Abstract: 【Abstract】 Objective To investigate the expression of fatty acid desaturase 2 （FADS2） in psoriatic skin lesions, as well as its regulatory factors. Methods FADS2 expression in psoriatic skin lesions was analyzed by using the dataset GDS4602 in Gene Expression Omnibus （GEO） database. Skin tissues were obtained from the back of 5 C57BL/6 mouse models of imiquimod-induced psoriasis, normal skin of 4 patients without psoriasis or other immune skin diseases, lesions of 4 patients with psoriasis before and after 10-week treatment with infliximab, as well as lesions of 3 patients with psoriasis before and after 12-week treatment with secukinumab in Shanghai Skin Disease Hospital. FADS2 expression was determined by both immunohistochemical staining and Western blot analysis in the epidermis of mouse skin tissues, and by immunohistochemical staining in that of human skin tissues. In vitro cultured human immortalized keratinocytes （HaCaT） were divided into several groups to be treated with 50 ng/ml tumor necrosis factor-α （TNF-α） alone for 0, 6, 12 and 24 hours respectively, 200 ng/ml interleukin-17A （IL-17A） alone for 0, 6 and 12 hours respectively, or treated with 50 ng/ml TNF-α and 5 μmol/L BAY 11-7082 （a nuclear factor-κB pathway inhibitor） for 6 hours （TNF-α+ BAY 11-7082 6 h group）, and the cells receiving normal culture served as the control group. After the above treatment, real-time fluorescence-based quantitative PCR（qPCR）and Western blot analysis were conducted to determine the mRNA and protein expression of FADS2 respectively. Statistical analysis was carried out by using one-way analysis of variance and t test. Results Analysis of the dataset GDS4602 showed that the FADS2 mRNA expression was significantly lower in the lesional and non-lesional skin tissues from the patients with psoriasis （0.656 ± 0.475, 1.503 ± 1.062, respectively） than in the normal skin tissues （2.035 ± 1.226; F = 55.17, 3.07, P < 0.001, = 0.012, respectively）, and was significantly lower in the lesional skin tissues than in the non-lesional skin tissues from the patients with psoriasis （F = 26.27, P < 0.001）. Western blot analysis and immunohistochemical staining both showed significantly decreased FADS2 protein expression in the mouse skin tissues in the imiquimod group （gray-value ratio: 0.463 ± 0.172; fluorescence intensity: 21.840 ± 3.125） compared with the normal control group （gray-value ratio: 1.000, t = 7.00, P = 0.002; fluorescence intensity: 30.720 ± 6.850, t = 3.15, P = 0.035）. Compared with the skin lesions before treatment, the FADS2 protein expression significantly increased in the skin lesions from the patients with psoriasis after 10-week treatment with infliximab （43.775± 3.342 vs. 27.950 ±1.218, t = -6.95, P = 0.006）, but was not significantly changed in the skin lesions from the patients with psoriasis after 12-week treatment with secukinumab （28.667 ± 3.402 vs. 31.933 ± 2.987, t = 2.72, P = 0.113）. qPCR revealed that the FADS2 mRNA expression significantly decreased in HaCaT cells in the TNF-α 6 h group and TNF-α 12 h group compared with the TNF-α 0 h group （P = 0.002, 0.003, respectively）, while there was no significant change in the FADS2 mRNA expression in the IL-17A 6 h group and IL-17A 12 h group compared with the IL-17A 0 h group （P = 0.849, 0.961, respectively）. The FADS2 mRNA expression significantly decreased in HaCaT cells in the TNF-α 6 h group （0.682 ± 0.132） compared with the control group （1.000, t = 4.82, P = 0.017）, but significantly increased in the TNF-α + BAY 11-7082 6 h group （1.541 ± 0.525） compared with the TNF-α 6 h group （t = -3.58, P = 0.037）. Western blot analysis revealed significantly decreased FADS2 protein expression in HaCaT cells in the TNF-α 24 h group compared with the TNF-α 0 h group （F = 6.24, P = 0.013）. Conclusion FADS2 expression was downregulated in psoriatic lesions, which may be related to TNF-α.

Key words: Psoriasis, Fatty acid desaturases, Tumor necrosis factor-alpha, Interleukin-17A, Keratinocytes, FADS2