Deevska Gergana M, Dotson Patrick P, Karakashian Alexander A, Isaac Giorgis, Wrona Mark, Kelly Samuel B, Merrill Alfred H, Nikolova-Karakashian Mariana N
From the Department of Physiology, University of Kentucky, Lexington, Kentucky 40536.
Pharmaceutical Discovery and Life Sciences, Waters Corporation, Milford, Massachusetts 01757, and.
J Biol Chem. 2017 Mar 24;292(12):5110-5122. doi: 10.1074/jbc.M116.751602. Epub 2017 Jan 13.
This study investigates the consequences of elevating sphingomyelin synthase 1 (SMS1) activity, which generates the main mammalian sphingolipid, sphingomyelin. HepG2 cells stably transfected with SMS1 (HepG2-SMS1) exhibit elevated enzyme activity and increased sphingomyelin content (mainly C22:0- and C24:0-sphingomyelin) but lower hexosylceramide (Hex-Cer) levels. HepG2-SMS1 cells have fewer triacylglycerols than controls but similar diacylglycerol acyltransferase activity, triacylglycerol secretion, and mitochondrial function. Treatment with 1 mm palmitate increases ceramide synthesis in both cell lines to a similar degree, causing accumulation of C16:0-ceramide (and some C18:0-, C20:0-, and C22:0-ceramides) as well as C16:0- and C18:0-Hex-Cers. In these experiments, the palmitic acid is delivered as a complex with delipidated BSA (2:1, mol/mol) and does not induce significant lipotoxicity. Based on precursor labeling, the flux through SM synthase also increases, which is exacerbated in HepG2-SMS1 cells. In contrast, palmitate-induced lipid droplet formation is significantly reduced in HepG2-SMS1 cells. [C]Choline and [H]palmitate tracking shows that SMS1 overexpression apparently affects the partitioning of palmitate-enriched diacylglycerol between the phosphatidylcholine and triacylglycerol pathways, to the benefit of the former. Furthermore, triacylglycerols from HepG2-SMS1 cells are enriched in polyunsaturated fatty acids, which is indicative of active remodeling. Together, these results delineate novel metabolic interactions between glycerolipids and sphingolipids.
本研究调查了提高鞘磷脂合酶1（SMS1）活性的后果，该酶可生成主要的哺乳动物鞘脂——鞘磷脂。稳定转染SMS1的HepG2细胞（HepG2-SMS1）表现出酶活性升高和鞘磷脂含量增加（主要是C22:0-和C24:0-鞘磷脂），但己糖神经酰胺（Hex-Cer）水平较低。HepG2-SMS1细胞的三酰甘油比对照细胞少，但二酰甘油酰基转移酶活性、三酰甘油分泌和线粒体功能相似。用1 mM棕榈酸处理可使两种细胞系中的神经酰胺合成增加到相似程度，导致C16:0-神经酰胺（以及一些C18:0-、C20:0-和C22:0-神经酰胺）以及C16:0-和C18:0-Hex-Cers积累。在这些实验中，棕榈酸以与脱脂牛血清白蛋白的复合物形式（2:1，摩尔/摩尔）递送，不会诱导明显的脂毒性。基于前体标记，通过SM合酶的通量也增加，在HepG2-SMS1细胞中这种增加更为明显。相比之下，HepG2-SMS1细胞中棕榈酸诱导的脂滴形成显著减少。[C]胆碱和[H]棕榈酸追踪显示，SMS1过表达明显影响富含棕榈酸的二酰甘油在磷脂酰胆碱和三酰甘油途径之间的分配，有利于前者。此外，HepG2-SMS1细胞的三酰甘油富含多不饱和脂肪酸，这表明存在活跃的重塑过程。总之，这些结果描绘了甘油脂和鞘脂之间新的代谢相互作用。
