Atrial fibrillation (AF) affects over 33 million individuals worldwide1 and has a complex heritability.2 We conducted the largest meta-analysis of genome-wide association studies for AF to date, consisting of over half a million individuals including 65,446 with AF. In total, we identified 97 loci significantly associated with AF including 67 of which were novel in a combined-ancestry analysis, and 3 in a European specific analysis. We sought to identify AF-associated genes at the GWAS loci by performing RNA-sequencing and expression quantitative trait loci (eQTL) analyses in 101 left atrial samples, the most relevant tissue for AF. We also performed transcriptome-wide analyses that identified 57 AF-associated genes, 42 of which overlap with GWAS loci. The identified loci implicate genes enriched within cardiac developmental, electrophysiological, contractile and structural pathways. These results extend our understanding of the biological pathways underlying AF and may facilitate the development of therapeutics for AF.

The molecular basis of the beneficial effects associated with exercise training (ET) on overall ventricular function (VF) in heart failure (HF) remains unclear. We investigated potential Ca(2+) handling abnormalities and whether ET would improve VF of mice lacking alpha(2A)- and alpha(2C)-adrenoceptors (alpha(2A)/alpha(2C)ARKO) that have sympathetic hyperactivity-induced HF. A cohort of male wild-type (WT) and congenic alpha(2A)/alpha(2C)ARKO mice in a C57BL/J genetic background (5-7 mo of age) was randomly assigned into untrained and trained groups. VF was assessed by two-dimensional guided M-mode echocardiography. Cardiac myocyte width and ventricular fibrosis were evaluated with a computer-assisted morphometric system. Sarcoplasmic reticulum Ca(2+) ATPase (SERCA2), phospholamban (PLN), phospho-Ser(16)-PLN, phospho-Thr(17)-PLN, phosphatase 1 (PP1), and Na(+)-Ca(2+) exchanger (NCX) were analyzed by Western blotting. ET consisted of 8-wk running sessions of 60 min, 5 days/wk. alpha(2A)/alpha(2C)ARKO mice displayed exercise intolerance, systolic dysfunction, increased cardiac myocyte width, and ventricular fibrosis paralleled by decreased SERCA2 and increased NCX expression levels. ET in alpha(2A)/alpha(2C)ARKO mice improved exercise tolerance and systolic function. ET slightly reduced cardiac myocyte width, but unchanged ventricular fibrosis in alpha(2A)/alpha(2C)ARKO mice. ET significantly increased the expression of SERCA2 (20%) and phospho-Ser(16)-PLN (63%), phospho-Thr(17)-PLN (211%) in alpha(2A)/alpha(2C)ARKO mice. Furthermore, ET restored NCX and PP1 expression in alpha(2A)/alpha(2C)ARKO to untrained WT mice levels. Thus, we provide evidence that Ca(2+) handling is impaired in this HF model and that overall VF improved upon ET, which was associated to changes in the net balance of cardiac Ca(2+) handling proteins.

Exercise training associated with robust conditioning can be useful for the study of molecular mechanisms underlying exercise-induced cardiac hypertrophy. A swimming apparatus is described to control training regimens in terms of duration, load, and frequency of exercise. Mice were submitted to 60-vs 90-min session/day, once vs twice a day, with 2 or 4% of the weight of the mouse or no workload attached to the tail, for 4 vs 6 weeks of exercise training. Blood pressure was unchanged in all groups while resting heart rate decreased in the trained groups (8-18%). Skeletal muscle citrate synthase activity, measured spectrophotometrically, increased (45-58%) only as a result of duration and frequency-controlled exercise training, indicating that endurance conditioning was obtained. In groups which received duration and endurance conditioning, cardiac weight (14-25%) and myocyte dimension (13-20%) increased. The best conditioning protocol to promote physiological hypertrophy, our primary goal in the present study, was 90 min, twice a day, 5 days a week for 4 weeks with no overload attached to the body. Thus, duration-and frequency-controlled exercise training in mice induces a significant conditioning response qualitatively similar to that observed in humans. Correspondence

Abstract-In the C57BL/6J mice model, we investigated whether obesity affects the function or expression of components of the tissue renin-angiotensin system and whether endothelin (ET)-1 contributes to these changes. ACE activity (nmol ⅐ L His-Leu ⅐ mg protein Ϫ1 ) was measured in lung, kidney, and liver in control (receiving standard chow) and obese animals treated for 30 weeks with a high-fat, low cholesterol diet alone or in combination with LU135252, an orally active ET A receptor antagonist. ACE mRNA expression was measured in the kidney, and the effects of LU135252 on purified human ACE were determined. Aortic and renal tissue ET-1 protein content was measured, and the vascular contractility to angiotensin II was assessed. Obesity was associated with a tissue-specific increase in ACE activity in the kidney (55Ϯ4 versus 33Ϯ3 nmol/L) but not in the lung (34Ϯ2 versus 32Ϯ2 nmol/L). Long-term LU135252 treatment completely prevented this activation (13.3Ϯ0.3 versus 55Ϯ4 nmol/L, PϽ0.05) independent of ACE mRNA expression, body weight, or renal ET-1 protein but did not affect pulmonary or hepatic ACE activity. Obesity potentiated contractions in response to angiotensin II in the aorta (from 6Ϯ2% to 33Ϯ5% KCl) but not in the carotid artery (4Ϯ1% to 3.6Ϯ1% KCl), an effect that was completely prevented with LU135252 treatment (6Ϯ0.4% versus 33Ϯ5% KCl). No effect of LU135252 on purified ACE was observed. Thus, obesity is associated with the activation of renal ACE in vivo independent of its mRNA expression and enhanced vascular contractility to angiotensin II. These effects are regulated by ET in an organ-specific manner, providing novel mechanisms by which ET antagonists may exert organ protection.

Genome-wide association analysis advanced understanding of blood pressure (BP), a major risk factor for vascular conditions such as coronary heart disease and stroke. Accounting for smoking behavior may help identify BP loci and extend our knowledge of its genetic architecture. We performed genome-wide association meta-analyses of systolic and diastolic BP incorporating gene-smoking interactions in 610,091 individuals. Stage 1 analysis examined ∼18.8 million SNPs and small insertion/deletion variants in 129,913 individuals from four ancestries (European, African, Asian, and Hispanic) with follow-up analysis of promising variants in 480,178 additional individuals from five ancestries. We identified 15 loci that were genome-wide significant (p < 5 × 10) in stage 1 and formally replicated in stage 2. A combined stage 1 and 2 meta-analysis identified 66 additional genome-wide significant loci (13, 35, and 18 loci in European, African, and trans-ancestry, respectively). A total of 56 known BP loci were also identified by our results (p < 5 × 10). Of the newly identified loci, ten showed significant interaction with smoking status, but none of them were replicated in stage 2. Several loci were identified in African ancestry, highlighting the importance of genetic studies in diverse populations. The identified loci show strong evidence for regulatory features and support shared pathophysiology with cardiometabolic and addiction traits. They also highlight a role in BP regulation for biological candidates such as modulators of vascular structure and function (CDKN1B, BCAR1-CFDP1, PXDN, EEA1), ciliopathies (SDCCAG8, RPGRIP1L), telomere maintenance (TNKS, PINX1, AKTIP), and central dopaminergic signaling (MSRA, EBF2).