Department of Biological Chemistry, School of Pharmacy, Showa University, Tokyo, Japan.
J Lipid Res. 2010 Sep;51(9):2571-80. doi: 10.1194/jlr.M004648. Epub 2010 Jun 6.
Cellular lipid droplets (LD) are organelles involved in cellular lipid metabolism. When liver cellular components were fractionated using sucrose density gradient centrifugation, adipose differentiation-related protein (ADRP) was distributed in both the top and bottom fractions, which correspond to the LD and membranous fractions, respectively, in the mouse liver under normal feeding conditions. After overnight fasting, triacylglycerol and ADRP increased nearly 2.5-fold in the mouse liver, and a portion appeared in the intermediate-density LD (iLD) fractions. ADRP in the iLD fractions was also increased in a mouse nonalcoholic steatohepatitis model induced by methione/choline-deficient diet. When HuH-7 human hepatoma cells were incubated with oleic acid for 24 h, the amount of ADRP increased, and it was distributed in both the LD and membrane fractions. However, ADRP appeared in the iLD fractions upon treatment of HuH-7 cells with glucagon. This behavior of ADRP was cAMP-dependent, as the ADRP-positive iLD fractions were induced by dibutylyl cAMP and were blocked by protein kinase A inhibitors. A portion of ADRP colocalized microscopically with calnexin, which is present in the iLD fractions, by treatment of HuH-7 cells or human primary hepatocytes with oleic acid and glucagon, but not by treatment with oleic acid alone. Glucagon has a role in the reorganization of endoplasmic reticulum membranes to generate ADRP-associated lipid-poor particles in hepatic cells, which is related to LD formation during lipid storage.
细胞脂质滴（LD）是参与细胞脂质代谢的细胞器。当使用蔗糖密度梯度离心法对肝脏细胞成分进行分级分离时，在正常进食条件下，脂肪分化相关蛋白（ADRP）分布在上部和下部两个部分，分别对应于小鼠肝脏中的 LD 和膜部分。经过一夜禁食后，小鼠肝脏中的三酰甘油和 ADRP 增加了近 2.5 倍，一部分出现在中间密度 LD（iLD）部分。在由蛋氨酸/胆碱缺乏饮食诱导的小鼠非酒精性脂肪性肝炎模型中，iLD 部分的 ADRP 也增加了。当 HuH-7 人肝癌细胞用油酸孵育 24 小时时，ADRP 增加，分布在 LD 和膜部分。然而，当用胰高血糖素处理 HuH-7 细胞时，ADRP 出现在 iLD 部分。ADRP 的这种行为是 cAMP 依赖性的，因为用二丁酰环腺苷酸处理 HuH-7 细胞或人原代肝细胞可诱导 ADRP 阳性 iLD 部分，而蛋白激酶 A 抑制剂则可阻断其诱导。用油酸和胰高血糖素处理 HuH-7 细胞或人原代肝细胞，但不用油酸单独处理时，ADRP 的一部分在显微镜下与 calnexin 共定位，calnexin 存在于 iLD 部分。胰高血糖素在重组内质网膜以在肝细胞中产生与 ADRP 相关的富含脂质的颗粒方面起作用，这与脂质储存过程中 LD 的形成有关。
