1030 Role of mast cells in psoriasis associated-pruritus

Abstract

Whilst a key role of mast cells in itch (pruritogenic pruritus) is well-established, the exact underlying mechanisms remain to be fully elucidated. Here, we have examined the role of mast cells in psoriasis-associated pruritus. By immunofluorescence microscopy we confirmed not only that lesional psoriasis skin showed increased mast cell numbers, degranulation activity and overall innervation, but also an increased density of PAR2-positive nerve fibres. Moreover, the proximity of visualized nerve fibres and mast cells was increased suggesting enhanced mast cell-nerve interaction. To characterized mast cell related-itch pathways, healthy human skin was exposed in vitro for 18 hours to known pruritogens which induce mast cell activation such as compound 48/80, substance P (SP), and the selective proteinase-activated receptor 2 (PAR2)-activating peptide, SLIGKV, to mimic conditions of itch and neurogenic skin inflammation and to compare the expression of itch-associated genes with unexposed skin. RNA-Seq with DESeq2 was used for analysis of transcript expression. In organ-cultured healthy human skin, TSLP transcripts were upregulated 1.65, 1.53, and 1.59 fold following stimulation with 100 μg/ml of compound 48/80, 2 μM of SP and 100 μM of SLIGKV, respectively. In addition, SP stimulation upregulated IL31RA and TLR7 gene expression 3.22 and 2.56 fold, respectively, whilst stimulation with SLIGKV also upregulated MRGPRX2, TRPA1, and IL2RA 1.56, 2.21, and 1.76 fold, respectively. The differences in itch-associated genes, other than TSLP, upregulated following stimulation of skin with compound 48/80, SP, and SLIGKV may suggest that SP and PAR-2 agonists could induce itch through multiple, distinct and synergistic signalling pathways. Furthermore, these findings indicate that SP stimulation increases the sensitivity of the skin to potent pruritogens, such as IL-31 or TLR7 ligands, by upregulating their receptors.