Stem cell-based therapies for Duchenne muscular dystrophy

Chimeric Cell Therapies as a Novel Approach for Duchenne Muscular Dystrophy (DMD) and Muscle Regeneration

Chimerism-based strategies represent a pioneering concept which has led to groundbreaking advancements in regenerative medicine and transplantation. This new approach offers therapeutic potential for the treatment of various diseases, including inherited disorders. The ongoing studies on chimeric cells prompted the development of Dystrophin-Expressing Chimeric (DEC) cells which were introduced as a potential therapy for Duchenne Muscular Dystrophy (DMD). DMD is a genetic condition that leads to premature death in adolescent boys and remains incurable with current methods. DEC therapy, created via the fusion of human myoblasts derived from normal and DMD-affected donors, has proven to be safe and efficacious when tested in experimental models of DMD after systemic-intraosseous administration. These studies confirmed increased dystrophin expression, which correlated with functional and morphological improvements in DMD-affected muscles, including cardiac, respiratory, and skeletal muscles. Furthermore, the application of DEC therapy in a clinical study confirmed its long-term safety and efficacy in DMD patients. This review summarizes the development of chimeric cell technology tested in preclinical models and clinical studies, highlighting the potential of DEC therapy in muscle regeneration and repair, and introduces chimeric cell-based therapies as a promising, novel approach for muscle regeneration and the treatment of DMD and other neuromuscular disorders.

Myalgic encephalomyelitis/chronic fatigue syndrome from current evidence to new diagnostic perspectives through skeletal muscle and metabolic disturbances

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a demanding medical condition for patients and society. It has raised much more public awareness after the COVID-19 pandemic since ME/CFS and long-COVID patients share many clinical symptoms such as debilitating chronic fatigue. However, unlike long COVID, the etiopathology of ME/CFS remains a mystery despite several decades' research. This review moves from pathophysiology of ME/CFS through the compelling evidence and most interesting hypotheses. It focuses on the pathophysiology of skeletal muscle by proposing the hypothesis that skeletal muscle tissue offers novel opportunities for diagnosis and treatment of this syndrome and that new evidence can help resolve the long-standing debate on terminology.

Cell Therapy Strategies on Duchenne Muscular Dystrophy: A Systematic Review of Clinical Applications

Duchenne Muscular Dystrophy (DMD) is an inherited genetic disorder characterized by progressive degeneration of muscle tissue, leading to functional disability and premature death. Despite extensive research efforts, the discovery of a cure for DMD continues to be elusive, emphasizing the need to investigate novel treatment approaches. Cellular therapies have emerged as prospective approaches to address the underlying pathophysiology of DMD. This review provides an examination of the present situation regarding cell-based therapies, including CD133 + cells, muscle precursor cells, mesoangioblasts, bone marrow-derived mononuclear cells, mesenchymal stem cells, cardiosphere-derived cells, and dystrophin-expressing chimeric cells. A total of 12 studies were found eligible to be included as they were completed cell therapy clinical trials, clinical applications, or case reports with quantitative results. The evaluation encompassed an examination of limitations and potential advancements in this particular area of research, along with an assessment of the safety and effectiveness of cell-based therapies in the context of DMD. In general, the available data indicates that diverse cell therapy approaches may present a new, safe, and efficacious treatment modality for patients diagnosed with DMD. However, further studies are required to comprehensively understand the most advantageous treatment approach and therapeutic capacity.

Tenascin-C-EGFR activation induces functional human satellite cell proliferation and promotes wound-healing of skeletal muscles via oleanic acid

Human satellite cells (HuSCs) have been deemed to be the potential cure to treat muscular atrophy diseases such as Duchenne muscular dystrophy. However, the clinical trials of HuSCs were restricted to the inadequacy of donors because of that freshly isolated HuSCs quickly lost the Pax7 expression and myogenesis capacity in vivo after a few days of culture. Here we found that oleanic acid, a kind of triterpenoid endowed with diverse biological functions with treatment potential, could efficiently promote HuSCs proliferation. The HuSCs cultured in the medium supplement with oleanic acid could maintain a high expression level of Pax7 and retain the ability to differentiate into myotubes as well as facilitate muscle regeneration in injured muscles of recipient mice. We further revealed that Tenascin-C acts as the core mechanism to activate the EGFR signaling pathway followed by HuSCs proliferation. Taken together, our data provide an efficient method to expand functional HuSCs and a novel mechanism that controls HuSCs proliferation, which sheds light on the HuSCs-based therapy to treat muscle diseases.

Safety and Efficacy of DT-DEC01 Therapy in Duchenne Muscular Dystrophy Patients: A 12 - Month Follow-Up Study After Systemic Intraosseous Administration

Duchenne Muscular Dystrophy (DMD) is a progressive and fatal muscle-wasting disease with no known cure. We previously reported the preliminary safety and efficacy up to six months after the administration of DT-DEC01, a novel Dystrophin Expressing Chimeric (DEC) cell therapy created by fusion of myoblasts of DMD patient and the normal donor. In this 12-month follow-up study, we report on the safety and functional outcomes of three DMD patients after the systemic intraosseous administration of DT-DEC01. The safety of DT-DEC01 was confirmed by the absence of Adverse Events (AE) and Severe Adverse Events (SAE) up to 21 months after intraosseous DT-DEC01 administration. The lack of presence of anti-HLA antibodies and Donors Specific Antibodies (DSA) further confirmed DT-DEC01 therapy safety. Functional assessments in ambulatory patients revealed improvements in 6-Minute Walk Test (6MWT) and timed functions of North Star Ambulatory Assessment (NSAA). Additionally, improvements in PUL2.0 test and grip strength correlated with increased Motor Unit Potentials (MUP) duration recorded by Electromyography (EMG) in both ambulatory and non-ambulatory patients. DT-DEC01 systemic effect was confirmed by improved cardiac and pulmonary parameters and daily activity recordings. This follow-up study confirmed the safety and preliminary efficacy of DT-DEC01 therapy in DMD-affected patients up to 12 months after intraosseous administration. DT-DEC01 introduces a novel concept of personalized myoblast-based cellular therapy that is irrespective of the mutation type, does not require immunosuppression or the use of viral vectors, and carries no risk of off target mutations. This establishes DT-DEC01 as a promising and universally effective treatment option for all DMD patients.

Cellular pathogenesis of Duchenne muscular dystrophy: progressive myofibre degeneration, chronic inflammation, reactive myofibrosis and satellite cell dysfunction

Duchenne muscular dystrophy is a highly progressive muscle wasting disease of early childhood and characterized by complex pathophysiological and histopathological changes in the voluntary contractile system, including myonecrosis, chronic inflammation, fat substitution and reactive myofibrosis. The continued loss of functional myofibres and replacement with non-contractile cells, as well as extensive tissue scarring and decline in tissue elasticity, leads to severe skeletal muscle weakness. In addition, dystrophic muscles exhibit a greatly diminished regenerative capacity to counteract the ongoing process of fibre degeneration. In normal muscle tissues, an abundant stem cell pool consisting of satellite cells that are localized between the sarcolemma and basal lamina, provides a rich source for the production of activated myogenic progenitor cells that are involved in efficient myofibre repair and tissue regeneration. Interestingly, the self-renewal of satellite cells for maintaining an essential pool of stem cells in matured skeletal muscles is increased in dystrophin-deficient fibres. However, satellite cell hyperplasia does not result in efficient recovery of dystrophic muscles due to impaired asymmetric cell divisions. The lack of expression of the full-length dystrophin isoform Dp427-M, which is due to primary defects in the DMD gene,  appears to affect key regulators of satellite cell polarity causing a reduced differentiation of myogenic progenitors, which are essential for myofibre regeneration. This review outlines the complexity of dystrophinopathy and describes the importance of the pathophysiological role of satellite cell dysfunction. A brief discussion of the bioanalytical usefulness of single cell proteomics for future studies of satellite cell biology is provided.

Dystrophin Expressing Chimeric (DEC) Cell Therapy for Duchenne Muscular Dystrophy: A First-in-Human Study with Minimum 6 Months Follow-up

Duchenne Muscular Dystrophy (DMD) is a X-linked progressive lethal muscle wasting disease for which there is no cure. We present first-in-human study assessing safety and efficacy of novel Dystrophin Expressing Chimeric (DEC) cell therapy created by fusion of patient myoblasts with myoblasts of normal donor origin. We report here on safety and functional outcomes of the first 3 DMD patients. No study related adverse events (AE) and no serious adverse events (SAE) were observed up to 14 months after systemic-intraosseous administration of DEC01. Ambulatory patients showed improvements in functional tests (6-Minute Walk Test (6MWT), North Star Ambulatory Assessment (NSAA)) and both, ambulatory and non-ambulatory in PUL, strength and fatigue resistance which correlated with improvement of Electromyography (EMG) parameters. DEC01 therapy does not require immunosuppression, involves no risks of off target mutations, is not dependent upon the causative mutation and is therefore a universal therapy that does not use viral vectors and therefore can be readministered, if needed. This study was approved by the Bioethics Committee (approval No. 46/2019). Mechanism of action of the Dystrophin Expressing Chimeric Cell (DEC) cells created via ex vivo fusion of human myoblast from normal and DMD-affected donors. Following systemic-intraosseous administration, DEC engraft and fuse with the myoblasts of DMD patients, deliver dystrophin and improve muscle strength and function. (Created with BioRender.com).

A Brief Review of Duchenne Muscular Dystrophy Treatment Options, with an Emphasis on Two Novel Strategies

Despite the full cloning of the Dystrophin cDNA 35 years ago, no effective treatment exists for the Duchenne Muscular Dystrophy (DMD) patients who have a mutation in this gene. Many treatment options have been considered, investigated preclinically and some clinically, but none have circumvented all barriers and effectively treated the disease without burdening the patients with severe side-effects. However, currently, many novel therapies are in the pipelines of research labs and pharmaceutical companies and many of these have progressed to clinical trials. A brief review of these promising therapies is presented, followed by a description of two novel technologies that when utilized together effectively treat the disease in the mdx mouse model. One novel technology is to generate chimeric cells from the patient’s own cells and a normal donor. The other technology is to systemically transplant these cells into the femur via the intraosseous route.

The spatiotemporal matching pattern of Ezrin/Periaxin involved in myoblast differentiation and fusion and Charcot-Marie-Tooth disease-associated muscle atrophy

BACKGROUND

Clinically, Charcot-Marie-Tooth disease (CMT)-associated muscle atrophy still lacks effective treatment. Deletion and mutation of L-periaxin can be involved in CMT type 4F (CMT4F) by destroying the myelin sheath form, which may be related to the inhibitory role of Ezrin in the self-association of L-periaxin. However, it is still unknown whether L-periaxin and Ezrin are independently or interactively involved in the process of muscle atrophy by affecting the function of muscle satellite cells.

METHOD

A gastrocnemius muscle atrophy model was prepared to mimic CMT4F and its associated muscle atrophy by mechanical clamping of the peroneal nerve. Differentiating C2C12 myoblast cells were treated with adenovirus-mediated overexpression or knockdown of Ezrin. Then, overexpression of L-periaxin and NFATc1/c2 or knockdown of L-periaxin and NFATc3/c4 mediated by adenovirus vectors were used to confirm their role in Ezrin-mediated myoblast differentiation, myotube formation and gastrocnemius muscle repair in a peroneal nerve injury model. RNA-seq, real-time PCR, immunofluorescence staining and Western blot were used in the above observation.

RESULTS

For the first time, instantaneous L-periaxin expression was highest on the 6th day, while Ezrin expression peaked on the 4th day during myoblast differentiation/fusion in vitro. In vivo transduction of adenovirus vectors carrying Ezrin, but not Periaxin, into the gastrocnemius muscle in a peroneal nerve injury model increased the numbers of muscle myosin heavy chain (MyHC) I and II type myofibers, reducing muscle atrophy and fibrosis. Local muscle injection of overexpressed Ezrin combined with incubation of knockdown L-periaxin within the injured peroneal nerve or injection of knockdown L-periaxin into peroneal nerve-injured gastrocnemius muscle not only increased the number of muscle fibers but also recovered their size to a relatively normal level in vivo. Overexpression of Ezrin promoted myoblast differentiation/fusion, inducing increased MyHC-I⁺ and MyHC-II + muscle fiber specialization, and the specific effects could be enhanced by the addition of adenovirus vectors for knockdown of L-periaxin by shRNA. Overexpression of L-periaxin did not alter the inhibitory effects on myoblast differentiation and fusion mediated by knockdown of Ezrin by shRNA in vitro but decreased myotube length and size. Mechanistically, overexpressing Ezrin did not alter protein kinase A gamma catalytic subunit (PKA-γ cat), protein kinase A I alpha regulatory subunit (PKA reg Iα) or PKA reg Iβ levels but increased PKA-α cat and PKA reg II α levels, leading to a decreased ratio of PKA reg I/II. The PKA inhibitor H-89 remarkably abolished the effects of overexpressing-Ezrin on increased myoblast differentiation/fusion. In contrast, knockdown of Ezrin by shRNA significantly delayed myoblast differentiation/fusion accompanied by an increased PKA reg I/II ratio, and the inhibitory effects could be eliminated by the PKA reg activator N6-Bz-cAMP. Meanwhile, overexpressing Ezrin enhanced type I muscle fiber specialization, accompanied by an increase in NFATc2/c3 levels and a decrease in NFATc1 levels. Furthermore, overexpressing NFATc2 or knocking down NFATc3 reversed the inhibitory effects of Ezrin knockdown on myoblast differentiation/fusion.

CONCLUSIONS

The spatiotemporal pattern of Ezrin/Periaxin expression was involved in the control of myoblast differentiation/fusion, myotube length and size, and myofiber specialization, which was related to the activated PKA-NFAT-MEF2C signaling pathway, providing a novel L-Periaxin/Ezrin joint strategy for the treatment of muscle atrophy induced by nerve injury, especially in CMT4F.

Biological and genetic therapies for the treatment of Duchenne muscular dystrophy

INTRODUCTION

Duchenne muscular dystrophy is a lethal genetic disease which currently has no cure, and poor standard treatment options largely focused on symptom relief. The development of multiple biological and genetic therapies is underway across various stages of clinical progress which could markedly affect how DMD patients are treated in the future.

AREAS COVERED

The purpose of this review is to provide an introduction to the different therapeutic modalities currently being studied, as well as a brief description of their progress to date and relative advantages and disadvantages for the treatment of DMD. This review discusses exon skipping therapy, microdystrophin therapy, stop codon readthrough therapy, CRISPR-based gene editing, cell-based therapy, and utrophin upregulation. Secondary therapies addressing nonspecific symptoms of DMD were excluded.

EXPERT OPINION

Despite the vast potential held by gene replacement therapy options such as microdystrophin production and utrophin upregulation, safety risks inherent to the adeno-associated virus delivery vector might hamper the clinical viability of these approaches until further improvements can be made. Of the mutation-specific therapies, exon skipping therapy remains the most extensively validated and explored option, and the cell-based CAP-1002 therapy may prove to be a suitable adjunct therapy filling the urgent need for cardiac-specific therapies.

A new immunodeficient Duchenne muscular dystrophy rat model to evaluate engraftment after human cell transplantation

Duchenne muscular dystrophy (DMD) is an X-linked fatal muscular disease, affecting one in 3,500 live male births worldwide. Currently, there is no cure for this disease, except for steroid-based treatment to attenuate disease progression. Cell transplantation therapy is a promising therapeutic approach, however, there is a lack of appropriate animal models to conduct large-scale preclinical studies using human cells, including biochemical and functional tests. Here, we established an immunodeficient DMD rat model and performed exhaustive pathological analysis and transplantation efficiency evaluation to assess its suitability to study DMD. Our DMD rat model exhibited histopathological characteristics similar to those observed in human patients with DMD. Human myoblasts demonstrated successful engraftment following transplantation into these rats. Therefore, this immunodeficient DMD rat model would be useful in preclinical studies to develop cellular transplantation therapies for DMD.

Ageing and rejuvenation of tissue stem cells and their niches

Most adult organs contain regenerative stem cells, often organized in specific niches. Stem cell function is critical for tissue homeostasis and repair upon injury, and it is dependent on interactions with the niche. During ageing, stem cells decline in their regenerative potential and ability to give rise to differentiated cells in the tissue, which is associated with a deterioration of tissue integrity and health. Ageing-associated changes in regenerative tissue regions include defects in maintenance of stem cell quiescence, differentiation ability and bias, clonal expansion and infiltration of immune cells in the niche. In this Review, we discuss cellular and molecular mechanisms underlying ageing in the regenerative regions of different tissues as well as potential rejuvenation strategies. We focus primarily on brain, muscle and blood tissues, but also provide examples from other tissues, such as skin and intestine. We describe the complex interactions between different cell types, non-cell-autonomous mechanisms between ageing niches and stem cells, and the influence of systemic factors. We also compare different interventions for the rejuvenation of old regenerative regions. Future outlooks in the field of stem cell ageing are discussed, including strategies to counter ageing and age-dependent disease.

Identification of immune-related features involved in Duchenne muscular dystrophy: A bidirectional transcriptome and proteome-driven analysis

Background

We aimed to investigate the biological mechanism and feature genes of Duchenne muscular dystrophy (DMD) by multi-omics and experimental verification strategy.

Methods

We integrated the transcriptomic and proteomic methods to find the differentially expressed mRNAs (DEMs) and proteins (DEPs) between DMD and Control groups. Weighted gene co-expression network analysis (WGCNA) was then used to identify modules of highly correlated genes and hub genes. In the following steps, the immune and stromal cells infiltrations were accomplished by xCELL algorithm. Furthermore, TF and miRNA prediction were performed with Networkanalyst. ELISA, western blot and external datasets were performed to verify the key proteins/mRNAs in DMD patient and mouse. Finally, a nomogram model was established based on the potential biomarkers.

Results

4515 DEMs and 56 DEPs were obtained from the transcriptomic and proteomic study respectively. 14 common genes were identified, which is enriched in muscle contraction and inflammation-related pathways. Meanwhile, we observed 33 significant differences in the infiltration of cells in DMD. Afterwards, a total of 22 miRNAs and 23 TF genes interacted with the common genes, including TFAP2C, MAX, MYC, NFKB1, RELA, hsa-miR-1255a, hsa-miR-130a, hsa-miR-130b, hsa-miR-152, and hsa-miR-17. In addition, three genes (ATP6AP2, CTSS, and VIM) showed excellent diagnostic performance on discriminating DMD in GSE1004, GSE3307, GSE6011 and GSE38417 datasets (all AUC > 0.8), which is validated in patients (10 DMD vs. 10 controls), DMD with exon 55 mutations, mdx mouse, and nomogram model.

Conclusion

Taken together, ATP6AP2, CTSS, and VIM play important roles in the inflammatory response in DMD, which may serve as diagnostic biomarkers and therapeutic targets.

Stem Cells in Clinical Trials on Neurological Disorders: Trends in Stem Cells Origins, Indications, and Status of the Clinical Trials

Neurological diseases can significantly reduce the quality and duration of life. Stem cells provide a promising solution, not only due to their regenerative features but also for a variety of other functions, including reducing inflammation and promoting angiogenesis. Although only hematopoietic cells have been approved by the FDA so far, the number of trials continues to expand. We analyzed 492 clinical trials and illustrate the trends in stem cells origins, indications, and phase and status of the clinical trials. The most common neurological disorders treated with stem cells were injuries of brain, spinal cord, and peripheral nerves (14%), stroke (13%), multiple sclerosis (12%), and brain tumors (11%). Mesenchymal stem cells dominated (83%) although the choice of stem cells was highly dependent on the neurological disorder. Of the 492 trials, only two trials have reached phase 4, with most of all other trials being in phases 1 or 2, or transitioning between them (83%). Based on a comparison of the obtained results with similar works and further analysis of the literature, we discuss some of the challenges and future directions of stem cell therapies in the treatment of neurological diseases.

Clinical trials of stem cell-based therapies for pediatric diseases: a comprehensive analysis of trials registered on ClinicalTrials.gov and the ICTRP portal site

BACKGROUND

Research on clinical trials that employ stem cells to treat children's diseases is limited. The clinical trial registry database provides a unique window to us to get known about clinical trial researches with different statuses. However, few studies aimed to perform a comprehensive and thorough analysis of those registered trials in the aforementioned field based on ClinicalTrials.gov and the ICTRP portal site.

METHODS

Our study covered the clinical researches about stem cell therapy enrolling subjects aged under 18 years old registered on ClinicalTrials.gov and WHO ICTRP before May 18, 2021. A cross-sectional study was implemented to comprehensively describe and analyze the included trials that met the criteria. Results were available on ClinicalTrials.gov, and publications related to the included trials were identified. All analyses were performed utilizing the SPSS 25.0 software.

RESULTS

Eventually, 202 clinical trials were included and evaluated. The participant number of trials tended to be small; 71.3% were enrolled < 50. And 93.5% of the subjects were without gender restrictions. Till May 2020, 112 trials had been preliminary completed, of which only 39 trials had published papers or uploaded results. Most (73.6%) of 186 interventional trials were in phase 1 and phase 2, where 131 (70.4%) trials were conducted without masking, and 26.3% trials were randomized; 55.4% trials were performed single group assignment. Of 16 observational trials, case-only/series took up 37.5%. Hematopoietic stem cells (37.1%) and mesenchymal stem cells (36.1%) were mostly employed, while umbilical cord blood (UCB)-derived cells (24.3%) and bone marrow (BM)-derived cells (20.8%) were the major sources.

CONCLUSIONS

This study provided an overall picture of utilizing stem cells for treatment and management of childhood diseases. Since clinical trials in this area are insufficient in quantity and quality, there is an urgent need of larger, better-designed trials. Increased investment in clinical research of stem cell treatment products should be carried out to achieve the transformation of results as soon as possible. Moreover, it is important to optimize the management of the registration platform and shorten the time it takes for research results to be published.

Fasting induces a highly resilient deep quiescent state in muscle stem cells via ketone body signaling

Short-term fasting is beneficial for the regeneration of multiple tissue types. However, the effects of fasting on muscle regeneration are largely unknown. Here, we report that fasting slows muscle repair both immediately after the conclusion of fasting as well as after multiple days of refeeding. We show that ketosis, either endogenously produced during fasting or a ketogenic diet or exogenously administered, promotes a deep quiescent state in muscle stem cells (MuSCs). Although deep quiescent MuSCs are less poised to activate, slowing muscle regeneration, they have markedly improved survival when facing sources of cellular stress. Furthermore, we show that ketone bodies, specifically β-hydroxybutyrate, directly promote MuSC deep quiescence via a nonmetabolic mechanism. We show that β-hydroxybutyrate functions as an HDAC inhibitor within MuSCs, leading to acetylation and activation of an HDAC1 target protein p53. Finally, we demonstrate that p53 activation contributes to the deep quiescence and enhanced resilience observed during fasting.

Long-Term Protective Effect of Human Dystrophin Expressing Chimeric (DEC) Cell Therapy on Amelioration of Function of Cardiac, Respiratory and Skeletal Muscles in Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is a lethal disease caused by mutations in dystrophin encoding gene, causing progressive degeneration of cardiac, respiratory, and skeletal muscles leading to premature death due to cardiac and respiratory failure. Currently, there is no cure for DMD. Therefore, novel therapeutic approaches are needed for DMD patients.

We have previously reported functional improvements which correlated with increased dystrophin expression following administration of dystrophin expressing chimeric (DEC) cells of myoblast origin to the mdx mouse models of DMD.

In the current study, we confirmed dose-dependent protective effect of human DEC therapy created from myoblasts of normal and DMD-affected donors, on restoration of dystrophin expression and amelioration of cardiac, respiratory, and skeletal muscle function at 180 days after systemic-intraosseous DEC administration to mdx/scid mouse model of DMD. Functional improvements included maintenance of ejection fraction and fractional shortening levels on echocardiography, reduced enhanced pause and expiration time on plethysmography and improved grip strength and maximum stretch induced contraction of skeletal muscles. Improved function was associated with amelioration of mdx muscle pathology revealed by reduced muscle fibrosis, reduced inflammation and improved muscle morphology confirmed by reduced number of centrally nucleated fibers and normalization of muscle fiber diameters. Our findings confirm the long-term systemic effect of DEC therapy in the most severely affected by DMD organs including heart, diaphragm, and long skeletal muscles.

These encouraging preclinical data introduces human DEC as a novel therapeutic modality of Advanced Therapy Medicinal Product (ATMP) with the potential to improve or halt the progression of DMD and enhance quality of life of DMD patients.

Human Dystrophin Dp71ab Enhances the Proliferation of Myoblasts Across Species But Not Human Nonmyoblast Cells

Dystrophin Dp71 is an isoform produced from the Dp71 promoter in intron 62 of the DMD gene, mutations in which cause Duchenne muscular dystrophy. Dp71 is involved in various cellular processes and comprises more than 10 isoforms produced by alternative splicing. Dp71ab, in which both exons 71 and 78 are deleted, has a hydrophobic C-terminus that is hydrophilic in Dp71. Therefore, Dp71ab is believed to have different roles from Dp71. Previously, we reported that Dp71ab enhanced the proliferation of human myoblasts. Here, we further characterized Dp71ab, focusing on the activation of cell proliferation. Dp71ab increased the proliferation of immortalized human myoblasts in a dose-dependent manner. In contrast, Dp71 suppressed proliferation in a dose-dependent manner. Consistent with these opposite effects, eGFP-tagged Dp71ab and mCherry-tagged Dp71 showed different cellular distributions, with Dp71ab mostly in the nucleus. Notably, human Dp71ab enhanced the proliferation of rat and mouse myoblasts. Despite these findings, human Dp71ab did not enhance the proliferation of human nonmyoblast cells, including rhabdomyosarcoma cells. We concluded that Dp71ab is a myoblast-specific proliferation enhancer. In further studies, Dp71ab will be employed for the expansion of myoblasts in clinical settings.

Therapeutic Strategies for Dystrophin Replacement in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked hereditary disease characterized by progressive muscle wasting due to modifications in the DMD gene (exon deletions, nonsense mutations, intra-exonic insertions or deletions, exon duplications, splice site defects, and deep intronic mutations) that result in a lack of functional dystrophin expression. Many therapeutic approaches have so far been attempted to induce dystrophin expression and improve the patient phenotype. In this manuscript, we describe the relevant updates for some therapeutic strategies for DMD aiming to restore dystrophin expression. We also present and analyze in vitro and in vivo ongoing experimental approaches to treat the disease.

Transplantation of human iPSC-derived muscle stem cells in the diaphragm of Duchenne muscular dystrophy model mice

Duchenne muscular dystrophy (DMD) is an intractable genetic muscular disorder characterized by the loss of DYSTROPHIN. The restoration of DYSTROPHIN is expected to be a curative therapy for DMD. Because muscle stem cells (MuSCs) can regenerate damaged myofibers with full-length DYSTROPHIN in vivo, their transplantation is being explored as such a therapy. As for the transplanted cells, primary satellite cells have been considered, but donor shortage limits their clinical application. We previously developed a protocol that differentiates induced pluripotent stem cells (iPSCs) to MuSCs (iMuSCs). To ameliorate the respiratory function of DMD patients, cell transplantation to the diaphragm is necessary but difficult, because the diaphragm is thin and rapidly moves. In the present study, we explored the transplantation of iMuSCs into the diaphragm. First, we show direct cell injection into the diaphragm of mouse was feasible. Then, to enhance the engraftment of the transplanted cells in a rapidly moving diaphragm, we mixed polymer solutions of hyaluronic acid, alginate and gelatin to the cell suspension, finding a solution of 20% dissolved hyaluronic acid and 80% dissolved gelatin improved the engraftment. Thus, we established a method for cell transplantation into mouse diaphragm and show that an injectable hyaluronic acid-gelatin solution enables the engraftment of iMuSCs in the diaphragm.

Non-Invasive Optical Motion Tracking Allows Monitoring of Respiratory Dynamics in Dystrophin-Deficient Mice

Duchenne muscular dystrophy (DMD) is the most common x-chromosomal inherited dystrophinopathy which leads to progressive muscle weakness and a premature death due to cardiorespiratory dysfunction. The mdx mouse lacks functional dystrophin protein and has a comparatively human-like diaphragm phenotype. To date, diaphragm function can only be inadequately mapped in preclinical studies and a simple reliable translatable method of tracking the severity of the disease still lacks. We aimed to establish a sensitive, reliable, harmless and easy way to assess the effects of respiratory muscle weakness and subsequent irregularity in breathing pattern. Optical respiratory dynamics tracking (ORDT) was developed utilising a camera to track the movement of paper markers placed on the thoracic-abdominal region of the mouse. ORDT successfully distinguished diseased mdx phenotype from healthy controls by measuring significantly higher expiration constants (k) in mdx mice compared to wildtype (wt), which were also observed in the established X-ray based lung function (XLF). In contrast to XLF, with ORDT we were able to distinguish distinct fast and slow expiratory phases. In mdx mice, a larger part of the expiratory marker displacement was achieved in this initial fast phase as compared to wt mice. This phenomenon could not be observed in the XLF measurements. We further validated the simplicity and reliability of our approach by demonstrating that it can be performed using free-hand smartphone acquisition. We conclude that ORDT has a great preclinical potential to monitor DMD and other neuromuscular diseases based on changes in the breathing patterns with the future possibility to track therapy response.

Challenges in cell transplantation for muscular dystrophy

For decades now, cell transplantation has been considered a possible therapeutic strategy for muscular dystrophy, but failures have largely outnumbered success or at least encouraging outcomes. In this review we will briefly recall the history of cell transplantation, discuss the peculiar features of skeletal muscle, and dystrophic skeletal muscle in particular, that make the procedure complicated and inefficient. As there are many recent and exhaustive reviews on the various myogenic cell types that have been or will be transplanted, we will only briefly describe them and refer the reader to these reviews. Finally, we will discuss possible strategies to overcome the hurdles that prevent biological efficacy and hence clinical success.

Rheological properties of skeletal muscles in a Duchenne muscular dystrophy murine model before and after autologous cell therapy

Duchenne muscular dystrophy (DMD) is still an incurable muscle degenerative disease; thus, numerous studies focused on novel therapeutic approaches. However, a simple assay of muscle function restoration remains needed. Herein, we used an oscillatory shear rheometer to evaluate changes in rheological properties of mouse muscles (tibialis anterior, TA) and their restoration upon autologous cell therapy by comparing the viscoelastic properties of normal, diseased and treated muscles. Amplitude sweep tests of muscle samples were performed under 20% compression over a range of shear strain between 0.01 and 2% and frequency of 1 rad/s. The samples were tested in plane-plane geometry and horizontal myofiber alignment. Typical linear viscoelastic region (LVER) patterns were found for each muscle type. For healthy muscles, a broad LVER between shear deformations (γ) of 0.013-0.62% was observed. The LVER of DMD mdx/SCID muscles was found at 0.14% to 0.46% shear deformation, and no shear dependence of storage (G') and loss (G") moduli at γ range changing from 0.034% to 0.26% was found for transplanted tissues. G'_LVER and G"_LVER moduli of healthy muscles were significantly higher than G'_LVER and G"_LVER of dystrophic tissues. Additionally, muscle resistance assessment by rheometer indicated that muscles transplanted with stem cells restored elastic properties to levels close to those of healthy muscles. Interestingly, histological staining and rheological data indicate that the loss factor is strongly related to structural changes of examined muscles.

Human muscle production in vitro from pluripotent stem cells: Basic and clinical applications

Human pluripotent stem cells (PSCs), which have the capacity to self-renew and differentiate into multiple cell types, offer tremendous therapeutic potential and invaluable flexibility as research tools. Recently, remarkable progress has been made in directing myogenic differentiation of human PSCs. The differentiation strategies, which were inspired by our knowledge of myogenesis in vivo, have provided an important platform for the study of human muscle development and modeling of muscular diseases, as well as a promising source of cells for cell therapy to treat muscular dystrophies. In this review, we summarize the current state of skeletal muscle generation from human PSCs, including transgene-based and transgene-free differentiation protocols, and 3D muscle tissue production through bioengineering approaches. We also highlight their basic and clinical applications, which facilitate the study of human muscle biology and deliver new hope for muscular disease treatment.

Comparison of Differentiation Pattern and WNT/SHH Signaling in Pluripotent Stem Cells Cultured under Different Conditions

Pluripotent stem cells (PSCs) are characterized by the ability to self-renew as well as undergo multidirectional differentiation. Culture conditions have a pivotal influence on differentiation pattern. In the current study, we compared the fate of mouse PSCs using two culture media: (1) chemically defined, free of animal reagents, and (2) standard one relying on the serum supplementation. Moreover, we assessed the influence of selected regulators (WNTs, SHH) on PSC differentiation. We showed that the differentiation pattern of PSCs cultured in both systems differed significantly: cells cultured in chemically defined medium preferentially underwent ectodermal conversion while their endo- and mesodermal differentiation was limited, contrary to cells cultured in serum-supplemented medium. More efficient ectodermal differentiation of PSCs cultured in chemically defined medium correlated with higher activity of SHH pathway while endodermal and mesodermal conversion of cells cultured in serum-supplemented medium with higher activity of WNT/JNK pathway. However, inhibition of either canonical or noncanonical WNT pathway resulted in the limitation of endo- and mesodermal conversion of PSCs. In addition, blocking WNT secretion led to the inhibition of PSC mesodermal differentiation, confirming the pivotal role of WNT signaling in this process. In contrast, SHH turned out to be an inducer of PSC ectodermal, not mesodermal differentiation.

The Immune System in Duchenne Muscular Dystrophy Pathogenesis

Growing evidence demonstrates the crosstalk between the immune system and the skeletal muscle in inflammatory muscle diseases and dystrophic conditions such as Duchenne Muscular Dystrophy (DMD), as well as during normal muscle regeneration. The rising of inflammation and the consequent activation of the immune system are hallmarks of DMD: several efforts identified the immune cells that invade skeletal muscle as CD4+ and CD8+ T cells, Tregs, macrophages, eosinophils and natural killer T cells. The severity of muscle injury and inflammation dictates the impairment of muscle regeneration and the successive replacement of myofibers with connective and adipose tissue. Since immune system activation was traditionally considered as a consequence of muscular wasting, we recently demonstrated a defect in central tolerance caused by thymus alteration and the presence of autoreactive T-lymphocytes in DMD. Although the study of innate and adaptive immune responses and their complex relationship in DMD attracted the interest of many researchers in the last years, the results are so far barely exhaustive and sometimes contradictory. In this review, we describe the most recent improvements in the knowledge of immune system involvement in DMD pathogenesis, leading to new opportunities from a clinical point-of-view.

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.

Duchenne muscular dystrophy cell culture models created by CRISPR/Cas9 gene editing and their application in drug screening

Gene editing methods are an attractive therapeutic option for Duchenne muscular dystrophy, and they have an immediate application in the generation of research models. To generate myoblast cultures that could be useful in in vitro drug screening, we have optimised a CRISPR/Cas9 gene edition protocol. We have successfully used it in wild type immortalised myoblasts to delete exon 52 of the dystrophin gene, modelling a common Duchenne muscular dystrophy mutation; and in patient's immortalised cultures we have deleted an inhibitory microRNA target region of the utrophin UTR, leading to utrophin upregulation. We have characterised these cultures by demonstrating, respectively, inhibition of dystrophin expression and overexpression of utrophin, and evaluating the expression of myogenic factors (Myf5 and MyH3) and components of the dystrophin associated glycoprotein complex (α-sarcoglycan and β-dystroglycan). To demonstrate their use in the assessment of DMD treatments, we have performed exon skipping on the DMDΔ52-Model and have used the unedited DMD cultures/ DMD-UTRN-Model combo to assess utrophin overexpression after drug treatment. While the practical use of DMDΔ52-Model is limited to the validation to our gene editing protocol, DMD-UTRN-Model presents a possible therapeutic gene edition target as well as a useful positive control in the screening of utrophin overexpression drugs.

Current Pharmacological Strategies for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a lethal, X-linked neuromuscular disorder caused by the absence of dystrophin protein, which is essential for muscle fiber integrity. Loss of dystrophin protein leads to recurrent myofiber damage, chronic inflammation, progressive fibrosis, and dysfunction of muscle stem cells. There is still no cure for DMD so far and the standard of care is principally limited to symptom relief through glucocorticoids treatments. Current therapeutic strategies could be divided into two lines. Dystrophin-targeted therapeutic strategies that aim at restoring the expression and/or function of dystrophin, including gene-based, cell-based and protein replacement therapies. The other line of therapeutic strategies aims to improve muscle function and quality by targeting the downstream pathological changes, including inflammation, fibrosis, and muscle atrophy. This review introduces the important developments in these two lines of strategies, especially those that have entered the clinical phase and/or have great potential for clinical translation. The rationale and efficacy of each agent in pre-clinical or clinical studies are presented. Furthermore, a meta-analysis of gene profiling in DMD patients has been performed to understand the molecular mechanisms of DMD.

[Update on Duchenne muscular dystrophy]

Duchenne muscular dystrophy, DMD*(ICD-9-C: 359.1; ICD-10-ES: G71.01, ORPHA: 98896) is a dystrophic type, autosomal recessive myopathy linked to the X chromosome, low incidence 1/3300, with full penetrance and multi-organ involvement (neuro-muscular, respiratory, digestive and metabolic). It has great clinical variability. Symptoms begin in pediatric age (mobility limitation and early respiratory complications). Respiratory complications reduce the life expectancy of those affected. There is no treatment that modifies its evolution, although corticosteroids and new gene therapies are increasing the half-life of this disease. The role of the Primary Care Physician (PCP) is decisive in the monitoring and control of the complications of DMD, either coordinating the different specialties involved in it.

Drosophila, an Integrative Model to Study the Features of Muscle Stem Cells in Development and Regeneration

Muscle stem cells (MuSCs) are essential for muscle growth, maintenance and repair. Over the past decade, experiments in Drosophila have been instrumental in understanding the molecular and cellular mechanisms regulating MuSCs (also known as adult muscle precursors, AMPs) during development. A large number of genetic tools available in fruit flies provides an ideal framework to address new questions which could not be addressed with other model organisms. This review reports the main findings revealed by the study of Drosophila AMPs, with a specific focus on how AMPs are specified and properly positioned, how they acquire their identity and which are the environmental cues controlling their behavior and fate. The review also describes the recent identification of the Drosophila adult MuSCs that have similar characteristics to vertebrates MuSCs. Integration of the different levels of MuSCs analysis in flies is likely to provide new fundamental knowledge in muscle stem cell biology largely applicable to other systems.

Myogenic Cell Transplantation in Genetic and Acquired Diseases of Skeletal Muscle

This article will review myogenic cell transplantation for congenital and acquired diseases of skeletal muscle. There are already a number of excellent reviews on this topic, but they are mostly focused on a specific disease, muscular dystrophies and in particular Duchenne Muscular Dystrophy. There are also recent reviews on cell transplantation for inflammatory myopathies, volumetric muscle loss (VML) (this usually with biomaterials), sarcopenia and sphincter incontinence, mainly urinary but also fecal. We believe it would be useful at this stage, to compare the same strategy as adopted in all these different diseases, in order to outline similarities and differences in cell source, pre-clinical models, administration route, and outcome measures. This in turn may help to understand which common or disease-specific problems have so far limited clinical success of cell transplantation in this area, especially when compared to other fields, such as epithelial cell transplantation. We also hope that this may be useful to people outside the field to get a comprehensive view in a single review. As for any cell transplantation procedure, the choice between autologous and heterologous cells is dictated by a number of criteria, such as cell availability, possibility of in vitro expansion to reach the number required, need for genetic correction for many but not necessarily all muscular dystrophies, and immune reaction, mainly to a heterologous, even if HLA-matched cells and, to a minor extent, to the therapeutic gene product, a possible antigen for the patient. Finally, induced pluripotent stem cell derivatives, that have entered clinical experimentation for other diseases, may in the future offer a bank of immune-privileged cells, available for all patients and after a genetic correction for muscular dystrophies and other myopathies.

Inhibition of the Combinatorial Signaling of Transforming Growth Factor-Beta and NOTCH Promotes Myotube Formation of Human Pluripotent Stem Cell-Derived Skeletal Muscle Progenitor Cells

Understanding the signaling pathways that regulate the final differentiation of human myoblasts is essential for successful cell transplantation and drug screening for the treatment of muscular dystrophy. In an effort to improve myotube formation from hiPSC-derived myoblasts, we validated a collection of 13 small molecules in a newly established in vitro screening platform for the assessment of myotube formation. The analysis of myotube formation as measured by the fusion index showed that the combinational inhibition of the TGFβ signaling with NOTCH signaling enhances the ability of multi-nucleated myotube production. Combinational treatment of inhibitors for TGFβ and NOTCH signaling pathways improved myotube formation in a dose-dependent manner. This effect was achieved by inhibiting the combinatorial mechanism of signaling. The combination treatment of small molecules effective in inducing multinucleated myotubes was validated in healthy human primary myoblasts. In addition, it was also applied to DMD patient iPSC-derived myoblasts to enhance the generation of multinucleated myotubes.

Autologous Induced Pluripotent Stem Cell-Based Cell Therapies: Promise, Progress, and Challenges

The promise of human induced pluripotent stem cells (iPSCs) lies in their ability to serve as a starting material for autologous, or patient-specific, stem cell-based therapies. Since the first publications describing the generation of iPSCs from human tissue in 2007, a Phase I/IIa clinical trial testing an autologous iPSC-derived cell therapy has been initiated in the U.S., and several other autologous iPSC-based therapies have advanced through various stages of development. Three single-patient in-human transplants of autologous iPSC-derived cells have taken place worldwide. None of the patients suffered serious adverse events, despite not undergoing immunosuppression. These promising outcomes support the proposed advantage of an autologous approach: a cell therapy product that can engraft without the risk of immune rejection, eliminating the need for immunosuppression and the associated side effects. Despite this advantage, there are currently more allogeneic than autologous iPSC-based cell therapy products in development due to the cost and complexity of scaling out manufacturing for each patient. In this review, we highlight recent progress toward clinical translation of autologous iPSC-based cell therapies. We also highlight technological advancements that would reduce the cost and complexity of autologous iPSC-based cell therapy production, enabling autologous iPSC-based therapies to become a more commonplace treatment modality for patients. © 2021 The Authors.

MiRNAs and Muscle Regeneration: Therapeutic Targets in Duchenne Muscular Dystrophy

microRNAs (miRNAs) are small non-coding RNAs required for the post-transcriptional control of gene expression. MicroRNAs play a critical role in modulating muscle regeneration and stem cell behavior. Muscle regeneration is affected in muscular dystrophies, and a critical point for the development of effective strategies for treating muscle disorders is optimizing approaches to target muscle stem cells in order to increase the ability to regenerate lost tissue. Within this framework, miRNAs are emerging as implicated in muscle stem cell response in neuromuscular disorders and new methodologies to regulate the expression of key microRNAs are coming up. In this review, we summarize recent advances highlighting the potential of miRNAs to be used in conjunction with gene replacement therapies, in order to improve muscle regeneration in the context of Duchenne Muscular Dystrophy (DMD).

Assessment of Weighted Gene Co-Expression Network Analysis to Explore Key Pathways and Novel Biomarkers in Muscular Dystrophy

Purpose

This study aimed to explore the key molecular pathways involved in Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) and thereby identify hub genes to be potentially used as novel biomarkers using a bioinformatics approach.

Methods

Raw GSE109178 data were collected from the Gene Expression Omnibus (GEO) database. Weighted gene co-expression network analysis (WGCNA) was conducted on the top 50% of altered genes. The key modules associated with the clinical features of DMD and BMD were identified. Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed using the DAVID website. A protein-protein interaction (PPI) network was constructed using the STRING website. MCODE, together with the Cytohubba plug-ins of Cytoscape, screened out the potential hub genes, which were subsequently verified via receiver operating characteristic (ROC) curves in other datasets.

Results

Among the 11 modules obtained, the black module was predominantly associated with pathology and DMD, whereas the light-green module was primarily related to age and BMD. Functional enrichment assessments indicated that the genes in the black module were primarily clustered in “immune response” and “phagosome,” whereas the ones in the light-green module were chiefly enriched in “protein polyubiquitination”. Eleven essential genes were eventually identified, including VCAM1, TYROBP, CD44, ITGB2, CSF1R, LCP2, C3AR1, CCL2, and ITGAM for DMD, along with UBA5 and UBR2 for BMD.

Conclusion

Overall, our findings may be useful for investigating the mechanisms underlying DMD and BMD. In addition, the hub genes discovered might serve as novel molecular markers correlated with dystrophinopathies.

Therapeutic aspects of cell signaling and communication in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a devastating chromosome X-linked disease that manifests predominantly in progressive skeletal muscle wasting and dysfunctions in the heart and diaphragm. Approximately 1/5000 boys and 1/50,000,000 girls suffer from DMD, and to date, the disease is incurable and leads to premature death. This phenotypic severity is due to mutations in the DMD gene, which result in the absence of functional dystrophin protein. Initially, dystrophin was thought to be a force transducer; however, it is now considered an essential component of the dystrophin-associated protein complex (DAPC), viewed as a multicomponent mechanical scaffold and a signal transduction hub. Modulating signal pathway activation or gene expression through epigenetic modifications has emerged at the forefront of therapeutic approaches as either an adjunct or stand-alone strategy. In this review, we propose a broader perspective by considering DMD to be a disease that affects myofibers and muscle stem (satellite) cells, as well as a disorder in which abrogated communication between different cell types occurs. We believe that by taking this systemic view, we can achieve safe and holistic treatments that can restore correct signal transmission and gene expression in diseased DMD tissues.

Beneficial Role of Exercise in the Modulation of mdx Muscle Plastic Remodeling and Oxidative Stress

Duchenne muscular dystrophy (DMD) is an X-linked recessive progressive lethal disorder caused by the lack of dystrophin, which determines myofibers mechanical instability, oxidative stress, inflammation, and susceptibility to contraction-induced injuries. Unfortunately, at present, there is no efficient therapy for DMD. Beyond several promising gene- and stem cells-based strategies under investigation, physical activity may represent a valid noninvasive therapeutic approach to slow down the progression of the pathology. However, ethical issues, the limited number of studies in humans and the lack of consistency of the investigated training interventions generate loss of consensus regarding their efficacy, leaving exercise prescription still questionable. By an accurate analysis of data about the effects of different protocol of exercise on muscles of mdx mice, the most widely-used pre-clinical model for DMD research, we found that low intensity exercise, especially in the form of low speed treadmill running, likely represents the most suitable exercise modality associated to beneficial effects on mdx muscle. This protocol of training reduces muscle oxidative stress, inflammation, and fibrosis process, and enhances muscle functionality, muscle regeneration, and hypertrophy. These conclusions can guide the design of appropriate studies on human, thereby providing new insights to translational therapeutic application of exercise to DMD patients.

Stem Cell Therapy in the Management of Fracture Non-Union - Evaluating Cellular Mechanisms and Clinical Progress

Bone, as a physiological and anatomical construct, displays remarkable intrinsic healing capacity. The overwhelming majority of fractures will heal satisfactorily, if aligned anatomically, compressed and immobilised appropriately. Of the 10% of fractures that do not heal, even under ideal mechanical and biological conditions, further consideration must be given to augment bone healing. Management strategies for non-union pose a significant clinical challenge to the practicing orthopaedic surgeon. Stem cell therapy is beginning to demonstrate significant potential for augmented bone repair in the context of non-union. This review attempts to contextualise the function of stem cells within this clinical setting, reviewing the relevant cellular mechanisms and clinical applications. From evaluating the literature base, there is a lack of high-quality evidence examining the role of mesenchymal stem cells (MSCs) within this research focus. Appropriately designed randomised controlled trials are required to evaluate this research area further, with a view to guiding future treatment options for the practicing orthopaedic surgeon.

Innovative Therapeutic Approaches for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is the most common childhood muscular dystrophy affecting ~1:5000 live male births. Following the identification of pathogenic variations in the dystrophin gene in 1986, the underlining genotype/phenotype correlations emerged and the role of the dystrophin protein was elucidated in skeletal, smooth, and cardiac muscles, as well as in the brain. When the dystrophin protein is absent or quantitatively or qualitatively modified, the muscle cannot sustain the stress of repeated contractions. Dystrophin acts as a bridging and anchoring protein between the sarcomere and the sarcolemma, and its absence or reduction leads to severe muscle damage that eventually cannot be repaired, with its ultimate substitution by connective tissue and fat. The advances of an understanding of the molecular pathways affected in DMD have led to the development of many therapeutic strategies that tackle different aspects of disease etiopathogenesis, which have recently led to the first successful approved orphan drugs for this condition. The therapeutic advances in this field have progressed exponentially, with second-generation drugs now entering in clinical trials as gene therapy, potentially providing a further effective approach to the condition.

Pluripotent stem cell-induced skeletal muscle progenitor cells with givinostat promote myoangiogenesis and restore dystrophin in injured Duchenne dystrophic muscle

Background

Duchenne muscular dystrophy (DMD) is caused by mutations of the gene that encodes the protein dystrophin. A loss of dystrophin leads to severe and progressive muscle wasting in both skeletal and heart muscles. Human induced pluripotent stem cells (hiPSCs) and their derivatives offer important opportunities to treat a number of diseases. Here, we investigated whether givinostat (Givi), a histone deacetylase inhibitor, with muscle differentiation properties could reprogram hiPSCs into muscle progenitor cells (MPC) for DMD treatment.

Methods

MPC were generated from hiPSCs by treatment with CHIR99021 and givinostat called Givi-MPC or with CHIR99021 and fibroblast growth factor as control-MPC. The proliferation and migration capacity were investigated by CCK-8, colony, and migration assays. Engraftment, pathological changes, and restoration of dystrophin were evaluated by in vivo transplantation of MPC. Conditioned medium from cultured MPC was collected and analyzed for extracellular vesicles (EVs).

Results

Givi-MPC exhibited superior proliferation and migration capacity compared to control-MPC. Givi-MPC produced less reactive oxygen species (ROS) after oxidative stress and insignificant expression of IL6 after TNF-α stimulation. Upon transplantation in cardiotoxin (CTX)-injured hind limb of Mdx/SCID mice, the Givi-MPC showed robust engraftment and restored dystrophin in the treated muscle than in those treated with control-MPC or human myoblasts. Givi-MPC significantly limited infiltration of inflammatory cells and reduced muscle necrosis and fibrosis. Additionally, Givi-MPC seeded the stem cell pool in the treated muscle. Moreover, EVs released from Givi-MPC were enriched in several miRNAs related to myoangiogenesis including miR-181a, miR-17, miR-210 and miR-107, and miR-19b compared with EVs from human myoblasts.

Conclusions

It is concluded that hiPSCs reprogrammed into MPC by givinostat possessing anti-oxidative, anti-inflammatory, and muscle gene-promoting properties effectively repaired injured muscle and restored dystrophin in the injured muscle.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02174-3.

MOTS-c promotes phosphorodiamidate morpholino oligomer uptake and efficacy in dystrophic mice

Antisense oligonucleotide (AO)-mediated exon-skipping therapies show promise in Duchenne muscular dystrophy (DMD), a devastating muscular disease caused by frame-disrupting mutations in the DMD gene. However, insufficient systemic delivery remains a hurdle to clinical deployment. Here, we demonstrate that MOTS-c, a mitochondria-derived bioactive peptide, with an intrinsic muscle-targeting property, augmented glycolytic flux and energy production capacity of dystrophic muscles in vitro and in vivo, resulting in enhanced phosphorodiamidate morpholino oligomer (PMO) uptake and activity in mdx mice. Long-term repeated administration of MOTS-c (500 μg) and PMO at the dose of 12.5 mg/kg/week for 3 weeks followed by 12.5 mg/kg/month for 3 months (PMO-M) induced therapeutic levels of dystrophin expression in peripheral muscles, with up to 25-fold increase in diaphragm of mdx mice over PMO alone. PMO-M improved muscle function and pathologies in mdx mice without detectable toxicity. Our results demonstrate that MOTS-c enables enhanced PMO uptake and activity in dystrophic muscles by providing energy and may have therapeutic implications for exon-skipping therapeutics in DMD and other energy-deficient disorders.

Targeted addition of mini-dystrophin into rDNA locus of Duchenne muscular dystrophy patient-derived iPSCs

Duchenne muscular dystrophy (DMD), the most common lethal muscular disorder, affects 1 in 5000 male births. It is caused by mutations in the X-linked dystrophin gene (DMD), and there is no effective treatment currently. Gene addition is a promising strategy owing to its universality for patients with all gene mutations types. In this study, we describe a site-specific gene addition strategy in induced pluripotent stem cells (iPSCs) derived from a DMD patient with exon 50 deletion. By using transcription activator-like effector nickases (TALENickases), the mini-dystrophin cassette was precisely targeted at the ribosomal RNA gene (rDNA) locus via homologous recombination with high targeting efficiency. The targeted clone retained the main pluripotent properties and was differentiated into cardiomyocytes. Significantly, the dystrophin expression and membrane localization were restored in the genetic corrected iPSCs and their derived cardiomyocytes. More importantly, the enhanced spontaneous contraction was observed in modified cardiomyocytes. These results provide a proof of principle for an efficient targeted gene addition for DMD gene therapy and represents a significant step toward precisely therapeutic for DMD.

Cellular therapies in organ transplantation

Cellular therapy is a promising tool for improving the outcome of organ transplantation. Various cell types with different immunoregulatory and regenerative properties may find application for specific transplant rejection or injury-related indications. The current era is crucial for the development of cellular therapies. Preclinical models have demonstrated the feasibility of efficacious cell therapy in transplantation, early clinical trials have shown safety of several of these therapies, and the first steps towards efficacy studies in humans have been made. In this review, we address the current state of the art of cellular therapies in clinical transplantation and discuss monitoring tools and endpoints for these studies.

Molecular correction of Duchenne muscular dystrophy by splice modulation and gene editing

Duchenne muscular dystrophy (DMD) is a currently incurable X-linked neuromuscular disorder, characterized by progressive muscle wasting and premature death, typically as a consequence of cardiac failure. DMD-causing mutations in the dystrophin gene are highly diverse, meaning that the development of a universally-applicable therapy to treat all patients is very challenging. The leading therapeutic strategy for DMD is antisense oligonucleotide-mediated splice modulation, whereby one or more specific exons are excluded from the mature dystrophin mRNA in order to correct the translation reading frame. Indeed, three exon skipping oligonucleotides have received FDA approval for use in DMD patients. Second-generation exon skipping drugs (i.e. peptide-antisense oligonucleotide conjugates) exhibit enhanced potency, and also induce dystrophin restoration in the heart. Similarly, multiple additional antisense oligonucleotide drugs targeting various exons are in clinical development in order to treat a greater proportion of DMD patient mutations. Relatively recent advances in the field of genome engineering (specifically, the development of the CRISPR/Cas system) have provided multiple promising therapeutic approaches for the RNA-directed genetic correction of DMD, including exon excision, exon reframing via the introduction of insertion/deletion mutations, disruption of splice signals to promote exon skipping, and the templated correction of point mutations by seamless homology directed repair or base editing technology. Potential limitations to the clinical translation of the splice modulation and gene editing approaches are discussed, including drug delivery, the importance of uniform dystrophin expression in corrected myofibres, safety issues (e.g. renal toxicity, viral vector immunogenicity, and off-target gene editing), and the high cost of therapy.

Regenerative rehabilitation of catastrophic extremity injury in military conflicts and a review of recent developmental efforts

AIM OF THE REVIEW

This review aims to describe the current state of regenerative rehabilitation of severe military extremity injuries, and promising new therapies on the horizon.

DISCUSSION

The nature of warfare is rapidly shifting with information operations, autonomous weapons, and the threat of full-scale peer adversary conflicts threatening to create contested environments with delayed medical evacuation to definitive care. More destructive weapons will lead to more devastating injuries, creating new challenges for limb repair and restoration. Current paradigms of delayed rehabilitation following initial stabilization, damage control surgery, and prolonged antibiotic therapy will need to shift. Advances in regenerative medicine technologies offer the possibility of treatment along the continuum of care. Regenerative rehabilitation will begin at the point of injury and require a holistic, organ-systems approach.

CONCLUSIONS

Both technological improvements and a rapidly advancing understanding of injury pathophysiology will contribute to improved limb-salvage outcomes, and shift the calculus away from early limb amputation.