Lysophosphatidic Acid Signaling Research Articles

Effects of diet and hyperlipidemia on levels and distribution of circulating lysophosphatidic acid

Lysophosphatidic acids (LPAs) are bioactive radyl hydrocarbon-substituted derivatives of glycerol 3-phosphate. LPA metabolism and signaling are implicated in heritable risk of coronary artery disease. Genetic and pharmacological inhibition of these processes attenuate experimental atherosclerosis. LPA accumulates in atheromas, which may be a consequence of association with LDLs. The source, regulation, and biological activity of LDL-associated LPA are unknown. We examined the effects of experimental hyperlipidemia on the levels and distribution of circulating LPA in mice. The majority of plasma LPA was associated with albumin in plasma from wild-type mice fed normal chow. LDL-associated LPA was increased in plasma from high-fat Western diet-fed mice that are genetically prone to hyperlipidemia (LDL receptor knockout or activated proprotein convertase subtilisin/kexin type 9-overexpressing C57Bl6). Adipose-specific deficiency of the ENPP2 gene encoding the LPA-generating secreted lysophospholipase D, autotaxin (ATX), attenuated these Western diet-dependent increases in LPA. ATX-dependent increases in LDL-associated LPA were observed in isolated incubated plasma. ATX acted directly on LDL-associated lysophospholipid substrates in vitro. LDL from all human subjects examined contained LPA and was decreased by lipid-lowering drug therapies. Human and mouse plasma therefore contains a diet-sensitive LDL-associated LPA pool that might contribute to the cardiovascular disease-promoting effects of LPA.

Lysophosphatidic Acid Receptor Signaling Underlying Chronic Pain and Neuroprotective Mechanisms through Prothymosin α

For my Ph.D. research topic, I isolated endogenous morphine-like analgesic dipeptide, kyotorphin, which mediates Met-enkephalin release, and discovered kyotorphin synthetase, a putative receptor and antagonist. Furthermore, I succeeded in purifying μ-opioid receptor and functional reconstitution with purified G proteins. After receiving my full professor position at Nagasaki University in 1996, I worked on two topics of research, molecular mechanisms of chronic pain through lysophosphatidic acid (LPA) and identification and characterization of neuroprotective protein, prothymosin α. In a series of studies, we have shown that LPA signaling defines the molecular mechanisms of neuropathic pain and fibromyalgia in terms of development and maintenance. Above all, the discovery of feed-forward system in LPA production and pain memory may contribute to better understanding of chronic pain and future analgesic drug discovery. Regarding prothymosin α, we first discovered it as neuronal necrosis-inhibitory molecule through two independent mechanisms, such as toll-like receptor and F0/F1 ATPase, both which protect neurons through indirect mechanisms. Prothymosin α is released by non-classical and non-vesicular mechanisms on various stresses, such as ischemia, starvation, and heat-shock. Thus it may be called a new type of neuroprotective damage-associated molecular patterns (DAMPs)/Alarmins. Heterozygotic mice showed a defect in memory-learning and neurogenesis as well as anxiogenic behaviors. Small peptide, P6Q derived from prothymosin α retains neuroprotective actions, which include blockade of cerebral hemorrhage caused by late treatment with tissue plasminogen activator in the stroke model in mice.

Deregulated Lysophosphatidic Acid Metabolism and Signaling in Liver Cancer.

Liver cancer is one of the leading causes of death worldwide due to late diagnosis and scarcity of treatment options. The major risk factor for liver cancer is cirrhosis with the underlying causes of cirrhosis being viral infection (hepatitis B or C), metabolic deregulation (Non-alcoholic fatty liver disease (NAFLD) in the presence of obesity and diabetes), alcohol or cholestatic disorders. Lysophosphatidic acid (LPA) is a bioactive phospholipid with numerous effects, most of them compatible with the hallmarks of cancer (proliferation, migration, invasion, survival, evasion of apoptosis, deregulated metabolism, neoangiogenesis, etc.). Autotaxin (ATX) is the enzyme responsible for the bulk of extracellular LPA production, and together with LPA signaling is involved in chronic inflammatory diseases, fibrosis and cancer. This review discusses the most important findings and the mechanisms related to ATX/LPA/LPAR involvement on metabolic, viral and cholestatic liver disorders and their progression to liver cancer in the context of human patients and mouse models. It focuses on the role of ATX/LPA in NAFLD development and its progression to liver cancer as NAFLD has an increasing incidence which is associated with the increasing incidence of liver cancer. Bearing in mind that adipose tissue accounts for the largest amount of LPA production, many studies have implicated LPA in adipose tissue metabolism and inflammation, liver steatosis, insulin resistance, glucose intolerance and lipogenesis. At the same time, LPA and ATX play crucial roles in fibrotic diseases. Given that hepatocellular carcinoma (HCC) is usually developed on the background of liver fibrosis, therapies that both delay the progression of fibrosis and prevent its development to malignancy would be very promising. Therefore, ATX/LPA signaling appears as an attractive therapeutic target as evidenced by the fact that it is involved in both liver fibrosis progression and liver cancer development.

Modulation of lysophosphatidic acid (LPA) receptor activity: the key to successful neural regeneration?

Modulation of lysophosphatidic acid (LPA) receptor activity: the key to successful neural regeneration?

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.

Regulation of PLPP3 gene expression by NF-κB family transcription factors

Lipid phosphate phosphatase 3 (LPP3), encoded by the PLPP3 gene, is an integral membrane enzyme that dephosphorylates phosphate esters of glycero- and sphingophospholipids. Cell surface LPP3 can terminate the signaling actions of bioactive lysophosphatidic acid (LPA) and sphingosine 1 phosphate, which likely explains its role in developmental angiogenesis, vascular injury responses, and cell migration. Heritable variants in the final intron PLPP3 associate with interindividual variability in coronary artery disease risk that may result from disruption of enhancer sequences that normally act in cis to increase expression of the gene. However, the mechanisms regulating PLPP3 expression are not well understood. We show that the human PLPP3 promoter contains three functional NF-κB response elements. All of these are required for maximal induction of PLPP3 promoter activity in reporter assays. The identified sequences recruit RelA and RelB components of the NF-κB transcription complex to chromatin, and these transcription factors bind to the identified target sequences in two different cell types. LPA promotes binding of Rel family transcription factors to the PLPP3 promoter and increases PLPP3 gene expression through mechanisms that are attenuated by an NF-κB inhibitor, LPA receptor antagonists, and inhibitors of phosphoinositide 3 kinase. These findings indicate that up-regulation of PLPP3 during inflammation and atherosclerosis results from canonical activation of the NF-κB signaling cascade to increase PLPP3 expression through nuclear import and binding of RelA and RelB transcription factors to the PLPP3 promoter and suggest a mechanism by which the LPP3 substrate, LPA, can regulate PLPP3 expression.

Lysophosphatidic acid and its receptors: pharmacology and therapeutic potential in atherosclerosis and vascular disease.

Lysophosphatidic acid (LPA) is a collective name for a set of bioactive lipid species. Via six widely distributed G protein-coupled receptors (GPCRs), LPA elicits a plethora of biological responses, contributing to inflammation, thrombosis and atherosclerosis. There have recently been considerable advances in GPCR signaling especially recognition of the extended role for GPCR transactivation of tyrosine and serine/threonine kinase growth factor receptors. This review covers LPA signaling pathways in the light of new information. The use of transgenic and gene knockout animals, gene manipulated cells, pharmacological LPA receptor agonists and antagonists have provided many insights into the biological significance of LPA and individual LPA receptors in the progression of atherosclerosis and vascular diseases. This review provides a comprehensive presentation of LPA with the highlight of the distinct role of its receptors in cell and animal models that relate to atherosclerosis and vascular diseases, and therefore provides new opportunities to reduce the burden of cardiovascular diseases. The recent drug development strategies that target LPA signaling pathways are also included in this review.

Modulation of chemoresistance by lysophosphatidic acid (LPA) signaling through LPA5 in melanoma cells treated with anticancer drugs

Lysophosphatidic acid (LPA) signaling via LPA receptors (LPA1 to LPA6) contributes to the promotion of malignant potency in cancer cells. The cell motile activity are stimulated through the induction of LPA5 in melanoma cells treated with anticancer drugs. The present study aimed to investigate whether LPA signaling via LPA5 regulates chemoresistance in melanoma A375 cells. Cells were treated with cisplatin (CDDP) or dacarbazine (DTIC) every 24 h for 2 days. CDDP and DTIC treatment increased LPAR5 expressions. The cell survival rates of A375 cells treated with CDDP and DTIC were significantly decreased by LPA. In addition, LPAR5 expression was markedly elevated in long-term CDDP treated (A375-CDDP) cells. LPA decreased the cell survival rate of A375-CDDP cells treated with CDDP. To evaluate the roles of LPA5 in chemoresistance during tumor progression, highly migratory (A375-R11) cells were established from A375 cells. LPAR5 expression level was significantly lower in A375-R11 cells than in A375 cells. The cell survival rates of A375-R11 cells treated with CDDP and DTIC were increased, compared with A375 cells. Moreover, we generated LPA5 knockdown cells from A375 cells. The cell survival rates of A375 cells treated with CDDP and DTIC were significantly elevated by LPA5 knockdown. These results suggest that LPA signaling via LPA5 is involved in the modulation of chemoresistance in melanoma A375 cells.

Lysophosphatidic Acid and Autotaxin-associated Effects on the Initiation and Progression of Colorectal Cancer.

The intestinal epithelium interacts dynamically with the immune system to maintain its barrier function to protect the host, while performing the physiological roles in absorption of nutrients, electrolytes, water and minerals. The importance of lysophosphatidic acid (LPA) and its receptors in the gut has been progressively appreciated. LPA signaling modulates cell proliferation, invasion, adhesion, angiogenesis, and survival that can promote cancer growth and metastasis. These effects are equally important for the maintenance of the epithelial barrier in the gut, which forms the first line of defense against the milieu of potentially pathogenic stimuli. This review focuses on the LPA-mediated signaling that potentially contributes to inflammation and tumor formation in the gastrointestinal tract.

Lysophosphatidic Acid Signaling in Diabetic Nephropathy.

Lysophosphatidic acid (LPA) is a bioactive phospholipid present in most tissues and body fluids. LPA acts through specific LPA receptors (LPAR1 to LPAR6) coupled with G protein. LPA binds to receptors and activates multiple cellular signaling pathways, subsequently exerting various biological functions, such as cell proliferation, migration, and apoptosis. LPA also induces cell damage through complex overlapping pathways, including the generation of reactive oxygen species, inflammatory cytokines, and fibrosis. Several reports indicate that the LPA–LPAR axis plays an important role in various diseases, including kidney disease, lung fibrosis, and cancer. Diabetic nephropathy (DN) is one of the most common diabetic complications and the main risk factor for chronic kidney diseases, which mostly progress to end-stage renal disease. There is also growing evidence indicating that the LPA–LPAR axis also plays an important role in inducing pathological alterations of cell structure and function in the kidneys. In this review, we will discuss key mediators or signaling pathways activated by LPA and summarize recent research findings associated with DN.

Lysophosphatidic Acid and Glutamatergic Transmission.

Signaling through bioactive lipids regulates nervous system development and functions. Lysophosphatidic acid (LPA), a membrane-derived lipid mediator particularly enriched in brain, is able to induce many responses in neurons and glial cells by affecting key processes like synaptic plasticity, neurogenesis, differentiation and proliferation. Early studies noted sustained elevations of neuronal intracellular calcium, a primary response to LPA exposure, suggesting functional modifications of NMDA and AMPA glutamate receptors. However, the crosstalk between LPA signaling and glutamatergic transmission has only recently been shown. For example, stimulation of presynaptic LPA receptors in hippocampal neurons regulates glutamate release from the presynaptic terminal, and excess of LPA induce seizures. Further evidence indicating a role of LPA in the modulation of neuronal transmission has been inferred from animal models with deficits on LPA receptors, mainly LPA1 which is the most prevalent receptor in human and mouse brain tissue. LPA1 null-mice exhibit cognitive and attention deficits characteristic of schizophrenia which are related with altered glutamatergic transmission and reduced neuropathic pain. Furthermore, silencing of LPA1 receptor in mice induced a severe down-regulation of the main glutaminase isoform (GLS) in cerebral cortex and hippocampus, along with a parallel sharp decrease on active matrix-metalloproteinase 9. The downregulation of both enzymes correlated with an altered morphology of glutamatergic pyramidal cells dendritic spines towards a less mature phenotype, indicating important implications of LPA in synaptic excitatory plasticity which may contribute to the cognitive and memory deficits shown by LPA1-deficient mice. In this review, we present an updated account of current evidence pointing to important implications of LPA in the modulation of synaptic excitatory transmission.

A Stromal Lysolipid-Autotaxin Signaling Axis Promotes Pancreatic Tumor Progression.

Pancreatic ductal adenocarcinoma (PDAC) develops a pronounced stromal response reflecting an aberrant wound-healing process. This stromal reaction features transdifferentiation of tissue-resident pancreatic stellate cells (PSC) into activated cancer-associated fibroblasts, a process induced by PDAC cells but of unclear significance for PDAC progression. Here, we show that PSCs undergo a dramatic lipid metabolic shift during differentiation in the context of pancreatic tumorigenesis, including remodeling of the intracellular lipidome and secretion of abundant lipids in the activated, fibroblastic state. Specifically, stroma-derived lysophosphatidylcholines support PDAC cell synthesis of phosphatidylcholines, key components of cell membranes, and also facilitate production of the potent wound-healing mediator lysophosphatidic acid (LPA) by the extracellular enzyme autotaxin, which is overexpressed in PDAC. The autotaxin-LPA axis promotes PDAC cell proliferation, migration, and AKT activation, and genetic or pharmacologic autotaxin inhibition suppresses PDAC growth in vivo. Our work demonstrates how PDAC cells exploit the local production of wound-healing mediators to stimulate their own growth and migration. SIGNIFICANCE: Our work highlights an unanticipated role for PSCs in producing the oncogenic LPA signaling lipid and demonstrates how PDAC tumor cells co-opt the release of wound-healing mediators by neighboring PSCs to promote their own proliferation and migration.See related commentary by Biffi and Tuveson, p. 578.This article is highlighted in the In This Issue feature, p. 565.

Lysophosphatidic acid induces integrin β6 expression in human oral squamous cell carcinomas cells via LPAR1 coupling to Gαi and downstream SMAD3 and ETS-1 activation

Integrin β6 (ITGB6), an epithelial-specific integrin, is upregulated in oral squamous cell carcinomas (OSCC) and is associated with progression and metastasis of OSCC. Lysophosphatidic acid (LPA), an important bioactive phospholipid present in saliva, has also been related to OSCC cell migration and invasiveness. LPA exerts its biological effects through signal transduction pathways that ultimately regulate gene expression. However, it is unclear whether LPA signaling is involved in ITGB6 upregulation in OSCC. Therefore, the aim of the current study was to investigate the role of LPA in the regulation of ITGB6 expression in OSCC cells, and to delineate the molecular signaling pathways involved. Using SAS and HSC-3 OSCC cell lines, we found that LPA increases ITGB6 mRNA expression without affecting mRNA stability, suggesting that LPA acts by regulating ITGB6 gene transcription. In addition, we show that LPA stimulation increases phosphorylation and binding of the transcription factors SMAD3 and ETS-1 to the ITGB6 promoter resulting in ITGB6 active transcription. Finally, we demonstrate that LPA-induced ITGB6 expression is mediated via the LPA receptors 1 (LPAR1) coupling to Gαi. Our findings provide insights into the molecular mechanism underlying ITGB6 overexpression in OSCC and may have important implications for therapeutic purposes.

Lysophosphatidic acid signaling restores mislocalization of brush border proteins in MYO5B deficient mice

Background & AimMyosin Vb (MYO5B) is an essential trafficking protein for membrane protein recycling in gastrointestinal (GI) epithelial cells and its mutation causes the congenital diarrheal disease, microvillus inclusion disease (MVID). Our group has reported that MYO5B loss results in a decrease in the brush border localization of nutrient transporters and enzymes, but CFTR expression is maintained, causing malabsorption and secretory diarrhea in MVID patients and MYO5B KO mice. Activation of lysophosphatidic acid (LPA) receptors (LPA2 and LPA5) can inhibit CFTR and activate NHE3 in the intestinal epithelium. This study tested whether LPA treatment reverses the functional expression of apical proteins in MYO5B knockout (KO) mice.MethodsAdult tamoxifen‐induced, intestine‐specific, MYOB KO mice (VilCreERT2;Myo5bflox/flox) and littermate control mice were treated with LPA (18:1 at 1 or 3 mg/kg/day) or vehicle, orally or intraperitoneally for 4 days after a single injection of tamoxifen (2 mg/mouse, i.p.). Apical transporter activities in jejunum and ileum were measured by an Üssing chamber system and the localization of apical proteins were evaluated immunostaining with whole‐slide imaging and digital image analysis.ResultsFollowing tamoxifen injection, F‐actin‐positive inclusions appeared in the upper small intestine of VilCreERT2;Myo5bflox/flox mice and the brush border localization of phospho‐ezrin, SGLT1, NHE3, DRA, PEPT1, alkaline phosphatase, and DPPIV were lost throughout the intestine. Treatment with LPA partially restored apical localization of phospho‐ezrin, SGLT1, NHE3, alkaline phosphatase, and DPPIV particularly in villus epithelial cells. Consistent with these observations, SGLT1‐dependent short‐circuit current (Isc) was 3 times higher in LPA (3 mg/kg)‐treated jejunum and ileum than that of vehicle‐treated VilCreERT2;Myo5bflox/flox mice. LPA dose‐dependently decreased CFTR‐dependent Isc in the steady state, but had no effect on CFTR dependence in carbachol‐ and forskolin‐stimulated Isc, which was increased by MYO5B loss.ConclusionsThese results suggest that LPA signaling may modulate a MYO5B‐independent trafficking mechanism for some brush border proteins in the small intestine, demonstrating a therapeutic potential for LPA in the treatment of MVID.Support or Funding InformationSupported by The Christine Volpe FoundationThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Induction of asthma causes sensitization of the carotid bodies to lysophosphatidic acid

Previously, we demonstrated an important role for the carotid bodies in asthmatic bronchoconstriction. Specifically, we showed that an allergen‐induced increase in circulating lysophosphatidic acid (LPA) in asthmatic rats activates LPA receptors (LPAr) in the carotid bodies and post‐ganglionic TRPV1 channels, provoking vagal activity and thereby triggering acute bronchoconstriction (Jendzjowsky et al. 2018 Nat Comm. 9, 4030). Here we report that induction of asthma causes molecular and functional changes to the carotid bodies that sensitize them to LPA.Experiments were carried out using the standard ovalbumin‐sensitized brown Norway rat model of asthma. Carotid bodies and petrosal ganglia were extracted 3 hours after the third ovalbumin challenge in asthmatic (OVA) or third saline challenge in naïve (N) rats. Using qPCR (Δctt OVA vs N), LPAr expression was increased in the carotid body (LPAr1: 556x; LPAr2: 20x; LPAr3: 2x; LPAr4: 150x; LPAr5 only detected in OVA: LPAr6: 175x; TRPV1 not detected, as demonstrated previously Roy et al. 2012 J Appl Physiol 112:212–224) whereas LPAr 1–6 and TRPV1 were similarly expressed in petrosal ganglia of OVA and N rats. Using the perfused ex vivo carotid body preparation, baseline normalized carotid sinus nerve responses to increasing doses of LPA activity, were significantly augmented in OVA compared to N rats (2.5uM‐ OVA: 1.12 ± 0.01 N: 1.05 ± 0.02, p=0.162; 5uM: OVA: 1.23 ± 0.03 N:1.10 ± 0.02, p=0.009; 10uM: OVA: 1.40 ± 0.07 N: 1.17 ± 0.03, p<0.001). In contrast, carotid body activity in response to hypoxia was not different between OVA (2.54 ± 0.47) and N (1.95 ± 0.10) rats (p=0.243).Our data suggest that asthmatic carotid bodies have enhanced responsiveness to LPA, independent of hypoxic sensitivity. These changes likely contribute to the acute allergen‐induced bronchoconstriction which is the hallmark of asthma that appears to be mediated, in part, by a novel carotid body‐vagal‐lung neuronal pathway. Targeting carotid body LPA signalling may reduce asthmatic bronchoconstriction and provide new pharmaceutical targets for inflammatory lung disease.Support or Funding InformationThis project was funded by The Lung Association and Canadian Institute for Health Research.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Atorvastatin attenuates lysophosphatidic acid‐induced tau hyperphosphorylation through p38 MAPK kinase pathway in an Alzheimer's disease model

The prevalence of Alzheimer's disease (AD) is currently estimated to be around 6 million cases and is predicted to rapidly increase in the coming decades. The currently approved treatments fail to alter the underlying pathophysiology, provide only modest and temporary symptomatic relief and are associated with several side effects. Recent evidence suggests that vascular factors, in particular, lysophosphatidic acid (LPA), the most bioactive component of oxidized low‐density lipoprotein (oxLDL), play a crucial role in the pathophysiology of AD. Increased levels of LPA lead to activation of several intracellular signaling cascades thereby leading to neuroinflammation and neurodegeneration. Statins are cholesterol lowering agents of proven benefit in vascular disease and are also associated with reduction in circulating oxLDL levels. Additionally, several clinical studies suggest the risk of AD was substantially reduced with statins. Hence, the goal of the proposed research is to evaluate the role of the LPA signaling in AD pathogenesis and the effect of statin (atorvastatin) in attenuating LPA induced cognitive dysfunction. In vitro studies utilizing ShSy5y neuronal cell line showed atorvastatin attenuated LPA induced Amyloid beta and tau hyperphosphorylation. The effect of LPA on p38 MAPK Kinase and it's downstream signaling markers of apoptosis (BAX, BCL2) and inflammation (NF‐Kβ, IL‐6, TNFα) was analyzed through biochemical assays. We will utilize a high fat diet mouse model, to investigate the neuroprotective effects of atorvastatin. Novel object location test, Y‐maze and contextual fear conditioning will be performed to evaluate cognitive and behavioral deficits. To assess the effects of LPA and atorvastatin on hippocampal synaptic plasticity, we will measure long term potentiation and long‐term depression, which are the cellular correlates of learning and memory. Golgi cox staining to study the effect of LPA and atorvastatin on dendritic spine morphology is being performed. Western blot will also be used to measure levels of AMPA and NMDA receptor subunits. Biochemical assays will be performed to quantify levels of PSD‐95, synaptophysin, and ARC protein, which are proteins essential for synaptic maturity and plasticity. Finally, the neuroprotective effect of atorvastatin on LPA induced cognitive dysfunction will be analyzed by measuring the levels of autotaxin (ATX), an enzyme important for LPA synthesis. 4, 8‐ and 12‐months aged age. We believe our study will demonstrate that that atorvastatin through its pleotropic effects, attenuate LPA induced cognitive dysfunction by improving behavioral and cognitive deficits, synaptic dysfunction, and reducing the pathologies of AD thereby uncovering a molecular mechanism of LPA induced dyshomeostasis in AD.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Autotaxin‐LPA‐LPP3 axis regulates mitochondrial respiration prompting myocardial dysfunction

Background and ObjectiveAcute myocardial infarction (AMI) and ischemic heart disease are the two most prevalent causes of morbidity and mortality in the western world. Lysophosphatidic acid (LPA) a pro‐inflammatory, pro‐thrombotic bioactive glycerophospholipid plays a well‐known role in atherosclerotic disease; its role in myocardial dysfunction remains virtually unexplored. Following AMI, serum LPA concentration increases six‐fold over control subjects. Since LPA has a rapid turnover in the circulation, LPA production involves hydrolysis of lysophosphatidylcholine by the secreted enzyme autotaxin.In contrast, LPP3 catalyzes LPA dephosphorylation to generate lipid products that are not receptor active. The steady state of local and circulating LPA is balanced between these opposing pathways of LPA synthesis and degradation. The goal of this study was to determine the role of the autotaxin‐LPA‐LPP3 axis in myocardial dysfunction along with cardiomyocyte responses.MethodsTo study the role of the autotaxin‐LPA‐LPP3 axis in the myocardium, we used human induced pluripotent stem cell (IPS) cardiomyocytes and generated a cardiac‐specific Plpp3 deficient mouse strain. Mitochondrial bioenergetics was measured using the Seahorse XF24 analyzer.ResultsOur results show that exposure to LPA significantly decreased oxygen consumption rate (OCR; P<0.001) and increased extracellular acidification rate (ECAR; P<0.001) in IPS cardiomyocytes. Similar results were seen after subjecting the IPS cardiomyocytes to hypoxia where in the addition of autotaxin inhibitors had the reverse effect on OCR (P<0.001) and ECAR (P<0.001). LPA receptors blockade with pan‐Brp‐LPA restored the mitochondrial OCR (P<0.001) and decreased the ECAR (P<0.001). Generation of Plpp3 knockout mice (Plpp3Δ) showed increased mortality ~8 months. Plpp3Δ myocardium showed a distorted intercalated disc with damaged mitochondria with disorganized cristae and amorphous matrix densities as compared to lpp3fl in transmission electron microscopy. Lack of LPP3 resulted in deteriorating cardiac function. Plpp3Δ cardiomyocyte exposure to LPA significantly decreased oxygen consumption rate (OCR; P<0.001) and increased extracellular acidification rate (ECAR; P<0.001). Together these findings show that the absence of LPP3 increases LPA signaling and results in impaired mitochondrial function.Discussion and ConclusionsThe results presented in this study indicate that the autotaxin‐LPA‐LPP3 axis plays a critical role in the mitochondrial respiration and loss of LPP3 in cardiomyocytes from Plpp3Δ mice further confirms the impairment of myocardial function. Importantly, we demonstrate that autotaxin‐LPA‐LPP3 axis regulates mitochondrial respiration to limit myocardial function.Support or Funding InformationNational Institutes of Health Grants 1P20GM121307‐01A1 (Dr. Kevil) Sub‐Project ID: 8571 to Dr. Panchatcharam.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Doxorubicin in myocardial lysophosphatidic acid signaling

Generation of reactive oxygen species has been implicated in the toxicity of nearly 50% of the current FDA approved cancer therapeutic drugs. Mitochondrial respiration is a major source of reactive oxygen species production and that the presence of the mitochondrial antioxidant enzyme, manganese superoxide dismutase, is essential for the survival of all aerobic life. Our studies of animals using the prototype redox‐active anticancer drug, doxorubicin, indicate that overexpression of manganese superoxide dismutase protects the heart against doxorubicin‐induced cardiac injury and reduction of manganese superoxide dismutase by heterozygous knockout mice increases cardiac injury after exposure to doxorubicin. While the bioactive glycerophospholipid lysophosphatidic acid rises by seven‐fold over control subjects, suggesting lysophosphatidic acid may contribute to the doxorubicin‐induced cardiac toxicity. Lysophosphatidic acid production involves hydrolysis of lysophosphatidylcholine by the secreted enzyme autotaxin, whereas lipid phosphate phosphatase‐3 (LPP3) catalyzes lysophosphatidic acid dephosphorylation to generate lipid products that are not receptor active. In this application, we present the first evidence that doxorubicin‐induced cardiac injury enhances myocardial autotaxin levels and decreases myocardial LPP3 expression, and this is associated with increased serum lysophosphatidic acid levels. Reactive oxygen species production arises as a burst of superoxide from mitochondria following doxorubicin‐induced cardiac injury. The redox‐sensitive transcription factor NFAT (a nuclear factor of activated T‐cells) has been shown to bind to the autotaxin promoter and induce its expression. Similarly, oxidant stress may deplete LPP3 levels in the context of cardiac injury through reduced LPP3 expression or enhanced LPP3 degradation. Thus, we hypothesize that doxorubicin‐induced cardiac injury alters autotaxin and LPP3 expression through mitochondrial superoxide production to drive lysophosphatidic acid signaling and cardiomyocyte dysfunction. The following interrelated specific aims are designed to provide step‐wise and in‐depth studies in vitro, in vivo, and in experimental therapeutics settings. Specific aim 1 will assess the role of myocardial superoxide production in autotaxin expression and lysophosphatidic acid production in doxorubicin‐induced cardiac injury. Specific aim 2 will determine the role of mitochondrial superoxide production in LPP3 depletion and lysophosphatidic acid regulation in doxorubicin‐induced cardiac injury. We could identify whether modulation of cellular versus mitochondrial antioxidant status confers a differential protective effect in doxorubicin‐induced cardiac injury models.Support or Funding InformationAAA‐ FGAP Fellow grant funded by the American Association of Anatomists.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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.

Mutant p53 regulates LPA signaling through lysophosphatidic acid phosphatase type 6

Emerging evidence has indicated that high-grade serous ovarian cancer (HGSOC) originates in the fallopian tube, where the earliest known genetic lesion is the mutation of TP53. In addition to such genetic changes, HGSOC is characterized by altered metabolism, including the production of oncogenic lipids such as lysophosphatidic acid (LPA). To understand the crosstalk between TP53 mutations and LPA signaling, we utilized primary fallopian tube epithelial cells (FTEC) engineered to overexpress mutant p53. We found that gain-of-function (GOF) p53 mutations downregulated the LPA-degrading enzyme lysophosphatidic acid phosphatase type 6 (ACP6), leading to upregulation of focal adhesion signaling in an LPA-dependent manner. Although highly expressed in normal fallopian tube epithelium, ACP6 expression was significantly reduced in ovarian cancer tumors and early in situ lesions. Downregulation of ACP6 in ovarian cancer cells was necessary and sufficient to support HGSOC proliferation, adhesion, migration, and invasion. Using mouse models of metastasis, we established that attenuation of ACP6 expression was associated with increased tumor burden. Conversely, overexpression of ACP6 suppressed invasive behavior. These data identify an involvement of oncogenic p53 mutations in LPA signaling and HGSOC progression through regulation of ACP6 expression.