Glucocorticoid exacerbation of gp120 neurotoxicity: role of microglia

Gp120 protein, part of the HIV coat, may be a causative agent in AIDS-Related Dementia (ARD) because of its demonstrated neurotoxicity in vitro and in vivo. There are two possible mechanisms for this toxicity, namely through release of toxins from the microglia or through direct action on neuronal chemokine receptors. In tissue culture, glucocorticoids (GCs), the adrenal steroids released during stress, exacerbate gp120 neurotoxicity. In this paper, we examine the means by which GCs may increase toxicity, focusing on interactions with microglia and glia. Media from microglia treated with gp120 was toxic to neurons but not to glia. The effects of GCs upon the extent of gp120-induced release of toxins by microglia seemed to be dependent on the time of exposure to the hormone. Twenty-four-hour exposure of microglia to GCs decreased the toxicity of gp120-treated microglial conditioned media. In contrast, longer-term GC exposure enhanced neurotoxicity. There also appeared to be a component of gp120 neurotoxicity in hippocampal cultures that was exacerbated by GCs, independent of the amount of microglia present. Thus, GCs appear to act at a number of different sites in the multi-cellular pathway to exacerbate the neurotoxic effects of gp120.