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

Sphingosine-1-phosphate Attenuates Endoplasmic Reticulum Stress-induced Cardiomyocyte Apoptosis Through Sphingosine-1-phosphate Receptor 1

BACKGROUND

Endoplasmic reticulum stress (ER stress) is involved in the development and progression of various forms of heart disease and may lead to myocardial apoptosis. Sphingosine-1-phosphate (S1P) possesses cardioprotective properties, including anti-apoptosis. However, little is known about the link between S1P and ER stress-induced myocardial apoptosis. This study investigated the regulatory role of S1P in ER stress-induced apoptosis in cardiomyocytes.

METHODS

ER stress and myocardial apoptosis were induced by transverse aortic constriction (TAC) or tunicamycin in mice, which were then treated with 2-acetyl-5-tetrahydroxybutyl imidazole (THI) or S1P. AC16 cells were treated with tunicamycin or thapsigargin, or pretreated with S1P, sphingosine-1-phosphate receptor (S1PR) subtype antagonists, S1PR1 agonist, and PI3K and MEK inhibitors. Cardiac function, the level of S1P in plasma and heart, ER stress markers, cell viability, and apoptosis were detected.

RESULTS

S1P reduced the expression of ER stress-related molecules and ER stress-induced myocardial apoptosis in mice subjected to TAC or an injection of tunicamycin. Furthermore, in AC16 cells exposed to thapsigargin or tunicamycin, S1P decreased the expression of ER stress-related molecules, promoting cell viability and survival. Nevertheless, the S1PR1 antagonist abrogated the protection of S1P. Subsequently, in TAC S1PR1 heterozygous (S1PR1^+/-) mice, S1P had no effect on ER stress and apoptosis in cardiomyocytes. Notably, in vitro, the impact of anti-ER stress-induced myocardial apoptosis by the S1PR1 agonist was reversed by PI3K and MEK inhibitors.

CONCLUSION

This study is the first to demonstrate that S1P relieves ER stress-induced myocardial apoptosis via S1PR1/AKT and S1PR1/ERK1/2, which are potential therapeutic targets for heart disease.

Mfsd2b and Spns2 are essential for maintenance of blood vessels during development and in anaphylactic shock

Sphingosine-1-phosphate (S1P) is a potent lipid mediator that is secreted by several cell types. We recently showed that Mfsd2b is an S1P transporter from hematopoietic cells that contributes approximately 50% plasma S1P. Here we report the characterization of compound deletion of Mfsd2b and Spns2, another S1P transporter active primarily in endothelial cells. Global deletion of Mfsd2b and Spns2 (global double knockout [gDKO]) results in embryonic lethality beyond embryonic day 14.5 (E14.5), with severe hemorrhage accompanied by defects of tight junction proteins, indicating that Mfsd2b and Spns2 provide S1P for signaling, which is essential for blood vessel integrity. Compound postnatal deletion of Mfsd2b and Spns2 using Mx1Cre (ctDKO-Mx1Cre) results in maximal 80% reduction of plasma S1P. ctDKO-Mx1Cre mice exhibit severe susceptibility to anaphylaxis, indicating that S1P from Mfsd2b and Spns2 is indispensable for vascular homeostasis. Our results show that S1P export from Mfsd2b and Spns2 is essential for developing and mature vasculature.

Sphingosine-1-phosphate receptor modulators in stroke treatment

Sphingosine-1-phosphate (S1P) is a bioactive lysophospholipid that can influence a broad range of biological processes through its binding to five distinct G protein-coupled receptors. S1P receptor modulators are a new group of immunosuppressive agents currently used in the immunotherapy of multiple sclerosis. Inflammation following stroke may exacerbate injury. Given that S1P signaling is linked to multiple immune processes, therapies targeting the S1P axis may be suitable for treating stroke. In this review, we outline S1P metabolism and S1P receptors, discuss the mechanisms of action of S1P receptor modulators in lymphocyte migration and their direct action on cells of the central nervous system, and provide a concise summary of the efficacy of S1P receptor modulators in animal studies and clinical trials on treatments for stroke.

Lymphatic endothelial sphingosine 1-phosphate receptor 1 enhances macrophage clearance via lymphatic system following myocardial infarction

Lymphatic endothelial cell homeostasis plays important roles in normal physiological cardiac functions, and its dysfunction significantly influences pathological cardiac remodeling after myocardial infarction (MI). Our results revealed that sphingosine 1-phosphate receptor 1 (S1pr1) expression in cardiac lymphatic endothelial cells (LECs) was sharply changed after MI. It has been shown that S1pr1 tightly controlled LEC functions and homeostasis. We thus hypothesized that lymphatic endothelial S1pr1 might be involved in post-MI cardiac remodeling. We generated LEC-conditional S1pr1 transgenic mice, in which S1pr1 expression was reduced in cardiac LECs. We performed the left anterior descending coronary artery (LAD) ligation operation to induce MI in these mice. Cardiac functions and remodeling were examined by echocardiography analysis and serial histological analysis. Meanwhile, we performed adoptive cell transfer experiments to monitor macrophage trafficking in post-MI myocardium and their draining lymphatic system. Furthermore, in vitro cell culture experiments and mechanism studies were undertaken to uncover the molecular mechanism by which LEC-S1pr1 regulated cardiac inflammation and remodeling after MI. Our results showed that S1pr1 expression significantly decreased in cardiac LECs after MI. Our in vivo experiments showed that the reduced expression of LEC-S1pr1 deteriorated cardiac function and worsened pathological cardiac remodeling after MI. Our further results demonstrated that the reduced expression of LEC-S1pr1 did not influence macrophage infiltration in an early inflammatory phase of MI, but significantly affected macrophages clearance in the later phase of MI via afferent cardiac lymphatics, and thus influenced inflammatory responses and cardiac outcome after MI. Further study showed that S1P/S1pr1 activated ERK signaling pathway and enhanced CCL2 expression, which promoted macrophage trafficking in a paracrine manner. This study reveals that cardiac lymphatic endothelial cells tightly control macrophage trafficking via lymphatic vessels in injured hearts via S1P/S1pr1/ERK/CCL2 pathway and thus regulate post-MI immune modulation and heart repair. This study highlights the importance of cardiac lymphatic vessel system in orchestrating post-MI immune responses and cardiac remodeling by regulating macrophage transit in injured hearts. Our finding implies that a feasible modulation of S1pr1 signaling in LECs might provide a promising target to resolve excessive inflammation and to ameliorate adverse cardiac remodeling after MI.

Protective and therapeutic potentials of HDL and ApoA1 in COVID-19 elderly and chronic illness patients

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for coronavirus disease-2019 (COVID-19). Elderly subjects, obese, and patients with chronic illnesses, are the most affected group. HDL has pleiotropic physiological functions that are affected with alteration(s) in its structure.

MAIN TEXT

Inflammation whether septic, immune, or other affects HDL structure and function. COVID-19 is associated with systemic immune-inflammation due to cytokine surge. Viral interaction with erythrocytes and hemoglobin-related compounds (may cause anemia and hypoxia) and other factors may affect HDL function. Trials have been conducted to resume HDL functions using peptide preparation, nutritional, and herbal elements.

CONCLUSIONS

In this review article, I'll discuss the use of reconstituted HDL (rHDL), Apo-A1 mimetic peptide D-4F, ω-3 polyunsaturated fatty acids, and the powdered roots and/or extract of Saussurea lappa (costus) to avoid comorbidity and mortality of COVID-19 in patients with chronic illness or elderly-age mortality.

Fight the Cancer, Hit the CAF!

Simple Summary

In the last 20 years, the tumor microenvironment (TME) has raised an increasing interest from the therapeutic point of view. Indeed, different strategies targeting either the endothelial or the immune component have been implemented. Furthermore, cancer-associated fibroblasts (CAF) have attracted even more interest due to their ability to prime the TME in order to favor tumor progression and metastasis. This current review provides a comprehensive overview on the latest discoveries regarding CAF, more specifically on their complex characterization and on preclinical studies and clinical trials that target CAF within the TME.

Abstract

The tumor microenvironment (TME) is comprised of different cellular components, such as immune and stromal cells, which co-operate in unison to promote tumor progression and metastasis. In the last decade, there has been an increasing focus on one specific component of the TME, the stromal component, often referred to as Cancer-Associated Fibroblasts (CAF). CAF modulate the immune response and alter the composition of the extracellular matrix with a decisive impact on the response to immunotherapies and conventional chemotherapy. The most recent publications based on single-cell analysis have underlined CAF heterogeneity and the unique plasticity that strongly impact the TME. In this review, we focus not only on the characterization of CAF based on the most recent findings, but also on their impact on the immune system. We also discuss clinical trials and preclinical studies where targeting CAF revealed controversial results. Therefore, future efforts should focus on understanding the functional properties of individual subtypes of CAF, taking into consideration the peculiarities of each pathological context.

Endothelial S1pr2 regulates post-ischemic angiogenesis via AKT/eNOS signaling pathway

Aims: It is important to understand the mechanism that regulates post-ischemic angiogenesis and to explore a new therapeutic target for an effective improvement of revascularization in peripheral artery disease (PAD) patients. Post-ischemic angiogenesis is a highly orchestrated process, which involves vascular endothelial cells (ECs) proliferation, migration and assembly into capillaries. We found a significant reduction of S1pr2 (sphingosine 1-phosphate receptor 2) in endothelial cells after hindlimb ischemia (HLI). We thus hypothesized that EC-S1pr2 might be involved in the regulation of post-ischemic angiogenesis and blood flow recovery during peripheral arterial disease (PAD). Methods and Results: We generated both EC-specific S1pr2 loss-of-function and S1pr2 gain-of-function mice. Our study showed that EC-specific S1pr2 loss-of-function significantly enhanced post-ischemic angiogenesis and improved blood flow recovery upon femoral artery ligation, whereas the EC-specific S1pr2 gain-of-function severely hindered post-ischemic angiogenesis and reduced blood flow recovery in ischemic limbs. We next identified that S1pr2 inhibited AKT/eNOS signaling pathway, and thus inhibited EC proliferation/migration and angiogenic activity. As expected, pharmacological inhibition of S1pr2 by JTE013 improved post-ischemic angiogenesis and improved blood flow perfusion after femoral artery ligation. Moreover, we developed RGD-peptide magnetic nanoparticles packaging S1pr2-siRNA which specifically targeted ECs and achieved an efficient silencing of S1pr2 expression in ECs in vivo. This EC-targeted strategy to dampen S1pr2 significantly enhanced post-ischemic angiogenesis and boosted blood perfusion after HLI, supplying a novel therapy target for patients with peripheral arterial disease. Conclusions: This present study demonstrates that EC-expressing S1pr2 tightly controls post-ischemic angiogenesis and blood flow perfusion recovery. This research provides a novel strategy for EC-target knockdown of S1pr2 as a new therapeutic intervention for patients with peripheral artery disease.

DOCK4 Regulation of Rho GTPases Mediates Pulmonary Vascular Barrier Function

BACKGROUND

The vascular endothelium maintains tissue-fluid homeostasis by controlling the passage of large molecules and fluid between the blood and interstitial space. The interaction of catenins and the actin cytoskeleton with VE-cadherin (vascular endothelial cadherin) is the primary mechanism for stabilizing AJs (adherens junctions), thereby preventing lung vascular barrier disruption. Members of the Rho (Ras homology) family of GTPases and conventional GEFs (guanine exchange factors) of these GTPases have been demonstrated to play important roles in regulating endothelial permeability. Here, we evaluated the role of DOCK4 (dedicator of cytokinesis 4)-an unconventional Rho family GTPase GEF in vascular function.

METHODS

We generated mice deficient in DOCK4' used DOCK4 silencing and reconstitution approaches in human pulmonary artery endothelial cells' used assays to evaluate protein localization, endothelial cell permeability, and small GTPase activation.

RESULTS

Our data show that DOCK4-deficient mice are viable. However, these mice have hemorrhage selectively in the lung, incomplete smooth muscle cell coverage in pulmonary vessels, increased basal microvascular permeability, and impaired response to S1P (sphingosine-1-phosphate)-induced reversal of thrombin-induced permeability. Consistent with this, DOCK4 rapidly translocates to the cell periphery and associates with the detergent-insoluble fraction following S1P treatment, and its absence prevents S1P-induced Rac-1 activation and enhancement of barrier function. Moreover, DOCK4-silenced pulmonary artery endothelial cells exhibit enhanced basal permeability in vitro that is associated with enhanced Rho GTPase activation.

CONCLUSIONS

Our findings indicate that DOCK4 maintains AJs necessary for lung vascular barrier function by establishing the normal balance between RhoA (Ras homolog family member A) and Rac-1-mediated actin cytoskeleton remodeling, a previously unappreciated function for the atypical GEF family of molecules. Our studies also identify S1P as a potential upstream regulator of DOCK4 activity.

Role of Sphingolipids in Multiple Myeloma Progression, Drug Resistance, and Their Potential as Therapeutic Targets

Multiple myeloma (MM) is an incapacitating hematological malignancy characterized by accumulation of cancerous plasma cells in the bone marrow (BM) and production of an abnormal monoclonal protein (M-protein). The BM microenvironment has a key role in myeloma development by facilitating the growth of the aberrant plasma cells, which eventually interfere with the homeostasis of the bone cells, exacerbating osteolysis and inhibiting osteoblast differentiation. Recent recognition that metabolic reprograming has a major role in tumor growth and adaptation to specific changes in the microenvironmental niche have led to consideration of the role of sphingolipids and the enzymes that control their biosynthesis and degradation as critical mediators of cancer since these bioactive lipids have been directly linked to the control of cell growth, proliferation, and apoptosis, among other cellular functions. In this review, we present the recent progress of the research investigating the biological implications of sphingolipid metabolism alterations in the regulation of myeloma development and its progression from the pre-malignant stage and discuss the roles of sphingolipids in in MM migration and adhesion, survival and proliferation, as well as angiogenesis and invasion. We introduce the current knowledge regarding the role of sphingolipids as mediators of the immune response and drug-resistance in MM and tackle the new developments suggesting the manipulation of the sphingolipid network as a novel therapeutic direction for MM.

E-Selectin/AAV2/2 Gene Therapy Alters Angiogenesis and Inflammatory Gene Profiles in Mouse Gangrene Model

For patients with chronic limb-threatening ischemia and limited revascularization options, alternate means for therapeutic angiogenesis and limb salvage are needed. E-selectin is a cell adhesion molecule that is critical for inflammation and neovascularization in areas of wound healing and ischemia. Here, we tested the efficacy of modifying ischemic limb tissue by intramuscular administration of E-selectin/AAV2/2 (adeno-associated virus serotype 2/2) to modulate angiogenic and inflammatory responses in a murine hindlimb gangrene model. Limb appearance, reperfusion, and functional recovery were assessed for 3 weeks after induction of ischemia. Mice receiving E-selectin/AAV2/2 gene therapy had reduced gangrene severity, increased limb and footpad perfusion, enhanced recruitment of endothelial progenitor cells, and improved performance on treadmill testing compared to control group. Histologically, E-selectin/AAV2/2 gene therapy was associated with increased vascularity and preserved myofiber integrity. E-selectin/AAV2/2 gene therapy also upregulated a panel of pro-angiogenic genes yet downregulated another group of genes associated with the inflammatory response. This novel gene therapy did not induce adverse effects on coagulability, or hematologic, hepatic, and renal function. Our findings highlight the potential of E-selectin/AAV2/2 gene therapy for improving limb perfusion and function in patients with chronic limb-threatening ischemia.

Discovery of In Vivo Active Sphingosine-1-phosphate Transporter (Spns2) Inhibitors

Sphingosine 1-phosphate (S1P) is a pleiotropic signaling molecule that interacts with five G-protein-coupled receptors (S1P1-5) to regulate cellular signaling pathways. S1P export is facilitated by Mfsd2b and spinster homologue 2 (Spns2). While mouse genetic studies suggest that Spns2 functions to maintain lymph S1P, Spns2 inhibitors are necessary to understand its biology and to learn whether Spns2 is a viable drug target. Herein, we report a structure-activity relationship study that identified the first Spns2 inhibitor 16d (SLF1081851). In vitro studies in HeLa cells demonstrated that 16d inhibited S1P release with an IC50 of 1.93 μM. Administration of 16d to mice and rats drove significant decreases in circulating lymphocyte counts and plasma S1P concentrations, recapitulating the phenotype observed in mice made deficient in Spns2. Thus, 16d has the potential for development and use as a probe to investigate Spns2 biology and to determine the potential of Spns2 as a drug target.

Sphingosine-1-phosphate and Sphingosine-1-phosphate receptors in the cardiovascular system: pharmacology and clinical implications

Sphingosine-1-phosphate (S1P) is a lipid that binds and activates five distinct receptor subtypes, S1P₁, S1P₂, S1P₃, S1P₄, S1P₅, widely expressed in different cells, tissues and organs. In the cardiovascular system these receptors have been extensively studied, but no drug acting on them has been approved so far for treating cardiovascular diseases. In contrast, a number of S1P receptor agonists are approved as immunomodulators, mainly for multiple sclerosis, because of their action on lymphocyte trafficking. This chapter summarizes the available information on S1P receptors in the cardiovascular system and discusses their potential for treating cardiovascular conditions and/or their role on the clinical pharmacology of drugs so far approved for non-cardiovascular conditions. Basic research has recently produced data useful to understand the molecular pharmacology of S1P and S1P receptors, regarding biased agonism, S1P storage, release and vehiculation and chaperoning by lipoproteins, paracrine actions, intracellular non-receptorial S1P actions. On the other hand, the approval of fingolimod and newer generation S1P receptor ligands as immunomodulators, provides information on a number of clinical observations on the impact of these drugs on cardiovascular system which need to be integrated with preclinical data. S1P receptors are potential targets for prevention and treatment of major cardiovascular conditions, including hypertension, myocardial infarction, heart failure and stroke.

Lysophosphatidic acid stimulates pericyte migration via LPA receptor 1

Lysophosphatidic acid (LPA) is a bioactive compound known to regulate various vascular functions. However, despite the fact that many vascular functions are regulated by peri-vascular cells such as pericytes, the effect of LPA on brain pericytes has not been fully evaluated. Thus, we designed this study to evaluate the effects of LPA on brain pericytes. These experiments revealed that while LPA receptors (LPARs) are expressed in cultured pericytes from mouse brains, LPA treatment does not influence the proliferation of these cells but does have a profound impact on their migration, which is regulated via the expression of LPAR1. LPAR1 expression was also detected in human pericyte culture and LPA treatment of these cells also induced migration. Taken together these findings imply that LPA-LPAR1 signaling is one of the key mechanisms modulating pericyte migration, which may help to control vascular function during development and repair processes.

Sphingosine 1-phosphate receptor-targeted therapeutics in rheumatic diseases

Sphingosine 1-phosphate (S1P), which acts via G protein-coupled S1P receptors (S1PRs), is a bioactive lipid essential for vascular integrity and lymphocyte trafficking. The S1P-S1PR signalling axis is a key component of the inflammatory response in autoimmune rheumatic diseases. Several drugs that target S1PRs have been approved for the treatment of multiple sclerosis and inflammatory bowel disease and are under clinical testing for patients with systemic lupus erythematosus (SLE). Preclinical studies support the hypothesis that targeting the S1P-S1PR axis would be beneficial to patients with SLE, rheumatoid arthritis (RA) and systemic sclerosis (SSc) by reducing pathological inflammation. Whereas most preclinical research and development efforts are focused on reducing lymphocyte trafficking, protective effects of circulating S1P on endothelial S1PRs, which maintain the vascular barrier and enable blood circulation while dampening leukocyte extravasation, have been largely overlooked. In this Review, we take a holistic view of S1P-S1PR signalling in lymphocyte and vascular pathobiology. We focus on the potential of S1PR modulators for the treatment of SLE, RA and SSc and summarize the rationale, pathobiology and evidence from preclinical models and clinical studies. Improved understanding of S1P pathobiology in autoimmune rheumatic diseases and S1PR therapeutic modulation is anticipated to lead to efficacious and safer management of these diseases.

KRP-203 Is a Desirable Immunomodulator for Islet Allotransplantation

BACKGROUND

The current standard immunosuppressive regimens, calcineurin inhibitors, have diabetogenic and anti-vascularization effects on islet grafts. KRP-203, a sphingosine-1-phosphate functional antagonist, exerts its immunomodulatory function through lymphocyte sequestration. However, the effect of this antagonist on islets is unclear. We examined the effect of KRP-203 on the islet function and vascularization and sought a calcineurin-free regimen for islet allotransplantation.

METHODS

KRP-203 was administered for 14 d to mice, then diabetogenic effect was evaluated by blood glucose levels and a glucose tolerance test. Static glucose stimulation, the breathing index, and insulin/DNA were examined using isolated islets. Islet neovascularization was evaluated using a multiphoton laser scanning microscope. After islet allotransplantation with either KRP-203 alone, sirolimus alone, or both in combination, the graft survival was evaluated by blood glucose levels and immunohistochemical analyses. A mixed lymphocyte reaction was also performed to investigate the immunologic characteristics of KRP-203 and sirolimus.

RESULTS

No significant differences in the blood glucose levels or glucose tolerance were observed between the control and KRP-203 groups. Functional assays after islet isolation were also comparable. The multiphoton laser scanning microscope showed no inhibitory effect of KRP-203 on islet neovascularization. Although allogeneic rejection was effectively inhibited by KRP-203 monotherapy (44%), combination therapy prevented rejection in most transplanted mice (83%).

CONCLUSIONS

KRP-203 is a desirable immunomodulator for islet transplantation because of the preservation of the endocrine function and lack of interference with islet neovascularization. The combination of KRP-203 with low-dose sirolimus may be promising as a calcineurin-free regimen for islet allotransplantation.

Lipids in Liver Failure Syndromes: A Focus on Eicosanoids, Specialized Pro-Resolving Lipid Mediators and Lysophospholipids

Lipids are organic compounds insoluble in water with a variety of metabolic and non-metabolic functions. They not only represent an efficient energy substrate but can also act as key inflammatory and anti-inflammatory molecules as part of a network of soluble mediators at the interface of metabolism and the immune system. The role of endogenous bioactive lipid mediators has been demonstrated in several inflammatory diseases (rheumatoid arthritis, inflammatory bowel disease, atherosclerosis, cancer). The liver is unique in providing balanced immunotolerance to the exposure of bacterial components from the gut transiting through the portal vein and the lymphatic system. This balance is abruptly deranged in liver failure syndromes such as acute liver failure and acute-on-chronic liver failure. In these syndromes, researchers have recently focused on bioactive lipid mediators by global metabonomic profiling and uncovered the pivotal role of these mediators in the immune dysfunction observed in liver failure syndromes explaining the high occurrence of sepsis and subsequent organ failure. Among endogenous bioactive lipids, the mechanistic actions of three classes (eicosanoids, pro-resolving lipid mediators and lysophospholipids) in the pathophysiological modulation of liver failure syndromes will be the topic of this narrative review. Furthermore, the therapeutic potential of lipid-immune pathways will be described.

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 Gαi and further stabilize the complex by increasing the Gαi 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.

Fingolimod (FTY720), a Sphinogosine-1-Phosphate Receptor Agonist, Mitigates Choroidal Endothelial Proangiogenic Properties and Choroidal Neovascularization

Neovascular or wet age-related macular degeneration (nAMD) causes vision loss due to inflammatory and vascular endothelial growth factor (VEGF)-driven neovascularization processes in the choroid. Due to the excess in VEGF levels associated with nAMD, anti-VEGF therapies are utilized for treatment. Unfortunately, not all patients have a sufficient response to such therapies, leaving few if any other treatment options for these patients. Sphingosine-1-phosphate (S1P) is a bioactive lipid mediator found in endothelial cells that participates in modulating barrier function, angiogenesis, and inflammation. S1P, through its receptor (S1PR1) in endothelial cells, prevents illegitimate sprouting angiogenesis during vascular development. In the present paper, we show that, in choroidal endothelial cells, S1PR1 is the most abundantly expressed S1P receptor and agonism of S1PR1-prevented choroidal endothelial cell capillary morphogenesis in culture. Given that nAMD pathogenesis draws from enhanced inflammation and angiogenesis as well as a loss of barrier function, we assessed the impact of S1PR agonism on choroidal neovascularization in vivo. Using laser photocoagulation rupture of Bruch’s membrane to induce choroidal neovascularization, we show that S1PR non-selective (FTY720) and S1PR1 selective (CYM5442) agonists significantly inhibit choroidal neovascularization in this model. Thus, utilizing S1PR agonists to temper choroidal neovascularization presents an additional novel use for these agonists presently in clinical use for multiple sclerosis as well as other inflammatory diseases.

HDL Composition, Heart Failure, and Its Comorbidities

Although research on high-density lipoprotein (HDL) has historically focused on atherosclerotic coronary disease, there exists untapped potential of HDL biology for the treatment of heart failure. Anti-oxidant, anti-inflammatory, and endothelial protective properties of HDL could impact heart failure pathogenesis. HDL-associated proteins such as apolipoprotein A-I and M may have significant therapeutic effects on the myocardium, in part by modulating signal transduction pathways and sphingosine-1-phosphate biology. Furthermore, because heart failure is a complex syndrome characterized by multiple comorbidities, there are complex interactions between heart failure, its comorbidities, and lipoprotein homeostatic mechanisms. In this review, we will discuss the effects of heart failure and associated comorbidities on HDL, explore potential cardioprotective properties of HDL, and review novel HDL therapeutic targets in heart failure.

Sphingosine-1-phosphate receptor 1 agonist SEW2871 alters membrane properties of late-firing somatostatin expressing neurons in the central lateral amygdala

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that mediates a wide spectrum of biological processes including apoptosis, immune response and inflammation. Here, we sought to understand how S1P signaling affects neuronal excitability in the central amygdala (CeA), which is a brain region associated with fear learning, aversive memory, and the affective dimension of pain. Because the G-protein coupled S1P receptor 1 (S1PR1) has been shown to be the primary mediator of S1P signaling, we utilized S1PR1 agonist SEW2871 and S1PR1 antagonist NIBR to determine a potential role of S1PR1 in altering the cellular physiology of neurons in the lateral division of the CeA (CeL) that share the neuronal lineage marker somatostatin (Sst). CeL-Sst neurons play a critical role in expression of conditioned fear and pain modulation. Here we used transgenic breeding strategies to identify fluorescently labeled CeL-Sst neurons for electrophysiological recordings. Using principal component analysis, we identified two primary subtypes of Sst neurons within the CeL in both male and female mice. We denoted the two types regular-firing (type A) and late-firing (type B) CeL-Sst neurons. In response to SEW2871 application, Type A neurons exhibited increased input resistance, while type B neurons displayed a depolarized resting membrane potential and voltage threshold, increased current threshold, and decreased voltage height. NIBR application had no effect on CeL Sst neurons, indicating the absence of tonic S1P-induced S1PR1. Our findings reveal subtypes of Sst neurons within the CeL that are uniquely affected by S1PR1 activation, which may have implications for how S1P alters supraspinal circuits.

Hypogelsolinemia and Decrease in Blood Plasma Sphingosine-1-Phosphate in Patients Diagnosed with Severe Acute Pancreatitis

BACKGROUND

Acute pancreatitis (AP) is a frequent hospitalization cause of patients suffering from gastrointestinal disorders. Gelsolin has an ability to bind bioactive lipids including different sphingolipids engaged in inflammatory response. Importantly, hypogelsolinemia was observed in patients with different states of acute and chronic inflammation.

AIMS

The aim of the present study was to assess the interplay of blood plasma gelsolin and blood plasma sphingosine-1-phosphate (S1P) concentration in patients diagnosed with acute pancreatitis.

MATERIALS AND METHODS

To assess the concentration of gelsolin and S1P, immunoblotting and HPLC technique were employed, respectively. Additionally, the concentrations of amylase, lipase, C-reactive protein (CRP), procalcitonin (PCT) and the number of white blood cells (WBC) and platelet (PLT) were recorded.

RESULTS

We found that both pGSN and S1P concentrations in the plasma of the AP patients were significantly lower (pGSN ~ 15-165 mg/L; S1P ~ 100-360 pmol/mL) when compared to the levels of pGSN and S1P in a control group (pGSN ~ 130-240 mg/L; S1P ~ 260-400 pmol/mL). Additionally, higher concentrations of CRP, WBC, amylase and lipase were associated with low level of gelsolin in the blood of AP patients. No correlations between the level of PCT and PLT with gelsolin concentration were noticed.

CONCLUSION

Plasma gelsolin and S1P levels decrease during severe acute pancreatitis. Simultaneous assessment of pGSN and S1P can be useful in development of more accurate diagnostic strategies for patients with severe acute pancreatitis.

Vitamin B6 prevents Isocarbophos-induced posterior cerebral artery injury in offspring rats through up-regulating S1P receptor expression

We have previously reported that the long-term exposure of Isocarbophos, a kind of organophosphorus compounds, induces vascular dementia (VD) in rats. Studies have also shown that organophosphorus compounds have adverse effects on offsprings. Vitamin B6 is a coenzyme mainly involved in the regulation of metabolism and has been demonstrated to ameliorate VD. Sphingosine-1-phosphate (S1P), a biologically active lipid, plays a vital role in the cardiovascular system. However, whether S1P is involved in the therapeutic effects of Vitamin B6 on posterior cerebral artery injury has yet to be further answered. In the present study, we aimed to explore the potential influence of Vitamin B6 on Isocarbophos-induced posterior cerebral artery injury in offspring rats and the role of the S1P receptor in this process. We found that Vitamin B6 significantly improves the vasoconstriction function of the posterior cerebral artery in rats induced by Isocarbophos by the blood gas analysis and endothelium-dependent relaxation function assay. We further demonstrated that Vitamin B6 alleviates the Isocarbophos-induced elevation of ICAM-1, VCAM-1, IL-1, and IL-6 by using the enzyme-linked immunosorbent assay kits. By performing immunofluorescence and the western blot assay, we revealed that Vitamin B6 prevents the down-regulation of S1P in posterior cerebral artery injury. It is worth noting that Fingolimod, the S1P inhibitor, significantly inhibits the Vitamin B6-induced up-regulation of S1P in posterior cerebral artery injury. Collectively, our data indicate that Vitamin B6 may be a novel drug for the treatment of posterior cerebral artery injury and that S1P may be a drug target for its treatment.

Biologically active lipids in the regulation of lymphangiogenesis in disease states

Lymphatic vessels have crucial roles in the regulation of interstitial fluids, immune surveillance, and the absorption of dietary fat in the intestine. Lymphatic function is also closely related to the pathogenesis of various disease states such as inflammation, lymphedema, endometriosis, liver dysfunction, and tumor metastasis. Lymphangiogenesis, the formation of new lymphatic vessels from pre-existing lymphatic vessels, is a critical determinant in the above conditions. Although the effect of growth factors on lymphangiogenesis is well-characterized, and biologically active lipids are known to affect smooth muscle contractility and vasoaction, there is accumulating evidence that biologically active lipids are also important inducers of growth factors and cytokines that regulate lymphangiogenesis. This review discusses recent advances in our understanding of biologically active lipids, including arachidonic acid metabolites, sphingosine 1-phosphate, and lysophosphatidic acid, as regulators of lymphangiogenesis, and the emerging importance of the lymphangiogenesis as a therapeutic target.

Deletion of Sphingosine 1-Phosphate receptor 1 in cardiomyocytes during development leads to abnormal ventricular conduction and fibrosis

Sphingosine 1-Phosphate receptor 1 (S1P1 , encoded by S1pr1) is a G protein-coupled receptor that signals in multiple cell types including endothelial cells and cardiomyocytes. Cardiomyocyte-specific deletion of S1pr1 during mouse development leads to ventricular noncompaction, with 44% of mutant mice surviving to adulthood. Adult survivors of embryonic cardiomyocyte S1pr1 deletion showed cardiac hypertrabeculation consistent with ventricular noncompaction. Surprisingly, systolic function in mutant mice was preserved through at least 1 year of age. Cardiac conduction was abnormal in cardiomyocyte S1pr1 mutant mice, with prolonged QRS intervals in mutants as compared with littermate control mice. Immunostaining of hearts from S1pr1 mutant embryos displayed a zone of intermediate Connexin 40 (Cx40) expression in the trabecular myocardium. However, we observed no significant differences in Cx40 and Connexin 43 immunostaining in hearts from adult survivors of embryonic cardiomyocyte S1pr1 deletion, which suggests normalized development of the ventricular conduction system in mutant mice. By contrast, the adult survivors of embryonic cardiomyocyte S1pr1 deletion showed increased cardiac fibrosis as compared with littermate controls. These results demonstrate that ventricular hypertrabeculation caused by embryonic deletion of cardiomyocyte S1pr1 correlates with cardiac fibrosis, which contributes to abnormal ventricular conduction. These results also reveal conduction abnormalities in the setting of hypertrabeculation with normal systolic function, which may be of clinical relevance in humans with ventricular hypertrabeculation.

Uncovering the 'sphinx' of sphingosine 1-phosphate signalling: from cellular events to organ morphogenesis

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid metabolite, functioning as a signalling molecule in diverse cellular processes. Over the past few decades, studies of S1P signalling have revealed that the physiological activity of S1P largely depends on S1P metabolizing enzymes, transporters and receptors on the plasma membrane, as well as on the intracellular proteins that S1P binds directly to. In addition to its roles in cancer signalling, immunity and inflammation, a large body of evidence has identified a close link of S1P signalling with organ morphogenesis. Here we discuss the vital role of S1P signalling in orchestrating various cellular events during organ morphogenesis through analysing each component along the extracellular and intracellular S1P signalling axes. For each component, we review advances in our understanding of S1P signalling and function from the upstream regulators to the downstream effectors and from cellular behaviours to tissue organization, primarily in the context of morphogenetic mechanisms. S1P-mediated vesicular trafficking is also discussed as a function independent of its signalling function. A picture emerges that reveals a multifaceted role of S1P-dependent pathways in the development and maintenance of organ structure and function.

Apolipoprotein M and its impact on endothelial dysfunction and inflammation in the cardiovascular system

Apolipoprotein M (apoM) is a member of the lipocalin superfamily and is predominantly associated with high-density lipoprotein (HDL). It was found that apoM is the chaperon to the bioactive sphingolipid, sphingosine-1-phosphate (S1P). Several studies have since contributed to expand the knowledge on apoM, S1P, and the apoM/S1P-complex in cardiovascular diseases. For instance, the HDL-bound apoM/S1P complex serves as a bridge between HDL and endothelial cells, maintaining a healthy endothelial barrier. Evidence indicates, however, that the apoM/S1P complex may has both protective and harmful effects on the cardiovascular system, which suggests the need for more research to understand the interplay between these molecules. This review aims to shed light on the most recent findings on apoM/S1P-signaling and its impact on endothelial dysfunction, inflammation, and cardiovascular diseases. Finally, it will be discussed whether drugs that target apoM and/or S1P-signaling may be beneficial to patients with cardiovascular and inflammatory diseases.

Targeting S1PR1 May Result in Enhanced Migration of Cancer Cells in Bladder Carcinoma

Clinical bladder tumor histological analysis shows that high expression of S1PR1 is associated with poor patient prognosis. However, there are no studies that describe the underlying mechanism. To investigate the relative distribution and actual function of S1PR1 in bladder tumors, we analyzed multiple clinical databases in combination with tumor purity and immune cell infiltration simulations, as well as databases of well-defined histological phenotypes of bladder cancer, and single-cell sequencing of adjacent normal tissues and bladder tumors, and further compared them with bladder cancer cell lines. The results showed that S1PR1 expression was generally higher in normal tissues than in bladder cancer tissues, and its distribution was mainly in endothelial cells or immune cells. The association between high S1PR1 expression and poor prognosis may be due to tumor invasion of adjacent normal tissues, where highly expressed S1PR1 may affect prognostic interpretation. The effect of S1PR1 itself on cancer cells was associated with cell adhesion, and in bladder cancer cells, S1PR1 expression was negatively correlated with cell motility. Moreover, the use of FTY-720 will cause an increased metastatic ability of bladder cancer cells. In conclusion, we suggest that the use of S1PR1-specific inhibition as a synergistic treatment requires more observation and consideration.

Hyperoxia-induced S1P1 signaling reduced angiogenesis by suppression of TIE-2 leading to experimental bronchopulmonary dysplasia

INTRODUCTION

We have earlier shown that hyperoxia (HO)-induced sphingosine kinase 1 (SPHK1)/sphingosine-1-phosphate (S1P) signaling contribute to bronchopulmonary dysplasia (BPD). S1P acts through G protein-coupled receptors, S1P1 through S1P5. Further, we noted that heterozygous deletion of S1pr1 ameliorated the HO-induced BPD in the murine model. The mechanism by which S1P1 signaling contributes to HO-induced BPD was explored.

METHODS

S1pr1+/+ and S1pr1+/- mice pups were exposed to either room air (RA) or HO (75% oxygen) for 7 days from PN 1-7. Lung injury and alveolar simplification was evaluated. Lung protein expression was determined by Western blotting and immunohistochemistry (IHC). In vitro experiments were performed using human lung microvascular endothelial cells (HLMVECs) with S1P1 inhibitor, NIBR0213 to interrogate the S1P1 signaling pathway.

RESULTS

HO increased the expression of S1pr1 gene as well as S1P1 protein in both neonatal lungs and HLMVECs. The S1pr1+/- neonatal mice showed significant protection against HO-induced BPD which was accompanied by reduced inflammation markers in the bronchoalveolar lavage fluid. HO-induced reduction in ANG-1, TIE-2, and VEGF was rescued in S1pr1+/- mouse, accompanied by an improvement in the number of arterioles in the lung. HLMVECs exposed to HO increased the expression of KLF-2 accompanied by reduced expression of TIE-2, which was reversed with S1P1 inhibition.

CONCLUSION

HO induces S1P1 followed by reduced expression of angiogenic factors. Reduction of S1P1 signaling restores ANG-1/ TIE-2 signaling leading to improved angiogenesis and alveolarization thus protecting against HO-induced neonatal lung injury.

Early Life Stress and Metabolic Plasticity of Brain Cells: Impact on Neurogenesis and Angiogenesis

Early life stress (ELS) causes long-lasting changes in brain plasticity induced by the exposure to stress factors acting prenatally or in the early postnatal ontogenesis due to hyperactivation of hypothalamic-pituitary-adrenal axis and sympathetic nervous system, development of neuroinflammation, aberrant neurogenesis and angiogenesis, and significant alterations in brain metabolism that lead to neurological deficits and higher susceptibility to development of brain disorders later in the life. As a key component of complex pathogenesis, ELS-mediated changes in brain metabolism associate with development of mitochondrial dysfunction, loss of appropriate mitochondria quality control and mitochondrial dynamics, deregulation of metabolic reprogramming. These mechanisms are particularly critical for maintaining the pool and development of brain cells within neurogenic and angiogenic niches. In this review, we focus on brain mitochondria and energy metabolism related to tightly coupled neurogenic and angiogenic events in healthy and ELS-affected brain, and new opportunities to develop efficient therapeutic strategies aimed to restore brain metabolism and reduce ELS-induced impairments of brain plasticity.

From remodeling to quiescence: The transformation of the vascular network

The vascular system is essential for embryogenesis, healing, and homeostasis. Dysfunction or deregulated blood vessel function contributes to multiple diseases, including diabetic retinopathy, cancer, hypertension, or vascular malformations. A balance between the formation of new blood vessels, vascular remodeling, and vessel quiescence is fundamental for tissue growth and function. Whilst the major mechanisms contributing to the formation of new blood vessels have been well explored in recent years, vascular remodeling and quiescence remain poorly understood. In this review, we highlight the cellular and molecular mechanisms responsible for vessel remodeling and quiescence during angiogenesis. We further underline how impaired remodeling and/or destabilization of vessel networks can contribute to vascular pathologies. Finally, we speculate how addressing the molecular mechanisms of vascular remodeling and stabilization could help to treat vascular-related disorders.

GPCR Partners as Cancer Driver Genes: Association with PH-Signal Proteins in a Distinctive Signaling Network

The essential role of G-protein coupled receptors (GPCRs) in tumor growth is recognized, yet a GPCR based drug in cancer is rare. Understanding the molecular path of a tumor driver gene may lead to the design and development of an effective drug. For example, in members of protease-activated receptor (PAR) family (e.g., PAR1 and PAR2), a novel PH-binding motif is allocated as critical for tumor growth. Animal models have indicated the generation of large tumors in the presence of PAR1 or PAR2 oncogenes. These tumors showed effective inhibition when the PH-binding motif was either modified or were inhibited by a specific inhibitor targeted to the PH-binding motif. In the second part of the review we discuss several aspects of some cardinal GPCRs in tumor angiogenesis.

Differential Expression of Hypoxia-Related Genes in Primary Brain Tumors and Correlation with Clinicopathologic Data

OBJECTIVE

Meningiomas and gliomas are common benign and malignant primary brain tumors, respectively. One of the most prominent features of aggressive malignancies contributing to their progression is their ability to cope with hypoxia. Therefore, glioma tumors are expected to better cope with adverse hypoxic conditions and, consequently, display significantly different expression levels of hypoxia-adaptive genes.

METHODS

Thirty-three glioma (17 glioblastoma multiforme [GBM], 16 low-grade glioma [LGG]) and 32 meningioma samples were investigated for expression of hypoxia adaptation- related genes by real-time polymerase chain reaction. The same investigation was carried out for GBM, the most malignant form of glioma, versus LGG. The findings were further checked by bioinformatics analysis of expression levels using RNA-seq data. Additional investigations conducted include receiver operating characteristic curve analysis to assess the power for each gene in differential diagnosis of glioma from meningioma.

RESULTS

A greater level of hypoxia-inducible factor (HIF) 1α expression in glioma samples compared with meningioma and greater expression levels of Yes-associated protein (YAP) 1 and G-protein-coupled receptor class C group 5 member A (GPRC5A) in meningioma were observed, with P values 0.0005, <0.0001, and <0.0001 for GPRC5A, HIF1α, and YAP1, respectively. Comparison of GBM with LGG also revealed GPRC5A to have significantly greater expression in GBM with P = 0.0381. The calculated area under the curve was 0.7536, 0.8438, and 0.8272 for GPRC5A, HIF1α, and YAP1, respectively, which represented acceptable power for these genes in differential diagnosis of glioma tumor types from meningioma and tumor subtypes GBM from LGG under study.

CONCLUSIONS

These results imply that these genes can possibly be implicated in brain tumor hypoxia-adaptation response with tumor-specific roles and patterns of expression.

SPNS2 enables T cell egress from lymph nodes during an immune response

T cell expression of sphingosine 1-phosphate (S1P) receptor 1 (S1PR1) enables T cell exit from lymph nodes (LNs) into lymph, while endothelial S1PR1 expression regulates vascular permeability. Drugs targeting S1PR1 treat autoimmune disease by trapping pathogenic T cells within LNs, but they have adverse cardiovascular side effects. In homeostasis, the transporter SPNS2 supplies lymph S1P and enables T cell exit, while the transporter MFSD2B supplies most blood S1P and supports vascular function. It is unknown whether SPNS2 remains necessary to supply lymph S1P during an immune response, or whether in inflammation other compensatory transporters are upregulated. Here, using a model of dermal inflammation, we demonstrate that SPNS2 supplies the S1P that guides T cells out of LNs with an ongoing immune response. Furthermore, deletion of Spns2 is protective in a mouse model of multiple sclerosis. These results support the therapeutic potential of SPNS2 inhibitors to achieve spatially specific modulation of S1P signaling.

Endothelial Spns2 and ApoM Regulation of Vascular Tone and Hypertension Via Sphingosine-1-Phosphate

Background Most of the circulating sphingosine-1-phosphate (S1P) is bound to ApoM (apolipoprotein M) of high-density lipoprotein (HDL) and mediates many beneficial effects of HDL on the vasculature via G protein-coupled S1P receptors. HDL-bound S1P is decreased in atherosclerosis, myocardial infarction, and diabetes mellitus. In addition to being the target, the endothelium is a source of S1P, which is transported outside of the cells by Spinster-2, contributing to circulating S1P as well as to local signaling. Mice lacking endothelial S1P receptor 1 are hypertensive, suggesting a vasculoprotective role of S1P signaling. This study investigates the role of endothelial-derived S1P and ApoM-bound S1P in regulating vascular tone and blood pressure. Methods and Results ApoM knockout (ApoM KO) mice and mice lacking endothelial Spinster-2 (ECKO-Spns2) were infused with angiotensin II for 28 days. Blood pressure, measured by telemetry and tail-cuff, was significantly increased in both ECKO-Spns2 and ApoM KO versus control mice, at baseline and following angiotensin II. Notably, ECKO-Spns2 presented an impaired vasodilation to flow and blood pressure dipping, which is clinically associated with increased risk for cardiovascular events. In hypertension, both groups presented reduced flow-mediated vasodilation and some degree of impairment in endothelial NO production, which was more evident in ECKO-Spns2. Increased hypertension in ECKO-Spns2 and ApoM KO mice correlated with worsened cardiac hypertrophy versus controls. Conclusions Our study identifies an important role for Spinster-2 and ApoM-HDL in blood pressure homeostasis via S1P-NO signaling and dissects the pathophysiological impact of endothelial-derived S1P and ApoM of HDL-bound S1P in hypertension and cardiac hypertrophy.

Programming to S1PR1+ Endothelial Cells Promotes Restoration of Vascular Integrity

[Figure: see text].

S1P signaling, its interactions and cross-talks with other partners and therapeutic importance in colorectal cancer

Sphingosine-1-Phosphate (S1P) plays an important role in normal physiology, inflammation, initiation and progression of cancer. Deregulation of S1P signaling causes aberrant proliferation, affects survival, leads to angiogenesis and metastasis. Sphingolipid rheostat is crucial for cellular homeostasis. Discrepancy in sphingolipid metabolism is linked to cancer and drug insensitivity. Owing to these diverse functions and being a potent mediator of tumor growth, S1P signaling might be a suitable candidate for anti-tumor therapy or combination therapy. In this review, with a focus on colorectal cancer we have summarized the interacting partners of S1P signaling pathway, its therapeutic approaches along with the contribution of S1P signaling to various cancer hallmarks.

Targeting sphingosine kinase-1 with the low MW inhibitor SKI-5C suppresses the development of endometriotic lesions in mice

BACKGROUND AND PURPOSE

Limited evidence suggests that the sphingosine-1-phosphate/sphingosine kinase 1 (S1P/SPHK1) signalling pathway is involved in the pathogenesis of endometriosis. Therefore, we analyzed in this study whether the inhibition of SPHK1 and, consequently, decreased levels of S1P affected the vascularization and growth of endometriotic lesions.

EXPERIMENTAL APPROACH

Endometriotic lesions were surgically induced in the peritoneal cavity and the dorsal skinfold chamber of female BALB/c mice. The animals received a daily dose of the SPHK1 inhibitor SKI-5C or vehicle (control). Analyses involved the determination of lesion growth, cyst formation, microvessel density and cell proliferation within peritoneal endometriotic lesions by means of high-resolution ultrasound imaging, caliper measurement, histology and immunohistochemistry. In the dorsal skinfold chamber model the development of newly formed microvascular networks and their microhemodynamic parameters within endometriotic lesions were investigated by means of intravital fluorescence microscopy.

KEY RESULTS

SKI-5C significantly inhibited the development and vascularization of peritoneal endometriotic lesions, as indicated by a reduced growth and cyst formation, a lower microvessel density and a suppressed cell proliferation, when compared to vehicle-treated controls. Endometriotic lesions in dorsal skinfold chambers of SKI-5C-treated animals exhibited a significantly smaller lesion size, lower functional microvessel density, smaller microvessel diameters and a reduced blood perfusion of the newly developing microvascular networks.

CONCLUSIONS AND IMPLICATIONS

SPHK1/S1P signalling promotes the establishment and progression of endometriotic lesions. The inhibition of this pathway suppresses the development of endometriotic lesions, suggesting SPHK1 as a potential novel target for future endometriosis therapy.

Barrier maintenance by S1P during inflammation and sepsis

Sphingosine 1-phosphate (S1P) is a multifaceted lipid signaling molecule that activates five specific G protein-coupled S1P receptors. Despite the fact that S1P is known as one of the strongest barrier-enhancing molecules for two decades, no medical application is available yet. The reason for this lack of translation into clinical practice may be the complex regulatory network of S1P signaling, metabolism and transportation.In this review, we will provide an overview about the physiology and the network of S1P signaling with the focus on endothelial barrier maintenance in inflammation. We briefly describe the physiological role of S1P and the underlying S1P signaling in barrier maintenance, outline differences of S1P signaling and metabolism in inflammatory diseases, discuss potential targets and compounds for medical intervention, and summarize our current knowledge regarding the role of S1P in the maintenance of specialized barriers like the blood-brain barrier and the placenta.

Sphingosine 1-phosphate and its receptors in ischemia

Sphingosine 1-phosphate (S1P), a metabolite of sphingolipids, is mainly derived from red blood cells (RBCs), platelets and endothelial cells (ECs). It plays important roles in regulating cell survival, vascular integrity and inflammatory responses through its receptors. S1P receptors (S1PRs), including 5 subtypes (S1PR1-5), are G protein-coupled receptors and have been proved to mediate various and complex roles of S1P in atherosclerosis, myocardial infarction (MI) and ischemic stroke by regulating endothelial function and inflammatory response as well as immune cell behavior. This review emphasizes the functions of S1PRs in atherosclerosis and ischemic diseases such as MI and ischemic stroke, enabling mechanistic studies and new S1PRs targeted therapies in atherosclerosis and ischemia in the future.

Glomerular Endothelial Cells Are the Coordinator in the Development of Diabetic Nephropathy

The prevalence of diabetes is consistently rising worldwide. Diabetic nephropathy is a leading cause of chronic renal failure. The present study aimed to explore the crosstalk among the different cell types inside diabetic glomeruli, including glomerular endothelial cells, mesangial cells, podocytes, and immune cells, by analyzing an online single-cell RNA profile (GSE131882) of patients with diabetic nephropathy. Differentially expressed genes in the glomeruli were processed by gene enrichment and protein-protein interactions analysis. Glomerular endothelial cells, as well as podocytes, play a critical role in diabetic nephropathy. A subgroup of glomerular endothelial cells possesses characteristic angiogenesis genes, indicating that angiogenesis takes place in the progress of diabetic nephropathy. Immune cells such as macrophages, T lymphocytes, B lymphocytes, and plasma cells also contribute to the disease progression. By using iTALK, the present study reports complicated cellular crosstalk inside glomeruli. Dysfunction of glomerular endothelial cells and immature angiogenesis result from the activation of both paracrine and autocrine signals. The present study reinforces the importance of glomerular endothelial cells in the development of diabetic nephropathy. The exploration of the signaling pathways involved in aberrant angiogenesis reported in the present study shed light on potential therapeutic target(s) for diabetic nephropathy.

Association of SNPs in AKIRIN2, TTN, EDG1 and MYBPC1 genes with growth and carcass traits in Qinchuan cattle

Growth and carcass traits are the main breeding objectives in beef cattle. The aim of this study was to confirm genetic effects of the c.*188G>A SNP of AKIRIN2, the g.231054C>T SNP of TTN, the g.1471620G>T SNP of EDG1 and the g.70014208A>G SNP of MYBPC1 on growth and carcass traits in Chinese Qinchuan (QC) cattle, as well as to compare the frequencies of the well-characterized alleles of these SNPs among six Chinese cattle populations, three Japanese cattle populations, two European cattle populations and one Korean cattle population. In this study, a total of 665 cattle samples were genotyped using MassARRAY and PCR-RFLP. Association analysis explored effects of four SNPs on growth and carcass traits including body length, wither height, hip height, hip width, rump length, chest depth, chest circumference, back fat thickness, ultrasound longissimus muscle area and ultrasound longissimus muscle depth in QC (P<0.05 to P<0.001). The well-characterized A (c.*188G>A), T (g.231054C>T) and T (g.1471620G>T) alleles in Japanese Black cattle were significantly higher than Chinese cattle breeds, on the contrary, the G allele (g.70014208A>G) was markedly higher in Chinese cattle breeds than other cattle breeds. These results suggest that the four SNPs might be useful as a molecular marker for growth-related traits in Chinese QC cattle.

Physiological and pathological functions of sphingolipids in pregnancy

Signaling by the bioactive sphingolipid, sphingosine 1-phosphate (S1P), and its precursors are emerging areas in pregnancy research. S1P and ceramide levels increase towards end of gestation, suggesting a physiological role in parturition. However, high levels of circulating S1P and ceramide are correlated with pregnancy disorders such as preeclampsia, gestational diabetes mellitus and intrauterine growth restriction. Expression of placental and decidual enzymes that metabolize S1P and S1P receptors are also dysregulated during pregnancy complications. In this review, we provide an in-depth examination of the signaling mechanism of S1P and ceramide in various reproductive tissues during gestation. These factors determine implantation and early pregnancy success by modulating corpus luteum function from progesterone production to luteolysis through to apoptosis. We also highlight the role of S1P through receptor signaling in inducing decidualization and angiogenesis in the decidua, as well as regulating extravillous trophoblast migration to anchor the placenta into the uterine wall. Recent advances on the role of the S1P:ceramide rheostat in controlling the fate of villous trophoblasts and the role of S1P as a negative regulator of trophoblast syncytialization to a multinucleated placental barrier are discussed. This review also explores the role of S1P in anti-inflammatory and pro-inflammatory signaling, its role as a vasoconstrictor, and the effects of S1P metabolizing enzymes and receptors in pregnancy.

Bioactive Sphingolipids as Major Regulators of Coronary Artery Disease

Atherosclerosis is the deposition of plaque in the main arteries. It is an inflammatory condition involving the accumulation of macrophages and various lipids (low-density lipoprotein [LDL] cholesterol, ceramide, S1P). Moreover, endothelial cells, macrophages, leukocytes, and smooth muscle cells are the major players in the atherogenic process. Sphingolipids are now emerging as important regulators in various pathophysiological processes, including the atherogenic process. Various sphingolipids exist, such as the ceramides, ceramide-1-phosphate, sphingosine, sphinganine, sphingosine-1-phosphate (S1P), sphingomyelin, and hundreds of glycosphingolipids. Among these, ceramides, glycosphingolipids, and S1P play important roles in the atherogenic processes. The atherosclerotic plaque consists of higher amounts of ceramide, glycosphingolipids, and sphingomyelin. The inhibition of the de novo ceramide biosynthesis reduces the development of atherosclerosis. S1P regulates atherogenesis via binding to the S1P receptor (S1PR). Among the five S1PRs (S1PR1-5), S1PR1 and S1PR3 mainly exert anti-atherosclerotic properties. This review mainly focuses on the effects of ceramide and S1P via the S1PR in the development of atherosclerosis. Moreover, it discusses the recent findings and potential therapeutic implications in atherosclerosis.

S1PR1 signaling in cancer: A current perspective

Sphingosine-1-phosphate receptor 1 (S1PR1) is a G-protein coupled receptor for the bioactive lysosphingolipid sphingosine 1-phosphate (S1P). S1PR1 belongs to the sphingosine-1-phosphate receptor subfamily comprising five members (S1PR1-5). It has prominent roles in regulating endothelial cell cytoskeletal structure, cell migration, immunomodulation, vasculogenesis during embryogenesis, T cell egress and Multiple sclerosis. This review is addressing the role of S1PR1 in tumorigenesis and therapeutic opportunities to target S1PR1 in cancer.

Silencing of Sphingosine kinase 1 Affects Maturation Pathways in Mouse Neonatal Cardiomyocytes

Sphingosine kinase-1 (Sphk1) and its product, sphingosine-1-phosphate (S1P) are important regulators of cardiac growth and function. Numerous studies have reported that Sphk1/S1P signaling is essential for embryonic cardiac development and promotes pathological cardiac hypertrophy in adulthood. However, no studies have addressed the role of Sphk1 in postnatal cardiomyocyte (CM) development so far. The present study aimed to assess the molecular mechanism(s) by which Sphk1 silencing might influence CMs development and hypertrophy in vitro. Neonatal mouse CMs were transfected with siRNA against Sphk1 or negative control, and subsequently treated with 1 µM angiotensin II (AngII) or a control buffer for 24 h. The results of RNASeq analysis revealed that diminished expression of Sphk1 significantly accelerated neonatal CM maturation by inhibiting cell proliferation and inducing developmental pathways in the stress (AngII-induced) conditions. Importantly, similar effects were observed in the control conditions. Enhanced maturation of Sphk1-lacking CMs was further confirmed by the upregulation of the physiological hypertrophy-related signaling pathway involving Akt and downstream glycogen synthase kinase 3 beta (Gsk3β) downregulation. In summary, we demonstrated that the Sphk1 silencing in neonatal mouse CMs facilitated their postnatal maturation in both physiological and stress conditions.

Direct uptake of sphingosine-1-phosphate independent of phospholipid phosphatases

Sphingosine-1-phosphate (S1P) is a lipid mediator that is relatively abundant in plasma and plays an important role in the vascular and immune systems. To date, the only known mechanism for removing S1P from plasma has been dephosphorylation by phospholipid phosphatases (PLPPs) on the surface of cells in contact with the plasma. However, there remains a possibility that PLPP-independent dephosphorylation or direct S1P uptake into cells could occur. To examine these possibilities, here we generated triple KO (TKO) HAP1 cells that lacked all PLPPs (PLPP1–3) present in mammals. In the TKO cells, the intracellular metabolism of externally added deuterium-labeled S1P to ceramide was reduced to 17% compared with the WT cells, indicating that most extracellular S1P is dephosphorylated by PLPPs and then taken up into cells. However, this result also reveals the existence of a PLPP-independent S1P uptake pathway. Tracer experiments using [³²P]S1P showed the existence of a direct S1P uptake pathway that functions without prior dephosphorylation. Overexpression of sphingolipid transporter 2 (SPNS2) or of major facilitator superfamily domain containing 2B (MFSD2B), both known S1P efflux transporters, in TKO cells increased the direct uptake of S1P, whereas KO of MFSD2B in TKO cells reduced this uptake. These results suggest that these are channel-type transporters and capable of not only exporting but also importing S1P. Furthermore, we observed that erythroid cells expressing MFSD2B, exhibited high S1P uptake activity. Our findings describing direct S1P uptake may contribute to the elucidation of the molecular mechanisms that regulate plasma S1P concentration.

Deletion of Mir223 Exacerbates Lupus Nephritis by Targeting S1pr1 in Faslpr/lpr Mice

Objective

The micro RNAs (miRNAs) and their target mRNAs are differentially expressed in various immune-mediated cells. Here, we investigated the role of Mir223 and sphingosine-1-phosphate receptor 1 (S1pr1) in the pathogenesis of systemic lupus erythematosus.

Methods

We analyzed miRNA and mRNA profiling data of CD4+ splenic T cells derived from MRL/MpJ-Faslpr /J mice. We performed 3' untranslated region (UTR) luciferase reporter gene assay using human umbilical vein endothelial cells (HUVECs). We generated the B6-Mir223-/-Faslpr/lpr mice and the lupus phenotypes were analyzed.

Results

In CD4+ splenic T cells, we identified upregulation of miR-223-3p and downregulation of the possible target, S1pr1 by RNA sequencing of MRL/MpJ-Faslpr /J mice. The transfection with miR-223-3p mimic significantly suppressed a luciferase activity in HUVEC treated with a Lentivirus vector containing 3' UTR of S1pr1. The mRNA levels of S1pr1 were significantly decreased after miR-223-3p overexpression. In B6-Mir223-/-Faslpr/lpr mice, the proportion of CD3+ T cells, CD3+CD4-CD8- cells, B cells, plasma cells, and S1PR1+CD4+ T cells in the spleen was significantly increased compared with that in B6-Mir223+/+Faslpr/lpr mice by flow cytometry. B6-Mir223-/-Faslpr/lpr mice demonstrated the elevation of glomerular and renal vascular scores associated with enhanced intraglomerular infiltration of S1PR1+CD4+ T cells.

Conclusion

Unexpectedly, the deletion of Mir223 exacerbated the lupus phenotypes associated with increased population of S1PR1+CD4+ T in spleen and the enhanced infiltration of S1PR1+CD4+ T cells in inflamed kidney tissues, suggesting compensatory role of Mir223 in the pathogenesis of lupus nephritis.

Vascular endothelial S1pr1 ameliorates adverse cardiac remodelling via stimulating reparative macrophage proliferation after myocardial infarction

AIMS

Endothelial cell (EC) homoeostasis plays an important role in normal physiological cardiac functions, and its dysfunction significantly influences pathological cardiac remodelling after myocardial infarction (MI). It has been shown that the sphingosine 1-phosphate receptor 1 (S1pr1) was highly expressed in ECs and played an important role in maintaining endothelial functions. We thus hypothesized that the endothelial S1pr1 might be involved in post-MI cardiac remodelling.

METHODS AND RESULTS

Our study showed that the specific loss of endothelial S1pr1 exacerbated post-MI cardiac remodelling and worsened cardiac dysfunction. We found that the loss of endothelial S1pr1 significantly reduced Ly6clow macrophage accumulation, which is critical for the resolution of inflammation and cardiac healing following MI. The reduced reparative macrophages in post-MI myocardium contributed to the detrimental effects of endothelial S1pr1 deficiency on post-MI cardiac remodelling. Further investigations showed that the loss of endothelial S1pr1-reduced Ly6clow macrophage proliferation, while the pharmacological activation of S1pr1-enhanced Ly6clow macrophage proliferation, thereby ameliorated cardiac remodelling after MI. A mechanism study showed that S1P/S1pr1 activated the ERK signalling pathway and enhanced colony-stimulating factor 1 (CSF1) expression, which promoted Ly6clow macrophage proliferation in a cell-contact manner. The blockade of CSF1 signalling reversed the enhancing effect of S1pr1 activation on Ly6clow macrophage proliferation and worsened post-MI cardiac remodelling.

CONCLUSION

This study reveals that cardiac microvascular endothelium promotes reparative macrophage proliferation in injured hearts via the S1P/S1PR1/ERK/CSF1 pathway and thus ameliorates post-MI adverse cardiac remodelling.

Sphingosine-1 phosphate induces cAMP/PKA-independent phosphorylation of the cAMP response element-binding protein (CREB) in granulosa cells

BACKGROUND AND AIMS

Sphingosine-1 phosphate (S1P) is a lysosphingolipid present in the ovarian follicular fluid. The role of the lysosphingolipid in gonads of the female is widely unclear. At nanomolar concentrations, S1P binds and activates five specific G protein-coupled receptors (GPCRs), known as S1P_1-5, modulating different signaling pathways. S1P₁ and S1P₃ are highly expressed in human primary granulosa lutein cells (hGLC), as well as in the immortalized human primary granulosa cell line hGL5. In this study, we evaluated the signaling cascade activated by S1P and its synthetic analogues in hGLC and hGL5 cells, exploring the biological relevance of S1PR-stimulation in this context.

METHODS AND RESULTS

hGLC and hGL5 cells were treated with a fixed dose (0.1 μM) of S1P, or by S1P₁- and S1P₃-specific agonists SEW2871 and CYM5541. In granulosa cells, S1P and, at a lesser extent, SEW2871 and CYM5541, potently induced CREB phosphorylation. No cAMP production was detected and pCREB activation occurred even in the presence of the PKA inhibitor H-89. Moreover, S1P-dependent CREB phosphorylation was dampened by the mitogen-activate protein kinase (MEK) inhibitor U0126 and by the L-type Ca²⁺ channel blocker verapamil. The complete inhibition of CREB phosphorylation occurred by blocking either S1P₂ or S1P₃ with the specific receptor antagonists JTE-013 and TY52156, or under PLC/PI3K depletion. S1P-dependent CREB phosphorylation induced FOXO1 and the EGF-like epiregulin-encoding gene (EREG), confirming the exclusive role of gonadotropins and interleukins in this process, but did not affect steroidogenesis. However, S1P or agonists did not modulate granulosa cell viability and proliferation in our conditions.

CONCLUSIONS

This study demonstrates for the first time that S1P may induce a cAMP-independent activation of pCREB in granulosa cells, although this is not sufficient to induce intracellular steroidogenic signals and progesterone synthesis. S1P-induced FOXO1 and EREG gene expression suggests that the activation of S1P-S1PR axis may cooperate with gonadotropins in modulating follicle development.