Imai Norihiro, Suzuki Michitaka, Hayashi Kazuhiko, Ishigami Masatoshi, Hirooka Yoshiki, Abe Takaya, Shioi Go, Goto Hidemi, Fujimoto Toyoshi
Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Nagoya, Japan; Department of Gastroenterology and Hepatology, Nagoya University Graduate School of Medicine, Nagoya, Japan.
Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Nagoya, Japan.
PLoS One. 2015 May 13;10(5):e0127114. doi: 10.1371/journal.pone.0127114. eCollection 2015.
We showed previously that UBXD8 plays a key role in proteasomal degradation of lipidated ApoB in hepatocarcinoma cell lines. In the present study, we aimed to investigate the functions of UBXD8 in liver in vivo. For this purpose, hepatocyte-specific UBXD8 knockout (UBXD8-LKO) mice were generated. They were fed with a normal or high-fat diet, and the phenotypes were compared with those of littermate control mice. Hepatocytes obtained from UBXD8-LKO and control mice were analyzed in culture. After 26 wk of a high-fat diet, UBXD8-LKO mice exhibited macrovesicular steatosis in the periportal area and microvesicular steatosis in the perivenular area, whereas control mice exhibited steatosis only in the perivenular area. Furthermore, UBXD8-LKO mice on a high-fat diet had significantly lower concentrations of serum triglyceride and VLDL than control mice. A Triton WR-1339 injection study revealed that VLDL secretion from hepatocytes was reduced in UBXD8-LKO mice. The decrease of ApoB secretion upon UBXD8 depletion was recapitulated in cultured primary hepatocytes. Accumulation of lipidated ApoB in lipid droplets was observed only in UBXD8-null hepatocytes. The results showed that depletion of UBXD8 in hepatocytes suppresses VLDL secretion, and could lead to periportal steatosis when mice are fed a high-fat diet. This is the first demonstration that an abnormality in the intracellular ApoB degradation mechanism can cause steatosis, and provides a useful model for periportal steatosis, which occurs in several human diseases.
我们之前表明，UBXD8在肝癌细胞系中脂化载脂蛋白B的蛋白酶体降解过程中起关键作用。在本研究中，我们旨在探究UBXD8在体内肝脏中的功能。为此，构建了肝细胞特异性UBXD8基因敲除（UBXD8-LKO）小鼠。给它们喂食正常或高脂饮食，并将其表型与同窝对照小鼠进行比较。对从UBXD8-LKO小鼠和对照小鼠获取的肝细胞进行体外分析。高脂饮食26周后，UBXD8-LKO小鼠在汇管区出现大泡性脂肪变性，在中央静脉周围区域出现小泡性脂肪变性，而对照小鼠仅在中央静脉周围区域出现脂肪变性。此外，高脂饮食的UBXD8-LKO小鼠血清甘油三酯和极低密度脂蛋白（VLDL）浓度显著低于对照小鼠。一项Triton WR-1339注射研究表明，UBXD8-LKO小鼠肝细胞的VLDL分泌减少。在原代培养肝细胞中也重现了UBXD8缺失后载脂蛋白B分泌减少的现象。仅在UBXD8基因敲除的肝细胞中观察到脂化载脂蛋白B在脂滴中的积累。结果表明，肝细胞中UBXD8的缺失会抑制VLDL分泌，并且在小鼠喂食高脂饮食时可能导致汇管区脂肪变性。这首次证明细胞内载脂蛋白B降解机制异常可导致脂肪变性，并为几种人类疾病中出现的汇管区脂肪变性提供了一个有用的模型。
