Puri V, Virbasius J V, Guilherme A, Czech M P
Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Acta Physiol (Oxf). 2008 Jan;192(1):103-15. doi: 10.1111/j.1748-1716.2007.01786.x.
Adipose tissue modulates whole body metabolism and insulin sensitivity by controlling circulating lipid levels and producing molecules that can regulate fatty acid metabolism in such tissues as muscle and liver. We have developed RNA interference (RNAi) screens to identify genes in cultured adipocytes that regulate insulin signalling and key metabolic pathways. These short interfering RNA (siRNA)-based screens identified the transcriptional corepressor receptor interacting protein 140 (RIP140) (J Clin Invest 116: 125, 2006) and the mitogen-activated protein kinase (MAP4k4) (Proc Natl Acad Sci USA 103: 2087, 2006) as negative regulators of insulin-responsive hexose uptake and oxidative metabolism. Gene expression profiling revealed that RIP140 depletion upregulates the expression of clusters of genes in the pathways of glucose uptake, glycolysis, tricarboxylic acid cycle, fatty acid oxidation, mitochondrial biogenesis and oxidative phosphorylation. RIP140-null mice resist weight gain on a high-fat diet and display enhanced glucose tolerance. MAP4k4 depletion in adipocytes increases many of the RIP140-sensitive genes, increases adipogenesis and mediates some actions of tumour necrosis factor-alpha (TNF-alpha). Remarkably, another hit in our RNAi screens was fat specific protein 27 (FSP27), a highly expressed isoform of Cidea. We discovered that FSP27 unexpectedly associates specifically with lipid droplets and regulates fat storage. We conclude that RIP140, MAP4k4 and the novel lipid droplet protein FSP27 are powerful regulators of adipose tissue metabolism and are potential therapeutic targets for controlling metabolic disease. The discovery of these novel proteins validates the power of RNAi screening for discovery of new therapeutic approaches to type 2 diabetes and obesity.
脂肪组织通过控制循环脂质水平和产生可调节肌肉和肝脏等组织中脂肪酸代谢的分子，来调节全身代谢和胰岛素敏感性。我们开发了RNA干扰（RNAi）筛选方法，以鉴定培养的脂肪细胞中调节胰岛素信号传导和关键代谢途径的基因。这些基于小干扰RNA（siRNA）的筛选确定了转录共抑制因子受体相互作用蛋白140（RIP140）（《临床研究杂志》116: 125, 2006）和丝裂原活化蛋白激酶（MAP4k4）（《美国国家科学院院刊》103: 2087, 2006）是胰岛素反应性己糖摄取和氧化代谢的负调节因子。基因表达谱分析显示，RIP140缺失上调了葡萄糖摄取、糖酵解、三羧酸循环、脂肪酸氧化、线粒体生物发生和氧化磷酸化途径中基因簇的表达。RIP140基因敲除小鼠在高脂饮食下抵抗体重增加，并表现出增强的葡萄糖耐量。脂肪细胞中MAP4k4缺失增加了许多对RIP140敏感的基因，增加了脂肪生成，并介导肿瘤坏死因子-α（TNF-α）的一些作用。值得注意的是，我们的RNAi筛选中的另一个发现是脂肪特异性蛋白27（FSP27），它是Cidea的一种高表达异构体。我们发现FSP27意外地特异性与脂滴结合并调节脂肪储存。我们得出结论，RIP140、MAP4k4和新型脂滴蛋白FSP27是脂肪组织代谢的强大调节因子，是控制代谢疾病的潜在治疗靶点。这些新型蛋白质的发现验证了RNAi筛选在发现2型糖尿病和肥胖症新治疗方法方面的作用。
