Department of Physiology, Medical University of Bialystok, 15-089 Bialystok, Poland.
Int J Mol Sci. 2021 Nov 19;22(22):12478. doi: 10.3390/ijms222212478.
Increased lipid bioavailability in a diet favors lipid accumulation, enhancing hepatic lipotoxicity and contributing to insulin resistance (IR) development. The aim of our study was to examine time-dependent alterations in the intrahepatic content of sphingolipids and insulin signaling pathway in rats fed a high-fat diet (HFD). The experiment was conducted on male Wistar rats receiving a standard diet or HFD for five weeks. At the end of each experimental feeding week, liver sphingolipids were determined using high-performance liquid chromatography. The expression of proteins from the sphingolipid pathway and glucose transporter expression were assessed by Western blot. The content of phosphorylated form of proteins from the insulin pathway was detected by a multiplex assay kit. Our results revealed that HFD enhanced hepatic ceramide deposition by increasing the expression of selected proteins from sphingomyelin and salvage pathways in the last two weeks. Importantly, we observed a significant inhibition of Akt phosphorylation in the first week of HFD and stimulation of PTEN and mTOR phosphorylation at the end of HFD. These changes worsened the PI3K/Akt/mTOR signaling pathway. We may postulate that HFD-induced reduction in the insulin action in the time-dependent matter was exerted by excessive accumulation of sphingosine and sphinganine rather than ceramide.
饮食中脂质生物利用度的增加有利于脂质积累，增强肝毒性和导致胰岛素抵抗（IR）的发展。我们的研究目的是研究高脂饮食（HFD）喂养的大鼠肝内鞘脂含量和胰岛素信号通路的时间依赖性变化。该实验在接受标准饮食或 HFD 喂养五周的雄性 Wistar 大鼠上进行。在每个实验喂养周结束时，使用高效液相色谱法测定肝鞘脂含量。通过 Western blot 评估糖转运蛋白表达和鞘脂途径中蛋白质的表达。通过多指标测定试剂盒检测胰岛素途径中磷酸化蛋白的含量。我们的结果表明，HFD 在最后两周通过增加鞘磷脂和补救途径中选定蛋白质的表达来增强肝Cer 的沉积。重要的是，我们在 HFD 的第一周观察到 Akt 磷酸化的显著抑制，并且在 HFD 的最后阶段观察到 PTEN 和 mTOR 磷酸化的刺激。这些变化恶化了 PI3K/Akt/mTOR 信号通路。我们可以假设，HFD 诱导的胰岛素作用在时间依赖性上的降低是通过鞘氨醇和鞘氨醇的过度积累而不是 Cer 引起的。
