Mast cell-5-HT-HTR2A axis involvement in chronic itch induced by SADBE.

Although 5-hydroxytryptamine (5-HT) contributes to pruritus associated with allergic contact dermatitis (ACD), the role of 5-HT derived from mast cells (MC) in chronic pruritus induced by squaric acid dibutyl ester (SADBE), and the expression and distribution of 5-HT2A receptor (HTR2A) in sensory neurons remain unclear. In this study, a SADBE-induced ACD mouse model was established to evaluate pruritus behavior, MC activation, and 5-HTproduction. The mechanism was verified through pharmacological intervention (MC stabilizer cromolyn, HTR2A antagonist Ketanserin) and FcεRIα-KO mice. It was found that SADBE triggered time-dependent MC recruitment (peaking at Day 14-21) and Mc-derived 5-HT release, which were associated with persistent pruritus. The intervention of MC stabilizer cromolyn and FcεRIα-KO mice confirmed MC/IgE-dependent 5-HT release, and inhibiting MC degranulation could reduce pruritus. Single-cell RNA sequencing and RNAscope in situ hybridization techniques revealed that HTR2A was mainly expressed in the NF3/PEP2/NP3 subsets of DRG neurons. The co-expression level of HTR2A and Nppb was relatively high, partially overlapping with TRPV1/TRPA1. HTR2A antagonists can relieve SADBE-induced pruritus. In conclusion, we have determined that the MC-5-HT-HTR2A axis is involved in chronic pruritus in SADBE-induced ACD, and targeting this axis provides a very promising therapeutic strategy.