Targeting the Ubiquitin-Proteasome System in Limb-Girdle Muscular Dystrophy With CAPN3 Mutations

Front Cell Dev Biol. 2022 Mar 2;10:822563. doi: 10.3389/fcell.2022.822563.

PMID: 35309930

Jaione Lasa-Elgarresta, Laura Mosqueira-Martín, Klaudia González-Imaz

Highlights: This study investigates the potential contribution of the ubiquitin-proteasome pathway to increased SERCA degradation in LGMDR1.

Abstract

Background: Mutations in the CAPN3 gene, which produces calpain 3 (CAPN3), a non-lysosomal cysteine protease required for healthy muscle function, result in LGMDR1. Our earlier research has demonstrated that a lack of CAPN3 causes accelerated protein degradation, which lowers SERCA levels.

Objective: In this study, the role of the ubiquitin-proteasome pathway in LGMDR1's enhanced SERCA degradation is examined.

Results: In line with the earlier findings, it is found that low SERCA protein levels and high cytosolic calcium concentration are present in CAPN3-deficient human myotubes. In CAPN3-deficient myotubes, treatment with the proteasome inhibitor bortezomib (Velcade) raised SERCA2 protein levels and restored intracellular calcium levels. Bortezomib also helped a patient with the missense mutations R289W and R546L restore the mutant CAPN3 protein. It is discovered that SERCA deficiencies in skeletal muscle were present in CAPN3 knockout mice (C3KO) in the early stages of the disease, before the appearance of muscle abnormalities. Bortezomib therapy (0.8 mg/kg every 72 hours) was administered for three weeks, however SERCA levels were not improved. Bortezomib-treated animals' muscle proteasome activity did not alter, indicating that greater bortezomib dosages are required to restore SERCA levels in this model.

Conclusion: Overall, the findings of this study provide the groundwork for investigating ubiquitin-proteasome inhibition as a new therapeutic approach to treat LGMDR1 patients. Additionally, patients with CAPN3 missense mutations and maybe additional genes may gain from proteasome inhibition by restoring levels of mutant protein. To demonstrate the therapeutic effectiveness of proteasome inhibition for diverse missense mutations, additional research in appropriate animals would be required.

Keywords: LGMD2A, SERCA1, SERCA2, bortezomib (BTZ), calcium, calpain 3 (CAPN3), muscular dystrophies