Astrocyte production of tissue inhibitor of metalloproteinase (TIMP)-1 plays an important role in central nervous system homeostasis and inflammatory diseases such as HIV-1-associated dementia (HAD). While originally discovered as an inhibitor of matrix metalloproteinases (MMPs), recently, TIMP-1 has emerged as a multifunctional molecule promoting cell survival. MMP/TIMP imbalance is implicated in several neuro-inflammatory diseases. Our previous studies uniquely demonstrate that HAD patients have reduced levels of TIMP-1 in the brain. Astrocyte-TIMP-1 expression is differentially regulated in acute and chronic inflammatory conditions with elevated levels in acute and diminished levels in chronic. These observations indicate that TIMP-1 replenishment in HAD may have therapeutic value. We propose that astrocyte-TIMP-1 regulates neuronal survival in HAD, either through neurotrophic activities and/or via activation of anti-apoptotic proteins. TIMP-1 neuroprotection may or may not involve MMPs. To understand the mechanisms of TIMP-1 regulation and neuroprotection in HAD, the following questions are proposed: 1. How is TIMP-1 regulated in immune-activated astrocytes at the molecular level and what is the temporal relationship between TIMP-1 expression and chronic glial activation? 2. What is the mechanism of TIMP-1-mediated neuronal survival? Is TIMP-1 neuroprotection mediated through interactions with MMP? 3. Can TIMP-1 be utilized as a therapeutic agent to attenuate HIV-1-mediated neurodegeneration? To address these questions, cellular and animal models for HAD will be utilized to mimic acute and chronic inflammatory disease processes. Laboratory in vitro systems consisting of primary human astrocytes, human neurons, neurotoxins, virus and viral proteins will be used. Molecular manipulations such as TIMP-1 promoter-luciferase reporter constructs, adenoviral infections and gene silencing with siRNA molecules will be used to examine TIMP-1 promoter elements and signal transduction pathways involved in astrocvte-TIMP-1 regulation and neuroprotective effects. Neuroprotective mechanisms of TIMP-1 including induction of anti-apoptotic pathways and neurotrophic activities will be evaluated. MMP-dependence of these phenomena will be investigated using TIMP-1 mutants with differential MMP binding abilities. To examine if TIMP-1 can attenuate neurodegeneration, adenoviral-expressed TIMP-1 will be delivered to areas of injury in an HIV encephalitis SCID mouse model using intra-cranial or intra-ventricular injections. These studies will shed light on glial inflammatory responses in HAD, unravel novel mechanisms of glial-neuronal interactions, and may uncover potential future therapeutic strategies for neurodegenerative diseases.
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