Laboratory of Cell Signaling and Obesity and Comorbidities Research Center, University of Campinas, 13084-970 Campinas, SP, Brazil.
Laboratory of Cell Signaling and Obesity and Comorbidities Research Center, University of Campinas, 13084-970 Campinas, SP, Brazil; Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, 05508-000 São Paulo, Brazil.
Mol Cell Endocrinol. 2018 Jan 15;460:238-245. doi: 10.1016/j.mce.2017.07.029. Epub 2017 Jul 29.
Hypothalamic dysfunction is a common feature of experimental obesity. Studies have identified at least three mechanisms involved in the development of hypothalamic neuronal defects in diet-induced obesity: i, inflammation; ii, endoplasmic reticulum stress; and iii, mitochondrial abnormalities. However, which of these mechanisms is activated earliest in response to the consumption of large portions of dietary fats is currently unknown. Here, we used immunoblot, real-time PCR, mitochondrial respiration assays and transmission electron microscopy to evaluate markers of inflammation, endoplasmic reticulum stress and mitochondrial abnormalities in the hypothalamus of Swiss mice fed a high-fat diet for up to seven days. In the present study we show that the expression of the inflammatory chemokine fractalkine was the earliest event detected. Its hypothalamic expression increased as early as 3 h after the introduction of a high-fat diet and was followed by the increase of cytokines. GPR78, an endoplasmic reticulum chaperone, was increased 6 h after the introduction of a high-fat diet, however the actual triggering of endoplasmic reticulum stress was only detected three days later, when IRE-1α was increased. Mitofusin-2, a protein involved in mitochondrial fusion and tethering of mitochondria to the endoplasmic reticulum, underwent a transient reduction 24 h after the introduction of a high-fat diet and then increased after seven days. There were no changes in hypothalamic mitochondrial respiration during the experimental period, however there were reductions in mitochondria/endoplasmic reticulum contact sites, beginning three days after the introduction of a high-fat diet. The inhibition of TNF-α with infliximab resulted in the normalization of mitofusin-2 levels 24 h after the introduction of the diet. Thus, inflammation is the earliest mechanism activated in the hypothalamus after the introduction of a high-fat diet and may play a mechanistic role in the development of mitochondrial abnormalities in diet-induced obesity.
下丘脑功能障碍是实验性肥胖的常见特征。研究已经确定了至少三种与饮食诱导肥胖中下丘脑神经元缺陷发展有关的机制：i、炎症；ii、内质网应激；iii、线粒体异常。然而，目前尚不清楚这些机制中哪一种最早被激活以响应大量食用膳食脂肪。在这里，我们使用免疫印迹、实时 PCR、线粒体呼吸测定和透射电子显微镜来评估高脂肪饮食喂养的瑞士小鼠下丘脑的炎症、内质网应激和线粒体异常的标志物，最长可达七天。在本研究中，我们发现炎症趋化因子 fractalkine 的表达是最早检测到的事件。其在下丘脑的表达早在高脂肪饮食引入后 3 小时就增加了，随后细胞因子增加。内质网伴侣 GPR78 在高脂肪饮食引入后 6 小时增加，但内质网应激的实际触发仅在三天后 IRE-1α 增加时检测到。参与线粒体融合和将线粒体与内质网连接的线粒体融合蛋白 2（mitofusin-2）在高脂肪饮食引入后 24 小时短暂减少，然后在七天后增加。在实验期间，下丘脑线粒体呼吸没有变化，但是在高脂肪饮食引入三天后，线粒体/内质网接触点减少。用英夫利昔单抗抑制 TNF-α 可使饮食引入后 24 小时 mitofusin-2 水平正常化。因此，炎症是高脂肪饮食引入后下丘脑最早激活的机制，并可能在饮食诱导肥胖中线粒体异常的发展中发挥机制作用。
