GT-11 impairs insulin signaling through modulation of sphingolipid metabolism in C2C12 myotubes

AIMS

Sphingolipids are involved in the regulation of insulin signaling, which is linked to the development of insulin resistance, leading to diabetes mellitus. We aimed to study whether modulation of sphingolipid levels by GT-11 may regulate insulin signaling in C2C12 myotubes.

MAIN METHODS

We investigated the effects of sphingolipid metabolism on Akt phosphorylation and glucose uptake using C2C12 myotubes. Either GT-11, an inhibitor of dihydroceramide desaturase 1 and S1P lyase, or siRNA targeting Sgpl1, the gene encoding the enzyme, was employed to determine the effect of sphingolipid metabolism modulation on insulin signaling. Western blotting and glucose uptake assays were used to evaluate the effect of treatments on insulin signaling. Sphingolipid metabolites were analyzed by high performance liquid chromatography (HPLC).

KEY FINDINGS

Treatment with GT-11 resulted in decreased Akt phosphorylation and reduced glucose uptake. Silencing the Sgpl1 gene, which encodes S1P lyase, mimicked these findings, suggesting the potential for regulating insulin signaling through S1P lyase modulation. GT-11 modulated sphingolipid metabolism, inducing the accumulation of sphingolipids. Using PF-543 and ARN14974 to inhibit sphingosine kinases and acid ceramidase, respectively, we identified a significant interplay between sphingosine, S1P lyase, and insulin signaling. Treatment with either exogenous sphingosine or palmitic acid inhibited Akt phosphorylation, and reduced S1P lyase activity.

SIGNIFICANCE

Our findings highlight the importance of close relationship between sphingolipid metabolism and insulin signaling in C2C12 myotubes, pointing to its potential therapeutic relevance for diabetes mellitus.

Signaling sphingolipids are biomarkers for atopic dermatitis prone to disseminated viral infections

BACKGROUND

Life-threatening viral diseases such as eczema herpeticum (EH) and eczema vaccinatum (EV) occur in <5% of individuals with atopic dermatitis (AD). The diagnosis of AD, however, excludes all individuals with AD from smallpox vaccination.

OBJECTIVES

We sought to identify circulatory and skin lipid biomarkers associated with EH and EV.

METHODS

Stratum corneum and plasma samples from 15 subjects with AD and a history of EH, 13 age- and gender-matched subjects with AD and without EH history, and 13 healthy nonatopic (NA) controls were analyzed by liquid chromatography tandem mass spectrometry for sphingolipid content. Sphingosine-1-phosphate (S1P) and ceramide levels were validated in plasma samples from the Atopic Dermatitis Vaccinia Network/Atopic Dermatitis Research Network repository (12 NA, 12 AD, 23 EH) and plasma from 7 subjects with EV and 7 matched subjects with AD. S1P lyase was downregulated in human primary keratinocytes to evaluate its effect on herpes simplex virus 1 (HSV-1) replication in vitro.

RESULTS

The stratum corneum of patients with EH demonstrated significantly higher levels of free sphingoid bases than those in patients who were NA, indicating enhanced sphingolipid turnover in keratinocytes (P < .05). Plasma from 2 independent cohorts of patients with EH had a significantly increased S1P/ceramide ratio in subjects with EH versus those with AD and or who were NA (P < .01). The S1P level in plasma from subjects with EV was twice the level in plasma from subjects with AD (mean = 1,533 vs 732 pmol/mL; P < .001). Downregulation of S1P lyase expression with silencing RNA led to an increased S1P level and doubled HSV-1 titer in keratinocytes.

CONCLUSIONS

Our data point to long-term abnormalities in the S1P signaling system as a biomarker for previous disseminated viral diseases and a potential treatment target in recurring infections.

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.

Nuclear Sphingosine-1-phosphate Lyase Generated ∆2-hexadecenal is A Regulator of HDAC Activity and Chromatin Remodeling in Lung Epithelial Cells

Sphingosine-1-phosphate (S1P), a bioactive lipid mediator, is generated from sphingosine by sphingosine kinases (SPHKs) 1 and 2 and is metabolized to ∆2-hexadecenal (∆2-HDE) and ethanolamine phosphate by S1P lyase (S1PL) in mammalian cells. We have recently demonstrated the activation of nuclear SPHK2 and the generation of S1P in the nucleus of lung epithelial cells exposed to Pseudomonas aeruginosa. Here, we have investigated the nuclear localization of S1PL and the role of ∆2-HDE generated from S1P in the nucleus as a modulator of histone deacetylase (HDAC) activity and histone acetylation. Electron micrographs of the nuclear fractions isolated from MLE-12 cells showed nuclei free of ER contamination, and S1PL activity was detected in nuclear fractions isolated from primary lung bronchial epithelial cells and alveolar epithelial MLE-12 cells. Pseudomonas aeruginosa-mediated nuclear ∆2-HDE generation, and H3/H4 histone acetylation was attenuated by S1PL inhibitors in MLE-12 cells and human bronchial epithelial cells. In vitro, the addition of exogenous ∆2-HDE (100-10,000 nM) to lung epithelial cell nuclear preparations inhibited HDAC1/2 activity, and increased acetylation of Histone H3 and H4, whereas similar concentrations of S1P did not show a significant change. In addition, incubation of ∆2-HDE with rHDAC1 generated five different amino acid adducts as detected by LC-MS/MS; the predominant adduct being ∆2-HDE with lysine residues of HDAC1. Together, these data show an important role for the nuclear S1PL-derived ∆2-HDE in the modification of HDAC activity, histone acetylation, and chromatin remodeling in lung epithelial cells.

S1P Lyase Regulates Intestinal Stem Cell Quiescence via Ki-67 and FOXO3

Background: Reduction of the Sphingosine-1-phosphate (S1P) degrading enzyme S1P lyase 1 (SGPL1) initiates colorectal cancer progression with parallel loss of colon function in mice. We aimed to investigate the effect of SGPL1 knockout on the stem cell niche in these mice. Methods: We performed immunohistochemical and multi-fluorescence imaging on tissue sections of wildtype and SGPL1 knockout colons under disease conditions. Furthermore, we generated SGPL1 knockout DLD-1 cells (SGPL1^−/−M.Ex1) using CRISPR/Cas9 and characterized cell cycle and AKT signaling pathway via Western blot, immunofluorescence, and FACS analysis. Results: SGPL1 knockout mice were absent of anti-Ki-67 staining in the stem cell niche under disease conditions. This was accompanied by an increase of the negative cell cycle regulator FOXO3 and attenuation of CDK2 activity. SGPL1^−/−M.Ex1 cells show a similar FOXO3 increase but no arrest of proliferation, although we found a suppression of the PDK1/AKT signaling pathway, a prolonged G1-phase, and reduced stem cell markers. Conclusions: While already established colon cancer cells find escape mechanisms from cell cycle arrest, in vivo SGPL1 knockout in the colon stem cell niche during progression of colorectal cancer can contribute to cell cycle quiescence. Thus, we propose a new function of the S1P lyase 1 in stemness.

Lipid rafts as platforms for sphingosine 1-phosphate metabolism and signalling

Spontaneous segregation of cholesterol and sphingolipids as a liquid-ordered phase leads to their clustering in selected membrane areas, the lipid rafts. These specialized membrane domains enriched in gangliosides, sphingomyelin, cholesterol and selected proteins involved in signal transduction, organize and determine the function of multiprotein complexes involved in several aspects of signal transduction, thus regulating cell homeostasis. Sphingosine 1-phosphate, an important biologically active mediator, is involved in several signal transduction processes regulating a plethora of cell functions and, not only several of its downstream effectors tend to localize in lipid rafts, some of the enzymes involved in its pathway, of receptors involved in its signalling and its transporters have been often found in these membrane microdomains. Considering this, in this review we address what is currently known regarding the relationship between sphingosine 1-phosphate metabolism and signalling and plasma membrane lipid rafts.

S1P Lyase siRNA Dampens Malignancy of DLD-1 Colorectal Cancer Cells

Sphingosine-1-phosphate lyase 1 (S1P lyase or SGPL1) is an essential sphingosine-1-phosphate-degrading enzyme. Its manipulation favors onset and progression of colorectal cancer and others in vivo. Thus, SGPL1 is an important modulator of cancer initiation. However, in established cancer, the impact of retrospective SGPL1 modulation is elusive. Herein, we analyzed how SGPL1 siRNA affects malignancy of the human colorectal cancer cells DLD-1 and found that in parallel to the reduction of SGPL1 expression levels, migration, invasion, and differentiation status changed. Diminished SGPL1 expression was accompanied with reduced cell migration and cell invasion in scratch assays and transwell assays, whereas metabolic activity and proliferation was not altered. Decreased migration was attended by increased cell-cell-adhesion through upregulation of E-cadherin and formation of cadherin-actin complexes. Spreading cell islets showed lower vimentin abundance in border cells. Furthermore, SGPL1 siRNA treatment induced expression of epithelial cell differentiation markers, such as intestinal alkaline phosphatase and cytokeratin 20. Hence, interference with SGPL1 expression augmented a partial redifferentiation of colorectal cancer cells toward normal colon epithelial cells. Our investigation showed that SGPL1 siRNA influenced tumorigenic activity of established colorectal cancer cells. We therefore suggest SGPL1 as a target for lowering malignant potential of already existing cancer.

Migratory cues controlling B-lymphocyte trafficking in human lymph nodes

B-cell migration within lymph nodes (LNs) is crucial to adaptive immune responses. Chemotactic gradients are proposed to drive migration of B cells into follicles, followed by their relocation to specific zones of the follicle during activation, and ultimately egress. However, the molecular drivers of these processes and the cells generating chemotactic signals that affect B cells in human LNs are not well understood. We used immunofluorescence microscopy, flow cytometry and functional assays to study molecular mechanisms of B-cell migration within human LNs, and found subtle but important differences to previous murine models. In human LNs we find CXCL13 is prominently expressed at the follicular edge, often associated with fibroblastic reticular cells located in these areas, whereas follicular dendritic cells show minimal contribution to CXCL13 expression. Human B cells rapidly downregulate CXCR5 on encountering CXCL13, but recover CXCR5 expression in the CXCL13-low environment. These data suggest that the CXCL13 gradient in human LNs is likely to be different from that proposed in mice. We also identify CD68⁺ CD11c⁺ PU.1⁺ tingible body macrophages within both primary and secondary follicles as likely drivers of the sphingosine-1-phosphate (S1P) gradient that mediates B-cell egress from LNs, through their expression of the S1P-degrading enzyme, S1P lyase. Based on our findings, we present a model of B-cell migration within human LNs, which has both similarities and interesting differences to that proposed for mice.

Suppression of sphingosine 1-phosphate lyase retards the liver regeneration in mice after partial hepatectomy

Background: Liver regeneration is an extremely complicated process that is regulated by a number of signaling pathways. Sphingosine 1-phosphate (S1P), a potent bioactive lipid mediator playing crucial roles in various cellular responses through its receptors, has been attracting attention in the fields of hepatology, where S1P lyase (SPL), an irreversibly degrading enzyme of S1P, reportedly has a stimulatory role in growth of hepatocellular carcinoma (HCC).

Aim of the study: To examine whether SPL might play a stimulatory role in liver regeneration.

Method: Using in-vivo siRNA technology, we inhibited SPL expression. Seventy percent of the liver was resected in mice as partial hepatectomy (PH). Liver tissue samples were collected and mRNA expression level of the SPL, IHC of the proliferating cell nuclear antigen (PCNA), protein levels of various proliferation factors and lipid measurements were performed in different groups.

Results: The mRNA levels of SPL increased in PH mice on the third day after PH surgery. When we suppressed the expression of SPL by in-vivo siRNA, we observed a significant decline of the PCNA positive cell numbers. Furthermore, the Cyclin D1 expressions and phosphorylation of ERK also were decreased in the siSPL injected PH group.

Conclusion: We verified the importance of the SPL in liver regeneration, using the mice PH model. SPL might be a potential target to facilitate liver regeneration.

Downregulation of S1P Lyase Improves Barrier Function in Human Cerebral Microvascular Endothelial Cells Following an Inflammatory Challenge

Sphingosine 1-phosphate (S1P) is a key bioactive lipid that regulates a myriad of physiological and pathophysiological processes, including endothelial barrier function, vascular tone, vascular inflammation, and angiogenesis. Various S1P receptor subtypes have been suggested to be involved in the regulation of these processes, whereas the contribution of intracellular S1P (iS1P) through intracellular targets is little explored. In this study, we used the human cerebral microvascular endothelial cell line HCMEC/D3 to stably downregulate the S1P lyase (SPL-kd) and evaluate the consequences on endothelial barrier function and on the molecular factors that regulate barrier tightness under normal and inflammatory conditions. The results show that in SPL-kd cells, transendothelial electrical resistance, as a measure of barrier integrity, was regulated in a dual manner. SPL-kd cells had a delayed barrier build up, a shorter interval of a stable barrier, and, thereafter, a continuous breakdown. Contrariwise, a protection was seen from the rapid proinflammatory cytokine-mediated barrier breakdown. On the molecular level, SPL-kd caused an increased basal protein expression of the adherens junction molecules PECAM-1, VE-cadherin, and β-catenin, increased activity of the signaling kinases protein kinase C, AMP-dependent kinase, and p38-MAPK, but reduced protein expression of the transcription factor c-Jun. However, the only factors that were significantly reduced in TNFα/SPL-kd compared to TNFα/control cells, which could explain the observed protection, were VCAM-1, IL-6, MCP-1, and c-Jun. Furthermore, lipid profiling revealed that dihydro-S1P and S1P were strongly enhanced in TNFα-treated SPL-kd cells. In summary, our data suggest that SPL inhibition is a valid approach to dampenan inflammatory response and augmente barrier integrity during an inflammatory challenge.

Sphingolipids in Ventilator Induced Lung Injury: Role of Sphingosine-1-Phosphate Lyase

Mechanical ventilation (MV) performed in respiratory failure patients to maintain lung function leads to ventilator-induced lung injury (VILI). This study investigates the role of sphingolipids and sphingolipid metabolizing enzymes in VILI using a rodent model of VILI and alveolar epithelial cells subjected to cyclic stretch (CS). MV (0 PEEP (Positive End Expiratory Pressure), 30 mL/kg, 4 h) in mice enhanced sphingosine-1-phosphate lyase (S1PL) expression, and ceramide levels, and decreased S1P levels in lung tissue, thereby leading to lung inflammation, injury and apoptosis. Accumulation of S1P in cells is a balance between its synthesis catalyzed by sphingosine kinase (SphK) 1 and 2 and catabolism mediated by S1P phosphatases and S1PL. Thus, the role of S1PL and SphK1 in VILI was investigated using Sgpl1+/- and Sphk1-/- mice. Partial genetic deletion of Sgpl1 protected mice against VILI, whereas deletion of SphK1 accentuated VILI in mice. Alveolar epithelial MLE-12 cells subjected to pathophysiological 18% cyclic stretch (CS) exhibited increased S1PL protein expression and dysregulation of sphingoid bases levels as compared to physiological 5% CS. Pre-treatment of MLE-12 cells with S1PL inhibitor, 4-deoxypyridoxine, attenuated 18% CS-induced barrier dysfunction, minimized cell apoptosis and cytokine secretion. These results suggest that inhibition of S1PL that increases S1P levels may offer protection against VILI.

Evidence Suggests Sphingosine 1-Phosphate Might Be Actively Generated, Degraded, and Transported to Extracellular Spaces With Increased S1P2 and S1P3 Expression in Colon Cancer

BACKGROUND

A pivotal role of sphingosine 1-phosphate (S1P) in cancer has been suggested based on the ceramide-S1P rheostat theory that the intracellular balance between prosurvival S1P and proapoptotic ceramide determines cell fate. Upregulation of S1P-generating sphingosine kinases (SKs) and downregulation of S1P-degrading S1P lyase (SPL) might increase intracellular S1P levels to exert a prosurvival effect in cancer in general, such as colon cancer. However, we recently observed a distinct S1P metabolism in hepatocellular carcinoma tissues that increased SPL mRNA levels with reduced S1P levels. Thus, we investigated S1P metabolism in colon cancer.

PATIENTS AND METHODS

We enrolled 26 consecutive colon cancer patients, who had undergone surgical treatment.

RESULTS

Not only SK, but also SPL, mRNA levels were increased in colon cancer tissues compared with the adjacent nontumorous tissues. Furthermore, the mRNA levels of another S1P degrading enzyme, S1P phosphatase 1, S1P transporters, spinster homolog 2, adenosine triphosphate-binding cassette subfamily C member 1, and S1P receptors, S1P₂ and S1P₃ were also increased, but the S1P levels were not increased in the colon cancer tissues. The reduction of SPL expression by silencing led to reduced proliferation and invasion, and overexpression of SPL caused enhanced proliferation in colon cancer cell lines.

CONCLUSION

In human colon cancer tissues, mRNA levels of S1P-generating and S1P-degrading enzymes, transporters from inside to outside the cells, and S1P receptors, S1P₂ and S1P₃ were elevated, suggesting active S1P metabolism and movement. This altered S1P metabolism might play a role in colon cancer pathophysiology.

Epigenetic regulation of pro-inflammatory cytokine secretion by sphingosine 1-phosphate (S1P) in acute lung injury: Role of S1P lyase

Cellular level of sphingosine-1-phosphate (S1P), the simplest bioactive sphingolipid, is tightly regulated by its synthesis catalyzed by sphingosine kinases (SphKs) 1 & 2 and degradation mediated by S1P phosphatases, lipid phosphate phosphatases, and S1P lyase. The pleotropic actions of S1P are attributed to its unique inside-out (extracellular) signaling via G-protein-coupled S1P1-5 receptors, and intracellular receptor independent signaling. Additionally, S1P generated in the nucleus by nuclear SphK2 modulates HDAC1/2 activity, regulates histone acetylation, and transcription of pro-inflammatory genes. Here, we present data on the role of S1P lyase mediated S1P signaling in regulating LPS-induced inflammation in lung endothelium. Blocking S1P lyase expression or activity attenuated LPS-induced histone acetylation and secretion of pro-inflammatory cytokines. Degradation of S1P by S1P lyase generates Δ2-hexadecenal and ethanolamine phosphate and the long-chain fatty aldehyde produced in the cytoplasmic compartment of the endothelial cell seems to modulate histone acetylation pattern, which is different from the nuclear SphK2/S1P signaling and inhibition of HDAC1/2. These in vitro studies suggest that S1P derived long-chain fatty aldehyde may be an epigenetic regulator of pro-inflammatory genes in sepsis-induced lung inflammation. Trapping fatty aldehydes and other short chain aldehydes such as 4-hydroxynonenal derived from S1P degradation and lipid peroxidation, respectively by cell permeable agents such as phloretin or other aldehyde trapping agents may be useful in treating sepsis-induced lung inflammation via modulation of histone acetylation. .

Scintillation Proximity Assay to Detect the Changes in Cellular Dihydrosphingosine 1-Phosphate Levels

Compounds that modulate the activity of sphingosine 1-phosphate (S1P)-metabolizing enzymes are expected to be potential therapeutic agents for various diseases. Investigation of their potencies requires not only cell-free but also cell-based assays in which intracellular accumulation/depletion of S1P could be monitored. However, conventional methods have limitations to their simplicity, mainly due to the necessity of a separation process that separates S1P from its related substances. Here, we describe a method utilizing a scintillation proximity assay (SPA) for semi-quantifying intracellular [(3)H]-labeled dihydroS1P ([(3)H]dhS1P), which is also a substrate for S1P-metabolizing enzymes. We found that uncoated yttrium silicate SPA beads could selectively bind to and detect [(3)H]dhS1P rather than [(3)H]dihydrosphingosine (the non-phosphorylated form of [(3)H]dhS1P). Based on this, we developed a novel cell-based assay system which does not require any organic solvent extraction or chromatographic separation, and confirmed its practicality by using siRNA targeting S1P lyase (S1PL) and known S1PL inhibitors as models. Our results demonstrated that this assay is useful for rapid and easy evaluation of S1PL inhibitors, and could be potentially applicable for all compounds that modulate the activity of S1P-metabolizing enzymes.

Therapeutic Strategies and Pharmacological Tools Influencing S1P Signaling and Metabolism

During the last two decades the study of the sphingolipid anabolic, catabolic, and signaling pathways has attracted enormous interest. Especially the introduction of fingolimod into market as first p.o. therapeutic for the treatment of multiple sclerosis has boosted this effect. Although the complex regulation of sphingosine-1-phosphate (S1P) and other catabolic and anabolic sphingosine-related compounds is not fully understood, the influence on different (patho)physiological states from inflammation to cytotoxicity as well as the availability of versatile pharmacological tools that represent new approaches to study these states are described. Here, we have summarized various aspects concerning the many faces of sphingolipid function modulation by different pharmacological tools up to clinical candidates. Due to the immense heterogeneity of physiological or pharmacological actions and complex cross regulations, it is difficult to predict their role in upcoming therapeutic approaches. Currently, inflammatory, immunological, and/or antitumor aspects are discussed.

Sphingolipids in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a devastating disease characterized by alveolar epithelial cell injury, accumulation of fibroblasts/myofibroblasts and deposition of extracellular matrix proteins. Levels of sphingosine-1-phosphate (S1P), a naturally occurring bioactive lipid, are elevated in bronchoalveolar fluids and lung tissues from IPF patients and animal models of pulmonary fibrosis. However, the in vivo contribution of S1P, regulated by its synthesis catalyzed by Sphingosine kinases (SphKs) 1 & 2 and catabolism by S1P phosphatases and S1P lyase (S1PL), in the pathogenesis of pulmonary fibrosis is not well defined. Microarray analysis of blood mononuclear cells from patients with IPF and SphK1-, SphK2- or S1PL-knockout mice and SphK inhibitor were used to assess the role of S1P in fibrogenesis. The expression of SphK1 negatively correlated with lung function and survival of patients with IPF. Further, the expressions of SphK1 and S1PL were increased in lung tissues from patients with IPF and bleomycin-challenged mice. Genetic knockdown of SphK1, but not SphK2, ameliorated bleomycin-induced pulmonary fibrosis in mice while deletion of S1PL (SGPL1(+/-)) in mice potentiated fibrosis post-bleomycin challenge. TGF-β increased the expression of SphK1 and S1PL in human lung fibroblasts and knockdown of SphK1 or treatment with SphK inhibitor attenuated S1P generation and TGF-β mediated signal transduction. Over-expression of S1PL attenuated bleomycin-induced TGF-β secretion and S1P mediated differentiation of human lung fibroblasts through regulation of autophagy. Administration of SphK1 inhibitor 8 days post-bleomycin challenge reduced bleomycin-induced mortality and pulmonary fibrosis. Our results suggest that SphK1 and S1PL play critical roles in the pathology of lung fibrosis and may be novel therapeutic targets.

S1P lyase in thymic perivascular spaces promotes egress of mature thymocytes via up-regulation of S1P receptor 1

Sphingosine 1-phosphate (S1P) and S1P receptor 1 (S1P1) play an important role in the egress of mature CD4 or CD8 single-positive (SP) thymocytes from the thymus. Fingolimod hydrochloride (FTY720), an S1P1 functional antagonist, induced significant accumulation of CD62L(high)CD69(low) mature SP thymocytes in the thymic medulla. Immunohistochemical staining using anti-S1P1 antibody revealed that S1P1 is predominantly expressed on thymocytes in the thymic medulla and is strongly down-regulated even at 3h after FTY720 administration. 2-Acetyl-4-tetrahydroxybutylimidazole (THI), an S1P lyase inhibitor, also induced accumulation of mature SP thymocytes in the thymic medulla with an enlargement of the perivascular spaces (PVS). At 6h after THI administration, S1P1-expressing thymocytes reduced partially as if to form clusters and hardly existed in the proximity of CD31-expressing blood vessels in the thymic medulla, suggesting S1P lyase expression in the cells constructing thymic medullary PVS. To determine the cells expressing S1P lyase in the thymus, we newly established a mAb (YK19-2) specific for mouse S1P lyase. Immunohistochemical staining with YK19-2 revealed that S1P lyase is predominantly expressed in non-lymphoid thymic stromal cells in the thymic medulla. In the thymic medullary PVS, S1P lyase was expressed in ER-TR7-positive cells (reticular fibroblasts and pericytes) and CD31-positive vascular endothelial cells. Our findings suggest that S1P lyase expressed in the thymic medullary PVS keeps the tissue S1P concentration low around the vessels and promotes thymic egress via up-regulation of S1P1.

Inhibition of sphingosine-1-phosphate lyase rescues sphingosine kinase-1-knockout phenotype following murine cardiac arrest

AIMS

To test the role of sphingosine-1-phosphate (S1P) signaling system in the in vivo setting of resuscitation and survival after cardiac arrest.

MAIN METHODS

A mouse model of potassium-induced cardiac arrest and resuscitation was used to test the importance of S1P homeostasis in resuscitation and survival. C57BL/6 and sphingosine kinase-1 knockout (SphK1-KO) female mice were arrested for 8 min then subjected to 5 minute CPR with epinephrine bolus given at 90s after the beginning of CPR. Animal survival was monitored for 4h post-resuscitation. Upregulation of tissue and circulatory S1P levels were achieved via inhibition of S1P lyase by 2-acetyl-5-tetrahydroxybutyl imidazole (THI). Plasma and heart tissue S1P and ceramide levels were quantified by targeted ESI-LC/MS/MS.

KEY FINDINGS

Lack of SphK1 and low tissue/circulatory S1P levels in SphK1-KO mice led to poor animal resuscitation after cardiac arrest and to impaired survival post-resuscitation. Inhibition of S1P lyase in SphK1-KO mice drastically improved animal resuscitation and survival. Improved resuscitation and survival of THI-treated SphK1-KO mice were better correlated with cardiac dihydro-S1P (DHS1P) than S1P levels. The lack of SphK1 and the inhibition of S1P lyase by THI were accompanied by modulation in cardiac S1PR1 and S1PR2 expression and by selective changes in plasma N-palmitoyl- and N-behenoyl-ceramide levels.

SIGNIFICANCE

Our data provide evidence for the crucial role for SphK1 and S1P signaling system in resuscitation and survival after cardiac arrest, which may form the basis for development of novel therapeutic strategy to support resuscitation and long-term survival of cardiac arrest patients.