Li Bing-Hang, He Fang-Ping, Yang Xin, Chen Yuan-Wen, Fan Jian-Gao
Department of Gastroenterology, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
Department of Hepatology, First Affiliated Hospital of Xinjiang Medical University, Urumqi, Xinjiang Uygur Autonomous Region, China.
Transl Res. 2017 Feb;180:103-117.e4. doi: 10.1016/j.trsl.2016.08.006. Epub 2016 Aug 31.
The rapidly increasing prevalence of nonalcoholic fatty liver disease (NAFLD) has become one of the major public health threats in China and worldwide. However, during the development of NAFLD, the key mechanism underlying the progression of related fibrosis remains unclear, which greatly impedes the development of optimal NAFLD therapy. In the current study, we were endeavored to characterize a proinflammatory cytokine, CCL5, as a major contributor for fibrosis in NAFLD. The results showed that CCL5 was highly expressed in fatty liver and NASH patients. In NAFLD rats induced by 8-week-HFD, CCL5 and its receptor, CCR5, were significantly up-regulated and liver fibrosis exclusively occurred in this group. In addition, we showed that hepatocytes are the major source contributing to this CCL5 elevation. Interestingly, a CCL5 inhibitor Met-CCL5, significantly decreased liver fibrosis but not hepatic steatosis. Using a cell model of hepatic steatosis, we found that the conditioned medium of lipid-overloaded hepatocytes (Fa2N-4 cells) which produced excessive CCL5 stimulated the profibrotic activities of hepatic stellate cells (LX-2) as manifested by increased migration rate, proliferation and collagen production of LX-2 cells. CCL5 knockdown in Fa2N-4 cells, Met-CCL5 or CCR5 antibody treatment on LX-2 cells all significantly inhibited the conditioned medium of FFA-treated Fa2N-4 cells to exert stimulatory effects on LX-2 cells. Consistently, the conditioned medium of Fa2N-4 cells with CCL5 over-expression significantly enhanced migration rate, cell proliferation and collagen production of LX-2 cells. All these results support that CCL5 produced by steatotic hepatocytes plays an essential role in fibrotic signaling machinery of NAFLD. In addition, we were able to identify C/EBP-β as the up-stream regulator of CCL5 gene transcription in hepatocytes treated with free fatty acid (FFA). Our data strongly supported that CCL5 plays a pivotal regulatory role in hepatic fibrosis during NAFLD, which constitutes a novel and exciting observation that may call for potential future development of specific CCL5-targeted NAFLD therapy.
非酒精性脂肪性肝病（NAFLD）患病率的迅速上升已成为中国乃至全球主要的公共卫生威胁之一。然而，在NAFLD的发展过程中，相关纤维化进展的关键机制仍不清楚，这极大地阻碍了最佳NAFLD治疗方法的开发。在本研究中，我们致力于将促炎细胞因子CCL5鉴定为NAFLD纤维化的主要促成因素。结果显示，CCL5在脂肪肝和非酒精性脂肪性肝炎（NASH）患者中高表达。在8周高脂饮食（HFD）诱导的NAFLD大鼠中，CCL5及其受体CCR5显著上调，且肝纤维化仅在该组中出现。此外，我们表明肝细胞是导致CCL5升高的主要来源。有趣的是，CCL5抑制剂Met-CCL5可显著降低肝纤维化，但不影响肝脂肪变性。使用肝脂肪变性细胞模型，我们发现产生过量CCL5的脂质过载肝细胞（Fa2N-4细胞）的条件培养基刺激肝星状细胞（LX-2）的促纤维化活性，表现为LX-2细胞迁移率增加、增殖和胶原蛋白产生增加。在Fa2N-4细胞中敲低CCL5、在LX-2细胞上用Met-CCL5或CCR5抗体处理，均显著抑制经游离脂肪酸（FFA）处理的Fa2N-4细胞的条件培养基对LX-2细胞产生刺激作用。一致地，过表达CCL5的Fa2N-4细胞的条件培养基显著提高了LX-2细胞的迁移率、细胞增殖和胶原蛋白产生。所有这些结果支持脂肪变性肝细胞产生的CCL5在NAFLD的纤维化信号传导机制中起重要作用。此外，我们能够确定C/EBP-β是游离脂肪酸（FFA）处理的肝细胞中CCL5基因转录的上游调节因子。我们的数据有力地支持CCL5在NAFLD期间的肝纤维化中起关键调节作用，这构成了一个新颖且令人兴奋的发现，可能需要未来开发针对CCL5的特异性NAFLD治疗方法。
