Dilated cardiomyopathy mutations in thin-filament regulatory proteins reduce contractility, suppress systolic Ca²⁺, and activate NFAT and Akt signaling

Abstract

<jats:p> Dilated cardiomyopathy (DCM) is clinically characterised by dilated ventricular cavities and reduced ejection fraction, leading to heart failure and increased thromboembolic risk. Mutations in thin filament regulatory proteins can cause DCM and have been shown in vitro to reduce contractility and myofilament Ca<jats:sup>2+</jats:sup>-affinity. In this work we have studied the functional consequences of mutations in cardiac troponin T (R131W), cardiac troponin I (K36Q) and α-tropomyosin (E40K) using adenovirally transduced isolated guinea pig left ventricular cardiomyocytes. We find significantly reduced fractional shortening with reduced systolic Ca<jats:sup>2+</jats:sup>. We also observe slowed contraction and Ca<jats:sup>2+</jats:sup>-reuptake times, which contrast with some findings in murine models of myofilament Ca<jats:sup>2+</jats:sup>-desensitisation. We also observe increased sarco-endoplasmic reticulum (SR) Ca<jats:sup>2+</jats:sup> load and smaller fractional SR Ca2+ release. This corresponds to a reduction in SR Ca<jats:sup>2+</jats:sup>-ATPase activity and increase in Sodium-Calcium Exchanger activity. The disequilibrium of Ca<jats:sup>2+</jats:sup> handling promotes dephosphorylation and nuclear translocation of the Nuclear-Factor-of-Activated T-cells (NFAT), with concordant RAC-alpha serine/threonine-protein kinase (AKT) phosphorylation but no change to Extracellular‐Signal‐Regulated Kinase activation in chronically paced cardiomyocytes expressing DCM mutations. These changes in Ca<jats:sup>2+</jats:sup>-handling and signalling are common to all three mutations, indicating a common pathway of disease pathogenesis in thin filament sarcomeric DCM. Previous work has shown changes to myofilament Ca2+ sensitivity caused by DCM mutations are qualitatively opposite those resulting from hypertrophic cardiomyopathy (HCM) mutations. However, we find several common pathways such as increased relaxation times and NFAT activation that are also hallmarks of HCM. This suggests more complex intracellular signalling underpinning DCM, driven by the primary mutation. </jats:p>

Effective use of genetically-encoded optical biosensors for profiling signalling signatures in iPSC-CMs derived from idiopathic dilated cardiomyopathy patients

“…Mitogen activated protein kinase inhibitors have been demonstrated to improve the LMNA dilated cardiomyopathic phenotype (79–82). However, ERK 1/2 signalling was not altered in guinea pig left ventricular cardiomyocytes modeling DCM mutations of the thin-filament regulatory proteins (83). Thus, there is a clear phenotypic spectrum in terms of signalling when assessing different mutations and models of dilated cardiomyopathy.…”

“…Mitogen activated protein kinase inhibitors have been demonstrated to improve the LMNA dilated cardiomyopathic phenotype (79)(80)(81)(82). However, ERK1/2 signalling was not altered in guinea pig left ventricular cardiomyocytes modeling DCM mutations of the thin-filament regulatory proteins (83).…”

Case Report: Mutation in TNNI3(c. 544G>A): a novel likely pathogenic mechanism of neonatal dilated cardiomyopathy

“…Gomes et al ( 16 ) investigations showed that mutations in cTnI increase Ca 2+ sensitivity and could lead to a decrease in the ability of cTnI, which inhibits actomyosin ATPase activity, causing impaired relaxation properties and diastolic dysfunction. Robinson et al ( 17 ). Found that changes in Ca 2+ handling and signaling are common to all mutations, indicating an analogous pathway of pathogenesis of disease in thin-filament sarcomeric DCM.…”

Bioinformatics prediction of potential mechanisms and biomarkers underlying dilated cardiomyopathy

“…Li et al [ 11 ] reported that mutation of aryl hydrocarbon receptor nuclear translocator-like protein 1 (known as BMAL1) plays a critical role in the development of DCM through the regulation of mitochondrial fission and mitophagy via mitochondrial protein B cell leukemia/lymphoma 2 interacting protein 3. Mutations in thin filament regulatory proteins including cardiac troponin T, cardiac troponin I, and α-tropomyosin can cause DCM with systolic dysfunction by reducing fractional shortening and systolic calcium level[ 12 ]. Moreover, some biomarkers associated with the development of DCM have been reported.…”