Lysophosphatidic acid promotes ESCC progression by increasing the level of CCL2 secreted by esophageal epithelial cells.

BACKGROUND: Lysophosphatidic acid (LPA) is a small bioactive lipid which acts as a potent regulator in various tumor progressions through six G-protein-coupled receptors (LPA1-LPA6). Our previous study demonstrated that the LPA-producing enzyme, autotaxin (ATX), was upregulated in esophageal squamous cell carcinoma (ESCC) and ATX high expression levels indicated a poor prognosis. Esophageal squamous cell carcinoma is a type of malignant tumor which originates from epithelial cells. Its progression can be affected by the interaction between cancer cells and normal cells. However, the impact of LPA on the interaction between esophageal epithelial cells and cancer cells in the development of ESCC remains uncertain. METHODS: MTS and Edu assays were performed to determine ESCC cell proliferation in culture medium (CM) derived from LPA-stimulated esophageal epithelial cells (Het-1a). A wound healing assay, transwell migration and an invasion assay were performed to assess the metastatic ability of ESCC cells. Cytokine array analysis was conducted to detect the differentially secreted cytokines in CM. The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases were utilized to uncover the pathways and cytokines that are influenced by LPA in ESCC. Immunohistochemical staining was employed to measure the expression of ATX and CCL2 in early-stage ESCC. Quantitative real-time PCR, western blot, enzyme-linked immunosorbent assay and an antibody neutralization assay were employed to measure the mechanism of LPA-mediated communication between epithelial cells and cancer cells. RESULTS: Functional experiments showed that exposing ESCC cancer cells to CM from LPA-treated Het-1a results in promoting proliferation, migration, invasion and epithelial-mesenchymal transition processes. Using cytokine array analysis, we discovered that LPA triggers the release of multiple cytokines from epithelial cells. After screening of the TCGA and GEO databases, CCL2 was identified and found to be correlated with ATX expression in ESCC. Furthermore, CCL2 levels in both mRNA expression and secretion were observed to be upregulated in epithelial cells upon stimulation with LPA. Blocking CCL2 effectively reduced the pro-migration influence of CM derived from LPA-treated Het-1a. Mechanism studies have demonstrated that LPA activated the NF-κB signaling pathway through LPA1/3, ultimately causing an increase in CCL2 expression and secretion in Het-1a. CONCLUSIONS: Our findings, taken together, demonstrate that CM from LPA-treated esophageal epithelial cells plays a significant role in promoting the progression of ESCC, with CCL2 acting as the primary regulator.

LPA suppresses HLA-DR expression in human melanoma cells: a potential immune escape mechanism involving LPAR1 and DR6-mediated release of IL-10.

While immune checkpoint inhibitors (ICIs) are promising in the treatment of metastatic melanoma, about half of patients do not respond well to them. Low levels of human leukocyte antigen-DR (HLA-DR) in tumors have been shown to negatively influence prognosis and response to ICIs. Lysophosphatidic acid (LPA) is produced in large amounts by melanoma and is abundantly present in the tumor microenvironment. LPA induces the release of various cytokines and chemokines from tumor cells, which affect cancer development, metastasis, and tumor immunity. In the present study, we investigated the role of LPA-induced IL-10 release in regulating HLA-DR expression and the underlying mechanisms in human melanoma cells. We showed that LPA (0.001-10 µM) dose-dependently increased DR6 transcript levels through activating LPAR1 in HEK293T cells. Knockdown of NF-κB1 abrogated the LPA-increased DR6 expression without affecting basal DR6 expression in both A2058 and A375 melanoma cell lines. LPA (10 µM) significantly increased IL-10 transcripts in A2058 and A375 melanoma cells, the effect was abolished by pharmacological inhibition of LPAR1 or knockdown of DR6. We found a statistically significant correlation between the expression of LPAR1, DR6 and IL-10 in human melanoma tissue and an association between increased expression of LPAR1 and reduced effectiveness of ICI therapy. We demonstrated that LPA (10 µM) markedly suppressed HLA-DR expression in both A375 and A2058 melanoma cells via activating the LPAR1-DR6-IL-10 pathway. These data suggest that the LPAR1-DR6-IL-10 autocrine loop could constitute a novel mechanism used by tumor cells to evade immunosurveillance by decreasing HLA-DR expression.

Lysophosphatidic Acid (LPA) and Its Receptors in Mood Regulation: A Systematic Review of the Molecular Mechanisms and Therapeutic Potential.

Mood disorders affect over 300 million individuals worldwide, often characterized by their chronic and refractory nature, posing significant threats to patient life. There has been a notable increase in mood disorders among American adolescents and young adults, with a rising number of suicide attempts and fatalities, highlighting a growing association between mood disorders and suicidal outcomes. Dysregulation within the neuroimmune-endocrine system is now recognized as one of the fundamental biological mechanisms underlying mood and mood disorders. Lysophosphatidic acid (LPA), a novel mediator of mood behavior, induces anxiety-like and depression-like phenotypes through its receptors LPA1 and LPA5, regulating synaptic neurotransmission and plasticity. Consequently, LPA has garnered substantial interest in the study of mood regulation. This study aimed to elucidate the molecular mechanisms of lysophosphatidic acid and its receptors, along with LPA receptor ligands, in mood regulation and to explore their potential therapeutic efficacy in treating mood disorders. A comprehensive literature search was conducted using the PubMed and Web of Science databases, identifying 208 articles through keyword searches up to June 2024. After excluding duplicates, irrelevant publications, and those restricted by open access limitations, 21 scientific papers were included in this review. The findings indicate that LPA/LPA receptor modulation could be beneficial in treating mood disorders, suggesting that pharmacological agents or gintonin, an extract from ginseng, may serve as effective therapeutic strategies. This study opens new avenues for future research into how lysophosphatidic acid and its receptors, as well as lysophosphatidic acid receptor ligands, influence emotional behavior in animals and humans.

LPA3 Receptor Phosphorylation Sites: Roles in Signaling and Internalization.

Lysophosphatidic acid (LPA) type 3 (LPA3) receptor mutants were generated in which the sites detected phosphorylated were substituted by non-phosphorylatable amino acids. Substitutions were made in the intracellular loop 3 (IL3 mutant), the carboxyl terminus (Ctail), and both domains (IL3/Ctail). The wild-type (WT) receptor and the mutants were expressed in T-REx HEK293 cells, and the consequences of the substitutions were analyzed employing different functional parameters. Agonist- and LPA-mediated receptor phosphorylation was diminished in the IL3 and Ctail mutants and essentially abolished in the IL3/Ctail mutant, confirming that the main phosphorylation sites are present in both domains and their role in receptor phosphorylation eliminated by substitution and distributed in both domains. The WT and mutant receptors increased intracellular calcium and ERK 1/2 phosphorylation in response to LPA and PMA. The agonist, Ki16425, diminished baseline intracellular calcium, which suggests some receptor endogenous activity. Similarly, baseline ERK1/2 phosphorylation was diminished by Ki16425. An increase in baseline ERK phosphorylation was detected in the IL3/Ctail mutant. LPA and PMA-induced receptor interaction with ß-arrestin 2 and LPA3 internalization were severely diminished in cells expressing the mutants. Mutant-expressing cells also exhibit increased baseline proliferation and response to different stimuli, which were inhibited by the antagonist Ki16425, suggesting a role of LPA receptors in this process. Migration in response to different attractants was markedly increased in the Ctail mutant, which the Ki16425 antagonist also attenuated. Our data experimentally show that receptor phosphorylation in the distinct domains is relevant for LPA3 receptor function.

Autotaxin-Lysophosphatidate Axis: Promoter of Cancer Development and Possible Therapeutic Implications.

Autotaxin (ATX) is a member of the ectonucleotide pyrophosphate/phosphodiesterase (ENPP) family; it is encoded by the ENPP2 gene. ATX is a secreted glycoprotein and catalyzes the hydrolysis of lysophosphatidylcholine to lysophosphatidic acid (LPA). LPA is responsible for the transduction of various signal pathways through the interaction with at least six G protein-coupled receptors, LPA Receptors 1 to 6 (LPAR1-6). The ATX-LPA axis is involved in various physiological and pathological processes, such as angiogenesis, embryonic development, inflammation, fibrosis, and obesity. However, significant research also reported its connection to carcinogenesis, immune escape, metastasis, tumor microenvironment, cancer stem cells, and therapeutic resistance. Moreover, several studies suggested ATX and LPA as relevant biomarkers and/or therapeutic targets. In this review of the literature, we aimed to deepen knowledge about the role of the ATX-LPA axis as a promoter of cancer development, progression and invasion, and therapeutic resistance. Finally, we explored its potential application as a prognostic/predictive biomarker and therapeutic target for tumor treatment.

Recent research advances in ATX inhibitors: An overview of primary literature.

The autoglobulin gene is the main enzyme for circulating LPA production and has lysophosphatidylcholine D activity, which catalyzes the production of lysophosphatidic acid and choline with lysophosphatidylcholine as substrate. A growing body of experimental evidence suggests that autoglobulin is involved in the pathogenesis of a variety of diseases. This review summarizes the different structural ATX inhibitors classified according to their binding mode to the ATX triple orientation site, and summarizes the conformational relationships and molecular docking of each type with ATX structure, hoping to contribute to the development of novel ATX inhibitors.

Lysophosphatidic Acid Induces Podocyte Pyroptosis in Diabetic Nephropathy by an Increase of Egr1 Expression via Downregulation of EzH2.

Podocyte damage and renal inflammation are the main features and pathogenesis of diabetic nephropathy (DN). Inhibition of lysophosphatidic acid (LPA) receptor 1 (LPAR1) suppresses glomerular inflammation and improves DN. Herein, we investigated LPA-induced podocyte damage and its underlying mechanisms in DN. We investigated the effects of AM095, a specific LPAR1 inhibitor, on podocytes from streptozotocin (STZ)-induced diabetic mice. E11 cells were treated with LPA in the presence or absence of AM095, and the expression of NLRP3 inflammasome factors and pyroptosis were measured. A chromatin immunoprecipitation assay and Western blotting were performed to elucidate underlying molecular mechanisms. Gene knockdown by transfecting small interfering RNA was used to determine the role of the transcription factor Egr1 (early growth response protein 1) and histone methyltransferase EzH2 (Enhancer of Zeste Homolog 2) in LPA-induced podocyte injury. AM095 administration inhibited podocyte loss, NLRP3 inflammasome factor expression, and cell death in STZ-induced diabetic mice. In E11 cells, LPA increased NLRP3 inflammasome activation and pyroptosis via LPAR1. Egr1 mediated NLRP3 inflammasome activation and pyroptosis in LPA-treated E11 cells. LPA decreased H3K27me3 enrichment at the Egr1 promoter in E11 cells by downregulating EzH2 expression. EzH2 knockdown further increased LPA-induced Egr1 expression. In podocytes from STZ-induced diabetic mice, AM095 suppressed Egr1 expression increase and EzH2/H3K27me3 expression reduction. Collectively, these results demonstrate that LPA induces NLRP3 inflammasome activation by downregulating EzH2/H3K27me3 and upregulating Egr1 expression, resulting in podocyte damage and pyroptosis, which may be a potential mechanism of DN progression.

Designing Dual Inhibitors of Autotaxin-LPAR GPCR Axis.

The ATX-LPA-LPAR1 signaling pathway plays a universal role in stimulating diverse cellular responses, including cell proliferation, migration, survival, and invasion in almost every cell type. The ATX-LPAR1 axis is linked to several metabolic and inflammatory diseases including cancer, fibrosis, and rheumatoid arthritis. Numerous selective ATX or LPAR1 inhibitors have been developed and so far, their clinical efficacy has only been evaluated in idiopathic pulmonary fibrosis. None of the ATX and LPAR1 inhibitors have advanced to clinical trials for cancer and rheumatoid arthritis. Nonetheless, several research groups, including ours, have shown considerable benefit of simultaneous ATX and LPAR1 inhibition through combination therapy. Recent research suggests that dual-targeting therapies are superior to combination therapies that use two selective inhibitors. However, limited reports are available on ATX-LPAR1 dual inhibitors, potentially due to co-expression of multiple different LPARs with close structural similarities at the same target. In this review, we discuss rational design and future directions of dual ATX-LPAR1 inhibitors.

Crystalline silica particles induce DNA damage in respiratory epithelium by ATX secretion and Rac1 activation.

Autotaxin (ATX) and its product lysophosphatidic acid (LPA) have been implicated in lung fibrosis and cancer. We have studied their roles in DNA damage induced by carcinogenic crystalline silica particles (CSi). In an earlier study on bronchial epithelia, we concluded that ATX, via paracrine signaling, amplifies DNA damage. This effect was seen at 6-16 h. A succeeding study showed that CSi induced NLRP3 phosphorylation, mitochondrial depolarization, double strand breaks (DSBs), and NHEJ repair enzymes within minutes. In the current study we hypothesized a role for the ATX-LPA axis also in this rapid DNA damage. Using 16HBE human bronchial epithelial cells, we show ATX secretion at 3 min, and that ATX inhibitors (HA130 and PF8380) prevented both CSi-induced mitochondrial depolarization and DNA damage (detected by γH2AX and Comet assay analysis). Experiments with added LPA gave similar rapid effects as CSi. Furthermore, Rac1 was activated at 3 min, and a Rac1 inhibitor (NSC23766) prevented mitochondrial depolarization and genotoxicity. In mice the bronchial epithelia exhibited histological signs of ATX activation and signs of DSBs (53BP1 positive nuclei) minutes after a single inhalation of CSi. Our data indicate that CSi rapidly activate the ATX-LPA axis and within minutes this leads to DNA damage in bronchial epithelial cells. Thus, ATX mediates very rapid DNA damaging effects of inhaled particles.

LPA1 signaling drives Schwann cell dedifferentiation in experimental autoimmune neuritis.

BACKGROUND: Lysophosphatidic acid (LPA) is a pleiotropic lipid messenger that addresses at least six specific G-protein coupled receptors. Accumulating evidence indicates a significant involvement of LPA in immune cell regulation as well as Schwann cell physiology, with potential relevance for the pathophysiology of peripheral neuroinflammation. However, the role of LPA signaling in inflammatory neuropathies has remained completely undefined. Given the broad expression of LPA receptors on both Schwann cells and cells of the innate and adaptive immune system, we hypothesized that inhibition of LPA signaling may ameliorate the course of disease in experimental autoimmune neuritis (EAN). METHODS: We induced active EAN by inoculation of myelin protein 2 peptide (P255-78) in female Lewis rats. Animals received the orally available LPA receptor antagonist AM095, specifically targeting the LPA1 receptor subtype. AM095 was administered daily via oral gavage in a therapeutic regimen from 10 until 28 days post-immunization (dpi). Analyses were based on clinical testing, hemogram profiles, immunohistochemistry and morphometric assessment of myelination. RESULTS: Lewis rats treated with AM095 displayed a significant improvement in clinical scores, most notably during the remission phase. Cellular infiltration of sciatic nerve was only discretely affected by AM095. Hemogram profiles indicated no impact on circulating leukocytes. However, sciatic nerve immunohistochemistry revealed a reduction in the number of Schwann cells expressing the dedifferentiation marker Sox2 paralleled by a corresponding increase in differentiating Sox10-positive Schwann cells. In line with this, morphometric analysis of sciatic nerve semi-thin sections identified a significant increase in large-caliber myelinated axons at 28 dpi. Myelin thickness was unaffected by AM095. CONCLUSION: Thus, LPA1 signaling may present a novel therapeutic target for the treatment of inflammatory neuropathies, potentially affecting regenerative responses in the peripheral nerve by modulating Schwann cell differentiation.

Positron Emission Tomography Imaging of Autotaxin in Thyroid and Breast Cancer Models Using [18F]PRIMATX.

Autotaxin (ATX) is a secreted enzyme responsible for producing lysophosphatidic acid (LPA). The ATX/LPA signaling axis is typically activated in wound healing and tissue repair processes. The ATX/LPA axis is highjacked and upregulated in the progression and persistence of several chronic inflammatory diseases, including cancer. As ATX inhibitors are now progressing to clinical testing, innovative diagnostic tools such as positron emission tomography (PET) are needed to measure ATX expression in vivo accurately. The radiotracer, [18F]PRIMATX, was recently developed and tested for PET imaging of ATX in vivo in a murine melanoma model. The goal of the present work was to further validate [18F]PRIMATX as a PET imaging agent by analyzing its in vivo metabolic stability and suitability for PET imaging of ATX in models of human 8305C thyroid tumor and murine 4T1 breast cancer. [18F]PRIMATX displayed favorable metabolic stability in vivo (65% of intact radiotracer after 60 min p.i.) and provided sufficient tumor uptake profiles in both tumor models. Radiotracer uptake could be blocked by 8-12% in 8305C thyroid tumors in the presence of ATX inhibitor AE-32-NZ70 as determined by PET and ex vivo biodistribution analyses. [18F]PRIMATX also showed high brain uptake, which was reduced by 50% through the administration of ATX inhibitor AE-32-NZ70. [18F]PRIMATX is a suitable radiotracer for PET imaging of ATX in the brain and peripheral tumor tissues.

Lysophosphatidic Acid Mediates Imiquimod-Induced Psoriasis-like Symptoms by Promoting Keratinocyte Proliferation through LPAR1/ROCK2/PI3K/AKT Signaling Pathway.

Psoriasis is a chronic inflammatory skin disease. Recently, lysophosphatidic acid (LPA)/LPAR5 signaling has been reported to be involved in both NLRP3 inflammasome activation in macrophages and keratinocyte activation to produce inflammatory cytokines, contributing to psoriasis pathogenesis. However, the effect and molecular mechanisms of LPA/LPAR signaling in keratinocyte proliferation in psoriasis remain unclear. In this study, we investigated the effects of LPAR1/3 inhibition on imiquimod (IMQ)-induced psoriasis-like mice. Treatment with the LPAR1/3 antagonist, ki16425, alleviated skin symptoms in IMQ-induced psoriasis-like mouse models and decreased keratinocyte proliferation in the lesion. It also decreased LPA-induced cell proliferation and cell cycle progression via increased cyclin A2, cyclin D1, cyclin-dependent kinase (CDK)2, and CDK4 expression and decreased p27Kip1 expression in HaCaT cells. LPAR1 knockdown in HaCaT cells reduced LPA-induced proliferation, suppressed cyclin A2 and CDK2 expression, and restored p27Kip1 expression. LPA increased Rho-associated protein kinase 2 (ROCK2) expression and PI3K/AKT activation; moreover, the pharmacological inhibition of ROCK2 and PI3K/AKT signaling suppressed LPA-induced cell cycle progression. In conclusion, we demonstrated that LPAR1/3 antagonist alleviates IMQ-induced psoriasis-like symptoms in mice, and in particular, LPAR1 signaling is involved in cell cycle progression via ROCK2/PI3K/AKT pathways in keratinocytes.

Increased Autotaxin Levels in Severe COVID-19, Correlating with IL-6 Levels, Endothelial Dysfunction Biomarkers, and Impaired Functions of Dendritic Cells.

Autotaxin (ATX; ENPP2) is a secreted lysophospholipase D catalyzing the extracellular production of lysophosphatidic acid (LPA), a pleiotropic signaling phospholipid. Genetic and pharmacologic studies have previously established a pathologic role for ATX and LPA signaling in pulmonary injury, inflammation, and fibrosis. Here, increased ENPP2 mRNA levels were detected in immune cells from nasopharyngeal swab samples of COVID-19 patients, and increased ATX serum levels were found in severe COVID-19 patients. ATX serum levels correlated with the corresponding increased serum levels of IL-6 and endothelial damage biomarkers, suggesting an interplay of the ATX/LPA axis with hyperinflammation and the associated vascular dysfunction in COVID-19. Accordingly, dexamethasone (Dex) treatment of mechanically ventilated patients reduced ATX levels, as shown in two independent cohorts, indicating that the therapeutic benefits of Dex include the suppression of ATX. Moreover, large scale analysis of multiple single cell RNA sequencing datasets revealed the expression landscape of ENPP2 in COVID-19 and further suggested a role for ATX in the homeostasis of dendritic cells, which exhibit both numerical and functional deficits in COVID-19. Therefore, ATX has likely a multifunctional role in COVID-19 pathogenesis, suggesting that its pharmacological targeting might represent an additional therapeutic option, both during and after hospitalization.

Lysophosphatidic acid improves corneal endothelial density in tissue culture by stimulating stromal secretion of interleukin-1ß.

The short supply of donor corneas is exacerbated by the unsuitability of donors with insufficient endothelial cell density. Few studies have investigated promoting corneal endothelial cell proliferation to increase the endothelial cell density. We hypothesize that pre-transplantation treatment of proliferative tissue-cultivated corneas may increase corneal endothelial cell density. We observed that the airlift cultures were superior to immersion cultures with respect to both transparency and thickness. In this tissue culture system, we observed that lysophosphatidic acid increased the rabbit corneal endothelial cell density, number of BrdU-positive cells and improve wound healing. We also observed an indirect effect of lysophosphatidic acid on corneal endothelial cell proliferation mediated by the stimulation of interleukin-1ß secretion from stromal cells. Human corneal tissues treated with lysophosphatidic acid or interleukin-1ß contained significantly more Ki-67-positive cells than untreated group. The lysophosphatidic acid- or interleukin-1ß-treated cultured tissue remained hexagon-shaped, with ZO-1 expression and no evidence of the endothelial-mesenchymal transition. Our novel protocol of tissue culture may be applicable for eye banks to optimize corneal grafting.

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.

Autotaxin and chronic inflammatory diseases.

Autotaxin (ATX) is a secreted glycoprotein, widely present in biological fluids including blood. ATX catalyzes the hydrolysis of lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA), a growth factor-like, signaling phospholipid. LPA exerts pleiotropic effects mediated by its G-protein-coupled receptors that are widely expressed and exhibit overlapping specificities. Although ATX also possesses matricellular properties, the majority of ATX reported functions in adulthood are thought to be mediated through the extracellular production of LPA. ATX-mediated LPA synthesis is likely localized at the cell surface through the possible interaction of ATX with integrins or other molecules, while LPA levels are further controlled by a group of membrane-associated lipid-phosphate phosphatases. ATX expression was shown to be necessary for embryonic development, and ATX deficient embryos exhibit defective vascular homeostasis and aberrant neuronal system development. In adult life, ATX is highly expressed in the adipose tissue and has been implicated in diet-induced obesity and glucose homeostasis with multiple implications in metabolic disorders. Additionally, LPA has been shown to affect multiple cell types, including stromal and immune cells in various ways. Therefore, LPA participates in many processes that are intricately involved in the pathogenesis of different chronic inflammatory diseases such as vascular homeostasis, skeletal and stromal remodeling, lymphocyte trafficking and immune regulation. Accordingly, increased ATX and LPA levels have been detected, locally and/or systemically, in patients with chronic inflammatory diseases, most notably idiopathic pulmonary fibrosis (IPF), chronic liver diseases, and rheumatoid arthritis. Genetic and pharmacological studies in mice have confirmed a pathogenetic role for ATX expression and LPA signaling in chronic inflammatory diseases, and provided the proof of principle for therapeutic interventions, as exemplified by the ongoing clinical trials for IPF.

Lysophosphatidic acid: Its role in bone cell biology and potential for use in bone regeneration.

Lysophosphatidic acid (LPA) is a simple phospholipid that exerts pleiotropic effects on numerous cell types by activating its family of cognate G protein-coupled receptors (GPCRs) and participates in many biological processes, including organismal development, wound healing, and carcinogenesis. Bone cells, such as bone marrow mesenchymal stromal (stem) cells (BMSCs), osteoblasts, osteocytes and osteoclasts play essential roles in bone homeostasis and repair. Previous studies have identified the presence of specific LPA receptors in these bone cells. In recent years, an increasing number of cellular effects of LPA, such as the induction of cell proliferation, survival, migration, differentiation and cytokine secretion, have been found in different bone cells. Moreover, some biomaterials containing LPA have shown the ability to enhance osteogenesis. This review will focus on findings associated with LPA functions in these bone cells and present current studies related to the application of LPA in bone regenerative medicine. Further understanding this information will help us develop better strategies for bone healing.

Lysophosphatidic Acid Induces Ligamentum Flavum Hypertrophy Through the LPAR1/Akt Pathway.

BACKGROUND/AIMS: Hypertrophic ligamentum flavum (LF) is a major cause of lumbar spinal stenosis. Our previous work showed that high levels of lysophosphatidic acid (LPA) expression are positively correlated with LF hypertrophy. This study aimed to further unveil how LPA regulates LF hypertrophy Methods: We studied LPAR1 expression in human LF cells using PCR and western blotting. Cell viability cell cycle, apoptosis rate and molecular mechanisms were assayed in LPAR1 knockdown or overexpression LF cells. LF hypertrophy and the molecular mechanism was confirmed in human samples and in in vivo studies. RESULTS: The expression of LPA and its receptor LPAR1 is significantly higher in tissues or cells harvested from hypertrophic LF compared to healthy controls. Moreover, LPA promoted LF cell proliferation by interacting with LPAR1. This conclusion is supported by the fact that depletion or overexpression of LPAR1 changed the effect of LPA on LF cell proliferation. LPA also inhibits apoptosis in LF cells through the receptor LPAR1. Importantly, we demonstrated that the LPA-LPAR1 interaction initiated Akt phosphorylation and determined cell proliferation and apoptosis. Our in vitro findings were supported by our in vivo evidence that lyophilized LPA significantly induced LF hypertrophy via the LPAR1-Akt signaling pathway. More importantly, targeted inhibition of LPAR1 by Ki16425 with a gel sponge implant effectively reduced LPA-associated LF hypertrophy. Taken together, these data indicate that LPA binds to the receptor LPAR1 to induce LF cell proliferation and inhibit apoptosis by activating AKT signaling cascades. Targeting this signaling cascade with Ki16425 is a potential therapeutic strategy for preventing LF hypertrophy. CONCLUSION: LPA-LPAR1-Akt activation is positively correlated with the proliferation and survival of LF cells. LPAR1 could be a target for new drugs and the development of new therapeutic methods for treating LF hypertrophy.

Pharmacologic targeting of the ATX/LPA axis attenuates bleomycin-induced pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a chronic fibrosing lung disease with a dismal prognosis and a largely unknown etiology. Autotaxin (ATX) is a secreted lysophospholipase D, largely responsible for extracellular production of lysophosphatidic acid (LPA), a bioactive phospholipid. LPA has numerous effects in most cell types, signaling through at least 6 receptors (LPAR) exhibiting wide spread distribution and overlapping specificities. The ATX/LPA axis has been suggested as a therapeutic target in different chronic inflammatory and fibroproliferative disorders, including pulmonary fibrosis. In this report, we examined head-to-head the efficacy of a potent inhibitor of ATX (PF-8380), that has not been tested in pulmonary fibrosis models, and an antagonist of LPAR1 (AM095) in bleomycin (BLM)-induced pulmonary fibrosis. Both compounds abrogated the development of pulmonary fibrosis and prevented the distortion of lung architecture, exhibiting qualitative and quantitative differences in different manifestations of the modeled disease.

Lysophosphatidic Acid Signaling Axis Mediates Ceramide 1-Phosphate-Induced Proliferation of C2C12 Myoblasts.

Sphingolipids are not only crucial for membrane architecture but act as critical regulators of cell functions. The bioactive sphingolipid ceramide 1-phosphate (C1P), generated by the action of ceramide kinase, has been reported to stimulate cell proliferation, cell migration and to regulate inflammatory responses via activation of different signaling pathways. We have previously shown that skeletal muscle is a tissue target for C1P since the phosphosphingolipid plays a positive role in myoblast proliferation implying a role in muscle regeneration. Skeletal muscle displays strong capacity of regeneration thanks to the presence of quiescent adult stem cells called satellite cells that upon trauma enter into the cell cycle and start proliferating. However, at present, the exact molecular mechanism by which C1P triggers its mitogenic effect in myoblasts is lacking. Here, we report for the first time that C1P stimulates C2C12 myoblast proliferation via lysophosphatidic acid (LPA) signaling axis. Indeed, C1P subsequently to phospholipase A2 activation leads to LPA1 and LPA3 engagement, which in turn drive Akt (protein kinase B) and ERK1/2 (extracellular signal-regulated kinases 1/2) activation, thus stimulating DNA synthesis. The present findings shed new light on the key role of bioactive sphingolipids in skeletal muscle and provide further support to the notion that these pleiotropic molecules might be useful therapeutic targets for skeletal muscle regeneration.