Cardiovascular Disease CRISPR Cell Models for Drug Discovery

Cardiovascular disease (CVD) remains the leading cause of death globally, accounting for an estimated 17.9 million deaths per year according to the World Health Organization (WHO, 2021). Major risk factors include hypertension, hyperlipidemia, diabetes, smoking, and physical inactivity. The 5-year survival rate for heart failure is approximately 50%, and for myocardial infarction, in-hospital mortality is around 5-10% depending on region (NCI SEER data). The economic burden is immense, with direct and indirect costs exceeding $350 billion annually in the United States alone.

CVD encompasses a spectrum of conditions including coronary artery disease, cardiomyopathy, arrhythmias, and heart failure. The availability of large public datasets (e.g., UK Biobank, GTEx) and the complexity of genetic and environmental interactions make CVD ideal for mechanistic studies. Key open questions include the role of somatic mutations in cardiac aging, the contribution of non-coding variants to disease risk, and the mechanisms of drug-induced cardiotoxicity. Gene-edited cell models provide a controlled system to dissect these pathways.

CVD pathogenesis involves several interconnected pathways:

1. Lipid Metabolism and Atherosclerosis

• • LDL receptor (LDLR) dysfunction leads to elevated plasma LDL cholesterol.
• • Oxidized LDL uptake by macrophages promotes foam cell formation.
• • Plaque rupture triggers thrombosis and myocardial infarction.

2. Cardiac Hypertrophy and Fibrosis

• • Pressure overload activates MAPK and calcineurin-NFAT signaling.
• • TGF-beta signaling drives fibroblast-to-myofibroblast transition.
• • Extracellular matrix remodeling leads to diastolic dysfunction.

3. Ion Channel Dysfunction and Arrhythmia

• • Mutations in sodium (SCN5A), potassium (KCNQ1), and calcium (CACNA1C) channels disrupt action potential.
• • Prolonged QT interval increases risk of torsades de pointes.

4. Oxidative Stress and Inflammation

• • Reactive oxygen species (ROS) from mitochondria damage cardiomyocytes.
• • NLRP3 inflammasome activation releases IL-1beta and IL-18.

Data from ClinVar, COSMIC, and TCGA (for cardiac tumors).

• • MAPK/ERK Pathway: Activated by growth factors and mechanical stress; promotes hypertrophy and fibrosis.
• • Key nodes: EGFR, RAS, RAF, MEK, ERK.
• • PI3K/AKT Pathway: Regulates cell survival, metabolism, and growth.
• • Key nodes: PI3K, AKT, mTOR, PTEN (negative regulator).
• • Wnt/beta-catenin Pathway: Involved in cardiac development and adult remodeling.
• • Key nodes: Wnt, LRP5/6, beta-catenin, TCF/LEF.
• • TGF-beta/Smad Pathway: Drives fibroblast activation and extracellular matrix deposition.
• • Key nodes: TGFBR1/2, SMAD2/3, SMAD4.

Organoid models, such as cardiac microtissues and engineered heart tissues, provide 3D architecture and multicellular interactions, enabling studies of contractile function, drug response, and disease modeling.

• • Genetically Engineered Mouse Models (GEMMs): Knock-in of human mutations (e.g., MYH7 R403Q) or knockout of protective genes (e.g., LDLR-/-).
• • Patient-Derived Xenografts (PDX): Not common for CVD; more relevant for cardiac tumors.
• • Induced Models: Angiotensin II infusion for hypertension, transverse aortic constriction (TAC) for pressure overload, and isoproterenol for cardiac hypertrophy.
• • Zebrafish Models: Used for high-throughput drug screening and cardiac regeneration studies.

CRISPR/Cas9 technology enables the creation of isogenic cell lines with precise genetic modifications. For example:

• • LDLR knockout in HepG2 cells: Models familial hypercholesterolemia for lipid metabolism studies.
• • MYH7 R403Q knock-in in iPSC-CMs: Recapitulates hypertrophic cardiomyopathy phenotype.
• • PCSK9 D374Y knock-in in Huh7 cells: Gain-of-function mutation for LDLR degradation studies.
• • SCN5A knockout in HEK293 cells: Used for electrophysiology and drug screening.

Commercially available, sequence-verified gene-edited cell models accelerate research by providing reproducible, validated tools. These models are available from commercial sources and can be customized for specific mutations or reporter constructs.

Knockout and knock-in cell lines are used to validate the functional impact of genetic variants identified in GWAS and sequencing studies. For example:

• • TTN truncating variants: Knockout of TTN in iPSC-CMs leads to sarcomere disorganization and reduced contractility, confirming pathogenicity.
• • MYBPC3 frameshift: Knock-in of a frameshift mutation in rat cardiomyocytes causes haploinsufficiency and hypertrophy.
• • PCSK9 gain-of-function: Overexpression in hepatocytes increases LDLR degradation, validating the role in cholesterol homeostasis.

Isogenic pairs (wild-type vs. mutant) enable high-throughput screening for compounds that selectively target mutant cells. For example:

• • LDLR-/- cells: Used to screen for PCSK9 inhibitors and LDLR upregulators.
• • MYH7 R403Q iPSC-CMs: Used to test compounds that reverse hypertrophy or improve contractility.
• • SCN5A knockout cells: Used to evaluate antiarrhythmic drugs and identify off-target effects.

Resistance mechanisms can be modeled by chronic drug exposure and subsequent sequencing of resistant clones.

CRISPR-based synthetic lethality screens identify genes that are essential only in the context of a specific mutation. For example:

• • MYH7 mutant cells: Screen for kinases that, when knocked out, selectively kill mutant cells, revealing potential therapeutic targets.
• • LDLR-/- cells: Identify genes that regulate cholesterol efflux or LDL uptake, serving as biomarkers for atherosclerosis.
• • PCSK9 D374Y cells: Screen for genes that modulate LDLR recycling, uncovering novel regulators of lipid metabolism.