Isogenic Pairs of hiPSC-CMs with Hypertrophic Cardiomyopathy/LVNC-Associated ACTC1 E99K Mutation Unveil Differential Functional Deficits

Abstract

SummaryHypertrophic cardiomyopathy (HCM) is a primary disorder of contractility in heart muscle. To gain mechanistic insight and guide pharmacological rescue, this study models HCM using isogenic pairs of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) carrying the E99K-ACTC1 cardiac actin mutation. In both 3D engineered heart tissues and 2D monolayers, arrhythmogenesis was evident in all E99K-ACTC1 hiPSC-CMs. Aberrant phenotypes were most common in hiPSC-CMs produced from the heterozygote father. Unexpectedly, pathological phenotypes were less evident in E99K-expressing hiPSC-CMs from the two sons. Mechanistic insight from Ca2+ handling expression studies prompted pharmacological rescue experiments, wherein dual dantroline/ranolazine treatment was most effective. Our data are consistent with E99K mutant protein being a central cause of HCM but the three-way interaction between the primary genetic lesion, background (epi)genetics, and donor patient age may influence the pathogenic phenotype. This illustrates the value of isogenic hiPSC-CMs in genotype-phenotype correlations.

Modelling of Genetic Cardiac Diseases

“…Similar haploinsufficiency results were also shown in HCM hiPSC-CMs with mutation in MYBPC3 gene [25,80], and gene replacement in HCM hiPSC-CMs partially improves the haploinsufficiency and reduces cellular hypertrophy [80]. Similar to higher myofilament Ca 2+ sensitivity observed in isolated cardiac biopsies from HCM with E99K mutation in cardiac actin [81], in vitro model of HCM hiPSC-CMs carrying E99K mutation in cardiac actin demonstrated significantly stronger contraction and increased arrhythmogenic events [82] Furthermore, a study in HCM mice harboring I79N mutation in cTnT resulted in increased cardiac contractility, altered Ca 2+ transients, and remodeling of action potential [83]. These phenotypes were faithfully recapitulated by HCM hiPSC-CMs carrying the same I79N mutation in cTnT [84].…”

Modeling Hypertrophic Cardiomyopathy: Mechanistic Insights and Pharmacological Intervention

“…Smith et al generated isogenic sets of E99K-ACTC1 variants, either by correcting or inserting the mutation in patient-derived hPSCs [78]. Notably, inserting the E99K-ACTC1 mutation in healthy lines did not induce the pathological phenotypes observed in patients with the same genotype (3.6-fold higher contraction force in EHTs, increased Ca 2+ sensitivity, and double the prevalence of arrhythmogenic events).…”

“…These reduce intracellular Ca 2+ by targeting the Na + /Ca 2+ exchanger and promoting Ca 2+ efflux to restore intracellular Na + levels. Ranolazine halved the number of arrhythmias in R453C-β-MHC hPSC-CMs [81] and reduced hypertrophic brain natriuretic peptide (BNP) signaling in E99K-ACTC1 hPSC-CMs [78]. Hypertrophic signaling was reduced further in combination with dantrolene, a drug that blocks SR Ca 2+ release through inhibiting…”

“…the ryanodine receptor (RYR2) [78]. However, Phase II clinical trials (clinicaltrialsregister.eu 2011-004507-20) have not shown efficacy of ranolazine to improve functional capacity in HCM [99].…”

Inherited cardiac diseases, pluripotent stem cells, and genome editing combined—the past, present, and future

“…Another study from the same group underscored the need to study such primary genetic mutations in the same genetic background. 106 Isogenic pairs of hiPSC-CMs were generated from three family members by either correcting or introducing a mutation in alpha-cardiac actin (ACTC1) associated with HCM. Although arrhythmogenesis was evident in all hiPSC-CMs with the ACTC1 mutation, considerable variation in contractile abnormalities was observed between the cell lines including the absence of some contractile defects in the hiPSC-CMs generated from the line derived from the healthy brother in which the mutation had been introduced.…”