Faculty of Biological Sciences, School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK.
Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds LS2 9JT, UK.
Cell Death Differ. 2017 Dec;24(12):1999-2012. doi: 10.1038/cdd.2017.118. Epub 2017 Jul 28.
Rise in plasma free fatty acids (FFAs) represents a major risk factor for obesity-induced type 2 diabetes. Saturated FFAs cause a progressive decline in insulin secretion by promoting pancreatic β-cell death through increased production of reactive oxygen species (ROS). Recent studies have demonstrated that palmitate (a C-FFA)-induced rise in ROS causes β-cell death by triggering mitochondrial fragmentation, but the underlying mechanisms are unclear. Using the INS1-832/13 β-cell line, here we demonstrate that palmitate generates the ROS required for mitochondrial fission by activating NOX (NADPH oxidase)-2. More importantly, we show that chemical inhibition, RNAi-mediated silencing and knockout of ROS-sensitive TRPM (transient receptor potential melastatin)-2 channels prevent palmitate-induced mitochondrial fission. Although TRPM2 activation affects the intracellular dynamics of Ca and Zn, chelation of Zn alone was sufficient to prevent mitochondrial fission. Consistent with the role of Zn, palmitate caused a rise in mitochondrial Zn, leading to Zn-dependent mitochondrial recruitment of Drp-1 (a protein that catalyses mitochondrial fission) and loss of mitochondrial membrane potential. In agreement with the previous reports, Ca caused Drp-1 recruitment, but it failed to induce mitochondrial fission in the absence of Zn. These results indicate a novel role for Zn in mitochondrial dynamics. Inhibition or knockout of TRPM2 channels in mouse islets and RNAi-mediated silencing of TRPM2 expression in human islets prevented FFA/cytokine-induced β-cell death, findings that are consistent with the role of abnormal mitochondrial fission in cell death. To conclude, our results reveal a novel, potentially druggable signalling pathway for FFA-induced β-cell death. The cascade involves NOX-2-dependent production of ROS, activation of TRPM2 channels, rise in mitochondrial Zn, Drp-1 recruitment and abnormal mitochondrial fission.
血浆游离脂肪酸（FFAs）的升高是肥胖引起的 2 型糖尿病的一个主要危险因素。饱和 FFAs 通过增加活性氧物种（ROS）的产生来促进胰腺β细胞死亡，从而导致胰岛素分泌逐渐下降。最近的研究表明，棕榈酸（一种 C-FFA）诱导的 ROS 升高通过触发线粒体片段化导致β细胞死亡，但潜在机制尚不清楚。在这里，我们使用 INS1-832/13β细胞系证明，棕榈酸通过激活 NADPH 氧化酶-2（NOX-2）产生线粒体裂变所需的 ROS。更重要的是，我们表明，ROS 敏感的瞬时受体电位 melastatin-2（TRPM）通道的化学抑制、RNAi 介导的沉默和敲除可防止棕榈酸诱导的线粒体裂变。尽管 TRPM2 激活会影响 Ca 和 Zn 的细胞内动力学，但单独螯合 Zn 就足以防止线粒体裂变。与 Zn 的作用一致，棕榈酸导致线粒体 Zn 升高，导致 Zn 依赖性 Drp-1（一种催化线粒体裂变的蛋白质）募集和线粒体膜电位丧失。与之前的报告一致，Ca 引起 Drp-1 募集，但在没有 Zn 的情况下未能诱导线粒体裂变。这些结果表明 Zn 在线粒体动力学中具有新的作用。在小鼠胰岛中抑制或敲除 TRPM2 通道以及在人胰岛中 RNAi 介导的 TRPM2 表达沉默可防止 FFA/细胞因子诱导的β细胞死亡，这与异常线粒体裂变在细胞死亡中的作用一致。总之，我们的研究结果揭示了一种新的、潜在可药物治疗的 FFA 诱导的β细胞死亡信号通路。该级联反应涉及 NOX-2 依赖性 ROS 产生、TRPM2 通道激活、线粒体 Zn 升高、Drp-1 募集和异常线粒体裂变。
