Intense myosin binding of hALC-1 provides a mechanism for preferential sarcomeric sorting and Ca(2+)-independent positive inotropic activity.
Disturbed myosin binding of mutated hVLC-1 may provide a pathomechanism for the development of HCM.
KCNE5 is an X‐linked gene encoding KCNE5, an ancillary subunit to voltage‐gated potassium (Kv) channels. Human KCNE5 mutations are associated with atrial fibrillation (AF)– and Brugada syndrome (BrS)–induced cardiac arrhythmias that can arise from increased potassium current in cardiomyocytes. Seeking to establish underlying molecular mechanisms, we created and studied Kcne5 knockout (Kcne5−/0) mice. Intracardiac ECG revealed that Kcne5 deletion caused ventricular premature beats, increased susceptibility to induction of polymorphic ventricular tachycardia (60 vs. 24% in Kcne5+/0 mice), and 10% shorter ventricular refractory period. Kcne5 deletion increased mean ventricular myocyte Kv current density in the apex and also in the subpopulation of septal myocytes that lack fast transient outward current (Ito,f). The current increases arose from an apex‐specific increase in slow transient outward current‐1 (IKslow,1) (conducted by Kv1.5) and Ito,f (conducted by KV4) and an increase in IKslow,2 (conducted by Kv2.1) in both apex and septum. Kcne5 protein localized to the intercalated discs in ventricular myocytes, where KV2.1 was also detected in both Kcne5−/0 and Kcne5+/0 mice. In HL‐1 cardiac cells and human embryonic kidney cells, KCNE5 and KV2.1 colocalized at the cell surface, but predominantly in intracellular vesicles, suggesting that Kcne5 deletion increases IK,slow2 by reducing KV2.1 intracellular sequestration. The human AF‐associated mutation KCNE5‐L65F negative shifted the voltage dependence of KV2.1‐KCNE5 channels, increasing their maximum current density >2‐fold, whereas BrS‐associated KCNE5 mutations produced more subtle negative shifts in KV2.1 voltage dependence. The findings represent the first reported native role for Kcne5 and the first demonstrated Kcne regulation of KV2.1 in mouse heart. Increased KV current is a manifestation of KCNE5 disruption that is most likely common to both mouse and human hearts, providing a plausible mechanistic basis for human KCNE5‐linked AF and BrS.—David, J.‐P., Lisewski, U., Crump, S. M., Jepps, T. A., Bocksteins, E., Wilck, N., Lossie, J., Roepke, T. K., Schmitt, N., Abbott, G. W. Deletion in mice of X‐linked, Brugada syndrome—and atrial fibrillation–associated Kcne5 augments ventricular KV currents and predisposes to ventricular arrhythmia. FASEB J. 33, 2537–2552 (2019). http://www.fasebj.org
The essential myosin light chain (ELC) is involved in modulation of force generation of myosin motors and cardiac contraction, while its mechanism of action remains elusive. We hypothesized that ELC could modulate myosin stiffness which subsequently determines its force production and cardiac contraction. We therefore generated heterologous transgenic mouse (TgM) strains with cardiomyocyte-specific expression of ELC with human ventricular ELC (hVLC-1; TgM hVLC-1 ) or E56G-mutated hVLC-1 (hVLC-1 E56G ; TgM E56G ). hVLC-1 or hVLC-1 E56G expression in TgM was around 39% and 41%, respectively of total VLC-1. Laser trap and in vitro motility assays showed that stiffness and actin sliding velocity of myosin with hVLC-1 prepared from TgM hVLC-1 (1.67pN/nm and 2.3µm/s, respectively) were significantly higher than myosin with hVLC-1 E56G prepared from TgM E56G (1.25pN/nm and 1.7µm/s, respectively) or myosin with mouse VLC-1 (mVLC-1) prepared from C57/BL6 (1.41 pN/nm and 1.5±0.03 µm/s , respectively). Maximal left ventricular pressure development of isolated perfused hearts in vitro prepared from TgM hVLC-1 (80.0mmHg) were significantly higher than hearts from TgM E56G (66.2mmHg) or C57/BL6 (59.3±3.9 mmHg). These findings show that ELCs decreased myosin stiffness, in vitro motility, and thereby cardiac functions in the order hVLC-1 > hVLC-1 E56G ≈ mVLC-1. They also suggest a molecular pathomechanism of cardiomyopathies caused by hVLC-1 mutations.
IntroductionTransgenic mice overexpressing mutated NEBL, encoding the cardiac-specific Z-disk protein nebulette, develop severe cardiac phenotypes. Since cardiomyopathies are commonly familial and because mutations in a single gene may result in variable phenotypes, we tested the hypothesis that NEBL mutations are associated with cardiomyopathy.Material and methodsWe analyzed 389 patients, including cohorts of patients with dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), and left ventricular non-compaction cardiomyopathy (LVNC). The 28 coding exons of the NEBL gene were sequenced. Further bioinformatic analysis was used to distinguish variants.ResultsIn total, we identified six very rare heterozygous missense mutations in NEBL in 7 different patients (frequency 1.8%) in highly conserved codons. The mutations were not detectable in 320 Caucasian sex-matched unrelated individuals without cardiomyopathy and 192 Caucasian sex-matched blood donors without heart disease. Known cardiomyopathy genes were excluded in these patients. The mutations p.H171R and p.I652L were found in 2 HCM patients. Further, p.Q581R and p.S747L were detected in 2 DCM patients, while the mutation p.A175T was identified independently in two unrelated patients with DCM. One LVNC patient carried the mutation p.P916L. All HCM and DCM related mutations were located in the nebulin-like repeats, domains responsible for actin binding. Interestingly, the mutation associated with LVNC was located in the C-terminal serine-rich linker region.ConclusionsOur data suggest that NEBL mutations may cause various cardiomyopathies. We herein describe the first NEBL mutations in HCM and LVNC. Our findings underline the notion that the cardiomyopathies are true allelic diseases.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.