Abnormal contractility in human heart myofibrils from patients with dilated cardiomyopathy due to mutations in TTN and contractile protein genes

Petr G Vikhorev,Natalia Smoktunowicz,Sean Lal,Manfred Richter,O’Neal Copeland,Ralph Knöll,Cheavar A Blair,Maya Guglin,Kenneth S Campbell,Cristobal G Dos Remedios,Amy Li,Alex B Munster,Andrew E Messer,Mohammad R Toliat,Sawa Kostin,Steven B Marston,Cecile Montgiraud

doi:10.1038/s41598-017-13675-8

Abstract

Dilated cardiomyopathy (DCM) is an important cause of heart failure. Single gene mutations in at least 50 genes have been proposed to account for 25–50% of DCM cases and up to 25% of inherited DCM has been attributed to truncating mutations in the sarcomeric structural protein titin (TTNtv). Whilst the primary molecular mechanism of some DCM-associated mutations in the contractile apparatus has been studied in vitro and in transgenic mice, the contractile defect in human heart muscle has not been studied. In this study we isolated cardiac myofibrils from 3 TTNtv mutants, and 3 with contractile protein mutations (TNNI3 K36Q, TNNC1 G159D and MYH7 E1426K) and measured their contractility and passive stiffness in comparison with donor heart muscle as a control. We found that the three contractile protein mutations but not the TTNtv mutations had faster relaxation kinetics. Passive stiffness was reduced about 38% in all the DCM mutant samples. However, there was no change in maximum force or the titin N2BA/N2B isoform ratio and there was no titin haploinsufficiency. The decrease in myofibril passive stiffness was a common feature in all hearts with DCM-associated mutations and may be causative of DCM.

Highlights

Dilated cardiomyopathy (DCM) is an important cause of heart failure
To investigate whether there was any mechanical dysfunction caused by putative DCM mutations we isolated cardiac myofibrils and measured their passive stiffness and contractility using an apparatus for single myofibril force studies
We found that there were no significant differences between the N2BA/ N2B ratio of donor heart or any of the mutant DCM heart muscle samples, we did observe a higher ratio in myofibrils from idiopathic DCM as expected (Figs 3 and 4)

Summary

Introduction

Single gene mutations in at least 50 genes have been proposed to account for 25–50% of DCM cases and up to 25% of inherited DCM has been attributed to truncating mutations in the sarcomeric structural protein titin (TTNtv). In this study we isolated cardiac myofibrils from 3 TTNtv mutants, and 3 with contractile protein mutations (TNNI3 K36Q, TNNC1 G159D and MYH7 E1426K) and measured their contractility and passive stiffness in comparison with donor heart muscle as a control. In a previous study of human heart tissue samples we identified 26 potentially disease-causing mutations in 14 genes, 5 of which were in contractile proteins, 4 were in OBSCN and 6 were truncating mutations in the titin gene (TTNtv)[4]. In this study we have directly investigated TTNtv heterozygous mutations in human heart tissue samples in comparison with donor heart and DCM-causing mutations in other sarcomeric proteins.

Methods

Results

Conclusion