Sustaining cardiac claudin-5 levels prevents functional hallmarks of cardiomyopathy in a muscular dystrophy mouse model

A novel function of claudin-5 in maintaining the structural integrity of the heart and its implications in cardiac pathology

This study aims to investigate the role of claudin-5 (Cldn5) in cardiac structural integrity. Proteomic analysis was performed to screen the protein profiles in enlarged left atrium from atrial fibrillation (AF) patients. Cldn5 shRNA adeno-associated virus (AAV) or siRNA was injected into the mouse left ventricle or added into HL1 cells respectively to knockdown Cldn5 in cardiomyocytes to observe whether the change of Cldn5 influences cardiac morphology and function, and affects those protein expressions stem from the proteomic analysis. Mitochondrial density and membrane potential were also measured by Mitotracker staining and JC-1 staining under the confocal microscope in HL1 cells. Cldn5 was reduced in cardiomyocytes from the left atrial appendage of AF patients compared to non-AF donors. Proteomic analysis showed 83 proteins were less abundant and 102 proteins were more abundant in AF patients. KEGG pathway analysis showed less abundant CACNA2D2, CACNB2, MYL2 and MAP6 were highly associated with dilated cardiomyopathy. Cldn5 shRNA AAV injection caused severe cardiac atrophy, dilation and myocardial dysfunction in mice. The decreases in mitochondrial numbers and mitochondrial membrane potentials in HL1 cells were observed after Cldn5 knockdown. We demonstrated for the first time the mechanism of Cldn5 downregulation-induced myocyte atrophy and myocardial dysfunction might be associated with the downregulation of CACNA2D2, CACNB2, MYL2 and MAP6, and mitochondrial dysfunction in cardiomyocytes.

CLDN5: From structure and regulation to roles in tumors and other diseases beyond CNS disorders

Claudin-5 (CLDN5) is an essential component of tight junctions (TJs) and is critical for the integrity of the blood-brain barrier (BBB), ensuring homeostasis and protection from damage to the central nervous system (CNS). Currently, many researchers have summarized the role and mechanisms of CLDN5 in CNS diseases. However, it is noteworthy that CLDN5 also plays a significant role in tumor growth and metastasis. In addition, abnormal CLDN5 expression is involved in the development of respiratory diseases, intestinal diseases, cardiac diseases, and diabetic ocular complications. This paper aims to review the structure, expression, and regulation of CLDN5, focusing on its role in tumors, including its expression and regulation, effects on malignant phenotypes, and clinical significance. Furthermore, this paper will provide an overview of the role and mechanisms of CLDN5 in respiratory diseases, intestinal diseases, cardiac diseases, and diabetic ocular complications.

Hypoxia-induced vascular remodeling responses in the brain are much more robust than other organs

Exposure to chronic mild hypoxia (CMH; 8-10% O2) promotes a robust vascular remodeling response in the brain resulting in 50% increased vessel density over a period of two weeks. It is currently unknown whether blood vessels in other organs show similar responses. To address this question, mice were exposed to CMH for 4 days and various markers of vascular remodeling were examined in the brain along with heart, skeletal muscle, kidney, and liver. In contrast to brain, where CMH strongly promoted endothelial proliferation, none of the peripheral organs showed this response and in heart and liver, CMH notably reduced endothelial proliferation. While the MECA-32 endothelial activation marker was strongly induced by CMH in brain, in peripheral organs it was constitutively expressed either on a sub-population of vessels (heart and skeletal muscle) or on all vessels (kidney and liver), and notably, CMH did not affect expression. Endothelial expression of the tight junction proteins claudin-5 and ZO-1 were markedly increased on cerebral vessels, but in the peripheral organs examined, CMH either had no effect or reduced ZO-1 expression (liver). Finally, while CMH had no impact on the number of Mac-1 positive macrophages in the brain, heart, or skeletal muscle, this number was markedly decreased in the kidney but increased in the liver. Our findings show that the vascular remodeling responses to CMH are organ-specific, with the brain showing a strong angiogenic response and enhanced tight junction protein expression, but heart, skeletal muscle, kidney, and liver failing to show these responses.

Micro-dystrophin gene therapy demonstrates long-term cardiac efficacy in a severe Duchenne muscular dystrophy model

Micro-dystrophin gene replacement therapies for Duchenne muscular dystrophy (DMD) are currently in clinical trials, but have not been thoroughly investigated for their efficacy on cardiomyopathy progression to heart failure. We previously validated Fiona/dystrophin-utrophin-deficient (dko) mice as a DMD cardiomyopathy model that progresses to reduced ejection fraction indicative of heart failure. Adeno-associated viral (AAV) vector delivery of an early generation micro-dystrophin prevented cardiac pathology and functional decline through 1 year of age in this new model. We now show that gene therapy using a micro-dystrophin optimized for skeletal muscle efficacy (AAV-μDys5), and which is currently in a clinical trial, is able to fully prevent cardiac pathology and cardiac strain abnormalities and maintain normal (>45%) ejection fraction through 18 months of age in Fiona/dko mice. Early treatment with AAV-μDys5 prevents inflammation and fibrosis in Fiona/dko hearts. Collagen in cardiac fibrotic scars becomes more tightly packed from 12 to 18 months in Fiona/dko mice, but the area of fibrosis containing tenascin C does not change. Increased tight collagen correlates with unexpected improvements in Fiona/dko whole-heart function that maintain impaired cardiac strain and strain rate. This study supports micro-dystrophin gene therapy as a promising intervention for preventing DMD cardiomyopathy progression.

Cardiac-specific overexpression of Claudin-5 exerts protection against myocardial ischemia and reperfusion injury

Claudin-5 has recently attracted increasing attention by its potential as a novel treatment target in the early stage of heart failure. However, whether Claudin-5 produces beneficial effects on myocardial ischemia and reperfusion (IR) injury has not been elucidated yet. In this study, we identified reduced levels of Claudin-5 in the hearts of mice subjected to acute myocardial IR injury and murine HL-1 cardiomyocytes subjected to hypoxia and reoxygenation (HR). We then constructed cardiac-specific Cldn5-overexpressing mice using an adeno-associated virus (AAV9) vector and demonstrated that Cldn5 overexpression ameliorated cardiac dysfunction and myocardial damage in mice subjected to myocardial IR injury. Moreover, Cldn5 overexpression attenuated myocardial oxidative stress (DHE and protein levels of Nrf2, HO-1, and NQO1), inflammatory response (levels of MPO, F4/80, Ly6C, and circulating inflammatory cells), mitochondrial dysfunction (protein levels of PGC-1α, NRF1, and TFAM), endoplasmic reticulum stress (protein levels of GRP78, ATF6, and CHOP and p-PERK), energy metabolism disorder (p-AMPK and ACC), and apoptosis (TUNEL assay and protein levels of Bax and Bcl2) in mice subjected to myocardial IR. Next, we generated Cldn5 knockdown cells by lentiviral shRNA and observed that Cldn5 knockdown inhibited cell viability and affected the expression or activation of these IR-related signalings in HL-1 cardiomyocytes subjected to HR. Mechanistically, SIRT1 was proved to be involved in regulating the expression of Claudin-5 by co-immunoprecipitation analysis and Sirt1 knockdown experiments. Our data demonstrated that targeting Claudin-5 may represent a promising approach for preventing and treating acute myocardial IR injury.

Micro-dystrophin gene therapy prevents heart failure in an improved Duchenne muscular dystrophy cardiomyopathy mouse model

Gene replacement for Duchenne muscular dystrophy (DMD) with micro-dystrophins has entered clinical trials, but efficacy in preventing heart failure is unknown. Although most patients with DMD die from heart failure, cardiomyopathy is undetectable until the teens, so efficacy from trials in young boys will be unknown for a decade. Available DMD animal models were sufficient to demonstrate micro-dystrophin efficacy on earlier onset skeletal muscle pathology underlying loss of ambulation and respiratory insufficiency in patients. However, no mouse models progressed into heart failure, and dog models showed highly variable progression insufficient to evaluate efficacy of micro-dystrophin or other therapies on DMD heart failure. To overcome this barrier, we have generated the first DMD mouse model to our knowledge that reproducibly progresses into heart failure. This model shows cardiac inflammation and fibrosis occur prior to reduced function. Fibrosis does not continue to accumulate, but inflammation persists after function declines. We used this model to test micro-dystrophin gene therapy efficacy on heart failure prevention for the first time. Micro-dystrophin prevented declines in cardiac function and prohibited onset of inflammation and fibrosis. This model will allow identification of committed pathogenic steps to heart failure and testing of genetic and nongenetic therapies to optimize cardiac care for patients with DMD.

A novel role of claudin-5 in prevention of mitochondrial fission against ischemic/hypoxic stress in cardiomyocytes

BACKGROUND

Downregulation of claudin-5 in the heart is associated with the end-stage heart failure. However, the underlying mechanism of claudin-5 is unclear. Here we investigated the molecular actions of claudin-5 in perspective of mitochondria in cardiomyocytes to better understand the role of claudin-5 in cardioprotection during ischemia.

METHODS AND RESULTS

Claudin-5 was detected in the murine heart tissue and the neonatal rat cardiomyocytes (NRCM). Its protein level was severely decreased after myocardial ischemia/reperfusion (I/R; 30 min/24 h) or hypoxia/reoxygenation (H/R; 24 h/4 h). Claudin-5 was present in the mitochondria of NRCM as determined by confocal microscopy. H/R-induced downregulation of claudin-5 was accompanied by mitochondrial fragmentation. The protein level of mitofusin 2 (Mfn2) was dramatically decreased while the expression of dynamin-related protein (Drp) 1 was significantly increased after H/R. H/R-induced mitochondrial swelling and fission were observed by transmission electron microscope (TEM). Overexpression of claudin-5 by adenoviral infection reversed these structural disintegration of mitochondria. The mitochondria-centered intrinsic pathway of apoptosis triggered by H/R and indicated by the expression of cytochrome c and cleaved caspase 3 in the cytoplasm of NRCMs was also reduced by overexpressing claudin-5. Overexpression of claudin-5 in mouse heart also significantly decreased cleaved caspase 3 expression and the infarct size in ischemic heart with improved systolic function.

CONCLUSION

We demonstrated for the first time the presence of claudin-5 in the mitochondria in cardiomyocytes and provided the firm evidence for the cardioprotective role of claudin-5 in the preservation of mitochondrial dynamics and cell fate against hypoxia- or ischemia-induced stress.

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.

In the line-up: deleted genes associated with DiGeorge/22q11.2 deletion syndrome: are they all suspects?

BACKGROUND

22q11.2 deletion syndrome (22q11DS), a copy number variation (CNV) disorder, occurs in approximately 1:4000 live births due to a heterozygous microdeletion at position 11.2 (proximal) on the q arm of human chromosome 22 (hChr22) (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011). This disorder was known as DiGeorge syndrome, Velo-cardio-facial syndrome (VCFS) or conotruncal anomaly face syndrome (CTAF) based upon diagnostic cardiovascular, pharyngeal, and craniofacial anomalies (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011; Burn et al., J Med Genet 30:822-4, 1993) before this phenotypic spectrum was associated with 22q11.2 CNVs. Subsequently, 22q11.2 deletion emerged as a major genomic lesion associated with vulnerability for several clinically defined behavioral deficits common to a number of neurodevelopmental disorders (Fernandez et al., Principles of Developmental Genetics, 2015; Robin and Shprintzen, J Pediatr 147:90-6, 2005; Schneider et al., Am J Psychiatry 171:627-39, 2014).

RESULTS

The mechanistic relationships between heterozygously deleted 22q11.2 genes and 22q11DS phenotypes are still unknown. We assembled a comprehensive "line-up" of the 36 protein coding loci in the 1.5 Mb minimal critical deleted region on hChr22q11.2, plus 20 protein coding loci in the distal 1.5 Mb that defines the 3 Mb typical 22q11DS deletion. We categorized candidates based upon apparent primary cell biological functions. We analyzed 41 of these genes that encode known proteins to determine whether haploinsufficiency of any single 22q11.2 gene-a one gene to one phenotype correspondence due to heterozygous deletion restricted to that locus-versus complex multigenic interactions can account for single or multiple 22q11DS phenotypes.

CONCLUSIONS

Our 22q11.2 functional genomic assessment does not support current theories of single gene haploinsufficiency for one or all 22q11DS phenotypes. Shared molecular functions, convergence on fundamental cell biological processes, and related consequences of individual 22q11.2 genes point to a matrix of multigenic interactions due to diminished 22q11.2 gene dosage. These interactions target fundamental cellular mechanisms essential for development, maturation, or homeostasis at subsets of 22q11DS phenotypic sites.

Claudin-5: gatekeeper of neurological function

Tight junction proteins of the blood–brain barrier are vital for maintaining integrity of endothelial cells lining brain blood vessels. The presence of these protein complexes in the space between endothelial cells creates a dynamic, highly regulated and restrictive microenvironment that is vital for neural homeostasis. By limiting paracellular diffusion of material between blood and brain, tight junction proteins provide a protective barrier preventing the passage of unwanted and potentially damaging material. Simultaneously, this protective barrier hinders the therapeutic effectiveness of central nervous system acting drugs with over 95% of small molecule therapeutics unable to bypass the blood–brain barrier. At the blood–brain barrier, claudin-5 is the most enriched tight junction protein and its dysfunction has been implicated in neurodegenerative disorders such as Alzheimer’s disease, neuroinflammatory disorders such as multiple sclerosis as well as psychiatric disorders including depression and schizophrenia. By regulating levels of claudin-5, it is possible to abrogate disease symptoms in many of these disorders. This review will give an overview of the blood–brain barrier and the role of tight junction complexes in maintaining blood–brain barrier integrity before focusing on the role of claudin-5 and its regulation in homeostatic and pathological conditions. We will also summarise therapeutic strategies to restore integrity of cerebral vessels by targeting tight junction protein complexes.

Duchenne muscular dystrophy: an updated review of common available therapies

BACKGROUND AND PURPOSE

Duchenne muscular dystrophy (DMD) is a lethal progressive pediatric muscle disorder and genetically inherited as an X-linked disease that caused by mutations in the dystrophin gene. DMD leads to progressive muscle weakness, degeneration, and wasting; finally, follows with the premature demise in affected individuals due to respiratory and/or cardiac failure typically by age of 30. For decades, scientists tried massively to find an effective therapy method, but there is no absolute cure currently for patients with DMD, nevertheless, recent advanced progressions on the treatment of DMD will be hopeful in the future. Several promising gene therapies are currently under investigation. These include gene replacement, exon skipping, suppression of stop codons. More recently, a promising gene editing tool referred to as CRISPR/Cas9 offers exciting perspectives for restoring dystrophin expression in patients with DMD. This review intents to briefly describe these methods and comment on their advances. Since DMD is a genetic disorder, it should be treated by replacing the deficient DMD copy with a functional one. However, there are different types of mutations in this gene, so such therapeutic approaches are highly mutation specific and thus are personalized. Therefore, DMD has arisen as a model of genetic disorder for understanding and overcoming of the challenges of developing personalized genetic medicines, consequently, the lessons learned from these approaches will be applicable to many other disorders.

CONCLUSIONS

This review provides an update on the recent gene therapies for DMD that aim to compensate for dystrophin deficiency and the related clinical trials.

Claudin-1, -2, -4, and -5: comparison of expression levels and distribution in equine tissues

Claudins, which are known as transmembrane proteins play an essential role in tight junctions (TJs) to form physical barriers and regulate paracellular transportation. To understand equine diseases, it is helpful to measure the tissue-specific expression of TJs in horses. Major equine diseases such as colic and West Nile cause damage to TJs. In this study, the expression level and distribution of claudin-1, -2, -4, and -5 in eight tissues were assessed by Western blotting and immunohistochemistry methods. Claudin-1 was primarily identified in the lung, duodenum, and uterus, claudin-2 was evenly observed in equine tissues, claudin-4 was abundantly detected in the liver, kidney and uterus, and claudin-5 was strongly expressed in the lung, duodenum, ovary, and uterus, as determined by Western blotting method. The localization of equine claudins was observed by immunohistochemistry methods. These findings provide knowledge regarding the expression patterns and localization of equine claudins, as well as valuable information to understand tight junction-related diseases according to tissue specificity and function of claudins in horses.

Myocardial Contractile Dysfunction Is Present without Histopathology in a Mouse Model of Limb-Girdle Muscular Dystrophy-2F and Is Prevented after Claudin-5 Virotherapy

Mutations in several members of the dystrophin glycoprotein complex lead to skeletal and cardiomyopathies. Cardiac care for these muscular dystrophies consists of management of symptoms with standard heart medications after detection of reduced whole heart function. Recent evidence from both Duchenne muscular dystrophy patients and animal models suggests that myocardial dysfunction is present before myocardial damage or deficiencies in whole heart function, and that treatment prior to heart failure symptoms may be beneficial. To determine whether this same early myocardial dysfunction is present in other muscular dystrophy cardiomyopathies, we conducted a physiological assessment of cardiac function at the tissue level in the δ-sarcoglycan null mouse model (Sgcd^−/−) of Limb-girdle muscular dystrophy type 2F. Baseline cardiac contractile force measurements using ex vivo intact linear muscle preparations, were severely depressed in these mice without the presence of histopathology. Virotherapy withclaudin-5 prevents the onset of cardiomyopathy in another muscular dystrophy model. After virotherapy with claudin-5, the cardiac contractile force deficits in Sgcd^−/− mice are no longer significant. These studies suggest that screening Limb-girdle muscular dystrophy patients using methods that detect earlier functional changes may provide a longer therapeutic window for cardiac care.

Identification of Transcription Factor-Gene Regulatory Network in Acute Myocardial Infarction

BACKGROUND

Acute myocardial infarction (AMI) is a common disease with serious mortality and morbidity, worldwide. The present study aimed to identify differentially expressed genes (DEGs) and construct a transcription factor-gene regulatory network to further study the early diagnosis of AMI.

METHODS

The integrated analysis of publicly available Gene Expression Omnibus datasets of AMI was performed. Differentially expressed genes were identified between AMI and normal blood samples. Gene Ontology enrichment analyses, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, and the transcription factor-gene regulatory network were used to obtain insights into the functions of DEGs. Quantitative real-time polymerase chain reactions (qRT-PCR) were performed to validate the expression level of DEGs.

RESULTS

A total of 2,502 DEGs, including 917 up-regulated genes and 1,585 down-regulated genes, were identified between AMI and normal blood samples by integrating four expression profiles of AMI. Differentially expressed genes were significantly enriched in pathways including complement and coagulation cascades, Staphylococcus aureus infection, and cell adhesion molecules. Transcription factors were screened and performed to construct the regulatory network. The transcription factor-gene regulatory network consisted of 871 interactions between 80 transcription factors and 716 DEGs. ETS homologous factor (EHF) was one of transcription factors that had high connectivity with DEGs and regulated CACNB4 in the network. Verification by qRT-PCR revealed that EHF, KRT6A and DSG3 were significantly up-regulated, while CACNG4 was significantly down-regulated in AMI. Furthermore, CACNG6, CACNB4 and CLDN18 had a tendency to be down-regulated, and CALML3 had a tendency to be up-regulated in AMI.

CONCLUSIONS

The identification of important differentially expressed transcription factors and genes in the development of AMI would be the groundwork for the early diagnosis and early intervention of AMI.

Dysfunction of mitochondria and deformed gap junctions in the heart of IL-18-deficient mice

Interleukin-18 (IL-18) was discovered as an interferon-γ-inducing factor and has been regarded as a proinflammatory cytokine. However, IL-18 is ubiquitously expressed both in immune/inflammatory cells and in nonimmune cells, and its biological roles have not been sufficiently elucidated. Here, we demonstrate that IL-18-deficient [IL-18 knockout (KO)] mice have heart abnormalities that may be related to impaired autophagy. In endurance running tests, IL-18KO mice ran significantly shorter distances compared with wild-type (WT) mice. Echocardiographs indicated disability in the systolic and diastolic functions of the IL-18KO mouse heart. Immunostaining of connexin 43 showed heterogeneous localization of gap junctions in the lateral membranes of the IL-18KO cardiac myocytes. Western blotting analysis revealed decreased phosphorylated connexin 43 in the IL-18KO heart. Electron microscopy revealed unusual localization of intercalated disks, swollen or damaged mitochondria, and broad, indistinct Z-lines in the IL-18KO heart. In accordance with the morphological observation, mitochondrial respiratory function, including that of complexes I and IV, was impaired, and production of reactive oxygen species was augmented in IL-18KO hearts. Notably, levels of LC3-II were markedly lower in the IL-18KO hearts than in WT hearts. In the culture of cardiac myocytes of IL-18KO neonates, exogenous IL-18 upregulated LC3-II and increased the number of intact mitochondria with high mitochondrial membrane potential. These results indicated that IL-18 has roles apart from those as a proinflammatory cytokine in cardiac myocytes and suggested that IL-18 contributes to the homeostatic maintenance of mitochondrial function and gap-junction turnover in cardiac myocytes, possibly by upregulating autophagy.

Claudin-5 levels are reduced from multiple cell types in human failing hearts and are associated with mislocalization of ephrin-B1

Claudin-5 is transcriptionally downregulated resulting in dramatically reduced protein levels in human heart failure. Studies in mice have demonstrated that reduced claudin-5 levels occur prior to cardiac damage and far before reduced whole heart function. Therefore, claudin-5 may be a useful early therapeutic target for human heart failure. However, the cell types in which claudin-5 is localized in human heart and from which claudin-5 is reduced in heart failure is not known. The recent identification of claudin-5's interaction with ephrin-B1 in mouse hearts has also not been investigated in non-failing or failing human hearts. In this study we collected human left ventricular mid-myocardium histological samples from 7 non-failing hearts and 16 end-stage failing hearts. Immunoblots demonstrate severe reductions of claudin-5 protein in 14 of 16 failing hearts compared to non-failing controls. Claudin-5 was observed to localize to cardiomyocytes, endothelial cells, and a subset of fibroblasts in non-failing human heart sections. In isolated cardiomyocytes, the transmembrane claudin-5 protein localized in longitudinal striations in lateral membranes. In failing heart, both cardiomyocyte and endothelial claudin-5 localization was severely reduced, but claudin-5 remained in fibroblasts. Absence of claudin-5 staining also correlated with the reduction of the endothelial cell marker CD31. Ephrin-B1 localization, but not protein levels, was altered in failing hearts supporting that claudin-5 is required for ephrin-B1 localization. These data support that loss of claudin-5 in cardiomyocytes and endothelial cells is prevalent in human heart failure. Investigating claudin-5/ephrin-B1 protein complexes and gene regulation may lead to novel therapies.

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.