Non-alcoholic steatohepatitis (NASH), a metabolic disorder consisting of steatosis and inflammation, is considered the hepatic equivalent of metabolic syndrome and can result in irreversible liver damage. Macrophage-stimulating protein (MSP) is a hepatokine that potentially has a beneficial role in hepatic lipid and glucose metabolism via the activation of AMP-activated protein kinase (AMPK). In the current study, we investigated the regulatory role of MSP in the development of inflammation and lipid metabolism in various NASH models, both in vitro and ex vivo. We observed that MSP treatment activated the AMPK signaling pathway and inhibited lipopolysaccharide (LPS)- and palmitic acid (PA)-induced gene expression of pro-inflammatory cytokines in primary mouse hepatocytes. In addition, MSP treatment resulted in a significant reduction in PA-induced lipid accumulation and inhibited the gene expression of key lipogenic enzymes in HepG2 cells. Upon short hairpin RNA-induced knockdown of RON (the membrane-bound receptor for MSP), the anti-inflammatory and anti-lipogenic effects of MSP were markedly ablated. Finally, to mimic NASH ex vivo, we challenged bone marrow-derived macrophages with oxidized low-density lipoprotein (oxLDL) in combination with LPS. OxLDL+LPS exposure led to a marked inhibition of AMPK activity and a robust increase in inflammation. MSP treatment significantly reversed these effects by restoring AMPK activity and by suppressing pro-inflammatory cytokine gene expression and secretion under this condition. Taken together, these data suggest that MSP is an effective inhibitor of inflammation and lipid accumulation in the stressed liver, thereby indicating that MSP has a key regulatory role in NASH.
AMP-Activated Protein Kinases ; Animals ; Cytokines ; Fatty Liver* ; Gene Expression ; Glucose ; Hep G2 Cells ; Hepatocytes ; In Vitro Techniques ; Inflammation* ; Lipid Metabolism ; Lipogenesis* ; Lipoproteins ; Liver ; Macrophages ; Metabolism ; Mice ; Palmitic Acid

[摘 要] 目的：探讨甲硫氨酸限制对肺腺癌（LUAD）细胞增殖、凋亡及磷酸戊糖途径的影响。方法：将H1299、A549细胞分为Met+组和Met−组，分别用含100 μmol/L或不含甲硫氨酸的培养基连续培养4 d，采用细胞计数法评估甲硫氨酸处理对H1299和A549细胞增殖的影响，PI染色法检测细胞周期分布，Annexin Ⅴ-PE/7AAD标记细胞凋亡，利用DCFH-DA探针检测细胞内ROS水平，WST-8法和DTNB法分别测定细胞内NADPH与GSH含量；通过癌症基因组图谱（TCGA）数据库分析葡萄糖-6-磷酸脱氢酶（G6PD）和6-磷酸葡萄糖酸脱氢酶（6PGD）表达与甲硫氨酸代谢通路的关系；采用WB法检测甲硫氨酸处理及回补甲硫氨酸下游代谢产物S-腺苷甲硫氨酸（SAM）对LUAD细胞中磷酸戊糖途径关键酶G6PD和6PGD表达的影响。结果：甲硫氨酸限制显著抑制H1299和A549细胞增殖（均P < 0.01），将细胞周期阻滞于G2/M期（均P < 0.05），显著升高细胞内总ROS水平（均P < 0.001）并促进细胞凋亡（均P < 0.001）；同时，甲硫氨酸限制显著降低了细胞内NADPH和GSH水平（均P < 0.01），抑制DNA合成（均P < 0.01）。分析TCAG数据发现，G6PD和6PGD表达水平与甲硫氨酸代谢通路呈正相关（均P < 0.001），甲硫氨酸限制下调G6PD和6PGD蛋白表达（均P < 0.01），而回补SAM可部分逆转甲硫氨酸限制对G6PD和6PGD的表达的抑制（均P < 0.01），提示甲硫氨酸通过SAM合成调控磷酸戊糖途径。结论：甲硫氨酸限制通过抑制磷酸戊糖途径抑制LUAD细胞增殖，为甲硫氨酸限制疗法治疗LUAD提供实验依据。