Mas-related G protein-coupled receptor X1 (MRGPRX1), Mas-related G protein-coupled receptor X2 (MRGPRX2), and related subtypes (MRGPRX1, MRGPRX2, MRGPRX4)

"Itch receptors" is an imprecise term that generally refers to a group of membrane-bound proteins—primarily **Mas-related G protein-coupled receptors** (*MRGPRs*)—that mediate the sensation of itch. The most studied human members are **MRGPRX1**, **MRGPRX2**, and **MRGPRX4**. These GPCRs are expressed on sensory neurons and mast cells; they detect various endogenous and exogenous pruritogens including neuropeptides, drugs like chloroquine, inflammatory peptides, and allergens. Upon activation by their ligands, these receptors initiate intracellular signaling cascades that result in the transmission of itch signals from peripheral nerves to the central nervous system. In humans: * **MRGPRX1** mediates chloroquine-induced itch and has been targeted for both pain inhibition and anti-pruritic drug development. * **MRGPRX2** is highly expressed on mast cells where it mediates non-histaminergic itch as well as pseudoallergic drug reactions. * **MRGPRX4** has emerged as a potential target for chronic pain and skin inflammation therapies. Other molecular players in human itch include histamine H1/H4 GPCRs for histaminergic pathways; protease activated-receptors such as PAR2/PAR4; transient receptor potential channels like TRPV1/TRPA1; cytokine pathways involving IL31RA/OSM/TSLP; opioid μ/kappa-receptors; among others[3][4][6]. Therapeutically targeting these GPCRs offers promise for treating chronic pruritus associated with atopic dermatitis, allergic diseases, neuropathic pain syndromes, liver disease–related cholestatic pruritus—and potentially other inflammatory conditions. However, specificity remains challenging due to overlapping expression patterns with pain pathways or immune functions. Notably "Itch receptors" should be replaced by precise names such as "Mas-related G protein-coupled receptor X2" when referring to individual therapeutic targets[1][2][5].

Other names

Itch receptorpruriceptorpruritogen receptorMrgprA3 (mouse ortholog)MrgprC11 (mouse ortholog)

Agonists or antagonists modulate GPCR signaling to either induce or inhibit itch sensation[5][7]