HIV-1 associated encephalopathy can show either minor or severe cognitive impariments refered to as the AIDS dementia complex as well as motor dysfunction. HIV-1 causes damage in the human brain through both direct infection and indirect mechanisms through viral structural or non-structural proteins. 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 infection in glial cells 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 and that transcriptional control may be the key factor. The MCP-1 released chemoattracts monocytes across the barrier and upregulates the beta-chemokine HIV-1 co-receptor, CCR5, on migrating monocytes. 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. However we are testing the physiological effects of the viral gp 120 protein binding to astrocytes and regulation of glutamate uptake, an important physiological role for astrocytes. With the emphasis on the development of an AIDS vaccine, understanding the mechanisms of HIV-1 infection in human brain is critical to the use of vaccines as eitehr prophylactic or therapeutic. 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 have collected many different strains of HIV-1 from several clades of virus from Asia, Africa, South and North America to do this study. Using a novel cell culture model of human brain cells, we have been able to directly infect multipotential progenitor cells and have identified HIV-1 infected cells in pediatric brain tissue in anatomical regions that are the primary site for stem cell migration.
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