A brain-specific isoform of apoptosis-inducing factor 2 attenuates ischemia-induced oxidative stress in HT22 cells

Apoptosis-inducing factor (AIF) is a family of conserved mitochondrial flavoproteins that have both vital and lethal functions in cells. The function and regulation of AIF-1, the original described and most abundant isoform, has been extensively studied, whereas three other AIF isoforms have not been further characterized. Here, we investigated the role of AIF-2, a brain-specific isoform of AIF, in an in vitro ischemia model in neuronal HT22 cells. We showed that AIF-2 was constitutively expressed in HT22 cells, and the oxygen and glucose deprivation (OGD) did not alter AIF-2 expression. Downregulation of AIF-2 with specific siRNA aggravated OGD-induced lactate dehydrogenase (LDH) release, apoptosis and loss of cell viability, whereas overexpression of AIF-2 through lentivirus transfection exerted the opposite effects. In OGD-treated cells, AIF-2 overexpression promoted the endogenous antioxidant enzyme activities, preserved mitochondrial membrane potential (MMP), inhibited cytochrome c release, and thereby prevented reactive oxygen species (ROS) generation and lipid peroxidation. In addition, AIF-2 significantly prevented the OGD-induced AIF-1 translocation from cytoplasm to the nuclei. In view of these considerations, AIF-2 might represent an ideal strategy to avoid AIF-1 associated neurotoxicity, and could be tested against brain ischemia in animal models.