HIV-1 infection of the central nervous system (CNS) induces conditions of stress that trigger an array of cellular responses with the capacity to affect HIV-1 gene expression, alter the homeostatic state of the host cell, and stimulate co-existing opportunistic pathogens. Recent results from evaluating brain tissue obtained from AIDS patients with neurologic disorders have revealed enhanced expression of BAG3 in astrocytes and perivascular microglial cells. BAG3 is an anti-apoptotic/pro-survival protein that associates with a key stress response chaperone protein, HSP70, and modulates its activity on re-folding of damaged proteins and delivery of its cargo to proteasomes. These events influence several pathways involved in cell survival and apoptosis including mitochondrial membrane depolarization, caspase activation, DNA damage, cell cycle progression, and others. Activation of BAG3 can also be observed during the course of HIV-1 infection of microglia, a cell type that supports viral replication in the brain. Interestingly, activation of BAG3 appears to augment cell survival as silencing of BAG3 by siRNA increases the rate of apoptosis in HIV-1 infected microglial cells. Induction of BAG3 may have a negative impact on HIV-1 replication as BAG3 possesses the ability to suppress HIV-1 gene transcription in both microglia and astrocytes. Indeed these events may be reversed once the level of BAG3 is reduced in the cells. In glial cells this can be accomplished upon activation of the human opportunistic virus, JCV, whose early protein suppresses BAG3 transcription and may alleviate the negative effect of BAG3 on HIV-1 and promote apoptotic pathways. These observations are relevant to the neuropathogenesis of AIDS as replication of JCV, which results in the development of progressive multifocal leukoencephalopthy (PML), is frequently seen in AIDS patients. All of these observations have led us to hypothesize that BAG3, by assisting cells to survive the initial infection with HIV-1, can play a critical role in converting cells to become a long-term reservoir for the virus. With this notion, we plan to investigate the molecular events involved in the differential regulation of BAG3 in CNS cells, identify the pathway by which BAG3 suppresses HIV-1 expression and replication, investigate the impact of JCV via suppression of BAG3 upon HIV-1 expression, and determine the mechanism involved in BAG3 mediated cell survival in HIV-1 infected cells. We will employ molecular, cellular, and virological approaches to address these questions and examine the biological relevance of our findings by immunohistochemical evaluation of clinical samples from patients with HIV-1 CNS disease.
The ability of certain cell types to survive for long periods following HIV-1 infection and thereby to function as long-term viral reservoirs is a critical consideration in HIV-1 therapy and appears to be a major obstacle to eradicating the virus from infected hosts particularly from brain. The studies proposed in this application explore the involvement of one of the key cellular proteins, BAG3, in this event.
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