Improvement of left ventricular dysfunction and of survival prognosis of dilated cardiomyopathy by administration of calcium sensitizer SCH00013 in a mouse model

Emerin deficiency does not exacerbate cardiomyopathy in a murine model of Emery-Dreifuss muscular dystrophy caused by an LMNA gene mutation

Emery-Dreifuss muscular dystrophy (EDMD), caused by mutations in genes encoding nuclear envelope proteins, is clinically characterized by muscular dystrophy, early joint contracture, and life-threatening cardiac abnormalities. To elucidate the pathophysiological mechanisms underlying striated muscle involvement in EDMD, we previously established a murine model with mutations in Emd and Lmna (Emd-/-/LmnaH222P/H222P; EH), and reported exacerbated skeletal muscle phenotypes and no notable cardiac phenotypes at 12 weeks of age. We predicted that lack of emerin in LmnaH222P/H222P mice causes an earlier onset and more pronounced cardiac dysfunction at later stages. In this study, cardiac abnormalities of EDMD mice were compared at 18 and 30 weeks of age. Contrary to our expectations, physiological and histological analyses indicated that emerin deficiency causes no prominent differences of cardiac involvement in LmnaH222P/H222P mice. These results suggest that emerin does not contribute to cardiomyopathy progression in LmnaH222P/H222P mice.

Activation of sarcolipin expression and altered calcium cycling in LMNA cardiomyopathy

Cardiomyopathy caused by A-type lamins gene (LMNA) mutations (LMNA cardiomyopathy) is associated with dysfunction of the heart, often leading to heart failure. LMNA cardiomyopathy is highly penetrant with bad prognosis with no specific therapy available. Searching for alternative ways to halt the progression of LMNA cardiomyopathy, we studied the role of calcium homeostasis in the evolution of this disease. We showed that sarcolipin, an inhibitor of the sarco/endoplasmic reticulum (SR) Ca²⁺ ATPase (SERCA) was abnormally elevated in the ventricular cardiomyocytes of mutated mice compared with wild type mice, leading to an alteration of calcium handling. This occurs early in the progression of the disease, when the left ventricular function was not altered. We further demonstrated that down regulation of sarcolipin using adeno-associated virus (AAV) 9-mediated RNA interference delays cardiac dysfunction in mouse model of LMNA cardiomyopathy. These results showed a novel role for sarcolipin on calcium homeostasis in heart and open perspectives for future therapeutic interventions to LMNA cardiomyopathy.

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Sarcolipin, an inhibitor of the sarco/endoplasmic reticulum (SR) Ca²⁺ ATPase (SERCA) was abnormally elevated in the cardiac muscle of a mouse model of cardiomyopathy caused by LMNA mutations.

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The elevation of sarcolipin expression leads to an alteration of calcium handling.

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Down regulation of sarcolipin using adeno-associated virus (AAV) 9-mediated RNA interference delays cardiac dysfunction in mouse model of cardiomyopathy caused by LMNA mutations.

TBX5 R264K acts as a modifier to develop dilated cardiomyopathy in mice independently of T-box pathway

Background

TBX5 is a transcription factor that has an important role in development of heart. TBX5 variants in the region encoding the T-box domain have been shown to cause cardiac defects, such as atrial septal defect or ventricular septal defect, while TBX5 variants have also been identified in a few cardiomyopathy patients and considered causative. We identified a TBX5 variant (c.791G>A, p.Arg264Lys), that is over-represented in cardiomyopathy patients. This variant is located outside of the T-box domain, and its pathogenicity has not been confirmed by functional analyses.

Objective

To investigate whether the TBX5 R264K is deleterious and could contribute to the pathogenesis of cardiomyopathy.

Methods and results

We developed mice expressing Tbx5 R264K. Mice homozygous for this variant displayed compensated dilated cardiomyopathy; mild decreased fractional shortening, dilatation of the left ventricle, left ventricular wall thinning and increased heart weight without major heart structural disorders. There was no difference in activation of the ANF promotor, a transcriptional target of Tbx5, compared to wild-type. However, analysis of RNA isolated from left ventricular samples showed significant increases in the expression of Acta1 in left ventricle with concomitant increases in the protein level of ACTA1.

Conclusions

Mice homozygous for Tbx5 R264K showed compensated dilated cardiomyopathy. Thus, TBX5 R264K may have a significant pathogenic role in some cardiomyopathy patients independently of T-box domain pathway.

Deficiency of emerin contributes differently to the pathogenesis of skeletal and cardiac muscles in LmnaH222P/H222P mutant mice

Laminopathies are tissue-selective diseases that affect differently in organ systems. Mutations in nuclear envelopes, emerin (Emd) and lamin A/C (Lmna) genes, cause clinically indistinguishable myopathy called Emery-Dreifuss muscular dystrophy (EDMD) and limb-girdle muscular dystrophy. Several murine models for EDMD have been generated; however, emerin-null (Emd) mice do not show obvious skeletal and cardiac muscle phenotypes, and Lmna H222P/H222P mutant (H222P) mice show only a mild phenotype in skeletal muscle when they already have severe cardiomyopathy. Thus, the underlying molecular mechanism of muscle involvement due to nuclear abnormalities is still unclarified. We generated double mutant (Emd-/-/LmnaH222P/H222P; EH) mice to characterize dystrophic changes and to elucidate interactions between emerin and lamin A/C in skeletal and cardiac muscles. As H222P mice, EH mice grow normally and have breeding productivity. EH mice showed severer muscle involvement compared with that of H222P mice which was an independent of cardiac abnormality at 12 weeks of age. Nuclear abnormalities, reduced muscle fiber size and increased fibrosis were prominent in EH mice. Roles of emerin and lamin A/C in satellite cells function and regeneration of muscle fiber were also evaluated by cardiotoxin-induced muscle injury. Delayed increases in myog and myh3 expression were seen in both H222P and EH mice; however, the expression levels of those genes were similar with control and regenerated muscle fiber size was not different at day 7 after injury. These results indicate that EH mouse is a suitable model for studying skeletal muscle involvement, independent of cardiac function, in laminopathies and an interaction between emerin and lamin A/C in different tissues.

N-acetyl cysteine alleviates oxidative stress and protects mice from dilated cardiomyopathy caused by mutations in nuclear A-type lamins gene

Cardiomyopathy caused by lamin A/C gene (LMNA) mutations (hereafter referred as LMNA cardiomyopathy) is an anatomic and pathologic condition associated with muscular and electrical dysfunction of the heart, often leading to heart failure-related disability. There is currently no specific therapy available for patients that target the molecular pathophysiology of LMNA cardiomyopathy. We showed here an increase in oxidative stress levels in the hearts of mice carrying LMNA mutation, associated with a decrease of the key cellular antioxidant glutathione (GHS). Oral administration of N-acetyl cysteine, a GHS precursor, led to a marked improvement of GHS content, a decrease in oxidative stress markers including protein carbonyls and an improvement of left ventricular structure and function in a model of LMNA cardiomyopathy. Collectively, our novel results provide therapeutic insights into LMNA cardiomyopathy.

The Pathogenesis and Therapies of Striated Muscle Laminopathies

Emery-Dreifuss muscular dystrophy (EDMD) is a genetic condition characterized by early contractures, skeletal muscle weakness, and cardiomyopathy. During the last 20 years, various genetic approaches led to the identification of causal genes of EDMD and related disorders, all encoding nuclear envelope proteins. By their respective localization either at the inner nuclear membrane or the outer nuclear membrane, these proteins interact with each other and establish a connection between the nucleus and the cytoskeleton. Beside this physical link, these proteins are also involved in mechanotransduction, responding to environmental cues, such as increased tension of the cytoskeleton, by the activation or repression of specific sets of genes. This ability of cells to adapt to environmental conditions is altered in EDMD. Increased knowledge on the pathophysiology of EDMD has led to the development of drug or gene therapies that have been tested on mouse models. This review proposed an overview of the functions played by the different proteins involved in EDMD and related disorders and the current therapeutic approaches tested so far.

Role of Lamin A/C Gene Mutations in the Signaling Defects Leading to Cardiomyopathies

Nuclear lamin A/C are crucial components of the intricate protein mesh that underlies the inner nuclear membrane and confers mainly nuclear and cytosolic rigidity. However, throughout the years a number of other key physiological processes have been associated with lamins such as modulation of both genes expression and the activity of signaling mediators. To further solidify its importance in cell physiology, mutations in the lamin A/C gene (LMNA) have been associated to diverse pathological phenotypes with skeletal muscles and the heart being the most affected systems. When affected, the heart develops a wide array of phenotypes spanning from dilated cardiomyopathy with conduction defects to arrhythmogenic right ventricular cardiomyopathy. The surprising large number of cardiac phenotypes reflects the equally large number of specific mutations identified in the LMNA gene. In this review, we underlie how mutations in LMNA can impact the activity and the spatial/temporal organization of signaling mediators and transcription factors. We analyzed the ever-increasing amount of findings collected in Lmna^H222P/H222P mice whose cardiomyopathy resemble the most important features of the disease in humans and a number of key evidences from other experimental models. With this mini review, we attempt to combine the newest insights regarding both the pathogenic effects of LMNA mutations in terms of signaling abnormalities and cardiac laminopathies.

Overexpression of heart-specific small subunit of myosin light chain phosphatase results in heart failure and conduction disturbance

Mutations in genes encoding components of the sarcomere cause cardiomyopathy, which is often associated with abnormal Ca²⁺ sensitivity of muscle contraction. We have previously shown that a heart-specific myosin light chain phosphatase small subunit (hHS-M₂₁) increases the Ca²⁺ sensitivity of muscle contraction. The aim of the present study was to investigate the function of hHS-M₂₁ in vivo and the causative role of abnormal Ca²⁺ sensitivity in cardiomyopathy. We generated transgenic mice with cardiac-specific overexpression of hHS-M₂₁. We confirmed that hHS-M₂₁ increased the Ca²⁺ sensitivity of cardiac muscle contraction in vivo, which was not followed by an increased phosphorylation of myosin light chain 2 isoforms. hHS-M₂₁ transgenic mice developed severe systolic dysfunction with myocardial fibrosis and degeneration of cardiomyocytes in association with sinus bradycardia and atrioventricular conduction defect. The contractile dysfunction and cardiac fibrosis were improved by treatment with the Rho kinase inhibitor fasudil. Our findings suggested that the overexpression of hHS-M₂₁ results in cardiac dysfunction and conduction disturbance via non-myosin light chain 2 phosphorylation-dependent regulation. NEW & NOTEWORTHY The present study is the first to develop mice with transgenic overexpression of a heart-specific myosin light chain phosphatase small subunit (hHS-M₂₁) and to examine the effects of hHS-M₂₁ on cardiac function. Elevation of hHS-M₂₁ induced heart failure with myocardial fibrosis and degeneration of cardiomyocytes accompanied by supraventricular arrhythmias.

Lamin and the heart

Lamins A and C are intermediate filament nuclear envelope proteins encoded by the LMNA gene. Mutations in LMNA cause autosomal dominant severe heart disease, accounting for 10% of dilated cardiomyopathy (DCM). Characterised by progressive conduction system disease, arrhythmia and systolic impairment, lamin A/C heart disease is more malignant than other common DCMs due to high event rates even when the left ventricular impairment is mild. It has several phenotypic mimics, but overall it is likely to be an under-recognised cause of DCM. In certain clinical scenarios, particularly familial DCM with early conduction disease, the pretest probability of finding an LMNA mutation may be quite high.

Recognising lamin A/C heart disease is important because implantable cardioverter defibrillators need to be implanted early. Promising oral drug therapies are within reach thanks to research into the mitogen-activated protein kinase (MAPK) and affiliated pathways. Personalised heart failure therapy may soon become feasible for LMNA, alongside personalised risk stratification, as variant-related differences in phenotype severity and clinical course are being steadily elucidated.

Genotyping and family screening are clinically important both to confirm and to exclude LMNA mutations, but it is the three-pronged integration of such genetic information with functional data from in vivo cardiomyocyte mechanics, and pathological data from microscopy of the nuclear envelope, that is properly reshaping our LMNA knowledge base, one variant at a time. This review explains the biology of lamin A/C heart disease (genetics, structure and function of lamins), clinical presentation (diagnostic pointers, electrocardiographic and imaging features), aspects of screening and management, including current uncertainties, and future directions.

What Should the Cardiologist know about Lamin Disease?

Lamins are intermediate filament proteins able to polymerise and form an organised meshwork underlying the inner nuclear membrane in most differentiated somatic cells. Mutations in the LMNA gene, which encodes the two major lamin A and C isoforms, cause a diverse range of diseases, called laminopathies, including dilated cardiomyopathy, associated with a poor prognosis and high rate of sudden death due to conduction defect and early ventricular arrhythmia. Identification of mutations in LMNA gene in clinical practice is rapidly increasing, as well as comprehensive cardiac and genetic family screening. As a consequence, cardiologists are more and more frequently faced to difficult questions regarding optimal management of patients and relatives, especially timing for prophylactic cardioverter defibrillator. This review focuses on recent data useful for the clinician, as well as therapeutic perspectives both in human and animal models.

Striated muscle laminopathies

Lamins A and C, encoded by LMNA, are constituent of the nuclear lamina, a meshwork of proteins underneath the nuclear envelope first described as scaffolding proteins of the nucleus. Since the discovery of LMNA mutations in highly heterogeneous human disorders (including cardiac and muscular dystrophies, lipodystrophies and progeria), the number of functions described for lamin A/C has expanded. Lamin A/C is notably involved in the regulation of chromatin structure and gene transcription, and in the resistance of cells to mechanical stress. This review focuses on studies performed on knock-out and knock-in Lmna mouse models, which have led to decipher some of the lamin A/C functions in striated muscles and to the first preclinical trials of pharmaceutical therapies.

Depletion of extracellular signal-regulated kinase 1 in mice with cardiomyopathy caused by lamin A/C gene mutation partially prevents pathology before isoenzyme activation

Mutations in the lamin A/C gene (LMNA) encoding A-type nuclear lamins cause dilated cardiomyopathy with variable muscular dystrophy. These mutations enhance mitogen-activated protein kinase signaling in the heart and pharmacological inhibition of extracellular signal-regulated kinase (ERK) 1 and 2 improves cardiac function in Lmna(H222P/H222P) mice. In the current study, we crossed mice lacking ERK1 to Lmna(H222P/H222P) mice and examined cardiac performance and survival. Male Lmna(H222P/H222P)/Erk1(-/-) mice lacking ERK1 had smaller left ventricular end systolic diameters and increased fractional shortening (FS) at 16 weeks of age than Lmna(H222P/H222P/)Erk1(+/+) mice. Their mean survival was also significantly longer. However, the improved cardiac function was abrogated at 20 weeks of age concurrent with an increased activity of ERK2. Lmna(H222P/H222P)/Erk1(-/-) mice treated with an inhibitor of ERK1/2 activation had smaller left ventricular diameters and increased FS at 20 weeks of age. These results provide genetic evidence that ERK1 and ERK2 contribute to the development of cardiomyopathy caused by LMNA mutations and reveal interplay between these isoenzymes in maintaining a combined pathological activity in heart.

Treatment with selumetinib preserves cardiac function and improves survival in cardiomyopathy caused by mutation in the lamin A/C gene

AIMS

Mutations in A-type nuclear lamins gene, LMNA, lead to a dilated cardiomyopathy. We have reported abnormal activation of the extracellular signal-regulated kinase1/2 (ERK1/2) signalling in hearts from Lmna(H222P/H222P) mice, which develop dilated cardiomyopathy. We therefore determined whether an inhibitor of ERK1/2 signalling that has been investigated in clinical trials for cancer has the potential to be translated to humans with LMNA cardiomyopathy.

METHODS AND RESULTS

To evaluate the relevance of this finding in mice to patients, we analysed the ERK1/2 signalling in heart tissue from human subjects with LMNA cardiomyopathy and showed that it was abnormally activated. To determine whether pharmacological inhibitors of the ERK1/2 signalling pathway could potentially be used to treat LMNA cardiomyopathy, we administered selumetinib to male Lmna(H222P/H222P) mice starting at 16 weeks of age, after they show signs of cardiac deterioration, up to 20 weeks of age. Selumetinib is an inhibitor of ERK1/2 signalling and has been given safely to human subjects in clinical trials for cancer. Systemic treatment with selumetinib inhibited cardiac ERK1/2 phosphorylation and blocked increased expression of RNAs encoding natriuretic peptide precursors and proteins involved in sarcomere architecture that occurred in placebo-treated mice. Echocardiography and histological analysis demonstrated that treatment increases cardiac fractional shortening, prevents myocardial fibrosis, and prolongs survival. Selumetinib treatment did not induce biochemical abnormalities suggestive of renal or hepatic toxicity.

CONCLUSION

Our results suggest that selumetinib or other related inhibitors that have been safely administered to humans in clinical trials could potentially be used to treat LMNA cardiomyopathy.

Contribution of genetic factors to the pathogenesis of dilated cardiomyopathy: the cause of dilated cardiomyopathy: genetic or acquired? (genetic-side)

Dilated cardiomyopathy (DCM) is characterized by dilated ventricles and systolic dysfunction. Its etiology is not fully unraveled, but both extrinsic and intrinsic factors are considered to be involved. The intrinsic factors include genetic variations in the genes (ie, disease-causing mutations and disease-associated polymorphisms), which play key roles in controlling the susceptibility to the disease by affecting the performance, regulation, and/or maintenance of cardiac function. DCM can be classified into 2 types: hereditary and non-hereditary. The genetic variations, or disease-causing mutations, contributing to the pathogenesis of hereditary DCM can be found in various genes, especially those for sarcolemma elements, contractile elements, Z-disc elements, sarcoplasmic elements, and nuclear lamina elements of cardiomyocytes. On the other hand, disease-associated polymorphisms, which control the susceptibility to non-hereditary DCM, may be found in genes expressing not only in cardiomyocytes but also other non-cardiac cells involved in the immune system. Because functional alterations caused by these genetic variations can be classified into several categories, it is necessary to understand the pathogenesis and hence to develop diagnostic and therapeutic strategies for both hereditary and non-hereditary DCM from the viewpoint of genetic factors.

Mitogen-activated protein kinase inhibitors improve heart function and prevent fibrosis in cardiomyopathy caused by mutation in lamin A/C gene

BACKGROUND

Mutations in the lamin A/C gene, LMNA, can cause dilated cardiomyopathy. We have shown abnormal activation of the extracellular signal-regulated kinase (ERK) and the c-jun N-terminal kinase (JNK) branches of the mitogen-activated protein kinase signaling cascade in hearts from Lmna(H222P/H222P) mice that develop dilated cardiomyopathy. We recently showed that partial inhibition of ERK and JNK signaling before the onset of cardiomyopathy in Lmna(H222P/H222P) mice prevented the development of left ventricle dilatation and decreased cardiac ejection fraction at a time when they occurred in untreated mice.

METHODS AND RESULTS

To determine whether pharmacological inhibitors of ERK and JNK signaling could be clinically useful to treat cardiomyopathy caused by LMNA mutation, we administered them to Lmna(H222P/H222P) mice after they developed left ventricular dilatation and decreased ejection fraction. Lmna(H222P/H222P) mice were treated with ERK and JNK signaling inhibitors from 16 to 20 or, in pilot experiments, 19 to 24 weeks of age. The inhibitors blocked increased expression of RNAs encoding natriuretic peptide precursors and proteins involved in sarcomere architecture that occurred in placebo-treated mice. Echocardiography and histological analysis demonstrated that treatment prevented left ventricular end-systolic dilatation, increased ejection fraction, and decreased myocardial fibrosis.

CONCLUSION

Inhibitors of ERK and JNK signaling could potentially be used to treat humans with cardiomyopathy caused by LMNA mutations.