Caroli Disease Cell Models for Research

Caroli disease is a rare congenital disorder characterized by cystic dilation of the intrahepatic bile ducts. Its prevalence is estimated at 1 in 1,000,000 individuals, with no clear gender predominance. The disease often presents in childhood or young adulthood with symptoms such as recurrent cholangitis, abdominal pain, and jaundice. Complications include biliary stones, abscesses, and an increased risk of cholangiocarcinoma (CCA), with a reported incidence of 7-14% in Caroli disease patients. The 5-year survival rate for Caroli disease is variable, but early diagnosis and management can improve outcomes. According to the National Cancer Institute (NCI), the overall 5-year survival for cholangiocarcinoma is around 20%, but for Caroli disease-associated CCA, it may be lower due to late detection. The disease is a significant research model for understanding biliary development and carcinogenesis.

Caroli disease provides a unique opportunity to study the molecular mechanisms underlying bile duct malformations and neoplastic transformation. The disease is primarily caused by mutations in the PKHD1 gene, which encodes fibrocystin, a protein involved in ciliary function and planar cell polarity. Research on Caroli disease can shed light on the role of primary cilia in biliary epithelial homeostasis and the progression from congenital cystic disease to cholangiocarcinoma. Public datasets, such as those from TCGA and COSMIC, include genomic and transcriptomic data from cholangiocarcinoma samples, which can be compared with Caroli disease models to identify early events in malignant transformation. Open questions include the precise signaling pathways downstream of fibrocystin and the factors that determine which patients develop CCA. Gene-edited cell models are essential for functional studies to answer these questions.

The progression from Caroli disease to cholangiocarcinoma involves several key pathways:

• • Wnt/β-catenin pathway: Activation of Wnt signaling promotes cell proliferation and survival. Mutations in CTNNB1 or APC can lead to nuclear accumulation of β-catenin, driving tumorigenesis.
• • RAS/MAPK pathway: Mutations in KRAS and BRAF are common in cholangiocarcinoma, leading to constitutive activation of the MAPK cascade, which promotes cell growth and invasion.
• • PI3K/AKT/mTOR pathway: Alterations in PIK3CA, PTEN, and AKT are frequent, enhancing cell survival and metabolism.
• • p53 pathway: TP53 mutations are present in a significant proportion of cholangiocarcinomas, disrupting cell cycle checkpoints and apoptosis.

These pathways interact to drive malignant transformation in the context of chronic inflammation and bile stasis.

Data from TCGA and COSMIC databases.

In Caroli disease and associated cholangiocarcinoma, several signaling networks are deregulated:

• • Hedgehog signaling: Overactivation of the Hedgehog pathway has been observed, contributing to cell proliferation and desmoplasia.
• • Notch signaling: Notch receptors and ligands are upregulated, promoting stem cell-like properties and epithelial-mesenchymal transition.
• • IL-6/JAK/STAT3 pathway: Chronic inflammation leads to IL-6 secretion, activating STAT3, which promotes cell survival and immune evasion.
• • Growth factor receptors: EGFR and HER2 are often overexpressed, providing targets for therapy.

Key nodes in these networks include:

• • β-catenin
• • KRAS
• • PI3K
• • STAT3
• • Notch intracellular domain (NICD)

Organoids derived from Caroli disease patients are also valuable, as they recapitulate the cystic phenotype and can be used for drug screening. They retain the genetic background of the patient and can be genetically manipulated.

Animal models for Caroli disease and cholangiocarcinoma include:

• • Patient-derived xenografts (PDX): Immunodeficient mice implanted with patient tumor tissue, preserving the original tumor heterogeneity.
• • Genetically engineered mouse models (GEMM): Mice with conditional knockouts of Pkhd1 or overexpression of oncogenes (e.g., Kras) in biliary epithelium.
• • Induced models: Chemical carcinogen-induced (e.g., thioacetamide) models that mimic chronic inflammation and fibrosis.

These models are useful for studying disease progression and testing therapeutic interventions.

CRISPR-based gene editing allows the creation of isogenic cell lines with specific mutations in PKHD1 or other genes. For example:

• • PKHD1 knockout cell lines: Generated by introducing frameshift mutations in exon 3, leading to loss of fibrocystin expression. These lines mimic the loss-of-function seen in Caroli disease.
• • KRAS G12D knock-in cell lines: Introduce the oncogenic point mutation into a wild-type background, enabling studies of pathway activation.
• • TP53 knockout cell lines: Disrupt the tumor suppressor to study its role in cholangiocarcinoma development.

Commercially available, sequence-verified gene-edited cell models are available from various suppliers. These models accelerate research by providing consistent, validated tools for functional studies, drug screening, and target validation.

Gene-edited cell lines are used to validate the function of genes implicated in Caroli disease and cholangiocarcinoma. For example:

• • PKHD1 knockout in cholangiocyte cell lines leads to increased proliferation and abnormal ciliary signaling, confirming its role in biliary development.
• • TP53 knockout enhances cell survival and resistance to apoptosis, demonstrating its tumor suppressor function.
• • KRAS G12D knock-in activates the MAPK pathway, promoting cell invasion and migration.

These models allow researchers to dissect the contribution of individual mutations to disease phenotypes.

Isogenic cell line pairs (e.g., wild-type vs. PKHD1 knockout) are powerful tools for drug screening. By comparing drug responses, researchers can identify compounds that specifically target the mutant phenotype. For example:

• • Screening a library of kinase inhibitors against KRAS-mutant cells can identify selective inhibitors of the MAPK pathway.
• • Resistance studies: exposing cells to increasing concentrations of a drug can select for resistant clones, which can be analyzed to identify resistance mechanisms.

Gene-edited models enable high-throughput screening to discover novel therapeutic agents.

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

• • In PKHD1-deficient cells, a genome-wide CRISPR knockout screen can reveal genes whose loss is lethal, providing potential therapeutic targets.
• • In KRAS-mutant cells, synthetic lethal partners such as TBK1 or STK33 have been identified.

These screens can uncover novel biomarkers and drug targets for Caroli disease and associated cancers.