Macrophage ABCA1 and ABCG1, but not SR-BI, promote macrophage reverse cholesterol transport in vivo

Macrophage ATP-binding cassette transporter A1 (ABCA1), scavenger receptor class B type I (SR-BI), and ABCG1 have been shown to promote cholesterol efflux to extracellular acceptors in vitro and influence atherosclerosis in mice, but their roles in mediating reverse cholesterol transport (RCT) from macrophages in vivo are unknown. Using an assay of macrophage RCT in mice, we found that primary macrophages lacking ABCA1 had a significant reduction in macrophage RCT in vivo, demonstrating the importance of ABCA1 in promoting macrophage RCT, however substantial residual RCT exists in the absence of macrophage ABCA1. Using primary macrophages deficient in SR-BI expression, we found that macrophage SR-BI, which was shown to promote cholesterol efflux in vitro, does not contribute to macrophage RCT in vivo. To investigate whether macrophage ABCG1 is involved in macrophage RCT in vivo, we used ABCG1-overexpressing, -knockdown, and -knockout macrophages. We show that increased macrophage ABCG1 expression significantly promoted while knockdown or knockout of macrophage ABCG1 expression significantly reduced macrophage RCT in vivo. Finally, we show that there was a greater decrease in macrophage RCT from cells where both ABCA1 and ABCG1 expression were knocked down than from ABCG1-knockdown cells. These results demonstrate that ABCA1 and ABCG1, but not SR-BI, promote macrophage RCT in vivo and are additive in their effects.     

Modulation of sphingosine-1-phosphate in ulcerative colitis

ABSTRACT

Introduction: Sphingosine-1-phosphate (S1P) is a membrane-derived lysophospholipid signaling molecule implicated in various physiological and pathological processes, such as regulation of the immune, cardiovascular, pulmonary, and nervous systems and theoretical cancer-related risks, through extracellular activation of S1P1-5 receptors.

Areas covered: S1P receptor agonism is a novel strategy for the treatment of UC targeting lymphocyte recirculation, through blockade of lymphocyte egress from lymph nodes. We conducted an extensive literature review on PUBMED on currently available data on molecular aspects of S1P modulation, the mechanisms of action of S1PR agonists (fingolimod, ozanimod, etrasimod, and KRP-203), and their potential efficacy and safety for the treatment of patients with ulcerative colitis.

Expert opinion: Selective S1P modulators have emerged to enlarge the efficacy and safety profile of this class of agents. Phase 3 programs should add the potential body of evidence to prove their benefit for the management of UC patients.     

Development of small-molecule inhibitors of sphingosine-1-phosphate signaling

The pleiotropic sphingolipid mediator, sphingosine-1-phosphate, produced in cells by two sphingosine kinase isoenzymes, SphK1 and SphK2, regulates many cellular and physiological processes important for homeostasis and development and pathophysiology. Many of the actions of S1P are mediated by a family of five specific cell surface receptors that are ubiquitously and specifically expressed, although important direct intracellular targets of S1P have also recently been identified. S1P, SphK1, and or S1P receptors have been linked to onset and progression of numerous diseases, including many types of cancer, and especially inflammatory disorders, such as multiple sclerosis, asthma, rheumatoid arthritis, inflammatory bowel disease, and sepsis. S1P formation and signaling are attractive targets for development of new therapeutics. The effects of a number of inhibitors of SphKs and S1PRs have been examined in animal models of human diseases. The effectiveness of the immunosuppressant FTY720 (known as Fingolimod or Gilenya), recently approved for the treatment of multiple sclerosis, whose actions are mediated by downregulation of S1PR1, has become the gold standard for S1P-centric drugs. Here, we review S1P biology and signaling with an emphasis on potential therapeutic benefits of specific interventions and discuss recent development of small molecule antagonists and agonists that target specific subtypes of S1P receptors as well as inhibitors of SphKs.     

Emerging biology of sphingosine-1-phosphate: its role in pathogenesis and therapy

Membrane sphingolipids are metabolized to sphingosine-1-phosphate (S1P), a bioactive lipid mediator that regulates many processes in vertebrate development, physiology, and pathology. Once exported out of cells by cell-specific transporters, chaperone-bound S1P is spatially compartmentalized in the circulatory system. Extracellular S1P interacts with five GPCRs that are widely expressed and transduce intracellular signals to regulate cellular behavior, such as migration, adhesion, survival, and proliferation. While many organ systems are affected, S1P signaling is essential for vascular development, neurogenesis, and lymphocyte trafficking. Recently, a pharmacological S1P receptor antagonist has won approval to control autoimmune neuroinflammation in multiple sclerosis. The availability of pharmacological tools as well as mouse genetic models has revealed several physiological actions of S1P and begun to shed light on its pathological roles. The unique mode of signaling of this lysophospholipid mediator is providing novel opportunities for therapeutic intervention, with possibilities to target not only GPCRs but also transporters, metabolic enzymes, and chaperones.     

Elevated sphingosine-1-phosphate promotes sickling and sickle cell disease progression

Sphingosine-1-phosphate (S1P) is a bioactive lipid that regulates multicellular functions through interactions with its receptors on cell surfaces. S1P is enriched and stored in erythrocytes; however, it is not clear whether alterations in S1P are involved in the prevalent and debilitating hemolytic disorder sickle cell disease (SCD). Here, using metabolomic screening, we found that S1P is highly elevated in the blood of mice and humans with SCD. In murine models of SCD, we demonstrated that elevated erythrocyte sphingosine kinase 1 (SPHK1) underlies sickling and disease progression by increasing S1P levels in the blood. Additionally, we observed elevated SPHK1 activity in erythrocytes and increased S1P in blood collected from patients with SCD and demonstrated a direct impact of elevated SPHK1-mediated production of S1P on sickling that was independent of S1P receptor activation in isolated erythrocytes. Together, our findings provide insights into erythrocyte pathophysiology, revealing that a SPHK1-mediated elevation of S1P contributes to sickling and promotes disease progression, and highlight potential therapeutic opportunities for SCD.     

鞘氨醇-1-磷酸在脓毒症中调节作用的研究进展

鞘氨醇-1-磷酸(sphingosine-1-phosphate,S1P)是具有多种生物活性的鞘磷脂代谢产物,通过激活细胞膜表面的G蛋白偶联受体即S1P受体(sphingosine-1-phosphate receptors,S1PRs),参与细胞生长和凋亡、免疫与凝血系统调节等多种生理功能。脓毒症是由于感染引起免疫反应失调所致的严重危及生命的疾病,常导致多器官功能障碍甚至衰竭。脓毒症导致的器官衰竭主要与内皮细胞和免疫细胞在炎症环境中的病理生理变化有关,包括血管通透性增加、血栓形成、炎症及免疫反应失调。S1P可参与调节脓毒症的多种病理生理过程,有望成为预测脓毒症患者病情严重程度的重要标志物,也是治疗脓毒症的潜在靶点。本文通过对S1P在脓毒症发生发展过程中的调节作用及相关临床研究进行总结,旨在为该领域的后续研究提供参考。     

Edg-1, the G protein-coupled receptor for sphingosine-1-phosphate, is essential for vascular maturation

Sphingolipid signaling pathways have been implicated in many critical cellular events. Sphingosine-1-phosphate (SPP), a sphingolipid metabolite found in high concentrations in platelets and blood, stimulates members of the endothelial differentiation gene (Edg) family of G protein-coupled receptors and triggers diverse effects, including cell growth, survival, migration, and morphogenesis. To determine the in vivo functions of the SPP/Edg signaling pathway, we disrupted the Edg1 gene in mice. Edg1(-/-) mice exhibited embryonic hemorrhage leading to intrauterine death between E12.5 and E14.5. Vasculogenesis and angiogenesis appeared normal in the mutant embryos. However, vascular maturation was incomplete due to a deficiency of vascular smooth muscle cells/pericytes. We also show that Edg-1 mediates an SPP-induced migration response that is defective in mutant cells due to an inability to activate the small GTPase, Rac. Our data reveal Edg-1 to be the first G protein-coupled receptor required for blood vessel formation and show that sphingolipid signaling is essential during mammalian development.     

Combined deficiency of ABCA1 and ABCG1 promotes foam cell accumulation and accelerates atherosclerosis in mice

HDLs protect against the development of atherosclerosis, but the underlying mechanisms are poorly understood. HDL and its apolipoproteins can promote cholesterol efflux from macrophage foam cells via the ATP-binding cassette transporters ABCA1 and ABCG1. Experiments addressing the individual roles of ABCA1 and ABCG1 in the development of atherosclerosis have produced mixed results, perhaps because of compensatory upregulation in the individual KO models. To clarify the role of transporter-mediated sterol efflux in this disease process, we transplanted BM from Abca1(-/-)Abcg1(-/-) mice into LDL receptor-deficient mice and administered a high-cholesterol diet. Compared with control and single-KO BM recipients, Abca1(-/-)Abcg1(-/-) BM recipients showed accelerated atherosclerosis and extensive infiltration of the myocardium and spleen with macrophage foam cells. In experiments with isolated macrophages, combined ABCA1 and ABCG1 deficiency resulted in impaired cholesterol efflux to HDL or apoA-1, profoundly decreased apoE secretion, and increased secretion of inflammatory cytokines and chemokines. In addition, these cells showed increased apoptosis when challenged with free cholesterol or oxidized LDL loading. These results suggest that the combined effects of ABCA1 and ABCG1 in mediating macrophage sterol efflux are central to the antiatherogenic properties of HDL.     

Enhanced sphingosine-1-phosphate receptor 2 expression underlies female CNS autoimmunity susceptibility

Multiple sclerosis (MS) is an inflammatory disease of the CNS that is characterized by BBB dysfunction and has a much higher incidence in females. Compared with other strains of mice, EAE in the SJL mouse strain models multiple features of MS, including an enhanced sensitivity of female mice to disease; however, the molecular mechanisms that underlie the sex- and strain-dependent differences in disease susceptibility have not been described. We identified sphingosine-1-phosphate receptor 2 (S1PR2) as a sex- and strain-specific, disease-modifying molecule that regulates BBB permeability by destabilizing adherens junctions. S1PR2 expression was increased in disease-susceptible regions of the CNS of both female SJL EAE mice and female patients with MS compared with their male counterparts. Pharmacological blockade or lack of S1PR2 signaling decreased EAE disease severity as the result of enhanced endothelial barrier function. Enhanced S1PR2 signaling in an in vitro BBB model altered adherens junction formation via activation of Rho/ROCK, CDC42, and caveolin endocytosis-dependent pathways, resulting in loss of apicobasal polarity and relocation of abluminal CXCL12 to vessel lumina. Furthermore, S1PR2-dependent BBB disruption and CXCL12 relocation were observed in vivo. These results identify a link between S1PR2 signaling and BBB polarity and implicate S1PR2 in sex-specific patterns of disease during CNS autoimmunity.     

Brain sphingosine-1-phosphate receptors: implication for FTY720 in the treatment of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune, neurological disability with unknown etiology. The current therapies available for MS work by an immunomodulatory action, preventing T-cell- and macrophage-mediated destruction of brain-resident oligodendrocytes and axonal loss. Recently, FTY720 (fingolimod) was shown to significantly reduce relapse rates in MS patients and is currently in Phase III clinical trials. This drug attenuates trafficking of harmful T cells entering the brain by regulating sphingosine-1-phosphate (S1P) receptors. Here, we outline the direct roles that S1P receptors play in the central nervous system (CNS) and discuss additional modalities by which FTY720 may provide direct neuroprotection in MS.     

高密度脂蛋白中的1-磷酸鞘氨醇对心肌细胞生存信号通路的影响

目的:观察高密度脂蛋白(HDL)不同组分中1-磷酸鞘氨醇(S1P)的含量对心肌细胞AKT和ERK1/2信号转导通路的影响,探讨HDL对心肌细胞的保护作用。方法:应用超速离心法和层析法,分离不同组分HDL;应用地高辛核素标记法检测各组分中S1P含量。给予小鼠心肌细胞不同S1P含量的HDL组分和S1P1、S1P3受体抑制剂VPC23019刺激后,用蛋白印迹法检测AKT和ERK1/2转导通路磷酸化水平的变化。结果 :与对照组比较,受不同HDL组分刺激后,成年小鼠心肌细胞AKT和ERK1/2磷酸化水平升高,且随着各组分中S1P含量升高,磷酸化水平呈上升趋势,而S1P1及S1P 3受体抑制剂VPC23019能明显阻断此种作用。结论:不同HDL组分通过细胞膜上的S1P受体,激活PI3K-AKT和MEK-ERK1/2信号通路,该作用通过S1P1和S1P3受体介导;HDL可能通过S1P发挥心肌保护作用。     

Cyclical modulation of sphingosine-1-phosphate receptor 1 surface expression during lymphocyte recirculation and relationship to lymphoid organ transit

Sphingosine-1-phosphate receptor 1 (S1P(1)) was recently shown to be required for lymphocyte egress from lymphoid organs. Here we have examined the relationship between S1P(1) abundance on the cell and egress efficiency. Using an integrin neutralization approach to separate the processes of entry and exit, we show that pertussis toxin treatment reduces lymphocyte egress from lymph nodes. Retrovirally mediated S1P(1) overexpression is sufficient to reduce B cell accumulation in the splenic white pulp and to promote egress of activated T cells from lymph nodes, whereas S1P(1)(+/-) cells have reduced lymph node exit efficiency. Furthermore, lymphocyte S1P(1) is down-regulated in the blood, up-regulated in lymphoid organs, and down-regulated again in the lymph. We propose that cyclical ligand-induced modulation of S1P(1) on circulating lymphocytes contributes to establishing their lymphoid organ transit time.     

Sphingosine-1-phosphate-induced airway hyper-reactivity in rodents is mediated by the sphingosine-1-phosphate type 3 receptor

There is a need to better understand the mechanism of airway hyper-reactivity, a key feature of asthma. Evidence suggests that sphingosine-1-phosphate (S1P) could be a major player in this phenomenon. The purpose of this work was to define the S1P receptor responsible for this phenomenon. We have studied, in the rat, the effect of two S1P synthetic receptor ligands, 2-amino-2-[2-(4-octylphenyl)ethyl]propane-1,3-diol (FTY720) (which in its phosphorylated form is a potent agonist at each S1P receptor except S1P(2)) and 3-[[2-[4-phenyl-3-(trifluoromethyl)phenyl]-1-benzothiophen-5-yl]methylamino]propanoic acid (AUY954) (a selective S1P(1) agonist) on lung function in vivo. This was complemented by in vitro studies using isolated trachea from the rat, the S1P(3) receptor-deficient mouse, and its wild-type counterpart. After oral administration, FTY720 induced a generalized airway hyper-reactivity to a range of contractile stimuli. This was observed as early as 1 h postdosing, lasted for at least 24 h, and was not subject to desensitization. In both rat and wild-type mouse isolated trachea, preincubation with the active phosphorylated metabolite of FTY720 induced hyper-responsiveness to 5-hydroxytryptamine. This effect was not seen in the isolated tracheas from S1P(3) receptor-deficient mice. AUY954, did not mimic the effect of FTY720 either in vivo or in vitro. Our data are consistent with activation of the S1P pathway inducing a generalized airway hyper-reactivity in rats and mice that is mediated by the S1P(3) receptor. S1P(3) receptor antagonists might prove to be useful as new therapeutic strategies aimed at blocking the airway hyper-reactivity observed in asthma.     

鞘氨醇-1-磷酸酯受体拮抗剂对抗肾小球基底膜肾炎的影响

目的观察鞘氨醇-1-磷酸酯受体拮抗剂720(sphingosine-1-phosphate receptor agonist 720,FTY720)对C57BL/6小鼠抗肾小球基底膜肾炎模型(Anti-GBM GN)的干预作用并对其作用机制进行探讨。方法选择健康雄性C57BL/6小鼠52只,给予兔IgG(500μg)加完全弗氏佐剂皮下注射进行预免疫,5d后从中随机抽取8只作为正常对照组,经尾静脉注射同剂量的非抗体性的正常兔血清,其余44只小鼠取灭活兔抗小鼠GBM抗血清0.3mL/20g经尾静脉注射。44只小鼠按随机化原则分组,FTY0.3mg/(kg·d)组(n=8)尾静脉注射6h后0.3mg/(kg·d)FTY720灌胃;FTY3mg/(kg·d)组(n=8)3mg/(kg·d)FTY720灌胃;FTY5mg/(kg·d)组(n=8)5mg/(kg·d)FTY720灌胃;FTY10mg/(kg·d)组(n=8)10mg/(kg·d)FTY720灌胃;Anti-GBM GN组(n=12)为模型组,同等剂量的无菌生理盐水灌胃。观察小鼠实验室指标及肾脏组织病理学改变情况。实时定量PCR检测小鼠脾脏鞘氨醇-1-磷酸脂(sphingosine-1-phosphate,S1P)受体S1P1～S1P5mRNA表达变化。流式细胞仪检测CD4+T细胞的凋亡情况。结果治疗组小鼠的尿蛋白、血肌酐、尿素氮和血胆固醇水平明显降低,血浆白蛋白明显增高;治疗组小鼠肾脏组织学病变明显减轻。与模型组相比,用药各组随着用药剂量增加S1P1、S1P2、S1P5的表达量逐渐减少,差异有显著性;S1P3、S1P4的表达量无明显变化,差异无显著性。流式细胞仪检测结果表明FTY720促进小鼠脾脏CD4+T细胞凋亡。结论 FTY720可能通过下调S1P1、S1P2、S1P5mRNA表达,促进CD4+T细胞凋亡,减轻抗肾小球基底膜肾炎模型的肾脏组织学改变,从而减少蛋白尿、稳定肾功能。     

The sphingosine-1-phosphate transporter Spns2 expressed on endothelial cells regulates lymphocyte trafficking in mice

The bioactive lysophospholipid mediator sphingosine-1-phosphate (S1P) promotes the egress of newly formed T cells from the thymus and the release of immature B cells from the bone marrow. It has remained unclear, however, where and how S1P is released. Here, we show that in mice, the S1P transporter spinster homolog 2 (Spns2) is responsible for the egress of mature T cells and immature B cells from the thymus and bone marrow, respectively. Global Spns2-KO mice exhibited marked accumulation of mature T cells in thymi and decreased numbers of peripheral T cells in blood and secondary lymphoid organs. Mature recirculating B cells were reduced in frequency in the bone marrow as well as in blood and secondary lymphoid organs. Bone marrow reconstitution studies revealed that Spns2 was not involved in S1P release from blood cells and suggested a role for Spns2 in other cells. Consistent with these data, endothelia-specific deletion of Spns2 resulted in defects of lymphocyte egress similar to those observed in the global Spns2-KO mice. These data suggest that Spns2 functions in ECs to establish the S1P gradient required for T and B cells to egress from their respective primary lymphoid organs. Furthermore, Spns2 could be a therapeutic target for a broad array of inflammatory and autoimmune diseases.     

Transactivation of sphingosine-1-phosphate receptors by FcepsilonRI triggering is required for normal mast cell degranulation and chemotaxis

Mast cells secrete various substances that initiate and perpetuate allergic responses. Cross-linking of the high-affinity receptor for IgE (FcepsilonRI) in RBL-2H3 and bone marrow-derived mast cells activates sphingosine kinase (SphK), which leads to generation and secretion of the potent sphingolipid mediator, sphingosine-1-phosphate (S1P). In turn, S1P activates its receptors S1P1 and S1P2 that are present in mast cells. Moreover, inhibition of SphK blocks FcepsilonRI-mediated internalization of these receptors and markedly reduces degranulation and chemotaxis. Although transactivation of S1P1 and Gi signaling are important for cytoskeletal rearrangements and migration of mast cells toward antigen, they are dispensable for FcepsilonRI-triggered degranulation. However, S1P2, whose expression is up-regulated by FcepsilonRI cross-linking, was required for degranulation and inhibited migration toward antigen. Together, our results suggest that activation of SphKs and consequently S1PRs by FcepsilonRI triggering plays a crucial role in mast cell functions and might be involved in the movement of mast cells to sites of inflammation.     

ABCA1: regulation,trafficking and association with heteromeric proteins

HDL metabolism is crucial in maintaining cellular cholesterol and phospholipid homeostasis and prevention of atherosclerosis progression. Recent work identified the ATP-binding cassette transporter A1 (ABCA1) as the major regulator of plasma high density lipoprotein (HDL) cholesterol responsible for the removal of excess cholesterol from peripheral cells and tissues. Here we discuss some novel aspects of the ABCA1 network: 1) the cellular pathways involved in cholesterol and phospholipid efflux, 2) regulation of ABCA1, 3) sulfonylurea receptor 1 (SUR1)- or cystic fibrosis transmembrane conductance regulator (CFTR)-like function of ABCA1, 4) interaction of the ABCA1 C-terminus with &#103 2-syntrophin, 5) ABCA1 modulation of the Rho GTPase Cdc42, 6) localization of ABCA1 in plasma membrane microdomains and intracellular sites, 7) differential effects of pre &#103 -HDL precursors on ABCA1 mediated &#102 -HDL particle formation and 8) ABCA1 in platelets and its relation to phosphatidylserine-flippase activity. A complex regulatory network and additional antiatherogenic features that may depend on the composition of pre &#103 -HDL precursor particles are believed to coordinate ABCA1 function in reverse cholesterol and phospholipid transport. Distinct pre &#103 -HDL ligand-specific receptor-clusters are involved that may modulate specific signaling pathways with varying outcomes related to pre &#103 -HDL particle composition, the cell-type and the cellular response status.     

ABCA1: regulation,trafficking and association with heteromeric proteins

HDL metabolism is crucial in maintaining cellular cholesterol and phospholipid homeostasis and prevention of atherosclerosis progression. Recent work identified the ATP-binding cassette transporter A1 (ABCA1) as the major regulator of plasma high density lipoprotein (HDL) cholesterol responsible for the removal of excess cholesterol from peripheral cells and tissues. Here we discuss some novel aspects of the ABCA1 network: 1) the cellular pathways involved in cholesterol and phospholipid efflux, 2) regulation of ABCA1, 3) sulfonylurea receptor 1 (SUR1)- or cystic fibrosis transmembrane conductance regulator (CFTR)-like function of ABCA1, 4) interaction of the ABCA1 C-terminus with beta2-syntrophin, 5) ABCA1 modulation of the Rho GTPase Cdc42, 6) localization of ABCA1 in plasma membrane microdomains and intracellular sites, 7) differential effects of prebeta-HDL precursors on ABCA1 mediated alpha-HDL particle formation and 8) ABCA1 in platelets and its relation to phosphatidylserine-flippase activity. A complex regulatory network and additional antiatherogenic features that may depend on the composition of prebeta-HDL precursor particles are believed to coordinate ABCA1 function in reverse cholesterol and phospholipid transport. Distinct prebeta-HDL ligand-specific receptor-clusters are involved that may modulate specific signaling pathways with varying outcomes related to prebeta-HDL particle composition, the cell-type and the cellular response status.     

联合使用1-磷酸鞘氨醇和溶血磷脂酸对小鼠卵母细胞体外成熟和受精后胚胎发育的影响

目的通过在成熟培养液中联合添加或单独添加1-磷酸鞘氨醇(S1P)和溶血磷脂酸(LPA)研究对小鼠卵母细胞体外成熟和受精后胚胎发育的影响,以期为优化人卵母细胞的体外成熟系统和提高体外胚胎发育率奠定实验基础。方法 (1)成熟培养液中单独添加50~2 000 nmol/L S1P或1~100μmol/L LPA,体外成熟后的卵母细胞体外受精,得到的胚胎观察并统计卵裂率、8-细胞率、囊胚率。(2)成熟培养液中联合添加不同浓度组合S1P和LPA,体外成熟后的卵母细胞体外受精,得到的胚胎观察并统计卵裂率、8-细胞率、囊胚率。(3)对各组体外成熟得到的卵母细胞进行免疫荧光法染色,以评估MⅡ期卵母细胞纺锤体的完整性。(4)对各组得到的数据应用卡方检验进行分析。结果添加100 nmol/L S1P组的成熟率(81.0%)和8-细胞率(81.9%)显著高于0 nmol/L和2 000 nmol/L组;添加30μmol/L LPA的成熟率(81.8%)和8-细胞率(81.5%)显著高于0μmol/L和100μmol/L组;500 nmol/L S1P+30μmol/L LPA组的成熟率(90.7%)显著高于100 nmol/L S1P组、30μmol/L LPA组合和不添加组;500 nmol/L S1P+30μmol/L LPA组的囊胚率(77.6%)显著高于100 nmol/L S1P组和不添加组。结论联合添加S1P和LPA可能要比单独添加更能促进小鼠卵母细胞成熟,虽然在正常纺锤体百分率方面没有显示出优势,但通过体外受精得到的胚胎得到了较高的囊胚发育率。