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Background— Cardiac dysfunction in failing hearts of human patients and animal models is associated with both microtubule densification and transverse-tubule (T-tubule) remodeling. Our objective was to investigate whether microtubule densification contributes to T-tubule remodeling and excitation–contraction coupling dysfunction in heart disease. Methods and Results— In a mouse model of pressure overload–induced cardiomyopathy by transaortic banding, colchicine, a microtubule depolymerizer, significantly ameliorated T-tubule remodeling and cardiac dysfunction. In cultured cardiomyocytes, microtubule depolymerization with nocodazole or colchicine profoundly attenuated T-tubule impairment, whereas microtubule polymerization/stabilization with taxol accelerated T-tubule remodeling. In situ immunofluorescence of heart tissue sections demonstrated significant disorganization of junctophilin-2 (JP2), a protein that bridges the T-tubule and sarcoplasmic reticulum membranes, in transaortic banded hearts as well as in human failing hearts, whereas colchicine injection significantly preserved the distribution of JP2 in transaortic banded hearts. In isolated mouse cardiomyocytes, prolonged culture or treatment with taxol resulted in pronounced redistribution of JP2 from T-tubules to the peripheral plasma membrane, without changing total JP2 expression. Nocodazole treatment antagonized JP2 redistribution. Moreover, overexpression of a dominant-negative mutant of kinesin 1, a microtubule motor protein responsible for anterograde trafficking of proteins, protected against JP2 redistribution and T-tubule remodeling in culture. Finally, nocodazole treatment improved Ca 2+ handling in cultured myocytes by increasing the amplitude of Ca 2+ transients and reducing the frequency of Ca 2+ sparks. Conclusion— Our data identify a mechanistic link between microtubule densification and T-tubule remodeling and reveal microtubule-mediated JP2 redistribution as a novel mechanism for T-tubule disruption, loss of excitation–contraction coupling, and heart failure.

Introduction: Cystic fibrosis is among the most common inherited disorders, with ∼ 3% of Caucasians being heterozygous for the common CFTR ΔF508 mutation. Cardiomyopathy is a major cause of morbidity and mortality. While a small preliminary study suggested that cardiomyopathy patients heterozygous for the CFTR ΔF508 mutation have poorer outcomes, the finding has not been replicated and it is not known whether the poor outcomes are related to sudden death and/or heart failure progression. Methods: We screened 1347 Caucasian cardiomyopathy subjects (EF 21%, 82% male, 75% ischemic) with implantable cardioverter defibrillators (ICDs) from the prospective, multicenter, NIH-funded Genetic Risk Assessment of Defibrillator Events (GRADE) study. CFTR ΔF508 alleles were discriminated by real time fluorescence PCR. GRADE subjects were followed for up to 5 years to the primary endpoint of freedom from appropriate ICD shocks and the secondary endpoints of death and death/heart transplant/VAD placement. The results were compared by genotype using Kaplan-Meier analysis and Log Rank testing. Results: Genotyping revealed 33 CFTR ΔF508 heterozygotes (allele frequency 2.4%). ΔF508 carriers were older (68 vs 64 yrs, p=0.03); more likely to be diabetic (55 vs 34%, p=0.02), to have had an MI (77 vs 57%, p=0.02), and to have a RBBB on ECG (18 vs 7%, p=0.03); and had lower EFs (19 vs 21%, p=0.01). CFTR ΔF508 carriers had markedly higher rates of death (HR>2; p Conclusion: We have confirmed that carrying one CFTR ΔF508 allele is associated with an increased mortality in cardiomyopathy patients, and that this is likely not due to increased arrhythmic death. These findings may have implications for the treatment of this high risk heart failure subgroup. Future studies are needed to determine whether the increased mortality stems from a cardiac and/or pulmonary etiology.

Mutations that disrupt the coding sequence of Nav1.5, the cardiac Na+ channel encoded by SCN5A, cause inherited arrhythmias and cardiomyopathy. Changes in Nav1.5 splice isoforms, localization and function have also been associated with prognosis in acquired heart disease. However, the role of genetic variants in SCN5A gene regulatory sequences (e.g. those modulating expression) remains poorly understood. MicroRNAs (miRs) have emerged as vital gene regulators in heart, having roles in cardiogenesis, contractile function, and disease. These small non-coding RNAs are loaded into Argonaute proteins to direct post-transcriptional gene suppression by base-pairing with target transcripts, and genetic variants altering miR binding sequences may influence disease. Here, we used high-throughput biochemical means (HITS-CLIP) to generate the first transcriptome-wide map of miR binding events in human heart (4000 sites across >2200 genes). Our query of the data uncovered >500 common SNPs residing in or nearby miR target sites. Among these, we identified a synonymous SNP (rs1805126, T/C) which alters a conserved miR-24 binding site in the terminal coding exon of SCN5A. We hypothesized that this SNP affects Nav1.5 expression and contributes to clinical outcomes in heart failure. In vitro experiments showed that miR-24 suppresses Na+ current on patch clamp analysis (~5-fold; p1800 subjects with EFs≤30% and implantable cardioverter defibrillators (ICDs) from GRADE, a prospective multicenter study of genetic modulators of heart failure outcomes. We found that CC homozygotes had worse survival rates than T-allele carriers (HR=1.5, p=0.001), but no change in appropriate ICD shocks, a surrogate for sudden death. Together, these data reveal a novel miR-24:SCN5A:SNP regulatory axis that points to a surprising link between cardiac Na+ channel levels and non-arrhythmic death in heart failure. Overall, this work represents a key advance in exploring the interface of cardiac miRs with genetics and disease, perhaps signifying a broader functional relevance for “silent” SNPs.

A 32-year-old man was referred to our medical center for chest pain and dyspnea of 2 days duration. Past medical history was unremarkable. Vital signs and physical examination were normal. ECG (Figure 1) showed a right bundle-branch block but no changes suggestive of ischemia. Troponin T level was 4.01 ng/mL (normal

Background— Apelin is among the most potent stimulators of cardiac contractility known. However, no physiological or pathological role for apelin–angiotensin receptor-like 1 (APJ) signaling has ever been described. Methods and Results— We performed transcriptional profiling using a spotted cDNA microarray with 12 814 unique clones on paired samples of left ventricle obtained before and after placement of a left ventricular assist device in 11 patients. The significance analysis of microarrays and a novel rank consistency score designed to exploit the paired structure of the data confirmed that natriuretic peptides were among the most significantly downregulated genes after offloading. The most significantly upregulated gene was the G-protein–coupled receptor APJ, the specific receptor for apelin. We demonstrate here using immunoassay and immunohistochemical techniques that apelin is localized primarily in the endothelium of the coronary arteries and is found at a higher concentration in cardiac tissue after mechanical offloading. These findings imply an important paracrine signaling pathway in the heart. We additionally extend the clinical significance of this work by reporting for the first time circulating human apelin levels and demonstrating increases in the plasma level of apelin in patients with left ventricular dysfunction. Conclusions— The apelin-APJ signaling pathway emerges as an important novel mediator of cardiovascular control.