Hypertrophic Cardiomyopathy Cell Models for Research

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disorder, affecting approximately 1 in 500 individuals worldwide (WHO, 2023). It is a leading cause of sudden cardiac death in young adults and athletes. The clinical course is highly variable, ranging from asymptomatic carriers to severe heart failure. According to the National Cancer Institute (NCI), HCM is not a cancer, but its genetic basis and molecular mechanisms share similarities with oncogenic signaling pathways. The 5-year survival for symptomatic HCM patients is approximately 80% with appropriate management, but sudden cardiac death remains a significant risk. Key risk factors include family history, specific sarcomeric gene mutations, and left ventricular hypertrophy.

HCM is an ideal model for studying genotype-phenotype correlations, sarcomere function, and cardiac signaling. The disease is primarily caused by mutations in genes encoding sarcomeric proteins, making it a monogenic disorder with high penetrance. Public datasets such as ClinVar and the HCM Variant Database provide extensive genetic information. Open questions include the mechanisms of disease progression, the role of modifier genes, and the development of targeted therapies. Gene-edited cell models are crucial for dissecting these mechanisms and for drug discovery.

HCM is primarily caused by mutations in sarcomeric genes, leading to impaired contractility and altered calcium handling. The main pathways involved are:

1. Sarcomere dysfunction: Mutations in MYH7, MYBPC3, TNNT2, TNNI3, and other genes disrupt the sarcomere structure and function, leading to hypercontractility or hypocontractility.

2. Calcium handling abnormalities: Altered calcium flux affects excitation-contraction coupling and triggers hypertrophic signaling.

3. Signaling cascades: Activation of MAPK/ERK, PI3K/AKT, and calcineurin/NFAT pathways promotes cardiomyocyte hypertrophy and fibrosis.

4. Metabolic remodeling: Shift from fatty acid to glucose metabolism, leading to energy deficit and oxidative stress.

Data from TCGA and COSMIC are not directly applicable to HCM, but ClinVar and the HCM Variant Database provide similar frequency data.

The following signaling networks are deregulated in HCM:

• • MAPK/ERK pathway: Activated by stress signals and growth factors, leading to hypertrophy.
• • PI3K/AKT pathway: Regulates cell growth and survival; hyperactivation promotes hypertrophy.
• • Calcineurin/NFAT pathway: Calcium-dependent, promotes hypertrophic gene expression.
• • TGF-beta/SMAD pathway: Involved in fibrosis and remodeling.
• • G-protein coupled receptor (GPCR) signaling: Beta-adrenergic and angiotensin II receptors modulate contractility and hypertrophy.

Organoids: 3D cardiac organoids derived from iPSCs can recapitulate tissue-level features of HCM, including hypertrophy and fibrosis, and are useful for drug testing.

Animal models for HCM include:

• • Genetically engineered mouse models (GEMMs): Knock-in of specific mutations (e.g., MYH7 R403Q) or knockout of MYBPC3.
• • Rabbit models: Larger heart size, more similar to human physiology.
• • Zebrafish models: High fecundity, easy genetic manipulation.
• • Induced models: Pharmacological induction with angiotensin II or isoproterenol to mimic hypertrophy.
• • Patient-derived xenografts (PDX) are not applicable to HCM as it is not a cancer.

CRISPR-based gene editing enables the creation of isogenic cell lines with precise mutations in sarcomeric genes. For example:

• • MYH7 knockout cell lines: Used to study the loss-of-function effects and haploinsufficiency.
• • MYBPC3 knockout lines: Model the most common cause of HCM.
• • TNNT2 knock-in lines: Introduce specific point mutations to study altered calcium sensitivity.

These models are commercially available from various sources, and sequence-verified clones accelerate research by providing consistent and reproducible results. They are essential for functional genomics, drug screening, and mechanistic studies.

Gene-edited cell lines allow researchers to validate the functional impact of HCM-associated variants. For example, knocking out MYBPC3 in iPSC-derived cardiomyocytes leads to reduced contractility and altered calcium handling, confirming its role in disease. Knock-in of specific mutations can be used to study genotype-phenotype correlations.

Isogenic pairs (wild-type vs. mutant) are ideal for high-throughput screening of potential therapeutics. For instance, testing drugs that modulate calcium handling or sarcomere function on MYH7 mutant cells can identify compounds that reverse the hypertrophic phenotype. Resistance mechanisms can be studied by exposing cells to chronic drug treatment and selecting for resistant clones.

CRISPR-based synthetic lethality screens can identify genes that are essential for the survival of HCM mutant cells but not wild-type cells. This can reveal novel therapeutic targets and biomarkers. For example, a screen in MYBPC3 knockout cells might identify genes involved in compensatory mechanisms.