Background Mycoprotein is a fungal-derived sustainable protein-rich food source, and its ingestion results in systemic amino acid and leucine concentrations similar to that following milk protein ingestion. Objective We assessed the mixed skeletal muscle protein synthetic response to the ingestion of a single bolus of mycoprotein compared with a leucine-matched bolus of milk protein, in rested and exercised muscle of resistance-trained young men. Methods Twenty resistance-trained healthy young males (age: 22 ± 1 y, body mass: 82 ± 2 kg, BMI: 25 ± 1 kg·m−2) took part in a randomized, double-blind, parallel-group study. Participants received primed, continuous infusions of L-[ring-2H5]phenylalanine and ingested either 31 g (26.2 g protein: 2.5 g leucine) milk protein (MILK) or 70 g (31.5 g protein: 2.5 g leucine) mycoprotein (MYCO) following a bout of unilateral resistance-type exercise (contralateral leg acting as resting control). Blood and m. vastus lateralis muscle samples were collected before exercise and protein ingestion, and following a 4-h postprandial period to assess mixed muscle fractional protein synthetic rates (FSRs) and myocellular signaling in response to the protein beverages in resting and exercised muscle. Results Mixed muscle FSRs increased following MILK ingestion (from 0.036 ± 0.008 to 0.052 ± 0.006%·h−1 in rested, and 0.035 ± 0.008 to 0.056 ± 0.005%·h−1 in exercised muscle; P <0.01) but to a greater extent following MYCO ingestion (from 0.025 ± 0.006 to 0.057 ± 0.004%·h−1 in rested, and 0.024 ± 0.007 to 0.072 ± 0.005%·h−1 in exercised muscle; P <0.0001) (treatment × time interaction effect; P <0.05). Postprandial FSRs trended to be greater in MYCO compared with MILK (0.065 ± 0.004 compared with 0.054 ± 0.004%·h−1, respectively; P = 0.093) and the postprandial rise in FSRs was greater in MYCO compared with MILK (Delta 0.040 ± 0.006 compared with Delta 0.018 ± 0.005%·h−1, respectively; P <0.01). Conclusions The ingestion of a single bolus of mycoprotein stimulates resting and postexercise muscle protein synthesis rates, and to a greater extent than a leucine-matched bolus of milk protein, in resistance-trained young men. This trial was registered at clinicaltrials.gov as 660065600.

The present study investigated the contribution of myofibrillar protein synthesis (MyoPS) and associated gene signaling to recovery from 300 muscle-damaging, eccentric contractions. Measured with D2O, MyoPS rates were elevated during recovery and observed alongside expression of inflammatory and regenerative signaling pathways. A nutritional intervention accelerated recovery; however, MyoPS and gene signaling were unchanged compared with placebo. These data indicate that MyoPS and associated signaling do not explain accelerated recovery from muscle damage.

Burn trauma results in prolonged hypermetabolism and skeletal muscle wasting. How hypermetabolism contributes to muscle wasting in burn patients remains unknown. We hypothesized that oxidative stress, cytosolic protein degradation, and mitochondrial stress as a result of hypermetabolism contribute to muscle cachexia postburn. Patients (n = 14) with burns covering >30% of their total body surface area were studied. Controls (n = 13) were young healthy adults. We found that burn patients were profoundly hypermetabolic at both the skeletal muscle and systemic levels, indicating increased oxygen consumption by mitochondria. In skeletal muscle of burn patients, concurrent activation of mTORC1 signaling and elevation in the fractional synthetic rate paralleled increased levels of proteasomes and elevated fractional breakdown rate. Burn patients had greater levels of oxidative stress markers as well as higher expression of mtUPR-related genes and proteins, suggesting that burns increased mitochondrial stress and protein damage. Indeed, upregulation of cytoprotective genes suggests hypermetabolism-induced oxidative stress postburn. In parallel to mtUPR activation postburn, mitochondrial-specific proteases (LONP1 and CLPP) and mitochondrial translocases (TIM23, TIM17B, and TOM40) were upregulated, suggesting increased mitochondrial protein degradation and transport of preprotein, respectively. Our data demonstrate that proteolysis occurs in both the cytosolic and mitochondrial compartments of skeletal muscle in severely burned patients. Increased mitochondrial protein turnover may be associated with increased protein damage due to hypermetabolism-induced oxidative stress and activation of mtUPR. Our results suggest a novel role for the mitochondria in burn-induced cachexia.

Context The early events regulating the remodelling programme following skeletal muscle damage are poorly understood. Objective The objective of this study was to determine the association between myofibrillar protein synthesis (myoPS) and nuclear factor-kappa B (NF-κB) signalling by nutritionally accelerating recovery of muscle function following damage. Design, setting, participants, and interventions Healthy males and females consumed daily post-exercise and pre-bed protein-polyphenol (PP; n=9; 4 females) or isocaloric maltodextrin placebo (PLA; n=9; 3 females) drinks (parallel design), 6 days before and 3 days after 300 unilateral eccentric quadriceps contractions (EC) during complete dietary control. Main outcome measures Muscle function was assessed daily, and skeletal muscle biopsies were taken after 24, 27 and 36 h for measurements of myoPS rates using deuterated water, and gene ontology and NF-κB signalling analysis using an RT-qPCR gene array. Results EC impaired muscle function for 48 h in PLA, but for just 24 h in PP (P=0.047). EC increased myoPS compared to the control leg during post-exercise (24–27 h; 0.14±0.01 vs 0.11±0.01%·h -1, respectively; P=0.075) and overnight periods (27–36 h; 0.10±0.01 vs 0.07±0.01%·h -1, respectively; P=0.020), but was not further increased by PP (P>0.05). PP decreased post-exercise and overnight muscle IL1R1 (PLA=2.8±0.4, PP=1.1±0.4 and PLA=1.9±0.4, PP=0.3±0.4 log2 fold change, respectively) and IL1RL1 (PLA=4.9±0.7, PP=1.6±0.8 and PLA=3.7±0.6, PP=0.7±0.7 log2 fold change, respectively) mRNA expression (P<0.05) and downstream NF-κB signalling compared to PLA. Conclusion PP ingestion likely accelerates recovery of muscle function by attenuating inflammatory NF-κB transcriptional signalling, possibly to reduce aberrant tissue degradation rather than increase myoPS rates.