Activation of CD11b+ Kupffer Cells/Macrophages as a Common Cause for Exacerbation of TNF/Fas-Ligand-Dependent Hepatitis in Hypercholesterolemic Mice

We have reported that the mouse hepatic injury induced by either α-galactosylceramide (α-GalCer) or bacterial DNA motifs (CpG-ODN) is mediated by the TNF/NKT cell/Fas-ligand (FasL) pathway. In addition, F4/80+ Kupffer cells can be subclassified into CD68+ subset with a phagocytosing capacity and CD11b+ subset with a TNF-producing capacity. CD11b+ subset increase if mice are fed high-fat and cholesterol diet (HFCD). The present study examined how a HFCD affects the function of NKT cells and F4/80+ CD11b+ subset and these hepatitis models. After the C57BL/6 mice received a HFCD, high-cholesterol diet (HCD), high-fat diet (HFD) and control diet (CD) for four weeks, the HFCD mice increased surface CD1d and intracellular TLR-9 expression by the CD11b+ population compared to CD mice. Hepatic injury induced either by α-GalCer or CpG-ODN was more severe in HCD and HFCD mice compared to CD mice, which was in proportion to the serum TNF levels. In addition, liver cholesterol levels but not serum cholesterol levels nor liver triglyceride levels were involved in the aggravation of hepatitis. The FasL expression of NKT cells induced by both reagents was upregulated in HFCD mice. Furthermore, the liver mononuclear cells and purified F4/80+ CD11b+ subset from HFCD mice stimulated with either reagent in vitro produced a larger amount of TNF than did those from CD mice. Intracellular TNF production in F4/80+ CD11b+ cells was confirmed. The increased number of F4/80+ CD11b+ Kupffer cells/macrophages by HFCD and their enhanced TNF production thus play a pivotal role in TNF/NKT cell/FasL dependent hepatic injury.

我们此前已有报道，由α-半乳糖苷神经酰胺(α-galactosylceramide, α-GalCer)或细菌DNA基序(CpG-寡聚脱氧核苷酸, CpG-ODN)诱导的小鼠肝损伤，是通过肿瘤坏死因子(TNF)/自然杀伤T细胞(NKT cell)/Fas配体(FasL)通路介导的。此外，F4/80阳性库普弗细胞(Kupffer cells)可被分为两个亚群：具有吞噬能力的CD68阳性亚群，以及具备肿瘤坏死因子产生能力的CD11b阳性亚群。当小鼠饲喂高脂高胆固醇饮食(high-fat and cholesterol diet, HFCD)时，CD11b阳性亚群的数量会增加。本研究探究了高脂高胆固醇饮食对自然杀伤T细胞(NKT细胞)、F4/80+CD11b+亚群功能的影响，以及其对上述肝炎模型的作用。将C57BL/6小鼠分别饲喂高脂高胆固醇饮食(HFCD)、高胆固醇饮食(high-cholesterol diet, HCD)、高脂饮食(high-fat diet, HFD)与对照饮食(control diet, CD)四周后，与对照饮食组小鼠相比，高脂高胆固醇饮食组小鼠的CD11b阳性群体的表面CD1d与胞内Toll样受体9(TLR-9)表达水平均显著升高。与对照饮食组小鼠相比，高胆固醇饮食组与高脂高胆固醇饮食组小鼠中，由α-GalCer或CpG-ODN诱导的肝损伤更为严重，且损伤程度与血清TNF水平呈正相关。此外，肝脏胆固醇水平而非血清胆固醇或肝脏甘油三酯水平，与肝炎病情的加重密切相关。两种试剂诱导的NKT细胞的Fas配体(FasL)表达，在高脂高胆固醇饮食组小鼠中均出现上调。此外，体外经两种试剂刺激后，取自高脂高胆固醇饮食组小鼠的肝脏单个核细胞，以及纯化得到的F4/80+CD11b+亚群，其分泌的TNF量均高于对照饮食组小鼠的对应样本。本研究同时证实了F4/80+CD11b+细胞的胞内TNF产生能力。综上，高脂高胆固醇饮食诱导的F4/80+CD11b+库普弗细胞/巨噬细胞数量增加，以及其增强的TNF产生能力，在依赖TNF/NKT细胞/FasL通路的肝损伤中发挥关键作用。