Methionine aminopeptidase 1D preserves myogenic cell integrity via maintaining mitochondrial activity

Mitochondria are essential organelles that regulate cellular energy production and homeostasis, and there are more than 40 resident proteases known to contribute to mitochondrial activity and dynamics. Among them, the mitochondrial aminopeptidase methionine aminopeptidase 1D (Metap1D) is primarily involved in protein processing, including N-terminal methionine removal. Despite its potential significance, the role of Metap1D in myoblast proliferation and myogenic differentiation remains unclear. In this study, we investigated the function of Metap1D in C2C12 myoblasts, focusing on mitochondrial regulation, cell proliferation, and myogenic differentiation. Suppression of Metap1D by siRNA increased Pgc1α expression and mitochondrial content as well as mitochondrial membrane potential and intracellular ATP levels. Short-term knockdown of Metap1D enhanced cell proliferation with increased phosphorylation of the retinoblastoma protein, a key regulator of the cell cycle; however, prolonged suppression reduced proliferation. Furthermore, Metap1D knockdown reduced the expression of myogenic markers, including myogenin and myosin heavy chain, and was associated with impaired myogenic differentiation, accompanied by the formation of multinucleated myotubes with abnormal spherical morphology. These findings suggest that mitochondria-localized Metap1D is involved in the regulation of mitochondrial content and activity and is associated with the control of C2C12 myoblast proliferation and myogenic differentiation.