Tissue-specific effects on TFAM amount, mtDNA and TFAM-binding to mtDNA in aged and calorie-restricted rat

Mitochondrial Transcription Factor A (TFAM) is a histone-like protein for mitochondrial DNA (mtDNA), involved in multiple functions for this genome. Aging markedly affects mitochondrial biogenesis and functions in a tissue-specific manner and calorie restriction (CR) diet is, so far, the only intervention able to delay or prevent the onset of several age-related alterations, also in mitochondria, in different organisms. TFAM amount, mtDNA content and TFAM-binding to mtDNA were analyzed in samples of frontal cortex and soleus skeletal muscle from 6- and 26-month-old ad libitum-fed and 26-month-old calorie-restricted rats and of liver from18- and 28-month-old ad libitum-fed and 28-month-old calorie-restricted rats. We found an age-related increase in TFAM amount in the frontal cortex, not affected by CR, whereas an age-related decrease was present in the soleus and liver, fully prevented by CR. The semi-quantitative analysis of in vivo binding of TFAM to specific mtDNA regions, by mtDNA immunoprecipitation assay and following PCR, showed a marked age-dependent decrease in TFAM-binding activity in the frontal cortex, partially prevented by CR. An age-related increase in TFAM-binding to mtDNA, fully prevented by CR, was found in the soleus and liver. A common age-related decrease in mtDNA content, completely prevented by CR, was found in the soleus and liver, but not in the frontal cortex. The modulation of TFAM expression, TFAM-binding to mtDNA and mtDNA content with aging and CR showed a trend shared by the skeletal muscle and liver, but not by the frontal cortex counterpart. Considering the above mentioned findings, aging and CR appear to induce similar mitochondrial molecular mechanisms in the skeletal muscle and liver, different from those elicited in the frontal cortex.