(12) REGULATION OF MITOCHONDRIAL GENE EXPRESSION DURING GLUTAMATE EXCITOTOXICITY IN RAT CEREBELLAR NEURONAL CULTURES

K. Chandrasekaran* and G. Fiskum
Dept. of Anesthesiology, University of Maryland School of Medicine, Baltimore, MD 21201

Mechanisms regulating mitochondrial gene expression are not well understood although altered expression likely contributes to the pathophysiology of neurodegenerative diseases. Previously, we have observed that elevation of intracellular sodium ([Na]i) markedly decreases levels of mitochondrial mRNA in cultured neurons. Thus, addition of ouabain or monensin to differentiated PC12 cells caused a 50% decrease in levels of mitochondrial DNA (mtDNA)-encoded cytochrome oxidase subunit III (C.O III) mRNA within 6h. This was unexpected since high [Na]i increases energy demand which normally up-regulates mitochondrial gene expression. We hypothesized that high [Na]i following exposure of neurons to excitotoxic levels of glutamate inhibits mitochondrial gene expression, affects their electron transport-dependent activities (e.g., [Ca 2+]i buffering, and free radical generation) and increases their vulnerability to both necrotic and apoptotic cell death. We evaluated this hypothesis by measuring the levels of mitochondrial mRNA, respective protein subunits and enzyme activity in primary rat cerebellar cultures after a transient exposure to glutamate. Addition of 100 uM glutamate + 10 uM glycine for 30 min followed by incubation in normal growth medium, resulted in a ~50% reduction in mtDNA-encoded C.O III mRNA in the absence of acute cell death. Experiments are in progress to determine the temporal relationship between reduction in mitochondrial mRNA, levels of protein subunits, enzyme activity and cell death. Supported by NS34152 and a grant from the IPSEN Institut Henri-Beaufour.