MOTS-C (mitochondrial open reading frame of the 12S rRNA-c) is a 16-amino-acid peptide (MRWQEMGYIFYPRKLR) encoded within the 12S rRNA gene of the mitochondrial genome — making it one of a small family of mitochondrial-derived peptides (MDPs) discovered in the past decade. Originally characterised by Changhan Lee and colleagues at USC (Lee et al., 2015, Cell Metabolism), MOTS-C has emerged as a critical regulator of metabolic homeostasis with relevance to diabetes, ageing, and exercise physiology.
Human mitochondrial DNA (mtDNA) encodes only 13 proteins involved in the electron transport chain, plus ribosomal RNAs and tRNAs. The discovery that the 12S rRNA gene also encodes functional peptides (including MOTS-C and humanin) represents a paradigm shift in understanding mitochondrial function beyond energy production. These MDPs appear to act as retrograde signals from mitochondria to the nucleus and to other tissues, coordinating the cellular response to metabolic stress.
The evolutionary conservation of MOTS-C across primates, and the location of its gene within a highly conserved region of mtDNA, suggest important biological functions maintained across evolution.
The primary characterised mechanism of MOTS-C is activation of AMP-activated protein kinase (AMPK), the master energy sensor of the cell. Lee et al. (2015) demonstrated that MOTS-C inhibits the folate cycle and de novo purine synthesis in muscle cells, leading to AICAR accumulation (5-aminoimidazole-4-carboxamide ribonucleotide) — a well-established direct AMPK activator. This MOTS-C → AICAR → AMPK pathway represents a novel mechanism of metabolic regulation originating from mitochondria.
AMPK activation by MOTS-C promotes:
Lee et al. (2015) demonstrated that MOTS-C administration improved insulin sensitivity in high-fat diet-fed obese mice, reducing fasting glucose and improving glucose tolerance test outcomes. Systemic MOTS-C increased glucose uptake in skeletal muscle independent of insulin, via AMPK-dependent GLUT4 translocation — a mechanism of particular interest in insulin resistance research.
Subsequent studies have extended these findings: MOTS-C prevents diet-induced insulin resistance in multiple rodent models and restores insulin sensitivity in aged animals, where endogenous MOTS-C levels are reduced.
Reynolds et al. (2021) demonstrated that MOTS-C levels increase in human plasma during and after exercise, and that exogenous MOTS-C administration significantly improved running performance in young and aged mice — the aged mice showing the most dramatic response. This effect was AMPK-dependent and associated with enhanced mitochondrial function, glucose utilisation, and reduced fatigue markers. These findings position MOTS-C as a potential tool for studying exercise adaptation and age-related physical decline.
Circulating MOTS-C levels decline with age in humans and animal models. Restoration of MOTS-C to youthful levels in aged mice improves metabolic health markers, physical performance, and lifespan in some models. The peptide modulates FOXO transcription factors and sirtuin pathways — core longevity mechanisms — and reduces markers of mitochondrial dysfunction and systemic inflammation in aged tissue.
A recent discovery demonstrated that MOTS-C, under stress conditions, translocates to the nucleus where it associates with Nrf2 and modulates antioxidant gene expression. This nuclear function represents an additional mechanism distinct from cytoplasmic AMPK activation and extends MOTS-C's role to direct transcriptional regulation of stress response genes.
