Introduction

Mast cell (MC) degranulation is an important step in the pathogenesis of inflammatory reactions and allergies; however, the mechanism of stabilizing MC membranes to reduce their degranulation is unclear.

Methods

SO₂ content in MC culture supernatant was measured by HPLC-FD. The protein and mRNA expressions of the key enzymes aspartate aminotransferase 1 (AAT1) and AAT2 and intracellular AAT activity were detected. The cAMP level in MCs was detected by immunofluorescence and ELISA. The release rate of MC degranulation marker β-hexosaminidase was measured. The expression of AAT1 and cAMP, the MC accumulation and degranulation in lung tissues were detected.

Objectives

To exam whether an endogenous sulfur dioxide (SO₂) pathway exists in MCs and if it serves as a novel endogenous MC stabilizer.

Results

We firstly show the existence of the endogenous SO₂/AAT pathway in MCs. Moreover, when AAT1 was knocked down in MCs, MC degranulation was significantly increased, and could be rescued by a SO₂ donor. Mechanistically, AAT1 knockdown decreased the cyclic adenosine monophosphate (cAMP) content in MCs, while SO₂ prevented this reduction in a dose-independent manner. Pretreatment with the cAMP-synthesizing agonist forskolin or the cAMP degradation inhibitor IBMX significantly blocked the increase in AAT1 knockdown-induced MC degranulation. Furthermore, in hypoxia-stimulated MCs, AAT1 protein expression and SO₂ production were markedly down regulated, and MC degranulation was activated, which were blunted by AAT1 overexpression. The cAMP synthesis inhibitor SQ22536 disrupted the suppressive effect of AAT1 overexpression on hypoxia-induced MC degranulation. In a hypoxic environment, mRNA and protein expression of AAT1 was significantly reduced in lung tissues of rats. Supplementation of SO₂ elevated the cAMP level and reduced perivascular MC accumulation and degranulation in lung tissues of rats exposed to a hypoxic environment in vivo.

Conclusion

SO₂ serves as an endogenous MC stabilizer via upregulating the cAMP pathway under hypoxic circumstance.

中文翻译：

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内源性二氧化硫是一种新型的缺氧诱导肥大细胞脱粒抑制剂

介绍

肥大细胞 (MC) 脱颗粒是炎症反应和过敏发病机制中的重要步骤；然而，稳定 MC 膜以减少其脱粒的机制尚不清楚。

方法

MC培养上清液中SO ₂含量通过HPLC-FD测定。检测关键酶天冬氨酸转氨酶1（AAT1）和AAT2的蛋白和mRNA表达及细胞内AAT活性。通过免疫荧光和ELISA检测MCs中的cAMP水平。测量了 MC 脱粒标志物 β-氨基己糖苷酶的释放速率。检测肺组织中AAT1和cAMP的表达，MC​​的积累和脱颗粒。

目标

检查内源性二氧化硫 (SO ₂ ) 途径是否存在于 MC​​s 中，以及它是否充当新的内源性 MC 稳定剂。

结果

我们首先表明MCs中存在内源性SO ₂ /AAT途径。此外，当 AAT1 在 MC 中被击倒时，MC 脱粒显着增加，并且可以被 SO ₂供体挽救。从机制上讲，AAT1 敲低降低了 MC 中环磷酸腺苷 (cAMP) 的含量，而 SO ₂以与剂量无关的方式阻止了这种降低。用 cAMP 合成激动剂毛喉素或 cAMP 降解抑制剂 IBMX 进行预处理显着阻止了 AAT1 组合式诱导的 MC 脱粒的增加。此外，在缺氧刺激的 MCs 中，AAT1 蛋白表达和 SO ₂产生显着下调，并激活 MC 脱颗粒，这被 AAT1 过表达钝化。cAMP 合成抑制剂 SQ22536 破坏了 AAT1 过表达对缺氧诱导的 MC 脱颗粒的抑制作用。在缺氧环境下，大鼠肺组织中AAT1的mRNA和蛋白表达显着降低。SO _{2 的}补充提高了 cAMP 水平，并减少了暴露于体内缺氧环境的大鼠肺组织中血管周围 MC 的积累和脱颗粒。

结论

SO ₂在缺氧环境下通过上调 cAMP 通路作为内源性 MC 稳定剂。