LPA(3), a unique G protein-coupled receptor for lysophosphatidic acid

Lysophosphatidic Acid Receptor 3 (LPA3): Signaling and Phosphorylation Sites

LPA3 receptors were expressed in TREx HEK 293 cells, and their signaling and phosphorylation were studied. The agonist, lysophosphatidic acid (LPA), increased intracellular calcium and ERK phosphorylation through pertussis toxin-insensitive processes. Phorbol myristate acetate, but not LPA, desensitizes LPA3-mediated calcium signaling, the agonists, and the phorbol ester-induced LPA3 internalization. Pitstop 2 (clathrin heavy chain inhibitor) markedly reduced LPA-induced receptor internalization; in contrast, phorbol ester-induced internalization was only delayed. LPA induced rapid β-arrestin-LPA3 receptor association. The agonist and the phorbol ester-induced marked LPA3 receptor phosphorylation, and phosphorylation sites were detected using mass spectrometry. Phosphorylated residues were detected in the intracellular loop 3 (S221, T224, S225, and S229) and in the carboxyl terminus (S321, S325, S331, T333, S335, Y337, and S343). Interestingly, phosphorylation sites are within sequences predicted to constitute β-arrestin binding sites. These data provide insight into LPA3 receptor signaling and regulation.

LPA1 receptors in the lateral habenula regulate negative affective states associated with alcohol withdrawal

The role of lysophosphatidic acid (LPA) signaling in psychiatric disorders and drug abuse is significant. LPA receptors are widely expressed in the central nervous system, including the lateral habenula (LHb). Recent studies suggest that LHb is involved in a negative emotional state during alcohol withdrawal, which can lead to relapse. The current study examines the role of LHb LPA signaling in the negative affective state associated with alcohol withdrawal. Adult male Long-Evans rats were trained to consume either alcohol or water for eight weeks. At 48 h of withdrawal, alcohol-drinking rats showed anxiety- and depression-like symptoms, along with a significant increase in LPA signaling and related neuronal activation molecules, including autotaxin (ATX, Enpp2), LPA receptor 1/3 (LPA1/3), βCaMKII, and c-Fos. However, there was a decrease in lipid phosphate phosphatase-related protein type 4 (LPPR4) in the LHb. Intra-LHb infusion of the LPA1/3 receptor antagonist ki-16425 or PKC-γ inhibitor Go-6983 reduced the abnormal behaviors and elevated relapse-like ethanol drinking. It also normalized high LPA1/3 receptors and enhanced AMPA GluA1 phosphorylation in Ser831 and GluA1/GluA2 ratio. Conversely, selective activation of LPA1/3 receptors by intra-LHb infusion of 18:1 LPA induced negative affective states and upregulated βCaMKII-AMPA receptor phosphorylation in Naive rats, which were reversed by pretreatment with intra-LHb Go-6983. Our findings suggest that disturbances in LPA signaling contribute to adverse affective disorders during alcohol withdrawal, likely through PKC-γ/βCaMKII-linked glutamate signaling. Targeting LPA may therefore be beneficial for individuals suffering from alcohol use disorders.

Usefulness of lysophosphatidylcholine measurement in the cerebrospinal fluid for differential diagnosis of neuropathic pain: Possible introduction into clinical laboratory testing

BACKGROUND

The differential diagnosis of neuropathic pain, especially discrimination between neuropathic pain caused by spinal canal stenosis (SCS) and neuropathic pain associated with causes other than SCS, is sometimes difficult; however, it is important for surgical application.

METHODS

We established a reliable method for measuring lysophosphatidylcholine (LPC), a precursor of lysophosphatidic acids which are known as being pain initiators, using a liquid chromatography-tandem mass spectrometry method, and measured the LPC concentrations in the cerebrospinal fluid (CSF) in patients with SCS (SCS group; n = 76), patients with neuropathic pain caused by non-SCS diseases (Others group; n = 49), and control subjects without pain (control group; n = 92).

RESULTS

Both within-run and between-run CV(%) were almost < 10 %, suggesting an enough performance for clinical introduction. The CSF concentrations of LPC (16:0) and LPC (18:0) were higher in the SCS group than those in the Control or Others group; the concentrations of LPC (18:1), LPC (18:2), LPC (20:4), LPC (22:6) levels were higher in the SCS group than those in the control or others group, but they were also higher in the Others group than those in the control group. The areas under the curve in the ROC curve analyses of LPC (18:1) for discriminating between the SCS and control groups, others and control groups, and SCS and others groups were 0.994, 0.860, and 0.869, respectively.

CONCLUSIONS

LPC measurement in the CSF is useful for the differential diagnosis of neuropathic pain, especially for surgical decision-making, which is expected for clinical introduction.

Dynamic modulations of sphingolipids and glycerophospholipids in COVID-19

BACKGROUND

A heterogeneous clinical phenotype is a characteristic of coronavirus disease 2019 (COVID-19). Therefore, investigating biomarkers associated with disease severity is important for understanding the mechanisms responsible for this heterogeneity and for developing novel agents to prevent critical conditions. This study aimed to elucidate the modulations of sphingolipids and glycerophospholipids, which have been shown to possess potent biological properties.

METHODS

We measured the serum sphingolipid and glycerophospholipid levels in a total of 887 samples from 215 COVID-19 subjects, plus 115 control subjects without infectious diseases and 109 subjects with infectious diseases other than COVID-19.

RESULTS

We observed the dynamic modulations of sphingolipids and glycerophospholipids in the serum of COVID-19 subjects, depending on the time course and severity. The elevation of C16:0 ceramide and lysophosphatidylinositol and decreases in C18:1 ceramide, dihydrosphingosine, lysophosphatidylglycerol, phosphatidylglycerol and phosphatidylinositol were specific to COVID-19. Regarding the association with maximum severity, phosphatidylinositol and phosphatidylcholine species with long unsaturated acyl chains were negatively associated, while lysophosphatidylethanolamine and phosphatidylethanolamine were positively associated with maximum severity during the early phase. Lysophosphatidylcholine and phosphatidylcholine had strong negative correlations with CRP, while phosphatidylethanolamine had strong positive ones. C16:0 ceramide, lysophosphatidylcholine, phosphatidylcholine and phosphatidylethanolamine species with long unsaturated acyl chains had negative correlations with D-dimer, while phosphatidylethanolamine species with short acyl chains and phosphatidylinositol had positive ones. Several species of phosphatidylcholine, phosphatidylethanolamine and sphingomyelin might serve as better biomarkers for predicting severe COVID-19 during the early phase than CRP and D-dimer. Compared with the lipid modulations seen in mice treated with lipopolysaccharide, tissue factor, or histone, the lipid modulations observed in severe COVID-19 were most akin to those in mice administered lipopolysaccharide.

CONCLUSION

A better understanding of the disturbances in sphingolipids and glycerophospholipids observed in this study will prompt further investigation to develop laboratory testing for predicting maximum severity and/or novel agents to suppress the aggravation of COVID-19.

Paradoxical downregulation of LPAR3 exerts tumor-promoting activity through autophagy induction in Ras-transformed cells

Background

Lysophosphatidic acid receptor 3 (LPAR3) is coupled to Gα_i/o and Gα_11/q signaling. Previously, we reported that LPAR3 is highly methylated in carcinogen-induced transformed cells. Here, we demonstrate that LPAR3 exhibits malignant transforming activities, despite being downregulated in transformed cells.

Methods

The LPAR3 knockout (KO) in NIH 3 T3 and Bhas 42 cells was established using the CRISPR/Cas9 system. Both RT-PCR and DNA sequencing were performed to confirm the KO of LPAR3. The cellular effects of LPAR3 KO were further examined by WST-1 assay, immunoblotting analysis, transwell migration assay, colony formation assay, wound scratch assday, in vitro cell transformation assay, and autophagy assay.

Results

In v-H-ras-transformed cells (Ras-NIH 3 T3) with LPAR3 downregulation, ectopic expression of LPAR3 significantly enhanced the migration. In particular, LPAR3 knockout (KO) in Bhas 42 (v-Ha-ras transfected Balb/c 3 T3) and NIH 3 T3 cells caused a decrease in cell survival, transformed foci, and colony formation. LPAR3 KO led to the robust accumulation of LC3-II and autophagosomes and inhibition of autophagic flux by disrupting autophagosome fusion with lysosome. Conversely, autolysosome maturation proceeded normally in Ras-NIH 3 T3 cells upon LPAR3 downregulation. Basal phosphorylation of MEK and ERK markedly increased in Ras-NIH 3 T3 cells, whereas being significantly lower in LPAR3 KO cells, suggesting that increased MEK signaling is involved in autophagosome–lysosome fusion in Ras-NIH 3 T3 cells.

Conclusions

Paradoxical downregulation of LPAR3 exerts cooperative tumor-promoting activity with MEK activation through autophagy induction in Ras-transformed cells. Our findings have implications for the development of cancer chemotherapeutic approaches.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-10053-0.

Lipid metabolism and endometrial receptivity

BACKGROUND

Obesity has now been recognized as a high-risk factor for reproductive health. Although remarkable advancements have been made in ART, a considerable number of infertile obese women still suffer from serial implantation failure, despite the high quality of embryos transferred. Although obesity has long been known to exert various deleterious effects on female fertility, the underlying mechanisms, especially the roles of lipid metabolism in endometrial receptivity, remain largely elusive.

OBJECTIVE AND RATIONALE

This review summarizes current evidence on the impacts of several major lipids and lipid-derived mediators on the embryonic implantation process. Emerging methods for evaluating endometrial receptivity, for example transcriptomic and lipidomic analysis, are also discussed.

SEARCH METHODS

The PubMed and Embase databases were searched using the following keywords: (lipid or fatty acid or prostaglandin or phospholipid or sphingolipid or endocannabinoid or lysophosphatidic acid or cholesterol or progesterone or estrogen or transcriptomic or lipidomic or obesity or dyslipidemia or polycystic ovary syndrome) AND (endometrial receptivity or uterine receptivity or embryo implantation or assisted reproductive technology or in vitro fertilization or embryo transfer). A comprehensive literature search was performed on the roles of lipid-related metabolic pathways in embryo implantation published between January 1970 and March 2022. Only studies with original data and reviews published in English were included in this review. Additional information was obtained from references cited in the articles resulting from the literature search.

OUTCOMES

Recent studies have shown that a fatty acids-related pro-inflammatory response in the embryo-endometrium boundary facilitates pregnancy via mediation of prostaglandin signaling. Phospholipid-derived mediators, for example endocannabinoids, lysophosphatidic acid and sphingosine-1-phosphate, are associated with endometrial receptivity, embryo spacing and decidualization based on evidence from both animal and human studies. Progesterone and estrogen are two cholesterol-derived steroid hormones that synergistically mediate the structural and functional alterations in the uterus ready for blastocyst implantation. Variations in serum cholesterol profiles throughout the menstrual cycle imply a demand for steroidogenesis at the time of window of implantation (WOI). Since 2002, endometrial transcriptomic analysis has been serving as a diagnostic tool for WOI dating. Numerous genes that govern lipid homeostasis have been identified and, based on specific alterations of lipidomic signatures differentially expressed in WOI, lipidomic analysis of endometrial fluid provides a possibility for non-invasive diagnosis of lipids alterations during the WOI.

WIDER IMPLICATIONS

Given that lipid metabolic dysregulation potentially plays a role in infertility, a better understanding of lipid metabolism could have significant clinical implications for the diagnosis and treatment of female reproductive disorders.

Understanding modulations of lipid mediators in cancer using a murine model of carcinomatous peritonitis

Background

Numerous studies have investigated the possible involvement of eicosanoids, lysophospholipids, and sphingolipids in cancer. We considered that comprehensive measurement of these lipid mediators might provide a better understanding of their involvement in the pathogenesis of cancer. In the present study, we attempted to elucidate the modulations of sphingolipids, lysophospholipids, diacyl‐phospholipids, eicosanoids, and related mediators in cancer by measuring their levels simultaneously by a liquid chromatography‐mass spectrometry method in a mouse model of carcinomatous peritonitis.

Methods

We investigated the modulations of these lipids in both ascitic fluid and plasma specimens obtained from Balb/c mice injected intraperitoneally with Colon‐26 cells, as well as the modulations of the lipid contents in the cancer cells obtained from the tumor xenografts.

Results

The results were as follows: the levels of sphingosine 1‐phosphate were increased, while those of lysophosphatidic acid (LysoPA), especially unsaturated long‐chain LysoPA, tended to be increased, in the ascitic fluid. Our findings suggested that ceramides, sphingomyelin, and phosphatidylcholine, their precursors, were supplied by both de novo synthesis and from elsewhere in the body. The levels of lysophosphatidylserine (LysoPS), lysophosphatidylinositol, lysophosphatidylglycerol, and lysophosphatidylethanolamine were also increased in the ascitic fluid, while those of phosphatidylserine (PS), a precursor of LysoPS, were markedly decreased. The levels of arachidonic acid derivatives, especially PGE2‐related metabolites, were increased, while the plasma levels of eicosanoids and related mediators were decreased. Comprehensive statistical analyses mainly identified PS in the ascitic fluid and eicosanoids in the plasma as having highly negative predictive values for cancer.

Conclusions

The results proposed many unknown associations of lipid mediators with cancer, underscoring the need for further studies. In particular, the PS/LysoPS pathway could be a novel therapeutic target, and plasma eicosanoids could be useful biomarkers for cancer.

LPAR2 correlated with different prognosis and immune cell infiltration in head and neck squamous cell carcinoma and kidney renal clear cell carcinoma

Background

Lysophosphatidic acid (LPA) and its receptors play a key role in regulating cancer progression. Upregulation of LPA receptor 2 (LPAR2) plays a role in carcinogenesis; however, the exact role of LPAR2 in tumors remains elusive. This study aims to explore the correlation between LPAR2 expression with tumor prognosis and immune infiltration in pan-cancers.

Materials and methods

The expression of LPAR2 in pan-cancers was analyzed using the Online Cancer Microarray Database (Oncomine), Tumor Immune Estimation Resource (TIMER), and UALCAN databases. The effects of LPAR2 on the clinical prognosis in pan-cancer were examined using the Kaplan–Meier plotter (KM plotter) as well as Gene Expression Profiling Interactive Analysis (GEPIA), UALCAN, and Human Protein Atlas (HPA) databases. Moreover, the R software program was applied for validation of expression and prognostic value of LPAR2 in tumor patients in the Cancer Genome Atlas (TCGA) dataset and the Gene Expression Omnibus (GEO) database. The relationship between the expression level of LPAR2 and the clinical and molecular criteria of head and neck squamous cell carcinoma (HNSC) and kidney renal clear cell carcinoma (KIRC) was analyzed using UALCAN, whereas the relationship between LPAR2 expression and prognosis in patients with HNSC and KIRC with different clinical characteristics was examined using the KM plotter. Furthermore, the correlation between LPAR2 expression and tumor immune infiltration was examined using TIMER. The correlation between LPAR2 expression and gene markers of tumor immune infiltrates was analyzed using TIMER and GEPIA. In addition, the cBioPortal for Cancer Genomics was used to calculate the mutations, methylations, and altered neighbor genes of LPAR2.

Results

The expression of LPAR2 was significantly correlated with the outcome of multiple types of cancer, especially HNSC and KIRC. Furthermore, high expression of LPAR2 was significantly associated with various immune markers in the immune cell subsets of HNSC and KIRC.

Conclusions

High expression of LPAR2 plays significantly different prognostic roles in HNSC and KIRC possibly owing to its association with different immune markers. LPAR2 is correlated with tumor immune cell infiltration and is a valuable prognostic biomarker for HNSC and KIRC. However, further experiments are required to validate these findings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41065-022-00229-w.

Lysophosphatidic Acid Signaling in Cancer Cells: What Makes LPA So Special?

Lysophosphatidic acid (LPA) refers to a family of simple phospholipids that act as ligands for G protein-coupled receptors. While LPA exerts effects throughout the body in normal physiological circumstances, its pathological role in cancer is of great interest from a therapeutic viewpoint. The numerous LPA receptors (LPARs) are coupled to a variety of G proteins, and more than one LPAR is typically expressed on any given cell. While the individual receptors signal through conventional GPCR pathways, LPA is particularly efficacious in stimulating cancer cell proliferation and migration. This review addresses the mechanistic aspects underlying these pro-tumorigenic effects. We provide examples of LPA signaling responses in various types of cancers, with an emphasis on those where roles have been identified for specific LPARs. While providing an overview of LPAR signaling, these examples also reveal gaps in our knowledge regarding the mechanisms of LPA action at the receptor level. The current understanding of the LPAR structure and the roles of LPAR interactions with other receptors are discussed. Overall, LPARs provide insight into the potential molecular mechanisms that underlie the ability of individual GPCRs (or combinations of GPCRs) to elicit a unique spectrum of responses from their agonist ligands. Further knowledge of these mechanisms will inform drug discovery, since GPCRs are promising therapeutic targets for cancer.

Lysophosphatidic Acid Receptors: Biochemical and Clinical Implications in Different Diseases

Lysophosphatidic acid (LPA, 1-acyl-2-hemolytic-sn-glycerol-3-phosphate) extracted from membrane phospholipid is a kind of simple bioactive glycophospholipid, which has many biological functions such as stimulating cell multiplication, cytoskeleton recombination, cell survival, drug-fast, synthesis of DNA and ion transport. Current studies have shown that six G-coupled protein receptors (LPAR1-6) can be activated by LPA. They stimulate a variety of signal transduction pathways through heterotrimeric G-proteins (such as Gα12/13, Gαq/11, Gαi/o and GαS). LPA and its receptors play vital roles in cancers, nervous system diseases, cardiovascular diseases, liver diseases, metabolic diseases, etc. In this article, we discussed the structure of LPA receptors and elucidated their functions in various diseases, in order to better understand them and point out new therapeutic schemes for them.

Development of a Rapid Ultra High-Performance Liquid Chromatography/Tandem Mass Spectrometry Method for the Analysis of sn-1 and sn-2 Lysophosphatidic Acid Regioisomers in Mouse Plasma

Lysophosphatidic acids (lysoPtdOH) are involved in several physiological processes including cell proliferation, inflammation, and glucose metabolism. However, measuring lysoPtdOH is challenging due to inadequate extraction techniques, poor chromatographic resolution, or the inability to discriminate between sn-1 and sn-2 regioisomers. In the present work, we developed a high-throughput (10 min run times) ultra-high-performance liquid chromatography-tandem mass spectrometry method capable of discriminating lysoPtdOH species by their fatty acyl composition and sn-localization on glycerol backbones. We quantitated sn-1/sn-2 regioisomeric pairs of lysoPtdOH with 16:0, 18:0, 18:1, 18:2, 20:4, and 22:6 fatty acyl chains using 50 μL of mouse plasma. The method presented here can be expanded to profile more lysoPtdOH species, and has the potential to be used in clinical settings to quickly screen lysoPtdOH profiles. Finally, the ability to discriminate between sn-1 and sn-2 isomers can provide insights regarding the metabolic origins and fates of specific lysoPtdOH molecules.

Production of extracellular lysophosphatidic acid in the regulation of adipocyte functions and liver fibrosis

Lysophosphatidic acid (LPA), a glycerophospholipid, consists of a glycerol backbone connected to a phosphate head group and an acyl chain linked to sn-1 or sn-2 position. In the circulation, LPA is in sub-millimolar range and mainly derived from hydrolysis of lysophosphatidylcholine, a process mediated by lysophospholipase D activity in proteins such as autotaxin (ATX). Intracellular and extracellular LPAs act as bioactive lipid mediators with diverse functions in almost every mammalian cell type. The binding of LPA to its receptors LPA_1-6 activates multiple cellular processes such as migration, proliferation and survival. The production of LPA and activation of LPA receptor signaling pathways in the events of physiology and pathophysiology have attracted the interest of researchers. Results from studies using transgenic and gene knockout animals with alterations of ATX and LPA receptors genes, have revealed the roles of LPA signaling pathways in metabolic active tissues and organs. The present review was aimed to summarize recent progresses in the studies of extracellular and intracellular LPA production pathways. This includes the functional, structural and biochemical properties of ATX and LPA receptors. The potential roles of LPA production and LPA receptor signaling pathways in obesity, insulin resistance and liver fibrosis are also discussed.

Autotaxin-lysophosphatidic acid-LPA3 signaling at the embryo-epithelial boundary controls decidualization pathways

During pregnancy, up-regulation of heparin-binding (HB-) EGF and cyclooxygenase-2 (COX-2) in the uterine epithelium contributes to decidualization, a series of uterine morphological changes required for placental formation and fetal development. Here, we report a key role for the lipid mediator lysophosphatidic acid (LPA) in decidualization, acting through its G-protein-coupled receptor LPA₃ in the uterine epithelium. Knockout of Lpar3 or inhibition of the LPA-producing enzyme autotaxin (ATX) in pregnant mice leads to HB-EGF and COX-2 down-regulation near embryos and attenuates decidual reactions. Conversely, selective pharmacological activation of LPA₃ induces decidualization via up-regulation of HB-EGF and COX-2. ATX and its substrate lysophosphatidylcholine can be detected in the uterine epithelium and in pre-implantation-stage embryos, respectively. Our results indicate that ATX-LPA-LPA₃ signaling at the embryo-epithelial boundary induces decidualization via the canonical HB-EGF and COX-2 pathways.

Roles of LPA receptor signaling in breast cancer

INTRODUCTION

LPA and its receptors play an important role in mediating malignant behaviors in various cancers, including breast cancer. Aberrant expression of certain LPA receptors in breast cancer suggested that LPA receptors could be potential biomarkers in understanding malignant growth patterns of breast cancer. Further research considering molecular mechanisms for LPA receptors will contribute to new methods of malignant breast cancer diagnosis and treatment. Areas covered: Accumulating studies have indicated that LPA receptors correlated to proliferation, invasion, migration and metastasis both in vivo and in vitro. In this manuscript, we have reviewed LPA receptors expressions and LPA mediated biological behaviors in cell lines, mouse models and patients and their potential molecular pathways. Expert commentary: LPA receptors could be applied in early diagnosis, survival rate prediction, metastasis probability and potential treatment targets. However, further studies are required to clarify the upstream and downstream molecular mechanisms of LPA receptors in breast cancer.

G-Protein-Coupled Lysophosphatidic Acid Receptors and Their Regulation of AKT Signaling

A hallmark of G-protein-coupled receptors (GPCRs) is their ability to recognize and respond to chemically diverse ligands. Lysophospholipids constitute a relatively recent addition to these ligands and carry out their biological functions by activating G-proteins coupled to a large family of cell-surface receptors. This review aims to highlight salient features of cell signaling by one class of these receptors, known as lysophosphatidic acid (LPA) receptors, in the context of phosphatidylinositol 3-kinase (PI3K)-AKT pathway activation. LPA moieties efficiently activate AKT phosphorylation and activation in a multitude of cell types. The interplay between LPA, its receptors, the associated Gαi/o subunits, PI3K and AKT contributes to the regulation of cell survival, migration, proliferation and confers chemotherapy-resistance in certain cancers. However, detailed information on the regulation of PI3K-AKT signals induced by LPA receptors is missing from the literature. Here, some urgent issues for investigation are highlighted.

Mutational mapping of the transmembrane binding site of the G-protein coupled receptor TGR5 and binding mode prediction of TGR5 agonists

TGR5 (Gpbar-1, M-Bar) is a class A G-protein coupled bile acid-sensing receptor predominately expressed in brain, liver and gastrointestinal tract, and a promising drug target for the treatment of metabolic disorders. Due to the lack of a crystal structure of TGR5, the development of TGR5 agonists has been guided by ligand-based approaches so far. Three binding mode models of bile acid derivatives have been presented recently. However, they differ from one another in terms of overall orientation or with respect to the location and interactions of the cholane scaffold, or cannot explain all results from mutagenesis experiments. Here, we present an extended binding mode model based on an iterative and integrated computational and biological approach. An alignment of 68 TGR5 agonists based on this binding mode leads to a significant and good structure-based 3D QSAR model, which constitutes the most comprehensive structure-based 3D-QSAR study of TGR5 agonists undertaken so far and suggests that the binding mode model is a close representation of the "true" binding mode. The binding mode model is further substantiated in that effects predicted for eight mutations in the binding site agree with experimental analyses on the impact of these TGR5 variants on receptor activity. In the binding mode, the hydrophobic cholane scaffold of taurolithocholate orients towards the interior of the orthosteric binding site such that rings A and B are in contact with TM5 and TM6, the taurine side chain orients towards the extracellular opening of the binding site and forms a salt bridge with R79(EL1), and the 3-hydroxyl group forms hydrogen bonds with E169(5.44) and Y240(6.51). The binding mode thus differs in important aspects from the ones recently presented. These results are highly relevant for the development of novel, more potent agonists of TGR5 and should be a valuable starting point for the development of TGR5 antagonists, which could show antiproliferative effects in tumor cells.

Lysophosphatidic Acid and Sphingosine-1-Phosphate: A Concise Review of Biological Function and Applications for Tissue Engineering

The presentation and controlled release of bioactive signals to direct cellular growth and differentiation represents a widely used strategy in tissue engineering. Historically, work in this field has primarily focused on the delivery of large cytokines and growth factors, which can be costly to manufacture and difficult to deliver in a sustained manner. There has been a marked increase over the past decade in the pursuit of lipid mediators due to their wide range of effects over multiple cell types, low cost, and ease of scale-up. Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are two bioactive lysophospholipids (LPLs) that have gained attention for use as pharmacological agents in tissue engineering applications. While these lipids can have similar effects on cellular response, they possess distinct chemical backbones, mechanisms of synthesis and degradation, and signaling pathways using a discrete set of G-protein-coupled receptors (GPCRs). LPA and S1P predominantly act extracellularly on their GPCRs and can directly regulate cell survival, differentiation, cytokine secretion, proliferation, and migration--each of the important functions that must be considered in regenerative medicine. In addition to these potent physiological functions, these LPLs play pivotal roles in a number of pathophysiological processes. To capitalize on the promise of these molecules in tissue engineering, these lipids have been incorporated into biomaterials for in vivo delivery. Here, we survey the effects of LPA and S1P on both cellular- and tissue-level phenotypes, with an eye toward regulating stem/progenitor cell growth and differentiation. In particular, we examine work that has translational applications for cell-based tissue engineering strategies in promoting cell survival, bone and cartilage engineering, and therapeutic angiogenesis.

Curcumin inhibits LPA-induced invasion by attenuating RhoA/ROCK/MMPs pathway in MCF7 breast cancer cells

Breast cancer generally shows poor prognosis because of its invasion and metastasis. Lysophosphatidic acid (LPA) induces and aggravates cancer invasion and metastasis by activating its downstream signal pathways. RhoA/ROCK/MMP signaling was found one of the LPA-induced pathways, which may be involved in invasion of breast cancer. Furthermore, we investigated whether this pathway was involved in curcumin's effect against LPA-induced invasion. LPA incubation was used to enhance invasion of MCF-7 breast cancer cells. RhoA expression was knocked-down by siRNA technique. MTT assay was used to evaluate the proliferation. Transwell assay was utilized to investigate the invasion ability of MCF-7 cells. Real-time PCR and Western blotting were used to assess the expressions of RhoA, ROCK1, ROCK2, MMP2 and MMP9 at both translational and transcriptional levels. The RhoA and ROCK activities were also evaluated. LPA incubation significantly boosted invasion rate of MCF-7. RhoA silencing by siRNA dramatically inhibited LPA-enhanced invasion. Concurrently, RhoA and ROCK activities and expression levels of RhoA, ROCK1, ROCK2, MMP2 and MMP9 were down-regulated by RhoA siRNA transfection. In order to avoid influence of cytotoxicity of curcumin, concentrations below 45 μmol/L were selected to further investigate the mechanism of curcumin's anti-invasion effect. Invasion of LPA-incubated MCF-7 cells was impaired by curcumin in a concentration-dependent manner. Concurrently, RhoA and ROCK activities and expression levels of RhoA, ROCK1, ROCK2, MMP2 and MMP9 were down-regulated by curcumin in a concentration-dependent manner. In conclusion, RhoA/ROCK/MMPs pathway activation is involved in LPA-induced invasion in MCF-7 cells; curcumin inhibited LPA-induced invasion in MCF-7 cells by attenuating RhoA/ROCK/MMPs pathway.

Comparative structures and evolution of vertebrate lipase H (LIPH) genes and proteins: a relative of the phospholipase A1 gene families

Lipase H (LIPH) is a membrane-bound phospholipase generating 2-acyl lysophosphatidic acid (LPA) in the body. LPA is a lipid mediator required for maintaining homeostasis of diverse biological functions and in activating cell surface receptors such as P2Y5, which plays an essential role in hair growth. Bioinformatic methods were used to predict the amino acid sequences, secondary and tertiary structures, and gene locations for LIPH genes and encoded proteins using data from several vertebrate genome projects. Vertebrate LIPH genes contained ten coding exons transcribed on either the positive or negative DNA strands. Evidence is presented for duplicated LIPH genes for the chicken and zebra fish genomes. Vertebrate LIPH protein subunits shared 56–97 % sequence identities and exhibited sequence alignments and identities for key LIPH amino acid residues as well as extensive conservation of predicted secondary and tertiary structures with those previously reported for horse pancreatic lipase (LIPP), with ‘N-signal peptide’, ‘lipase,’ and ‘plat’ structural domains. Comparative studies of vertebrate LIPH sequences with other phospholipase A1-like lipases (LIPI and PS-PLA1), as well as vascular and pancreatic lipases, confirmed predictions for LIPH N-terminal signal peptides (residues 1–18); a conserved vertebrate LIPH N-glycosylation site (66NVT for human LIPH); active site ‘triad’ residues (Ser 154; Asp 178; His 248); disulfide bond residues (233–246; 270–281; 284–292; 427–446), and a ‘short’ 12 residue ‘active site lid’, which is comparable to other phospholipases examined. Phylogenetic analyses demonstrated the relationships and potential evolutionary origins of the vertebrate LIPH family of genes related to, but distinct from other phospholipase A1-like genes (LIPI and PS-PLA1), and from vascular lipase and pancreatic lipase gene families.

Conjugated bile acids activate the sphingosine-1-phosphate receptor 2 in primary rodent hepatocytes

Bile acids have been shown to be important regulatory molecules for cells in the liver and gastrointestinal tract. They can activate various cell signaling pathways including extracellular regulated kinase (ERK)1/2 and protein kinase B (AKT) as well as the G-protein-coupled receptor (GPCR) membrane-type bile acid receptor (TGR5/M-BAR). Activation of the ERK1/2 and AKT signaling pathways by conjugated bile acids has been reported to be sensitive to pertussis toxin (PTX) and dominant-negative Gα(i) in primary rodent hepatocytes. However, the GPCRs responsible for activation of these pathways have not been identified. Screening GPCRs in the lipid-activated phylogenetic family (expressed in HEK293 cells) identified sphingosine-1-phosphate receptor 2 (S1P(2) ) as being activated by taurocholate (TCA). TCA, taurodeoxycholic acid (TDCA), tauroursodeoxycholic acid (TUDCA), glycocholic acid (GCA), glycodeoxycholic acid (GDCA), and S1P-induced activation of ERK1/2 and AKT were significantly inhibited by JTE-013, a S1P(2) antagonist, in primary rat hepatocytes. JTE-013 significantly inhibited hepatic ERK1/2 and AKT activation as well as short heterodimeric partner (SHP) mRNA induction by TCA in the chronic bile fistula rat. Knockdown of the expression of S1P(2) by a recombinant lentivirus encoding S1P(2) shRNA markedly inhibited the activation of ERK1/2 and AKT by TCA and S1P in rat primary hepatocytes. Primary hepatocytes prepared from S1P(2) knock out (S1P(2) (-/-) ) mice were significantly blunted in the activation of the ERK1/2 and AKT pathways by TCA. Structural modeling of the S1P receptors indicated that only S1P(2) can accommodate TCA binding. In summary, all these data support the hypothesis that conjugated bile acids activate the ERK1/2 and AKT signaling pathways primarily through S1P(2) in primary rodent hepatocytes.

Lysophosphatidic Acid Stimulates the Proliferation of Ovarian Cancer Cells via the gep Proto-Oncogene Gα(12)

Lysophosphatidic acid (LPA), an agonist that activates specific G protein-coupled receptors, is present at an elevated concentration in the serum and ascitic fluid of ovarian cancer patients. Although the increased levels of LPA have been linked to the genesis and progression of different cancers including ovarian carcinomas, the specific signaling conduit utilized by LPA in promoting different aspects of oncogenic growth has not been identified. Here, we show that LPA stimulates both migration and proliferation of ovarian cancer cells. Using multiple approaches, we demonstrate that the stimulation of ovarian cancer cells with LPA results in a robust and statistically significant proliferative response. Our results also indicate that Gα(12), the gep proto-oncogene, which can be stimulated by LPA via specific LPA receptors, is overtly activated in a large array of ovarian cancer cells. We further establish that LPA stimulates the rapid activation of Gα(12) in SKOV-3 cells and the expression of CT12, an inhibitory minigene of Gα(12) that disrupts LPAR-Gα(12) interaction and potently inhibits such activation. Using this inhibitory molecule as well as the shRNA approach, we show that the inhibition of Gα(12) or silencing of its expression drastically and significantly attenuates LPA-mediated proliferation of ovarian cancer cell lines such as SKOV3, Hey, and OVCAR-3. Together with our findings that the silencing of Gα(12) does not have any significant effect on LPA-mediated migratory response of SKOV3 cells, our results point to a critical role for LPA-LPAR-Gα(12) signaling in ovarian cancer cell proliferation and not in migration. Thus, results presented here for the first time demonstrate that the gep proto-oncogene forms a specific node in LPA-LPAR-mediated mitogenic signaling in ovarian cancer cells.

Lysophosphatidic acid receptor 2/3-mediated IL-8-dependent angiogenesis in cervical cancer cells

The expression of lysophosphatidic acid (LPA)-specific receptors in cervical cancer has not been clearly defined. In this study, we identified LPA1, LPA2 and LPA3 receptors' mRNA in SiHa, HeLa and CaSki cell lines by RT-PCR. These receptors were not associated with tumor cell proliferation in vitro. We then used a xenograph animal model to evaluate the effects of these receptors on in vivo cervical cancer tumorigenicity. When SiHa cells with different receptor expression patterns were seeded on the backs of SCID mice, the resulting knockout of both LPA2 and LPA3 significantly attenuated tumor growth; this decrease in tumor growth was found to be linked with decreased angiogenesis (microvessel density), suggesting that LPA2 and LPA3 are crucial for in vivo tumor growth through an angiogenic mechanism. We further investigated this mechanism of LPA receptor 2/3-mediated angiogenic capability by analyzing angiogenic factors in protein lysates from receptor knockout tumors, by detecting interleukin (IL-8) mRNA expression after treating with siRNA, by evaluating the biological role of LPA-enhanced IL-8 via endothelial cell tube formation, monolayer permeability, migration and cell growth assays, and by IL-8 knockout xenograft mice modeling. We found that the angiogenesis is mediated through IL-8. Finally, we evaluated the regulation pathways involved in LPA-induced IL-8 expression. We found that LPA receptor 2/3-mediated IL-8 expression occurs through Gi/PI3K/AKT, Gi/PKC and IκB/NF-κB signaling. In conclusion, we propose that LPA2 and LPA3 might play an important role in cervical cancer tumor growth through IL-8-dependent angiogenesis.

Pulmonary fibrosis inducer, bleomycin, causes redox-sensitive activation of phospholipase D and cytotoxicity through formation of bioactive lipid signal mediator, phosphatidic acid, in lung microvascular endothelial cells

The mechanisms of lung microvascular complications and pulmonary hypertension known to be associated with idiopathic pulmonary fibrosis (IPF), a debilitating lung disease, are not known. Therefore, we investigated whether bleomycin, the widely used experimental IPF inducer, would be capable of activating phospholipase D (PLD) and generating the bioactive lipid signal-mediator phosphatidic acid (PA) in our established bovine lung microvascular endothelial cell (BLMVEC) model. Our results revealed that bleomycin induced the activation of PLD and generation of PA in a dose-dependent (5, 10, and 100 µg) and time-dependent (2-12 hours) fashion that were significantly attenuated by the PLD-specific inhibitor, 5-fluoro-2-indolyl des-chlorohalopemide (FIPI). PLD activation and PA generation induced by bleomycin (5 µg) were significantly attenuated by the thiol protectant (N-acetyl-L-cysteine), antioxidants, and iron chelators suggesting the role of reactive oxygen species (ROS), lipid peroxidation, and iron therein. Furthermore, our study demonstrated the formation of ROS and loss of glutathione (GSH) in cells following bleomycin treatment, confirming oxidative stress as a key player in the bleomycin-induced PLD activation and PA generation in ECs. More noticeably, PLD activation and PA generation were observed to happen upstream of bleomycin-induced cytotoxicity in BLMVECs, which was protected by FIPI. This was also supported by our current findings that exposure of cells to exogenous PA led to internalization of PA and cytotoxicity in BLMVECs. For the first time, this study revealed novel mechanism of the bleomycin-induced redox-sensitive activation of PLD that led to the generation of PA, which was capable of inducing lung EC cytotoxicity, thus suggesting possible bioactive lipid-signaling mechanism/mechanisms of microvascular disorders encountered in IPF.