Lysophosphatidic acid and its role in reproduction

Transplantation-based screen identifies inducers of muscle progenitor cell engraftment across vertebrate species

Stem cell transplantation presents a potentially curative strategy for genetic disorders of skeletal muscle, but this approach is limited by the deleterious effects of cell expansion in vitro and consequent poor engraftment efficiency. In an effort to overcome this limitation, we sought to identify molecular signals that enhance the myogenic activity of cultured muscle progenitors. Here, we report the development and application of a cross-species small-molecule screening platform employing zebrafish and mice, which enables rapid, direct evaluation of the effects of chemical compounds on the engraftment of transplanted muscle precursor cells. Using this system, we screened a library of bioactive lipids to discriminate those that could increase myogenic engraftment in vivo in zebrafish and mice. This effort identified two lipids, lysophosphatidic acid and niflumic acid, both linked to the activation of intracellular calcium-ion flux, which showed conserved, dose-dependent, and synergistic effects in promoting muscle engraftment across these vertebrate species.

Stockpiling by pups and self-sacrifice by their fasting mothers observed in birth to weaning serum metabolomes of Atlantic grey seals

During the uniquely short lactations of true seals, pups acquire a greater proportion of maternal body resources, at a greater rate, than in any other group of mammals. Mothers in many species enter a period of anorexia but must preserve sufficient reserves to fuel hunting and thermoregulation for return to cold seas. Moreover, pups may undergo a period of development after weaning during which they have no maternal care or nutrition. This nutritionally closed system presents a potentially extreme case of conflict between maternal survival and adequate provisioning of offspring, likely presenting strains on their metabolisms. We examined the serum metabolomes of five mother and pup pairs of Atlantic grey seals, Halichoerus grypus, from birth to weaning. Changes with time were particularly evident in pups, with indications of strain in the fat and energy metabolisms of both. Crucially, pups accumulate certain compounds to levels that are dramatically greater than in mothers. These include compounds that pups cannot synthesise themselves, such as pyridoxine/vitamin B6, taurine, some essential amino acids, and a conditionally essential amino acid and its precursor. Fasting mothers therefore appear to mediate stockpiling of critical metabolites in their pups, potentially depleting their own reserves and prompting cessation of lactation.

Local effect of lysophosphatidic acid on prostaglandin production in the bovine oviduct

The mammalian oviduct plays an important role in the fertilisation and transport of gametes and embryo. Prostaglandins (PGs) are local mediators of oviductal functions and are involved in fertilisation and the transport of gametes and embryo. Lysophosphatidic acid (LPA), a kind of phospholipid, is involved in various physiological actions. We hypothesised that LPA regulates PG production in the bovine oviduct. To test this hypothesis, we examined the mRNA expression of LPA receptors (LPAR1-6) and LPA-producing enzymes (ATX, PLA1α, PLA1β) in ampullary and isthmic tissues and in cultured epithelial and stromal cells isolated from the bovine oviduct. We also investigated the effects of LPA on PG synthase expression and PG production in cultured cells. The mRNA of LPAR1-4, 6, ATX and PLA1α were expressed in cultured epithelial and stromal cells. The expressions of LPAR1-3 were significantly lower and the expression of LPAR4 was significantly higher in the isthmic than in the ampullary tissues. Lysophosphatidic acid significantly stimulated PG production in the cultured isthmic stromal cells. The overall findings suggest that LPA stimulates PG production via LPAR4 in the bovine oviduct. Since PGs are important for fertilisation and the transport of gametes and embryo, these findings show that locally produced LPA regulates oviductal functions.

Lysophosphatidic acid modulates prostaglandin signalling in bovine steroidogenic luteal cells

We examined whether lysophosphatidic acid affects prostaglandin biosynthesis, transport, and signalling in bovine steroidogenic luteal cells. The aim of the present study was to determine the influence of LPA on PGE2 and PGF2α synthesis and on the expression of enzymes involved in PG biosynthesis (PTGS2, mPGES-1, cPGES, mPGES-2, PGFS and 9-KPR), prostaglandin transporter (PGT), and prostaglandin receptors (EP1, EP2, EP3, EP4 and FP) in bovine steroidogenic luteal cells. We found that LPA inhibited PGF2α synthesis in steroidogenic luteal cells. Moreover, LPA increased mPGES1 and cPGES and decreased PGFS expression in cultured bovine steroidogenic luteal cells. Additionally, LPA stimulated EP2 and EP4 receptor and PGT expression. This study suggests that LPA activity in the bovine CL directs the physiological intraluteal balance between the two main prostanoids towards luteotropic PGE2.

Detection and characterization of phospholipase A(2) (PLA(2)) in Caiman latirostris and Caiman yacare plasma

Reptiles have proven to have a versatile and efficient nonspecific immune system adapted to the environments in which they commonly live. Phospholipase A(2) (PLA(2)) is important hydrolytic enzyme involved in the regulation of specific types of messengers, with significant roles in the innate immune response. A number of agents that exert effects on cellular receptors emit a series of signals leading to the increased activity of PLA(2). Phospholipase A(2) has been identified and characterized in temperature, plasma concentration, and kinetic dependence in two species of caiman. The results of these studies suggest that the high PLA(2) activities observed in caiman plasma may be an important component of a well-developed innate immunity. Based on the knowledge of their properties, this powerful immunologic component should be evaluated as a possible application in the veterinary or even human therapeutic industry. Additionally, this is another reason to consider these animals excellent models for the study of immune phylogenetic mechanisms.

Participation of analogues of lysophosphatidic acid (LPA): oleoyl-sn-glycero-3-phosphate (L-α-LPA) and 1-oleoyl-2-O-methyl-rac-glycerophosphothionate (OMPT) in uterine smooth muscle contractility of the pregnant pigs

Recent studies show that a representative of phospholipids, namely lysophosphatidic acid (LPA) and its receptors (LPA1-3) play a significant role in the reproductive processes, i. a, in the modulation of the uterine contractility. The participation of LPA3 in the reproductive processes has been revealed in mice and has not been studied in gilts. Therefore, in the present study we investigated the role/action of LPA and its receptors LPA1, LPA2 and LPA3 on the contraction activity in the porcine uterus. The study was conducted on an experimental model in which the pig uterus consisted of the one whole uterine horn and a part of the second horn, both connected with the uterine corpus. Uterine strips consisting of the endometrium with the myometrium (ENDO/MYO) and myometrium (MYO) alone were collected on days 12-14 of the estrous cycle (control group; n = 5) or pregnancy (experimental group; n = 5). Two analogues of LPA at increasing doses were used: oleoyl-sn-glycero- 3-phosphate (L-α-LPA, a selective agonist of LPA1 and LPA2 receptors; 10-7 M; 10-6 M and 10-5 M) and 1-oleoyl-2-O-methyl-rac-glycerophosphothionate (OMPT, a selective agonist of LPA3 receptor; 68 nM; 136 nM and 680 nM). L-α-LPA caused an increase in the contraction tension, amplitude and frequency of ENDO/MYO from the uterine horn with the developing embryos. This effect was not observed in MYO in both groups examined. In the ENDO/MYO strips of the uterine horn with developing embryos, OMPT significantly increased the contraction tension at the highest dose (680 nM) and amplitude at all doses examined, while frequency of contractions was decreased at doses of 136 nM and 680 nM. In the MYO strips of the uterine horn with embryos a significant increase in the contraction tension and amplitude after the highest dose of OMPT was observed. The results obtained imply the important role of receptors LPA1 , LPA2 and LPA3 in the contraction activity of the porcine uterus during early pregnancy.

Lysophosphatidic acid receptors in ovine uterus during estrous cycle and early pregnancy and their regulation by progesterone

In the present study, we examined the lysophosphatidic acid (LPA) pathway in the ovine uterus during the estrous cycle and early pregnancy. With the use of quantitative reverse transcription PCR, expression of LPAR1 and LPAR3 was analyzed. Both receptors were present in the ovine uterus. Immunolocalization showed that LPAR1 was mainly present in the stroma of the ovine endometrium, whereas LPAR3 was mostly restricted to epithelial compartments. In luminal and glandular epithelia, LPAR1 and LPAR3 levels were affected by pregnancy status, day, or the day-by-status interaction, whereas in stroma the receptors were not modified. Analysis of the whole endometrium from ovariectomized ewes showed that the expression of LPAR3 but not LPAR1 was regulated by the administration of progesterone. However, the examination of receptors at cellular levels showed that progesterone increases LPAR1 and LPAR3 in glandular epithelium and, in a minor extent, in endometrial stroma. Emerging evidence suggests that LPA is an essential component in the estrous cycle and early pregnancy regulation. We demonstrated that LPA induced stress fiber formation in ovine uterine epithelial cells, suggesting that LPA may be involved in cytoskeleton reorganization occurring cyclically in ovine uterus.

LPA receptors: subtypes and biological actions

Lysophosphatidic acid (LPA) is a small, ubiquitous phospholipid that acts as an extracellular signaling molecule by binding to and activating at least five known G protein-coupled receptors (GPCRs): LPA(1)-LPA(5). They are encoded by distinct genes named LPAR1-LPAR5 in humans and Lpar1-Lpar5 in mice. The biological roles of LPA are diverse and include developmental, physiological, and pathophysiological effects. This diversity is mediated by broad and overlapping expression patterns and multiple downstream signaling pathways activated by cognate LPA receptors. Studies using cloned receptors and genetic knockout mice have been instrumental in uncovering the significance of this signaling system, notably involving basic cellular processes as well as multiple organ systems such as the nervous system. This has further provided valuable proof-of-concept data to support LPA receptors and LPA metabolic enzymes as targets for the treatment of medically important diseases that include neuropsychiatric disorders, neuropathic pain, infertility, cardiovascular disease, inflammation, fibrosis, and cancer.

Differential genome-wide gene expression profiling of bovine largest and second-largest follicles: identification of genes associated with growth of dominant follicles

BACKGROUND

Bovine follicular development is regulated by numerous molecular mechanisms and biological pathways. In this study, we tried to identify differentially expressed genes between largest (F1) and second-largest follicles (F2), and classify them by global gene expression profiling using a combination of microarray and quantitative real-time PCR (QPCR) analysis. The follicular status of F1 and F2 were further evaluated in terms of healthy and atretic conditions by investigating mRNA localization of identified genes.

METHODS

Global gene expression profiles of F1 (10.7 +/- 0.7 mm) and F2 (7.8 +/- 0.2 mm) were analyzed by hierarchical cluster analysis and expression profiles of 16 representative genes were confirmed by QPCR analysis. In addition, localization of six identified transcripts was investigated in healthy and atretic follicles using in situ hybridization. The healthy or atretic condition of examined follicles was classified by progesterone and estradiol concentrations in follicular fluid.

RESULTS

Hierarchical cluster analysis of microarray data classified the follicles into two clusters. Cluster A was composed of only F2 and was characterized by high expression of 31 genes including IGFBP5, whereas cluster B contained only F1 and predominantly expressed 45 genes including CYP19 and FSHR. QPCR analysis confirmed AMH, CYP19, FSHR, GPX3, PlGF, PLA2G1B, SCD and TRB2 were greater in F1 than F2, while CCL2, GADD45A, IGFBP5, PLAUR, SELP, SPP1, TIMP1 and TSP2 were greater in F2 than in F1. In situ hybridization showed that AMH and CYP19 were detected in granulosa cells (GC) of healthy as well as atretic follicles. PlGF was localized in GC and in the theca layer (TL) of healthy follicles. IGFBP5 was detected in both GC and TL of atretic follicles. GADD45A and TSP2 were localized in both GC and TL of atretic follicles, whereas healthy follicles expressed them only in GC.

CONCLUSION

We demonstrated that global gene expression profiling of F1 and F2 clearly reflected a difference in their follicular status. Expression of stage-specific genes in follicles may be closely associated with their growth or atresia. Several genes identified in this study will provide intriguing candidates for the determination of follicular growth.

Lysophosphatidic acid up-regulates expression of growth-regulated oncogene-alpha, interleukin-8, and monocyte chemoattractant protein-1 in human first-trimester trophoblasts: possible roles in angiogenesis and immune regulation

The serum lysophospholipase D activity and production of lysophosphatidic acid (LPA) increase in women with pregnancy. The effects of LPA on human placenta tissue remained unclear. We investigate the expression of LPA receptors and function of LPA in human first-trimester trophoblasts. Normal villous trophoblasts were obtained from termination of first-trimester gestation. We examined the expression of LPA receptors in primary culture of trophoblasts and the tissue. The effects of LPA on the expressions of chemokines of trophoblasts were examined using RT-PCR and enzyme immunoassay. We delineate signal pathways of LPA-inducing relevant chemokines in trophoblasts. The secretory chemokines were tested for angiogenic function using human endometrial microvascular endothelial cells and for immunological chemotaxis using decidual natural killer cells and THP-1 monocytes. The results revealed the expression of LPA1 receptors in trophoblast cells. LPA enhanced growth-regulated oncogene (GRO)-alpha, IL-8 and monocyte chemoattractant protein (MCP)-1 expressions in a time- and dose-dependent manner. Mechanistic dissection disclosed that LPA functioned mainly via the LPA1 receptor, Gi protein, various signal mediators of ERK, protein kinase C, p38, Akt, and c-Jun N-terminal kinase, and nuclear factor-kappaB pathways to secrete these chemokines. LPA-induced IL-8 protein secretion of trophoblasts enhanced permeability, migration, proliferation, and capillary tube formation of human endometrial microvascular endothelial cells. LPA-induced GRO-alpha and MCP-1 incited chemotaxis of natural killer cells and monocytes. We demonstrate that LPA mediates trophoblast cells to produce GRO-alpha, IL-8, and MCP-1 via LPA1 receptors and nuclear factor-kappaB-dependent signal pathways. Through LPA-induced chemokine production, human first-trimester trophoblast cells may regulate angiogenesis and innate immune system in early pregnancy.

Expression of autotaxin and acylglycerol kinase in prostate cancer: association with cancer development and progression

Lysophosphatidic acid (LPA) may enhance diverse biologic activities in prostate cancer. This study was conducted to analyze expression levels of LPA-producing enzymes, autotaxin (ATX) and acylglycerol kinase (AGK), in prostate cancer with relevance to clinicopathological parameters. Real-time RT-PCR and western blotting were performed for ATX and AGK in non-neoplastic prostate cells (PrECs and PrSCs) and prostate cancer cell-lines (DU-145, PC-3, LNCaP, and AILNCaP). Immunohistochemical analyses were conducted in tissue specimens of 132 localized prostate cancer patients who underwent radical prostatectomy between 2001 and 2007 (median observation period, 22 months). Both enzymes were negatively expressed in PrECs and PrSCs at mRNA and protein levels. ATX expression was higher than AGK in AILNCaP, DU-145, and PC-3 cell-lines, while AGK was mainly expressed in LNCaP cells. Immunohistochemically, ATX and AGK expressions were negative in non-neoplastic epithelia, while both were weakly expressed in the majority of high-grade intra-epithelial neoplasia (HG-PIN). In cancer foci, ATX and AGK expressions were strong in 49% and 62%, weak in 40% and 32%, and negative in 11% and 6%, respectively. Expressions of both enzymes were significantly correlated with primary Gleason grade of cancer foci (P < 0.0001) and capsular invasion (P = 0.03 and 0.003 respectively). ATX expression was significantly correlated with probability of prostate specific antigen (PSA)-failure after surgery (P < 0.0001). In conclusion, LPA-producing enzymes (ATX and AGK) were frequently expressed in prostate cancer cells and precancerous HG-PIN. In particular, high expression levels of ATX were associated with both malignant potentials and poor outcomes.

Lysophosphatidic acid mediates interleukin-8 expression in human endometrial stromal cells through its receptor and nuclear factor-kappaB-dependent pathway: a possible role in angiogenesis of endometrium and placenta

Lysophosphatidic acid (LPA) is a pleiotropic phospholipid molecule involved in inflammation, angiogenesis, would healing, and cancer invasion. Whereas serum lysophospholipase D activity increases in women with pregnancy, the role of LPA in pregnancy remains unclear. We investigated the expression of LPA receptors and function of LPA in endometrial stromal cells. Histologically normal endometrium was obtained from surgical specimens of women undergoing hysterectomy for leiomyoma. First-trimester decidua was obtained from women receiving elective termination of pregnancy. We examined the expressions of LPA1, LPA2, and LPA3 receptors in endometrial stromal cells. The effects of LPA on the expression of vascular endothelial growth factor, IL-6, and IL-8 were examined. Signal pathways of LPA were delineated. Functions of secretory angiogenic factors were tested using human endometrial microvascular endothelial cells. Immunoreactivity and mRNA of LPA1 receptors were identified in endometrial stromal cells. LPA enhanced IL-8 expression in a dose- and time-dependent manner, whereas vascular endothelial growth factor or IL-6 expression was not affected by LPA treatment. Mechanistic dissection disclosed that LPA functioned via the Gi protein, MAPK/p38 and nuclear factor-kappaB pathway. LPA-induced IL-8 enhanced migration, permeability, capillary tube formation, and proliferation of human endometrial microvascular endothelial cells. Endometrial stromal cells express LPA1 receptors. Through the LPA1 receptor, LPA induces IL-8 expression via a nuclear factor-kappaB-dependent signal pathway. These results could suggest that LPA may play a role in angiogenesis of endometrium and placenta through induction of IL-8 in endometrial stromal cells during pregnancy.

Lipidomics: new approaches to the studies of cell signaling and prospects of use in medicine

A new modern stage in the development of lipid biochemistry is presented: lipidomics, which emerged on the basic of new highly sensitive fractionation methods, primarily, mass spectroscopy. Lipidomics is defined mainly as systemic evaluation of all molecular types of lipids in an object, their cell functions, and molecules with which they react. Lipidomic approaches identifying picomole levels of individual lipids in combination with modern genome technology provide detailed information about the involvement of minor phospholipids in the cell signaling processes. Brief data on the functions of lysophospholipids as second messengers of signal transfer, their effects on cell processes, and possible involvement in the pathogenesis of some diseases are presented. It is expected that introduction of lipidomics in biomedical studies will promote the detection of targets for new drugs and development of new diagnostic tests.

Lysophospholipid signaling in the function and pathology of the reproductive system

BACKGROUND

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are two prominent signaling lysophospholipids (LPs) exerting their functions through a group of G protein-coupled receptors (GPCRs). This review covers current knowledge of the LP signaling in the function and pathology of the reproductive system.

METHODS

PubMed was searched up to May 2008 for papers on lysophospholipids/LPA/S1P/LPC/SPC in combination with each part of the reproductive system, such as testis/ovary/uterus.

RESULTS

LPA and SIP are found in significant amounts in serum and other biological fluids. To date, 10 LP receptors have been identified, including LPA(1-5) and S1P(1-5). In vitro and in vivo studies from the past three decades have demonstrated or suggested the physiological functions of LP signaling in reproduction, such as spermatogenesis, male sexual function, ovarian function, fertilization, early embryo development, embryo spacing, implantation, decidualization, pregnancy maintenance and parturition, as well as pathological roles in ovary, cervix, mammary gland and prostate cancers.

CONCLUSIONS

Receptor knock-out and other studies indicate tissue-specific and receptor-specific functions of LP signaling in reproduction. More comprehensive studies are required to define mechanisms of LP signaling and explore the potential use as a therapeutic target.

Age-dependent loss of sperm production in mice via impaired lysophosphatidic acid signaling

Approximately half of all infertility cases can be attributed to male reproductive dysfunction for which low sperm count is a major contributing factor. The current study identified receptor-mediated lysophosphatidic acid (LPA) signaling as a new molecular component influencing male fertility. LPA is a small signaling phospholipid, the effects of which are mediated through at least five G protein-coupled receptors, named LPA 1-5. LPA1/2/3, but not LPA4/5, show high expression in mouse testis. Mice deficient in LPA1/2/3 showed a testosterone-independent reduction of mating activity and sperm production, with an increased prevalence of azoospermia in aging animals. A significant increase of germ cell apoptosis also was observed in testes. Germ cell apoptosis led to a reduction in germ cell proliferation. These data demonstrate a novel in vivo function for LPA signaling as a germ cell survival factor during spermatogenesis.

Regulation of LPA receptor function by estrogens

17beta-Estradiol induced LPA(1) receptor desensitization in C9 cells stably expressing LPA(1) receptors and transiently expressing estrogen receptor alpha. Such desensitization was evidenced by a reduction in lysophosphatidic acid-mediated Ca(2+)mobilization and it was associated to receptor phosphorylation and internalization. These effects of 17beta-estradiol were rapid (taking place over 5 min) and were blocked by the estrogen receptor antagonist ICI 182780. Similarly, inhibitors of phosphoinositide 3-kinase (wortmannin and LY294002) and of protein kinase C (staurosporine and Gö 6976) blocked 17beta-estradiol-induced LPA(1) receptor desensitization and phosphorylation. Confocal microscopy evidenced LPA(1) receptor internalization in response to 17beta-estradiol treatment. Association between LPA(1) receptors and protein kinase C alpha was suggested by co-immunoprecipitation assays. Protein kinase C alpha was associated with LPA(1) receptors in the absence of stimulus and such association further increased in a dynamic fashion in response to 17beta-estradiol. The results demonstrated that in C9 cells estrogens modulate LPA(1) action through estrogen receptor alpha with the participation of protein kinase C alpha and phosphoinositide 3-kinase.

Stem cell regulation by lysophospholipids

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) regulate a diverse range of mammalian cell processes, largely through engaging multiple G protein-coupled receptors specific for these lysophospholipids. LPA and S1P have been clearly identified to have widespread physiological and pathophysiological actions, controlling events within the reproductive, gastrointestinal, vascular, nervous and immune systems, and also having a prominent role in cancer. Here we review the recent literature showing the additional emerging role for LPA and S1P in the regulation of stem cells and their progenitors. We discuss the role of these lysophospholipids in regulating the proliferation, survival, differentiation and migration of a range of adult and embryonic stem cells and progenitors, and thus are likely to play a substantial role in the maintenance, generation, mobilisation and homing of stem cell and progenitor populations in the body.

Lysophospholipid receptors in cell signaling

There is increasing evidence that different phospholipids are involved in regulation of various cell processes and cell-cell interactions. Lysophospholipids (lysophosphatidic acid, lysophosphatidylcholine) and a number of lysosphingolipids play particular roles in these regulations. Their effects are mediated by specific G-protein-coupled receptors. G-Protein coupled signal transduction to the cell nucleus involving a chain of intracellular protein kinases induces the main effects in cells--growth, proliferation, survival, or apoptosis. This review summarizes recent data on various groups of lysophospholipid receptors and their cell signal transduction pathways.

Lysophosphatidic acid induces interleukin-13 (IL-13) receptor alpha2 expression and inhibits IL-13 signaling in primary human bronchial epithelial cells

Interleukin-13 (IL-13), a Th2 cytokine, plays a pivotal role in pathogenesis of bronchial asthma via IL-13 receptor alpha1 (IL-13Ralpha1) and IL-4 receptor alpha (IL-4Ralpha). Recent studies show that a decoy receptor for IL-13, namely IL-13Ralpha2, mitigates IL-13 signaling and function. This study provides evidence for regulation of IL-13Ralpha2 production and release and IL-13-dependent signaling by lysophosphatidic acid (LPA) in primary cultures of human bronchial epithelial cells (HBEpCs). LPA treatment of HBEpCs in at imedependent fashion increased IL-13Ralpha2 gene expression without altering the mRNA levels of IL-13Ralpha1 and IL-4Ralpha. Pretreatment with pertussis toxin (100 ng/ml, 4 h) or transfection of c-Jun small interference RNA or an inhibitor of JNK attenuated LPA-induced IL-13Ralpha2 gene expression and secretion of soluble IL-13Ralpha2. Overexpression of catalytically inactive mutants of phospholipase D (PLD) 1 or 2 attenuated LPA-induced IL-13Ralpha2 gene expression and protein secretion as well as phosphorylation of JNK. Pretreatment of HBEpCs with 1 microM LPA for 6 h attenuated IL-13-but not IL-4-induced phosphorylation of STAT6. Transfection of HBEpCs with IL-13Ralpha2 small interference RNA blocked the effect of LPA on IL-13-induced phosphorylation of STAT6. Furthermore, pretreatment with LPA (1 microM, 6 h) attenuated IL-13-induced eotaxin-1 and SOCS-1 gene expression. These results demonstrate that LPA induces IL-13Ralpha2 expression and release via PLD and JNK/AP-1 signal transduction and that pretreatment with LPA down-regulates IL-13 signaling in HBEpCs. Our data suggest a novel mechanism of regulation of IL-13Ralpha2 and IL-13 signaling that may be of physiological relevance to airway inflammation and remodeling.

Emerging medicinal roles for lysophospholipid signaling

The two lysophospholipids (LPs) lysophosphatidic acid and sphingosine 1-phosphate (S1P) regulate diverse biological processes. Over the past decade, it has become clear that medically relevant LP activities are mediated by specific G protein-coupled receptors, implicating them in the etiology of a growing number of disorders. A new class of LP agonists shows promise for drug therapy: the experimental drug FTY720 is phosphorylated in vivo to produce a potent S1P receptor agonist (FTY720-P) and is currently in Phase III clinical trials for kidney transplantation and Phase II for multiple sclerosis. Recent genetic and pharmacological studies on LP signaling in animal disease models have identified new areas in which interventions in LP signaling might provide novel therapeutic approaches for the treatment of human diseases.

Actin polymerization in the equatorial and postacrosomal regions of guinea pig spermatozoa during the acrosome reaction is regulated by G proteins

The acrosome reaction (AR) is an exocytotic process of spermatozoa, and an absolute requirement for fertilization. During AR, actin polymerization is necessary in the equatorial and postacrosomal regions of guinea pig sperm for spermatozoa incorporation deep into the egg cytoplasm, but not for plasma membrane (PM) fusion nor the early steps of egg activation. To identify the mechanisms involved in this sperm actin polymerization, we searched for the protein members, known to be involved in a highly conserved model, that may apply to any cellular process in which de novo actin polymerization occurs from G protein activation. WASP, Arp 2/3, profilins I and II, and Cdc42, RhoA and RhoB GTPases were localized by indirect immunofluorescence (IIF) in guinea pig spermatozoa and their presence corroborated by Western blotting. WASP and profilin II were translocated to the postacrosomal region (Arp2/3 already were there) in long-term capacitated and acrosome-reacted spermatozoa, at the same time as actin polymerization occurred. These events were inhibited by GDP-beta-S and promoted by lysophosphatidic acid (LPA) and GTP-gamma-S, a small GTPase inhibitor and two activators, respectively. By immunoprecipitation, Cdc42-WASp association was identified in capacitated but not in noncapacitated gametes. Polymerized actin in the postacrosomal region is apparently anchored both to the postacrosomal perinuclear theca region and the overlying PM. Results suggest that GTPases are involved in sperm actin polymerization, in the postacrosomal region and the mechanism for polymerization might fit a previously proposed model (Mullins, 2000: Curr Opin Cell Biol 12:91-96).

[Lysophosphatidic acid: a "bioactive" phospholipid]

Lysophosphatidic acid (LPA) is a "bioactive" phospholipid able to generate growth factor-like activities in a wide variety of normal and malignant cell types. LPA is proposed to play an important role in normal physiological situations such as wound healing, vascular tone, vascular integrity, or reproduction. In parallel, LPA could also be involved in the etiology of some diseases such as atherosclerosis, cancer, or obesity. The bioactivity of LPA is mediated by the activation of specific G-protein coupled receptors (LPA1, LPA2, and LPA3) leading to the activation of a number of intracellular effectors. LPA is present in solution (bound to albumin) in various extracellular fluids (blood, ascites, aqueous humor), and is released in vitro by some cell types such as platelets, cancer cells, or adipocytes. LPA is a rather polar phospholipid, which cannot easily diffuse throughout plasma membrane, and its presence outside the cells requires soluble phospholipases (secreted phospholipase A2 and soluble lysophospholipase D/autotaxin), which synthesize LPA directly in the extracellular milieu, from precursors such as phosphatidic acid and lysophosphatidylcholine. In the future, LPA receptors, as well as the enzymes involved in LPA metabolism, will constitute promising pharmacological and transgenic targets to determine the physiopathological relevance of "bioactive" LPA in vivo.

Differential effects of lysolipids on steroid synthesis in cells expressing endogenous LPA2 receptor

Incubation of ovarian luteal cells with the bioactive lipid mediator lysophosphatidic acid (LPA) for 180 min abolishes gonadotropin-induced steroid production with no attenuation of the cyclic AMP accumulation. Treatment with the lysolipid also diminishes [14C]steroid production in cells preloaded with either [14C]cholesterol or [14C]acetate. Neither the expression of steroidogenic acute regulatory (StAR) protein nor in vitro steroid synthesis is affected in isolated mitochondrial fractions. The LPA-induced attenuation of steroid production occurs only in the mid-cycle corpus luteum and is associated with a transient endogenous expression of mRNA for the lysophosphatidic acid A2 (LPA2) receptor (with no concomitant changes in the expression of LPA1 receptor). Expression of LPA2 is accompanied by LPA-induced sphingosine-1-phosphate (S1P) production. Because luteal cells, in the presence of the sphingosine kinase inhibitor dihydrosphingosine, can overcome the inhibitory effects of LPA on steroid synthesis, we suggest the possible requirement of intracellular S1P production. Interestingly, no LPA-induced inhibition of 8Br-cAMP-stimulated progesterone synthesis can be detected in Leydig tumor cell line MA10 cells expressing only LPA2 receptor. Surprisingly, however, exogenous S1P inhibits agonist-stimulated progesterone in both cell types by inhibiting cyclic AMP accumulation, suggesting different mechanisms of action.

Lysophospholipid receptors: signaling and biology

Lysophospholipids (LPs), such as lysophosphatidic acid and sphingosine 1-phosphate, are membrane-derived bioactive lipid mediators. LPs can affect fundamental cellular functions, which include proliferation, differentiation, survival, migration, adhesion, invasion, and morphogenesis. These functions influence many biological processes that include neurogenesis, angiogenesis, wound healing, immunity, and carcinogenesis. In recent years, identification of multiple cognate G protein-coupled receptors has provided a mechanistic framework for understanding how LPs play such diverse roles. Generation of LP receptor-null animals has allowed rigorous examination of receptor-mediated physiological functions in vivo and has identified new functions for LP receptor signaling. Efforts to develop LP receptor subtype-specific agonists/antagonists are in progress and raise expectations for a growing collection of chemical tools and potential therapeutic compounds. The rapidly expanding literature on the LP receptors is herein reviewed.

Biology of LPA in health and disease

The functions of lysophosphatidic acid (LPA) can be broadly divided into two classes: (1) physiological and (2) pathological roles. The role of LPA in embryonic development can be seen as early as oocyte formation. It continues in postnatal homeostasis, through its ability to impart a level of protection from both stress and local injury, by regulating cellular proliferation, apoptosis, and the reorganization of cytoskeletal fibers. LPA may function as a double-edged sword. While it helps maintain homeostasis against stress and insult, it may also augment the development and spread of pathological processes, including cancers.

Discrimination between uterine serous papillary carcinomas and ovarian serous papillary tumours by gene expression profiling

High-grade ovarian serous papillary cancer (OSPC) and uterine serous papillary carcinoma (USPC) represent two histologically similar malignancies characterised by markedly different biological behavior and response to chemotherapy. Understanding the molecular basis of these differences may significantly refine differential diagnosis and management, and may lead to the development of novel, more specific and more effective treatment modalities for OSPC and USPC. We used an oligonucleotide microarray with probe sets complementary to >10 000 human genes to determine whether patterns of gene expression may differentiate OSPC from USPC. Hierarchical cluster analysis of gene expression in OSPC and USPC identified 116 genes that exhibited >two-fold differences (P<0.05) and that readily distinguished OSPC from USPC. Plasminogen activator inhibitor (PAI-2) was the most highly overexpressed gene in OSPC when compared to USPC, while c-erbB2 was the most strikingly overexpressed gene in USPC when compared to OSPC. Overexpression of the c-erbB2 gene and its expression product (i.e., HER-2/neu receptor) was validated by quantitative RT-PCR as well as by flow cytometry on primary USPC and OSPC, respectively. Immunohistochemical staining of serous tumour samples from which primary OSPC and USPC cultures were derived as well as from an independent set of 20 clinical tissue samples (i.e., 10 OSPC and 10 USPC) further confirmed HER-2/neu as a novel molecular diagnostic and therapeutic marker for USPC. Gene expression fingerprints have the potential to predict the anatomical site of tumour origin and readily identify the biologically more aggressive USPC from OSPC. A therapeutic strategy targeting HER-2/neu may be beneficial in patients harbouring chemotherapy-resistant USPC.

Stimulation of early gene induction and cell proliferation by lysophosphatidic acid in human amnion-derived WISH cells: role of phospholipase D-mediated pathway

Human-amniotic WISH cells express the lysophosphatidic acid (LPA) receptor, LPA(1), LPA(2) but not LPA(3). When WISH cells were stimulated with LPA, phospholipase D (PLD) activation was dramatically induced via a cytosolic calcium increase and protein kinase C activation. We also found that LPA stimulated two kinds of mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK) and p38 kinase via PLD-dependent signaling pathways in WISH cells. In terms of the LPA-mediated functional modulation of WISH cells, we observed that LPA stimulates the induction of two early genes (c-Jun and c-Fos) and cellular proliferation in WISH cells. We examined the signaling pathways involved in LPA-mediated cellular responses. LPA-induced early gene induction was completely blocked by normal butanol (n-butanol) but not by t-butanol, suggesting that PLD activity is essentially required for the process. PD98059 (2'-amino-3'-methoxyflavone) but not SB203580 (4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole) also significantly blocked LPA-induced early gene induction, suggesting a crucial role for ERK. Pertussis toxin (PTX) did not affect on the LPA-induced early gene induction and ERK activation, ruling out the role of Gi/o protein(s) in the process. The cellular proliferation of WISH cells was also dramatically inhibited by n-butanol or PD98059. This study demonstrates the physiological role of LPA on the modulation of early gene induction and on WISH cell proliferation, and the crucial role played by PLD in the process.

Lysophosphatidic acid signals through mitogen-activated protein kinase-extracellular signal regulated kinase in ovarian theca cells expressing the LPA1/edg2-receptor: involvement of a nonclassical pathway?

We investigated the mechanism of lysophosphatidic acid (LPA) signaling in ovarian theca cells and observed that stimulation with this bioactive lipid markedly enhanced Thr/Tyr phosphorylation of the MAPK ERK1/2. Activation of ERK was transient, showing a peak at 5 min that declined thereafter, and was not associated with a concomitant nuclear translocation of the enzyme, suggesting that a cytosolic tyrosine phosphatase may be responsible for switching off the signal. Epidermal growth factor (EGF)-induced activation of the enzyme in the same cell system was more rapid (peaking at 1 min), sustainable for at least 60 min, and could be suppressed by prior treatment with either pertussis toxin or a noncompetitive inhibitor of Ras acceptor protein, manumycin A. This functional inhibition of either Gi or Ras failed, however, to affect the LPA-induced ERK-phosphorylation. Surprisingly, functional inhibition of Rho-GTPase, in C3-exotoxin-lipofected cells, markedly reduced LPA-stimulated phosphorylation of ERK, without affecting the EGF-induced stimulation of MAPK. Theca cells labeled with anti-LPA1/edg2-type antibody showed a distinct cell surface labeling, which is reflected in the expression of (LPA1)-type LPA receptors at both mRNA and protein levels. The findings indicate that LPA transiently stimulates MAPK ERK in LPA1/edg2-expressing theca cells and suggest an alternative mechanism regulating the activation of ERK that differs from the canonical EGF-Ras-MAPK kinase pathway.