Department of Gastroenterology and Hepatology, Osaka University Graduate School of Medicine, Osaka, Japan.
Department of Genetics, Osaka University Graduate School of Medicine, Osaka, Japan.
Hepatology. 2016 Dec;64(6):1994-2014. doi: 10.1002/hep.28820. Epub 2016 Oct 21.
Nonalcoholic fatty liver disease (NAFLD) is the most prevalent liver disease worldwide. It encompasses a spectrum ranging from simple steatosis to fatty liver with hepatocellular injury, termed nonalcoholic steatohepatitis. Recent studies have demonstrated hepatic autophagy being impaired in NAFLD. In the present study, we investigated the impact of Rubicon, a Beclin1-interacting negative regulator for autophagosome-lysosome fusion, in the pathogenesis of NAFLD. In HepG2 cells, BNL-CL2 cells, and murine primary hepatocytes, Rubicon was posttranscriptionally up-regulated by supplementation with saturated fatty acid palmitate. Up-regulation of Rubicon was associated with suppression of the late stage of autophagy, as evidenced by accumulation of both LC3-II and p62 expression levels as well as decreased autophagy flux. Its blockade by small interfering RNA attenuated autophagy impairment and reduced palmitate-induced endoplasmic reticulum stress, apoptosis, and lipid accumulation. Rubicon was also up-regulated in association with autophagy impairment in livers of mice fed a high-fat diet (HFD). Hepatocyte-specific Rubicon knockout mice generated by crossing Rubicon floxed mice with albumin-Cre transgenic mice did not produce any phenotypes on a normal diet. In contrast, on an HFD, they displayed significant improvement of both liver steatosis and injury as well as attenuation of both endoplasmic reticulum stress and autophagy impairment in the liver. In humans, liver tissues obtained from patients with NAFLD expressed significantly higher levels of Rubicon than those without steatosis.
Rubicon is overexpressed and plays a pathogenic role in NAFLD by accelerating hepatocellular lipoapoptosis and lipid accumulation, as well as inhibiting autophagy. Rubicon may be a novel therapeutic target for regulating NAFLD development and progression. (Hepatology 2016;64:1994-2014).
非酒精性脂肪性肝病（NAFLD）是全球最常见的肝脏疾病。它包含了一个从单纯脂肪变性到伴有肝细胞损伤的脂肪性肝病的谱，称为非酒精性脂肪性肝炎。最近的研究表明，NAFLD 中存在肝自噬受损。在本研究中，我们研究了 Rubicon（Beclin1 相互作用的自噬体-溶酶体融合的负调控因子）在 NAFLD 发病机制中的作用。在 HepG2 细胞、BNL-CL2 细胞和小鼠原代肝细胞中，饱和脂肪酸棕榈酸补充后 Rubicon 的转录后水平上调。Rubicon 的上调与晚期自噬的抑制有关，这表现为 LC3-II 和 p62 表达水平的积累以及自噬流的减少。其小干扰 RNA 的阻断减弱了自噬的损害，并减少了棕榈酸诱导的内质网应激、凋亡和脂质积累。Rubicon 在高脂饮食喂养的小鼠肝脏中也与自噬损害有关。通过将 Rubicon floxed 小鼠与白蛋白-Cre 转基因小鼠杂交生成的肝细胞特异性 Rubicon 敲除小鼠在正常饮食下没有产生任何表型。相反，在高脂饮食下，它们显示出肝脏脂肪变性和损伤的显著改善，以及内质网应激和自噬损害的减弱。在人类中，从患有 NAFLD 的患者中获得的肝组织表达的 Rubicon 水平明显高于无脂肪变性的患者。
Rubicon 在 NAFLD 中过度表达并发挥致病作用，通过加速肝细胞脂肪凋亡和脂质积累，并抑制自噬。Rubicon 可能是调节 NAFLD 发展和进展的新的治疗靶点。（Hepatology 2016；64：1994-2014）。
