Insulin mitigates apoptosis of porcine follicular granulosa cells by downregulating BimEL.

Follicular growth or atresia is governed by the survival and apoptosis of granulosa cells. Increasing evidence shows that follicle growth is influenced by energy intake, which is positively related to insulin levels. However, the function of insulin in granulosa cell survival is poorly understood. This study focused on the effects of insulin on porcine medium follicle granulosa cell survival. In the present study, we showed that insulin markedly mitigated the apoptosis of porcine granulosa cells following serum starvation. Moreover, insulin activated the PI3K/Akt pathway to downregulate bim mRNA expression and simultaneously promoted the phosphorylation of BimEL through activating ERK 1/2, both of which reduced the level of BimEL. The results demonstrate that insulin protected the granulosa cells against apoptosis by reducing levels of the pro-apoptotic protein BimEL. However, the concentration of insulin (1 μg/ml) was relatively high. High levels of insulin partly combined with the IGF-1 receptor to play its roles in granulosa cells. This experiment provides new insight into the role of insulin in granulosa cells and sheds light on nutrition-reproduction interactions.