Pathogenic troponin T mutants with opposing effects on myofilament Ca2+ sensitivity attenuate cardiomyopathy phenotypes in mice

Abstract

Mutations in cardiac troponin T (TnT) associated with hypertrophic cardiomyopathy generally lead to an increase in the Ca2+ sensitivity of contraction and susceptibility to arrhythmias. In contrast, TnT mutations linked to dilated cardiomyopathy decrease the Ca2+ sensitivity of contraction. Here we tested the hypothesis that two TnT disease mutations with opposite effects on myofilament Ca2+ sensitivity can attenuate each other’s phenotype. We crossed transgenic mice expressing the HCM TnT-I79N mutation (I79N) with a DCM knock-in mouse model carrying the heterozygous TnT-R141W mutation (HET). The results of the Ca2+ sensitivity in skinned cardiac muscle preparations ranked from highest to lowest were as follow: I79N > I79N/HET > NTg > HET. Echocardiographic measurements revealed an improvement in hemodynamic parameters in I79N/HET compared to I79N and normalization of left ventricular dimensions and volumes compared to both I79N and HET. Ex vivo testing showed that the I79N/HET mouse hearts had reduced arrhythmia susceptibility compared to I79N mice. These results suggest that two disease mutations in TnT that have opposite effects on the myofilament Ca2+ sensitivity can paradoxically ameliorate each other’s disease phenotype. Normalizing myofilament Ca2+ sensitivity may be a promising new treatment approach for a variety of diseases.

Non‐negative blind deconvolution for signal processing in a CRISPR‐edited iPSC‐cardiomyocyte model of dilated cardiomyopathy

“…Moreover, the duration of contractile events is prolonged in MUT iPSC‐CMs. Our findings are in line with recent reports describing molecular disease phenotypes in patient‐specific iPSC‐CMs carrying inherited DCM mutations in sarcomeric proteins [13–15,17,44]. Our comparison of the NNBD‐based strategy with previously established methods for analysis of Ca 2+ handling, force recordings and contractility data in cardiac cells revealed overall comparable results.…”

“…It has been suggested that the TnT‐R141W mutation increases the TnT binding affinity for tropomyosin, thereby resulting in Ca 2+ desensitization of myocyte contraction [15]. Moreover, Ca 2+ desensitization in presence of TnT‐R141W has been elucidated in a double‐transgenic ‘rescue’ mouse model [44]. In line with these reports, we observed a prolonged transient duration and reduced amplitude in Ca 2+ transients from TnT‐R141W (MUT) iPSC‐CMs.…”

“…This mutation is located in the tropomyosin‐binding region of the troponin T1 domain [15,43] and has been reported in human DCM patients [16]. A murine model of TnT‐R141W demonstrated that the mutation leads to abnormal Ca 2+ handling [17,44]. Moreover, these findings were confirmed by studies with rabbit skinned cardiac muscle fibres into which human TnT‐WT or TnT‐R141W had been incorporated [15].…”

Familial Dilated Cardiomyopathy Associated With a Novel Combination of Compound Heterozygous TNNC1 Variants

“…In general, myofilament incorporation of troponin variants that cause opposing effects on thin filament Ca 2+ responsiveness are expected to normalize the myofilament Ca 2+ sensitivity Alves et al, 2014Alves et al, , 2017Dieseldorff Jones et al, 2018), and that was what was found in this study. Compared to WT, the 50%:50% mix of D132N/D145E showed similar myofilament Ca 2+ sensitivity and Hill coefficient (n Hill ) values, the latter generally reflecting cooperative processes associated with isometric force generation.…”

Sexual dimorphism in cardiac transcriptome associated with a troponin C murine model of hypertrophic cardiomyopathy

“…Echocardiography and analysis were performed using a Vevo 2100 high‐resolution in vivo imaging system and workstation as described previously (Dieseldorff Jones et al, 2019; Parvatiyar et al, 2019). Three‐month‐old male and female mice of both genotypes were maintained under light anesthesia with isoflurane (∼2%) during the procedure.…”