Tinman/Nkx2-5 acts via miR-1 and upstream of Cdc42 to regulate heart function across species

Cdc42 regulates cardiac function in mice and flies downstream of a conserved Tinman/Nkx2-5–miR-1 signaling network

Investigation of Association between PFO Complicated by Cryptogenic Stroke and a Common Variant of the Cardiac Transcription Factor GATA4

Patent foramen ovale (PFO) is associated with clinical conditions including cryptogenic stroke, migraine and varicose veins. Data from studies in humans and mouse suggest that PFO and the secundum form of atrial septal defect (ASDII) exist in an anatomical continuum of septal dysmorphogenesis with a common genetic basis. Mutations in multiple members of the evolutionarily conserved cardiac transcription factor network, including GATA4, cause or predispose to ASDII and PFO. Here, we assessed whether the most prevalent variant of the GATA4 gene, S377G, was significantly associated with PFO or ASD. Our analysis of world indigenous populations showed that GATA4 S377G was largely Caucasian-specific, and so subjects were restricted to those of Caucasian descent. To select for patients with larger PFO, we limited our analysis to those with cryptogenic stroke in which PFO was a subsequent finding. In an initial study of Australian subjects, we observed a weak association between GATA4 S377G and PFO/Stroke relative to Caucasian controls in whom ASD and PFO had been excluded (OR = 2.16; p = 0.02). However, in a follow up study of German Caucasians no association was found with either PFO or ASD. Analysis of combined Australian and German data confirmed the lack of a significant association. Thus, the common GATA4 variant S377G is likely to be relatively benign in terms of its participation in CHD and PFO/Stroke

Stretch-Sensitive KCNQ1Mutation A Link Between Genetic and Environmental Factors in the Pathogenesis of Atrial Fibrillation?

ObjectivesThis study sought to evaluate mutations in genes encoding the slow component of the cardiac delayed rectifier K+current (IKs) channel in familial atrial fibrillation (AF).BackgroundAlthough AF can have a genetic etiology, links between inherited gene defects and acquired factors such as atrial stretch have not been explored.MethodsMutation screening of the KCNQ1, KCNE1, KCNE2, and KCNE3genes was performed in 50 families with AF. The effects of mutant protein on cardiac IKsactivation were evaluated using electrophysiological studies and human atrial action potential modeling.ResultsOne missense KCNQ1mutation, R14C, was identified in 1 family with a high prevalence of hypertension. Atrial fibrillation was present only in older individuals who had developed atrial dilation and who were genotype positive. Patch-clamp studies of wild-type or R14C KCNQ1 expressed with KCNE1 in CHO cells showed no statistically significant differences between wild-type and mutant channel kinetics at baseline, or after activation of adenylate cyclase with forskolin. After exposure to hypotonic solution to elicit cell swelling/stretch, mutant channels showed a marked increase in current, a leftward shift in the voltage dependence of activation, altered channel kinetics, and shortening of the modeled atrial action potential duration.ConclusionsThese data suggest that the R14C KCNQ1 mutation alone is insufficient to cause AF. Rather, we suggest a model in which a “second hit”, such as an environmental factor like hypertension, which promotes atrial stretch and thereby unmasks an inherited defect in ion channel kinetics (the “first hit”), is required for AF to be manifested. Such a model would also account for the age-related increase in AF development

Epistatic Effects of Potassium Channel Variation on Cardiac Repolarization and Atrial Fibrillation Risk

ObjectivesThe aim of this study was to evaluate the role of cardiac K+ channel gene variants in families with atrial fibrillation (AF).BackgroundThe K+ channels play a major role in atrial repolarization but single mutations in cardiac K+ channel genes are infrequently present in AF families. The collective effect of background K+ channel variants of varying prevalence and effect size on the atrial substrate for AF is largely unexplored.MethodsGenes encoding the major cardiac K+ channels were resequenced in 80 AF probands. Nonsynonymous coding sequence variants identified in AF probands were evaluated in 240 control subjects. Novel variants were characterized using patch-clamp techniques and in silico modeling was performed using the Courtemanche atrial cell model.ResultsNineteen nonsynonymous variants in 9 genes were found, including 11 rare variants. Rare variants were more frequent in AF probands (18.8% vs. 4.2%, p < 0.001), and the mean number of variants was greater (0.21 vs. 0.04, p < 0.001). The majority of K+ channel variants individually had modest functional effects. Modeling simulations to evaluate combinations of K+ channel variants of varying population frequency indicated that simultaneous small perturbations of multiple current densities had nonlinear interactions and could result in substantial (>30 ms) shortening or lengthening of action potential duration as well as increased dispersion of repolarization.ConclusionsFamilies with AF show an excess of rare functional K+ channel gene variants of varying phenotypic effect size that may contribute to an atrial arrhythmogenic substrate. Atrial cell modeling is a useful tool to assess epistatic interactions between multiple variants

DMD-associated dilated cardiomyopathy : genotypes, phenotypes, and phenocopies

Background: Variants in the DMD gene, that encodes the cytoskeletal protein, dystrophin, cause a severe form of dilated cardiomyopathy (DCM) associated with high rates of heart failure, heart transplantation, and ventricular arrhythmias. Improved early detection of individuals at risk is needed. Methods: Genetic testing of 40 male probands with a potential X-linked genetic cause of primary DCM was undertaken using multi-gene panel sequencing, multiplex polymerase chain reaction, and array comparative genomic hybridization. Variant location was assessed with respect to dystrophin isoform patterns and exon usage. Telomere length was evaluated as a marker of myocardial dysfunction in left ventricular tissue and blood. Results: Four pathogenic/likely pathogenic DMD variants were found in 5 probands (5/40: 12.5%). Only one rare variant was identified by gene panel testing with 3 additional multi-exon deletion/duplications found following targeted assays for structural variants. All of the pathogenic/likely pathogenic DMD variants involved dystrophin exons that had percent spliced-in scores >90, indicating high levels of constitutive expression in the human adult heart. Fifteen DMD variant-negative probands (15/40: 37.5%) had variants in autosomal genes including TTN, BAG3, LMNA, and RBM20. Myocardial telomere length was reduced in patients with DCM irrespective of genotype. No differences in blood telomere length were observed between genotype-positive family members with/without DCM and controls. Conclusions: Primary genetic testing using multi-gene panels has a low yield and specific assays for structural variants are required if DMD-associated cardiomyopathy is suspected. Distinguishing X-linked causes of DCM from autosomal genes that show sex differences in clinical presentation is crucial for informed family management. © 2023 American Heart Association, Inc

Clinical characteristics of Australian cohort.

1<p>Includes 2 APVD, 2 LSVC, 2 Coarctation of the aorta, 2 Pulmonary Stenosis, 1 LSVC & Pulmonary Stenosis, 1 PDA, 3 MVP.</p>2<p>Includes 26 isolated VSD, 17 VSD with minor abnormalities, 1 functional single ventricle and 64 VSD with malformations of outflow tracts - these include 34 with Tetralogy/pulmonary atresia, 15 with transposition/DORV and 15 with other malformations.</p>3<p>Includes 1 Ebstein's Anomaly, 2 MVP, 1 prosthetic pulmonary valve, 1 prosthetic mitral valve.</p>4<p>Includes 1 Quadri-leaflet Aortic Valve, 3 MVP, 3 prosthetic AV, 1 prosthetic AV&MVR.</p>5<p>Includes 1 BAV, 4 MVP, 4 prosthetic AV, 2 MVR.</p>6<p>Includes 1 Ebstein's Anomaly, 8 BAV, 1 BAV & Coarctation of the Aorta, 1 BAV & MVR, 1 Sick Sinus Syndrome, 1 PDA, 1 aortic root replacement, 9 MVP, 3 prosthetic MV, 6 prosthetic AV, 2 prosthetic AV&MV, 1 MVR, 1 prosthetic AV & MVR, 1 MVR & tricuspid VR.</p>7<p>Family history was unknown for a small number of patients.</p>8<p>Grade of atherosclerosis was unknown for 14 cases with PFO and stroke, 2 cases with PFO and without stroke and 4 TEE controls.</p

Tinman/Nkx2-5 acts via miR-1 and upstream of Cdc42 to regulate heart function across species.

Unraveling the gene regulatory networks that govern development and function of the mammalian heart is critical for the rational design of therapeutic interventions in human heart disease. Using the Drosophila heart as a platform for identifying novel gene interactions leading to heart disease, we found that the Rho-GTPase Cdc42 cooperates with the cardiac transcription factor Tinman/Nkx2-5. Compound Cdc42, tinman heterozygous mutant flies exhibited impaired cardiac output and altered myofibrillar architecture, and adult heart-specific interference with Cdc42 function is sufficient to cause these same defects. We also identified K(+) channels, encoded by dSUR and slowpoke, as potential effectors of the Cdc42-Tinman interaction. To determine whether a Cdc42-Nkx2-5 interaction is conserved in the mammalian heart, we examined compound heterozygous mutant mice and found conduction system and cardiac output defects. In exploring the mechanism of Nkx2-5 interaction with Cdc42, we demonstrated that mouse Cdc42 was a target of, and negatively regulated by miR-1, which itself was negatively regulated by Nkx2-5 in the mouse heart and by Tinman in the fly heart. We conclude that Cdc42 plays a conserved role in regulating heart function and is an indirect target of Tinman/Nkx2-5 via miR-1