Genomic Reorganization of Lamin-Associated Domains in Cardiac Myocytes Is Associated With Differential Gene Expression and DNA Methylation in Human Dilated Cardiomyopathy

Pathogenic LMNA variants disrupt cardiac lamina-chromatin interactions and de-repress alternative fate genes

Pathogenic mutations in LAMIN A/C (LMNA) cause abnormal nuclear structure and laminopathies. These diseases have myriad tissue-specific phenotypes, including dilated cardiomyopathy (DCM), but how LMNA mutations result in tissue-restricted disease phenotypes remains unclear. We introduced LMNA mutations from individuals with DCM into human induced pluripotent stem cells (hiPSCs) and found that hiPSC-derived cardiomyocytes, in contrast to hepatocytes or adipocytes, exhibit aberrant nuclear morphology and specific disruptions in peripheral chromatin. Disrupted regions were enriched for transcriptionally active genes and regions with lower LAMIN B1 contact frequency. The lamina-chromatin interactions disrupted in mutant cardiomyocytes were enriched for genes associated with non-myocyte lineages and correlated with higher expression of those genes. Myocardium from individuals with LMNA variants similarly showed aberrant expression of non-myocyte pathways. We propose that the lamina network safeguards cellular identity and that pathogenic LMNA variants disrupt peripheral chromatin with specific epigenetic and molecular characteristics, causing misexpression of genes normally expressed in other cell types.

Establishment of an iPSC line (JSPHi001-A) from a patient with familial dilated cardiomyopathy and atrial fibrillation caused by LMNA missense mutation (c.1003C > T)

Peripheral blood mononuclear cells (PBMCs) were harvested and reprogramed to induced pluripotent stem cells (iPSCs) from a 46-year-old male patient with familial dilated cardiomyopathy and atrial fibrillation via a non-integrating system. A missense mutation in the LMNA gene (c.1003C > T) was identified by whole-exome sequencing and verified by Sanger sequencing. The pluripotency, differentiation potential, and karyotype of this cell line were also tested. This model is helpful to study the phenotype, mechanism, and therapy for laminopathy.

BET bromodomain inhibition attenuates cardiac phenotype in myocyte-specific lamin A/C-deficient mice

Mutation in the LMNA gene, encoding lamin A/C, causes a diverse group of diseases called laminopathies. Cardiac involvement is the major cause of death and manifests as dilated cardiomyopathy, heart failure, arrhythmias, and sudden death. There is no specific therapy for LMNA-associated cardiomyopathy. We report that deletion of Lmna in cardiomyocytes in mice leads to severe cardiac dysfunction, conduction defect, ventricular arrhythmias, fibrosis, apoptosis, and premature death within 4 weeks. The phenotype is similar to LMNA-associated cardiomyopathy in humans. RNA sequencing, performed before the onset of cardiac dysfunction, led to identification of 2338 differentially expressed genes (DEGs) in Lmna-deleted cardiomyocytes. DEGs predicted activation of bromodomain-containing protein 4 (BRD4), a regulator of chromatin-associated proteins and transcription factors, which was confirmed by complementary approaches, including chromatin immunoprecipitation sequencing. Daily injection of JQ1, a specific BET bromodomain inhibitor, partially reversed the DEGs, including those encoding secretome; improved cardiac function; abrogated cardiac arrhythmias, fibrosis, and apoptosis; and prolonged the median survival time 2-fold in the myocyte-specific Lmna-deleted mice. The findings highlight the important role of LMNA in cardiomyocytes and identify BET bromodomain inhibition as a potential therapeutic target in LMNA-associated cardiomyopathy, for which there is no specific effective therapy.

Exercise restores dysregulated gene expression in a mouse model of arrhythmogenic cardiomyopathy

AIMS

Arrhythmogenic cardiomyopathy (ACM) is a myocardial disease caused mainly by mutations in genes encoding desmosome proteins ACM patients present with ventricular arrhythmias, cardiac dysfunction, sudden cardiac death, and a subset with fibro-fatty infiltration of the right ventricle predominantly. Endurance exercise is thought to exacerbate cardiac dysfunction and arrhythmias in ACM. The objective was to determine the effects of treadmill exercise on cardiac phenotype, including myocyte gene expression in myocyte-specific desmoplakin (Dsp) haplo-insufficient (Myh6-Cre:DspW/F) mice.

METHODS AND RESULTS

Three months old sex-matched wild-type (WT) and Myh6-Cre:DspW/F mice with normal cardiac function, as assessed by echocardiography, were randomized to regular activity or 60 min of daily treadmill exercise (5.5 kJ work per run). Cardiac myocyte gene expression, cardiac function, arrhythmias, and myocardial histology, including apoptosis, were analysed prior to and after 3 months of routine activity or treadmill exercise. Fifty-seven and 781 genes were differentially expressed in 3- and 6-month-old Myh6-Cre:DspW/F cardiac myocytes, compared to the corresponding WT myocytes, respectively. Genes encoding secreted proteins (secretome), including inhibitors of the canonical WNT pathway, were among the most up-regulated genes. The differentially expressed genes (DEGs) predicted activation of epithelial-mesenchymal transition (EMT) and inflammation, and suppression of oxidative phosphorylation pathways in the Myh6-Cre:DspW/F myocytes. Treadmill exercise restored transcript levels of two-third (492/781) of the DEGs and the corresponding dysregulated transcriptional and biological pathways, including EMT, inflammation, and secreted inhibitors of the canonical WNT. The changes were associated with reduced myocardial apoptosis and eccentric cardiac hypertrophy without changes in cardiac function.

CONCLUSION

Treadmill exercise restored transcript levels of the majority of dysregulated genes in cardiac myocytes, reduced myocardial apoptosis, and induced eccentric cardiac hypertrophy without affecting cardiac dysfunction in a mouse model of ACM. The findings suggest that treadmill exercise has potential beneficial effects in a subset of cardiac phenotypes in ACM.

Three-dimensional chromatin organization in cardiac development and disease

Recent technological advancements in the field of chromatin biology have rewritten the textbook on nuclear organization. We now appreciate that the folding of chromatin in the three-dimensional space (i.e. its 3D "architecture") is non-random, hierarchical, and highly complex. While 3D chromatin structure is partially encoded in the primary sequence and thereby broadly conserved across cell types and states, a substantial portion of the genome seems to be dynamic during development or in disease. Moreover, there is growing evidence that at least some of the 3D structure of chromatin is functionally linked to gene regulation, both being modulated by and impacting on multiple nuclear processes (including DNA replication, transcription, and RNA splicing). In recent years, these new concepts have nourished several investigations about the functional role of 3D chromatin topology dynamics in the heart during development and disease. This review aims to provide a comprehensive overview of our current understanding in this field, and to discuss how this knowledge can inform further research as well as clinical practice.

Integrated analysis reveals the alterations that LMNA interacts with euchromatin in LMNA mutation-associated dilated cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is a serious cardiac heterogeneous pathological disease, which may be caused by mutations in the LMNA gene. Lamins interact with not only lamina-associated domains (LADs) but also euchromatin by alone or associates with the lamina-associated polypeptide 2 alpha (LAP2α). Numerous studies have documented that LMNA regulates gene expression by interacting with LADs in heterochromatin. However, the role of LMNA in regulating euchromatin in DCM is poorly understood. Here, we determine the differential binding genes on euchromatin in DCM induced by LMNA mutation by performing an integrated analysis of bioinformatics and explore the possible molecular pathogenesis mechanism.

RESULTS

Six hundred twenty-three and 4484 differential binding genes were identified by ChIP-seq technology. The ChIP-seq analysis results and matched RNA-Seq transcriptome data were integrated to further validate the differential binding genes of ChIP-seq. Five and 60 candidate genes involved in a series of downstream analysis were identified. Finally, 4 key genes (CREBBP, PPP2R2B, BMP4, and BMP7) were harvested, and these genes may regulate LMNA mutation-induced DCM through WNT/β-catenin or TGFβ-BMP pathways.

CONCLUSIONS

We identified four key genes that may serve as potential biomarkers and novel therapeutic targets. Our study also illuminates the possible molecular pathogenesis mechanism that the abnormal binding between LMNA or LAP2α-lamin A/C complexes and euchromatin DNA in LMNA mutations, which may cause DCM through the changes of CREBBP, PPP2R2B, BMP4, BMP7 expressions, and the dysregulation of WNT/β-catenin or TGFβ-BMP pathways, providing valuable insights to improve the occurrence and development of DCM.

State of the Art Review on Genetics and Precision Medicine in Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiomyopathy characterised by ventricular arrhythmia and an increased risk of sudden cardiac death (SCD). Numerous genetic determinants and phenotypic manifestations have been discovered in ACM, posing a significant clinical challenge. Further to this, wider evaluation of family members has revealed incomplete penetrance and variable expressivity in ACM, suggesting a complex genotype-phenotype relationship. This review details the genetic basis of ACM with specific genotype-phenotype associations, providing the reader with a nuanced perspective of this condition; whilst also proposing a future roadmap to delivering precision medicine-based management in ACM.

Identification of Genes and Pathways Regulated by Lamin A in Heart

Background Mutations in the LMNA gene, encoding LMNA (lamin A/C), causes distinct disorders, including dilated cardiomyopathies, collectively referred to as laminopathies. The genes (coding and noncoding) and regulatory pathways controlled by LMNA in the heart are not completely defined. Methods and Results We analyzed cardiac transcriptome from wild-type, loss-of-function (Lmna-/-), and gain-of-function (Lmna-/- injected with adeno-associated virus serotype 9 expressing LMNA) mice with normal cardiac function. Deletion of Lmna (Lmna-/-) led to differential expression of 2193 coding and 629 long noncoding RNA genes in the heart (q<0.05). Re-expression of LMNA in the Lmna-/- mouse heart, completely rescued 501 coding and 208 non-coding and partially rescued 1862 coding and 607 lncRNA genes. Pathway analysis of differentially expressed genes predicted activation of transcriptional regulators lysine-specific demethylase 5A, lysine-specific demethylase 5B, tumor protein 53, and suppression of retinoblastoma 1, paired-like homeodomain 2, and melanocyte-inducing transcription factor, which were completely or partially rescued upon reexpression of LMNA. Furthermore, lysine-specific demethylase 5A and 5B protein levels were increased in the Lmna-/- hearts and were partially rescued upon LMNA reexpression. Analysis of biological function for rescued genes identified activation of tumor necrosis factor-α, epithelial to mesenchymal transition, and suppression of the oxidative phosphorylation pathway upon Lmna deletion and their restoration upon LMNA reintroduction in the heart. Restoration of the gene expression and transcriptional regulators in the heart was associated with improved cardiac function and increased survival of the Lmna-/- mice. Conclusions The findings identify LMNA-regulated cardiac genes and their upstream transcriptional regulators in the heart and implicate lysine-specific demethylase 5A and B as epigenetic regulators of a subset of the dysregulated genes in laminopathies.

Arrhythmogenic Cardiomyopathy and Skeletal Muscle Dystrophies: Shared Histopathological Features and Pathogenic Mechanisms

Arrhythmogenic cardiomyopathy (ACM) is a heritable cardiac disease characterized by fibrotic or fibrofatty myocardial replacement, associated with an increased risk of ventricular arrhythmias and sudden cardiac death. Originally described as a disease of the right ventricle, ACM is currently recognized as a biventricular entity, due to the increasing numbers of reports of predominant left ventricular or biventricular involvement. Research over the last 20 years has significantly advanced our knowledge of the etiology and pathogenesis of ACM. Several etiopathogenetic theories have been proposed; among them, the most attractive one is the dystrophic theory, based on the observation of similar histopathological features between ACM and skeletal muscle dystrophies (SMDs), such as progressive muscular degeneration, inflammation, and tissue replacement by fatty and fibrous tissue. This review will describe the pathophysiological and molecular similarities shared by ACM with SMDs.

Role of Non-coding RNA in Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) is the leading cause of morbidity and mortality in diabetic population worldwide, characteristic by cardiomyocyte hypertrophy, apoptosis and myocardial interstitial fibrosis and eventually developing into heart failure. Non-coding RNAs, such as microRNAs (miRNAs), circular RNAs (circRNAs), long non-coding RNAs (lncRNAs) and other RNAs without the protein encoding function were emerging as a popular regulator in various types of processes during human diseases. The evidences have shown that miRNAs are regulators in diabetic cardiomyopathy, such as insulin resistance, cardiomyocytes apoptosis, and inflammatory, especially their protective effect on heart function. Besides that, the functions of lncRNAs and circRNAs have been gradually confirmed in recent years, and their functions in DCM have become increasingly prominent. We highlighted the nonnegligible roles of non-coding RNAs in the pathological process of DCM and showed the future possibilities of these non-coding RNAs in DCM treatment. In this chapter, we summarized the present advance of the researches in this filed and raised the concern and the prospect in the future.

An Omics View of Emery-Dreifuss Muscular Dystrophy

Recent progress in Omics technologies has started to empower personalized healthcare development at a thorough biomolecular level. Omics have subsidized medical breakthroughs that have started to enter clinical proceedings. The use of this scientific know-how has surfaced as a way to provide a more far-reaching view of the biological mechanisms behind diseases. This review will focus on the discoveries made using Omics and the utility of these approaches for Emery–Dreifuss muscular dystrophy.

Lamin A/C Mechanotransduction in Laminopathies

Mechanotransduction translates forces into biological responses and regulates cell functionalities. It is implicated in several diseases, including laminopathies which are pathologies associated with mutations in lamins and lamin-associated proteins. These pathologies affect muscle, adipose, bone, nerve, and skin cells and range from muscular dystrophies to accelerated aging. Although the exact mechanisms governing laminopathies and gene expression are still not clear, a strong correlation has been found between cell functionality and nuclear behavior. New theories base on the direct effect of external force on the genome, which is indeed sensitive to the force transduced by the nuclear lamina. Nuclear lamina performs two essential functions in mechanotransduction pathway modulating the nuclear stiffness and governing the chromatin remodeling. Indeed, A-type lamin mutation and deregulation has been found to affect the nuclear response, altering several downstream cellular processes such as mitosis, chromatin organization, DNA replication-transcription, and nuclear structural integrity. In this review, we summarize the recent findings on the molecular composition and architecture of the nuclear lamina, its role in healthy cells and disease regulation. We focus on A-type lamins since this protein family is the most involved in mechanotransduction and laminopathies.

Emery-Dreifuss muscular dystrophy: focal point nuclear envelope

PURPOSE OF REVIEW

Emery-Dreifuss muscular dystrophy (EDMD) is caused by mutations in EMD encoding emerin and LMNA encoding A-type lamins, proteins of the nuclear envelope. In the past decade, there has been an extraordinary burst of research on the nuclear envelope. Discoveries resulting from this basic research have implications for better understanding the pathogenesis and developing treatments for EDMD.

RECENT FINDINGS

Recent clinical research has confirmed that EDMD is one of several overlapping skeletal muscle phenotypes that can result from mutations in EMD and LMNA with dilated cardiomyopathy as a common feature. Basic research on the nuclear envelope has provided new insights into how A-type lamins and emerin function in force transmission throughout the cell, which may be particularly important in striated muscle. Much of the recent research has focused on the heart and LMNA mutations. Prevalence and outcome studies have confirmed the relative severity of cardiac disease. Robust mouse models of EDMD caused by LMNA mutations has allowed for further insight into pathogenic mechanisms and potentially beneficial therapeutic approaches.

SUMMARY

Recent clinical and basic research on EDMD is gradually being translated to clinical practice and possibly novel therapies.

Human-induced pluripotent stem cells for modelling metabolic perturbations and impaired bioenergetics underlying cardiomyopathies

Normal cardiac contractile and relaxation functions are critically dependent on a continuous energy supply. Accordingly, metabolic perturbations and impaired mitochondrial bioenergetics with subsequent disruption of ATP production underpin a wide variety of cardiac diseases, including diabetic cardiomyopathy, dilated cardiomyopathy, hypertrophic cardiomyopathy, anthracycline cardiomyopathy, peripartum cardiomyopathy, and mitochondrial cardiomyopathies. Crucially, there are no specific treatments for preventing the onset or progression of these cardiomyopathies to heart failure, one of the leading causes of death and disability worldwide. Therefore, new treatments are needed to target the metabolic disturbances and impaired mitochondrial bioenergetics underlying these cardiomyopathies in order to improve health outcomes in these patients. However, investigation of the underlying mechanisms and the identification of novel therapeutic targets have been hampered by the lack of appropriate animal disease models. Furthermore, interspecies variation precludes the use of animal models for studying certain disorders, whereas patient-derived primary cell lines have limited lifespan and availability. Fortunately, the discovery of human-induced pluripotent stem cells has provided a promising tool for modelling cardiomyopathies via human heart tissue in a dish. In this review article, we highlight the use of patient-derived iPSCs for studying the pathogenesis underlying cardiomyopathies associated with metabolic perturbations and impaired mitochondrial bioenergetics, as the ability of iPSCs for self-renewal and differentiation makes them an ideal platform for investigating disease pathogenesis in a controlled in vitro environment. Continuing progress will help elucidate novel mechanistic pathways, and discover novel therapies for preventing the onset and progression of heart failure, thereby advancing a new era of personalized therapeutics for improving health outcomes in patients with cardiomyopathy.

In situ nuclear DNA methylation in dilated cardiomyopathy: an endomyocardial biopsy study

AIMS

Although distinct DNA methylation patterns have been reported, its localization and roles remain to be defined in heart failure. We investigated the cellular and subcellular localization of DNA methylation and its pathophysiological significance in human failing hearts.

METHODS AND RESULTS

Using left ventricular (LV) endomyocardial biopsy specimens from 75 patients with dilated cardiomyopathy (DCM; age: 58 ± 14 years old, %female: 32%) and 20 patients without heart failure (controls; age: 56 ± 17 years old, %female: 45%), we performed immunohistochemistry and immunoelectron microscopy for methylated DNA, 5-methylcytosine (5-mC). We next investigated possible relations of the incidence of 5-mC-positive (%5-mC⁺ ) cardiomyocytes with clinicopathological parameters. Immunopositivity for 5-mC was detected in the cardiomyocytes and other cell types. The %5-mC⁺ cardiomyocytes was significantly greater in DCM hearts than in controls (57 ± 13% in DCM vs. 25 ± 12% in controls, P < 0.0001). The localization of 5-mC immunopositivity in cardiomyocyte nuclei coincided well with that of heterochromatin, as confirmed by immunoelectron microscopy. Substantial DNA methylation was also observed in interstitial non-cardiomyocytes, but the incidences did not differ between control and DCM hearts (39 ± 7.9% in DCM vs. 41 ± 10% in controls, P = 0.4099). In DCM patients, the %5-mC⁺ cardiomyocytes showed a significant inverse correlation with LV functional parameters such as heart rate (r = 0.2391, P = 0.0388), end-diastolic pressure (r = 0.2397, P = 0.0397), and ejection fraction (r = -0.2917, P = 0.0111) and a positive correlation with LV dilatation (volume index at diastole; r = 0.2442, P = 0.0347; and volume index at systole; r = 0.3136, P = 0.0062) and LV hypertrophy (mass index; r = 0.2287, P = 0.0484)-that is, LV remodelling parameters. No significant correlations between DNA methylation and the histological parameters of the biopsies, including cardiomyocyte hypertrophy, fibrosis, and inflammatory cell infiltration, were noted.

CONCLUSIONS

The present study revealed increased nuclear DNA methylation in cardiomyocytes, but not other cell types, from DCM hearts, with predominant localization in the heterochromatin. Its significant relations with LV functional and remodelling parameters imply a pathophysiological significance of DNA methylation in heart failure.

Case reports of a c.475G>T, p.E159* lamin A/C mutation with a family history of conduction disorder, dilated cardiomyopathy and sudden cardiac death

Background

Patients with some mutations in the lamin A/C (LMNA) gene are characterized by the presence of dilated cardiomyopathy (DCM), conduction abnormalities, ventricular tachyarrhythmias (VT), and sudden cardiac death (SCD). Various clinical features have been observed among patients who have the same LMNA mutation. Here, we show a family with cardiac laminopathy with a c.475G > T, p.E159* LMNA mutation, and a family history of conduction disorder, DCM, VT, and SCD.

Case presentation

A proband (female) with atrial fibrillation and bradycardia was implanted with a pacemaker in her fifties. Twenty years later, she experienced a loss of consciousness due to polymorphic VT. She had a serious family history; her mother and elder sister died suddenly in their fifties and sixties, respectively, and her nephew and son were diagnosed as having DCM. Genetic screening of the proband, her son, and nephew identified a nonsense mutation (c.475G > T, p.E159*) in the LMNA gene. Although the proband’s left ventricular ejection fraction remained relatively preserved, her son and nephew’s left ventricular ejection fraction were reduced, resulting in cardiac resynchronization therapy by implantation of a defibrillator.

Conclusions

In this family with cardiac laminopathy with a c.475G > T, p.E159* LMNA mutation, DCM, SCD, and malignant VT occurred. Clinical manifestation of various atrial and ventricular arrhythmias and heart failure with reduced ejection fraction occurred in an age-dependent manner in all family members who had the nonsense mutation. It appears highly likely that the E159* LMNA mutation is related to various cardiac problems in the family of the current report.

Yin Yang 1 Suppresses Dilated Cardiomyopathy and Cardiac Fibrosis Through Regulation of Bmp7 and Ctgf

RATIONALE

Pathogenic variations in the lamin gene (LMNA) cause familial dilated cardiomyopathy (DCM). LMNA insufficiency caused by LMNA pathogenic variants is believed to be the basic mechanism underpinning LMNA-related DCM.

OBJECTIVE

To assess whether silencing of cardiac Lmna causes DCM and investigate the role of Yin Yang 1 (Yy1) in suppressing Lmna DCM.

METHODS AND RESULTS

We developed a Lmna DCM mouse model induced by cardiac-specific Lmna short hairpin RNA. Silencing of cardiac Lmna induced DCM with associated cardiac fibrosis and inflammation. We demonstrated that upregulation of Yy1 suppressed Lmna DCM and cardiac fibrosis by inducing Bmp7 expression and preventing upregulation of Ctgf. Knockdown of upregulated Bmp7 attenuated the suppressive effect of Yy1 on DCM and cardiac fibrosis. However, upregulation of Bmp7 alone was not sufficient to suppress DCM and cardiac fibrosis. Importantly, upregulation of Bmp7 together with Ctgf silencing significantly suppressed DCM and cardiac fibrosis. Mechanistically, upregulation of Yy1 regulated Bmp7 and Ctgf reporter activities and modulated Bmp7 and Ctgf gene expression in cardiomyocytes. Downregulation of Ctgf inhibited TGF-β (transforming growth factor-β)/Smad signaling in DCM hearts. Regulation of both Bmp7 and Ctgf further suppressed TGFβ/Smad signaling. In addition, co-modulation of Bmp7 and Ctgf reduced CD3+ T cell numbers in DCM hearts.

CONCLUSIONS

Our findings demonstrate that upregulation of Yy1 or co-modulation of Bmp7 and Ctgf offer novel therapeutic strategies for the treatment of DCM caused by LMNA insufficiency.

Atrial Fibrillation Genetics Update: Toward Clinical Implementation

Atrial fibrillation (AF) is the most common heart rhythm disorder worldwide and may have serious cardiovascular health consequences. AF is associated with increased risk of stroke, dementia, heart failure, and death. There are several known robust, clinical risk predictors for AF, such as male sex, increasing age, and hypertension; however, during the last couple of decades, a substantive genetic component has also been established. Over the last 10 years, the discovery of novel AF-related genetic variants has accelerated, increasing our understanding of mechanisms behind AF. Current studies are focusing on mapping the polygenic structure of AF, improving risk prediction, therapeutic development, and patient-specific management. Nevertheless, it is still difficult for clinicians to interpret the role of genetics in AF prediction and management. Here, we provide an overview of relevant topics within the genetics of AF and attempt to provide some guidance on how to interpret genetic advances and their implementation into clinical decision-making.

Cardiac microtubules in health and heart disease

Cardiomyocytes are large (∼40,000 µm3), rod-shaped muscle cells that provide the working force behind each heartbeat. These highly structured cells are packed with dense cytoskeletal networks that can be divided into two groups—the contractile (i.e. sarcomeric) cytoskeleton that consists of filamentous actin-myosin arrays organized into myofibrils, and the non-sarcomeric cytoskeleton, which is composed of β- and γ-actin, microtubules, and intermediate filaments. Together, microtubules and intermediate filaments form a cross-linked scaffold, and these networks are responsible for the delivery of intracellular cargo, the transmission of mechanical signals, the shaping of membrane systems, and the organization of myofibrils and organelles. Microtubules are extensively altered as part of both adaptive and pathological cardiac remodeling, which has diverse ramifications for the structure and function of the cardiomyocyte. In heart failure, the proliferation and post-translational modification of the microtubule network is linked to a number of maladaptive processes, including the mechanical impediment of cardiomyocyte contraction and relaxation. This raises the possibility that reversing microtubule alterations could improve cardiac performance, yet therapeutic efforts will strongly benefit from a deeper understanding of basic microtubule biology in the heart. The aim of this review is to summarize the known physiological roles of the cardiomyocyte microtubule network, the consequences of its pathological remodeling, and to highlight the open and intriguing questions regarding cardiac microtubules.

Impact statement

Advancements in cell biological and biophysical approaches and super-resolution imaging have greatly broadened our view of tubulin biology over the last decade. In the heart, microtubules and microtubule-based transport help to organize and maintain key structures within the cardiomyocyte, including the sarcomere, intercalated disc, protein clearance machinery and transverse-tubule and sarcoplasmic reticulum membranes. It has become increasingly clear that post translational regulation of microtubules is a key determinant of their sub-cellular functionality. Alterations in microtubule network density, stability, and post-translational modifications are hallmarks of pathological cardiac remodeling, and modified microtubules can directly impede cardiomyocyte contractile function in various forms of heart disease. This review summarizes the functional roles and multi-leveled regulation of the cardiac microtubule cytoskeleton and highlights how refined experimental techniques are shedding mechanistic clarity on the regionally specified roles of microtubules in cardiac physiology and pathophysiology.

The structural and gene expression hypotheses in laminopathic diseases-not so different after all

Laminopathies are a diverse group of rare diseases with various pathologies in different tissues, which are linked to mutations in the LMNA gene. Historically, the structural disease model proposed mechanical defects of the lamina and nuclear fragility, the gene expression model impairment of spatial chromatin organization and signaling pathways as underlying mechanisms leading to the pathologies. Exciting findings in the past few years showing that mechanical forces are directly transmitted into the nucleus, where they affect chromatin organization and mechanoresponsive signaling molecules, have led to a revised concept of an integrative unified disease model, in which lamin-mediated pathways in mechanotransduction and chromatin regulation are highly interconnected and mutually dependent. In this Perspective we highlight breakthrough findings providing new insight into lamin-linked mechanisms of mechanotransduction and chromatin regulation and discuss how a combined and interrelated impairment of these functions by LMNA mutations may impair the complex mechanosignaling network and cause tissue-specific pathologies in laminopathies.

Genomic reorganization underlies LMNA -associated cardiomyopathies

Mutations in LMNA result in dilated cardiomyopathy through disruption of chromatin organization, methylation, and aberrant gene expression.