Treatment of dystrophin cardiomyopathies

Cardiomyopathy in Duchenne Muscular Dystrophy and the Potential for Mitochondrial Therapeutics to Improve Treatment Response

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease caused by mutations to the dystrophin gene, resulting in deficiency of dystrophin protein, loss of myofiber integrity in skeletal and cardiac muscle, and eventual cell death and replacement with fibrotic tissue. Pathologic cardiac manifestations occur in nearly every DMD patient, with the development of cardiomyopathy-the leading cause of death-inevitable by adulthood. As early cardiac abnormalities are difficult to detect, timely diagnosis and appropriate treatment modalities remain a challenge. There is no cure for DMD; treatment is aimed at delaying disease progression and alleviating symptoms. A comprehensive understanding of the pathophysiological mechanisms is crucial to the development of targeted treatments. While established hypotheses of underlying mechanisms include sarcolemmal weakening, upregulation of pro-inflammatory cytokines, and perturbed ion homeostasis, mitochondrial dysfunction is thought to be a potential key contributor. Several experimental compounds targeting the skeletal muscle pathology of DMD are in development, but the effects of such agents on cardiac function remain unclear. The synergistic integration of small molecule- and gene-target-based drugs with metabolic-, immune-, or ion balance-enhancing compounds into a combinatorial therapy offers potential for treating dystrophin deficiency-induced cardiomyopathy, making it crucial to understand the underlying mechanisms driving the disorder.

Inhibition of miR-25 ameliorates cardiac and skeletal muscle dysfunction in aged mdx/utrn haploinsufficient (+/-) mice

Dystrophic cardiomyopathy is a significant feature of Duchenne muscular dystrophy (DMD). Increased cardiomyocyte cytosolic calcium (Ca2+) and interstitial fibrosis are major pathophysiological hallmarks that ultimately result in cardiac dysfunction. MicroRNA-25 (miR-25) has been identified as a suppressor of both sarcoplasmic reticulum calcium ATPase 2a (SERCA2a) and mothers against decapentaplegic homolog-7 (Smad7) proteins. In this study, we created a gene transfer using an miR-25 tough decoy (TuD) RNA inhibitor delivered via recombinant adeno-associated virus serotype 9 (AAV9) to evaluate the effect of miR-25 inhibition on cardiac and skeletal muscle function in aged dystrophin/utrophin haploinsufficient mice mdx/utrn (+/-), a validated transgenic murine model of DMD. We found that the intravenous delivery of AAV9 miR-25 TuD resulted in strong and stable inhibition of cardiac miR-25 levels, together with the restoration of SERCA2a and Smad7 expression. This was associated with the amelioration of cardiomyocyte interstitial fibrosis as well as recovered cardiac function. Furthermore, the direct quadricep intramuscular injection of AAV9 miR-25 TuD significantly restored skeletal muscle Smad7 expression, reduced tissue fibrosis, and enhanced skeletal muscle performance in mdx/utrn (+/-) mice. These results imply that miR-25 TuD gene transfer may be a novel therapeutic approach to restore cardiomyocyte Ca2+ homeostasis and abrogate tissue fibrosis in DMD.

Influence of β1 Adrenergic Receptor Genotype on Longitudinal Measures of Left Ventricular Ejection Fraction and Responsiveness to ß-Blocker Therapy in Patients With Duchenne Muscular Dystrophy

The purpose of this study was to determine whether the longitudinal progression of decline in left ventricular ejection fraction (LVEF) in Duchenne muscular dystrophy (DMD) patients is moderated by ADRB1 genotype and whether the efficacy of ß-blocker therapy is influenced by genotype status. About 147 DMD patients (6-34 years.) were analyzed with a focus on β₁ adrenergic receptor (ADRB1) genotype variants. Patients were grouped by ADRB1 genotype resulting in Gly389 patients and Arg389 patients. A generalized additive mixed effects model was used to examine differences in the nonlinear trend of LVEF across patient ages between genotype groups and for ß-blocker use. Both genotype groups displayed a progressive decline in LVEF starting around the mean age of ambulation loss (~12 years). However, there was no difference between genotype groups in the progression of decline in LVEF. There was a significant effect of ß-blocker use on longitudinal LVEF, wherein patients on ß-blockers had systematically lower LVEF when compared to patients not on ß-blockers. However, the effect of ß-blocker therapy on LVEF was not affected by ADRB1 genotype. The current study did not demonstrate an influence of patient ADRB1 genotype on longitudinal LVEF in our cohort. Despite previous literature suggesting a positive influence of ß-blocker use on cardiac function in DMD patients and of an ADRB1 genotypic difference in responsiveness to ß-blocker use, we did not observe this in our cohort. Interestingly, our cohort did not demonstrate a positive influence of ß-blocker use on LVEF measures.

Longitudinal changes in cardiac function in Duchenne muscular dystrophy population as measured by magnetic resonance imaging

BACKGROUND

The lack of dystrophin in cardiomyocytes in Duchenne muscular dystrophy (DMD) is associated with progressive decline in cardiac function eventually leading to death by 20-40 years of age. The aim of this prospective study was to determine rate of progressive decline in left ventricular (LV) function in Duchenne muscular dystrophy (DMD) over 5 years.

METHODS

Short axis cine and grid tagged images of the LV were acquired in individuals with DMD (n = 59; age = 5.3-18.0 years) yearly, and healthy controls at baseline (n = 16, age = 6.0-18.3 years) on a 3 T MRI scanner. Grid-tagged images were analyzed for composite circumferential strain (ℇcc%) and ℇcc% in six mid LV segments. Cine images were analyzed for left ventricular ejection fraction (LVEF), LV mass (LVM), end-diastolic volume (EDV), end-systolic volume (ESV), LV atrioventricular plane displacement (LVAPD), and circumferential uniformity ratio estimate (CURE). LVM, EDV, and ESV were normalized to body surface area for a normalized index of LVM (LVMI), EDV (EDVI) and ESV (ESVI).

RESULTS

At baseline, LV ℇcc% was significantly worse in DMD compared to controls and five of the six mid LV segments demonstrated abnormal strain in DMD. Longitudinal measurements revealed that ℇcc% consistently declined in individuals with DMD with the inferior segments being more affected. LVEF progressively declined between 3 to 5 years post baseline visit. In a multivariate analysis, the use of cardioprotective drugs trended towards positively impacting cardiac measures while loss of ambulation and baseline age were associated with negative impact. Eight out of 17 cardiac parameters reached a minimal clinically important difference with a threshold of 1/3 standard deviation.

CONCLUSION

The study shows a worsening of circumferential strain in dystrophic myocardium. The findings emphasize the significance of early and longitudinal assessment of cardiac function in DMD and identify early biomarkers of cardiac dysfunction to help design clinical trials to mitigate cardiac pathology. This study provides valuable non-invasive and non-contrast based natural history data of cardiac changes which can be used to design clinical trials or interpret the results of current trials aimed at mitigating the effects of decreased cardiac function in DMD.

Cardiac MRI of Hereditary Cardiomyopathy

Hereditary cardiomyopathy comprises a heterogeneous group of diseases of the cardiac muscle that are characterized by the presence of genetic mutations. Cardiac MRI is central to evaluation of patients with cardiomyopathy owing to its ability to allow evaluation of many different tissue properties in a single examination. For example, cine MRI is the standard of care for assessment of myocardial structure and function. It clearly shows regions of asymmetric wall thickening that are typical of hypertrophic cardiomyopathy and allows it to be differentiated from other hereditary disorders such as Fabry disease or transthyretin cardiac amyloidosis that produce concentric hypertrophy. Late gadolinium enhancement provides a different tissue property and allows these latter two causes of concentric hypertrophy to be distinguished on the basis of their enhancement appearances (Fabry disease shows midwall basal inferolateral enhancement, and amyloidosis shows global subendocardial enhancement). Native T1 mapping may similarly allow differentiation between Fabry disease and amyloidosis without the use of contrast material. T2*-weighted MRI is important in the detection and quantification of iron overload cardiomyopathy. Other hereditary entities for which comprehensive MRI has proven essential include Danon disease, familial dilated cardiomyopathy, hereditary muscular dystrophy, arrhythmogenic right ventricular cardiomyopathy, and ventricular noncompaction. As a result of the diagnostic power of cardiac MRI, cardiac MRI examinations are being requested with increasing frequency, not only in academic centers but also in community practices. The genetic background, pathophysiologic characteristics, and clinical presentation of patients with hereditary cardiomyopathy are described; the characteristic cardiac MRI features of hereditary cardiomyopathy are discussed; and the role of MRI in risk stratification, treatment, and prognostication in patients with cardiomyopathy is reviewed. ^©RSNA, 2022 Online supplemental material is available for this article.

Therapeutic Exon Skipping Through a CRISPR-Guided Cytidine Deaminase Rescues Dystrophic Cardiomyopathy in Vivo

BACKGROUND

Loss of dystrophin protein causes Duchenne muscular dystrophy (DMD), characterized by progressive degeneration of cardiac and skeletal muscles, and mortality in adolescence or young adulthood. Although cardiac failure has risen as the leading cause of mortality in patients with DMD, effective therapeutic interventions remain underdeveloped, in part, because of the lack of a suitable preclinical model.

METHODS

We analyzed a novel murine model of DMD created by introducing a 4-bp deletion into exon 4, one of the exons encoding the actin-binding domain 1 of dystrophin (referred to as Dmd^E4* mice). Echocardiography, microcomputed tomography, muscle force measurement, and histological analysis were performed to determine cardiac and skeletal muscle defects in these mice. Using this model, we examined the feasibility of using a cytidine base editor to install exon skipping and rescue dystrophic cardiomyopathy in vivo. AAV9-based CRISPR/Cas9-AID (eTAM) together with AAV9-sgRNA was injected into neonatal Dmd^E4* mice, which were analyzed 2 or 12 months after treatment to evaluate the extent of exon skipping, dystrophin restoration, and phenotypic improvements of cardiac and skeletal muscles.

RESULTS

Dmd^E4* mice recapitulated many aspects of human DMD, including shortened life span (by ≈50%), progressive cardiomyopathy, kyphosis, profound loss of muscle strength, and myocyte degeneration. A single-dose administration of AAV9-eTAM instituted >50% targeted exon skipping in the Dmd transcripts and restored up to 90% dystrophin in the heart. As a result, early ventricular remodeling was prevented and cardiac and skeletal muscle functions were improved, leading to an increased life span of the Dmd^E4* mice. Despite gradual decline of AAV vector and base editor expression, dystrophin restoration and pathophysiological rescue of muscular dystrophy were long lasted for at least 1 year.

CONCLUSIONS

Our study demonstrates the feasibility and efficacy to institute exon skipping through an enhanced TAM (eTAM) for therapeutic application(s).

Increased tissue stiffness triggers contractile dysfunction and telomere shortening in dystrophic cardiomyocytes

Duchenne muscular dystrophy (DMD) is a rare X-linked recessive disease that is associated with severe progressive muscle degeneration culminating in death due to cardiorespiratory failure. We previously observed an unexpected proliferation-independent telomere shortening in cardiomyocytes of a DMD mouse model. Here, we provide mechanistic insights using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Using traction force microscopy, we show that DMD hiPSC-CMs exhibit deficits in force generation on fibrotic-like bioengineered hydrogels, aberrant calcium handling, and increased reactive oxygen species levels. Furthermore, we observed a progressive post-mitotic telomere shortening in DMD hiPSC-CMs coincident with downregulation of shelterin complex, telomere capping proteins, and activation of the p53 DNA damage response. This telomere shortening is blocked by blebbistatin, which inhibits contraction in DMD cardiomyocytes. Our studies underscore the role of fibrotic stiffening in the etiology of DMD cardiomyopathy. In addition, our data indicate that telomere shortening is progressive, contraction dependent, and mechanosensitive, and suggest points of therapeutic intervention.

Multiomic Approaches to Uncover the Complexities of Dystrophin-Associated Cardiomyopathy

Despite major progress in treating skeletal muscle disease associated with dystrophinopathies, cardiomyopathy is emerging as a major cause of death in people carrying dystrophin gene mutations that remain without a targeted cure even with new treatment directions and advances in modelling abilities. The reasons for the stunted progress in ameliorating dystrophin-associated cardiomyopathy (DAC) can be explained by the difficulties in detecting pathophysiological mechanisms which can also be efficiently targeted within the heart in the widest patient population. New perspectives are clearly required to effectively address the unanswered questions concerning the identification of authentic and effectual readouts of DAC occurrence and severity. A potential way forward to achieve further therapy breakthroughs lies in combining multiomic analysis with advanced preclinical precision models. This review presents the fundamental discoveries made using relevant models of DAC and how omics approaches have been incorporated to date.

Targeting of CAT and VCAM1 as Novel Therapeutic Targets for DMD Cardiomyopathy

Duchenne muscular dystrophy (DMD) related cardiomyopathy is the leading cause of early mortality in DMD patients. There is an urgent need to gain a better understanding of the disease molecular pathogenesis and develop effective therapies to prevent the onset of heart failure. In the present study, we used DMD human induced pluripotent stem cells (DMD-hiPSCs) derived cardiomyocytes (CMs) as a platform to explore the active compounds in commonly used Chinese herbal medicine (CHM) herbs. Single CHM herb (DaH, ZK, and CQZ) reduced cell beating rate, decreased cellular ROS accumulation, and improved structure of DMD hiPSC-CMs. Cross-comparison of transcriptomic profiling data and active compound library identified nine active chemicals targeting ROS neutralizing Catalase (CAT) and structural protein vascular cell adhesion molecule 1 (VCAM1). Treatment with Quecetin, Kaempferol, and Vitamin C, targeting CAT, conferred ROS protection and improved contraction; treatment with Hesperidin and Allicin, targeting VCAM1, induced structure enhancement via induction of focal adhesion. Lastly, overexpression of CAT or VCAM1 in DMD hiPSC-CMs reconstituted efficacious effects and conferred increase in cardiomyocyte function. Together, our results provide a new insight in treating DMD cardiomyopathy via targeting of CAT and VCAM1, and serves as an example of translating Bed to Bench back to Bed using a muti-omics approach.

Essential roles of the dystrophin-glycoprotein complex in different cardiac pathologies

The dystrophin-glycoprotein complex (DGC), situated at the sarcolemma dynamically remodels during cardiac disease. This review examines DGC remodeling as a common denominator in diseases affecting heart function and health. Dystrophin and the DGC serve as broad cytoskeletal integrators that are critical for maintaining stability of muscle membranes. The presence of pathogenic variants in genes encoding proteins of the DGC can cause absence of the protein and/or alterations in other complex members leading to muscular dystrophies. Targeted studies have allowed the individual functions of affected proteins to be defined. The DGC has demonstrated its dynamic function, remodeling under a number of conditions that stress the heart. Beyond genetic causes, pathogenic processes also impinge on the DGC, causing alterations in the abundance of dystrophin and associated proteins during cardiac insult such as ischemia-reperfusion injury, mechanical unloading, and myocarditis. When considering new therapeutic strategies, it is important to assess DGC remodeling as a common factor in various heart diseases. The DGC connects the internal F-actin-based cytoskeleton to laminin-211 of the extracellular space, playing an important role in the transmission of mechanical force to the extracellular matrix. The essential functions of dystrophin and the DGC have been long recognized. DGC based therapeutic approaches have been primarily focused on muscular dystrophies, however it may be a beneficial target in a number of disorders that affect the heart. This review provides an account of what we now know, and discusses how this knowledge can benefit persistent health conditions in the clinic.

Biochemical and biomechanical characteristics of dystrophin-deficient mdx3cv mouse lens

The molecular and cellular basis for cataract development in mice lacking dystrophin, a scaffolding protein that links the cytoskeleton to the extracellular matrix, is poorly understood. In this study, we characterized lenses derived from the dystrophin-deficient mdx3cv mouse model. Expression of Dp71, a predominant isoform of dystrophin in the lens, was induced during lens fiber cell differentiation. Dp71 was found to co-distribute with dystroglycan, connexin-50 and 46, aquaporin-0, and NrCAM as a large cluster at the center of long arms of the hexagonal fibers. Although mdx3cv mouse lenses exhibited dramatically reduced levels of Dp71, only older lenses revealed punctate nuclear opacities compared to littermate wild type (WT) lenses. The levels of dystroglycan, syntrophin, and dystrobrevin which comprise the dystrophin-associated protein complex (DAPC), and NrCAM, connexin-50, and aquaporin-0, were significantly lower in the lens membrane fraction of adult mdx3cv mice compared to WT mice. Additionally, decreases were observed in myosin light chain phosphorylation and lens stiffness together with a significant elevation in the levels of utrophin, a functional homolog of dystrophin in mdx3cv mouse lenses compared to WT lenses. The levels of perlecan and laminin (ligands of α-dystroglycan) remained normal in dystrophin-deficient lens fibers. Taken together, although mdx3cv mouse lenses exhibit only minor defects in lens clarity possibly due to a compensatory increase in utrophin, the noted disruptions of DAPC, stability, and organization of membrane integral proteins of fibers, and stiffness of mdx3cv lenses reveal the importance of dystrophin and DAPC in maintaining lens clarity and function.

Proteome-wide Changes in the mdx-4cv Spleen due to Pathophysiological Cross Talk with Dystrophin-Deficient Skeletal Muscle

Duchenne muscular dystrophy is primarily characterized by progressive muscle wasting due to deficiency in the membrane cytoskeletal protein dystrophin but is also associated with body-wide cellular disturbances in a variety of non-muscle tissues. In this study, we have focused on the comparative proteomic analysis of the spleen and established considerable changes in this crucial secondary lymphoid organ from the genetic mdx-4cv mouse model of dystrophinopathy. An apparent short isoform of dystrophin and associated glycoproteins were identified in spleen by mass spectrometry but appear not be affected in muscular dystrophy. In contrast, the mdx-4cv spleen showed significant proteome-wide changes in other protein species that are involved in metabolism, signaling, and cellular architecture. Since the spleen plays a key role in the immune response, these proteomic alterations may reflect pathophysiological cross talk between the lymphoid system and dystrophic muscles, which are affected by both fiber degeneration and inflammation.

"Betwixt Mine Eye and Heart a League Is Took": The Progress of Induced Pluripotent Stem-Cell-Based Models of Dystrophin-Associated Cardiomyopathy

The ultimate goal of precision disease modeling is to artificially recreate the disease of affected people in a highly controllable and adaptable external environment. This field has rapidly advanced which is evident from the application of patient-specific pluripotent stem-cell-derived precision therapies in numerous clinical trials aimed at a diverse set of diseases such as macular degeneration, heart disease, spinal cord injury, graft-versus-host disease, and muscular dystrophy. Despite the existence of semi-adequate treatments for tempering skeletal muscle degeneration in dystrophic patients, nonischemic cardiomyopathy remains one of the primary causes of death. Therefore, cardiovascular cells derived from muscular dystrophy patients' induced pluripotent stem cells are well suited to mimic dystrophin-associated cardiomyopathy and hold great promise for the development of future fully effective therapies. The purpose of this article is to convey the realities of employing precision disease models of dystrophin-associated cardiomyopathy. This is achieved by discussing, as suggested in the title echoing William Shakespeare's words, the settlements (or "leagues") made by researchers to manage the constraints ("betwixt mine eye and heart") distancing them from achieving a perfect precision disease model.

Transition from Childhood to Adulthood in Patients with Duchenne Muscular Dystrophy

Recently, progress has been observed in the knowledge about Duchenne Muscular Dystrophy (DMD), which is a severe and commonly diagnosed genetic myopathy in childhood, historically resulting in early death. Currently, there are a lot of methods available to improve the clinical course of DMD and extend patients’ life expectancy to more than 30 years of age. The key issue for DMD patients is the period between 16–18 years of age, which is described as a transition from pediatric- to adult-oriented healthcare. Adolescents and adults with DMD have highly complex healthcare needs associated with long-term steroid usage, orthopedic, ventilation, cardiac, and gastrointestinal problems. The current paper provides a comprehensive overview of special healthcare needs related to the transfer of a patient with DMD from child-oriented to adult-oriented care. Additionally, the need to organize effective care for adults with DMD is presented.

Antagonism of the Thromboxane-Prostanoid Receptor as a Potential Therapy for Cardiomyopathy of Muscular Dystrophy

Background Muscular dystrophy (MD) causes a progressive cardiomyopathy characterized by diffuse fibrosis, arrhythmia, heart failure, and early death. Activation of the thromboxane-prostanoid receptor (TPr) increases calcium transients in cardiomyocytes and is proarrhythmic and profibrotic. We hypothesized that TPr activation contributes to the cardiac phenotype of MD, and that TPr antagonism would improve cardiac fibrosis and function in preclinical models of MD. Methods and Results Three different mouse models of MD (mdx/utrn double knockout, second generation mdx/mTR double knockout, and delta-sarcoglycan knockout) were given normal drinking water or water containing 25 mg/kg per day of the TPr antagonist ifetroban, beginning at weaning. After 6 months (10 weeks for mdx/utrn double knockout), mice were evaluated for cardiac and skeletal muscle function before euthanization. There was a 100% survival rate of ifetroban-treated mice to the predetermined end point, compared with 60%, 43%, and 90% for mdx/utrn double knockout, mdx/mTR double knockout, and delta-sarcoglycan knockout mice, respectively. TPr antagonism improved cardiac output in mdx/utrn double knockout and mdx/mTR mice, and normalized fractional shortening, ejection fraction, and other parameters in delta-sarcoglycan knockout mice. Cardiac fibrosis in delta-sarcoglycan knockout was reduced with TPr antagonism, which also normalized cardiac expression of claudin-5 and neuronal nitric oxide synthase proteins and multiple signature genes of Duchenne MD. Conclusions TPr antagonism reduced cardiomyopathy and spontaneous death in mouse models of Duchenne and limb-girdle MD. Based on these studies, ifetroban and other TPr antagonists could be novel therapeutics for treatment of the cardiac phenotype in patients with MD.

Natural History of Cardiomyopathy in Adult Dogs With Golden Retriever Muscular Dystrophy

Background

Duchenne muscular dystrophy (DMD) is an X‐linked disease that causes progressive muscle weakness. Affected boys typically die from respiratory or cardiac failure. Golden retriever muscular dystrophy (GRMD) is genetically homologous with DMD and causes analogous skeletal and cardiac muscle disease. Previous studies have detailed features of GRMD cardiomyopathy in mostly young dogs. Cardiac disease is not well characterized in adult GRMD dogs, and cardiac magnetic resonance (CMR) imaging studies have not been completed.

Methods and Results

We evaluated echocardiography and CMR in 24 adult GRMD dogs at different ages. Left ventricular systolic and diastolic functions, wall thickness, and myocardial strain were assessed with echocardiography. Features evaluated with CMR included left ventricular function, chamber size, myocardial mass, and late gadolinium enhancement. Our results largely paralleled those of DMD cardiomyopathy. Ejection fraction and fractional shortening correlated well with age, with systolic dysfunction occurring at ≈30 to 45 months. Circumferential strain was more sensitive than ejection fraction in early disease detection. Evidence of left ventricular chamber dilatation provided proof of dilated cardiomyopathy. Late gadolinium enhancement imaging showed DMD‐like left ventricular lateral wall lesions and earlier involvement of the anterior septum. Multiple functional indexes were graded objectively and added, with and without late gadolinium enhancement, to give cardiac and cardiomyopathy scores of disease severity. Consistent with DMD, there was parallel skeletal muscle involvement, as tibiotarsal joint flexion torque declined in tandem with cardiac function.

Conclusions

This study established parallels of progressive cardiomyopathy between dystrophic dogs and boys, further validating GRMD as a model of DMD cardiac disease.

Human induced pluripotent stem cell models for the study and treatment of Duchenne and Becker muscular dystrophies

Duchenne and Becker muscular dystrophies are the most common muscle diseases and are both currently incurable. They are caused by mutations in the dystrophin gene, which lead to the absence or reduction/truncation of the encoded protein, with progressive muscle degeneration that clinically manifests in muscle weakness, cardiac and respiratory involvement and early death. The limits of animal models to exactly reproduce human muscle disease and to predict clinically relevant treatment effects has prompted the development of more accurate in vitro skeletal muscle models. However, the challenge of effectively obtaining mature skeletal muscle cells or satellite stem cells as primary cultures has hampered the development of in vitro models. Here, we discuss the recently developed technologies that enable the differentiation of skeletal muscle from human induced pluripotent stem cells (iPSCs) of Duchenne and Becker patients. These systems recapitulate key disease features including inflammation and scarce regenerative myogenic capacity that are partially rescued by genetic and pharmacological therapies and can provide a useful platform to study and realize future therapeutic treatments. Implementation of this model also takes advantage of the developing genome editing field, which is a promising approach not only for correcting dystrophin, but also for modulating the underlying mechanisms of skeletal muscle development, regeneration and disease. These data prove the possibility of creating an accurate Duchenne and Becker in vitro model starting from iPSCs, to be used for pathogenetic studies and for drug screening to identify strategies capable of stopping or reversing muscular dystrophinopathies and other muscle diseases.

Stabilization of the cardiac sarcolemma by sarcospan rescues DMD-associated cardiomyopathy

In the current preclinical study, we demonstrate the therapeutic potential of sarcospan (SSPN) overexpression to alleviate cardiomyopathy associated with Duchenne muscular dystrophy (DMD) utilizing dystrophin-deficient mdx mice with utrophin haploinsufficiency that more accurately represent the severe disease course of human DMD. SSPN interacts with dystrophin, the DMD disease gene product, and its autosomal paralog utrophin, which is upregulated in DMD as a partial compensatory mechanism. SSPN transgenic mice have enhanced abundance of fully glycosylated α-dystroglycan, which may further protect dystrophin-deficient cardiac membranes. Baseline echocardiography reveals SSPN improves systolic function and hypertrophic indices in mdx and mdx:utr-heterozygous mice. Assessment of SSPN transgenic mdx mice by hemodynamic pressure-volume methods highlights enhanced systolic performance compared to mdx controls. SSPN restores cardiac sarcolemma stability, the primary defect in DMD disease, reduces fibrotic response and improves contractile function. We demonstrate that SSPN ameliorates more advanced cardiac disease in the context of diminished sarcolemma expression of utrophin and β1D integrin that mitigate disease severity and partially restores responsiveness to β-adrenergic stimulation. Overall, our current and previous findings suggest SSPN overexpression in DMD mouse models positively impacts skeletal, pulmonary and cardiac performance by addressing the stability of proteins at the sarcolemma that protect the heart from injury, supporting SSPN and membrane stabilization as a therapeutic target for DMD.

Comprehensive evaluation of structural and functional myocardial impairments in Becker muscular dystrophy using quantitative cardiac magnetic resonance imaging

Aims

Becker muscular dystrophy (BMD) is a genetic neuromuscular disease characterized by an alteration of the dystrophin protein. Myocardial involvement is frequent, eventually progressing to a dilated cardiomyopathy, and represents the most common cause of death for this pathology. We performed a comprehensive evaluation of myocardial functional and structural alterations encountered in a large cohort of BMD patients using quantitative cardiac magnetic resonance (CMR) imaging.

Methods and results

Eighty-eight BMD patients and 26 age-matched volunteers underwent standard cine and tag imaging to assess myocardial function and dyssynchrony, while native T1, T2, and extracellular volume fraction (ECV) were measured for tissue characterization. The left ventricular ejection fraction (LV-EF) was significantly reduced in 26% of the BMD patients. Patients exhibited higher dyssynchrony index than controls (6.94 ± 3.17 vs. 5.09 ± 1.25, P = 0.005). Diastolic dyssynchrony also exists in patients where systolic function was normal. BMD subjects, compared with controls, had significantly higher native T1, T2, and ECV (1183 ± 60 ms vs. 1164 ± 22 ms, 47.5 ± 4.5 ms vs. 45.6 ± 3.4 ms, 0.282 ± 0.050 vs. 0.231 ± 0.027, respectively, P < 0.05). Native T1, T2, and ECV correlated with LV-EF (R = −0.79, −0.70, and −0.71, respectively, P < 0.001) and N-terminal-pro brain natriuretic peptide (R = 0.51, 0.58, and 0.44, respectively, P < 0.001).

Conclusion

Quantitative CMR represents a powerful tool to evaluate structural and functional impairments in the myocardium of BMD subjects. Native T1, T2, and ECV provided quantitative biomarkers related to inflammation and fibrosis, and could stratify disease severity.

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.

NF-κB inhibition rescues cardiac function by remodeling calcium genes in a Duchenne muscular dystrophy model

Duchenne muscular dystrophy (DMD) is a neuromuscular disorder causing progressive muscle degeneration. Although cardiomyopathy is a leading mortality cause in DMD patients, the mechanisms underlying heart failure are not well understood. Previously, we showed that NF-κB exacerbates DMD skeletal muscle pathology by promoting inflammation and impairing new muscle growth. Here, we show that NF-κB is activated in murine dystrophic (mdx) hearts, and that cardiomyocyte ablation of NF-κB rescues cardiac function. This physiological improvement is associated with a signature of upregulated calcium genes, coinciding with global enrichment of permissive H3K27 acetylation chromatin marks and depletion of the transcriptional repressors CCCTC-binding factor, SIN3 transcription regulator family member A, and histone deacetylase 1. In this respect, in DMD hearts, NF-κB acts differently from its established role as a transcriptional activator, instead promoting global changes in the chromatin landscape to regulate calcium genes and cardiac function.

Neuromuscular diseases with hypertrophic cardiomyopathy

[first paragraph of article]Neuromuscular disorders are frequently associated with cardiac abnormalities, even in pediatric population. Cardiac involvement includes both structural changes and conduction disease. In general, HCM is a rare manifestation of neuromuscular diseases. Autosomal dominant inheritance with mutations in sarcomeric genes are described in about 60% of young adults and adult population with HCM. Other genetic disorders, such as inherited metabolic and neuromuscular diseases and other chromosome abnormalities are responsible of 5–10% of HCM in adults. We review the most frequent neuromuscular diseases related with HCM.

A novel mutation of dystrophin in a Becker muscular dystrophy family with severe cardiac involvement: from genetics to clinicopathology

BACKGROUND

Dystrophin gene defects are the pathogenic molecular basis of Becker muscular dystrophy (BMD), characterised by skeletal myopathy and cardiomyopathy. Because of the broad phenotype spectrum, it was difficult to use the traditional diagnostic method to achieve an early accurate diagnosis of BMD-associated cardiomyopathy.

METHODS

We applied an in-house gene panel testing and a gene-filtering strategy to investigate the genetic defect in a four-generation family with 73 members. The proband had a heart transplant due to heart failure; the explanted heart was subjected to a careful pathological analysis.

RESULTS

A novel small in-frame mutation (c.4998_5000 del CAG, p.1667 del Ala) of the dystrophin gene was identified and co-segregated in the affected family members. By using the image segmentation technology, we found the left ventricular free wall demonstrated severe fibrofatty replacement of cardiac myocytes from the epicardium to the endocardium.

CONCLUSION

We identified a novel dystrophin mutation (p.1667 del Ala), resulting in BMD-associated cardiomyopathy that demonstrated the pathological features of significant fibrofatty replacement in the sub-epicardial layer of the ventricle; further, the high-throughput sequencing is helpful for making an early diagnosis of BMD.

Consensus on the diagnosis, treatment and follow-up of patients with Duchenne muscular dystrophy

INTRODUCTION

Duchenne muscular dystrophy (DMD) is the most common myopathy in children, with a worldwide prevalence of approximately 0.5 cases per 10,000 male births. It is characterised by a progressive muscular weakness manifesting in early childhood, with the subsequent appearance of musculoskeletal, respiratory, and cardiac complications, causing disability, dependence, and premature death. Currently, DMD is mainly managed with multidisciplinary symptomatic treatment, with favourable results in terms of the progression of the disease. It is therefore crucial to establish clear, up-to-date guidelines enabling early detection, appropriate treatment, and monitoring of possible complications.

DEVELOPMENT

We performed a literature search of the main biomedical databases for articles published in the last 10years in order to obtain an overview of the issues addressed by current guidelines and to identify relevant issues for which no consensus has yet been established. The degree of evidence and level of recommendation of the information obtained were classified and ordered according to the criteria of the American Academy of Neurology.

CONCLUSIONS

DMD management should be multidisciplinary and adapted to the patient's profile and the stage of clinical progression. In addition to corticotherapy, treatment targeting gastrointestinal, respiratory, cardiac, and orthopaedic problems, as well as physiotherapy, should be provided with a view to improving patients' quality of life. Genetic studies play a key role in the management of the disease, both in detecting cases and potential carriers and in characterising the mutation involved and developing new therapies.

Diagnosis and management of Duchenne muscular dystrophy, part 2: respiratory, cardiac, bone health, and orthopaedic management

A coordinated, multidisciplinary approach to care is essential for optimum management of the primary manifestations and secondary complications of Duchenne muscular dystrophy (DMD). Contemporary care has been shaped by the availability of more sensitive diagnostic techniques and the earlier use of therapeutic interventions, which have the potential to improve patients' duration and quality of life. In part 2 of this update of the DMD care considerations, we present the latest recommendations for respiratory, cardiac, bone health and osteoporosis, and orthopaedic and surgical management for boys and men with DMD. Additionally, we provide guidance on cardiac management for female carriers of a disease-causing mutation. The new care considerations acknowledge the effects of long-term glucocorticoid use on the natural history of DMD, and the need for care guidance across the lifespan as patients live longer. The management of DMD looks set to change substantially as new genetic and molecular therapies become available.

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.

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.

Pharmacological therapy for the prevention and management of cardiomyopathy in Duchenne muscular dystrophy: A systematic review

Cardiomyopathy is a major source of morbidity and mortality in Duchenne muscular dystrophy (DMD) patients now that respiratory care has improved. There is currently no definitive evidence guiding the management of DMD-associated cardiomyopathy (DMD-CM). The objective of this systematic review was to evaluate the effectiveness of pharmacotherapies for the prevention and/or management of DMD-CM and to determine the optimal timing to commence these interventions. A systematic search was conducted in January 2016 using MEDLINE, EMBASE and CINAHL databases and grey literature sources for studies evaluating the use of angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers, beta-blockers or aldosterone antagonists. Study quality assessment was conducted using the Downs and Black quality assessment checklist. PRISMA reporting guidelines were used. Of the 15 studies included in this review, most were of low methodological quality. Meta-analysis was not possible due to heterogeneity of studies. ACE inhibitors, angiotensin receptor blockers, beta-blockers and/or aldosterone antagonists tended to improve or preserve left ventricular systolic function and delay the progression of DMD-CM. While there is evidence supporting the use of heart failure medication in patients with DMD, data regarding these interventions for delaying the onset of DMD-CM and when to initiate therapy are lacking. PROSPERO registration: CRD42015029555.

Young at Heart: Pioneering Approaches to Model Nonischaemic Cardiomyopathy with Induced Pluripotent Stem Cells

A mere 9 years have passed since the revolutionary report describing the derivation of induced pluripotent stem cells from human fibroblasts and the first in-patient translational use of cells obtained from these stem cells has already been achieved. From the perspectives of clinicians and researchers alike, the promise of induced pluripotent stem cells is alluring if somewhat beguiling. It is now evident that this technology is nascent and many areas for refinement have been identified and need to be considered before induced pluripotent stem cells can be routinely used to stratify, treat and cure patients, and to faithfully model diseases for drug screening purposes. This review specifically addresses the pioneering approaches to improve induced pluripotent stem cell based models of nonischaemic cardiomyopathy.

miR-410 and miR-495 Are Dynamically Regulated in Diverse Cardiomyopathies and Their Inhibition Attenuates Pathological Hypertrophy

Noncoding RNAs have emerged as important modulators in cardiac development and pathological remodeling. Recently, we demonstrated that regulation of the Gtl2-Dio3 noncoding RNA locus is dependent on the MEF2 transcription factor in cardiac muscle, and that two of its encoded miRNAs, miR-410 and miR-495, induce robust cardiomyocyte proliferation. Given the possibility of manipulating the expression of these miRNAs to repair the damaged heart by stimulating cardiomyocyte proliferation, it is important to determine whether the Gtl2-Dio3 noncoding RNAs are regulated in cardiac disease and whether they function downstream of pathological cardiac stress signaling. Therefore, we examined expression of the above miRNAs processed from the Gtl2-Dio3 locus in various cardiomyopathies. These noncoding RNAs were upregulated in all cardiac disease models examined including myocardial infarction (MI) and chronic angiotensin II (Ang II) stimulation, and in the cardiomyopathies associated with muscular dystrophies. Consistent with these observations, we show that the Gtl2-Dio3 proximal promoter is activated by stress stimuli in cardiomyocytes and requires MEF2 for its induction. Furthermore, inhibiting miR-410 or miR-495 in stressed cardiomyocytes attenuated the hypertrophic response. Thus, the Gtl2-Dio3 noncoding RNA locus is a novel marker of cardiac disease and modulating the activity of its encoded miRNAs may mitigate pathological cardiac remodeling in these diseases.

Heart Disease in Disorders of Muscle, Neuromuscular Transmission, and the Nerves

Little is known regarding cardiac involvement (CI) by neuromuscular disorders (NMDs). The purpose of this review is to summarise and discuss the major findings concerning the types, frequency, and severity of cardiac disorders in NMDs as well as their diagnosis, treatment, and overall outcome. CI in NMDs is characterized by pathologic involvement of the myocardium or cardiac conduction system. Less commonly, additional critical anatomic structures, such as the valves, coronary arteries, endocardium, pericardium, and even the aortic root may be involved. Involvement of the myocardium manifests most frequently as hypertrophic or dilated cardiomyopathy and less frequently as restrictive cardiomyopathy, non-compaction, arrhythmogenic right-ventricular dysplasia, or Takotsubo-syndrome. Cardiac conduction defects and supraventricular and ventricular arrhythmias are common cardiac manifestations of NMDs. Arrhythmias may evolve into life-threatening ventricular tachycardias, asystole, or even sudden cardiac death. CI is common and carries great prognostic significance on the outcome of dystrophinopathies, laminopathies, desminopathies, nemaline myopathy, myotonias, metabolic myopathies, Danon disease, and Barth-syndrome. The diagnosis and treatment of CI in NMDs follows established guidelines for the management of cardiac disease, but cardiotoxic medications should be avoided. CI in NMDs is relatively common and requires complete work-up following the establishment of a neurological diagnosis. Appropriate cardiac treatment significantly improves the overall long-term outcome of NMDs.

SIRT1: A Novel Target for the Treatment of Muscular Dystrophies

Muscular dystrophies are inherited myogenic disorders accompanied by progressive skeletal muscle weakness and degeneration. Duchenne muscular dystrophy (DMD) is the most common and severe form of muscular dystrophy and is caused by mutations in the gene that encodes the cytoskeletal protein dystrophin. The treatment for DMD is limited to glucocorticoids, which are associated with multiple side effects. Thus, the identification of novel therapeutic targets is urgently needed. SIRT1 is an NAD⁺-dependent histone/protein deacetylase that plays roles in diverse cellular processes, including stress resistance and cell survival. Studies have shown that SIRT1 activation provides beneficial effects in the dystrophin-deficient mdx mouse, a model of DMD. SIRT1 activation leads to the attenuation of oxidative stress and inflammation, a shift from the fast to slow myofiber phenotype, and the suppression of tissue fibrosis. Although further research is needed to clarify the molecular mechanisms underlying the protective role of SIRT1 in mdx mice, we propose SIRT1 as a novel therapeutic target for patients with muscular dystrophies.

Animal models of Duchenne muscular dystrophy: from basic mechanisms to gene therapy

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disorder. It is caused by loss-of-function mutations in the dystrophin gene. Currently, there is no cure. A highly promising therapeutic strategy is to replace or repair the defective dystrophin gene by gene therapy. Numerous animal models of DMD have been developed over the last 30 years, ranging from invertebrate to large mammalian models. mdx mice are the most commonly employed models in DMD research and have been used to lay the groundwork for DMD gene therapy. After ~30 years of development, the field has reached the stage at which the results in mdx mice can be validated and scaled-up in symptomatic large animals. The canine DMD (cDMD) model will be excellent for these studies. In this article, we review the animal models for DMD, the pros and cons of each model system, and the history and progress of preclinical DMD gene therapy research in the animal models. We also discuss the current and emerging challenges in this field and ways to address these challenges using animal models, in particular cDMD dogs.

An overview of muscle diseases presenting in adulthood

Patients with muscle disease present not only to neurologists, but also to rheumatologists and general physicians. This article provides a framework of how to approach patients with suspected muscle disease, and reviews the clinical features of the most frequently encountered acquired and genetic conditions in adult practice.

Nanopatterned Human iPSC-based Model of a Dystrophin-Null Cardiomyopathic Phenotype

Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) offer unprecedented opportunities to study inherited heart conditions in vitro, but are phenotypically immature, limiting their ability to effectively model adult-onset diseases. Cardiomyopathy is becoming the leading cause of death in patients with Duchenne muscular dystrophy (DMD), but the pathogenesis of this disease phenotype is not fully understood. Therefore, we aimed to test whether biomimetic nanotopography could further stratify the disease phenotype of DMD hiPSC-CMs to create more translationally relevant cardiomyocytes for disease modeling applications. We found that anisotropic nanotopography was necessary to distinguish structural differences between normal and DMD hiPSC-CMs, as these differences were masked on conventional flat substrates. DMD hiPSC-CMs exhibited a diminished structural and functional response to the underlying nanotopography compared to normal cardiomyocytes at both the macroscopic and subcellular levels. This blunted response may be due to a lower level of actin cytoskeleton turnover as measured by fluorescence recovery after photobleaching. Taken together these data suggest that DMD hiPSC-CMs are less adaptable to changes in their extracellular environment, and highlight the utility of nanotopographic substrates for effectively stratifying normal and structural cardiac disease phenotypes in vitro.

X-Linked Dilated Cardiomyopathy: A Cardiospecific Phenotype of Dystrophinopathy

X-linked dilated cardiomyopathy (XLDCM) is a distinct phenotype of dystrophinopathy characterized by preferential cardiac involvement without any overt skeletal myopathy. XLDCM is caused by mutations of the Duchenne muscular dystrophy (DMD) gene and results in lethal heart failure in individuals between 10 and 20 years. Patients with Becker muscular dystrophy, an allelic disorder, have a milder phenotype of skeletal muscle involvement compared to Duchenne muscular dystrophy (DMD) and sometimes present with dilated cardiomyopathy. The precise relationship between mutations in the DMD gene and cardiomyopathy remain unclear. However, some hypothetical mechanisms are being considered to be associated with the presence of some several dystrophin isoforms, certain reported mutations, and an unknown dystrophin-related pathophysiological mechanism. Recent therapy for Duchenne muscular dystrophy, the severe dystrophinopathy phenotype, appears promising, but the presence of XLDCM highlights the importance of focusing on cardiomyopathy while elucidating the pathomechanism and developing treatment.

Dysregulation of calcium homeostasis in muscular dystrophies

Muscular dystrophies are a group of diseases characterised by the primary wasting of skeletal muscle, which compromises patient mobility and in the most severe cases originate a complete paralysis and premature death. Existing evidence implicates calcium dysregulation as an underlying crucial event in the pathophysiology of several muscular dystrophies, such as dystrophinopathies, calpainopathies or myotonic dystrophy among others. Duchenne muscular dystrophy is the most frequent myopathy in childhood, and calpainopathy or LGMD2A is the most common form of limb-girdle muscular dystrophy, whereas myotonic dystrophy is the most frequent inherited muscle disease worldwide. In this review, we summarise recent advances in our understanding of calcium ion cycling through the sarcolemma, the sarcoplasmic reticulum and mitochondria, and its involvement in the pathogenesis of these dystrophies. We also discuss some of the clinical implications of recent findings regarding Ca2+ handling as well as novel approaches to treat muscular dystrophies targeting Ca2+ regulatory proteins.

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.