Altered muscle niche contributes to myogenic deficit in the D2-mdx model of severe DMD.

Lack of dystrophin expression is the underlying genetic basis for Duchenne muscular dystrophy (DMD). However, disease severity varies between patients, based on specific genetic modifiers. D2-mdx is a model for severe DMD that exhibits exacerbated muscle degeneration and failure to regenerate even in the juvenile stage of the disease.

Altered muscle niche contributes to myogenic deficit in the D2- model of severe DMD.

Lack of dystrophin is the genetic basis for the Duchenne muscular dystrophy (DMD). However, disease severity varies between patients, based on specific genetic modifiers. D2- is a model for severe DMD that exhibits exacerbated muscle degeneration and failure to regenerate even in the juvenile stage of the disease.

The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.

Background: Becker muscular dystrophy (BMD) is a genetic neuromuscular disease of growing importance caused by in-frame, partial loss-of-function mutations in the dystrophin (DMD) gene. BMD presents with reduced severity compared with Duchenne muscular dystrophy (DMD), the allelic disorder of complete dystrophin deficiency. Significant therapeutic advancements have been made in DMD, including four FDA-approved drugs.

Characterization of the dystrophin-associated protein complex by mass spectrometry.

The dystrophin-associated protein complex (DAPC) is a highly organized multiprotein complex that plays a pivotal role in muscle fiber structure integrity and cell signaling. The complex is composed of three distinct interacting subgroups, intracellular peripheral proteins, transmembrane glycoproteins, and extracellular glycoproteins subcomplexes. Dystrophin protein nucleates the DAPC and is important for connecting the intracellular actin cytoskeletal filaments to the sarcolemma glycoprotein complex that is connected to the extracellular matrix via laminin, thus stabilizing the sarcolemma during muscle fiber contraction and relaxation.

Anoctamin 5 Knockout Mouse Model Recapitulates LGMD2L Muscle Pathology and Offers Insight Into in vivo Functional Deficits.

Mutations in the Anoctamin 5 (Ano5) gene that result in the lack of expression or function of ANO5 protein, cause Limb Girdle Muscular Dystrophy (LGMD) 2L/R12, and Miyoshi Muscular Dystrophy (MMD3). However, the dystrophic phenotype observed in patient muscles is not uniformly recapitulated by ANO5 knockout in animal models of LGMD2L. Here we describe the generation of a mouse model of LGMD2L generated by targeted out-of-frame deletion of the Ano5 gene.

Interrogation of Dystrophin and Dystroglycan Complex Protein Turnover After Exon Skipping Therapy.

Recently, the Food and Drug Administration granted accelerated approvals for four exon skipping therapies -Eteplirsen, Golodirsen, Viltolarsen, and Casimersen -for Duchenne Muscular Dystrophy (DMD). However, these treatments have only demonstrated variable and largely sub-therapeutic levels of restored dystrophin protein in DMD patients, limiting their clinical impact. To better understand variable protein expression and the behavior of truncated dystrophin protein in vivo, we assessed turnover dynamics of restored dystrophin and dystrophin glycoprotein complex (DGC) proteins in mdx mice after exon skipping therapy, compared to those dynamics in wild type mice, using a targeted, highly-reproducible and sensitive, in vivo stable isotope labeling mass spectrometry approach in multiple muscle tissues.

Human muscle stem cells are refractory to aging.

Age-related loss of muscle mass and strength is widely attributed to limitation in the capacity of muscle resident satellite cells to perform their myogenic function. This idea contains two notions that have not been comprehensively evaluated by experiment. First, it entails the idea that we damage and lose substantial amounts of muscle in the course of our normal daily activities.

Membrane Repair Deficit in Facioscapulohumeral Muscular Dystrophy.

Deficits in plasma membrane repair have been identified in dysferlinopathy and Duchenne Muscular Dystrophy, and contribute to progressive myopathy. Although Facioscapulohumeral Muscular Dystrophy (FSHD) shares clinicopathological features with these muscular dystrophies, it is unknown if FSHD is characterized by plasma membrane repair deficits. Therefore, we exposed immortalized human FSHD myoblasts, immortalized myoblasts from unaffected siblings, and myofibers from a murine model of FSHD () to focal, pulsed laser ablation of the sarcolemma.

TGF-β-driven muscle degeneration and failed regeneration underlie disease onset in a DMD mouse model.

Duchenne muscular dystrophy (DMD) is a chronic muscle disease characterized by poor myogenesis and replacement of muscle by extracellular matrix. Despite the shared genetic basis, severity of these deficits varies among patients. One source of these variations is the genetic modifier that leads to increased TGF-β activity.

Morpholino-induced exon skipping stimulates cell-mediated and humoral responses to dystrophin in mdx mice.

Exon skipping is a promising genetic therapeutic strategy for restoring dystrophin expression in the treatment of Duchenne muscular dystrophy (DMD). The potential for newly synthesized dystrophin to trigger an immune response in DMD patients, however, is not well established. We have evaluated the effect of chronic phosphorodiamidate morpholino oligomer (PMO) treatment on skeletal muscle pathology and asked whether sustained dystrophin expression elicits a dystrophin-specific autoimmune response.

Shorter Phosphorodiamidate Morpholino Splice-Switching Oligonucleotides May Increase Exon-Skipping Efficacy in DMD.

Duchenne muscular dystrophy is a fatal muscle disease, caused by mutations in DMD, leading to loss of dystrophin expression. Phosphorodiamidate morpholino splice-switching oligonucleotides (PMO-SSOs) have been used to elicit the restoration of a partially functional truncated dystrophin by excluding disruptive exons from the DMD messenger. The 30-mer PMO eteplirsen (EXONDYS51) developed for exon 51 skipping is the first dystrophin-restoring, conditionally FDA-approved drug in history.

Author Correction: Myoblasts and macrophages are required for therapeutic morpholino antisense oligonucleotide delivery to dystrophic muscle.

The originally published version of this Article contained an error in Figure 6. In panel b, the top graph (BrdU 21-24d) and the bottom graph (BrdU 28-31d) were inadvertently swapped. This error has now been corrected in both the PDF and HTML versions of the Article.

Author Correction: Myoblasts and macrophages are required for therapeutic morpholino antisense oligonucleotide delivery to dystrophic muscle.

In the original version of this Article, financial support was not fully acknowledged. The PDF and HTML versions of the Article have now been corrected to include support from the CRI Light Microscopy and Image Analysis Core.

Myoblasts and macrophages are required for therapeutic morpholino antisense oligonucleotide delivery to dystrophic muscle.

Exon skipping is a promising therapeutic strategy for Duchenne muscular dystrophy (DMD), employing morpholino antisense oligonucleotides (PMO-AO) to exclude disruptive exons from the mutant DMD transcript and elicit production of truncated dystrophin protein. Clinical trials for PMO show variable and sporadic dystrophin rescue. Here, we show that robust PMO uptake and efficient production of dystrophin following PMO administration coincide with areas of myofiber regeneration and inflammation.

Quantitative Antisense Screening and Optimization for Exon 51 Skipping in Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD), the most common lethal genetic disorder, is caused by mutations in the dystrophin (DMD) gene. Exon skipping is a therapeutic approach that uses antisense oligonucleotides (AOs) to modulate splicing and restore the reading frame, leading to truncated, yet functional protein expression. In 2016, the US Food and Drug Administration (FDA) conditionally approved the first phosphorodiamidate morpholino oligomer (morpholino)-based AO drug, eteplirsen, developed for DMD exon 51 skipping.

Effect of endurance exercise on microRNAs in myositis skeletal muscle-A randomized controlled study.

Objective: To identify changes in skeletal muscle microRNA expression after endurance exercise and associate the identified microRNAs with mRNA and protein expression to disease-specific pathways in polymyositis (PM) and dermatomyositis (DM) patients.

Methods: Following a parallel clinical trial design, patients with probable PM or DM, exercising less than once a week, and on stable medication for at least one month were randomized into two groups at Karolinska University Hospital: a 12-week endurance exercise group (n = 12) or a non-exercised control group (n = 11). Using an Affymetrix microarray, microRNA expression was determined in paired muscle biopsies taken before and after the exercise intervention from 3 patients in each group.

Elusive sources of variability of dystrophin rescue by exon skipping.

Background: Systemic delivery of anti-sense oligonucleotides to Duchenne muscular dystrophy (DMD) patients to induce de novo dystrophin protein expression in muscle (exon skipping) is a promising therapy. Treatment with Phosphorodiamidate morpholino oligomers (PMO) lead to shorter de novo dystrophin protein in both animal models and DMD boys who otherwise lack dystrophin; however, restoration of dystrophin has been observed to be highly variable. Understanding the factors causing highly variable induction of dystrophin expression in pre-clinical models would likely lead to more effective means of exon skipping in both pre-clinical studies and human clinical trials.

Effect of genetic background on the dystrophic phenotype in mdx mice.

Genetic background significantly affects phenotype in multiple mouse models of human diseases, including muscular dystrophy. This phenotypic variability is partly attributed to genetic modifiers that regulate the disease process. Studies have demonstrated that introduction of the γ-sarcoglycan-null allele onto the DBA/2J background confers a more severe muscular dystrophy phenotype than the original strain, demonstrating the presence of genetic modifier loci in the DBA/2J background.

TNF-α-Induced microRNAs Control Dystrophin Expression in Becker Muscular Dystrophy.

The amount and distribution of dystrophin protein in myofibers and muscle is highly variable in Becker muscular dystrophy and in exon-skipping trials for Duchenne muscular dystrophy. Here, we investigate a molecular basis for this variability. In muscle from Becker patients sharing the same exon 45-47 in-frame deletion, dystrophin levels negatively correlate with microRNAs predicted to target dystrophin.

Germline quality control: eEF2K stands guard to eliminate defective oocytes.

The control of germline quality is critical to reproductive success and survival of a species; however, the mechanisms underlying this process remain unknown. Here, we demonstrate that elongation factor 2 kinase (eEF2K), an evolutionarily conserved regulator of protein synthesis, functions to maintain germline quality and eliminate defective oocytes. We show that disruption of eEF2K in mice reduces ovarian apoptosis and results in the accumulation of aberrant follicles and defective oocytes at advanced reproductive age.