The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance

This 2015 *Cell Metabolism* paper from Pinchas Cohen's laboratory at the University of Southern California is the discovery and foundational characterization of MOTS-c and one of the most important mitochondrial-biology papers of the last decade. The authors identified a small open reading frame within the mitochondrial 12S ribosomal RNA gene encoding a 16-amino-acid peptide they named MOTS-c (mitochondrial open reading frame of the 12S rRNA-c). The peptide is detectable in plasma at physiological concentrations across mammalian species, behaving as a circulating signaling molecule rather than a structural mitochondrial component. Mechanistically, MOTS-c's primary tissue target is skeletal muscle, where it inhibits the folate cycle, raises AICAR (5-aminoimidazole-4-carboxamide ribonucleotide) levels, and activates AMP-activated protein kinase (AMPK). The phenotypic consequences in mice are striking: exogenous MOTS-c administration prevented both age-dependent and high-fat-diet-induced insulin resistance, improved glucose tolerance, lowered circulating insulin levels, and enhanced skeletal-muscle glucose uptake. The paper opened the modern field of mitochondrial-derived peptide signaling and is the basis for nearly every subsequent claim about MOTS-c's metabolic and longevity activity.

This is a discovery and rodent-pharmacology paper, not a human clinical trial. The metabolic phenotypes described are robust in mice but have not been demonstrated in humans through controlled exogenous administration — human evidence to date is correlational (serum MOTS-c levels associated with metabolic and aging biomarkers across cohorts) rather than interventional. The AMPK-activation pathway is well-characterized, but the precise contribution of MOTS-c to that pathway in vivo, relative to other inputs (exercise, AMP/ADP ratios, fasting), is still being parsed. The dose-response curves established here are wide and rodent-specific; translation to human dosing is inferential rather than empirical. The paper does not address chronic-administration safety, cancer-biology interaction (an open question for any AMPK-activating intervention in cancer-prone populations), or interaction with diabetes pharmacotherapy. The mitochondrial-derived peptide class as a whole has expanded since this paper, with humanin, SHLP1-6, and other peptides now characterized — readers seeking the broader picture should follow the citation network from this paper rather than treating MOTS-c as the entire field.