Dp412e: a novel human embryonic dystrophin isoform induced by BMP4 in early differentiated cells

Duchenne muscular dystrophy skeletal muscle cells derived from human induced pluripotent stem cells recapitulate various calcium dysregulation pathways

Duchenne muscular dystrophy (DMD) is an X-linked progressive muscle degenerative disease, caused by mutations in the dystrophin gene and resulting in premature death. As a major secondary event, an abnormal elevation of the intracellular calcium concentration in the dystrophin-deficient muscle contributes to disease progression in DMD. In this study, we investigated the specific functional features of induced pluripotent stem cell-derived muscle cells (hiPSC-skMCs) generated from DMD patients to regulate intracellular calcium concentration. As compared to healthy hiPSC-skMCs, DMD hiPSC-skMCs displayed specific spontaneous calcium signatures with high levels of intracellular calcium concentration. Furthermore, stimulations with electrical field or with acetylcholine perfusion induced higher calcium response in DMD hiPSC-skMCs as compared to healthy cells. Finally, Mn2+ quenching experiments demonstrated high levels of constitutive calcium entries in DMD hiPSC-skMCs as compared to healthy cells. Our findings converge on the fact that DMD hiPSC-skMCs display intracellular calcium dysregulation as demonstrated in several other models. Observed calcium disorders associated with RNAseq analysis on these DMD cells highlighted some mechanisms, such as spontaneous and activated sarcoplasmic reticulum (SR) releases or constitutive calcium entries, known to be disturbed in other dystrophin-deficient models. However, store operated calcium entries (SOCEs) were not found to be dysregulated in our DMD hiPSC-skMCs model. These results suggest that all the mechanisms of calcium impairment observed in other animal models may not be as pronounced in humans and could point to a preference for certain mechanisms that could correspond to major molecular targets for DMD therapies.

Dystrophin deficiency impairs cell junction formation during embryonic myogenesis from pluripotent stem cells

Mutations in the DMD gene lead to Duchenne muscular dystrophy (DMD), a severe neuromuscular disorder affecting young boys as they acquire motor functions. DMD is typically diagnosed at 2-4 years of age, but the absence of dystrophin has negative impacts on skeletal muscles before overt symptoms appear in patients, which poses a serious challenge in current standards of care. Here, we investigated the consequences of dystrophin deficiency during skeletal muscle development. We used single-cell transcriptome profiling to characterize the myogenic trajectory of human pluripotent stem cells and showed that DMD cells bifurcate to an alternative branch when they reach the somite stage. Dystrophin deficiency was linked to marked dysregulations of cell junction proteins involved in the cell state transitions characteristic of embryonic somitogenesis. Altogether, this work demonstrates that in vitro, dystrophin deficiency has deleterious effects on cell-cell communication during myogenic development, which should be considered in future therapeutic strategies for DMD.

Ablation of the dystrophin Dp71f alternative C-terminal variant increases sarcoma tumour cell aggressiveness

Alterations in Dp71 expression, the most ubiquitous dystrophin isoform, have been associated with patient survival across tumours. Intriguingly, in certain malignancies, Dp71 acts as a tumour suppressor, while manifesting oncogenic properties in others. This diversity could be explained by the expression of two Dp71 splice variants encoding proteins with distinct C-termini, each with specific properties. Expression of these variants has impeded the exploration of their unique roles. Using CRISPR/Cas9, we ablated the Dp71f variant with the alternative C-terminus in a sarcoma cell line not expressing the canonical C-terminal variant, and conducted molecular (RNAseq) and functional characterisation of the knockout cells. Dp71f ablation induced major transcriptomic alterations, particularly affecting the expression of genes involved in calcium signalling and ECM-receptor interaction pathways. The genome-scale metabolic analysis identified significant downregulation of glucose transport via membrane vesicle reaction (GLCter) and downregulated glycolysis/gluconeogenesis pathway. Functionally, these molecular changes corresponded with, increased calcium responses, cell adhesion, proliferation, survival under serum starvation and chemotherapeutic resistance. Knockout cells showed reduced GLUT1 protein expression, survival without attachment and their migration and invasion in vitro and in vivo were unaltered, despite increased matrix metalloproteinases release. Our findings emphasise the importance of alternative splicing of dystrophin transcripts and underscore the role of the Dp71f variant, which appears to govern distinct cellular processes frequently dysregulated in tumour cells. The loss of this regulatory mechanism promotes sarcoma cell survival and treatment resistance. Thus, Dp71f is a target for future investigations exploring the intricate functions of specific DMD transcripts in physiology and across malignancies.

Dystrophin deficiency impairs cell junction formation during embryonic myogenesis

Mutations in the DMD gene lead to Duchenne muscular dystrophy, a severe X-linked neuromuscular disorder that manifests itself as young boys acquire motor functions. DMD is typically diagnosed at 2 to 4 years of age, but the absence of dystrophin negatively impacts muscle structure and function before overt symptoms appear in patients, which poses a serious challenge in the optimization of standards of care. In this report, we investigated the early consequences of dystrophin deficiency during skeletal muscle development. We used single-cell transcriptome profiling to characterize the myogenic trajectory of human pluripotent stem cells and showed that DMD cells bifurcate to an alternative branch when they reach the somite stage. Here, dystrophin deficiency was linked to marked dysregulations of cell junction protein families involved in the cell state transitions characteristic of embryonic somitogenesis. Altogether, this work demonstrates that in vitro, dystrophin deficiency has deleterious effects on cell-cell communication during myogenic development, which should be considered in future therapeutic strategies for DMD.

Primary mouse myoblast metabotropic purinoceptor profiles and calcium signalling differ with their muscle origin and are altered in mdx dystrophinopathy

Mortality of Duchenne Muscular Dystrophy (DMD) is a consequence of progressive wasting of skeletal and cardiac muscle, where dystrophinopathy affects not only muscle fibres but also myogenic cells. Elevated activity of P2X7 receptors and increased store-operated calcium entry have been identified in myoblasts from the mdx mouse model of DMD. Moreover, in immortalized mdx myoblasts, increased metabotropic purinergic receptor response was found. Here, to exclude any potential effects of cell immortalization, we investigated the metabotropic response in primary mdx and wild-type myoblasts. Overall, analyses of receptor transcript and protein levels, antagonist sensitivity, and cellular localization in these primary myoblasts confirmed the previous data from immortalised cells. However, we identified significant differences in the pattern of expression and activity of P2Y receptors and the levels of the "calcium signalling toolkit" proteins between mdx and wild-type myoblasts isolated from different muscles. These results not only extend the earlier findings on the phenotypic effects of dystrophinopathy in undifferentiated muscle but, importantly, also reveal that these changes are muscle type-dependent and endure in isolated cells. This muscle-specific cellular impact of DMD may not be limited to the purinergic abnormality in mice and needs to be taken into consideration in human studies.

The Role of P2X7 Purinoceptors in the Pathogenesis and Treatment of Muscular Dystrophies

Muscular dystrophies are inherited neuromuscular diseases, resulting in progressive disability and often affecting life expectancy. The most severe, common types are Duchenne muscular dystrophy (DMD) and Limb-girdle sarcoglycanopathy, which cause advancing muscle weakness and wasting. These diseases share a common pathomechanism where, due to the loss of the anchoring dystrophin (DMD, dystrophinopathy) or due to mutations in sarcoglycan-encoding genes (LGMDR3 to LGMDR6), the α-sarcoglycan ecto-ATPase activity is lost. This disturbs important purinergic signaling: An acute muscle injury causes the release of large quantities of ATP, which acts as a damage-associated molecular pattern (DAMP). DAMPs trigger inflammation that clears dead tissues and initiates regeneration that eventually restores normal muscle function. However, in DMD and LGMD, the loss of ecto-ATPase activity, that normally curtails this extracellular ATP (eATP)-evoked stimulation, causes exceedingly high eATP levels. Thus, in dystrophic muscles, the acute inflammation becomes chronic and damaging. The very high eATP over-activates P2X7 purinoceptors, not only maintaining the inflammation but also tuning the potentially compensatory P2X7 up-regulation in dystrophic muscle cells into a cell-damaging mechanism exacerbating the pathology. Thus, the P2X7 receptor in dystrophic muscles is a specific therapeutic target. Accordingly, the P2X7 blockade alleviated dystrophic damage in mouse models of dystrophinopathy and sarcoglycanopathy. Therefore, the existing P2X7 blockers should be considered for the treatment of these highly debilitating diseases. This review aims to present the current understanding of the eATP-P2X7 purinoceptor axis in the pathogenesis and treatment of muscular dystrophies.

Integrated Proteomics Unveils Nuclear PDE3A2 as a Regulator of Cardiac Myocyte Hypertrophy

BACKGROUND

Signaling by cAMP is organized in multiple distinct subcellular nanodomains regulated by cAMP-hydrolyzing PDEs (phosphodiesterases). Cardiac β-adrenergic signaling has served as the prototypical system to elucidate cAMP compartmentalization. Although studies in cardiac myocytes have provided an understanding of the location and properties of a handful of cAMP subcellular compartments, an overall view of the cellular landscape of cAMP nanodomains is missing.

METHODS

Here, we combined an integrated phosphoproteomics approach that takes advantage of the unique role that individual PDEs play in the control of local cAMP, with network analysis to identify previously unrecognized cAMP nanodomains associated with β-adrenergic stimulation. We then validated the composition and function of one of these nanodomains using biochemical, pharmacological, and genetic approaches and cardiac myocytes from both rodents and humans.

RESULTS

We demonstrate the validity of the integrated phosphoproteomic strategy to pinpoint the location and provide critical cues to determine the function of previously unknown cAMP nanodomains. We characterize in detail one such compartment and demonstrate that the PDE3A2 isoform operates in a nuclear nanodomain that involves SMAD4 (SMAD family member 4) and HDAC-1 (histone deacetylase 1). Inhibition of PDE3 results in increased HDAC-1 phosphorylation, leading to inhibition of its deacetylase activity, derepression of gene transcription, and cardiac myocyte hypertrophic growth.

CONCLUSIONS

We developed a strategy for detailed mapping of subcellular PDE-specific cAMP nanodomains. Our findings reveal a mechanism that explains the negative long-term clinical outcome observed in patients with heart failure treated with PDE3 inhibitors.

Dlk1-Dio3 cluster miRNAs regulate mitochondrial functions in the dystrophic muscle in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a severe muscle disease caused by impaired expression of dystrophin. Whereas mitochondrial dysfunction is thought to play an important role in DMD, the mechanism of this dysfunction remains to be clarified. Here we demonstrate that in DMD and other muscular dystrophies, a large number of Dlk1-Dio3 clustered miRNAs (DD-miRNAs) are coordinately up-regulated in regenerating myofibers and in the serum. To characterize the biological effect of this dysregulation, 14 DD-miRNAs were simultaneously overexpressed in vivo in mouse muscle. Transcriptomic analysis revealed highly similar changes between the muscle ectopically overexpressing 14 DD-miRNAs and the mdx diaphragm, with naturally up-regulated DD-miRNAs. Among the commonly dysregulated pathway we found repressed mitochondrial metabolism, and oxidative phosphorylation (OxPhos) in particular. Knocking down the DD-miRNAs in iPS-derived skeletal myotubes resulted in increased OxPhos activities. The data suggest that (1) DD-miRNAs are important mediators of dystrophic changes in DMD muscle, (2) mitochondrial metabolism and OxPhos in particular are targeted in DMD by coordinately up-regulated DD-miRNAs. These findings provide insight into the mechanism of mitochondrial dysfunction in muscular dystrophy.

Loss of full-length dystrophin expression results in major cell-autonomous abnormalities in proliferating myoblasts

Duchenne muscular dystrophy (DMD) affects myofibers and muscle stem cells, causing progressive muscle degeneration and repair defects. It was unknown whether dystrophic myoblasts-the effector cells of muscle growth and regeneration-are affected. Using transcriptomic, genome-scale metabolic modelling and functional analyses, we demonstrate, for the first time, convergent abnormalities in primary mouse and human dystrophic myoblasts. In Dmdmdx myoblasts lacking full-length dystrophin, the expression of 170 genes was significantly altered. Myod1 and key genes controlled by MyoD (Myog, Mymk, Mymx, epigenetic regulators, ECM interactors, calcium signalling and fibrosis genes) were significantly downregulated. Gene ontology analysis indicated enrichment in genes involved in muscle development and function. Functionally, we found increased myoblast proliferation, reduced chemotaxis and accelerated differentiation, which are all essential for myoregeneration. The defects were caused by the loss of expression of full-length dystrophin, as similar and not exacerbated alterations were observed in dystrophin-null Dmdmdx-βgeo myoblasts. Corresponding abnormalities were identified in human DMD primary myoblasts and a dystrophic mouse muscle cell line, confirming the cross-species and cell-autonomous nature of these defects. The genome-scale metabolic analysis in human DMD myoblasts showed alterations in the rate of glycolysis/gluconeogenesis, leukotriene metabolism, and mitochondrial beta-oxidation of various fatty acids. These results reveal the disease continuum: DMD defects in satellite cells, the myoblast dysfunction affecting muscle regeneration, which is insufficient to counteract muscle loss due to myofiber instability. Contrary to the established belief, our data demonstrate that DMD abnormalities occur in myoblasts, making these cells a novel therapeutic target for the treatment of this lethal disease.

Dystrophin Dp71 Subisoforms Localize to the Mitochondria of Human Cells

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease caused by deficiency in dystrophin, a protein product encoded by the DMD gene. Mitochondrial dysfunction is now attracting much attention as a central player in DMD pathology. However, dystrophin has never been explored in human mitochondria. Here, we analyzed dystrophin in cDNAs and mitochondrial fractions of human cells. Mitochondrial fraction was obtained using a magnetic-associated cell sorting (MACS) technology. Dystrophin was analyzed by reverse transcription (RT)-PCR and western blotting using an antibody against the dystrophin C-terminal. In isolated mitochondrial fraction from HEK293 cells, dystrophin was revealed as a band corresponding to Dp71b and Dp71ab subisoforms. Additionally, in mitochondria from HeLa, SH-SY5Y, CCL-136 and HepG2 cells, signals for Dp71b and Dp71ab were revealed as well. Concomitantly, dystrophin mRNAs encoding Dp71b and Dp71ab were disclosed by RT-PCR in these cells. Primary cultured myocytes from three dystrophinopathy patients showed various levels of mitochondrial Dp71 expression. Coherently, levels of mRNA were different in all cells reflecting the protein content, which indicated predominant accumulation of Dp71. Dystrophin was demonstrated to be localized to human mitochondrial fraction, specifically as Dp71 subisoforms. Myocytes derived from dystrophinopathy patients manifested different levels of mitochondrial Dp71, with higher expression revealed in myocytes from Becker muscular dystrophy (BMD) patient-derived myocytes.

De novo revertant fiber formation and therapy testing in a 3D culture model of Duchenne muscular dystrophy skeletal muscle

The biological basis of Duchenne muscular dystrophy (DMD) pathology is only partially characterized and there are still few disease-modifying therapies available, therein underlying the value of strategies to model and study DMD. Dystrophin, the causative gene of DMD, is responsible for linking the cytoskeleton of muscle fibers to the extracellular matrix beyond the sarcolemma. We posited that disease-associated phenotypes not yet captured by two-dimensional culture methods would arise by generating multinucleated muscle cells within a three-dimensional (3D) extracellular matrix environment. Herein we report methods to produce 3D human skeletal muscle microtissues (hMMTs) using clonal, immortalized myoblast lines established from healthy and DMD donors. We also established protocols to evaluate immortalized hMMT self-organization and myotube maturation, as well as calcium handling, force generation, membrane stability (i.e., creatine kinase activity and Evans blue dye permeability) and contractile apparatus organization following electrical-stimulation. In examining hMMTs generated with a cell line wherein the dystrophin gene possessed a duplication of exon 2, we observed rare dystrophin-positive myotubes, which were not seen in 2D cultures. Further, we show that treating DMD hMMTs with a β1-integrin activating antibody, improves contractile apparatus maturation and stability. Hence, immortalized myoblast-derived DMD hMMTs offer a pre-clinical system with which to investigate the potential of duplicated exon skipping strategies and those that protect muscle cells from contraction-induced injury. STATEMENT OF SIGNIFICANCE: Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disorder that is caused by mutation of the dystrophin gene. The biological basis of DMD pathology is only partially characterized and there is no cure for this fatal disease. Here we report a method to produce 3D human skeletal muscle microtissues (hMMTs) using immortalized human DMD and healthy myoblasts. Morphological and functional assessment revealed DMD-associated pathophysiology including impaired calcium handling and de novo formation of dystrophin-positive revertant muscle cells in immortalized DMD hMMTs harbouring an exon 2 duplication, a feature of many DMD patients that has not been recapitulated in culture prior to this report. We further demonstrate that this "DMD in a dish" system can be used as a pre-clinical assay to test a putative DMD therapeutic and study the mechanism of action.

Myogenesis modelled by human pluripotent stem cells: a multi-omic study of Duchenne myopathy early onset

BACKGROUND

Duchenne muscular dystrophy (DMD) causes severe disability of children and death of young men, with an incidence of approximately 1/5000 male births. Symptoms appear in early childhood, with a diagnosis made mostly around 4 years old, a time where the amount of muscle damage is already significant, preventing early therapeutic interventions that could be more efficient at halting disease progression. In the meantime, the precise moment at which disease phenotypes arise-even asymptomatically-is still unknown. Thus, there is a critical need to better define DMD onset as well as its first manifestations, which could help identify early disease biomarkers and novel therapeutic targets.

METHODS

We have used both human tissue-derived myoblasts and human induced pluripotent stem cells (hiPSCs) from DMD patients to model skeletal myogenesis and compared their differentiation dynamics with that of healthy control cells by a comprehensive multi-omic analysis at seven time points. Results were strengthened with the analysis of isogenic CRISPR-edited human embryonic stem cells and through comparisons against published transcriptomic and proteomic datasets from human DMD muscles. The study was completed with DMD knockdown/rescue experiments in hiPSC-derived skeletal muscle progenitor cells and adenosine triphosphate measurement in hiPSC-derived myotubes.

RESULTS

Transcriptome and miRnome comparisons combined with protein analyses demonstrated that hiPSC differentiation (i) leads to embryonic/foetal myotubes that mimic described DMD phenotypes at the differentiation endpoint and (ii) homogeneously and robustly recapitulates key developmental steps-mesoderm, somite, and skeletal muscle. Starting at the somite stage, DMD dysregulations concerned almost 10% of the transcriptome. These include mitochondrial genes whose dysregulations escalate during differentiation. We also describe fibrosis as an intrinsic feature of DMD skeletal muscle cells that begins early during myogenesis. All the omics data are available online for exploration through a graphical interface at https://muscle-dmd.omics.ovh/.

CONCLUSIONS

Our data argue for an early developmental manifestation of DMD whose onset is triggered before the entry into the skeletal muscle compartment, data leading to a necessary reconsideration of dystrophin roles during muscle development. This hiPSC model of skeletal muscle differentiation offers the possibility to explore these functions as well as find earlier DMD biomarkers and therapeutic targets.

Dystrophin Dp71ab is monoclonally expressed in human satellite cells and enhances proliferation of myoblast cells

Dystrophin Dp71 is the smallest isoform of the DMD gene, mutations in which cause Duchenne muscular dystrophy (DMD). Dp71 has also been shown to have roles in various cellular processes. Stem cell-based therapy may be effective in treating DMD, but the inability to generate a sufficient number of stem cells remains a significant obstacle. Although Dp71 is comprised of many variants, Dp71 in satellite cells has not yet been studied. Here, the full-length Dp71 consisting of 18 exons from exons G1 to 79 was amplified by reverse transcription-PCR from total RNA of human satellite cells. The amplified product showed deletion of both exons 71 and 78 in all sequenced clones, indicating monoclonal expression of Dp71ab. Western blotting of the satellite cell lysate showed a band corresponding to over-expressed Dp71ab. Transfection of a plasmid expressing Dp71ab into human myoblasts significantly enhanced cell proliferation when compared to the cells transfected with the mock plasmid. However, transfection of the Dp71 expression plasmid encoding all 18 exons did not enhance myoblast proliferation. These findings indicated that Dp71ab, but not Dp71, is a molecular enhancer of myoblast proliferation and that transfection with Dp71ab may generate a high yield of stem cells for DMD treatment.

miR-379 links glucocorticoid treatment with mitochondrial response in Duchenne muscular dystrophy

Duchenne Muscular Dystrophy (DMD) is a lethal muscle disorder, caused by mutations in the DMD gene and affects approximately 1:5000-6000 male births. In this report, we identified dysregulation of members of the Dlk1-Dio3 miRNA cluster in muscle biopsies of the GRMD dog model. Of these, we selected miR-379 for a detailed investigation because its expression is high in the muscle, and is known to be responsive to glucocorticoid, a class of anti-inflammatory drugs commonly used in DMD patients. Bioinformatics analysis predicts that miR-379 targets EIF4G2, a translational factor, which is involved in the control of mitochondrial metabolic maturation. We confirmed in myoblasts that EIF4G2 is a direct target of miR-379, and identified the DAPIT mitochondrial protein as a translational target of EIF4G2. Knocking down DAPIT in skeletal myotubes resulted in reduced ATP synthesis and myogenic differentiation. We also demonstrated that this pathway is GC-responsive since treating mice with dexamethasone resulted in reduced muscle expression of miR-379 and increased expression of EIF4G2 and DAPIT. Furthermore, miR-379 seric level, which is also elevated in the plasma of DMD patients in comparison with age-matched controls, is reduced by GC treatment. Thus, this newly identified pathway may link GC treatment to a mitochondrial response in DMD.

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.

Advances in Stem Cell Modeling of Dystrophin-Associated Disease: Implications for the Wider World of Dilated Cardiomyopathy

Familial dilated cardiomyopathy (DCM) is mostly caused by mutations in genes encoding cytoskeletal and sarcomeric proteins. In the pediatric population, DCM is the predominant type of primitive myocardial disease. A severe form of DCM is associated with mutations in the DMD gene encoding dystrophin, which are the cause of Duchenne Muscular Dystrophy (DMD). DMD-associated cardiomyopathy is still poorly understood and orphan of a specific therapy. In the last 5 years, a rise of interest in disease models using human induced pluripotent stem cells (hiPSCs) has led to more than 50 original studies on DCM models. In this review paper, we provide a comprehensive overview on the advances in DMD cardiomyopathy disease modeling and highlight the most remarkable findings obtained from cardiomyocytes differentiated from hiPSCs of DMD patients. We will also describe how hiPSCs based studies have contributed to the identification of specific myocardial disease mechanisms that may be relevant in the pathogenesis of DCM, representing novel potential therapeutic targets.

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

Background

The DMD gene is one of the largest human genes, being composed of 79 exons. Dystrophin Dp116 expressed from the promoter in intron 55 is a Schwann cell-specific isoform. The pathophysiological roles of Dp116 are largely unknown, because of its limited expression. This study assessed the expression of Dp116 in glioblastoma cells and evaluated the splicing patterns of the DMD gene in these cells.

Methods

Full-length Dp116 cDNA was PCR amplified from U-251 glioblastoma cells. Dp116 protein was analyzed by Western blotting.

Results

Full-length Dp116 cDNA, extending from exon S1 to exon 79, was PCR amplified to avoid confusion with other DMD isoforms. The full-length Dp116 transcript was amplified as nearly 3 kb in size. Western blotting of U-251 cell lysates revealed a signal at a position corresponding to vector-expressed Dp116 protein, indicating that Dp116 is expressed in glioblastoma cells. Sequencing of the amplified product revealed five splice variants, all skipping exon 78. The most abundant transcript lacked only exon 78 (Dp116b), whereas the second most abundant transcript lacked both exons 71 and 78 (Dp116ab). A third transcript lacking exons 71–74 and 78 was also identified (Dp116bc). Two novel splicing patterns were also observed, one with a deletion of exons 68 and 69 (Dp116bΔ68-69) and the other with a 100 bp deletion in the 5’ terminal end of exon 75 (75s), which was produced by the activation of a cryptic splice acceptor site (Dp116b75s). However, the splicing patterns in glioblastoma cells of DMD exons in Dp116 and Dp71 showed no significant differences.

Conclusions

Dp116 is expressed in glioblastoma cells as five splicing variants, with Dp116b being the most abundant. Two novel splicing patterns of DMD exons were observed.

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Dp116 is a Schwann cell-specific dystrophin isoform.

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Dp116 was shown to be expressed in glioblastoma, a lethal cerebral malignancy.

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Skipping of exon 78 was the default pathway.

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Of the five alternatively spliced variants detected, Dp116b was the most abundant.

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DMD exons showed two novel splicing patterns, one with cryptic splice activation.

Dystrophin Deficiency Leads to Genomic Instability in Human Pluripotent Stem Cells via NO Synthase-Induced Oxidative Stress

Recent data on Duchenne muscular dystrophy (DMD) show myocyte progenitor's involvement in the disease pathology often leading to the DMD patient's death. The molecular mechanism underlying stem cell impairment in DMD has not been described. We created dystrophin-deficient human pluripotent stem cell (hPSC) lines by reprogramming cells from two DMD patients, and also by introducing dystrophin mutation into human embryonic stem cells via CRISPR/Cas9. While dystrophin is expressed in healthy hPSC, its deficiency in DMD hPSC lines induces the release of reactive oxygen species (ROS) through dysregulated activity of all three isoforms of nitric oxide synthase (further abrev. as, NOS). NOS-induced ROS release leads to DNA damage and genomic instability in DMD hPSC. We were able to reduce both the ROS release as well as DNA damage to the level of wild-type hPSC by inhibiting NOS activity.

Genome editing in primary cells and in vivo using viral-derived Nanoblades loaded with Cas9-sgRNA ribonucleoproteins

Programmable nucleases have enabled rapid and accessible genome engineering in eukaryotic cells and living organisms. However, their delivery into target cells can be technically challenging when working with primary cells or in vivo. Here, we use engineered murine leukemia virus-like particles loaded with Cas9-sgRNA ribonucleoproteins (Nanoblades) to induce efficient genome-editing in cell lines and primary cells including human induced pluripotent stem cells, human hematopoietic stem cells and mouse bone-marrow cells. Transgene-free Nanoblades are also capable of in vivo genome-editing in mouse embryos and in the liver of injected mice. Nanoblades can be complexed with donor DNA for "all-in-one" homology-directed repair or programmed with modified Cas9 variants to mediate transcriptional up-regulation of target genes. Nanoblades preparation process is simple, relatively inexpensive and can be easily implemented in any laboratory equipped for cellular biology.

The paracrine effects of human induced pluripotent stem cells promote bone-like structures via the upregulation of BMP expression in a mouse ectopic model

Use of human induced pluripotent stem cells (h-iPSCs) for bone tissue engineering is most appealing, because h-iPSCs are an inexhaustible source of osteocompetent cells. The present study investigated the contribution of undifferentiated h-iPSCs and elucidated aspects of the underlying mechanism(s) of the involvement of these cells to new bone formation. Implantation of undifferentiated h-iPSCs seeded on coral particles in ectopic sites of mice resulted in expression of osteocalcin and DMP-1, and in mineral content similar to that of the murine bone. The number of the implanted h-iPSCs decreased with time and disappeared by 30 days post-implantation. In contrast, expression of the murine osteogenic genes at day 15 and 30 post-implantation provided, for the first time, evidence that the implanted h-iPSCs affected the observed outcomes via paracrine mechanisms. Supporting evidence was provided because supernatant conditioned media from h-iPSCs (h-iPSC CM), promoted the osteogenic differentiation of human mesenchymal stem cells (h-MSCs) in vitro. Specifically, h-iPSC CM induced upregulation of the BMP-2, BMP-4 and BMP-6 genes, and promoted mineralization of the extracellular matrix. Given the current interest in the use of h-iPSCs for regenerative medicine applications, our study contributes new insights into aspects of the mechanism underlying the bone promoting capability of h-iPSCs.

Detection of Dystrophin Dp71 in Human Skeletal Muscle Using an Automated Capillary Western Assay System

Background: Dystrophin Dp71 is one of the isoforms produced by the DMD gene which is mutated in patients with Duchenne muscular dystrophy (DMD). Although Dp71 is expressed ubiquitously, it has not been detected in normal skeletal muscle. This study was performed to assess the expression of Dp71 in human skeletal muscle. Methods: Human skeletal muscle RNA and tissues were obtained commercially. Mouse skeletal muscle was obtained from normal and DMD^mdx mice. Dp71 mRNA and protein were determined by reverse-transcription PCR and an automated capillary Western assay system, the Simple Western, respectively. Dp71 was over-expressed or suppressed using a plasmid expressing Dp71 or antisense oligonucleotide, respectively. Results: Full-length Dp71 cDNA was PCR amplified as a single product from human skeletal muscle RNA. A ca. 70 kDa protein peak detected by the Simple Western was determined as Dp71 by over-expressing Dp71 in HEK293 cells, or suppressing Dp71 expression with antisense oligonucleotide in rhabdomyosarcoma cells. The Simple Western assay detected Dp71 in the skeletal muscles of both normal and DMD mice. In human skeletal muscle, Dp71 was also detected. The ratio of Dp71 to vinculin of human skeletal muscle samples varied widely, indicating various levels of Dp71 expression. Conclusions: Dp71 protein was detected in human skeletal muscle using a highly sensitive capillary Western blotting system.

Comparability of automated human induced pluripotent stem cell culture: a pilot study

Consistent and robust manufacturing is essential for the translation of cell therapies, and the utilisation automation throughout the manufacturing process may allow for improvements in quality control, scalability, reproducibility and economics of the process. The aim of this study was to measure and establish the comparability between alternative process steps for the culture of hiPSCs. Consequently, the effects of manual centrifugation and automated non-centrifugation process steps, performed using TAP Biosystems’ CompacT SelecT automated cell culture platform, upon the culture of a human induced pluripotent stem cell (hiPSC) line (VAX001024c07) were compared. This study, has demonstrated that comparable morphologies and cell diameters were observed in hiPSCs cultured using either manual or automated process steps. However, non-centrifugation hiPSC populations exhibited greater cell yields, greater aggregate rates, increased pluripotency marker expression, and decreased differentiation marker expression compared to centrifugation hiPSCs. A trend for decreased variability in cell yield was also observed after the utilisation of the automated process step. This study also highlights the detrimental effect of the cryopreservation and thawing processes upon the growth and characteristics of hiPSC cultures, and demonstrates that automated hiPSC manufacturing protocols can be successfully transferred between independent laboratories.