SUMMARY Caloric restriction (CR) mitigates many detrimental effects of aging and prolongs lifespan. CR has been suggested to increase mitochondrial biogenesis, thereby attenuating age-related declines in mitochondrial function; a concept that is challenged by recent studies. Here we show that lifelong CR in mice prevents age-related loss of mitochondrial oxidative capacity and efficiency, measured in isolated mitochondria and permeabilized muscle fibers. We find that these beneficial effects of CR occur without increasing mitochondrial abundance. Whole-genome expression profiling and large-scale proteomic surveys revealed expression patterns inconsistent with increased mitochondrial biogenesis, which is further supported by lower mitochondrial protein synthesis with CR. We find that CR decreases oxidant emission, increases antioxidant scavenging, and minimizes oxidative damage to DNA and protein. These results demonstrate that CR preserves mitochondrial function by protecting the integrity and function of existing cellular components rather than by increasing mitochondrial biogenesis.

Omega-3 polyunsaturated fatty acids (n3-PUFA) are recognized for their anti-inflammatory effects and may be beneficial in the context of sarcopenia. We determined the influence of n3-PUFA on muscle mitochondrial physiology and protein metabolism in older adults. Twelve young (18-35 years) and older (65-85 years) men and women were studied at baseline. Older adults were studied again following n3-PUFA supplementation (3.9g/day, 16 weeks). Muscle biopsies were used to evaluate respiratory capacity (high resolution respirometry) and oxidant emissions (spectrofluorometry) in isolated mitochondria. Maximal respiration was significantly lower in older compared to young. n3-PUFA did not change respiration, but significantly reduced oxidant emissions. Participants performed a single bout of resistance exercise, followed by biopsies at 15 and 18 hours post exercise. Several genes involved in muscle protein turnover were significantly altered in older adults at baseline and following exercise, yet muscle protein synthesis was similar between age groups under both conditions. Following n3-PUFA supplementation, mixed muscle, mitochondrial, and sarcoplasmic protein synthesis rates were increased in older adults before exercise. n3-PUFA increased post-exercise mitochondrial and myofibrillar protein synthesis in older adults. These results demonstrate that n3-PUFA reduce mitochondrial oxidant emissions, increase postabsorptive muscle protein synthesis, and enhance anabolic responses to exercise in older adults.

Acute aerobic exercise increases reactive oxygen species and could potentially damage proteins, but exercise training (ET) enhances mitochondrial respiration irrespective of age. Here, we report a differential impact of ET on protein quality in young and older participants. Using mass spectrometry we measured oxidative damage to skeletal muscle proteins before and after 8 weeks of ET and find that young but not older participants reduced oxidative damage to both total skeletal muscle and mitochondrial proteins. Young participants showed higher total and mitochondrial derived semitryptic peptides and 26S proteasome activity indicating increased protein degradation. ET however, increased the activity of the endogenous antioxidants in older participants. ET also increased skeletal muscle content of the mitochondrial deacetylase SIRT3 in both groups. A reduction in the acetylation of isocitrate dehydrogenase 2 was observed following ET that may counteract the effect of acute oxidative stress. In conclusion aging is associated with an inability to improve skeletal muscle and mitochondrial protein quality in response to ET by increasing degradation of damaged proteins. ET does however increase muscle and mitochondrial antioxidant capacity in older individuals, which provides increased buffering from the acute oxidative effects of exercise.

Jaleel A, Short KR, Asmann YW, Klaus KA, Morse DM, Ford GC, Nair KS. In vivo measurement of synthesis rate of individual skeletal muscle mitochondrial proteins.

EAAs increased MiPS and oxidative enzyme activity only with high insulin concentrations.