Ramadori Pierluigi, Drescher Hannah, Erschfeld Stephanie, Schumacher Fabienne, Berger Cordula, Fragoulis Athanassios, Schenkel Julia, Kensler Thomas W, Wruck Christoph J, Trautwein Christian, Kroy Daniela C, Streetz Konrad L
Department of Medicine III, RWTH Aachen University Hospital, Aachen, Germany.
Department of Medicine III, RWTH Aachen University Hospital, Aachen, Germany.
Free Radic Biol Med. 2016 Feb;91:114-26. doi: 10.1016/j.freeradbiomed.2015.12.014. Epub 2015 Dec 15.
Generation of reactive oxygen species (ROS) in response to fatty acids accumulation has been classically proposed as a possible "second hit" triggering progression from simple steatosis to non-alcoholic steatohepatitis (NASH). In this study we challenged hepatocyte-specific Keap1 knockout mice (Keap1(Δhepa)) and littermate Cre- controls (Keap1(fx/fx)) with two different diet models of NASH in order to evaluate the effects of the anti-oxidant transcription factor Nrf2 over-activation on hepatic metabolism and disease progression. After 4 weeks of MCD diet the liver/body weight ratio of Keap1(Δhepa) mice was significantly higher compared to littermate controls with no differences in total body weight. Strikingly, liver histology revealed a dramatic reduction of lipid droplets confirmed by a decreased content of intra-hepatic triglycerides in Keap1(Δhepa) compared to controls. In parallel to reduced expression of genes involved in lipid droplet formation, protein expression of Liver X Receptor (LXRα/β) and Peroxisome proliferator-activated receptor α (PPARα) was significantly decreased. In contrast, genes involved in mitochondrial lipid catabolism were markedly up-regulated in Keap1(Δhepa) livers. A similar phenotype characterized by inhibition of lipogenesis in favor of increased mitochondrial catabolic activity was also observed after 13 weeks of western diet administration. MCD-induced apoptosis was significantly dampened in Keap1(Δhepa) compared to Keap1(fx/fx) as detected by TUNEL, cleaved caspase-3 and Bcl-2 protein expression analyses. However, no differences in inflammatory F4/80- and CD11b-positive cells and pro-fibrogenic genes were detected between the two groups. Although hepatic lack of Keap1 did not ameliorate inflammation, the resulting constitutive Nrf2 over-activation in hepatocytes strongly reduced hepatic steatosis via enhanced lipid catabolism and repressed de novo lipogenesis during murine NASH development.
经典理论认为，脂肪酸积累引发的活性氧（ROS）生成可能是促使单纯性脂肪变性发展为非酒精性脂肪性肝炎（NASH）的“二次打击”。在本研究中，我们用两种不同的NASH饮食模型分别对肝细胞特异性Keap1基因敲除小鼠（Keap1(Δhepa)）及其同窝对照Cre小鼠（Keap1(fx/fx)）进行试验，以评估抗氧化转录因子Nrf2过度激活对肝脏代谢及疾病进展的影响。采用蛋氨酸-胆碱缺乏（MCD）饮食4周后，Keap1(Δhepa)小鼠的肝体比显著高于同窝对照，而总体体重无差异。令人惊讶的是，肝脏组织学检查显示，与对照组相比，Keap1(Δhepa)小鼠肝脏中的脂滴显著减少，肝内甘油三酯含量降低也证实了这一点。与脂滴形成相关基因表达降低同时出现的是，肝脏X受体（LXRα/β）和过氧化物酶体增殖物激活受体α（PPARα）的蛋白表达显著下降。相反，参与线粒体脂质分解代谢的基因在Keap1(Δhepa)小鼠肝脏中显著上调。给予西方饮食13周后，也观察到了类似的表型，即脂肪生成受到抑制，线粒体分解代谢活性增强。通过TUNEL、裂解的半胱天冬酶-3和Bcl-2蛋白表达分析检测发现，与Keap1(fx/fx)小鼠相比，MCD诱导的Keap1(Δhepa)小鼠细胞凋亡明显减少。然而，两组之间在炎性F4/80和CD11b阳性细胞以及促纤维化基因方面未检测到差异。虽然肝脏中缺乏Keap1并没有改善炎症，但在小鼠NASH发展过程中，肝细胞中Nrf2的持续过度激活通过增强脂质分解代谢和抑制从头脂肪生成，显著减轻了肝脏脂肪变性。
