Mas-related G-protein coupled receptor member X4
G protein-coupled bile acid receptor activity
MRGPRX4 is a G protein-coupled receptor activated by bile acids that may contribute to cholestatic pruritus.
Patients suffering from cholestasis, the slowing or stoppage of bile flow, commonly report experiencing an intense, chronic itch. Numerous pruritogens are up-regulated in cholestatic patient sera, including bile acids (BAs). Acute injection of BAs results in itch in both mice and humans, and BA-modulating therapy is effective in controlling patient itch. Here, we present evidence that human sensory neuron-expressed Mas-related G protein-coupled receptor X4 (MRGPRX4), an orphan member of the <i>Mrgpr</i> family of GPCRs, is a BA receptor. Using Ca<sup>2+</sup> imaging, we determined that pathophysiologically relevant levels of numerous BAs activated MRGPRX4. No mouse Mrgpr orthologs were activated by BAs. To assess the in vivo relevance of BA activation of MRGPRX4, we generated a humanized mouse with targeted expression of MRGPRX4 in itch-encoding sensory neurons. BAs activated MRGPRX4<sup>+</sup> sensory neurons at higher levels compared with WT neurons. Compared with control animals, MRGPRX4<sup>+</sup> mice scratched more upon acute injection of BAs and in a model of cholestatic itch. Overall, these data suggest that targeting MRGPRX4 is a promising strategy for alleviating cholestatic itch.