Miyagawa Koichiro, Oe Shinji, Honma Yuichi, Izumi Hiroto, Baba Ryoko, Harada Masaru
Third Department of Internal Medicine, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
Third Department of Internal Medicine, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
Am J Pathol. 2016 Jul;186(7):1861-1873. doi: 10.1016/j.ajpath.2016.03.003. Epub 2016 May 6.
Blockage of hepatic autophagic degradation system occurs in obesity and is associated with the development of nonalcoholic fatty liver disease. However, the mechanism of this blockage remains unclear. We found a high-fat diet induced accumulation of autophagosomes in the mice livers. However, autophagy substrates such as p62 and ubiquitinated proteins also accumulated in the livers in this model. These findings indicate the possibility that a high-fat diet impairs autophagic flux in the liver. Then, to assess the autophagic flux in more detail, we performed analyses of autophagic flux in cultured hepatocytes exposed to monounsaturated fatty acids (FAs) or saturated FAs (SFAs). SFAs but not monounsaturated FAs suppressed degradation of contents in the autophagosomes. We analyzed each stage of the autophagy pathway (ie, autophagosome formation, autophagosome-lysosome fusion, lysosomal degradation) in cultured hepatocytes treated with monounsaturated FAs or SFAs and found that SFAs impaired autophagosome-lysosome fusion. This impairment occurred in an endoplasmic reticulum stress-dependent manner. Moreover, ubiquitin and p62-positive inclusions observed in high-fat diet-fed mice livers and SFA-treated cells were sequestered within autophagosomes. We also found that SFA-induced accumulation of Ser351-phosphorylated p62, which is indispensable for selective autophagy, further increased on administration of a lysosomal proteinase inhibitor. Although lipid-induced endoplasmic reticulum stress interferes with the autophagosome-lysosome fusion, selective autophagic sequestration of aggregated proteins is not inhibited.
肝脏自噬降解系统的阻断发生在肥胖症中，并与非酒精性脂肪性肝病的发展有关。然而，这种阻断的机制仍不清楚。我们发现高脂饮食会导致小鼠肝脏中自噬体的积累。然而，在该模型中，自噬底物如p62和泛素化蛋白也在肝脏中积累。这些发现表明高脂饮食可能会损害肝脏中的自噬通量。然后，为了更详细地评估自噬通量，我们对暴露于单不饱和脂肪酸（FAs）或饱和脂肪酸（SFAs）的培养肝细胞中的自噬通量进行了分析。饱和脂肪酸而非单不饱和脂肪酸抑制了自噬体中内容物的降解。我们分析了用单不饱和脂肪酸或饱和脂肪酸处理的培养肝细胞中自噬途径的每个阶段（即自噬体形成、自噬体-溶酶体融合、溶酶体降解），发现饱和脂肪酸损害了自噬体-溶酶体融合。这种损害以内质网应激依赖的方式发生。此外，在高脂饮食喂养的小鼠肝脏和饱和脂肪酸处理的细胞中观察到的泛素和p62阳性包涵体被隔离在自噬体内。我们还发现，饱和脂肪酸诱导的选择性自噬所必需的Ser351磷酸化p62的积累在给予溶酶体蛋白酶抑制剂后进一步增加。尽管脂质诱导的内质网应激会干扰自噬体-溶酶体融合，但聚集蛋白的选择性自噬隔离并未受到抑制。
