Aortic Aneurysm Cell Models for Research

Aortic aneurysm (AA) is a life-threatening condition characterized by progressive dilation of the aorta, often asymptomatic until rupture, which carries a mortality rate exceeding 80% (WHO, 2020). The global incidence of abdominal aortic aneurysm (AAA) is estimated at 1-2% in men over 65, with a higher prevalence in smokers and hypertensive individuals (WHO, 2020). Thoracic aortic aneurysm (TAA) is less common but often associated with genetic syndromes. The 5-year survival for ruptured AA is less than 20%, while elective repair has a 5-year survival of over 70% (NCI, 2021). Major risk factors include age, male sex, smoking, hypertension, and genetic predisposition (e.g., Marfan syndrome, Loeys-Dietz syndrome).

Aortic aneurysm is ideal for mechanistic studies due to its well-defined genetic basis, availability of patient-derived tissue samples, and established animal models. Public datasets such as the GenTAC registry and dbGaP provide genomic and clinical data. Open questions include the molecular triggers of aortic wall degeneration, the role of smooth muscle cell phenotype switching, and the identification of biomarkers for early detection. Gene-edited cell models allow precise dissection of these pathways.

The pathogenesis of aortic aneurysm involves several interconnected pathways:

• • TGF-β Signaling: Mutations in TGFBR1, TGFBR2, and TGFB2 lead to dysregulated TGF-β signaling, causing extracellular matrix degradation and smooth muscle cell apoptosis.
• • ECM Remodeling: Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) imbalance results in elastin and collagen breakdown.
• • Inflammation: Chronic inflammation, with infiltration of macrophages and T-cells, promotes vascular wall weakening.
• • Smooth Muscle Cell Phenotype Switching: Contractile SMCs switch to synthetic/proliferative phenotype, contributing to wall remodeling.

These pathways are targets for therapeutic intervention and can be modeled using gene-edited cells.

Data from ClinVar and COSMIC.

Key signaling networks implicated in aortic aneurysm include:

• • TGF-β/Smad Pathway: Ligand binding to TGFBR1/2 activates Smad2/3, which translocate to the nucleus to regulate ECM genes. Mutations in receptors cause paradoxical activation or inhibition.
• • MAPK/ERK Pathway: Often hyperactivated in response to TGF-β, leading to cell proliferation and inflammation.
• • PI3K/AKT Pathway: Promotes SMC survival and proliferation, but dysregulation can lead to apoptosis.
• • NF-κB Pathway: Mediates inflammatory responses, upregulating MMPs and cytokines.

These networks are interconnected and can be studied using gene-edited cell lines.

Organoids derived from patient iPSCs can recapitulate 3D aortic structure and are increasingly used for disease modeling.

Animal models are essential for studying aortic aneurysm in vivo:

• • PDX (Patient-Derived Xenograft): Not commonly used for aortic aneurysm due to the lack of tumorigenic tissue, but can be used for vascular tumors.
• • GEMM (Genetically Engineered Mouse Models): Examples include Fbn1C1041G/+ (Marfan), Tgfbr2 knockout, and Acta2 knockout mice.
• • Induced Models: Angiotensin II infusion in ApoE-/- mice induces AAA; elastase perfusion models also used.

These models help validate findings from cell-based assays.

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

• • FBN1 knockout in human aortic smooth muscle cells to model Marfan syndrome.
• • TGFBR2 knock-in with a pathogenic point mutation (e.g., c.1379C>T) to study Loeys-Dietz syndrome.
• • ACTA2 knockout to investigate smooth muscle dysfunction.

These models are sequence-verified and commercially available, allowing researchers to study disease mechanisms and test therapeutics in a controlled genetic background. They are essential for drug discovery and functional genomics.

Gene-edited cell lines are used to validate the functional impact of genetic variants identified in patients. For example, knocking out FBN1 in SMCs can recapitulate the extracellular matrix abnormalities seen in Marfan syndrome, allowing researchers to study downstream effects on TGF-β signaling. Similarly, introducing a TGFBR2 mutation via knock-in can help elucidate the molecular consequences of specific mutations.

Isogenic pairs (wild-type vs. mutant) are powerful tools for drug screening. For instance, screening compounds that inhibit TGF-β signaling in FBN1 knockout cells can identify potential therapeutic agents. Additionally, gene-edited cells can be used to model drug resistance by introducing mutations that confer resistance to current therapies, enabling the development of next-generation drugs.

CRISPR-based synthetic lethality screens can identify genes that are essential for survival of cells with specific mutations. For example, in cells with TGFBR2 mutations, screening for genes that, when knocked out, cause cell death can reveal novel therapeutic targets. This approach can also uncover biomarkers for early detection of aortic aneurysm.