BACKGROUND:Dysregulated metabolism of bioactive sphingolipids, including ceramides and sphingosine-1-phosphate, has been implicated in cardiovascular disease, although the specific species, disease contexts, and cellular roles are not completely understood. Sphingolipids are produced by the serine palmitoyltransferase enzyme, canonically composed of 2 subunits, SPTLC1 (serine palmitoyltransferase long chain base subunit 1) and SPTLC2 (serine palmitoyltransferase long chain base subunit 2). Noncanonical sphingolipids are produced by a more recently described subunit, SPTLC3 (serine palmitoyltransferase long chain base subunit 3).METHODS:The noncanonical (d16) and canonical (d18) sphingolipidome profiles in cardiac tissues of patients with end-stage ischemic cardiomyopathy and in mice with ischemic cardiomyopathy were analyzed by targeted lipidomics. Regulation of SPTLC3 by HIF1α under ischemic conditions was determined with chromatin immunoprecipitation. Transcriptomics, lipidomics, metabolomics, echocardiography, mitochondrial electron transport chain, mitochondrial membrane fluidity, and mitochondrial membrane potential were assessed in the cSPTLC3^KO transgenic mice we generated. Furthermore, morphological and functional studies were performed on cSPTLC3^KO mice subjected to permanent nonreperfused myocardial infarction.RESULTS:Herein, we report that SPTLC3 is induced in both human and mouse models of ischemic cardiomyopathy and leads to production of atypical sphingolipids bearing 16-carbon sphingoid bases, resulting in broad changes in cell sphingolipid composition. This induction is in part attributable to transcriptional regulation by HIF1α under ischemic conditions. Furthermore, cardiomyocyte-specific depletion of SPTLC3 in mice attenuates oxidative stress, fibrosis, and hypertrophy in chronic ischemia, and mice demonstrate improved cardiac function and increased survival along with increased ketone and glucose substrate metabolism utilization. Depletion of SPTLC3 mechanistically alters the membrane environment and subunit composition of mitochondrial complex I of the electron transport chain, decreasing its activity.CONCLUSIONS:Our findings suggest a novel essential role for SPTLC3 in electron transport chain function and a contribution to ischemic injury by regulating complex I activity.

中文翻译：

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SPTLC3 对于复合物 I 活性至关重要，并导致缺血性心肌病

背景：生物活性鞘脂（包括神经酰胺和 1-磷酸鞘氨醇）的代谢失调与心血管疾病有关，尽管具体物种、疾病背景和细胞作用尚不完全清楚。鞘脂由丝氨酸棕榈酰转移酶产生，通常由 2 个亚基组成：SPTLC1（丝氨酸棕榈酰转移酶长链碱基亚基 1）和 SPTLC2（丝氨酸棕榈酰转移酶长链碱基亚基 2）。非典型鞘脂由最近描述的亚基 SPTLC3（丝氨酸棕榈酰转移酶长链碱基亚基 3）产生。方法：终末期缺血性心肌病患者和小鼠心脏组织中的非典型 (d16) 和典型 (d18) 鞘脂组谱通过靶向脂质组学分析缺血性心肌病。通过染色质免疫沉淀测定缺血条件下 HIF1α 对 SPTLC3 的调节。在我们生成的cSPTLC3 ^KO转基因小鼠中评估了转录组学、脂质组学、代谢组学、超声心动图、线粒体电子传递链、线粒体膜流动性和线粒体膜电位。此外，我们对遭受永久性非再灌注心肌梗死的 cSPTLC3 ^KO小鼠进行了形态学和功能研究。 结果：在此，我们报告 SPTLC3 在人类和小鼠缺血性心肌病模型中均被诱导，并导致产生带有 16 碳鞘氨醇的非典型鞘脂碱基，导致细胞鞘脂成分发生广泛变化。这种诱导部分归因于缺血条件下 HIF1α 的转录调节。此外，小鼠心肌细胞特异性去除 SPTLC3 可减轻慢性缺血中的氧化应激、纤维化和肥大，并且小鼠的心脏功能得到改善，存活率增加，酮和葡萄糖底物代谢利用率也增加。 SPTLC3 的耗尽会机械地改变电子传递链线粒体复合物 I 的膜环境和亚基组成，从而降低其活性。结论：我们的研究结果表明 SPTLC3 在电子传递链功能中具有新的重要作用，并通过调节复合物对缺血性损伤做出贡献我活动。