Group on Molecular and Cell Biology of Lipids, University of Alberta, Alberta, Canada; Department of Pediatrics, Faculty of Medicine and Dentistry, University of Alberta, Alberta, Canada.
Group on Molecular and Cell Biology of Lipids, University of Alberta, Alberta, Canada; Department of Pediatrics, Faculty of Medicine and Dentistry, University of Alberta, Alberta, Canada; Department of Cell Biology, Faculty of Medicine and Dentistry, University of Alberta, Alberta, Canada.
Biochim Biophys Acta Mol Cell Biol Lipids. 2023 Oct;1868(10):159376. doi: 10.1016/j.bbalip.2023.159376. Epub 2023 Jul 28.
Two distinct diacylglycerol acyltransferases (DGAT1 and DGAT2) catalyze the final committed step of triacylglycerol (TG) synthesis in hepatocytes. After its synthesis in the endoplasmic reticulum (ER) TG is either stored in cytosolic lipid droplets (LDs) or is assembled into very low-density lipoproteins in the ER lumen. TG stored in cytosolic LDs is hydrolyzed by adipose triglyceride lipase (ATGL) and the released fatty acids are converted to energy by oxidation in mitochondria. We hypothesized that targeting/association of ATGL to LDs would differ depending on whether the TG stores were generated through DGAT1 or DGAT2 activities. Individual inhibition of DGAT1 or DGAT2 in Huh7 hepatocytes incubated with oleic acid did not yield differences in TG accretion while combined inhibition of both DGATs completely prevented TG synthesis suggesting that either DGAT can efficiently esterify exogenously supplied fatty acid. DGAT2-made TG was stored in larger LDs, whereas TG formed by DGAT1 accumulated in smaller LDs. Inactivation of DGAT1 or DGAT2 did not alter expression (mRNA or protein) of ATGL, the ATGL activator ABHD5/CGI-58, or LD coat proteins PLIN2 or PLIN5, but inactivation of both DGATs increased PLIN2 abundance despite a dramatic reduction in the number of LDs. ATGL was found to preferentially target to LDs generated by DGAT1 and fatty acids released from TG in these LDs were also preferentially used for fatty acid oxidation. Combined inhibition of DGAT2 and ATGL resulted in larger LDs, suggesting that the smaller size of DGAT1-generated LDs is the result of increased lipolysis of TG in these LDs.
两种不同的二酰基甘油酰基转移酶（DGAT1 和 DGAT2）催化肝细胞中三酰基甘油（TG）合成的最后一个关键步骤。在粗面内质网（ER）中合成后，TG 要么储存在细胞质脂滴（LD）中，要么在 ER 腔中组装成极低密度脂蛋白。储存在细胞质 LD 中的 TG 被脂肪甘油三酯脂肪酶（ATGL）水解，释放的脂肪酸在线粒体中通过氧化转化为能量。我们假设 ATGL 与 LD 的靶向/结合会因 TG 储存是通过 DGAT1 还是 DGAT2 活性产生而有所不同。在油酸孵育的 Huh7 肝细胞中单独抑制 DGAT1 或 DGAT2 不会导致 TG 积累的差异，而同时抑制两种 DGAT 则完全阻止了 TG 的合成，这表明任何一种 DGAT 都能有效地酯化外源性供应的脂肪酸。DGAT2 生成的 TG 储存在更大的 LD 中，而由 DGAT1 形成的 TG 则积累在更小的 LD 中。DGAT1 或 DGAT2 的失活不会改变 ATGL 的表达（mRNA 或蛋白）、ATGL 激活剂 ABHD5/CGI-58 或 LD 外壳蛋白 PLIN2 或 PLIN5，但两种 DGAT 的失活尽管 LD 的数量急剧减少，但增加了 PLIN2 的丰度。发现 ATGL 优先靶向由 DGAT1 产生的 LD，并且这些 LD 中的 TG 释放的脂肪酸也优先用于脂肪酸氧化。DGAT2 和 ATGL 的联合抑制导致 LD 增大，这表明 DGAT1 生成的 LD 较小是由于这些 LD 中 TG 的水解增加所致。
