Primary ciliary dyskinesia Cell Models for Research

Primary ciliary dyskinesia (PCD) is a rare genetic disorder with an estimated prevalence of 1 in 10,000 to 20,000 individuals worldwide (WHO). It is characterized by impaired ciliary function, leading to chronic respiratory tract infections, infertility, and situs inversus in about 50% of cases. The disease is caused by mutations in genes encoding ciliary structural proteins, affecting mucociliary clearance. Clinical impact includes progressive lung damage, requiring lifelong management. Research significance is high due to the need for better therapies and understanding of ciliary biology.

PCD is an ideal model for studying ciliary function and mucociliary clearance. It offers a clear genotype-phenotype correlation, with over 40 genes implicated. Public datasets, such as the PCD Foundation registry and ClinVar, provide mutation data. Open questions include the role of specific genes in ciliary assembly and the development of targeted therapies. Gene-edited cell models allow precise manipulation of these genes to study their function and screen for potential drugs.

PCD is not a cancer, but the underlying pathways involve ciliary assembly and function. Key pathways include:

• • Dynein arm assembly: Defects in outer and inner dynein arms (e.g., DNAH5, DNAI1) disrupt ciliary motility.
• • Radial spoke and central pair defects: Mutations in genes like RSPH4A and HYDIN affect ciliary structure.
• • Ciliary biogenesis: Genes like CCDC39 and CCDC40 are involved in axonemal organization.
• • Signaling pathways: Cilia play roles in Hedgehog and Wnt signaling, which may be disrupted in PCD.

Data from TCGA (not applicable) and COSMIC (not applicable) – PCD is not a cancer, but ClinVar and NCBI Gene provide mutation data.

Although PCD is not cancer, ciliary dysfunction can affect signaling pathways:

• • Hedgehog signaling: Cilia are essential for Hedgehog signal transduction; defects can lead to developmental abnormalities.
• • Wnt signaling: Cilia modulate Wnt signaling, affecting cell polarity.
• • Planar cell polarity: Ciliary positioning is critical for tissue organization.
• • Inflammatory pathways: Chronic inflammation due to impaired mucociliary clearance activates NF-κB and other inflammatory mediators.

Organoids derived from patient nasal or bronchial biopsies can recapitulate ciliary function and are useful for drug testing.

• • Mouse models: Knockout mice for DNAH5, DNAI1, and CCDC39 show PCD-like phenotypes.
• • Zebrafish models: Used for studying ciliary motility due to ease of genetic manipulation.
• • Induced models: Chemical or genetic induction of ciliary dysfunction in cell lines.
• • PDX models: Not applicable for PCD as it is not a cancer.

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

• • DNAH5 knockout cell lines: Generated by introducing frameshift mutations, leading to loss of function.
• • DNAI1 knock-in cell lines: Introducing point mutations to study specific variants.
• • CCDC39 knockout lines: To investigate axonemal organization.

These models are commercially available from various sources and are sequence-verified. They allow precise study of gene function and drug response, accelerating research.

Gene-edited cell lines are used to validate the function of PCD genes. For example, knocking out DNAH5 in bronchial epithelial cells leads to reduced ciliary beat frequency, confirming its role. Knock-in of specific mutations can help assess pathogenicity. These models enable high-throughput screening to identify genetic modifiers.

Isogenic pairs (wild-type vs. mutant) are used to screen for drugs that rescue ciliary function. For instance, testing compounds that increase ciliary beat frequency in DNAH5 knockout cells. Resistance modeling is less relevant for PCD, but gene-edited cells can be used to study response to anti-inflammatory therapies.

CRISPR synthetic lethality screens can identify genes that, when inhibited, are lethal in PCD mutant cells but not wild-type. This can reveal potential drug targets. Gene-edited cells also help identify biomarkers for disease severity and progression.