G.P.284: Dysferlinopathy caused by protein misfolding: The novel murine animal model Dysf-MMex38

Abstract

Limb-girdle muscular dystrophy 2B (LGMD2B) is caused by mutations in the dysferlin gene (DYSF). There are no mutational hotspots. Approximately one third of all mutations are missense mutations causing misfolding and protein aggregation, premature degradation and amyloid formation. There is no therapy. We could show that by treating patients’ primary myotubes with short dysferlin-specific peptides the endogenous produced missense mutant dysferlin can be relocated to the sarcolemma. There, it regains its proper function as a membrane repair protein. The human missense mutation DYSF p.L1341P causes all characteristics of a protein misfolding disease in dysferlinopathy. We therefore generated the first knock-in mouse model carrying the analogous murine missense mutation in exon 38 (Dysf p.L1360P, NP_001071162.1) named MMex38 (B6;129P2-Dysftm1.1Mdcb). Natural disease course was investigated at 8, 13 and 21 weeks of age (n = 36). We performed body composition, analyzed treadmill performance and voluntary running as well as protein analysis and histology of proximal and distal muscles. Evaluation of ER stress and membrane resealing assays complete the assessment. The targeted mutation leads to a dystrophic phenotype in 13 week old mice with a continuous disease progression in adulthood. Total body weight of 21 week old MMex38 was increased compared to WT controls without changes in the percentage of fat, free body fluid and lean tissue. Three weeks of treadmill exercise exposed significant endurance impairment in 19 to 21 week old MMex38 compared to controls. Histology revealed a distinct dystrophic pattern in 13 week old MMex38 and number of necrotic and regenerating fibres increased highly significant with age. In the immunofluorescence no dysferlin was detected at the sarcolemma. The successful generation of an animal model for protein misfolding in dysferlinopathy allows the investigation of pharmacokinetics and -dynamics of dysferlin-derived peptides in vivo.