Sphingosine 1-phosphate induces vascular endothelial growth factor expression in endothelial cells

Sphingosine-1-phosphate promotes osteogenesis by stimulating osteoblast growth and neovascularization in a vascular endothelial growth factor-dependent manner

Sphingosine-1-phosphate (S1P) plays multiple roles in bone metabolism and regeneration. Here, we have identified a novel S1P-regulated osteoanabolic mechanism functionally connecting osteoblasts (OBs) to the highly specialized bone vasculature. We demonstrate that S1P/S1PR3 signaling in OBs stimulates vascular endothelial growth factor a (VEGFa) expression and secretion to promote bone growth in an autocrine and boost osteogenic H-type differentiation of bone marrow endothelial cells in a paracrine manner. VEGFa-neutralizing antibodies and VEGF receptor inhibition by axitinib abrogated OB growth in vitro and bone formation in male C57BL/6J in vivo following S1P stimulation and S1P lyase inhibition, respectively. Pharmacological S1PR3 inhibition and genetic S1PR3 deficiency suppressed VEGFa production, OB growth in vitro, and inhibited H-type angiogenesis and bone growth in male mice in vivo. Together with previous work on the osteoanabolic functions of S1PR2 and S1PR3, our data suggest that S1P-dependent bone regeneration employs several nonredundant positive feedback loops between OBs and the bone vasculature. The identification of this yet unappreciated aspect of osteoanabolic S1P signaling may have implications for regular bone homeostasis as well as diseases where the bone microvasculature is affected such as age-related osteopenia and posttraumatic bone regeneration.

Roles of follicle stimulating hormone and sphingosine 1-phosphate co-administered in the process in mouse ovarian vitrification and transplantation

Some major challenges of ovarian tissue vitrification and transplantation include follicle apoptosis induced by cryopreservation and ischemia-reperfusion injury, as well as ovarian follicle loss during post-transplantation. This research aimed to investigate the protective effects and underlying mechanisms of follicle-stimulating hormone (FSH) and Sphingosine-1-phosphate (S1P) on vitrified and post-transplantation ovaries. Ovaries from 21-day-old mice were cryopreservation by vitrification with 0.3 IU/mL FSH, 2 µM S1P, and 0.3 IU/mL FSH + 2 µM S1P, respectively, for follicle counting and detection of apoptosis-related indicators. The results demonstrated that FSH and S1P co-intervention during the vitrification process could preserve the primordial follicle pool and inhibit follicular atresia by suppressing cell apoptosis. The thawed ovaries were transplanted under the renal capsule of 6-8 week-old ovariectomized mice and removed 24 h or 7 days after transplantation. The results indicated that FSH and S1P co-intervention can inhibit apoptosis and autophagy in ovaries at 24 h after transplantation, and promote follicle survival by up-regulating Cx37 and Cx43 expression, enhanced angiogenesis in transplanted ovaries by promoting VEGF expression, as well as increased the E2 levels to restore ovarian endocrine function at 7 days after transplantation. The hypoxia and ischemia cell model was established by CoCl2 treatment for hypoxia in human granulosa-like tumor cell line (KGN), as well as serum-free culture system was used for ischemia. The results confirmed that ischemia-hypoxia-induced apoptosis in ovarian granulosa cells was reduced by FSH and S1P co-intervention, and granulosa cell autophagy was inhibited by up-regulating the AKT/mTOR signaling pathway. In summary, co-administration of FSH and S1P can maintain ovarian survival during ovarian vitrification and increase follicle survival and angiogenesis after transplantation.

Optimization of Culture Media and Cell Ratios for 3D In Vitro Skeletal Muscle Tissues with Endothelial Cells

A major challenge of engineering larger macroscale tissues in vitro is the limited diffusion of nutrients and oxygen to the interior. For skeletal muscle, this limitation results in millimeter scale outcomes to avoid necrosis. One method to address this constraint may be to vascularize in vitro-grown muscle tissue, to support nutrient (culture media) flow into the interior of the structure. In this exploratory study, we examine culture conditions that enable myogenic development and endothelial cell survival within tissue engineered 3D muscles. Myoblasts (C2C12s), endothelial cells (HUVECs), and endothelial support cells (C3H 10T1/2s) were seeded into Matrigel-fibrin hydrogels and cast into 3D printed frames to form 3D in vitro skeletal muscle tissues. Our preliminary results suggest that the simultaneous optimization of culture media formulation and cell concentrations is necessary for 3D cultured muscles to exhibit robust myosin heavy chain expression and GFP expression from GFP-transfected endothelial cells. The ability to form differentiated 3D muscles containing endothelial cells is a key step toward achieving vascularized 3D muscle tissues, which have potential use as tissue for implantation in a medical setting, as well as for future foods such as cultivated meats.

Sphingolipids and impaired hypoxic stress responses in Huntington disease

Huntington disease (HD) is a debilitating, currently incurable disease. Protein aggregation and metabolic deficits are pathological hallmarks but their link to neurodegeneration and symptoms remains debated. Here, we summarize alterations in the levels of different sphingolipids in an attempt to characterize sphingolipid patterns specific to HD, an additional molecular hallmark of the disease. Based on the crucial role of sphingolipids in maintaining cellular homeostasis, the dynamic regulation of sphingolipids upon insults and their involvement in cellular stress responses, we hypothesize that maladaptations or blunted adaptations, especially following cellular stress due to reduced oxygen supply (hypoxia) contribute to the development of pathology in HD. We review how sphingolipids shape cellular energy metabolism and control proteostasis and suggest how these functions may fail in HD and in combination with additional insults. Finally, we evaluate the potential of improving cellular resilience in HD by conditioning approaches (improving the efficiency of cellular stress responses) and the role of sphingolipids therein. Sphingolipid metabolism is crucial for cellular homeostasis and for adaptations following cellular stress, including hypoxia. Inadequate cellular management of hypoxic stress likely contributes to HD progression, and sphingolipids are potential mediators. Targeting sphingolipids and the hypoxic stress response are novel treatment strategies for HD.

Transcriptional Regulation of Thrombin-Induced Endothelial VEGF Induction and Proangiogenic Response

Thrombin, the ligand of the protease-activated receptor 1 (PAR1), is a well-known stimulator of proangiogenic responses in vascular endothelial cells (ECs), which are mediated through the induction of vascular endothelial growth factor (VEGF). However, the transcriptional events underlying this thrombin-induced VEGF induction and angiogenic response are less well understood at present. As reported here, we conducted detailed promotor activation and signal transduction pathway studies in human microvascular ECs, to decipher the transcription factors and the intracellular signaling events underlying the thrombin and PAR-1-induced endothelial VEGF induction. We found that c-FOS is a key transcription factor controlling thrombin-induced EC VEGF synthesis and angiogenesis. Upon the binding and internalization of its G-protein-coupled PAR-1 receptor, thrombin triggers ERK1/2 signaling and activation of the nuclear AP-1/c-FOS transcription factor complex, which then leads to VEGF transcription, extracellular secretion, and concomitant proangiogenic responses of ECs. In conclusion, exposure of human microvascular ECs to thrombin triggers signaling through the PAR-1–ERK1/2–AP-1/c-FOS axis to control VEGF gene transcription and VEGF-induced angiogenesis. These observations offer a greater understanding of endothelial responses to thromboinflammation, which may help to interpret the results of clinical trials tackling the conditions associated with endothelial injury and thrombosis.

A Rationale for Hypoxic and Chemical Conditioning in Huntington's Disease

Neurodegenerative diseases are characterized by adverse cellular environments and pathological alterations causing neurodegeneration in distinct brain regions. This development is triggered or facilitated by conditions such as hypoxia, ischemia or inflammation and is associated with disruptions of fundamental cellular functions, including metabolic and ion homeostasis. Targeting intracellular downstream consequences to specifically reverse these pathological changes proved difficult to translate to clinical settings. Here, we discuss the potential of more holistic approaches with the purpose to re-establish a healthy cellular environment and to promote cellular resilience. We review the involvement of important molecular pathways (e.g., the sphingosine, δ-opioid receptor or N-Methyl-D-aspartate (NMDA) receptor pathways) in neuroprotective hypoxic conditioning effects and how these pathways can be targeted for chemical conditioning. Despite the present scarcity of knowledge on the efficacy of such approaches in neurodegeneration, the specific characteristics of Huntington’s disease may make it particularly amenable for such conditioning techniques. Not only do classical features of neurodegenerative diseases like mitochondrial dysfunction, oxidative stress and inflammation support this assumption, but also specific Huntington’s disease characteristics: a relatively young age of neurodegeneration, molecular overlap of related pathologies with hypoxic adaptations and sensitivity to brain hypoxia. The aim of this review is to discuss several molecular pathways in relation to hypoxic adaptations that have potential as drug targets in neurodegenerative diseases. We will extract the relevance for Huntington’s disease from this knowledge base.

Combination of RAD001 (everolimus) and docetaxel reduces prostate and breast cancer cell VEGF production and tumour vascularisation independently of sphingosine-kinase-1

Resistance to docetaxel is a key problem in current prostate and breast cancer management. We have recently discovered a new molecular mechanism of prostate cancer docetaxel chemoresistance mediated by the mammalian target of rapamycin (mTOR)/sphingosine-kinase-1 (SK1) pathway. Here we investigated the influence of this pathway on vascular endothelial growth factor (VEGF) production and tumour vascularisation in hormone resistant prostate and breast cancer models. Immunofluorescent staining of tumour sections from human oestrogen receptor (ER)-negative breast cancer patients showed a strong correlation between phosphorylated P70S6 kinase (mTOR downstream target), VEGF and SK1 protein expression. In hormone-insensitive prostate (PC3) and breast (MDA-MB-231 and BT-549) cancer cell lines the mTOR inhibitor RAD001 (everolimus) has significantly inhibited SK1 and VEGF expression, while low dose (5 nM) docetaxel had no significant effect. In these cell lines, SK1 overexpression slightly increased the basal levels of VEGF, but did not block the inhibitory effect of RAD001 on VEGF. In a human prostate xenograft model established in nude mice, RAD001 alone or in combination with docetaxel has suppressed tumour growth, VEGF expression and decreased tumour vasculature. Overall, our data demonstrate a new mechanism of an independent regulation of SK1 and VEGF by mTOR in hormone-insensitive prostate and breast cancers.

C-terminally mutated tubby protein accumulates in aggresomes

The tubby protein (Tub), a putative transcription factor, plays important roles in the maintenance and function of neuronal cells. A splicing defect-causing mutation in the 3′-end of the tubby gene, which is predicted to disrupt the carboxy-terminal region of the Tub protein, causes maturity-onset obesity, blindness, and deafness in mice. Although this pathological Tub mutation leads to a loss of function, the precise mechanism has not yet been investigated. Here, we found that the mutant Tub proteins were mostly localized to puncta found in the perinuclear region and that the C-terminus was important for its solubility. Immunocytochemical analysis revealed that puncta of mutant Tub co-localized with the aggresome. Moreover, whereas wild-type Tub was translocated to the nucleus by extracellular signaling, the mutant forms failed to undergo such translocation. Taken together, our results suggest that the malfunctions of the Tub mutant are caused by its misfolding and subsequent localization to aggresomes.

Melatonin prevents deregulation of the sphingosine kinase/sphingosine 1-phosphate signaling pathway in a mouse model of diethylnitrosamine-induced hepatocellular carcinoma

The sphingosine kinase (SphK)/sphingosine 1-phosphate (S1P) pathway is involved in multiple biological processes, including carcinogenesis. Melatonin shows beneficial effects in cell and animal models of hepatocellular carcinoma, but it is unknown if they are associated with the modulation of the SphK/S1P system, along with different downstream signaling pathways modified in cancer. We investigated the effects of melatonin in mice which received diethylnitrosamine (DEN) (35 mg/kg body weight i.p) once a week for 8 weeks. Melatonin was given at 5 or 10 mg/kg/day i.p. beginning 4 weeks after the onset of DEN administration and ending at the sacrifice time (10, 20, 30, or 40 weeks). Melatonin alleviated the distortion of normal hepatic architecture, lowered the incidence of preneoplastic/neoplastic lesions, and inhibited the expression of proliferative/cell cycle regulatory proteins (Ki67, PCNA, cyclin D1, cyclin E, CDK4, and CDK6). S1P levels and expression of SphK1, SphK2, and S1P receptors (S1PR1/S1PR3) were significantly elevated in DEN-treated mice. However, there was a decreased expression of S1P lyase. These effects were significantly abrogated in a time- and dose-dependent manner by melatonin, which also increased S1PR2 expression. Following DEN treatment, mice exhibited increased phosphorylation of PI3K, AKT, mTOR, STAT3, ERK, and p38, and a higher expression of NF-κB p50 and p65 subunits. Melatonin administration significantly inhibited those changes. Data obtained suggest a contribution of the SphK/S1P system and related signaling pathways to the protective effects of melatonin in hepatocarcinogenesis.

ApoA-I induces S1P release from endothelial cells through ABCA1 and SR-BI in a positive feedback manner

Sphingosine-1-phosphate (S1P), which has emerged as a pivotal signaling mediator that participates in the regulation of multiple cellular processes, is derived from various cells, including vascular endothelial cells. S1P accumulates in lipoproteins, especially HDL, and the majority of free plasma S1P is bound to HDL. We hypothesized that HDL-associated S1P is released through mechanisms associated with the HDL maturation process. ApoA-I, a major HDL apolipoprotein, is a critical factor for nascent HDL formation and lipid trafficking via ABCA1. Moreover, apoA-I is capable of promoting bidirectional lipid movement through SR-BI. In the present study, we confirmed that apoA-I can facilitate the production and release of S1P by HUVECs. Furthermore, we demonstrated that ERK1/2 and SphK activation induced by apoA-I is involved in the release of S1P from HUVECs. Inhibitor and siRNA experiments showed that ABCA1 and SR-BI are required for S1P release and ERK1/2 phosphorylation induced by apoA-I. However, the effects triggered by apoA-I were not suppressed by inhibiting ABCA1/JAK2 or the SR-BI/Src pathway. S1P released due to apoA-I activation can stimulate the (ERK1/2)/SphK1 pathway through S1PR (S1P receptor) 1/3. These results indicated that apoA-I not only promotes S1P release through ABCA1 and SR-BI but also indirectly activates the (ERK1/2)/SphK1 pathway by releasing S1P to trigger their receptors. In conclusion, we suggest that release of S1P induced by apoA-I from endothelial cells through ABCA1 and SR-BI is a self-positive-feedback process: apoA-I-(ABCA1 and SR-BI)-(S1P release)-S1PR-ERK1/2-SphK1-(S1P production)-(more S1P release induced by apoA-I).

Concise Review: Pancreatic Cancer and Bone Marrow-Derived Stem Cells

Pancreatic adenocarcinoma remains one of the most challenging diseases of modern gastroenterology, and, even though considerable effort has been put into understanding its pathogenesis, the exact molecular mechanisms underlying the development and/or systemic progression of this malignancy still remain unclear. Recently, much attention has been paid to the potential role of bone marrow-derived stem cells (BMSCs) in this malignancy. Hence, herein, we comprehensively review the most recent discoveries and current achievements and concepts in this field. Specifically, we discuss the significance of identifying pancreatic cancer stem cells and novel therapeutic approaches involving molecular interference of their metabolism. We also describe advances in the current understanding of the biochemical and molecular mechanisms responsible for BMSC mobilization during pancreatic cancer development and systemic spread. Finally, we summarize experimental, translational, and/or clinical evidence regarding the contribution of bone marrow-derived mesenchymal stem cells, endothelial progenitor cells, hematopoietic stem/progenitor cells, and pancreatic stellate cells in pancreatic cancer development/progression. We also present their potential therapeutic value for the treatment of this deadly malignancy in humans.

SIGNIFICANCE

Different bone marrow-derived stem cell populations contribute to the development and/or progression of pancreatic cancer, and they might also be a promising "weapon" that can be used for anticancer treatments in humans. Even though the exact role of these stem cells in pancreatic cancer development and/or progression in humans still remains unclear, this concept continues to drive a completely novel scientific avenue in pancreatic cancer research and gives rise to innovative ideas regarding novel therapeutic modalities that can be safely offered to patients.

Polydatin attenuates AGEs-induced upregulation of fibronectin and ICAM-1 in rat glomerular mesangial cells and db/db diabetic mice kidneys by inhibiting the activation of the SphK1-S1P signaling pathway

We previously demonstrated that activation of sphingosine kinase 1 (SphK1)- sphingosine 1- phosphate (S1P) signaling pathway by high glucose (HG) plays a pivotal role in increasing the expression of fibronectin (FN), an important fibrotic component, by promoting the DNA-binding activity of transcription factor activator protein 1 (AP-1) in glomerular mesangial cells (GMCs) under diabetic conditions. As a multi-target anti-oxidative drug, polydatin (PD) has been shown to have renoprotective effects on experimental diabetes. However, whether PD could resist diabetic nephropathy (DN) by regulating SphK1-S1P signaling pathway needs further investigation. Here, we found that PD significantly reversed the upregulated FN and ICAM-1 expression in GMCs exposed to AGEs. Simultaneously, PD dose-dependently inhibited SphK1 levels at the protein expression and kinase activity and attenuated S1P production under AGEs treatment conditions. In addition, PD reduced SphK activity in GMCs transfected with wild-type SphK(WT) plasmid and significantly suppressed SphK1-mediated increase of FN and ICAM-1 levels under normal conditions. Furthermore, we found that the AGEs-induced upregulation of phosphorylation of c-Jun at Ser63 and Ser73 and c-Fos at Ser32, DNA-binding activity and transcriptional activity of AP-1 were blocked by PD. In comparison with db/db model group, PD treatment suppressed SphK1 levels (mRNA, protein expression, and activity) and S1P production, reversed the upregulation of FN, ICAM-1, c-Jun, and c-Fos in the kidney tissues of diabetic mice, and finally ameliorated renal injury in db/db mice. These findings suggested that the downregulation of SphK1-S1P signaling pathway is probably a novel mechanism by which PD suppressed AGEs-induced FN and ICAM-1 expression and improved renal dysfunction of diabetic models.

Lipid phosphate phosphatases and their roles in mammalian physiology and pathology

Lipid phosphate phosphatases (LPPs) are a group of enzymes that belong to a phosphatase/phosphotransferase family. Mammalian LPPs consist of three isoforms: LPP1, LPP2, and LPP3. They share highly conserved catalytic domains and catalyze the dephosphorylation of a variety of lipid phosphates, including phosphatidate, lysophosphatidate (LPA), sphingosine 1-phosphate (S1P), ceramide 1-phosphate, and diacylglycerol pyrophosphate. LPPs are integral membrane proteins, which are localized on plasma membranes with the active site on the outer leaflet. This enables the LPPs to degrade extracellular LPA and S1P, thereby attenuating their effects on the activation of surface receptors. LPP3 also exhibits noncatalytic effects at the cell surface. LPP expression on internal membranes, such as endoplasmic reticulum and Golgi, facilitates the metabolism of internal lipid phosphates, presumably on the luminal surface of these organelles. This action probably explains the signaling effects of the LPPs, which occur downstream of receptor activation. The three isoforms of LPPs show distinct and nonredundant effects in several physiological and pathological processes including embryo development, vascular function, and tumor progression. This review is intended to present an up-to-date understanding of the physiological and pathological consequences of changing the activities of the different LPPs, especially in relation to cell signaling by LPA and S1P.

Identification and characterization of a mirror-image oligonucleotide that binds and neutralizes sphingosine 1-phosphate, a central mediator of angiogenesis

The sphingolipid S1P (sphingosine 1-phosphate) is known to be involved in a number of pathophysiological conditions such as cancer, autoimmune diseases and fibrosis. It acts extracellularly through a set of five G-protein-coupled receptors, but its intracellular actions are also well documented. Employing in vitro selection techniques, we identified an L-aptamer (Spiegelmer®) to S1P designated NOX-S93. The binding affinity of NOX-S93 to S1P had a K_d value of 4.3 nM. The Spiegelmer® shows equal binding to dihydro-S1P, but no cross-reactivity to the related lipids sphingosine, lysophosphatidic acid, ceramide, ceramide-1-phosphate or sphingosine phosphocholine. In stably transfected CHO (Chinese-hamster ovary) cell lines expressing the S1P receptors S1PR1 or S1PR3, NOX-S93 inhibits S1P-mediated β-arrestin recruitment and intracellular calcium release respectively, with IC₅₀ values in the low nanomolar range. The pro-angiogenic activity of S1P, and of the growth factors VEGF-A (vascular endothelial growth factor-A), FGF-2 (fibroblast growth factor-2) and IGF-1 (insulin-like growth factor-1), was effectively blocked by NOX-S93 in a cellular angiogenesis assay employing primary human endothelial cells. These data provide further evidence for the relevance of extracellular S1P as a central mediator of angiogenesis, suggesting pharmacological S1P neutralization as a promising treatment alternative to current anti-angiogenesis approaches.

The mirror-image aptamer NOX-S93, identified by in vitro selection to bind specifically to S1P, inhibits signalling at S1P receptors. NOX-S93 inhibits the pro-angiogenic activity of S1P and other growth factors, revealing S1P neutralization as a promising anti-angiogenesis approach.

Sphingosine 1-phosphate: a potential molecular target for ovarian cancer therapy?

Sphingosine 1-phosphate (S1P) is an important signaling regulator involved in tumor progression in multiple neoplasms. However, the role of S1P in the pathogenesis of ovarian cancer remains unclear. Herein, we summarize recent advances in understanding the impact of S1P signaling in ovarian cancer progression. S1P, aberrantly produced in ovarian cancer patients, is involved in the regulation of key cellular processes that contribute to ovarian cancer initiation and progression. Moreover, agents that block the S1P signaling pathway inhibit ovarian cancer cell growth or induce apoptosis. Hence, current evidence suggests that S1P may become a potential molecular target for ovarian cancer therapy.

Roles of sphingosine-1-phosphate in reproduction

Sphingosine-1-phosphate (S1P) plays crucial roles in the regulation of cell growth, proliferation, differentiation, cell survival, migration, and angiogenesis. In the reproductive system, S1P protects mammalian germ cells from irradiation or chemotherapy-induced cell death in vivo and in vitro. Moreover, S1P could improve the survival rate of thawed ovary and transplanted ovary. Furthermore, S1P could improve the developmental potential of oocyte and preimplantation embryo. In conclusion, S1P plays important roles in reproduction.

Increased sphingosine-1-phosphate improves muscle regeneration in acutely injured mdx mice

BACKGROUND

Presently, there is no effective treatment for the lethal muscle wasting disease Duchenne muscular dystrophy (DMD). Here we show that increased sphingosine-1-phoshate (S1P) through direct injection or via the administration of the small molecule 2-acetyl-4(5)-tetrahydroxybutyl imidazole (THI), an S1P lyase inhibitor, has beneficial effects in acutely injured dystrophic muscles of mdx mice.

METHODS

We treated mdx mice with and without acute injury and characterized the histopathological and functional effects of increasing S1P levels. We also tested exogenous and direct administration of S1P on mdx muscles to examine the molecular pathways under which S1P promotes regeneration in dystrophic muscles.

RESULTS

Short-term treatment with THI significantly increased muscle fiber size and extensor digitorum longus (EDL) muscle specific force in acutely injured mdx limb muscles. In addition, the accumulation of fibrosis and fat deposition, hallmarks of DMD pathology and impaired muscle regeneration, were lower in the injured muscles of THI-treated mdx mice. Furthermore, increased muscle force was observed in uninjured EDL muscles with a longer-term treatment of THI. Such regenerative effects were linked to the response of myogenic cells, since intramuscular injection of S1P increased the number of Myf5nlacz/+ positive myogenic cells and newly regenerated myofibers in injured mdx muscles. Intramuscular injection of biotinylated-S1P localized to muscle fibers, including newly regenerated fibers, which also stained positive for S1P receptor 1 (S1PR1). Importantly, plasma membrane and perinuclear localization of phosphorylated S1PR1 was observed in regenerating muscle fibers of mdx muscles. Intramuscular increases of S1P levels, S1PR1 and phosphorylated ribosomal protein S6 (P-rpS6), and elevated EDL muscle specific force, suggest S1P promoted the upregulation of anabolic pathways that mediate skeletal muscle mass and function.

CONCLUSIONS

These data show that S1P is beneficial for muscle regeneration and functional gain in dystrophic mice, and that THI, or other pharmacological agents that raise S1P levels systemically, may be developed into an effective treatment for improving muscle function and reducing the pathology of DMD.

Sphingosine kinase 1 induces vasculogenic mimicry formation by up-regulating VEGF expression and secretion in human colon cancer cell line HT-29

AIM: To investigate the role of sphingosine kinase 1 (Sphk1) in vasculogenic mimicry (VM) formation in human colon cancer cell line HT-29 in vitro.

METHODS: HT-29 cells were divided into three groups and treated with 100 nm/L of phorbol 12-myristate 13-acetate (PMA, Sphk1 activation group), 50 μmol/L of N,N-dimethyl-D-erythro-sphingosine (DMS, suppression group), and equal volume of culture medium (control group), respectively. After treatment, cell proliferation was determined by MTT assay, and cell invasiveness and migration were assessed by Transwell chamber assays. Cell apoptosis was observed by transmission electron microscopy (TEM). VM formation was observed in a three-dimensional culture system. The mRNA and protein expression of vascular endothelial growth factor (VEGF) was evaluated by QT-PCR and Western blot, respectively. The secretion of VEGF was detected by ELISA.

RESULTS: Treatment with DMS significantly suppressed cell proliferation, invasion and migration, promoted apoptosis, down-regulated VEGF mRNA and protein expression and secretion, and did not induce VM formation. In contrast, treatment with PMA significantly promoted cell proliferation, invasion (112.00 ± 6.25 vs 57.00 ± 8.00, 142.00 ± 5.57, both P < 0.05) and migration (69.33 ± 4.04 vs 42.00 ± 4.16, 111.00 ± 8.03, both P < 0.05), suppressed apoptosis, up-regulated VEGF mRNA (1.000 vs 0.740 ± 0.122, 1.220 ± 0.075, both P < 0.05) and protein (0.39 ± 0.05 vs 0.23 ± 0.02, 0.65 ± 0.06, both P < 0.05) expression and secretion (103.00 ± 8.96 vs 63.89 ± 8.44, 201.01 ± 17.93, both P < 0.05), and induced the formation of tubular VM.

CONCLUSION: Sphk1 promotes cell proliferation, invasion and migration, suppresses cell apoptosis, and induces VM formation possibly by up-regulating VEGF expression and secretion in human HT-29 colon cancer cell line.

Sphingosine-1-phosphate modulates expression of vascular endothelial growth factor in human articular chondrocytes: a possible new role in arthritis

AIM

Although sphingosine-1-phosphate (S1P) is suggested to have an important role in arthritis, its function in chondrocytes remains unknown. In contrast, vascular endothelial growth factor (VEGF) has been speculated to contribute to the pathogenesis of osteoarthritis (OA), most likely by regulating angiogenesis. We here investigated the in vitro effect of S1P on VEGF expression in human articular chondrocytes from OA patients.

METHODS

Human articular cartilage samples were obtained from patients with OA under informed consent. Chondrocytes were isolated by an enzymatic procedure, grown in monolayer culture, and then stimulated with S1P in the presence or absence of mitogen-activated protein kinase (MAPK) inhibitors or the Gi protein inhibitor pertussis toxin (PTX). VEGF expression and secretion in culture supernatants were analyzed using real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

Although S1P did not enhance basal secretion of matrix metalloproteinase (MMP)-1 and MMP-13, it stimulated VEGF expression in human articular chondrocytes, both at the messenger RNA and protein levels. MAPK inhibitors SB203580 and PD98059 were not effective at suppressing VEGF induction; rather, blocking extracellular signal-regulated kinase (ERK) MAPK enhanced VEGF expression. The Gi protein inhibitor PTX partially attenuated S1P-induced VEGF secretion.

CONCLUSION

Our results suggest that S1P may contribute to the regulation of VEGF expression in human chondrocytes. S1P may therefore play a unique role in the pathophysiology of OA by regulating VEGF expression in chondrocytes.

Sphingosine analogue AAL-R increases TLR7-mediated dendritic cell responses via p38 and type I IFN signaling pathways

Sphingosine analogues display immunosuppressive activities and thus have therapeutic potential in the treatment of autoimmune diseases. In this study, we investigated the effects of the sphingosine analogue AAL-R (FTY720 derivative) on dendritic cell (DC) response upon TLR stimulation. Unlike its known immunosuppressive activity, AAL-R increased TLR7-mediated DC responses by elevating the levels of MHC class I and costimulatory molecules and type I IFN expression and by enhancing the capacity of DCs to induce CD8(+) T cell proliferation. Importantly, the stimulatory activity of AAL-R was dependent on type I IFN signaling, as type I IFN receptor-deficient DCs failed to respond to AAL-R. Also, AAL-R activated p38 MAPK to increase type I IFN synthesis and TLR7-mediated DC maturation. These findings enhance our understanding of sphingosine regulation of the host immune system, in particular upon pathogenic infections.

Extracellular and intracellular sphingosine-1-phosphate in cancer

Sphingosine-1-phosphate (S1P) was first described as a signaling molecule over 20 years ago. Since then, great strides have been made to reveal its vital roles in vastly different cellular and disease processes. Initially, S1P was considered nothing more than the terminal point of sphingolipid metabolism; however, over the past two decades, a large number of reports have helped unveil its full potential as an important regulatory, bioactive sphingolipid metabolite. S1P has a plethora of physiological functions, due in part to its many sites of actions and its different pools, which are both intra- and extracellular. S1P plays pivotal roles in many physiological processes, including the regulation of cell growth, migration, autophagy, angiogenesis, and survival, and thus, not surprisingly, S1P has been linked to cancer. In this review, we will summarize the vast body of knowledge, highlighting the connection between S1P and cancer. We will also suggest new avenues for future research.

Blocking S1P interaction with S1P₁ receptor by a novel competitive S1P₁-selective antagonist inhibits angiogenesis

Sphingosine 1-phosphate receptor type 1 (S1P(1)) was shown to be essential for vascular maturation during embryonic development and it has been demonstrated that substantial crosstalk exists between S1P(1) and other pro-angiogenic growth factors, such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor. We developed a novel S1P(1)-selective antagonist, TASP0277308, which is structurally unrelated to S1P as well as previously described S1P(1) antagonists. TASP0277308 inhibited S1P- as well as VEGF-induced cellular responses, including migration and proliferation of human umbilical vein endothelial cells. Furthermore, TASP0277308 effectively blocked a VEGF-induced tube formation in vitro and significantly suppressed tumor cell-induced angiogenesis in vivo. These findings revealed that S1P(1) is a critical component of VEGF-related angiogenic responses and also provide evidence for the efficacy of TASP0277308 for anti-cancer therapies.

α-Tocopheryl phosphate--an activated form of vitamin E important for angiogenesis and vasculogenesis?

Vitamin E was originally discovered as a dietary factor essential for reproduction in rats. Since then, vitamin E has revealed many important molecular properties such as the scavenging of reactive oxygen and nitrogen species or the modulation of signal transduction and gene expression in antioxidant and nonantioxidant manners. A congenital disease, ataxia with vitamin E deficiency, which is characterized by impaired enrichment of α-tocopherol (αT) in plasma due to mutations in the α-tocopherol transfer protein gene, has been discovered. An effect of vitamin E on angiogenesis and vasculogenesis has been observed in several studies, and recently, it has been demonstrated in the placenta of pregnant ewes, possibly involving the stimulation of vascular endothelial growth factor (VEGF) expression. We recently observed that the phosphorylated form of αT, α-tocopheryl phosphate (αTP), increases the expression of VEGF. We propose that the stimulatory effect of αT on angiogenesis and vasculogenesis is potentiated by phosphorylation to αTP, which may act as a cofactor or active lipid mediator increasing VEGF expression. Increased VEGF expression and consequent enhanced angiogenesis and vasculogenesis induced by αTP may explain not only the essential roles of vitamin E on reproduction, but also its beneficial effects against pre-eclampsia, ischemia/reperfusion injury, and during wound healing. It may also serve as a survival factor for brain and muscle cells. The finding that αTP may regulate vasculogenesis may indicate potential, important pathophysiological implications.

S1P is associated with protection in human and experimental cerebral malaria

Cerebral malaria (CM) is associated with excessive inflammatory responses and endothelial activation. Sphingosine 1-phosphate (S1P) is a signaling sphingolipid implicated in regulating vascular integrity, inflammation and T-cell migration. We hypothesized that altered S1P signaling during malaria contributes to endothelial activation and inflammation, and show that plasma S1P levels were decreased in Ugandan children with CM compared with children with uncomplicated malaria. Using the Plasmodium berghei ANKA (PbA) model of experimental CM (ECM), we demonstrate that humanized S1P lyase (hS1PL)(-/-) mice with reduced S1P lyase activity (resulting in increased bio-available S1P) had improved survival compared with wild-type littermates. Prophylactic and therapeutic treatment of infected mice with compounds that modulate the S1P pathway and are in human trials for other conditions (FTY720 or LX2931) significantly improved survival in ECM. FTY720 treatment improved vascular integrity as indicated by reduced levels of soluble intercellular adhesion molecule (sICAM), increased angiopoietin 1 (Ang1) (regulator of endothelial quiescence) levels, and decreased Evans blue dye leakage into brain parenchyma. Furthermore, treatment with FTY720 decreased IFNγ levels in plasma as well as CD4(+) and CD8(+) T-cell infiltration into the brain. Finally, when administered during infection in combination with artesunate, FTY720 treatment resulted in increased survival to ECM. These findings implicate dysregulation of the S1P pathway in the pathogenesis of human and murine CM and suggest a novel therapeutic strategy to improve clinical outcome in severe malaria.

Roles of sphingosine 1-phosphate on tumorigenesis

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid with a variety of biological activities. It is generated from the conversion of ceramide to sphingosine by ceramidase and the subsequent conversion of sphingosine to S1P, which is catalyzed by sphingosine kinases. Through increasing its intracellular levels by sphingolipid metabolism and binding to its cell surface receptors, S1P regulates several physiological and pathological processes, including cell proliferation, migration, angiogenesis and autophagy. These processes are responsible for tumor growth, metastasis and invasion and promote tumor survival. Since ceramide and S1P have distinct functions in regulating in cell fate decision, the balance between the ceramide/sphingosine/S1P rheostat becomes a potent therapeutic target for cancer cells. Herein, we summarize our current understanding of S1P signaling on tumorigenesis and its potential as a target for cancer therapy.

Regulation of lysophosphatidate signaling by autotaxin and lipid phosphate phosphatases with respect to tumor progression, angiogenesis, metastasis and chemo-resistance

Evidence from clinical, animal and cell culture studies demonstrates that increased autotaxin (ATX) expression is responsible for enhancing tumor progression, cell migration, metastases, angiogenesis and chemo-resistance. These effects depend mainly on the rapid formation of lysophosphatidate (LPA) by ATX. Circulating LPA has a half-life of about 3 min in mice and it is degraded by the ecto-activities of lipid phosphate phosphatases (LPPs). These enzymes also hydrolyze extracellular sphingosine 1-phosphate (S1P), a potent signal for cell division, survival and angiogenesis. Many aggressive tumor cells express high ATX levels and low LPP activities. This favors the formation of locally high LPA and S1P concentrations. Furthermore, LPPs attenuate signaling downstream of the activation of G-protein coupled receptors and receptor tyrosine kinases. Therefore, we propose that the low expression of LPPs in many tumor cells makes them hypersensitive to growth promoting and survival signals that are provided by LPA, S1P, platelet-derived growth factor (PDGF) and epidermal growth factor (EGF). One of the key signaling pathways in this respect appears to be activation of phospholipase D (PLD) and phosphatidate (PA) production. This is required for the transactivations of the EGFR and PDGFR and also for LPA-induced cell migration. PA also increases the activities of ERK, mTOR, myc and sphingosine kinase-1 (SK-1), which provide individual signals for cells division, survival, chemo-resistance and angiogenesis. This review focuses on the balance of signaling by bioactive lipids including LPA, phosphatidylinositol 3,4,5-trisphosphate, PA and S1P versus the action of ceramides. We will discuss how these lipid mediators interact to produce an aggressive neoplastic phenotype.

Sphingosine-1-phosphate induces human endothelial VEGF and MMP-2 production via transcription factor ZNF580: novel insights into angiogenesis

Sphingosine-1-phosphate (S1P)-induced migration and proliferation of endothelial cells are critical for angiogenesis. C2H2-zinc finger (ZNF) proteins usually play an essential role in altering gene expression and regulating the angiogenesis. The aim of this study is to investigate whether a novel human C2H2-zinc finger gene ZNF580 (Gene ID: 51157) is involved in the migration and proliferation of endothelial cells stimulated by S1P. Our study shows that EAhy926 endothelial cells express S1P1, S1P3 and S1P5 receptors. Furthermore, S1P upregulates both ZNF580 mRNA and protein levels in a concentration- and time-dependent manner. SB203580, the specific inhibitor of the p38 mitogen-activated protein kinase (p38 MAPK) pathway, blocks the S1P-induced upregulation of ZNF580. Moreover, overexpression/downexpression of ZNF580 in EAhy926 cells leads to the enhancement/decrease of matrix metalloproteinase-2 (MMP-2) and vascular endothelial growth factor (VEGF) expression as well as the migration and proliferation of EAhy926 endothelial cells. These results elucidate the important role that ZNF580 plays in the process of migration and proliferation of endothelial cells, which provides a foundation for a novel approach to regulate angiogenesis.