Dietary nitrate preserves mitochondrial bioenergetics and mitochondrial protein synthesis rates during short‐term immobilization in mice

Abstract

Skeletal muscle disuse reduces muscle protein synthesis rates and induces atrophy, events associated with decreased mitochondrial respiration and increased reactive oxygen species. Given that dietary nitrate can improve mitochondrial bioenergetics, we examined whether nitrate supplementation attenuates disuse‐induced impairments in mitochondrial function and muscle protein synthesis rates. Female C57Bl/6N mice were subjected to single‐limb casting (3 or 7 days) and consumed drinking water with or without 1 mM sodium nitrate. Compared with the contralateral control limb, 3 days of immobilization lowered myofibrillar fractional synthesis rates (FSR, P < 0.0001), resulting in muscle atrophy. Although FSR and mitophagy‐related proteins were higher in subsarcolemmal (SS) compared with intermyofibrillar (IMF) mitochondria, immobilization for 3 days decreased FSR in both SS (P = 0.009) and IMF (P = 0.031) mitochondria. Additionally, 3 days of immobilization reduced maximal mitochondrial respiration, decreased mitochondrial protein content, and increased maximal mitochondrial reactive oxygen species emission, without altering mitophagy‐related proteins in muscle homogenate or isolated mitochondria (SS and IMF). Although nitrate consumption did not attenuate the decline in muscle mass or myofibrillar FSR, intriguingly, nitrate completely prevented immobilization‐induced reductions in SS and IMF mitochondrial FSR. In addition, nitrate prevented alterations in mitochondrial content and bioenergetics after both 3 and 7 days of immobilization. However, in contrast to 3 days of immobilization, nitrate did not prevent the decline in SS and IMF mitochondrial FSR after 7 days of immobilization. Therefore, although nitrate supplementation was not sufficient to prevent muscle atrophy, nitrate may represent a promising therapeutic strategy to maintain mitochondrial bioenergetics and transiently preserve mitochondrial protein synthesis rates during short‐term muscle disuse. imageKey points Alterations in mitochondrial bioenergetics (decreased respiration and increased reactive oxygen species) are thought to contribute to muscle atrophy and reduced protein synthesis rates during muscle disuse. Given that dietary nitrate can improve mitochondrial bioenergetics, we examined whether nitrate supplementation could attenuate immobilization‐induced skeletal muscle impairments in female mice. Dietary nitrate prevented short‐term (3 day) immobilization‐induced declines in mitochondrial protein synthesis rates, reductions in markers of mitochondrial content, and alterations in mitochondrial bioenergetics. Despite these benefits and the preservation of mitochondrial content and bioenergetics during more prolonged (7 day) immobilization, nitrate consumption did not preserve skeletal muscle mass or myofibrillar protein synthesis rates. Overall, although dietary nitrate did not prevent atrophy, nitrate supplementation represents a promising nutritional approach to preserve mitochondrial function during muscle disuse.

Under‐fuelling the fire: mitochondrial implications for energy deficiency and muscle protein synthesis

“…Additionally, as alluded to above, it is possible that LEA enhances the breakdown of muscle protein to provide substrates for the production of ATP in an attempt to maintain cellular energy homeostasis, especially following exercise when substrates are not being adequately replenished. In line with this, it may be interesting for a follow-up study to investigate mitochondrial-specific protein synthesis rates given that: (1) mitochondria are primarily responsible for cellular energy production and are thus likely influenced by LEA; (2) mitochondrial FSR responds to nutritional/physical inactivity in rodent models (Petrick et al, 2023); and (3) impaired mitochondrial bioenergetics (i.e. decreased respiration, altered substrate preference and increased reactive oxygen species production) is thought to contribute to muscle atrophy and reduced protein synthesis in various physiological conditions (Trommelen et al, 2023).…”

Skeletal muscle immobilisation-induced atrophy: mechanistic insights from human studies

“…Current countermeasures for muscle disuse atrophy include, but are not limited to, contractile activity, i.e., electrical stimulation [ 22 , 23 ], pre-habilitation [ 7 ], in situ resistance exercise [ 24 ] or nutrition, i.e., omega-3 supplementation [ 25 , 26 ], protein/amino acid supplementation [ 27 , 28 ] and structured feeding patterns [ 29 ]. Each, however, displays limited consistent efficacy in humans, while effective interventions remain elusive given our incomplete understanding of the underlying mechanisms of disuse atrophy [ 30 ]. In addition to non-pharmacological interventions, novel drug therapies targeting muscle atrophy (e.g.…”