Inflammation-Linked Muscle Atrophy in Limb Girdle Muscular Dystrophy R1 (LGMDR1): Insights into Disease Mechanisms

Background: Muscle atrophy is a major feature of Limb Girdle Muscular Dystrophy R1 (LGMDR1) patients, but its underlying molecular mechanisms have not been fully explored. While the ubiquitin–proteasome system (UPS) is known to be involved in muscle protein degradation, inflammation commonly observed in LGMDR1 patients may further activate the UPS. This study aimed to explore the role of inflammation in the muscle atrophy of LGMDR1 patients. Methods: Muscle biopsies from six confirmed LGMDR1 patients (with CAPN3 variants and reduced calpain-3 protein expression) were analyzed for atrophy-related markers, MuRF1 and Atrogin-1, using qRT-PCR and Western blotting. The expression of cytokines, TNF-α, IL-1β, and IL-6 was analyzed by qRT-PCR from muscle biopsies and by ELISA from serum samples. The NFκB, FOXO1, and FOXO3 gene expression was analyzed using qRT-PCR and Western blotting from muscle biopsies. Results: Elevated TNF-α levels were associated with increased UPS activity, reflected by upregulated NFκB, FOXO1, MuRF1, and Atrogin-1 expression in LGMDR1. Conclusion: Our findings indicate that increased TNF-α expression is associated with muscle wasting in LGMDR1 patients by targeting UPS pathway mediators that activate ubiquitin ligases—MuRF1 and Atrogin-1. These findings suggest that targeting TNF-α signaling and its downstream factors may help develop therapeutic interventions to prevent muscle atrophy in LGMDR1 patients.