Changes in TFAM binding at both origins of mitochondrial DNA replication are involved in the mitochondrial biogenesis alterations related to aging and calorie restriction in rat liver.

Mitochondrial biogenesis is among the organelle’s features affected by aging in tissue-specific ways. The only intervention, so far, able to delay or prevent the onset of several age-related changes, also in mitochondria, is calorie restriction (CR). Aging and CR both influence in a relevant manner mitochondrial structure and function in rat liver. Using livers from 18-month-old, 28-month-old, 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. Also the proteins PGC-1 and NRF-1 as well as the nuclear-encoded cytochrome c oxidase subunit IV revealed an age-related decrease, confirming the reduction in mitochondrial biogenesis with aging, that was completely prevented by CR. The already described age-related increased oxidative stress was verified and also prevented by CR. We reported with aging a decrease in peroxiredoxin III (Prx III) and in mitochondrial superoxide dismutase 2 (SOD2) proteins, usually sensitive to an increased ROS presence and also involved in mitochondrial biogenesis, which suggested a prevailing relevance of the age-reduced mitochondrial biogenesis above the induction by ROS in the regulation of expression with aging. Furthermore, the full prevention of the decrease in Prx III and SOD2 by CR suggested that, in rat liver, the preservation of the mitochondrial biogenesis might be more relevant than the reduction of the oxidative stress in the anti-aging action of CR. We then analyzed the in vivo TFAM binding to specific mtDNA regions finding a marked increase in the TFAM-bound amounts of mtDNA at both origins of replication with aging, fully prevented by CR. Joining the data from the 18-month-old ad libitum-fed and the 28-month-old calorie-restricted samples we could find a novel, positive correlation between the coupled amounts of TFAM-bound mtDNA at the origins of replication, not present in the 28-month-old ad libitum-fed animals, thus suggesting a quite different modulation of TFAM binding at these sub-regions in aging and in CR, likely involved in the respective alterations of mitochondrial biogenesis.