Cardiac phenotype of Duchenne Muscular Dystrophy: insights from cellular studies

rAAVrh74.MCK.GALGT2 Protects against Loss of Hemodynamic Function in the Aging mdx Mouse Heart

Dilated cardiomyopathy is a common cause of death in patients with Duchenne muscular dystrophy (DMD). Gene therapies for DMD must, therefore, have a therapeutic impact in cardiac as well as skeletal muscles. Our previous studies have shown that GALGT2 overexpression in mdx skeletal muscles can prevent muscle damage. Here we have tested whether rAAVrh74.MCK.GALGT2 gene therapy in mdx cardiac muscle can prevent the loss of heart function. Treatment of mdx hearts with rAAVrh74.MCK.GALGT2 1 day after birth did not negatively alter hemodynamic function, tested at 3 months of age, and it prevented early left ventricular remodeling and expression of fibrotic gene markers. Intravenous treatment of mdx mice with rAAVrh74.MCK.GALGT2 at 2 months of age significantly improved stroke volume and cardiac output compared to mock-treated mice analyzed at 17 months, both at rest and after stimulation with dobutamine. rAAVrh74.MCK.GALGT2 treatment of mdx heart correlated with increased glycosylation of α-dystroglycan with the CT glycan and increased utrophin protein expression. These data provide the first demonstration that GALGT2 overexpression can inhibit the loss of cardiac function in the dystrophin-deficient heart and, thus, may benefit both cardiac and skeletal muscles in DMD patients.

Risk Stratification in Patients With Nonisquemic Dilated Cardiomyopathy. The Role of Genetic Testing

Dilated cardiomyopathy is inherited in nearly 50% of cases. More than 90 genes have been associated with this disease, which is one of the main causes of heart transplant and has been associated with an increased risk of sudden cardiac death. Risk stratification in these patients continues to be challenging. The identification of the specific etiology of the disease is very useful for the early detection of mutation carriers. Genetic study often provides prognostic information and can determine the therapeutic approach. Wide phenotypic variability is observed depending on the mutated gene, the type of mutation, and the presence of additional genetic and environmental factors.

A long-term treatment with taurine prevents cardiac dysfunction in mdx mice

Taurine is an amino acid abundantly present in heart and skeletal muscle. Duchenne muscular dystrophy (DMD) is a genetic disorder in which the absence of dystrophin leads to skeletal muscle wasting and heart failure. An altered taurine metabolism has been described in dystrophic animals and short-term taurine administration exerts promising amelioration of early muscular alterations in the mdx mouse model of DMD. To reinforce the therapeutic and nutraceutical taurine potential in DMD, we evaluated the effects of a long-term treatment on cardiac and skeletal muscle function of mdx mice in a later disease stage. Taurine was administered in drinking water (1 g/kg/day) to wt and mdx mice for 6 months, starting at 6 months of age. Ultrasonography evaluation of heart and hind limb was performed, in parallel with in vivo and ex vivo functional tests and biochemical, histological and gene expression analyses. 12-month-old mdx mice showed a significant worsening of left ventricular function parameters (shortening fraction, ejection fraction, stroke volume), which were significantly counteracted by the taurine treatment. In parallel, histologic signs of damage were reduced by taurine along with the expression of proinflammatory myocardial IL-6. Interestingly, no effects were observed on hind limb volume and percentage of vascularization or on in vivo and ex vivo muscle functional parameters, suggesting a tissue-specific action of taurine in relation to the disease phase. A trend toward increase in taurine was found in heart and quadriceps from treated animals, paralleled by a slight decrease in mdx mice plasma. Our study provides evidences that taurine can prevent late heart dysfunction in mdx mice, further corroborating the interest on this amino acid toward clinical trials.

Cardiac and skeletal muscle effects in the randomized HOPE-Duchenne trial

OBJECTIVE

To assess the feasibility, safety, and efficacy of intracoronary allogeneic cardiosphere-derived cells (CAP-1002) in patients with Duchenne muscular dystrophy (DMD).

METHODS

The Halt Cardiomyopathy Progression (HOPE)-Duchenne trial is a phase I/II, randomized, controlled, open-label trial (NCT02485938). Patients with DMD >12 years old, with substantial myocardial fibrosis, were randomized (1:1) to usual care (control) or global intracoronary infusion of CAP-1002 (75 million cells). Participants were enrolled at 3 US medical centers between January and August 2016 and followed for 12 months. An independent Data and Safety Monitoring Board provided safety oversight. Cardiac function and structure were assessed by MRI, and analyzed by a blinded core laboratory. Skeletal muscle function was assessed by performance of the upper limb (PUL).

RESULTS

Twenty-five eligible patients (mean age 17.8 years; 68% wheelchair-dependent) were randomized to CAP-1002 (n = 13) or control (n = 12). Incidence of treatment-emergent adverse events was similar between groups. Compared to baseline, MRI at 12 months revealed significant scar size reduction and improvement in inferior wall systolic thickening in CAP-1002 but not control patients. Mid-distal PUL improved at 12 months in 8 of 9 lower functioning CAP-1002 patients, and no controls (p = 0.007).

CONCLUSIONS

Intracoronary CAP-1002 in DMD appears safe and demonstrates signals of efficacy on both cardiac and upper limb function for up to 12 months. Thus, future clinical research on CAP-1002 treatment of DMD cardiac and skeletal myopathies is warranted.

CLASSIFICATION OF EVIDENCE

This phase I/II study provides Class II evidence that for patients with DMD, intracoronary CAP-1002 is feasible and appears safe and potentially effective.

Analysis of motor and respiratory function in Duchenne muscular dystrophy patients

INTRODUCTION

Duchenne muscular dystrophy(DMD) shows motor and respiratory impairment.

METHODS

19 DMD patients (DMDG) (nine ambulatory and 10 non-ambulatory) were evaluated through motor function measure (MFM), 6-minute walk test (6MWT), respiratory muscle strength, cough peak flow, spirometry and volumetric capnography (VCap) tools. Control group that performed spirometry and VCap (CG1-n = 17) were different from those that performed the 6MWT (CG2-n = 8).

RESULTS

The follow tools were assessed (p < 0.05): (i) MFM: Ambulatory patients showed higher values than non-ambulatory patients; (ii) 6MWT: DMDG walked a shorter distance and showed higher respiratory rate at rest and heart rate (HR) at rest than CG2; (iii) Spirometry: DMDG and non-ambulatory patients had minor values achieved in spirometry when compared with CG1 and ambulatory patients, respectively; (iv) VCap: DMDG when compared with CG1 showed: (<11 years-old) lower values in VCap parameters; (>11 years-old): higher HR and lower slope 2. There was correlation between spirometry, mainly for zFEV₁/FVC, and MFM.

CONCLUSION

DMDG showed motor (MFM/6MWT) and respiratory (spirometry/VCap) deterioration when compared with CG. Non-ambulatory condition was associated with worse MFM and spirometry.

Fibrosis Rescue Improves Cardiac Function in Dystrophin-Deficient Mice and Duchenne Patient-Specific Cardiomyocytes by Immunoproteasome Modulation

Patients affected by Duchenne muscular dystrophy (DMD) develop a progressive dilated cardiomyopathy characterized by inflammatory cell infiltration, necrosis, and cardiac fibrosis. Standard treatments consider the use of β-blockers and angiotensin-converting enzyme inhibitors that are symptomatic and unspecific toward DMD disease. Medications that target DMD cardiac fibrosis are in the early stages of development. We found immunoproteasome dysregulation in affected hearts of mdx mice (murine animal model of DMD) and cardiomyocytes derived from induced pluripotent stem cells of patients with DMD. Interestingly, immunoproteasome inhibition ameliorated cardiomyopathy in mdx mice and reduced the development of cardiac fibrosis. Establishing the immunoproteasome inhibition-dependent cardioprotective role suggests the possibility of modulating the immunoproteasome as new and clinically relevant treatment to rescue dilated cardiomyopathy in patients with DMD.

Rehabilitation Management of the Patient With Duchenne Muscular Dystrophy

Steadily improving management of Duchenne muscular dystrophy (DMD) continues to lead to improved physical and functional status, allowing increasingly successful transitions to independence and self-actualization in adulthood. Rehabilitation principles remain key to overall management for individuals with DMD with increasing options for ever more successful management, reflecting a changing natural history based on the use of glucocorticoids, more consistent comprehensive care, and the emergence of disease-modifying treatments. Advances and expansion in assessment, cardiorespiratory management, preventive management of contracture and deformity, assistive technology, "smart" technology, and robotics with increased emphasis on function, participation, self-advocacy, and independence in decision-making should allow individuals with DMD to experience childhood and transition to adulthood with support that allows for increasing success in the achievement of individual goals and fulfillment across the life span.

Dystrophin Cardiomyopathies: Clinical Management, Molecular Pathogenesis and Evolution towards Precision Medicine

Duchenne’s muscular dystrophy is an X-linked neuromuscular disease that manifests as muscle atrophy and cardiomyopathy in young boys. However, a considerable percentage of carrier females are often diagnosed with cardiomyopathy at an advanced stage. Existing therapy is not disease-specific and has limited effect, thus many patients and symptomatic carrier females prematurely die due to heart failure. Early detection is one of the major challenges that muscular dystrophy patients, carrier females, family members and, research and medical teams face in the complex course of dystrophic cardiomyopathy management. Despite the widespread adoption of advanced imaging modalities such as cardiac magnetic resonance, there is much scope for refining the diagnosis and treatment of dystrophic cardiomyopathy. This comprehensive review will focus on the pertinent clinical aspects of cardiac disease in muscular dystrophy while also providing a detailed consideration of the known and developing concepts in the pathophysiology of muscular dystrophy and forthcoming therapeutic options.

Reduced myocyte complex N-glycosylation causes dilated cardiomyopathy

Protein glycosylation is an essential posttranslational modification that affects a myriad of physiologic processes. Humans with genetic defects in glycosylation, which result in truncated glycans, often present with significant cardiac deficits. Acquired heart diseases and their associated risk factors were also linked to aberrant glycosylation, highlighting its importance in human cardiac disease. In both cases, the link between causation and corollary remains enigmatic. The glycosyltransferase gene, mannosyl (α-1,3-)-glycoprotein β-1,2- N-acetylglucosaminyltransferase (Mgat1), whose product, N-acetylglucosaminyltransferase 1 (GlcNAcT1) is necessary for the formation of hybrid and complex N-glycan structures in the medial Golgi, was shown to be at reduced levels in human end-stage cardiomyopathy, thus making Mgat1 an attractive target for investigating the role of hybrid/complex N-glycosylation in cardiac pathogenesis. Here, we created a cardiomyocyte-specific Mgat1 knockout (KO) mouse to establish a model useful in exploring the relationship between hybrid/complex N-glycosylation and cardiac function and disease. Biochemical and glycomic analyses showed that Mgat1KO cardiomyocytes produce predominately truncated N-glycan structures. All Mgat1KO mice died significantly younger than control mice and demonstrated chamber dilation and systolic dysfunction resembling human dilated cardiomyopathy (DCM). Data also indicate that a cardiomyocyte L-type voltage-gated Ca²⁺ channel (Ca_v) subunit (α2δ1) is a GlcNAcT1 target, and Mgat1KO Ca_v activity is shifted to more-depolarized membrane potentials. Consistently, Mgat1KO cardiomyocyte Ca²⁺ handling is altered and contraction is dyssynchronous compared with controls. The data demonstrate that reduced hybrid/complex N-glycosylation contributes to aberrant cardiac function at whole-heart and myocyte levels drawing a direct link between altered glycosylation and heart disease. Thus, the Mgat1KO provides a model for investigating the relationship between systemic reductions in glycosylation and cardiac disease, showing that clinically relevant changes in cardiomyocyte hybrid/complex N-glycosylation are sufficient to cause DCM and early death.-Ednie, A. R., Deng, W., Yip, K.-P., Bennett, E. S. Reduced myocyte complex N-glycosylation causes dilated cardiomyopathy.

Exacerbation of dystrophic cardiomyopathy by phospholamban deficiency mediated chronically increased cardiac Ca2+ cycling in vivo

Cardiomyopathy is a significant contributor to morbidity and mortality in Duchenne muscular dystrophy (DMD). Membrane instability, leading to intracellular Ca²⁺ mishandling and overload, causes myocyte death and subsequent fibrosis in DMD cardiomyopathy. On a cellular level, cardiac myocytes from mdx mice have dysregulated Ca²⁺ handling, including increased resting Ca²⁺ and slow Ca²⁺ decay, especially evident under stress conditions. Sarco(endo)plasmic reticulum Ca²⁺ ATPase and its regulatory protein phospholamban (PLN) are potential therapeutic targets for DMD cardiomyopathy owing to their key role in regulating intracellular Ca²⁺ cycling. We tested the hypothesis that enhanced cardiac Ca²⁺ cycling would remediate cardiomyopathy caused by dystrophin deficiency. We used a genetic complementation model approach by crossing dystrophin-deficient mdx mice with PLN knockout (PLNKO) mice [termed double-knockout (DKO) mice]. As expected, adult cardiac myocytes isolated from DKO mice exhibited increased contractility and faster relaxation associated with increased Ca²⁺ transient peak height and faster Ca²⁺ decay rate compared with control mice. However, compared with wild-type, mdx, and PLNKO mice, DKO mice unexpectedly had reduced in vivo systolic and diastolic function as measured by echocardiography. Furthermore, Evans blue dye uptake was increased in DKO hearts compared with control, mdx, and PLNKO hearts, demonstrating increased membrane damage, which subsequently led to increased fibrosis in the DKO myocardium in vivo. In conclusion, despite enhanced intracellular Ca²⁺ handling at the myocyte level, DMD cardiomyopathy was exacerbated owing to unregulated chronic increases in Ca²⁺ cycling in DKO mice in vivo. These findings have potentially important implications for ongoing therapeutic strategies for the dystrophic heart. NEW & NOTEWORTHY This study examined the effects of phospholamban ablation on the pathophysiology of cardiomyopathy in dystrophin-deficient mice. In this setting, contractility and Ca²⁺ cycling were enhanced in isolated myocytes; however, in vivo heart function was diminished. Additionally, sarcolemmal integrity was compromised and fibrosis was increased. This is the first study, to our knowledge, examining unregulated Ca²⁺ cycling in the dystrophin-deficient heart. Results from this study have implications for potential therapies targeting Ca²⁺ handling in dystrophic cardiomyopathy. Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/unregulated-ca2-cycling-exacerbates-dmd-cardiomyopathy/ .

A novel rabbit model of Duchenne muscular dystrophy generated by CRISPR/Cas9

Duchenne muscular dystrophy (DMD) is an X-linked muscle-wasting disorder caused by mutations in the dystrophin gene, with an incidence of 1 in 3500 in new male births. Mdx mice are widely used as an animal model for DMD. However, these mice do not faithfully recapitulate DMD patients in many aspects, rendering the preclinical findings in this model questionable. Although larger animal models of DMD, such as dogs and pigs, have been generated, usage of these animals is expensive and only limited to several facilities in the world. Here, we report the generation of a rabbit model of DMD by co-injection of Cas9 mRNA and sgRNA targeting exon 51 into rabbit zygotes. The DMD knockout (KO) rabbits exhibit the typical phenotypes of DMD, including severely impaired physical activity, elevated serum creatine kinase levels, and progressive muscle necrosis and fibrosis. Moreover, clear pathology was also observed in the diaphragm and heart at 5 months of age, similar to DMD patients. Echocardiography recording showed that the DMD KO rabbits had chamber dilation with decreased ejection fraction and fraction shortening. In conclusion, this novel rabbit DMD model generated with the CRISPR/Cas9 system mimics the histopathological and functional defects in DMD patients, and could be valuable for preclinical studies.

This article has an associated First Person interview with the first author of the paper.

Summary: The DMD KO rabbit engineered by CRISPR genome editing faithfully recapitulates the DMD pathologies, and could be a valuable tool for basic and translational studies to combat this disease.

A Morpholino Oligomer Therapy Regime That Restores Mitochondrial Function and Prevents mdx Cardiomyopathy

Current clinical trials demonstrate Duchenne muscular dystrophy (DMD) patients receiving phosphorodiamidate morpholino oligomer (PMO) therapy exhibit improved ambulation and stable pulmonary function; however, cardiac abnormalities remain. Utilizing the same PMO chemistry as current clinical trials, we have identified a non-toxic PMO treatment regimen that restores metabolic activity and prevents DMD cardiomyopathy. We propose that a treatment regimen of this nature may have the potential to significantly improve morbidity and mortality from DMD by improving ambulation, stabilizing pulmonary function, and preventing the development of cardiomyopathy.

Exosome-Mediated Benefits of Cell Therapy in Mouse and Human Models of Duchenne Muscular Dystrophy

Genetic deficiency of dystrophin leads to disability and premature death in Duchenne muscular dystrophy (DMD), affecting the heart as well as skeletal muscle. Here, we report that clinical-stage cardiac progenitor cells, known as cardiosphere-derived cells (CDCs), improve cardiac and skeletal myopathy in the mdx mouse model of DMD. Injection of CDCs into the hearts of mdx mice augments cardiac function, ambulatory capacity, and survival. Exosomes secreted by human CDCs reproduce the benefits of CDCs in mdx mice and in human induced pluripotent stem cell-derived Duchenne cardiomyocytes. Surprisingly, CDCs and their exosomes also transiently restored partial expression of full-length dystrophin in mdx mice. The findings further motivate the testing of CDCs in Duchenne patients, while identifying exosomes as next-generation therapeutic candidates.

Normalization of connexin 43 protein levels prevents cellular and functional signs of dystrophic cardiomyopathy in mice

Duchenne muscular dystrophy (DMD) associated cardiomyopathy remains incurable. Connexin 43 (Cx43) is upregulated and remodeled in the hearts of mdx mice, a mouse model of DMD. Hearts from Wild Type, mdx, and mdx:Cx43(+/-) mice were studied before (4-6 months) and after (10-15 months) the onset of cardiomyopathy to assess the impact of decreasing Cx43 levels on cardiac pathology in dystrophic mice. Increased connexin 43 protein levels in mdx hearts were not observed in mdx:Cx43(+/-) hearts. Cx43 remodeling in mdx hearts was attenuated in mdx:Cx43(+/-) hearts. At time-point 4-6 months, isolated cardiomyocytes from mdx hearts displayed enhanced ethidium bromide uptake, augmented intracellular calcium signals and increased production of reactive oxygen species. These pathological features were improved in mdx:Cx43(+/-) cardiomyocytes. Isoproterenol-challenged mdx:Cx43(+/-) mice did not show arrhythmias or acute lethality observed in mdx mice. Likewise, isoproterenol-challenged mdx:Cx43(+/-) isolated hearts were also protected from arrhythmogenesis. At time-point 10-15 months, mdx:Cx43(+/-) mice showed decreased cardiac fibrosis and improved ventricular function, relative to mdx mice. These results suggest that normalization of connexin 43 protein levels in mdx mice reduces overall cardiac pathology.

miR-25 Tough Decoy Enhances Cardiac Function in Heart Failure

MicroRNAs are promising therapeutic targets, because their inhibition has the potential to normalize gene expression in diseased states. Recently, our group found that miR-25 is a key SERCA2a regulating microRNA, and we showed that multiple injections of antagomirs against miR-25 enhance cardiac contractility and function through SERCA2a restoration in a murine heart failure model. However, for clinical application, a more stable suppressor of miR-25 would be desirable. Tough Decoy (TuD) inhibitors are emerging as a highly effective method for microRNA inhibition due to their resistance to endonucleolytic degradation, high miRNA binding affinity, and efficient delivery. We generated a miR-25 TuD inhibitor and subcloned it into a cardiotropic AAV9 vector to evaluate its efficacy. The AAV9 TuD showed selective inhibition of miR-25 in vitro cardiomyoblast culture. In vivo, AAV9-miR-25 TuD delivered to the murine pressure-overload heart failure model selectively decreased expression of miR-25, increased levels of SERCA2a protein, and ameliorated cardiac dysfunction and fibrosis. Our data indicate that miR-25 TuD is an effective long-term suppressor of miR-25 and a promising therapeutic candidate to treat heart failure.

Evaluation of cardiac functions in children with Duchenne Muscular Dystrophy: A prospective case-control study

Background

Duchenne muscular dystrophy (DMD) is the most common childhood form of muscular dystrophy. The incidence of cardiomyopathy in DMD increases with age, so its early detection is important because institution of cardioprotective medical therapies may slow adverse remodeling and attenuate heart failure symptoms in these patients.

Objective

To assess the cardiac functions in children clinically suspected to have DMD.

Methods

Over a one-year period, 28 male children aged from 3 to 18 years old, who met the criteria for diagnosis of DMD compared to 47 healthy controls children, were approached to participate in the study. The included children were subjected to full clinical examination, and blood samples were collected to determine creatinine phosphokinase (CPK), troponin I enzyme, myoglobin and lactate dehydrogenase (LDH) enzyme level. Echocardiography and 12-leads electrocardiogram (ECG) were also done for children in both groups. Data were analyzed using Independent-samples t-test, Mann-Whitney U, Chi square, and Fisher’s exact test.

Results

The mean age of the cases group was 7.29±3.24 years versus 8.06±2.86 years for controls. In DMD group, 25% had positive family history of DMD while 35.7% of them had positive consanguinity. All cases had elevated CPK level while CPK level in controls was normal (p<0.0001). LDH level was elevated in 19 cases (67.86%) of DMD while all controls children had normal LDH level (p<0.0001). Furthermore, the mean serum myoglobin level of DMD patients was higher relative to that of healthy controls (39.39±7.25 versus 33.68 ±12.38 ng/ml respectively) (p=0.01). Echocardiography of our patients revealed that seven cases (25%) had low ejection fraction (EF) and fraction shortening (FS). In addition, all controls children had normal EF (p<0.0001) and normal FS (p<0.0001). Interestingly, ECG showed that 28.57% of cases had sinus tachycardia vs. 6.88% for controls (p=0.0001). Prolonged QTc interval was present in 39.29% of cases (mean 431.39±43.60) while all controls had normal QTc duration for age (mean of 415.17±25.2) (p<0.0001).

Conclusion

ECG manifestations in children with DMD in the form of sinus tachycardia and prolonged QTc interval are an early alarm for developing cardiomyopathy before overt echocardiographic findings appear.

Neuromuscular Disorders and the Role of the Clinical Electrophysiologist

Cardiac involvement is common and may be the presenting or predominant manifestation in a variety of neuromuscular disorders, most notably the inherited muscle disorders, or muscular dystrophies. Cardiac manifestations of the neuromuscular disorders result from pathological involvement of the myocardium and the cardiac conduction system, with resulting cardiomyopathy or rhythm disturbances including supraventricular arrhythmias, life-threatening ventricular arrhythmias, and sudden cardiac death. Many of these neuromuscular disorders are rare and may be unrecognized by even experienced specialists in internal and cardiovascular medicine. Furthermore, the initial cardiac manifestations in these patients are often asymptomatic. The goal of this investigation is to review the scope of cardiac conduction defects and rhythm disturbances in these disorders and to propose some practical recommendations for arrhythmia monitoring and management of these patients.

Dystrophic Cardiomyopathy: Complex Pathobiological Processes to Generate Clinical Phenotype

Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), and X-linked dilated cardiomyopathy (XL-DCM) consist of a unique clinical entity, the dystrophinopathies, which are due to variable mutations in the dystrophin gene. Dilated cardiomyopathy (DCM) is a common complication of dystrophinopathies, but the onset, progression, and severity of heart disease differ among these subgroups. Extensive molecular genetic studies have been conducted to assess genotype-phenotype correlation in DMD, BMD, and XL-DCM to understand the underlying mechanisms of these diseases, but the results are not always conclusive, suggesting the involvement of complex multi-layers of pathological processes that generate the final clinical phenotype. Dystrophin protein is a part of dystrophin-glycoprotein complex (DGC) that is localized in skeletal muscles, myocardium, smooth muscles, and neuronal tissues. Diversity of cardiac phenotype in dystrophinopathies suggests multiple layers of pathogenetic mechanisms in forming dystrophic cardiomyopathy. In this review article, we review the complex molecular interactions involving the pathogenesis of dystrophic cardiomyopathy, including primary gene mutations and loss of structural integrity, secondary cellular responses, and certain epigenetic and other factors that modulate gene expressions. Involvement of epigenetic gene regulation appears to lead to specific cardiac phenotypes in dystrophic hearts.

Reduced Myocardial Reserve in Young X-Linked Muscular Dystrophy Mice Diagnosed by Two-Dimensional Strain Analysis Combined with Stress Echocardiography

BACKGROUND

Early, sensitive, and reproducible evaluation of left ventricular function is imperative for the diagnosis of cardiac dysfunction in patients with Duchene muscular dystrophy. The aim of this study was to test the hypothesis that combining two-dimensional strain analysis with catecholamine stress could be a sensitive method for detecting early cardiac dysfunction.

METHODS

Mdx (C57BL/10ScSn-Dmdmdx/J, a mouse model of DMD) and control (C57BL/10ScSn) mice were studied with conventional M-mode and high-frequency ultrasound-based two-dimensional speckle-tracking echocardiography using long- and short-axis images of the left ventricle at baseline and after intraperitoneal isoprenaline (ISO) administration (2 μg/g body weight).

RESULTS

Conventional M-mode analysis showed no differences in left ventricular fractional shortening, wall thickness, or internal diameter at diastole between mdx and control mice before the age of 6 months. ISO increased left ventricular ejection fraction and fractional shortening to the same extent in mdx and control mice at young ages (3, 4, and 5 months). No differences in basal peak systolic strain (PSS) but increased SDs of times to PSS between young mdx and control mice were found. After ISO, PSS and percentile changes of PSS were significantly diminished in mdx mice compared with control mice at young ages. ISO increased the normalized maximum difference of times to PSS in young mdx mice but not in young control mice, suggesting that ISO reduces cardiac contractile synchrony in young mdx mice.

CONCLUSIONS

This study suggests that catecholamine stress coupled with two-dimensional strain analysis is a feasible and sensitive approach for detecting early onset of cardiac dysfunction, which is instrumental for early diagnosis of cardiac dysfunction and early treatment.

Long-term dietary quercetin enrichment as a cardioprotective countermeasure in mdx mice

NEW FINDINGS

What is the central question of this study? The central question of this study is to understand whether dietary quercetin enrichment attenuates physiologic, histological, and biochemical indices of cardiac pathology. What is the main finding and its importance? Novel findings from this investigation, in comparison to prior published studies, suggest that mouse strain-dependent cardiac outcomes in performance and remodelling exist. Unlike Mdx/Utrn^-/+ mice, mdx mice receiving lifelong quercetin treatment did not exhibit improvements cardiac function. Similar to prior work in Mdx/Utrn^-/+ mice, histological evidence of remodelling suggests that quercetin consumption may have benefited hearts of mdx mice. Positive outcomes may be related to indirect markers that suggest improved mitochondrial wellbeing and to selected indices of inflammation that were lower in hearts from quercetin-fed mice. Duchenne muscular dystrophy causes a decline in cardiac health, resulting in premature mortality. As a potential countermeasure, quercetin is a polyphenol possessing inherent anti-inflammatory and antioxidant effects that activate proliferator-activated γ coactivator 1α (PGC-1α), increasing the abundance of mitochondrial biogenesis proteins. We investigated the extent to which lifelong 0.2% dietary quercetin enrichment attenuates dystrophic cardiopathology in mdx mice. Dystrophic animals were fed a quercetin-enriched or control diet for 12 months, while control C57 mice were fed a control diet. Cardiac function was assessed via 7 T magnetic resonance imaging at 2, 10 and 14 months. At 14 months, hearts were harvested for histology and Western blotting. The results indicated an mdx strain-dependent decline in cardiac performance at 14 months and that dietary quercetin enrichment did not attenuate functional losses. In contrast, histological analyses provided evidence that quercetin feeding was associated with decreased fibronectin and indirect damage indices (Haematoxylin and Eosin) compared with untreated mdx mice. Dietary quercetin enrichment increased cardiac protein abundance of PGC-1α, cytochrome c, electron transport chain complexes I-V, citrate synthase, superoxide dismutase 2 and glutathione peroxidase (GPX) versus untreated mdx mice. The protein abundance of the inflammatory markers nuclear factor-κB, phosphorylated nuclear factor kappa beta (P-NFκB) and phosphorylated nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (P-IKBα) was decreased by quercetin compared with untreated mdx mice, while preserving nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha( IKBα) compared with mdx mice. Furthermore, quercetin decreased transforming growth factor-β1, cyclooxygenase-2 (COX2) and macrophage-restricted F4/80 protein (F4/80) versus untreated mdx mice. The data suggest that long-term quercetin enrichment does not impact physiological parameters of cardiac function but improves indices of mitochondrial biogenesis and antioxidant enzymes, facilitates dystrophin-associated glycoprotein complex (DGC) assembly and decreases inflammation in dystrophic hearts.

Dystrophic Cardiomyopathy-Potential Role of Calcium in Pathogenesis, Treatment and Novel Therapies

Duchenne muscular dystrophy (DMD) is caused by defects in the DMD gene and results in progressive wasting of skeletal and cardiac muscle due to an absence of functional dystrophin. Cardiomyopathy is prominent in DMD patients, and contributes significantly to mortality. This is particularly true following respiratory interventions that reduce death rate and increase ambulation and consequently cardiac load. Cardiomyopathy shows an increasing prevalence with age and disease progression, and over 95% of patients exhibit dilated cardiomyopathy by the time they reach adulthood. Development of the myopathy is complex, and elevations in intracellular calcium, functional muscle ischemia, and mitochondrial dysfunction characterise the pathophysiology. Current therapies are limited to treating symptoms of the disease and there is therefore an urgent need to treat the underlying genetic defect. Several novel therapies are outlined here, and the unprecedented success of phosphorodiamidate morpholino oligomers (PMOs) in preclinical and clinical studies is overviewed.

GsMTx4: Mechanism of Inhibiting Mechanosensitive Ion Channels

GsMTx4 is a spider venom peptide that inhibits cationic mechanosensitive channels (MSCs). It has six lysine residues that have been proposed to affect membrane binding. We synthesized six analogs with single lysine-to-glutamate substitutions and tested them against Piezo1 channels in outside-out patches and independently measured lipid binding. Four analogs had ∼20% lower efficacy than the wild-type (WT) peptide. The equilibrium constants calculated from the rates of inhibition and washout did not correlate with the changes in inhibition. The lipid association strength of the WT GsMTx4 and the analogs was determined by tryptophan autofluorescence quenching and isothermal calorimetry with membrane vesicles and showed no significant differences in binding energy. Tryptophan fluorescence-quenching assays showed that both WT and analog peptides bound superficially near the lipid-water interface, although analogs penetrated deeper. Peptide-lipid association, as a function of lipid surface pressure, was investigated in Langmuir monolayers. The peptides occupied a large fraction of the expanded monolayer area, but that fraction was reduced by peptide expulsion as the pressure approached the monolayer-bilayer equivalence pressure. Analogs with compromised efficacy had pressure-area isotherms with steeper slopes in this region, suggesting tighter peptide association. The pressure-dependent redistribution of peptide between "deep" and "shallow" binding modes was supported by molecular dynamics (MD) simulations of the peptide-monolayer system under different area constraints. These data suggest a model placing GsMTx4 at the membrane surface, where it is stabilized by the lysines, and occupying a small fraction of the surface area in unstressed membranes. When applied tension reduces lateral pressure in the lipids, the peptides penetrate deeper acting as "area reservoirs" leading to partial relaxation of the outer monolayer, thereby reducing the effective magnitude of stimulus acting on the MSC gate.

Lifelong quercetin enrichment and cardioprotection in Mdx/Utrn+/− mice

Duchenne Muscular Dystrophy (DMD) is associated with progressive cardiac pathology; however, the SIRT1/PGC1-α activator quercetin may cardioprotect dystrophic hearts. We tested the extent to which long-term 0.2% dietary quercetin enrichment attenuates dystrophic cardiopathology in Mdx/Utrn+/− mice. At 2 mo, Mdx/Utrn+/− mice were fed quercetin-enriched (Mdx/Utrn+/−-Q) or control diet (Mdx/Utrn+/−) for 8 mo. Control C57BL/10 (C57) animals were fed a control diet for 10 mo. Cardiac function was quantified by MRI at 2 and 10 mo. Spontaneous physical activity was quantified during the last week of treatment. At 10 mo hearts were excised for histological and biochemical analysis. Quercetin feeding improved various physiological indexes of cardiac function in diseased animals. Mdx/Utrn+/−-Q also engaged in more high-intensity physical activity than controls. Histological analyses of heart tissues revealed higher expression and colocalization of utrophin and α-sarcoglycan. Lower abundance of fibronectin, cardiac damage (Hematoxylin Eosin-Y), and MMP9 were observed in quercetin-fed vs. control Mdx/Utrn+/− mice. Quercetin evoked higher protein abundance of PGC-1α, cytochrome c, ETC complexes I–V, citrate synthase, SOD2, and GPX compared with control-fed Mdx/Utrn+/−. Quercetin decreased abundance of inflammatory markers including NFκB, TGF-β1, and F4/80 compared with Mdx/Utrn+/−; however, P-NFκB, P-IKBα, IKBα, CD64, and COX2 were similar between groups. Dietary quercetin enrichment improves cardiac function in aged Mdx/Utrn+/− mice and increases mitochondrial protein content and dystrophin glycoprotein complex formation. Histological analyses indicate a marked attenuation in pathological cardiac remodeling and indicate that long-term quercetin consumption benefits the dystrophic heart.

NEW & NOTEWORTHY The current investigation provides first-time evidence that quercetin provides physiological cardioprotection against dystrophic pathology and is associated with improved spontaneous physical activity. Secondary findings suggest that quercetin-dependent outcomes are in part due to PGC-1α pathway activation.

Dysregulation of Intracellular Ca2+ in Dystrophic Cortical and Hippocampal Neurons

Duchenne muscular dystrophy (DMD) is an inherited X-linked disorder characterized by skeletal muscle wasting, cardiomyopathy, as well as cognitive impairment. Lack of dystrophin in striated muscle produces dyshomeostasis of resting intracellular Ca²⁺ ([Ca²⁺]_i), Na⁺ ([Na⁺]_i), and oxidative stress. Here, we test the hypothesis that similar to striated muscle cells, an absence of dystrophin in neurons from mdx mice (a mouse model for DMD) is also associated with dysfunction of [Ca²⁺]_i homeostasis and oxidative stress. [Ca²⁺]_i and [Na⁺]_i in pyramidal cortical and hippocampal neurons from 3 and 6 months mdx mice were elevated compared to WT in an age-dependent manner. Removal of extracellular Ca²⁺ reduced [Ca²⁺]_i in both WT and mdx neurons, but the decrease was greater and age-dependent in the latter. GsMTx-4 (a blocker of stretch-activated cation channels) significantly decreased [Ca²⁺]_i and [Na⁺]_i in an age-dependent manner in all mdx neurons. Blockade of ryanodine receptors (RyR) or inositol triphosphate receptors (IP3R) reduced [Ca²⁺]_i in mdx. Mdx neurons showed elevated and age-dependent reactive oxygen species (ROS) production and an increase in neuronal damage. In addition, mdx mice showed a spatial learning deficit compared to WT. GsMTx-4 intraperitoneal injection reduced neural [Ca²⁺]_i and improved learning deficit in mdx mice. In summary, mdx neurons show an age-dependent dysregulation in [Ca²⁺]_i and [Na⁺]_i which is mediated by plasmalemmal cation influx and by intracellular Ca²⁺ release through the RyR and IP3R. Also, mdx neurons have elevated ROS production and more extensive cell damage. Finally, a reduction of [Ca²⁺]_i improved cognitive function in mdx mice.

Uniform low-level dystrophin expression in the heart partially preserved cardiac function in an aged mouse model of Duchenne cardiomyopathy

Dystrophin deficiency results in Duchenne cardiomyopathy, a primary cause of death in Duchenne muscular dystrophy (DMD). Gene therapy has shown great promise in ameliorating the cardiac phenotype in mouse models of DMD. However, it is not completely clear how much dystrophin is required to treat dystrophic heart disease. We and others have shown that mosaic dystrophin expression at the wild-type level, depending on the percentage of dystrophin positive cardiomyocytes, can either delay the onset of or fully prevent cardiomyopathy in dystrophin-null mdx mice. Many gene therapy strategies will unlikely restore dystrophin to the wild-type level in a cardiomyocyte. To determine whether low-level dystrophin expression can reduce the cardiac manifestations in DMD, we examined heart histology, ECG and hemodynamics in 21-m-old normal BL6 and two strains of BL6-background dystrophin-deficient mice. Mdx3cv mice show uniform low-level expression of a near full-length dystrophin protein in every myofiber while mdx4cv mice have no dystrophin expression. Immunostaining and western blot confirmed marginal level dystrophin expression in the heart of mdx3cv mice. Although low-level expression did not reduce myocardial histopathology, it significantly ameliorated QRS prolongation and normalized diastolic hemodynamic deficiencies. Our study demonstrates for the first time that low-level dystrophin can partially preserve heart function.

Small Fractions of Muscular Dystrophy Embryonic Stem Cells Yield Severe Cardiac and Skeletal Muscle Defects in Adult Mouse Chimeras

Duchenne muscular dystrophy (DMD) is characterized by the loss of the protein dystrophin, leading to muscle fragility, progressive weakening, and susceptibility to mechanical stress. Although dystrophin-negative mdx mouse models have classically been used to study DMD, phenotypes appear mild compared to patients. As a result, characterization of muscle pathology, especially in the heart, has proven difficult. We report that injection of mdx embryonic stem cells (ESCs) into Wild Type blastocysts produces adult mouse chimeras with severe DMD phenotypes in the heart and skeletal muscle. Inflammation, regeneration and fibrosis are observed at the whole organ level, both in dystrophin-negative and dystrophin-positive portions of the chimeric tissues. Skeletal and cardiac muscle function are also decreased to mdx levels. In contrast to mdx heterozygous carriers, which show no significant phenotypes, these effects are even observed in chimeras with low levels of mdx ESC incorporation (10%-30%). Chimeric mice lack typical compensatory utrophin upregulation, and show pathological remodeling of Connexin-43. In addition, dystrophin-negative and dystrophin-positive isolated cardiomyocytes show augmented calcium response to mechanical stress, similar to mdx cells. These global effects highlight a novel role of mdx ESCs in triggering muscular dystrophy even when only low amounts are present. Stem Cells 2017;35:597-610.

Up-regulation of miR-31 in human atrial fibrillation begets the arrhythmia by depleting dystrophin and neuronal nitric oxide synthase

Atrial fibrillation (AF) is a growing public health burden, and its treatment remains a challenge. AF leads to electrical remodeling of the atria, which in turn promotes AF maintenance and resistance to treatment. Although remodeling has long been a therapeutic target in AF, its causes remain poorly understood. We show that atrial-specific up-regulation of microRNA-31 (miR-31) in goat and human AF depletes neuronal nitric oxide synthase (nNOS) by accelerating mRNA decay and alters nNOS subcellular localization by repressing dystrophin translation. By shortening action potential duration and abolishing rate-dependent adaptation of the action potential duration, miR-31 overexpression and/or disruption of nNOS signaling recapitulates features of AF-induced remodeling and significantly increases AF inducibility in mice in vivo. By contrast, silencing miR-31 in atrial myocytes from patients with AF restores dystrophin and nNOS and normalizes action potential duration and its rate dependency. These findings identify atrial-specific up-regulation of miR-31 in human AF as a key mechanism causing atrial dystrophin and nNOS depletion, which in turn contributes to the atrial phenotype begetting this arrhythmia. miR-31 may therefore represent a potential therapeutic target in AF.

Crosstalk between RyR2 oxidation and phosphorylation contributes to cardiac dysfunction in mice with Duchenne muscular dystrophy

BACKGROUND

Patients with Duchenne muscular dystrophy (DMD) are at risk of developing cardiomyopathy and cardiac arrhythmias. Studies in a mouse model of DMD revealed that enhanced sarcoplasmic reticulum (SR) Ca(2+) leak contributes to the pathogenesis of cardiac dysfunction. In view of recent data suggesting the involvement of altered phosphorylation and oxidation of the cardiac ryanodine receptor (RyR2)/Ca(2+) release channel, we hypothesized that inhibition of RyR2 phosphorylation in a mouse model of DMD can prevent SR Ca(2+) leak by reducing RyR2 oxidation.

METHODS AND RESULTS

Confocal Ca(2+) imaging and single RyR2 channel recordings revealed that both inhibition of S2808 or S2814 phosphorylation, and inhibition of oxidation could normalize RyR2 activity in mdx mice. Moreover, Western blotting revealed that genetic inhibition of RyR2 phosphorylation at S2808 or S2814 reduced RyR2 oxidation. Production of reactive oxygen species (ROS) in myocytes from mdx mice was reduced by both inhibition of RyR2 phosphorylation or the ROS scavenger 2-mercaptopropionyl glycine (MPG). Finally, it was shown that ROS production in mdx mice is proportional to the activity of RyR2-mediated SR Ca(2+) leak, and likely generated by Nox2.

CONCLUSIONS

Increased ROS production in the hearts of mdx mice drives the progression of cardiac dysfunction. Inhibition of RyR2 phosphorylation can suppress SR Ca(2+) leak in mdx mouse hearts in part by reducing RyR2 oxidation.

Pivotal role of miR-448 in the development of ROS-induced cardiomyopathy

AIMS

Nicotinamide adenine dinucleotide oxidases (NOXs) are important contributors to cellular oxidative stress in the cardiovascular system. The NOX2 isoform is upregulated in numerous disorders, including dystrophic cardiomyopathy, where it drives the progression of the disease. However, mechanisms underlying NOX2 overexpression are still unknown. We investigated the role of microRNAs (miRs) in the regulation of NOX2 expression.

METHODS AND RESULTS

Duchenne muscular dystrophy (DMD) was used as a model of cardiomyopathy. After screening with miRNA target prediction databases and following qRT-PCR analysis, we found drastic downregulation of miR-448-3p in hearts of mdx mice, an animal model of DMD. The downregulation correlated with overexpression of the Ncf1 gene, encoding the NOX2 regulatory subunit p47(phox). Specificity of Ncf1 targeting by miR-448-3p was validated by luciferase reporter assay. Silencing of miR-448-3p in wild-type mice had a dramatic effect on cellular and functional properties of cardiac muscle as assessed by western blotting, qRT-PCR, confocal imaging, echocardiography, and histology. Acute treatment of mice with LNA-miR-448 inhibitors led to increased Ncf1 expression, abnormally elevated reactive oxygen species (ROS) production and exacerbated Ca(2+) signalling in cardiomyocytes, reminiscent of features previously observed in dystrophic cardiac cells. In addition, chronic inhibition of miR-448-3p resulted in dilated cardiomyopathy and arrhythmia, hallmarks of dystrophic cardiomyopathy.

CONCLUSIONS

Our studies suggest that downregulation of miR-448-3p leads to the increase in the expression of Ncf1 gene and p47(phox) protein, as well as to the substantial increase in NOX2-derived ROS production. Cellular oxidative stress subsequently triggers events that finally culminate in cardiac tissue damage and development of cardiomyopathy.

Pathoproteomic profiling of the skeletal muscle matrisome in dystrophinopathy associated myofibrosis

The gradual accumulation of collagen and associated proteins of the extracellular matrix is a crucial myopathological parameter of many neuromuscular disorders. Progressive tissue damage and fibrosis play a key pathobiochemical role in the dysregulation of contractile functions and often correlates with poor motor outcome in muscular dystrophies. Following a brief introduction into the role of the extracellular matrix in skeletal muscles, we review here the proteomic profiling of myofibrosis and its intrinsic role in X-linked muscular dystrophy. Although Duchenne muscular dystrophy is primarily a disease of the membrane cytoskeleton, one of its most striking histopathological features is a hyperactive connective tissue and tissue scarring. We outline the identification of novel factors involved in the modulation of the extracellular matrix in muscular dystrophy, such as matricellular proteins. The establishment of novel proteomic markers will be helpful in improving the diagnosis, prognosis, and therapy monitoring in relation to fibrotic substitution of contractile tissue. In the future, the prevention of fibrosis will be crucial for providing optimum conditions to apply novel pharmacological treatments, as well as establish cell-based approaches or gene therapeutic interventions. The elimination of secondary abnormalities in the matrisome promises to reduce tissue scarring and the loss of skeletal muscle elasticity.

Naproxcinod shows significant advantages over naproxen in the mdx model of Duchenne Muscular Dystrophy

Background

In dystrophin-deficient muscles of Duchenne Muscular Dystrophy (DMD) patients and the mdx mouse model, nitric oxide (NO) signalling is impaired. Previous studies have shown that NO-donating drugs are beneficial in dystrophic mouse models. Recently, a long-term treatment (9 months) of mdx mice with naproxcinod, an NO-donating naproxen, has shown a significant improvement of the dystrophic phenotype with beneficial effects present throughout the disease progression. It remains however to be clearly dissected out which specific effects are due to the NO component compared with the anti-inflammatory activity associated with naproxen. Understanding the contribution of NO vs the anti-inflammatory effect is important, in view of the potential therapeutic perspective, and this is the final aim of this study.

Methods

Five-week-old mdx mice received either naproxcinod (30 mg/kg) or the equimolar dose of naproxen (20 mg/kg) in the diet for 6 months. Control mdx mice were used as reference. Treatments (or vehicle for control groups) were administered daily in the diet. For the first 3 months the study was performed in sedentary animals, then all mice were subjected to exercise until the sixth month. Skeletal muscle force was assessed by measuring whole body tension in sedentary animals as well as in exercised mice and resistance to fatigue was measured after 3 months of running exercise. At the end of 6 months of treatment, animals were sacrificed for histological analysis and measurement of naproxen levels in blood and skeletal muscle.

Results

Naproxcinod significantly ameliorated skeletal muscle force and resistance to fatigue in sedentary as well as in exercised mice, reduced inflammatory infiltrates and fibrosis deposition in both cardiac and diaphragm muscles. Conversely, the equimolar dose of naproxen showed no effects on fibrosis and improved muscle function only in sedentary mice, while the beneficial effects in exercised mice were lost demonstrating a limited and short-term effect.

Conclusion

In conclusion, this study shows that NO donation may have an important role, in addition to anti-inflammatory activity, in slowing down the progression of the disease in the mdx mouse model therefore positioning naproxcinod as a promising candidate for treatment of DMD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-015-0311-0) contains supplementary material, which is available to authorized users.

Genetic manipulation of cardiac ageing

Ageing in humans is associated with a significant increase in the prevalence of cardiovascular disease. We still do not fully understand the molecular mechanisms underpinning this correlation. However, a number of insights into which genes control cardiac ageing have come from studying hearts of the fruit fly, Drosophila melanogaster. The fly's simple heart tube has similar molecular structure and basic physiology to the human heart. Also, both fly and human hearts experience significant age-related morphological and functional decline. Studies on the fly heart have highlighted the involvement of key nutrient sensing, ion channel and sarcomeric genes in cardiac ageing. Many of these genes have also been implicated in ageing of the mammalian heart. Genes that increase oxidative stress, or are linked to cardiac hypertrophy or neurodegenerative diseases in mammals also affect cardiac ageing in the fruit fly. Moreover, fly studies have demonstrated the potential of exercise and statins to treat age-related cardiac disease. These results show the value of Drosophila as a model to discover the genetic causes of human cardiac ageing.

Current understanding of molecular pathology and treatment of cardiomyopathy in duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a genetic muscle disorder caused by mutations in the Dmd gene resulting in the loss of the protein dystrophin. Patients do not only experience skeletal muscle degeneration, but also develop severe cardiomyopathy by their second decade, one of the main causes of death. The absence of dystrophin in the heart renders cardiomyocytes more sensitive to stretch-induced damage. Moreover, it pathologically alters intracellular calcium (Ca²⁺) concentration, neuronal nitric oxide synthase (nNOS) localization and mitochondrial function and leads to inflammation and necrosis, all contributing to the development of cardiomyopathy. Current therapies only treat symptoms and therefore the need for targeting the genetic defect is immense. Several preclinical therapies are undergoing development, including utrophin up-regulation, stop codon read-through therapy, viral gene therapy, cell-based therapy and exon skipping. Some of these therapies are undergoing clinical trials, but these have predominantly focused on skeletal muscle correction. However, improving skeletal muscle function without addressing cardiac aspects of the disease may aggravate cardiomyopathy and therefore it is essential that preclinical and clinical focus include improving heart function. This review consolidates what is known regarding molecular pathology of the DMD heart, specifically focusing on intracellular Ca²⁺, nNOS and mitochondrial dysregulation. It briefly discusses the current treatment options and then elaborates on the preclinical therapeutic approaches currently under development to restore dystrophin thereby improving pathology, with a focus on the heart.

Mitochondrial dysfunctions during progression of dystrophic cardiomyopathy

Duchenne muscular dystrophy (DMD) is a progressive muscle disease with severe cardiac complications. It is believed that cellular oxidative stress and augmented Ca(2+) signaling drives the development of cardiac pathology. Some mitochondrial and metabolic dysfunctions have also been reported. Here we investigate cellular mechanisms responsible for impaired mitochondrial metabolism in dystrophic cardiomyopathy at early stages of the disease. We employed electrophysiological and imaging techniques to study mitochondrial structure and function in cardiomyocytes from mdx mice, an animal model of DMD. Here we show that mitochondrial matrix was progressively oxidized in myocytes isolated from mdx mice. Moreover, an abrupt increase in workload resulted in significantly more pronounced oxidation of mitochondria in dystrophic cells. Electron micrographs revealed a gradually increased number of damaged mitochondria in mdx myocytes. Degradation in mitochondrial structure was correlated with progressive increase in mitochondrial Ca(2+) sequestration and mitochondrial depolarization, despite a substantial and persistent elevation in resting cytosolic sodium levels. Treatment of mdx cells with cyclosporine A, an inhibitor of mitochondrial permeability transition pore (mPTP), shifted both resting and workload-dependent mitochondrial redox state to the levels recorded in control myocytes. It also significantly reduced workload dependent depolarization of mitochondrial membrane in dystrophic cardiomyocytes. Overall, our studies highlight age dependent deterioration of mitochondrial function in dystrophic cardiomyocytes, which seems to be associated with excessive opening of mPTP due to oxidative stress and cellular Ca(2+) overload.

A community-engaged approach to quantifying caregiver preferences for the benefits and risks of emerging therapies for Duchenne muscular dystrophy

BACKGROUND

There is growing agreement that regulators performing benefit-risk evaluations should take patients' and caregivers' preferences into consideration. The Patient-Focused Drug Development Initiative at the US Food and Drug Administration offers patients and caregivers an enhanced opportunity to contribute to regulatory processes by offering direct testimonials. This process may be advanced by providing scientific evidence regarding treatment preferences through engagement of a broad community of patients and caregivers.

OBJECTIVE

In this article, we demonstrate a community-engaged approach to measure caregiver preferences for potential benefits and risks of emerging therapies for Duchenne muscular dystrophy (DMD).

METHODS

An advocacy oversight team led the community-engaged study. Caregivers' treatment preferences were measured by using best-worst scaling (BWS). Six relevant and understandable attributes describing potential benefits and risks of emerging DMD therapies were identified through engagement with advocates (n = 5), clinicians (n = 9), drug developers from pharmaceutical companies and academic centers (n = 11), and other stakeholders (n = 5). The attributes, each defined across 3 levels, included muscle function, life span, knowledge about the drug, nausea, risk of bleeds, and risk of arrhythmia. Cognitive interviewing with caregivers (n = 7) was used to refine terminology and assess acceptability of the BWS instrument. The study was implemented through an online survey of DMD caregivers, who were recruited in the United States through an advocacy group and snowball sampling. Caregivers were presented with 18 treatment profiles, identified via a main-effect orthogonal experimental design, in which the dependent variable was the respondents' judgment as to the best and worst feature in each profile. Preference weights were estimated by calculating the relative number of times a feature was chosen as best and as worst, which were then used to estimate relative attribute importance.

RESULTS

A total of 119 DMD caregivers completed the BWS instrument; they were predominately biological mothers (67.2%), married (89.9%), and white (91.6%). Treatment effect on muscle function was the most important among experimental attributes (28.7%), followed by risk of heart arrhythmia (22.4%) and risk of bleeding (21.2%). Having additional postapproval data was relatively the least important attribute (2.3%).

CONCLUSIONS

We present a model process for advocacy organizations aiming to promote patient-centered drug development. The community-engaged approach was successfully used to develop and implement a survey to measure caregiver preferences. Caregivers were willing to accept a serious risk when balanced with a noncurative treatment, even absent improvement in life span. These preferences should inform the Food and Drug Administration's benefit-risk assessment of emerging DMD therapies. This study highlights the synergistic integration of traditional advocacy methods and scientific approach to quantify benefit-risk preferences.

Histological and biochemical outcomes of cardiac pathology in mdx mice with dietary quercetin enrichment

NEW FINDINGS

What is the central question of this study? Does dietary quercetin enrichment improve biochemical and histological outcomes in hearts from mdx mice? What is the main finding and what is its importance? Biochemical and histological findings suggest that chronic quercetin feeding of mdx mice may improve mitochondrial function and attenuate tissue pathology. Patients with Duchenne muscular dystrophy suffer from cardiac pathology, which causes up to 40% of all deaths because of fibrosis and cardiac complications. Quercetin is a flavonol with anti-inflammatory and antioxidant effects and is also an activator of peroxisome proliferator-activated receptor γ coactivator 1α capable of antioxidant upregulation, mitochondrial biogenesis and prevention of cardiac complications. We sought to determine the extent to which dietary quercetin enrichment prevents (experiment 1) and rescues cardiac pathology (experiment 2) in mdx mice. In experiment 1, 3-week-old mdx mice were fed control chow (C3w6m, n = 10) or chow containing 0.2% quercetin for 6 months (Q3w6m, n = 10). In experiment 2, 3-month-old mdx mice were fed control chow (C3m6m, n = 10) or 0.2% chow containing 0.2% quercetin for 6 months (Q3m6m, n = 10). Hearts were excised for histological and biochemical analyses. In experiment 1, Western blot targets for mitochondrial biogenesis (cytochrome c, P = 0.007) and antioxidant expression (superoxide dismutase 2, P = 0.014) increased in Q3w6m mice compared with C3w6m. Histology revealed increased utrophin (P = 0.025) and decreased matrix metalloproteinase 9 abundance (P = 0.040) in Q3w6m mice compared with C3w6m. In experiment 2, relative (P = 0.023) and absolute heart weights (P = 0.020) decreased in Q3m6m mice compared with C3m6m. Indications of damage (Haematoxylin- and Eosin-stained sections, P = 0.007) and Western blot analysis of transforming growth factor β1 (P = 0.009) were decreased in Q3m6m mice. Six months of quercetin feeding increased a mitochondrial biomarker, antioxidant protein and utrophin and decreased matrix metalloproteinase 9 in young mice. Given that these adaptations are associated with attenuated cardiac pathology and damage, the present findings may indicate that dietary quercetin enrichment attenuates dystrophic cardiac pathology, but physiological confirmation is needed.

Blunted cardiac beta-adrenergic response as an early indication of cardiac dysfunction in Duchenne muscular dystrophy

AIMS

To determine whether altered beta-adrenergic responses contribute to early cardiac dysfunction in mdx (X-linked muscular dystrophy) mice, an animal model for human Duchenne muscular dystrophy.

METHODS AND RESULTS

Replacement fibrosis in mdx hearts gradually increased with age, suggesting a gradual loss of cardiomyocytes. Echocardiography and intra-left ventricular haemodynamic measurements detected baseline cardiac dysfunction in mdx mice at ≥8 months. However, a reduction of cardiac beta-adrenergic response to isoproterenol (ISO) was already present in mdx mice at 4 months. Ventricular myocytes (VMs) isolated from 4- and 8-month-old mdx mice had greater baseline contractile function {fractional shortening, [Ca(2+)]i, and sarcoplasmic reticulum (SR) Ca(2+) content} and ICa-L than age-matched control VMs and than myocytes isolated from 2-month-old mdx mice. ISO increased myocyte function in the VMs of 4- and 8-month-old mdx mice to the same level as in age-matched control VMs. In the VMs of 12-month-old mdx mice, ISO failed to increase myocyte function to the level in VMs of 12-month-old control mice and could not further increaseICa-L. No differences were observed in the expression of Cav1.2α1c, Cav1.2β1, Cav1.2β2, sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA), and the Na(+)/Ca(2+) exchanger. In contrast, total ryanodine receptor 2 (RyR2) and basal phosphorylation of RyR2, phospholamban, and Cav1.2α1c were found to be increased in hearts of 4-month-old mdx mice; baseline protein kinase A activity was also increased. After ISO treatment, phosphorylation levels were the same in mdx and control hearts. VMs of 4-month-old mdx mice had reduced beta1-adrenergic receptor (β1-AR) density and beta-adrenergic sensitivity.

CONCLUSION

In young mdx mice, the myocyte increases its contractile function to compensate for myocyte loss. However, these myocytes with enhanced baseline function have reduced potential for stimulation, decreased β1-AR density/sensitivity, leading to blunted cardiac beta-adrenergic response.

Pharmacological prospects in the treatment of Duchenne muscular dystrophy

PURPOSE OF REVIEW

The most encouraging recent advances regarding pharmacological agents for treating Duchenne muscular dystrophy (DMD) are summarized. Emphasis is given to compounds acting downstream of dystrophin, the protein lacking in DMD, on cellular pathways leading to pathological consequences. The author highlights the progress that may have the greatest potential for clinical use in DMD.

RECENT FINDINGS

Modifying the transcripts of the mutated gene by exon skipping has led to expression of shortened dystrophins in DMD patients. Currently, the most promising potential drugs are the exon-skipping agents eteplirsen and drisapersen. Biglycan and SMTC1100 upregulate utrophin. The steroid receptor modulating compounds VBP15 and tamoxifen, and specific antioxidants appear promising agents for symptomatic therapy.

SUMMARY

The past 18 months have seen a strong increase in the number of exciting reports on novel therapeutic agents for DMD. Exon-skipping agents have been fine-tuned to improve tissue delivery and stability. Impressive discoveries regarding pathogenic events in cellular signalling have revealed targets that were unknown in the context of DMD, thus enabling approaches that limit inflammation, fibrosis and necrosis. The targets are nuclear hormone receptors, NADPH-oxidases and Ca channels. Inhibition of NF-KB, transforming growth factor-alpha (TGF-α) and transforming growth factor-beta (TGF-β)/myostatin production or action are also promising routes in counteracting the complex pathogenesis of DMD.

Proteomic profiling of the dystrophin-deficient mdx phenocopy of dystrophinopathy-associated cardiomyopathy

Cardiorespiratory complications are frequent symptoms of Duchenne muscular dystrophy, a neuromuscular disorder caused by primary abnormalities in the dystrophin gene. Loss of cardiac dystrophin initially leads to changes in dystrophin-associated glycoproteins and subsequently triggers secondarily sarcolemmal disintegration, fibre necrosis, fibrosis, fatty tissue replacement, and interstitial inflammation. This results in progressive cardiac disease, which is the cause of death in a considerable number of patients afflicted with X-linked muscular dystrophy. In order to better define the molecular pathogenesis of this type of cardiomyopathy, several studies have applied mass spectrometry-based proteomics to determine proteome-wide alterations in dystrophinopathy-associated cardiomyopathy. Proteomic studies included both gel-based and label-free mass spectrometric surveys of dystrophin-deficient heart muscle from the established mdx animal model of dystrophinopathy. Comparative cardiac proteomics revealed novel changes in proteins associated with mitochondrial energy metabolism, glycolysis, signaling, iron binding, antibody response, fibre contraction, basal lamina stabilisation, and cytoskeletal organisation. This review summarizes the importance of studying cardiomyopathy within the field of muscular dystrophy research, outlines key features of the mdx heart and its suitability as a model system for studying cardiac pathogenesis, and discusses the impact of recent proteomic findings for exploring molecular and cellular aspects of cardiac abnormalities in inherited muscular dystrophies.

Mouse models of heart failure: cell signaling and cell survival

Heart failure is one of the paramount global causes of morbidity and mortality. Despite this pandemic need, the available clinical counter-measures have not altered substantially in recent decades, most notably in the context of pharmacological interventions. Cell death plays a causal role in heart failure, and its inhibition poses a promising approach that has not been thoroughly explored. In previous approaches to target discovery, clinical failures have reflected a deficiency in mechanistic understanding, and in some instances, failure to systematically translate laboratory findings toward the clinic. Here, we review diverse mouse models of heart failure, with an emphasis on those that identify potential targets for pharmacological inhibition of cell death, and on how their translation into effective therapies might be improved in the future.

Tissue-resident Sca1+ PDGFRα+ mesenchymal progenitors are the cellular source of fibrofatty infiltration in arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (AC) is a disease of the heart involving myocardial dystrophy leading to fibrofatty scarring of the myocardium and is associated with an increased risk of both ventricular arrhythmias and sudden cardiac death. It often affects the right ventricle but may also involve the left. Although there has been significant progress in understanding the role of underlying desmosomal genetic defects in AC, there is still a lack of data regarding the cellular processes involved in its progression. The development of cardiac fibrofatty scarring is known to be a principal pathological process associated with ventricular arrhythmias, and it is vital that we elucidate the role of various cell populations involved in the disease if targeted therapeutics are to be developed. The known role of mesenchymal progenitor cells in the reparative process of both the heart and skeletal muscle has provided inspiration for the identification of the cellular basis of fibrofatty infiltration in AC. Here we hypothesize that reparative processes triggered by myocardial degeneration lead to the differentiation of tissue-resident Sca1+ PDGFRα+ mesenchymal progenitors into adipocytes and fibroblasts, which compose the fibrofatty lesions characteristic of AC.