Muscle-specific deletion of SLK/Stk2 enhances p38 activity and myogenesis in mdx mice.

Duchenne's muscular dystrophy (DMD) is a severe muscle wasting disorder characterized by the loss of dystrophin expression, muscle necrosis, inflammation and fibrosis. Ongoing muscle regeneration is impaired by persistent cytokine stress, further decreasing muscle function. Patients with DMD rarely survive beyond their early 20s, with cardiac and respiratory dysfunction being the primary cause of death. Despite an increase in our understanding of disease progression as well as promising preclinical animal models for therapeutic intervention, treatment options for muscular dystrophy remain limited and novel therapeutic targets are required. Many reports suggest that the TGFß signalling pathway is activated in dystrophic muscle and contributes to the pathology of DMD in part by impairing the differentiation of myoblasts into mature myofibers. Here, we show that in vitro knockdown of the Ste20-like kinase, SLK, can partially restore myoblast differentiation downstream of TGFß in a Smad2/3 independent manner. In an mdx model, we demonstrate that SLK is expressed at high levels in regenerating myofibers. Muscle-specific deletion of SLK reduced leukocyte infiltration, increased myogenin and utrophin expression and enhanced differentiation. This was accompanied by resistance to eccentric contraction-induced injury in slow fiber type-enriched soleus muscles. Finally, we found that these effects were partially dependent on the upregulation of p38 signalling. Collectively, these results demonstrate that SLK downregulation can restore some aspects of disease progression in DMD.

Impaired autophagy correlates with golden retriever muscular dystrophy phenotype.

INTRODUCTION: Duchenne muscular dystrophy (DMD) and golden retriever muscular dystrophy (GRMD) are X-linked disorders caused by mutations in the DMD gene. Autophagy was recently identified as a secondary therapeutic target for DMD. We hypothesized that autophagy would be reduced in GRMD. METHODS: Autophagic gene and protein expression was assessed in normal and GRMD skeletal muscles and correlated with phenotypic biomarkers. RESULTS: Muscles were differentially affected. Autophagy gene levels were lower than normal in the GRMD cranial sartorius (CS) but similar in the vastus lateralis (VL). Protein markers of autophagic flux, LC3B-II and p62, were higher in both GRMD muscles, in keeping with impaired autophagy. Protein levels correlated with a more severe phenotype. Autophagic structures were found in necrotic, fast-twitch GRMD myofibers. DISCUSSION: Our data suggest that autophagy is impaired in certain GRMD muscles. Differential GRMD CS involvement emphasizes that therapeutic modulation of autophagy could require specific muscle targeting. Muscle Nerve 58: 418-426, 2018.

Whole genome sequencing reveals a 7 base-pair deletion in DMD exon 42 in a dog with muscular dystrophy.

Dystrophin is a key cytoskeletal protein coded by the Duchenne muscular dystrophy (DMD) gene located on the X-chromosome. Truncating mutations in the DMD gene cause loss of dystrophin and the classical DMD clinical syndrome. Spontaneous DMD gene mutations and associated phenotypes occur in several other species. The mdx mouse model and the golden retriever muscular dystrophy (GRMD) canine model have been used extensively to study DMD disease pathogenesis and show efficacy and side effects of putative treatments. Certain DMD gene mutations in high-risk, the so-called hot spot areas can be particularly helpful in modeling molecular therapies. Identification of specific mutations has been greatly enhanced by new genomic methods. Whole genome, next generation sequencing (WGS) has been recently used to define DMD patient mutations, but has not been used in dystrophic dogs. A dystrophin-deficient Cavalier King Charles Spaniel (CKCS) dog was evaluated at the functional, histopathological, biochemical, and molecular level. The affected dog's phenotype was compared to the previously reported canine dystrophinopathies. WGS was then used to detect a 7 base pair deletion in DMD exon 42 (c.6051-6057delTCTCAAT mRNA), predicting a frameshift in gene transcription and truncation of dystrophin protein translation. The deletion was confirmed with conventional PCR and Sanger sequencing. This mutation is in a secondary DMD gene hotspot area distinct from the one identified earlier at the 5' donor splice site of intron 50 in the CKCS breed.