Distinct systemic metabolic features in limb-girdle muscular dystrophy type R1 mouse models as a potential early pathogenic signature

Limb-girdle muscular dystrophy type R1 (LGMDR1, formerly LGMD2A) is a genetic disorder caused by mutations in CAPN3 and is characterized by progressive proximal limb muscle weakness. The CAPN3 gene product, calpain-3/CAPN3/p94, is a member of the intracellular cysteine protease superfamily predominantly expressed in the skeletal muscle. LGMDR1 pathogenesis has been investigated separately using mouse models: CAPN3:C129S [knock-in (KI)] mice, which express a proteolytically inactive variant, and CAPN3 knockout (KO) mice. These studies propose that CAPN3 bears both proteolytic activity-dependent and -independent functions and that the loss of either or both affects phenotypes.

Here, we report a side-by-side, long-term analysis of KI and KO mice to comprehensively understand the LGMDR1 pathology in terms of CAPN3 function. Their physiques were comparable to those of wild-type animals, but age-dependent LGMDR1 symptoms were observed by histochemical analysis, with more severe symptoms observed in KO mice. Quantitative muscle proteomics and gene ontology analyses revealed more diverse changes in the KO mice than in the KI mice. Of the associated terms, “metabolic process” was the most affected across the genotype and age groups. Metabolomic analysis suggested that the skeletal muscles of these mice had an imbalance in the branched-chain amino acid catabolic pathway. Furthermore, a reduction in lipids and glycogen was observed in the liver of KO mice, suggesting that a systemic energy deficit occurs during CAPN3 deficiency.

Altogether, our results suggest that muscular dysfunction in LGMDR1 models is associated with compromised systemic energy balance and that the extent of perturbation is implicated in disease severity.