Morphological and Hormonal Identification of Porcine Atretic Follicles and Relationship Analysis of Hormone Receptor Levels During Granulosa Cell Apoptosis In vivo

Recent reports have demonstrated that follicular atresia is initiated or caused by granulosa cell apoptosis followed by theca cell degeneration in mammalian ovaries, but the mechanism of follicular atresia is still to be elucidated. Therefore, our present study was designed to examine our hypothesis that the changes of follicular microenvironment induce the granulosa cell apoptosis during pocrine follicular atresia in vivo. We firstly isolated intact porcine antral follicles and identified them into three groups, healthy follicles (HF), early atretic follicles (EAF) and progressed atretic follicles (PAF) through morphology and histology. To further confirm their status, we detected hormone levels in follicular fluids and the expression level of apoptosis gene Bax in granulosa cells. The rate of progesterone (P) and estradiol (E2) was increased with the expression of Bax, indicating hormone can be used as a marker of granulosa cell apoptosis or follicular atresia. Finally, we analyzed the expression level of hormone receptor genes in granulosa cells and their relationship with follicular atresia. In PAF, the expression of Progesterone receptor (PGR) was increased significantly while estradiol receptor (ER) had no notable changes, which suggesting the increased-PGR accelerated the effect of P-stimulated granulosa cell apoptosis. The dramatic increasing of androgen receptor (AR) expression in PAF and the obvious increase of tumor necrosis factor-α receptor (TNFR) in EAF indicated that there are different pathways regulating granulosa cell apoptosis during follicular atresia. Together, our results suggested that different pathways of granulosa cell apoptosis was induced by changing the follicular microenvironment during follicular atresia.