Hans Popper Laboratory of Molecular Hepatology, Division of Gastroenterology and Hepatology, Department of Internal Medicine III, Medical University of Vienna, 1090 Vienna, Austria.
Division of Gastroenterology and Hepatology, Joan and Sanford I. Weill Cornell Department of Medicine, Weill Cornell Medical College, New York, NY 10021, USA.
Int J Mol Sci. 2020 Nov 18;21(22):8711. doi: 10.3390/ijms21228711.
Liver fibrosis represents the wound healing response to sustained hepatic injury with activation of hepatic stellate cells (HSCs). The I148M variant of the gene represents a risk factor for development of severe liver fibrosis. Activated HSCs carrying the I148M variant display exacerbated pro-inflammatory and pro-fibrogenic features. We aimed to examine whether the I148M variant may impair Hedgehog and Yap signaling, as key pathways implicated in the control of energy expenditure and maintenance of myofibroblastic traits. First, we show that TGF-β rapidly up-regulated the PNPLA3 transcript and protein and Yap/Hedgehog target gene expression. In addition, HSCs overexpressing I148M boosted anaerobic glycolysis, as supported by higher lactate release and decreased phosphorylation of the energy sensor AMPK. These cells displayed higher Yap and Hedgehog signaling, due to accumulation of total Yap protein, Yap promoter activity and increased downstream targets expression, compared to WT cells. HSCs exposed to TGF-β and leptin rapidly increased total Yap, together with a reduction in its inhibited form, phosphorylated Yap. In line, Yap-specific inhibitor Verteporfin strongly abolished Yap-mediated genes expression, at baseline as well as after TGF-β and leptin treatments in HSCs with I148M . Finally, Yap transcriptional activity was strongly reduced by a combination of Verteporfin and Rosiglitazone, a PPARγ synthetic agonist. In conclusion, HSCs carrying the variant show activated Yap/Hedgehog pathways, resulting in altered anaerobic glycolysis and enhanced synthesis of Hedgehog markers and sustained Yap signaling. TGF-β and leptin exacerbate Yap/Hedgehog-related fibrogenic genes expression, while Yap inhibitors and PPARγ agonists abrogate these effects in I148M carrying HSCs.
肝纤维化代表了对持续肝损伤的愈合反应，肝星状细胞（HSCs）被激活。基因的 I148M 变体是发展严重肝纤维化的风险因素。携带 I148M 变体的活化 HSCs 表现出加剧的促炎和促纤维化特征。我们旨在研究 I148M 变体是否可能损害 Hedgehog 和 Yap 信号通路，因为这些信号通路是控制能量消耗和维持肌成纤维特征的关键途径。首先，我们表明 TGF-β 可快速上调 PNPLA3 转录本和蛋白以及 yap/Hedgehog 靶基因的表达。此外，过表达 I148M 的 HSCs 促进了无氧糖酵解，这得到了更高的乳酸释放和能量传感器 AMPK 磷酸化减少的支持。与 WT 细胞相比，这些细胞显示出更高的 yap 和 Hedgehog 信号，这是由于总 yap 蛋白的积累、yap 启动子活性和下游靶基因表达的增加。暴露于 TGF-β 和瘦素的 HSCs 可迅速增加总 yap，同时减少其抑制形式磷酸化 yap。与此一致，yap 特异性抑制剂 Verteporfin 强烈抑制了 HSCs 中 I148M 基因表达，无论是在基线水平还是在 TGF-β 和瘦素处理后。最后，Verteporfin 和 PPARγ 合成激动剂罗格列酮的组合强烈降低了 yap 转录活性。总之，携带 变体的 HSCs 显示出激活的 yap/Hedgehog 通路，导致改变的无氧糖酵解和增强的 Hedgehog 标志物合成以及持续的 yap 信号。TGF-β 和瘦素加剧了与 yap/Hedgehog 相关的纤维化基因表达，而 yap 抑制剂和 PPARγ 激动剂则消除了 I148M 携带 HSCs 中的这些作用。
