Quantitative electron microscopy shows uniform incorporation of triglycerides into existing lipid droplets
Quantitative electron microscopy shows uniform incorporation of triglycerides into existing lipid droplets
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DOI：
10.1007/s00418-009-0615-z
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发表时间：
2009-09-01
影响因子：
2.3
通讯作者：
Fujimoto, Toyoshi
中科院分区：
文献类型：
--
作者：
Cheng, Jinglei;Fujita, Akikazu;Fujimoto, Toyoshi
脂滴（LD）是一种细胞器，具有脂酯核心和表面磷脂单层。LD的生物成因机制还不清楚。本研究的目的是阐明LD的生长过程，为此，我们开发了一种新的电子显微镜方法，量化现有的和新合成的甘油三酯在个别LD的比例。我们的方法利用了不饱和脂肪酸和四氧化锇的反应性，这赋予LD反映脂肪酸组成的电子密度。使用这种方法，观察到3 Y1成纤维细胞中现有的富含甘油三酯的LD以高度均匀的速率掺入新合成的甘油三酯。这种均匀性和它的持久性，即使在微管解聚后，表明成纤维细胞中的甘油三酯在个别LD的局部附近合成，然后掺入。相比之下，3 T3-L1脂肪细胞中的LD在脂质酯掺入的速率上显示出异质性，表明成纤维细胞和脂肪细胞中LD生长的不同机制。
The lipid droplet (LD) is an organelle with a lipid ester core and a surface phospholipid monolayer. The mechanism of LD biogenesis is not well understood. The present study aimed to elucidate the LD growth process, for which we developed a new electron microscopic method that quantifies the proportion of existing and newly synthesized triglycerides in individual LDs. Our method takes advantage of the reactivity of unsaturated fatty acids and osmium tetroxide, which imparts LDs an electron density that reflects fatty acid composition. With this method, existing triglyceride-rich LDs in 3Y1 fibroblasts were observed to incorporate newly synthesized triglycerides at a highly uniform rate. This uniformity and its persistence even after microtubules were depolymerized suggest that triglycerides in fibroblasts are synthesized in the local vicinity of individual LDs and then incorporated. In contrast, LDs in 3T3-L1 adipocytes showed heterogeneity in the rate at which lipid esters were incorporated, indicating different mechanisms of LD growth in fibroblasts and adipocytes.