Lysophosphatidic acid stimulates inflammatory cascade in airway epithelial cells

KAI1/CD82 gene and autotaxin-lysophosphatidic acid axis in gastrointestinal cancers

The KAI1/CD82 gene inhibits the metastasis of most tumors and is remarkably correlated with tumor invasion and prognosis. Cell metabolism dysregulation is an important cause of tumor occurrence, development, and metastasis. As one of the important characteristics of tumors, cell metabolism dysregulation is attracting increasing research attention. Phospholipids are an indispensable substance in the metabolism in various tumor cells. Phospholipid metabolites have become important cell signaling molecules. The pathological role of lysophosphatidic acid (LPA) in tumors was identified in the early 1990s. Currently, LPA inhibitors have entered clinical trials but are not yet used in clinical treatment. Autotaxin (ATX) has lysophospholipase D (lysoPLD) activity and can regulate LPA levels in vivo. The LPA receptor family and ATX/lysoPLD are abnormally expressed in various gastrointestinal tumors. According to our recent pre-experimental results, KAI1/CD82 might inhibit the migration and metastasis of cancer cells by regulating the ATX-LPA axis. However, no relevant research has been reported. Clarifying the mechanism of ATX-LPA in the inhibition of cancer metastasis by KAI1/CD82 will provide an important theoretical basis for targeted cancer therapy. In this paper, the molecular compositions of the KAI1/CD82 gene and the ATX-LPA axis, their physiological functions in tumors, and their roles in gastrointestinal cancers and target therapy are reviewed.

Lysophosphatidic Acid Is a Proinflammatory Stimulus of Renal Tubular Epithelial Cells

Chronic kidney disease (CKD) refers to a spectrum of diseases defined by renal fibrosis, permanent alterations in kidney structure, and low glomerular-filtration rate. Prolonged epithelial-tubular damage involves a series of changes that eventually lead to CKD, highlighting the importance of tubular epithelial cells in this process. Lysophosphatidic acid (LPA) is a bioactive lipid that signals mainly through its six cognate LPA receptors and is implicated in several chronic inflammatory pathological conditions. In this report, we have stimulated human proximal tubular epithelial cells (HKC-8) with LPA and 175 other possibly pathological stimuli, and simultaneously detected the levels of 27 intracellular phosphoproteins and 32 extracellular secreted molecules with multiplex ELISA. This quantification revealed a large amount of information concerning the signaling and the physiology of HKC-8 cells that can be extrapolated to other proximal tubular epithelial cells. LPA responses clustered with pro-inflammatory stimuli such as TNF and IL-1, promoting the phosphorylation of important inflammatory signaling hubs, including CREB1, ERK1, JUN, IκΒα, and MEK1, as well as the secretion of inflammatory factors of clinical relevance, including CCL2, CCL3, CXCL10, ICAM1, IL-6, and IL-8, most of them shown for the first time in proximal tubular epithelial cells. The identified LPA-induced signal-transduction pathways, which were pharmacologically validated, and the secretion of the inflammatory factors offer novel insights into the possible role of LPA in CKD pathogenesis.

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.

Lysophosphatidic acid enhanced the osteogenic and angiogenic capability of osteoblasts via LPA1/3 receptor

Lysophosphatidic acid is a serum-derived growth factor that is involved in wound healing. Although in its infancy, a growing body of evidence has demonstrated that lysophosphatidic acid exerts a potentially significant role in regulating bone cell biology. However, previous studies mainly focused on the osteoinductive potential of lysophosphatidic acid, its effects on bone tissue vascularization, another essential element during bone regeneration, remains ill-defined so far. Here in this study, we examined the effects of lysophosphatidic acid on osteogenic differentiation as well as the angiogenesis-inducing capacity of pre-osteoblasts, a cell population that coordinates osteogenic and angiogenic processes in bone regenerating niche. Our results showed that treatment of MC3T3-E1 pre-osteoblastic cells with lysophosphatidic acid enhanced alkaline phosphatase activity and matrix mineralization, demonstrating in vitro osteoblastic differentiation. Of particular importance was the finding that vascular endothelial growth factor secretion also increased after lysophosphatidic acid treatment. Lysophosphatidic acid conditioned media of MC3T3-E1 cells was capable of promoting angiogenic behavior of endothelial cells, as evidenced by stimulating proliferation, migration, and tube formation. Besides, inhibition of LPA1/3 receptor abolished lysophosphatidic acid-induced elevation of the osteogenic and angiogenic capability of pre-osteoblasts. Our research demonstrated the important role of lysophosphatidic acid in coupling osteogenesis and angiogenesis during bone remodeling through orchestrating pre-osteoblast behavior, and implications therein for novel and effective treatment strategies for bone regeneration success.

The role of lysophosphatidic acid in the physiology and pathology of the skin

Lysophosphatidic acid (LPA) is the simplest phospholipid found in nature. LPA is mainly biosynthesized in tissues and cells by autotoxin and PA-PLA1α/PA-PLA1β and is degraded by lipid phosphate phosphatases (LPPs). It is an important component of biofilm, an extracellular signal transmitter and intracellular second messenger. After targeting to endothelial differentiation gene (Edg) family LPA receptors (LPA1, LPA2, LPA3) and non-Edg family LPA receptors (LPA4, LPA5, LPA6), LPA mediates physiological and pathological processes such as embryonic development, angiogenesis, tumor progression, fibrogenesis, wound healing, ischemia/reperfusion injury, and inflammatory reactions. These processes are induced through signaling pathways including mitogen-activated protein kinase (MAPK), phosphatidylinositol-3-kinase (PI3K)/Akt, protein kinase C (PKC)-GSK3β-β-catenin, Rho, Stat, and hypoxia-inducible factor 1-alpha (HIF-1α). LPA is involved in multiple physiological and pathological processes in the skin. It not only regulates skin function but also plays an important role in hair follicle development, skin wound healing, pruritus, skin tumors, and scleroderma. Pharmacological inhibition of LPA synthesis or antagonization of LPA receptors is a new strategy for the treatment of various skin disorders. This review focuses on the current understanding of the pathophysiologic role of LPA in the skin.

Chronic rhinosinusitis with nasal polyps and without nasal polyps is associated with increased expression of lysophosphatidic acid-related molecules

BACKGROUND

Chronic sinusitis with nasal polyps (CRSwNPs) or CRS without NPs (CRSsNPs) is associated with expression of various cytokines. Lysophosphatidic acid (LPA) generated by autotaxin (ATX), LPA-producing enzyme, initiates signaling cascade involved in the inflammatory responses and participates in diverse biological processes through LPA receptors, including cytokine production. We analyzed the expression and distribution patterns of LPA-related molecules in nasal secretion and sinus mucosa of normal controls and patients with CRSwNPs and CRSsNPs, to evaluate the possible effects of the ATX-LPA receptor axis on the pathogenesis of CRS.

METHODS

LPA levels in nasal secretion and the expression and distribution patterns of ATX and LPA receptors 1-3 (LPA1-3) in sinus mucosa were investigated using ELISA, real-time polymerase chain reaction, Western blot, and immunohistochemistry. We elucidated the effect of CRS-relevant cytokines on the expression of ATX and LPA receptors, using cultured sinus epithelial cells, and investigated the effect of LPA on the expression of CRS-relevant cytokines, using sinus mucosa explant culture.

RESULTS

LPA, ATX, and LPA1-3 levels are increased in CRSwNPs and CRSsNPs. ATX and LPA1-3 were localized to superficial epithelium, submucosal glands in normal and inflammatory mucosa, but in inflammatory mucosa, they were found in inflammatory cells. LPA1-3 were noted in endothelium. Sinus mucosa explant stimulated with LPA increasingly produced IL-4, IL-5, interferon gamma, and TNF-alpha, and in cultured epithelial cells stimulated with CRS-relevant cytokines, ATX, and LPA1-3 were differentially induced.

CONCLUSION

LPA in human sinus mucosa may play important roles in the pathogenesis of CRS, contributing to produce CRS-related cytokines. LPA-related molecules were increased in CRS, which may attribute to CRS-related cytokines.

The autotaxin-LPA axis emerges as a novel regulator of lymphocyte homing and inflammation

Lysophosphatidic acid (LPA) is a pleiotropic lipid molecule with potent effects on cell growth and motility. Major progress has been made in recent years in deciphering the mechanisms of LPA generation and how it acts on target cells. Most research has been conducted in other disciplines, but emerging data indicate that LPA has an important role to play in immunity. A key discovery was that autotaxin (ATX), an enzyme previously implicated in cancer cell motility, generates extracellular LPA from the precursor lysophosphatidylcholine. Steady-state ATX is expressed by only a few tissues, including high endothelial venules in lymph nodes, but inflammatory signals can upregulate ATX expression in different tissues. In this article, we review current thinking about the ATX/LPA axis in lymphocyte homing, as well as in models of allergic airway inflammation and asthma. New insights into the role of LPA in regulating immune responses should be forthcoming in the near future.

Lysophosphatidic acid aberrancies and hepatocellular carcinoma: studies in the MDR2 gene knockout mouse

Studies show that lysophosphatidic acid (LPA) reprogramming is associated with the development of hepatocellular carcinoma (HCC). This manuscript evaluates the MDR2(-/-) model of HCC as a tool to examine the role of LPA reprogramming in the initiation/progression of HCC and identify novel treatment targets. Hepatic tumors developed in MDR2(-/-) mice between 9-12 m and serum LPA levels were greater in MDR2(-/-) when compared to controls. Blocking LPA biosynthesis/signaling significantly reduced tumor burden. LPA biosynthesis/signaling plays an important role in murine MDR2(-/-) model and is potentially linked to regulation of TNFα or other cytokines that are relevant to high-risk patients.

ATX-LPA receptor axis in inflammation and cancer

Lysophosphatidic acid (LPA, 1- or 2-acyl-sn-glycerol 3-phosphate) mediates a plethora of physiological and pathological activities via interactions with a series of high affinity G protein-coupled receptors (GPCR). Both LPA receptor family members and autotaxin (ATX/LysoPLD), the primary LPA-producing enzyme, are aberrantly expressed in many human breast cancers and several other cancer lineages. Using transgenic mice expressing either an LPA receptor or ATX, we recently demonstrated that the ATX-LPA receptor axis plays a causal role in breast tumorigenesis and cancer-related inflammation, further validating the ATX-LPA receptor axis as a rich therapeutic target in cancer.

Lysophosphatidic acid signaling in airway epithelium: role in airway inflammation and remodeling

Lysophosphatidic acid (LPA), a potent bioactive phospholipid, induces diverse cellular responses, including cell proliferation, migration, and cytokine release. LPA can be generated intracellularly and extracellularly through multiple synthetic pathways by action of various enzymes, such as phospholipase A(1/2) (PLA(1/2)), phospholipase D (PLD), acylglycerol kinase (AGK), and lysophospholipase D (lysoPLD). Metabolism of LPA is regulated by a family of lipid phosphate phosphatases (LPPs). Significant amounts of LPA have been detected in various biological fluids, including serum, saliva, and bronchoalveolar lavage fluid (BALF). The most significant effects of LPA appear to be through activation of the G-protein-coupled receptors (GPCRs), termed LPA(1-6). LPA regulates gene expression through activation of several transcriptional factors, such as nuclear factor-kappaB (NF-kappaB), AP-1, and C/EBPbeta. In addition to GPCRs, cross-talk between LPA receptors and receptor tyrosine kinases (RTKs) partly regulates LPA-induced intracellular signaling and cellular responses. Airway epithelial cells participate in innate immunity through the release of cytokines, chemokines, lipid mediators, other inflammatory mediators and an increase in barrier function in response to a variety of inhaled stimuli. Expression of LPA receptors has been demonstrated in airway epithelial cells. This review summarizes our recent observations of the role of LPA/LPA-Rs in regulation of airway epithelium, especially in relation to the secretion of pro- and anti-inflammatory mediators and regulation of airway barrier function.

Role of acylglycerol kinase in LPA-induced IL-8 secretion and transactivation of epidermal growth factor-receptor in human bronchial epithelial cells

LPA (lysophosphatidic acid) is a potent bioactive phospholipid, which regulates a number of diverse cellular responses through G protein-coupled LPA receptors. Intracellular LPA is generated by the phosphorylation of monoacylglycerol by acylglycerol kinase (AGK); however, the role of intracellular LPA in signaling and cellular responses remains to be elucidated. Here, we investigated signaling pathways of IL-8 secretion mediated by AGK and intracellular LPA in human bronchial epithelial cells (HBEpCs). Expression of AGK in HBEpCs was detected by real-time PCR, and overexpressed AGK was mainly localized in mitochondria as determined by immunofluorescence and confocal microscopy. Overexpression of lentiviral AGK wild type increased intracellular LPA production ( approximately 1.8-fold), enhanced LPA-mediated IL-8 secretion, and stimulated tyrosine phosphorylation epidermal growth factor-receptor (EGF-R). Furthermore, downregulation of native AGK by AGK small interfering RNA decreased intracellular LPA levels ( approximately 2-fold) and attenuated LPA-induced p38 MAPK, JNK, and NF-kappaB activation, tyrosine phosphorylation of EGF-R, and IL-8 secretion. These results suggest that native AGK regulates LPA-mediated IL-8 secretion involving MAPKs, NF-kappaB, and transactivation of EGF-R. Thus AGK may play an important role in innate immunity and airway remodeling during inflammation.

Significance of susceptible gene expression profiles in nasal polyposis

Nasal polyposis (NP) is a common chronic inflammatory disease of the rhinosinus mucosa and a complex disease with strong genetic and environmental components. During the past 10 to 20 yr, many studies have been performed to determine differential gene expression profiles between NP and normal nasal tissues, in order to identify susceptible genes that are associated with NP-related traits. Despite achievement in the identification of candidate genes and their associated pathogenic pathways, the large challenges remain as the genetic and molecular alterations required for its development and progression are still unclear. Therefore, the development of novel, powerful tools for gene discovery, and a closer integration of genetics and medical biology would provide valuable insight into the pathogenesis of NP.

Lysophosphatidic acid is detectable in human bronchoalveolar lavage fluids at baseline and increased after segmental allergen challenge

BACKGROUND

Lysophosphatidic acid (LPA) is a biologically active lysophospholipid and a component of normal plasma. LPA binds to receptors expressed on circulating and structural lung cells and affects cell growth and activation. Whether LPA is present in the lung has not been previously reported.

OBJECTIVE

To develop an assay to measure LPA in bronchoalveolar lavage (BAL) fluids, and to study the association between LPA and allergic airway inflammation.

METHODS

Seventeen allergic subjects underwent bronchoscopy and segmental allergen challenge, followed 18 h later by BAL. Supernatants were analysed for LPA content using liquid chromatography and mass spectroscopy. Expression of LPA receptors on primary bronchial epithelial cells was analysed by immunolabelling, and the effects of LPA on epithelial cell barrier function was investigated by measuring transepithelial resistance.

RESULTS

LPA was detectable in BAL from control lung segments, and significantly increased 18 h after allergen challenge. Polyunsaturated species of LPA were especially increased following segmental allergen challenge. LPA levels did not strongly correlate with the number or percentages of eosinophils, neutrophils of lymphocytes, whereas MIP-3alpha (CCL20) levels correlated significantly with the allergen-driven influx of lymphocytes. The levels of LPA from control sites correlated inversely with BAL protein content, suggesting that LPA promoted epithelial barrier integrity at baseline. Experiments using primary human bronchial epithelial cells confirmed that LPA tightened the epithelial cell barrier.

CONCLUSION

Lysophosphatidic acid is detectable in human BAL fluids at baseline and its expression increases during allergic inflammation. LPA does not appear to be a dominant chemoattractant for eosinophils or lymphocytes during allergic airway inflammation. In the absence of ongoing inflammation, LPA may promote epithelial barrier integrity.