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The most significantly associated genetic locus for atrial fibrillation (AF) is in chromosomal region 4q25, where four independent association signals have been identified. Although model-system studies suggest that altered PITX2c expression might underlie the association, the link between specific variants and the direction of effect on gene expression remains unknown for all four signals. In the present study, we analyzed the AF-associated region most proximal to PITX2 at 4q25. First, we identified candidate regulatory variants that might confer AF risk through a combination of mammalian conservation, DNase hypersensitivity, and histone modification from ENCODE and the Roadmap Epigenomics Project, as well as through in vivo analysis of enhancer activity in embryonic zebrafish. Within candidate regions, we then identified a single associated SNP, rs2595104, which displayed dramatically reduced enhancer activity with the AF risk allele. CRISPR-Cas9-mediated deletion of the rs2595104 region and editing of the rs2595104 risk allele in human stem-cell-derived cardiomyocytes resulted in diminished PITX2c expression in comparison to that of the non-risk allele. This differential activity was mediated by activating enhancer binding protein 2 alpha (TFAP2a), which bound robustly to the non-risk allele at rs2595104, but not to the risk allele, in cardiomyocytes. In sum, we found that the AF-associated SNP rs2595104 altered PITX2c expression via interaction with TFAP2a. Such a pathway could ultimately contribute to AF susceptibility at the PITX2 locus associated with AF.

Objective: Nonsyndromic Mitral valve prolapse (MVP) is a common degenerative valvular heart disease with severe health consequences, including arrhythmia, heart failure and sudden death. MVP is cha...

Injury to muscle tissue plays a central role in various cardiovascular pathologies. Overexpression of the small heat shock protein Hsp27 protects muscle cells against thermal, oxidative and ischemic stress. However, underlying mechanisms of this protection have not been resolved. A distinctive feature of muscle cells is the stress-induced association of Hsp27 with the sarcomere. The association of Hsp27 with the cytoskeleton, in both muscle and non-muscle cells, is thought to represent interaction with Z-line components or filamentous actin. Here, we examined the association of Hsp27 with myofibrils in adult zebrafish myocardium subjected to hyperthermia and mechanical stretching. Consistent with previously published results, Hsp27 in resting length myofibrils localized to narrowly defined regions, or bands, which colocalized with Z-line markers. However, analysis of stretched myofibrils revealed that the association of Hsp27 with myofibrils was independent of desmin, alpha-actinin, myosin, and filamentous actin. Instead, Hsp27 maintained a consistent relationship with a marker for the titin A/I border over various sarcomeric lengths. Finally, extraction of actin filaments revealed that Hsp27 binds to a component of the remaining sarcomere. Together, these novel data support a mechanism of Hsp27 function where interactions with the titin filament system protect myofibrils from stress-induced degradation.

Background Fibromuscular dysplasia (FMD) is a nonatherosclerotic vascular disease leading to arterial stenosis, aneurysm and dissection, mainly in renal and carotid artery. FMD has higher prevalence in females (80-90%) and is associated with hypertension and stroke. The pathophysiology of FMD is unclear and a genetic origin is suspected. Methods We performed a genetic association study in European ancestry individuals. The discovery included 249 cases and 689 controls, in which we analyzed 25,606 common variants (MAF>0.05) using an exome-chip array. Results We followed up 13 loci ( p −4 ) in 393 cases and 2537 controls and replicated a signal on Chr6. Three additional studies (combined n cases = 512, n controls = 669) confirmed this association, with an overall OR of 1.39, ( p = 7.4×10 −10 , n all cases = 1154, n all controls = 3895). The FMD risk variant is intronic to the phosphatase and actin regulator 1 gene (PHACTR1), involved in angiogenesis and cell migration. PHACTR1 is a risk locus for coronary artery disease, migraine, and cervical artery dissection, which may occur in FMD. We found a significant association between the risk allele and higher central pulse pressure ( p =0.0009), increased intima media thickness ( p =0.001) and wall cross-sectional area ( p =0.003) of carotids assessed by echotracking in 3800 population-based individuals. RNA expression of PHACTR1 in primary cultured human fibroblasts is 1.7 fold higher in FMD patients ( n =20, matched to 20 controls) and we showed that FMD risk allele is an eQTL for PHACTR1 in fibroblast of 57 FMD patients ( p =0.02). Finally, Phactr1 knockdown of zebrafish showed significantly dilated vessels ( p =0.003) indicating impaired development of vasculature. Conclusions Here we report the first risk locus for FMD with the largest genetic association study conducted so far. Our data reveal a common genetic variant at PHACTR1 providing indices of shared pathophysiology between FMD and other cardiovascular and neurovascular diseases.

Nonsyndromic mitral valve prolapse (MVP) is a common degenerative valvulopathy of unknown aetiology that predisposes to heart failure and sudden death. Here we investigate functional evidence for candidate genes near genome-wide association study (GWAS) loci to understand the mechanisms underlying the genetic susceptibility to MVP. To prioritize genes, we used literature and databases (e. g ENCODE, eQTLs). We analysed the expression pattern of 3 candidate genes during valve development in mouse embryos by immunohistochemistry (IHC) i) completion of endothelial-to-mesenchymal transformation (E13.5), ii) valve sculpting and elongation (E17.5) and iii) adult form (9 months). Morpholino knockdown (KD) was performed for 8 genes in zebrafish and assayed the function of developing atrioventrocular (AV) canal by scoring the embryos according to the presence of erythrocyte regurgitation. On chr3, the association is in an intron of LMCD1, a repressor of GATA6 previously implicated in cardiac hypertrophy. KD of Lmcd1 in zebrafish resulted in a significant atrioventricular valve defect with regurgitation. On Chr2, the associated variants were upstream to TNS1 encoding a focal adhesion and actin-interacting protein. Tensin1 is expressed during valve morphogenesis in mice and maintained in the adult endothelial and valvular interstitial cells. Hematoxylin and eosin histological staining in 9-month Tns1-/- mice show enlarged posterior mitral leaflets with myxomatous aspects. In addition, zebrafish KD of Tns1 induced AV regurgitation. The functional validation of genes located in or near MVP susceptibility loci identifies new MVP mechanisms and stresses the role of cytoskeleton integrity in valve development. This study reveals LMCD1 and TNS1 at play as early as during valve development and can potentially be targeted during adulthood to improve the natural history of MVP.