IL-33 down-regulates CLDN1 expression through the ERK/STAT3 pathway in keratinocytes

Area of Science:

• Dermatology
• Molecular Biology
• Immunology

Background:

• Tight junctions (TJs) are crucial for skin barrier integrity.
• Claudin-1 (CLDN1) expression is diminished in atopic dermatitis (AD).
• The regulatory mechanisms behind CLDN1 downregulation remain unclear.

Purpose of the Study:

• To investigate the impact of Interleukin-33 (IL-33) on CLDN1 expression in keratinocytes.
• To elucidate the signaling pathways involved in IL-33-mediated CLDN1 regulation.

Main Methods:

• Cultured normal human epidermal keratinocytes (NHEKs) and human skin equivalent models (HSEMs) with IL-33.
• Quantified CLDN1, STAT3, and MAPK expression using RT-PCR, Western blot, and immunofluorescence.
• Utilized MAPK inhibitors, siRNA, and Electrophoretic Mobility Shift Assay to identify signaling pathways and STAT3 transcriptional activity.
• Assessed skin barrier function via TEER and FITC-dextran flux assays.

Main Results:

• IL-33 overexpression reduced CLDN1 levels in AD-model mice epidermis.
• IL-33 downregulated CLDN1 mRNA and protein in NHEKs and HSEMs.
• IL-33 impaired keratinocyte barrier function, indicated by reduced TEER and increased FITC-dextran flux.
• The IL-33 effect on CLDN1 was mediated by extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription 3 (STAT3).
• STAT3 directly bound to CLDN1 promoters, suppressing its expression.

Conclusions:

• IL-33 downregulates CLDN1 expression in keratinocytes.
• The ERK/STAT3 signaling pathway mediates IL-33's effect on CLDN1.
• This pathway may contribute to skin barrier defects in inflammatory skin diseases.