Dysferlin Deficiency Shows Compensatory Induction of Rab27A/Slp2a That May Contribute to Inflammatory Onset

Abstract

Mutations in the dysferlin gene cause limb girdle muscular dystrophy 2B (LGMD2B) and Miyoshi myopathy. Dysferlin-deficient cells show abnormalities in vesicular traffic and membrane repair although onset of symptoms is not commonly seen until the late teenage years and is often associated with subacute onset and marked muscle inflammation. To identify molecular networks specific to dysferlin-deficient muscle that might explain disease pathogenesis, muscle mRNA profiles from 10 mutation-positive LGMD2B/MM patients were compared with a disease control [LGMD2I; (n ‫؍‬ 9)], and normal muscle samples (n ‫؍‬ 11). Query of inflammatory pathways suggested LGMD2B-specific increases in co-stimulatory signaling between dendritic cells and T cells (CD86, CD28, and CTLA4), associated with localized expression of both versican and tenascin. LGMD2B muscle also showed an increase in vesicular trafficking pathway proteins not normally observed in muscle (synaptotagmin-like protein Slp2a/SYTL2 and the small GTPase Rab27A). We propose that Rab27A/Slp2a expression in LGMD2B muscle provides a compensatory vesicular trafficking pathway that is able to repair membrane damage in the absence of dysferlin. However, this same pathway may release endocytotic vesicle contents, resulting in an inflammatory microenvironment. As dysferlin deficiency has been shown to enhance phagocytosis by macrophages, together with our findings of abnormal myofiber endocytosis pathways and dendritic-T cell activation markers, these results suggest a model of immune and inflammatory network over-stimulation that may explain the subacute inflammatory presentation. Limb-girdle muscular dystrophies are a group of heterogeneous disorders typically showing an autosomal recessive mode of inheritance, progressive muscle weakness, and high serum creatine kinase levels.1 Two types of muscle disease, a distal myopathy (Miyoshi Myopathy, MM) and a form of limb girdle muscular dystrophy (LGMD2B) have both been shown to be caused by mutations of the dysferlin gene. 2,3 In both LGMD2B and MM, dysferlin gene mutations result in partial or complete loss of dysferlin protein in muscle as measured by immunoassays, although the reduction in dysferlin levels does not strictly correlate with clinical severity. 4 Both the proximal (LGMD2B) and distal (MM) phenotypes can be caused by identical mutations in the same family, suggesting the role of genetic modifiers and/or environmental influence on disease expression. 5 The dysferlin gene is localized to 2p13 with expression in various tissues ranging from kidney to monocytes, with highest levels in skeletal and cardiac muscle.6 Dysferlin is localized predominantly to the muscle surface membrane, and is also associated with cytoplasmic vesicles. 7The dysferlin protein was originally named based on its similarity to the Caenorhabditis elegans protein FER-1. FER-1 is responsible for mediating fusion of intracellular vesicles with the spermatid plasma membrane.8 Sequence homology between FER-1 and dysferlin includes Supplemental materia...

Genetic Manipulation of Dysferlin Expression in Skeletal Muscle

“…9,10 To directly test this hypothesis we crossed the skeletal muscle-specific Dysf-TG mouse (C57Bl/6 background) with A/J mice, a mouse strain that develops MD due to a mutation in the Dysf gene, which results in the absence of expression of the dysferlin protein. 12 To assess skeletal muscle disease in these mice, we quantified a number of common dystrophic parameters, such as central nucleation, fibrosis, distribution of myofiber cross-sectional areas, macrophage infiltration, functional recovery from injury, and total serum CK levels (Figure 2).…”

“…9 -11 For example, macrophages and dendritic-T cell activation markers are elevated in the SJL mouse model for Dysf deficiency and in human limb girdle muscular dystrophy 2B. 9 Thus, it is unclear whether disease due to dysferlin deficiency is primarily due to an autonomous effect in immune cells or skeletal muscle fibers. To address this issue, we generated transgenic mice that express dysferlin specifically in skeletal muscle and used them to evaluate the necessity of dysferlin within myofibers to initiate muscle disease in Dysf null A/J mice.…”

Upregulation of the Rab27a-Dependent Trafficking and Secretory Mechanisms Improves Lysosomal Transport, Alleviates Endoplasmic Reticulum Stress, and Reduces Lysosome Overload in Cystinosis

“…Rab27b, which has 72% homology with Rab27a at the amino acid level, is also expressed in the kidney's transitional epithelium and in corneal epithelial cells (23). These secretory factors are also expressed in many other organs that are affected by late cystinosis complications, including in the thyroid glands, pancreas, stomach, large and small intestines, trachea, lung, liver, and heart (23) and in skeletal muscle (27). Although Rab27a was originally associated with the secretory pathway of secretory lysosomes in hematopoietic cells (28,29), recent studies have highlighted a role for Rab27a in conventional lysosomal trafficking and exocytosis (30).…”

Translational Research and Therapeutic Perspectives in Dysferlinopathies

“…The authors suggest a possible role for B cells in dysferlin pathophysiology. After the transcriptomics studies performed in EP Hoffman's laboratory, demonstrating the upregulation of proteins involved in rho signaling, they started preclinical studies using an inhibitor of a rho kinase (Fasudil™) (99). This preclinical treatment demonstrated some benefits: notably, a lower level of inflammatory cells in the muscles and an increase in body weight, but no impact in another physiological process such as muscle fiber degeneration/regeneration or in muscle force (100).…”