PLC-IP3-ORAI pathway participates in the activation of the MRGPRB2 receptor in mouse peritoneal mast cells

Mrgprb2-mediated mast cell activation exacerbates Modic changes by regulating immune niches

Modic changes are radiographic features associated with microfracture, low-virulence organism infection and chronic inflammation with inflammatory cell infiltration in the vertebral endplate region. Mast cells, as innate immune cells similar to macrophages, are present in painful degenerated intervertebral discs. However, the involvement and mechanisms of mast cells in the development of Modic changes remain unclear. Herein, we found increased mast cell infiltration in samples from patients with Modic changes and in mouse models of Modic changes. To clarify the role of mast cells in the progression of Modic changes, we used mast cell-deficient (KITW-SH/W-SH) mice to construct a model of Modic changes and found that the severity of Modic changes in KITW-SH/W-SH mice was significantly lower than that in WT mice. These findings were further supported by the use of a mast cell-specific activator (compound 48/80) and a stabilizer (cromolyn). Furthermore, we found that mast cells were not activated via the classic IgE pathway in the Modic change models and that Mrgprb2 is the specific receptor for mast cell activation reported in recent studies. Then, we utilized Mrgprb2 knockout mice to demonstrate that Mrgprb2 knockout inhibited mast cell activation and thus reduced the degree of Modic changes. Transcriptomic sequencing revealed aberrant PI3K-AKT and MAPK pathway activation in the Mrgprb2-deficient mast cells. Additionally, Mrgpbrb2-activated mast cells regulate immune niches by recruiting macrophages, promoting M1 polarization and reducing M2 polarization, thereby promoting the progression of Modic changes. These findings suggest that mast cells may serve as a novel therapeutic target for addressing Modic changes.

Fisetin alleviates chronic urticaria by inhibiting mast cell activation via MRGPRX2

OBJECTIVES

The activation of mast cell (MC) plays an important part in the pathogenesis of chronic urticaria (CU), and the expression of MRGPRX2 (Mas-related G-protein coupled receptor X2) and the circulating levels of SP (substance P) in skin MC of CU patients increased. Fisetin is a natural flavonoid with anti-inflammatory and antiallergic pharmacological effects. This study aimed to investigate the inhibitory effect of fisetin on CU via MRGPRX2 and its possible molecular mechanisms.

METHODS

OVA/SP co-stimulated and SP-stimulated CU like murine models were used to evaluate the effect of fisetin on CU. MRGPRX2/HEK293 cells and LAD2 cells were used to perform the antagonism effect of fisetin on MC via MRGPRX2.

KEY FINDINGS

The results indicated that fisetin prevented urticaria-like symptoms in murine CU models, and inhibited MCs activation by suppressing calcium mobilization and degranulation of cytokines and chemokines via binding to MRGPRX2. The bioinformatics analysis showed that fisetin might have an interaction relationship with Akt in CU. The western blotting experiments showed that fisetin downregulated the phosphorylation levels of Akt, P38, NF-κB, and PLCγ in C48/80 activated LAD2 cells.

CONCLUSIONS

Fisetin alleviates CU progression by inhibiting mast cell activation via MRGPRX2, which may be a novel therapeutic candidate for CU.

Curcumin inhibits the pruritus in mice through mast cell MrgprB2 receptor

BACKGROUND

Curcumin is a diketone compound extracted from the rhizomes of some plants in the Zingiberaceae and Araceae family. It possesses a variety of biological activities, including antioxidant, anti-inflammatory and anti-cancer properties. However, the cellular and molecular antipruritic mechanisms of curcumin remain to be explored.

OBJECTIVE

Our objective was to study the role of curcumin in pruritus and determine whether its antipruritic effect is related to MrgprB2 receptor.

METHODS

The effect of curcumin on pruritus in mice was examined by scratching behavior test. The antipruritic mechanism of curcumin was explored by using transgenic mice (MrgprB2^-/- mice, MrgprB2Cre^Td/tomato mice), histological analysis, western blot and immunofluorescence. In addition, the relationship between curcumin and MrgprB2/X2 receptor was studied in vitro by using calcium imaging, plasmid transfection and molecular docking RESULTS: In the current study, we found that curcumin had obvious antipruritic effect. Its antipruritic effect was related to the regulation of MrgprB2 receptor activation and mast cells tryptase release. In vitro, mouse peritoneal mast cells activated by compound 48/80 could be inhibited by curcumin. In addition, curcumin was also found to suppress the calcium flux in MrgprX2 or MrgprB2-overexpression HEK cells induced by compound 48/80, substance P, and PAMP 9-20, displaying the specific relation with the MrgprB2/X2 receptor. Moreover, molecular docking results showed that curcumin had affinity to MrgprX2 protein.

CONCLUSIONS

Overall, these results indicated that curcumin has the potential to treat pruritus induced by mast cell MrgprB2 receptor.

Licochalcone A inhibits IgE-mediated allergic reaction through PLC/ERK/STAT3 pathway

Licochalcone (LicA) is a flavonoid commonly derived from the licorice plant that is reported to have a variety of pharmacological activities. However, few studies have focused on its anti-allergic properties. IgE-mediated passive and systemic anaphylaxis mice models were used to assess the in vivo anti-allergic effect of LicA and its underlying mechanism, while degranulation, cytokines, and chemokines released from laboratory of allergic disease (LAD2) cells were used to assess its in vitro anti-allergic effect. We used western blot analysis to explore the downstream signaling pathway of its anti-allergic effect. We found that in the mouse model, LicA attenuated IgE-mediated paw inflammation, recovered the allergy-induced drop in body temperature, and reduced the concentrations of tumor necrosis factor-alpha and monocyte chemo-attractant protein-1 in mouse serum in a dose-dependent manner. LicA inhibited the allergic reaction via inhibition of IgE-mediated LAD2 cell activation through the PLC/ERK/STAT3 pathway.