Abstract: 【Abstract】 Objective To investigate the expression of ephrin type-A receptor 2 （EPHA2） in psoriatic lesions and its effect on the proliferation and differentiation of normal human epidermal keratinocytes （NHEKs）. Methods The GDS4602 dataset from the Gene Expression Omnibus （GEO） database was analyzed to determine EPHA2 gene expression changes in psoriatic lesions. Skin tissue samples were collected from 3 psoriasis patients and 3 healthy controls, and EPHA2 expression was determined in the skin tissues by immunofluorescence staining. Twelve female BALB/c mice were randomly divided into 3 groups （4 mice in each group）: a normal control group （receiving no treatment）, an imiquimod group （topically treated with 62.5 mg of imiquimod 5% cream）, and an imiquimod + ALWⅡ-41-27 group （topically treated with 62.5 mg of imiquimod 5% cream, followed by intraperitoneal injections of the EPHA2 inhibitor ALWⅡ-41-27 at a dose of 20 mg·kg?1·d?1）; after 6 days of treatment, dorsal skin samples were harvested for hematoxylin-eosin （HE） staining, immunofluorescence staining was performed to determine the expression of EPHA2 and phosphorylated extracellular signal-regulated kinase 1/2 （p-ERK1/2）, and real-time fluorescence-based quantitative PCR （qPCR） was conducted to determine the mRNA expression of the nuclear proliferation antigen Ki67, involucrin （Ivl）, loricrin （Lor）, and keratin 10 （Krt10）. In vitro cultured NHEKs were divided into a control group （receiving no treatment）, an M5 group （treated with 10 ng/ml M5 cytokines ［including interleukin-17A, interleukin-22, interleukin-1α, oncostatin M and tumor necrosis factor-α］）, an ALWⅡ-41-27 group （treated with 1 μmol/L ALWⅡ-41-27）, and an M5 + ALWⅡ-41-27 group （treated with 10 ng/ml M5 and 1 μmol/L ALWⅡ-41-27）; after 24 hours of treatment, the 5-ethynyl-2'-deoxyuridine （EdU） assay was performed to assess cellular proliferative activity, Western blot analysis to determine the expression of EPHA2, ERK and their phosphorylated proteins, and qPCR to determine the mRNA expression of KI67, IVL, LOR, and KRT10. One-way analysis of variance, Dunnett's T3 test, two-independent-sample t test, and paired t test were used for statistical analysis. Results GEO database analysis revealed upregulated EPHA2 expression in psoriatic lesions compared with normal skin tissues from healthy controls （t = 21.07, P < 0.001）. Immunofluorescence staining showed increased EPHA2 expression in skin tissues from psoriasis patients and mouse models of psoriasis compared with those from healthy controls and normal control mice, respectively （both P < 0.01）. In the animal experiments, the imiquimod group showed thicker epidermis, increased Ki67 mRNA expression, decreased mRNA expression of Ivl, Lor, and Krt10, and elevated p-ERK1/2 expression compared with the normal control group and imiquimod + ALWⅡ-41-27 group （all P < 0.05）. In the cell experiments, the M5 group showed an increased proportion of EdU-positive cells （35.61% ± 1.18% vs. 24.83% ± 0.60% and 12.49% ± 1.52%, t = 8.12, 12.00, P = 0.015, 0.001, respectively）, increased KI67 mRNA expression, and decreased mRNA expression of IVL, LOR, and KRT10 compared with the control group and M5 + ALWⅡ-41-27 group （all P < 0.05）; Western blot analysis revealed that the expression levels of EPHA2, p-EPHA2, and p-ERK1/2 in NHEKs were significantly higher in the M5 group than in the control group and M5 + ALWⅡ-41-27 group （all P < 0.05）, but there was no significant difference in the ERK1/2 protein expression among groups （P > 0.05）. Conclusion EPHA2 expression was upregulated in psoriatic lesions, which may promote keratinocyte proliferation and inhibit its differentiation, possibly via the ERK pathway.

Key words: Psoriasis, EPHA2, Keratinocyte, Cell proliferation, Cell differentiation, ERK pathway