Hearts Of Mdx Mice Research Articles

Therapeutic potential of hiPSC-derived cardiomyocytes for Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) results in progressive and incurable cardiomyopathy, leading to significant morbidity and mortality due to heart failure. There is currently no effective cure for DMD that can correct the genetic defects and compensate for the lack of dystrophin. Therefore, the therapeutic strategies that focus on the transplantation of induced pluripotent stem cells (iPSCs) derived cardiomyocytes are promising options, and remain to be investigated to which extent they can restrain the cardiomyocyte loss phenotype and improve cardiac function. There has been significant progress in the differentiation of cardiomyocytes (CMs) from hiPSCs (human iPSCs). Three hiPSC lines: AICS-0011, 029 iPS clone 4-PCBC, and PCBC16iPS were investigated based on previously published culture and differentiation methods. We will inject differentiated CMs into the heart of Mdx mice that are mutated or deficient for NOD-scid, IL2Rg to allow for xenotransplantation engraftment. Having confirmed the effcient differentiation of CMs from all three hiPSC lines, the next step will be to transplant CMs. The engraftment rate after transplantation will be quantified by IHC staining for human lamin A/C and the relative level of genomic human DNA from isolated hearts. Correction of dystrophin expression will be measured via IHC for dystrophin. Echocardiography will be performed to measure improvement in cardiac systolic or diastolic function. If therapeutic transplantation of hiPSC-CMs is possible, it could improve the survival of DMD patients. This project was supported by RMM091621DS008, NIH155993, and NIH160665. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Cardioprotection and Suppression of Fibrosis by Diverse Cancer and Non-Cancer Cell Lines in a Murine Model of Duchenne Muscular Dystrophy.

The dynamic relationship between heart failure and cancer poses a dual challenge. While cardiac remodeling can promote cancer growth and metastasis, tumor development can ameliorate cardiac dysfunction and suppress fibrosis. However, the precise mechanism through which cancer influences the heart and fibrosis is yet to be uncovered. To further explore the interaction between heart failure and cancer, we used the MDX mouse model, which suffers from cardiac fibrosis and cardiac dysfunction. A previous study from our lab demonstrated that tumor growth improves cardiac dysfunction and dampens fibrosis in the heart and diaphragm muscles of MDX mice. We used breast Polyoma middle T (PyMT) and Lewis lung carcinoma (LLC) cancer cell lines that developed into large tumors. To explore whether the aggressiveness of the cancer cell line is crucial for the beneficial phenotype, we employed a PyMT breast cancer cell line lacking integrin β1, representing a less aggressive cell line compared to the original PyMT cells. In addition, we examined immortalized and primary MEF cells. The injection of integrin β1 KO PyMT cancer cells and Mouse Embryo Fibroblasts cells (MEF) resulted in the improvement of cardiac function and decreased fibrosis in the heart, diaphragm, and skeletal muscles of MDX mice. Collectively, our data demonstrate that the cancer line aggressiveness as well as primary MEF cells are sufficient to impose the beneficial phenotype. These discoveries present potential novel clinical therapeutic approaches with beneficial outcome for patients with fibrotic diseases and cardiac dysfunction that do not require tumor growth.

Uridine Administration Promotes Normalization of Heart Mitochondrial Function in Dystrophin-Deficient Mice and Decreases Tissue Fibrosis.

The work shows the effect of the metabolic modulator uridine on the functioning and ultrastructure of heart mitochondria in dystrophin-deficient mdx mice. Intraperitoneal administration of uridine (30 mg/kg/day for 28 days) improved K+ transport and increased its content in the heart mitochondria of mdx mice to the level of wild-type animals. This was accompanied by a significant decrease in the level of malondialdehyde and an increase in the number of mitochondria in the heart of mdx mice. At the same time, uridine did not affect the hyperfunctionality of mitochondria in mdx mice, which manifested in an increase in the calcium retention capacity. Nevertheless, we noted that uridine causes a significant decrease in the level of fibrosis in the heart of mdx mice, which attested to a positive effect of therapy.

Effect of the large-conductance calcium-dependent k<sup>+</sup> channel activator NS1619 on the function of mitochondria in the heart of dystrophin-deficient mice

Dystrophin-deficient muscular dystrophy (Duchenne dystrophy) is characterized by impaired ion homeostasis, in which mitochondria play an important role. In the present work, using a model of dystrophin-deficient mdx mice, we revealed a decrease in the efficiency of potassium ion transport and the total content of this ion in heart mitochondria. We evaluated the effect of chronic administration of the benzimidazole derivative NS1619, which is an activator of the large-conductance Ca2+-dependent K+ channel (mitoBKCa) on the structure and function of organelles and the state of the heart muscle. It was shown that NS1619 improves K+ transport and increases the content of the ion in the heart mitochondria of mdx mice, but this is not associated with changes in the level of the mitoBKCa protein and the expression of the encoding gene. The effect of NS1619 was accompanied by a decrease in the intensity of oxidative stress, assessed by the level of lipid peroxidation products (MDA products) and normalization of the mitochondrial ultrastructure in the heart of mdx mice. In addition, we found positive changes in the tissue, expressed in a decrease in the level of fibrosis in the heart of dystrophin-deficient animals treated with NS1619. It was noted that NS1619 had no significant effect on the structure and function of heart mitochondria in wild-type animals. The paper discusses the mechanisms of influence of NS1619 on the function of mouse heart mitochondria in Duchenne muscular dystrophy and the prospects for applying this approach to correct pathology.

Abstract 13964: A Microtubule-Connexin-43 Feed-Forward Loop Suppresses Arrhythmias in Duchenne Muscular Dystrophy Mice

Dilated cardiomyopathy is the leading cause of death in patients with Duchenne muscular dystrophy (DMD), a lethal neuromuscular disorder that affects 1 in 5,000 males. We identified pathological remodeling of gap-junction protein Connexin-43 (Cx43) is a strong contributor towards DMD-related cardiomyopathy, which occurs primarily through a reduction in post-translational phosphorylation of Cx43 serine residues 325/328/330. We hypothesized that the organization of the microtubules (MTs) regulates the phospho-status of Cx43, and that the phospho-status of Cx43 regulates the organization of the MTs. To study a potential regulation of Cx43 by MTs, we delivered colchicine (Colch), a MT-regulator that reduces oxidative stress and corrects MT organization, into the DMD mouse model (mdx) and in Cx43-phosphorylation-deficient mdx mice (mdxS3A). We found that, while Colch treatment prevented the formation and aberrant activity of remodeled Cx43 in the hearts of mdx mice, it did not prevent aberrant activities in the hearts of mdxS3A mice. Thereby, Colch treatment did not prevent severe cardiac conduction in Isoproterenol-stressed mdxS3A mice, while it protected against Isoproterenol-induced arrhythmias in mdx mice. To study a potential regulation of MTs by Cx43, we evaluated the MT cytoskeleton in Cx43-phospho-mimicking mdx mice (mdxS3E). We found that the MT organization of mdxS3E isolated cardiomyocytes resembled that of wild-type. Lastly, to assess the potency of S3E in rescuing fibrosis in severe models of DMD-cardiomyopathy, we studied mdxS3E mice with partial absence of utrophin (utr). We found that S3E conferred protection against fibrosis in mdxutr(+/-)S3E relative to mdxutr(+/-) mice. In sum, Cx43-triplet phosphorylation depends on proper organization of the MT cytoskeleton, and the organization of the MT cytoskeleton depends on Cx43-triplet phosphorylation. This dual dependency creates a feed-forward mechanistic loop, which is disrupted in DMD-cardiomyopathy leading to MT disarray, arrhythmias and long-term fibrosis. The pathology is prevented either by forcing corrections in the MTs with Colch or in Cx43 with S3E. Thus, the impactful intersection between MTs and Cx43 can be harnessed for future cardiovascular disease studies.

Reduced Na+ current in Purkinje fibers explains cardiac conduction defects and arrhythmias in Duchenne muscular dystrophy.

Cardiac arrhythmias significantly contribute to mortality in Duchenne muscular dystrophy (DMD), a degenerative muscle disease triggered by mutations in the gene encoding for the intracellular protein dystrophin. A major source for the arrhythmias in patients with DMD is impaired ventricular impulse conduction, which predisposes for ventricular asynchrony, decreased cardiac output, and the development of reentrant mechanisms. The reason for ventricular conduction impairments and the associated arrhythmias in the dystrophic heart has remained unidentified. In the present study, we explored the hypothesis that dystrophin-deficient cardiac Purkinje fibers have reduced Na+ currents (INa), which would represent a potential mechanism underlying slowed ventricular conduction in the dystrophic heart. Therefore, by using a Langendorff perfusion system, we isolated Purkinje fibers from the hearts of adult wild-type control and dystrophin-deficient mdx mice. Enhanced green fluorescent protein (eGFP) expression under control of the connexin 40 gene allowed us to discriminate Purkinje fibers from eGFP-negative ventricular working cardiomyocytes after cell isolation. Finally, we recorded INa from wild-type and dystrophic mdx Purkinje fibers for comparison by means of the whole cell patch clamp technique. We found substantially reduced INa densities in mdx compared with wild-type Purkinje fibers, suggesting that dystrophin deficiency diminishes INa. Because Na+ channels in the Purkinje fiber membrane represent key determinants of ventricular conduction velocity, we propose that reduced INa in Purkinje fibers at least partly explains impaired ventricular conduction and the associated arrhythmias in the dystrophic heart.NEW & NOTEWORTHY Dystrophic cardiac Purkinje fibers have abnormally reduced Na+ current densities. This explains impaired ventricular conduction in the dystrophic heart.

Expression of the organic cation/carnitine transporter family (Octn1,-2 and-3) in mdx muscle and heart: Implications for early carnitine therapy in Duchenne muscular dystrophy to improve cellular carnitine homeostasis

IntroductionCarnitine is essential for long-chain fatty acid oxidation in muscle and heart. Tissue stores are regulated by organic cation/Cn transporter plasmalemmal Octn2. We previously demonstrated low carnitine in quadriceps/gluteus and heart of adult mdx mice. MethodsWe studied protein and mRNA expression of Octn2, mitochondrial Octn1 and peroxisomal Octn3 in adult male C57BL/10ScSn-DMD mdx/J quadriceps, heart, and diaphragm compared to C57BL/10SnJ mice. ResultsWe demonstrated reduction in mOctn2 expression on Western blot and similar expression of mOctn1 and mOctn3 in mdx quadriceps, heart and diaphragm. There was a significant upregulation of mOctn1 and mOctn2 mRNA by qRT-PCR in mdx quadriceps and of mOctn2 and mOctn3 mRNA in mdx heart. We showed upregulation of mdx mOctn1 and mOctn3 mRNA but no increase in protein expression. DiscussionDystrophin deficiency likely disrupts Octn2 expression decreasing muscle carnitine uptake thus contributing to membranotoxic long-chain acyl-CoAs with sarcolemmal and organellar membrane oxidative injury providing a treatment rationale for early L-carnitine in DMD.

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 forDMD 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 1day after birth did not negatively alter hemodynamic function, tested at 3months 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 2months of age significantly improved stroke volume and cardiac output compared to mock-treated mice analyzed at 17months, 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.

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.

Resveratrol Ameliorates Mitophagy Disturbance and Improves Cardiac Pathophysiology of Dystrophin-deficient mdx Mice

Autophagy activation improves the phenotype in mdx mice, a Duchenne muscular dystrophy (DMD) model, although the underlying mechanisms are obscure. We previously found that resveratrol, a strong inducer of autophagy, ameliorates the cardiac pathology of mdx mice. Autophagy could eliminate damaged mitochondria, a major source of intracellular reactive oxygen species (ROS), although there is no evidence for mitochondriopathy in dystrophic cardiomyopathy. To elucidate resveratrol’s function, we investigated the deletion of mitochondrial DNA (mtDNA), autophagy of damaged mitochondria (mitophagy), and ROS accumulation in the mdx mouse heart. Low levels of normal mtDNA and abnormal accumulations of mitochondria-containing autophagosomes were found in the mdx mouse heart. Administering resveratrol to mdx mice for 56 weeks ameliorated the cardiomyopathy, with significant reductions in the amount of mtDNA deletion, the number of mitochondria-containing autophagosomes, and the ROS levels. Resveratrol induced nuclear FoxO3a accumulation and the expression of autophagy-related genes, which are targets of FoxOs. The most effective dose in mdx mice was 0.4 g resveratrol/kg food. In conclusion, resveratrol improved cardiomyopathy by promoting mitophagy in the mdx mouse heart. We propose that acquired mitochondriopathy worsens the pathology of DMD and is a potential therapeutic target for the cardiomyopathy in DMD patients.

Exosome-Derived Dystrophin from Allograft Myogenic Progenitors Improves Cardiac Function in Duchenne Muscular Dystrophic Mice.

Progressive cardiomyocyte loss in Duchenne muscular dystrophy (DMD) leads to cardiac fibrosis, cardiomyopathy, and eventually heart failure. In the present study, we observed that myogenic progenitor cells (MPC) carry mRNA for the dystrophin gene. We tested whether cardiac function can be improved in DMD by allograft transplantation of MPC-derived exosomes (MPC-Exo) into the heart to restore dystrophin protein expression. Exo from C2C12 cells (an MPC cell line) or vehicle were delivered locally into the hearts of MDX mice. After 2days of treatment, we observed that MPC-Exo restored dystrophin expression in the hearts of MDX mice, which correlated with improved myocardial function in dystrophin-deficient MDX mouse hearts. In conclusion, this study demonstrated that allogeneic WT-MPC-Exo transplantation transiently restored dystrophin gene expression and improved cardiac function in MDX mice, suggesting that allogenic exosomal delivery may serve as an alternative treatment for cardiomyopathy of DMD.

Increased sarco-endoplasmic reticulum – mitochondria interaction and mitochondrial dysfunction in dystrophin-deficient mdx heart

Sarco-endoplasmic reticulum (SR/ER) calcium leak due to post-transcriptional type-2 ryanodine receptor (RyR2) modifications and mitochondrial dysfunction are two main defects observed in the heart of mdx mice, the murine model of Duchenne muscular dystrophy. However, whether SR/ER-mitochondria interaction is involved in the development of the pathology remain unknown in heart. The aim of the present study was to determine the potential link between calcium leak and the mitochondrial metabolism dysfunction in mdx mice. In ventricular cardiomyocytes isolated from mdx mice, we characterized, by Western blot, the post-transcriptional RyR2 modifications at 1 month of age and we observed an increase of S-nitrosylation and carboxylation of the RyR2. Using Proximity Ligand Assay experiment, we showed an increase of contact points between the SR/ER and mitochondria, which induces higher mitochondrial calcium, content in 3 month-old mdx mice. Using oxygraphy experiments, we observed a severe decrease of the maximal respiration driven by β-oxidation pathway at the same age. This metabolism dysfunction is associated with an increase in the production of radical oxygen species (ROS) attested by a higher Mitosox fluorescence. Our data demonstrate for the first time that at the early stage of the pathology the excessive SR/ER-mitochondria coupling is associated with an increase of calcium uptake by mitochondria. Higher calcium content is in turn involved in a mitochondrial dysfunction which induces ROS production.

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

SummaryGenetic 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.

Deficit in PINK1/PARKIN-mediated mitochondrial autophagy at late stages of dystrophic cardiomyopathy.

Duchenne muscular dystrophy (DMD) is an inherited devastating muscle disease with severe and often lethal cardiac complications. Emerging evidence suggests that the evolution of the pathology in DMD is accompanied by the accumulation of mitochondria with defective structure and function. Here, we investigate whether defects in the housekeeping autophagic pathway contribute to mitochondrial and metabolic dysfunctions in dystrophic cardiomyopathy. We employed various biochemical and imaging techniques to assess mitochondrial structure and function as well as to evaluate autophagy, and specific mitochondrial autophagy (mitophagy), in hearts of mdx mice, an animal model of DMD. Our results indicate substantial structural damage of mitochondria and a significant decrease in ATP production in hearts of mdx animals, which developed cardiomyopathy. In these hearts, we also detected enhanced autophagy but paradoxically, mitophagy appeared to be suppressed. In addition, we found decreased levels of several proteins involved in the PINK1/PARKIN mitophagy pathway as well as an insignificant amount of PARKIN protein phosphorylation at the S65 residue upon induction of mitophagy. Our results suggest faulty mitophagy in dystrophic hearts due to defects in the PINK1/PARKIN pathway.

Dystrophin-glycoprotein complex sequesters Yap to inhibit cardiomyocyte proliferation.

SummaryThe regenerative capacity of the adult mammalian heart is limited because of the reduced ability of cardiomyocytes (CMs) to progress through mitosis1. The regenerative capacity of endogenous CMs exists at birth but is lost postnatally, with subsequent organ growth occurring through CM hypertrophy2,3. The Hippo pathway, a conserved kinase cascade, inhibits CM proliferation in the developing heart to control heart size and in the adult heart to prevent regeneration4,5. The dystrophin glycoprotein complex (DGC), a multicomponent transmembrane complex linking the actin cytoskeleton to extracellular matrix, is essential for CM homeostasis. DGC deficiency in humans results in muscular dystrophy, including lethal Duchenne muscular dystrophy (DMD). We found that the DGC component dystroglycan 1 (DAG1) directly binds to Hippo pathway effector Yap to inhibit CM proliferation. The Yap-DAG1 interaction was enhanced by Hippo-induced Yap phosphorylation, revealing a connection between Hippo pathway function and the DGC. After injury, Hippo-deficient postnatal hearts maintained organ size control by repairing the defect with correct dimensions, whereas postnatal hearts doubly deficient for Hippo and the DGC showed CM overproliferation at the injury site. In mature Mdx mouse hearts—a model of DMD—Hippo deficiency protected against overload-induced heart failure.

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

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 12months, while control C57 mice were fed a control diet. Cardiac function was assessed via 7T magnetic resonance imaging at 2, 10 and 14months. At 14months, hearts were harvested for histology and Western blotting. The results indicated an mdx strain-dependent decline in cardiac performance at 14months 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, cytochromec, electron transport chain complexes I-V, citrate synthase, superoxide dismutase2 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.

Chemotaxis and Immunoregulatory Function of Cardiac γδ T Cells in Dystrophin-Deficient Mice.

Duchenne muscular dystrophy (DMD) is a fatal X-linked disorder caused by mutations in the dystrophin gene that lead to degeneration of skeletal and cardiac muscles and to chronic inflammation. Despite the importance of γδ T cells in many diseases, this cellular subpopulation has not been described in DMD patients or in mdx mice, a widely used mouse model for studying DMD. Therefore, in this study, we aimed to evaluate the migration of γδ T cells to the cardiac muscle of mdx mice and to characterize their phenotype and functional activity. We observed no migration of γδ T cells to skeletal muscles, but these cells were found in the hearts of mdx mice during the study period, reaching a peak in 12-wk-old mice. These cells migrate primarily owing to CCL2 and CCL5 chemokines produced by cardiac tissue, and they are Vγ1+/CD27+ and thus produce high levels of IFN-γ. In vivo depletion of the γδ T cells revealed γδ T cell-dependent cardiac inflammatory immunoregulation, with increased numbers of CD3+CD4+, CD3+CD8+, and, in particular, F4/80+ cells in the heart and increased cardiac damage in mdx mice. We also observed in vitro that purified cardiac Γδ T cells are cytotoxic against adherent endomysial cardiac cells, mostly macrophages, but not against peritoneal cells, in a perforin/granzyme-dependent manner. Our present data indicate that γδ T cells exert protective effects on the hearts of mdx mice, possibly by selectively killing pathogenic macrophages, and this function may be important for the late onset of cardiac damage in DMD.

Nicorandil, a Nitric Oxide Donor and ATP-Sensitive Potassium Channel Opener, Protects Against Dystrophin-Deficient Cardiomyopathy.

Dystrophin-deficient cardiomyopathy is a growing clinical problem without targeted treatments. We investigated whether nicorandil promotes cardioprotection in human dystrophin-deficient induced pluripotent stem cell (iPSC)-derived cardiomyocytes and the muscular dystrophy mdx mouse heart. Dystrophin-deficient iPSC-derived cardiomyocytes had decreased levels of endothelial nitric oxide synthase and neuronal nitric oxide synthase. The dystrophin-deficient cardiomyocytes had increased cell injury and death after 2 hours of stress and recovery. This was associated with increased levels of reactive oxygen species and dissipation of the mitochondrial membrane potential. Nicorandil pretreatment was able to abolish these stress-induced changes through a mechanism that involved the nitric oxide-cyclic guanosine monophosphate pathway and mitochondrial adenosine triphosphate-sensitive potassium channels. The increased reactive oxygen species levels in the dystrophin-deficient cardiomyocytes were associated with diminished expression of select antioxidant genes and increased activity of xanthine oxidase. Furthermore, nicorandil was found to improve the restoration of cardiac function after ischemia and reperfusion in the isolated mdx mouse heart. Nicorandil protects against stress-induced cell death in dystrophin-deficient cardiomyocytes and preserves cardiac function in the mdx mouse heart subjected to ischemia and reperfusion injury. This suggests a potential therapeutic role for nicorandil in dystrophin-deficient cardiomyopathy.

20. A Novel Approach in the Treatment of Dystrophic Cardiomyopathy

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy with a worldwide incidence of one in 3500 live male births. It is caused by the lack of dystrophin, a critical muscle protein that connects the cytoskeleton and the extracellular matrix (ECM). Cardiomyopathy develops in at least 90% of patients and alone can shorten the life expectancy of DMD patients by at least 2 years and up to 40% of DMD patients eventually die from heart failure. Recently, RNA-guided, nuclease-mediated genome editing based on type II CRISPR (clustered regularly interspaced short palindromic repeat)/Cas (CRISPR-associated) system, has been emerged to alter the genome. In this study, we hypothesize that CRISPR-mediated genome editing could offer a novel therapy for DMD-associated cardiomyopathy in live mice. Two gRNA target sites were chosen from intron 20 and 23 of mouse Dmd. Co- transfection of the two gRNA with cas9 plasmids into mouse C2C12 cells resulted in the detection of a small PCR product as predicted, indicating successful CRISPR-mediated genome editing. DNA sequencing confirmed that the transcripts from C2C12 cells treated with gRNA/cas9 were formed due to successful deletion of exons 21-23 of mouse Dmd. Moreover, we injected the adenoviral vectors carrying GFP-2A-cas9 and gRNAs systemically and locally into the newborn pups. Four weeks after adenovirus transduction, dystrophin expression was restored in the heart muscles positive for GFP. Our PCR and western blotting data demonstrated that in-frame deletion of the genomic DNA covering exon 23 restored functional dystrophin expression in the hearts of mdx mice. Immunofluorescence staining also demonstrated that β-dystroglycan, which is normally located to the sarcolemma in healthy heart muscles via interaction with dystrophin-glycoprotein complex, was also restored at the sarcolemma of GFP-positive heart muscle fibers. These data provide the proof evidence of systemic restoration of dystrophin in the hearts of live mice.