Lysophosphatidic acids induce contraction of rat isolated colon by two different mechanisms

Uterine injury during diestrus leads to placental and embryonic defects in future pregnancies in mice†

Uterine injury from procedures such as Cesarean sections (C-sections) often have severe consequences on subsequent pregnancy outcomes, leading to disorders such as placenta previa, placenta accreta, and infertility. With rates of C-section at ~30% of deliveries in the USA and projected to continue to climb, a deeper understanding of the mechanisms by which these pregnancy disorders arise and opportunities for intervention are needed. Here we describe a rodent model of uterine injury on subsequent in utero outcomes. We observed three distinct phenotypes: increased rates of resorption and death, embryo spacing defects, and placenta accreta-like features of reduced decidua and expansion of invasive trophoblasts. We show that the appearance of embryo spacing defects depends entirely on the phase of estrous cycle at the time of injury. Using RNA-seq, we identified perturbations in the expression of components of the COX/prostaglandin pathway after recovery from injury, a pathway that has previously been demonstrated to play an important role in embryo spacing. Therefore, we demonstrate that uterine damage in this mouse model causes morphological and molecular changes that ultimately lead to placental and embryonic developmental defects.

Effects of lysophosphatidic acid on sling and clasp fibers of the human lower esophageal sphincter

Background

This study aims to explore the role of lysophosphatidic acid receptors in the regulation mechanisms of contraction and relaxation of human lower esophageal sphincter.

Methods

Between July 2015 and March 2016, muscle strips were collected from a total of 30 patients (19 males, 11 females; mean age: 62±9.9 years; range, 52 to 68 years) who underwent an esophagectomy for mid-third esophageal carcinomas. The specimens were maintained in oxygenated Krebs solution. Muscle tension measurement technique in vitro was used to examine the effects of non-selective lysophosphatidic acid receptors agonists and antagonists, as well as selective lysophosphatidic acid receptors agonists on the clasp and sling fibers of human lower esophageal sphincter.

Results

The non-selective dopamine receptor agonist lysophosphatidic acid induced the contraction of the clasp and sling fibers of the human lower esophageal sphincter. The response induced by nonselective lysophosphatidic acid receptor agonist was inhibited completely by non-selective lysophosphatidic acid receptor antagonist. The selective lysophosphatidic acid 1 and 2 receptor agonist and the selective lysophosphatidic acid 3 receptor agonist induced a concentration-dependent contractile response of the clasp and sling fibers of the human lower esophageal sphincter. There was no significant difference in contraction rates between the clasp and sling fibers (p>0.05).

Conclusion

This study indicates that lysophosphatidic acid regulates the lower esophageal sphincter is through its receptor; the lysophosphatidic acid receptors may be involved in the contractile response of the human lower esophageal sphincter.

Targeting Lysophosphatidic Acid in Cancer: The Issues in Moving from Bench to Bedside

Since the clear demonstration of lysophosphatidic acid (LPA)'s pathological roles in cancer in the mid-1990s, more than 1000 papers relating LPA to various types of cancer were published. Through these studies, LPA was established as a target for cancer. Although LPA-related inhibitors entered clinical trials for fibrosis, the concept of targeting LPA is yet to be moved to clinical cancer treatment. The major challenges that we are facing in moving LPA application from bench to bedside include the intrinsic and complicated metabolic, functional, and signaling properties of LPA, as well as technical issues, which are discussed in this review. Potential strategies and perspectives to improve the translational progress are suggested. Despite these challenges, we are optimistic that LPA blockage, particularly in combination with other agents, is on the horizon to be incorporated into clinical applications.

LPA1 receptor-mediated thromboxane A2 release is responsible for lysophosphatidic acid-induced vascular smooth muscle contraction

Lysophosphatidic acid (LPA) has been recognized recently as an endothelium-dependent vasodilator, but several lines of evidence indicate that it may also stimulate vascular smooth muscle cells (VSMCs), thereby contributing to vasoregulation and remodeling. In the present study, mRNA expression of all 6 LPA receptor genes was detected in murine aortic VSMCs, with the highest levels of LPA₁, LPA₂, LPA₄, and LPA₆ In endothelium-denuded thoracic aorta (TA) and abdominal aorta (AA) segments, 1-oleoyl-LPA and the LPA_1-3 agonist VPC31143 induced dose-dependent vasoconstriction. VPC31143-induced AA contraction was sensitive to pertussis toxin (PTX), the LPA_1&3 antagonist Ki16425, and genetic deletion of LPA₁ but not that of LPA₂ or inhibition of LPA₃, by diacylglycerol pyrophosphate. Surprisingly, vasoconstriction was also diminished in vessels lacking cyclooxygenase-1 [COX1 knockout (KO)] or the thromboxane prostanoid (TP) receptor (TP KO). VPC31143 increased thromboxane A₂ (TXA₂) release from TA of wild-type, TP-KO, and LPA₂-KO mice but not from LPA₁-KO or COX1-KO mice, and PTX blocked this effect. Our findings indicate that LPA causes vasoconstriction in VSMCs, mediated by LPA₁-, G_i-, and COX1-dependent autocrine/paracrine TXA₂ release and consequent TP activation. We propose that this new-found interaction between the LPA/LPA₁ and TXA₂/TP pathways plays significant roles in vasoregulation, hemostasis, thrombosis, and vascular remodeling.-Dancs, P. T., Ruisanchez, E., Balogh, A., Panta, C. R., Miklós, Z., Nüsing, R. M., Aoki, J., Chun, J., Offermanns, S., Tigyi, G., Benyó, Z. LPA₁ receptor-mediated thromboxane A₂ release is responsible for lysophosphatidic acid-induced vascular smooth muscle contraction.

A novel highly potent autotaxin/ENPP2 inhibitor produces prolonged decreases in plasma lysophosphatidic acid formation in vivo and regulates urethral tension

Autotaxin, also known as ectonucleotide pyrophosphatase/phosphodiesterase 2 (ENPP2), is a secreted enzyme that has lysophospholipase D activity, which converts lysophosphatidylcholine to bioactive lysophosphatidic acid. Lysophosphatidic acid activates at least six G-protein coupled recpetors, which promote cell proliferation, survival, migration and muscle contraction. These physiological effects become dysfunctional in the pathology of cancer, fibrosis, and pain. To date, several autotaxin/ENPP2 inhibitors have been reported; however, none were able to completely and continuously inhibit autotaxin/ENPP2 in vivo. In this study, we report the discovery of a highly potent autotaxin/ENPP2 inhibitor, ONO-8430506, which decreased plasma lysophosphatidic acid formation.

The IC₅₀ values of ONO-8540506 for lysophospholipase D activity were 6.4–19 nM for recombinant autotaxin/ENPP2 proteins and 4.7–11.6 nM for plasma from various animal species. Plasma lysophosphatidic acid formation during 1-h incubation was almost completely inhibited by the addition of >300 nM of the compound to human plasma. In addition, when administered orally to rats at a dose of 30 mg/kg, the compound demonstrated good pharmacokinetics in rats and persistently inhibited plasma lysophosphatidic acid formation even at 24 h after administration.

Smooth muscle contraction is a known to be promoted by lysophosphatidic acid. In this study, we showed that dosing rats with ONO-8430506 decreased intraurethral pressure accompanied by urethral relaxation. These findings demonstrate the potential of this autotaxin/ENPP2 inhibitor for the treatment of various diseases caused by lysophosphatidic acid, including urethral obstructive disease such as benign prostatic hyperplasia.

Expression of lysophosphatidic acid receptors in the human lower esophageal sphincter

Lysophosphatidic acid (LPA) is a bioactive lipid that is involved in a variety of physiological and pathological processes occurring in the gastrointestinal tract. It acts via six distinct types of receptors, LPA1, LPA2, LPA3, LPA4, LPA5 and LPA6, which belong to the family of G protein-coupled receptors. The aim of the present study was to detect the expression of the LPA receptors in the human lower esophageal sphincter (LES). Quantitative polymerase chain reaction and western blotting were used to analyze the expression of LPA1-6 receptors in sling and clasp fibers from the human LES. The results showed that the protein and mRNA expression levels of various LPA receptors were significantly different. Specifically, the mRNA and protein expression levels of the LPA1 receptor were higher compared with those of the other receptors. The prevalence of the LPA1 receptor mRNA and protein indicates that the LPA1 receptor is likely to be involved in the regulation of human LES functions.

Rat aortic smooth muscle cells contract in response to serum and its components in a calcium independent manner

Diluted serum provides a model of interstitial fluid that can be used to study the response of smooth muscle cells (SMCs) to interstitial flow. The effect of serum and some of its components on SMC contraction (area reduction) and intracellular calcium ([Ca2+]i) response were characterized in rat aortic SMC in vitro. Rat aortic SMCs contracted dramatically to fetal bovine serum (FBS), bovine serum albumin (BSA), and lysophosphatidic acid (LPA) within 5 min of exposure. By 30 min, cell areas were significantly reduced. Even at concentrations as low as 0.0005% FBS, 0.004% BSA and 0.25 microM LPA, cell areas were significantly different from controls at 30 min. The [Ca2+]i response was significant for serum and LPA at these low concentration levels, but BSA did not elicit a significant [Ca2+]i response at concentrations of 0.1% or lower. Under calcium controlled conditions in which SMCs were pretreated with 10 microM BAPTA-AM, contraction levels were not statistically different from non-calcium controlled conditions even when SMCs were exposed to the highest concentration of serum, BSA, or LPA. It appears that LPA and albumin are components of interstitial fluid that contribute to SMC contraction through calcium-independent mechanisms.

Lack of significant differences in the corrected activity of lysophospholipase D, producer of phospholipid mediator lysophosphatidic acid, in incubated serum from women with and without ovarian tumors

BACKGROUND

Several studies have shown that lysophosphatidic acid (LPA), a phospholipidic chemical mediator, is relevant to the pathogenesis of ovarian carcinoma. Higher plasma levels of LPA have been reported in patients with ovarian carcinoma than in healthy patients, and LPA is known to activate ovarian carcinoma cells. To determine the reason for the increased plasma LPA levels in ovarian carcinoma patients, we compared the activities of serum lysophospholipase D, a novel LPA-producing metallo-enzyme, in healthy volunteers, patients with benign ovarian tumor, and patients with ovarian carcinoma.

METHODS

Lysophospholipase D activity was assessed by measuring the percentage conversion of [14C]palmitoyl-lysophosphatidylcholine (LPC) added to human serum. The apparent enzyme activities were corrected based on the serum levels of palmitoyl-LPC determined by gas-liquid chromatography after its purification and conversion to fatty acid methyl esters.

RESULTS

The apparent activity of lysophospholipase D in serum preparations from four patients with ovarian carcinoma at Stage IV was significantly higher than those from five healthy subjects, five patients with benign ovarian tumors, and fourteen patients with ovarian carcinoma at Stages I (n = 5), II (n = 4), and III (n = 5). The serum levels of LPC, an endogenous substrate of lysophospholipase D, in ovarian carcinoma patients were less than those in patients with benign ovarian tumors. There were no significant differences in the corrected lysophospholipase D activity for the LPC levels in healthy women, patients with benign ovarian tumors, and patients with ovarian carcinoma at various stages.

CONCLUSIONS

The current results suggest that lysophospholipase D is not associated with the elevated plasma levels of LPA in ovarian carcinoma patients previously reported, although only a limited number of patients were analyzed.

Topical application of the phospholipid growth factor lysophosphatidic acid promotes wound healing in vivo

The lipid mediator lysophosphatidic acid (LPA) regulates cell proliferation and enhances cell motility in vitro, both of which are important events in wound healing. To evaluate the effects of LPA in vivo, it was applied to a full-thickness wound of rat skin. LPA in micromolar concentrations, or solvent, was applied daily. Animals were killed at 1, 3, 6, and 9 days after wounding and processed for histological evaluation, including hematoxylin-eosin staining and histochemical markers for macrophage-histiocytes, proliferating cells, and capillary endothelial cells. LPA treatment accelerated wound closing and increased neoepithelial thickness. Cytological evaluation showed no evidence for a secondary inflammation-mediated injury, infection, or increased keloid formation. Whereas LPA caused only a modest dose-dependent increase in proliferating cells, a marked increase in the immigration of histiocyte-macrophage cells was observed as early as day 1. The peaks of several cytological features and immunohistological markers preceded those of the untreated side. Our data suggest that exogenously applied LPA in this model promotes healing and that macrophage-histiocytes are the primary LPA-responsive cells in vivo.

Pharmacological characterization of phospholipid growth-factor receptors

The phospholipid growth-factor (PLGE) terminology is proposed to describe a group of endogenous glycerol- and sphingolipid mediators that regulate cell proliferation through plasma membrane receptors. In addition to LPA and SPP, multiple PLGFs are present in blood plasma and serum. PLGF activity is regulated by its stimulus-coupled production and by endogenous inhibitors. In addition to LPA and SPP, alkenyl-glycerophosphate, cyclic-phosphatidic acid, and sphingosylphosphorylcholine were detected in biological fluids using mass spectrometry. Heterologous desensitization studies indicate the expression of multiple LPA-activated receptors in a variety of cell types, which are differentially activated by the different PLGFs. Northern blot and RT-PCR results reinforce the coexpression of PSP24 alpha and different members of the EDG1-7 receptors in the same cell. Stable heterologous expression of the PSP24 alpha, EDG2, and EDG4 receptors in HEK293 cells show distinct PLGF specificities and dose-response properties for each receptor subtype. Thus, both the controlled availability of the different agonists/inhibitors and the regulated expression of their receptors regulate the biological effects of PLGFs.

Effect of lysophosphatidic acid on the ovum transport in mouse oviducts

The effects of lysophosphatidic acid (LPA) on ovum transport in mouse oviducts were studied. When excised oviducts were incubated at 37 degrees C under 5% CO2 in humidified air for 24 hours, addition of LPA at 10 microM to the medium significantly accelerated the rate of ovum transport, and 1 microM LPA slightly increased the ovum transport rate. These increases were not inhibited by 10 microM indomethacin, a cyclooxygense inhibitor, but were suppressed by 260 ng/ml of pertussis toxin or 10 microM verapamil, a voltage-sensitive calcium channel blocker. These data suggested that LPA stimulates mouse ovum transport by contracting oviductual smooth muscle via a voltage-sensitive calcium channel mediated by a pertussis toxin-sensitive G-protein-linked receptor.

Intercellular signaling by lysophosphatidate

Lysophosphatidate (LPA) is an intercellular phospholipid messenger with a wide range of biologic effects. The first discovered source of LPA in the human body were activated platelets, but several other sites of LPA generation are now known. The number of cellular interactions is also growing steadily and responses to the compound range wide, from induction of mitogenesis to neurite retraction. LPA acts via a specific G protein-coupled receptor, of which one or more subtypes may exist. Intracellularly, this receptor activates several heterotrimeric G proteins. LPA induces cell proliferation via the small GTP-binding proteins ras, and triggers actin-based cytoskeletal events through rho. This review describes the most relevant recent developments in our understanding of LPA signaling.

Characterization of a receptor subtype-selective lysophosphatidic acid mimetic

Despite an intriguing cell biology and the suggestion of a role in pathophysiological responses, the mechanism of action of such lipid phosphoric acid mediators as lysophosphatidic acid (LPA) remains obscure, in part because of an underdeveloped medicinal chemistry. We report now the agonist activity of a synthetic phospholipid in which the glycerol backbone of LPA is replaced by L-serine. Like LPA, the L-serine-based lipid mobilizes calcium and inhibits activation of adenylyl cyclase in the human breast cancer cell line MDA MB231. Treatment with LPA desensitizes MDA MB231 cells to subsequent application of the L-serine compound; when the order of application is reversed, however, the L-serine compound does not prevent calcium mobilization by LPA, which might indicate the existence of two LPA receptors in these cells. The analogous D-serine-based phospholipid was distinctly less potent than the L-isomer in those assays; this finding demonstrates stereoselectivity by an LPA receptor. Unlike LPA, the L-serine-based lipid does not evoke a chloride conductance in Xenopus laevis oocytes, but injection of poly(A)+ RNA from HEK 293 cells confers this phenotype on the oocyte. The latter result has practical importance in that it allows use of the frog oocyte for expression cloning of an LPA receptor DNA, an assay system made problematic by the oocyte's strong endogenous response to LPA.

Positive and negative controls by protein kinases of sodium-dependent Ca2+ efflux from cultured bovine adrenal chromaffin cells stimulated by lysophosphatidic acid

We previously found that lysophosphatidic acid (LPA), a bioactive phospholipid, induced Na+-dependent Ca2+ efflux from cultured bovine adrenal chromaffin cells, possibly by activating a Na+/Ca2+ exchanger. The present study on the structure-activity relationship of its action revealed that 1-acyl type LPAs were stronger stimulants than the corresponding 1-O-alkyl type LPAs having a long alkyl moiety with the same chain length. Lysophosphatidylglycerol, suramin and N-palmitoyl-tyrosine phosphoric acid have all been reported to inhibit the action of LPA in some animal cells and platelets, but only lysophosphatidylglycerol was found to inhibit selectively LPA-induced Ca2+ efflux from chromaffin cells. LPA-induced Ca2+ extrusion was suggested to be involved in both acceleration of return of intracellular Ca2+ in Fura 2-loaded bovine chromaffin cells after addition of carbachol, and inhibition of carbachol-induced catecholamine release when the cells were co-incubated with LPA. The Ca2+ efflux from chromaffin cells stimulated by LPA was augmented by their pretreatment with staurosporine or calphostin C, inhibitors of protein kinase C, but reduced by their preincubation with phorbol 12-myristate 13-acetate. Furthermore, the response to LPA was potentiated by sodium vanadate, a protein tyrosine phosphatase inhibitor, but inhibited by genistein, an inhibitor of protein tyrosine kinase. These results suggest that protein kinase C and protein tyrosine kinase are involved negatively and positively, respectively, in the signal transduction triggered by LPA, leading to activation of the Na+/Ca2+ exchanger.

Lysophosphatidic acid enhances contractility of isolated airway smooth muscle

The effects of the simple phospholipid mediator lysophosphatidic acid (LPA) on the contractile responsiveness of isolated tracheal rings from rabbits and cats were assessed. In both species, LPA increased the contractile response to the muscarinic agonist methacholine, but LPA did not induce contraction on its own. Conversely, LPA decreased the relaxation response to the beta-adrenergic-agonist isoproterenol in both species. Concentrations of LPA as low as 10(-8) M were effective, and the effects of LPA were rapidly reversed on washing. Phosphatidic acid was much less effective, requiring higher concentrations and producing only a minimal effect. Contractions induced by serotonin and by substance P also were enhanced by LPA, but KCl-induced contractions were unaffected. LPA inhibited the isoproterenol-induced relaxation of KCl-precontracted rings, similar to its effects on methacholine-precontracted rings, and relaxation induced by the direct adenylyl cyclase activator forskolin was inhibited in a manner similar to that induced by isoproterenol. Epithelium removal did not alter the contraction-enhancing effect of LPA. The ability of LPA to both enhance contraction and inhibit relaxation of airway smooth muscle suggests that LPA could contribute to airway hypercontractility in asthma, airway inflammation, or other types of lung injury.

Effects of lysophosphatidic acid, a novel lipid mediator, on cytosolic Ca2+ and contractility in cultured rat mesangial cells

Lysophosphatidic acid (LPA), the smallest and structurally simplest phospholipid, has the potential to modulate cellular signaling in diverse tissues and cell types, including fibroblasts. In the present study, we assessed the effects of LPA on cultured rat glomerular mesangial cells. Quantitative changes of [Ca2+]i in response to LPA were measured in monolayers of mesangial cells loaded with the fluorescent Ca2+ indicator fura 2. LPA (10 nmol/L to 100 mumol/L) increased [Ca2+]i in a dose-dependent manner and evoked inositol trisphosphate formation. LPA (1 mumol/L to 30 mumol/L) also elicited a marked, albeit transient, contractile response in mesangial cells cultured on collagen gel, as assessed by a decrease in cell surface area (CSA). The contraction persisted for 5 minutes (CSA decreased by 31%), whereupon the mesangial cells gradually relaxed with a consequent increase in CSA. Pretreatment of mesangial cells with isradipine (1 mumol/L), a dihydropyridine-sensitive Ca2+ channel blocker, completely blocked LPA-induced contraction. Isradipine also decreased resting [Ca2+]i levels as well as the peak and the subsequently sustained [Ca2+]i levels induced by LPA, suggesting that the contractile effects of LPA are dependent on Ca2+ entry through voltage-gated Ca2+ channels. Finally, LPA stimulated an increase in both prostaglandin E2 synthesis and cAMP accumulation, indicating that these mediators may modulate the contractile effects of LPA. Our study is the first demonstration that exogenous LPA induces mesangial cell contraction and suggests that the contraction is mediated by mobilization of intracellular Ca2+ by activation of the phosphoinositide cascade as well as by promotion of Ca2+ entry across the plasma membrane.

Lysophosphatidic acid as a stimulator of Na(+)-dependent Ca2+ efflux from adrenal chromaffin cells

The effect of lysophosphatidic acid (LPA) on Ca2+ efflux from cultured bovine adrenal chromaffin cells was examined. LPA stimulated the efflux of 45Ca2+ from the cells in a concentration dependent manner (10(-7)-10(-5)M). Other lysophospholipids (lysophosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylinositol and lysophosphatidylserine), phosphatidic acid, monoolein and oleic acid had not significant effect on 45Ca2+ efflux from the cells. The LPA-stimulated 45Ca2+ efflux was dependent on the extracellular Na+ concentration and was inhibited by amiloride, inhibitor of Na+/Ca2+ exchange. LPA increased 22Na+ uptake into the cells and this effect was also sensitive to amiloride. These results indicate that LPA stimulates extracellular Na(+)-dependent 45Ca2+ efflux from cultured bovine adrenal chromaffin cells, probably through its stimulatory effect on membrane Na+/Ca2+ exchange.

Lysophosphatidic acids induce proliferation of cultured vascular smooth muscle cells from rat aorta

Lysophosphatidic acids (LPA) with a C18 fatty acyl group accelerated thymidine incorporation into cultured rat aortic vascular smooth muscle cells and stimulated their cell division. LPA acted synergistically with epidermal growth factor and fibroblast growth factor but additively with platelet-derived growth factor. The stimulatory actions of LPA were suggested to be rather specific from the following findings: 1) their stimulation of DNA synthesis increased with an increase in their acyl moiety; 2) lysophosphatidylcholine, a neutral lysophospholipid, had no mitogenic action but was cytotoxic at high concentrations; and 3) LPA induced a rapid external Ca(2+)-independent increase in intracellular Ca2+ concentration ([Ca2+]i) in single fura 2-loaded cells that resembled the receptor-mediated increases in [Ca2+]i triggered by different agonists, whereas lysophosphatidylcholine provoked a slow sustained increase in [Ca2+]i in an external Ca(2+)-dependent manner. These results are discussed in relation to the possible pathophysiological role of LPA.

Lysophosphatidic acid induces a pertussis toxin-sensitive Ca(2+)-activated Cl- current in Xenopus laevis oocytes

Lysophosphatidic acid (LPA) induces a Ca(2+)-activated Cl- current in defolliculated Xenopus laevis oocytes. The response appears mediated by a specific membrane receptor, because no current is induced when related compounds [phosphatidic acid (PA), lysophosphatidylcholine (LPC), and lysophosphatidylserine (LPS)] are applied extracellularly or when LPA is injected intracellularly. Incubation in pertussis toxin prevents the response. The response is mediated by a Ca(2+)-activated Cl- current because 1) it is abolished by intracellular ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA; 5 mM) but not affected by changes in extracellular Ca2+ concentration and 2) the reversal potential becomes more positive at lower Cl- concentrations. Suramin (2 mM) blocks the LPA-induced current, but PA, LPS, LPC, and the platelet-activating factor antagonist WEB-2086 do not. The response is dose dependent for LPA concentrations from 10(-8) to 10(-3) M. Incubation of oocytes in LPA does not induce germinal vesicle breakdown. These findings suggest that this novel oocyte response to LPA is mediated by a specific membrane receptor linked to a pertussis toxin-sensitive G protein.