STABILIZATION OF THE PYRUVATE-DEHYDROGENASE E1-ALPHA SUBUNIT BY DICHLOROACETATE

Objective: To test the effects of dichloroacetate (DCA) treatment on t he rate of turnover of pyruvate dehydrogenase (PDH) subunits. Backgrou nd: PDH deficiency is a nuclear-encoded mitochondrial disorder and a m ajor recognized cause of neonatal encephalomyopathies associated with primary lactic acidosis. DCA has been used for its treatment. The prim ary mechanism of action of DCA has been thought to increase the propor tion of enzyme in the activated, dephosphorylated state. However, this mechanism does not readily account for responses to treatment with mu tations that do not obviously affect regulation of the enzyme complex. Methods: PDH subunit turnover rates were measured using pulse-chase m ethods in a normal fibroblastic cell line before and after chronic (5- day) treatment with 5 mM DCA. Results: Chronic DCA treatment causes a more than twofold decrease in the apparent first-order rate constant f or degradation of the PDH E1 alpha subunit (k(E1)alpha(pre-DCA) = 0.02 5 +/- 0.006 hr(-1), n = 6; k(E1)alpha(post-DCA) = 0.011 +/- 0.002 hr(- 1), n = 3; p < 0.01) and a selective, progressive increase in the tota l cell PDH activity by 150 +/- 5% (p < 0.0005). Conclusion: These resu lts suggest an additional novel mechanism of action for the chronic DC A treatment of lactic acidemia; namely, inhibition of mitochondrial E1 alpha subunit degradation leading to an increase in maximal PDH compl ex activity.