Stereoselective effects of lysophosphatidylserine in rodents

Lysophosphatidylserine: A Signaling Lipid with Implications in Human Diseases

Lysophosphatidylserine (lyso-PS) has emerged as yet another important signaling lysophospholipid in mammals, and deregulation in its metabolism has been directly linked to an array of human autoimmune and neurological disorders. It has an indispensable role in several biological processes in humans, and therefore, cellular concentrations of lyso-PS are tightly regulated to ensure optimal signaling and functioning in physiological settings. Given its biological importance, the past two decades have seen an explosion in the available literature toward our understanding of diverse aspects of lyso-PS metabolism and signaling and its association with human diseases. In this Review, we aim to comprehensively summarize different aspects of lyso-PS, such as its structure, biodistribution, chemical synthesis, and SAR studies with some synthetic analogs. From a biochemical perspective, we provide an exhaustive coverage of the diverse biological activities modulated by lyso-PSs, such as its metabolism and the receptors that respond to them in humans. We also briefly discuss the human diseases associated with aberrant lyso-PS metabolism and signaling and posit some future directions that may advance our understanding of lyso-PS-mediated mammalian physiology.

Metabolomics in early life and the association with body composition at age 2 years

BACKGROUND AND OBJECTIVES

Early life is a critical window for adiposity programming. Metabolic-profile in early life may reflect this programming and correlate with later life adiposity. We investigated if metabolic-profile at 3 months of age is predictive for body composition at 2 years and if there are differences between boys and girls and between infant feeding types.

METHODS

In 318 healthy term-born infants, we determined body composition with skinfold measurements and abdominal ultrasound at 3 months and 2 years of age. High-throughput-metabolic-profiling was performed on 3-month-blood-samples. Using random-forest-machine-learning-models, we studied if the metabolic-profile at 3 months can predict body composition outcomes at 2 years of age.

RESULTS

Plasma metabolite-profile at 3 months was found to predict body composition at 2 years, based on truncal: peripheral-fat-skinfold-ratio (T:P-ratio), with a predictive value of 75.8%, sensitivity of 100% and specificity of 50%. Predictive value was higher in boys (Q²  = 0.322) than girls (Q²  = 0.117). Of the 15 metabolite variables most strongly associated with T:P-ratio, 11 were also associated with visceral fat at 2 years of age.

CONCLUSION

Several plasma metabolites (LysoPC(22:2), dimethylarginine and others) at 3 months associate with body composition outcome at 2 years. These results highlight the importance of the first months of life for adiposity programming.

The Lysophosphatidylserines-An Emerging Class of Signalling Lysophospholipids

Lysophospholipids are potent hormone-like signalling biological lipids that regulate many important biological processes in mammals (including humans). Lysophosphatidic acid and sphingosine-1-phosphate represent the best studied examples for this lipid class, and their metabolic enzymes and/or cognate receptors are currently under clinical investigation for treatment of various neurological and autoimmune diseases in humans. Over the past two decades, the lysophsophatidylserines (lyso-PSs) have emerged as yet another biologically important lysophospholipid, and deregulation in its metabolism has been linked to various human pathophysiological conditions. Despite its recent emergence, an exhaustive review summarizing recent advances on lyso-PSs and the biological pathways that this bioactive lysophospholipid regulates has been lacking. To address this, here, we summarize studies that led to the discovery of lyso-PS as a potent signalling biomolecule, and discuss the structure, its detection in biological systems, and the biodistribution of this lysophospholipid in various mammalian systems. Further, we describe in detail the enzymatic pathways that are involved in the biosynthesis and degradation of this lipid and the putative lyso-PS receptors reported in the literature. Finally, we discuss the various biological pathways directly regulated by lyso-PSs in mammals and prospect new questions for this still emerging biomedically important signalling lysophospholipid.

Mapping the Neuroanatomy of ABHD16A, ABHD12, and Lysophosphatidylserines Provides New Insights into the Pathophysiology of the Human Neurological Disorder PHARC

Lysophosphatidylserine (lyso-PS), a lysophospholipid derived from phosphatidylserine (PS), has emerged as a potent signaling lipid in mammalian physiology. In vivo, the metabolic serine hydrolases ABHD16A and ABHD12 are major lipases that biosynthesize and degrade lyso-PS, respectively. Of biomedical relevance, deleterious mutations to ABHD12 cause accumulation of lyso-PS in the brain, and this deregulated lyso-PS metabolism leads to the human genetic neurological disorder PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract). While the roles of ABHD16A and ABHD12 in lyso-PS metabolism in the mammalian brain are well established, the anatomical and (sub)cellular localizations of both lipases and the functional cross-talk between them with respect to regulating lyso-PS lipids remain under investigated. Here, using subcellular organelle fractionation, biochemical assays, and immunofluorescence-based high-resolution microscopy, we show that the PS lipase ABHD16A is an endoplasmic reticulum-localized enzyme, an organelle intricately regulating cellular PS levels. In addition, leveraging immunohistochemical analysis using genetic ABHD16A and ABHD12 knockout mice as important controls, we map the anatomical distribution of both of these lipases in tandem in the murine brain and show for the first time the distinct localization of these lipases to different regions and cells of the cerebellum. We complement the aforementioned immunohistochemical studies by quantitatively measuring lyso-PS concentrations in various brain regions using mass spectrometry and find that the cerebellar lyso-PS levels are most affected by deletion of ABHD16A (decreased) or ABHD12 (increased). Taken together, our studies provide new insights into lyso-PS signaling in the cerebellum, the most atrophic brain region in human PHARC subjects.

Identification of lysophosphatidylthreonine with an aromatic fatty acid surrogate as a potent inducer of mast cell degranulation

Upon various stimulations, mast cells (MCs) release a wide variety of chemical mediators stored in their cytoplasmic granules, which then initiates subsequent allergic reactions. Lysophosphatidylserine (LysoPS), a kind of lysophospholipid, potentiates the histamine release from MCs triggered by antigen stimulation. We previously showed through structure-activity studies of LysoPS analogs that LysoPS with a methyl group at the carbon of the serine residue, i.e., lysophosphatidylthreonine (LysoPT), is extremely potent in stimulating the MC degranulation. In this study, as our continuing study to identify more potent LysoPS analogs, we developed LysoPS analogs with fatty acid surrogates. We found that the substitution of oleic acid to an aromatic fatty acid surrogate (C3-pH-p-O-C11) in 2-deoxy-1-LysoPS resulted in significant increase in the ability to induce MCs degranulation compared with 2-deoxy-1-LysoPS with oleic acid. Conversion of the serine residue into the threonine residue further increased the activity of MC degranulation both in vitro and in vivo. The resulting super agonist, 2-deoxy-LysoPT with C3-pH-p-O-C11, will be a useful tool to elucidate the mechanisms of stimulatory effect of LysoPS on MC degranulation.

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Lysophosphatidylserine (LysoPS) stimulates degranulation of mast cell (MC).

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We evaluated various LysoPS analogs for their MC degranulation-stimulating activity.

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We identified a threonine containing LysoPS analogs as a super agonist.

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The MC LysoPS receptor is different from the known LysoPS receptors.

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The super agonist helps to identify the putative MC LysoPS receptor.

Emerging roles for lysophosphatidylserine in resolution of inflammation

Despite overlapping structural aspects with other phospholipids, lysophosphatidylserine (lysoPS), the monoacyl derivative of phosphatidylserine (diacylPS), appears to exert unique signaling characteristics important in both the early stages of initiating acute inflammation and in the orchestration of its resolution. LysoPS has long been known as a signaling phospholipid in mast cell biology, markedly enhancing stimulated histamine release and eicosanoid production. More recently, there has been a resurgence of interest in lysoPS as new roles in the promotion of phagocytosis of apoptotic cells, so-called efferocytosis, and resolution of inflammation have been identified. With regard to the latter, lysoPS generated in/on activated or aged apoptotic neutrophils enhances their clearance by macrophages via signaling through the macrophage G-protein coupled receptor G2A. In macrophages, this early acting pathway results in PKA-dependent augmentation of Rac1 activity via increased production of PGE₂ and cAMP. As such, macrophages stimulated with lysoPS demonstrate significantly increased efferocytic capacity necessary to clear large numbers of recruited neutrophils typical of acute inflammation. Given that clearance of these cells is critical for restoration of tissue function, lysoPS, as a pro-resolving lipid mediator, is hypothesized to play a key role in promoting timely resolution of inflammation. This article will review our current knowledge of lysoPS biology including receptor signaling and mechanisms of generation as well as summarize the more recent evidence of its expanding roles in inflammation.

Identification of a lysophosphatidylserine receptor on mast cells

Lysophosphatidyl-L-serine (lysoPS) is thought to be an immunological regulator because it dramatically augments the degranulation of rat peritoneal mast cells (RPMCs). This stimulatory effect may be mediated by a lysoPS receptor, but its molecule has not been identified yet. During a ligand fishing study for the orphan G-protein-coupled receptor 34 (GPR34), we found that lysoPS caused a dose-dependent inhibition of forskolin-stimulated cAMP accumulation in human GPR34-expressing Chinese hamster ovary (CHO/hGPR34) cells. The CHO/hGPR34 cells were unresponsive to other structurally related phospholipids examined. Quantitative real-time-PCR demonstrated that mRNAs of GPR34 are particularly abundant in mast cells. The effective lysoPS concentration for RPMC degranulation was similar to that required for GPR34 activation, and the structural requirement of lysoPS for RPMC degranulation was in good agreement with that observed in CHO/hGPR34 cells. These results suggest that GPR34 is the functional mast cell lysoPS receptor.

Effect of intracerebroventricular administration of soybean lecithin transphosphatidylated phosphatidylserine on scopolamine-induced amnesic mice

The effect of intracerebroventricularly administered soybean lecithin transphosphatidylated phosphatidylserine (SB-tPS) on memory impairment was evaluated by a passive avoidance task. SB-tPS significantly prolonged the step-through latency induced by scopolamine treatment as in our previous report where SB-tPS was orally administered. The same doses of soybean phosphatidylcholine were ineffective. This result indicates that SB-tPS can act on the brain without any peripheral modification.

Ca2+ influx, phosphoinositide hydrolysis, and histamine release induced by lysophosphatidylserine in mast cells

We have previously demonstrated that snake venom phospholipases A2 (PLA2s) and mammalian PLA2s induced inflammatory processes. This effect was correlated with the activity of the enzymes and the release of lipid mediators. We have now determined the role of lysophosphatidylserine (LysoPS) as an inflammatory lipid mediator. Thus, we have studied the possibility that intracellular calcium concentration, phosphoinositide hydrolysis, and the subsequent histamine release in mast cells is due to the action of lysophosphatidylserine. Lysophosphatidylserine-stimulated release of histamine was significantly higher than release by other lysophospholipids. The contribution of increased phospholipase C activity and the intracellular Ca2+ influx were therefore examined. LysoPS increased mast cell calcium concentration, and this increment was associated with phospholipase C activation and release of inositol phosphates. The increase in intracellular calcium and histamine degranulation induced by LysoPS were inhibited by apomorphine. Pretreatment of mast cells with pertussis toxin decreased the secretagogic effect of LysoPS and compound 48/80 without modifying the effect of the ionophore A23187. These results suggest that pertussis toxin-sensitive G-protein might be involved in the mast cell degranulation produced by lysophosphatidylserine and allow the increase in phospholipase C activity, thus enhancing intracellular calcium concentration, which then induces exocytosis of histamine.

Lipid mediators of immune reactions: effect of a linked phosphorylserine group

Immunoregulation by lipids containing the phosphorylserine (PHS) group has been studied in rodent peritoneal mast cells and human peripheral blood lymphocytes. When PHS is linked to a phospholipid backbone (mono- and diacylglycerol), mast cell activation is produced. However, the effect decreases linking the PHS group to long chain alkanols and is abolished in cholesteryl-PHS, showing that the acylglycerol moiety participates in mast cell activation. Phospholipids containing the PHS group inhibit proliferation of activated peripheral blood lymphocytes. In contrast to mast cells, this effect is retained in alkyl-PHS and is enhanced in cholesteryl-PHS, indicating that in this case the PHS group is the main effector. Among non-phospholipid PHSs, cholesteryl-PHS has been the most interesting since it associates lack of mast cell activation and high inhibitory activity on peripheral blood lymphocytes. This selectivity suggests that this compound may have a potential as an immunosuppressive agent.

Inhibition of phospholipase C delta by hexadecylphosphorylcholine and lysophospholipids with antitumor activity

The antineoplastic compound hexadecylphosphorylcholine (HPC) was shown to be a highly effective inhibitor of phospholipase C delta (PLC delta 1), with an I50 of about 30 nmol/mL (30 microM) in the presence and absence of 200 microM spermine. A number of lysophospholipids, of which HPC can be considered to be a structural analog, also inhibited PLC. Lysosphingomyelin, lysophosphatidylserine, and lysophosphatidylcholine exhibited I50 values of 15, 10, and 7 nmol/mL, respectively, in the presence of 200 microM spermine. The I50 values were increased to 21-53 nmol/mL in the absence of spermine. N,N-Dimethylsphingosine and N,N,N-trimethylsphingosine, which inhibit the metastatic potential of human and murine tumor cells, were weak activators of PLC delta 1. It is postulated that HPC is more effective as an antineoplastic agent than lysophospholipids because HPC is metabolized slowly, while the lysophospholipids are metabolized rapidly in vivo.

Characteristics and possible functions of mast cell phospholipases A2

Phospholipase A2 activity in lysates of mast cells and their related cells [mouse bone marrow-derived IL-3 dependent mast cells (BMMC), rat connective tissue mast cells (CTMC), and rat mastocytoma RBL-2H3 cells] was measured using phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylcholine (PC) as exogenous substrates. Both BMMC and RBL cells showed rather high phospholipase A2 activity, whereas CTMC showed only weak activity. These cells contained at least three types of phospholipase A2. Type 1 enzyme showed no appreciable affinity to heparin, and preferentially hydrolyzed either PC or PE, both of which have an arachidonic acid at the sn-2 position. The activity was absorbed by monoclonal antibody against rabbit platelet cytosolic 85-kDa phospholipase A2. Type 2 enzyme had an affinity to heparin, and was completely inhibited by anti-rat platelet 14-kDa secretory phospholipase A2. This enzyme could be expressed as an "ecto-type" enzyme on the cell surface and might be secreted from cells when mast cells are activated. Type 3 enzyme also had an affinity to heparin, but was separated from type 2 enzyme on reverse-phase HPLC. This enzyme did not interact with anti-14-kDa secretory enzyme antibody. Purified type 3 enzyme (30-kDa) specifically hydrolyzed PS. p-Bromophenacylbromide inhibited all types of phospholipase A2, whereas mepacrine inhibited type 2 and type 3 enzymes, but not type 1 enzyme. Type 2 enzyme was also inhibited by the specific antibody, complement degradation product, and a small-molecular-weight inhibitor. Histamine release was inhibited by all these inhibitors, whereas PGD2 production was inhibited only by p-bromophenacylbromide. Possible roles for these phospholipases A2 in mast cell function are proposed.

Phosphatidylserine-induced modulation of the immune response in mice: effect of intravenous administration

The action of phosphatidylserine on the immune response has been examined in mice after the intravenous administration of phospholipid or exposing cultured splenocytes to the action of phosphatidylserine vesicles. Phosphatidylserine (5-25 mg/kg) reduces the T-dependent and the T-independent antibody production. This effect is observed when the phospholipid is injected before (4 h) but not after (24 h) the immunization. The decreased influence of phosphatidylserine injected 24 h before the immunization indicates the reversibility of the action of phospholipid. The effect on the immune system may in part reflect a direct interaction with lymphocytes, since phosphatidylserine (12-60 microM) decreases the production of T-cell growth factors (mainly interleukin-2) elicited by mitogens in cultured spleen cells and reduces the expression of growth factor receptors in the same cells activated by mitogens. In addition, the activity of T-helper cells is found to be reduced in mice receiving the injection of phosphatidylserine. By contrast, the antigen processing and presentation by macrophages is not affected. The data suggest that the intravenous injection of phosphatidylserine vesicles in mice is followed by a transient decrease of lymphocyte activity.

Activation of phosphoinositide hydrolysis by nerve growth factor and lysophosphatidylserine in rat peritoneal mast cells

Histamine secretion in rat peritoneal mast cells stimulated by nerve growth factor requires a synergistic signal delivered by lysophosphatidylserine. To study the signal-transducing system activated by these compounds, phospholipid metabolism has been investigated in these cells. Phospholipid labeling with 32PO4 reveals a 5-9-fold stimulation of phosphatidic acid, phosphatidylinositol and phosphatidylcholine synthesis. Increased synthesis of phosphatidylinositol is also monitored using [3H]inositol incorporation. When [3H]inositol-labeled mast cells are incubated in the presence of Li+, nerve growth factor and lysophosphatidylserine enhance the accumulation of inositol monophosphate, inositol bisphosphate and inositol trisphosphate. Similar to the induced histamine release, accumulation of inositol phosphates (a) does not occur when the two agonists are added separately; (b) is inhibited when lysophosphatidyl-L-serine is replaced by lysophosphatidyl-D-serine; and (c) is enhanced in the presence of extracellular Ca2+. The data suggest that the interactive stimulus of nerve growth factor and lysophosphatidylserine is transmitted through the polyphosphoinositide-phospholipase C system.