小鼠Cds1和Cds2调控糖脂代谢和与胰岛素信号通路相互调节的机制研究

CDP-diacylglycerol synthase (CDS) is an enzyme required for the generation of phosphatidylinositol, phosphatidylglycerol and cardiolipin in mammalian cells. It diverts phosphatidic acid from triglyceride synthesis to phospholipids synthesis, thus regulating the triglyceride and phospholipids contents in cells. CDS is conserved in eukaryotic cells and plays important roles in various biological processes based on studies in yeast, fly and zebrafish. We have demonstrated that Drosophila melanogaster CDS/CdsA coordinates cell growth and fat storage. Loss of CdsA results in substantial accumulation of neutral lipids in many organs and reduced cell/organ size. Moreover, loss of CdsA reduces PI levels, thus leading to low insulin signaling activity. There are two murine genes encoding CDS, Cds1 and Cds2. The role of mammalian CDS is currently unknown. Most recently, we found that insulin induced CDS1 mRNA levels in HepG2 cells and in mice, suggesting a reciprocal relation between Cds and insulin signaling. In addition, loss of murine Cds1 or 2 inhibits the differentiation of 3T3L1 preadipocytes, modulates phospholipids levels and promotes the formation of giant or supersized lipid droplets in cultured cells. So far, the role of mammalian CDS in regulation of lipid metabolism and in the pathogenesis of obesity and type II diabetes has not been characterized. We have generated liver-specific and adipocyte-specific Cds1 or Cds2 deficient mice. This proposal is aimed to determine: 1) whether hepatic and adipose Cds1 or 2 deletion affect lipid homeostasis and the pathogenesis of obesity; 2) the mechanism underlying Cds1 and Cds2 regulate lipid metabolism; 3) the mechanism underlying the reciprocal relation between Cds1 and 2 and insulin signaling. The successful completion of this study will open a new insight into the role of murine Cds1 and Cds2 in metabolic disorders.

胞嘧啶二脂酰甘油合成酶(CDP-diacylglycerol synthase，CDS)是调控磷脂生成的、高度保守的重要酶。 我们前期的研究发现果蝇CdsA协调了细胞生长与脂肪的储积。CdsA缺失后PI总体水平降低、Insulin信号通路的活性下降。同时，PA和中性脂含量增加并伴随器官/细胞大小减小。此外， 我们发现Insulin还可诱导Cds转录。这些现象提示我们CDS调控脂代谢，并与Insulin信号通路相互作用。目前，CDS在哺乳动物中的生物学功能基本上还不清楚。本实验室构建了肝脏和脂肪组织特异性Cds1和Cds2基因敲除小鼠。本项目将研究1）肝脏和脂肪组织Cds1和Cds2是否调控机体糖脂代谢以及是否影响肥胖症等代谢综合症的发生发展；2）Cds1和Cds2调控糖脂代谢的分子机制；3） Cds1和Cds2与Insulin信号通路相互调控的作用机制。由此进一步揭示CDS的生物学功能。

非酒精性脂肪肝(NAFLD)包括一系列肝损伤，从单纯脂肪变性到非酒精性肝炎(NASH)，后者可发展为肝硬化和肝癌(HCC)。目前常用的遗传小鼠模型不会自发进展到肝纤维化、硬化和肝癌，除非存在继发性饮食或化学肝毒性损伤。因此，创造严重疾病表型（如纤维化和HCC）快速进展的遗传模型，对理解该疾病的机制以及评估抗NASH和抗纤维化候选药物的治疗潜力大有裨益。. CDP-二酰基甘油（CDP-DAG）合酶（CDS）催化PA转化为CDP-DAG，随后在哺乳动物中用于合成磷脂酰肌醇（PI）和甘油磷脂（PG）。研究人员首先发现CDP-DAG合酶2/CDS2在遗传或饮食诱导的NAFLD小鼠模型中被下调。CDS2的肝脏特异性缺乏引起五周龄小鼠的肝脏脂肪变性、炎症和纤维化。CDS2在线粒体相关膜有定位，肝Cds2缺乏会损害线粒体功能并降低线粒体磷脂酰丝氨酸和磷脂酰乙醇胺水平。通过磷脂酰丝氨酸脱羧酶的过表达减轻了Cds2f/f;AlbCre 小鼠的NASH样表型以及肝细胞中CDS2缺乏引起的线粒体形态和功能异常。此外，还发现了饮食补充过氧化物酶体增殖物激活受体α激动剂可减轻线粒体缺陷并改善 Cds2f/f;AlbCre小鼠的NASH样表型。CDS2过表达可以防止高脂饮食引起的肝脂肪变性和肥胖。本研究为Cds2在维持线粒体形态、脂质组成和功能中的作用提供了证据，并提供了一个不需要二次饮食或化学肝毒性损伤的体内模型，以获得从脂肪变性到NASH和纤维化转变的机制见解。