Swift Larry L, Kakkad Bharati, Boone Cordelia, Jovanovska Aneta, Jerome W Gray, Mohler Peter J, Ong David E
Department of Pathology, C-3321 Medical Center North, Vanderbilt University School of Medicine, Nashville, TN 37232-2561, USA.
FEBS Lett. 2005 Jun 6;579(14):3183-9. doi: 10.1016/j.febslet.2005.05.009.
Microsomal triglyceride transfer protein (MTP) is a carrier of triglyceride essential for the assembly of apolipoprotein (apo)B-containing lipoproteins by the liver and the small intestine. Its role in triglyceride transfer in tissues that do not secrete lipoproteins has not been explored. In particular, MTP would seem to be a candidate for a role in triglyceride metabolism within the adipocyte. To test this hypothesis, we probed adipocytes for the presence of MTP. Immunohistochemical and biochemical studies demonstrate MTP in adipocytes from brown and white fat depots of mice and human, as well as in 3T3-L1 cells. Confocal microscopy revealed MTP throughout 3T3 cells; however, MTP fluorescence was prominent in juxtanuclear areas. In differentiated 3T3 cells MTP fluorescence was very striking around lipid droplets. In vitro lipid transfer assays demonstrated the presence of triglyceride transfer activity within microsomal fractions isolated from rat adipose tissue. In addition, quantitative rtPCR studies showed that MTP expression in mouse white fat depots was approximately 1% of MTP expression in mouse liver. MTP mRNA in differentiated 3T3 cells was approximately 13% of liver expression. Our results provide unequivocal evidence for the presence of MTP in adipocytes and present new possibilities for defining the mechanisms by which triglyceride is stored and/or hydrolyzed and mobilized.
微粒体甘油三酯转运蛋白（MTP）是甘油三酯的载体，对于肝脏和小肠组装含载脂蛋白（apo）B的脂蛋白至关重要。其在不分泌脂蛋白的组织中的甘油三酯转运作用尚未得到探索。特别是，MTP似乎是在脂肪细胞内甘油三酯代谢中发挥作用的一个候选者。为了验证这一假设，我们检测了脂肪细胞中MTP的存在情况。免疫组织化学和生化研究表明，在小鼠和人类棕色及白色脂肪库的脂肪细胞以及3T3-L1细胞中均存在MTP。共聚焦显微镜显示MTP遍布3T3细胞；然而，MTP荧光在近核区域较为突出。在分化的3T3细胞中，MTP荧光在脂滴周围非常明显。体外脂质转运试验证明从大鼠脂肪组织分离的微粒体部分存在甘油三酯转运活性。此外，定量逆转录聚合酶链反应（rtPCR）研究表明，小鼠白色脂肪库中MTP的表达约为小鼠肝脏中MTP表达的1%。分化的3T3细胞中MTP mRNA约为肝脏表达的13%。我们的结果为脂肪细胞中存在MTP提供了明确证据，并为确定甘油三酯储存、水解和动员的机制带来了新的可能性。
