Inhibition of Hypoxia-induced Apoptosis in PC12 Cells by Estradiol

ABSTRACT

Neuronal apoptotic events, which result in cell death, are occurred in hypoxic/ischemic conditions. Estradiol is a female sex hormone with steroid structure known to provide neuroprotection through multiple mechanisms in the central nervous system. This study was aimed to investigate the signal transduction pathway of CoCl2-induced neuronal cell death and the inhibitory effects of estradiol. Administration of CoCl2 decreased cell viability in both a dose- and time-dependent manner in PC12 cells. CoCl2-induced cell death produced genomic DNA fragmentation and morphologic changes such as cell shrinkage and condensed nuclei. It was found that CoCl2-treated cells increased the reactive oxygen species (ROS) as well as caspase-8, -9 and -3 activities. However, pretreatment with estradiol before exposure to CoCl2 prevented the reduction in cell viability reduction and attenuated DNA fragmentation and morphologic changes caused by CoCl2. Furthermore, the CoCl2-induced increases of ROS levels and caspases activities were attenuated by estradiol. Gene expression analysis revealed that estradiol blocked the underexpression of the Bcl-2 and ameliorated the increase in the release of cytochrome c from mitochondria into cytoplasm and Fas-ligand (Fas-L) upregulated by CoCl2. These results suggest that CoCl2 induce apoptosis in PC12 cells through both mitochondria- and death receptor-mediated cell death pathway. Estradiol was found to have a neuroprotective effect against CoCl2-induced apoptosis through the inhibition of ROS production and by modulating apoptotic effectors associated with the mitochondria- and death-dependent pathway in PC12 cells.