Sphingosylphosphocholine, a signaling molecule which accumulates in Niemann-Pick disease type A, stimulates DNA-binding activity of the transcription activator protein AP-1

Chemoselective Esterification of Natural and Prebiotic 1,2-Amino Alcohol Amphiphiles in Water

In cells, a vast number of membrane lipids are formed by the enzymatic O-acylation of polar head groups with acylating agents such as fatty acyl-CoAs. Although such ester-containing lipids appear to be a requirement for life on earth, it is unclear if similar types of lipids could have spontaneously formed in the absence of enzymatic machinery at the origin of life. There are few examples of enzyme-free esterification of amphiphiles in water and none that can occur in water at physiological pH using biochemically relevant acylating agents. Here we report the unexpected chemoselective O-acylation of 1,2-amino alcohol amphiphiles in water directed by Cu(II) and several other transition metal ions. In buffers containing Cu(II) ions, mixing biological 1,2-amino alcohol amphiphiles such as sphingosylphosphorylcholine with biochemically relevant acylating agents, namely, acyl adenylates and acyl-CoAs, leads to the formation of the O-acylation product with high selectivity. The resulting O-acylated sphingolipids self-assemble into vesicles with markedly different biophysical properties than those formed from their N-acyl counterparts. We also demonstrate that Cu(II) can direct the O-acylation of alternative 1,2-amino alcohols, including prebiotically relevant 1,2-amino alcohol amphiphiles, suggesting that simple mechanisms for aqueous esterification may have been prevalent on earth before the evolution of enzymes.

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

Acid Sphingomyelinase, a Lysosomal and Secretory Phospholipase C, Is Key for Cellular Phospholipid Catabolism

Here, we present the main features of human acid sphingomyelinase (ASM), its biosynthesis, processing and intracellular trafficking, its structure, its broad substrate specificity, and the proposed mode of action at the surface of the phospholipid substrate carrying intraendolysosomal luminal vesicles. In addition, we discuss the complex regulation of its phospholipid cleaving activity by membrane lipids and lipid-binding proteins. The majority of the literature implies that ASM hydrolyses solely sphingomyelin to generate ceramide and ignores its ability to degrade further substrates. Indeed, more than twenty different phospholipids are cleaved by ASM in vitro, including some minor but functionally important phospholipids such as the growth factor ceramide-1-phosphate and the unique lysosomal lysolipid bis(monoacylglycero)phosphate. The inherited ASM deficiency, Niemann-Pick disease type A and B, impairs mainly, but not only, cellular sphingomyelin catabolism, causing a progressive sphingomyelin accumulation, which furthermore triggers a secondary accumulation of lipids (cholesterol, glucosylceramide, GM2) by inhibiting their turnover in late endosomes and lysosomes. However, ASM appears to be involved in a variety of major cellular functions with a regulatory significance for an increasing number of metabolic disorders. The biochemical characteristics of ASM, their potential effect on cellular lipid turnover, as well as a potential impact on physiological processes will be discussed.

Toxoplasma gondii induces metabolic disturbances in the hippocampus of BALB/c mice

Toxoplasma gondii can cross the blood-brain barrier and infect different regions of the brain including the hippocampus. In the present study, we examined the impact of Toxoplasma gondii infection on the metabolism of the hippocampus of female BALB/c mice compared to control mice using ultra-high-performance liquid chromatography-tandem mass spectrometry. Multivariate analysis revealed significant differences between infected and control hippocampi and identified 25, 82, and 105 differential metabolites (DMs) in the infected hippocampi at 7, 14, and 21 days post-infection (dpi), respectively. One DM (sphingosyl-phosphocholine in the sphingolipid metabolism pathway) and 11 dysregulated pathways were detected at all time points post-infection, suggesting their important roles in the neuropathogenesis of T. gondii infection. These pathways were related to neural activity, such as inflammatory mediator regulation of TRP channels, retrograde endocannabinoid signaling, and arachidonic acid metabolism. Weighted correlation network analysis and receiver operating characteristic analysis identified 33 metabolites significantly associated with T. gondii infection in the hippocampus, and 30 of these were deemed as potential biomarkers for T. gondii infection. This study provides, for the first time, a global view of the metabolic perturbations that occur in the mouse hippocampus during T. gondii infection. The potential relevance of the identified metabolites and pathways to the pathogenesis of cognitive impairment and psychiatric disorders are discussed.

Adeno-associated viral vector serotype 9-based gene therapy for Niemann-Pick disease type A

Niemann-Pick disease type A (NPD-A) is a lysosomal storage disorder characterized by neurodegeneration and early death. It is caused by loss-of-function mutations in the gene encoding for acid sphingomyelinase (ASM), which hydrolyzes sphingomyelin into ceramide. Here, we evaluated the safety of cerebellomedullary (CM) cistern injection of adeno-associated viral vector serotype 9 encoding human ASM (AAV9-hASM) in nonhuman primates (NHP). We also evaluated its therapeutic benefit in a mouse model of the disease (ASM-KO mice). We found that CM injection in NHP resulted in widespread transgene expression within brain and spinal cord cells without signs of toxicity. CM injection in the ASM-KO mouse model resulted in hASM expression in cerebrospinal fluid and in different brain areas without triggering an inflammatory response. In contrast, direct cerebellar injection of AAV9-hASM triggered immune response. We also identified a minimally effective therapeutic dose for CM injection of AAV9-hASM in mice. Two months after administration, the treatment prevented motor and memory impairment, sphingomyelin (SM) accumulation, lysosomal enlargement, and neuronal death in ASM-KO mice. ASM activity was also detected in plasma from AAV9-hASM CM-injected ASM-KO mice, along with reduced SM amount and decreased inflammation in the liver. Our results support CM injection for future AAV9-based clinical trials in NPD-A as well as other lysosomal storage brain disorders.

Lipid Mediators Regulate Pulmonary Fibrosis: Potential Mechanisms and Signaling Pathways

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease of unknown etiology characterized by distorted distal lung architecture, inflammation, and fibrosis. The molecular mechanisms involved in the pathophysiology of IPF are incompletely defined. Several lung cell types including alveolar epithelial cells, fibroblasts, monocyte-derived macrophages, and endothelial cells have been implicated in the development and progression of fibrosis. Regardless of the cell types involved, changes in gene expression, disrupted glycolysis, and mitochondrial oxidation, dysregulated protein folding, and altered phospholipid and sphingolipid metabolism result in activation of myofibroblast, deposition of extracellular matrix proteins, remodeling of lung architecture and fibrosis. Lipid mediators derived from phospholipids, sphingolipids, and polyunsaturated fatty acids play an important role in the pathogenesis of pulmonary fibrosis and have been described to exhibit pro- and anti-fibrotic effects in IPF and in preclinical animal models of lung fibrosis. This review describes the current understanding of the role and signaling pathways of prostanoids, lysophospholipids, and sphingolipids and their metabolizing enzymes in the development of lung fibrosis. Further, several of the lipid mediators and enzymes involved in their metabolism are therapeutic targets for drug development to treat IPF.

Lysosphingolipids and sphingolipidoses: Psychosine in Krabbe's disease

Until recently, lipids were considered inert building blocks of cellular membranes. This changed three decades ago when lipids were found to regulate cell polarity and vesicle transport, and the "lipid raft" concept took shape. The lipid-driven membrane anisotropy in form of "rafts" that associate with proteins led to the view that organized complexes of lipids and proteins regulate various cell functions. Disturbance of this organization can lead to cellular, tissue, and organ malfunction. Sphingolipidoses, lysosomal storage diseases that are caused by enzyme deficiencies in the sphingolipid degradation pathway, were found to be particularly detrimental to the brain. These enzyme deficiencies result in accumulation of sphingolipid metabolites in lysosomes, although it is not yet clear how this accumulation affects the organization of lipids in cellular membranes. Krabbe's disease (KD), or globoid cell leukodystrophy, was one of the first sphingolipidosis for which the raft concept offered a potential mechanism. KD is caused by mutations in the enzyme β-galactocerebrosidase; however, elevation of its substrate, galactosylceramide, is not observed or considered detrimental. Instead, it was found that a byproduct of galactosylceramide metabolism, the lysosphingolipid psychosine, is accumulated. The "psychosine hypothesis" has been refined by showing that psychosine disrupts lipid rafts and vesicular transport critical for the function of glia and neurons. The role of psychosine in KD is an example of how the disruption of sphingolipid metabolism can lead to elevation of a toxic lysosphingolipid, resulting in disruption of cellular membrane organization and neurotoxicity. © 2016 Wiley Periodicals, Inc.

Choline kinase alpha-Putting the ChoK-hold on tumor metabolism

It is well established that lipid metabolism is drastically altered during tumor development and response to therapy. Choline kinase alpha (ChoKα) is a key mediator of these changes, as it represents the first committed step in the Kennedy pathway of phosphatidylcholine biosynthesis and ChoKα expression is upregulated in many human cancers. ChoKα activity is associated with drug resistant, metastatic, and malignant phenotypes, and represents a robust biomarker and therapeutic target in cancer. Effective ChoKα inhibitors have been developed and have recently entered clinical trials. ChoKα's clinical relevance was, until recently, attributed solely to its production of second messenger intermediates of phospholipid synthesis. The recent discovery of a non-catalytic scaffolding function of ChoKα may link growth receptor signaling to lipid biogenesis and requires a reinterpretation of the design and validation of ChoKα inhibitors. Advances in positron emission tomography, magnetic resonance spectroscopy, and optical imaging methods now allow for a comprehensive understanding of ChoKα expression and activity in vivo. We will review the current understanding of ChoKα metabolism, its role in tumor biology and the development and validation of targeted therapies and companion diagnostics for this important regulatory enzyme. This comes at a critical time as ChoKα-targeting programs receive more clinical interest.

A reflection of the lasting contributions from Dr. Robert Bittman to sterol trafficking, sphingolipid and phospholipid research

With the passing of Dr. Robert Bittman from pancreatic cancer on the 1st October 2014, the lipid research field lost one of the most influential and significant personalities. Robert Bittman's genius was in chemical design and his contribution to the lipid research field was truly immense. The reagents and chemicals he designed and synthesised allowed interrogation of the role of lipids in constituting complex biophysical membranes, sterol transfer and in cellular communication networks. Here we provide a review of these works which serve as a lasting memory to his life.

Inhibition of autophagy promoted sphingosylphosphorylcholine induced cell death in non-small cell lung cancer cells

Sphingosylphosphorylcholine (SPC) is a bioactive lipid mediated popular cell apoptosis in cancer cells. As a cell-specific sphingolipid, its function in lung cancer cells is unknown. Here we showed that SPC treatment triggered necrosis and autophagy but inhibited apoptosis in two non-small cell lung cancer cell lines: A549 cell line and H157 cell line. Then 3-methyladenine (3-MA), an autophagy inhibitor, was introduced to clarify the relationships between autophagy and necrosis or apoptosis. 3MA suppressed the survival furtherly by promoting apoptosis while had no influence on necrosis. Subsequent studies revealed that activity of AKT and mammalian target of rapamycin (mTOR) complex 1 (mTORC1) were downregulated during autophagy. Furthermore, SPC failed to promote autophagy in p53 deleted cells. Thus SPC induced autophagy in non-small cell lung cancer cells was through AKT/mTORC1 and P53 signal pathway. Besides, SPC reduced both the mitochondria membrane potential and ROS level in A549 cells. These findings provided a molecular basis of SPC-stimulated A549 cell death and support the notion that inhibition of autophagy is likely a novel anticancer mechanism.

Magnetic resonance imaging-guided delivery of adeno-associated virus type 2 to the primate brain for the treatment of lysosomal storage disorders

Gene replacement therapy for the neurological deficits caused by lysosomal storage disorders, such as in Niemann-Pick disease type A, will require widespread expression of efficacious levels of acid sphingomyelinase (ASM) in the infant human brain. At present there is no treatment available for this devastating pediatric condition. This is partly because of inherent constraints associated with the efficient delivery of therapeutic agents into the CNS of higher order models. In this study we used an adeno-associated virus type 2 (AAV2) vector encoding human acid sphingomyelinase tagged with a viral hemagglutinin epitope (AAV2-hASM-HA) to transduce highly interconnected CNS regions such as the brainstem and thalamus. On the basis of our data showing global cortical expression of a secreted reporter after thalamic delivery in nonhuman primates (NHPs), we set out to investigate whether such widespread expression could be enhanced after brainstem infusion. To maximize delivery of the therapeutic transgene throughout the CNS, we combined a single brainstem infusion with bilateral thalamic infusions in naive NHPs. We found that enzymatic augmentation in brainstem, thalamic, cortical, as well subcortical areas provided convincing evidence that much of the large NHP brain can be transduced with as few as three injection sites.

Functions of sphingolipid metabolism in mammals--lessons from genetic defects

Much is known about the pathways that control the biosynthesis, transport and degradation of sphingolipids. During the last two decades, considerable progress has been made regarding the roles this complex group of lipids play in maintaining membrane integrity and modulating responses to numerous signals. Further novel insights have been provided by the analysis of newly discovered genetic diseases in humans as well as in animal models harboring mutations in the genes whose products control sphingolipid metabolism and action. Through the description of the phenotypic consequences of genetic defects resulting in the loss of activity of the many proteins that synthesize, transport, bind, or degrade sphingolipids, this review summarizes the (patho)physiological functions of these lipids.

Sphingosylphosphorylcholine acts in an anti-inflammatory manner in renal mesangial cells by reducing interleukin-1β-induced prostaglandin E2 formation

Sphingosylphosphorylcholine (SPC) is a bioactive lipid that binds to G protein-coupled-receptors and activates various signaling cascades. Here, we show that in renal mesangial cells, SPC not only activates various protein kinase cascades but also activates Smad proteins, which are classical members of the transforming growth factor-beta (TGFbeta) signaling pathway. Consequently, SPC is able to mimic TGFbeta-mediated cell responses, such as an anti-inflammatory and a profibrotic response. Interleukin-1beta-stimulated prostaglandin E(2) formation is dose-dependently suppressed by SPC, which is paralleled by reduced secretory phospholipase A(2) (sPLA(2)) protein expression and activity. This effect is due to a reduction of sPLA(2) mRNA expression caused by inhibited sPLA(2) promoter activity. Furthermore, SPC upregulates the profibrotic connective tissue growth factor (CTGF) protein and mRNA expression. Blocking TGFbeta signaling by a TGFbeta receptor kinase inhibitor causes an inhibition of SPC-stimulated Smad activation and reverses both the negative effect of SPC on sPLA(2) expression and the positive effect on CTGF expression. In summary, our data show that SPC, by mimicking TGFbeta, leads to a suppression of proinflammatory mediator production and stimulates a profibrotic cell response that is often the end point of an anti-inflammatory reaction. Thus, targeting SPC receptors may represent a novel therapeutic strategy to cope with inflammatory diseases.

Agonist potency at P2X7 receptors is modulated by structurally diverse lipids

BACKGROUND AND PURPOSE

The P2X(7) receptor exhibits a high degree of plasticity with agonist potency increasing after prolonged receptor activation. In this study we investigated the ability of lipids to modulate agonist potency at P2X(7) receptors.

EXPERIMENTAL APPROACH

A variety of lipids, including lysophosphatidylcholine, sphingosylphosphorylcholine and hexadecylphosphorylcholine were studied for their effect on P2X(7) receptor-stimulated ethidium bromide accumulation in cells expressing human recombinant P2X(7) receptors and on P2X(7) receptor-stimulated interleukin-1 beta (IL1 beta) release from THP-1 cells. The effects of the lipids were also assessed in radioligand binding studies on human P2X(7) receptors.

KEY RESULTS

At concentrations (3-30 microM) below the threshold to cause cell lysis, the lipids increased agonist potency and/or maximal effects at P2X(7) receptors in both ethidium accumulation and IL1 beta release studies. There was little structure activity relationship (SAR) for this effect and sub-lytic concentrations of Triton X-100 partially mimicked the effects of the lipids. The lipids caused cell lysis and increased intracellular calcium at higher concentrations (30-100 microM) which complicated interpretation of their effects in functional studies. However, the lipids (3-100 microM) also increased agonist potency 30-100 fold in radioligand binding studies.

CONCLUSIONS AND IMPLICATIONS

This study demonstrates that a diverse range of lipids increase agonist potency at the P2X(7) receptor in functional and binding studies. The broad SAR, including the effect of Triton X-100, suggests this may reflect changes in membrane properties rather than a direct effect on the P2X(7) receptor. Since many of the lipids studied accumulate in disease states they may enhance P2X(7) receptor function under pathophysiological conditions.

Sphingosylphosphocholine effects on cultured astrocytes reveal mechanisms potentially involved in neurotoxicity in Niemann-Pick type A disease

Niemann-Pick type A is a disease characterized by the absence of a functional SMPD1 (acidic sphingomyelinase) gene and the abnormal accumulation of sphingomyelin. Under these conditions, also sphingosylphosphocholine (SPC, a sphingomyelin metabolite) accumulates in various tissues, including the brain, where it might act as a toxic stimulus, contributing to the appearance of the neurological symptoms. We studied the effects of SPC on astrocytic and neuronal cultures from rat. In particular, we investigated the possibility that SPC acts on astrocytes and that this represents the first step leading to neurodegeneration. Our results show that acute administration of SPC to astrocytes in culture promotes Ca2+ responses and a release of glutamate that, in turn, leads to cytosolic [Ca2+] elevation in neurons. We also show that chronic stimulation by SPC leads astrocytes to proliferate, but can also change their phenotype towards an activated state that might contribute to the inflammatory responses. Interestingly, upon acute SPC stimulation, activated astrocytes release more glutamate. In conclusion, we show that both chronic and acute exposure to SPC can constitute harmful signals that may have a role in the sequence of events leading to neurodegeneration.

The role of lysosphingolipids in the regulation of biological processes

This review summarizes data on the role of lysosphingolipids (glucosyl- and galactosylsphingosines, sphingosine-1-phosphate, sphingosine-1-phosphocholine) in the regulation of various biological processes in normal and pathological states.

Sphingosylphosphorylcholine-induced interleukin-6 production is mediated by protein kinase C and p42/44 extracellular signal-regulated kinase in human dermal fibroblasts

BACKGROUND

Sphingosylphosphorylcholine (SPC) has been reported as a novel lipid mediator that exerts various actions on wound healing process.

OBJECTIVE

The aim of this study is to evaluate the involvement of interleukin-6 (IL-6) in SPC-induced wound healing acceleration.

METHODS

We performed immunohistochemical analysis to demonstrate the IL-6 induction by SPC. To analyze the signaling events, skin fibroblasts were treated with SPC, and then RT-PCR, ELISA and Western blot analyses were carried out.

RESULTS

SPC markedly induced interleukin-6 (IL-6) expression in rabbit ear wound. SPC also induced IL-6 expression at both the mRNA and protein levels in human dermal fibroblasts cultured in vitro. SPC rapidly phosphorylated p42/44 extracellular signal-regulated kinase (ERK). Pretreatment with PD 98059, a specific MAPK kinase 1/2 inhibitor, markedly suppressed SPC-induced IL-6 expression in a dose-dependent manner. Protein kinase C (PKC) activation by phorbol myristate acetate (PMA) potentiated IL-6 mRNA expression, whereas PKC inhibition by bisindolylmaleimide blocked SPC-induced p42/44 ERK phosphorylation and IL-6 expression. Over-expression of PKCalpha markedly induced the IL-6 expression and p42/44 ERK activation.

CONCLUSION

These results suggest that SPC-induced IL-6 production is mediated by PKC-dependent p42/44 ERK activation in human dermal fibroblasts cultured in vitro.

Sphingosylphosphorylcholine stimulates human monocyte-derived dendritic cell chemotaxis

AIM

To investigate the effects of sphingosylphosphorylcholine (SPC) on human monocyte-derived dendritic cell (DC) chemotaxis.

METHODS

Human DC were generated from peripheral blood monocytes by culturing them with granulocyte macrophage-colony stimulating factor and interleukin-4. The effect of SPC on the DC chemotactic migration was measured by chemotaxis assay. Intracellular signaling event involved in the SPC-induced DC chemotaxis was investigated with several inhibitors for specific kinase. The expression of the SPC receptors was examined by reverse transcription polymerase chain reaction.

RESULTS

We found that SPC induced chemotactic migration in immature DC (iDC) and mature DC (mDC). In terms of SPC-induced signaling events, mitogen activated protein kinase activation and Akt activation in iDC and mDC were stimulated. SPC-induced chemotaxis was mediated by extracellular signal-regulated protein kinase and phosphoino-sitide-3-kinase, but not by calcium in both iDC and mDC. Although mDC express ovarian cancer G protein-coupled receptor 1, but not G protein-coupled receptor 4, iDC do not express any of these receptors. To examine the involvement of sphingosine-1-phosphate (S1P) receptors, we checked the effect of an S1P receptor antagonist (VPC23019) on SPC-induced DC chemotaxis. VPC23019 did not affect SPC-induced DC chemotaxis.

CONCLUSION

The results suggest that SPC may play a role in regulating DC trafficking during phagocytosis and the T cell-stimulating phase, and the unique SPC receptor, which is different from S1P receptors, is involved in SPC-induced chemotaxis.

Transcriptional repression of the CTP:phosphocholine cytidylyltransferase gene by sphingosine

We examined the effects of the bioactive lipid, sphingosine, on the expression of the rate-limiting enzyme involved in surfactant phosphatidylcholine synthesis, CCTalpha (CTP:phosphocholine cytidylyltransferase alpha). Sphingosine decreased phosphatidylcholine synthesis by inhibiting CCT activity in primary alveolar type II epithelia. Sphingosine decreased CCTalpha protein and mRNA levels by approx. 50% compared with control. The bioactive lipid did not alter CCTalpha mRNA stability, but significantly inhibited its transcriptional rate. In murine lung epithelia, sphingosine selectively reduced CCTalpha promoter-reporter activity when transfected with a 2 kb CCTalpha promoter/luciferase gene construct. Sphingosine also decreased transgene expression in murine type II epithelia isolated from CCTalpha promoter-reporter transgenic mice harbouring this 2 kb proximal 5'-flanking sequence. Deletional analysis revealed that sphingosine responsiveness was mapped to a negative regulatory element contained within 814 bp upstream of the coding region. The results indicate that bioactive sphingolipid metabolites suppress surfactant lipid synthesis by inhibiting gene transcription of a key surfactant biosynthetic enzyme.

GPR4 plays a critical role in endothelial cell function and mediates the effects of sphingosylphosphorylcholine

Angiogenesis is critical for many physiological and pathological processes. We show here that the lipid sphingosylphosphorylcholine (SPC) induces angiogenesis in vivo and GPR4 is required for the biological effects of SPC on endothelial cells (EC). In human umbilical vein EC, down-regulation of GPR4 specifically inhibits SPC-, but not sphingosine-1-phosphate-, or vascular endothelial growth factor (VEGF)-induced tube formation. Re-introduction of GPR4 fully restores the activity of SPC. In microvascular EC, GPR4 plays a pivotal role in cell survival, growth, migration, and tube formation through both SPC-dependent and -independent pathways. The biological effects resulting from SPC/GPR4 interactions involve the activation of both phosphatidylinositol-3 kinase and Akt. Moreover, the effects of SPC on EC require SPC induced trans-phosphorylation and activation of the VEGF receptor 2. These results identify SPC and its receptor, GPR4, as critical regulators of the angiogenic potential of EC.

Functional role of phospholipids in the nuclear events

This review presents the structural and functional role of phospholipids in chromatin and nuclear matrix as well as the difference in composition and turnover compared to those present in the nuclear membrane. Nuclei have a very active lipid metabolism which seems to play an important role in the transduction of the signals to the genome in response to agonists acting at the plasma membrane level. The evidence on the presence of phospholipid-calcium-dependent protein kinase C (PKC) in nuclei and enzymes of phospholipids turnover is given. Protein kinase C interacts with nuclear phosphoinositol and sphingomyelin cycles products. This fact evidences about possibility that signal transduction events could also occur at the nuclear level during induction of cell proliferation, differentiation and apoptosis.

Sphingosylphosphorylcholine is a ligand for ovarian cancer G-protein-coupled receptor 1

Sphingosylphosphorylcholine (SPC) is a bioactive lipid that acts as an intracellular and extracellular signalling molecule in numerous biological processes. Many of the cellular actions of SPC are believed to be mediated by the activation of unidentified G-protein-coupled receptors. Here we show that SPC is a high-affinity ligand for an orphan receptor, ovarian cancer G-protein-coupled receptor 1 (OGR1). In OGR1-transfected cells, SPC binds to OGR1 with high affinity (Kd = 33.3 nM) and high specificity and transiently increases intracellular calcium. The specific binding of SPC to OGR1 also activates p42/44 mitogen-activated protein kinases (MAP kinases) and inhibits cell proliferation. In addition, SPC causes internalization of OGR1 in a structurally specific manner.

Sphingosine 1-phosphate stimulates cell migration through a G(i)-coupled cell surface receptor. Potential involvement in angiogenesis

Sphingosine 1-phosphate (SPP) has been shown to inhibit chemotaxis of a variety of cells, in some cases through intracellular actions, while in others through receptor-mediated effects. Surprisingly, we found that low concentrations of SPP (10-100 nM) increased chemotaxis of HEK293 cells overexpressing the G protein-coupled SPP receptor EDG-1. In agreement with previous findings in human breast cancer cells (Wang, F., Nohara, K., Olivera, O., Thompson, E. W., and Spiegel, S. (1999) Exp. Cell Res. 247, 17-28), SPP, at micromolar concentrations, inhibited chemotaxis of both vector- and EDG-1-overexpressing HEK293 cells. Nanomolar concentrations of SPP also induced a marked increase in chemotaxis of human umbilical vein endothelial cells (HUVEC) and bovine aortic endothelial cells (BAEC), which express the SPP receptors EDG-1 and EDG-3, while higher concentrations of SPP were less effective. Treatment with pertussis toxin, which ADP-ribosylates and inactivates G(i)-coupled receptors, blocked SPP-induced chemotaxis. Checkerboard analysis indicated that SPP stimulates both chemotaxis and chemokinesis. Taken together, these data suggest that SPP stimulates cell migration by binding to EDG-1. Similar to SPP, sphinganine 1-phosphate (dihydro-SPP), which also binds to this family of SPP receptors, enhanced chemotaxis; whereas, another structurally related lysophospholipid, lysophosphatidic acid, did not compete with SPP for binding nor did it have significant effects on chemotaxis of endothelial cells. Furthermore, SPP increased proliferation of HUVEC and BAEC in a pertussis toxin-sensitive manner. SPP and dihydro-SPP also stimulated tube formation of BAEC grown on collagen gels (in vitro angiogenesis), and potentiated tube formation induced by basic fibroblast growth factor. Pertussis toxin treatment blocked SPP-, but not bFGF-stimulated in vitro angiogenesis. Our results suggest that SPP may play a role in angiogenesis through binding to endothelial cell G(i)-coupled SPP receptors.

Sphingosylphosphorylcholine induces a hypertrophic growth response through the mitogen-activated protein kinase signaling cascade in rat neonatal cardiac myocytes

The sphingolipid metabolites, sphingosine (SPH), SPH 1-phosphate (S1P), and sphingosylphosphorylcholine (SPC), can act as intracellular as well as extracellular signaling molecules. These compounds have been implicated in the regulation of cell growth, differentiation, and programmed cell death in nonmyocytes, but the effects of sphingolipid metabolites in cardiac myocytes are not known. Cultured neonatal rat cardiac myocytes were stimulated with SPH (1 to 10 micromol/L), S1P (1 to 10 micromol/L), or SPC (0.1 to 10 micromol/L) for 24 hours to determine the effects of sphingolipid metabolites on the rates of protein synthesis and degradation. Stimulation with SPC led to an increase in the total amount of protein, an accelerated rate of total protein synthesis, and a decrease in protein degradation in a dose-dependent manner. However, S1P had little effect and SPH had no effect on total protein synthesis. In addition, stimulation with SPC led to a 1.4-fold increase in myocardial cell size and enhanced atrial natriuretic factor gene expression. Pretreatment of the cardiac myocytes with pertussis toxin or PD98059 attenuated the SPC-induced hypertrophic growth response. Further, stimulation with SPC increased phosphorylation of mitogen-activated protein kinase (MAPK) and stimulated MAPK enzyme activity. Finally, endothelin-1 stimulated the generation of SPC in cardiac myocytes. The observation that SPC induces a hypertrophic growth response in cardiac myocytes suggests that SPC may play a critical role in the development of cardiac hypertrophy. The effects of SPC could be mediated, in part, by activation of a G protein-coupled receptor and a MAPK signaling cascade.

Sphingosylphosphorylcholine in Niemann-Pick disease brain: accumulation in type A but not in type B

A study of brain lipids in patients with the sphingomyelinase-deficient types of Niemann-Pick disease demonstrated that abnormal accumulation of sphingomyelin occurs only in the brain of neuronopathic type A patients but not in the non-neuronopathic type B. Additional lipid abnormalities were present in the type A brain. In contrast, the brain lipid profile was normal in type B patients. Since lysosphingolipids have been implicated in the biochemical pathogenesis of other genetic lysosomal sphingolipidoses, the occurrence of sphingosylphosphorylcholine (lysosphingomyelin) was specifically investigated in brain and extraneural tissues, using an HPLC method with fluorescent detection of orthophtalaldehyde derivatives. Levels close to or below the limit of detection (10 pmol/mg tissue protein) were observed in normal and pathological controls. A striking accumulation was observed in brain of two Niemann-Pick type A patients (830 and 430 pmol/mg protein in 27-and 16-month-old children with severe and milder neurological course, respectively), which was not present at the fetal stage of the disease. No significant increase was found in brain tissue from a 3.5 year-old type B patient. In liver and spleen, abnormally high sphingosylphosphorylcholine levels were observed in both types of the disease, with indication of a progressive increase during development. This study establishes the integrity of brain tissue in Niemann-Pick disease type B and suggests that the lysocompound sphingosylphosphorylcholine could play a role in the pathophysiology of brain dysfunction in the neuronopathic type A.

Discrimination between plasma membrane and intracellular target sites of sphingosylphosphorylcholine

On the background of the emerging concept of G protein-coupled sphingolipid receptors, Ca2+ mobilization by sphingosylphosphorylcholine (SPPC) in intact cells and SPPC-induced Ca2+ release in permeabilized cells, both occurring at similar, micromolar concentrations, were characterized and compared. In intact human embryonic kidney (HEK-293) cells, SPPC rapidly increased [Ca2+]i by mobilization of Ca2+ from thapsigargin-sensitive stores. In saponin-permeabilized HEK-293 cells, SPPC released stored Ca2+, in a manner similar to but independent of inositol 1,4,5-trisphosphate. Only the action of SPPC on intact cells, but not that in permeabilized cells, was, at least in part, sensitive to pertussis toxin. In addition and most important, Ca2+ release by SPPC in permeabilized cells was not stereoselective, whereas in intact cells only the naturally occurring D-erythro-SPPC, but not L-threo-SPPC, increased [Ca2+]i. Stereoselectivity of SPPC-induced [Ca2+]i increase was also demonstrated in bovine aortic endothelial cells. In conclusion, Ca2+ mobilization by SPPC in intact cells is independent of the previously described SPPC-gated Ca2+ channel on endoplasmic reticulum but probably mediated by a membrane sphingolipid receptor. Thus, SPPC can regulate Ca2+ homeostasis by acting apparently at two cellular targets, which exhibit clearly distinct recognition patterns.

Identification of a novel growth factor-like lipid, 1-O-cis-alk-1'-enyl-2-lyso-sn-glycero-3-phosphate (alkenyl-GP) that is present in commercial sphingolipid preparations

Lysophosphatidic acid, a member of the acidic phospholipid autacoid (APA) family of lipid mediators, elicits diverse cellular effects that range from mitogenesis to the prevention of programmed cell death. Sphingosine 1-phosphate and sphingosylphosphorylcholine have also been proposed to be ligands of the APA receptors. However, key observations that provide the foundation of this hypothesis have not been universally reproducible, leading to a controversy in the field. We provide evidence that 1-O-cis-alk-1'-enyl-2-lyso-sn-glycero-3-phosphate (alkenyl-GP) is present in some commercial sphingolipid preparations and is responsible for many of their APA-like effects, which were previously attributed to sphingosylphosphorylcholine. Alkenyl-GP was generated by acidic and basic methanolysis from ethanolamine lysoplasmalogen, which was present in the sphingomyelin fraction that is used to manufacture sphingosylphosphorylcholine. We present the structural identification of alkenyl-GP, using 1H and 13C NMR, Fourier transform infrared spectrometry, and mass spectrometry. Alkenyl-GP was a potent activator of the mitogen-activated protein kinases ERK1/2 and elicited a mitogenic response in Swiss 3T3 fibroblasts. In contrast, sphingosylphosphorylcholine at a concentration of 10 microM was only a weak mitogen and only weakly activated the extracellular signal-regulated protein kinases. Alkenyl-GP has recently been detected as an injury-induced component in the anterior chamber of the eye (Liliom, K., Guan, Z., Tseng, H., Desiderio, D. M., Tigyi, G., and Watsky, M. (1998) Am. J. Physiol. 274, C1065-C1074), indicating that this lipid is a naturally occurring member of the APA mediator family.

The potent lipid mitogen sphingosylphosphocholine activates the DNA binding activity of upstream stimulating factor (USF), a basic helix-loop-helix-zipper protein

We previously demonstrated that the sphingolipid, sphingosylphosphocholine (SPC) increased DNA binding activity of AP-1 proteins accompanying cellular proliferation. Herein, the effects of SPC on DNA binding activity and transcription of the basic, helix-loop-helix, leucine zipper (bHLH-ZIP) proteins Myc, Max, and USF were investigated because they regulate genes involved in mitogenesis. E-box (CACGTG) DNA binding proteins were detected by electrophoretic mobility shift assays in nuclear extracts from Swiss 3T3 fibroblasts. The slowest migrating complex (complex I) increased within 1-3 min after treatment with SPC, remained elevated for 10 min, and increased again after 12 h. Complexes I and II contained USF-1 and USF-2 proteins, and complex I migrated similarly to recombinant USF-1 protein/DNA complex. Treatment of nuclear extracts with alkaline phosphatase decreased these complexes suggesting USF might be a phosphoprotein, post-translationally modified by SPC. max and usf-1 mRNA levels were unaffected by SPC treatment. In contrast, c-myc mRNA was rapidly elevated, reached maximum levels at 0.5-1 h, and showed an additional increase after 12 h, just preceding S phase. Thus, certain bHLH-ZIP transcription factors may be involved in cell growth regulation by SPC.

Sphingosylphosphocholine reduces the calcium ion requirement for activating tissue transglutaminase

Tissue transglutaminase (tTG) catalyzes a Ca2+-dependent transglutaminase reaction resulting in the formation of gamma-glutamyl-epsilon-lysine bonds and is activated during apoptosis to catalyze the formation of apoptotic body. We investigate whether lipids that are membrane components and involved in cell signaling could modify the Ca2+-dependent activation of tTG. We found that sphingosylphosphocholine (lyso-SM) was the only lipid to activate transglutaminase at low Ca2+ concentrations. In the presence of lyso-SM (125 microM), transglutaminase was detectable at 10 microM Ca2+, whereas in the absence of lyso-SM, similar activity was obtained at 160 microM Ca2+. Furthermore, in the presence of lipid vesicles lyso-SM retained the ability to enhance the Ca2+-dependent activation of tTG. Lyso-SM did not significantly change the Km for the glutamyl and primary amine substrates. However, the Kact for Ca2+ was reduced from 300 microM to 90 microM. Structure-function studies of lyso-SM analogs indicate that phosphocholine group on C1, the free amino group at C2 and a C4-C5 double bond are critical for the activation of transglutaminase activity. This is the first demonstration that a specific sphingolipid could enhance the activity of tTG and could play a role in vivo in activation of the tTG at physiologic Ca2+ levels.

A new wound healing agent--sphingosylphosphorylcholine

Spingosylphosphorylcholine (lysosphingomyelin or SPC) is an effective and broad spectrum cell growth promoting agent and a candidate for evaluation on wound healing. The effect of SPC on full-thickness excision and incision wounds in genetically healing-impaired diabetic (db/db) mice was evaluated by measurement of wound area, skin strength, and tissue histology. The effect on cell proliferation was measured in vivo by incorporation of bromo-deoxyuridine and in vitro by [3H] thymidine incorporation. SPC increased the rate of wound closure, with a statistically significant improvement in measured wound areas (p < 0.02, compared with vehicle controls). The optimum concentration was 2-3 microM. SPC, alone and in combination with insulin, stimulated DNA synthesis in cells known to participate in wound healing, including microvascular endothelial cells. In vivo, SPC stimulated proliferation of keratinocytes, fibroblasts, endothelial cells, and cells around sebaceous glands and hair follicles at day 2-4 postwound, resulting in a complete re- epithelialization and profound granulation tissue formation in excisional and incisional wound sites of db.db and db/+ mice. Quantitative assessment of wound tissue section morphology indicated that SPC induced up to a 3-fold increase in the numbers of mitotic cells, resulted in smaller cross-sectional scar area, and led to more normalized tissue in the wound sites. SPC had no deleterious effect on wound skin strength. In conclusion, the acceleration of dermal wound healing animal models suggests that SPC could be an interesting candidate for clinical application.