Dysferlin and animal models for dysferlinopathy

Abstract

Dysferlin (DYSF) is involved in the membrane-repair process, in the intracellular vesicle system and in T-tubule development in skeletal muscle. It interacts with mitsugumin 53, annexins, caveolin-3, AHNAK, affixin, S100A10, calpain-3, tubulin and dihydropyridine receptor. Limb-girdle muscular dystrophy 2B (LGMD2B) and Miyoshi myopathy (MM) are muscular dystrophies associated with recessively inherited mutations in the DYSF gene. The diseases are characterized by weakness and muscle atrophy that progress slowly and symmetrically in the proximal muscles of the limb girdles. LGMD2B and MM, which are collectively termed "dysferlinopathy", both lead to abnormalities in vesicle traffic and membrane repair at the plasma membrane in muscle fibers. SJL/J (SJL) and A/J mice are naturally occurring animal models for dysferlinopathy. Since there has been no an approach to therapy for dysferlinopathy, the immediate development of a therapeutic method for this genetic disorder is desirable. The murine models are useful in verification experiments for new therapies and they are valuable tools for identifying factors that accelerate dystrophic changes in skeletal muscle. It could be possible that the genetic or immunological background in SJL or A/J mice could modify muscle damage in experiments involving these models, because SJL and A/J mice show differences in the progress and prevalent sites of skeletal muscle lesions as well as in the gene-expression profiles of their skeletal muscle. In this review, we provide up-to-date information on the function of dysferlin, the development of possible therapies for muscle dystrophies (including dysferlinopathy) and the detection of new therapeutic targets for dysferlinopathy by means of experiments using animal models for dysferlinopathy.

Keywords: A/J mouse; SJL/J mouse; complement; dysferlin; dysferlinopathy.

Fig. 1.

Schematic showing the organization of some of the integral and peripheral components involved in muscular dystrophies in skeletal muscles.

Fig. 2.

Conserved structure of the ferlin family. Proteins of the ferlin family have highly homologous structures. The proteins have a variable number of tandem C2 domains and a C-terminal transmembrane domain.

Fig. 3.

Schema for a model of the membrane-resealing processes associated with dysferlin in vitro. (A) shows the intact condition. Membrane disruption leads to an influx of calcium ions (B). Transport of intracellular vesicles toward the damaged site by the motor proteins kinesin and myosin may be facilitated by mitsugumin 53 (MG53) in an oxidation/cholesterol-dependent manner. The vesicles dock through oxidized MG53 and fuse with each other and the plasma membrane, possibly with mediation by annexin, soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and dysferlin in the presence of the calcium ion. Dysferlin interacts with annexins A1 and A2 and mediates wound healing of the sarcolemma. A membrane patch is consequently formed and reseals the membrane lesion (C). Although the proteins dysferlin and MG53 are known to be involved in muscle repair, there is still no direct evidence of an in vivo interaction between them.

Fig. 4.

Schema showing the interactions of proteins with dysferlin at the sarcolemma in skeletal muscle.

Fig. 5.

Histopathology of the rectus femoris in BALB/c, SJL/J and A/J mice. At 10 weeks of age (upper figures), no significant changes were observed in the skeletal muscle fibers of BALB/c (A) and A/J mice (C), and a few muscle fibers showed minimal degeneration with mononuclear cell infiltration in SJL/J mice (B). At 30 weeks of age (lower figures), BALB/c mice did not exhibit histopathological changes in any skeletal muscles (D). The histopathological lesions of skeletal muscles in SJL/J mice progressed in severity with age and were characterized by the following findings: degenerative/necrotic muscle fibers, centronuclear muscle fibers, fatty infiltration and variations in the size of the muscle fibers (E). The muscle fibers in A/J mice showed only degenerative/necrotic features and variations in size (F). Hematoxylin and eosin (HE) staining. Bar: 100 μm.

Fig. 6.

Estimated inflammatory process in dysferlin-deficient skeletal muscle. Plasma membrane damage to dysferlin-deficient muscle fibers causes a release of “danger” molecules (heat-shock proteins, high mobility group box-1, ATP, etc.). These “danger” molecules are recognized by receptors on innate immune cells and muscle cells and they stimulate the production of proinflammatory cytokines. Moreover, the released “danger” molecules activate the complement system and stimulate C3a or opsonizing C3b. The proinflammatory mediator C3a can trigger the production of proinflammatory cytokines from cells and render the local vascular endothelium “leaky”; this is followed by attraction of the migration of neutrophils and macrophages. C3b binds to the negatively charged sarcolemma, stimulating phagocytosis. These processes cause more-severe muscular degeneration/necrosis.