抑制中枢从头合成神经酰胺可恢复肥胖 Zucker 大鼠下丘脑中的胰岛素信号转导并增强β细胞功能。
Inhibition of central de novo ceramide synthesis restores insulin signaling in hypothalamus and enhances β-cell function of obese Zucker rats.
机构信息
Sorbonne Paris Cité, Université Denis Diderot, Unité de Biologie Fonctionnelle et Adaptative, CNRS UMR 8251, Bâtiment Buffon, PO box 7126, 4, rue Marie-Andrée Lagroua Weill-Halle, 75205 Paris Cedex 13, France.
INSERM U1016, Université Paris-Descartes, Institut Cochin, Paris, France.
出版信息
Mol Metab. 2018 Feb;8:23-36. doi: 10.1016/j.molmet.2017.10.013. Epub 2017 Nov 7.
OBJECTIVES
Hypothalamic lipotoxicity has been shown to induce central insulin resistance and dysregulation of glucose homeostasis; nevertheless, elucidation of the regulatory mechanisms remains incomplete. Here, we aimed to determine the role of de novo ceramide synthesis in hypothalamus on the onset of central insulin resistance and the dysregulation of glucose homeostasis induced by obesity.
METHODS
Hypothalamic GT1-7 neuronal cells were treated with palmitate. De novo ceramide synthesis was inhibited either by pharmacological (myriocin) or molecular (si-Serine Palmitoyl Transferase 2, siSPT2) approaches. Obese Zucker rats (OZR) were intracerebroventricularly infused with myriocin to inhibit de novo ceramide synthesis. Insulin resistance was determined by quantification of Akt phosphorylation. Ceramide levels were quantified either by a radioactive kinase assay or by mass spectrometry analysis. Glucose homeostasis were evaluated in myriocin-treated OZR. Basal and glucose-stimulated parasympathetic tonus was recorded in OZR. Insulin secretion from islets and β-cell mass was also determined.
RESULTS
We show that palmitate impaired insulin signaling and increased ceramide levels in hypothalamic neuronal GT1-7 cells. In addition, the use of deuterated palmitic acid demonstrated that palmitate activated several enzymes of the de novo ceramide synthesis pathway in hypothalamic cells. Importantly, myriocin and siSPT2 treatment restored insulin signaling in palmitate-treated GT1-7 cells. Protein kinase C (PKC) inhibitor or a dominant-negative PKCζ also counteracted palmitate-induced insulin resistance. Interestingly, attenuating the increase in levels of hypothalamic ceramides with intracerebroventricular infusion of myriocin in OZR improved their hypothalamic insulin-sensitivity. Importantly, central myriocin treatment partially restored glucose tolerance in OZR. This latter effect is related to the restoration of glucose-stimulated insulin secretion and an increase in β-cell mass of OZR. Electrophysiological recordings also showed an improvement of glucose-stimulated parasympathetic nerve activity in OZR centrally treated with myriocin.
CONCLUSION
Our results highlight a key role of hypothalamic de novo ceramide synthesis in central insulin resistance installation and glucose homeostasis dysregulation associated with obesity.
目的
已证实下丘脑脂肪毒性会导致中枢胰岛素抵抗和葡萄糖稳态失调；然而，其调控机制仍不完全清楚。本研究旨在确定脂肪酰基辅酶 A 合成酶（ceramide synthase，CerS）在肥胖诱导的中枢胰岛素抵抗和葡萄糖稳态失调中的作用。
方法
用棕榈酸处理下丘脑 GT1-7 神经元细胞。通过药理学（曲古抑菌素）或分子（si-Serine Palmitoyl Transferase 2，siSPT2）方法抑制从头合成的神经酰胺合成。用曲古抑菌素通过脑室内输注抑制肥胖型 Zucker 大鼠（OZR）中的从头合成神经酰胺合成。通过定量 Akt 磷酸化来测定胰岛素抵抗。通过放射性激酶测定或质谱分析来定量神经酰胺水平。用曲古抑菌素处理 OZR 来评估葡萄糖稳态。在 OZR 中记录基础和葡萄糖刺激的副交感神经张力。还测定胰岛胰岛素分泌和β细胞质量。
结果
我们发现棕榈酸可损害下丘脑神经元 GT1-7 细胞中的胰岛素信号，并增加神经酰胺水平。此外，使用氘代棕榈酸表明棕榈酸可激活下丘脑细胞中从头合成神经酰胺途径的几种酶。重要的是，曲古抑菌素和 siSPT2 处理可恢复棕榈酸处理的 GT1-7 细胞中的胰岛素信号。蛋白激酶 C（protein kinase C，PKC）抑制剂或显性失活的 PKCζ 也可拮抗棕榈酸诱导的胰岛素抵抗。有趣的是，用曲古抑菌素脑室内输注抑制下丘脑神经酰胺水平的增加可改善 OZR 的下丘脑胰岛素敏感性。重要的是，中枢曲古抑菌素治疗部分恢复了 OZR 的葡萄糖耐量。这种作用与恢复 OZR 的葡萄糖刺激胰岛素分泌和β细胞质量增加有关。电生理记录还显示，经曲古抑菌素中枢治疗的 OZR 中葡萄糖刺激的副交感神经活性得到改善。
结论
我们的结果强调了下丘脑从头合成神经酰胺合成在肥胖相关的中枢胰岛素抵抗和葡萄糖稳态失调中的关键作用。
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