HIV: gp120, Chemokine Receptors & Macrophage Activation

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DESCRIPTION (provided by applicant): Clinical disease in HIV encephalopathy (HIVE) is closely correlated with the degree of macrophage/microglia (M/M) activation, and many models have shown that HIV-1 induces M/M to release soluble mediators that injure neurons & have inflammatory or chemotactic potential. Both exposure to the HIV-1 Env glycoprotein gp120 & direct infection can induce these responses. These results implicate a major pathogenic role for HIV-elicited M/M activation & neurotoxin production. Many studies have addressed inflammatory mediators in HIVE & neurotoxins released by M/M in response to HIV. However, little is known about the specific mechanism by which HIV triggers M/M activation & neurotoxin release, which is an important gap in our understanding of HIV neuropathogenesis. To enter cells, HIV-1 uses the chemokine receptors CCR5 & CXCR4, which normally trigger activation & migration in response to extracellular stimuli. In studies supported by the previous funding period, we found that gp120 elicits intracellular signals in primary macrophages through the chemokine receptors including ionic signals, Ca2+ elevations & protein kinase phosphorylation. In addition, activation through these pathways leads to release of inflammatory mediators that may contribute to further activation & cell recruitment. Furthermore, we found that gp120-activated macrophages produce factors that injure neurons, and identified specific MAP kinase pathways activated through chemokine receptor interactions responsible. This project will focus on mechanisms of gp120- elicited M/M activation in HIVE pathogenesis. Our hypothesis is that HIV-1 Env interacts with chemokine receptors on brain macrophage/microglia to trigger intracellular signaling cascades that lead to inappropriate activation, inflammatory mediator secretion, and neurotoxin production. The goals of this project are to better understand pathways elicited by HIV-1 Env in macrophages, and how these signaling cascades contribute to macrophage activation & dysfunction relevant to HIVE. We will: (1) Define the intracellular signals activated by HIV-1 through the chemokine receptors in primary human macrophages; (2) Determine the specific pathways involved in HIV-elicited macrophage cytokine & neurotoxin production; and (3) Identify signaling pathways linked to primary, viruses & primary cells directly relevant to HIVE pathogenesis, using primary isolates derived from HIVE tissue, and primary human brain-derived macrophage/microglia to validate results obtained in monocyte-derived macrophages. We anticipate that these studies will provide insight into the afferent mechanisms of M/M activation & neurotoxin production in HIVE and, ultimately, provide a rational basis for targeted strategies to interfere with this process.