Schwann cell-specific Dp116 is expressed in glioblastoma cells, revealing two novel DMD gene splicing patterns

Dystrophin- and Utrophin-Based Therapeutic Approaches for Treatment of Duchenne Muscular Dystrophy: A Comparative Review

Duchenne muscular dystrophy is a devastating disease that leads to progressive muscle loss and premature death. While medical management focuses mostly on symptomatic treatment, decades of research have resulted in first therapeutics able to restore the affected reading frame of dystrophin transcripts or induce synthesis of a truncated dystrophin protein from a vector, with other strategies based on gene therapy and cell signaling in preclinical or clinical development. Nevertheless, recent reports show that potentially therapeutic dystrophins can be immunogenic in patients. This raises the question of whether a dystrophin paralog, utrophin, could be a more suitable therapeutic protein. Here, we compare dystrophin and utrophin amino acid sequences and structures, combining published data with our extended in silico analyses. We then discuss these results in the context of therapeutic approaches for Duchenne muscular dystrophy. Specifically, we focus on strategies based on delivery of micro-dystrophin and micro-utrophin genes with recombinant adeno-associated viral vectors, exon skipping of the mutated dystrophin pre-mRNAs, reading through termination codons with small molecules that mask premature stop codons, dystrophin gene repair by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9)-mediated genetic engineering, and increasing utrophin levels. Our analyses highlight the importance of various dystrophin and utrophin domains in Duchenne muscular dystrophy treatment, providing insights into designing novel therapeutic compounds with improved efficacy and decreased immunoreactivity. While the necessary actin and β-dystroglycan binding sites are present in both proteins, important functional distinctions can be identified in these domains and some other parts of truncated dystrophins might need redesigning due to their potentially immunogenic qualities. Alternatively, therapies based on utrophins might provide a safer and more effective approach.

Dystrophin deficiency affects human astrocyte properties and response to damage

In addition to progressive muscular degeneration due to dystrophin mutations, 1/3 of Duchenne muscular dystrophy (DMD) patients present cognitive deficits. However, there is currently an incomplete understanding about the function of the multiple dystrophin isoforms in human brains. Here, we tested the hypothesis that dystrophin deficiency affects glial function in DMD and could therefore contribute to neural impairment. We investigated human dystrophin isoform expression with development and differentiation and response to damage in human astrocytes from control and induced pluripotent stem cells from DMD patients. In control cells, short dystrophin isoforms were up-regulated with development and their expression levels changed differently upon neuronal and astrocytic differentiation, as well as in 2-dimensional versus 3-dimensional astrocyte cultures. All DMD-astrocytes tested displayed altered morphology, proliferative activity and AQP4 expression. Furthermore, they did not show any morphological change in response to inflammatory stimuli and their number was significantly lower as compared to stimulated healthy astrocytes. Finally, DMD-astrocytes appeared to be more sensitive than controls to oxidative damage as shown by their increased cell death. Behavioral and metabolic defects in DMD-astrocytes were consistent with gene pathway dysregulation shared by lines with different mutations as demonstrated by bulk RNA-seq analysis. Together, our DMD model provides evidence for altered astrocyte function in DMD suggesting that defective astrocyte responses may contribute to neural impairment and might provide additional potential therapeutic targets.

Complexity of skeletal muscle degeneration: multi-systems pathophysiology and organ crosstalk in dystrophinopathy

Duchenne muscular dystrophy is a highly progressive muscle wasting disorder due to primary abnormalities in one of the largest genes in the human genome, the DMD gene, which encodes various tissue-specific isoforms of the protein dystrophin. Although dystrophinopathies are classified as primary neuromuscular disorders, the body-wide abnormalities that are associated with this disorder and the occurrence of organ crosstalk suggest that a multi-systems pathophysiological view should be taken for a better overall understanding of the complex aetiology of X-linked muscular dystrophy. This article reviews the molecular and cellular effects of deficiency in dystrophin isoforms in relation to voluntary striated muscles, the cardio-respiratory system, the kidney, the liver, the gastrointestinal tract, the nervous system and the immune system. Based on the establishment of comprehensive biomarker signatures of X-linked muscular dystrophy using large-scale screening of both patient specimens and genetic animal models, this article also discusses the potential usefulness of novel disease markers for more inclusive approaches to differential diagnosis, prognosis and therapy monitoring that also take into account multi-systems aspects of dystrophinopathy. Current therapeutic approaches to combat muscular dystrophy are summarised.

The Dystrophin Node as Integrator of Cytoskeletal Organization, Lateral Force Transmission, Fiber Stability and Cellular Signaling in Skeletal Muscle

The systematic bioanalytical characterization of the protein product of the DMD gene, which is defective in the pediatric disorder Duchenne muscular dystrophy, led to the discovery of the membrane cytoskeletal protein dystrophin. Its full-length muscle isoform Dp427-M is tightly linked to a sarcolemma-associated complex consisting of dystroglycans, sarcoglyans, sarcospan, dystrobrevins and syntrophins. Besides these core members of the dystrophin-glycoprotein complex, the wider dystrophin-associated network includes key proteins belonging to the intracellular cytoskeleton and microtubular assembly, the basal lamina and extracellular matrix, various plasma membrane proteins and cytosolic components. Here, we review the central role of the dystrophin complex as a master node in muscle fibers that integrates cytoskeletal organization and cellular signaling at the muscle periphery, as well as providing sarcolemmal stabilization and contractile force transmission to the extracellular region. The combination of optimized tissue extraction, subcellular fractionation, advanced protein co-purification strategies, immunoprecipitation, liquid chromatography and two-dimensional gel electrophoresis with modern mass spectrometry-based proteomics has confirmed the composition of the core dystrophin complex at the sarcolemma membrane. Importantly, these biochemical and mass spectrometric surveys have identified additional members of the wider dystrophin network including biglycan, cavin, synemin, desmoglein, tubulin, plakoglobin, cytokeratin and a variety of signaling proteins and ion channels.

Intronic Alternative Polyadenylation in the Middle of the DMD Gene Produces Half-Size N-Terminal Dystrophin with a Potential Implication of ECG Abnormalities of DMD Patients

The DMD gene is one of the largest human genes, being composed of 79 exons, and encodes dystrophin Dp427m which is deficient in Duchenne muscular dystrophy (DMD). In some DMD patient, however, small size dystrophin reacting with antibody to N-terminal but not to C-terminal has been identified. The mechanism to produce N-terminal small size dystrophin remains unknown. Intronic polyadenylation is a mechanism that produces a transcript with a new 3′ terminal exon and a C-terminal truncated protein. In this study, intronic alternative polyadenylation was disclosed to occur in the middle of the DMD gene and produce the half-size N-terminal dystrophin Dp427m, Dpm234. The 3′-rapid amplification of cDNA ends revealed 421 bp sequence in the downstream of DMD exon 41 in U-251 glioblastoma cells. The cloned sequence composing of the 5′ end sequence of intron 41 was decided as the terminal exon, since it encoded poly (A) signal followed by poly (A) stretch. Subsequently, a fragment from DMD exon M1 to intron 41 was obtained by PCR amplification. This product was named Dpm234 after its molecular weight. However, Dpm234 was not PCR amplified in human skeletal and cardiac muscles. Remarkably, Dpm234 was PCR amplified in iPS-derived cardiomyocytes. Accordingly, Western blotting of cardiomyocyte proteins showed a band of 234 kDa reacting with dystrophin antibody to N-terminal, but not C-terminal. Clinically, DMD patients with mutations in the Dpm234 coding region were found to have a significantly higher likelihood of two ECG abnormal findings. Intronic alternative splicing was first revealed in Dp427m to produce small size dystrophin.