A novel mechanism involving four-and-a-half LIM domain protein-1 and extracellular signal-regulated kinase-2 regulates titin phosphorylation and mechanics.
ABSTRACT Understanding mechanisms underlying titin regulation in cardiac muscle function is of critical importance given recent compelling evidence that highlight titin mutations as major determinants of human cardiomyopathy. We previously identified a cardiac biomechanical stress-regulated complex at the cardiac-specific N2B region of titin that includes four-and-a-half LIM domain protein-1 (Fhl1) and components of the mitogen-activated protein signaling cascade, which impacted muscle compliance in Fhl1 knock-out cardiac muscle. However, direct regulation of these molecular components in mediating titin N2B function remained unresolved. Here we identify Fhl1 as a novel negative regulator of titin N2B levels and phosphorylation-mediated mechanics. We specifically identify titin N2B as a novel substrate of extracellular signal regulated-kinase-2 (Erk2) and demonstrate that Fhl1 directly interferes with Erk2-mediated titin-N2B phosphorylation. We highlight the critical region in titin-N2B that interacts with Fhl1 and residues that are dependent on Erk2-mediated phosphorylation in situ. We also propose a potential mechanism for a known titin-N2B cardiomyopathy-causing mutation that involves this regulatory complex. These studies shed light on a novel mechanism regulating titin-N2B mechano-signaling as well as suggest that dysfunction of these pathways could be important in cardiac disease states affecting muscle compliance.
Article: Cardiac Titin and Heart Disease.[Show abstract] [Hide abstract]
ABSTRACT: The giant sarcomeric protein titin is a key determinant of myocardial passive stiffness and stress sensitive signaling. Titin stiffness is modulated by isoform variation, phosphorylation by protein kinases and possibly oxidative stress through disulfide bond formation. Titin has also emerged as an important human disease gene. Early studies in patients with dilated cardiomyopathy (DCM) revealed shifts toward more compliant isoforms, an adaptation that offsets increases in passive stiffness based in the extracellular matrix. Similar shifts are observed in heart failure with preserved ejection fraction (HFpEF). In contrast, hypophosphorylation of PKA/G sites contributes to a net increase in cardiomyocyte resting tension in HFpEF. More recently, titin mutations have been recognized as the most common etiology of inherited DCM. In addition, some DCM-causing mutations affect RBM20, a titin splice factor. Titin mutations are a rare cause of hypertrophic cardiomyopathy (HCM) and also underlie some cases of arrhythmogenic right ventricular dysplasia. Finally, mutations of genes encoding proteins that interact with and/or bind to titin are responsible for both DCM and HCM. Targeting titin as a therapeutic strategy is in its infancy, but could potentially involve manipulation of isoforms, post-translational modifications, and up-regulation of normal protein in patients with disease causing mutations.Journal of cardiovascular pharmacology 09/2013; · 2.83 Impact Factor
- Journal of Molecular and Cellular Cardiology 04/2014; · 5.15 Impact Factor
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ABSTRACT: As part of this series devoted to heart failure (HF), we review the epidemiology, diagnosis, pathophysiology, and treatment of HF with preserved ejection fraction (HFpEF). Gaps in knowledge and needed future research are discussed.Pflügers Archiv - European Journal of Physiology 03/2014; · 4.87 Impact Factor