Leamy Alexandra K, Hasenour Clinton M, Egnatchik Robert A, Trenary Irina A, Yao Cong-Hui, Patti Gary J, Shiota Masakazu, Young Jamey D
Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN, USA.
Department of Chemistry, Washington University in St. Louis, St. Louis, MO, USA; Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA.
Biochim Biophys Acta. 2016 Sep;1861(9 Pt A):1005-1014. doi: 10.1016/j.bbalip.2016.05.013. Epub 2016 May 29.
Experiments in a variety of cell types, including hepatocytes, consistently demonstrate the acutely lipotoxic effects of saturated fatty acids, such as palmitate (PA), but not unsaturated fatty acids, such as oleate (OA). PA+OA co-treatment fully prevents PA lipotoxicity through mechanisms that are not well defined but which have been previously attributed to more efficient esterification and sequestration of PA into triglycerides (TGs) when OA is abundant. However, this hypothesis has never been directly tested by experimentally modulating the relative partitioning of PA/OA between TGs and other lipid fates in hepatocytes. In this study, we found that addition of OA to PA-treated hepatocytes enhanced TG synthesis, reduced total PA uptake and PA lipid incorporation, decreased phospholipid saturation and rescued PA-induced ER stress and lipoapoptosis. Knockdown of diacylglycerol acyltransferase (DGAT), the rate-limiting step in TG synthesis, significantly reduced TG accumulation without impairing OA-mediated rescue of PA lipotoxicity. In both wild-type and DGAT-knockdown hepatocytes, OA co-treatment significantly reduced PA lipid incorporation and overall phospholipid saturation compared to PA-treated hepatocytes. These data indicate that OA's protective effects do not require increased conversion of PA into inert TGs, but instead may be due to OA's ability to compete against PA for cellular uptake and/or esterification and, thereby, normalize the composition of cellular lipids in the presence of a toxic PA load.
在包括肝细胞在内的多种细胞类型中进行的实验一致表明，饱和脂肪酸（如棕榈酸酯，PA）具有急性脂毒性作用，而不饱和脂肪酸（如油酸酯，OA）则没有。PA与OA联合处理可完全预防PA的脂毒性，其机制尚不完全清楚，但此前认为，当OA充足时，这是由于PA能更有效地酯化并封存到甘油三酯（TGs）中。然而，这一假设从未通过实验调节肝细胞中PA/OA在TGs和其他脂质代谢途径之间的相对分配来直接验证。在本研究中，我们发现，向经PA处理的肝细胞中添加OA可增强TG合成，减少总PA摄取和PA脂质掺入，降低磷脂饱和度，并挽救PA诱导的内质网应激和脂肪凋亡。敲低甘油二酯酰基转移酶（DGAT，TG合成的限速步骤）可显著减少TG积累，但不影响OA介导的对PA脂毒性的挽救作用。与经PA处理的肝细胞相比，在野生型和DGAT敲低的肝细胞中，OA联合处理均显著降低了PA脂质掺入和总体磷脂饱和度。这些数据表明，OA的保护作用并不需要将PA更多地转化为惰性TGs，而是可能归因于OA能够与PA竞争细胞摄取和/或酯化，从而在存在毒性PA负荷的情况下使细胞脂质组成正常化。
