Proteomics of Cytochrome c Oxidase-Negative versus -Positive Muscle Fiber Sections in Mitochondrial Myopathy

Abstract

Summary: The mosaic distribution of cytochrome c oxidase+ (COX+) and COX− muscle fibers in mitochondrial disorders allows the sampling of fibers with compensated and decompensated mitochondrial function from the same individual. We apply laser capture microdissection to excise individual COX+ and COX− fibers from the biopsies of mitochondrial myopathy patients. Using mass spectrometry-based proteomics, we quantify >4,000 proteins per patient. While COX+ fibers show a higher expression of respiratory chain components, COX− fibers display protean adaptive responses, including upregulation of mitochondrial ribosomes, translation proteins, and chaperones. Upregulated proteins include C1QBP, required for mitoribosome formation and protein synthesis, and STOML2, which organizes cardiolipin-enriched microdomains and the assembly of respiratory supercomplexes. Factoring in fast/slow fiber type, COX− slow fibers show a compensatory upregulation of beta-oxidation, the AAA+ protease AFG3L1, and the OPA1-dependent cristae remodeling program. These findings reveal compensatory mechanisms in muscle fibers struggling with energy shortage and metabolic stress. : Murgia et al. use mass spectrometry-based proteomics to dissect the pathological mosaicism of compensated COX+ fibers and decompensated COX− fibers in mitochondrial myopathy. On this single-cell level, COX− fibers show protean adaptive responses. These findings reveal compensatory mechanisms in muscle fibers struggling with energy shortage and metabolic stress. Keywords: mitochondrial myopathy, chronic progressive external ophthalmoplegia, CPEO, cytochrome c oxidase, COX, single muscle fibers, laser microdissection, mass spectrometry, proteomics