Psoriasis activation of cells important in cardiovascular disease

Abstract

Psoriasis is an immune mediated inflammatory disease which affects 2-3% of the world’s population. Over the last decade, psoriasis has been acknowledged as an independent risk factor for atherosclerosis. The precise mechanism or mechanisms of the heightened risk is widely speculated. Endothelial cells and macrophages are central players in the immunopathological development of both diseases. Interleukin-36 cytokines (IL-36) have been heavily implicated in psoriasis immunopathology. Significant upregulation of epidermal IL-36 is a recognised characteristic of psoriatic skin inflammation. IL-36 induces inflammatory responses in dendritic cells, fibroblasts and epithelial cells. While vascular alterations are a hallmark of psoriatic lesions and dermal endothelial cells are well known to play a critical role in dermal inflammation, the effects of IL-36 on endothelial cells have not been defined. We report that endothelial cells including dermal microvascular cells express a functionally active IL-36 receptor. Adhesion molecules VCAM-1 and ICAM-1 are upregulated following IL-36γ stimulation, and this is reversed in the presence of the endogenous IL-36 receptor antagonist. IL-36γ-stimulated endothelial cells secrete the proinflammatory chemokines IL-8, CCL2 and CCL20. Chemotaxis assays showed increased migration of T-cells following IL-36γ stimulation of endothelial cells. Both resident and infiltrating inflammatory myeloid cells contribute to the immunopathology of psoriasis by promoting the IL-23/IL-17 axis. We show that IL-36γ induces the production of psoriasis-associated cytokines from macrophages (IL-23, TNFα) and that this response is enhanced in macrophages from psoriasis patients. This effect is specific for IL-36γ and could not be mimicked by other IL-1 family cytokines such as IL-1α. Furthermore, IL-36γ stimulated macrophages potently activated endothelial cells as illustrated by ICAM-1(CD54) upregulation, and led to increased adherence of monocytes, effects that were markedly more pronounced for psoriatic macrophages. Interestingly, regardless of stimulus, monocytes isolated from psoriasis patients showed increased adherence to both the stimulated and unstimulated endothelium when compared to monocytes from healthy individuals. Collectively, these findings add to the growing evidence for IL-36γ having roles in psoriatic responses, by enhancing endothelium directed leukocyte infiltration into the skin and strengthening the IL-23/IL-17 pathway. Our findings also point to a cellular response which could potentially support cardiovascular comorbidities in psoriasis.