Kim Francis, Pham Matilda, Luttrell Ian, Bannerman Douglas D, Tupper Joan, Thaler Joshua, Hawn Thomas R, Raines Elaine W, Schwartz Michael W
Department of Medicine, University of Washington, Seattle, WA 98104, USA.
Circ Res. 2007 Jun 8;100(11):1589-96. doi: 10.1161/CIRCRESAHA.106.142851. Epub 2007 May 3.
Vascular dysfunction is a major complication of metabolic disorders such as diabetes and obesity. The current studies were undertaken to determine whether inflammatory responses are activated in the vasculature of mice with diet-induced obesity, and if so, whether Toll-Like Receptor-4 (TLR4), a key mediator of innate immunity, contributes to these responses. Mice lacking TLR4 (TLR4(-/-)) and wild-type (WT) controls were fed either a low fat (LF) control diet or a diet high in saturated fat (HF) for 8 weeks. In response to HF feeding, both genotypes displayed similar increases of body weight, body fat content, and serum insulin and free fatty acid (FFA) levels compared with mice on a LF diet. In lysates of thoracic aorta from WT mice maintained on a HF diet, markers of vascular inflammation both upstream (IKKbeta activity) and downstream of the transcriptional regulator, NF-kappaB (ICAM protein and IL-6 mRNA expression), were increased and this effect was associated with cellular insulin resistance and impaired insulin stimulation of eNOS. In contrast, vascular inflammation and impaired insulin responsiveness were not evident in aortic samples taken from TLR4(-/-) mice fed the same HF diet, despite comparable increases of body fat mass. Incubation of either aortic explants from WT mice or cultured human microvascular endothelial cells with the saturated FFA, palmitate (100 micromol/L), similarly activated IKKbeta, inhibited insulin signal transduction and blocked insulin-stimulated NO production. Each of these effects was subsequently shown to be dependent on both TLR4 and NF-kappaB activation. These findings identify the TLR4 signaling pathway as a key mediator of the deleterious effects of palmitate on endothelial NO signaling, and are the first to document a key role for TLR4 in the mechanism whereby diet-induced obesity induces vascular inflammation and insulin resistance.
血管功能障碍是糖尿病和肥胖症等代谢紊乱的主要并发症。目前的研究旨在确定饮食诱导肥胖小鼠的血管中炎症反应是否被激活，如果是，先天免疫的关键介质Toll样受体4（TLR4）是否促成这些反应。缺乏TLR4（TLR4(-/-)）的小鼠和野生型（WT）对照小鼠分别喂食低脂（LF）对照饮食或高饱和脂肪（HF）饮食8周。与喂食LF饮食的小鼠相比，两种基因型的小鼠在喂食HF饮食后体重、体脂含量、血清胰岛素和游离脂肪酸（FFA）水平均有相似程度的增加。在维持HF饮食的WT小鼠胸主动脉裂解物中，转录调节因子NF-κB上游（IKKβ活性）和下游（ICAM蛋白和IL-6 mRNA表达）的血管炎症标志物均增加，且这种效应与细胞胰岛素抵抗以及胰岛素对eNOS的刺激受损有关。相比之下，尽管体脂量有相当程度的增加，但喂食相同HF饮食的TLR4(-/-)小鼠的主动脉样本中未出现明显的血管炎症和胰岛素反应性受损。用饱和脂肪酸棕榈酸（100 μmol/L）孵育WT小鼠的主动脉外植体或培养的人微血管内皮细胞，同样会激活IKKβ，抑制胰岛素信号转导并阻断胰岛素刺激的NO生成。随后发现这些效应均依赖于TLR4和NF-κB的激活。这些发现确定TLR4信号通路是棕榈酸对内皮NO信号产生有害影响的关键介质，并且首次证明了TLR4在饮食诱导肥胖引发血管炎症和胰岛素抵抗机制中的关键作用。
