The over arching hypothesis is that the brain is an important reservoir for retroviruses because of their ability to infect long lived terminally differentiated cells and viral products released from these cells can cause immune activation and neuronal injury Aim 1: To understand the mechanism of viral persistence in brain While my lab has been studying the mechanism of viral persistence in the brain in the context of HIV infection for several years, we have now studying the same phenomenon in the context of endogenous retroviruses and chronic dengue viral infection in the brain. Lessons learnt from HIv are widely applicable to other viral infections. Recent studies suggest that these viruses may play an important role in the pathophysiology of several neurodegenerative diseases. Hence the study of viral persistence and transmission within the brain is an excellent opportunity to shed new light in the pathophysiology of these diseases and to identify new therapeutic targets. The brain is a unique site of viral latency since the cells have a very low turn over rate and hence viral sequences can reside there for the life of the individual. For example we have found that HIV can be transmitted from cell to cell without complete viral production. We are now developing in vitro and in vivo models to study this phenomenon and determine if other retroviruses and those that cause chronic encephalitis can also similarly persist in the brain and transmit from cell to cell and thus escape the immune system.
Aim 2 : To investigate the mechanism of neuronal injury by HIV and endogenous retroviruses. Despite the use of antiretroviral agents and excellent control of the virus in the periphery, HIV infected patients continue to develop cognitive impairment. Currently available antiretroviral agents have no effect on the production of early viral proteins once the virus has integrated into the chromosome. One of these proteins, Tat, has been shown to be neurotoxic. Our laboratory was one of the first to demonstrate its toxic potential and has extensively investigated the mechanism by which it causes neurotoxicity. We have shown that Tat can complex with amyloid beta peptide to form highly neurotoxic protein aggregates. We have developed an assay to quantify Tat in spinal fluid. We have also discovered that Tat protein of HIV is present in the CSF of 1/3 of HIV infected patients despite undetectable virus while on antiretroviral therapy. We are developing therapeutics that incliudes antisense molecules and small molecules to block the effect of Tat on HIV replication and neurotoxicity. We have recently shown that the envelope protein of an endogenous retrovirus (HERV-K) can also cause toxicity and have implicated it in the pathophysiology of motor neuron diseases. We are studying the mechanism underlying the toxicity and screened a panel of anti-retroviral drugs against HERV-K. Based on these findings a clinical trial has been initiated for treatment of patients with ALS.
Aim 3 : To develop therapeutic approaches to prevent viral activation and formation of viral reservoirs in the brain. We have generated cell lines with inducible expression of HIV-Tat protein and the HERV-K virus. These cell lines are being used in high through put screening assays to screen for small pharmacological compounds that suppress their production. We have identified several potential candidates for further characterization. We have also developed antisense molecules to Tat that are being father characterized for their therapeutic potential. In summary, we have shown that astrocytes in the brain are an important reservoir for HIV and that cell to cell contact with lymphocytes is necessary for viral entry and the lysosomal pathway in these cells regulates the intracellular trafficking of the virus and its ultimate ability to successfully infect these cells. Further, we have shown that the HIV protein Tat and the env protein of endogenous retrovirus-K are neurotoxic and we are now studying the underlying mechanisms involved in these effects. We are now developing therapeutic strategies for preventing the activation of these genes.
Aim 4 : Study of undiagnosed neuroinflammatory diseases. Many patients with neuroinflammatory diseases go undiagnosed for years until proper treatment. We have developed a protocol to study these patients to determine the underlying pathophysiology and initiate appropriate therapy. We have recently identified some new neuroimmune disorders triggered by an infection. Clinical protocols related to this annual report: 1. Natural History Study of Inflammatory and Infectious Diseases of the Nervous System 2. HERV-K Suppression Using Antiretroviral Therapy in Volunteers with Amyotrophic Lateral Sclerosis (ALS) 4.Screening and Recruitment for HIV-associated Neurocognitive Disorders (HAND) Studies
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