LPA5-Dependent Signaling Regulates Regeneration of the Intestinal Epithelium Following Irradiation

Lysophosphatidic acid (LPA) is a bioactive lipid molecule that regulates a wide array of cellular functions, including proliferation, differentiation, and survival, via activation of cognate receptors. The LPA5 receptor is highly expressed in the intestinal epithelium, but its function in restoring intestinal epithelial integrity following injury has not been examined. Here, we use a radiation-induced injury model to study the role of LPA5 in regulating intestinal epithelial regeneration. Control mice (Lpar5f/f) and mice with an inducible, epithelial cell-specific deletion of Lpar5 in the small intestine (Lpar5IECKO) were subjected to 10 Gy total body X-ray irradiation and analyzed during recovery. Repair of the intestinal mucosa was delayed in Lpar5IECKO mice, with reduced epithelial proliferation and increased crypt cell apoptosis. These effects were accompanied by reduced numbers of OLFM4+ intestinal stem cells (ISCs). The effects of LPA5 on ISCs were corroborated by studies using organoids derived from Lgr5-lineage tracking reporter mice with deletion of Lpar5 in Lgr5+-stem cells (Lgr5Cont or Lgr5ΔLpar5). Irradiation of organoids resulted in fewer numbers of Lgr5ΔLpar5 organoids retaining Lgr5+-derived progenitor cells compared to Lgr5Cont organoids. Finally, we observed that impaired regeneration in Lpar5IECKO mice was associated with reduced numbers of Paneth cells and decreased expression of YAP, a critical factor for intestinal epithelial repair. Our study highlights a novel role for LPA5 in regeneration of the intestinal epithelium following irradiation and its effect on the maintenance of Paneth cells that support the stem cell niche.

The Emerging Role of LPA as an Oncometabolite

Lysophosphatidic acid (LPA) is a phospholipid that displays potent signalling activities that are regulated in both an autocrine and paracrine manner. It can be found both extra- and intracellularly, where it interacts with different receptors to activate signalling pathways that regulate a plethora of cellular processes, including mitosis, proliferation and migration. LPA metabolism is complex, and its biosynthesis and catabolism are under tight control to ensure proper LPA levels in the body. In cancer patient specimens, LPA levels are frequently higher compared to those of healthy individuals and often correlate with poor responses and more aggressive disease. Accordingly, LPA, through promoting cancer cell migration and invasion, enhances the metastasis and dissemination of tumour cells. In this review, we summarise the role of LPA in the regulation of critical aspects of tumour biology and further discuss the available pre-clinical and clinical evidence regarding the feasibility and efficacy of targeting LPA metabolism for effective anticancer therapy.

Lysophosphatidic Acid/Polydopamine-Modified nHA Composite Scaffolds for Enhanced Osteogenesis via Upregulating the Wnt/Beta-Catenin Pathway

Guided bone regeneration (GBR) technology has been widely used for the regeneration of periodontal bone defects. However, the limited mechanical properties and bone regeneration potential of the currently available GBR membranes often limit their repair effectiveness. In this paper, serum-derived growth factor lysophosphatidic acid (LPA) nanoparticles and dopamine-decorative nanohydroxyapatite (pDA/nHA) particles were double-loaded into polylactic-glycolic acid/polycaprolactone (PLGA/PCL) scaffolds as an organic/inorganic biphase delivery system, namely, PP-pDA/nHA-LPA scaffolds. Physicochemical properties and osteogenic ability in vitro and in vivo were performed. Scanning electron microscopy and mechanical tests showed that the PP-pDA/nHA-LPA scaffolds had a 3D bionic scaffold structure with improved mechanical properties. In vitro cell experiments demonstrated that the PP-pDA/nHA-LPA scaffolds could significantly enhance the attachment, proliferation, osteogenic differentiation, and mineralization of MC3T3-E1 cells. In vivo, the PP-pDA/nHA-LPA scaffolds exhibited great cytocompatibility and cell recruitment ability in 2- and 4-week subcutaneous implantation experiments and significantly promoted bone regeneration in the periodontal defect scaffold implantation experiment. Moreover, LPA-loaded scaffolds were confirmed to enhance osteogenic activities by upregulating the expression of β-catenin and further activating the Wnt/β-catenin pathway. These results demonstrate that the biphase PP-pDA/nHA-LPA delivery system is a promising material for the GBR.

Lysophosphatidic Acid Receptor 3 Activation Is Involved in the Regulation of Ferroptosis

Ferroptosis, a unique form of programmed cell death trigged by lipid peroxidation and iron accumulation, has been implicated in embryonic erythropoiesis and aging. Our previous research demonstrated that lysophosphatidic acid receptor 3 (LPA3) activation mitigated oxidative stress in progeria cells and accelerated the recovery of acute anemia in mice. Given that both processes involve iron metabolism, we hypothesized that LPA3 activation might mediate cellular ferroptosis. In this study, we used an LPA3 agonist, 1-Oleoyl-2-O-methyl-rac-glycerophosphothionate (OMPT), to activate LPA3 and examine its effects on the ferroptosis process. OMPT treatment elevated anti-ferroptosis gene protein expression, including solute carrier family 7 member 11 (SLC7A11), glutathione peroxidase 4 (GPX4), heme oxygenase-1 (HO-1), and ferritin heavy chain (FTH1), in erastin-induced cells. Furthermore, OMPT reduced lipid peroxidation and intracellular ferrous iron accumulation, as evidenced by C11 BODIPY™ 581/591 Lipid Peroxidation Sensor and FerroOrange staining. These observations were validated by applying LPAR3 siRNA in the experiments mentioned above. In addition, the protein expression level of nuclear factor erythroid 2-related factor (NRF2), a key regulator of oxidative stress, was also enhanced in OMPT-treated cells. Lastly, we verified that LPA3 plays a critical role in erastin-induced ferroptotic human erythroleukemia K562 cells. OMPT rescued the erythropoiesis defect caused by erastin in K562 cells based on a Gly A promoter luciferase assay. Taken together, our findings suggest that LPA3 activation inhibits cell ferroptosis by suppressing lipid oxidation and iron accumulation, indicating that ferroptosis could potentially serve as a link among LPA3, erythropoiesis, and aging.

Experimental autotaxin inhibitors for the treatment of idiopathic pulmonary fibrosis

INTRODUCTION

Idiopathic Pulmonary Fibrosis (IPF) is a progressive, irreversible, and fatal lung disease with unmet medical needs. Autotaxin (ATX) is an extracellular enzyme involved in the generation of lysophosphatidic acid (LPA). Preclinical and clinical data have suggested the ATX-LPAR signaling axis plays an important role in the pathogenesis and the progression of IPF.

AREAS COVERED

The aim of this review is to provide an update on the available evidence on autotaxin inhibitors in IPF and further details on the ongoing clinical studies involving these molecules.

EXPERT OPINION

The development of autotaxin inhibitors as a potential therapy for idiopathic pulmonary fibrosis has gained attention due to evidence of their involvement in the disease. Preclinical and early-phase clinical studies have explored these inhibitors' efficacy and safety, offering a novel approach in treating this disease. Combining autotaxin inhibitors with existing anti-fibrotic agents is considered for enhanced therapeutic effects. Large phase III trials assessed Ziritaxestat but yielded disappointing results, highlighting the importance of long-term observation and clinical outcomes in clinical research. Patient stratification and personalized medicine are crucial, as pulmonary fibrosis is a heterogeneous disease. Ongoing research and collaboration are essential for this advancement.

Disruption of LPA-LPAR1 pathway results in lung tumor growth inhibition by downregulating B7-H3 expression in fibroblasts

BACKGROUND

Lysophosphatidic acids (LPAs) belong to a class of bioactive lysophospholipids with multiple functions including immunomodulatory roles in tumor microenvironment (TME). LPA exerts its biological effects via its receptors that are highly expressed in fibroblasts among other cell types. As cancer-associated fibroblasts (CAFs) are a key component of the TME, it is important to understand LPA signaling and regulation of receptors in fibroblasts or CAFs and associated regulatory roles on immunomodulation-related molecules.

METHODS

Cluster analysis, immunoblotting, real-time quantitative-PCR, CRISPR-Cas9 gene editing system, immunohistochemical staining, coculture model, and in vivo xenograft model were used to investigate the effects of LPA-LPAR1 on B7-H3 in tumor promotion of CAFs.

RESULTS

In this study, we found that LPAR1 and CD276 (B7-H3) were generally highly expressed in fibroblasts with good expression correlation. LPA induced B7-H3 up-expression through LPAR1, and stimulated fibroblasts proliferation that could be inhibited by silencing LPAR1 or B7-H3 as well as small molecule LPAR1 antagonist (Ki16425). Using engineered fibroblasts and non-small cell lung carcinoma (NSCLC) cell lines, subsequent investigations demonstrated that CAFs promoted the proliferation of NSCLC in vitro and in vivo, and such effect could be inhibited by knocking out LPAR1 or B7-H3.

CONCLUSION

The present study provided new insights for roles of LPA in CAFs, which could lead to the development of innovative therapies targeting CAFs in the TME. It is also reasonable to postulate a combinatory approach to treat malignant fibrous tumors (such as NSCLC) with LPAR1 antagonists and B7-H3 targeting therapies.

A dual role of lysophosphatidic acid type 2 receptor (LPAR2) in nonsteroidal anti-inflammatory drug-induced mouse enteropathy

Lysophosphatidic acid (LPA) is a bioactive phospholipid mediator that has been found to ameliorate nonsteroidal anti-inflammatory drug (NSAID)-induced gastric injury by acting on lysophosphatidic acid type 2 receptor (LPAR2). In this study, we investigated whether LPAR2 signaling was implicated in the development of NSAID-induced small intestinal injury (enteropathy), another major complication of NSAID use. Wild-type (WT) and Lpar2 deficient (Lpar2-/-) mice were treated with a single, large dose (20 or 30 mg/kg, i.g.) of indomethacin (IND). The mice were euthanized at 6 or 24 h after IND treatment. We showed that IND-induced mucosal enteropathy and neutrophil recruitment occurred much earlier (at 6 h after IND treatment) in Lpar2-/- mice compared to WT mice, but the tissue levels of inflammatory mediators (IL-1β, TNF-α, inducible COX-2, CAMP) remained at much lower levels. Administration of a selective LPAR2 agonist DBIBB (1, 10 mg/kg, i.g., twice at 24 h and 30 min before IND treatment) dose-dependently reduced mucosal injury and neutrophil activation in enteropathy, but it also enhanced IND-induced elevation of several proinflammatory chemokines and cytokines. By assessing caspase-3 activation, we found significantly increased intestinal apoptosis in IND-treated Lpar2-/- mice, but it was attenuated after DBIBB administration, especially in non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice. Finally, we showed that IND treatment reduced the plasma activity and expression of autotaxin (ATX), the main LPA-producing enzyme, and also reduced the intestinal expression of Lpar2 mRNA, which preceded the development of mucosal damage. We conclude that LPAR2 has a dual role in NSAID enteropathy, as it contributes to the maintenance of mucosal integrity after NSAID exposure, but also orchestrates the inflammatory responses associated with ulceration. Our study suggests that IND-induced inhibition of the ATX-LPAR2 axis is an early event in the pathogenesis of enteropathy.

Group III secreted phospholipase A2 -driven lysophospholipid pathway protects against allergic asthma

Asthma is a chronic inflammatory disease of the airways characterized by recurrent episodes of airway obstruction, hyperresponsiveness, remodeling, and eosinophilia. Phospholipase A2 s (PLA2 s), which release fatty acids and lysophospholipids from membrane phospholipids, have been implicated in exacerbating asthma by generating pro-asthmatic lipid mediators, but an understanding of the association between individual PLA2 subtypes and asthma is still incomplete. Here, we show that group III-secreted PLA2 (sPLA2 -III) plays an ameliorating, rather than aggravating, role in asthma pathology. In both mouse and human lungs, sPLA2 -III was expressed in bronchial epithelial cells and decreased during the asthmatic response. In an ovalbumin (OVA)-induced asthma model, Pla2g3-/- mice exhibited enhanced airway hyperresponsiveness, eosinophilia, OVA-specific IgE production, and type 2 cytokine expression as compared to Pla2g3+/+ mice. Lipidomics analysis showed that the pulmonary levels of several lysophospholipids, including lysophosphatidylcholine, lysophosphatidylethanolamine, and lysophosphatidic acid (LPA), were decreased in OVA-challenged Pla2g3-/- mice relative to Pla2g3+/+ mice. LPA receptor 2 (LPA2 ) agonists suppressed thymic stromal lymphopoietin (TSLP) expression in bronchial epithelial cells and reversed airway hyperresponsiveness and eosinophilia in Pla2g3-/- mice, suggesting that sPLA2 -III negatively regulates allergen-induced asthma at least by producing LPA. Thus, the activation of the sPLA2 -III-LPA pathway may be a new therapeutic target for allergic asthma.

Involvement of Lysophospholipids in Pulmonary Vascular Functions and Diseases

Extracellular lysophospholipids (lysophosphatidic acid, lysophosphatidylcholine, sphingosine 1-phosphate, etc.), which are synthesized from phospholipids in the cell membrane, act as lipid mediators, and mediate various cellular responses in constituent cells in the respiratory system, such as contraction, proliferation, migration, and cytoskeletal organization. In addition to these effects, the expression of the adhesion molecules is enhanced by these extracellular lysophospholipids in pulmonary endothelial cells. These effects are exerted via specific G protein-coupled receptors. Rho, Ras, and phospholipase C (PLC) have been proven to be their signaling pathways, related to Ca2+ signaling due to Ca2+ dynamics and Ca2+ sensitization. Therefore, lysophospholipids probably induce pulmonary vascular remodeling through phenotype changes in smooth muscle cells, endothelial cells, and fibroblasts, likely resulting in acute respiratory distress syndrome due to vascular leak, pulmonary hypertension, and pulmonary fibrosis. Moreover, lysophospholipids induce the recruitment of inflammatory cells to the lungs via the enhancement of adhesion molecules in endothelial cells, potentially leading to the development of asthma. These results demonstrate that lysophospholipids may be novel therapeutic targets not only for injury, fibrosis, and hypertension in the lung, but also for asthma. In this review, we discuss the mechanisms of the effects of lysophospholipids on the respiratory system, and the possibility of precision medicine targeting lysophospholipids as treatable traits of these diseases.

Lysophosphatidic acid triggers inflammation in the liver and white adipose tissue in rat models of 1-acyl-sn-glycerol-3-phosphate acyltransferase 2 deficiency and overnutrition

AGPAT2 (1-acyl-sn-glycerol-3-phosphate-acyltransferase-2) converts lysophosphatidic acid (LPA) into phosphatidic acid (PA), and mutations of the AGPAT2 gene cause the most common form of congenital generalized lipodystrophy which leads to steatohepatitis. The underlying mechanism by which AGPAT2 deficiency leads to lipodystrophy and steatohepatitis has not been elucidated. We addressed this question using an antisense oligonucleotide (ASO) to knockdown expression of Agpat2 in the liver and white adipose tissue (WAT) of adult male Sprague-Dawley rats. Agpat2 ASO treatment induced lipodystrophy and inflammation in WAT and the liver, which was associated with increased LPA content in both tissues, whereas PA content was unchanged. We found that a controlled-release mitochondrial protonophore (CRMP) prevented LPA accumulation and inflammation in WAT whereas an ASO against glycerol-3-phosphate acyltransferase, mitochondrial (Gpam) prevented LPA content and inflammation in the liver in Agpat2 ASO-treated rats. In addition, we show that overnutrition, due to high sucrose feeding, resulted in increased hepatic LPA content and increased activated macrophage content which were both abrogated with Gpam ASO treatment. Taken together, these data identify LPA as a key mediator of liver and WAT inflammation and lipodystrophy due to AGPAT2 deficiency as well as liver inflammation due to overnutrition and identify LPA as a potential therapeutic target to ameliorate these conditions.

Infliximab, a Monoclonal Antibody against TNF-α, Inhibits NF-κB Activation, Autotaxin Expression and Breast Cancer Metastasis to Lungs

An inflammatory milieu in the tumor microenvironment leads to immune evasion, resistance to cell death, metastasis and poor prognosis in breast cancer patients. TNF-α is a proinflammatory cytokine that regulates multiple aspects of tumor biology from initiation to progression. TNF-α-induced NF-κB activation initiates inflammatory pathways, which determine cell survival, death and tumor progression. One candidate pathway involves the increased secretion of autotaxin, which produces lysophosphatidate that signals through six G-protein-coupled receptors. Significantly, autotaxin is one of the 40-50 most upregulated genes in metastatic tumors. In this study, we investigated the effects of TNF-α by blocking its action with a monoclonal antibody, Infliximab, and studied the effects on autotaxin secretion and tumor progression. Infliximab had little effect on tumor growth, but it decreased lung metastasis by 60% in a syngeneic BALB/c mouse model using 4T1 breast cancer cells. Infliximab-treated mice also showed a decrease in proliferation and metastatic markers like Ki-67 and vimentin in tumors. This was accompanied by decreases in NF-κB activation, autotaxin expression and the concentrations of plasma and tumor cytokines/chemokines which are involved in metastasis. We also demonstrated a positive correlation of TNF-α -NF-κB and ATX expression in breast cancer patients using cancer databases. Studies in vitro showed that TNF-α-induced NF-κB activation increases autotaxin expression and the clone forming ability of 4T1 breast cancer cells. This report highlights the potential role of Infliximab as an additional approach to attenuate signaling through the autotaxin-lysophosphatidate-inflammatory cycle and decrease mortality from metastatic cancer.

Association between plasma lysophosphatidic acid levels and bronchopulmonary dysplasia in extremely preterm infants: A prospective study

BACKGROUND

Lysophosphatidic acid (LPA) is implicated in bronchopulmonary dysplasia (BPD) pathogenesis, but clinical evidence is lacking. This study aimed to investigate LPA levels in preterm infants with and without BPD and explore LPA as a biomarker for predicting BPD occurrence.

METHODS

Premature infants with a gestational age of <28 weeks or a birth weight of <1000 g were enrolled. Blood samples were collected at postnatal day (PD) 7, 28, and postmenstrual age (PMA) 36 weeks, and plasma LPA levels were measured using a commercial ELISA kit. Receiver operating characteristic curve (ROC) curve analysis determined the PD 28 cutoff for LPA, and multivariable regression analyzed LPA's independent contribution to BPD and exploratory outcomes.

RESULT

Among the 91 infants enrolled in this study, 35 were classified into the non-BPD group and 56 into the BPD group. Infants with BPD had higher plasma LPA levels at PD 28 (6.467 vs. 4.226 μg/mL, p = 0.034) and PMA 36 weeks (2.330 vs. 1.636 μg/mL, p = 0.001). PD 28 LPA level of 6.132 μg/mL was the cutoff for predicting BPD development. Higher PD 28 LPA levels (≥6.132 μg/mL) independently associated with BPD occurrence (OR 3.307, 95% CI 1.032-10.597, p = 0.044). Higher LPA levels correlated with longer oxygen therapy durations [regression coefficients (β) 0.147, 95% CI 0.643-16.133, p = .034].

CONCLUSIONS

Infants with BPD had higher plasma LPA levels at PD 28 and PMA 36 weeks. Higher PD 28 LPA levels independently associated with an increased BPD risk.

Dual role of autotaxin as novel biomarker and therapeutic target in pancreatic neuroendocrine neoplasms

Pancreatic neuroendocrine neoplasms (panNENs) are rare pancreatic neoplasms, and descriptions of treatment remain limited. Autotaxin (ATX) is a secreted autocrine motility factor involved in the production of lysophosphatidic acid (LPA), a lipid mediator that promotes the progression of various cancers. The aim of this study was to clarify the importance of the ATX-LPA axis in panNENs and to confirm its contribution to panNEN progression using clinical data, cell lines, and a mouse model. Serum ATX level was higher in patients with panNEN than in patients with other pancreatic diseases (chronic pancreatitis, pancreatic ductal adenocarcinoma [PDAC], intraductal papillary mucinous neoplasm, autoimmune pancreatitis) and healthy controls, and 61% of clinical specimens stained strongly for ATX. In a case we encountered, serum ATX level fluctuated with disease progression. An in vitro study showed higher ATX mRNA expression in panNEN cell lines than in PDAC cell lines. Cell proliferation and migration in panNEN cell lines were stimulated via the ATX-LPA axis and suppressed by RNA interference or inhibitors. An in vivo study showed that intraperitoneal injection of GLPG1690, an ATX inhibitor, suppressed tumor progression in a xenograft model. These findings revealed that ATX expression is significantly elevated in panNEN and is related to the progression of panNEN. We showed the potential of ATX as a novel biomarker and therapeutic target.

In vitro pharmacological characterization of standard and new lysophosphatidic acid receptor antagonists using dynamic mass redistribution assay

Lysophosphatidic acid (LPA) is a bioactive phospholipid that acts as an agonist of six G protein-coupled receptors named LPA receptors (LPA1-6). LPA elicits diverse intracellular events and modulates several biological functions, including cell proliferation, migration, and invasion. Overactivation of the LPA-LPA receptor system is reported to be involved in several pathologies, including cancer, neuropathic pain, fibrotic diseases, atherosclerosis, and type 2 diabetes. Thus, LPA receptor modulators may be clinically relevant in numerous diseases, making the identification and pharmacodynamic characterization of new LPA receptor ligands of strong interest. In the present work, label-free dynamic mass redistribution (DMR) assay has been used to evaluate the pharmacological activity of some LPA1 and LPA2 standard antagonists at the recombinant human LPA1 and LPA2 receptors. These results are compared to those obtained in parallel experiments with the calcium mobilization assay. Additionally, the same experimental protocol has been used for the pharmacological characterization of the new compound CHI. KI 16425, RO 6842262, and BMS-986020 behaved as LPA1 inverse agonists in DMR experiments and as LPA1 antagonists in calcium mobilization assays. Amgen compound 35 behaved as an LPA2 antagonist, while Merck compound 20 from WO2012028243 was detected as an LPA2 inverse agonist using the DMR test. Of note, for all the compounds, similar potency values were estimated by DMR and calcium assay. The new compound CHI was found to be an LPA1 inverse agonist, but with potency lower than that of the standard compounds. In conclusion, we have demonstrated that DMR assay can be successfully used to characterize LPA1 and LPA2 ligands. Compared to the classical calcium mobilization assay, DMR offers some advantages, in particular allowing the identification of inverse agonists. Finally, in the frame of this study, a new LPA1 inverse agonist has been identified.

Expression of lysophosphatidic acid receptors in the rat uterus: cellular distribution of protein and gestation-associated changes in gene expression

Though lysophosphatidic acid (LPA) shows a variety of regulatory roles in reproduction, its action mechanisms in the gestational organs are still largely unknown. We here characterized cellular distribution of its six kinds of specific receptors (LPA1-6) in rat uteri by immunohistochemistry and quantitatively analyzed changes in Lpar1-6 mRNAs expression throughout pregnancy. Among LPA1-6, evident expression of LPA3, LPA4, and LPA6 was immunologically detected and less expression of immunoreactive LPA1 and LPA2 was also found. Luminal and glandular epithelial cells, stromal cells, and myometrial cells are sites of positive immunoreactions, and they are all likely to express three or more subtypes. All of Lpar1-6 mRNAs were expressed, and their alterations were variable depending on subtypes and gestational age. The present information suggests that diverse actions of LPA in the uterus involve varied expression of LPA receptors dependent on tissue/cell types, receptor subtype(s), and organ reproductive states and helps to understand uterine biology of LPA.

Association of lysophosphatidic acid molecules with liver fibrosis: different roles indicated

Lysophosphatidic acid is composed of lysophosphatidic acid (LPA) molecules with varied chemical forms. The present cross-sectional study was conducted to investigate the associations of various LPA molecules with liver fibrosis. Forty-six patients affected by various types of liver disease who underwent an ultrasound-guided liver biopsy were recruited for this study. Liver fibrosis was evaluated using histological grading, as well as shear wave velocity (Vs) and serum level of type IV collagen 7S (T4c7s). Serum levels of LPA molecules were determined using liquid-chromatography tandem mass-spectrometry (LC-MSMS). Total LPA showed a significant positive association with fibrosis severity evaluated based on histological grading, Vs, and T4c7s used as parameters, following adjustment for other confounding factors, including disease type, age, gender, body mass index, and high-sensitivity C-reactive protein. This association was replicated when 16:0-LPA was substituted for total LPA. In contrast, when 20:4-LPA was substituted for total LPA, no significant association with liver fibrosis was observed. In conclusion, the degree of association varied among the different LPA molecule chemical forms, suggesting different pathophysiological roles of individual LPA molecules, although total LPA concentration was shown to be associated with liver fibrosis.

Plasma Lysophosphatidic Acid Concentrations in Sex Differences and Psychiatric Comorbidity in Patients with Cocaine Use Disorder

We have recently reported sex differences in the plasma concentrations of lysophosphatidic acid (LPA) and alterations in LPA species in patients with alcohol and cocaine use disorders. Preclinical evidence suggests a main role of lysophosphatidic acid (LPA) signaling in anxiogenic responses and drug addiction. To further explore the potential role of the LPA signaling system in sex differences and psychiatric comorbidity in cocaine use disorder (CUD), we conducted a cross-sectional study with 88 patients diagnosed with CUD in outpatient treatment and 60 healthy controls. Plasma concentrations of total LPA and LPA species (16:0, 18:0, 18:1, 18:2 and 20:4) were quantified and correlated with cortisol and tryptophan metabolites [tryptophan (TRP), serotonin (5-HT), kynurenine (KYN), quinolinic acid (QUIN) and kynurenic acid (KYNA)]. We found sexual dimorphism for the total LPA and most LPA species in the control and CUD groups. The total LPA and LPA species were not altered in CUD patients compared to the controls. There was a significant correlation between 18:2 LPA and age at CUD diagnosis (years) in the total sample, but total LPA, 16:0 LPA and 18:2 LPA correlated with age at onset of CUD in male patients. Women with CUD had more comorbid anxiety and eating disorders, whereas men had more cannabis use disorders. Total LPA, 18:0 LPA and 20:4 LPA were significantly decreased in CUD patients with anxiety disorders. Both 20:4 LPA and total LPA were significantly higher in women without anxiety disorders compared to men with and without anxiety disorders. Total LPA and 16:0 LPA were significantly decreased in CUD patients with childhood ADHD. Both 18:1 LPA and 20:4 LPA were significantly augmented in CUD patients with personality disorders. KYNA significantly correlated with total LPA, 16:0 LPA and 18:2 LPA species, while TRP correlated with the 18:1 LPA species. Our results demonstrate that LPA signaling is affected by sex and psychiatric comorbidity in CUD patients, playing an essential role in mediating their anxiety symptoms.

Autotaxin-lysophosphatidic acid receptor 5 axis evokes endothelial dysfunction via reactive oxygen species signaling

Lysophosphatidylcholine (LPC) is a bioactive lipid that has been shown to attenuate endothelium-dependent vasorelaxation contributing to endothelial dysfunction; however, the underlying mechanisms are not well understood. In this study, we investigated the molecular mechanisms involved in the development of LPC-evoked impairment of endothelium-dependent vasorelaxation. In aortic rings isolated from wild-type (WT) mice, a 20-min exposure to LPC significantly reduced the acetylcholine chloride (ACh)-induced vasorelaxation indicating the impairment of normal endothelial function. Interestingly, pharmacological inhibition of autotaxin (ATX) by GLPG1690 partially reversed the endothelial dysfunction, suggesting that lysophosphatidic acid (LPA) derived from LPC may be involved in the effect. Therefore, the effect of LPC was also tested in aortic rings isolated from different LPA receptor knock-out (KO) mice. LPC evoked a marked reduction in ACh-dependent vasorelaxation in Lpar1, Lpar2, and Lpar4 KO, but its effect was significantly attenuated in Lpar5 KO vessels. Furthermore, addition of superoxide dismutase reduced the LPC-induced endothelial dysfunction in WT but not in the Lpar5 KO mice. In addition, LPC increased H2O2 release from WT vessels, which was significantly reduced in Lpar5 KO vessels. Our findings indicate that the ATX-LPA-LPA5 receptor axis is involved in the development of LPC-induced impairment of endothelium-dependent vasorelaxation via LPA5 receptor-mediated reactive oxygen species production. Taken together, in this study, we identified a new pathway contributing to the development of LPC-induced endothelial dysfunction.

Coupled Electrostatic and Hydrophobic Destabilisation of the Gelsolin-Actin Complex Enables Facile Detection of Ovarian Cancer Biomarker Lysophosphatidic Acid

Lysophosphatidic acid (LPA) is a promising biomarker candidate to screen for ovarian cancer (OC) and potentially stratify and treat patients according to disease stage. LPA is known to target the actin-binding protein gelsolin which is a key regulator of actin filament assembly. Previous studies have shown that the phosphate headgroup of LPA alone is inadequate to bind to the short chain of amino acids in gelsolin known as the PIP2-binding domain. Thus, the molecular-level detail of the mechanism of LPA binding is poorly understood. Here, we model LPA binding to the PIP2-binding domain of gelsolin in the gelsolin-actin complex through extensive ten-microsecond atomistic molecular dynamics (MD) simulations. We predict that LPA binding causes a local conformational rearrangement due to LPA interactions with both gelsolin and actin residues. These conformational changes are a result of the amphipathic nature of LPA, where the anionic phosphate, polar glycerol and ester groups, and lipophilic aliphatic tail mediate LPA binding via charged electrostatic, hydrogen bonding, and van der Waals interactions. The negatively-charged LPA headgroup binds to the PIP2-binding domain of gelsolin-actin while its hydrophobic tail is inserted into actin, creating a strong LPA-insertion pocket that weakens the gelsolin-actin interface. The computed structure, dynamics, and energetics of the ternary gelsolin-LPA-actin complex confirms that a quantitative OC assay is possible based on LPA-triggered actin release from the gelsolin-actin complex.

Lysophosphatidic Acid Signalling Regulates Human Sperm Viability via the Phosphoinositide 3-Kinase/AKT Pathway

Lysophosphatidic acid (LPA) signalling is essential for maintaining germ cell viability during mouse spermatogenesis; however, its role in human spermatozoa is unknown. We previously demonstrated that peroxiredoxin 6 (PRDX6) calcium-independent phospholipase A2 (iPLA2) releases lysophospholipids such as LPA or arachidonic acid (AA) and that inhibiting PRDX6 iPLA2 activity impairs sperm cell viability. The exogenous addition of LPA bypassed the inhibition of PRDX6 iPLA2 activity and maintained the active phosphoinositide 3-kinase (PI3K)/AKT pathway. Here, we aimed to study PI3K/AKT pathway regulation via LPA signalling and protein kinases in maintaining sperm viability. The localization of LPARs in human spermatozoa was determined using immunocytochemistry, and P-PI3K and P-AKT substrate phosphorylations via immunoblotting. Sperm viability was determined using the hypo-osmotic swelling test. LPAR1, 3, 5 and 6 were located on the sperm plasma membrane. The inhibition of LPAR1-3 with Ki16425 promoted the impairment of sperm viability and decreased the phosphorylation of PI3K AKT substrates. Inhibitors of PKC, receptor-type PTK and PLC impaired sperm viability and the PI3K/AKT pathway. Adding 1-oleoyl-2-acetyl-snglycerol (OAG), a cell-permeable analog of diacylglycerol (DAG), prevented the loss of sperm viability and maintained the phosphorylation of PI3K. In conclusion, human sperm viability is supported by LPAR signalling and regulated by PLC, PKC and RT-PTK by maintaining phosphorylation levels of PI3K and AKT substrates.

The pharmacological actions of Danzhi-xiaoyao-San on depression involve lysophosphatidic acid and microbiota-gut-brain axis: novel insights from a systems pharmacology analysis of a double-blind, randomized, placebo-controlled clinical trial

Danzhi-xiaoyao-San (DZXYS), a Traditional Chinese Medicine, plays an essential role in the clinical treatment of depression, but its mechanisms in humans remain unclear. To investigate its pharmacological effects and mechanisms as an add-on therapy for depression, we conducted a double-blind, placebo-controlled trial with depressed patients receiving selective serotonin reuptake inhibitors (SSRIs). Serum and fecal samples were collected for metabolomic and microbiome analysis using UHPLC-QTRAP-MS/MS and 16S rRNA gene sequencing technologies, respectively. Depression symptoms were assessed using the 24-item Hamilton Depression Scale. We employed network pharmacology, metabolomics, and molecular docking to identify potential targets associated with DZXYS. We also examined the correlation between gut microbes and metabolites to understand how DZXYS affects the microbiota-gut-brain axis. The results showed that DZXYS combined with SSRIs was more effective than SSRIs alone in improving depression. We identified 39 differential metabolites associated with DZXYS treatment and found seven upregulated metabolic pathways. The active ingredients quercetin and luteolin were docked to targets (AVPR2, EGFR, F2, and CDK6) associated with the enriched pathways 'pancreatic cancer' and 'phospholipase D signaling pathway', which included the metabolite lysophosphatidic acid [LPA(0:0/16:0)]. Additionally, we identified 32 differential gut microbiota species related to DZXYS treatment, with Bacteroides coprophilus and Ruminococcus gnavus showing negative correlations with specific metabolites such as L-2-aminobutyric acid and LPA(0:0/16:0). Our findings indicate that DZXYS's antidepressant mechanisms involve multiple targets, pathways, and the regulation of LPA and the microbiota-gut-brain axis. These insights from our systems pharmacology analysis contribute to a better understanding of DZXYS's potential pharmacological mechanisms in depression treatment.Communicated by Ramaswamy H. Sarma.

The Evaluation of Adropin and Autotaxin as Potential Markers of Endothelial Dysfunction in Preeclampsia

Endothelial dysfunction (ED) plays a prominent role in the pathogenesis of preeclampsia (PE). There is a need for non-invasive methods to assess endothelial function in preeclamptic patients. In the present study, adropin, autotaxin (ATX), and lysophosphatidic acid (LPA) were evaluated as indicators of ED. Patients diagnosed with PE and healthy pregnant women (n = 42 for each group) were compared. After measuring flow-mediated dilation (FMD), the participants were stratified as ED (+) or ED (-) based on a cut-off value of 6.5%. The PE patients were divided as early/late onset PE and severe/mild PE. Adropin, ATX, and LPA levels were measured, and their relevance to ED was evaluated. Student t, Mann-Whitney U, or ANOVA tests were used for statistics, as appropriate. Adropin levels were diminished in the ED (+) group, whereas ATX and LPA levels were increased. The decrease in adropin levels was more pronounced in severe PE, showing a positive correlation with the FMD. In the logistic regression model, adropin was the only parameter that was an independent variable for the FMD test (P < .001). Adropin measurements in serum may be of value for disease follow-up in patients with PE.

Emerging Roles of Lysophosphatidic Acid in Macrophages and Inflammatory Diseases

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

Emerging roles of lysophosphatidylserine as an immune modulator

In addition to direct activation by pathogens and antigens, immune cell functions are further modulated by factors in their environment. Recent studies have revealed that lysophospholipids (LPL) derived from membrane glycerophospholipids are such environmental factors. They are produced by the action of various phospholipases and modulate immune responses positively or negatively via G-protein-coupled receptor-type receptors. These include lysophosphatidic acid, lysophosphatidylserine (LysoPS), and lysophosphatidylinositol. Here, we summarize what is known about the synthetic pathways, receptors, and immunomodulatory functions of these LPLs. Particular focus is given to LysoPS, which have recently been identified, and recent findings on their immunomodulatory actions are presented.

Autotaxin production in the human breast cancer tumor microenvironment mitigates tumor progression in early breast cancers

Autotaxin (ATX) is a secreted enzyme that produces extracellular lysophosphatidate in physiological wound healing. ATX is overexpressed in many cancers to promote growth, metastasis, and treatment resistance. However, ATX expression is very low in breast cancer cells, and is instead secreted by the tumor microenvironment (TME). Paracrine ATX expression, and its effects on tumor progression, has not been robustly studied in human breast tumors. In this study, ATX expression was analyzed in over 5000 non-metastatic breast cancers from databases TCGA, METABRIC and GSE96058, dichotomized by the median. Gene set enrichment analysis (GSEA) and the xCell algorithm investigated biological functions of ATX and correlation to TME cell populations. TME ATX production was verified by single cell RNA sequencing. The highest ATX expression occurred in endothelial cells and cancer-associated fibroblasts (P<0.0001). High tumor ATX expression correlated to increased adipocyte, fibroblast, and endothelial cell fractions (P<0.01), and GSEA demonstrated enriched immune system, tumor suppressor, pro-survival, stemness, and pro-inflammatory signaling in multiple gene sets. Tumor mutational burden was decreased, Ki67 scores were decreased, tumor infiltrating immune cell populations increased, and immune cytolytic activity scores increased (all P<0.01) for ATX-high tumors. Overall survival trends favored ATX-high tumors (hazard ratios 0.75-0.80). In summary, in human breast cancers, ATX is produced by the TME, and in non-metastatic tumors, high levels correlate with an anti-tumor phenotype. Because pre-clinical models use aggressive pro-metastatic cell lines where ATX-mediated signaling promotes tumorigenesis, further research is required to verify an anti-to-pro-tumor phenotype switch with breast cancer progression and/or treatment resistance.

Entering, Linked with the Sphinx: Lysophosphatidic Acids Everywhere, All at Once, in the Oral System and Cancer

Oral health is crucial to overall health, and periodontal disease (PDD) is a chronic inflammatory disease. Over the past decade, PDD has been recognized as a significant contributor to systemic inflammation. Here, we relate our seminal work defining the role of lysophosphatidic acid (LPA) and its receptors (LPARs) in the oral system with findings and parallels relevant to cancer. We discuss the largely unexplored fine-tuning potential of LPA species for biological control of complex immune responses and suggest approaches for the areas where we believe more research should be undertaken to advance our understanding of signaling at the level of the cellular microenvironment in biological processes where LPA is a key player so we can better treat diseases such as PDD, cancer, and emerging diseases.

GPAM mediated lysophosphatidic acid synthesis regulates mitochondrial dynamics in acute myeloid leukemia

Metabolic alterations, especially in the mitochondria, play important roles in several kinds of cancers, including acute myeloid leukemia (AML). However, AML-specific molecular mechanisms that regulate mitochondrial dynamics remain elusive. Through the metabolite screening comparing CD34⁺ AML cells and healthy hematopoietic stem/progenitor cells, we identified enhanced lysophosphatidic acid (LPA) synthesis activity in AML. LPA is synthesized from glycerol-3-phosphate by glycerol-3-phosphate acyltransferases (GPATs), rate-limiting enzymes of the LPA synthesis pathway. Among the four isozymes of GPATs, glycerol-3-phosphate acyltransferases, mitochondrial (GPAM) was highly expressed in AML cells, and the inhibition of LPA synthesis by silencing GPAM or FSG67 (a GPAM-inhibitor) significantly impaired AML propagation through the induction of mitochondrial fission, resulting in the suppression of oxidative phosphorylation and the elevation of reactive oxygen species. Notably, inhibition of this metabolic synthesis pathway by FSG67 administration did not affect normal human hematopoiesis in vivo. Therefore, the GPAM-mediated LPA synthesis pathway from G3P represents a critical metabolic mechanism that specifically regulates mitochondrial dynamics in human AML, and GPAM is a promising potential therapeutic target.

Transplantation-based screen identifies inducers of muscle progenitor cell engraftment across vertebrate species

Stem cell transplantation presents a potentially curative strategy for genetic disorders of skeletal muscle, but this approach is limited by the deleterious effects of cell expansion in vitro and consequent poor engraftment efficiency. In an effort to overcome this limitation, we sought to identify molecular signals that enhance the myogenic activity of cultured muscle progenitors. Here, we report the development and application of a cross-species small-molecule screening platform employing zebrafish and mice, which enables rapid, direct evaluation of the effects of chemical compounds on the engraftment of transplanted muscle precursor cells. Using this system, we screened a library of bioactive lipids to discriminate those that could increase myogenic engraftment in vivo in zebrafish and mice. This effort identified two lipids, lysophosphatidic acid and niflumic acid, both linked to the activation of intracellular calcium-ion flux, which showed conserved, dose-dependent, and synergistic effects in promoting muscle engraftment across these vertebrate species.

COVID-19, Blood Lipid Changes, and Thrombosis

Although there is increasing evidence that oxidative stress and inflammation induced by COVID-19 may contribute to increased risk and severity of thromboses, the underlying mechanism(s) remain to be understood. The purpose of this review is to highlight the role of blood lipids in association with thrombosis events observed in COVID-19 patients. Among different types of phospholipases A₂ that target cell membrane phospholipids, there is increasing focus on the inflammatory secretory phospholipase A₂ IIA (sPLA₂-IIA), which is associated with the severity of COVID-19. Analysis indicates increased sPLA₂-IIA levels together with eicosanoids in the sera of COVID patients. sPLA₂ could metabolise phospholipids in platelets, erythrocytes, and endothelial cells to produce arachidonic acid (ARA) and lysophospholipids. Arachidonic acid in platelets is metabolised to prostaglandin H2 and thromboxane A₂, known for their pro-coagulation and vasoconstrictive properties. Lysophospholipids, such as lysophosphatidylcholine, could be metabolised by autotaxin (ATX) and further converted to lysophosphatidic acid (LPA). Increased ATX has been found in the serum of patients with COVID-19, and LPA has recently been found to induce NETosis, a clotting mechanism triggered by the release of extracellular fibres from neutrophils and a key feature of the COVID-19 hypercoagulable state. PLA2 could also catalyse the formation of platelet activating factor (PAF) from membrane ether phospholipids. Many of the above lipid mediators are increased in the blood of patients with COVID-19. Together, findings from analyses of blood lipids in COVID-19 patients suggest an important role for metabolites of sPLA₂-IIA in COVID-19-associated coagulopathy (CAC).

Decreased Lipid Phosphate Phosphatase 1/3 and Increased Lipid Phosphate Phosphatase 2 Expression in the Human Breast Cancer Tumor Microenvironment Promotes Tumor Progression and Immune System Evasion

The LPP family is comprised of three enzymes that dephosphorylate bioactive lipid phosphates both intracellularly and extracellularly. Pre-clinical breast cancer models have demonstrated that decreased LPP1/3 with increased LPP2 expression correlates to tumorigenesis. This though has not been well verified in human specimens. In this study, we correlate LPP expression data to clinical outcomes in over 5000 breast cancers from three independent cohorts (TCGA, METABRIC, and GSE96058), investigate biological function using gene set enrichment analysis (GSEA) and the xCell cell-type enrichment analysis, and confirm sources of LPP production in the tumor microenvironment (TME) using single-cell RNA-sequencing (scRNAseq) data. Decreased LPP1/3 and increased LPP2 expression correlated to increased tumor grade, proliferation, and tumor mutational burden (all p < 0.001), as well as worse overall survival (hazard ratios 1.3-1.5). Further, cytolytic activity was decreased, consistent with immune system invasion. GSEA data demonstrated multiple increased inflammatory signaling, survival, stemness, and cell signaling pathways with this phenotype across all three cohorts. scRNAseq and the xCell algorithm demonstrated that most tumor LPP1/3 was expressed by endothelial cells and tumor-associated fibroblasts and LPP2 by cancer cells (all p < 0.01). Restoring the balance in LPP expression levels, particularly through LPP2 inhibition, could represent novel adjuvant therapeutic options in breast cancer treatment.

Schwann cell stimulation induces functional and structural changes in peripheral nerves

Signal propagation is the essential function of nerves. Lysophosphatidic acid 18:1 (LPA) allows the selective stimulation of calcium signaling in Schwann cells but not neurons. Here, the time course of slowing and amplitude reduction on compound action potentials due to LPA exposure was observed in myelinated and unmyelinated fibers of the mouse, indicating a clear change of axonal function. Teased nerve fiber imaging showed that Schwann cell activation is also present in axon-attached Schwann cells in freshly isolated peripheral rat nerves. The LPA receptor 1 was primarily localized at the cell extensions in isolated rat Schwann cells, suggesting a role in cell migration. Structural investigation of rat C-fibers demonstrated that LPA leads to an evagination of the axons from their Schwann cells. In A-fibers, the nodes of Ranvier appeared unchanged, but the Schmidt-Lanterman incisures were shortened and myelination reduced. The latter might increase leak current, reducing the potential spread to the next node of Ranvier and explain the changes in conduction velocity. The observed structural changes provide a plausible explanation for the functional changes in myelinated and unmyelinated axons of peripheral nerves and the reported sensory sensations such as itch and pain.

Hypoxia increases cellular levels of phosphatidic acid and lysophospholipids in undifferentiated Caco-2 cells

Cancer cells are known to survive in a hypoxic microenvironment by altering their lipid metabolism as well as their energy metabolism. In this study, Caco-2 cells derived from human colon cancer, were found to have elevated intracellular levels of phosphatidic acid and its lysoform, lysophosphatidic acid (LPA), under hypoxic conditions. Our results suggested that the elevation of LPA in Caco-2 cells was mainly due to the combined increases in cellular levels of lysophosphatidylcholine and lysophosphatidylethanolamine by phospholipase A₂ and subsequent hydrolysis to LPA by lysophospholipase D. We detected the Ca²⁺ -stimulated choline-producing activities toward exogenous lysophosphatidylcholines in whole Caco-2 cell homogenates, indicating their involvement in the LPA production in intact Caco-2 cells.

Inhibition of lysophosphatidic acid receptor 6 upregulated by the choline-deficient l-amino acid-defined diet prevents hepatocarcinogenesis in mice

Hepatocellular carcinoma (HCC) is one of the most worrying tumors worldwide today, and its epidemiology is on the rise. Traditional pharmacological approaches have shown unfavorable results and exhibited many side effects. Hence, there is a need for new efficacious molecules with fewer side effects and improvements on traditional approaches. We previously showed that lysophosphatidic acid (LPA) supports hepatocarcinogenesis, and its effects are mainly mediated by LPA receptor 6 (LPAR6). We also reported that 9-xanthylacetic acid (XAA) acts as an antagonist of LPAR6 to inhibit the growth of HCC. Here, we report that LPAR6 is involved in the choline-deficient l-amino acid-defined (CDAA) diet-induced hepatocarcinogenesis in mice. Our data demonstrate that CDAA diet-induced metabolic imbalance stimulates LPAR6 expression in mice and that XAA counteracts diet-induced effects on hepatic lipid accumulation, fibrosis, inflammation, and HCC development. These conclusions are corroborated by results on LPAR6 gain and loss-of-function in HCC cells.

Cellular and Molecular Control of Lipid Metabolism in Idiopathic Pulmonary Fibrosis: Clinical Application of the Lysophosphatidic Acid Pathway

Idiopathic pulmonary fibrosis (IPF) is a representative disease that causes fibrosis of the lungs. Its pathogenesis is thought to be characterized by sustained injury to alveolar epithelial cells and the resultant abnormal tissue repair, but it has not been fully elucidated. IPF is currently difficult to cure and is known to follow a chronic progressive course, with the patient's survival period estimated at about three years. The disease occasionally exacerbates acutely, leading to a fatal outcome. In recent years, it has become evident that lipid metabolism is involved in the fibrosis of lungs, and various reports have been made at the cellular level as well as at the organic level. The balance among eicosanoids, sphingolipids, and lipid composition has been reported to be involved in fibrosis, with particularly close attention being paid to a bioactive lipid "lysophosphatidic acid (LPA)" and its pathway. LPA signals are found in a wide variety of cells, including alveolar epithelial cells, vascular endothelial cells, and fibroblasts, and have been reported to intensify pulmonary fibrosis via LPA receptors. For instance, in alveolar epithelial cells, LPA signals reportedly induce mitochondrial dysfunction, leading to epithelial damage, or induce the transcription of profibrotic cytokines. Based on these mechanisms, LPA receptor inhibitors and the metabolic enzymes involved in LPA formation are now considered targets for developing novel means of IPF treatment. Advances in basic research on the relationships between fibrosis and lipid metabolism are opening the path to new therapies targeting lipid metabolism in the treatment of IPF.

The Autotaxin-LPA Axis Emerges as a Novel Regulator of Smooth Muscle Cell Phenotypic Modulation during Intimal Hyperplasia

Neointimal hyperplasia is characterized by a loss of the contractile phenotype of vascular smooth muscle cells (VSMCs). Our group has recently shown that VSMC proliferation and migration are mediated by lysophosphatidic acid (LPA) during restenosis, but the role of autotaxin (ATX; lysophospholipase D), which produces LPA, remains unclear. Endothelial denudation of the mouse carotid artery was performed to induce neointimal hyperplasia, and the extent of damage caused by the ATX-LPA axis was assessed in VSMCs. We observed the upregulation of ATX activity (p < 0.0002) in the injured carotid artery using an AR2 probe fluorescence assay. Further, the tissue carotid LPA levels were elevated 2.7-fold in carotid vessels, augmenting neointimal hyperplasia. We used an electrical cell-substrate impedance sensor (ECIS) to measure VSMC proliferation and migration. Treatment with an ATX inhibitor (PF8380) or LPA receptor inhibitor (Ki16425) attenuated VSMC proliferation (extracellular signal-regulated kinases) activity and migration in response to recombinant ATX. Indeed, PF8380 treatment rescued the aggravated post-wire injury neointima formation of carotid arteries. The upregulation of ATX following vessel injury leads to LPA production in VSMCs, favoring restenosis. Our observations suggest that inhibition of the ATX-LPA axis could be therapeutically targeted in restenosis to minimize VSMC phenotypic modulation and inflammation after vascular injury.

Lpar1-mediated Effects in Endothelial Progenitor Cells Are Crucial for Lung Repair in Acute Respiratory Distress Syndrome/Acute Lung Injury

Acute respiratory distress syndrome/acute lung injury (ARDS/ALI) involves acute respiratory failure characterized by vascular endothelial and lung alveolar epithelial injury. Endothelial progenitor cells (EPCs) can mediate vasculogenesis. However, the limitations of EPCs, such as low survival and differentiation, are believed to inhibit the effectiveness of autologous cell therapies. This study demonstrated that lysophosphatidic acid (LPA), a bioactive small molecule without immunogenicity, is involved in the survival and antiapoptotic effects in human umbilical cord mesenchymal stem cells. This study aimed to explore whether LPA improves the survival of EPCs, enhancing the cellular therapeutic efficacy in ARDS, and these results will expand the application of LPA in stem cells and regenerative medicine. LPA promoted the colony formation, proliferation, and migration of EPCs and upregulated the expression of vascular endothelial-derived growth factor (VEGF) in EPCs. LPA pretreatment of transplanted EPCs improved the therapeutic effect by increasing EPC numbers in the rat lungs. LPA enhanced EPC proliferation and migration through Lpar1 coupled to G_i/o and G_q/11, respectively. Activation of extracellular signal-related kinase 1/2, or ERK1/2, was related to LPA-induced EPC proliferation but not migration. LPA/Lpar1-mediated G_i/o protein was also shown to be involved in promoting VEGF expression and inhibiting IL-1α expression in EPCs. Low LPA concentrations are present after lung injury; thus, the restoration of LPA may promote endothelial cell homeostasis and lung repair in ARDS. Inhalation of LPA significantly promoted the homing of endogenous EPCs to the lung and reduced lung injury in both rats with LPS-induced ALI and Streptococcus pneumoniae-infected mice. Taken together, these data indicated that LPA/Lpar1-mediated effects in EPCs are involved in maintaining endothelial cell homeostasis and lung tissue repair under physiological conditions.

Autotaxin facilitates selective LPA receptor signaling

Autotaxin (ATX; ENPP2) produces the lipid mediator lysophosphatidic acid (LPA) that signals through disparate EDG (LPA1-3) and P2Y (LPA4-6) G protein-coupled receptors. ATX/LPA promotes several (patho)physiological processes, including in pulmonary fibrosis, thus serving as an attractive drug target. However, it remains unclear if clinical outcome depends on how different types of ATX inhibitors modulate the ATX/LPA signaling axis. Here, we show that the ATX "tunnel" is crucial for conferring key aspects of ATX/LPA signaling and dictates cellular responses independent of ATX catalytic activity, with a preference for activation of P2Y LPA receptors. The efficacy of the ATX/LPA signaling responses are abrogated more efficiently by tunnel-binding inhibitors, such as ziritaxestat (GLPG1690), compared with inhibitors that exclusively target the active site, as shown in primary lung fibroblasts and a murine model of radiation-induced pulmonary fibrosis. Our results uncover a receptor-selective signaling mechanism for ATX, implying clinical benefit for tunnel-targeting ATX inhibitors.

Modes of action of lysophospholipids as endogenous activators of the TRPV4 ion channel

The Transient Receptor Potential Vanilloid 4 (TRPV4) channel has been shown to function in many physiological and pathophysiological processes. Despite abundant information on its importance in physiology, very few endogenous agonists for this channel have been described, and very few underlying mechanisms for its activation have been clarified. TRPV4 is expressed by several types of cells, such as vascular endothelial, and skin and lung epithelial cells, where it plays pivotal roles in their function. In the present study, we show that TRPV4 is activated by lysophosphatidic acid (LPA) in both endogenous and heterologous expression systems, pinpointing this molecule as one of the few known endogenous agonists for TRPV4. Importantly, LPA is a bioactive glycerophospholipid, relevant in several physiological conditions, including inflammation and vascular function, where TRPV4 has also been found to be essential. Here we also provide mechanistic details of the activation of TRPV4 by LPA and another glycerophospholipid, lysophosphatidylcholine (LPC), and show that LPA directly interacts with both the N- and C-terminal regions of TRPV4 to activate this channel. Moreover, we show that LPC activates TRPV4 by producing an open state with a different single-channel conductance to that observed with LPA. Our data suggest that the activation of TRPV4 can be finely tuned in response to different endogenous lipids, highlighting this phenomenon as a regulator of cell and organismal physiology. KEY POINTS: The Transient Receptor Potential Vaniloid (TRPV) 4 ion channel is a widely distributed protein with important roles in normal and disease physiology for which few endogenous ligands are known. TRPV4 is activated by a bioactive lipid, lysophosphatidic acid (LPA) 18:1, in a dose-dependent manner, in both a primary and a heterologous expression system. Activation of TRPV4 by LPA18:1 requires residues in the N- and C-termini of the ion channel. Single-channel recordings show that TRPV4 is activated with a decreased current amplitude (conductance) in the presence of lysophosphatidylcholine (LPC) 18:1, while LPA18:1 and GSK101 activate the channel with a larger single-channel amplitude. Distinct single-channel amplitudes produced by LPA18:1 and LPC18:1 could differentially modulate the responses of the cells expressing TRPV4 under different physiological conditions.

Role of autotaxin in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a prototypic systemic autoimmune disease characterized by the production of various autoantibodies and deposition of immune complexes. SLE is a heterogenous disease, and the pattern of organ involvement and response to treatment differs significantly among patients. Novel biological markers are necessary to assess the extent of organ involvement and predict treatment response in SLE. Lysophosphatidic acid is a lysophospholipid involved in various biological processes, and autotaxin (ATX), which catalyzes the production of lysophosphatidic acid in the extracellular space, has gained attention in various diseases as a potential biomarker. The concentration of ATX is increased in the serum and urine of patients with SLE and lupus nephritis. Recent evidence suggests that ATX produced by plasmacytoid dendritic cells may play an important role in the immune system and pathogenesis of SLE. Furthermore, the production of ATX is associated with type I interferons, a key cytokine in SLE pathogenesis, and ATX may be a potential biomarker and key molecule in SLE.

Autotaxin and Lysophosphatidic Acid Signalling: the Pleiotropic Regulatory Network in Cancer

Autotaxin, also known as ecto-nucleotide pyrophosphatase/phosphodiesterase family member 2, is a secreted glycoprotein that plays multiple roles in human physiology and cancer pathology. This protein, by converting lysophosphatidylcholine into lysophosphatidic acid, initiates a complex signalling cascade with significant biological implications. The article outlines the autotaxin gene and protein structure, expression regulation and physiological functions, but focuses mainly on the role of autotaxin in cancer development and progression. Autotaxin and lysophosphatidic acid signalling influence several aspects of cancer, including cell proliferation, migration, metastasis, therapy resistance, and interactions with the immune system. The potential of autotaxin as a diagnostic biomarker and promising drug target is also examined.

The lysophosphatidic acid-regulated signal transduction network in ovarian cancer cells and its role in actomyosin dynamics, cell migration and entosis

Lysophosphatidic acid (LPA) species accumulate in the ascites of ovarian high-grade serous cancer (HGSC) and are associated with short relapse-free survival. LPA is known to support metastatic spread of cancer cells by activating a multitude of signaling pathways via G-protein-coupled receptors of the LPAR family. Systematic unbiased analyses of the LPA-regulated signal transduction network in ovarian cancer cells have, however, not been reported to date. Methods: LPA-induced signaling pathways were identified by phosphoproteomics of both patient-derived and OVCAR8 cells, RNA sequencing, measurements of intracellular Ca²⁺ and cAMP as well as cell imaging. The function of LPARs and downstream signaling components in migration and entosis were analyzed by selective pharmacological inhibitors and RNA interference. Results: Phosphoproteomic analyses identified > 1100 LPA-regulated sites in > 800 proteins and revealed interconnected LPAR1, ROCK/RAC, PKC/D and ERK pathways to play a prominent role within a comprehensive signaling network. These pathways regulate essential processes, including transcriptional responses, actomyosin dynamics, cell migration and entosis. A critical component of this signaling network is MYPT1, a stimulatory subunit of protein phosphatase 1 (PP1), which in turn is a negative regulator of myosin light chain 2 (MLC2). LPA induces phosphorylation of MYPT1 through ROCK (T853) and PKC/ERK (S507), which is majorly driven by LPAR1. Inhibition of MYPT1, PKC or ERK impedes both LPA-induced cell migration and entosis, while interference with ROCK activity and MLC2 phosphorylation selectively blocks entosis, suggesting that MYPT1 figures in both ROCK/MLC2-dependent and -independent pathways. We finally show a novel pathway governed by LPAR2 and the RAC-GEF DOCK7 to be indispensable for the induction of entosis. Conclusion: We have identified a comprehensive LPA-induced signal transduction network controlling LPA-triggered cytoskeletal changes, cell migration and entosis in HGSC cells. Due to its pivotal role in this network, MYPT1 may represent a promising target for interfering with specific functions of PP1 essential for HGSC progression.

Mitochondrial GPAT-derived LPA controls auxin-dependent embryonic and postembryonic development

Membrane properties are emerging as important cues for the spatiotemporal regulation of hormone signaling. Lysophosphatidic acid (LPA) evokes multiple biological responses by activating G protein-coupled receptors in mammals. In this study, we demonstrated that LPA derived from the mitochondrial glycerol-3-phosphate acyltransferases GPAT1 and GPAT2 is a critical lipid-based cue for auxin-controlled embryogenesis and plant growth in Arabidopsis thaliana. LPA levels decreased, and the polarity of the auxin efflux carrier PIN-FORMED1 (PIN1) at the plasma membrane (PM) was defective in the gpat1 gpat2 mutant. As a consequence of distribution defects, instructive auxin gradients and embryonic and postembryonic development are severely compromised. Further cellular and genetic analyses revealed that LPA binds directly to PIN1, facilitating the vesicular trafficking of PIN1 and polar auxin transport. Our data support a model in which LPA provides a lipid landmark that specifies membrane identity and cell polarity, revealing an unrecognized aspect of phospholipid patterns connecting hormone signaling with development.

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.

Autotaxin in Breast Cancer: Role, Epigenetic Regulation and Clinical Implications

Autotaxin (ATX), the protein product of Ectonucleotide Pyrophosphatase Phosphodiesterase 2 (ENPP2), is a secreted lysophospholipase D (lysoPLD) responsible for the extracellular production of lysophosphatidic acid (LPA). ATX-LPA pathway signaling participates in several normal biological functions, but it has also been connected to cancer progression, metastasis and inflammatory processes. Significant research has established a role in breast cancer and it has been suggested as a therapeutic target and/or a clinically relevant biomarker. Recently, ENPP2 methylation was described, revealing a potential for clinical exploitation in liquid biopsy. The current review aims to gather the latest findings about aberrant signaling through ATX-LPA in breast cancer and discusses the role of ENPP2 expression and epigenetic modification, giving insights with translational value.

A defective lysophosphatidic acid-autophagy axis increases miscarriage risk by restricting decidual macrophage residence

Massive infiltrated and enriched decidual macrophages (dMφ) have been widely regarded as important regulators of maternal-fetal immune tolerance and trophoblast invasion, contributing to normal pregnancy. However, the characteristics of metabolic profile and the underlying mechanism of dMφ residence remain largely unknown. Here, we observe that dMφ display an active glycerophospholipid metabolism. The activation of ENPP2-lysophosphatidic acid (LPA) facilitates the adhesion and retention, and M2 differentiation of dMφ during normal pregnancy. Mechanistically, this process is mediated through activation of the LPA receptors (LPAR1 and PPARG/PPARγ)-DDIT4-macroautophagy/autophagy axis, and further upregulation of multiple adhesion factors (e.g., cadherins and selectins) in a CLDN7 (claudin 7)-dependent manner. Additionally, poor trophoblast invasion and placenta development, and a high ratio of embryo loss are observed in Enpp2^±, lpar1^-/- or PPARG-blocked pregnant mice. Patients with unexplained spontaneous abortion display insufficient autophagy and cell residence of dMφ. In therapeutic studies, supplementation with LPA or the autophagy inducer rapamycin significantly promotes dMφ autophagy and cell residence, and improves embryo resorption in Enpp2^± and spontaneous abortion mouse models, which should be dependent on the activation of DDIT4-autophagy-CLDN7-adhesion molecules axis. This observation reveals that inactivation of ENPP2-LPA metabolism and insufficient autophagy of dMφ result in resident obstacle of dMφ and further increase the risk of spontaneous abortion, and provides potential therapeutic strategies to prevent spontaneous abortion.Abbreviations: ACTB: actin beta; ADGRE1/F4/80: adhesion G protein-coupled receptor E1; Atg5: autophagy related 5; ATG13: autophagy related 13; BECN1: beclin 1; CDH1/E-cadherin: cadherin 1; CDH5/VE-cadherin: cadherin 5; CFSE: carboxyfluorescein succinimidyl ester; CLDN7: claudin 7; CSF1/M-CSF: colony stimulating factor 1; CSF2/GM-CSF: colony stimulating factor 2; Ctrl: control; CXCL10/IP-10: chemokine (C-X-C) ligand 10; DDIT4: DNA damage inducible transcript 4; dMφ: decidual macrophage; DSC: decidual stromal cells; ENPP2/ATX: ectonucleotide pyrophosphatase/phosphodiesterase 2; Enpp2^±: Enpp2 heterozygous knockout mouse; ENPP2i/PF-8380: ENPP2 inhibitor; EPCAM: epithelial cell adhesion molecule; ESC: endometrial stromal cells; FGF2/b-FGF: fibroblast growth factor 2; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GPCPD1: glycerophosphocholine phosphodiesterase 1; HE: heterozygote; HIF1A: hypoxia inducible factor 1 subunit alpha; HNF4A: hepatocyte nuclear factor 4 alpha; HO: homozygote; ICAM2: intercellular adhesion molecule 2; IL: interleukin; ITGAV/CD51: integrin subunit alpha V; ITGAM/CD11b: integrin subunit alpha M; ITGAX/CD11b: integrin subunit alpha X; ITGB3/CD61: integrin subunit beta 3; KLRB1/NK1.1: killer cell lectin like receptor B1; KRT7/cytokeratin 7: keratin 7; LPA: lysophosphatidic acid; LPAR: lysophosphatidic acid receptor; lpar1^-/-: lpar1 homozygous knockout mouse; LPAR1i/AM966: LPAR1 inhibitor; LY6C: lymphocyte antigen 6 complex, locus C1; LYPLA1: lysophospholipase 1; LYPLA2: lysophospholipase 2; Lyz2: lysozyme 2; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MARVELD2: MARVEL domain containing 2; 3-MA: 3-methyladenine; MBOAT2: membrane bound O-acyltransferase domain containing 2; MGLL: monoglyceride lipase; MRC1/CD206: mannose receptor C-type 1; MTOR: mechanistic target of rapamycin kinase; NP: normal pregnancy; PDGF: platelet derived growth factor; PLA1A: phospholipase A1 member A; PLA2G4A: phospholipase A2 group IVA; PLPP1: phospholipid phosphatase 1; pMo: peripheral blood monocytes; p-MTOR: phosphorylated MTOR; PPAR: peroxisome proliferator activated receptor; PPARG/PPARγ: peroxisome proliferator activated receptor gamma; PPARGi/GW9662: PPARG inhibitor; PTPRC/CD45: protein tyrosine phosphatase receptor type, C; Rapa: rapamycin; RHEB: Ras homolog, mTORC1 binding; SA: spontaneous abortion; SELE: selectin E; SELL: selectin L; siCLDN7: CLDN7-silenced; STAT: signal transducer and activator of transcription; SQSTM1: sequestosome 1; TJP1: tight junction protein 1; VCAM1: vascular cell adhesion molecule 1; WT: wild type.

Spatial Delivery of Triple Functional Nanoparticles via an Extracellular Matrix-Mimicking Coaxial Scaffold Synergistically Enhancing Bone Regeneration

It remains a major challenge to simultaneously achieve bone regeneration and prevent infection in the complex microenvironment of repairing bone defects. Here, we developed a novel ECM-mimicking scaffold by coaxial electrospinning to be endowed with multibiological functions. Lysophosphatidic acid (LPA) and zinc oxide (ZnO) nanoparticles were loaded into the poly-lactic-co-glycolic acid/polycaprolactone (PLGA/PCL, PP) sheath layer of coaxial nanofibers, and deferoxamine (DFO) nanoparticles were loaded into its core layer. The novel scaffold PP-LPA-ZnO/DFO maintained a porous nanofibrous architecture after incorporating three active nanoparticles, showing better physicochemical properties and eximious biocompatibility. In vitro studies showed that the bio-scaffold loaded with LPA nanoparticles had excellent cell adhesion, proliferation, and differentiation for MC3T3-E1 cells and synergistic osteogenesis with the addition of ZnO and DFO nanoparticles. Further, the PP-LPA-ZnO/DFO scaffold promoted tube formation and facilitated the expression of vascular endothelial markers in HUVECs. In vitro antibacterial studies against Escherichia Coli and Staphylococcus aureus demonstrated effective antibacterial activity of the PP-LPA-ZnO/DFO scaffold. In vivo studies showed that the PP-LPA-ZnO/DFO scaffold exhibited excellent biocompatibility after subcutaneous implantation and remarkable osteogenesis at 4 weeks post-implantation in the mouse alveolar bone defects. Importantly, the PP-LPA-ZnO/DFO scaffold showed significant antibacterial activity, prominent neovascularization, and new bone formation in the rat fenestration defect model. Overall, the spatially sustained release of LPA, ZnO, and DFO nanoparticles through the coaxial scaffold synergistically enhanced biocompatibility, osteogenesis, angiogenesis, and effective antibacterial properties, which is ultimately beneficial for bone regeneration. This project provides the optimized design of bone regenerative biomaterials and a new strategy for bone regeneration, especially in the potentially infected microenvironment.

RAGE pathway activation and function in chronic kidney disease and COVID-19

The multi-ligand receptor for advanced glycation end-products (RAGE) and its ligands are contributing factors in autoimmunity, cancers, and infectious disease. RAGE activation is increased in chronic kidney disease (CKD) and coronavirus disease 2019 (COVID-19). CKD may increase the risk of COVID-19 severity and may also develop in the form of long COVID. RAGE is expressed in essentially all kidney cell types. Increased production of RAGE isoforms and RAGE ligands during CKD and COVID-19 promotes RAGE activity. The downstream effects include cellular dysfunction, tissue injury, fibrosis, and inflammation, which in turn contribute to a decline in kidney function, hypertension, thrombotic disorders, and cognitive impairment. In this review, we discuss the forms and mechanisms of RAGE and RAGE ligands in the kidney and COVID-19. Because various small molecules antagonize RAGE activity in animal models, targeting RAGE, its co-receptors, or its ligands may offer novel therapeutic approaches to slowing or halting progressive kidney disease, for which current therapies are often inadequate.

Mesenteric Adipose Tissue Contributes to Intestinal Fibrosis in Crohn's Disease Through the ATX-LPA Axis

BACKGROUND AND AIMS

Intestinal fibrostenosis is an important cause of surgical intervention in patients with Crohn's disease [CD]. Hypertrophic mesenteric adipose tissue [MAT] is associated with the disease process of CD. The purpose of this study was to investigate the contribution of MAT to intestinal fibrosis.

METHODS

MAT from surgical specimens of fibrostenotic CD patients and controls was collected for measurement of the levels of autotaxin [ATX] and lysophosphatidic acid [LPA]. ATX was inhibited in vivo in DNBS [dinitrobenzene sulfonic acid]-induced colitis mice, which were evaluated for colonic inflammation and fibrosis. 3T3-L1 cells and primary colonic fibroblasts were used in vitro to investigate the interaction between MAT and intestinal fibrosis, as well as the molecular mechanism underlying this interaction.

RESULTS

MAT adjacent to the fibrostenotic intestine in CD patients showed an activated ATX-LPA axis. An in vivo study indicated that inhibition of ATX was associated with the improvement of morphology and function of diseased MAT, which was combined with ameliorated intestinal inflammation and fibrosis in DNBS-instilled mice. In vitro studies showed that hypoxia stimulated adipocyte ATX expression and that LPA stabilized adipocyte HIF-1α protein, forming an ATX-LPA-HIF-1α amplification loop and aggravating adipocyte dysfunction. LPA secreted by adipocytes bound to LPA1 on the surface of fibroblasts, promoted their proliferation and differentiation, and increased the expression of fibrosis-related factors.

CONCLUSIONS

The ATX-LPA axis regulated intestinal fibrosis by influencing the proliferation and differentiation of intestinal fibroblasts. Inhibiting this axis may be a therapeutic target for intestinal fibrosis in CD.