Hypoxia Induces the Apoptosis of Mouse Spleen Lymphocytes through the Fas Receptor-Dependent and Mitochondrial Pathways

Background: Hypoxia induces lymphocyte apoptosis and affects their function. However, there is limited information about the mechanisms underlying the hypoxia-induced apoptosis of lymphocytes.Objective: Apoptosis is mainly mediated by Fas (factor associated suicide) receptor-dependent apoptosis pathway and mito-chondria pathway. Therefore, this study aimed to investigate whether hypoxia-induced lymphocyte apoptosis occurs via the Fas receptor-dependent pathway and/or the mitochondrial pathway.Methods: Mouse spleen lymphocytes were exposed to hypoxia (1%) and normoxia (21%) for 6, 12, and 24 h. Cell viability, cell morphological changes and apoptosis were studied. Reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) production were also measured. The expression of apoptosis-related proteins was analyzed by quantitative real-time PCR (qRT-PCR) and western blotting.Results: Hypoxia-treated reduced lymphocyte survival and increased lymphocyte apoptosis, inducing morphological changes characteristic to early apoptosis. Hypoxia exposure enhanced the ROS formation. The MMP of lymphocytes decreased after 12 and 24 h of hypoxia exposure. Factor associated suicide (Fas), factor associated suicide ligand (FasL), Bcl-2 homologous antagonist-killer protein (Bak), Cytochrome C, apoptotic peptidase activating factor 1 (Apaf-1), and cysteinyl aspartate specific proteinase (caspase)-3,-6,-7,-8, and-9 transcript expression was upregulated and B-cell lymphoma 2 (Bcl-2) transcript expres-sion was downregulated in lymphocytes exposed to hypoxia for different time points. Then, the expression of Fas, FasL Bak, Cytochrome C, and caspase-3 were upregulated and that of Bcl-2 was downregulated at the protein level after hypoxia exposure.Conclusions: Hypoxia may induce lymphocyte apoptosis through both the Fas death receptor-dependent and mitochondria -dependent apoptosis pathways, thus mediating lymphocyte injury and causing immune dysfunction. Our findings provide the experimental basis for the mechanism of action of hypoxia in immune function impairment.