Dilated Cardiomyopathy Gene-Edited Cell Models for Drug Discovery

Dilated cardiomyopathy (DCM) is a leading cause of heart failure and the most common indication for heart transplantation worldwide. According to the World Health Organization (WHO), cardiovascular diseases, including DCM, account for approximately 17.9 million deaths annually. DCM has an estimated prevalence of 1 in 250 to 1 in 500 individuals, with an incidence of 5-8 cases per 100,000 person-years. The 5-year survival rate for DCM patients is approximately 50%, with many progressing to end-stage heart failure. Key risk factors include genetic predisposition, viral myocarditis, alcohol abuse, chemotherapy (e.g., doxorubicin), and peripartum cardiomyopathy. The National Cancer Institute (NCI) notes that cancer therapy-related cardiac dysfunction is a growing concern, with DCM being a major phenotype.

DCM is ideal for mechanistic studies due to its well-defined genetic etiology, with over 60 genes identified. The disease is characterized by left ventricular dilation and systolic dysfunction, making it a model for studying sarcomere function, cytoskeletal integrity, and calcium handling. Public datasets from the NCBI Gene Expression Omnibus (GEO) and the ClinVar database provide extensive genomic and transcriptomic data. Open questions include the role of non-coding variants, modifier genes, and the mechanisms of variable penetrance. Gene-edited cell models are crucial for dissecting these pathways.

DCM pathogenesis involves several interconnected pathways:

• • Sarcomere dysfunction: Mutations in sarcomeric proteins (e.g., MYH7, TNNT2, TPM1) impair force generation and transmission.
• • Cytoskeletal disruption: Mutations in genes encoding cytoskeletal proteins (e.g., DMD, DES, LMNA) compromise structural integrity.
• • Calcium handling defects: Altered expression or function of calcium-handling proteins (e.g., PLN, RYR2, SLC8A1) leads to impaired excitation-contraction coupling.
• • Nuclear envelope abnormalities: LMNA mutations disrupt nuclear structure and gene expression.
• • Mitochondrial dysfunction: Mutations in mitochondrial genes (e.g., TAZ, SCO2) cause energy deficiency.

Data from ClinVar, NCBI Gene, and published cohort studies.

Key signaling networks in DCM include:

• • MAPK/ERK pathway: Mutations in genes like RAF1 and MAP2K1 can lead to hypertrophic signaling and subsequent dilation.
• • PI3K/AKT pathway: Altered signaling affects cardiomyocyte survival and growth.
• • Wnt/beta-catenin pathway: Dysregulation contributes to fibrosis and remodeling.
• • TGF-beta pathway: Promotes fibroblast activation and extracellular matrix deposition.
• • Calcium/calcineurin/NFAT pathway: Impaired calcium handling leads to altered gene expression.

Key nodes: ERK1/2, AKT, beta-catenin, SMAD2/3, NFATc4.

Organoids: 3D cardiac microtissues derived from iPSC-CMs or primary cells recapitulate tissue-level contractile function and fibrosis, offering advantages over 2D cultures for studying cell-cell interactions and drug responses.

• • Genetically engineered mouse models (GEMMs): Knock-in of DCM mutations (e.g., Tnnt2 R92Q, Myh7 R403Q) recapitulate human disease.
• • Induced models: Doxorubicin-induced DCM in mice or rats for studying chemotherapy-related cardiotoxicity.
• • Patient-derived xenograft (PDX) models: Not commonly used for DCM due to technical challenges; primarily for cancer-related cardiac dysfunction.
• • Zebrafish models: Transgenic lines with mutant myh6 or tnnt2 for high-throughput screening.

CRISPR/Cas9 technology enables the generation of isogenic cell lines with precise DCM-associated mutations. Examples include:

• • TP53 knockout: Used to study the role of p53 in doxorubicin-induced cardiotoxicity.
• • TTN truncating variant knock-in: iPSC-CMs with TTNtv (e.g., TTN A198V) show reduced contractility.
• • LMNA R225X knock-in: iPSC-CMs exhibit nuclear envelope defects and altered gene expression.
• • MYH7 R403Q knock-in: iPSC-CMs display sarcomere disarray and impaired calcium handling.

Commercially available, sequence-verified isogenic cell models accelerate research by providing reproducible, well-characterized systems for target validation and drug screening. These models are available from commercial sources and can be customized for specific mutations.

Knockout and knock-in lines validate the causal role of genetic variants. For example:

• • TTN knockout in iPSC-CMs demonstrates reduced contractile force and sarcomere disorganization.
• • LMNA knockout in cardiomyocytes leads to nuclear blebbing and altered lamin A/C expression.
• • PLN R14del knock-in iPSC-CMs show impaired calcium reuptake and arrhythmogenic potential.

Isogenic pairs (e.g., wild-type vs. MYH7 R403Q) enable high-throughput screening for compounds that rescue contractile function. Resistance modeling: gene-edited cells with specific mutations (e.g., in calcium handling genes) can be used to test drug efficacy and identify resistance mechanisms.

CRISPR synthetic lethality screens identify genes that, when knocked out, selectively kill DCM mutant cells. For example, screening for genes that are essential in TTNtv cardiomyocytes but not in wild-type cells can reveal novel therapeutic targets. Proteomic and transcriptomic analyses of isogenic lines can identify secreted biomarkers (e.g., NT-proBNP, troponin) and signaling pathway alterations.