Mechanisms of CD4+ T cell apoptosis and the role of ethanol as a cofactor in HIV pathogenesis.

摘要

Acquired Immunodeficiency Syndrome (AIDS) was first reported in the United States in 1981 and has since become a major worldwide epidemic. The typical course of HIV disease begins with a primary infection followed by a relatively long latency phase and finally ends in the advance phase also called AIDS. There are two aspects considered the most important in HIV pathogenesis, namely viral replication and CD4+ T cell depletion.; During the latency phase, tumor necrosis factor α (TNFα) has been shown to play a predominant role in HIV-1 replication and disease progression. Since ethanol is also an important risk factor and has been implicated in HIV-1 replication, we investigate the effects of ethanol on TNFα inducible signaling associated with HIV-1 replication in human CD4 + T cells. We demonstrate that clinically relevant ethanol concentrations significantly potentiate TNFα inducible NFκB. Although ethanol effectively collaborated with TNFα by itself it does not have a direct effect on NFκB activation. The ethanol dependent potentiation of TNFα inducible NFκB nuclear translocation is observed to involve the enhanced degradation of IκBα. Additionally, the ethanol mediated potentiation of TNFα inducible NFκB activation is abrogated by the known antioxidant pyrrolidinedithiocarbamate (PDTC), suggesting an important mechanistic role for reactive oxygen species (ROS) in this process. In correspondence with its effect on NFκB, ethanol is also able to significantly enhance HIV-1 long terminal repeat (HIV-1-LTR) dependent transcription induced by TNFα.; Apoptosis has been proposed as a critical mechanism for CD4+ T cell depletion in HIV pathogenesis. Ceramide, a sphingolipid metabolite, is a common apoptotic transducer involved in CD4+ T cell apoptosis. In the current study, we show that ceramide potently induces CD4+ T cell apoptosis through activating caspase 3, which may further increase Fas Ligand expression to amplify the apoptotic signaling. Interestingly, the apoptotic effect of ceramide is completely blocked by pretreatment with zinc and the underneath mechanism is suggested to be a direct inhibition of caspase 3 activity by zinc.; Survival factors are equally important in the regulation of apoptotic process. We demonstrate that PI₃-kinase/Akt pathway is indispensable for the survival of CD4+ T cells. Further, Akt kinase is significantly inactivated and downregulated in oxidative stress induced CD4+ T cell apoptosis. N-acetyl-cysteine (NAC) can rescue CD4+ T cell from H₂O₂ induced caspase 3 activation and apoptosis, while depletion of glutathione (GSH) exacerbate it.; Overall, this work identifies several mechanisms underlying CD4 + T cell apoptosis and provides molecular basis for the role of ethanol as a cofactor that can adversely affect HIV-1 infection and pathogenesis.