MOTS-c: A Research Overview

Introduction

MOTS-c (mitochondrial open reading frame of the 12S rRNA-c) is a 16-amino-acid peptide encoded within the mitochondrial genome's 12S ribosomal RNA gene (MT-RNR1). It belongs to a class of small bioactive molecules termed mitochondrial-derived peptides (MDPs). Lee and colleagues first described the peptide in a 2015 publication in Cell Metabolism, characterizing it as a mitochondrially encoded regulator of cellular metabolic signaling [1]. The discovery was notable because MOTS-c originates from the organellar genome—not the nuclear genome—placing it at the intersection of mitochondrial biology and intercellular communication and expanding researchers' understanding of what the mitochondrial genome encodes.

Background

The human mitochondrial genome (mtDNA) is a circular, double-stranded molecule of approximately 16,569 base pairs. It encodes 13 proteins involved in oxidative phosphorylation, two ribosomal RNAs, and 22 transfer RNAs. For decades, the two rRNA genes (MT-RNR1 and MT-RNR2) were not thought to contain protein-coding sequences. The identification of MOTS-c within MT-RNR1—and the earlier identification of humanin within MT-RNR2—revised this understanding and established that ribosomal RNA-encoding regions of mitochondrial DNA harbor additional open reading frames whose products are biologically active [1, 2].

Humanin, a 24-amino-acid peptide encoded in the MT-RNR2 region, was the first MDP characterized, originally described in 2001 in studies of neuronal cell death [2]. The subsequent discovery of MOTS-c extended the MDP class to include peptides from the MT-RNR1 region with distinct target tissues and signaling mechanisms, opening an active research frontier in mitochondrial biology.

Chemistry and Structure

MOTS-c has the amino acid sequence Met-Arg-Trp-Gln-Glu-Met-Gly-Tyr-Ile-Phe-Tyr-Pro-Arg-Lys-Leu-Arg (MRWQEMGYIFYPRKLR). Its molecular formula is C₁₀₁H₁₅₂N₂₈O₂₂S₂ with a molar mass of approximately 2,174.6 g/mol. The 16-amino-acid sequence is encoded by a 75-base-pair open reading frame within MT-RNR1 [1].

The first 11 residues are highly conserved across at least 14 mammalian species, suggesting functional constraint on this region of the peptide. The C-terminal Arg-Lys-Leu-Arg motif contributes to the peptide's basic charge character and has been implicated in nuclear targeting activity documented in later research [3]. Circulating MOTS-c has been measured in human plasma and detected in skeletal muscle tissue, indicating that it is secreted and may function as a signaling molecule beyond its cell of origin [4].

Pharmacological Classification

Within the framework of peptide pharmacology, MOTS-c is classified as a mitochondrial-derived peptide with intracellular and intercellular signaling properties. The 2015 discovery paper characterized it as an activator of AMP-activated protein kinase (AMPK) signaling—a central cellular energy sensor—through an indirect mechanism involving inhibition of the folate cycle and accumulation of the endogenous AMPK activator AICAR (5-aminoimidazole-4-carboxamide ribonucleotide) [1].

A 2018 Cell Metabolism paper further characterized MOTS-c's capacity for nuclear translocation, where it participates in regulation of nuclear gene expression under metabolic stress conditions [3]. This dual activity—cytoplasmic metabolic modulation and nuclear gene regulation—distinguishes MOTS-c from earlier-characterized MDPs and positions it as a form of mitochondrial-nuclear retrograde signaling molecule. The MOTS-c mechanism of action article covers each of these pathways in detail.

The World Anti-Doping Agency (WADA) added MOTS-c to its Prohibited List under category S4.4 (Metabolic Modulators, AMPK activators subcategory) in 2024, effective at all times for competitive athletes subject to WADA rules. The listing reflects regulatory recognition of the peptide's biological characterization as an AMPK pathway modulator. SS-31 is another mitochondrial-targeted compound in this research cluster; the SS-31 research overview provides a parallel reference on mitochondrial peptide research.

Regulatory Status

MOTS-c is not approved by the US Food and Drug Administration (FDA) for any therapeutic indication. No New Drug Application (NDA) or Biologics License Application (BLA) for MOTS-c as a pharmaceutical product appears in publicly available FDA databases as of the date of this article. The compound occupies a research-use-only category consistent with its current stage of scientific development—a phase of active preclinical characterization with ongoing human observational studies and an evolving mechanistic literature. Clinical investigation remains an open area for future research.

Discovery History

The identification of MOTS-c arose from systematic bioinformatics interrogation of the mitochondrial genome for previously uncharacterized open reading frames, combined with mass spectrometry-based peptide detection. Lee and colleagues at the Leonard Davis School of Gerontology, University of Southern California (USC), under the direction of Pinchas Cohen, published the initial characterization in Cell Metabolism in March 2015 [1].

The USC/Cohen laboratory had previously contributed to characterization of humanin and its roles in neuronal protection. The discovery of MOTS-c extended the group's research into mitochondrial-nuclear communication and metabolic regulation—themes that have driven subsequent publications from the same group and from independent investigators across multiple continents [1, 3, 5].

The name MOTS-c (mitochondrial open reading frame of the 12S rRNA-c) was assigned to distinguish the peptide from earlier MDPs and to denote its genomic origin. The "type-c" suffix distinguishes it from other open reading frames identified within the same genomic region [1].

References

1. Lee C, Zeng J, Drew BG, Sallam T, Martin-Montalvo A, Wan J, Kim SJ, Mehta H, Hevener AL, de Cabo R, Cohen P. The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance. Cell Metab. 2015 Mar 3;21(3):443–454. doi: 10.1016/j.cmet.2015.02.009. PMID: 25738459. https://pubmed.ncbi.nlm.nih.gov/25738459/

2. Hashimoto Y, Niikura T, Tajima H, Yasukawa T, Sudo H, Ito Y, Kita Y, Kawasumi M, Kouyama K, Doyu M, Sobue G, Koide T, Tsuji S, Lang J, Kurokawa K, Nishimoto I. A rescue factor abolishing neuronal cell death by a wide spectrum of familial Alzheimer's disease genes and Abeta. Proc Natl Acad Sci U S A. 2001 May 22;98(11):6336–6341. doi: 10.1073/pnas.101133498. PMID: 11371646. https://pubmed.ncbi.nlm.nih.gov/11371646/

3. Kim KH, Son JM, Benayoun BA, Lee C. The mitochondrial-encoded peptide MOTS-c translocates to the nucleus to regulate nuclear gene expression in response to metabolic stress. Cell Metab. 2018 Sep 4;28(3):516–524.e7. doi: 10.1016/j.cmet.2018.06.015. PMID: 29983246. https://pubmed.ncbi.nlm.nih.gov/29983246/

4. Reynolds JC, Lai RW, Woodhead JST, Joly JH, Mitchell CJ, Cameron-Smith D, Lu R, Cohen P, Graham NA, Benayoun BA, Merry TL, Lee C. MOTS-c is an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis. Nat Commun. 2021 Jan 20;12(1):470. doi: 10.1038/s41467-020-20790-0. PMID: 33473109. https://pubmed.ncbi.nlm.nih.gov/33473109/

5. Wan W, Zhang L, Lin Y, Rao X, Wang X, Hua F, Ying J. Mitochondria-derived peptide MOTS-c: effects and mechanisms related to stress, metabolism and aging. J Transl Med. 2023 Jan 20;21(1):36. doi: 10.1186/s12967-023-03885-2. PMID: 36670507. https://pubmed.ncbi.nlm.nih.gov/36670507/