Effect of ryanodine on histamine release from rat peritoneal mast cells induced by anti-IgE

Activation of ryanodine-sensitive calcium store drives pseudo-allergic dermatitis via Mas-related G protein-coupled receptor X2 in mast cells

Mast cell (MC) activation is implicated in the pathogenesis of multiple immunodysregulatory skin disorders. Activation of an IgE-independent pseudo-allergic route has been recently found to be mainly mediated via Mas-Related G protein-coupled receptor X2 (MRGPRX2). Ryanodine receptor (RYR) regulates intracellular calcium liberation. Calcium mobilization is critical in the regulation of MC functional programs. However, the role of RYR in MRGPRX2-mediated pseudo-allergic skin reaction has not been fully addressed. To study the role of RYR in vivo, we established a murine skin pseudo-allergic reaction model. RYR inhibitor attenuated MRGPRX2 ligand substance P (SP)-induced vascular permeability and neutrophil recruitment. Then, we confirmed the role of RYR in an MC line (LAD2 cells) and primary human skin-derived MCs. In LAD2 cells, RYR inhibitor pretreatment dampened MC degranulation (detected by β-hexosaminidase retlease), calcium mobilization, IL-13, TNF-α, CCL-1, CCL-2 mRNA, and protein expression activated by MRGPRX2 ligands, namely, compound 48/80 (c48/80) and SP. Moreover, the inhibition effect of c48/80 by RYR inhibitor was verified in skin MCs. After the confirmation of RYR2 and RYR3 expression, the isoforms were silenced by siRNA-mediated knockdown. MRGPRX2-induced LAD2 cell exocytosis and cytokine generation were substantially inhibited by RYR3 knockdown, while RYR2 had less contribution. Collectively, our finding suggests that RYR activation contributes to MRGPRX2-triggered pseudo-allergic dermatitis, and provides a potential approach for MRGPRX2-mediated disorders.

Cross talk between polysulfide and nitric oxide in rat peritoneal mast cells

The aim of this study was to define the effects of polysulfide on intracellular Ca(2+) concentration ([Ca(2+)]i) and the underlying machinery, especially from the hydrogen sulfide (H2S) and nitric oxide (NO) perspectives, in rat peritoneal mast cells. We found that a polysulfide donor, Na2S4, increased [Ca(2+)]i, which is both extracellular and intracellular Ca(2+) dependent. Intracellular Ca(2+) release induced by Na2S4 was attenuated by the addition of a ryanodine receptor blocker. A slow-releasing H2S donor, GYY4137, dose dependently increased [Ca(2+)]i that was independent from extracellular Ca(2+) influx. The GYY4137-induced [Ca(2+)]i release was partially attenuated in the presence of the ryanodine receptor blocker. Both polysulfide and H2S donors increased the intracellular NO levels in DAF-2-loaded mast cells, which were abolished by an NO scavenger, cPTIO. Inhibition of NO synthase (NOS) significantly abolished the polysulfide- or H2S-donor-induced [Ca(2+)]i elevation in the absence of extracellular Ca(2+) An NO donor, diethylamine (DEA) NONOate, increased [Ca(2+)]i in a concentration-dependent manner, in which both extracellular and intracellular Ca(2+) are associated. At higher concentrations, the DEA NONOate-induced [Ca(2+)]i increases were attenuated in the absence of extracellular Ca(2+) and by the addition of the ryanodine receptor blocker. H2S and NO dose dependently induced polysulfide production. Curiously, polysulfide, H2S, and NO donors had no effect on mast cell degranulation. Among synthases, cystathionine-γ-lyase, and neuronal NOS seemed to be the major H2S- and NO-producing synthases, respectively. These results indicate that polysulfide acts as a potential signaling molecule that regulates [Ca(2+)]i homeostasis in rat peritoneal mast cells via a cross talk with NO and H2S.

Histamine release from mast cells of EAE rats by Gi protein-dependent and IgE-dependent pathways

We investigated both Gi protein-dependent and IgE-dependent pathways that control release of histamine by PMCs derived from EAE or Complete Freund's Adjuvant (CFA) immunized rats. The number and histamine content of MCs per rat were the same between normal and EAE rats. Activation of Gi pathway by substance P (SP), DSA, 48/80, and mastoparan resulted in a dose-dependent increase in release of histamine by PMCs in normal, EAE-, and CFA-immunized rats. In EAE and CFA rats, however, the induction was decreased by 10-20% compared to normal rats. The histamine release induced by MP was decreased at a concentration of 3 microM, but not at 10 microM in severe active EAE rats. Activation of the IgE pathway by MAM and concanavalin A (Con A) in the presence of phosphatidylserine led to dose-dependent histamine release in normal rats, and a 10-25% lower level of induction was observed in EAE rats. In CFA rats, the induction of histamine release was equivalent to normal rats. There was an increase in intracellular calcium stores following activation of both pathways in normal rats, whereas depletion of calcium stores by ryanodine reduced the level of induction by 48/80 and MP by 9-11% in normal rats. In EAE rats, 48/80, Con A, and MAM induced a smaller increase, but SP and MP induced larger or similar increases in calcium stores compared to normal rats. It was unlikely that the calcium stores of the PMCs from EAE rats were depleted, because MP stimulated calcium movement subsequent to the release of histamine. These results suggested that the Gi pathway may not be correlated to clinical manifestation of EAE, but cold be involved in the inflammatory process, and that the IgE pathway is better associated with clinical symptoms of EAE and may be more directly related to disease outcome.