Cardiovascular and Metabolism Disease Area, Novartis Institutes for BioMedical Research, Inc., Cambridge, Massachusetts 02139, USA.
J Biol Chem. 2010 Oct 15;285(42):31995-2002. doi: 10.1074/jbc.M110.124164. Epub 2010 Aug 4.
SIRT4, a member of the sirtuin family, has been implicated in the regulation of insulin secretion by modulation of glutamate dehydrogenase. However, the role of this enzyme in the regulation of metabolism in other tissues is unknown. In this study we investigated whether depletion of SIRT4 would enhance liver and muscle metabolic functions. To do this SIRT4 was knocked down using an adenoviral shRNA in mouse primary hepatocytes and myotubes. We observed a significant increase in gene expression of mitochondrial and fatty acid metabolism enzymes in hepatocytes with reduced SIRT4 levels. SIRT4 knockdown also increased SIRT1 mRNA and protein levels both in vitro and in vivo. In agreement with the increased fatty acid oxidation (FAO) gene expression, we showed a significant increase in FAO in SIRT4 knockdown primary hepatocytes compared with control, and this effect was dependent on SIRT1. In primary myotubes, knockdown of SIRT4 resulted in increased FAO, cellular respiration, and pAMPK levels. When SIRT4 was knocked down in vivo by tail vein injection of a shRNA adenovirus, we observed a significant increase in hepatic mitochondrial and FAO gene expression consistent with the findings in primary hepatocytes. Taken together these findings demonstrate that SIRT4 inhibition increases fat oxidative capacity in liver and mitochondrial function in muscle, which might provide therapeutic benefits for diseases associated with ectopic lipid storage such as type 2 diabetes.
SIRT4 是 sirtuin 家族的一员，其通过调节谷氨酸脱氢酶参与胰岛素分泌的调节。然而，该酶在其他组织代谢调节中的作用尚不清楚。在这项研究中，我们研究了 SIRT4 的耗竭是否会增强肝脏和肌肉的代谢功能。为此，我们使用腺病毒 shRNA 在小鼠原代肝细胞和肌管中敲低 SIRT4。我们观察到 SIRT4 水平降低的肝细胞中线粒体和脂肪酸代谢酶的基因表达显著增加。SIRT4 敲低还增加了体外和体内的 SIRT1 mRNA 和蛋白水平。与增加的脂肪酸氧化 (FAO) 基因表达一致，我们显示 SIRT4 敲低的原代肝细胞中的 FAO 显著增加，与对照相比，并且这种作用依赖于 SIRT1。在原代肌管中，SIRT4 的敲低导致 FAO、细胞呼吸和 pAMPK 水平增加。当通过尾静脉注射 shRNA 腺病毒在体内敲低 SIRT4 时，我们观察到肝线粒体和 FAO 基因表达的显著增加，与原代肝细胞中的发现一致。这些发现表明，SIRT4 抑制增加了肝脏的脂肪氧化能力和肌肉中的线粒体功能，这可能为与异位脂质储存相关的疾病（如 2 型糖尿病）提供治疗益处。
