Abstract: 【Abstract】 Objective To evaluate the effect of Notch-Hes1 signaling blockade by a γ-secretase inhibitor on the expression of γδT17 cells in a mouse model of psoriasis-like skin inflammation. Methods Forty-five healthy specific pathogen-free （SPF） male BALB/c mice were randomly divided into control group, model group and intervention group by simple random sampling. The model group and intervention group were both topically treated with imiquimod 5% cream （62.5 mg once a day） on the shaved back, the intervention group were then intraperitoneally injected with the γ-secretase inhibitor DAPT （10 mg/kg once a day） immediately after topical application of imiquimod, and the control group were topically treated with equivalent amount of vaseline once a day. After 6-day treatment, psoriasis area and severity index （PASI） was used to evaluate changes of skin lesions. On day 7, blood samples were obtained from all the mice through heart puncture after anesthetization, and spleen and skin tissues were acquired to prepare single cell suspension. Spleen index was compared among the 3 groups. Skin tissues on the mouse back were resected and subjected to hematoxylin-eosin staining to observe histopathological changes. Flow cytometry was performed to determine the percentage of γδT17 cells in the spleen and skin tissues, real-time reverse transcription （RT）-PCR to measure the mRNA expression of Hes1 in single cell suspension of the spleen, and enzyme-linked immunosorbent assay （ELISA） to determine the serum level of interleukin （IL）-17A. Statistical analysis was carried out by using one-way analysis of variance and repeated measures analysis of variance for comparison of indices among groups, and Pearson correlation analysis for evaluating the correlation between different indices. Results Twenty-four hours after the final treatment, the intervention group showed milder psoriasis-like skin inflammation, lower PASI score, and milder degree of epidermal thickening and dermal inflammatory cell infiltration compared with the model group. The model group showed significantly increased spleen index（12.534 ± 1.636）, proportions of γδT17 cells in the spleen （24.659% ± 4.603%） and skin tissues （22.127% ± 5.670%）, mRNA expression of Hes1 in the spleen （4.867 ± 0.543）, and serum level of IL-17A （［22.478 ± 2.776］ ng/L） compared with the control group （all P < 0.01）. However, the above indices were significantly lower in the intervention group （9.449 ± 1.040, 14.966% ± 5.770%, 13.631% ± 5.946%, 2.541 ± 0.347, ［18.639 ± 1.816］ ng/L） than in the model group （all P < 0.01）. In the model group and intervention group, there were positive correlations between the proportions of γδT17 cells in the spleen and serum levels of IL-17A （r = 0.56, 0.53 respectively, both P < 0.05）, between the proportions of γδT17 cells in skin lesions and PASI scores （r = 0.56, 0.52 respectively, both P < 0.05）, as well as between the mRNA expression of Hes1 in the spleen and the proportions of γδT17 cells （r = 0.61, 0.58 respectively, both P < 0.05） or serum levels of IL-17A （r = 0.60, 0.54 respectively, both P < 0.05）. Conclusion Notch-Hes1 signaling blockade by γ-secretase inhibitor can markedly inhibit the expression of γδT17 cells, and effectively alleviate the severity of psoriasis-like skin inflammation in mouse models.

Key words: Psoriasis, Amyloid precursor protein secretases, Receptors, Notch, Th17 cells, Interleukin-17, Hes1, γδT17 cells, γ-Secretase inhibitor