Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29403, USA.
J Biol Chem. 2013 May 10;288(19):13397-409. doi: 10.1074/jbc.M112.428185. Epub 2013 Mar 25.
Myristate is a novel potential substrate for sphingoid base synthesis.
Myocardial sphingoid base synthesis utilizes myristate; these sphingolipids are functionally non-redundant with canonical sphingoid bases.
d16:0 and d16:1 sphingolipids constitute an appreciable proportion of cardiac dihydrosphingosine and dihydroceramide, with distinct biological roles.
This pool of sphingolipids may play a heretofore unsuspected role in myocardial pathology or protection. The enzyme serine palmitoyltransferase (SPT) catalyzes the formation of the sphingoid base "backbone" from which all sphingolipids are derived. Previous studies have shown that inhibition of SPT ameliorates pathological cardiac outcomes in models of lipid overload, but the metabolites responsible for these phenotypes remain unidentified. Recent in vitro studies have shown that incorporation of the novel subunit SPTLC3 broadens the substrate specificity of SPT, allowing utilization of myristoyl-coenzyme A (CoA) in addition to its canonical substrate palmitoyl-CoA. However, the relevance of these findings in vivo has yet to be determined. The present study sought to determine whether myristate-derived d16 sphingolipids are represented among myocardial sphingolipids and, if so, whether their function and metabolic routes were distinct from those of palmitate-derived d18 sphingolipids. Data showed that d16:0 sphingoid bases occurred in more than one-third of total dihydrosphingosine and dihydroceramides in myocardium, and a diet high in saturated fat promoted their de novo production. Intriguingly, d16-ceramides demonstrated highly limited N-acyl chain diversity, and in vitro enzyme activity assays showed that these bases were utilized preferentially to canonical bases by CerS1. Functional differences between myristate- and palmitate-derived sphingolipids were observed in that, unlike d18 sphingolipids and SPTLC2, d16 sphingolipids and SPTLC3 did not appear to contribute to myristate-induced autophagy, whereas only d16 sphingolipids promoted cell death and cleavage of poly(ADP-ribose) polymerase in cardiomyocytes. Thus, these results reveal a previously unappreciated component of cardiac sphingolipids with functional differences from canonical sphingolipids.
豆蔻酸是一种新型潜在的神经酰胺合成底物。
心肌鞘氨醇碱基合成利用豆蔻酸；这些鞘脂与典型鞘氨醇碱基在功能上并非冗余。
d16:0 和 d16:1 鞘脂构成了心脏二氢鞘氨醇和二氢神经酰胺的可观比例，具有独特的生物学作用。
这一池鞘脂可能在心肌病理或保护中发挥了迄今未被察觉的作用。丝氨酸棕榈酰转移酶（SPT）酶催化鞘氨醇碱基“骨干”的形成，所有鞘脂都由此衍生。先前的研究表明，SPT 的抑制可改善脂质过载模型中的病理性心脏结局，但负责这些表型的代谢物仍未确定。最近的体外研究表明，新型亚基 SPTLC3 的掺入拓宽了 SPT 的底物特异性，允许除其典型底物棕榈酰-CoA 之外，还利用豆蔻酰-CoA。然而，这些发现在体内的相关性尚未确定。本研究旨在确定豆蔻酰基衍生的 d16 鞘脂是否存在于心肌鞘脂中，如果存在，其功能和代谢途径是否与棕榈酰基衍生的 d18 鞘脂不同。研究数据表明，d16:0 鞘氨醇碱基存在于心肌中二氢鞘氨醇和二氢神经酰胺的三分之一以上，并且富含饱和脂肪的饮食促进了它们的从头合成。有趣的是，d16-神经酰胺表现出高度受限的 N-酰基链多样性，体外酶活性测定表明，这些碱基优先被 CerS1 利用而不是典型碱基。与 d18 鞘脂和 SPTLC2 不同，豆蔻酰基衍生的鞘脂和 SPTLC3 似乎不参与豆蔻酸诱导的自噬，而只有 d16 鞘脂促进心肌细胞中的细胞死亡和聚（ADP-核糖）聚合酶的裂解，观察到豆蔻酸和棕榈酸衍生的鞘脂之间存在功能差异。因此，这些结果揭示了心脏鞘脂的一个以前未被重视的组成部分，与典型鞘脂具有功能差异。
