Mutation‐Specific Phenotypes in hiPSC‐Derived Cardiomyocytes Carrying Either Myosin‐Binding Protein C Or α‐Tropomyosin Mutation for Hypertrophic Cardiomyopathy

Abstract

Hypertrophic cardiomyopathy (HCM) is a genetic cardiac disease, which affects the structure of heart muscle tissue. The clinical symptoms include arrhythmias, progressive heart failure, and even sudden cardiac death but the mutation carrier can also be totally asymptomatic. To date, over 1400 mutations have been linked to HCM, mostly in genes encoding for sarcomeric proteins. However, the pathophysiological mechanisms of the disease are still largely unknown. Two founder mutations for HCM in Finland are located in myosin-binding protein C (MYBPC3-Gln1061X) and α-tropomyosin (TPM1-Asp175Asn) genes. We studied the properties of HCM cardiomyocytes (CMs) derived from patient-specific human induced pluripotent stem cells (hiPSCs) carrying either MYBPC3-Gln1061X or TPM1-Asp175Asn mutation. Both types of HCM-CMs displayed pathological phenotype of HCM but, more importantly, we found differences between CMs carrying either MYBPC3-Gln1061X or TPM1-Asp175Asn gene mutation in their cellular size, Ca2+ handling, and electrophysiological properties, as well as their gene expression profiles. These findings suggest that even though the clinical phenotypes of the patients carrying either MYBPC3-Gln1061X or TPM1-Asp175Asn gene mutation are similar, the genetic background as well as the functional properties on the cellular level might be different, indicating that the pathophysiological mechanisms behind the two mutations would be divergent as well.

Disease modeling of a mutation in α‐actinin 2 guides clinical therapy in hypertrophic cardiomyopathy

“…However, we provide several lines of evidence for this novel ACTN2 mutation to be HCM-causing: (i) It was segregated in three HCM-affected members of the family, (ii) it was not found in the gnomAD browser, assembling > 130,000 exome or whole-genome sequences from unrelated control individuals, and (iii) the patientderived hiPSC-CMs developed a phenotype, which was corrected in the isogenic control. Our disease modeling approach revealed HCM phenotypes in 2D-and 3D-cultured hiPSC-CMs that were also reported previously in hiPSC-CMs and animal models, such as myofibrillar disarray and CM hypertrophy (Lan et al, 2013;Dambrot et al, 2014;Tanaka et al, 2014;Ojala et al, 2016;Prondzynski et al, 2017), higher contraction force, longer relaxation time (Wijnker et al, 2016), and higher myofilament Ca 2+ sensitivity (Fraysse et al, 2012;Eschenhagen & Carrier, 2019). The fact that all parameters were significantly different between the HCM and the isogenic control line carrying the same genetic background provides evidence for the mutation to be causative.…”

Modelling of Genetic Cardiac Diseases

“…Furthermore, isolated CMs from HCM patients displayed the prolonged APDs, increased Ca 2+ current densities, reduced transient outward K + current densities, abnormal Ca 2+ handling, and increased frequency of arrhythmias [21]. These electrophysiological and Ca 2+ transient irregularity phenotypes have been faithfully recapitulated in HCM hiPSC-CMs [25,75,76,78]. When HCM tissues carrying a mutation in MYBPC3 gene were compared with donor heart sample, no specific truncated MyBP-C peptides were detected, but the overall level of MyBP-C in myofibrils was significantly reduced [79].…”

“…In addition, these cardiac biopsies are typically obtained from the end stage of cardiac diseases; hence it is not possible to understand the mechanism of cardiac diseases [20,21]. These obstacles are mostly overcome by the groundbreaking discovery of reprogramming adult somatic cells into induced pluripotent stem cells (iPSCs) [22,23] which can be differentiated into cardiomyocytes (CMs) (hiPSC-CMs) [24][25][26]. The main advantages of hiPSC-CMs are iPSCs can be generated at any period of a patient's life, they have unlimited supply, and these retain the same genetic information as the donor, i.e., hiPSC-CMs are patient specific (Figure 2).…”

“…Mutations in sarcomeric proteins account for ~60% of all HCM cases including mutation in β-myosin heavy chain (MYH7), cardiac myosinbinding protein C (MYBPC3), cardiac troponin I (cTnI), cardiac troponin T (cTnT), and tropomyosin (TPM1) [73]. Hypertrophy of myocytes and disarray of sarcomere are the histological hallmarks of HCM seen in cardiac biopsies from HCM patients [74], and these histological phenotypes are also observed in hiPSC-CM model of HCM [25,[75][76][77]. In addition, HCM hiPSC-CMs also demonstrated other hallmarks of HCM such as nuclear translocation of nuclear factor of activated T cells (NFAT) [75][76][77], elevation of β-myosin/α-myosin ratio, and calcineurin activation [75].…”

Phenotypic assays for analyses of pluripotent stem cell–derived cardiomyocytes

“…25,30-32 1.1.1 | Disease modeling for hPSC-CMs Historically, the first human diseases to be modeled using hPSC-CMs were monogenic channelopathies. Reported cardiac disease models exploiting hiPSC-derived CMs (hiPSC-CMs) include hypertrophic cardiomyopathy, 33,34 familiar dilated cardiomyopathy, 35 Barth syndrome, 36 long-QT syndromes (1-3 and Timothy syndrome), 37 catecholaminergic polymorphic ventricular tachycardia, 38 arrhythmogenic right ventricular cardiomyopathy, 39 LEOPARD syndrome, 40 Duchenne muscular dystrophy, 41 diabetic cardiomyopathy, 42 and others. 43 A recent review from Sinnecker et al points out the paramount issue of controlled selection in mutation-derived disease modeling and characterization.…”