DNA double-stranded breaks, a hallmark of aging, defined at the nucleotide resolution, are increased and associated with transcription in the cardiac myocytes in LMNA-cardiomyopathy.

AIMS: An intrinsic feature of gene transcription is the formation of DNA superhelices near the transcription bubble, which are resolved upon induction of transient double-stranded breaks (DSBs) by topoisomerases. Unrepaired DSBs are pathogenic as they lead to cell cycle arrest, senescence, inflammation, and organ dysfunction. We posit that DSBs would be more prevalent at the genomic sites that are associated with gene expression. The objectives were to identify and characterize genome-wide DSBs at the nucleotide resolution and determine the association of DSBs with transcription in cardiac myocytes. METHODS AND RESULTS: We identified the genome-wide DSBs in ∼1 million cardiac myocytes per heart in three wild-type and three myocyte-specific LMNA-deficient (Myh6-Cre:LmnaF/F) mice by END-Sequencing. The prevalence of DSBs was 0.8% and 2.2% in the wild-type and Myh6-Cre:LmnaF/F myocytes, respectively. The END-Seq signals were enriched for 8 and 6764 DSBs in the wild-type and Myh6-Cre:LmnaF/F myocytes, respectively (q < 0.05). The DSBs were preferentially localized to the gene regions, transcription initiation sites, cardiac transcription factor motifs, and the G quadruplex forming structures. Because LMNA regulates transcription through the lamin-associated domains (LADs), we defined the LADs in cardiac myocytes by a Cleavage Under Targets & Release Using Nuclease (CUT&RUN) assay (N = 5). On average there were 818 LADs per myocyte. Constitutive LADs (cLADs), defined as LADs that were shared by at least three genomes (N = 2572), comprised about a third of the mouse cardiac myocyte genomes. Transcript levels of the protein-coding genes located at the cLADs (N = 3975) were ∼16-fold lower than those at the non-LAD regions (N = ∼17 778). The prevalence of DSBs was higher in the non-LAD as compared to the cLAD regions. Likewise, DSBs were more common in the loss-of-LAD regions, defined as the genomic regions in the Myh6-Cre:LmnaF/F that were juxtaposed to the LAD regions in the wild-type myocytes. CONCLUSION: To our knowledge, this is the first identification of the DSBs, at the nucleotide resolution in the cardiovascular system. The prevalence of DSBs was higher in the genomic regions associated with transcription. Because transcription is pervasive, DSBs are expected to be common and pathogenic in various states and aging.

Histone demethylase KDM5 regulates cardiomyocyte maturation by promoting fatty acid oxidation, oxidative phosphorylation, and myofibrillar organization.

AIMS: Human pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) provide a platform to identify and characterize factors that regulate the maturation of CMs. The transition from an immature foetal to an adult CM state entails coordinated regulation of the expression of genes involved in myofibril formation and oxidative phosphorylation (OXPHOS) among others. Lysine demethylase 5 (KDM5) specifically demethylates H3K4me1/2/3 and has emerged as potential regulators of expression of genes involved in cardiac development and mitochondrial function. The purpose of this study is to determine the role of KDM5 in iPSC-CM maturation. METHODS AND RESULTS: KDM5A, B, and C proteins were mainly expressed in the early post-natal stages, and their expressions were progressively downregulated in the post-natal CMs and were absent in adult hearts and CMs. In contrast, KDM5 proteins were persistently expressed in the iPSC-CMs up to 60 days after the induction of myogenic differentiation, consistent with the immaturity of these cells. Inhibition of KDM5 by KDM5-C70 -a pan-KDM5 inhibitor, induced differential expression of 2372 genes, including upregulation of genes involved in fatty acid oxidation (FAO), OXPHOS, and myogenesis in the iPSC-CMs. Likewise, genome-wide profiling of H3K4me3 binding sites by the cleavage under targets and release using nuclease assay showed enriched of the H3K4me3 peaks at the promoter regions of genes encoding FAO, OXPHOS, and sarcomere proteins. Consistent with the chromatin and gene expression data, KDM5 inhibition increased the expression of multiple sarcomere proteins and enhanced myofibrillar organization. Furthermore, inhibition of KDM5 increased H3K4me3 deposits at the promoter region of the ESRRA gene and increased its RNA and protein levels. Knockdown of ESRRA in KDM5-C70-treated iPSC-CM suppressed expression of a subset of the KDM5 targets. In conjunction with changes in gene expression, KDM5 inhibition increased oxygen consumption rate and contractility in iPSC-CMs. CONCLUSION: KDM5 inhibition enhances maturation of iPSC-CMs by epigenetically upregulating the expressions of OXPHOS, FAO, and sarcomere genes and enhancing myofibril organization and mitochondrial function.

A human mitofusin 2 mutation can cause mitophagic cardiomyopathy.

Cardiac muscle has the highest mitochondrial density of any human tissue, but mitochondrial dysfunction is not a recognized cause of isolated cardiomyopathy. Here, we determined that the rare mitofusin (MFN) 2 R400Q mutation is 15-20× over-represented in clinical cardiomyopathy, whereas this specific mutation is not reported as a cause of MFN2 mutant-induced peripheral neuropathy, Charcot-Marie-Tooth disease type 2A (CMT2A). Accordingly, we interrogated the enzymatic, biophysical, and functional characteristics of MFN2 Q400 versus wild-type and CMT2A-causing MFN2 mutants. All MFN2 mutants had impaired mitochondrial fusion, the canonical MFN2 function. Compared to MFN2 T105M that lacked catalytic GTPase activity and exhibited normal activation-induced changes in conformation, MFN2 R400Q and M376A had normal GTPase activity with impaired conformational shifting. MFN2 R400Q did not suppress mitochondrial motility, provoke mitochondrial depolarization, or dominantly suppress mitochondrial respiration like MFN2 T105M. By contrast to MFN2 T105M and M376A, MFN2 R400Q was uniquely defective in recruiting Parkin to mitochondria. CRISPR editing of the R400Q mutation into the mouse Mfn2 gene induced perinatal cardiomyopathy with no other organ involvement; knock-in of Mfn2 T105M or M376V did not affect the heart. RNA sequencing and metabolomics of cardiomyopathic Mfn2 Q/Q400 hearts revealed signature abnormalities recapitulating experimental mitophagic cardiomyopathy. Indeed, cultured cardiomyoblasts and in vivo cardiomyocytes expressing MFN2 Q400 had mitophagy defects with increased sensitivity to doxorubicin. MFN2 R400Q is the first known natural mitophagy-defective MFN2 mutant. Its unique profile of dysfunction evokes mitophagic cardiomyopathy, suggesting a mechanism for enrichment in clinical cardiomyopathy.

Mitochondria are organelles with an essential role in providing energy to the cells of the body. If damaged, they are repaired by fusing and exchanging contents with sister mitochondria in a process that requires mitofusin proteins. While mutations in the gene for mitofusin 2 have been linked to nerve damage, they do not appear to affect the heart ­ despite high concentrations of mitochondria in heart muscle cells. However, previous research showed that experimentally disrupting the programmed removal of mitochondria, a process also regulated by mitofusin 2, can cause heart muscle disease known as cardiomyopathy. This suggests that mutations affecting different mitofusin 2 roles might harm individual cell types in different ways. To investigate, Franco et al. carried out a genetic screen of people with cardiomyopathy, identifying a rare mitofusin 2 mutation, called R400Q, that was more common in this group. Experiments showed that R400Q caused cardiomyopathy in mice and affected mitochondrial repair and replacement, but not movement. By contrast, a mutation linked to Charcot-Marie-Tooth disease type 2A ­ which causes nerve damage ­ affected mitochondrial movement but not clearance, leading to nerve cell damage but not cardiomyopathy. This led Franco et al. to suggest that mitochondrial movement is central to nerve cell health, whereas mitochondrial repair and replacement plays an important role in cardiac development. Genetic cardiomyopathies affect around 1 in 500 people, but only half of the gene mutations responsible are known. These results suggest that mutations affecting mitochondrial quality control factors could be involved, highlighting a direction for future studies into modifiers of cardiomyopathy.

Genetic inactivation of ß-catenin is salubrious, whereas its activation is deleterious in desmoplakin cardiomyopathy.

AIMS: Mutations in the DSP gene encoding desmoplakin, a constituent of the desmosomes at the intercalated discs (IDs), cause a phenotype that spans arrhythmogenic cardiomyopathy (ACM) and dilated cardiomyopathy. It is typically characterized by biventricular enlargement and dysfunction, myocardial fibrosis, cell death, and arrhythmias. The canonical wingless-related integration (cWNT)/ß-catenin pathway is implicated in the pathogenesis of ACM. The ß-catenin is an indispensable co-transcriptional regulator of the cWNT pathway and a member of the IDs. We genetically inactivated or activated ß-catenin to determine its role in the pathogenesis of desmoplakin cardiomyopathy. METHODS AND RESULTS: The Dsp gene was conditionally deleted in the 2-week-old post-natal cardiac myocytes using tamoxifen-inducible MerCreMer mice (Myh6-McmTam:DspF/F). The cWNT/ß-catenin pathway was markedly dysregulated in the Myh6-McmTam:DspF/F cardiac myocytes, as indicated by a concomitant increase in the expression of cWNT/ß-catenin target genes, isoforms of its key co-effectors, and the inhibitors of the pathway. The ß-catenin was inactivated or activated upon inducible deletion of its transcriptional or degron domain, respectively, in the Myh6-McmTam:DspF/F cardiac myocytes. Genetic inactivation of ß-catenin in the Myh6-McmTam:DspF/F mice prolonged survival, improved cardiac function, reduced cardiac arrhythmias, and attenuated myocardial fibrosis, and cell death caused by apoptosis, necroptosis, and pyroptosis, i.e. PANoptosis. In contrast, activation of ß-catenin had the opposite effects. The deleterious and the salubrious effects were independent of changes in the expression levels of the cWNT target genes and were associated with changes in several molecular and biological pathways, including cell death programmes. CONCLUSION: The cWNT/ß-catenin was markedly dysregulated in the cardiac myocytes in a mouse model of desmoplakin cardiomyopathy. Inactivation of ß-catenin attenuated, whereas its activation aggravated the phenotype, through multiple molecular pathways, independent of the cWNT transcriptional activity. Thus, suppression but not activation of ß-catenin might be beneficial in desmoplakin cardiomyopathy.

Cytosolic DNA sensing protein pathway is activated in human hearts with dilated cardiomyopathy.

Introduction: The genome is constantly exposed to numerous stressors, which induce DNA lesions, including double-stranded DNA breaks (DSBs). DSBs are the most dangerous, as they induce genomic instability. In response to DNA damage, the cell activates nuclear DNA damage response (DDR) and the cytosolic DNA sensing protein (CDSP) pathways, the latter upon release of the DSBs to the cytosol. The CDSP pathway activates NFκB and IRF3, which induce the expression of the pro-inflammatory genes. There is scant data on the activation of the CDSP pathway in human hearts with dilated cardiomyopathy (DCM). Aim: We aimed to determine expression levels of selected components of the CDSP pathway in human hearts with DCM. Methods: The DNA strand breaks were detected by the single-cell gel electrophoresis or the comet assay and expression of selected proteins by immunoblotting. Transcript levels were quantified in the RNA-Seq data. Results: Single-cell gel electrophoresis showed an approximately 2-fold increase in the number of COMET cells in the DCM hearts. Immunoblotting showed increased levels of cyclic GMP-AMP synthase (CGAS), the canonical CDSP; TANK-binding kinase 1 (TBK1), an intermediary kinase in the pathway; and RELB, P52, and P50 components of the NFκB pathway in human heart samples from patients with DCM. Likewise, transcript levels of over 2 dozen genes involved in inflammatory responses were increased. Conclusions: The findings provide the first set of evidence for the activation of the CDSP pathway in human hearts with DCM. The data in conjunction with the previous evidence of activation of the DDR pathway implicate the DSBs in the pathogenesis of human DCM.

PANoptosis is a prominent feature of desmoplakin cardiomyopathy.

Introduction: Arrhythmogenic cardiomyopathy (ACM) is hereditary cardiomyopathy caused by pathogenic variants (mutations) in genes encoding the intercalated disc (ID), particularly desmosome proteins. ACM caused by mutations in the DSP gene encoding desmoplakin (DSP) is characterized by the prominence of cell death, myocardial fibrosis, and inflammation, and is referred to as desmoplakin cardiomyopathy. Aim: The aim of this article was to gain insight into the pathogenesis of DSP cardiomyopathy. Methods and Results: The Dsp gene was exclusively deleted in cardiac myocytes using tamoxifen-inducible MerCreMer (Myh6-Mcm Tam) and floxed Dsp (Dsp F/F) mice (Myh6-Mcm Tam:Dsp F/F). Recombination was induced upon subcutaneous injection of tamoxifen (30 mg/kg/d) for 5 days starting post-natal day 14. Survival was analyzed by Kaplan-Meier plots, cardiac function by echocardiography, arrhythmias by rhythm monitoring, and gene expression by RNA-Seq, immunoblotting, and immunofluorescence techniques. Cell death was analyzed by the TUNEL assay and the expression levels of specific markers were by RT-PCR and immunoblotting. Myocardial fibrosis was assessed by picrosirius red staining of the myocardial sections, RT-PCR, and immunoblotting. The Myh6-Mcm Tam: Dsp F/F mice showed extensive molecular remodeling of the IDs and the differential expression of ~10,000 genes, which predicted activation of KDM5A, IRFs, and NFκB and suppression of PPARGC1A and RB1, among others in the DSP-deficient myocytes. Gene set enrichment analysis predicted activation of the TNFα/NFκB pathway, inflammation, cell death programs, and fibrosis. Analysis of cell death markers indicated PANoptosis, comprised of apoptosis (increased CASP3, CASP8, BAD and reduced BCL2), necroptosis (increased RIPK1, RIPK3, and MLKL), and pyroptosis (increased GSDMD and ASC or PYCARD) in the DSP-deficient myocytes. Transcript levels of the pro-inflammatory and pro-fibrotic genes were increased and myocardial fibrosis comprised ~25% of the myocardium in the DSP-deficient hearts. The Myh6-Mcm Tam:Dsp F/F mice showed severe cardiac systolic dysfunction and ventricular arrhythmias, and died prematurely with a median survival rate of ~2 months. Conclusion: The findings identify PANoptosis as a prominent phenotypic feature of DSP cardiomyopathy and set the stage for delineating the specific molecular mechanisms involved in its pathogenesis. The model also provides the opportunity to test the effects of pharmacological and genetic interventions on myocardial fibrosis and cell death.

Meeting report - Desmosome dysfunction and disease: Alpine desmosome disease meeting.

Desmosome diseases are caused by dysfunction of desmosomes, which anchor intermediate filaments (IFs) at sites of cell-cell adhesion. For many decades, the focus of attention has been on the role of actin filament-associated adherens junctions in development and disease, especially cancer. However, interference with the function of desmosomes, their molecular constituents or their attachments to IFs has now emerged as a major contributor to a variety of diseases affecting different tissues and organs including skin, heart and the digestive tract. The first Alpine desmosome disease meeting (ADDM) held in Grainau, Germany, in October 2022 brought together international researchers from the basic sciences with clinical experts from diverse fields to share and discuss their ideas and concepts on desmosome function and dysfunction in the different cell types involved in desmosome diseases. Besides the prototypic desmosomal diseases pemphigus and arrhythmogenic cardiomyopathy, the role of desmosome dysfunction in inflammatory bowel diseases and eosinophilic esophagitis was discussed.

Deletion of the Lmna gene in fibroblasts causes senescence-associated dilated cardiomyopathy by activating the double-stranded DNA damage response and induction of senescence-associated secretory phenotype.

Introduction: Mutations in the LMNA gene, encoding Lamin A/C (LMNA), are established causes of dilated cardiomyopathy (DCM). The phenotype is typically characterized by progressive cardiac conduction defects, arrhythmias, heart failure, and premature death. DCM is primarily considered a disease of cardiac myocytes. However, LMNA is also expressed in other cardiac cell types, including fibroblasts. Aim: The purpose of the study was to determine the contribution of the fibroblasts to DCM caused by LMNA deficiency. Methods and Results: The Lmna gene was deleted by crossing the platelet-derived growth factor receptor α-Cre recombinase (Pdgfra-Cre) and floxed Lmna (Lmna F/F) mice. The LMNA protein was nearly absent in ~80% of the cardiac fibroblasts and ~25% of cardiac myocytes in the Pdgfra-Cre:Lmna F/F mice. The Pdgfra-Cre:Lmna F/F mice showed an early phenotype characterized by cardiac conduction defects, arrhythmias, cardiac dysfunction, myocardial fibrosis, apoptosis, and premature death within the first six weeks of life. The Pdgfra-Cre:Lmna wild type/F (Lmna W/F) mice also showed a similar but slowly evolving phenotype that was expressed within one year of age. RNA sequencing of LMNA-deficient and wild-type cardiac fibroblasts identified differential expression of ~410 genes, which predicted activation of the TP53 and TNFA/NFκB and suppression of the cell cycle pathways. In agreement with these findings, levels of phospho-H2AFX, ATM, phospho-TP53, and CDKN1A, markers of the DNA damage response (DDR) pathway, were increased in the Pdgfra-Cre:Lmna F/F mouse hearts. Moreover, expression of senescence-associated beta-galactosidase was induced and levels of the senescence-associated secretory phenotype (SASP) proteins TGFß1, CTGF (CCN2), and LGLAS3 were increased as well as the transcript levels of additional genes encoding SASP proteins in the Pdgfra-Cre:Lmna F/F mouse hearts. Finally, expression of pH2AFX, a bonafide marker of the double-stranded DNA breaks, was increased in cardiac fibroblasts isolated from the Pdgfra-Cre:Lmna F/F mouse hearts. Conclusion: Deletion of the Lmna gene in fibroblasts partially recapitulates the phenotype of the LMNA-associated DCM, likely through induction of double-stranded DNA breaks, activation of the DDR pathway, and induction of expression of the SASP proteins. The findings indicate that the phenotype in the LMNA-associated DCM is the aggregate consequence of the LMNA deficiency in multiple cardiac cells, including cardiac fibroblasts.

Genetic basis of cardiovascular aging is at the core of human longevity.

Aging is an archetypical complex process influenced by genetic and environmental factors. Genetic variants impart a gradient of effect sizes, albeit the effect sizes seem to be skewed toward those with small effect sizes. On one end of the spectrum are the rare monogenic premature aging syndromes, such as Hutchinson Gilford Progeria Syndrome, whereby single nucleotide changes lead to rapidly progressive premature aging. On the end of the spectrum is the complex, slowly progressive process of living to an arbitrary-defined old age, i.e., longevity. Whereas the genetic basis of rare premature aging syndromes has been elucidated, only a small fraction of the genetic determinants of longevity and life span, time from birth to death, have been identified. The latter point to the complexity of the process and involvement of myriad of genetic and non-genetic factors and hence, the diluted effect of each determinant on longevity. The genetic discoveries point to the involvement of the DNA damage and activation of the DNA damage response pathway, particularly in the premature aging syndromes. Likewise, the insulin/insulin-like growth factor 1/mTOR/FOXO pathways have emerged as major regulators of life span. A notable fraction of the genetic variants that are associated with life span is also associated with age-related cardiovascular diseases, such as coronary artery disease and dyslipidemia, which places cardiovascular aging at the core of human life span. The clinical impact of the discoveries pertains to the identification of the pathways that are involved in life span, which might serve as targets of interventions to prevent, slow, and even possibly reverse aging.

The WNT/ß-catenin pathway regulates expression of the genes involved in cell cycle progression and mitochondrial oxidative phosphorylation in the postmitotic cardiac myocytes.

INTRODUCTION: Aging is associated with cardiac myocyte loss, sarcopenia, and cardiac dysfunction. Adult cardiac myocytes are postmitotic cells with an insufficient proliferative capacity to compensate for myocyte loss. The canonical WNT (cWNT) pathway is involved in the regulation of cell cycle reentry in various cell types. The effects of the cWNT pathway on the expression of genes involved in cell cycle reentry in the postmitotic cardiac myocytes are unknown. AIM: The aim of the study was to identify genes whose expression is regulated by the ß-catenin, the indispensable component to the cWNT signaling, in the postmitotic myocytes. METHODS AND RESULTS: Cardiac myocyte-specific tamoxifen-inducible MerCreMer (Myh6-Mcm) mice were used to delete the floxed exon 3 or exons 8 to 13 of the Ctnnb1 gene to induce gain-of-function (GoF) or loss-of-function (LoF) the ß-catenin, respectively. Deletion of exon 3 leads to the expression of a stable ß-catenin. In contrast, deletion of exons 8-13 leads to the expression of transcriptionally inactive truncated ß-catenin, which is typically degraded. GoF or LoF of the ß-catenin was verified by reverse transcription-polymerase chain reaction (RT-PCR), immunoblotting, and immunofluorescence. Myocyte transcripts were analyzed by RNA-Sequencing (RNA-Seq) at 4 weeks of age. The GoF of ß-catenin was associated with differential expression of ~1700 genes, whereas its LoF altered expression of ~400 genes. The differentially expressed genes in the GoF myocytes were enriched in pathways regulating the cell cycle, including karyokinesis and cytokinesis, whereas the LoF was associated with increased expression of genes involved in mitochondrial oxidative phosphorylation. These findings were validated by RT-PCR in independent samples. Short-term GoF nor LoF of ß-catenin did not affect the number of cardiac myocytes, cardiac function, myocardial fibrosis, myocardial apoptosis, or adipogenesis at 4 weeks of age. CONCLUSION: Activation of the ß-catenin of the cWNT pathway in postmitotic myocytes leads to cell cycle reentry and expression of genes involved in cytokinesis without leading to an increase in the number of myocytes. In contrast, suppression of the ß-catenin modestly increases the expression of genes involved in oxidative phosphorylation. The findings provide insights into the role of ß-catenin of the cWNT pathway in the regulation of cell cycle reentry and oxidative phosphorylation in the postmitotic cardiac myocytes.

Effects of tamoxifen inducible MerCreMer on gene expression in cardiac myocytes in mice.

The Cre-LoxP technology, including the tamoxifen (TAM) inducible MerCreMer (MCM), is increasingly used to delineate gene function, understand the disease mechanisms, and test therapeutic interventions. We set to determine the effects of TAM-MCM on cardiac myocyte transcriptome. Expression of the MCM was induced specifically in cardiac myocytes upon injection of TAM to myosin heavy chain 6-MCM (Myh6-Mcm) mice for 5 consecutive days. Cardiac function, myocardial histology, and gene expression (RNA-sequencing) were analyzed 2 weeks after TAM injection. A total of 346 protein coding genes (168 up- and 178 down-regulated) were differentially expressed. Transcript levels of 85 genes, analyzed by a reverse transcription-polymerase chain reaction in independent samples, correlated with changes in the RNA-sequencing data. The differentially expressed genes were modestly enriched for genes involved in the interferon response and the tumor protein 53 (TP53) pathways. The changes in gene expression were relatively small and mostly transient and had no discernible effects on cardiac function, myocardial fibrosis, and apoptosis or induction of double-stranded DNA breaks. Thus, TAM-inducible activation of MCM alters cardiac myocytes gene expression, provoking modest and transient interferon and DNA damage responses without exerting other discernible phenotypic effects. Thus, the effects of TAM-MCM on gene expression should be considered in discerning the bona fide changes that result from the targeting of the gene of interest.

The EP300/TP53 pathway, a suppressor of the Hippo and canonical WNT pathways, is activated in human hearts with arrhythmogenic cardiomyopathy in the absence of overt heart failure.

AIMS: Arrhythmogenic cardiomyopathy (ACM) is a primary myocardial disease that typically manifests with cardiac arrhythmias, progressive heart failure, and sudden cardiac death (SCD). ACM is mainly caused by mutations in genes encoding desmosome proteins. Desmosomes are cell-cell adhesion structures and hubs for mechanosensing and mechanotransduction. The objective was to identify the dysregulated molecular and biological pathways in human ACM in the absence of overt heart failure. METHODS AND RESULTS: Transcriptomes in the right ventricular endomyocardial biopsy samples from three independent individuals carrying truncating mutations in the DSP gene and five control samples were analysed by RNA-Seq (discovery group). These cases presented with cardiac arrhythmias and had a normal right ventricular function. The RNA-Seq analysis identified ∼5000 differentially expressed genes (DEGs), which predicted suppression of the Hippo and canonical WNT pathways, among others. Dysregulated genes and pathways, identified by RNA-Seq, were tested for validation in the right and left ventricular tissues from five independent autopsy-confirmed ACM cases with defined mutations (validation group), who were victims of SCD and had no history of heart failure. Protein levels and nuclear localization of the cWNT and Hippo pathway transcriptional regulators were reduced in the right and left ventricular validation samples. In contrast, levels of acetyltransferase EP300, known to suppress the Hippo and canonical WNT pathways, were increased and its bona fide target TP53 was acetylated. RNA-Seq data identified apical junction, reflective of cell-cell attachment, as the most disrupted biological pathway, which were corroborated by disrupted desmosomes and intermediate filament structures. Moreover, the DEGs also predicted dysregulation of over a dozen canonical signal transduction pathways, including the Tec kinase and integrin signalling pathways. The changes were associated with increased apoptosis and fibro-adipogenesis in the ACM hearts. CONCLUSION: Altered apical junction structures are associated with activation of the EP300-TP53 and suppression of the Hippo/cWNT pathways in human ACM caused by defined mutations in the absence of an overt heart failure. The findings implicate altered mechanotransduction in the pathogenesis of ACM.

Genetic Ablation of the DNA Damage Response Pathway Attenuates Lamin-Associated Dilated Cardiomyopathy in Mice.

Hereditary dilated cardiomyopathy (DCM) is a primary disease of cardiac myocytes caused by mutations in genes encoding proteins with a diverse array of functions. Mutations in the LMNA gene, encoding the nuclear envelope protein lamin A/C, are the second most common causes of DCM. The phenotype is characterized by progressive cardiac dysfunction, leading to refractory heart failure, myocardial fibrosis, cardiac arrhythmias, and sudden cardiac death. The molecular pathogenesis of DCM caused by the LMNA mutations is not well known. The LMNA protein is involved in nuclear membrane stability. It is also a guardian of the genome involved in the processing of the topoisomerases at the transcriptionally active domain and the repair of double-stranded DNA breaks (DSBs). Deletion of the mouse Lmna gene in cardiac myocytes leads to premature death, DCM, myocardial fibrosis, and apoptosis. The phenotype is associated with increased expression of the cytosolic DNA sensor cyclic GMP-AMP synthase (CGAS) and activation of the DNA damage response (DDR) pathway. Genetic blockade of the DDR pathway, upon knockout of the Mb21d1 gene encoding CGAS, prolonged survival, improved cardiac function, partially restored levels of molecular markers of heart failure, and attenuated myocardial apoptosis and fibrosis in the LMNA-deficient mice. The findings indicate that targeting the CGAS/DDR pathway might be beneficial in the treatment of DCM caused by mutations in the LMNA gene.