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

RATIONALE: Mutations in the LMNA gene, encoding LMNA (lamin A/C), are responsible for laminopathies. Dilated cardiomyopathy (DCM) is a major cause of mortality and morbidity in laminopathies. OBJECTIVE: To gain insights into the molecular pathogenesis of DCM in laminopathies. METHODS AND RESULTS: We generated a tet-off bigenic mice expressing either a WT (wild type) or a mutant LMNA (D300N) protein in cardiac myocytes. LMNAD300N mutation is associated with DCM in progeroid syndromes. Expression of LMNAD300N led to severe myocardial fibrosis, apoptosis, cardiac dysfunction, and premature death. Administration of doxycycline suppressed LMNAD300N expression and prevented the phenotype. Whole-heart RNA sequencing in 2-week-old WT and LMNAD300N mice led to identification of ≈6000 differentially expressed genes. Gene Set Enrichment and Hallmark Pathway analyses predicted activation of E2F (E2F transcription factor), DNA damage response, TP53 (tumor protein 53), NFκB (nuclear factor κB), and TGFß (transforming growth factor-ß) pathways, which were validated by Western blotting, quantitative polymerase chain reaction of selected targets, and immunofluorescence staining. Differentially expressed genes involved cell death, cell cycle regulation, inflammation, and epithelial-mesenchymal differentiation. RNA sequencing of human hearts with DCM associated with defined LMNA pathogenic variants corroborated activation of the DNA damage response/TP53 pathway in the heart. Increased expression of CDKN2A (cyclin-dependent kinase inhibitor 2A)-a downstream target of E2F pathway and an activator of TP53-provided a plausible mechanism for activation of the TP53 pathway. To determine pathogenic role of TP53 pathway in DCM, Tp53 gene was conditionally deleted in cardiac myocytes in mice expressing the LMNAD300N protein. Deletion of Tp53 partially rescued myocardial fibrosis, apoptosis, proliferation of nonmyocyte cells, left ventricular dilatation and dysfunction, and slightly improved survival. CONCLUSIONS: Cardiac myocyte-specific expression of LMNAD300N, associated with DCM, led to pathogenic activation of the E2F/DNA damage response/TP53 pathway in the heart and induction of myocardial fibrosis, apoptosis, cardiac dysfunction, and premature death. The findings denote the E2F/DNA damage response/TP53 axis as a responsible mechanism for DCM in laminopathies and as a potential intervention target.

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.