Division of Molecular Medicine, Department of Medicine, University of Minnesota, Minneapolis, Minnesota, USA.
Center for Metabolic Origins of Disease, Sanford Burnham Prebys Medical Discovery Institute, Orlando, Florida, USA.
JCI Insight. 2018 Jun 21;3(12). doi: 10.1172/jci.insight.99762.
While several molecular targets are under consideration, mechanistic underpinnings of the transition from uncomplicated nonalcoholic fatty liver disease (NAFLD) to nonalcoholic steatohepatitis (NASH) remain unresolved. Here we apply multiscale chemical profiling technologies to mouse models of deranged hepatic ketogenesis to uncover potential NAFLD driver signatures. Use of stable-isotope tracers, quantitatively tracked by nuclear magnetic resonance (NMR) spectroscopy, supported previous observations that livers of wild-type mice maintained long term on a high-fat diet (HFD) exhibit a marked increase in hepatic energy charge. Fed-state ketogenesis rates increased nearly 3-fold in livers of HFD-fed mice, a greater proportionate increase than that observed for tricarboxylic acid (TCA) cycle flux, but both of these contributors to overall hepatic energy homeostasis fueled markedly increased hepatic glucose production (HGP). Thus, to selectively determine the role of the ketogenic conduit on HGP and oxidative hepatic fluxes, we studied a ketogenesis-insufficient mouse model generated by knockdown of the mitochondrial isoform of 3-hydroxymethylglutaryl-CoA synthase (HMGCS2). In response to ketogenic insufficiency, TCA cycle flux in the fed state doubled and HGP increased more than 60%, sourced by a 3-fold increase in glycogenolysis. Finally, high-resolution untargeted metabolomics and shotgun lipidomics performed using ketogenesis-insufficient livers in the fed state revealed accumulation of bis(monoacylglycero)phosphates, which also accumulated in livers of other models commonly used to study NAFLD. In summary, natural and interventional variations in ketogenesis in the fed state strongly influence hepatic energy homeostasis, glucose metabolism, and the lipidome. Importantly, HGP remains tightly linked to overall hepatic energy charge, which includes both terminal fat oxidation through the TCA cycle and partial oxidation via ketogenesis.
虽然有几个分子靶点正在研究中，但从简单的非酒精性脂肪性肝病（NAFLD）向非酒精性脂肪性肝炎（NASH）的转变的机制基础仍未解决。在这里，我们应用多尺度化学分析技术研究肝脏酮生成异常的小鼠模型，以揭示潜在的 NAFLD 驱动特征。使用稳定同位素示踪剂，通过核磁共振（NMR）光谱进行定量跟踪，支持了先前的观察结果，即长期高脂肪饮食（HFD）喂养的野生型小鼠肝脏表现出明显的肝能量电荷增加。HFD 喂养的小鼠肝脏中的进食状态酮生成率增加了近 3 倍，这比三羧酸（TCA）循环通量的比例增加更大，但这两者都是整体肝能量平衡的贡献者，导致肝葡萄糖生成（HGP）显著增加。因此，为了选择性地确定酮生成途径对 HGP 和氧化肝通量的作用，我们研究了一种由线粒体同工型 3-羟甲基戊二酰辅酶 A 合酶（HMGCS2）敲低产生的酮生成不足的小鼠模型。在酮生成不足的情况下，进食状态下的 TCA 循环通量增加了一倍，HGP 增加了 60%以上，来源是糖原分解增加了 3 倍。最后，使用酮生成不足的肝脏在进食状态下进行的高分辨率非靶向代谢组学和鸟枪法脂质组学研究表明，双（单酰基甘油）磷酸酯的积累，这也在其他常用的 NAFLD 研究模型的肝脏中积累。总之，进食状态下酮生成的自然和干预变化强烈影响肝能量平衡、葡萄糖代谢和脂质组。重要的是，HGP 仍然与整体肝能量电荷紧密相关，其中包括通过 TCA 循环的末端脂肪氧化和通过酮生成的部分氧化。
