Fibre-specific mitochondrial protein abundance is linked to resting and post-training mitochondrial content in human muscle

Abstract

Analyses of mitochondrial adaptations in human skeletal muscle have mostly used whole-muscle samples, where results may be confounded by the presence of a mixture of type I and II muscle fibres. Using our MS-based proteomics workflow, we provide new insights into fibre-specific mitochondrial adaptations following two types of exercise training that were very different in terms of metabolic demands and fibre recruitment patterns: moderate intensity continuous training (MICT) and sprint interval training (SIT). There was a larger number of differentially expressed proteins in each fibre type following MICT than SIT. Our novel mitochondrial normalisation strategy highlighted that most training-induced changes in mitochondrial protein abundances were stoichiometrically linked to the overall increase in mitochondrial content, except for the decreased abundance of complex IV subunits in both type I and II fibres following SIT, and the increase in proteins associated with fatty acid oxidation in type I fibres.

Increased mitochondrial surface area and cristae density in the skeletal muscle of strength athletes

“…Increased mitochondrial volumetric density is a characteristic of human type I fibres (Sjöström et al ., 1982; Reisman et al ., 2022) and of mouse oxidative fibres (Glancy et al ., 2017; Bleck et al ., 2018). Our results indicate that mitochondrial morphological characteristics are largely similar between type I and II fibres (Figure 4), which would suggest that the number of mitochondrial profiles, rather than morphological differences, may be the primary factor that distinguishes skeletal muscle fibre types in humans.…”

Increased mitochondrial surface area and cristae density in the skeletal muscle of strength athletes

“…Increased mitochondrial volumetric density is a characteristic of human type I fibres (Reisman et al., 2022; Sjöström, Angquist et al., 1982) and of mouse oxidative fibres (Bleck et al., 2018; Glancy et al., 2017). Our results indicate that mitochondrial morphological characteristics are largely similar between type I and II fibres (Figure 4), which would suggest that the number of mitochondrial profiles, rather than morphological differences, may be the primary factor that distinguishes skeletal muscle fibre types in humans.…”