Changes in dihydrolipoamide dehydrogenase expression and activity during postnatal development and aging in the rat brain

Brain energy metabolism is increased during postnatal development and diminished in neurodegenerative diseases linked to senescence. The objective of this study was to determine if these conditions could involve postnatal or senescence-related shifts in activity or expression of dihydrolipoamide dehydrogenase (DLDH), a key mitochondrial oxidoreductase. Rats ranging from 10 to 60 days of age were used in studies of postnatal development, whereas rats aged 5 or 30 months were used in the aging studies. The expression of DLDH was determined by Western blot analysis using anti-DLDH antibodies and DLDH diaphorase activity was measured by an in-gel activity staining method using nitroblue tetrazolium (NBT)/NADH. Activity of DLDH dehydrogenase was measured as NAD⁺ oxidation of dihydrolipoamide. When these measures were considered in separate groups of 10-, 20-, 30-, or 60-day-old rats, all three showed an increase between 10 and 20 days of age. However, dehydrogenase activity of DLDH showed a further, progressive increase from 20 days to adulthood, in the absence of any further change in DLDH expression or diaphorase activity. No age-related decline in DLDH activity or expression was evident over the period from 5 to 30 months of age. Moreover, aging did not render DLDH more susceptible to oxidative inactivation by mitochondria-generated reactive oxygen species (ROS). Taken together, results of the present study indicate that (1) brain DLDH expression and activity undergo independent postnatal maturational increases; (2) senescence does not confer any detectable change in the activity of DLDH or its susceptibility to inactivation by mitochondrial oxidative stress.