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Atrial fibrillation (AF) is a common cardiac arrhythmia resulting in increased risk of stroke. Despite highly heritable etiology, our understanding of the genetic architecture of AF remains incomplete. Here we performed a genome-wide association study in the Japanese population comprising 9,826 cases among 150,272 individuals and identified East Asian-specific rare variants associated with AF. A cross-ancestry meta-analysis of >1 million individuals, including 77,690 cases, identified 35 new susceptibility loci. Transcriptome-wide association analysis identified IL6Ras a putative causal gene, suggesting the involvement of immune responses. Integrative analysis with ChIP-seq data and functional assessment using human induced pluripotent stem cell-derived cardiomyocytes demonstrated ERRg as having a key role in the transcriptional regulation of AF-associated genes. A polygenic risk score derived from the cross-ancestry meta-analysis predicted increased risks of cardiovascular and stroke mortalities and segregated individuals with cardioembolic stroke in undiagnosed AF patients. Our results provide new biological and clinical insights into AF genetics and suggest their potential for clinical applications.

To elucidate the genetics of coronary artery disease (CAD) in the Japanese population, we conducted a large-scale genome-wide association study of 168,228 individuals of Japanese ancestry (25,892 cases and 142,336 controls) with genotype imputation using a newly developed reference panel of Japanese haplotypes including 1,781 CAD cases and 2,636 controls. We detected eight new susceptibility loci and Japanese-specific rare variants contributing to disease severity and increased cardiovascular mortality. We then conducted a trans-ancestry meta-analysis and discovered 35 additional new loci. Using the meta-analysis results, we derived a polygenic risk score (PRS) for CAD, which outperformed those derived from either Japanese or European genome-wide association studies. The PRS prioritized risk factors among various clinical parameters and segregated individuals with increased risk of long-term cardiovascular mortality. Our data improve the clinical characterization of CAD genetics and suggest the utility of trans-ancestry meta-analysis for PRS derivation in non-European populations.

Foxp3+regulatory T cells (Tregcells) are the central component of peripheral immune tolerance. Whereas a dysregulated Tregcytokine signature has been observed in autoimmune diseases, the regulatory mechanisms underlying pro- and anti-inflammatory cytokine production are elusive. Here, we identify an imbalance between the cytokines IFN-? and IL-10 as a shared Tregsignature present in patients with multiple sclerosis and under high-salt conditions. RNA-sequencing analysis on human Tregsubpopulations revealed ß-catenin as a key regulator of IFN-? and IL-10 expression. The activated ß-catenin signature was enriched in human IFN-?+Tregcells, as confirmed in vivo with Treg-specific ß-catenin-stabilized mice exhibiting lethal autoimmunity with a dysfunctional Tregphenotype. Moreover, we identified prostaglandin E receptor 2 (PTGER2) as a regulator of IFN-? and IL-10 production under a high-salt environment, with skewed activation of the ß-catenin–SGK1–Foxo axis. Our findings reveal a novel PTGER2–ß-catenin loop in Tregcells linking environmental high-salt conditions to autoimmunity.

Variants in TGFBR1have been reported to induce two completely distinct diseases, namely Loeys–Dietz syndrome (LDS) and multiple self-healing squamous epithelioma (MSSE). However, detailed mechanisms underlying this effect remain unknown. We report a Japanese familial case of LDS with a novel splice donor site variant in TGFBR1gene (c.973 + 1 G > A; NG_007461.1). The intronic variant was predicted to mediate in-frame exon 5 skipping within the serine/threonine kinase (STK) domain, which may also be mediated by a similar TGFBR1variant of a splice acceptor site in intron 4 (c.806-2 A > C), identified in a British familial case of MSSE. Therefore, ex vivo splicing and functional assays were performed in mammalian cells to evaluate the effect of these sequence variants. The MSSE variant activated a cryptic acceptor site at 76 bp downstream of the 3′ natural splice acceptor site, which produced an out-of-frame transcript (r.807_882del, p.Asn270Thrfs*8). In contrast, the LDS variant generated two types of in-frame transcription products, r.[806_973del, 965_973 del], and produced two functionally inactivated proteins, p.[Asp269_Gln324del, Thr323_Gly325del], as a result of exon 5 skipping and the activation of a cryptic donor splice site at 9 bp upstream of the 5′ natural splice donor site, respectively. Our results support the previously proposed but not yet approved mechanism that dominant-negative and truncating variants in STK domain induce LDS and MSSE, respectively.

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Many studies have explored cardiac progenitor cell (CPC) therapy for heart disease. However, optimal scaffolds are needed to ensure the engraftment of transplanted cells. We produced a three-dimensional hydrogel scaffold (CPC-PRGmx) in which high-viability CPCs were cultured for up to 8 weeks. CPC-PRGmx contained an RGD peptide-conjugated self-assembling peptide with insulin-like growth factor-1 (IGF-1). Immediately after creating myocardial infarction (MI), we transplanted CPC-PRGmx into the pericardial space on to the surface of the MI area. Four weeks after transplantation, red fluorescent protein-expressing CPCs and in situhybridization analysis in sex-mismatched transplantations revealed the engraftment of CPCs in the transplanted scaffold (which was cellularized with host cells). The average scar area of the CPC-PRGmx-treated group was significantly smaller than that of the non-treated group (CPC-PRGmx-treated group = 46 ± 5.1%, non-treated MI group = 59 ± 4.5%; p< 0.05). Echocardiography showed that the transplantation of CPC-PRGmx improved cardiac function and attenuated cardiac remodeling after MI. The transplantation of CPCs-PRGmx promoted angiogenesis and inhibited apoptosis, compared to the untreated MI group. CPCs-PRGmx secreted more vascular endothelial growth factor than CPCs cultured on two-dimensional dishes. Genetic fate mapping revealed that CPC-PRGmx-treated mice had more regenerated cardiomyocytes than non-treated mice in the MI area (CPC-PRGmx-treated group = 0.98 ± 0.25%, non-treated MI group = 0.25 ± 0.04%; p< 0.05). Our findings reveal the therapeutic potential of epicardial-transplanted CPC-PRGmx. Its beneficial effects may be mediated by sustainable cell viability, paracrine function, and the enhancement of de novo cardiomyogenesis.

Early human mummies examined recently by computed tomography demonstrated a high prevalence of vascular calcification, a pathognomonic sign of atherosclerosis, which was correlated with estimated age at death. Early populations had little exposure to modern-day metabolic risk factors: these observations thus suggest that humans have an inherent age-dependent predisposition to atherosclerosis. Premature aging syndromes are extremely rare genetic disorders that exhibit clinical phenotypes resembling accelerated aging, including severe atherosclerosis, but those phenotypes are usually segmental. Controversy persists, therefore, regarding the extent to which the molecular mechanisms underlying premature aging syndromes overlap with those of physiological aging. Hutchinson-Gilford progeria syndrome (HGPS) and Werner syndrome are well-characterized premature aging syndromes. HGPS is caused by gain-of-function mutations in the LMNAgene, which result in the accumulation of a mutant nuclear protein, called “progerin,” at the nuclear rim. In contrast, loss-of-function mutations in Werner syndrome ATP-dependent helicase (WRN) lead to Werner syndrome. Mesenchymal stem cells (MSCs), which can differentiate into vascular cells to maintain vascular homeostasis in response to injury, are severely affected in these syndromes. Mechanistically, either aberrant expression of progerin or loss of WRN protein in MSCs alters heterochromatin structure, resulting in premature senescence and exhaustion of functional MSCs in premature aging syndromes. Surprisingly, vascular cells and MSCs in elderly healthy individuals have shown progerin expression and decreased expression levels of WRN, respectively. Studying these rare genetic disorders could thus provide valuable insights into age-related vascular diseases that occur in the general population.

The octapeptide angiotensin II (Ang II) plays a homeostatic role in the regulation of blood pressure and water and electrolyte balance, and also contributes to the progression of cardiovascular remodeling. Ang II activates Ang II type 1 (AT1) receptor and type 2 (AT2) receptor, both of which belong to the seven-transmembrane, G protein-coupled receptor family. Most of the actions of Ang II such as promotion of cellular prolifaration, hypertrophy, and fibrosis are mediated by AT1 receptor. However, in some pathological situations, AT2 receptor shows an increase in tissue expression and functions to antagonize the actions induced by AT1 receptor. Recent studies have advanced our understanding of the molecular mechanisms underlying receptor activation and signal transduction of AT1 and AT2 receptor in the cardiovascular system.

Reactive oxygen species (ROS) are proposed to contribute to the deterioration of cardiac function in patients with heart diseases. It has been reported that ROS are increased in the failing heart and involved in atherosclerosis, myocardial ischemia/reperfusion injury, and heart failure. Antioxidant enzymes are decreased in the decompensated heart, depressing defense mechanisms against oxidative stress. A variety of proteins, including receptors, ionic channels, transporters, and components of signal transduction pathways, are substrates of oxidation by ROS. ROS also function as signal transduction intermediates to induce transcription factor activation, gene expression, cell growth, and apoptosis. Recently, the upstream and downstream molecules of ROS in signal transduction pathways have been the subjects of intense investigation. These molecules include the mitogen-activated protein kinase family, the Rho family of small GTP binding proteins, the Src family of tyrosine kinases, Ras, and cytokines. The modulation of oxidative stress-induced signaling pathways is effective for preventing the progression of heart diseases.

Csx/Nkx2-5, which is essential for cardiac development of the embryo, is abundantly expressed in the adult heart. We here examined the role ofCsx/Nkx2-5in the adult heart using two kinds of transgenic mice. Transgenic mice that overexpress a dominant negative mutant of Csx/Nkx2-5(DN-TG mice) showed degeneration of cardiac myocytes and impairment of cardiac function. Doxorubicin induced more marked cardiac dysfunction in DN-TG mice and less in transgenic mice that overexpress wild typeCsx/Nkx2-5(WT-TG mice) compared with non-transgenic mice. Doxorubicin induced cardiomyocyte apoptosis, and the number of apoptotic cardiomyocytes was high in the order of DN-TG mice, non-transgenic mice, and WT-TG mice. Overexpression of the dominant negative mutant of Csx/Nkx2-5induced apoptosis in cultured cardiomyocytes, while expression of wild typeCsx/Nkx2-5protected cardiomyocytes from doxorubicin-induced apoptotic death. These results suggest thatCsx/Nkx2-5plays a critical role in maintaining highly differentiated cardiac phenotype and in protecting the heart from stresses including doxorubicin.

The Na+‐Ca2+exchanger (NCX) on the plasma membrane is thought to be the main calcium extrusion system from the cytosol to the extracellular space in many mammalian excitable cells, including cardiac myocytes. However, the pathophysiological role of NCX in the heart is still unclear because of the lack of known specific inhibitors of NCX. To determine the role of NCX in cardiac contraction and the development of cardiac hypertrophy, we imposed pressure overload on the heart of heterozygous NCX knockout (KO) mice by constricting transverse aorta, and examined cardiac function and morphology 3 wk after operation. Although there was no difference in cardiac function between sham‐operated KO mice and sham‐operated wild‐type (WT) mice, KO mice showed higher left ventricular pressure and better systolic function than WT mice in response to pressure overload. Northern blot analysis revealed that mRNA levels of sarcoplasmic reticulum Ca2+‐ATPase were reduced by pressure overload in left ventricles of WT but not of KO mice. However, hypertrophic changes with interstitial fibrosis were more prominent in KO mice than WT mice. These results suggest that reduction of NCX results in supernormalized cardiac function and causes marked cardiac hypertrophy in response to pressure overload.—Takimoto, E., Yao, A., Toko, H., Takano, H., Shimoyama, M., Sonoda, M., Wakimoto, K., Takahashi, T., Akazawa, H., Mizukami, M., Nagai, T., Nagai, R., Komuro, I. Sodium calcium exchanger plays a key role in alteration of cardiac function in response to pressure overload. FASEB J.16, 373–378 (2002)

Mechanical stress induces various hypertrophic responses including activation of mitogen-activated protein kinases (MAPKs) in cardiac myocytes. Here we examined the role of the small GTP-binding proteins of Rho family and reactive oxygen species (ROS) in stretch-induced activation of p38MAPK in cardiomyocytes. Overexpression of dominant-negative mutants of Rac1 (D.N. Rac1), D.N.RhoA and D.N.Cdc42 suppressed stretch-induced activation of p38MAPK. Overexpression of constitutively active mutants of Rac1 (C.A.Rac1) and C.A.Cdc42 increased the p38MAPK activity in the absence of mechanical stress. Pretreatment with N-acetyl-l-cysteine and N-(2-mercaptopropionyl)-glycine (NAC) suppressed stretch-induced activation of p38MAPK. Mechanical stretch increased intracellular ROS generation, which was abrogated by overexpression of D.N.Rac1 and attenuated by overexpression of D.N.RhoA and D.N.Cdc42. An increase in protein synthesis evoked by mechanical stretch was suppressed by overexpression of D.N.Rac1 and pretreatment with NAC. These results suggest that mechanical stress induces cardiac hypertrophy through the Rac1-ROS-p38MAPK pathway in cardiac myocytes.

A homeodomain-containing transcription factorCsx/Nkx-2.5is an important regulator of cardiogenesis in mammals. Three different mutants, Gln170ter (designated A) and Thr178Met (designated B) in the helix 2 of the homeodomain and Gln198ter mutation (designated C) just after homeodomain, have been reported to cause atrial septal defect with atrial ventricular block. We here examined the functions of these three mutants of Csx/Nkx-2.5. The atrial natriuretic peptide (ANP) promoter was activated by wild typeCsx/Nkx-2.5(WT, ∼8-fold), B(∼2-fold), and C(∼6-fold) but not by A. When A, B,or Cwas cotransfected into COS-7 cells with the same amount of WT,WT-induced activation of the ANPpromoter was attenuated by Aand B(A>B), whereas Cfurther enhanced the activation. Immunocytochemical analysis using anti-Myc tag antibody indicated that transfected Myc-tagged WT, B,and Cwere localized in the nucleus of both COS-7 cells and cardiomyocytes of neonatal rats, whereas Awas distributed diffusely in the cytoplasm and nucleus in COS-7 cells. Electrophoretic mobility shift assay showed that Csx/Nkx-2.5-binding sequences were bound strongly by WT and C, weakly by B, but not by A. Immunoprecipitation and GST pull-down assay revealed that WT and all mutants interacted with GATA-4. The synergistic activation of the ANPpromoter by WTand GATA-4was further enhanced by Cbut was inhibited by Aand B. In the cultured cardiomyocytes, overexpression of Cbut notWT, A,or B,induced apoptosis. These results suggest that although the three mutants induce the same cardiac phenotype, transactivation ability and DNA binding ability are different among the three mutants and that apoptosis may be a cause forC-induced cardiac defect.

Atrial fibrillation (AF) is the most common cardiac arrhythmia associated with increased risks of morbidity and mortality. We performed a large-scale genome-wide association study (GWAS) of 150,272 individuals of Japanese ancestry (9,826 cases and 140,446 controls) and identified five new susceptibility loci including Japanese-specific rare variants associated with the pathogenesis of cardiomyopathy. We then conducted a trans-ancestry meta-analysis of more than 1 million individuals including 77,690 cases and discovered 35 novel loci in total. Using the GWAS result, epigenetic-feature and gene-set analyses revealed the transcriptional landscape of AF, elucidating the underlying biological pathways. Additionally, we created polygenic risk scores (PRS) for AF, where PRS derived from trans-ancestry GWAS surpassed those derived from a single population. The PRS was associated with increased risk of long-term cardiovascular and stroke mortalities and segregated individuals with cardioembolic stroke in undiagnosed AF patients, suggesting that it may play an important role in early detection of subclinical AF or the pathophysiology underlying thromboembolism. Our results provide novel biological and clinical insights into AF genetics and broaden its clinical applications.

Cell transplantation could be a potential therapy for heart damage. Skeletal myoblasts have been expected to be a good cell source for autologous transplantation; however, the safety and efficacy of their transplantation are still controversial. Recent studies have revealed that skeletal muscle possesses the stem cell population that is distinct from myoblasts. To elucidate whether skeletal muscle stem cells can transdifferentiate into cardiomyocytes, we cocultured skeletal muscle cells isolated from transgenic mice expressing green fluorescent protein with cardiomyocytes of neonatal rats. Skeletal muscle‐derived cells expressed cardiac‐specific proteins such as cardiac troponin T and atrial natriuretic peptide as well as cardiac‐enriched transcription factors such as Nkx2E (formerly called Csx/Nkx2.5) and GATA4 by coculture with cardiomyocytes. Skeletal muscle‐derived cells also expressed cadherin and connexin 43 at the junctions with neighboring cardiomyocytes. Cardiomyocyte‐like action potentials were recorded from beating skeletal muscle‐derived cells. Treatment of nifedipine or culture in Ca2+‐free media suppressed contraction of cardiomyocytes and inhibited skeletal muscle cells to express cardiac‐specific proteins. Cyclic stretch completely restored this inhibitory effect. These results suggest that some part of skeletal muscle cells can transdifferentiate into cardiomyocytes and that direct cell‐to‐cell contact and contraction of neighboring cardiomyocytes are important for the transdifferentiation.

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