Namatame I, Tomoda H, Arai H, Inoue K, Omura S
Graduate School of Pharmaceutical Sciences, Kitasato University, and Research Center for Biological Function, The Kitasato Institute, Shirokane, Minato-ku, Tokyo, 108-8642, Japan.
J Biochem. 1999 Feb;125(2):319-27. doi: 10.1093/oxfordjournals.jbchem.a022289.
Primary mouse peritoneal macrophages effectively take up and metabolize phosphatidylcholine/cholesterol liposomes containing a small amount of phosphatidylserine, which results in the massive accumulation in the cytoplasm of oil red O positive lipid droplets consisting of cholesteryl ester (CE) and triacylglycerol (TG) [Nishikawa et al. (1990) J. Biol. Chem. 265, 5226-5231]. A number of inhibitors of CE synthesis have been reported, but their effects on the lipid droplet formation have not been fully examined. Furthermore, the contribution of TG synthesis to lipid droplet formation has been poorly investigated. We have investigated the relationship between CE and TG syntheses and cytosolic lipid droplet formation in macrophages cultured in the presence of inhibitors with different modes of action. When macrophages were cultured with liposomes and [14C]oleic acid in the presence of triacsin C, a potent inhibitor of long chain acyl-CoA synthetase, both [14C]CE and [14C]TG syntheses were inhibited to similar extents with IC50 values of 0.19 and 0.10 microM, respectively. On the other hand, pregnenolone, a well-known inhibitor of cellular cholesterol transport, and CL-283,546, a potent inhibitor of acyl-CoA:cholesterol acyltransferase, inhibited [14C]CE synthesis specifically with IC50 values of 5.0 and 0.038 microM, respectively. Microscopic observation revealed that the inhibitors of cholesterol metabolism produce only a partial decrease in cytosolic lipid droplets even at the highest doses which cause almost complete inhibition of [14C]CE synthesis. However, the triacsin C-dose dependent inhibition of lipid droplet formation was almost complete at 0.59 microM, a concentration that inhibits [14C]CE and [14C]TG syntheses by about 90%. These results show that inhibiton of acyl-CoA synthetase by triacsin C causes a decrease in the cellular levels of acyl-CoA, the common substrate for CE and TG syntheses, leading to an inhibiton of neutral lipid synthesis and eventually to the complete disappearance of cytosolic lipid droplets from macrophages. These findings suggest that TG synthesis, as well as CE synthesis, is responsible for macrophage-derived foam cell formation, and is therefore a potential target for new antiatherosclerotic agents.
原代小鼠腹腔巨噬细胞能有效地摄取和代谢含有少量磷脂酰丝氨酸的磷脂酰胆碱/胆固醇脂质体，这导致油红O阳性脂滴在细胞质中大量积累，这些脂滴由胆固醇酯（CE）和三酰甘油（TG）组成[西川等人（1990年）《生物化学杂志》265卷，5226 - 5231页]。已有许多胆固醇酯合成抑制剂的报道，但它们对脂滴形成的影响尚未得到充分研究。此外，三酰甘油合成对脂滴形成的作用也研究较少。我们研究了在存在不同作用方式抑制剂的情况下培养的巨噬细胞中胆固醇酯和三酰甘油合成与胞质脂滴形成之间的关系。当巨噬细胞在三辛素C（一种长链酰基辅酶A合成酶的有效抑制剂）存在的情况下与脂质体和[14C]油酸一起培养时，[14C]胆固醇酯和[14C]三酰甘油的合成均受到类似程度的抑制，IC50值分别为0.19和0.10微摩尔。另一方面，孕烯醇酮（一种著名的细胞胆固醇转运抑制剂）和CL - 283,546（一种酰基辅酶A：胆固醇酰基转移酶的有效抑制剂）分别以5.0和0.038微摩尔的IC50值特异性地抑制[14C]胆固醇酯的合成。显微镜观察显示，即使在导致[14C]胆固醇酯合成几乎完全抑制的最高剂量下，胆固醇代谢抑制剂也只会使胞质脂滴部分减少。然而，在0.59微摩尔时，三辛素C对脂滴形成的剂量依赖性抑制几乎是完全的，该浓度可使[14C]胆固醇酯和[14C]三酰甘油的合成抑制约90%。这些结果表明，三辛素C对酰基辅酶A合成酶的抑制导致细胞内酰基辅酶A水平降低，酰基辅酶A是胆固醇酯和三酰甘油合成的共同底物，从而导致中性脂质合成受到抑制，最终巨噬细胞胞质脂滴完全消失。这些发现表明，三酰甘油合成以及胆固醇酯合成均与巨噬细胞源性泡沫细胞的形成有关，因此是新型抗动脉粥样硬化药物的潜在靶点。
