The expression of IGF-I, TGF beta and Fas-L in granulosa cells of ovarian follicle with relation to the onset of atresia in rats

This study was designed to investigate the effects of IGF-I, TGF beta and Fas-L on the sustaining of granulosa cells of ovarian follicle and the modulation of apoptosis of those cells, and to understand the molecular mechanisms of ovarian follicle atresia. Paraffin-embedded sections of SD rat ovary were made. Both TUNEL method and PCNA immunohistochemistry were employed to recognize atretic and healthy follicles. The expression of IGF-I, TGF beta, Fas-L and their receptors was displayed by immunostaining. The results showed that most of the granulosa cells within the healthy preantral and antral follicles were PCNA(+). At the early stage of atretic antral follicle, more than 5 granulosa cells were labelled by TUNEL method, and some granulosa cells were PCNA(+). At the late stage of atretic antral follicle, were labelled by TUNEL method. The immunoreactive products of IGF-I, IGF-IR, TGF beta, TGF beta R, Fas and Fas-L could be seen in the granulosa cells of healthy antral follicles. But, Granulosa cells were only TGF beta, TGF beta R and Fas immunopositive in all atretic antral follicles. In conclusion, combination of TUNEL method and PCNA immunochemistry is of benefit for distinguishing atretic follicles from healthy follicles. IGF-I might play an important role in stimulating proliferation of the granulosa cells and sustaining them. The lower expression or disappearance of IGF-I in the antral follicle might cause the onset of atresia. TGF beta, Fas-L and Fas might mediate apoptosis of the granulosa cells in antral follicles, causing follicle atresia. But, their effects of mediation could be inhibited as IGF-I exists in the follicles.