7th Conference - Abstract 289

a-Chemokines and their Receptors in Neuronal Signaling: Relevance for HIV-1-Associated Dementia

J. ZHENG*, D. NIEMANN, M. BAUER, G. B. LEISMAN, R. L. COTTER, L. A. RYAN, A. LOPEZ, C. WILLIAMS, A. GHORPADE, and H. E. GENDELMAN. Univ. Nebraska Med. Ctr., Omaha

Chemokines and their receptors, which regulate HIV-1 infection in CD4⁺ T lymphocytes and macrophages, are also expressed on neural cells (microglia, astrocytes and/or neurons). The interaction between chemokine receptors, their ligand(s) and viral products affect the onset and/or tempo of HIV-1 associated dementia. We investigated the expression of a-chemokines as well as their receptors (including CXCR2, CXCR4 and CXCR5) in neural cells following viral infection and their abilities to influence neuronal signaling. Receptor function in neurons was assessed through the analysis of GTP binding protein (G-protein) linked intracellular signaling. Neuronal injury was determined by assessment of neurofilament expression and neuronal apoptosis. FACS analysis revealed that 10-30% of human neurons expressed CXCR2, CXCR4 and CXCR5. Immunocytochemical tests showed that CXCR5 was present on neuronal dendrites while CXCR2 and CXCR4 were on neuronal cell bodies and their processes. ELISA assays demonstrated interleukin-8 (IL-8), the ligand for CXCR2, secretion by macrophages/microglia (MP) and astrocytes. IL-8 was upregulated in HIV-1 infected macrophages and progeny virion-treated astrocytes. Activation of HIV-1 infected MP by lipopolysaccharide or CD40 ligand significantly increased IL-8 levels compared to unactivated cells. IL-8 induced a modest G inhibitory (Gi) protein linked decrease in cyclic AMP (cAMP) and increased inositol 1,4,5-triphosphate (IP₃) in human astrocytes and neurons while BLC-1 (ligand for CXCR5) had no effect on these pathways. Importantly, IL-8, at 100-500 ng/ml, induced neuronal apoptosis (determined by fragmented DNA ELISA) and decreased neuronal dendrite formation (assayed by neurofilament ELISA). BLC-1, at 10-500 ng/ml had only a modest effect on neuronal dendrites but not apoptosis. Importantly, BLC-1 showed a partial protective role for HIV-1 virion-induced neuronal injury while IL-8 had no such effect. These results, taken together, demonstrate potential pathogenic role(s) for a-chemokines and their receptors during HIV-1 infection of neural cells.

Key Words: Alpha-Chemokines, Chemokine Receptors, HIV-1 Dementia