Model Of Duchenne Muscular Dystrophy Research Articles

Immunomodulatory amnion-derived mesenchymal stromal cells preserve muscle function in a mouse model of Duchenne muscular dystrophy

BackgroundDuchenne muscular dystrophy (DMD) is an incurable genetic disease characterized by degeneration and necrosis of myofibers, chronic inflammation, and progressive muscle weakness resulting in premature mortality. Immunosuppressive multipotent mesenchymal stromal cell (MSC) therapy could be an option for DMD patients. We focused on amnion-derived mesenchymal stromal cells (AMSCs), a clinically viable cell source owing to their unique characteristics, such as non-invasive isolation, mitotic stability, ethical acceptability, and minimal risk of immune reaction and cancer. We aimed to identify novel immunomodulatory effects of AMSCs on macrophage polarization and their transplantation strategies for the functional recovery of skeletal and cardiac muscles.MethodsWe used flow cytometry to analyze the expression of anti-inflammatory M2 macrophage markers on peripheral blood mononuclear cells (PBMCs) co-cultured with human AMSCs (hAMSCs). hAMSCs were intravenously injected into DMD model mice (mdx mice) to assess the safety and efficacy of therapeutic interventions. hAMSC-treated and untreated mdx mice were monitored using blood tests, histological examinations, spontaneous wheel-running activities, grip strength, and echocardiography.ResultshAMSCs induced M2 macrophage polarization in PBMCs via prostaglandin E2 production. After repeated systemic hAMSC injections, mdx mice exhibited a transient downregulation of serum creatin kinase. Limited mononuclear cell infiltration and a decreased number of centrally nucleated fibers were indicative of regenerated myofibers following degeneration, suggesting an improved histological appearance of the skeletal muscle of hAMSC-treated mdx mice. Upregulated M2 macrophages and altered cytokine/chemokine expressions were observed in the muscles of hAMSC-treated mdx mice. During long-term experiments, a significant decrease in the grip strength in control mdx mice significantly improved in the hAMSC-treated mdx mice. hAMSC-treated mdx mice maintained running activity and enhanced daily running distance. Notably, the treated mice could run longer distances per minute, indicating high running endurance. Left ventricular function in DMD mice improved in hAMSC-treated mdx mice.ConclusionsEarly systemic hAMSC administration in mdx mice ameliorated progressive phenotypes, including pathological inflammation and motor dysfunction, resulting in the long-term improvement of skeletal and cardiac muscle function. The therapeutic effects might be associated with the immunosuppressive properties of hAMSCs via M2 macrophage polarization. This treatment strategy could provide therapeutic benefits to DMD patients.

Develop a Compact RNA Base Editor by Fusing ADAR with Engineered EcCas6e.

Catalytically inactive CRISPR-Cas13 (dCas13)-based base editors can achieve the conversion of adenine-to-inosine (A-to-I) or cytidine-to-uridine (C-to-U) at the RNA level, however, the large size of dCas13 protein limits its in vivo applications. Here, a compact and efficient RNA base editor (ceRBE) is reported with high in vivo editing efficiency. The larger dCas13 protein is replaced with a 199-amino acid EcCas6e protein, derived from the Class 1 CRISPR family involved in pre-crRNA processing, and conducted optimization for toxicity and editing efficiency. The ceRBE efficiently achieves both A-to-I and C-to-U base editing with low transcriptome off-target in HEK293T cells. The efficient repair of the DMD Q1392X mutation (68.3±10.1%) is also demonstrated in a humanized mouse model of Duchenne muscular dystrophy (DMD) after AAV delivery, achieving restoration of expression for gene products. The study supports that the compact and efficient ceRBE has great potential for treating genetic diseases.

PK/PD Modeling to Inform Clinical Development of an Adeno-associated Virus Gene Transfer Therapy for Duchenne Muscular Dystrophy (S48.005)

<h3>Objective:</h3> To evaluate the pharmacokinetic (PK)/pharmacodynamic (PD) relationship between tissue vector genome exposure, biological efficacy and functional outcome in an animal model of Duchenne muscular dystrophy (DMD) (DMD^mdx mice) following treatment with delandistrogene moxeparvovec (SRP-9001). <h3>Background:</h3> Delandistrogene moxeparvovec is an investigational gene transfer therapy developed to address the root cause of DMD through targeted skeletal and cardiac muscle expression of SRP-9001 dystrophin protein, which contains key functional domains of dystrophin. <h3>Design/Methods:</h3> We evaluated vector biodistribution, expression, and clinical dose selection of delandistrogene moxeparvovec using a novel application of a PK and PD modeling approach applied to data collected from DMD^mdx mice. We analyzed PK/PD relationships between dose, tissue vector genome exposure, SRP-9001 dystrophin protein expression (percent dystrophin positive fibers [PDPF] and western blot), and functional improvement (relative specific force from tibialis anterior and diaphragm). <h3>Results:</h3> Linear kinetics with a dose-proportional increase in tissue drug exposure were demonstrated across the nearly 10-fold dose range (4.43×10¹³–4.01×10¹⁴ vg/kg), and in all tissues. The relationship between tissue vector exposure and PD endpoints (PDPF, motor function outcome) showed a saturable response across a wide range of vector exposures. The vector exposure at 1.33×10¹⁴ vg/kg (the clinical dose) approached the maximum treatment response. Relative specific force and PDPF were significantly correlated (<i>P</i>=4.43×10⁻⁶). However, the relationship appeared to be nonlinear, with increased PDPF expression approaching the maximal functional improvement. Relative specific force and western blot were not significantly correlated. <h3>Conclusions:</h3> For the first time, biodistribution, biomarker and functional efficacy data were used to quantify and demonstrate PK/PD relationships for an adeno-associated virus (AAV)-based gene transfer therapy in a DMD animal model. The results continue to support the expected therapeutic benefit and clinical dose of delandistrogene moxeparvovec, an AAV-based gene transfer therapy. <b>Disclosure:</b> Mrs. East has received personal compensation for serving as an employee of Sarepta Therapeutics. Rachael Potter has received stock or an ownership interest from Sarepta Therapeutics. Dr. Snedeker has received personal compensation for serving as an employee of Sarepta Therapeutics. Dr. Snedeker has stock in Sarepta Therapeutics. Dr. Haile has nothing to disclose. Christopher Wier has received personal compensation for serving as an employee of Sarepta Therapeutics. Christopher Wier has stock in Sarepta Therapeutics. Ms. Rodino-Klapac has received personal compensation for serving as an employee of Sarepta Therapeutics, Inc.. Ms. Rodino-Klapac has received stock or an ownership interest from Sarepta Therapeutics. Ms. Rodino-Klapac has received intellectual property interests from a discovery or technology relating to health care.

Evaluation of the Biodistribution, Efficacy, and Side-Effect Profile of Deflazacort, Prednisolone and Vamorolone in a DMD Mouse Model (S34.010)

Evaluation of the Biodistribution, Efficacy, and Side-Effect Profile of Deflazacort, Prednisolone and Vamorolone in a DMD Mouse Model (S34.010)

Evaluating Pharmacology and Efficacy of Delandistrogene Moxeparvovec in Young and Aged DMDmdx Rats (P3-8.008)

<h3>Objective:</h3> The purpose of this preclinical study is to evaluate the myocardial efficacy and safety of intended commercial process delandistrogene moxeparvovec (SRP-9001) material in Duchenne muscular dystrophy (DMD)^mdx rats. DMD^mdx rats are a valuable alternative animal model of DMD, as they demonstrate cardiac dysfunction that recapitulates cardiac dysfunction of patients with DMD. <h3>Background:</h3> Gene transfer therapy is a promising treatment for patients with DMD. Delandistrogene moxeparvovec is an investigational gene transfer therapy developed to address the root cause of DMD through targeted skeletal and cardiac muscle expression of SRP-9001 dystrophin protein, which contains key functional domains of dystrophin. <h3>Design/Methods:</h3> We performed systemic, intravenous delivery of intended commercial process delandistrogene moxeparvovec material in young (21–35 days old) and aged (3–5 months old) DMD^mdx rats. The older rats demonstrate a more severe phenotype in terms of fibrosis or cardiac disease progression. Rats received a dose of 1.33×10¹⁴ vg/kg or 7.00×10¹³ vg/kg. Ambulation activity was recorded via the Photobeam Activity System Open Field. Echocardiograms and histological analysis of fibrosis were used to evaluate cardiac disease. <h3>Results:</h3> Data from 12 weeks and 24 weeks post-systemic delivery demonstrated no evidence of cardiac toxicity. Importantly, there were no deaths attributed to treatment. Compared with the saline control, intended commercial process delandistrogene moxeparvovec material increased ambulation and vertical activity in young DMD^mdx rats and improved cardiac function. Protein expression was broadly distributed across skeletal muscle, the diaphragm and the heart. <h3>Conclusions:</h3> Taken together, these findings confirm expression in cardiac muscle of rats, as expected, and support the potential myocardial efficacy and safety of delandistrogene moxeparvovec. Further results of cardiac disease phenotypes at 12 and 24 weeks post-systemic delivery utilizing several indicators of cardiac function will also be presented. <b>Disclosure:</b> Rachael Potter has received stock or an ownership interest from Sarepta Therapeutics. Christopher Wier has received personal compensation for serving as an employee of Sarepta Therapeutics. Christopher Wier has stock in Sarepta Therapeutics. Dr. Cooper-Olson has received personal compensation for serving as an employee of Sarepta Therapeutics. Dr. Cooper-Olson has stock in Sarepta Therapeutics. Ms. Wheeler has nothing to disclose. Miss Anderbery has nothing to disclose. Ms. Kempton has received personal compensation for serving as an employee of Sarepta Therapeutics. Ms. Kempton has stock in Sarepta Therapeutics. Ms. Clements has received personal compensation for serving as an employee of Sarepta Therapeutics . Ms. Clements has stock in Sarepta Therapeutics. Mrs. Adegboye has nothing to disclose. Dr. Haile has nothing to disclose. Ms. Peterson has nothing to disclose. Ms. Rodino-Klapac has received personal compensation for serving as an employee of Sarepta Therapeutics, Inc.. Ms. Rodino-Klapac has received stock or an ownership interest from Sarepta Therapeutics. Ms. Rodino-Klapac has received intellectual property interests from a discovery or technology relating to health care.

Indicators of increased ER stress and UPR in aged D2-mdx and human dystrophic skeletal muscles.

Duchenne muscular dystrophy (DMD) is a progressive muscle disease that results in muscle wasting, wheelchair dependence, and eventual death due to cardiac and respiratory complications. In addition to muscle fragility, dystrophin deficiency also results in multiple secondary dysfunctions, which may lead to the accumulation of unfolded proteins causing endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). The purpose of this investigation was to understand how ER stress and the UPR are modified in muscle from D2-mdx mice, an emerging DMD model, and from humans with DMD. We hypothesized that markers of ER stress and the UPR are upregulated in D2-mdx and human dystrophic muscles compared to their healthy counterparts. Immunoblotting in diaphragms from 11-month-old D2-mdx and DBA mice indicated increased ER stress and UPR in dystrophic diaphragms compared to healthy, including increased relative abundance of ER stress chaperone CHOP, canonical ER stress transducers ATF6 and pIRE1α S724, and transcription factors that regulate the UPR such as ATF4, XBP1s, and peIF2α S51. The publicly available Affymetrix dataset (GSE38417) was used to analyze the expression of ER stress and UPR-related transcripts and processes. Fifty-eight upregulated genes related to ER stress and the UPR in human dystrophic muscles suggest pathway activation. Further, based on analyses using iRegulon, putative transcription factors that regulate this upregulation profile were identified, including ATF6, XBP1, ATF4, CREB3L2, and EIF2AK3. This study adds to and extends the emerging knowledge of ER stress and the UPR in dystrophin deficiency and identifies transcriptional regulators that may be responsible for these changes and be of therapeutic interest.

Evaluation of Cardiac Function in Young Mdx Mice Using MRI with Feature Tracking and Self-Gated Magnetic Resonance Cine Imaging

This study aimed to evaluate cardiac function in a young mouse model of Duchenne muscular dystrophy (mdx) using cardiac magnetic resonance imaging (MRI) with feature tracking and self-gated magnetic resonance cine imaging. Cardiac function was evaluated in mdx and control mice (C57BL/6JJmsSlc mice) at 8 and 12 weeks of age. Preclinical 7-T MRI was used to capture short-axis, longitudinal two-chamber view and longitudinal four-chamber view cine images of mdx and control mice. Strain values were measured and evaluated from cine images acquired using the feature tracking method. The left ventricular ejection fraction was significantly less (p < 0.01 each) in the mdx group at both 8 (control, 56.6 ± 2.3% mdx, 47.2 ± 7.4%) and 12 weeks (control, 53.9 ± 3.3% mdx, 44.1 ± 2.7%). In the strain analysis, all strain value peaks were significantly less in mdx mice, except for the longitudinal strain of the four-chamber view at both 8 and 12 weeks of age. Strain analysis with feature tracking and self-gated magnetic resonance cine imaging is useful for assessing cardiac function in young mdx mice.

A Protocol for Simultaneous In Vivo Imaging of Cardiac and Neuroinflammation in Dystrophin-Deficient MDX Mice Using [18F]FEPPA PET.

Duchenne muscular dystrophy (DMD) is a neuromuscular disorder caused by dystrophin loss-notably within muscles and the central neurons system. DMD presents as cognitive weakness, progressive skeletal and cardiac muscle degeneration until pre-mature death from cardiac or respiratory failure. Innovative therapies have improved life expectancy; however, this is accompanied by increased late-onset heart failure and emergent cognitive degeneration. Thus, better assessment of dystrophic heart and brain pathophysiology is needed. Chronic inflammation is strongly associated with skeletal and cardiac muscle degeneration; however, neuroinflammation's role is largely unknown in DMD despite being prevalent in other neurodegenerative diseases. Here, we present an inflammatory marker translocator protein (TSPO) positron emission tomography (PET) protocol for in vivo concomitant assessment of immune cell response in hearts and brains of a dystrophin-deficient mouse model [mdx:utrn(+/-)]. Preliminary analysis of whole-body PET imaging using the TSPO radiotracer, [18F]FEPPA in four mdx:utrn(+/-) and six wildtype mice are presented with ex vivo TSPO-immunofluorescence tissue staining. The mdx:utrn(+/-) mice showed significant elevations in heart and brain [18F]FEPPA activity, which correlated with increased ex vivo fluorescence intensity, highlighting the potential of TSPO-PET to simultaneously assess presence of cardiac and neuroinflammation in dystrophic heart and brain, as well as in several organs within a DMD model.

Enveloped viruses pseudotyped with mammalian myogenic cell fusogens target skeletal muscle for gene delivery

Entry of enveloped viruses into cells is mediated by viral fusogenic proteins that drive membrane rearrangements needed for fusion between viral and target membranes. Skeletal muscle development also requires membrane fusion events between progenitor cells to form multinucleated myofibers. Myomaker and Myomerger are muscle-specific cell fusogens but do not structurally or functionally resemble classical viral fusogens. We asked whether the muscle fusogens could functionally substitute for viral fusogens, despite their structural distinctiveness, and fuse viruses to cells. We report that engineering of Myomaker and Myomerger on the membrane of enveloped viruses leads to specific transduction of skeletal muscle. We also demonstrate that locally and systemically injected virions pseudotyped with the muscle fusogens can deliver μDystrophin to skeletal muscle of a mouse model of Duchenne muscular dystrophy and alleviate pathology. Through harnessing the intrinsic properties of myogenic membranes, we establish a platform for delivery of therapeutic material to skeletal muscle.

Growth hormone secretagogues modulate inflammation and fibrosis in mdx mouse model of Duchenne muscular dystrophy.

Growth hormone secretagogues (GHSs) exert multiple actions, being able to activate GHS-receptor 1a, control inflammation and metabolism, to enhance GH/insulin-like growth factor-1 (IGF-1)-mediated myogenesis, and to inhibit angiotensin-converting enzyme. These mechanisms are of interest for potentially targeting multiple steps of pathogenic cascade in Duchenne muscular dystrophy (DMD). Here, we aimed to provide preclinical evidence for potential benefits of GHSs in DMD, via a multidisciplinary in vivo and ex vivo comparison in mdx mice, of two ad hoc synthesized compounds (EP80317 and JMV2894), with a wide but different profile. 4-week-old mdx mice were treated for 8 weeks with EP80317 or JMV2894 (320 µg/kg/d, s.c.). In vivo, both GHSs increased mice forelimb force (recovery score, RS towards WT: 20% for EP80317 and 32% for JMV2894 at week 8). In parallel, GHSs also reduced diaphragm (DIA) and gastrocnemius (GC) ultrasound echodensity, a fibrosis-related parameter (RS: ranging between 26% and 75%). Ex vivo, both drugs ameliorated DIA isometric force and calcium-related indices (e.g., RS: 40% for tetanic force). Histological analysis highlighted a relevant reduction of fibrosis in GC and DIA muscles of treated mice, paralleled by a decrease in gene expression of TGF-β1 and Col1a1. Also, decreased levels of pro-inflammatory genes (IL-6, CD68), accompanied by an increment in Sirt-1, PGC-1α and MEF2c expression, were observed in response to treatments, suggesting an overall improvement of myofiber metabolism. No detectable transcript levels of GHS receptor-1a, nor an increase of circulating IGF-1 were found, suggesting the presence of a novel receptor-independent mechanism in skeletal muscle. Preliminary docking studies revealed a potential binding capability of JMV2894 on metalloproteases involved in extracellular matrix remodeling and cytokine production, such as ADAMTS-5 and MMP-9, overactivated in DMD. Our results support the interest of GHSs as modulators of pathology progression in mdx mice, disclosing a direct anti-fibrotic action that may prove beneficial to contrast pathological remodeling.

The Implication of Hinge 1 and Hinge 4 in Micro-Dystrophin Gene Therapy for Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD) is a fatal muscle disease caused by dystrophin deficiency. Dystrophin consists of the amino terminus, central rod domain with 24 spectrin-like repeats and four hinges (H), cysteine-rich domain, and carboxyl terminus. Several highly abbreviated micro-dystrophins (μDys) are currently in clinical trials. They all carry H1 and H4. In this study, we investigated whether these two hinges are essential for μDy function in murine DMD models. Three otherwise identical μDys were engineered to contain H1 and/or H4 and were named H1/H4 (with both H1 and H4), ΔH1 (without H1), and ΔH4 (without H4). These constructs were packaged in adeno-associated virus serotype-9 and delivered to the tibialis anterior muscle of 3-month-old male mdx4cv mice (1E12 vector genome particles/muscle). Three months later, we detected equivalent μDys expression in total muscle lysate. However, only H1/H4 and ΔH1 showed correct sarcolemmal localization. ΔH4 mainly existed as sarcoplasmic aggregates. H1/H4 and ΔH1, but not ΔH4, fully restored the dystrophin-associated protein complex and significantly improved the specific muscle force. Eccentric contraction-induced force decline was best protected by H1/H4, followed by ΔH1, but not by ΔH4. Next, we compared H1/H4 and ΔH1 in 6-week-old male mdx mice by intravenous injection (1E13 vector genome particles/mouse). Four months postinjection, H1/H4 significantly outperformed ΔH1 in extensor digitorum longus muscle force measurements but two constructs yielded comparable electrocardiography improvements. We conclude that H4 is essential for μDys function and H1 facilitates force production. Our findings will help develop next-generation μDys gene therapy.

Ivabradine acutely improves cardiac Ca handling and function in a rat model of Duchenne muscular dystrophy.

The muscular dystrophies caused by dystrophin deficiency, the so-called dystrophinopathies, are associated with impaired cardiac contractility and arrhythmias, which considerably contribute to disease morbidity and mortality. Impaired Ca handling in ventricular cardiomyocytes has been identified as a causative factor for complications in the dystrophic heart, and restoration of normal Ca handling in myocytes has emerged as a promising new therapeutic strategy. In the present study, we explored the hypothesis that ivabradine, a drug clinically approved for the treatment of heart failure and stable angina pectoris, improves Ca handling in dystrophic cardiomyocytes and thereby enhances contractile performance in the dystrophic heart. Therefore, ventricular cardiomyocytes were isolated from the hearts of adult dystrophin-deficient DMDmdx rats, and the effects of acutely applied ivabradine on intracellular Ca transients were tested. In addition, the drug's acute impact on cardiac function in DMDmdx rats was assessed by transthoracic echocardiography. We found that administration of ivabradine to DMDmdx rats significantly improved cardiac function. Moreover, the amplitude of electrically induced intracellular Ca transients in ventricular cardiomyocytes isolated from DMDmdx rats was increased by the drug. We conclude that ivabradine enhances Ca release from the sarcoplasmic reticulum in dystrophic cardiomyocytes and thereby improves contractile performance in the dystrophic heart.

Multiomic characterization of disease progression in mice lacking dystrophin.

Duchenne muscular dystrophy (DMD) is caused by genetic mutations leading to lack of dystrophin in skeletal muscle. A better understanding of how objective biomarkers for DMD vary across subjects and over time is needed to model disease progression and response to therapy more effectively, both in pre-clinical and clinical research. We present an in-depth characterization of disease progression in 3 murine models of DMD by multiomic analysis of longitudinal trajectories between 6 and 30 weeks of age. Integration of RNA-seq, mass spectrometry-based metabolomic and lipidomic data obtained in muscle and blood samples by Multi-Omics Factor Analysis (MOFA) led to the identification of 8 latent factors that explained 78.8% of the variance in the multiomic dataset. Latent factors could discriminate dystrophic and healthy mice, as well as different time-points. MOFA enabled to connect the gene expression signature in dystrophic muscles, characterized by pro-fibrotic and energy metabolism alterations, to inflammation and lipid signatures in blood. Our results show that omic observations in blood can be directly related to skeletal muscle pathology in dystrophic muscle.

Comparison of Pronase versus Manual Dechorionation of Zebrafish Embryos for Small Molecule Treatments.

Zebrafish are a powerful animal model for small molecule screening. Small molecule treatments of zebrafish embryos usually require that the chorion, an acellular envelope enclosing the embryo, is removed in order for chemical compounds to access the embryo from the bath medium. For large-scale studies requiring hundreds of embryos, manual dechorionation, using forceps, can be a time-consuming and limiting process. Pronase is a non-specific protease that is widely used as an enzymatic alternative for dechorionating zebrafish embryos. However, whether pronase treatments alter the effects of subsequent small molecule treatments has not been addressed. Here, we provide a detailed protocol for large-scale pronase dechorionation of zebrafish embryos. We tested whether pronase treatment can influence the efficacy of drug treatments in zebrafish embryos. We used a zebrafish model for Duchenne muscular dystrophy (DMD) to investigate whether the efficacies of trichostatin-A (TSA) or salermide + oxamflatin, small molecule inhibitors known to ameliorate the zebrafish dmd muscle degeneration phenotype, are significantly altered when embryos are treated with pronase versus manual dechorionation. We also tested the effects of pronase on the ability of the anthracycline cancer drug doxorubicin to induce cardiotoxicity in zebrafish embryos. When comparing pronase- versus forceps-dechorionated embryos used in these small molecule treatments, we found no appreciable effects of pronase on animal survival or on the effects of the small molecules. The significant difference that was detected was a small improvement in the ability of salermide + oxamflatin to ameliorate the dmd phenotype in pronase-treated embryos when compared with manual dechorionation. Our study supports the use of pronase treatment as a dechorionation method for zebrafish drug screening experiments.

Brain magnetic resonance imaging in the DE50-MD dog model of Duchenne muscular dystrophy reveals regional reductions in cerebral gray matter

BackgroundDuchenne muscular dystrophy is a X-linked disease characterized by severe and progressive muscle weakness, alongside cognitive impairment and a range of neurobehavioral disorders secondary to brain dystrophin deficiency. Duchenne muscular dystrophy patients have reduced cerebral gray matter and altered white matter ultrastructure (detected by magnetic resonance imaging) compared to age-matched controls.MethodsWe studied the DE50-MD canine model of Duchenne muscular dystrophy, which is deficient in full length brain dystrophin (Dp427) isoforms and has a neurocognitive phenotype. Eight DE50-MD and 6 age-matched littermate wild type male dogs underwent serial brain magnetic resonance imaging from 14 to 33 months of age.ResultsReduced regional gray matter was detected in DE50-MD dogs compared with wildtype, including the piriform lobe, hippocampus and cingulate gyrus. Lateral ventricle volume was larger in DE50-MD dogs. Differences did not progress over time. White matter volume did not differ between DE50-MD and wildtype dogs. There was no difference in brain nor cranial vault volume between DE50-MD and wildtype dogs.ConclusionDystrophin deficiency in the canine brain results in structural changes that likely contribute to the neurocognitive phenotype.

Investigating the Impact of Delivery Routes for Exon Skipping Therapies in the CNS of DMD Mouse Models

Nucleic acid-based therapies have demonstrated great potential for the treatment of monogenetic diseases, including neurologic disorders. To date, regulatory approval has been received for a dozen antisense oligonucleotides (ASOs); however, these chemistries cannot readily cross the blood-brain barrier when administered systemically. Therefore, an investigation of their potential effects within the central nervous system (CNS) requires local delivery. Here, we studied the brain distribution and exon-skipping efficacy of two ASO chemistries, PMO and tcDNA, when delivered to the cerebrospinal fluid (CSF) of mice carrying a deletion in exon 52 of the dystrophin gene, a model of Duchenne muscular dystrophy (DMD). Following intracerebroventricular (ICV) delivery (unilateral, bilateral, bolus vs. slow rate, repeated via cannula or very slow via osmotic pumps), ASO levels were quantified across brain regions and exon 51 skipping was evaluated, revealing that tcDNA treatment invariably generates comparable or more skipping relative to that with PMO, even when the PMO was administered at higher doses. We also performed intra-cisterna magna (ICM) delivery as an alternative route for CSF delivery and found a biased distribution of the ASOs towards posterior brain regions, including the cerebellum, hindbrain, and the cervical part of the spinal cord. Finally, we combined both ICV and ICM injection methods to assess the potential of an additive effect of this methodology in inducing efficient exon skipping across different brain regions. Our results provide useful insights into the local delivery and associated efficacy of ASOs in the CNS in mouse models of DMD. These findings pave the way for further ASO-based therapy application to the CNS for neurological disease.

Inhibition of ATP synthase reverse activity restores energy homeostasis in mitochondrial pathologies.

The maintenance of cellular function relies on the close regulation of adenosine triphosphate (ATP) synthesis and hydrolysis. ATP hydrolysis by mitochondrial ATP Synthase (CV) is induced by loss of proton motive force and inhibited by the mitochondrial protein ATPase inhibitor (ATPIF1). The extent of CV hydrolytic activity and its impact on cellular energetics remains unknown due to the lack of selective hydrolysis inhibitors of CV. We find that CV hydrolytic activity takes place in coupled intact mitochondria and is increased by respiratory chain defects. We identified (+)-Epicatechin as a selective inhibitor of ATP hydrolysis that binds CV while preventing the binding of ATPIF1. In cells with Complex-III deficiency, we show that inhibition of CV hydrolytic activity by (+)-Epichatechin is sufficient to restore ATP content without restoring respiratory function. Inhibition of CV-ATP hydrolysis in a mouse model of Duchenne Muscular Dystrophy is sufficient to improve muscle force without any increase in mitochondrial content. We conclude that the impact of compromised mitochondrial respiration can be lessened using hydrolysis-selective inhibitors of CV.

Thyroid-stimulating hormone receptor signaling restores skeletal muscle stem cell regeneration in rats with muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a severe and progressive myopathy leading to motor and cardiorespiratory impairment. We analyzed samples from patients with DMD and a preclinical rat model of severe DMD and determined that compromised repair capacity of muscle stem cells in DMD is associated with early and progressive muscle stem cell senescence. We also found that extraocular muscles (EOMs), which are spared by the disease in patients, contain muscle stem cells with long-lasting regenerative potential. Using single-cell transcriptomics analysis of muscles from a rat model of DMD, we identified the gene encoding thyroid-stimulating hormone receptor (Tshr) as highly expressed in EOM stem cells. Further, TSHR activity was involved in preventing senescence. Forskolin, which activates signaling downstream of TSHR, was found to reduce senescence of skeletal muscle stem cells, increase stem cell regenerative potential, and promote myogenesis, thereby improving muscle function in DMD rats. These findings indicate that stimulation of adenylyl cyclase leads to muscle repair in DMD, potentially providing a therapeutic approach for patients with the disease.

Smooth Muscle Cells of Dystrophic (mdx) Mice Are More Susceptible to Hypoxia; The Protective Effect of Reducing Ca2+ Influx

Duchenne muscular dystrophy (DMD) is an inherited muscular disorder caused by mutations in the dystrophin gene. DMD patients have hypoxemic events due to sleep-disordered breathing. We reported an anomalous regulation of resting intracellular Ca2+ ([Ca2+]i) in vascular smooth muscle cells (VSMCs) from a mouse (mdx) model of DMD. We investigated the effect of hypoxia on [Ca2+]i in isolated and quiescent VSMCs from C57BL/10SnJ (WT) and C57BL/10ScSn-Dmd (mdx) male mice. [Ca2+]i was measured using Ca2+-selective microelectrodes under normoxic conditions (95% air, 5% CO2) and after hypoxia (glucose-free solution aerated with 95% N2-5% CO2 for 30 min). [Ca2+]i in mdx VSMCs was significantly elevated compared to WT under normoxia. Hypoxia-induced [Ca2+]i overload, which was significantly greater in mdx than in WT VSMCs. A low Ca2+ solution caused a reduction in [Ca2+]i and prevented [Ca2+]i overload secondary to hypoxia. Nifedipine (10 µM), a Ca2+ channel blocker, did not modify resting [Ca2+]i in VSMCs but partially prevented the hypoxia-induced elevation of [Ca2+]i in both genotypes. SAR7334 (1 µM), an antagonist of TRPC3 and TRPC6, reduced the basal and [Ca2+]i overload caused by hypoxia. Cell viability, assessed by tetrazolium salt (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, was significantly reduced in mdx compared to WT VSMCs. Pretreatment with SAR7341 increases cell viability in normoxic mdx (p < 0.001) and during hypoxia in WT and mdx VSMCs. These results provide evidence that the lack of dystrophin makes VSMCs more susceptible to hypoxia-induced [Ca2+]i overload, which appears to be mediated by increased Ca2+ entry through L-type Ca2+ and TRPC channels.

Six weeks of N-acetylcysteine antioxidant in drinking water decreases pathological fiber branching in MDX mouse dystrophic fast-twitch skeletal muscle.

Introduction: It has been proposed that an increased susceptivity to oxidative stress caused by the absence of the protein dystrophin from the inner surface of the sarcolemma is a trigger of skeletal muscle necrosis in the destructive dystrophin deficient muscular dystrophies. Here we use the mdx mouse model of human Duchenne Muscular Dystrophy to test the hypothesis that adding the antioxidant NAC at 2% to drinking water for six weeks will treat the inflammatory phase of the dystrophic process and reduce pathological muscle fiber branching and splitting resulting in a reduction of mass in mdx fast-twitch EDL muscles. Methods: Animal weight and water intake was recorded during the six weeks when 2% NAC was added to the drinking water. Post NAC treatment animals were euthanised and the EDL muscles dissected out and placed in an organ bath where the muscle was attached to a force transducer to measure contractile properties and susceptibility to force loss from eccentric contractions. After the contractile measurements had been made the EDL muscle was blotted and weighed. In order to assess the degree of pathological fiber branching mdx EDL muscles were treated with collagenase to release single fibers. For counting and morphological analysis single EDL mdx skeletal muscle fibers were viewed under high magnification on an inverted microscope. Results: During the six-week treatment phase NAC reduced body weight gain in three- to nine-week-old mdx and littermate control mice without effecting fluid intake. NAC treatment also significantly reduced the mdx EDL muscle mass and abnormal fiber branching and splitting. Discussion: We propose chronic NAC treatment reduces the inflammatory response and degenerative cycles in the mdx dystrophic EDL muscles resulting in a reduction in the number of complexed branched fibers reported to be responsible for the dystrophic EDL muscle hypertrophy.