Multilevel impairment of mitochondrial respiration with sex-specific signatures in inclusion body myositis

BackgroundOxidative phosphorylation (OXPHOS) is a central function and a key indicator of mitochondrial fitness, yet studies in human tissue remain limited. Inclusion body myositis (IBM) is a progressive myopathy that lies at the intersection of aging, inflammation and mitochondrial dysfunction. We aimed to perform a comprehensive profiling of mitochondrial respiration in muscle tissue from patients with IBM. MethodsA wide battery of complementary tests from RNA level to high-resolution respirometry on permeabilized muscle fibers was performed. The relationship between respiration, mitochondrial content, mitochondrial DNA (mtDNA) abnormalities and mitophagy was examined, along with the correlation with various clinical parameters to determine the clinical significance of the findings. ResultsThe study included a total of 67 patients with IBM and 45 controls. IBM muscle tissue exhibited reduced maximal respiration per tissue weight in State 3 (high substrates, high ADP) and uncoupled state with decreased coupling efficiency and higher leak control ratios. When adjusting for citrate synthase reflecting mitochondrial content, males had decreased State 3 intrinsic respiration, whereas females had greater intrinsic respiration in leak states. Complex II control ratio strongly correlated with disease duration and severity only in females. IBM was associated with decreased RNA and protein expression of OXPHOS complexes. Complex I activity was decreased mainly in females. IBM samples exhibited lower maximal H2O2 emission, accompanied by a higher total antioxidant capacity that correlated with disease duration in females. In IBM, there was decreased mtDNA content, and impaired mitophagy, both of which strongly correlated with respirometry measures and markers of disease severity, indicating these pathways are likely interconnected and of clinical significance. ConclusionIBM is characterized by multilevel impairments in mitochondrial coupling efficiency, revealing several potential therapeutic targets to improve mitochondrial fitness, while accounting for sex-specific differences.