HIV enters the CNS within 2 weeks after peripheral infection and viral presence persists despite cART. CNS HIV infection results in HIV Associated Neurocognitive Disorders, or HAND, in greater than 50% of the infected population. HAND is mediated, at least in part, by ongoing neuroinflammation and low level viral persistence that causes CNS damage. A major mechanism by which virus enters the brain is by the transmigration of HIV-infected monocytes across the BBB. These monocytes differentiate into macrophages in the CNS parenchyma. They elaborate neurotoxic and chemotactic factors that recruit additional infected and uninfected monocytes into the CNS, as well as virus that infects perivascular macrophages and microglia. Thus, chronic inflammation persists within the CNS. NeuroAIDS is characterized by neuronal damage and loss, but HIV does not infect neurons. Therefore, the altered function and damage seen in neurons must be due to indirect effects of HIV infection, primarily of macrophages and microglia as the major targets of infection, including the elaboration of the neurotoxic viral protein, tat. Tat is the transactivator of the virus and isstill produced despite cART. Tat also interacts with host genes to alter their expression. We and others demonstrated that tat induced cytokine secretion in macrophages, including CCL2, that mediates neuroinflammation and is highly expressed in the CNS of HIV infected people with HAND. Tat also increased the expression of CCR5 and CXCR4 on macrophages. Thus, we hypothesize that the HIV tat protein interacts with human macrophage host genes, altering their expression, resulting in macrophage dysfunction, neuroinflammation, CNS damage and subsequent development of HAND. To address this hypothesis we will use data we obtained from ChIP-seq assays that identified specific tat binding sites in the macrophage host genome and from Ingenuity Pathway Analysis (IPA) of these 67 sites. We propose three Aims.
Aim 1 is to confirm and characterize the genes identified by ChIP-seq in THP-1-Tat-Flag cell lines.
Aim 2 is to demonstrate alterations in expression of the genes confirmed in AIM 1 in primary human macrophages infected with adenovirus containing Tat-Flag, and with HIV, as compared to uninfected macrophages, and in tissue sections of brains obtained from HIV infected people with and without HAND.
Aim 3 is to demonstrate the amino acids of tat that mediate host gene expression. Our approaches will provide new information about how tat alters host gene expression and the contribution of these dysregulated genes to the pathogenesis of HAND. It is anticipated that these data will indicate innovative strategies for therapeutic intervention to limt the consequences of HIV CNS infection.
HIV enters the CNS soon after peripheral infection and persists despite effective antiretroviral therapy. Macrophages are the major cells infected in the brain, and unlike T cells, HIV infected macrophages are long lived. These cells elaborate mediators that promote inflammation as well as neurotoxic factors, all of which lead to HIV associated neurocognitive impairment, or HAND, in greater than 50% of HIV infected people even when on successful antiretrovirals. Tat is an HIV protein produced early in the life cycle of the virus that interacts with the host genome and alters host gene expression. It is important to identify the host genes dysregulated by tat in macrophages, as well as how this interaction is mediated, to develop appropriate therapeutic interventional strategies to limit CNS HIV pathogenesis and HAND. We used ChIP-seq assays of human macrophage infected with lentiviruses containing tat to identify host genes to which the tat complex binds and now we propose to examine the regulation of expression of these genes and which specific amino acids of tat mediate this regulation using molecular and cellular biologic approaches.
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