IL‐21 promoting angiogenesis contributes to the development of psoriasis

Background Elevated IL‐21 expression which can effectively induce Th17 cell differentiation has been implicated in the pathogenesis of psoriasis, but its role in angiogenesis remains poorly understood. Methods PASI and PSI score assessment was applied to evaluate the severity of psoriatic lesions. The expression of IL‐21, IL‐21 receptor (IL‐21R), CD31, VEGFA, MMP‐9, and ICAM‐1 in skin was determined by immunohistochemistry or quantitative real‐time polymerase chain reaction. The serum level of IL‐21 was measured by enzyme‐linked immunosorbent assay (ELISA). Then, their correlation was analyzed statistically. Human umbilical vein endothelial cells (HUVECs) cocultured with conditional medium from normal human epidermal keratinocytes (NHEKs) were treated with IL‐21 and/or M5 cocktail (mixture of IL‐1α, IL‐17A, IL‐22, TNF‐α, and oncostatin M). The migration and tube formation of HUVECs were detected, and the levels of VEGFA, MMP‐9, and ICAM‐1 in NHEKs were measured by Western blotting or ELISA. Results Increased IL‐21 and IL‐21R expression was observed in psoriatic sera or skin specimens, with IL‐21R mainly locating in keratinocytes and IL‐21 in immune cells. Pearson analysis showed significantly positive correlation between IL‐21/IL‐21R and erythema scores/microvessel density in psoriatic lesions. Moreover, the expression of proangiogenic genes, VEGFA, ICAM‐1, and MMP‐9 was upregulated in skins of psoriasis. Additionally, in M5 microenvironment, migration and tube formation could be magnified in HUVECs using IL‐21 pre‐treated NHEK medium. Mechanically, the co‐stimulation of IL‐21 and M5 to NEHKs increased the expression of ICAM‐1. Conclusion IL‐21 could regulate keratinocytes to secrete ICAM‐1, thereby promoting angiogenesis in psoriasis. Elevated IL‐21 could contribute to angiogenesis of endothelial cells in psoriasis through promoting keratinocytes to secrete proangiogenic factors, such as ICAM‐1 in psoriatic microenvironment.