The study tested a mitochondrial peptide called MOTS‑c on cells with a common mitochondrial DNA mutation that causes poor energy production. Adding MOTS‑c from outside or making the cells produce it themselves didn’t boost the cells’ ATP levels, respiratory function, or the proteins that run the energy factories. In short, MOTS‑c didn’t fix the mitochondrial problem in this model.

Mitochondrial derived peptides (MDPs) are a class of peptide encoded in small open reading frames of mitochondrial DNA (mtDNA). MOTS-c, a recently discovered MDP, participates in retrograde signaling from the mitochondria to the nucleus to control cellular metabolism. Humanin, another MDP, has cytoprotective properties and enhances mitochondrial function. However, it has not yet been tested whether MOTS-c can affect mitochondrial function. We investigated the effect of exogenous and endogenous MOTS-c on mitochondrial function in a cybrid cell harboring 3243 A to G mutant mtDNA, which causes significant mitochondrial dysfunction. To test the effects of endogenous MOTS-c, the cybrid cell was transfected with a MOTS-c EGFP expression vector. Exogenous (synthetic) MOTS-c did not show a significant effect on the ATP content or the mRNA and protein levels of the mitochondrial complex in the mutant cybrid cells. Basal and stimulated mitochondrial respiration were also not affected by exogenous MOTS-c. The mutant cybrid cells transfected with the MOTS-c EGFP expression vector stably expressed MOTS-c, but ATP production and mRNA and protein levels of the mitochondrial complex were not affected. In contrast to other MDPs, MOTS-c does not improve mitochondrial dysfunction in cybrid cells with mutant mtDNA, which suggests the heterogeneous nature of MDPs.