Intracellular serotonin modulates insulin secretion from pancreatic beta-cells by protein serotonylation.
Intracellular serotonin modulates insulin secretion from pancreatic beta-cells by protein serotonylation.
复制标题
细胞内5-羟色胺通过蛋白质素化调节胰腺β细胞的胰岛素分泌。
DOI：
10.1371/journal.pbio.1000229
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发表时间：
2009-10
期刊：
影响因子：
9.8
通讯作者：
Walther DJ
中科院分区：
文献类型：
--
作者：
Paulmann N;Grohmann M;Voigt JP;Bert B;Vowinckel J;Bader M;Skelin M;Jevsek M;Fink H;Rupnik M;Walther DJ
非神经元性外周血清素缺乏导致糖尿病，并确定血清素在调节胰岛素分泌中的细胞内作用。虽然5-羟色胺（5-HT）与胰岛素在胰腺β细胞颗粒中的共定位在三十多年前就已被证实，但其在糖尿病病因学中的生理作用仍不清楚。我们对外周色氨酸羟化酶（Tph1−/−）和5-HT选择性缺乏的小鼠进行了生化和电生理分析，结果表明细胞内5-HT调节胰岛素分泌。我们发现这些小鼠患有糖尿病，由于胰腺中缺乏5-HT，胰岛素分泌受损。体外5-羟色胺水平的药理学恢复挽救了体内受损的胰岛素分泌。膜片钳实验进一步证实了这些发现，这清楚地表明分泌缺陷是Ca2+信号的下游，可以通过膜片移液管直接在细胞内应用5-HT来修复。为了进一步阐明潜在的机制，我们证明了在胰岛素分泌过程中，5-HT通过转谷氨酰胺酶与胰岛素分泌的两个关键分子，小gtpase Rab3a和Rab27a的共价偶联。这使得它们在一种不依赖受体的信号机制中具有组成性活性，我们最近称之为血清素化。与此同时，抑制β细胞中这种活化的血清素化作用会减弱胰岛素的分泌。我们还观察到，通过增强蛋白酶体降解，5 -羟色胺化Rab3a失活，这与其他5 -羟色胺化gtpase的失活一致。我们的研究结果表明，5-HT通过胰腺β细胞内gtpase的5-羟色胺化调节胰岛素分泌，并表明细胞内5-HT通过这种机制与已知的受体介导的信号传导相一致，在各种微环境中发挥作用。糖尿病是最普遍的代谢性疾病，影响着每一个社会和经济地位的个体。这种疾病可由于胰腺β细胞分泌胰岛素减少或胰岛素对其靶器官的作用减少而引起。因此，了解如何预防和治疗糖尿病需要广泛的胰岛素分泌调节知识。在这项研究中，我们确定了激素5 -羟色胺作为胰岛素分泌的新调节剂，从而将其功能归因于30年前首次观察到的胰腺β细胞中5 -羟色胺和胰岛素的共定位，但直到现在才被理解。我们首先证明了转基因小鼠β细胞中血清素的缺乏导致胰岛素分泌减少和糖尿病，而在这些小鼠中补充血清素可以挽救胰岛素分泌。有趣的是，5 -羟色胺主要不是通过其传统的表面受体作为细胞间信号分子，而是通过5 -羟色胺与靶蛋白的共价偶联来调节靶蛋白的活性。这种耦合称为血清素化，激活特定的小gtpase，进而促进葡萄糖介导的胰岛素分泌。将这种不依赖受体的信号机制加入到血清素的多种调节功能中，我们假设蛋白质血清素化调节所有含血清素组织的生理分泌过程。
Non-neuronal, peripheral serotonin deficiency causes diabetes mellitus and identifies an intracellular role for serotonin in the regulation of insulin secretion. While serotonin (5-HT) co-localization with insulin in granules of pancreatic β-cells was demonstrated more than three decades ago, its physiological role in the etiology of diabetes is still unclear. We combined biochemical and electrophysiological analyses of mice selectively deficient in peripheral tryptophan hydroxylase (Tph1−/−) and 5-HT to show that intracellular 5-HT regulates insulin secretion. We found that these mice are diabetic and have an impaired insulin secretion due to the lack of 5-HT in the pancreas. The pharmacological restoration of peripheral 5-HT levels rescued the impaired insulin secretion in vivo. These findings were further evidenced by patch clamp experiments with isolated Tph1−/− β-cells, which clearly showed that the secretory defect is downstream of Ca2+-signaling and can be rescued by direct intracellular application of 5-HT via the clamp pipette. In elucidating the underlying mechanism further, we demonstrate the covalent coupling of 5-HT by transglutaminases during insulin exocytosis to two key players in insulin secretion, the small GTPases Rab3a and Rab27a. This renders them constitutively active in a receptor-independent signaling mechanism we have recently termed serotonylation. Concordantly, an inhibition of such activating serotonylation in β-cells abates insulin secretion. We also observed inactivation of serotonylated Rab3a by enhanced proteasomal degradation, which is in line with the inactivation of other serotonylated GTPases. Our results demonstrate that 5-HT regulates insulin secretion by serotonylation of GTPases within pancreatic β-cells and suggest that intracellular 5-HT functions in various microenvironments via this mechanism in concert with the known receptor-mediated signaling. Diabetes is the most prevalent metabolic disease and one that affects individuals of every social and economic status. The disease can arise as a result of reduced secretion of insulin from pancreatic β-cells or reduced action of insulin on its target organs. Therefore, understanding how to prevent and treat diabetes requires an extensive knowledge of the regulation of insulin secretion. In this study, we identify the hormone serotonin as a new regulator of insulin secretion and thereby attribute a function to the co-localization of serotonin and insulin in pancreatic β-cells that was first observed 30 years ago but until now not understood. We first demonstrate that a lack of serotonin in β-cells of transgenic mice leads to reduced insulin secretion and diabetes mellitus and that pharmacological replenishment of serotonin rescues insulin secretion in these mice. Interestingly, serotonin mainly acts not as an intercellular signaling molecule via its traditional surface receptors but intracellularly via regulation of the activity of target proteins through covalent coupling of serotonin to them. This coupling, called serotonylation, activates specific small GTPases, which in turn promote glucose-mediated insulin secretion. Adding this receptor-independent signaling mechanism to the multifarious regulatory functions of serotonin, we hypothesize that protein serotonylation modulates physiological secretion processes in all serotonin-containing tissues.
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