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Titin-truncating mutations associated with dilated cardiomyopathy alter length-dependent activation and its modulation via phosphorylation

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journal contribution
posted on 03.05.2022, 06:49 authored by Petr G Vikhorev, Natalia N Vikhoreva, WaiChun Yeung, Amy LiAmy Li, Sean Lal, Cristobal G dos Remedios, Cheavar A Blair, Maya Guglin, Kenneth S Campbell, Magdi H Yacoub, Pieter de Tombe, Steven B Marston
Aims: Dilated cardiomyopathy (DCM) is associated with mutations in many genes encoding sarcomere proteins. Truncating mutations in the titin gene TTN are the most frequent. Proteomic and functional characterizations are required to elucidate the origin of the disease and the pathogenic mechanisms of TTN-truncating variants. Methods and results: We isolated myofibrils from DCM hearts carrying truncating TTN mutations and measured the Ca2+ sensitivity of force and its length dependence. Simultaneous measurement of force and adenosine triphosphate (ATP) consumption in skinned cardiomyocytes was also performed. Phosphorylation levels of troponin I (TnI) and myosin binding protein-C (MyBP-C) were manipulated using protein kinase A and λ phosphatase. mRNA sequencing was employed to overview gene expression profiles. We found that Ca2+ sensitivity of myofibrils carrying TTN mutations was significantly higher than in myofibrils from donor hearts. The length dependence of the Ca2+ sensitivity was absent in DCM myofibrils with TTN-truncating variants. No significant difference was found in the expression level of TTN mRNA between the DCM and donor groups. TTN exon usage and splicing were also similar. However, we identified down-regulation of genes encoding Z-disk proteins, while the atrial-specific regulatory myosin light chain gene, MYL7, was up-regulated in DCM patients with TTN-truncating variants. Conclusion: Titin-truncating mutations lead to decreased length-dependent activation and increased elasticity of myofibrils. Phosphorylation levels of TnI and MyBP-C seen in the left ventricles are essential for the length-dependent changes in Ca2+ sensitivity in healthy donors, but they are reduced in DCM patients with TTN-truncating variants. A decrease in expression of Z-disk proteins may explain the observed decrease in myofibril passive stiffness and length-dependent activation.

Funding

The work was supported by a grant from the British Heart Foundation [PG/17/5/32705 to P.G.V. and S.B.M.]; the National Institutes of Health grant [HL-PO1 HL62426 to P.d.T.]; the Fondation Leducq [17CVD04 to M.H.Y.]; and by the Magdi Yacoub Institute [Charity number 1082750].

History

Publication Date

01/01/2022

Journal

Cardiovascular Research

Volume

118

Issue

1

Pagination

13p. (p. 241-253)

Publisher

Oxford University Press

ISSN

0008-6363

Rights Statement

© The Author(s) 2020. Published by Oxford University Press on behalf of the European Society of Cardiology. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.