Myocardial DNA strand breaks are detected in biopsy tissues from patients with dilated cardiomyopathy

Association between SCN5A R225Q variant and dilated cardiomyopathy: potential role of intracellular pH and WNT/β-catenin pathway

BACKGROUND

The SCN5A variant is a common cause of familial dilated cardiomyopathy (DCM). We previously reported a SCN5A variant (c.674G>A), located in the high-risk S4 segment of domain I (DI-S4) region in patients with idiopathic DCM and R225Q knockin (p.R225Q) mice carrying the c.674G>A variant exhibited prolonged baseline PR intervals without DCM phenotypes. In this study, we explored the association and mechanism between R225Q variant and DCM phenotype.

METHODS

Prevalence of DI-S4 variant was compared between patients with idiopathic DCM and the control participants. R225Q knockin and wild-type (WT) mice were subjected to doxorubicin (DOX), D-galactose (D-gal) or D-gal combined with DOX.

RESULTS

Clinical data suggested that the prevalence of DI-S4 variant was higher in DCM group than in the control group (4/90 (4.4%) vs 3/1339 (0.2%), p<0.001). Cardiomyocytes from R225Q knockin mice treated with D-gal and DOX exhibited more significant hypertrophic phenotype and weaker contraction/dilation function and an increased level of apoptosis as compared with WT mice. Mechanistically, we found that R225Q variant could increase intracellular pH and further induce the activation of the WNT/β-catenin pathway as well as the overexpression of pro-hypertrophic and pro-apoptotic targets. WNT-C59 inhibitor improved cardiac function in the R225Q knockin mice treated with D-gal and DOX.

CONCLUSION

Our results suggest that R225Q variant is associated with increased susceptibility to DCM. Ageing could enhance this process via activating WNT/β-catenin signaling in response to increased intracellular pH. Antagonising the WNT/β-catenin pathway might be a potential therapeutic strategy for mitigating R225Q variant-related DCM pathogenesis.

Molecular biology and pathogenesis of viral myocarditis

Myocarditis is a cardiac disease associated with inflammation and injury of the myocardium. Several viruses have been associated with myocarditis in humans. However, coxsackievirus B3 is still considered the dominant etiological agent. The observed pathology in viral myocarditis is a result of cooperation or teamwork between viral processes and host immune responses at various stages of disease. Both innate and adaptive immune responses are crucial determinants of the severity of myocardial damage, and contribute to the development of chronic myocarditis and dilated cardiomyopathy following acute viral myocarditis. Advances in genomics and proteomics, and in the use of informatics and biostatistics, are allowing unbiased initial evaluations that can be the basis for testable hypotheses about virus pathogenesis and new therapies.

Apoptotic cardiomyocyte death in fatal myocarditis

Acute myocarditis is often a self-limited process with a good outcome. Experimental animal studies have found that cardiomyocyte apoptosis occurs in severe forms of myocarditis. We studied whether cardiomyocyte apoptosis plays a role in the development of fatal acute human myocarditis. Myocardial autopsy samples from subjects who died of acute myocarditis in Finland between 1970 and 1998 were studied. Thirty-three of these cases(16 men and 17 women; 45 +/- 6 years old) were randomly selected for this study. All cases fulfilled the histopathologic Dallas criteria for myocarditis. Eight subjects who had died accidentally served as controls. Apoptotic DNA fragmentation (terminal transferase-mediated DNA nick end labeling) and activation of caspase-3 (immunohistochemistry) were detected. The mode of death was determined retrospectively from all available clinical data. In fatal myocarditis, large amounts of cardiomyocytes showed apoptotic DNA fragmentation or contained active caspase-3 (2.0 +/- 0.3% and 2.8 +/- 0.4%, respectively). In the controls, few apoptotic cardiomyocytes were found (0.008 +/- 0.003% by terminal transferase-mediated DNA nick end labeling and 0.009 +/- 0.003% by detection of active caspase-3, p <0.001 vs myocarditis). The amount of apoptosis did not correlate with the age or gender of the cases, recognized viral etiology, histologic features, or duration of disease. However, more apoptotic cardiomyocytes were detected in the subjects who had myocarditis and had died of heart failure (n = 18) than in those who had myocarditis and died suddenly of cardiac arrest (n = 15; 2.6 +/- 0.4% vs 1.1 +/- 0.2%, p <0.001). In conclusion, cardiomyocyte apoptosis is a common mechanism of myocardial damage in severe acute human myocarditis. Moreover, higher rates of cardiomyocyte apoptosis are associated with the development of fatal heart failure in acute myocarditis.

Detection of apoptosis usingin situ markers for DNA strand breaks in the failing human heart. Fact or epiphenomenon?

The role of apoptosis and the methods used for its detection in failing human hearts are controversial. Recent data have challenged the hypothesis that in situ markers for DNA strand breaks mirror apoptotic (TUNEL and Taq in situ ligation assay) and/or necrotic (Pfu in situ ligation assay) cell death, and thus provide evidence that apoptotic cell loss contributes to the progression of heart failure. Experimental data cast doubt not only upon the specificity of the TUNEL technique but also the Taq in situ ligation assay as a reliable method for the detection of apoptotic cell death and provide compelling new evidence that the occurrence of cardiomyocyte cell death as defined by the detection of DNA strand breaks using either TUNEL or Taq and Pfu in situ ligation assays is an epiphenomena that is not related to the evolution of heart failure. Cardiomyocyte positivity for in situ markers of DNA strand breaks is a feature of hypertrophic cardiomyopathic hearts, irrespective of the underlying pathology or the presence or absence of heart failure. These data raise concerns regarding the extent of apoptosis in cardiomyopathy and the contribution of this process to the progression of heart failure.

Role of Fas/FasL pathway in the activation of infiltrating cells in murine acute myocarditis caused by Coxsackievirus B3

OBJECTIVES

This study was designed to investigate the roles of Fas/FasL pathway in myocardial damage in murine acute myocarditis caused by Coxsackie virus B3 (CVB3).

BACKGROUND

Cardiac myocyte apoptosis rarely occurs in murine acute myocarditis caused by CVB3. Fas/FasL belong to the tumor necrosis factor receptor/ligand superfamily of costimulatory molecules and are known to play a critical role in the induction of apoptosis, as well as in the cytotoxicty mediated by T-cells and natural killer cells.

METHODS

We first analyzed the expression of Fas on cardiac myocytes in vivo and in vitro. Second, we examined the development of myocardial damage, in C3H/He mice treated with an anti-FasL monoclonal antibody (mAb), and in C3H/He-lpr/lpr mice and C3H/He-gld/gld mice infected with CVB3. Third, to investigate the effects of anti-FasL mAb treatment on the activation of the infiltrating cells, we examined the expression of interferon (IFN)-gamma and interleukin (IL)-2 as activation markers in the heart of mice by semiquantitative polymerase chain reaction.

RESULTS

Fas was markedly induced on cardiac myocytes with acute myocarditis. Myocardial inflammation was decreased in mice treated with anti-Fas L mAb, C3H/He-lpr/lpr mice and C3H/He-gld/gld mice. Anti-FasL mAb-treatment also decreased the expression of IFN-gamma, IL-2, inducible nitric oxide synthase and CVB3 genomes in myocardial tissue.

CONCLUSIONS

Our findings strongly suggested that the Fas/FasL pathway played a critical role in the development of massive myocardial necrosis through activation of infiltrating cells, and raise the possibility of immunotherapy by blocking the Fas/FasL pathway to prevent myocardial damage and improve the prognosis of patients with viral myocarditis.

Apoptosis in myocarditis and dilated cardiomyopathy: does enterovirus genome persistence protect from apoptosis? An endomyocardial biopsy study

The purpose of this study was to examine the role of apoptosis in myocarditis and dilated cardiomyopathy. Apoptosis is an active energy-consuming mechanism of cell death in several cardiac diseases in different quality and quantity.

METHODS

Endomyocardial biopsies from 81 patients with active (1) and chronic myocarditis (10), dilated cardiomyopathy with inflammation (DCMi; 10) and without inflammation (DCM; 20), with borderline myocarditis and positive PCR for cytomegalovirus-DNA (6), adenovirus-DNA, or enterovirus-RNA (7), and controls (17) were analysed. Apoptosis was detected by using the TUNEL method. The highest rate of apoptotic cardiocytes was found in active and chronic myocarditis. One patient with severe active myocarditis demonstrated 6.15% of apoptotic cardiocytes. Mean percentage of apoptotic cardiocytes in chronic myocarditis was significantly increased (0.61+/-1.25%) when compared to controls (0.01+/-0.04%, P<.05). Particularly, patients with cytomegalovirus-DNA persistence in borderline myocarditis had an elevated rate of apoptosis (0.34+/-0.68%, P<.05). Increased rates of apoptosis were found in borderline myocarditis with adenovirus-DNA persistence (0.20+/-0.57%) and in DCM (0.06+/-0.15%). Only a nonsignificant increase of apoptotic cardiocytes was found in DCMi (0.03+/-0.08%). No apoptosis was found in patients with enteroviral genome persistence in borderline myocarditis.

CONCLUSIONS

Apoptosis of cardiac cells is increased in myocarditis and dilated cardiomyopathy, being highest in severe active myocarditis. Apoptosis thus contributes to cell death in active myocarditis and may play a role not to be neglected in dilated cardiomyopathy. Enteroviruses seem to have anti-apoptotic effects, because no apoptosis at all was found in the myocardium.

Apoptotic versus autophagic cell death in heart failure

OBJECTIVE

Progressive loss of cardiomyocytes is one of the most important pathogenic characteristics of heart failure. Apoptosis may be an important mode of cell death in heart failure but it must be demonstrated by multiple criteria and not just TUNEL staining alone. Previously, we and others have demonstrated that besides apoptosis other phenomena like active gene transcription can result in TUNEL positivity. Moreover, other types of cell death that are caspase-independent could be important in heart failure. This study examined the hypothesis whether TUNEL labeling parallels caspase activation.

METHODS

Cardiac tissue of patients in the terminal stage of heart failure as a consequence of ischaemic cardiomyopathy (ICM) or dilated cardiomyopathy (DCM) were studied. Embryonic mice hearts were used for positive control for detection of the classical apoptosis.

RESULTS

In mice embryonic hearts we could clearly find apoptotic cell death detected by TUNEL labeling and immunohistochemistry for activated caspase-3. In heart failure, TUNEL-positive cardiomyocytes were negative for active caspase-3 but showed signs of active gene transcription (SC-35). However, autophagic cell death could be found in 0.3% of the cardiomyocytes. Autophagic cell death was demonstrated by granular cytoplasmic ubiquitin inclusions, an established marker of autophagocytosis in neurons. Interestingly, these autophagic cardiomyocytes were TUNEL and activated caspase-3 negative but were also negative for C9, a marker for necrosis. Western blot analysis confirmed that in cardiomyopathies no cleavage of caspase-3 and caspase-7 occurred.

CONCLUSION

The present study demonstrates two fundamentally different situations of cell death in cardiac tissue. In embryonic mice, cardiomyocytes undergo caspase-dependent cell death. However, cardiomyocytes in heart failure show caspase-independent autophagic cell death rather than apoptotic cell death.

Malalignment of the sarcomeric filaments in hypertrophic cardiomyopathy with cardiac myosin heavy chain gene mutation

OBJECTIVE

To investigate changes in the alignment of the sarcomeric filaments in hypertrophic cardiomyopathy and the effects of cardiac beta myosin heavy chain (beta-MHC) mutation on the sarcomeric ultrastructure.

DESIGN

A retrospective analysis.

PATIENTS

Endomyocardial biopsy samples were examined by transmission electron microscopy in seven patients with hypertrophic cardiomyopathy and beta-MHC mutation, six with hypertrophic cardiomyopathy but without the mutation, and five controls (with chest pain syndromes).

MAIN OUTCOME MEASURE

Alignment of the sarcomeric filaments and the distance between neighbouring thick myosin filaments.

RESULTS

In controls, cross sections of the sarcomere at the A band showed a highly organised orthohexagonal array with 6 thin actin filaments surrounding one thick myosin filament, whereas in hypertrophic cardiomyopathy the alignment of the sarcomeric filaments was sparse and disrupted. In hypertrophic cardiomyopathy with a mutation, the distance between neighbouring thick myosin filaments was greater than in controls (mean (SD) 45.3 (4.7) v 38.5 (3.5) nm, p < 0.05), and the variance of the distance was greater than in controls (8.0 (0.7) v 4.8 (1.0) nm, p < 0.001) or in patients with hypertrophic cardiomyopathy without a mutation (6.7 (0.6) nm, p < 0.05). In the latter, the variance of the distance was also greater than in the controls (p < 0.01). A significant correlation was found between the grade of the myocyte hypertrophy and the variance of the distance (r = 0.654; p < 0.01).

CONCLUSIONS

The alignment of the sarcomeric filaments is disrupted in hypertrophic cardiomyopathy, particularly when there is beta-MHC mutation.