Atopic dermatitis Cell Models for Research

Atopic dermatitis (AD) is a chronic inflammatory skin disease affecting up to 20% of children and 10% of adults worldwide, with increasing prevalence in industrialized countries (WHO). The global burden is substantial, with significant impacts on quality of life and healthcare costs. AD is characterized by intense pruritus, eczematous lesions, and a relapsing course. It is often the first manifestation of the atopic march, leading to asthma, allergic rhinitis, and food allergies. While mortality is low, severe AD is associated with increased risk of skin infections and psychosocial morbidity. The disease has a complex etiology involving genetic, immunological, and environmental factors. Research models are essential to dissect pathogenic mechanisms and develop targeted therapies.

AD is an ideal model for studying skin barrier dysfunction, immune dysregulation, and gene-environment interactions. The availability of well-characterized keratinocyte cell lines (e.g., HaCaT, NHEK) and immune cell lines (e.g., THP-1, Jurkat) allows mechanistic studies. Public datasets, such as those from the Human Skin Microbiome Project and GEO, provide transcriptomic and epigenetic data. Open questions include the role of specific genetic variants (e.g., FLG mutations), the interplay between keratinocytes and immune cells, and the mechanisms of itch. Gene-edited cell models enable functional validation of candidate genes and drug targets.

Although AD is not a cancer, it shares inflammatory and proliferative pathways with skin cancers. Key pathways include:

• • Th2/Th22 immune response: Overproduction of IL-4, IL-13, IL-22, and TSLP drives inflammation and barrier dysfunction.
• • JAK-STAT signaling: Activation of JAK1/2 and STAT3/6 mediates cytokine signaling.
• • NF-κB pathway: Pro-inflammatory cytokines activate NF-κB, leading to chemokine production.
• • MAPK/ERK pathway: Involved in keratinocyte proliferation and differentiation.
• • Aryl hydrocarbon receptor (AhR) pathway: Regulates skin barrier genes and oxidative stress response.

Data from ClinVar, NCBI Gene, and population studies.

AD involves complex signaling networks:

• • Keratinocyte differentiation: FLG, loricrin, involucrin, and keratin 1/10 are downregulated.
• • Innate immunity: Antimicrobial peptides (LL-37, HBD-2) are suppressed, increasing infection risk.
• • Adaptive immunity: Th2 cells produce IL-4, IL-13, IL-31; Th22 cells produce IL-22; Th17 cells are also involved.
• • Itch pathway: IL-31, substance P, and TRPV1 activation.
• • Skin microbiome: Staphylococcus aureus colonization triggers inflammation.

Organoids: 3D skin organoids derived from primary keratinocytes and fibroblasts recapitulate barrier function and inflammation. They are useful for studying cell-cell interactions and drug responses.

• • Flaky tail mouse: Spontaneous FLG mutation, exhibits skin barrier defects and AD-like inflammation.
• • NC/Nga mouse: Spontaneous AD-like lesions under conventional conditions.
• • Oxazolone-induced AD: Topical application of oxazolone induces Th2-mediated dermatitis.
• • DNCB-induced AD: Dinitrochlorobenzene induces skin inflammation.
• • IL-4/IL-13 overexpressing mice: Transgenic mice with skin-specific overexpression of IL-4 or IL-13 develop AD-like phenotype.
• • PDX models: Patient-derived xenografts of skin lesions can be used to test therapies.

CRISPR-Cas9 gene editing enables the creation of isogenic cell lines with specific mutations. For AD, key models include:

• • FLG knockout HaCaT cells: Mimic filaggrin deficiency, allowing study of barrier dysfunction and immune responses.
• • IL4R knockout NHEK cells: Elucidate IL-4/IL-13 signaling in keratinocytes.
• • TSLP reporter lines: Monitor TSLP expression in response to stimuli.
• • SPINK5 knockout keratinocytes: Model Netherton syndrome.

These sequence-verified, commercially available models accelerate research by providing consistent, reproducible systems. They are essential for target validation and drug screening.

Gene-edited cell lines are used to validate the role of genes in AD pathogenesis. For example:

• • FLG knockout in keratinocytes leads to reduced filaggrin expression, impaired barrier function, and increased cytokine release.
• • IL13 knockout in immune cells reduces Th2 cytokine production.
• • TSLP knockout in keratinocytes decreases TSLP secretion, affecting dendritic cell activation.

These models help identify novel therapeutic targets and understand disease mechanisms.

Isogenic pairs (e.g., wild-type vs. FLG knockout) are used to screen compounds that restore barrier function or reduce inflammation. For example:

• • Testing JAK inhibitors on IL4R knockout vs. wild-type cells to assess on-target effects.
• • Screening for drugs that upregulate filaggrin expression in FLG-deficient cells.
• • Resistance mechanisms: Long-term exposure to corticosteroids can be modeled in keratinocyte lines to study resistance.

CRISPR screens can identify genes that modulate disease-relevant phenotypes. For example:

• • Synthetic lethality screens in keratinocytes with FLG mutation to identify genes essential for survival.
• • Genome-wide knockout screens to find regulators of TSLP expression.
• • Secretome analysis of edited cells to discover novel biomarkers.