Cytochrome c dysregulation induced by HIV infection of astrocytes results in bystander apoptosis of uninfected astrocytes by an IP₃ and calcium-dependent mechanism

HIV entry into the CNS is an early event after peripheral infection, resulting in neurologic dysfunction in a significant number of individuals despite successful anti-retroviral therapy. The mechanisms by which HIV mediates CNS dysfunction are not well understood. Our group recently demonstrated that HIV infection of astrocytes results in survival of HIV infected cells and apoptosis of surrounding uninfected astrocytes by the transmission of toxic intracellular signals through gap junctions. In the current report, we characterize the intracellular signaling responsible for this bystander apoptosis. Here, we demonstrate that HIV infection of astrocytes results in release of cytochrome C from the mitochondria into the cytoplasm, and dysregulation of inositol trisphosphate/intracellular calcium that leads to toxicity to neighboring uninfected astrocytes. Blocking these dysregulated pathways results in protection from bystander apoptosis. These secondary messengers that are toxic in uninfected cells are not toxic in HIV infected cells, suggesting that HIV protects these cells from apoptosis. Thus, our data provide novel mechanisms of HIV mediated toxicity and generation of HIV reservoirs. Our findings provide new potential therapeutic targets to reduce the CNS damage resulting from HIV infection and to eradicate the generation of viral reservoirs. We demonstrated that HIV infection of astrocytes protects infected cells from apoptosis but results in cell death of surrounding uninfected astrocytes by a mechanism that is dependent on gap junction channels, dysregulation of mitochondrial cytochrome C (CytC), and cell to cell diffusion of inositol trisphosphate (IP₃) and calcium. Our data provide essential information about generation of brain reservoirs and the mechanism of toxicity mediated by the virus. We demonstrated that HIV infection of astrocytes protects infected cells from apoptosis but results in cell death of surrounding uninfected astrocytes by a mechanism that is dependent on gap junction channels, dysregulation of mitochondrial cytochrome C (CytC), and cell to cell diffusion of inositol trisphosphate (IP₃) and calcium. Our data provide essential information about generation of brain reservoirs and the mechanism of toxicity mediated by the virus.