Cleavage of poly (ADP-ribose) polymerase-1 is involved in the process of porcine ovarian follicular atresia

Ovarian follicle atresia is a common phenomenon in vertebrate ovaries and this process is characterized by follicular wall degeneration. The molecular mechanism underlying follicle atresia is apoptotic granulusa cell death; however, the exact signaling pathway is still unclear. PARP-1, the founding member of the poly (ADP-ribose) polymerase (PARP) family, plays an important role in a large variety of physiological processes. Although its cleavage has recently been implicated in a variety of physiological and pathological processes, its role in the process of follicular atresia is not yet completely defined. We identified the cleavage of PARP-1 involved in the process of follicle degeneration, which is known as "follicular atresia", both from in vivo models and cell culture data. The results from immunohistochemistry (IHC) showed that cleaved PARP-1 was mainly located in apoptotic granulosa cells (GCs); and the expression of PARP-1 and caspase-3 were decreased in apoptotic granulosa cells (GCs). The results from western blotting showed that PARP-1 expression was significantly decreased in atretic follicles compared with healthy (H) follicles, and the cleavage of caspase-3 (17kDa) significantly increased in atretic follicles. Along with the cleavage of caspase-3, the expression of cleaved PARP-1 (24kDa) product was significantly increased, which confirmed caspase-3 activation. Serum starvation led to a reduction in PARP-1 and an increase in cleaved PARP-1 (24kDa) and caspase-3 (17kDa), suggesting that caspase-3 was activated under the stress of withdrawal of growth factors, in accordance with the in vivo study. In the present study, the concentrations of estradiol (E2) and progesterone (P4) as well as the P4/E2 (P/E) ratio were combined with morphological features to determine follicular classification. In summary, the present study demonstrated that cleavage of PARP-1 by caspase-3 was involved in the process of granulosa cell apoptosis. PARP-1 may through its cleavage act as a critical regulator in the process of porcine follicular atresia. Our results identified that cleavage of PARP-1 by activated (cleaved) caspase-3 may serve a key role in controlling follicular atresia through granulosa cell degeneration. These findings should prove helpful in understanding the regulatory mechanisms controlling follicular development and atresia.