HIV-1 associated encephalopathy which may develop into severe cognitive impariments refered to as the AIDS dementia complex causes damage in the human brain through both direct and indirect mechanisms. An example of HIV-1 non-structural proteins which participates in brain pathogenesis is the viral tat protein. The ability of HIV-1 proteins, particularly tat, which is a transactivating protein to regulate cellular functions helps explain the dysfunction of the nervous system in brain tissue where there is little evidence of active virus multiplication. We found that HIV-1 up regulates the synthesis and release of the beta-chemokine MCP-1 which is also found in elevated levels in the CSF of AIDS patients with dementia. We are now investigating a cohort of HIV-1 infected patients with clinically diagnosed cognitive impairments and no history of treatment, i.e. anti-retroviral drugs like HAART. These patients are part of a collaborative study with the Medical Center in Honduras. Elevated levels of MCP-1 in the CSF is being studied by other AIDS Neuro Centers and has been confirmed by several other laboratories. It may serve as a surrogate marker for AIDS assoicated dementia. We have also shown that human astrocytes are responsible for MCP-1 release in a model of the blood:brain: barrier with endothelial cells. The MCP-1 released chemoattracts monocytes across the barrier and upregulates the beta-chemokine HIV-1 co-receptor, CCR5, on migrating monocytes. The molecular regulation of MCP-1 in astrocytes may be controlled by transcription factors which also regulate JCV infection, namely NF-1. The promoter sequences of the human MCP- 1 promoter shows inducible NF-1/AP-1 sites which are sensitive to the HIV-1 protein tat. We have identified the distal region of the human MCP-1 promoter as most active in regulating MCP-1 synthesis in astrocytes, indicating a role for DNA binding proteins in astrocytes that are responsive to cytokines like TNF-alpha. We had previoulsy established a cell culture model of HIV-1 infection in human astrocytes closely resembling a viral latency. Upon treatment of HIV-1 latenly infected cells with proinflammatory cytokines like TNF-a, the viral genome is activated and new progeny virions are released. We have now shown that IL-1 beta and the tat also activate new virus synthesis. This infectious process however is not cytopathic to the cells which suggests that the astrocyte may serve as a reservoir for HIV-1 in the brain. We have also shown that clinical isolates of HIV-1 from patient CSF or blood are able to infect astrocytes in an CD4 and/or chemokine co-receptor independent manner. We also have determined that sequences of the viral gp120 glycoprotein in the V3 loop are not involved in binding to astrocytes unlike binding to lymphoid cells. With the emphasis on the development of an AIDS vaccine, understanding the mechanisms of HIV-1 infection in human brain is critical to the performance and either prophylactic or therapeutic use of a vaccine. If reactivation of a latent infection from a sequestered site such as the brain can take place, immune reactivity as a result of vacination would be necessary to clear the neuroinvasive virus as well as virus in the periphery. Considering the diverse nature of HIV-1 strains and their re-occurrence, it is necessary to investigate both the neruovirulence of HIV-1 and the emergence of neurotropic strains. We are also investigating the regulation of glutamate uptake and release from astrocytes in the presence of HIV-1 infection. We have identified a dual phase uptake of glutamate in astrocytes that are derived from human fetal progenitor cells. HIV-1 proteins do interrupt glutamate uptake and release as well making this mechanism a part of the pathogenesis of AIDS encephalopathy.
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