Tick peptides evoke itch by activating MrgprC11/X1 to sensitize TRPV1 in pruriceptors

Abstract

Background: Tick bites severely threaten human health because they allow the transmission of many deadly pathogens, including viruses, bacteria, protozoa and helminths. Pruritus is a leading symptom of tick bites, but its molecular and neural bases remain elusive.

Objective: To discover potent drugs and targets for the specific prevention and treatment of tick bite-induced pruritus and arthropod-related itch. Methods We used live-cell calcium imaging, patch-clamp recordings, and genetic ablation and evaluated mouse behavior to investigate the molecular and neural bases of tick bite-induced pruritus.

Results: We found that two tick salivary peptides, IPDef1 and IRDef2, induced itch in mice. IPDef1 was further revealed to have a stronger pruritogenic potential than IRDef2 and to induce pruritus in a histamine-independent manner. IPDef1 evoked itch by activating mouse MrgprC11 and human MrgprX1 on dorsal root ganglion (DRG) neurons. IPDef1-activated MrgprC11/X1 signaling sensitized downstream ion channel TRPV1 on DRG neurons. Moreover, IPDef1 also activated mouse MrgprB2 and its ortholog human MrgprX2 selectively expressed on mast cells, inducing the release of inflammatory cytokines and driving acute inflammation in mice, although mast cell activation did not contribute to IP-O-induced itch. Conclusion Our study identifies tick salivary peptides as a new class of pruritogens that initiate itch through MrgprC11/X1-TRPV1 signaling in pruritoceptors. Our work will provide potential drug targets for the prevention and treatment of pruritus induced by the bites or stings of tick and maybe other arthropods.

Key words: Tick; Peptide; Itch; Mrgprs; TRP channel