HIV‐1 Envelope Proteins gp120 and gp160 Potentiate NMDA‐induced [Ca²⁺]_i Increase, Alter [Ca²⁺]_i Homeostasis and Induce Neurotoxicity in Human Embryonic Neurons

Abstract

The envelope glycoprotein gp120 of the human immunodeficiency virus HIV-1 has been proposed to cause neuron death in developing murine hippocampal cultures and rat retinal ganglion cells. In the present study, cultured human embryonic cerebral and spinal neurons from 8- to 10-week-old embryos were used to study the neurotoxic effect of gp120 and gp160. Electrophysiological properties as well as N-methyl-D-aspartate (NMDA)-induced current were recorded from neurons maintained in culture for 10-30 days. Neither voltage-activated sodium or calcium currents nor NMDA-induced currents were affected by exposure of neurons to 250 pM gp120 or gp160. In contrast, when neurons were subjected to photometric measurements using the calcium dye indo-1 to monitor the intracellular free Ca2+ concentration ([Ca2+])i, gp120 and gp160 (20-250 pM) potentiated the large rises in [Ca2+]i induced by 50 microM NMDA. The potentiation of NMDA-induced Ca2+ responses required the presence of Ca2+ in the medium, and was abolished by the NMDA antagonist D-2-amino-5-phosphonovalerate (AP5) and the voltage-gated Ca2+ channel inhibitor nifedipine. Moreover, exposure of a subpopulation of spinal neurons (25% of the cells tested) to 20-250 pM gp120 or gp160 resulted in an increase in [Ca2+]i that followed three patterns: fluctuations not affected by AP5, a single peak, and the progressive and irreversible rise of [Ca2+]i. The neurotoxicity of picomolar doses of gp120 and gp160 cultures was estimated by immunofluorescence and colorimetric assay. Treatment of cultures with AP5 or nifedipine reduced gp120-induced toxicity by 70 and