Mitochondrial-derived Microprotein Mots-c Attenuates Immobilization-induced Skeletal Muscle Atrophy By Inhibiting Fat Infiltration

PURPOSE: MOTS-c, a mitochondrial microprotein, has been described as a novel regulator of glucose and lipid metabolism. In addition to its role as a metabolic regulator, MOTS-c prevents skeletal muscle atrophy in high-fat-fed mice. These observations suggest that MOTS-c may have additional muscle-preserving and sarcopenia-preventing effects. Here, we examined the preventive effect of MOTS-c on skeletal muscle mass using an immobilization-induced muscle atrophy model and explored its underlying mechanisms. METHODS: Young (10-weeks old) male C57BL/6 mice were randomly assigned to one of three experimental groups: A) non-cast immobilization control, B) cast immobilization with sterile water injection, and C) cast immobilization with MOTS-c injection groups. Both the right and left hindlimbs of the mice were immobilized by using casting tape under light anesthesia and mice were injected with sterilized water or MOTS-c (7.5 mg/kg) (2 times per day) for 8 days. Plasma and skeletal muscle samples were collected at the end of the experiment. RESULTS: Immobilization reduced ~15% of muscle mass, while MOTS-c treatment attenuated muscle loss with only a 5% reduction. MOTS-c treatment also normalized phospho-AKT, phospho-FOXO1, and phospho-FOXO3a expression levels, and reduced circulating inflammatory cytokines, such as interleukin-1b (IL-1β), interleukin-6 (IL-6), chemokine C-X-C motif ligand 1 (CXCL1), and monocyte chemoattractant protein 1 (MCP-1), in immobilized mice. An unbiased RNA sequencing and its downstream analyses demonstrated that MOTS-c modified adipogenic-modulating gene expression within the peroxisome proliferator-activated receptors (PPARs) pathway. Supporting this observation, muscle fatty acid levels were lower in the MOTS-c treated group than in the casted controls. CONCLUSIONS: This study demonstrates that MOTS-c treatment inhibits skeletal muscle fat infiltration by regulating adipogenesis-related genes and prevents immobilization-induced muscle atrophy. This study was supported by NIH grants R01AG069698, RF1AG061834, R01AG068405, P30AG068345, P01AG055369, R01CA231219, and R01HL158691.