Molecular cloning and characterization of a novel human G-protein-coupled receptor, EDG7, 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.

The interaction of platelet-related factors with tumor cells promotes tumor metastasis

Platelets not only participate in thrombosis and hemostasis but also interact with tumor cells and protect them from mechanical damage caused by hemodynamic shear stress and natural killer cell lysis, thereby promoting their colonization and metastasis to distant organs. Platelets can affect the tumor microenvironment via interactions between platelet-related factors and tumor cells. Metastasis is a key event in cancer-related death and is associated with platelet-related factors in lung, breast, and colorectal cancers. Although the factors that promote platelet expression vary slightly in terms of their type and mode of action, they all contribute to the overall process. Recognizing the correlation and mechanisms between these factors is crucial for studying the colonization of distant target organs and developing targeted therapies for these three types of tumors. This paper reviews studies on major platelet-related factors closely associated with metastasis in lung, breast, and colorectal cancers.

Structural basis for lysophosphatidylserine recognition by GPR34

GPR34 is a recently identified G-protein coupled receptor, which has an immunomodulatory role and recognizes lysophosphatidylserine (LysoPS) as a putative ligand. Here, we report cryo-electron microscopy structures of human GPR34-Gi complex bound with one of two ligands bound: either the LysoPS analogue S3E-LysoPS, or M1, a derivative of S3E-LysoPS in which oleic acid is substituted with a metabolically stable aromatic fatty acid surrogate. The ligand-binding pocket is laterally open toward the membrane, allowing lateral entry of lipidic agonists into the cavity. The amine and carboxylate groups of the serine moiety are recognized by the charged residue cluster. The acyl chain of S3E-LysoPS is bent and fits into the L-shaped hydrophobic pocket in TM4-5 gap, and the aromatic fatty acid surrogate of M1 fits more appropriately. Molecular dynamics simulations further account for the LysoPS-regioselectivity of GPR34. Thus, using a series of structural and physiological experiments, we provide evidence that chemically unstable 2-acyl LysoPS is the physiological ligand for GPR34. Overall, we anticipate the present structures will pave the way for development of novel anticancer drugs that specifically target GPR34.

Synthesis and Biological Evaluation of Lysophosphatidic Acid Analogues Using Conformational Restriction and Bioisosteric Replacement Strategies

Lysophosphatidic acid (LPA) is a key player in many physiological and pathophysiological processes. The biological activities of LPA are mediated through interactions with-at least-six subtypes of G-protein-coupled receptors (GPCRs) named LPA1-6. Developing a pharmacological tool molecule that activates LPA subtype receptors selectively will allow a better understanding of their specific physiological roles. Here, we designed and synthesized conformationally restricted 25 1-oleoyl LPA analogues MZN-001 to MZN-025 by incorporating its glycerol linker into dihydropyran, tetrahydropyran, and pyrrolidine rings and variating the lipophilic chain. The agonistic activities of these compounds were evaluated using the TGFα shedding assay. Overall, the synthesized analogues exhibited significantly reduced agonistic activities toward LPA1, LPA2, and LPA6, while demonstrating potent activities toward LPA3, LPA4, and LPA5 compared to the parent LPA. Specifically, MZN-010 showed more than 10 times greater potency (EC50 = 4.9 nM) than the standard 1-oleoyl LPA (EC50 = 78 nM) toward LPA5 while exhibiting significantly lower activity on LPA1, LPA2, and LPA6 and comparable potency toward LPA3 and LPA4. Based on the MZN-010 scaffold, we synthesized additional analogues with improved selectivity and potency toward LPA5. Compound MZN-021, which contains a saturated lipophilic chain, exhibited 50 times more potent activity (EC50 = 1.2 nM) than the natural LPA against LPA5 with over a 45-fold higher selectivity when compared to those of other LPA receptors. Thus, MZN-021 was found to be a potent and selective LPA5 agonist. The findings of this study could contribute to broadening the current knowledge about the stereochemical and three-dimensional arrangement of LPA pharmacophore components inside LPA receptors and paving the way toward synthesizing other subtype-selective pharmacological probes.

Emerging Roles of Lysophosphatidic Acid in Macrophages and Inflammatory Diseases

Lysophosphatidic acid (LPA) is a bioactive phospholipid that regulates physiological and pathological processes in numerous cell biological functions, including cell migration, apoptosis, and proliferation. Macrophages are found in most human tissues and have multiple physiological and pathological functions. There is growing evidence that LPA signaling plays a significant role in the physiological function of macrophages and accelerates the development of diseases caused by macrophage dysfunction and inflammation, such as inflammation-related diseases, cancer, atherosclerosis, and fibrosis. In this review, we summarize the roles of LPA in macrophages, analyze numerous macrophage- and inflammation-associated diseases triggered by LPA, and discuss LPA-targeting therapeutic strategies.

Lysophosphatidic acid, a simple phospholipid with myriad functions

Lysophosphatidic acid (LPA) is a simple phospholipid consisting of a phosphate group, glycerol moiety, and only one hydrocarbon chain. Despite its simple chemical structure, LPA plays an important role as an essential bioactive signaling molecule via its specific six G protein-coupled receptors, LPA_1-6. Recent studies, especially those using genetic tools, have revealed diverse physiological and pathological roles of LPA and LPA receptors in almost every organ system. Furthermore, many studies are illuminating detailed mechanisms to orchestrate multiple LPA receptor signaling pathways and to facilitate their coordinated function. Importantly, these extensive "bench" works are now translated into the "bedside" as exemplified by approaches targeting LPA₁ signaling to combat fibrotic diseases. In this review, we discuss the physiological and pathological roles of LPA signaling and their implications for clinical application by focusing on findings revealed by in vivo studies utilizing genetic tools targeting LPA receptors.

LPAR1 and aberrantly expressed LPAR3 differentially promote the migration and proliferation of malignant peripheral nerve sheath tumor cells

Schwann cell-derived neoplasms known as malignant peripheral nerve sheath tumors (MPNSTs) are the most common malignancy and the leading cause of death in individuals with neurofibromatosis Type 1. Using genome-scale shRNA screens, we have previously found evidence suggesting that lysophosphatidic acid receptors (LPARs) are essential for MPNST proliferation and/or survival. Here, we examine the expression and mutational status of all six LPA receptors in MPNSTs, assess the role that individual LPA receptors play in MPNST physiology and examine their ability to activate key neurofibromin-regulated signaling cascades. We found that human Schwann cells express LPAR1 and LPAR6, while MPNST cells express predominantly LPAR1 and LPAR3. Whole exome sequencing of 16 MPNST cell lines showed no evidence of mutations in any LPAR genes or ENPP2, a gene encoding a major LPA biosynthetic enzyme. Oleoyl-LPA, an LPA variant with an unsaturated side chain, promoted MPNST cell proliferation and migration. LPAR1 knockdown ablated the promigratory effect of LPA, while LPAR3 knockdown decreased proliferation. Inhibition of R-Ras signaling with a doxycycline-inducible dominant negative (DN) R-Ras mutant, which inhibits both R-Ras and R-Ras2, blocked LPA's promigratory effect. In contrast, DN R-Ras did not affect migration induced by neuregulin-1β (NRG1β), suggesting that LPA and NRG1β promote MPNST migration via distinct pathways. LPA-induced migration was also inhibited by Y27632, an inhibitor of the ROCK1/2 kinases that mediate R-Ras effects in MPNSTs. Thus, LPAR1 and aberrantly expressed LPAR3 mediate distinct effects in MPNSTs. These receptors and the signaling pathways that they regulate are potentially useful therapeutic targets in MPNSTs.

In Vitro Animal Model for Estimating the Time since Death with Attention to Early Postmortem Stage

Estimating the postmortem interval (PMI) has remained the subject of investigations in forensic medicine for many years. Every kind of death results in changes in metabolites in body tissues and fluids due to lack of oxygen, altered circulation, enzymatic reactions, cellular degradation, and cessation of anabolic production of metabolites. Metabolic changes may provide markers determining the time since death, which is challenging in current analytical and observation-based methods. The study includes metabolomics analysis of blood with the use of an animal model to determine the biochemical changes following death. LC-MS is used to fingerprint postmortem porcine blood. Metabolites, significantly changing in blood after death, are selected and identified using univariate statistics. Fifty-one significant metabolites are found to help estimate the time since death in the early postmortem stage. Hypoxanthine, lactic acid, histidine, and lysophosphatidic acids are found as the most promising markers in estimating an early postmortem stage. Selected lysophosphatidylcholines are also found as significantly increased in blood with postmortal time, but their practical utility as PMI indicators can be limited due to a relatively low increasing rate. The findings demonstrate the great potential of LC-MS-based metabolomics in determining the PMI due to sudden death and provide an experimental basis for applying this attitude in investigating various mechanisms of death. As we assume, our study is also one of the first in which the porcine animal model is used to establish PMI metabolomics biomarkers.

LPAR2-mediated action promotes human renal cell carcinoma via MAPK/NF-κB signaling to regulate cytokine network

PURPOSE

Lysophosphatidic acid (LPA) exerts various physiological and pathological effects by activating its distinct G-protein-coupled LPA receptors. We demonstrated that LPA can increase the migration and proliferation of renal carcinoma cells. Meanwhile, LPAR1 and LPAR2 were preferentially expressed in renal cancer (RC) cell lines. So, the study aimed to determine the LPA receptor subtypes involved in LPA-induced actions and whether they could be used as a precision therapeutic target for renal cancer.

METHODS

Biological approaches combined with big data analysis were used to demonstrate the role of LPAR2 in the progression of renal cancer.

RESULTS

We found that the proliferation, clone formation, and migration in response to LPA were enhanced in LPAR2-overexpressing renal cancer cells, whereas, the actions were suppressed by LPAR2 antagonist in the cells. LPAR2 has also shown clinical diagnostic and prognostic value in renal carcinoma based on bioinformatics analysis and clinical tissue microarray analysis. In vivo study shown that tumor growth and metastasis were significantly increased in the LPAR2-overexpressing cells-derived solid tumors. LPA stimulated MAPK and NF-κB activation, and LPA-induced actions were inhibited by MAPKs and NF-κB inhibitors, respectively. Subsequently, the transcriptomic results revealed that LPAR2 strongly affected the cytokines production, and the increased IL6, CXCL8, and TNF were confirmed again using Kit assay.

CONCLUSIONS

We have identified that LPAR2 is critical for LPA-promoted renal cancer progression, and the actions mainly dependent the MAPK and NF-κB activation mechanism. Then, the expression of inflammatory factors activated by NF-κB is also suspected to be involved in LPAR2-mediated carcinogenesis. Thus, LPAR2 may be a promising therapeutic target for renal cancer.

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.

Current Knowledge on Mammalian Phospholipase A1, Brief History, Structures, Biochemical and Pathophysiological Roles

Phospholipase A₁ (PLA₁) is an enzyme that cleaves an ester bond at the sn-1 position of glycerophospholipids, producing a free fatty acid and a lysophospholipid. PLA₁ activities have been detected both extracellularly and intracellularly, which are well conserved in higher eukaryotes, including fish and mammals. All extracellular PLA₁s belong to the lipase family. In addition to PLA₁ activity, most mammalian extracellular PLA₁s exhibit lipase activity to hydrolyze triacylglycerol, cleaving the fatty acid and contributing to its absorption into the intestinal tract and tissues. Some extracellular PLA₁s exhibit PLA₁ activities specific to phosphatidic acid (PA) or phosphatidylserine (PS) and serve to produce lysophospholipid mediators such as lysophosphatidic acid (LPA) and lysophosphatidylserine (LysoPS). A high level of PLA₁ activity has been detected in the cytosol fractions, where PA-PLA₁/DDHD1/iPLA₁ was responsible for the activity. Many homologs of PA-PLA₁ and PLA₂ have been shown to exhibit PLA₁ activity. Although much has been learned about the pathophysiological roles of PLA₁ molecules through studies of knockout mice and human genetic diseases, many questions regarding their biochemical properties, including their genuine in vivo substrate, remain elusive.

Lysophospholipid Mediators in Health and Disease

Lysophospholipids, exemplified by lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P), are produced by the metabolism and perturbation of biological membranes. Both molecules are established extracellular lipid mediators that signal via specific G protein-coupled receptors in vertebrates. This widespread signaling axis regulates the development, physiological functions, and pathological processes of all organ systems. Indeed, recent research into LPA and S1P has revealed their important roles in cellular stress signaling, inflammation, resolution, and host defense responses. In this review, we focus on how LPA regulates fibrosis, neuropathic pain, abnormal angiogenesis, endometriosis, and disorders of neuroectodermal development such as hydrocephalus and alopecia. In addition, we discuss how S1P controls collective behavior, apoptotic cell clearance, and immunosurveillance of cancers. Advances in lysophospholipid research have led to new therapeutics in autoimmune diseases, with many more in earlier stages of development for a wide variety of diseases, such as fibrotic disorders, vascular diseases, and cancer.

Motility Dynamics of T Cells in Tumor-Draining Lymph Nodes: A Rational Indicator of Antitumor Response and Immune Checkpoint Blockade

The migration status of T cells within the densely packed tissue environment of lymph nodes reflects the ongoing activation state of adaptive immune responses. Upon encountering antigen-presenting dendritic cells, actively migrating T cells that are specific to cognate antigens slow down and are eventually arrested on dendritic cells to form immunological synapses. This dynamic transition of T cell motility is a fundamental strategy for the efficient scanning of antigens, followed by obtaining the adequate activation signals. After receiving antigenic stimuli, T cells begin to proliferate, and the expression of immunoregulatory receptors (such as CTLA-4 and PD-1) is induced on their surface. Recent findings have revealed that these 'immune checkpoint' molecules control the activation as well as motility of T cells in various situations. Therefore, the outcome of tumor immunotherapy using checkpoint inhibitors is assumed to be closely related to the alteration of T cell motility, particularly in tumor-draining lymph nodes (TDLNs). In this review, we discuss the migration dynamics of T cells during their activation in TDLNs, and the roles of checkpoint molecules in T cell motility, to provide some insight into the effect of tumor immunotherapy via checkpoint blockade, in terms of T cell dynamics and the importance of TDLNs.

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.

The LPA3 Receptor: Regulation and Activation of Signaling Pathways

The lysophosphatidic acid 3 receptor (LPA₃) participates in different physiological actions and in the pathogenesis of many diseases through the activation of different signal pathways. Knowledge of the regulation of the function of the LPA₃ receptor is a crucial element for defining its roles in health and disease. This review describes what is known about the signaling pathways activated in terms of its various actions. Next, we review knowledge on the structure of the LPA₃ receptor, the domains found, and the roles that the latter might play in ligand recognition, signaling, and cellular localization. Currently, there is some information on the action of LPA₃ in different cells and whole organisms, but very little is known about the regulation of its function. Areas in which there is a gap in our knowledge are indicated in order to further stimulate experimental work on this receptor and on other members of the LPA receptor family. We are convinced that knowledge on how this receptor is activated, the signaling pathways employed and how the receptor internalization and desensitization are controlled will help design new therapeutic interventions for treating diseases in which the LPA₃ receptor is implicated.

BRET analysis reveals interaction between the lysophosphatidic acid receptor LPA2 and the lysophosphatidylinositol receptor GPR55 in live cells

Lysophosphatidic acid (LPA) and lysophosphatidylinositol bind to the G protein-coupled receptors (GPCRs) LPA and GPR55, respectively. LPA₂ , a type 2 LPA receptor, and GPR55 are highly expressed in colon cancer and involved in cancer progression. However, crosstalk between the two receptors and potential effects on cellular physiology are not fully understood. Here, using BRET analysis, we found that LPA₂ and GPR55 interact in live cells. In the presence of both receptors, LPA₂ and/or GPR55 activation facilitated co-internalization, and activation of GPR55, uncoupled with Gα_i , induced reduction of intracellular cAMP. Notably, co-activation of receptors synergistically triggered further decline in the cAMP level, promoted cell proliferation, and increased the expression of cancer progression-related genes, suggesting that physical and functional crosstalk between LPA₂ and GRR55 is involved in cancer progression.

Lysophosphatidic Acid Signalling in Nervous System Development and Function

One class of molecules that are now coming to be recognized as essential for our understanding of the nervous system are the lysophospholipids. One of the major signaling lysophospholipids is lysophosphatidic acid, also known as LPA. LPA activates a variety of G protein-coupled receptors (GPCRs) leading to a multitude of physiological responses. In this review, I describe our current understanding of the role of LPA and LPA receptor signaling in the development and function of the nervous system, especially the central nervous system (CNS). In addition, I highlight how aberrant LPA receptor signaling may underlie neuropathological conditions, with important clinical application.

Evaluation of serum ATX and LPA as potential diagnostic biomarkers in patients with pancreatic cancer

BACKGROUND

Pancreatic cancer (PC) is a devastating disease that has a poor prognosis and a total 5-year survival rate of around 5%. The poor prognosis of PC is due in part to a lack of suitable biomarkers that can allow early diagnosis. The lysophospholipase autotaxin (ATX) and its product lysophosphatidic acid (LPA) play an essential role in disease progression in PC patients and are associated with increased morbidity in several types of cancer. In this study, we evaluated both the potential role of serum LPA and ATX as diagnostic markers in PC and their prognostic value for PC either alone or in combination with CA19-9.

METHODS

ATX, LPA and CA19-9 levels were evaluated using ELISA of serum obtained from PC patients (n = 114) healthy volunteers (HVs: n = 120) and patients with benign pancreatic diseases (BPDs: n = 94).

RESULTS

Serum levels of ATX, LPA and CA19-9 in PC patients were substantially higher than that for BPD patients or HVs (p < 0.001). The sensitivity of LPA in early phase PC was 91.74% and the specificity of ATX was 80%. The levels of ATX, LPA and CA19-9 were all substantially higher for early stage PC patients compared to levels in serum from BPD patients and HVs. The diagnostic efficacy of CA19-9 for PC was significantly enhanced by the addition of ATX and LPA (p = 0.0012).

CONCLUSION

Measurement of LPA and ATX levels together with CA19-9 levels can be used for early detection of PC and diagnosis of PC in general.

Role of lysophosphatidic acid and its receptors in health and disease: novel therapeutic strategies

Lysophosphatidic acid (LPA) is an abundant bioactive phospholipid, with multiple functions both in development and in pathological conditions. Here, we review the literature about the differential signaling of LPA through its specific receptors, which makes this lipid a versatile signaling molecule. This differential signaling is important for understanding how this molecule can have such diverse effects during central nervous system development and angiogenesis; and also, how it can act as a powerful mediator of pathological conditions, such as neuropathic pain, neurodegenerative diseases, and cancer progression. Ultimately, we review the preclinical and clinical uses of Autotaxin, LPA, and its receptors as therapeutic targets, approaching the most recent data of promising molecules modulating both LPA production and signaling. This review aims to summarize the most update knowledge about the mechanisms of LPA production and signaling in order to understand its biological functions in the central nervous system both in health and disease.

Pathogenic mechanisms of lipid mediator lysophosphatidic acid in chronic pain

A number of membrane lipid-derived mediators play pivotal roles in the initiation, maintenance, and regulation of various types of acute and chronic pain. Acute pain, comprising nociceptive and inflammatory pain warns us about the presence of damage or harmful stimuli. However, it can be efficiently reversed by opioid analgesics and anti-inflammatory drugs. Prostaglandin E₂ and I₂, the representative lipid mediators, are well-known causes of acute pain. However, some lipid mediators such as lipoxins, resolvins or endocannabinoids suppress acute pain. Various types of peripheral and central neuropathic pain (NeuP) as well as fibromyalgia (FM) are representatives of chronic pain and refractory owing to abnormal pain processing distinct from acute pain. Accumulating evidence demonstrated that lipid mediators represented by lysophosphatidic acid (LPA) are involved in the initiation and maintenance of both NeuP and FM in experimental animal models. The LPAR₁-mediated peripheral mechanisms including dorsal root demyelination, Ca_vα2δ1 expression in dorsal root ganglion, and LPAR₃-mediated amplification of central LPA production via glial cells are involved in the series of molecular mechanisms underlying NeuP. This review also discusses the involvement of lipid mediators in emerging research directives, including itch-sensing, sexual dimorphism, and the peripheral immune system.

Association of lysophosphatidic acids with cerebrospinal fluid biomarkers and progression to Alzheimer's disease

Background

Lysophosphatidic acids (LPAs) are bioactive signaling phospholipids that have been implicated in Alzheimer’s disease (AD). It is largely unknown whether LPAs are associated with AD pathology and progression from mild cognitive impairment (MCI) to AD.

Methods

The current study was performed on cerebrospinal fluid (CSF) and plasma samples of 182 MCI patients from two independent cohorts. We profiled LPA-derived metabolites using liquid chromatography-mass spectrometry. We evaluated the association of LPAs with CSF biomarkers of AD, Aβ-42, p-tau, and total tau levels overall and stratified by APOE genotype and with MCI to AD progression.

Results

Five LPAs (C16:0, C16:1, C22:4, C22:6, and isomer-LPA C22:5) showed significant positive association with CSF biomarkers of AD, Aβ-42, p-tau, and total tau, while LPA C14:0 and C20:1 associated only with Aβ-42 and alkyl-LPA C18:1, and LPA C20:1 associated with tau pathology biomarkers. Association of cyclic-LPA C16:0 and two LPAs (C20:4, C22:4) with Aβ-42 levels was found only in APOE ε4 carriers. Furthermore, LPA C16:0 and C16:1 also showed association with MCI to AD dementia progression, but results did not replicate in an independent cohort.

Conclusions

Our findings provide evidence that LPAs may contribute to early AD pathogenesis. Future studies are needed to determine whether LPAs play a role in upstream of AD pathology or are downstream markers of neurodegeneration.

Druggable Lipid GPCRs: Past, Present, and Prospects

G protein-coupled receptors (GPCRs) have seven transmembrane spanning domains and comprise the largest superfamily with ~800 receptors in humans. GPCRs are attractive targets for drug discovery because they transduce intracellular signaling in response to endogenous ligands via heterotrimeric G proteins or arrestins, resulting in a wide variety of physiological and pathophysiological responses. The endogenous ligands for GPCRs are highly chemically diverse and include ions, biogenic amines, nucleotides, peptides, and lipids. In this review, we follow the KonMari method to better understand druggable lipid GPCRs. First, we have a comprehensive tidying up of lipid GPCRs including receptors for prostanoids, leukotrienes, specialized pro-resolving mediators (SPMs), lysophospholipids, sphingosine 1-phosphate (S1P), cannabinoids, platelet-activating factor (PAF), free fatty acids (FFAs), and sterols. This tidying up consolidates 46 lipid GPCRs and declutters several perplexing lipid GPCRs. Then, we further tidy up the lipid GPCR-directed drugs from the literature and databases, which identified 24 clinical drugs targeting 16 unique lipid GPCRs available in the market and 44 drugs under evaluation in more than 100 clinical trials as of 2019. Finally, we introduce drug designs for GPCRs that spark joy, such as positive or negative allosteric modulators (PAM or NAM), biased agonism, functional antagonism like fingolimod, and monoclonal antibodies (MAbs). These strategic drug designs may increase the efficacy and specificity of drugs and reduce side effects. Technological advances will help to discover more endogenous lipid ligands from the vast number of remaining orphan GPCRs and will also lead to the development novel lipid GPCR drugs to treat various diseases.

The Role of Lysophosphatidic Acid in Adult Stem Cells

Stem cells are undifferentiated multipotent precursor cells that are capable both of perpetuating themselves as stem cells (self-renewal) and of undergoing differentiation into one or more specialized types of cells. And these stem cells have been reported to reside within distinct anatomic locations termed “niches”. The long-term goals of stem cell biology range from an understanding of cell-lineage determination and tissue organization to cellular therapeutics for degenerative diseases. Stem cells maintain tissue function throughout an organism’s lifespan by replacing differentiated cells. To perform this function, stem cells provide a unique combination of multilineage developmental potential and the capacity to undergo self-renewing divisions. The loss of self-renewal capacity in stem cells underlies certain degenerative diseases and the aging process. This self-renewal regulation must balance the regenerative needs of tissues that persist throughout life. Recent evidence suggests lysophosphatidic acid (LPA) signaling pathway plays an important role in the regulation of a variety of stem cells. In this review, we summarize the evidence linking between LPA and stem cell regulation. The LPA-induced signaling pathway regulates the proliferation and survival of stem cells and progenitors, and thus are likely to play a role in the maintenance of stem cell population in the body. This lipid mediator regulatory system can be a novel potential therapeutics for stem cell maintenance.

Unlabeled lysophosphatidic acid receptor binding in free solution as determined by a compensated interferometric reader

Native interactions between lysophospholipids (LPs) and their cognate LP receptors are difficult to measure because of lipophilicity and/or the adhesive properties of lipids, which contribute to high levels of nonspecific binding in cell membrane preparations. Here, we report development of a free-solution assay (FSA) where label-free LPs bind to their cognate G protein-coupled receptors (GPCRs), combined with a recently reported compensated interferometric reader (CIR) to quantify native binding interactions between receptors and ligands. As a test case, the binding parameters between lysophosphatidic acid (LPA) receptor 1 (LPA₁; one of six cognate LPA GPCRs) and LPA were determined. FSA-CIR detected specific binding through the simultaneous real-time comparison of bound versus unbound species by measuring the change in the solution dipole moment produced by binding-induced conformational and/or hydration changes. FSA-CIR identified K_D values for chemically distinct LPA species binding to human LPA₁ and required only a few nanograms of protein: 1-oleoyl (18:1; K_D = 2.08 ± 1.32 nM), 1-linoleoyl (18:2; K_D = 2.83 ± 1.64 nM), 1-arachidonoyl (20:4; K_D = 2.59 ± 0.481 nM), and 1-palmitoyl (16:0; K_D = 1.69 ± 0.1 nM) LPA. These K_D values compared favorably to those obtained using the previous generation back-scattering interferometry system, a chip-based technique with low-throughput and temperature sensitivity. In conclusion, FSA-CIR offers a new increased-throughput approach to assess quantitatively label-free lipid ligand-receptor binding, including nonactivating antagonist binding, under near-native conditions.

Fingolimod: Lessons Learned and New Opportunities for Treating Multiple Sclerosis and Other Disorders

Fingolimod (FTY720, Gilenya) was the first US Food and Drug Administration-approved oral therapy for relapsing forms of multiple sclerosis (MS). Research on modified fungal metabolites converged with basic science studies that had identified lysophospholipid (LP) sphingosine 1-phosphate (S1P) receptors, providing mechanistic insights on fingolimod while validating LP receptors as drug targets. Mechanism of action (MOA) studies identified receptor-mediated processes involving the immune system and the central nervous system (CNS). These dual actions represent a more general theme for S1P and likely other LP receptor modulators. Fingolimod's direct CNS activities likely contribute to its efficacy in MS, with particular relevance to treating progressive disease stages and forms that involve neurodegeneration. The evolving understanding of fingolimod's MOA has provided strategies for developing next-generation compounds with superior attributes, suggesting new ways to target S1P as well as other LP receptor modulators for novel therapeutics in the CNS and other organ systems.

A Novel Function of the Lysophosphatidic Acid Receptor 3 (LPAR3) Gene in Zebrafish on Modulating Anxiety, Circadian Rhythm Locomotor Activity, and Short-Term Memory

Lysophosphatidic acid (LPA) is a small lysophospholipid molecule that activates multiple cellular functions through pathways with G-protein-coupled receptors. So far, six LPA receptors (LPAR1 to LPAR6) have been discovered and each one of them can connect to the downstream cell message-transmitting network. A previous study demonstrated that LPA receptors found in blood-producing stem cells can enhance erythropoietic processes through the activation of LPAR3. In the current study, newly discovered functions of LPAR3 were identified through extensive behavioral tests in lpar3 knockout (KO) zebrafish. It was found that the adult lpar3 KO zebrafish display an abnormal movement orientation and altered exploratory behavior compared to that of the control group in the three-dimensional locomotor and novel tank tests, respectively. Furthermore, consistent with those results, in the circadian rhythm locomotor activity test, the lpar3 KO zebrafish showed a lower level of angular velocity and average speed during the light cycles, indicating an hyperactivity-like behavior. In addition, the mutant fish also exhibited considerably higher locomotor activity during the dark cycle. Supporting those findings, this phenomenon was also displayed in the lpar3 KO zebrafish larvae. Furthermore, several important behavior alterations were also observed in the adult lpar3 KO fish, including a lower degree of aggression, less interest in conspecific social interaction, and looser shoal formation. However, there was no significant difference regarding the predator avoidance behavior between the mutant and the control fish. In addition, lpar3 KO zebrafish displayed memory deficiency in the passive avoidance test. These in vivo results support for the first time that the lpar3 gene plays a novel role in modulating behaviors of anxiety, aggression, social interaction, circadian rhythm locomotor activity, and memory retention in zebrafish.

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.

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.

MicroRNA Regulation of the Autotaxin-Lysophosphatidic Acid Signaling Axis

The revelation that microRNAs (miRNAs) exist within the human genome uncovered an underappreciated mechanism of gene expression. For cells to regulate expression of their genes, miRNA molecules and argonaute proteins bind to mRNAs and interfere with efficient translation of the RNA transcript. Although miRNAs have important roles in normal tissues, miRNAs may adopt aberrant functions in malignant cells depending on their classification as either a tumor suppressor or oncogenic miRNA. Within this review, the current status of miRNA regulation is described in the context of signaling through the lysophosphatidic acid receptors, including the lysophosphatidic acid-producing enzyme, autotaxin. Thus far, research has revealed miRNAs that increase in response to lysophosphatidic acid stimulation, such as miR-21, miR-30c-2-3p, and miR-122. Other miRNAs inhibit the translation of lysophosphatidic acid receptors, such as miR-15b, miR-23a, and miR200c, or proteins that are downstream of lysophosphatidic acid signaling, such as miR-146 and miR-21. With thousands of miRNAs still uncharacterized, it is anticipated that the complex regulation of lysophosphatidic acid signaling by miRNAs will continue to be elucidated. RNA-based therapeutics have entered the clinic with enormous potential in precision medicine. This exciting field is rapidly emerging and it will be fascinating to witness its expansion in scope.

Osteoglycin attenuates cardiac fibrosis by suppressing cardiac myofibroblast proliferation and migration through antagonizing lysophosphatidic acid 3/matrix metalloproteinase 2/epidermal growth factor receptor signalling

Aims

Cardiac myofibroblasts (CMFs) play a crucial role in the progression of pathological fibrotic cardiac remodelling. The expression of osteoglycin (OGN) is increased in diseased hearts; however, the role of OGN in pathological cardiac remodelling is not understood. Here, we sought to determine the effect of OGN on cardiac interstitial fibrosis and investigate the molecular mechanisms of OGN in CMF activation and matrix production.

Methods and results

We found that OGN expression was significantly upregulated in mouse hearts in response to chronic 14-day angiotensin II (Ang II) infusion. Mice lacking OGN (OGN-/-) exhibited enhanced cardiac interstitial fibrosis and significantly more severe cardiac dysfunction following Ang II infusion compared to wild-type mice. OGN deficiency did not alter blood pressure, nor had effect on transforming growth factor-beta signalling activation, but presented with increased proliferative activity in hearts. In vitro studies with isolated CMFs revealed that OGN deficiency significantly increased proliferation and migration and enhanced the transactivation of epidermal growth factor receptor (EGFR) signalling by Ang II. On the other hand, OGN overexpression in CMFs decreased their proliferation and migration via reducing EGFR activation. Overexpression of OGN also suppressed the shedding of membrane anchored EGFR ligand. Moreover, OGN was found to interact with a lysophosphatidic acid (LPA) receptor isoform 3 and thus to attenuate EGFR transactivation through blocking cell surface translocation of membrane type 1 matrix metalloproteinase (MT1-MMP) and subsequent pro-MMP-2 activation in a Ras homolog gene family, member A (RhoA)/Rho-associated, coiled-coil containing protein kinase (ROCK)-dependent manner.

Conclusion

These findings suggest that OGN negatively regulates cardiac fibrotic remodelling by attenuating CMF proliferation and migration through LPA3-mediated and Rho/ROCK-dependent inhibition of MT1-MMP translocation, MMP2 activation and EGFR transactivation.

Lysophosphatidic acid up-regulates IL-10 production to inhibit TNF-α synthesis in Mϕs stimulated with LPS

Bacterial LPS strongly induces pro-inflammatory responses of Mϕs after binding to CD14 protein and the TLR4/MD-2 receptor complex. The LPS-triggered signaling can be modulated by extracellular lysophosphatidic acid (LPA), which is of substantial importance for Mϕ functioning under specific pathophysiological conditions, such as atherosclerosis. The molecular mechanisms of the crosstalk between the LPS- and LPA-induced signaling, and the LPA receptors involved, are poorly known. In this report, we show that LPA strongly inhibits the LPS-induced TNF-α production at the mRNA and protein levels in primary Mϕs and Mϕ-like J774 cells. The decreased TNF-α production in LPA/LPS-stimulated cells is to high extent independent of NF-κB but is preceded by enhanced expression and secretion of the anti-inflammatory cytokine IL-10. The IL-10 elevation and TNF-α reduction are both abrogated upon depletion of the LPA₅ and LPA₆ receptors in J774 cells and can be linked with LPA-mediated activation of p38. We propose that the binding of LPA to LPA₅ and LPA₆ fine-tunes the LPS-induced inflammatory response by activating p38, and up-regulating IL-10 and down-regulating TNF-α production.

LPA1 , LPA2 , LPA4 , and LPA6 receptor expression during mouse brain development

Background

LPA is a small bioactive phospholipid that acts as an extracellular signaling molecule and is involved in cellular processes, including cell proliferation, migration, and differentiation. LPA acts by binding and activating at least six known G protein–coupled receptors: LPA_1–6. In recent years, LPA has been suggested to play an important role both in normal neuronal development and under pathological conditions in the nervous system.

Results

We show the expression pattern of LPA receptors during mouse brain development by using qRT‐PCR, in situ hybridization, and immunocytochemistry. Only LPA₁, LPA_2,LPA_4, and LPA₆ mRNA transcripts were detected throughout development stages from embryonic day 16 until postnatal day 30 of hippocampus, neocortex, cerebellum, and bulbus olfactorius in our experiments, while expression of LPA₃ and LPA₅ genes was below detection level. In addition to our qRT‐PCR results, we also analyzed the cellular protein expression of endogenous LPA receptors, with focus on LPA₁ and LPA₂ within postnatal brain slices and primary neuron differentiation with and without cytoskeleton stabilization and destabilization.

Conclusions

The expression of LPA receptors changes depends on the developmental stage in mouse brain and in cultured hippocampal primary neurons. Interestingly, we found that commercially available antibodies for LPA receptors are largely unspecific.

LPA1, ‐2, ‐4, and ‐6 genes are dynamically expressed during postnatal brain development.

LPA1, ‐2, ‐4, and ‐6 genes are differently expressed in the hippocampus, neocortex, cerebellum, and bulbus olfactorius.

LPA1 and ‐2 gene expression alters during neuronal differentiation.

LPA1, ‐2, ‐3, ‐4, and ‐6 genes are expressed in glia cells, but differed in gene expression levels.

Targeting the autotaxin - Lysophosphatidic acid receptor axis in cardiovascular diseases

Lysophosphatidic acid (LPA) is a well-characterized bioactive lipid mediator, which is involved in development, physiology, and pathological processes of the cardiovascular system. LPA can be produced both inside cells and in biological fluids. The majority of extracellularLPAis produced locally by the secreted lysophospholipase D, autotaxin (ATX), through its binding to various β integrins or heparin sulfate on cell surface and hydrolyzing various lysophospholipids. LPA initiates cellular signalling pathways upon binding to and activation of its G protein-coupled receptors (LPA1-6). LPA has potent effects on various blood cells and vascular cells involved in the development of cardiovascular diseases such as atherosclerosis and aortic valve sclerosis. LPA signalling drives cell migration and proliferation, cytokine production, thrombosis, fibrosis, as well as angiogenesis. For instance, LPA promotes activation and aggregation of platelets through LPA5, increases expression of adhesion molecules in endothelial cells, and enhances expression of tissue factor in vascular smooth muscle cells. Furthermore, LPA induces differentiation of monocytes into macrophages and stimulates oxidized low-density lipoproteins (oxLDLs) uptake by macrophages to form foam cells during formation of atherosclerotic lesions through LPA1-3. This review summarizes recent findings of the roles played by ATX, LPA and LPA receptors (LPARs) in atherosclerosis and calcific aortic valve disease. Targeting the ATX-LPAR axis may have potential applications for treatment of patients suffering from various cardiovascular diseases.

ADSCs and adipocytes are the main producers in the autotaxin-lysophosphatidic acid axis of breast cancer and healthy mammary tissue in vitro

Background

Breast cancer is the most common malignancy in women affecting one out of eight females throughout their lives. Autotaxin (ATX) is upregulated in breast cancer which results in increased lysophosphatidic acid (LPA) formation within the tumor. This study’s aim was to identify the role of different mammary cell populations within the ATX–LPA axis.

Methods

Epithelial-cell-adhesion-molecule-positive (EpCAM) and -negative cells from breast tumors, adipose-derived stem cells (ADSCs) of tumor-adjacent and tumor-distant mammary fat were isolated and compared to healthy ADSCs, mammary epithelial cells (HMECs), and mesenchymal cells (MES) of healthy mammary tissue (n = 4 each) and further to well-established breast (cancer) cell lines.

Results

mRNA expression analyses revealed that ADSCs and MES largely expressed LPA receptor 1 (LPAR1) while epithelial cells mainly expressed LPAR6. LPA 18:1 activated all the cell populations and cell lines by rise in cytosolic free calcium concentrations. MES and ADSCs expressed ATX whereas epithelial cells did not. ADSCs revealed the highest expression in ATX with a significant decline after adipogenic differentiation in healthy ADSCs, whereas ATX expression increased in ADSCs from tumor patients. Breast (cancer) cell lines did not express ATX. Transmigration of MES was stimulated by LPA whereas an inhibitory effect was observed in epithelial cells with no differences between tumors and healthy cells. Triple-negative breast cancer (TNBC) cell lines were also stimulated and the transmigration partly inhibited using the LPA receptor antagonist Ki16425.

Conclusions

We here show that each mammary cell population plays a different role in the ATX–LPA axis with ADSCs and adipocytes being the main source of ATX in tumor patients in our experimental setting. Inhibitors of this axis may therefore present a valuable target for pharmacological therapies.

Arginine 313 of the putative 8th helix mediates Gαq/14 coupling of human CC chemokine receptors CCR2a and CCR2b

In man, two CC chemokine receptor isoforms, CCR2a and CCR2b, are present that belong to the rhodopsin-like G protein-coupled receptor family, and couple to G_i and G_q family members. The CCR2 receptors are known to regulate canonical functions of chemokines such as directed migration of leukocytes, and to potentially control non-canonical functions such as differentiation, proliferation, and gene transcription of immune and non-immune cells. We recently reported on the activation of phospholipase C isoenzymes and RhoA GTPases by coupling of the two CCR2 receptors to members of the G_q family, in particular Gα_q and Gα₁₄. So far little is known about the structural requirements for the CCR2/G_q/14 interaction. Interestingly, the CCR2 receptor isoforms are identical up to arginine 313 (R³¹³) that is part of the putative 8th helix in CCR2 receptors, and the 8th helix has been implicated in the interaction of rhodopsin-like G protein-coupled receptors with Gα_q. In the present work we describe that the 8th helix of both CCR2a and CCR2b is critically involved in selectively activating Gα_q/14-regulated signaling. Refined analysis using various CCR2a and CCR2b mutants and analyzing their cellular signaling, e.g. ligand-dependent (i) activation of phospholipase C isoenzymes, (ii) stimulation of serum response factor-mediated gene transcription, (iii) activation of mitogen-activated protein kinases, (iv) internalization, and (v) changes in intracellular calcium concentrations, identified arginine 313 within the amino terminal portion of helix 8 to play a role for the agonist-mediated conformational changes and the formation of a Gα_q/14 binding surface. We show that R³¹³ determines Gα_q/14 protein-dependent but not G_i protein-dependent cellular signaling, and plays no role in G_q/G_i-independent receptor internalization, indicating a role of R³¹³ in biased signaling of CCR2 receptors.

Regulation of tumor cell - Microenvironment interaction by the autotaxin-lysophosphatidic acid receptor axis

The lipid mediator lysophosphatidic acid (LPA) in biological fluids is primarily produced by cleavage of lysophospholipids by the lysophospholipase D enzyme Autotaxin (ATX). LPA has been identified and abundantly detected in the culture medium of various cancer cell types, tumor effusates, and ascites fluid of cancer patients. Our current understanding of the physiological role of LPA established its role in fundamental biological responses that include cell proliferation, metabolism, neuronal differentiation, angiogenesis, cell migration, hematopoiesis, inflammation, immunity, wound healing, regulation of cell excitability, and the promotion of cell survival by protecting against apoptotic death. These essential biological responses elicited by LPA are seemingly hijacked by cancer cells in many ways; transcriptional upregulation of ATX leading to increased LPA levels, enhanced expression of multiple LPA GPCR subtypes, and the downregulation of its metabolic breakdown. Recent studies have shown that overexpression of ATX and LPA GPCR can lead to malignant transformation, enhanced proliferation of cancer stem cells, increased invasion and metastasis, reprogramming of the tumor microenvironment and the metastatic niche, and development of resistance to chemo-, immuno-, and radiation-therapy of cancer. The fundamental role of LPA in cancer progression and the therapeutic inhibition of the ATX-LPA axis, although highly appealing, remains unexploited as drug development to these targets has not reached into the clinic yet. The purpose of this brief review is to highlight some unique signaling mechanisms engaged by the ATX-LPA axis and emphasize the therapeutic potential that lies in blocking the molecular targets of the LPA system.

Lysophosphatidic acid enhances human umbilical cord mesenchymal stem cell viability without differentiation via LPA receptor mediating manner

Human umbilical cord mesenchymal stem cells (hUC-MSCs) are potential stromal cells which are regarded as the most feasible stem cell group in cell therapy. The maintenance of cell survival without differentiation is important in cell transplantation and stem cell therapy. However, negative factors exist in cell transplantation. Lysophosphatidic acid (LPA) is a non-antigenic small molecule phospholipid which induced several fundamental cellular responses, such as cell proliferation, apoptosis and migration. In this study we aimed to explore the effects of LPA on the survival and differentiation of MSCs and its availability in cell therapy. We found that LPA stimulated hUC-MSC proliferation and protected hUC-MSCs from lipopolysaccharide (LPS) induced apoptosis. We also observed that CD29, CD44, CD73, CD90 and CD105 were expressed, whereas CD34 and CD45 were not expressed in hUC-MSCs, and these makers have no change in LPA containing medium, which indicated that LPA accelerated the survival of hUC-MSCs in an undifferentiating status. We also demonstrated that higher expressed LPAR1 involved in LPA stimulated cell survival action. LPA stimulated cell proliferation was associated with LPAR1 mediated G_i/o-proteins/ERK1/2 pathway. On the other hand, LPA protected hUC-MSCs from LPS-induced apoptosis through suppressing caspase-3 activation by LPAR1 coupled with a G protein, but not G_i/o or G_q/11 in hUC-MSC. Collectively, this study demonstrated that LPA increased the proliferation and survival of hUC-MSCs without differentiation through LPAR1 mediated manner. Our findings provide that LPA as a anti-apoptotic agent having potential application prospect in cell transplantation and stem cell therapy.

LPAR2 and LPAR4 are the Main Receptors Responsible for LPA Actions in Ovarian Endometriotic Cysts

Endometriosis has been considered as an estrogen (E2)-dependent and progesterone (P4)-resistant disease. On the other hand, lysophosphatidic acid (LPA) has been suggested as a significant modulator of ovarian pathology, acting via both LPA levels and LPA receptor (LPAR) upregulation. Therefore, the objective of the present study was to evaluate LPA concentration as well as LPARs, autotaxin (ATX), and phospholipase A2 (PLA2) expression in ovarian endometriotic cysts and normal endometrium with correlation of the expression of E2 and P4 receptors in endometriotic cysts. The analyses were carried out using the tissues derived from 37 patients with ovarian endometriosis and 20 endometrial samples collected from women without endometriosis were used as a control. We found that ovarian endometriotic cysts are a site of LPA synthesis due to the presence of enzymes involved in LPA synthesis in the tissue. Additionally, when we compared endometriotic cysts versus normal endometrium, we were able to show overexpression of 3 from 6 examined LPARs and both enzymes responsible for LPA synthesis in endometriotic cysts. Finally, we found the correlations between LPARs, ATX, and PLA2 and the expression of E2 and P4 receptors in endometriotic cysts. Owing to the high LPAR2 and LPAR4 transcript and protein expression in endometriotic ovarian cysts and positive correlations of both these receptors with the PR-B and ERβ, respectively, those receptors seem to be the most promising predictors of the endometriotic cysts as well as the main receptors responsible for LPA action in the ovarian endometriosis.

Lysophosphatidic Acid Signaling in Obesity and Insulin Resistance

Although simple in structure, lysophosphatidic acid (LPA) is a potent bioactive lipid that profoundly influences cellular signaling and function upon binding to G protein-coupled receptors (LPA1-6). The majority of circulating LPA is produced by the secreted enzyme autotaxin (ATX). Alterations in LPA signaling, in conjunction with changes in autotaxin (ATX) expression and activity, have been implicated in metabolic and inflammatory disorders including obesity, insulin resistance, and cardiovascular disease. This review summarizes our current understanding of the sources and metabolism of LPA with focus on the influence of diet on circulating LPA. Furthermore, we explore how the ATX-LPA pathway impacts obesity and obesity-associated disorders, including impaired glucose homeostasis, insulin resistance, and cardiovascular disease.

Lpar2b Controls Lateral Line Tissue Size by Regulating Yap1 Activity in Zebrafish

LPA signaling plays important roles during cell migration and proliferation in normal and pathological conditions. However, its role during sensory organ development remains unknown. Here we show a LPA receptor Lpar2b is expressed in the posterior lateral line primordium (pLLP) and mechanosensory organs called neuromasts (NMs) in zebrafish embryos. Lpar2b loss-of-function significantly reduces the number of NMs and hair cells in the posterior lateral line (pLL). Further analysis reveals that Lpar2b regulates the patterning and tissue size of the pLLP. Interestingly, we show that knocking down a Hippo effector Yap1 phenocopies the result of Lpar2b depletion, and Lpar2b regulates the phosphorylation and activity of Yap1 in the pLLP. Importantly, a phosphorylation-resistant Yap1 rescues pLLP size and NM number in Lpar2b-depleted embryos. Our results indicate Lpar2b controls primordium size and NM number by regulating Yap1 activity in the lateral line system.

Autotaxin-Lysophosphatidic Acid: From Inflammation to Cancer Development

Lysophosphatidic acid (LPA) is a ubiquitous lysophospholipid and one of the main membrane-derived lipid signaling molecules. LPA acts as an autocrine/paracrine messenger through at least six G protein-coupled receptors (GPCRs), known as LPA_1–6, to induce various cellular processes including wound healing, differentiation, proliferation, migration, and survival. LPA receptors and autotaxin (ATX), a secreted phosphodiesterase that produces this phospholipid, are overexpressed in many cancers and impact several features of the disease, including cancer-related inflammation, development, and progression. Many ongoing studies aim to understand ATX-LPA axis signaling in cancer and its potential as a therapeutic target. In this review, we discuss the evidence linking LPA signaling to cancer-related inflammation and its impact on cancer progression.

Bovine ovarian follicular growth and development correlate with lysophosphatidic acid expression

The basis of successful reproduction is proper ovarian follicular growth and development. In addition to prostaglandins and vascular endothelial growth factor, a number of novel factors are suggested as important regulators of follicular growth and development: PGES, TFG, CD36, RABGAP1, DBI and BTC. This study focuses on examining the expression of these factors in granulosa and thecal cells that originate from different ovarian follicle types and their link with the expression of lysophosphatidic acid (LPA), known local regulator of reproductive functions in the cow. Ovarian follicles were divided into healthy, transitional, and atretic categories. The mRNA expression levels for PGES, TFG, CD36, RABGAP1, DBI and BTC in granulosa and thecal cells in different follicle types were measured by real-time PCR. The correlations among expression of enzymes synthesizing LPA (autotaxin, phospholipase A2), receptors for LPA and examined factors were measured. Immunolocalization of PGES, TFG, CD36, RABGAP1, DBI and BTC was examined by immunohistochemistry. We investigated follicle-type dependent mRNA expression of factors potentially involved in ovarian follicular growth and development, both in granulosa and thecal cells of bovine ovarian follicles. Strong correlations among receptors for LPA, enzymes synthesizing LPA, and the examined factors in healthy and transitional follicles were observed, with its strongest interconnection with TFG, DBI and RABGAP1 in granulosa cells, and TFG in thecal cells; whereas no correlations in atretic follicles were detected. A greater number of correlations were found in thecal cells than in granulosa cells as well as in healthy follicles than in transitional follicles. These data indicate the role of LPA in the growth, development and physiology of the bovine ovarian follicle.

Expression of factors involved in apoptosis and cell survival is correlated with enzymes synthesizing lysophosphatidic acid and its receptors in granulosa cells originating from different types of bovine ovarian follicles

BACKGROUND

Lysophosphatidic acid (LPA) regulates reproductive processes in the cow. Ovarian granulosa cells play a pivotal role in follicle growth and development. Nevertheless, the role of LPA in the local regulation of granulosa cell function in different follicle categories in the bovine ovary has not been investigated.

METHODS

Ovarian follicles were divided into healthy, transitional and atretic categories. The expression levels of AX, PLA2, LPARs and factors involved in apoptosis and cell survival processes in granulosa cells in different types of follicles were measured by real-time PCR. The correlations between the expression levels of AX, PLA2, LPARs and the examined factors were measured. The immunolocalization of AX, PLA2 and LPARs in different ovarian follicles was examined by immunohistochemistry. Statistical analyses were conducted in GraphPad using a one-way ANOVA followed by the Kruskal-Wallis multiple comparison test or a correlation analysis followed by Pearson's test.

RESULTS

The expression levels of AX, PLA2 and LPARs, with the major role of LPAR2 and PLA2, were found in the granulosa cells originating from different follicle types. The expression levels of the factors involved in cell apoptosis (TNFα and its receptors, FAS, FASL, CASP3, CASP8, β-glycan, and DRAK2) were significantly higher in the granulosa cells of the atretic follicles compared to the healthy follicles. A number of correlations between LPARs, AX, PLA2 and factors associated with apoptosis were observed in the atretic but not in the healthy follicles. A greater expression of the factors involved in differentiation and proliferation in the granulosa cells (DICE1 and SOX2) was found in the healthy follicles in comparison with the atretic. A number of correlations between LPARs, AX, PLA2 and the factors associated with cell survival were observed in the healthy but not in the atretic follicles.

CONCLUSIONS

Granulosa cells are the target of LPA action and the source of LPA synthesis in the bovine ovarian follicle. We suggest that the participation of LPA in apoptosis in the atretic follicles mainly occurs through the regulation of TNF-α-dependent and caspase-induced pathways. In the transitional follicles, LPA might influence the inhibins to shift the balance between the number of healthy and atretic follicles. In the healthy follicle type, LPA, acting via LPAR1, might regulate MCL1 and estradiol-stimulating ERβ mRNA expression, leading to the stimulation of anti-apoptotic processes in the granulosa cells and their differentiation and proliferation.

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.

Implications of the lysophosphatidic acid signaling axis in liver cancer

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death in western countries. The major risk factors for HCC are hepatitis C or B viruses, alcohol and metabolic disorders. The increasing risk of HCC in patients with metabolic disorders (i.e. obesity, diabetes and non-alcoholic steatohepatitis/NASH) regardless of the presence of liver cirrhosis is becoming relevant. Nevertheless, molecular mechanisms linking these risk factors to liver oncogenesis are unclear. This review focuses on the pathogenic role of the lysophosphatidic acid (LPA) pathway in HCC, highlighting the implications of this bioactive phospholipid in liver cancer biology and metabolism and as potential therapeutic target.