Toral-Ojeda, I. 1, 2 , Aldanondo, G. 1 , Lasa-Elgarresta, J. 1 , Fernández-Torrón, R. 1, 2, 5 , López de Munain, A. 1, 2, 4, 5 & Vallejo-Illarramendi, A. 1, 2, 3
1 Neuroscience Area, Biodonostia Research Institute, San Sebastian, Spain
2 CIBERNED, Instituto de Salud Carlos III, Madrid, Spain
3 Euskampus
4 Department of Neuroscience, University of the Basque Country, San Sebastian, Spain
5 Department of Neurology, Donostia Hospital, San Sebastian, Spain
Limb girdle muscular dystrophy 2A (LGMD2A) is a rare neuromuscular disease affecting skeletal muscle that is caused by mutations in calpain 3 (CAPN3). This study focuses on the expression of several calcium related proteins using CAPN3 knockdown myotubes and muscle biopsies. In CAPN3 deficient human and mouse myotubes, we found significant reduction of SERCA expression and function, which resulted in impairment of calcium homeostasis. Furthermore, small Ankyrin 1 (sAnk1), a protein involved in the integrity of the sarcoplasmic reticulum network, was also reduced in CAPN3 deficient fibres. Analysis of muscle biopsies from LGMD2A patients revealed virtual absence of SERCA2 protein, whereas SERCA1 and sAnk1 were mostly reduced in patients with the lowest CAPN3 levels. Otherwise, muscle samples from patients affected by other kinds of muscular dystrophies displayed presence of SERCA2, suggesting that its absence is characteristic of LGMD2A patients. Moreover, correlation analysis of protein levels performed with 13 control and dystrophic muscle samples revealed significant positive correlations between levels of CAPN3 and those of SERCA1, SERCA2 and sAnk1. In fact, these proteins exhibited direct interaction with CAPN3, as showed by immunoprecipitation experiments in mouse skeletal muscle. In conclusion, our study supplies new evidence of the impact of CAPN3 deficiency on LGMD2A pathological development through destabilization of SERCA1, SERCA2 and sAnk1, which, in turn, compromises calcium homeostasis and sarcoplasmic reticulum stability.