DNA Damage Response/TP53 Pathway Is Activated and Contributes to the Pathogenesis of Dilated Cardiomyopathy Associated With LMNA (Lamin A/C) Mutations

Research landscape of genetics in dilated cardiomyopathy: insight from a bibliometric analysis

Background

Dilated cardiomyopathy (DCM) is a heterogeneous myocardial disorder with diverse genetic or acquired origins. Notable advances have been achieved in discovering and understanding the genetics of DCM. This study aimed to depict the distribution of the main research forces, hotspots, and frontiers in the genetics of DCM, thus shaping future research directions.

Methods

Based on the documents published in the Web of Science Core Collection database from 2013 to 2022, co-authorship of authors, institutions, and countries/regions, co-citation of references, and co-occurrence of keywords were conducted respectively to present the distribution of the leading research forces, research hotspots, and emerging trends in the genetics of DCM.

Results

4,141 documents were included, and the annual publications have steadily increased. Seidman, Christine E, Meder, Benjamin, Sinagra, Gianfranco were the most productive authors, German Centre for Cardiovascular Research was the most productive institution, and the USA, China, and Germany were the most prolific countries. The co-occurrence of keywords has generated 8 clusters, including DCM, lamin a/c, heart failure, sudden cardiac death, hypertrophic cardiomyopathy, cardiac hypertrophy, arrhythmogenic cardiomyopathy, and next-generation sequencing. Frequent keywords with average publication time after 2019 mainly included arrhythmogenic cardiomyopathy, whole-exome sequencing, RBM 20, phenotype, risk stratification, precision medicine, genotype, and machine learning.

Conclusion

The research landscape of genetics in DCM is continuously evolving. Deciphering the genetic profiles by next-generation sequencing and illustrating pathogenic mechanisms of gene variants, establishing innovative treatments for heart failure and improved risk stratification for SCD, uncovering the genetic overlaps between DCM and other inherited cardiomyopathies, as well as identifying genotype-phenotype correlations are the main research hotspots and frontiers in this field.

The E2F family: a ray of dawn in cardiomyopathy

Cardiomyopathies are a group of heterogeneous diseases, characterized by abnormal structure and function of the myocardium. For many years, it has been a hot topic because of its high morbidity and mortality as well as its complicated pathogenesis. The E2Fs, a group of transcription factors found extensively in eukaryotes, play a crucial role in governing cell proliferation, differentiation, and apoptosis, meanwhile their deregulated activity can also cause a variety of diseases. Based on accumulating evidence, E2Fs play important roles in cardiomyopathies. In this review, we describe the structural and functional characteristics of the E2F family and its role in cardiomyocyte processes, with a focus on how E2Fs are associated with the onset and development of cardiomyopathies. Moreover, we discuss the great potential of E2Fs as biomarkers and therapeutic targets, aiming to provide a reference for future research.

TRIM35 Monoubiquitinates H2B in Cardiac Cells, Implications for Heart Failure

BACKGROUND

The tumor suppressor and proapoptotic transcription factor P53 is induced (and activated) in several forms of heart failure, including cardiotoxicity and dilated cardiomyopathy; however, the precise mechanism that coordinates its induction with accessibility to its transcriptional promoter sites remains unresolved, especially in the setting of mature terminally differentiated (nonreplicative) cardiomyocytes.

METHODS

Male and female control or TRIM35 (tripartite motif containing 35) overexpression adolescent (aged 1-3 months) and adult (aged 4-6 months) transgenic mice were used for all in vivo experiments. Primary adolescent or adult mouse cardiomyocytes were isolated from control or TRIM35 overexpression transgenic mice for all in vitro experiments. Adenovirus or small-interfering RNA was used for all molecular experiments to overexpress or knockdown, respectively, target genes in primary mouse cardiomyocytes. Patient dilated cardiomyopathy or nonfailing left ventricle samples were used for translational and mechanistic insight. Chromatin immunoprecipitation and DNA sequencing or quantitative real-time polymerase chain reaction (qPCR) was used to assess P53 binding to its transcriptional promoter targets, and RNA sequencing was used to identify disease-specific signaling pathways.

RESULTS

Here, we show that E3-ubiquitin ligase TRIM35 can directly monoubiquitinate lysine-120 (K120) on histone 2B in postnatal mature cardiomyocytes. This epigenetic modification was sufficient to promote chromatin remodeling, accessibility of P53 to its transcriptional promoter targets, and elongation of its transcribed mRNA. We found that increased P53 transcriptional activity (in cardiomyocyte-specific Trim35 overexpression transgenic mice) was sufficient to initiate heart failure and these molecular findings were recapitulated in nonischemic human LV dilated cardiomyopathy samples.

CONCLUSIONS

These findings suggest that TRIM35 and the K120Ub-histone 2B epigenetic modification are molecular features of cardiomyocytes that can collectively predict dilated cardiomyopathy pathogenesis.

Pervasive nuclear envelope ruptures precede ECM signaling and disease onset without activating cGAS-STING in Lamin-cardiomyopathy mice

Nuclear envelope (NE) ruptures are emerging observations in Lamin-related dilated cardiomyopathy, an adult-onset disease caused by loss-of-function mutations in Lamin A/C, a nuclear lamina component. Here, we test a prevailing hypothesis that NE ruptures trigger the pathological cGAS-STING cytosolic DNA-sensing pathway using a mouse model of Lamin cardiomyopathy. The reduction of Lamin A/C in cardio-myocyte of adult mice causes pervasive NE ruptures in cardiomyocytes, preceding inflammatory transcription, fibrosis, and fatal dilated cardiomyopathy. NE ruptures are followed by DNA damage accumulation without causing immediate cardiomyocyte death. However, cGAS-STING-dependent inflammatory signaling remains inactive. Deleting cGas or Sting does not rescue cardiomyopathy in the mouse model. The lack of cGAS-STING activation is likely due to the near absence of cGAS expression in adult cardiomyocytes at baseline. Instead, extracellular matrix (ECM) signaling is activated and predicted to initiate pro-inflammatory communication from Lamin-reduced cardiomyocytes to fibroblasts. Our work nominates ECM signaling, not cGAS-STING, as a potential inflammatory contributor in Lamin cardiomyopathy.

Multi-level transcriptomic analysis of LMNA -related dilated cardiomyopathy identifies disease-driving processes

LMNA- related dilated cardiomyopathy ( LMNA -DCM) is one of the most severe forms of DCM. The incomplete understanding of the molecular disease mechanisms results in lacking treatment options, leading to high mortality amongst patients. Here, using an inducible, cardiomyocyte-specific lamin A/C depletion mouse model, we conducted a comprehensive transcriptomic study, combining both bulk and single nucleus RNA sequencing, and spanning LMNA -DCM disease progression, to identify potential disease drivers. Our refined analysis pipeline identified 496 genes already misregulated early in disease. The expression of these genes was largely driven by disease specific cardiomyocyte sub-populations and involved biological processes mediating cellular response to DNA damage, cytosolic pattern recognition, and innate immunity. Indeed, DNA damage in LMNA -DCM hearts was significantly increased early in disease and correlated with reduced cardiomyocyte lamin A levels. Activation of cytosolic pattern recognition in cardiomyocytes was independent of cGAS, which is rarely expressed in cardiomyocytes, but likely occurred downstream of other pattern recognition sensors such as IFI16. Altered gene expression in cardiac fibroblasts and immune cell infiltration further contributed to tissue-wide changes in gene expression. Our transcriptomic analysis further predicted significant alterations in cell-cell communication between cardiomyocytes, fibroblasts, and immune cells, mediated through early changes in the extracellular matrix (ECM) in the LMNA -DCM hearts. Taken together, our work suggests a model in which nuclear damage in cardiomyocytes leads to activation of DNA damage responses, cytosolic pattern recognition pathway, and other signaling pathways that activate inflammation, immune cell recruitment, and transcriptional changes in cardiac fibroblasts, which collectively drive LMNA -DCM pathogenesis.

Global Proteomic Analysis Reveals Alterations in Differentially Expressed Proteins between Cardiopathic Lamin A/C Mutations

Lamin A/C (LMNA) is an important component of nuclear lamina. Mutations cause arrhythmia, heart failure, and sudden cardiac death. While LMNA-associated cardiomyopathy typically has an aggressive course that responds poorly to conventional heart failure therapies, there is variability in severity and age of penetrance between and even within specific mutations, which is poorly understood at the cellular level. Further, this heterogeneity has not previously been captured to mimic the heterozygous state, nor have the hundreds of clinical LMNA mutations been represented. Herein, we have overexpressed cardiopathic LMNA variants in HEK cells and utilized state-of-the-art quantitative proteomics to compare the global proteomic profiles of (1) aggregating Q353 K alone, (2) Q353 K coexpressed with WT, (3) aggregating N195 K coexpressed with WT, and (4) nonaggregating E317 K coexpressed with WT to help capture some of the heterogeneity between mutations. We analyzed each data set to obtain the differentially expressed proteins (DEPs) and applied gene ontology (GO) and KEGG pathway analyses. We found a range of 162 to 324 DEPs from over 6000 total protein IDs with differences in GO terms, KEGG pathways, and DEPs important in cardiac function, further highlighting the complexity of cardiac laminopathies. Pathways disrupted by LMNA mutations were validated with redox, autophagy, and apoptosis functional assays in both HEK 293 cells and in induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) for LMNA N195 K. These proteomic profiles expand our repertoire for mutation-specific downstream cellular effects that may become useful as druggable targets for personalized medicine approach for cardiac laminopathies.

Eliminating elevated p53 signaling fails to rescue skeletal muscle defects or extend survival in lamin A/C-deficient mice

Lamins A and C, encoded by the LMNA gene, are nuclear intermediate filaments that provide structural support to the nucleus and contribute to chromatin organization and transcriptional regulation. LMNA mutations cause muscular dystrophies, dilated cardiomyopathy, and other diseases. The mechanisms by which many LMNA mutations result in muscle-specific diseases have remained elusive, presenting a major hurdle in the development of effective treatments. Previous studies using striated muscle laminopathy mouse models found that cytoskeletal forces acting on mechanically fragile Lmna-mutant nuclei led to transient nuclear envelope rupture, extensive DNA damage, and activation of DNA damage response (DDR) pathways in skeletal muscle cells in vitro and in vivo. Furthermore, hearts of Lmna mutant mice have elevated activation of the tumor suppressor protein p53, a central regulator of DDR signaling. We hypothesized that elevated p53 activation could present a pathogenic mechanism in striated muscle laminopathies, and that eliminating p53 activation could improve muscle function and survival in laminopathy mouse models. Supporting a pathogenic function of p53 activation in muscle, stabilization of p53 was sufficient to reduce contractility and viability in wild-type muscle cells in vitro. Using three laminopathy models, we found that increased p53 activity in Lmna-mutant muscle cells primarily resulted from mechanically induced damage to the myonuclei, and not from altered transcriptional regulation due to loss of lamin A/C expression. However, global deletion of p53 in a severe muscle laminopathy model did not reduce the disease phenotype or increase survival, indicating that additional drivers of disease must contribute to the disease pathogenesis.

Exploring the mechanism of Tingli Pill in the treatment of HFpEF based on network pharmacology and molecular docking

To explore the mechanism of action of Tingli Pill (TLP) in the treatment of heart failure with preserved ejection fraction (HFpEF) by using network pharmacology and molecular docking technology. The active components and targets of TLP were screened using the TCMSP and UniProt databases. HFpEF-related targets were identified using the OMIM and GeneCards databases. Drug-disease intersection targets were obtained via Venny 2.1.0, as well as establishing the "component-target" network and screening out the core active components. Construct a protein-protein interaction network of intersecting targets using the STRING database as well as Cytoscape software and filter the core targets. Gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis of core targets were performed using the Metascape database. The core active components of TLP for HFpEF were quercetin, kaempferol, β-sitosterol, isorhamnetin and hederagenin. The core targets of TLP for HFpEF were JUN, MAPK1, TP53, AKT1, RELA, TNF, MAPK14, and IL16. Gene ontology enrichment analysis obtained 1528 biological processes, 85 cell components, and 140 molecular functions. The Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis yielded 1940 signaling pathways, mainly involved in lipid and atherosclerosis, regulation of apoptotic signaling pathway, PI3K-Akt signaling pathway, HIF-1 signaling pathway, oxidative stress, TNF signaling pathway, and IL-17 signaling pathway. TLP has the characteristics of multi-component, multi-target, and multi-pathway in the treatment of HFpEF. This study lays the foundation for revealing the pharmacodynamic substances and mechanism of TLP in the treatment of HFpEF.

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.

Myocardial DNA Damage Predicts Heart Failure Outcome in Various Underlying Diseases

BACKGROUND

Reliable predictors of treatment efficacy in heart failure have been long awaited. DNA damage has been implicated as a cause of heart failure.

OBJECTIVES

The purpose of this study was to investigate the association of DNA damage in myocardial tissue with treatment response and prognosis of heart failure.

METHODS

The authors performed immunostaining of DNA damage markers poly(ADP-ribose) (PAR) and γ-H2A.X in endomyocardial biopsy specimens from 175 patients with heart failure with reduced ejection fraction (HFrEF) of various underlying etiologies. They calculated the percentage of nuclei positive for each DNA damage marker (%PAR and %γ-H2A.X). The primary outcome was left ventricular reverse remodeling (LVRR) at 1 year, and the secondary outcome was a composite of cardiovascular death, heart transplantation, and ventricular assist device implantation.

RESULTS

Patients who did not achieve LVRR after the optimization of medical therapies presented with significantly higher %PAR and %γ-H2A.X. The ROC analysis demonstrated good performance of both %PAR and %γ-H2A.X for predicting LVRR (AUCs: 0.867 and 0.855, respectively). There was a negative correlation between the mean proportion of DNA damage marker-positive nuclei and the probability of LVRR across different underlying diseases. In addition, patients with higher %PAR or %γ-H2A.X had more long-term clinical events (PAR HR: 1.63 [95% CI: 1.31-2.01]; P < 0.001; γ-H2A.X HR: 1.48 [95% CI: 1.27-1.72]; P < 0.001).

CONCLUSIONS

DNA damage determines the consequences of human heart failure. Assessment of DNA damage is useful to predict treatment efficacy and prognosis of heart failure patients with various underlying etiologies.

The structure and function of lamin A/C: Special focus on cardiomyopathy and therapeutic interventions

Lamins are inner nuclear membrane proteins that belong to the intermediate filament family. Lamin A/C lie adjacent to the heterochromatin structure in polymer form, providing skeletal to the nucleus. Based on the localization, lamin A/C provides nuclear stability and cytoskeleton to the nucleus and modulates chromatin organization and gene expression. Besides being the structural protein making the inner nuclear membrane in polymer form, lamin A/C functions as a signalling molecule involved in gene expression as an enhancer inside the nucleus. Lamin A/C regulates various cellular pathways like autophagy and energy balance in the cytoplasm. Its expression is highly variable in differentiated tissues, higher in hard tissues like bone and muscle cells, and lower in soft tissues like the liver and brain. In muscle cells, including the heart, lamin A/C must be expressed in a balanced state. Lamin A/C mutation is linked with various diseases, such as muscular dystrophy, lipodystrophy, and cardiomyopathies. It has been observed that a good number of mutations in the LMNA gene impact cardiac activity and its function. Although several works have been published, there are still several unexplored areas left regarding the lamin A/C function and structure in the cardiovascular system and its pathological state. In this review, we focus on the structural organization, expression pattern, and function of lamin A/C, its interacting partners, and the pathophysiology associated with mutations in the lamin A/C gene, with special emphasis on cardiovascular diseases. With the recent finding on lamin A/C, we have summarized the possible therapeutic interventions to treat cardiovascular symptoms and reverse the molecular changes.

Primate Model Carrying LMNA Mutation Develops Dilated Cardiomyopathy

To solve the clinical transformation dilemma of lamin A/C (LMNA)-mutated dilated cardiomyopathy (LMD), we developed an LMNA-mutated primate model based on the similarity between the phenotype of primates and humans. We screened out patients with LMD and compared the clinical data of LMD with TTN-mutated and mutation-free dilated cardiomyopathy to obtain the unique phenotype. After establishment of the LMNA c.357-2A>G primate model, primates were continuously observed for 48 months, and echocardiographic, electrophysiological, histologic, and transcriptional data were recorded. The LMD primate model was found to highly simulate the phenotype of clinical LMD. In addition, the LMD primate model shared a similar natural history with humans.

Genetic inactivation of β-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)/β-catenin pathway is implicated in the pathogenesis of ACM. The β-catenin is an indispensable co-transcriptional regulator of the cWNT pathway and a member of the IDs. We genetically inactivated or activated β-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/β-catenin pathway was markedly dysregulated in the Myh6-McmTam:DspF/F cardiac myocytes, as indicated by a concomitant increase in the expression of cWNT/β-catenin target genes, isoforms of its key co-effectors, and the inhibitors of the pathway. The β-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 β-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 β-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/β-catenin was markedly dysregulated in the cardiac myocytes in a mouse model of desmoplakin cardiomyopathy. Inactivation of β-catenin attenuated, whereas its activation aggravated the phenotype, through multiple molecular pathways, independent of the cWNT transcriptional activity. Thus, suppression but not activation of β-catenin might be beneficial in desmoplakin cardiomyopathy.

An effective disease diagnostic model related to pyroptosis in ischemic cardiomyopathy

Pyroptosis is involved in ischemic cardiomyopathy (ICM). The study aimed to investigate the pyroptosis-related genes and clarify their diagnostic value in ICM. The bioinformatics method identified the differential pyroptosis genes between the normal control and ICM samples from online datasets. Then, protein-protein interaction (PPI) and function analysis were carried out to explore the function of these genes. Following, subtype analysis was performed using ConsensusClusterPlus, functions, immune score, stromal score, immune cell proportion and human leukocyte antigen (HLA) genes between subtypes were investigated. Moreover, optimal pyroptosis genes were selected using the least absolute shrinkage and selection operator (LASSO) analysis to construct a diagnostic model and evaluate its effectiveness using receiver operator characteristic (ROC) analysis. Twenty-one differential expressed pyroptosis genes were identified, and these genes were related to immune and pyroptosis. Subtype analysis identified two obvious subtypes: sub-1 and sub-2. And LASSO identified 13 optimal genes used to construct the diagnostic model. The diagnostic model in ICM diagnosis with the area under ROC (AUC) was 0.965. Our results suggested that pyroptosis was tightly associated with ICM.

Molecular targets and mechanisms of Jiawei Jiaotai Pill on diabetic cardiomyopathy based on network pharmacology

BACKGROUND

Jiawei Jiaotai Pill is commonly used in clinical practice to reduce apoptosis, increase insulin secretion, and improve blood glucose tolerance. However, its mechanism of action in the treatment of diabetic cardiomyopathy (DCM) remains unclear, hindering research efforts aimed at developing drugs specifically for the treatment of DCM.

AIM

To explore the pharmacodynamic basis and molecular mechanism of Jiawei Jiaotai Pill in DCM treatment.

METHODS

We explored various databases and software, including the Traditional Chinese Medicine Systems Pharmacology Database, Uniport, PubChem, GenCards, String, and Cytoscape, to identify the active components and targets of Jiawei Jiaotai Pill, and the disease targets in DCM. Protein-protein interaction network, gene ontology, and Kyoto Encyclopedia of Genes and Genomes analyses were used to determine the mechanism of action of Jiawei Jiaotai Pill in treating DCM. Molecular docking of key active components and core targets was verified using AutoDock software.

RESULTS

Total 42 active ingredients and 142 potential targets of Jiawei Jiaotai Pill were identified. There were 100 common targets between the DCM and Jiawei Jiaotai Pills. Through this screening process, TNF, IL6, TP53, EGFR, INS, and other important targets were identified. These targets are mainly involved in the positive regulation of the mitogen-activated protein kinase (MAPK) MAPK cascade, response to xenobiotic stimuli, response to hypoxia, positive regulation of gene expression, positive regulation of cell proliferation, negative regulation of the apoptotic process, and other biological processes. It was mainly enriched in the AGE-RAGE signaling pathway in diabetic complications, DCM, PI3K-Akt, interleukin-17, and MAPK signaling pathways. Molecular docking results showed that Jiawei Jiaotai Pill's active ingredients had good docking activity with DCM's core target.

CONCLUSION

The active components of Jiawei Jiaotai Pill may play a role in the treatment of DCM by reducing oxidative stress, cardiomyocyte apoptosis and fibrosis, and maintaining metabolic homeostasis.

Naturally occurring canine laminopathy leading to a dilated and fibrosing cardiomyopathy in the Nova Scotia Duck Tolling Retriever

Dilated cardiomyopathy (DCM) is characterized by decreased systolic function and dilation of one or both ventricles, often leading to heart failure or sudden death. Two 10-month-old sibling Nova Scotia Duck Tolling Retrievers (NSDTR) died acutely with evidence of dilated cardiomyopathy with myocardial fibrosis. Association analysis using two cases and 35 controls identified three candidate regions homozygous in the two cases. Whole genome sequencing identified a frameshift deletion in the LMNA gene (NC_049228.1:g.41688530del, NP_001274080:p.(Asp576ThrfsTer124)). Three retrospectively identified NSDTRs with sudden death before 2 years of age and severe myocardial fibrosis were also homozygous for the deletion. One 5 year old with sudden death and myocardial fibrosis was heterozygous for the deletion. This variant was not identified in 722 dogs of other breeds, nor was it identified to be homozygous in 784 NSDTR. LMNA codes for lamin A/C proteins, which are type V intermediate filaments that provide structural support to the nuclear membrane. In humans, LMNA variants can cause DCM with sudden death as well as diseases of striated muscles, lipodystrophy, neuropathies, and accelerated aging disorders. This frameshift deletion is predicted to affect processing of prelamin A into lamin A. Pedigree analysis in the NSDTR and functional evaluation of heterozygotes is consistent with a predominantly recessive mode of inheritance and possibly low penetrance in heterozygotes in contrast to people, where most pathogenic LMNA variants are dominantly inherited.

Systematic in vivo candidate evaluation uncovers therapeutic targets for LMNA dilated cardiomyopathy and risk of Lamin A toxicity

BACKGROUND

Dilated cardiomyopathy (DCM) is a severe, non-ischemic heart disease which ultimately results in heart failure (HF). Decades of research on DCM have revealed diverse aetiologies. Among them, familial DCM is the major form of DCM, with pathogenic variants in LMNA being the second most common form of autosomal dominant DCM. LMNA DCM is a multifactorial and complex disease with no specific treatment thus far. Many studies have demonstrated that perturbing candidates related to various dysregulated pathways ameliorate LMNA DCM. However, it is unknown whether these candidates could serve as potential therapeutic targets especially in long term efficacy.

METHODS

We evaluated 14 potential candidates including Lmna gene products (Lamin A and Lamin C), key signaling pathways (Tgfβ/Smad, mTor and Fgf/Mapk), calcium handling, proliferation regulators and modifiers of LINC complex function in a cardiac specific Lmna DCM model. Positive candidates for improved cardiac function were further assessed by survival analysis. Suppressive roles and mechanisms of these candidates in ameliorating Lmna DCM were dissected by comparing marker gene expression, Tgfβ signaling pathway activation, fibrosis, inflammation, proliferation and DNA damage. Furthermore, transcriptome profiling compared the differences between Lamin A and Lamin C treatment.

RESULTS

Cardiac function was restored by several positive candidates (Smad3, Yy1, Bmp7, Ctgf, aYAP1, Sun1, Lamin A, and Lamin C), which significantly correlated with suppression of HF/fibrosis marker expression and cardiac fibrosis in Lmna DCM. Lamin C or Sun1 shRNA administration achieved consistent, prolonged survival which highly correlated with reduced heart inflammation and DNA damage. Importantly, Lamin A treatment improved but could not reproduce long term survival, and Lamin A administration to healthy hearts itself induced DCM. Mechanistically, we identified this lapse as caused by a dose-dependent toxicity of Lamin A, which was independent from its maturation.

CONCLUSIONS

In vivo candidate evaluation revealed that supplementation of Lamin C or knockdown of Sun1 significantly suppressed Lmna DCM and achieve prolonged survival. Conversely, Lamin A supplementation did not rescue long term survival and may impart detrimental cardiotoxicity risk. This study highlights a potential of advancing Lamin C and Sun1 as therapeutic targets for the treatment of LMNA DCM.

OPA1, a molecular regulator of dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a disease with no specific treatment, poor prognosis and high mortality. During DCM development, there is apoptosis, mitochondrial dynamics imbalance and changes in cristae structure. Optic atrophy 1 (OPA1) appears at high frequency in these three aspects. DCM LMNA (LaminA/C) gene mutation can activate TP53, and the study of P53 shows that P53 affects OPA1 through Bak/Bax and OMA1 (a metalloprotease). OPA1 can be considered the missing link between DCMp53 and DCM apoptosis, mitochondrial dynamics imbalance and changes in cristae structure. OPA1 regulates apoptosis by regulating the release of cytochrome c from the mitochondrial matrix through CJs (crisp linkages, located in the inner mitochondrial membrane) and unbalances mitochondrial fusion and fission by affecting mitochondrial inner membrane (IM) fusion. OPA1 is also associated with the formation and maintenance of mitochondrial cristae. OPA1 is not the root cause of DCM, but it is an essential mediator in P53 mediating the occurrence and development of DCM, so OPA1 also becomes a molecular regulator of DCM. This review discusses the implication of OPA1 for DCM from three aspects: apoptosis, mitochondrial dynamics and ridge structure.

Regulated cell death pathways in cardiomyopathy

Heart disease is a worldwide health menace. Both intractable primary and secondary cardiomyopathies contribute to malignant cardiac dysfunction and mortality. One of the key cellular processes associated with cardiomyopathy is cardiomyocyte death. Cardiomyocytes are terminally differentiated cells with very limited regenerative capacity. Various insults can lead to irreversible damage of cardiomyocytes, contributing to progression of cardiac dysfunction. Accumulating evidence indicates that majority of cardiomyocyte death is executed by regulating molecular pathways, including apoptosis, ferroptosis, autophagy, pyroptosis, and necroptosis. Importantly, these forms of regulated cell death (RCD) are cardinal features in the pathogenesis of various cardiomyopathies, including dilated cardiomyopathy, diabetic cardiomyopathy, sepsis-induced cardiomyopathy, and drug-induced cardiomyopathy. The relevance between abnormity of RCD with adverse outcome of cardiomyopathy has been unequivocally evident. Therefore, there is an urgent need to uncover the molecular and cellular mechanisms for RCD in order to better understand the pathogenesis of cardiomyopathies. In this review, we summarize the latest progress from studies on RCD pathways in cardiomyocytes in context of the pathogenesis of cardiomyopathies, with particular emphasis on apoptosis, necroptosis, ferroptosis, autophagy, and pyroptosis. We also elaborate the crosstalk among various forms of RCD in pathologically stressed myocardium and the prospects of therapeutic applications targeted to various cell death pathways.

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.

Exploring novel biomarkers in dilated cardiomyopathy‑induced heart failure by integrated analysis and in vitro experiments

Despite the availability of several effective and promising treatment methods, heart failure (HF) remains a significant public health concern that requires advanced therapeutic strategies and techniques. Dilated cardiomyopathy (DCM) is a crucial factor that contributes to the development and deterioration of HF. The aim of the present study was to identify novel biomarkers and biological pathways to enhance the diagnosis and treatment of patients with DCM-induced HF using weighted gene co-expression network analysis (WGCNA). A total of 24 co-expressed gene modules connected with DCM-induced HF were obtained by WGCNA. Among these, the blue module had the highest correlation with DCM-induced HF (r=0.91; P<0.001) and was enriched in the AGE-RAGE signaling pathway in diabetic complications, the p53 and MAPK signaling pathway, adrenergic signaling in cardiomyocytes, the Janus kinase-STAT signaling pathway and cGMP/PKG signaling. Eight key genes, including secreted protein acidic and rich in cysteine-related modular calcium-binding protein 2 (SMOC2), serpin family A member 3 (SERPINA3), myosin heavy chain 6 (MYH6), S100 calcium binding protein A9 (S100A9), tubulin α (TUBA)3E, TUBA3D, lymphatic vessel endothelial hyaluronic acid receptor 1 (LYVE1) and phospholipase C ε1 (PLCE1), were selected as the therapeutic targets of DCM-induced HF based on WGCNA and differentially expressed gene analysis. Immune cell infiltration analysis revealed that the proportion of naive B cells and CD4-activated memory T cells was markedly upregulated in DCM-induced HF tissues compared with tissues from healthy controls. Furthermore, reverse transcription-quantitative PCR in AC16 human cardiomyocyte cells treated with doxorubicin showed that among the eight key genes, only SERPINA3, MYH6, S100A9, LYVE1 and PLCE1 exhibited expression levels identical to those revealed by bioinformatics analysis, suggesting that these genes may be involved in the development of DCM-induced HF.

AAV-based gene therapy prevents and halts the progression of dilated cardiomyopathy in a mouse model of phosphoglucomutase 1 deficiency (PGM1-CDG)

Phosphoglucomutase 1 (PGM1) deficiency is recognized as the third most common N-linked congenital disorders of glycosylation (CDG) in humans. Affected individuals present with liver, musculoskeletal, endocrine, and coagulation symptoms; however, the most life-threatening complication is the early onset of dilated cardiomyopathy (DCM). Recently, we discovered that oral D-galactose supplementation improved liver disease, endocrine, and coagulation abnormalities, but does not alleviate the fatal cardiomyopathy and the associated myopathy. Here we report on left ventricular ejection fraction (LVEF) in 6 individuals with PGM1-CDG. LVEF was pathologically low in most of these individuals and varied between 10% and 65%. To study the pathobiology of the cardiac disease observed in PGM1-CDG, we constructed a novel cardiomyocyte-specific conditional Pgm2 gene (mouse ortholog of human PGM1) knockout (Pgm2 cKO) mouse model. Echocardiography studies corroborated a DCM phenotype with significantly reduced ejection fraction and left ventricular dilation similar to those seen in individuals with PGM1-CDG. Histological studies demonstrated excess glycogen accumulation and fibrosis, while ultrastructural analysis revealed Z-disk disarray and swollen/fragmented mitochondria, which was similar to the ultrastructural pathology in the cardiac explant of an individual with PGM1-CDG. In addition, we found decreased mitochondrial function in the heart of KO mice. Transcriptomic analysis of hearts from mutant mice demonstrated a gene signature of DCM. Although proteomics revealed only mild changes in global protein expression in left ventricular tissue of mutant mice, a glycoproteomic analysis unveiled broad glycosylation changes with significant alterations in sarcolemmal proteins including different subunits of laminin-211, which was confirmed by immunoblot analyses. Finally, augmentation of PGM1 in KO mice via AAV9-PGM1 gene replacement therapy prevented and halted the progression of the DCM phenotype.

Identification of Novel Targets for Treatment of Dilated Cardiomyopathy Based on the Ferroptosis and Immune Heterogeneity

Purpose

This study aimed to investigate the role of ferroptosis in dilated cardiomyopathy (DCM) and to identify new targets for treatment and diagnosis of DCM.

Methods

GSE116250 and GSE145154 were downloaded from the Gene Expression Omnibus database. Unsupervised consensus clustering of DCM patients was used to confirm the impact of ferroptosis. Ferroptosis-related hub genes were identified by WGCNA and single cell sequencing analyses. Finally, we established a DCM mouse model via injection of Doxorubicin to verify the expression level of OTUD1 and colocalization between cell markers and OTUD1 in DCM mouse heart.

Results

A total of 13 ferroptosis-related differentially expressed genes (DEGs) were identified. The DCM patients were divided into two clusters according to the expression of 13 DEGs. The DCM patients in different clusters showed discrepancies in immune infiltration. Four hub genes were further identified by WGCNA analysis. Single cell data analysis revealed that OTUD1 may regulate B cells and DC cells and then participate in immune infiltration discrepancy. The upregulation of OTUD1 and the colocalization of OTUD1 with CD19 (B cell maker) and CD11c (DCs markers) markers were confirmed in DCM mouse hearts.

Conclusion

Ferroptosis and the immune microenvironment are closely associated with DCM, and OTUD1 may play an important role through B cells and DCs.

CCND1 Overexpression in Idiopathic Dilated Cardiomyopathy: A Promising Biomarker?

Cardiomyopathy, a disorder of electrical or heart muscle function, represents a type of cardiac muscle failure and culminates in severe heart conditions. The prevalence of dilated cardiomyopathy (DCM) is higher than that of other types (hypertrophic cardiomyopathy and restrictive cardiomyopathy) and causes many deaths. Idiopathic dilated cardiomyopathy (IDCM) is a type of DCM with an unknown underlying cause. This study aims to analyze the gene network of IDCM patients to identify disease biomarkers. Data were first extracted from the Gene Expression Omnibus (GEO) dataset and normalized based on the RMA algorithm (Bioconductor package), and differentially expressed genes were identified. The gene network was mapped on the STRING website, and the data were transferred to Cytoscape software to determine the top 100 genes. In the following, several genes, including VEGFA, IGF1, APP, STAT1, CCND1, MYH10, and MYH11, were selected for clinical studies. Peripheral blood samples were taken from 14 identified IDCM patients and 14 controls. The RT-PCR results revealed no significant differences in the expression of the genes APP, MYH10, and MYH11 between the two groups. By contrast, the STAT1, IGF1, CCND1, and VEGFA genes were overexpressed in patients more than in controls. The highest expression was found for VEGFA, followed by CCND1 (p < 0.001). Overexpression of these genes may contribute to disease progression in patients with IDCM. However, more patients and genes need to be analyzed in order to achieve more robust results.

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

Rationale

Human pluripotent stem cell-derived CMs (iPSC-CMs) are a valuable tool for disease modeling, cell therapy and to reconstruct the CM maturation process and identify, characterize factors that regulate maturation. The transition from immature fetal to adult CM entails coordinated regulation of the mature gene programming, which is characterized by the induction of myofilament and OXPHOS gene expression among others. Recent studies in Drosophila , C. elegans, and C2C12 myoblast cell lines have implicated the histone H3K4me3 demethylase KDM5 and its homologs, as a potential regulator of developmental gene program and mitochondrial function. We speculated that KDM5 may potentiate the maturation of iPSC-CMs by targeting a conserved epigenetic program that encompass mitochondrial OXPHOS and other CM specific maturation genes.

Objectives

The purpose of this study is to determine the role of KDM5 in iPSC-CM maturation.

Methods and Results

Immunoblot analysis revealed that KDM5A, B, and C expression was progressively downregulated in postnatal cardiomyocytes and absent in adult hearts and CMs. Additionally, KDM5 proteins were found to be persistently expressed in iPSC-CMs up to 60 days after the onset of myogenic differentiation, consistent with the immaturity of these cells. Inhibition of KDM5 by KDM5-C70 -a pan-KDM5 inhibitor-resulted in differential regulation of 2,372 genes including upregulation of Fatty acid oxidation (FAO), OXPHOS, and myogenic gene programs in iPSC-CMs. Likewise, genome-wide profiling of H3K4me3 binding sites by the CUT&RUN assay revealed enriched H3K4me3 peaks at the promoter regions of FAO, OXPHOS, and sarcomere genes. Consistent with the chromatin and gene expression data, KDM5 inhibition led to increased expression of multiple sarcomere proteins, enhanced myofibrillar organization and improved calcium handling. Furthermore, inhibition of KDM5 increased H3K4me3 deposits at the promoter region of the ESRRA gene, which is known to regulate OXPHOS and cardiomyocyte maturation, and resulted in its increased RNA and protein levels. Finally, KDM5 inhibition increased baseline, peak, and spare oxygen consumption rates in iPSC-CMs.

Conclusions

KDM5 regulates the maturation of iPSC-CMs by epigenetically regulating the expression of ESRRA, OXPHOS, FAO, and sarcomere genes and enhancing myofibril organization and mitochondrial function.

Epigenetics in LMNA-Related Cardiomyopathy

Mutations in the gene for lamin A/C (LMNA) cause a diverse range of diseases known as laminopathies. LMNA-related cardiomyopathy is a common inherited heart disease and is highly penetrant with a poor prognosis. In the past years, numerous investigations using mouse models, stem cell technologies, and patient samples have characterized the phenotypic diversity caused by specific LMNA variants and contributed to understanding the molecular mechanisms underlying the pathogenesis of heart disease. As a component of the nuclear envelope, LMNA regulates nuclear mechanostability and function, chromatin organization, and gene transcription. This review will focus on the different cardiomyopathies caused by LMNA mutations, address the role of LMNA in chromatin organization and gene regulation, and discuss how these processes go awry in heart disease.

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.

Integrated whole transcriptome analysis for the crucial regulators and functional pathways related to cardiac fibrosis in rats

BACKGROUND

Cardiac fibrosis has gradually gained significance in the field of cardiovascular disease; however, its specific pathogenesis remains unclear. This study aims to establish the regulatory networks based on whole-transcriptome RNA sequencing analyses and reveal the underlying mechanisms of cardiac fibrosis.

METHODS

An experimental model of myocardial fibrosis was induced using the chronic intermittent hypoxia (CIH) method. Expression profiles of long non-coding RNA (lncRNA), microRNA (miRNA), and messenger RNA (mRNA) were acquired from right atrial tissue samples of rats. Differentially expressed RNAs (DERs) were identified, and functional enrichment analysis was performed. Moreover, a protein-protein interaction (PPI) network and competitive endogenous RNA (ceRNA) regulatory network that are related to cardiac fibrosis were constructed, and the relevant regulatory factors and functional pathways were identified. Finally, the crucial regulators were validated using qRT-PCR.

RESULTS

DERs, including 268 lncRNAs, 20 miRNAs, and 436 mRNAs, were screened. Further, 18 relevant biological processes, such as "chromosome segregation, " and 6 KEGG signaling pathways, such as "cell cycle, " were significantly enriched. The regulatory relationship of miRNA-mRNA-KEGG pathways showed eight overlapping disease pathways, including "pathways in cancer." In addition, crucial regulatory factors, such as Arnt2, WNT2B, GNG7, LOC100909750, Cyp1a1, E2F1, BIRC5, and LPAR4, were identified and verified to be closely related to cardiac fibrosis.

CONCLUSION

This study identified the crucial regulators and related functional pathways in cardiac fibrosis by integrating the whole transcriptome analysis in rats, which might provide novel insights into the pathogenesis of cardiac fibrosis.

Emerging roles of interferon-stimulated gene-15 in age-related telomere attrition, the DNA damage response, and cardiovascular disease

Population aging and age-related cardiovascular disease (CVD) are becoming increasingly prevalent worldwide, generating a huge medical and socioeconomic burden. The complex regulation of aging and CVD and the interaction between these processes are crucially dependent on cellular stress responses. Interferon-stimulated gene-15 (ISG15) encodes a ubiquitin-like protein expressed in many vertebrate cell types that can be found both free and conjugated to lysine residues of target proteins via a post-translational process termed ISGylation. Deconjugation of ISG15 (deISGylation) is catalyzed by the ubiquitin-specific peptidase 18 (USP18). The ISG15 pathway has mostly been studied in the context of viral and bacterial infections and in cancer. This minireview summarizes current knowledge on the role of ISG15 in age-related telomere shortening, genomic instability, and DNA damage accumulation, as well as in hypertension, diabetes, and obesity, major CVD risk factors prevalent in the elderly population.

Mechanism of Epimedium intervention in heart failure based on network pharmacology and molecular docking technology

To analyze the pharmacological mechanism of Epimedium in regulating heart failure (HF) based on the network pharmacology method, and to provide a reference for the clinical application of Epimedium in treating HF. Obtaining the main active ingredients and their targets of Epimedium through TCMSP (Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform) database. Access to major HF targets through Genecards, OMIM, PharmGKB, Therapeutic Target Database, Drug Bank database. Protein interaction analysis using String platform and construction of PPI network. Subsequently, Cytoscape software was used to construct the "Epimedium active ingredient-heart failure target" network. Finally, the molecular docking is verified through the Systems Dock Web Site. The core active ingredients of Epimedium to regulate HF are quercetin, luteolin, kaempferol, etc. The core targets are JUN, MYC, TP53, HIF1A, ESR1, RELA, MAPK1, etc. Molecular docking validation showed better binding activity of the major targets of HF to the core components of Epimedium. The biological pathways that Epimedium regulates HF mainly act on lipid and atherosclerotic pathways, PI3K-Akt signaling pathway, and chemoattractant-receptor activation. And its molecular functions are mainly DNA-binding transcription factor binding, RNA polymerase II-specific DNA-binding transcription factor binding, and neurotransmitter receptor activity. This study reveals the multi-component, multi-target and multi-pathway mechanism of action of Epimedium in regulating mental failure, and provides a basis for the clinical development and utilization of Epimedium to intervene in HF.

Loss of function of the nuclear envelope protein LEMD2 causes DNA damage-dependent cardiomyopathy

Mutations in nuclear envelope proteins (NEPs) cause devastating genetic diseases, known as envelopathies, that primarily affect the heart and skeletal muscle. A mutation in the NEP LEM domain-containing protein 2 (LEMD2) causes severe cardiomyopathy in humans. However, the roles of LEMD2 in the heart and the pathological mechanisms responsible for its association with cardiac disease are unknown. We generated knockin (KI) mice carrying the human c.T38>G Lemd2 mutation, which causes a missense amino acid exchange (p.L13>R) in the LEM domain of the protein. These mice represent a preclinical model that phenocopies the human disease, as they developed severe dilated cardiomyopathy and cardiac fibrosis leading to premature death. At the cellular level, KI/KI cardiomyocytes exhibited disorganization of the transcriptionally silent heterochromatin associated with the nuclear envelope. Moreover, mice with cardiac-specific deletion of Lemd2 also died shortly after birth due to heart abnormalities. Cardiomyocytes lacking Lemd2 displayed nuclear envelope deformations and extensive DNA damage and apoptosis linked to p53 activation. Importantly, cardiomyocyte-specific Lemd2 gene therapy via adeno-associated virus rescued cardiac function in KI/KI mice. Together, our results reveal the essentiality of LEMD2 for genome stability and cardiac function and unveil its mechanistic association with human disease.

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.

Heart Failure Pathogenesis Elucidation and New Treatment Method Development

Heart failure (HF) is a leading cause of death worldwide. In Japan, the number of HF patients has increased with its aging population, resulting in "HF pandemic." HF is the final stage of various cardiovascular diseases, including valvular heart disease, ischemic heart disease, atrial fibrillation, and hypertension. Cardiac hypertrophy is a compensatory response to increased workload and maintains cardiac function. Pressure overload due to mechanical stress causes cardiac hypertrophy, whereas continuous cardiac stress reduces wall thickness and consequently causes HF. Understanding the molecular mechanisms underlying this process is crucial to elucidate HF pathophysiology. We demonstrated that ischemia and DNA damage are important in the progression of hypertrophy to HF. Genetic mutations associated with cardiomyopathy and prognosis has been identified. To realize precision medicines for HF, the underlying molecular mechanisms need to be elucidated. In this review, we introduce new paradigms for understanding HF pathophysiology discovered through basic research.

Loss of Nuclear Envelope Integrity and Increased Oxidant Production Cause DNA Damage in Adult Hearts Deficient in PKP2: A Molecular Substrate of ARVC

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by high propensity to life-threatening arrhythmias and progressive loss of heart muscle. More than 40% of reported genetic variants linked to ARVC reside in the PKP2 gene, which encodes the PKP2 protein (plakophilin-2).

METHODS

We describe a comprehensive characterization of the ARVC molecular landscape as determined by high-resolution mass spectrometry, RNA sequencing, and transmission electron microscopy of right ventricular biopsy samples obtained from patients with ARVC with PKP2 mutations and left ventricular ejection fraction >45%. Samples from healthy relatives served as controls. The observations led to experimental work using multiple imaging and biochemical techniques in mice with a cardiac-specific deletion of Pkp2 studied at a time of preserved left ventricular ejection fraction and in human induced pluripotent stem cell-derived PKP2-deficient myocytes.

RESULTS

Samples from patients with ARVC present a loss of nuclear envelope integrity, molecular signatures indicative of increased DNA damage, and a deficit in transcripts coding for proteins in the electron transport chain. Mice with a cardiac-specific deletion of Pkp2 also present a loss of nuclear envelope integrity, which leads to DNA damage and subsequent excess oxidant production (O2.- and H2O2), the latter increased further under mechanical stress (isoproterenol or exercise). Increased oxidant production and DNA damage is recapitulated in human induced pluripotent stem cell-derived PKP2-deficient myocytes. Furthermore, PKP2-deficient cells release H2O2 into the extracellular environment, causing DNA damage and increased oxidant production in neighboring myocytes in a paracrine manner. Treatment with honokiol increases SIRT3 (mitochondrial nicotinamide adenine dinucleotide-dependent protein deacetylase sirtuin-3) activity, reduces oxidant levels and DNA damage in vitro and in vivo, reduces collagen abundance in the right ventricular free wall, and has a protective effect on right ventricular function.

CONCLUSIONS

Loss of nuclear envelope integrity and subsequent DNA damage is a key substrate in the molecular pathology of ARVC. We show transcriptional downregulation of proteins of the electron transcript chain as an early event in the molecular pathophysiology of the disease (before loss of left ventricular ejection fraction <45%), which associates with increased oxidant production (O2.- and H2O2). We propose therapies that limit oxidant formation as a possible intervention to restrict DNA damage in ARVC.

Identification and validation of differentially expressed chromatin regulators for diagnosis of aortic dissection using integrated bioinformatics analysis and machine-learning algorithms

Background: Aortic dissection (AD) is a life-threatening disease. Chromatin regulators (CRs) are indispensable epigenetic regulators. We aimed to identify differentially expressed chromatin regulators (DECRs) for AD diagnosis.

Methods: We downloaded the GSE52093 and GSE190635 datasets from the Gene Expression Omnibus database. Following the merging and processing of datasets, bioinformatics analysis was applied to select candidate DECRs for AD diagnosis: CRs exertion; DECR identification using the “Limma” package; analyses of enrichment of function and signaling pathways; construction of protein–protein interaction (PPI) networks; application of machine-learning algorithms; evaluation of receiver operating characteristic (ROC) curves. GSE98770 served as the validation dataset to filter DECRs. Moreover, we collected peripheral-blood samples to further validate expression of DECRs by real-time reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Finally, a nomogram was built for clinical use.

Results: A total of 841 CRs were extracted from the merged dataset. Analyses of functional enrichment of 23 DECRs identified using Limma showed that DECRs were enriched mainly in epigenetic-regulation processes. From the PPI network, 17 DECRs were selected as node DECRs. After machine-learning calculations, eight DECRs were chosen from the intersection of 13 DECRs identified using support vector machine recursive feature elimination (SVM-RFE) and the top-10 DECRs selected using random forest. DECR expression between the control group and AD group were considerably different. Moreover, the area under the ROC curve (AUC) of each DECR was >0.75, and four DECRs (tumor protein 53 (TP53), chromobox protein homolog 7 (CBX7), Janus kinase 2 (JAK2) and cyclin-dependent kinase 5 (CDK5)) were selected as candidate biomarkers after validation using the external dataset and clinical samples. Furthermore, a nomogram with robust diagnostic value was established (AUC = 0.960).

Conclusion: TP53, CBX7, JAK2, and CDK5 might serve as diagnostic DECRs for AD diagnosis. These DECRs were enriched predominantly in regulating epigenetic processes.

LMNA mutation leads to cardiac sodium channel dysfunction in the Emery-Dreifuss muscular dystrophy patient

Pathogenic variants in the LMNA gene are known to cause laminopathies, a broad range of disorders with different clinical phenotypes. LMNA genetic variants lead to tissue-specific pathologies affecting various tissues and organs. Common manifestations of laminopathies include cardiovascular system abnormalities, in particular, cardiomyopathies and conduction disorders. In the present study, we used induced pluripotent stem cells from a patient carrying LMNA p.R249Q genetic variant to create an in vitro cardiac model of laminopathy. Induced pluripotent stem cell-derived cardiomyocytes with LMNA p.R249Q genetic variant showed a decreased sodium current density and an impaired sodium current kinetics alongside with changes in transcription levels of cardiac-specific genes. Thus, we obtained compelling in vitro evidence of an association between LMNA p.R249Q genetic variant and cardiac-related abnormalities.

Pediatric and adult dilated cardiomyopathy are distinguished by distinct biomarker profiles

BACKGROUND

Emerging evidence suggests that pediatric and adult dilated cardiomyopathy (DCM) represent distinct diseases. Few diagnostic tools exist for pediatric cardiologists to assess clinical status and prognosis. We hypothesized that pediatric DCM would have a unique biomarker profile compared to adult DCM and controls.

METHODS

We utilized a DNA aptamer array (SOMAScan) to compare biomarker profiles between pediatric and adult DCM. We simultaneously measured 1310 plasma proteins and peptides from 39 healthy children (mean age 3 years, interquartile range (IQR) 1-14), 39 ambulatory subjects with pediatric DCM (mean age 2.7 years, IQR 1-13), and 40 ambulatory adults with DCM (mean age 53 years, IQR 46-63).

RESULTS

Pediatric and adult DCM patients displayed distinct biomarker profiles, despite similar clinical characteristics. We identified 20 plasma peptides and proteins that were increased in pediatric DCM compared to age- and sex-matched controls. Unbiased multidimensionality reduction analysis suggested previously unrecognized heterogeneity among pediatric DCM subjects. Biomarker profile analysis identified four subgroups of pediatric DCM with distinguishing clinical characteristics.

CONCLUSIONS

These findings support the emerging concept that pediatric and adult DCM are distinct disease entities, signify the need to develop pediatric-specific biomarkers for disease prognostication, and challenge the paradigm that pediatric DCM should be viewed as a single disease.

IMPACT

Pediatric and adult DCM patients displayed distinct biomarker profiles, despite similar clinical characteristics and outcomes. Our findings suggest that pediatric DCM may be a heterogeneous disease with various sub-phenotypes, including differing biomarker profiles and clinical findings. These data provide prerequisite information for future prospective studies that validate the identified pediatric DCM biomarkers, address their diagnostic accuracy and prognostic significance, and explore the full extent of heterogeneity amongst pediatric DCM patients.

Ferroptosis and its role in cardiomyopathy

Heart disease is the leading cause of death worldwide. Cardiomyopathy is a disease characterized by the heart muscle damage, resulting heart in a structurally and functionally change, as well as heart failure and sudden cardiac death. The key pathogenic factor of cardiomyopathy is the loss of cardiomyocytes, but the related molecular mechanisms remain unclear. Ferroptosis is a newly discovered regulated form of cell death, characterized by iron accumulation and lipid peroxidation during cell death. Recent studies have shown that ferroptosis plays an important regulatory roles in the occurrence and development of many heart diseases such as myocardial ischemia/reperfusion injury, cardiomyopathy and heart failure. However, the systemic association of ferroptosis and cardiomyopathy remains largely unknown and needs to be elucidated. In this review, we provide an overview of the molecular mechanisms of ferroptosis and its role in individual cardiomyopathies, highlight that targeting ferroptosis maybe a potential therapeutic strategy for cardiomyopathy therapy in the future.

Functional Evaluation of Human Bioengineered Cardiac Tissue Using iPS Cells Derived from a Patient with Lamin Variant Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM) is caused by various gene variants and characterized by systolic dysfunction. Lamin variants have been reported to have a poor prognosis. Medical and device therapies are not sufficient to improve the prognosis of DCM with the lamin variants. Recently, induced pluripotent stem (iPS) cells have been used for research on genetic disorders. However, few studies have evaluated the contractile function of cardiac tissue with lamin variants. The aim of this study was to elucidate the function of cardiac cell sheet tissue derived from patients with lamin variant DCM. iPS cells were generated from a patient with lamin A/C (LMNA) -mutant DCM (LMNA p.R225X mutation). After cardiac differentiation and purification, cardiac cell sheets that were fabricated through cultivation on a temperature-responsive culture dish were transferred to the surface of the fibrin gel, and the contractile force was measured. The contractile force and maximum contraction velocity, but not the maximum relaxation velocity, were significantly decreased in cardiac cell sheet tissue with the lamin variant. A qRT-PCR analysis revealed that mRNA expression of some contractile proteins, cardiac transcription factors, Ca²⁺-handling genes, and ion channels were downregulated in cardiac tissue with the lamin variant.Human iPS-derived bioengineered cardiac tissue with the LMNA p.R225X mutation has the functional properties of systolic dysfunction and may be a promising tissue model for understanding the underlying mechanisms of DCM.

Clinical Profile, Arrhythmias, and Adverse Cardiac Outcomes in Emery–Dreifuss Muscular Dystrophies: A Systematic Review of the Literature

Cardiolaminopathies are a heterogeneous group of disorders which are due to mutations in the genes encoding for nuclear lamins or their binding proteins. The whole spectrum of cardiac manifestations encompasses atrial arrhythmias, conduction disturbances, progressive systolic dysfunction, and malignant ventricular arrhythmias. Despite the prognostic significance of cardiac involvement in this setting, the current recommendations lack strong evidence. The aim of our work was to systematically review the current data on the main cardiovascular outcomes in cardiolaminopathies. We searched PubMed/Embase for studies focusing on cardiovascular outcomes in LMNA mutation carriers (atrial arrhythmias, ventricular arrhythmias, sudden cardiac death, conduction disturbances, thromboembolic events, systolic dysfunction, heart transplantation, and all-cause and cardiovascular mortality). In total, 11 studies were included (1070 patients, mean age between 26–45 years, with follow-up periods ranging from 2.5 years up to 45 ± 12). When available, data on the EMD-mutated population were separately reported (40 patients). The incidence rates (IR) were individually assessed for the outcomes of interest. The IR for atrial fibrillation/atrial flutter/atrial tachycardia ranged between 6.1 and 13.9 events/100 pts–year. The IR of atrial standstill ranged between 0 and 2 events/100 pts-year. The IR for malignant ventricular arrhythmias reached 10.2 events/100 pts–year and 15.6 events/100 pts–year for appropriate implantable cardioverter–defibrillator (ICD) interventions. The IR for advanced conduction disturbances ranged between 3.2 and 7.7 events/100 pts–year. The IR of thromboembolic events reached up to 8.9 events/100 pts–year. Our results strengthen the need for periodic cardiological evaluation focusing on the early recognition of atrial arrhythmias, and possibly for the choice of preventive strategies for thromboembolic events. The frequent need for cardiac pacing due to advanced conduction disturbances should be counterbalanced with the high risk of malignant ventricular arrhythmias that would justify ICD over pacemaker implantation.

Cytoskeletal Protein Variants Driving Atrial Fibrillation: Potential Mechanisms of Action

The most common clinical tachyarrhythmia, atrial fibrillation (AF), is present in 1-2% of the population. Although common risk factors, including hypertension, diabetes, and obesity, frequently underlie AF onset, it has been recognized that in 15% of the AF population, AF is familial. In these families, genome and exome sequencing techniques identified variants in the non-coding genome (i.e., variant regulatory elements), genes encoding ion channels, as well as genes encoding cytoskeletal (-associated) proteins. Cytoskeletal protein variants include variants in desmin, lamin A/C, titin, myosin heavy and light chain, junctophilin, nucleoporin, nesprin, and filamin C. These cytoskeletal protein variants have a strong association with the development of cardiomyopathy. Interestingly, AF onset is often represented as the initial manifestation of cardiac disease, sometimes even preceding cardiomyopathy by several years. Although emerging research findings reveal cytoskeletal protein variants to disrupt the cardiomyocyte structure and trigger DNA damage, exploration of the pathophysiological mechanisms of genetic AF is still in its infancy. In this review, we provide an overview of cytoskeletal (-associated) gene variants that relate to genetic AF and highlight potential pathophysiological pathways that drive this arrhythmia.

Genetic predisposition study of heart failure and its association with cardiomyopathy

Heart failure (HF) is a clinical condition distinguished by structural and functional defects in the myocardium, which genetic and environmental factors can induce. HF is caused by various genetic factors that are both heterogeneous and complex. The incidence of HF varies depending on the definition and area, but it is calculated to be between 1 and 2% in developed countries. There are several factors associated with the progression of HF, ranging from coronary artery disease to hypertension, of which observed the most common genetic cause to be cardiomyopathy. The main objective of this study is to investigate heart failure and its association with cardiomyopathy with their genetic variants. The selected novel genes that have been linked to human inherited cardiomyopathy play a critical role in the pathogenesis and progression of HF. Research sources collected from the human gene mutation and several databases revealed that numerous genes are linked to cardiomyopathy and thus explained the hereditary influence of such a condition. Our findings support the understanding of the genetics aspect of HF and will provide more accurate evidence of the role of changing disease accuracy. Furthermore, a better knowledge of the molecular pathophysiology of genetically caused HF could contribute to the emergence of personalized therapeutics in future.

Tachycardiomyopathy entails a dysfunctional pattern of interrelated mitochondrial functions

Tachycardiomyopathy is characterised by reversible left ventricular dysfunction, provoked by rapid ventricular rate. While the knowledge of mitochondria advanced in most cardiomyopathies, mitochondrial functions await elucidation in tachycardiomyopathy. Pacemakers were implanted in 61 rabbits. Tachypacing was performed with 330 bpm for 10 days (n = 11, early left ventricular dysfunction) or with up to 380 bpm over 30 days (n = 24, tachycardiomyopathy, TCM). In n = 26, pacemakers remained inactive (SHAM). Left ventricular tissue was subjected to respirometry, metabolomics and acetylomics. Results were assessed for translational relevance using a human-based model: induced pluripotent stem cell derived cardiomyocytes underwent field stimulation for 7 days (TACH-iPSC-CM). TCM animals showed systolic dysfunction compared to SHAM (fractional shortening 37.8 ± 1.0% vs. 21.9 ± 1.2%, SHAM vs. TCM, p < 0.0001). Histology revealed cardiomyocyte hypertrophy (cross-sectional area 393.2 ± 14.5 µm² vs. 538.9 ± 23.8 µm², p < 0.001) without fibrosis. Mitochondria were shifted to the intercalated discs and enlarged. Mitochondrial membrane potential remained stable in TCM. The metabolite profiles of ELVD and TCM were characterised by profound depletion of tricarboxylic acid cycle intermediates. Redox balance was shifted towards a more oxidised state (ratio of reduced to oxidised nicotinamide adenine dinucleotide 10.5 ± 2.1 vs. 4.0 ± 0.8, p < 0.01). The mitochondrial acetylome remained largely unchanged. Neither TCM nor TACH-iPSC-CM showed relevantly increased levels of reactive oxygen species. Oxidative phosphorylation capacity of TCM decreased modestly in skinned fibres (168.9 ± 11.2 vs. 124.6 ± 11.45 pmol·O₂·s^-1·mg^-1 tissue, p < 0.05), but it did not in isolated mitochondria. The pattern of mitochondrial dysfunctions detected in two models of tachycardiomyopathy diverges from previously published characteristic signs of other heart failure aetiologies.

OUP accepted manuscript

Cardiovascular diseases (CVDs) arise from a complex interplay among genomic, proteomic, and metabolomic abnormalities. Emerging evidence has recently consolidated the presence of robust DNA damage in a variety of cardiovascular disorders. DNA damage triggers a series of cellular responses termed DNA damage response (DDR) including detection of DNA lesions, cell cycle arrest, DNA repair, cellular senescence, and apoptosis, in all organ systems including hearts and vasculature. Although transient DDR in response to temporary DNA damage can be beneficial for cardiovascular function, persistent activation of DDR promotes the onset and development of CVDs. Moreover, therapeutic interventions that target DNA damage and DDR have the potential to attenuate cardiovascular dysfunction and improve disease outcome. In this review, we will discuss molecular mechanisms of DNA damage and repair in the onset and development of CVDs, and explore how DDR in specific cardiac cell types contributes to CVDs. Moreover, we will highlight the latest advances regarding the potential therapeutic strategies targeting DNA damage signalling in CVDs.

Phenotypic Variability in iPSC-Induced Cardiomyocytes and Cardiac Fibroblasts Carrying Diverse LMNA Mutations

Mutations in the LMNA gene (encoding lamin A/C) are a significant cause of familial arrhythmogenic cardiomyopathy. Although the penetrance is high, there is considerable phenotypic variability in disease onset, rate of progression, arrhythmias, and severity of myopathy. To begin to address whether this variability stems from specific LMNA mutation sites and types, we generated seven patient-specific induced pluripotent stem cell (iPSC) lines with various LMNA mutations. IPSC-derived cardiomyocytes (iCMs) and cardiac fibroblasts (iCFs) were differentiated from each line for phenotypic analyses. LMNA expression and extracellular signal-regulated kinase pathway activation were perturbed to differing degrees in both iCMs and iCFs from the different lines. Enhanced apoptosis was observed in iCMs but not in iCFs. Markedly diverse irregularities of nuclear membrane morphology were present in iCFs but not iCMs, while iCMs demonstrated variable sarcomere disarray. Heterogenous electrophysiological aberrations assayed by calcium indicator imaging and multi-electrode array suggest differing substrates for arrhythmia that were accompanied by variable ion channel gene expression in the iCMs. Coculture studies suggest enhancement of the LMNA mutation effects on electrophysiological function exerted by iCFs. This study supports the utility of patient-specific iPSC experimental platform in the exploration of mechanistic and phenotypic heterogeneity of different mutations within a cardiac disease-associated gene. The addition of genetically defined coculture of cardiac-constituent non-myocytes further expands the capabilities of this approach.

Recent Findings Related to Cardiomyopathy and Genetics

With the development and advancement of next-generation sequencing (NGS), genetic analysis is becoming more accessible. High-throughput genetic studies using NGS have contributed to unraveling the association between cardiomyopathy and genetic background, as is the case with many other diseases. Rare variants have been shown to play major roles in the pathogenesis of cardiomyopathy, which was empirically recognized as a monogenic disease, and it has been elucidated that the clinical course of cardiomyopathy varies depending on the causative genes. These findings were not limited to dilated and hypertrophic cardiomyopathy; similar trends were reported one after another for peripartum cardiomyopathy (PPCM), cancer therapy-related cardiac dysfunction (CTRCD), and alcoholic cardiomyopathy (ACM). In addition, as the association between clinical phenotypes and the causative genes becomes clearer, progress is being made in elucidating the mechanisms and developing novel therapeutic agents. Recently, it has been suggested that not only rare variants but also common variants contribute to the development of cardiomyopathy. Cardiomyopathy and genetics are approaching a new era, which is summarized here in this overview.

Identification and Validation of Autophagy-Related Genes as Potential Biomarkers and Therapeutic Targets in Atrial Fibrillation

Background

Autophagy is an evolutionary conserved important process for the turnover of intracellular substances in eukaryotes and is closely related to the development of atrial fibrillation (AF). The aim of this study is to identify and validate potential autophagy-related genes (ARGs) of AF through bioinformatics analysis and experimental validation.

Methods

We downloaded two data sets from the Gene Expression Omnibus (GEO) database, GSE14975 and GSE31821. After merging the data of the two microarrays, adjusting the batch effect, and integrating the differentially expressed genes (DEGs) with ARGs to obtain differentially expressed autophagy-related genes (DEARGs). Functional and pathway enrichment analyses were carried out based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). Use the STRING database to construct a protein–protein interaction (PPI) network. Finally, mRNA expression levels of DEARGs were validated in right atrial tissue samples from AF patients and non-AF controls by qRT-PCR.

Results

Through bioinformatics analysis, we finally identified 11 DEARGs (CDKN1A, CXCR4, DIRAS3, HSP90AB1, ITGA3, PRKCD, TP53INP2, DAPK2, IFNG, PTK6, and TNFSF10) in AF using [log2 (fold change)] > 0.5 and P < 0.05. In the pathway enrichment analysis, the most significantly enriched pathway was the autophagy pathway. The results of validation showed that the expression levels of CXCR4, DAPK2, and TNFSF10 corroborating with our computational findings, and the results were statistically significant (P<0.05).

Conclusion

Our study demonstrates that these 11 potential crucial ARGs, especially CXCR4, DAPK2, and TNFSF10, may be potential biomarkers and therapeutic targets in AF, which will help the personalized treatment of AF patients.

Diversity of Nuclear Lamin A/C Action as a Key to Tissue-Specific Regulation of Cellular Identity in Health and Disease

A-type lamins are the main structural components of the nucleus, which are mainly localized at the nucleus periphery. First of all, A-type lamins, together with B-type lamins and proteins of the inner nuclear membrane, form a stiff structure-the nuclear lamina. Besides maintaining the nucleus cell shape, A-type lamins play a critical role in many cellular events, such as gene transcription and epigenetic regulation. Nowadays it is clear that lamins play a very important role in determining cell fate decisions. Various mutations in genes encoding A-type lamins lead to damages of different types of tissues in humans, collectively known as laminopathies, and it is clear that A-type lamins are involved in the regulation of cell differentiation and stemness. However, the mechanisms of this regulation remain unclear. In this review, we discuss how A-type lamins can execute their regulatory role in determining the differentiation status of a cell. We have summarized recent data focused on lamin A/C action mechanisms in regulation of cell differentiation and identity development of stem cells of different origin. We also discuss how this knowledge can promote further research toward a deeper understanding of the role of lamin A/C mutations in laminopathies.

Fortilin inhibits p53, halts cardiomyocyte apoptosis, and protects the heart against heart failure

Heart failure (HF) has reached epidemic proportions in developed countries, affecting over 20 million people worldwide. Despite modern medical and device therapies, 60–70% of HF patients still die within 5 years of diagnosis as it relentlessly progresses through pervasive apoptotic loss of cardiomyocytes. Although fortilin, a 172-amino-acid anti-p53 molecule, is one of the most expressed proteins in the heart, its precise role there has remained unknown. Also unclear is how cardiomyocytes are protected against apoptosis. Here, we report that failing human hearts express less fortilin than do non-failing hearts. We also found that mice lacking fortilin in the heart (fortilin^KO-heart) die by 9 weeks of age due to extensive cardiomyocyte apoptosis and severe HF, which suggests that fortilin sustains cardiomyocyte viability. The lack of fortilin is also associated with drastic upregulation of p53 target genes in the hearts. The heart-specific deletion of p53 in fortilin^KO-heart mice extends their life spans from 9 to 18 weeks by mitigating cardiomyocyte apoptosis. Our data suggest that fortilin is a novel cardiac p53 inhibitor and that its inadequate expression in failing hearts and subsequent overactivation of the p53 apoptosis pathway in cardiomyocytes exacerbates HF.

Haploinsufficiency of Tmem43 in cardiac myocytes activates the DNA damage response pathway leading to a late-onset senescence-associated pro-fibrotic cardiomyopathy

AIMS

Arrhythmogenic cardiomyopathy (ACM) encompasses a genetically heterogeneous group of myocardial diseases whose manifestations are sudden cardiac death, cardiac arrhythmias, heart failure, and in a subset fibro-adipogenic infiltration of the myocardium. Mutations in the TMEM43 gene, encoding transmembrane protein 43 (TMEM43) are known to cause ACM. The purpose of the study was to gain insights into the molecular pathogenesis of ACM caused by TMEM43 haploinsufficiency.

METHODS AND RESULTS

The Tmem43 gene was specifically deleted in cardiac myocytes by crossing the Myh6-Cre and floxed Tmem43 mice. Myh6-Cre:Tmem43W/F mice showed an age-dependent phenotype characterized by an increased mortality, cardiac dilatation and dysfunction, myocardial fibrosis, adipogenesis, and apoptosis. Sequencing of cardiac myocyte transcripts prior to and after the onset of cardiac phenotype predicted early activation of the TP53 pathway. Increased TP53 activity was associated with increased levels of markers of DNA damage response (DDR), and a subset of senescence-associated secretary phenotype (SASP). Activation of DDR, TP53, SASP, and their selected downstream effectors, including phospho-SMAD2 and phospho-SMAD3 were validated by alternative methods, including immunoblotting. Expression of SASP was associated with epithelial-mesenchymal transition and age-dependent expression of myocardial fibrosis and apoptosis in the Myh6-Cre:Tmem43W/F mice.

CONCLUSION

TMEM43 haploinsufficiency is associated with activation of the DDR and the TP53 pathways, which lead to increased expression of SASP and an age-dependent expression of a pro-fibrotic cardiomyopathy. Given that TMEM43 is a nuclear envelope protein and our previous data showing deficiency of another nuclear envelope protein, namely lamin A/C, activates the DDR/TP53 pathway, we surmise that DNA damage is a shared mechanism in the pathogenesis of cardiomyopathies caused by mutations involving nuclear envelope proteins.