Modelling Hypertrophic Cardiomyopathy with hiPSC-Derived Cardiomyocytes: Mini-Review of Current hiPSC-based Models of Hypertrophic Cardiomyopathy and 2D Monolayer Model of JPH2 Variant

Abstract

Hypertrophic cardiomyopathy (HCM) is the most inherited heart disease with estimated prevalence of 1:500 worldwide. The distinguishing characteristic of HCM is thickening and stiffening of the left ventricle, called left ventricular hypertrophy, which cannot be explained by other medical conditions. The vast majority of HCM cases are explained by pathogenic gene variants affecting various parts of the cardiac sarcomere, the base contractile unit of the heart. Understanding the molecular and cellular mechanisms underlying HCM is crucial to advance HCM treatments and to inspire HCM drug discovery.

Human induced pluripotent stem cell (hiPSC) is a type of pluripotent stem cell that is derived from a somatic cell, such skin fibroblast or peripheral blood mononuclear cells. Reprogramming these somatic cells with known factors that induce pluripotency can generate hiPSC, which are able to differentiate into nearly any cell type, including cardiomyocytes. Cardiomyocytes are heart muscle cells responsible for the contraction of the heart, and modern hiPSC and gene editing technologies have opened the doors for most advanced, human-based disease models of HCM.

This thesis includes a mini literature review part that introduces the state-of-the-art hiPSC-based heart models and their application in modelling HCM and an experimental part that explores HCM caused by a junctophilin-2 (JPH2) variant in a simple 2D cardiomyocyte monolayer model. This model compared the cardiac phenotype of a hiPSC line bearing the pathogenic JPH2 variant and an unaffected wild-type (WT) variant through video measurements of contracting cells and fluorescence imaging of troponin T and DAPI to quantify average cell size and multinucleation.

The results of fluorescence imaging were in-line with prior research on JPH2 variant. The cells bearing the pathogenic JPH2 had a statistically significant increase in cell size and a statistically insignificant increase in multinucleation. Increased beating rate was observed, albeit quantitative analysis of the videos failed due to poor video quality.

In present, HCM modelling with hiPSC-based 2D and 3D models of the heart provides us with insight into cellular and molecular mechanisms that drive HCM. These hiPSC-based models, when equipped with isogenic controls, can be used to establish cause-and-effect relationships between singular gene variations and cardiac cell phenotypes.

In the future, HCM modelling must overcome significant challenges to reach physiologically relevant models of the heart that may replace animal testing in pre-clinical trials. Cardiomyocyte maturation, that has been especially promoted through various stimulation methods, remains a challenge in many HCM models. Another challenge is lack of vascularization, which may be overcome through organoid models in future. Lack of a multicellular model that utilizes all the different major cell types found in heart tissue remains to be a limitation that no present hiPSC-based heart model has been able to overcome yet. Future HCM models will evolve alongside developing heart models that will advance over time as hiPSC, gene editing, and cell culture technology advances and novel tissue engineering designs amalgamate into more encompassing and physiologically accurate heart models.