Withdrawn Melbourne Protein Group Student Symposium 2013

Limb girdle muscular dystrophy type 2A (LGMD2A) is one of the more commonly occurring LGMD’s, where onset of the disease is the result of a mutation in a protein called calpain-3 (CAPN3). CAPN3 is a non-lysosomal, Ca²⁺-dependent protease expressed almost exclusively within skeletal muscle. The specific function(s) and cellular target(s) of CAPN3 remain elusive, with a proposed role in skeletal muscle repair and remodeling. Previous work in CAPN3 reveals it too be sensitive to very low Ca²⁺ concentrations, an attribute thought pivotal to its function. Also, in the absence of CAPN3 it has been seen that Ca²⁺-release is impaired, a characteristic that has been linked to glycogen depletion with skeletal muscle. This study investigated the expression of specific Ca²⁺-handling proteins, combined with glycogen phosphorylase (GP) and glycogen debranching enzyme (GDE), within skeletal muscle of healthy individuals (Control) and LGMD2A patients.

            Muscle biopsies were collected from the vastus lateralis muscle of both Control (n=5) and Patient (n=8) individuals. All muscle samples were utilised for experiments where the expression of specific Ca²⁺-handling proteins, such as dihydropyridine receptor, SR Ca²⁺-ATPase and calsequestrin proteins were examined. Using Western blotting, the expression of a little known calsequestrin-like protein isoform was increased ~1000% (Control: 0.66 ± 0.35; Patient: 7.6 ± 1.4) in Patients compared to Control individuals. No other Ca²⁺-handling protein was found to alter between control individuals and patients. The expression of both GP and GDE decreased ~50% (Control: 1.00 ± 0.26; Patient: 0.46 ± 0.12) and (Control: 1.00 ± 0.09; Patient: 0.54±0.03) in Patients compared to Control individuals respectively. All values are mean±SEM, p<0.05, unpaired t-test.

Based on these findings, it cannot be concluded if a relationship between CAPN3 and the Ca²⁺-handling proteins exists. Conversely, based on the observed decrease the catabolic enzyme in LGMD2A patients, it would appear that perhaps an unknown relationship has been uncovered.