线粒体 NAD 转运蛋白 SLC25A51 是一种饥饿诱导基因，影响 SIRT3 功能。
The mitochondrial NAD transporter SLC25A51 is a fasting-induced gene affecting SIRT3 functions.
机构信息
Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI 48201, USA.
Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, USA.
出版信息
Metabolism. 2022 Oct;135:155275. doi: 10.1016/j.metabol.2022.155275. Epub 2022 Aug 4.
INTRODUCTION
Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism and energy production. NAD-dependent deacetylase sirtuin 3 (SIRT3) regulates the acetylation levels of mitochondrial proteins that are involved in mitochondrial homeostasis. Fasting up-regulates hepatic SIRT3 activity, which requires mitochondrial NAD. What is the mechanism, then, to transport more NAD into mitochondria to sustain enhanced SIRT3 activity during fasting?
OBJECTIVE
SLC25A51 is a recently discovered mitochondrial NAD transporter. We tested the hypothesis that, during fasting, increased expression of SLC25A51 is needed for enhanced mitochondrial NAD uptake to sustain SIRT3 activity. Because the fasting-fed cycle and circadian rhythm are closely linked, we further tested the hypothesis that SLC25A51 is a circadian regulated gene.
METHODS
We examined Slc25a51 expression in the liver of fasted mice, and examined its circadian rhythm in wild-type mice and those with liver-specific deletion of the clock gene BMAL1 (LKO). We suppressed Slc25a51 expression in hepatocytes and the mouse liver using shRNA-mediated knockdown, and then examined mitochondrial NAD levels, SIRT3 activities, and acetylation levels of SIRT3 target proteins (IDH2 and ACADL). We measured mitochondrial oxygen consumption rate using Seahorse analysis in hepatocytes with reduced Slc25a51 expression.
RESULTS
We found that fasting induced the hepatic expression of Slc25a51, and its expression showed a circadian rhythm-like pattern that was disrupted in LKO mice. Reduced expression of Slc25a51 in hepatocytes decreased mitochondrial NAD levels and SIRT3 activity, reflected by increased acetylation of SIRT3 targets. Slc25a51 knockdown reduced the oxygen consumption rate in intact hepatocytes. Mice with reduced Slc25a51 expression in the liver manifested reduced hepatic mitochondrial NAD levels, hepatic steatosis and hypertriglyceridemia.
CONCLUSIONS
Slc25a51 is a fasting-induced gene that is needed for hepatic SIRT3 functions.
简介
烟酰胺腺嘌呤二核苷酸（NAD）是一种辅酶，对代谢和能量产生至关重要。依赖 NAD 的去乙酰化酶 SIRT3 调节参与线粒体动态平衡的线粒体蛋白的乙酰化水平。禁食上调肝 SIRT3 活性，这需要线粒体 NAD。那么，在禁食期间，将更多的 NAD 转运到线粒体中以维持禁食期间增强的 SIRT3 活性的机制是什么？
目的
SLC25A51 是一种新发现的线粒体 NAD 转运体。我们测试了这样一个假设，即在禁食期间，SLC25A51 的表达增加是增强线粒体 NAD 摄取以维持 SIRT3 活性所必需的。由于禁食-喂养周期和昼夜节律密切相关，我们进一步测试了 SLC25A51 是昼夜节律调节基因的假设。
方法
我们检查了禁食小鼠肝脏中 Slc25a51 的表达，并检查了野生型小鼠和肝脏特异性敲除时钟基因 BMAL1（LKO）的小鼠中 Slc25a51 的昼夜节律。我们使用 shRNA 介导的敲低在肝细胞和小鼠肝脏中抑制 Slc25a51 的表达，然后检查线粒体 NAD 水平、SIRT3 活性以及 SIRT3 靶蛋白（IDH2 和 ACADL）的乙酰化水平。我们使用 Seahorse 分析测量了表达降低的 Slc25a51 的肝细胞中的线粒体耗氧率。
结果
我们发现禁食诱导了肝脏中 Slc25a51 的表达，其表达呈现出一种类似昼夜节律的模式，而在 LKO 小鼠中这种模式被打乱。肝细胞中 Slc25a51 表达降低会降低线粒体 NAD 水平和 SIRT3 活性，反映出 SIRT3 靶标的乙酰化增加。Slc25a51 敲低降低了完整肝细胞中的耗氧率。肝脏中 Slc25a51 表达降低的小鼠表现出肝线粒体 NAD 水平降低、肝脂肪变性和高三酰甘油血症。
结论
Slc25a51 是一种诱导性基因，是肝 SIRT3 功能所必需的。
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