Psoriasis Cell Models for Research

Psoriasis is a chronic immune-mediated inflammatory skin disease affecting approximately 2-3% of the global population, with an estimated 125 million people affected worldwide (WHO, 2023). The disease has a significant impact on quality of life, with moderate-to-severe psoriasis associated with increased risk of comorbidities such as cardiovascular disease, metabolic syndrome, and psoriatic arthritis. The prevalence varies by region, with higher rates in Europe and North America. Although psoriasis is not directly fatal, severe cases can lead to complications that increase mortality risk. The economic burden is substantial, with direct and indirect costs exceeding billions annually. Key risk factors include genetic predisposition (HLA-C*06:02), environmental triggers (stress, infections, medications), and lifestyle factors (smoking, obesity).

Psoriasis is an ideal model for studying immune-mediated inflammatory mechanisms, keratinocyte hyperproliferation, and aberrant differentiation. The disease has distinct subtypes (plaque, guttate, inverse, pustular, erythrodermic) with varying genetic and environmental contributions. Public datasets, such as the Psoriasis Transcriptome Project and GEO, provide extensive gene expression and epigenetic data. Open questions include the exact interplay between innate and adaptive immunity, the role of specific cytokines (IL-17, IL-23, TNF-alpha), and the mechanisms of keratinocyte response to immune signals. Gene-edited cell models enable precise dissection of these pathways and validation of therapeutic targets.

Psoriasis pathogenesis involves dysregulation of the IL-23/IL-17 axis, TNF-alpha signaling, and keratinocyte proliferation. The following steps outline the key pathways:

1. IL-23/IL-17 Axis:

• • Dendritic cells produce IL-23, which stimulates Th17 cells to release IL-17A, IL-17F, and IL-22.
• • IL-17 acts on keratinocytes to induce proliferation and production of antimicrobial peptides (e.g., LL-37) and chemokines (e.g., CXCL8).
• • This creates a positive feedback loop, amplifying inflammation.

2. TNF-alpha Signaling:

• • TNF-alpha is produced by macrophages and T cells, activating NF-kB pathway in keratinocytes and endothelial cells.
• • This leads to upregulation of adhesion molecules (ICAM-1) and recruitment of immune cells.

3. Keratinocyte Hyperproliferation:

• • Aberrant signaling through STAT3 and MAPK pathways promotes excessive keratinocyte growth and abnormal differentiation.
• • Dysregulation of apoptosis and cell cycle regulators (e.g., p53, p21) contributes to epidermal thickening.

Psoriasis is not a classic cancer, but genetic variants in immune-related genes are associated with susceptibility. The following table summarizes key genes with high-frequency risk variants (from GWAS and sequencing studies):

Data from GWAS and ImmunoChip studies (e.g., Tsoi et al., 2012).

Psoriasis involves complex signaling networks that are interconnected. Key networks include:

• • NF-kB Pathway: Central to inflammation, activated by TNF-alpha and IL-17. Key nodes: TNFAIP3, NFKB1, RELA.
• • JAK-STAT Pathway: Mediates IL-23 and IL-6 signaling. Key nodes: JAK2, TYK2, STAT3.
• • MAPK Pathway: Regulates keratinocyte proliferation. Key nodes: ERK, JNK, p38.
• • PI3K/AKT Pathway: Promotes cell survival and proliferation. Key nodes: PI3K, AKT, mTOR.
• • Wnt Pathway: Involved in epidermal differentiation. Key nodes: beta-catenin, LEF1.

These networks interact, and dysregulation in one can affect others, leading to sustained inflammation and hyperproliferation.

Common cell lines used in psoriasis research include:

Organoids derived from psoriatic skin or healthy skin can recapitulate epidermal differentiation and immune interactions. They are valuable for studying cell-cell communication and drug responses.

Animal models for psoriasis include:

• • Imiquimod (IMQ)-induced mouse model: Topical application of IMQ induces psoriasiform dermatitis, driven by IL-17/IL-23 axis.
• • Xenograft models (PDX): Human psoriatic skin transplanted onto immunodeficient mice (e.g., SCID) to study human-specific mechanisms.
• • Genetically engineered mouse models (GEMM): Overexpression of IL-17A, IL-23, or knockout of TNFAIP3 in keratinocytes leads to spontaneous psoriasiform lesions.
• • Induced models: Using cytokines (IL-23 injection) or adoptive transfer of T cells to induce disease.

These models are useful for preclinical testing of therapeutics.

CRISPR-based gene editing enables the creation of isogenic cell lines with precise genetic modifications, such as knockouts (KO) or knock-ins (KI) of psoriasis-associated genes. These models allow researchers to study the functional impact of specific variants in a controlled genetic background.

• • Examples include:
• • IL17RA knockout in HaCaT cells: To study the role of IL-17 signaling in keratinocyte proliferation.
• • TNFAIP3 knockout in NHEK: To investigate NF-kB dysregulation and inflammatory responses.
• • IL23R knock-in (R381Q) in HaCaT: To examine protective effects on IL-23 signaling.

Commercially available, sequence-verified gene-edited cell lines accelerate research by providing consistent, validated models. These are available from commercial sources and are essential for drug discovery and functional genomics.

Gene-edited cells are used to validate the role of specific genes in psoriasis pathogenesis. For example:

• • Knockout of IL17RA in keratinocytes reduces IL-17-induced expression of inflammatory cytokines (IL-6, CXCL8), confirming its role.
• • Knock-in of IL23R R381Q in immune cells reduces IL-23-mediated STAT3 phosphorylation, supporting its protective function.
• • Knockout of TNFAIP3 in keratinocytes enhances NF-kB activity and increases production of pro-inflammatory mediators, mimicking disease-associated loss-of-function.

These models enable precise dissection of signaling pathways and identification of potential therapeutic targets.

Isogenic pairs (wild-type vs. gene-edited) are powerful tools for drug screening. For example:

• • Screening for inhibitors of IL-17 signaling: Using IL17RA knockout cells as a negative control to identify specific inhibitors.
• • Testing TNF-alpha inhibitors: TNFAIP3 knockout cells can be used to assess the efficacy of NF-kB pathway inhibitors.
• • Resistance modeling: Chronic exposure to drugs (e.g., methotrexate) can select for resistant clones, and gene editing can introduce mutations to study resistance mechanisms.

These approaches accelerate the development of targeted therapies.

CRISPR screens can identify genes that, when knocked out, sensitize cells to certain treatments or alter disease-relevant phenotypes. For example:

• • Synthetic lethality screens: In keratinocytes with TNFAIP3 knockout, knocking out additional genes may reveal vulnerabilities that can be targeted therapeutically.
• • Reporter lines: Gene-edited cells with fluorescent reporters (e.g., IL-8 promoter-driven GFP) can be used to screen for compounds that modulate inflammatory responses.

These approaches facilitate the discovery of novel biomarkers and drug targets.