The mechanism of glutamate-induced degeneration of cultured Huntington's disease and control fibroblasts

Abstract

Human cultured skin fibroblasts undergo rapid cellular degeneration and cell death when exposed to moderate levels of glutamate (10–30 mM). Huntington's disease (HD) skin fibroblast cultures are more sensitive to the toxic effects of glutamate (Gray et al. 1980) and elucidation of the toxic mechanism may bear on degenerative processes occurring in the HD brain. Glutamate toxicity was found to be inversely related to cystine content in the culture medium. Supplementing culture media with cystine effectively suppressed toxicity of l-Glu and that of a closely related but more potent analogue, l-homocysteic acid ( l-HCA). Glutamate and l-HCA treatment provoked a rapid and marked decrease in cellular glutathione levels prior to cell death. Depletion of cellular glutathione with buthionine sulfoximine potentiated the toxicity of glutamate and l-HCA. Glutamate- or l-HCA-induced cell death also could be reduced or inhibited by co-treatment with antioxidants, thereby suggesting that free radical-induced peroxidative damage may ultimately be responsible for the loss of cell viability. While no site for the differential sensitivity of HD and normal fibroblasts to glutamate was clearly discerned, our results suggest that HD fibroblasts are more susceptible to peroxidative damage. The increased deposition of lipofuscin (Tellez-Nagel et al. 1974) and abnormal neuronal membrane ultrastructure seen in HD (Roizin et al. 1979) suggest similar degenerative processes may occur in HD brain.