resulting from insulin resistance, plays a role in the pathophysiology of polycystic ovary syndrome (PCOS). The aim of this study was to investigate if ovarian follicular development and atresia are impaired in obese hyperinsulinemic (fa/fa) Zucker rats. To gain insight into the molecular mechanism of follicular atresia, we also examined the expression and localization of forkhead transcription factor FOXO1, a major regulator of cell fate decisions such as differentiation, cell-cycle arrest, and cell death. Serum insulin but not gonadotropin levels were significantly higher in obese (fa/fa) rats when compared to lean controls. Total ovarian follicle number and the percentage of atretic follicles were also significantly increased in obese (fa/fa) rats. Follicle atresia was associated with nuclear accumulation of FOXO1 transcription factor in TUNEL-positive granulosa cells. These results suggest a role for FOXO1 in granulosa cell apoptosis and increased ovarian follicle atresia associated with hyperinsulinemia.