An inherited life-threatening arrhythmia model established by screening randomly mutagenized mice.

Inherited arrhythmia syndromes (IASs) can cause life-threatening arrhythmias and are responsible for a significant proportion of sudden cardiac deaths (SCDs). Despite progress in the development of devices to prevent SCDs, the precise molecular mechanisms that induce detrimental arrhythmias remain to be fully investigated, and more effective therapies are desirable. In the present study, we screened a large-scale randomly mutagenized mouse library by electrocardiography to establish a disease model of IASs and consequently found one pedigree that exhibited spontaneous ventricular arrhythmias (VAs) followed by SCD within 1 y after birth. Genetic analysis successfully revealed a missense mutation (p.I4093V) of the ryanodine receptor 2 gene to be a cause of the arrhythmia. We found an age-related increase in arrhythmia frequency accompanied by cardiomegaly and decreased ventricular contractility in the Ryr2I4093V/+ mice. Ca2+ signaling analysis and a ryanodine binding assay indicated that the mutant ryanodine receptor 2 had a gain-of-function phenotype and enhanced Ca2+ sensitivity. Using this model, we detected the significant suppression of VA following flecainide or dantrolene treatment. Collectively, we established an inherited life-threatening arrhythmia mouse model from an electrocardiogram-based screen of randomly mutagenized mice. The present IAS model may prove feasible for use in investigating the mechanisms of SCD and assessing therapies.

Novel preventive effect of isorhamnetin on electrical and structural remodeling in atrial fibrillation.

Isorhamnetin, a natural flavonoid, has strong antioxidant and antifibrotic effects, and a regulatory effect against Ca2+-handling. Atrial remodeling due to fibrosis and abnormal intracellular Ca2+ activities contributes to initiation and persistence of atrial fibrillation (AF). The present study investigated the effect of isorhamnetin on angiotensin II (AngII)-induced AF in mice. Wild-type male mice (C57BL/6J, 8 weeks old) were assigned to three groups: (1) control group, (2) AngII-treated group, and (3) AngII- and isorhamnetin-treated group. AngII (1000 ng/kg/min) and isorhamnetin (5 mg/kg) were administered continuously via an implantable osmotic pump for two weeks and intraperitoneally one week before initiating AngII administration, respectively. AF induction and electrophysiological studies, Ca2+ imaging with isolated atrial myocytes and HL-1 cells, and action potential duration (APD) measurements using atrial tissue and HL-1 cells were performed. AF-related molecule expression was assessed and histopathological examination was performed. Isorhamnetin decreased AF inducibility compared with the AngII group and restored AngII-induced atrial effective refractory period prolongation. Isorhamnetin eliminated abnormal diastolic intracellular Ca2+ activities induced by AngII. Isorhamnetin also abrogated AngII-induced APD prolongation and abnormal Ca2+ loading in HL-1 cells. Furthermore, isorhamnetin strongly attenuated AngII-induced left atrial enlargement and atrial fibrosis. AngII-induced elevated expression of AF-associated molecules, such as ox-CaMKII, p-RyR2, p-JNK, p-ERK, and TRPC3/6, was improved by isorhamnetin treatment. The findings of the present study suggest that isorhamnetin prevents AngII-induced AF vulnerability and arrhythmogenic atrial remodeling, highlighting its therapeutic potential as an anti-arrhythmogenic pharmaceutical or dietary supplement.

Identification of potential dilated cardiomyopathy-related targets by meta-analysis and co-expression analysis of human RNA-sequencing datasets.

AIMS: Dilated cardiomyopathy (DCM) remains among the most refractory heart diseases because of its complicated pathogenesis, and the key molecules that cause it remain unclear. MAIN METHODS: To elucidate the molecules and upstream pathways critical for DCM pathogenesis, we performed meta-analysis and co-expression analysis of RNA-sequencing (RNA-seq) datasets from publicly available databases. We analyzed three RNA-seq datasets containing comparisons of RNA expression in left ventricles between healthy controls and DCM patients. We extracted differentially expressed genes (DEGs) and clarified upstream regulators of cardiovascular disease-related DEGs by Ingenuity Pathway Analysis (IPA). Weighted Gene Co-expression Network Analysis (WGCNA) and Protein-Protein Interaction (PPI) analysis were also used to identify the hub gene candidates strongly associated with DCM. KEY FINDINGS: In total, 406 samples (184 healthy, 222 DCM) were used in this study. Overall, 391 DEGs [absolute fold change (FC) ≥ 1.5; P < 0.01], including 221 upregulated and 170 downregulated ones in DCM, were extracted. Seven common hub genes (LUM, COL1A2, CXCL10, FMOD, COL3A1, ADAMTS4, MRC1) were finally screened. IPA showed several upstream transcriptional regulators, including activating (NFKBIA, TP73, CALR, NFKB1, KLF4) and inhibiting (CEBPA, PPARGC1A) ones. We further validated increased expression of several common hub genes in the transverse aortic constriction-induced heart failure model. SIGNIFICANCE: In conclusion, meta-analysis and WGCNA using RNA-seq databases of DCM patients identified seven hub genes and seven upstream transcriptional regulators.

Electrical, structural, and autonomic atrial remodeling underlies atrial fibrillation in inflammatory atrial cardiomyopathy.

Background: There is growing evidence indicating a close relationship between inflammation and atrial fibrillation (AF). Although underlying inflammatory atrial cardiomyopathy may contribute to the development of AF, the arrhythmogenic remodeling caused by atrial inflammation has not been elucidated in detail. Herein, we examined electrical, structural, and autonomic changes in the atria in a mouse model of autoimmune myocarditis. Methods: BALB/c mice were immunized with cardiac myosin peptide (MyHC-α614-629) conjugated with complete Freund's adjuvant on days 0 and 7. Susceptibility to AF was assessed using right-atrial burst pacing. Results: The mice immunized with MyHC-α614-629 showed an inflammatory atrial cardiomyopathy phenotype, with enlarged atria; a high degree of inflammatory cell infiltration primarily consisting of CD4+ T cells, CD8+ T cells, Ly6GlowCD11b+ macrophages, and CD11c+ dendritic cells; and severe interstitial fibrosis with collagen deposition. These mice demonstrated significantly enhanced susceptibility to AF, as indicated by their increased AF induction rate and duration. In addition, the expression of potassium channels (Kcnh2, Kcnd3, and Kcnj2) and calcium handling-associated genes (Cacna1c, Camk2, Ryr2, and Atp2a2) was downregulated. Connexin 40 expression was significantly downregulated, leading to frequent lateralization to the inflamed atrium. Sympathetic and parasympathetic innervation and neurotrophin expression (nerve growth factor and brain-derived neurotrophic factor) were upregulated in the inflamed atria. Conclusion: Inflammatory atrial cardiomyopathy promotes susceptibility to AF via arrhythmogenic electrical, structural, and autonomic remodeling of the atria.

Xanthine oxidase inhibitor febuxostat reduces atrial fibrillation susceptibility by inhibition of oxidized CaMKII in Dahl salt-sensitive rats.

Oxidative stress could be a possible mechanism and a therapeutic target of atrial fibrillation (AF). However, the effects of the xanthine oxidase (XO) inhibition for AF remain to be fully elucidated. We investigated the effects of a novel XO inhibitor febuxostat on AF compared with allopurinol in hypertension rat model. Five-week-old Dahl salt-sensitive rats were fed either low-salt (LS) (0.3% NaCl) or high-salt (HS) (8% NaCl) diet. After 4 weeks of diet, HS diet rats were divided into three groups: orally administered to vehicle (HS-C), febuxostat (5 mg/kg/day) (HS-F), or allopurinol (50 mg/kg/day) (HS-A). After 4 weeks of treatment, systolic blood pressure (SBP) was significantly higher in HS-C than LS, and it was slightly but significantly decreased by treatment with each XO inhibitor. AF duration was significantly prolonged in HS-C compared with LS, and significantly suppressed in both HS-F and HS-A (LS; 5.8 ± 3.5 s, HS-C; 33.9 ± 23.7 s, HS-F; 15.0 ± 14.1 s, HS-A; 20.1 ± 11.9 s: P<0.05). Ca2+ spark frequency was obviously increased in HS-C rats and reduced in the XO inhibitor-treated rats, especially in HS-F group. Western blotting revealed that the atrial expression levels of Met281/282-oxidized Ca2+/Calmodulin-dependent kinase II (CaMKII) and Ser2814-phosphorylated ryanodine receptor 2 were significantly increased in HS-C, and those were suppressed in HS-F and HS-A. Decreased expression of gap junction protein connexin 40 in HS-C was partially restored by treatment with each XO inhibitor. In conclusion, XO inhibitor febuxostat, as well as allopurinol, could reduce hypertension-related increase in AF perpetuation by restoring Ca2+ handling and gap junction.

Programmed Death-Ligand 2 Deficiency Exacerbates Experimental Autoimmune Myocarditis in Mice.

Programmed death ligand 2 (PD-L2) is the second ligand of programmed death 1 (PD-1) protein. In autoimmune myocarditis, the protective roles of PD-1 and its first ligand programmed death ligand 1 (PD-L1) have been well documented; however, the role of PD-L2 remains unknown. In this study, we report that PD-L2 deficiency exacerbates myocardial inflammation in mice with experimental autoimmune myocarditis (EAM). EAM was established in wild-type (WT) and PD-L2-deficient mice by immunization with murine cardiac myosin peptide. We found that PD-L2-deficient mice had more serious inflammatory infiltration in the heart and a significantly higher myocarditis severity score than WT mice. PD-L2-deficient dendritic cells (DCs) enhanced CD4+ T cell proliferation in the presence of T cell receptor and CD28 signaling. These data suggest that PD-L2 on DCs protects against autoreactive CD4+ T cell expansion and severe inflammation in mice with EAM.

MAIR-II deficiency ameliorates cardiac remodelling post-myocardial infarction by suppressing TLR9-mediated macrophage activation.

Macrophages are fundamental components of inflammation in post-myocardial infarction (MI) and contribute to adverse cardiac remodelling and heart failure. However, the regulatory mechanisms in macrophage activation have not been fully elucidated. Previous studies showed that myeloid-associated immunoglobulin-like receptor II (MAIR-II) is involved in inflammatory responses in macrophages. However, its role in MI is unknown. Thus, this study aimed to determine a novel role and mechanism of MAIR-II in MI. We first identified that MAIR-II-positive myeloid cells were abundant from post-MI days 3 to 5 in infarcted hearts of C57BL/6J (WT) mice induced by permanent left coronary artery ligation. Compared to WT, MAIR-II-deficient (Cd300c2-/- ) mice had longer survival, ameliorated cardiac remodelling, improved cardiac function and smaller infarct sizes. Moreover, we detected lower pro-inflammatory cytokine and fibrotic gene expressions in Cd300c2-/- -infarcted hearts. These mice also had less infiltrating pro-inflammatory macrophages following MI. To elucidate a novel molecular mechanism of MAIR-II, we considered macrophage activation by Toll-like receptor (TLR) 9-mediated inflammation. In vitro, we observed that Cd300c2-/- bone marrow-derived macrophages stimulated by a TLR9 agonist expressed less pro-inflammatory cytokines compared to WT. In conclusion, MAIR-II may enhance inflammation via TLR9-mediated macrophage activation in MI, leading to adverse cardiac remodelling and poor prognosis.

Effects of Isorhamnetin in Human Amniotic Epithelial Stem Cells in vitro and Its Cardioprotective Effects in vivo.

Cardiac hypertrophy and fibrosis are major pathophysiologic disorders that lead to serious cardiovascular diseases (CVDs), such as heart failure and arrhythmia. It is well known that transforming growth factor ß (TGFß) signaling pathways play a major role in the proliferation of cardiac hypertrophy and fibrosis, which is mainly stimulated by angiotensin II (AgII). This study aimed to investigate the cardioprotective potential of isorhamnetin (ISO) in human amniotic epithelial stem cells (hAESCs) through global gene expression analysis and to confirm its beneficial effects on cardiac hypertrophy and fibrosis in the AgII-induced in vivo model. In vitro, biological processes including TGFß, collagen-related functions, and inflammatory processes were significantly suppressed in ISO pretreated hAESCs. In vivo, continuous AgII infusion using an osmotic pump induced significant pathological fibrosis and myocardial hypertrophy, which were remarkably suppressed by ISO pretreatment. ISO was found to reverse the enhanced TGFß and Collagen type I alpha 1 mRNA expression induced by AgII exposure, which causes cardiovascular remodeling in ventricular tissue. These findings indicate that ISO could be a potential agent against cardiac hypertrophy and fibrosis.