Chemokine receptor expression and signaling in macaque and human fetal neurons and astrocytes: implications for the neuropathogenesis of AIDS

Abstract

Chemokines are believed to play a role in the neuropathogenesis of AIDS through their recruitment of neurotoxin-secreting, virally infected leukocytes into the CNS. Levels of chemokines are elevated in brains of patients and macaques with HIV/SIV-induced encephalitis. The chemokine receptors CCR3, CCR5, and CXCR4 are found on subpopulations of neurons in the cortex of human and macaque brain. We have developed an in vitro system using both macaque and human fetal neurons and astrocytes to further investigate the roles of these receptors in neuronal response to inflammation. Here we report the presence of functional HIV/SIV coreceptors CCR3, CCR5, and CXCR4 on fetal human and macaque neurons and CCR5 and CXCR4 on astrocytes immediately ex vivo and after several weeks in culture. Confocal imaging of immunostained neurons demonstrated different patterns of distribution for these receptors, which may have functional implications. Chemokine receptors were shown to respond to their appropriate chemokine ligands with increases in intracellular calcium that, in the case of neurons, required predepolarization with KCl. These responses were blocked by neutralizing chemokine receptor in mAbs. Pretreatment of neural cells with pertussis toxin abolished responses to stromal-derived factor-1alpha, macrophage inflammatory protein-1beta, and RANTES, indicating coupling of CCR5 and CXCR4 to a Gialpha protein, as in leukocytes. Cultured macaque neurons demonstrated calcium flux response to treatment with recombinant SIVmac239 envelope protein, suggesting a mechanism by which viral envelope could affect neuronal function in SIV infection. The presence of functional chemokine receptors on neurons and astrocytes suggests that chemokines could serve to link inflammatory and neuronal responses.