Consequences of the alpha-Ketoglutarate Dehydrogenase Inhibition for Neuronal Metabolism and Survival: Implications for Neurodegenerative Diseases

Neurodegenerative diseases are accompanied by reduced activity of mitochondrial alpha-ketoglutarate dehydrogenase multienzyme complex (KGDHC). We present a new cellular model to study molecular mechanisms of this association. By application of the highly specific and efficient inhibitor of KGDHC, succinyl phosphonate (SP), to cultured neurons, we characterized the concentration-and time-dependent consequences of decreased KGDHC activity for neuronal metabolism and viability. Metabolic profiling of SP-treated neurons established accumulation of alpha-ketoglutarate and pyruvate as indicators of the KGDHC inhibition and ensuing impairment of pyruvate oxidation in the tricarboxylic acid cycle. Concomitant increases in alanine, glutamate and gamma-aminobutyrate indicated a scavenging of the accumulated pyruvate and alpha-ketoglutarate by transamination and further decarboxylation of glutamate. Changes among other amino acids were in accordance with their potential to react with alpha-ketoglutarate or products of its transamination and serve as fuel compensating for the KGDHC block. Disturbances in neuronal amino acid pool were accompanied by changed polyamines, decreased total protein and increased thymine, suggesting increased catabolism of amino acids to decrease translation and affect DNA turnover/repair. The ensuing ATP salvage was observed as the paradoxical increase in neuronal ATP by mitochondrial inhibitor SP. Extensive exposure of neurons to SP reduced viability, as revealed by both the ATP- and NAD(P)H-dependent viability tests. Thus, we provide experimental evidence on the KGDHC impairment as a cause of neurodegeneration and decipher underlying molecular mechanisms, exposing the key regulatory complex of the tricarboxylic acid cycle as a promising target for directed regulation of neuronal function and survival.