Impaired myogenesis in limb girdle muscular dystrophy type 2B

The skeletal muscle tissue has a remarkable capacity of growth and regeneration. Fusion of myoblasts and myotubes elongation are fundamental processes in muscle development. Previous studies have depicted impaired myogenic processes in animal models and myoblast from human patients with muscle diseases. Here, we evaluated the myogenesis in patients with Limb-girdle Muscle Dystrophy 2B (LGMD2B). Aiming to explain why dysferlin-deficient muscle cells lose its myogenic potential, we used immortalized myoblasts from LGMD2B patients and a cellular DYSF knocking-out model. Myotubes from patients were smaller and containing less myonuclei than control myotubes. Main muscle regulatory factors expression were not altered in these cells. The analysis of the expression of newly described genes associated with muscle fusion and growth, such as MYMK, MYMX, PALMD, SHISA2, COL25A, didn´t show any difference with controls, which is a novel finding. It was also observed that dysferlin deficiency doesn't alter the expression of FAM65B and HDAC6 genes, components of a proposed protein complex that needs to be formed to allow muscle differentiation. Interestingly, morphometric analysis of DYSF knock-out myotubes induced by CRISPR/Cas9 also revealed reduced myogenic capacity with formation of smaller myotubes. These findings suggest that the absence of DYSF itself is sufficient to impair muscle formation in vitro, and that downstream gene and protein expression related to muscle development might depend on the presence and proper function of dysferlin.