Role of SIRT1 in diet-induced metabolic diseases

The purpose of this study is to investigate the role of SIRT1 in high-fat diet-induced liver steatosis and insulin resistance. SIRT1 is a nuclear enzyme that could remove an acetyl-group from target proteins by using NAD as co-substrate. Homologs of this protein in yeast and the roundworm C. elegans are able to delay the aging process in response to nutrients. However, the molecular mechanism by which SIRT1 sense the environment to mediate this response are poorly understood. We have shown that when chronically fed with a 40%-fat diet, SIRT1 heterozygous animals gain significantly more weight compared to wild type littermates. They are also hyperinsulimia, more insulin-resistant, and accumulate more lipids in liver. Interestingly, these animals also show signs of premature aging, such as an early appearance of gray fur, defective motor activity, and decreased fertility. In this microarray study, we analyzed the gene expression profiles in the liver of WT low-fat diet, Het low-fat diet, WT high-fat diet, and Het high-fat diet using Agilent Whole Genome Mouse 4x44 multiplex format oligo arrays following the Agilent-1-color microarray-based gene expression analysis protocol. This microarray analysis concluded that SIRT1 Het mice reponsed to the high-fat diet differently from the WT control mice. Liver total RNAs from SIRT1 WT and Het mice that were fed with either a low-fat diet or a high-fat diet for 34 weeks were used for a microarray gene expression study. Three biological replicates for each group were used.本研究旨在探讨沉默信息调节因子1（SIRT1）在高脂饮食诱导的肝脂肪变性与胰岛素抵抗中的作用。SIRT1是一种核酶，可利用烟酰胺腺嘌呤二核苷酸（NAD）作为辅底物，从靶蛋白上移除乙酰基团。该蛋白在酵母与秀丽隐杆线虫（C. elegans）中的同源物能够响应营养信号延缓衰老进程。然而，SIRT1如何感知环境以介导该应答的分子机制仍不甚明晰。我们的研究显示，长期饲喂40%脂肪含量的高脂饲料时，SIRT1杂合子（heterozygous, Het）动物较野生型（wild type, WT）同窝对照小鼠体重显著增加；此类动物还表现出高胰岛素血症、更严重的胰岛素抵抗，且肝脏脂质沉积更多。值得注意的是，这些动物还出现了早衰相关表型，例如早期出现灰毛、运动功能缺陷以及生育能力下降。在本次微阵列（microarray）研究中，我们遵循安捷伦单色微阵列基因表达分析流程，使用安捷伦全基因组小鼠4x44多重格式寡核苷酸微阵列（Agilent Whole Genome Mouse 4x44 multiplex format oligo arrays），对低脂饲料饲喂野生型、低脂饲料饲喂杂合子、高脂饲料饲喂野生型以及高脂饲料饲喂杂合子小鼠的肝脏基因表达谱进行分析。本次微阵列分析结果表明，SIRT1杂合子小鼠对高脂饮食的应答模式与野生型对照小鼠存在显著差异。本研究使用了饲喂低脂或高脂饲料达34周的SIRT1野生型与杂合子小鼠的肝脏总RNA，开展微阵列基因表达研究，每组设置3个生物学重复样本。