Genotype-specific pathogenic effects in human dilated cardiomyopathy

Abstract

Background

Dilated cardiomyopathy (DCM) can be caused by mutations in sarcomeric and non-sarcomeric genes. In this study we defined the pathogenic effects of three DCM causing mutations: the sarcomeric mutations in genes encoding cardiac troponin I (TNNI3_{p.98truncation}) and cardiac troponin T (TNNT2_{p.K217deletion}; also known as the K210del) and the non-sarcomeric gene mutation encoding lamin A/C (LMNA_p.R331Q).

Methods

We assessed sarcomeric protein expression and phosphorylation and contractile behaviour in single membrane-permeabilized cardiomyocytes in human left ventricular heart tissue. Exchange with recombinant troponin complex was used to establish the direct pathogenic effects of the mutations in TNNI3 and TNNT2.

Results

The TNNI3_p.98trunc and TNNT2_p.K217del mutation showed reduced expression of troponin I to 39% and 51%, troponin T to 64% and 53% and troponin C to 73% and 97% of controls, respectively, and altered stoichiometry between the 3 cardiac troponin subunits. The TNNI3_p.98trunc showed pure haploinsufficiency, increased Ca²⁺-sensitivity and impaired length-dependent activation. The TNNT2_p.K217del mutation showed a significant increase in passive tension that was not due to changes in titin isoform composition or phosphorylation. Exchange with wildtype troponin complex corrected troponin protein levels to 83% of controls in the TNNI3_p.98trunc sample. Moreover, upon exchange all functional deficits in the TNNI3_p.98trunc and TNNT2_p.K217del samples were normalized to control values confirming the pathogenic effects of the troponin mutations. The LMNA_p.R331Q mutation resulted in reduced maximal force development due to disease remodelling. Our study shows that different gene mutations induce DCM via diverse cellular pathways.

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