Insulin-like growth factor-1 regulates follicle selection of hens by promoting proliferation and inhibiting apoptosis of granulosa cells in prehierarchical follicles in vitro

Abstract

During the reproduction stage of poultry, a single follicle is selected from a cohort of 6–8 mm small yellow follicles to initiate rapid growth and final ovulation almost daily. In the process, follicle-stimulating hormone (FSH) plays a pivotal role by interacting with intraovarian factors, including insulin-like growth Factor 1 (IGF1). The objective of this study was to analyze whether IGF1 coordinates with FSH to affect the characteristics of granulosa cells from prehierarchical follicles. After treating granulosa cells with 50 ng/mL FSH and 200 ng/mL IGF1, we detected the proliferation and apoptosis of granulosa cells using flow cytometry. The percentage of G1 phase granulosa cells was increased, and the percentage of mitotic cells and apoptotic cells was reduced under IGF1 treatment. The expression levels of the steroidogenic acute regulatory protein gene, cytochrome P450 side-chain cleavage gene and 3β-hydroxysteroid dehydrogenase gene, which are related to steroidogenic synthesis, were reduced by cotreatment with FSH and IGF1. The expression of the cell proliferation- or apoptosis-related genes cyclin dependent kinase 2, cyclin D2, B-cell leukemia/lymphoma 2, and BCL2 like 1 and the ratio of B-cell leukemia/lymphoma 2/BCL2-associated X were increased by treatment with IGF1. There was a decrease in the expression of caspase3 after treatment with FSH and IGF1. All these results showed that IGF1 reduced the expression of genes involved in progesterone synthesis, stimulated proliferation and inhibited apoptosis in granulosa cells. Thus, IGF1 may be one of the factors involved in affecting FSH responsiveness and maintaining the undifferentiated state of prehierarchical follicles before follicle selection.