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.