Promising pharmacological directions in the world of lysophosphatidic Acid signaling

Lysophosphatidic acid (LPA) receptor-mediated signaling regulates hypoxia-induced biological functions of lymphatic endothelial cells

The tumor microenvironment is an extremely complex composed of cancer cells and various non-cancer cells, including lymphatic endothelial cells. Lysophosphatidic acid (LPA) receptors (LPA1 to LPA6) activate a variety of malignant properties in human malignancies. In the present study, we examined the roles of LPA receptor-mediated signaling in biological responses of lymphatic endothelial SVEC4-10 cells induced by hypoxia. Lpar1, Lpar2 and Lpar3 expressions were decreased in SVEC4-10 cells cultured at hypoxic conditions (1 % O2). LPA had no impact on the cell growth activity of SVEC4-10 cells in 21 % O2 culture conditions. Conversely, the cell growth activity of SVEC4-10 cells in 1 % O2 culture conditions was reduced by LPA. The cell motile activity of SVEC4-10 cells was elevated by 1 % O2 culture conditions. GRI-977143 (LPA2 agonist) and (2S)-OMPT (LPA3 agonist) stimulated SVEC4-10 cell motility as well as AM966 (LPA1 antagonist). In tube formation assay, the tube formation of SVEC4-10 cells in 1 % O2 culture conditions was markedly increased, in comparison with 21 % O2. GRI-977143 and (2S)-OMPT elevated the tube formation of SVEC4-10 cells. Furthermore, the tube formation of SVEC4-10 cells was increased by AM966. These results suggest that LPA receptor-mediated signaling contributes to the modulation of hypoxic-induced biological functions of lymphatic endothelial cells.

Roles of lysophosphatidic acid (LPA) receptor-mediated signaling in cancer cell biology

Lysophosphatidic acid (LPA) is a simple lipid which is endogenously synthesized from lysophosphatidylcholine (LPC) by autotaxin (ATX). LPA mediates a variety of cellular responses through the binding of G protein-coupled LPA receptors (LPA1 to LPA6). It is considered that LPA receptor-mediated signaling plays an important role in the pathogenesis of human malignancy. Genetic alterations and epigenetic changes of LPA receptors have been detected in some cancer cells as well as LPA per se. Moreover, LPA receptors contribute to the promotion of tumor progression, including cell proliferation, invasion, metastasis, tumorigenicity, and angiogenesis. In recent studies, the activation of LPA receptor-mediated signaling regulates chemoresistance and radiosensitivity in cancer cells. This review provides an updated overview on the roles of LPA receptor-mediated signaling in the regulation of cancer cell functions and its potential utility as a molecular target for novel therapies in clinical cancer approaches.

Involvement of lysophosphatidic acid (LPA) receptor-mediated signaling in breast cancer cell functions by long-term tamoxifen treatment under hypoxic and estrogen-deprived conditions

BACKGROUND

Tamoxifen (TAM) is a selective estrogen receptor modulator and has anti-estrogenic activity. Breast cancer cells acquire drug resistance to TAM as a consequence of long-term treatment. Lysophosphatidic acid (LPA) receptor-mediated signaling contributes to the promotion of tumor progression. This study aimed to evaluate the role of LPA receptors in the modulation of biological functions by long-term TAM treatment in breast cancer MCF-7 cells under hypoxic and estrogen-deprived conditions.

METHODS

Long-term TAM treated (MCF-TAM) cells were generated from MCF-7 cells. Cells were cultured in estrogen-free medium at 1 % O2. LPA receptor expressions were measured by quantitative real-time RT-PCR analysis. Cell motile activity was investigated using Cell Culture Inserts. The CCK-8 kit was used to determine the cell proliferation rate.

RESULTS

LPAR1 and LPAR3 expressions were elevated in MCF-TAM cells. MCF-TAM cell motility was enhanced by culturing at 1 % O2, compared with MCF-7 cells. When cells were cultured in estrogen-deprived medium at 1 % O2, the cell proliferation rate of MCF-TAM cells was significantly higher than that of MCF-7 cells.

CONCLUSION

These results suggest that LPA receptor-mediated signaling plays an important role in the acquisition of malignant properties in long-term TAM treated MCF-7 cells under hypoxic and estrogen-deprived conditions.

LPA-induced expression of CCN2 in muscular fibro/adipogenic progenitors (FAPs): Unraveling cellular communication networks

Cellular Communication Network Factor 2, CCN2, is a profibrotic cytokine implicated in physiological and pathological processes in mammals. The expression of CCN2 is markedly increased in dystrophic muscles. Interestingly, diminishing CCN2 genetically or inhibiting its function improves the phenotypes of chronic muscular fibrosis in rodent models. Elucidating the cell-specific mechanisms behind the induction of CCN2 is a fundamental step in understanding its relevance in muscular dystrophies. Here, we show that the small lipids LPA and 2S-OMPT induce CCN2 expression in fibro/adipogenic progenitors (FAPs) through the activation of the LPA1 receptor and, to a lower extent, by also the LPA6 receptor. These cells show a stronger induction than myoblasts or myotubes. We show that the LPA/LPARs axis requires ROCK kinase activity and organized actin cytoskeleton upstream of YAP/TAZ signaling effectors to upregulate CCN2 levels, suggesting that mechanical signals are part of the mechanism behind this process. In conclusion, we explored the role of the LPA/LPAR axis on CCN2 expression, showing a strong cytoskeletal-dependent response in muscular FAPs.

Lysophosphatidic Acid Receptor 1 Plays a Pathogenic Role in Permanent Brain Ischemic Stroke by Modulating Neuroinflammatory Responses

Lysophosphatidic acid receptor 1 (LPA1) plays a critical role in brain injury following a transient brain ischemic stroke. However, its role in permanent brain ischemic stroke remains unknown. To address this, we investigated whether LPA1 could contribute to brain injury of mice challenged by permanent middle cerebral artery occlusion (pMCAO). A selective LPA1 antagonist (AM152) was used as a pharmacological tool for this investigation. When AM152 was given to pMCAO-challenged mice one hour after occlusion, pMCAO-induced brain damage such as brain infarction, functional neurological deficits, apoptosis, and blood-brain barrier disruption was significantly attenuated. Histological analyses demonstrated that AM152 administration attenuated microglial activation and proliferation in injured brain after pMCAO challenge. AM152 administration also attenuated abnormal neuroinflammatory responses by decreasing expression levels of pro-inflammatory cytokines while increasing expression levels of anti-inflammatory cytokines in the injured brain. As underlying effector pathways, NF-κB, MAPKs (ERK1/2, p38, and JNKs), and PI3K/Akt were found to be involved in LPA1-dependent pathogenesis. Collectively, these results demonstrate that LPA1 can contribute to brain injury by permanent ischemic stroke, along with relevant pathogenic events in an injured brain.

Lysophosphatidic acid (LPA) receptor-mediated signaling and cellular responses to anticancer drugs and radiation of cancer cells

Lysophosphatidic acid (LPA) is a simple physiological lipid and structurally consists of a fatty, a phosphate and a glycerol. LPA binds to G protein-coupled LPA receptors (LPA1 to LPA6). LPA receptor-mediated signaling mediates a variety of biological responses, such as cell growth, migration, morphogenesis, differentiation and protection from apoptosis. It is considered that LPA receptor-mediated signaling plays an important role in the pathogenesis of human malignancies. So far, genetic and epigenetic alterations of LPA receptors have been found in several cancer cells as well as abnormal LPA production. In addition, LPA receptor-mediated signaling regulates the promotion of malignant behaviors, including chemo- and/or radiation-resistance. Chemotherapy and radiotherapy are the common approaches to the treatments of cancers. However, resistance to anticancer drugs and irradiation is the most critical limitation for chemotherapy and radiotherapy. In this review, we provide the roles of LPA receptor-mediated signaling in the regulation of cellular responses induced by chemotherapeutic agents and irradiation and its biological utility as a possible molecular target for improving cancer cell responses to chemotherapy and radiotherapy.

Regulation of cellular responses to X-ray irradiation through the activation of lysophosphatidic acid (LPA) receptor-3 (LPA3) and LPA2 in osteosarcoma cells

Lysophosphatidic acid (LPA) binds to its specific G protein-coupled LPA receptors (LPA1 to LPA6), resulting in the activation of various cellular functions. LPA receptor-mediated signaling facilitates tumor progression in human malignancies. In the present study, we investigated whether LPA receptor-mediated signaling contributes to cellular responses to X-ray irradiation in osteosarcoma MG-63 cells. After X-ray irradiation (2, 4 and 8 Gy), LPAR2 and LPAR3 expression levels in MG-63 cells were significantly elevated in a dose-dependent manner, but no change of LPAR1 expression level was observed. The cell growth activities of MG-63 cells irradiated with X-rays (2, 4 and 8 Gy) were reduced by LPA. Conversely, LPA3 agonist (2 S)-OMPT enhanced the cell growth activities of X-ray irradiated MG-63 cells. The cell movement of MG-63 cells exposed to X-ray irradiation (8 Gy) was inhibited by (2 S)OMPT. In cell survival assay, (2 S)-OMPT suppressed the cell survival to cisplatin (CDDP) of MG-63 cells irradiated with X-rays (8 Gy). The cell survival to CDDP of X-ray irradiated cells was elevated by LPA3 knockdown. Moreover, we evaluated the effects of LPA2 on the cell survival to CDDP of MG-63 cells exposed to X-ray irradiation (8 Gy). The cell survival to CDDP of X-ray irradiated cells was increased by LPA2 agonist GRI-977143 and reduced by LPA2 knockdown. These results suggest that LPA receptor-signaling participates in the modulation of cellular functions induced by X-ray irradiation in osteosarcoma cells.

High expression of autotaxin is associated with poor recurrence-free survival in cholangiocarcinoma

BACKGROUND AND AIM

Autotaxin (ATX) is an extracellular lysophospholipase D that catalyzes the hydrolysis of lysophosphatidylcholine into lysophosphatidic acid (LPA). Recent accumulating evidence indicates the biological roles of ATX in malignant tumors. However, the expression and clinical implications of ATX in human cholangiocarcinoma (CCA) remain elusive.

METHODS

In this study, the expression of ATX in 97 human CCA tissues was evaluated by immunohistochemistry. Serum ATX levels were determined in CCA patients (n = 26) and healthy subjects (n = 8). Autotaxin expression in cell types within the tumor microenvironment was characterized by immunofluorescence staining.

RESULTS

High ATX expression in CCA tissue was significantly associated with a higher frequency of lymph node metastasis (p = 0.050). High ATX expression was correlated with shorter overall survival (p = 0.032) and recurrence-free survival (RFS) (p = 0.001) than low ATX expression. In multivariate Cox analysis, high ATX expression (p = 0.019) was an independent factor for shorter RFS. Compared with low ATX expression, high ATX expression was significantly associated with higher Ki-67-positive cell counts (p < 0.001). Serum ATX levels were significantly higher in male CCA patients than in healthy male subjects (p = 0.030). In the tumor microenvironment of CCA, ATX protein was predominantly expressed in tumor cells, cancer-associated fibroblasts, plasma cells, and biliary epithelial cells.

CONCLUSIONS

Our study highlights the clinical evidence and independent prognostic value of ATX in human CCA.

Roles of lysophosphatidic acid (LPA) receptor-mediated signaling in cellular functions modulated by endothelial cells in pancreatic cancer cells under hypoxic conditions

BACKGROUND

In the tumor environment, malignant characteristics of cancer cells are promoted by stromal cells under hypoxia. It is unknown whether lysophosphatidic acid (LPA) receptor-mediated signaling is involved in the regulation of cellular functions by endothelial cells in pancreatic cancer cells under hypoxic conditions.

METHODS

Pancreatic cancer (PANC-1) cells were co-cultured with endothelial (F2) cells and F2 cell supernatants at 21% and 1% O2. The Cell Culture Insert was used to assess the cell motile activity. The cell growth and viability to cisplatin (CDDP) were measured, using the Cell Counting Kit-8.

RESULTS

LPA receptor expression levels were changed in PANC-1 cells co-cultured with F2 cells at 21% and 1% O2. The cell motile activities of PANC-1 cells co-cultured with F2 cells at 21% and 1% O2 were markedly elevated, compared with PANC-1 cells alone. The cell viabilities to CDDP of PANC-1 cells co-cultured with F2 cell supernatants at 21% and 1% O2 were regulated by the activation of LPA receptors.

CONCLUSION

These results suggest that LPA receptor-mediated signaling plays an important role in the modulation of pancreatic cancer cell functions by endothelial cells under hypoxic conditions.

Screening Ultra-Large Encoded Compound Libraries Leads to Novel Protein-Ligand Interactions and High Selectivity

The DNA-encoded library (DEL) discovery platform has emerged as a powerful technology for hit identification in recent years. It has become one of the major parallel workstreams for small molecule drug discovery along with other strategies such as HTS and data mining. For many researchers working in the DEL field, it has become increasingly evident that many hits and leads discovered via DEL screening bind to target proteins with unique and unprecedented binding modes. This Perspective is our attempt to analyze reports of DEL screening with the purpose of providing a rigorous and useful account of the binding modes observed for DEL-derived ligands with a focus on binding mode novelty.

Differential targeting of lysophosphatidic acid LPA1, LPA2, and LPA3 receptor signalling by tricyclic and tetracyclic antidepressants

We previously reported that in different cell types antidepressant drugs activate lysophosphatidic acid (LPA) LPA1 receptor to induce proliferative and prosurvival responses. Here, we further characterize this unique action of antidepressants by examining their effects on two additional LPA receptor family members, LPA2 and LPA3. Human LPA1-3 receptors were stably expressed in HEK-293 cells (HEK-LPA1, -LPA2 and -LPA3 cells) and their functional activity was determined by Western blot and immunofluorescence. LPA effectively stimulated the phosphorylation of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) in HEK-LPA1, -LPA2, and -LPA3 cells. The tricyclic antidepressants amitriptyline, clomipramine, imipramine and desipramine increased phospho-ERK1/2 levels in HEK-LPA1 and -LPA3 cells but were relatively poor agonists in LPA2-expressing cells. The tetracyclic antidepressants mianserin and mirtazapine were active at all three LPA receptors. When combined with LPA, both amitriptyline and mianserin potentiated Gi/o-mediated phosphorylation of ERK1/2 induced by LPA in HEK-LPA1, -LPA2 and -LPA3 cells, CHO-K1 fibroblasts and HT22 hippocampal neuroblasts. This potentiation was associated with enhanced phosphorylation of CREB and S6 ribosomal protein, two molecular targets of activated ERK1/2. The antidepressants also potentiated LPA-induced Gq/11-mediated phosphorylation of AMP-activated protein kinase in HEK-LPA1 and -LPA3 cells. Conversely, amitriptyline and mianserin were found to inhibit LPA-induced Rho activation in HEK-LPA1 and LPA2 cells. These results indicate that tricyclic and tetracyclic antidepressants can act on LPA1, LPA2 and LPA3 receptor subtypes and exert differential effects on LPA signalling through these receptors.

LPA1-mediated inhibition of CXCR4 attenuates CXCL12-induced signaling and cell migration

BACKGROUND

G protein-coupled receptor heteromerization is believed to exert dynamic regulatory impact on signal transduction. CXC chemokine receptor 4 (CXCR4) and its ligand CXCL12, both of which are overexpressed in many cancers, play a pivotal role in metastasis. Likewise, lysophosphatidic acid receptor 1 (LPA1) is implicated in cancer cell proliferation and migration. In our preliminary study, we identified LPA1 as a prospective CXCR4 interactor. In the present study, we investigated in detail the formation of the CXCR4-LPA1 heteromer and characterized the unique molecular features and function of this heteromer.

METHODS

We employed bimolecular fluorescence complementation, bioluminescence resonance energy transfer, and proximity ligation assays to demonstrate heteromerization between CXCR4 and LPA1. To elucidate the distinctive molecular characteristics and functional implications of the CXCR4-LPA1 heteromer, we performed various assays, including cAMP, BRET for G protein activation, β-arrestin recruitment, ligand binding, and transwell migration assays.

RESULTS

We observed that CXCR4 forms heteromers with LPA1 in recombinant HEK293A cells and the human breast cancer cell line MDA-MB-231. Coexpression of LPA1 with CXCR4 reduced CXCL12-mediated cAMP inhibition, ERK activation, Gαi/o activation, and β-arrestin recruitment, while CXCL12 binding to CXCR4 remained unaffected. In contrast, CXCR4 had no impact on LPA1-mediated signaling. The addition of lysophosphatidic acid (LPA) further hindered CXCL12-induced Gαi/o recruitment to CXCR4. LPA or alkyl-OMPT inhibited CXCL12-induced migration in various cancer cells that endogenously express both CXCR4 and LPA1. Conversely, CXCL12-induced calcium signaling and migration were increased in LPAR1 knockout cells, and LPA1-selective antagonists enhanced CXCL12-induced Gαi/o signaling and cell migration in the parental MDA-MB-231 cells but not in LPA1-deficient cells. Ultimately, complete inhibition of cell migration toward CXCL12 and alkyl-OMPT was only achieved in the presence of both CXCR4 and LPA1 antagonists.

CONCLUSIONS

The presence and impact of CXCR4-LPA1 heteromers on CXCL12-induced signaling and cell migration have been evidenced across various cell lines. This discovery provides crucial insights into a valuable regulatory mechanism of CXCR4 through heteromerization. Moreover, our findings propose a therapeutic potential in combined CXCR4 and LPA1 inhibitors for cancer and inflammatory diseases associated with these receptors, simultaneously raising concerns about the use of LPA1 antagonists alone for such conditions. Video Abstract.

Roles of lysophosphatidic acid (LPA) receptor-2 (LPA2) in the regulation of cellular responses induced by X-ray irradiation and hydrogen peroxide in pancreatic cancer cells

PURPOSE

Lysophosphatidic acid (LPA) receptor-mediated signaling regulates various biological functions in cancer cells. This study aimed to evaluate the roles of LPA receptor-2 (LPA2) in cellular responses induced by X-ray irradiation in pancreatic cancer PANC-1 cells. Since X-ray irradiation generates reactive oxygen species (ROS), PANC-1 cells were treated with hydrogen peroxide (H2O2). H2O2 is a key member of ROS.

METHODS

To investigate the cell survival rate to X-ray irradiation, PANC-1 cells were irradiated with X-rays (2.5-15 Gy). LPAR2 expression levels were measured by quantitative real-time RT-PCR analysis. The effects of LPA2 on the cell survival and motility were evaluated using LPA2 knockdown cells. To establish H2O2 treated cells, PANC-1 cells were cultured in 10% FBS-DMEM with H2O2 (30 µM) for 2 weeks. The cell motility and survival rate to cisplatin (CDDP) of H2O2 treated cells were examined.

RESULTS

LPAR2 expression was significantly increased in PANC-1 cells irradiated with X-rays. PANC-1 cell motility was markedly decreased by X-ray irradiation. The reduced cell motility activity by X-ray irradiation was enhanced by LPA2 knockdown. The cell survival to X-ray irradiation was elevated in PANC-1 cells treated with GRI-977143 (LPA2 agonist) and suppressed by LPA2 knockdown. On the other hand, LPAR2 expression was markedly higher in H2O2 treated cells than in H2O2 untreated cells. H2O2 treated cells showed the high cell survival to CDDP in comparison with H2O2 untreated cells. GRI-977143 increased the cell survival to CDDP of H2O2 treated cells, while LPA2 knockdown suppressed.

CONCLUSIONS

The present results suggest that the activation of LPA2-mediated signaling plays an important role in the modulation of cellular functions induced by X-ray irradiation and H2O2 in PANC-1 cells.

Induction of lysophosphatidic acid (LPA) receptor-mediated signaling regulates cell motility and survival to anticancer drugs in cancer cells treated with hydrogen peroxide

Hydrogen peroxide (H2O2) is one of reactive oxygen species (ROS) and promotes malignant properties of cancer cells. Lysophosphatidic acid (LPA) signaling via LPA receptor (LPA1 to LPA6) regulates a variety of cellular functions, such as cell growth, migration and differentiation. This study aimed to evaluate the effects of LPA receptors on the cell motility and survival to anticancer drugs by H2O2 in colon cancer DLD-1 cells. To obtain H2O2 treated (DLD- H2O2) cells, cells were maintained in culture medium containing H2O2 (60 μM) for 2 months. LPAR2 and LPAR4 gene expressions were markedly elevated in DLD-H2O2 cells. The cell motility of DLD-H2O2 cells was significantly lower than that of DLD-1 cells. DLD-H2O2 cell motility was suppressed by LPA2 knockdown and stimulated by LPA4 knockdown. The cell survival rates to fluorouracil (5-FU), irinotecan (CPT-11) and oxaliplatin (L-OHP) of DLD-H2O2 cells were significantly higher than those of DLD-1 cells. The cell survival rate to 5-FU of DLD-H2O2 cells was decreased by LPA2 knockdown. Conversely, LPA4 knockdown enhanced the cell survival rate to 5-FU of DLD-H2O2 cells. In the tumor microenvironment, high levels of H2O2 production are observed under hypoxic conditions. The cell survival rate to 5-FU of DLD-H2O2 cells cultured at 1% O2 was significantly higher than that of DLD-1 cells cultured at 1% O2, correlating with LPAR2 gene expression. The present results suggest that the induction of LPA receptor-mediated signaling plays an important role in regulating cellular functions of DLD-1 cells treated with H2O2.

Effects of LPA receptor-mediated signaling on the modulation of cellular functions of pancreatic cancer cells cultured in fibroblast supernatants under hypoxic conditions

The tumor microenvironment (TME) consists of various cell types, including fibroblasts. The TME plays a central role in the promotion of tumor progression. In the present study, we investigated whether lysophosphatidic acid (LPA) receptor-mediated signaling regulates cellular functions by the TME of pancreatic cancer PANC-1 cells. To obtain fibroblast 3T3 cell supernatants, 3T3 cells were cultured in 5% charcoal stripped FCS-DMEM for 48 h. LPAR2 and LPAR3 expression levels were elevated in PANC-1 cells cultured in 3T3 cell supernatants. While PANC-1 cell motility was decreased by 3T3 cell supernatants, the cell survival to cisplatin (CDDP) of PANC-1 cells was markedly enhanced. Moreover, the cell survival to CDDP of PANC-1 cells cultured in 3T3 cell supernatants was increased by GRI-977,143 (LPA₂ agonist) and (2 S)-OMPT (LPA₃ agonist). Since hypoxia is caused by the restriction of adequate vascular networks to deliver oxygen into solid tumors, PANC-1 cells were cultured in 3T3 cell supernatants at 1% O₂ conditions. The cell survival to CDDP of PANC-1 cells cultured in 3T3 cell supernatants at 1% O₂ was significantly elevated, correlating with LPAR2 and LPAR3 expressions. These results suggest that LPA signaling via LPA₂ and LPA₃ is involved in the promotion of malignant properties by the TME in PANC-1 cells.

LPA receptor-mediated signaling regulates cell motility and survival to anticancer drug of pancreatic cancer cells under glucose-deprived and hypoxic conditions

In tumor microenvironment, cancer cells can adapt to low conditions of nutrients and oxygen. Lysophosphatidic acid (LPA) receptor-mediated signaling is involved in the promotion of malignant properties in cancer cells. In the present study, to examine the roles of LPA receptors in the regulation of cell motility and survival to cisplatin (CDDP) of pancreatic cancer PANC-1 cells under glucose-deprived and hypoxic conditions, cells were cultured in 4500 mg/L high glucose (HG)-DMEM, 500 mg/L middle glucose (MG)-DMEM and 100 mg/L low glucose (LG)-DMEM at 21% and 1% O₂. The expression levels of LPAR1 and LPAR2 genes in cells cultured in MG-DMEM and LG-DMEM were significantly elevated, compared with HG-DMEM cells. The cell motility and survival rate to CDDP of cells cultured in MG-DMEM and LG-DMEM were significantly lower than those of cells cultured in HG-DMEM. The cell survival to CDDP was enhanced by LPA₁ knockdown and suppressed by LPA₂ knockdown. Under hypoxic conditions (1% O₂), LPAR1, LPAR2 and LPAR3 expressions were markedly higher in cells cultured in MG-DMEM and LG-DMEM than in cells cultured in HG-DMEM. The cell survival rates to CDDP of cells cultured in MG-DMEM and LG-DMEM were elevated in comparison with HG-DMEM. The cell survival to CDDP was reduced by LPA₃ knockdown. These results suggest that LPA receptor-mediated signaling is involved in the regulation of malignant properties of PANC-1 cells under glucose-deprived and hypoxic conditions.

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.

Alteration of Cellular Energy Metabolism through LPAR2-Axin2 Axis in Gastric Cancer

Lysophosphatidic acid (LPA), a multifunctional endogenous phospholipid, plays a vital role in cellular homeostasis and the malignant behavior of cancer cells through G-protein-coupled receptors. However, the role of LPA in β-catenin-mediated gastric cancer is unknown. Here, we have noted the high expression of LPAR2 in human gastric cancer tissues, and that LPA treatment significantly increased the proliferation, migration, and invasion of human gastric cancer cells. Results from our biochemical experiments showed that an LPA exposure increased the expression of β-catenin and its nuclear localization, increased the phosphorylation of glycogen synthase kinase 3β (GSK-3β), decreased the expression of Axin2, and increased the expression of the target genes of the β-catenin signaling pathway. The LPA2 receptor (LPAR2) antagonist significantly reduced the LPA-induced nuclear localization of β-catenin, the primary signaling event. The knockdown of LPAR2 in the gastric cancer cell lines robustly reduced the LPA-induced β-catenin activity. An LPA exposure increased the ATP production by both oxidative phosphorylation and glycolysis, and this effect was abrogated with the addition of an LPAR2 antagonist and XAV393, which stabilizes the Axin and inhibits the β-catenin signaling pathway. Based on our findings, the possibility that LPA contributes to gastric cancer initiation and progression through the β-catenin signaling pathway as well as by the dysregulation of the energy metabolism via the LPAR2 receptor and Axin2, respectively, provides a novel insight into the mechanism of and possible therapeutic targets of gastric cancer.

Lysophosphatidic acid signaling via LPA6 : A negative modulator of developmental oligodendrocyte maturation

The developmental process of central nervous system (CNS) myelin sheath formation is characterized by well-coordinated cellular activities ultimately ensuring rapid and synchronized neural communication. During this process, myelinating CNS cells, namely oligodendrocytes (OLGs), undergo distinct steps of differentiation, whereby the progression of earlier maturation stages of OLGs represents a critical step toward the timely establishment of myelinated axonal circuits. Given the complexity of functional integration, it is not surprising that OLG maturation is controlled by a yet fully to be defined set of both negative and positive modulators. In this context, we provide here first evidence for a role of lysophosphatidic acid (LPA) signaling via the G protein-coupled receptor LPA6 as a negative modulatory regulator of myelination-associated gene expression in OLGs. More specifically, the cell surface accessibility of LPA6 was found to be restricted to the earlier maturation stages of differentiating OLGs, and OLG maturation was found to occur precociously in Lpar6 knockout mice. To further substantiate these findings, a novel small molecule ligand with selectivity for preferentially LPA6 and LPA6 agonist characteristics was functionally characterized in vitro in primary cultures of rat OLGs and in vivo in the developing zebrafish. Utilizing this approach, a negative modulatory role of LPA6 signaling in OLG maturation could be corroborated. During development, such a functional role of LPA6 signaling likely serves to ensure timely coordination of circuit formation and myelination. Under pathological conditions as seen in the major human demyelinating disease multiple sclerosis (MS), however, persistent LPA6 expression and signaling in OLGs can be seen as an inhibitor of myelin repair. Thus, it is of interest that LPA6 protein levels appear elevated in MS brain samples, thereby suggesting that LPA6 signaling may represent a potential new druggable pathway suitable to promote myelin repair in MS.

Effects of lysophosphatidic acid (LPA) signaling via LPA receptors on cellular functions associated with ATP reduction in osteosarcoma cells treated with ethidium bromide

Lysophosphatidic acid (LPA) signaling via LPA receptors (LPA₁ to LPA₆) exhibits a variety of malignant properties in cancer cells. Intracellular ATP depletion leads to the development of necrosis and apoptosis. The present study aimed to evaluate the effects of LPA receptor-mediated signaling on the regulation of cancer cell functions associated with ATP reduction. Long-term ethidium bromide (EtBr) treated (MG63-EtBr) cells were established from osteosarcoma MG-63 cells. The intracellular ATP levels of MG63-EtBr cells were significantly lower than that of MG-63 cells. LPAR2, LPAR3, LPAR4 and LPAR6 gene expressions were elevated in MG63-EtBr cells. The cell motile and invasive activities of MG63-EtBr cells were markedly higher than those of MG-63 cells. The cell motile activity of MG-63 cells was increased by LPA₄ and LPA₆ knockdowns. In cell survival assay, cells were treated with cisplatin (CDDP) every 24 h for 3 days. The cell survival to CDDP of MG63-EtBr cells was lower than that of MG-63 cells. LPA₂ knockdown decreased the cell survival to CDDP of MG-63 cells. The cell survival to CDDP of MG-63 cells was inhibited by (2 S)-OMPT (LPA₃ agonist). Moreover, the cell survival to CDDP of MG-63 cells was enhanced by LPA₄ and LPA₆ knockdowns. These results indicate that LPA signaling via LPA receptors is involved in the regulation of cellular functions associated with ATP reduction in MG-63 cells treated with EtBr.

Emerging therapeutic targets for idiopathic pulmonary fibrosis: preclinical progress and therapeutic implications

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive lung disease with high associated morbidity and mortality. The therapeutic landscape has significantly changed in the last 20 years with two drugs currently approved that have demonstrated the ability to slow disease progression. Despite these developments, survival in IPF is limited, so there is a major interest in therapeutic targets which could serve to open up new therapeutic avenues.

AREAS COVERED

We review the most recent information regarding drug targets and therapies currently being investigated in preclinical and early-stage clinical trials.

EXPERT OPINION

The complex pathogenesis of IPF and variability in disease course and response to therapy highlights the importance of a precision approach to therapy. Novel technologies including transcriptomics and the use of serum biomarkers, will become essential tools to guide future drug development and therapeutic decision making particularly as it pertains to combination therapy.

Changes in Plasma Phospholipid Metabolism Are Associated with Clinical Manifestations of Systemic Sclerosis

Systemic sclerosis (SSc) is an autoimmune disease with fibrosis of the skin and/or internal organs, causing a decrease in quality of life and survival. There is no causative therapy, and the pathophysiology of the SSc remains unclear. Studies showed that lipid metabolism was relevant for autoimmune diseases, but little is known about the role of lipids in SSc. In the present study, we sought to explore the phospholipid profile of SSc by using the lipidomics approach. We also aimed to analyze lipidomics results for different clinical manifestations of SSc. Experiments were performed using high-performance liquid chromatography coupled to mass spectrometry for the lipidomic profiling of plasma samples from patients with SSc. Our study showed, for the first time, significant changes in the level of phospholipids such as plasmalogens and sphingomyelins from the plasma of SSc patients as compared to controls. Phosphatidylcholine plasmalogens species and sphingomyelins were significantly increased in SSc patients as compared to controls. Our results also demonstrated a significant association of changes in the metabolism of phospholipids (phosphatidylcholine and phosphatidylethanolamine plasmalogens species and sphingomyelins) with different clinical manifestations of SSc. Further lipidomic studies might lead to the detection of lipids as new biomarkers or therapeutic targets of SSc.

Singlet-Oxygen-Induced Phospholipase A2 Inhibition: A Major Role for Interfacial Tryptophan Dioxidation

Several studies have revealed that various diseases such as cancer have been associated with elevated phospholipase A2 (PLA2 ) activity. Therefore, the regulation of PLA2 catalytic activity is undoubtedly vital. In this study, effective inactivation of PLA2 due to reactive species produced from cold physical plasma as a source to model oxidative stress is reported. We found singlet oxygen to be the most relevant active agent in PLA2 inhibition. A more detailed analysis of the plasma-treated PLA2 identified tryptophan 128 as a hot spot, rich in double oxidation. The significant dioxidation of this interfacial tryptophan resulted in an N-formylkynurenine product via the oxidative opening of the tryptophan indole ring. Molecular dynamics simulation indicated that the efficient interactions between the tryptophan residue and phospholipids are eliminated following tryptophan dioxidation. As interfacial tryptophan residues are predominantly involved in the attaching of membrane enzymes to the bilayers, tryptophan dioxidation and indole ring opening leads to the loss of essential interactions for enzyme binding and, consequently, enzyme inactivation.

Inhibition of lysophosphatidic acid receptor 1-3 deteriorates experimental autoimmune encephalomyelitis by inducing oxidative stress

Background

Lysophosphatidic acid receptors (LPARs) are G-protein-coupled receptors involved in many physiological functions in the central nervous system. However, the role of the LPARs in multiple sclerosis (MS) has not been clearly defined yet.

Methods

Here, we investigated the roles of LPARs in myelin oligodendrocyte glycoprotein peptides-induced experimental autoimmune encephalomyelitis (EAE), an animal model of MS.

Results

Pre-inhibition with LPAR1–3 antagonist Ki16425 deteriorated motor disability of EAE^low. Specifically, LPAR1–3 antagonist (intraperitoneal) deteriorated symptoms of EAE^low associated with increased demyelination, chemokine expression, cellular infiltration, and immune cell activation (microglia and macrophage) in spinal cords of mice compared to the sham group. This LPAR1–3 antagonist also increased the infiltration of CD4⁺/IFN-γ⁺ (Th1) and CD4⁺/IL-17⁺ (Th17) cells into spinal cords of EAE^low mice along with upregulated mRNA expression of IFN-γ and IL-17 and impaired blood–brain barrier (BBB) in the spinal cord. The underlying mechanism for negative effects of LPAR1–3 antagonist was associated with the overproduction of reactive oxygen species (ROS)-generating nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) 2 and NOX3. Interestingly, LPAR1/2 agonist 1-oleoyl-LPA (LPA 18:1) (intraperitoneal) ameliorated symptoms of EAE^high and improved representative pathological features of spinal cords of EAE^high mice.

Conclusions

Our findings strongly suggest that some agents that can stimulate LPARs might have potential therapeutic implications for autoimmune demyelinating diseases such as MS.

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.

Lysophosphatidic Acid: Promoter of Cancer Progression and of Tumor Microenvironment Development. A Promising Target for Anticancer Therapies?

Increased expression of the enzyme autotaxin (ATX) and the consequently increased levels of its product, lysophosphatidic acid (LPA), have been reported in several primary tumors. The role of LPA as a direct modulator of tumor cell functions—motility, invasion and migration capabilities as well as resistance to apoptotic death—has been recognized by numerous studies over the last two decades. Notably, evidence has recently been accumulating that shows that LPA also contributes to the development of the tumor microenvironment (TME). Indeed, LPA plays a crucial role in inducing angiogenesis and lymphangiogenesis, triggering cellular glycolytic shift and stimulating intratumoral fibrosis. In addition, LPA helps tumoral cells to escape immune surveillance. Treatments that counter the TME components, in order to deprive cancer cells of their crucial support, have been emerging among the promising new anticancer therapies. This review aims to summarize the latest knowledge on how LPA influences both tumor cell functions and the TME by regulating the activity of its different elements, highlighting why and how LPA is worth considering as a molecular target for new anticancer therapies.

Lysophosphatidic acid (LPA) receptor modulators: Structural features and recent development

Lysophosphatidic acid (LPA) activates six LPA receptors (LPAR_1-6) and regulates various cellular activities such as cell proliferation, cytoprotection, and wound healing. Many studies elucidated the pathological outcomes of LPA are due to the alteration in signaling pathways, which include migration and invasion of cancer cells, fibrosis, atherosclerosis, and inflammation. Current pathophysiological research on LPA and its receptors provides a means that LPA receptors are new therapeutic targets for disorders associated with LPA. Various chemical modulators are developed and are under investigation to treat a wide range of pathological complications. This review summarizes the physiological and pathological roles of LPA signaling, development of various LPA modulators, their structural features, patents, and their clinical outcomes.

The lysophosphatidic acid axis in fibrosis: Implications for glaucoma

Glaucoma is a common progressive optic neuropathy that results in visual field defects and can lead to irreversible blindness. The pathophysiology of glaucoma involves dysregulated extracellular matrix remodelling in both the trabecular meshwork in the anterior chamber and in the lamina cribrosa of the optic nerve head. Fibrosis in these regions leads to raised intraocular pressure and retinal ganglion cell degeneration, respectively. Lysophosphatidic acid (LPA) is a bioactive lipid mediator which acts via six G-protein coupled receptors on the cell surface to activate intracellular pathways that promote cell proliferation, transcription and survival. LPA signalling has been implicated in both normal wound healing and pathological fibrosis. LPA enhances fibroblast proliferation, migration and contraction, and induces expression of pro-fibrotic mediators such as connective tissue growth factor. The LPA axis plays a major role in diseases such as idiopathic pulmonary fibrosis, where it has been identified as an important pharmacological target. In glaucoma, LPA is present in high levels in the aqueous humour, and its signalling has been found to increase resistance to aqueous humour outflow through altered trabecular meshwork cellular contraction and extracellular matrix deposition. LPA signalling may, therefore, also represent an attractive target for treatment of glaucoma. In this review we wish to describe the role of LPA and its related proteins in tissue fibrosis and glaucoma.

Innovative Approaches in the Battle Against Cancer Recurrence: Novel Strategies to Combat Dormant Disseminated Tumor Cells

Cancer recurrence remains a great fear for many cancer survivors following their initial, apparently successful, therapy. Despite significant improvement in the overall survival of many types of cancer, metastasis accounts for ~90% of all cancer mortality. There is a growing understanding that future therapeutic practices must accommodate this unmet medical need in preventing metastatic recurrence. Accumulating evidence supports dormant disseminated tumor cells (DTCs) as a source of cancer recurrence and recognizes the need for novel strategies to target these tumor cells. This review presents strategies to target dormant quiescent DTCs that reside at secondary sites. These strategies aim to prevent recurrence by maintaining dormant DTCs at bay, or eradicating them. Various approaches are presented, including: reinforcing the niche where dormant DTCs reside in order to keep dormant DTCs at bay; promoting cell intrinsic mechanisms to induce dormancy; preventing the engagement of dormant DTCs with their supportive niche in order to prevent their reactivation; targeting cell-intrinsic mechanisms mediating long-term survival of dormant DTCs; sensitizing dormant DTCs to chemotherapy treatments; and, inhibiting the immune evasion of dormant DTCs, leading to their demise. Various therapeutic approaches, some of which utilize drugs that are already approved, or have been tested in clinical trials and may be considered for repurposing, will be discussed. In addition, clinical evidence for the presence of dormant DTCs will be reviewed, along with potential prognostic biomarkers to enable the identification and stratification of patients who are at high risk of recurrence, and who could benefit from novel dormant DTCs targeting therapies. Finally, we will address the shortcomings of current trial designs for determining activity against dormant DTCs and provide novel approaches.

LPAR5 promotes thyroid carcinoma cell proliferation and migration by activating class IA PI3K catalytic subunit p110β

Lysophosphatidic acid receptor 5 (LPAR5) is involved in mediating thyroid cancer progression, but the underlying mechanism needs to be further revealed. In this study, we confirmed that LPAR5 is upregulated in papillary thyroid carcinoma (PTC), especially in BRAF‐like PTC, by analyzing The Cancer Genome Atlas (TCGA) database and performing immunohistochemistry assay in human thyroid cancer tissues. LPAR5‐specific antagonist TC LPA5 4 treatment inhibited CGTH‐W3, TPC‐1, B‐CPAP, and BHT‐101 cell proliferation, CGTH‐W3 and TPC‐1 cell migration significantly. In vivo, TC LPA5 4 treatment could delay CGTH‐W3 xenograft growth in nude mice. We also found that LPAR5‐specific antagonist TC LPA5 4, PI3K inhibitor wortmannin, or mTOR inhibitor rapamycin pretreatment abrogated phosphorylation of Akt and p70S6K1 stimulated by LPA in CGTH‐W3 and TPC‐1 cells. Stimulating CGTH‐W3 cells transfected with pEGFPC1‐Grp1‐PH fusion protein with LPA resulted in the generation of phosphatidylinositol (3,4,5)‐triphosphate, which indicates that PI3K was activated by LPA directly. The p110β‐siRNA instead of p110α‐siRNA transfection abrogated the increase of levels of phosphorylated Akt and S6K1 stimulated by LPA. Furthermore, immunoprecipitation assay confirmed an interaction between LPAR5 and p110β. Overall, we provide new insights that the downregulation of LPAR5 decreased the proliferation and migration phenotype via the PI3K/Akt pathway. Inhibition of LPAR5 or the PI3K/Akt signal may be a novel therapeutic strategy for treating thyroid cancer.

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.

Interfering with lysophosphatidic acid receptor edg2/lpa1 signalling slows down disease progression in SOD1-G93A transgenic mice

AIMS

Alterations in excitability represent an early hallmark in Amyotrophic Lateral Sclerosis (ALS). Therefore, deciphering the factors that impact motor neuron (MN) excitability offers an opportunity to uncover further aetiopathogenic mechanisms, neuroprotective agents, therapeutic targets, and/or biomarkers in ALS. Here, we hypothesised that the lipokine lysophosphatidic acid (lpa) regulates MN excitability via the G-protein-coupled receptor lpa₁ . Then, modulating lpa₁ -mediated signalling might affect disease progression in the ALS SOD1-G93A mouse model.

METHODS

The influence of lpa-lpa₁ signalling on the electrical properties, Ca²⁺ dynamic and survival of MNs was tested in vitro. Expression of lpa₁ in cultured MNs and in the spinal cord of SOD1-G93A mice was analysed. ALS mice were chronically treated with a small-interfering RNA against lpa₁ (siRNA_lpa1 ) or with the lpa₁ inhibitor AM095. Motor skills, MN loss, and lifespan were evaluated.

RESULTS

AM095 reduced MN excitability. Conversely, exogenous lpa increased MN excitability by modulating task1 'leak' potassium channels downstream of lpa₁ . Lpa-lpa₁ signalling evoked an excitotoxic response in MNs via voltage-sensitive calcium channels. Cultured SOD1-G93A MNs displayed lpa₁ upregulation and heightened vulnerability to lpa. In transgenic mice, lpa₁ was upregulated mostly in spinal cord MNs before cell loss. Chronic administration of either siRNA_lpa1 or AM095 reduced lpa₁ expression at least in MNs, delayed MN death, improved motor skills, and prolonged life expectancy of ALS mice.

CONCLUSIONS

These results suggest that stressed lpa-lpa₁ signalling contributes to MN degeneration in SOD1-G93A mice. Consequently, disrupting lpa₁ slows down disease progression. This highlights LPA₁ signalling as a potential target and/or biomarker in ALS.

Inhibition of lysophosphatidic acid receptor 1 attenuates neuroinflammation via PGE2/EP2/NOX2 signalling and improves the outcome of intracerebral haemorrhage in mice

Lysophosphatidic acid receptor 1 (LPA1) plays a critical role in proinflammatory processes in the central nervous system by modulating microglia activation. The aim of this study was to explore the anti-inflammatory effects and neurological function improvement of LPA1 inhibition after intracerebral haemorrhage (ICH) in mice and to determine whether prostaglandin E2 (PGE2), E-type prostaglandin receptor 2 (EP2), and NADPH oxidase 2 (NOX2) signalling are involved in LPA1-mediated neuroinflammation. ICH was induced in CD1 mice by autologous whole blood injection. AM966, a selective LPA1 antagonist, was administered by oral gavage 1 h and 12 h after ICH. The LPA1 endogenous ligand, LPA was administered to verify the effect of LPA1 activation. To elucidate potential inflammatory mechanisms of LPA1, the selective EP2 activator butaprost was administered by intracerebroventricular injection with either AM966 or LPA1 CRISPR knockout (KO). Water content of the brain, neurobehavior, immunofluorescence staining, and western blot were performed. After ICH, EP2 was expressed in microglia whereas LPA1 was expressed in microglia, neurons, and astrocytes, which peaked after 24 h. AM966 inhibition of LPA1 improved neurologic function, reduced brain oedema, and suppressed perihematomal inflammatory cells after ICH. LPA administration aggravated neurological deficits after ICH. AM966 treatment and LPA1 CRISPR KO both decreased the expressions of PGE2, EP2, NOX2, NF-κB, TNF-α, IL-6, and IL-1β expressions after ICH, which was reversed by butaprost. This study demonstrated that inhibition of LPA1 attenuated neuroinflammation caused by ICH via PGE2/EP2/NOX2 signalling pathway in mice, which consequently improved neurobehavioral functions and alleviated brain oedema. LPA1 may be a promising therapeutic target to attenuate ICH-induced secondary brain injury.

Roles of endothelial cells in the regulation of cell motility via lysophosphatidic acid receptor-2 (LPA2) and LPA3 in osteosarcoma cells

Lysophosphatidic acid (LPA) signaling via LPA receptors (LPA₁ to LPA₆) exhibits a variety of biological responses. In tumor microenvironment, endothelial cells promote cancer cell functions. In this study, we investigated the roles of endothelial cells in the regulation of cell motile activity via LPA₂ and LPA₃ in human osteosarcoma MG-63 cells. In cell motility assay, the cell motile activity of MG-63 cells was markedly increased by the supernatants of endothelial F2 cells. MG-63 cell motility elevated by the supernatants was enhanced by GRI-977143 (LPA₂ agonist) and reduced by (2S)-OMPT (LPA₃ agonist). LPAR2 and LPAR3 expressions were increased in highly migratory MG63-CR7(F2) cells, which were generated from MG-63 cells by co-culture with F2 cell supernatants. MG63-CR7(F2) cell motility was stimulated by LPA treatment. In the presence of F2 cell supernatants, MG63-CR7(F2) cell motility was markedly enhanced by GRI-977143 and suppressed by (2S)-OMPT. Autotaxin (ATX) enzymatically converts lysophosphatidylcholine (LPC) to LPA. ATX expression was higher in MG63-CR(F2) cells than in MG-63 cells. MG63-CR7(F2) cell motility was markedly increased by LPC in comparison with MG-63 cells. In addition, MG63-CR(F2) cell motility was significantly stimulated by the supernatants of LPC treated F2 cells. The present results suggest that the activation of LPA signaling via LPA₂ and LPA₃ by endothelial cells is involved in the modulation of cell motile activity of MG-63 cells.

NLRP3 Inflammasome Activation Is Involved in LPA1-Mediated Brain Injury after Transient Focal Cerebral Ischemia

Lysophosphatidic acid receptor 1 (LPA₁) contributes to brain injury following transient focal cerebral ischemia. However, the mechanism remains unclear. Here, we investigated whether nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome activation might be an underlying mechanism involved in the pathogenesis of brain injury associated with LPA₁ following ischemic challenge with transient middle cerebral artery occlusion (tMCAO). Suppressing LPA₁ activity by its antagonist attenuated NLRP3 upregulation in the penumbra and ischemic core regions, particularly in ionized calcium-binding adapter molecule 1 (Iba1)-expressing cells like macrophages of mouse after tMCAO challenge. It also suppressed NLRP3 inflammasome activation, such as caspase-1 activation, interleukin 1β (IL-1β) maturation, and apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) speck formation, in a post-ischemic brain. The role of LPA₁ in NLRP3 inflammasome activation was confirmed in vitro using lipopolysaccharide-primed bone marrow-derived macrophages, followed by LPA exposure. Suppressing LPA₁ activity by either pharmacological antagonism or genetic knockdown attenuated NLRP3 upregulation, caspase-1 activation, IL-1β maturation, and IL-1β secretion in these cells. Furthermore, nuclear factor-κB (NF-κB), extracellular signal-regulated kinase 1/2 (ERK1/2), and p38 were found to be LPA₁-dependent effector pathways in these cells. Collectively, results of the current study first demonstrate that LPA₁ could contribute to ischemic brain injury by activating NLRP3 inflammasome with underlying effector mechanisms.

BMS-986020, a Specific LPA1 Antagonist, Provides Neuroprotection against Ischemic Stroke in Mice

Stroke is a leading cause of death. Stroke survivors often suffer from long-term functional disability. This study demonstrated neuroprotective effects of BMS-986020 (BMS), a selective lysophosphatidic acid receptor 1 (LPA₁) antagonist under clinical trials for lung fibrosis and psoriasis, against both acute and sub-acute injuries after ischemic stroke by employing a mouse model with transient middle cerebral artery occlusion (tMCAO). BMS administration immediately after reperfusion significantly attenuated acute brain injuries including brain infarction, neurological deficits, and cell apoptosis at day 1 after tMCAO. Neuroprotective effects of BMS were preserved even when administered at 3 h after reperfusion. Neuroprotection by BMS against acute injuries was associated with attenuation of microglial activation and lipid peroxidation in post-ischemic brains. Notably, repeated BMS administration daily for 14 days after tMCAO exerted long-term neuroprotection in tMCAO-challenged mice, as evidenced by significantly attenuated neurological deficits and improved survival rate. It also attenuated brain tissue loss and cell apoptosis in post-ischemic brains. Mechanistically, it significantly enhanced neurogenesis and angiogenesis in injured brains. A single administration of BMS provided similar long-term neuroprotection except survival rate. Collectively, BMS provided neuroprotection against both acute and sub-acute injuries of ischemic stroke, indicating that BMS might be an appealing therapeutic agent to treat ischemic stroke.

Cooperation of G12/13 and Gi proteins via lysophosphatidic acid receptor-2 (LPA2) signaling enhances cancer cell survival to cisplatin

Lysophosphatidic acid (LPA) through six subtypes of G protein-coupled LPA receptors (LPA₁ to LPA₆) mediates a variety of cancer cell functions. The aim of this study was to evaluate the cooperative effects of G12/13 and Gi proteins through LPA₂ on cancer cell survival to cisplatin (CDDP). In cell survival assay, cells were treated with CDDP every 24 h for 2 days. The long-term CDDP treated (HT-CDDP) cells established from fibrosarcoma HT1080 cells were pretreated with an LPA₂ agonist, GRI-977143. The cell survival rate to CDDP of HT-CDDP cells was significantly increased by GRI-977143. The elevated cell survival to CDDP was suppressed by LPA₂ knockdown. Since G12/13 protein stimulates Rho-mediated signaling, RhoA and RhoC knockdown cells were generated from HT1080 cells (HT1080-RhoA and HT1080-RhoC cells, respectively). In the presence of GRI-977143, HT1080-RhoA and HT1080-RhoC cells showed the low cell survival rates to CDDP. On the other hand, Gi protein inhibits adenylyl cyclase (AC) activity. Before cell survival assay, cells were treated with a Gi protein inhibitor, pertussis toxin (PTX) for 24 h. The cell survival rate to CDDP of HT1080 cells was significantly reduced by PTX. Furthermore, when HT1080-RhoA and HT1080-RhoC cells were pretreated with PTX, the cell survival rates to CDDP of both cells were markedly inhibited by PTX. The present results suggest that cooperation of G12/13 and Gi proteins activated by LPA₂ enhances the cell survival of HT1080 cells treated with CDDP.

Lysophosphatidic Acid Receptor 5 Contributes to Imiquimod-Induced Psoriasis-Like Lesions through NLRP3 Inflammasome Activation in Macrophages

The pathogenesis of psoriasis, an immune-mediated chronic skin barrier disease, is not fully understood yet. Here, we identified lysophosphatidic acid (LPA) receptor 5 (LPA₅)-mediated signaling as a novel pathogenic factor in psoriasis using an imiquimod-induced psoriasis mouse model. Amounts of most LPA species were markedly elevated in injured skin of psoriasis mice, along with LPA₅ upregulation in injured skin. Suppressing the activity of LPA₅ with TCLPA5, a selective LPA₅ antagonist, improved psoriasis symptoms, including ear thickening, skin erythema, and skin scaling in imiquimod-challenged mice. TCLPA5 administration attenuated dermal infiltration of macrophages that were found as the major cell type for LPA₅ upregulation in psoriasis lesions. Notably, TCLPA5 administration attenuated the upregulation of macrophage NLRP3 in injured skin of mice with imiquimod-induced psoriasis. This critical role of LPA₅ in macrophage NLRP3 was further addressed using lipopolysaccharide-primed bone marrow-derived macrophages. LPA exposure activated NLRP3 inflammasome in lipopolysaccharide-primed cells, which was evidenced by NLRP3 upregulation, caspase-1 activation, and IL-1β maturation/secretion. This LPA-driven NLRP3 inflammasome activation in lipopolysaccharide-primed cells was significantly attenuated upon LPA₅ knockdown. Overall, our findings establish a pathogenic role of LPA₅ in psoriasis along with an underlying mechanism, further suggesting LPA₅ antagonism as a potential strategy to treat psoriasis.

Different effects of lysophosphatidic acid receptor-2 (LPA2) and LPA5 on the regulation of chemoresistance in colon cancer cells

Lysophosphatidic acid (LPA) is a simple physiological lipid and exhibits several biological functions by binding to G-protein-coupled LPA receptors (LPA receptor-1 (LPA₁) to LPA₆). The present study aimed to evaluate whether LPA signaling via LPA₂ and LPA₅ is involved in the chemoresistance to anticancer drugs in colon cancer DLD1 cells. In cell survival assay, cells were treated with fluorouracil (5-FU) every 24 h for 2 days. The cell survival rate to 5-FU of DLD1 cells was significantly decreased by LPA treatment. In the presence of LPA, the cell survival rate to 5-FU was significantly elevated by LPA₅ knockdown. Before initiation of the cell survival assay, cells were pretreated with an LPA₂ agonist, GRI-977143. The cell survival rate to 5-FU was markedly increased in DLD1 cells treated with GRI-977143. In the presence of GRI-977143, the elevated cell survival rate of DLD1 cells was reduced by LPA₂ knockdown. To assess the effects of LPA₂ and LPA₅ on the enhancement of chemoresistance, long-term 5-FU treated (DLD-5FU) cells were generated from DLD1 cells. The cell survival rate to 5-FU of DLD-5FU cells were significantly elevated by LPA₅ knockdown. GRI-977143 treatment increased the cell survival rate to 5-FU of DLD-5FU cells. These results suggest that LPA₂ promotes and LPA₅ suppresses the acquisition of chemoresistance in colon cancer cells treated with anticancer drugs.

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.

Lysophosphatidic acid receptor-2 (LPA2)-mediated signaling enhances chemoresistance in melanoma cells treated with anticancer drugs

Lysophosphatidic acid (LPA) signaling through LPA receptors (LPA₁ to LPA₆) regulates a variety of malignant properties in cancer cells. Recently, we show that LPA₂ expression is elevated by long-term cisplatin (CDDP) treatment in melanoma A375 cells. In the present study, we investigated whether LPA₂-mediated signaling is involved in the modulation of chemoresistance in A375 cells. In cell survival assay, cells were treated with CDDP and dacarbazine (DTIC) every 24 h for 2 days. The cell survival rates to CDDP and DTIC were markedly increased by an LPA₂ agonist, GRI-977143. To validate the effects of LPA₂ on cell survival, LPA₂ knockdown cells were generated from A375 cells. The cell survival rates elevated by GRI-977143 were suppressed by LPA₂ knockdown. To evaluate the roles of LPA₂-mediated signaling in cell survival, cells were pretreated with a Gi protein inhibitor, pertussis toxin (PTX). In the presence of GRI-977143, the cell survival rates to CDDP and DTIC were significantly lower in PTX-treated cells than in untreated cells. In addition, pretreatment of an adenylyl cyclase inhibitor, SQ22536, increased the cell survival of A375 cells treated with CDDP and DTIC. These results suggest that LPA₂-mediated signaling plays an important role in the enhancement of chemoresistance of A375 cells treated with anticancer drugs.

Lysophosphatidic Acid Inhibits Simvastatin-Induced Myocytoxicity by Activating LPA Receptor/PKC Pathway

Statins such as simvastatin have many side effects, including muscle damage, which is known to be the most frequent undesirable side effect. Lysophosphatidic acid (LPA), a kind of biolipid, has diverse cellular activities, including cell proliferation, survival, and migration. However, whether LPA affects statin-linked muscle damage has not been reported yet. In the present study, to determine whether LPA might exert potential protective effect on statin-induced myocyotoxicity, the effect of LPA on cytotoxicity in rat L6 myoblasts exposed to simvastatin was explored. Viability and apoptosis of rat L6 myoblasts were detected via 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5- [(phenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT) assay and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, respectively. Protein expression levels were detected via Western blotting. Simvastatin decreased viability of L6 cells. Such decrease in viability was recovered in the presence of LPA. Treatment with LPA suppressed simvastatin-induced apoptosis in L6 cells. In addition, treatment with LPA receptor inhibitor Ki16425, protein kinase C (PKC) inhibitor GF109203X, or intracellular calcium chelator BAPTA-AM attenuated the recovery effect of LPA on simvastatin-induced L6 cell toxicity. These findings indicate that LPA may inhibit simvastatin-induced toxicity in L6 cells probably by activating the LPA receptor-PKC pathway. Therefore, LPA might have potential as a bioactive molecule to protect muscles against simvastatin-induced myotoxicity.

Circ0004390 promotes cell proliferation through sponging miR-198 in ovarian cancer

Circular RNAs (circRNAs) are a novel class of non-coding RNAs which play important roles in human diseases and tumor progression. However, the function of circRNAs in ovarian cancer remains to be uncovered. Here we found a large amount of circRNAs that are differentially expressed in ovarian cancer tissues compared with normal ovarian tissues. We further identified one circRNA derived from the LPAR3 gene and termed Circ0004390, which was frequently upregulated in ovarian cancer tissues. The knockdown of Circ0004390 can significantly reduce the proliferation of ovarian cancer cells. We further demonstrated that Circ0004390 may promote cell proliferation by acting as a sponge for the miR-198 family to regulated the MET expression in ovarian cancer cells. The level of Circ0004390 was closely related with overall survival of ovarian cancer patients. Our findings suggested that Circ0004390 regulated ovarian cancer proliferation by miR-198/MET axis, which might provide a potential target for the treatment of ovarian cancer.

Lysophosphatidic Acid and Hematopoiesis: From Microenvironmental Effects to Intracellular Signaling

Vertebrate hematopoiesis is a complex physiological process that is tightly regulated by intracellular signaling and extracellular microenvironment. In recent decades, breakthroughs in lineage-tracing technologies and lipidomics have revealed the existence of numerous lipid molecules in hematopoietic microenvironment. Lysophosphatidic acid (LPA), a bioactive phospholipid molecule, is one of the identified lipids that participates in hematopoiesis. LPA exhibits various physiological functions through activation of G-protein-coupled receptors. The functions of these LPARs have been widely studied in stem cells, while the roles of LPARs in hematopoietic stem cells have rarely been examined. Nonetheless, mounting evidence supports the importance of the LPA-LPAR axis in hematopoiesis. In this article, we have reviewed regulation of hematopoiesis in general and focused on the microenvironmental and intracellular effects of the LPA in hematopoiesis. Discoveries in these areas may be beneficial to our understanding of blood-related disorders, especially in the context of prevention and therapy for anemia.

Inhibition of store-operated calcium channels by N-arachidonoyl glycine (NAGly): no evidence for the involvement of lipid-sensing G protein coupled receptors

N-arachidonoyl glycine (NAGly) is an endogenous lipid deriving from the endocannabinoid anandamide (AEA). Identified as a ligand of several G-protein coupled receptors (GPCRs), it can however exert biological responses independently of GPCRs. NAGly was recently shown to depress store-operated Ca²⁺ entry (SOCE) but its mechanism of action remains elusive. The major aim of this study was to gain a better knowledge on the NAGly-dependent impairment of SOCE in neurons of the central nervous system (CNS) from mice. First, we examined the expression of genes encoding for putative lipid sensing GPCRs using transcriptomic data publicly available. This analysis showed that the most abundant GPCRs transcripts present in the cerebral cortices of embryonic brains were coding for lysophosphatidic acid (LPA) and sphingosine-1 phosphate (S1P) receptors. Next, the presence of functional receptors was assessed with live-cell calcium imaging experiments. In primary cortical cells S1P and LPA mobilize Ca²⁺ from internal stores via a mechanism sensitive to the S1P and LPA receptor antagonists Ex26, H2L5186303, or Ki16425. However, none of these compounds prevented or attenuated the NAGly-dependent impairment of SOCE. We found no evidence for the requirement of lipid sensing GPCRs in this inhibitory process, indicating that NAGly is an endogenous modulator interfering with the core machinery of SOCE. Moreover, these data also raise the intriguing possibility that the depression of SOCE could play a role in the central effects of NAGly.

Effects of lysophosphatidic acid (LPA) receptor-2 (LPA2) and LPA3 on the regulation of chemoresistance to anticancer drug in lung cancer cells

Lysophosphatidic acid (LPA) mediates a variety of biological functions via the binding of G protein-coupled LPA receptors (LPA receptor-1 (LPA₁) to LPA₆). This study aimed to investigate the roles of LPA₂ and LPA₃ in the modulation of chemoresistance to anticancer drug in lung cancer A549 cells. In cell survival assay, cells were treated with cisplatin (CDDP) every 24 h for 2 days. The cell survival rate to CDDP of A549 cells was significantly elevated by an LPA₂ agonist, GRI-977143. To evaluate the roles of LPA₂-mediated signaling in cell survival during tumor progression, highly migratory (A549-R10) cells were generated from A549 cells. In the presence of GRI-977143, the cell survival rate to CDDP of A549-R10 cells were markedly higher than that of A549 cells, correlating with LPAR2 expression level. Moreover, to assess the effects of long-term anticancer drug treatment on cell survival, the long-term CDDP treated (A549-CDDP) cells were established from A549 cells. The cell survival rate to CDDP of A549-CDDP cells was elevated by GRI-977143. Since LPAR3 expression level was significantly higher in A549-CDDP cells than in A549 cells, we investigated the roles of LPA₃ in the cell survival to CDDP of A549 cells, using an LPA₃ agonist, 1-oleoyl-2-methyl-sn-glycero-3-phosphothionate ((2S)-OMPT). The cell survival rate to CDDP of A549 cells was significantly reduced by (2S)-OMPT treatment. In the presence of (2S)-OMPT, the cell survival rate to CDDP of A549 cells was elevated by LPA₃ knockdown. These results suggest that LPA signaling via LPA₂ and LPA₃ is involved in the regulation of chemoresistance in A549 cells treated with CDDP.

A Novel Agonist of the Type 1 Lysophosphatidic Acid Receptor (LPA1), UCM-05194, Shows Efficacy in Neuropathic Pain Amelioration

Neuropathic pain (NP) is a complex chronic pain state with a prevalence of almost 10% in the general population. Pharmacological options for NP are limited and weakly effective, so there is a need to develop more efficacious NP attenuating drugs. Activation of the type 1 lysophosphatidic acid (LPA₁) receptor is a crucial factor in the initiation of NP. Hence, it is conceivable that a functional antagonism strategy could lead to NP mitigation. Here we describe a new series of LPA₁ agonists among which derivative (S)-17 (UCM-05194) stands out as the most potent and selective LPA₁ receptor agonist described so far (E_max = 118%, EC₅₀ = 0.24 μM, K_D = 19.6 nM; inactive at autotaxin and LPA_2-6 receptors). This compound induces characteristic LPA₁-mediated cellular effects and prompts the internalization of the receptor leading to its functional inactivation in primary sensory neurons and to an efficacious attenuation of the pain perception in an in vivo model of NP.