RESUMEN
BACKGROUND: Mas-related G-protein coupled receptor X2 (MRGPRX2) is a promiscuous receptor on mast cells that mediates IgE-independent degranulation and has been implicated in multiple mast cell-mediated disorders, including chronic urticaria, atopic dermatitis, and pain disorders. Although it is a promising therapeutic target, few potent, selective, small molecule antagonists have been identified, and functional effects of human MRGPRX2 inhibition have not been evaluated in vivo. OBJECTIVE: We identified and characterized novel, potent, and selective orally active small molecule MRGPRX2 antagonists for potential treatment of mast cell-mediated disease. METHODS: Antagonists were identified using multiple functional assays in cell lines overexpressing human MRGPRX2, LAD2 mast cells, human peripheral stem cell-derived mast cells, and isolated skin mast cells. Skin mast cell degranulation was evaluated in Mrgprb2em(-/-) knockout (KO) and Mrgprb2em(MRGPRX2) transgenic human MRGPRX2 knock-in (KI) mice by assessment of agonist-induced skin vascular permeability. Ex vivo skin mast cell degranulation and associated histamine release was evaluated by microdialysis of human skin tissue samples. RESULTS: MRGPRX2 antagonists potently inhibited agonist-induced MRGPRX2 activation and mast cell degranulation in all mast cell types tested, in an IgE-independent manner. Orally administered MRGPRX2 antagonists also inhibited agonist-induced degranulation and resulting vascular permeability in MRGPRX2 KI mice. In addition, antagonist treatment dose dependently inhibited agonist-induced degranulation in ex vivo human skin. CONCLUSION: MRGPRX2 small molecule antagonists potently inhibited agonist-induced mast cell degranulation in vitro and in vivo as well as ex vivo in human skin, supporting potential therapeutic utility as a novel treatment for multiple human diseases involving clinically relevant mast cell activation.
RESUMEN
The liver X receptors LXRalpha and LXRbeta play critical roles in maintaining lipid homeostasis by functioning as transcription factors that regulate genetic networks controlling the transport, catabolism, and excretion of cholesterol. The studies described in this report examine the individual anti-atherogenic activity of LXRalpha and LXRbeta and determine the ability of each subtype to mediate the biological response to LXR agonists. Utilizing individual knockouts of LXRalpha and LXRbeta in the Ldlr(-/-) background, we demonstrate that LXRalpha has a dominant role in limiting atherosclerosis in vivo. Functional studies in macrophages indicate that LXRalpha is required for a robust response to LXR ligands, whereas LXRbeta functions more strongly as a repressor. Furthermore, selective knockout of LXRalpha in hematopoietic cells and rescue experiments indicate that the anti-atherogenic activity of this LXR subtype is not restricted to macrophages. These studies indicate that LXRalpha plays a selective role in limiting atherosclerosis in response to hyperlipidemia.
