Notch-1 mediates endothelial cell activation and invasion in psoriasis.

Notch receptor-ligand interactions are critical for cell proliferation, differentiation and survival; however, the role of Notch signalling in psoriasis remains to be elucidated. Serum amyloid A (A-SAA) is an acute-phase protein with cytokine-like properties, regulates cell survival pathways and is implicated in many inflammatory conditions. To examine the role of Notch-1 signalling in the pathogenesis of psoriasis, Notch-1, DLL-4, Jagged-1, Hrt-1/Hrt-2, A-SAA, Factor VIII and vascular endothelial growth factor (VEGF) mRNA and/or protein expression in psoriasis skin biopsies, serum and dHMVEC were assessed by immunohistology, dual-immunofluorescence, real-time PCR, ELISA and Western blotting. A-SAA-induced angiogenesis and invasion in the presence of Notch-1 siRNA was assessed by matrigel tube formation assays and Transwell invasion assay. Increased Notch-1, its ligand DLL-4 and Hrt-1 expression were demonstrated in lesional skin compared with non-lesional skin, with greatest expression observed in the dermal vasculature (P < 0.05). Dual-immunofluorescent staining demonstrated co-localization of Notch-1 to endothelial cell marker Factor VIII. A significant increase in A-SAA levels was demonstrated in psoriasis serum compared with healthy control serum (P < 0.05), and A-SAA expression was higher in lesional skin compared with non-lesional. In dHMVEC, A-SAA significantly induced Jagged-1, Hrt-1 and VEGF mRNA expression (P < 0.05) and activated Notch-1 IC indicative of transcriptional regulation. In contrast, A-SAA significantly inhibited DLL-4 mRNA expression (P < 0.05). Finally A-SAA-induced angiogenesis and invasion were inhibited by Notch-1 siRNA (P < 0.05). Notch receptor-ligand interactions mediate vascular dysfunction in psoriasis and may represent a potential therapeutic target.