Structural insights into sphingosine-1-phosphate receptor activation

As a critical sphingolipid metabolite, sphingosine-1-phosphate (S1P) plays an essential role in immune and vascular systems. There are five S1P receptors, designated as S1PR1 to S1PR5, encoded in the human genome, and their activities are governed by endogenous S1P, lipid-like S1P mimics, or nonlipid-like therapeutic molecules. Among S1PRs, S1PR1 stands out due to its nonredundant functions, such as the egress of T and B cells from the thymus and secondary lymphoid tissues, making it a potential therapeutic target. However, the structural basis of S1PR1 activation and regulation by various agonists remains unclear. Here, we report four atomic resolution cryo-electron microscopy (cryo-EM) structures of Gi-coupled human S1PR1 complexes: bound to endogenous agonist d18:1 S1P, benchmark lipid-like S1P mimic phosphorylated Fingolimod [(S)-FTY720-P], or nonlipid-like therapeutic molecule CBP-307 in two binding modes. Our results revealed the similarities and differences of activation of S1PR1 through distinct ligands binding to the amphiphilic orthosteric pocket. We also proposed a two-step “shallow to deep” transition process of CBP-307 for S1PR1 activation. Both binding modes of CBP-307 could activate S1PR1, but from shallow to deep transition may trigger the rotation of the N-terminal helix of G_αi and further stabilize the complex by increasing the G_αi interaction with the cell membrane. We combine with extensive biochemical analysis and molecular dynamic simulations to suggest key steps of S1P binding and receptor activation. The above results decipher the common feature of the S1PR1 agonist recognition and activation mechanism and will firmly promote the development of therapeutics targeting S1PRs.

Sphingolipids, named after the sphinx in Egypt to represent its mysterious role, include sphingosine-1-phosphate (S1P), sphingosine, ceramide, and other complex sphingolipids, like glycosphingolipids and sphingomyelins (1–3). S1P, acting as a bioactive lipid mediator, is mainly derived from the deacylation of ceramide or interconverted with sphingosine and secreted by vascular endothelial cells to the circulation predominantly (4–7). Intracellular S1P promotes cellular proliferation (8) and close links to a myriad of essential cellular processes, including immune-cell trafficking (9), angiogenesis (10, 11), and vascular maturation (12). Plasma S1P helps maintain vascular integrity and regulate vascular leaks (13). Besides, S1P is identified as an early risk factor of lung cancer (14) and a crucial mediator of cardioprotection (15, 16). Thus, abnormal S1P production leads to the occurrence and progression of numerous severe diseases, such as metabolic syndrome, cancers, autoimmune disorders such as multiple sclerosis (MS), and kidney and cardiovascular diseases (7, 17–20).Currently, the therapeutic molecules targeting S1P receptors (S1PRs) can be divided into two classes: the lipid-like S1P mimics, such as (S)-FTY720-P (21), or the nonlipid-like molecules, such as clinical drugs BAF-312 (siponimod) (22), RPC-1063 (ozanimod) (23), and CBP-307, which is still in clinical trials (Fig. 1A). (S)-FTY720-P is the in vivo phosphorylated product of Fingolimod to treat relapsing MS (3, 24). Siponimod and ozanimod were also launched to treat relapsing MS or ulcerative colitis in recent years (25, 26). Despite the broad indications and urgent need, the development of therapeutics is primarily limited by the high sequence similarity of S1PRs and less-characterized functions of S1PR2 to S1PR5. The inactive structure of S1PR1 bound with an antagonist was reported in 2012 (27). Recently, the crystal structure of active S1PR3 bound to Fab and endogenous agonist S1P and active-state structures of S1PR1,3,5 bound to the G_i complex and different agonists were reported (28–30). Here, we report four atomic resolution cryo-electron microscopy (cryo-EM) structures of G_i-coupled human S1PR1 complexes bound to d18:1 S1P, (S)-FTY720-P, or CBP-307 in two binding modes. This structural information further supplements the binding details of different agonists and explores the activation mechanism of S1PR1, which will firmly promote the development of therapeutics targeting S1PRs.Open in a separate windowFig. 1.Cryo-EM maps and structures of human S1PR1 with G_i and agonist d18:1 S1P, (S)-FTY720-P, or CBP-307. (A) Structural formulas of three agonists: d18:1 S1P, (S)-FTY720-P, and CBP-307. (B) Cryo-EM maps of human S1PR1 with Gi and agonist d18:1 S1P, (S)-FTY720-P, or CBP-307. The densities of S1PR1, G_αi, G_β, G_γ, and scFv16 are shown in marine, pale green, pink, wheat, and gray, respectively. (C) Structural models of human S1PR1 with G_i, scFv16, and agonist d18:1 S1P (PDB ID code 7VIE), (S)-FTY720-P (PDB ID code 7VIF), or CBP-307 (PDB ID code 7VIG). S1PR1, G_αi, G_β, G_γ, and scFv16 are shown in marine, pale green, light blue, wheat, and gray, respectively. Ligands in density (yellow) are shown on the right side of the models. (D) The extracellular lid of S1PR1 is shown in the top and side views (surface and cartoon modes). N-helix, ECL1/2, and TM helices are pink, orange, and marine, respectively.     

Platelet-derived sphingosine-1-phosphate and inflammation: from basic mechanisms to clinical implications

Beyond key functions in hemostasis and thrombosis, platelets are recognized as key players of inflammation, an underlying feature of a variety of diseases. In this regard, platelets act as a circulating source of several pro- and anti-inflammatory molecules, which are secreted from their intracellular stores upon activation. Among them, mounting evidence highlights a crucial role of sphingosine-1-phosphate (S1P), a multifunctional sphingoid mediator. S1P-induced pleiotropic effects include those crucial in inflammatory processes, such as the maintenance of the endothelial barrier integrity, and leukocyte activation and recruitment at the injured site. This review outlines the peculiar features and molecular mechanisms that allow platelets for acting as a unique factory that produces and stores S1P in large quantities. A particular emphasis is placed on the autocrine and paracrine roles of S1P derived from the “inflamed” platelets, highlighting the role of its cross-talk with endothelial and blood cells involved in inflammation, and the mechanisms of its contribution to the development and progression of inflammatory diseases. Finally, potential clinical implications of platelet-derived S1P as diagnostic tool of inflammatory severity, and as therapeutic target in inflammation are discussed.     

心肌缺血预适应对单支动脉闭塞性急性心肌梗死患者的影响

目的 :观察心肌缺血预适应 （IPC）对急性心肌梗死 （AMI）患者并发症及预后的影响。方法 :对照分析 40例无 IPC的 AMI患者 （A组 ）和 5 0例有 IPC的 AMI患者 （B组 ）的近期临床资料。结果 :B组梗死后泵功能障碍发生率及程度、磷酸肌酸激酶 （CPK）峰值、并发症均显著低于 A组 ,近期预后有改善。结论 :缺血预适应组 CPK的峰值降低 ,梗死后所致心肌坏死面积减小 ,从而使泵功能障碍的发生率降低、梗死后室性心律失常、 度以上房室传导阻滞及再灌注性心律失常发生率减少。这可能是 IPC使 AMI患者死亡率降低的主要原因。     

1-磷酸鞘氨醇受体3在心血管系统中的作用

1-磷酸鞘氨醇受体是1-磷酸鞘氨醇在细胞内发挥作用的重要靶点,包括5种亚型,广泛存在于包括心血管系统在内的各系统。近年来,许多研究发现1-磷酸鞘氨醇受体3在血管舒张、血管屏障功能、缺血再灌注损伤和动脉粥样硬化等过程中具有重要的生物学作用。现就1-磷酸鞘氨醇受体3在心血管系统中的作用及其机制做一综述。     

抑制1-磷酸鞘氨醇裂解酶活性加重缺血性心力衰竭

目的:观察1-磷酸鞘氨醇(S1P)裂解酶(SPL)在小鼠缺血性心衰(HF)模型中的作用。方法:将60只成年雄性C57/BL6J小鼠随机分为以下4组:假手术(Sham)组、心肌梗死(MI)组、假手术+THI(Sham+THI)组[THI是SPL的抑制剂]及MI+THI组,每组15只(n=15),将25 mg/L THI溶于饮水中,于手术24 h后连续饲喂2周。MI4周后,采用ELISA试剂盒测定心肌中S1P的含量。根据心脏质量/体质量(HW/BW)评价心肌肥厚。用小动物心脏超声评估小鼠心脏结构和功能,经Masson三色染剂染色法观察心脏纤维化。用Western blot检测转化生长因子-β(TGF-β)蛋白的表达。实时PCR检测Ⅰ、Ⅲ型胶原、心房钠尿肽(ANP)、脑钠尿肽(BNP)和平滑肌肌动蛋白-α(α-SMA)mRNA的水平。结果:与MI组相比,MI+THI组小鼠心肌组织中S1P的含量增加(P0.01);左心室射血分数(LVEF)降低(P0.01),左心室收缩末期内径(LVESD)和舒张末期内径(LVEDD)均增加(均P0.05),HW/BW增加(P0.01),心脏纤维化加重;TGF-β蛋白的表达增加(P0.01);Ⅰ、Ⅲ型胶原、ANP、BNP和α-SMA mRNA的水平均显著增加(均P0.01)。与Sham组相比,Sham+THI组小鼠上述指标无显著差异。结论:抑制SPL的活性可能增加梗死后心肌病理性S1P信号的激活,加重MI后的心脏重构和HF。     

HDL and its sphingosine-1-phosphate content in cardioprotection

Increasing evidence suggests that High-density lipoproteins (HDL) are a direct cardioprotective agent in the setting of acute myocardial ischemia/reperfusion injury, and that this cardioprotection occurs independently of their atheroprotective effect. Studies on the involved mechanisms have revealed that the biologically active HDL-compound sphingosine-1-phosphate (S1P) is responsible for the beneficial effect of HDL on the myocardium. There appears to be an intricate interplay between known preconditioning agents and components of the S1P synthesis machinery in the heart, which makes S1P signalling an attractive downstream convergence point of preconditioning and cardioprotection at the level of its G protein-coupled receptors. While local S1P production has been known to protect the heart against ischemia/reperfusion injury and to mediate preconditioning, systemic S1P supply via HDL adds a novel aspect to the regulation of cardioprotection. Thus the S1P-content of HDL may serve both as a potential cardiovascular risk marker and a novel therapeutic target. Strategies for short-term “acute” HDL elevation as well as S1P analogues may prove beneficial not only in the high-risk patient but also in any patient at risk of myocardial ischemia.     

鞘氨醇-1-磷酸在支气管哮喘中作用的研究进展

鞘类脂质是一类广泛存在于各种真核细胞膜上的分子类物质.鞘脂类最初被认为是细胞膜的结构组成部分,随着研究的深入发现此类物质同时也是重要的信号分子.鞘氨醇-1-磷酸(sphingosine-1-phosphate,S1P)是鞘脂类的代谢产物,在细胞的变异、增殖、凋亡以及血管生成的过程中是重要的生物活性信号.S1P在支气管哮喘的发病机制中扮演了重要角色.近期研究表明在肥大细胞中鞘氨醇激酶的激活通过FcεRI信号通路使鞘氨醇转变为S1P,参与诱导了气道平滑肌的收缩和气道重塑.这些新发现的信号途径为支气管哮喘患者提供了潜在的治疗靶点.     

溃疡性结肠炎中信号转导和转录活化因子6的活化表达及作用

目的检测信号转导和转录活化因子6（STAT6）在溃疡性结肠炎（UC）中的表达，探讨其在UC发病中的作用机制。方法选择结肠镜诊断并经病理证实的UC患者30例，均为活动期患者，且未用激素及免疫抑制剂治疗。同时选择性别年龄相匹配的正常对照者30例。用Western印迹法分别检测标本核蛋白与胞质蛋白中磷酸化和非磷酸化STAT6的表达，同时用凝焦电泳迁移率改变分析法（EMSA）检测STAT6的DNA结合活性。结果Western印迹结果显示，在轻度UC患者，细胞核磷酸化STAT6表达低于细胞质，而在中、重度UC患者则胞核表达高于胞质。EMSA结果亦显示，UC组STAT6的DNA结合活性高于对照组，且随炎症程度加重而有逐渐增强的趋势。结论STAT6可能参与UC的发病过程并在UC的发病中起作用。     

阿托伐他汀在1-磷酸鞘氨醇诱导心肌细胞肥大中的作用

目的研究阿托伐他汀对1-磷酸鞘氨醇(S1P)诱导乳鼠心肌细胞肥大反应中的作用。方法原代培养乳鼠心肌细胞,测定心肌细胞体积和[3H]-亮氨酸掺入量作为心肌细胞肥大的指标。乳鼠心肌细胞使用不同浓度的阿托伐他汀(atorvastatin),加入S1P,[3H]-亮氨酸掺入量作为心肌细胞蛋白摄取量;分别用qPCR和Western blot法检测心肌细胞的β-肌球蛋白(β-MHC)的mRNA和蛋白质表达水平;用qPCR检测心肌细胞的心房利钠肽(ANF)的mRNA表达水平。结果与S1P组比较,阿托伐他汀10μmol/L处理组[3H]-亮氨酸掺入率减少[(234.89%±31.23%)比(342.23%±31.60%),P=0.205],β-MHC的mRNA和蛋白表达水平下降[(0.59±0.14)比(0.84±0.20),P=0.318]和[(0.55±0.09)比(0.98±0.15),P=0.223],ANF的mRNA表达水平降低[(0.51±0.13)比(0.76±0.19),P=0.445];与S1P组比较,阿托伐他汀20μmol/L处理组[3H]-亮氨酸掺入率明显减少[(189.07%±17.69%)比(342.23%±31.60%),P<0.01],β-MHC的mRNA和蛋白表达水平显著下降[(0.50±0.12)比(0.84±0.20),P<0.01]和[(0.35±0.08)比(0.98±0.15),P<0.01],ANF的mRNA水平明显降低[(0.47±0.12)比(0.76±0.19),P<0.01]。结论阿托伐他汀可抑制S1P诱导的心肌细胞肥大,并可减少S1P诱导的β-MHC和ANF表达。     

非心脏缺血预处理对未成熟心肌和心肌间质保护作用的研究

目的 :研究非心脏缺血预处理对未成熟心肌和心肌间质的保护作用。方法 :建立动物离体心脏 L angendorff灌注模型 ,分为 4组 :1缺血 /再灌注 （I/R,n=6 ） ,离体心灌注 15 min转为工作心 15 min;2心脏缺血预处理组 （IPC,n=6 ） ,离体灌注 15 min转为工作心 15 m in,缺血 5 m in/再灌 5 min各 2次 ;3双下肢缺血预处理组 （DL- IPC,n=6 ） ,反复 3次阻断双下肢血流 5 min/松开 5 m in,建立离体心脏 L angendorff灌注模型 ,灌注 15 min转为工作心 15min;4肾缺血预处理组 （K- IPC,n=6 ） ,反复 3次阻断左肾动脉 5 m in/放开 5 min,建立离体心脏 L angendorff灌注模型 ,灌注 15 min转为工作心 15 min。然后各组全心缺血 45 min,恢复灌注 15 m in改为工作心 30 m in。以左室功能恢复、心肌含水量、血清肌酸激酶 （CK）和乳酸脱氢酶 （L DH）漏出率、心肌组织 ATP和丙二醛 （MDA）含量、超氧化物歧化酶 （SOD）活性、心肌羟脯氨酸 （HP）含量及血清内皮素 （ET）含量作为观察指标。结果 :IPC,DL- IPC及 K-IPC组左室功能恢复优于 I/R组 （P<0 .0 5 ） ,ATP含量、SOD活性、HP含量均优于 I/R组 （P<0 .0 1） ,心肌含水量低于 I/R组 （P<0 .0 5 ） ,MDA含量 ,CK,L DH漏出率及 ET含量均低于 I/R组 （P<0 .0 1）。结论 :非心脏缺血预处理与心脏缺     

鞘氨醇-1-磷酸对心脏肥大的作用及对心脏微血管内皮细胞的影响

目的探讨鞘氨醇-1-磷酸(S1P)对心脏肥大(CH)的作用与对心脏微血管内皮细胞(CMECs)功能及血管新生的调控,及对磷脂酰肌醇3-激酶/蛋白激酶B/血管内皮生长因子(PI3K/AKT/VEGF)通路的影响。方法收集51例CH患者和65例正常志愿者外周血,及其死亡捐赠的左心室心肌组织,采用免疫组织化学法(IHC)检测两组心肌组织S1P含量,酶联免疫吸附测定法(ELISA)检测外周血S1P、人二氢-S1P(DH-S1P)和血管内皮生长因子(VEGF)的含量。采用免疫荧光法(IF)分别对两组心肌组织进行S1P和分化簇31(CD31)、S1P和Alpha-平滑肌肌动蛋白(α-SMA)共定位染色。采用免疫印迹法(WB)检测心肌组织S1P、S1P受体1-3(S1PR1-3)、α-SMA、CD31及PI3K/AKT通路的变化。分离培养原代CMECs,将第3代CMECs接种于12孔板中,建立肥大CMECs模型,分为两组:去氧肾上腺素(PE)组和PE+S1P(OE)组,每组6孔。OE组转染1μg的PDEST42-S1P-V5质粒24 h,IF对细胞进行染色。结果CH患者心肌组织S1P和血清S1P、DH-S1P和VEGF含量显著低于正常志愿者(t=6.994、7.822、5.982、9.811,P<0.05),且血清VEGF和S1P含量呈显著正相关性(r=0.427,P>0.01)。相比于正常志愿者,CH患者心肌组织CD31+S1P+双阳性共定位细胞占CD31阳性细胞比例显著降低(t=18.214,P<0.05);α-SMA+S1P+双阳性共定位细胞占α-SMA阳性细胞比例也显著降低(t=12.451,P<0.05)。与正常志愿者相比,CH患者心肌组织S1P、S1PR3、CD31和α-SMA蛋白含量明显降低(t=4.254、4.492、15.803、9.941,P<0.05),S1PR2含量明显增高(t=6.828,P<0.05),S1PR1含量无明显变化,差异无统计学意义(P>0.05)。CH患者心脏组织p-PI3K、p-AKT和p-eNOS蛋白表达量明显低于正常志愿者(t=12.340、15.597、8.624,P<0.05)。相比于PE组,OE组中S1P和α-SMA双阳性共定位细胞占α-SMA阳性细胞比例显著增加,细胞培养上清中S1P和VEGF蛋白水平显著增加(t=6.894、5.213,P<0.05)。结论低水平的S1P可能通过抑制CMECs血管新生和间充质转换,及下调PI3K/AKT/eNOS通路在CH的发生发展中发挥重要作用。