The pathogenesis of neurodegenerative disorders, including Human Immunodeficiency Virus (HIV)-1 associated dementia (HAD-now called HAND: HIV-1-associated neurocognitive disorder), is exacerbated by an imbalance between metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of metalloproteinases (TIMPs). As the TIMPs exhibit diverse non-classical functions including anti-apoptotic effects, the induction of TIMP-1 in neuroinflammatory conditions likely serves multiple roles in addition to modulating MMP activity. Our work in the previous funding cycle demonstrated that differential TIMP-1 expression in acute versus chronic activation of astrocytes and HAD brain tissues. We showed that in acute activation IL-12 upregulates TIMP-1 through multiple mechanisms, while chronic activation leads to TIMP-1 downregulation primarily through transcriptional control. We identified a novel CCAAT displacement protein (CDP) binding repressor element involved in astrocyte TIMP-1 regulation. Further, neurotoxicity assays were performed using staurosporine, macrophage-tropic HIV-1 virus and glutamate to induce cell death in cultured human neurons. In these assays, TIMP-1 had equivalent neuroprotective effects as brain derived neurotrophic factor (BDNF). These neuroprotective effects were independent of MMP binding as shown with the TIMP-1 T2G mutant. Neurotrophic signaling through Bcl-2/Bcl-xL is a possible pathway for TIMP-1 neuroprotection and recently a tetraspanin has been identified as a potential TIMP-1 binding partner. Thus, the overarching hypothesis for this proposal is that astrocyte-TIMP-1 is differentially regulated in disease through CDP repression and contributes to loss of TIMP-1-mediated neuroprotection rendered via tetraspanin receptors on neurons. Furthermore, TIMP-1 CNS delivery strategies will be explored using novel nanomedicine approaches. Combined molecular, cellular, in vitro, in vivo and translational approaches will be used. In this competing renewal, we continue an in depth investigation into the mechanisms of astrocyte-TIMP-1 regulation via CDP, neuroprotective effects of TIMP-1 and explore a potential therapeutic nanomedicine strategy, based on our progress in the previous round of funding. We will first investigate the role of CDP in the regulation of astrocyte-TIMP-1 in HAD (Aim 1). Next, we will study the mechanisms of TIMP-1-mediated neuroprotection via tetraspanin signaling (Aim 2). Specifically, we will delineate the TIMP-1 neuronal tetraspanin receptors and related signal transduction mechanism leading to neuroprotection. Finally, we will explore the therapeutic application of GFAP-driven TIMP-1 expression using CNS-targeted nanoparticles (Aim 3). GFAP-TIMP- 1/luciferase constructs in Tat-conjugated PLGA nanoparticles will be intravenously administered to mice and CNS-specific TIMP-1 and luciferase expression will be evaluated. Thus, studies proposed in this renewal will unravel novel mechanisms underlying astrocyte responses during chronic neuroinflammation in HAD, have broader implications in other inflammatory diseases that involve MMP/TIMP imbalance and provide critical proof-of-concept data for future therapeutic strategies.
HIV-1-associated dementia (HAD), now referred to as HIV-1-associated neurocognitive disorder, is an important neurological complication of HIV-1 infection and is characterized by cognitive, behavioral and motor dysfunction. An estimated 10-15% of HIV-seropositive (HIV+) patients progress to develop HAD in developed worlds such as the United States, despite the availability of highly active antiretroviral therapy. Reactive astrogliosis, recruitment to and proliferation of astrocytes at the site of injury, is the pathological hallmark of all neuroinflammatory conditions and is observed in areas of inflammation in HAD. How neuroprotective responses of astrocytes are altered in neuroinflammation and contribute to disease is intriguing and is the focus of our and many other recent investigations. Our studies will provide a better understanding of the specific mechanistic contributions of activated astrocytes to HIV-1-neuropathogensis and neuroinflammation.
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