Kwon Bumsup, Querfurth Henry W
Department of Neurology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, RI 02903, USA.
Department of Neurology, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, RI 02903, USA.
Biochimie. 2015 Nov;118:141-50. doi: 10.1016/j.biochi.2015.09.006. Epub 2015 Sep 5.
Excessive saturated free fatty acids (SFFAs; e.g. palmitate) in blood are a pathogenic factor in diabetes, obesity, cardiovascular disease and liver failure. In contrast, monounsaturated free fatty acids (e.g. oleate) prevent the toxic effect of SFFAs in various types of cells. The mechanism is poorly understood and involvement of the mTOR complex is untested. In the present study, we demonstrate that oleate preconditioning, as well as coincubation, completely prevented palmitate-induced markers of inflammatory signaling, insulin resistance and cytotoxicity in C2C12 myotubes. We then examined the effect of palmitate and/or oleate on the mammalian target of rapamycin (mTOR) signal path and whether their link is mediated by AMP-activated protein kinase (AMPK). Palmitate decreased the phosphorylation of raptor and 4E-BP1 while increasing the phosphorylation of p70S6K. Palmitate also inhibited phosphorylation of AMPK, but did not change the phosphorylated levels of mTOR or rictor. Oleate completely prevented the palmitate-induced dysregulation of mTOR components and restored pAMPK whereas alone it produced no signaling changes. To understand this more, we show activation of AMPK by metformin also prevented palmitate-induced changes in the phosphorylations of raptor and p70S6K, confirming that the mTORC1/p70S6K signaling pathway is responsive to AMPK activity. By contrast, inhibition of AMPK phosphorylation by Compound C worsened palmitate-induced changes and correspondingly blocked the protective effect of oleate. Finally, metformin modestly attenuated palmitate-induced insulin resistance and cytotoxicity, as did oleate. Our findings indicate that palmitate activates mTORC1/p70S6K signaling by AMPK inhibition and phosphorylation of raptor. Oleate reverses these effects through a metformin-like facilitation of AMPK.
血液中过量的饱和游离脂肪酸（SFFAs；如棕榈酸酯）是糖尿病、肥胖症、心血管疾病和肝衰竭的致病因素。相比之下，单不饱和游离脂肪酸（如油酸）可防止SFFAs在各类细胞中的毒性作用。其机制尚不清楚，且mTOR复合物的参与情况未经测试。在本研究中，我们证明油酸预处理以及共孵育可完全预防棕榈酸酯诱导的C2C12肌管中炎症信号、胰岛素抵抗和细胞毒性标志物的产生。然后，我们研究了棕榈酸酯和/或油酸对雷帕霉素哺乳动物靶标（mTOR）信号通路的影响，以及它们之间的联系是否由AMP激活的蛋白激酶（AMPK）介导。棕榈酸酯降低了raptor和4E-BP1的磷酸化水平，同时增加了p70S6K的磷酸化水平。棕榈酸酯还抑制了AMPK的磷酸化，但未改变mTOR或rictor的磷酸化水平。油酸完全预防了棕榈酸酯诱导的mTOR组分失调，并恢复了pAMPK，而单独使用油酸则未产生信号变化。为了进一步了解这一点，我们表明二甲双胍激活AMPK也可预防棕榈酸酯诱导的raptor和p70S6K磷酸化变化，证实mTORC1/p70S6K信号通路对AMPK活性有反应。相比之下，化合物C抑制AMPK磷酸化会加剧棕榈酸酯诱导的变化，并相应地阻断油酸的保护作用。最后，二甲双胍适度减轻了棕榈酸酯诱导的胰岛素抵抗和细胞毒性，油酸也有同样的效果。我们的研究结果表明，棕榈酸酯通过抑制AMPK和raptor磷酸化激活mTORC1/p70S6K信号通路。油酸通过类似二甲双胍的方式促进AMPK来逆转这些作用。
