Fig. 2

Mitochondrial composition is altered with age. Mitochondrial-encoded (ND1-6, CytB, COX1-3, ATP6, and ATP8) and nuclear-encoded (NDUFAB1, SDHb, SDHd, UQCRC1-2, ATP5a1) mRNA analyzed by quantitative RT-PCR in skeletal muscle of young (Y), middle-aged (M), and old (O) mice (M) (a–c), rhesus monkeys (Rh) (d–f) and humans (H) (g–i). Relative expression values were normalized to young within each species. j Citrate synthase activity measured in skeletal muscle of young (Y), middle-aged (M), and old (O) species. k Mitochondrial DNA content analyzed by quantitative PCR in skeletal muscle of young (Y), middle-aged (M), and old (O) mice, rhesus monkeys and humans. Relative expression values were normalized to young. Electronic microscopy analysis of skeletal muscle of young (Y), middle-aged (M), and old (O) mice (l) and rhesus monkeys (m) and the respective mitochondrial area quantification and circularity. Arrows indicate intermyofibrillar mitochondria; asterisks indicate sarcoplasmic reticulum. Bars equal to 1 µm. n Cellular ATP content from skeletal muscle of young (Y), middle-aged (M), and old (O) mice and rhesus monkeys. *p < 0.05 vs. young. Values are expressed as mean ± SEM