Daily protein supplementation attenuates immobilization-induced blunting of postabsorptive muscle mTORC1 activation in middle-aged men.

Disuse-induced muscle atrophy is accompanied by a blunted postprandial response of the mammalian target of rapamycin complex 1 (mTORC1) pathway. Conflicting observations exist as to whether postabsorptive mTORC1 pathway activation is also blunted by disuse and plays a role in atrophy. It is unknown whether changes in habitual protein intake alter mTORC1 regulatory proteins and how they may contribute to the development of anabolic resistance. The primary objective of this study was to characterize the downstream responsiveness of skeletal muscle mTORC1 activation and its upstream regulatory factors, following 14 days of lower limb disuse in middle-aged men (45-60 yr). The participants were further randomized to receive daily supplementation of 20 g/d of protein (n = 12; milk protein concentrate) or isocaloric carbohydrate placebo (n = 13). Immobilization reduced postabsorptive skeletal muscle phosphorylation of the mTORC1 downstream targets, 4E-BP1, P70S6K, and ribosomal protein S6 (RPS6), with phosphorylation of the latter two decreasing to a greater extent in the placebo, compared with the protein supplementation groups (37% ± 13% vs. 14% ± 11% and 38% ± 20% vs. 25% ± 8%, respectively). Sestrin2 protein was also downregulated following immobilization irrespective of supplement group, despite a corresponding increase in its mRNA content. This decrease in Sestrin2 protein was negatively correlated with the immobilization-induced change in the in silico-predicted regulator miR-23b-3p. No other measured upstream proteins were altered by immobilization or supplementation. Immobilization downregulated postabsorptive mTORC1 pathway activation, and 20 g/day of protein supplementation attenuated the decrease in phosphorylation of targets regulating muscle protein synthesis.

MitoQ and CoQ10 supplementation mildly suppresses skeletal muscle mitochondrial hydrogen peroxide levels without impacting mitochondrial function in middle-aged men.

PURPOSE: Excess production of reactive oxygen species (ROS) from the mitochondria can promote mitochondrial dysfunction and has been implicated in the development of a range of chronic diseases. As such there is interest in whether mitochondrial-targeted antioxidant supplementation can attenuate mitochondrial-associated oxidative stress. We investigated the effect of MitoQ and CoQ10 supplementation on oxidative stress and skeletal muscle mitochondrial ROS levels and function in healthy middle-aged men. METHODS: Skeletal muscle and blood samples were collected from twenty men (50 ± 1 y) before and following six weeks of daily supplementation with MitoQ (20 mg) or CoQ10 (200 mg). High-resolution respirometry was used to determine mitochondrial respiration and H2O2 levels, markers of mitochondrial mass and antioxidant defences were measured in muscle samples and oxidative stress markers in urine and blood samples. RESULTS: Both MitoQ and CoQ10 supplementation suppressed mitochondrial net H2O2 levels during leak respiration, while MitoQ also elevated muscle catalase expression. However, neither supplement altered urine F2-isoprostanes nor plasma TBARS levels. Neither MitoQ nor CoQ10 supplementation had a significant impact on mitochondrial respiration or mitochondrial density markers (citrate synthase, mtDNA/nDNA, PPARGC1A, OXPHOS expression). CONCLUSION: Our results suggest that neither MitoQ and CoQ10 supplements impact mitochondrial function, but both can mildly suppress mitochondrial ROS levels in healthy middle-aged men, with some indication that MitoQ may be more effective than CoQ10.