A new role for the muscle repair protein dysferlin in endothelial cell adhesion and angiogenesis

Amyloidosis and exercise intolerance in ANO5 muscular dystrophy

Anoctamin 5 and dysferlin mutations can result in myopathies with similar clinical phenotype. Amyloid deposits can occur in the muscle of patients with dysferlinopathy. We describe a 53-year-old woman with exercise intolerance since childhood, recurrent rhabdomyolysis and late-onset weakness. Muscle biopsy showed amyloid deposits within the blood vessel walls and around muscle fibers. Mutation analysis identified two pathogenic heterozygous mutations in anoctamin 5 and no mutations in dysferlin. To our knowledge this is the first report of muscle amyloidosis in anoctamin 5 muscular dystrophy. This finding suggests that patients with amyloid in muscle should be screened for anoctamin 5 muscular dystrophy.

Myoferlin gene silencing decreases Tie-2 expression in vitro and angiogenesis in vivo

Angiogenesis consists in the growth of new blood vessels from pre-existing ones. Although anti-angiogenesis interventions have been shown to have therapeutic properties in human diseases such as cancer, their effect is only partial and the identification of novel modulators of angiogenesis is warranted. Recently, we reported the unexpected proteomic identification in endothelial cells (EC) of Myoferlin, a member of the Ferlin family of transmembrane proteins. Ferlins are well known to regulate the fusion of lipid vesicles at the plasma membrane in muscle cells, and we showed that Myoferlin gene knockdown not only decreases lipid vesicle fusion in EC but also attenuates Vascular Endothelial Growth Factor (VEGF) Receptor-2 (VEGFR-2) expression. Herein, we show that Myoferlin gene silencing in cultured EC also results in attenuated expression of a second tyrosine kinase receptor, Tie-2, which is another well-described angiogenic receptor. Most importantly, we provide evidence that delivery of a low-volume Myoferlin siRNA preparation in mouse tissues results in attenuated angiogenesis and edema formation. This provides the first evidence that acute Myoferlin knockdown has anti-angiogenic effects and validates Myoferlin as an anti-angiogenesis target. Furthermore, this supports the unexpected but increasingly accepted concept that proper tyrosine kinase receptors expression at the plasma membrane requires Myoferlin.

Muscle membrane repair and inflammatory attack in dysferlinopathy

Repair of plasma membrane tears is an important normal physiological process that enables the cells to survive a variety of physiological and pathological membrane lesions. Dysferlin was the first protein reported to play a crucial role in this repair process in muscle, and recently, several other proteins including Mitsugumin 53 (MG53), annexin and calpain were also found to participate. These findings have now established the framework of the membrane repair mechanism. Defective membrane repair in dysferlin-deficient muscle leads to the development of muscular dystrophy associated with remarkable muscle inflammation. Recent studies have demonstrated a crosstalk between defective membrane repair and immunological attack, thus unveiling a new pathophysiological mechanism of dysferlinopathy. Here I summarize and discuss the latest progress in the molecular mechanisms of membrane repair and the pathogenesis of dysferlinopathy. Discussion about potential therapeutic applications of these findings is also provided.