•Mrgpr gene family gathers more than 50 members in rodents and humans.•Mrgprs are mainly expressed in nociceptive neurons and specialized immune cells.•Mrgprs are essential player in pain, itch and ...neuroimmune interactions.•Some Mrgprs are still orphan receptors with unknown ligand and pathophysiological role.•Mrgprs represent promising future therapeutic targets in pain, itch and chronic inflammatory diseases.
Interplay between physiological systems in the body plays a prominent role in health and disease. At the cellular level, such interplay is orchestrated through the binding of specific ligands to their receptors expressed on cell surface. G protein-coupled receptors (GPCR) are seven-transmembrane domain receptors that initiate various cellular responses and regulate homeostasis. In this review, we focus on particular GPCRs named Mas-related G protein-coupled receptors (Mrgprs) mainly expressed by sensory neurons and specialized immune cells. We describe the different subfamilies of Mrgprs and their specific ligands, as well as recent advances in the field that illustrate the role played by these receptors in neuro-immune biological processes, including itch, pain and inflammation in diverse organs.
Quorum-sensing molecules (QSMs) are secreted by bacteria to signal population density. Upon reaching a critical concentration, QSMs induce transcriptional alterations in bacteria, which enable ...virulence factor expression and biofilm formation. It is unclear whether mammalian hosts can recognize QSMs to trigger responsive antibacterial immunity. We report that mouse mast-cell-specific G-protein-coupled receptor Mrgprb2 and its human homolog MRGPRX2 are receptors for Gram-positive QSMs, including competence-stimulating peptide (CSP)-1. CSP-1 activates Mrgprb2 and MRGPRX2, triggering mast cell degranulation, which inhibits bacterial growth and prevents biofilm formation. Such antibacterial functions are reduced in Mrgprb2-deficient mast cells, while wild-type mast cells fail to inhibit the growth of bacterial strains lacking CSP-1. Mrgprb2-knockout mice exhibit reduced bacterial clearance, while pharmacologically activating Mrgprb2 in vivo eliminates bacteria and improves disease score. These findings identify a host defense mechanism that uses QSMs as an “Achilles heel” and suggest MRGPRX2 as a potential therapeutic target for controlling bacterial infections.
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•The mammalian receptor Mrgprb2 and MRGPRX2 can detect bacterial QSMs•QSM detection by Mrgprb2 and MRGPRX2 in mast cells elicits antibacterial mediator release•Mrgprb2 recognition of QSMs is critical for an effective immune response to bacteria•Pharmacologic activation of Mrgprb2 and MRGPRX2 enhances bacterial clearance
Bacteria use quorum-sensing signaling for cross-species communication. Pundir et al. report that host mast cells detect Gram-positive-bacteria-derived quorum-sensing molecules via the Mrgpr receptors. Mrgpr activation triggers antibacterial activity and immune cell recruitment to efficiently clear bacteria, while animals deficient in Mrgpr are hypersusceptible to bacterial infection.
Gain-of-function mutations in NLRP3 are responsible for a spectrum of autoinflammatory diseases collectively referred to as "cryopyrin-associated periodic syndromes" (CAPS). Treatment of CAPS ...patients with IL-1-targeted therapies is effective, confirming a central pathogenic role for IL-1β. However, the specific myeloid cell population(s) exhibiting inflammasome activity and sustained IL-1β production in CAPS remains elusive. Previous reports suggested an important role for mast cells (MCs) in this process. Here, we report that, in mice, gain-of-function mutations in Nlrp3 restricted to neutrophils, and to a lesser extent macrophages/dendritic cells, but not MCs, are sufficient to trigger severe CAPS. Furthermore, in patients with clinically established CAPS, we show that skin-infiltrating neutrophils represent a substantial biological source of IL-1β. Together, our data indicate that neutrophils, rather than MCs, can represent the main cellular drivers of CAPS pathology.
Allergic skin diseases, such as atopic dermatitis, are clinically characterized by severe itching and type 2 immunity-associated hypersensitivity to widely distributed allergens, including those ...derived from house dust mites (HDMs). Here we found that HDMs with cysteine protease activity directly activated peptidergic nociceptors, which are neuropeptide-producing nociceptive sensory neurons that express the ion channel TRPV1 and Tac1, the gene encoding the precursor for the neuropeptide substance P. Intravital imaging and genetic approaches indicated that HDM-activated nociceptors drive the development of allergic skin inflammation by inducing the degranulation of mast cells contiguous to such nociceptors, through the release of substance P and the activation of the cationic molecule receptor MRGPRB2 on mast cells. These data indicate that, after exposure to HDM allergens, activation of TRPV1
Tac1
nociceptor-MRGPRB2
mast cell sensory clusters represents a key early event in the development of allergic skin reactions.
The body is innervated by a meshwork of heterogeneous peripheral neurons (including sensory neurons) which project virtually to all the organs. Peripheral neurons have been studied extensively in the ...context of their primary function of initiation of voluntary and involuntary movement, transmission of sensations and induction of appropriate behavioral response such as withdrawal to avoid tissue injury or scratching to remove irritating molecules. More recently, breakthrough articles have shown that, on top of their primary function of signal transmission to the spinal cord and brain, peripheral neurons (including afferent neurons) could directly sense environmental alarms and consequently regulate the development of various type of immune responses through the release of neuropeptides or growth factors. In this review, we discuss recent advances in the neural regulation of the immune response, both in physiological and pathological contexts by taking into account the type of organs (lungs, skin and gut), subtypes of peripheral neurons (sympathetic, nociceptive and intrinsic gut neurons) or immune cells and strains of pathogens studied. We also highlight future challenges in the field and potential therapeutic innovations targeting neuro‐immune interactions.
Immune and peripheral nervous systems are virtually present in all organs, where they detect potential threats and constitute a first line of defense. Here, we describe recent advances in neural regulation of immune response and how neuro‐immune interactions participate to health and diseases.
Mast cells (MCs) are tissue-resident immune cells that exhibit homeostatic and neuron-associated functions. Here, we combined whole-tissue imaging and single-cell RNA sequencing datasets to generate ...a pan-organ analysis of MCs in mice and humans at steady state. In mice, we identify two mutually exclusive MC populations, MrgprB2+ connective tissue-type MCs and MrgprB2neg mucosal-type MCs, with specific transcriptomic core signatures. While MrgprB2+ MCs develop in utero independently of the bone marrow, MrgprB2neg MCs develop after birth and are renewed by bone marrow progenitors. In humans, we unbiasedly identify seven MC subsets (MC1-7) distributed across 12 organs with different transcriptomic core signatures. MC1 are preferentially enriched in the bladder, MC2 in the lungs, and MC4, MC6, and MC7 in the skin. Conversely, MC3 and MC5 are shared by most organs but not skin. This comprehensive analysis offers valuable insights into the natural diversity of MC subtypes in both mice and humans.
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.
We identified and characterized novel, potent, and selective orally active small molecule MRGPRX2 antagonists for potential treatment of mast cell-mediated disease.
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.
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.
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.
Routine clinical assays, such as conventional immunohistochemistry, often fail to resolve the regional heterogeneity of complex inflammatory skin conditions. We introduce MANTIS (Multiplex Annotated ...Tissue Imaging System), a flexible analytic pipeline compatible with routine practice, specifically designed for spatially resolved immune phenotyping of the skin in experimental or clinical samples. On the basis of phenotype attribution matrices coupled to α-shape algorithms, MANTIS projects a representative digital immune landscape while enabling automated detection of major inflammatory clusters and concomitant single-cell data quantification of biomarkers. We observed that severe pathological lesions from systemic lupus erythematosus, Kawasaki syndrome, or COVID-19-associated skin manifestations share common quantitative immune features while displaying a nonrandom distribution of cells with the formation of disease-specific dermal immune structures. Given its accuracy and flexibility, MANTIS is designed to solve the spatial organization of complex immune environments to better apprehend the pathophysiology of skin manifestations.
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