Abstract

Bitter taste receptors (T2Rs) are GPCRs involved in detection of bitter compounds by type 2 taste cells of the tongue, but are also expressed in other tissues throughout the body, including the airways, gastrointestinal tract, and brain. These T2Rs can be activated by several bacterial products and regulate innate immune responses in several cell types. Expression of T2Rs has been demonstrated in immune cells like neutrophils; however, the molecular details of their signaling are unknown. We examined mechanisms of T2R signaling in primary human monocyte-derived unprimed (M0) macrophages (M\(\Phi\)s) using live cell imaging techniques. Known bitter compounds and bacterial T2R agonists activated low-level calcium signals through a pertussis toxin (PTX)-sensitive, phospholipase C-dependent, and inositol trisphosphate receptor-dependent calcium release pathway. These calcium signals activated low-level nitric oxide (NO) production via endothelial and neuronal NO synthase (NOS) isoforms. NO production increased cellular cGMP and enhanced acute phagocytosis ~ threefold over 30–60 min via protein kinase G. In parallel with calcium elevation, T2R activation lowered cAMP, also through a PTX-sensitive pathway. The cAMP decrease also contributed to enhanced phagocytosis. Moreover, a co-culture model with airway epithelial cells demonstrated that NO produced by epithelial cells can also acutely enhance M\(\Phi\) phagocytosis. Together, these data define M\(\Phi\) T2R signal transduction and support an immune recognition role for T2Rs in M\(\Phi\) cell physiology.

中文翻译：

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苦味受体通过钙、一氧化氮和环 GMP 信号刺激人类巨噬细胞的吞噬作用。

摘要

苦味受体 (T2R) 是一种 GPCR，它涉及通过舌头的 2 型味觉细胞检测苦味化合物，但也在整个身体的其他组织中表达，包括气道、胃肠道和大脑。这些 T2R 可以被多种细菌产物激活，并调节多种细胞类型的先天免疫反应。T2R 的表达已在中性粒细胞等免疫细胞中得到证实；然而，它们信号的分子细节是未知的。我们研究了原代人类单核细胞衍生的未引发 (M0) 巨噬细胞 (M \(\Phi\)s) 使用活细胞成像技术。已知的苦味化合物和细菌 T2R 激动剂通过百日咳毒素 (PTX) 敏感性、磷脂酶 C 依赖性和肌醇三磷酸受体依赖性钙释放途径激活低水平钙信号。这些钙信号通过内皮和神经元一氧化氮合酶 (NOS) 异构体激活低水平一氧化氮 (NO) 的产生。NO 产生通过蛋白激酶 G 在 30-60 分钟内增加细胞 cGMP 并增强急性吞噬作用约三倍。与钙升高平行，T2R 激活降低 cAMP，也是通过 PTX 敏感途径。cAMP 的减少也有助于增强吞噬作用。此外，与气道上皮细胞的共培养模型表明，上皮细胞产生的 NO 也可以急剧增强 M \(\Phi\)吞噬作用。总之，这些数据定义了 M \(\Phi\) T2R 信号转导，并支持 T2R 在 M \(\Phi\)细胞生理学中的免疫识别作用。