Aging and calorie restriction oppositely affect mitochondrial biogenesis through TFAM binding at both origins of mitochondrial DNA replication in rat liver

Aging affects mitochondria in a tissue-specific manner. Calorie restriction (CR) is, so far, the only intervention able to delay or prevent the onset of several age-related changes also in mitochondria. Using livers from middle age (18-month-old), 28-month-old and 32-month-old ad libitum-fed and 28-month-old calorie-restricted rats we found an age-related decrease in mitochondrial DNA (mtDNA) content and mitochondrial transcription factor A (TFAM) amount, fully prevented by CR. We revealed also an age-related decrease, completely prevented by CR, for the proteins PGC-1α NRF-1 and cytochrome c oxidase subunit IV, supporting the efficiency of CR to forestall the age-related decrease in mitochondrial biogenesis. Furthermore, CR counteracted the age-related increase in oxidative damage to proteins, represented by the increased amount of oxidized peroxiredoxins (PRX-SO3) in the ad libitum-fed animals. An unexpected age-related decrease in the mitochondrial proteins peroxiredoxin III (Prx III) and superoxide dismutase 2 (SOD2), usually induced by increased ROS and involved in mitochondrial biogenesis, suggested a prevailing relevance of the age-reduced mitochondrial biogenesis above the induction by ROS in the regulation of expression of these genes with aging. The partial prevention of the decrease in Prx III and SOD2 proteins by CR also supported the preservation of mitochondrial biogenesis in the anti-aging action of CR. To investigate further the age-and CR-related effects on mitochondrial biogenesis we analyzed the in vivo binding of TFAM to specific mtDN