This proposal is directed toward determining the molecular basis of neuropathogenesis induced by a murine retrovirus mutant, ts1, of Moloney murine leukemia virus (MoMuLV). ts1, unlike its wild type (WT) leukemogenic virus, causes degenerative neurologic and immunologic disease when inoculated into susceptible strains of mice. The disease syndrome is characterized by development of noninflammatory spongiform encephalomyelopathy resulting in hind limb paralysis and marked thymic atrophy. The neurovirulence of ts1 has been attributed to two critical mutations in the env gene resulting in inefficient transport and processing of the precursor envelope protein gPr80(env) and an enhanced ability of ts1, relative to WT virus, to replicate in the CNS. We hypothesize that high level of viral expression, together with rate limiting transport of gPr80(env) in neural cells leading to accumulation of gPr80(env) in the ER may perturb vital cellular functions which ultimately lead to cell death. Instead of or in addition to exerting a direct effect on neuronal cells, ts1 may participate indirectly in the destruction of neurons through the infection impairment of neighboring neuronal helper cells such as astrocytes. We therefore propose to use several novel experimental approaches and transgenic studies to investigate virus-cell interaction at the molecular and cellular levels to elucidate viral and cellular factors involved in neurodegeneration. Our studies will focus on the role of viral envelope protein in neuropathogenesis.
Our specific aims are: 1. To investigate the interaction of viral envelope protein and cell-type specific receptors in neuropathogenesis by performing the following experiments: A) to investigate the presence of cell type-specific receptors for ts1 in CNS; B) to investigate whether glutamate transporter serve as a cell type specific receptor for ts1; C) to evaluate if ts1 infection influences glutamate uptake activity by glutamate transporter or arginine uptake by the cationic amino acid transporter (MCAT-1); and D) to determine whether glutamate transporter and/or MCAT-1 receptor and/or other protein are retained intracellularly by accumulation of viral envelope protein. 2. To use transgenic mice expressing the env gene of ts1 or its mutants to further study the effect of expression of the envelope glycoprotein alone in causing neurodegenerative syndrome by performing the following experiments A) to establish high expression lines of Tg mice and to assess the effect of high levels of expression of ts1 env transgene in neuronal degeneration; B) to study direct effects of ts1 envelope protein by targeting ts1 env gene expression to specific CNS cell types; and C) to test the hypothesis that ts1 envelope precursor protein alone is sufficient to cause neuronal degeneration by establishing Tg mice carrying ts1-env (YC4) transgene and/or env gene of other site directed mutants of ts1 at position 25. It is increasingly apparent that envelope protein of retrovirus, including that of HIV, plays a critical role in pathogenesis. We believe that by understanding how a retrovirus envelope protein interacts with specific target cells to cause cell damage, may not only help to elucidate the pathogenic mechanism of neurodegenerative diseases associated with retroviruses but may help to develop successful therapies for these diseases.
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