Lysophosphatidic Acid Receptors: Biochemical and Clinical Implications in Different Diseases

Lysophosphatidic Acid Receptor 1 (LPA1) Antagonists as Potential Migrastatics for Triple Negative Breast Cancer

Metastasis is responsible for about 90 % of cancer deaths. Anti-metastatic drugs, termed as migrastatics, offer a distinctive therapeutic approach to address cancer migration and invasion. However, therapeutic exploitation of metastasis-specific targets remains limited, and the effective prevention and suppression of metastatic cancer continue to be elusive. Lysophosphatidic acid receptor 1 (LPA1) is activated by an endogenous lipid molecule LPA, leading to a diverse array of cellular activities. Previous studies have shown that the LPA/LPA1 axis supports the progression of metastasis for many types of cancer. In this study, we report the synthesis and biological evaluation of fluorine-containing triazole derivatives as potent LPA1 antagonists, offering potential as migrastatic drugs for triple negative breast cancer (TNBC). In particular, compound 12 f, the most potent and highly selective in this series with an IC50 value of 16.0 nM in the cAMP assay and 18.4 nM in the calcium mobilization assay, inhibited cell survival, migration, and invasion in the TNBC cell line. Interestingly, the compound did not induce apoptosis in TNBC cells and demonstrated no cytotoxic effects. These results highlight the potential of LPA1 as a migrastatic target. Consequently, the LPA1 antagonists developed in this study hold promise as potential migrastatic candidates for TNBC.

Network analysis-guided drug repurposing strategies targeting LPAR receptor in the interplay of COVID, Alzheimer's, and diabetes

The COVID-19 pandemic caused by the SARS-CoV-2 virus has greatly affected global health. Emerging evidence suggests a complex interplay between Alzheimer's disease (AD), diabetes (DM), and COVID-19. Given COVID-19's involvement in the increased risk of other diseases, there is an urgent need to identify novel targets and drugs to combat these interconnected health challenges. Lysophosphatidic acid receptors (LPARs), belonging to the G protein-coupled receptor family, have been implicated in various pathological conditions, including inflammation. In this regard, the study aimed to investigate the involvement of LPARs (specifically LPAR1, 3, 6) in the tri-directional relationship between AD, DM, and COVID-19 through network analysis, as well as explore the therapeutic potential of selected anti-AD, anti-DM drugs as LPAR, SPIKE antagonists. We used the Coremine Medical database to identify genes related to DM, AD, and COVID-19. Furthermore, STRING analysis was used to identify the interacting partners of LPAR1, LPAR3, and LPAR6. Additionally, a literature search revealed 78 drugs on the market or in clinical studies that were used for treating either AD or DM. We carried out docking analysis of these drugs against the LPAR1, LPAR3, and LPAR6. Furthermore, we modeled the LPAR1, LPAR3, and LPAR6 in a complex with the COVID-19 spike protein and performed a docking study of selected drugs with the LPAR-Spike complex. The analysis revealed 177 common genes implicated in AD, DM, and COVID-19. Protein-protein docking analysis demonstrated that LPAR (1,3 & 6) efficiently binds with the viral SPIKE protein, suggesting them as targets for viral infection. Furthermore, docking analysis of the anti-AD and anti-DM drugs against LPARs, SPIKE protein, and the LPARs-SPIKE complex revealed promising candidates, including lupron, neflamapimod, and nilotinib, stating the importance of drug repurposing in the drug discovery process. These drugs exhibited the ability to bind and inhibit the LPAR receptor activity and the SPIKE protein and interfere with LPAR-SPIKE protein interaction. Through a combined network and targeted-based therapeutic intervention approach, this study has identified several drugs that could be repurposed for treating COVID-19 due to their expected interference with LPAR(1, 3, and 6) and spike protein complexes. In addition, it can also be hypothesized that the co-administration of these identified drugs during COVID-19 infection may not only help mitigate the impact of the virus but also potentially contribute to the prevention or management of post-COVID complications related to AD and DM.

Dysregulated autotaxin expression by T cells in multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disease characterized by infiltration of autoreactive T cells into the central nervous system (CNS). In order to understand how activated, autoreactive T cells are able to cross the blood brain barrier, the unique molecular characteristics of pathogenic T cells need to be more thoroughly examined. In previous work, our laboratory found autotaxin (ATX) to be upregulated by activated autoreactive T cells in the mouse model of MS. ATX is a secreted glycoprotein that promotes T cell chemokinesis and transmigration through catalysis of lysophoshphatidic acid (LPA). ATX is elevated in the serum of MS patients during active disease phases, and we previously found that inhibiting ATX decreases severity of neurological deficits in the mouse model. In this study, ATX expression was found to be lower in MS patient immune cells during rest, but significantly increased during early activation in a manner not seen in healthy controls. The ribosomal binding protein HuR, which stabilizes ATX mRNA, was also increased in MS patients in a similar pattern to that of ATX, suggesting it may be helping regulate ATX levels after activation. The proinflammatory cytokine interleukin-23 (IL-23) was shown to induce prolonged ATX expression in MS patient Th1 and Th17 cells. Finally, through ChIP, re-ChIP analysis, we show that IL-23 may be signaling through pSTAT3/pSTAT4 heterodimers to induce expression of ATX. Taken together, these findings elucidate cell types that may be contributing to elevated serum ATX levels in MS patients and identify potential drivers of sustained expression in encephalitogenic T cells.

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.

Lead generation from N-[benzyl(4-phenylbutyl)carbamoyl]amino acid as a novel LPA1 antagonist for the treatment of systemic sclerosis

Lysophosphatidic acid (LPA), a bioactive phospholipid, binds to the G protein-coupled LPA1 receptor on the surfaces of immune cells, to promote progression of fibrosis of the skin and organs through inducing infiltration of immune cells into tissues, chemokine production, inflammatory cytokine production, and fibroblast transformation. Anti-fibrotic effects of LPA1 blockade have been reported in animal models of scleroderma and scleroderma patients. In the study reported herein, we identified the novel urea compound 5 as a hit compound with LPA1 antagonist activity from our in-house library and synthesized the lead compound TP0541640 (18) by structural transformation utilizing a structure-based drug design (SBDD) approach. Compound 18 possessed potent in vitro LPA1 antagonist activity and exhibited a dose-dependent inhibitory effect against LPA-induced histamine release in mice. Furthermore, 18 significantly suppressed collagen production and skin thickening in a mouse model of bleomycin-induced skin fibrosis. Herein, we describe the compound design strategies and in vivo studies in greater detail.

Discovery of Chemical Scaffolds as Lysophosphatidic Acid Receptor 1 Antagonists: Virtual Screening, In Vitro Validation, and Molecular Dynamics Analysis

Lysophosphatidic acid receptor 1 (LPAR1) is an emerging therapeutic target for numerous human diseases including fibrosis. However, the limited number of available core structures of LPAR1 antagonists has prompted the need for novel chemical templates. In this study, we conducted a high-throughput virtual screening to discover potential new scaffolds. We tested three existing crystal structures alongside an AlphaFold model to evaluate their suitability in structure-based virtual screening, finding that the crystal structures show superior performance compared with the predictive model. Furthermore, we also found that enhancing the precision in the screening process did not necessarily improve the enrichment of hits. From the screening campaign, we identified five structures that were validated using an LPAR1-dependent calcium flux assay. To gain a deeper insight into the protein-ligand interaction, we extensively analyzed the binding modes of these compounds using in silico techniques, laying the groundwork for the discovery of novel LPAR1 antagonists.

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.

Emerging roles of lysophosphatidic acid receptor subtype 5 (LPAR5) in inflammatory diseases and cancer

Lysophosphatidic acid (LPA) is a bioactive lipid mediator that regulates a variety of cellular functions such as cell proliferation, migration, survival, calcium mobilization, cytoskeletal rearrangements, and neurite retraction. The biological actions of LPA are mediated by at least six G protein-coupled receptors known as LPAR1-6. Given that LPAR1-3 were among the first LPARs identified, the majority of research efforts have focused on understanding their biology. This review provides an in-depth discussion of LPAR5, which has recently emerged as a key player in regulating normal intestinal homeostasis and modulating pathological conditions such as pain, itch, inflammatory diseases, and cancer. We also present a chronological overview of the efforts made to develop compounds that target LPAR5 for use as tool compounds to probe or validate LPAR5 biology and therapeutic agents for the treatment of inflammatory diseases and cancer.

Gα13-Mediated Signaling Cascade Is Related to the Tau Pathology Caused by Anesthesia and Surgery in 5XFAD Transgenic Mice

BACKGROUND

Our previous studies indicated that anesthesia and surgery could aggravate cognitive impairment of 5XFAD transgenic (Tg) mice, and this aggravation was associated with tau hyperphosphorylation. We previously identified that GNA13 (the gene encoding Gα13) was a hub gene with tau hyperphosphorylation.

OBJECTIVE

This study aims to further investigate the mechanism that whether the Gα13-mediated signaling pathway acts as an instigator to regulate cofilin activation and autophagy impairment in this process.

METHODS

5XFAD Tg mice and their littermate (LM) mice were randomly allocated into four groups: LM Control group, LM Anesthesia/Surgery group, AD Control group, and AD Anesthesia/Surgery group. For mice in the Anesthesia/Surgery groups, abdominal surgery was performed under 1.4% isoflurane anesthesia followed by sustaining anesthetic inhalation for up to 2 h.

RESULTS

Compared with the AD Control group, protein levels of Gα13, ROCK2, LPAR5, and p-tau/tau46 ratio were increased, while p-cofilin/cofilin protein expression ratio was decreased in the AD Anesthesia/Surgery group. However, the differences in these protein levels were not significant among LM groups.

CONCLUSION

This study demonstrated that anesthesia and surgery might exacerbate p-tau accumulation in 5XFAD Tg mice but not in LM mice. And this might be closely related to cofilin activation via Gα13-mediated signaling cascade.

Endothelial Specific Deletion of Autotaxin Improves Stroke Outcomes

Autotaxin (ATX) is an extracellular secretory enzyme (lysophospholipase D) that catalyzes the hydrolysis of lysophosphatidyl choline to lysophosphatidic acid (LPA). The ATX-LPA axis is a well-known pathological mediator of liver fibrosis, metastasis in cancer, pulmonary fibrosis, atherosclerosis, and neurodegenerative diseases. Additionally, it is believed that LPA may cause vascular permeability. In ischemic stroke, vascular permeability leading to hemorrhagic transformation is a major limitation for therapies and an obstacle to stroke management. Therefore, in this study, we generated an endothelial-specific ATX deletion in mice (ERT2 ATX-/-) to observe stroke outcomes in a mouse stroke model to analyze the role of endothelial ATX. The AR2 probe and Evans Blue staining were used to perform the ATX activity and vascular permeability assays, respectively. Laser speckle imaging was used to observe the cerebral blood flow following stroke. In this study, we observed that stroke outcomes were alleviated with the endothelial deletion of ATX. Permeability and infarct volume were reduced in ERT2 ATX-/- mice compared to ischemia-reperfusion (I/R)-only mice. In addition, the cerebral blood flow was retained in ERT2 ATX-/- compared to I/R mice. The outcomes in the stroke model are alleviated due to the limited LPA concentration, reduced ATX concentration, and ATX activity in ERT2 ATX-/- mice. This study suggests that endothelial-specific ATX leads to increased LPA in the brain vasculature following ischemic-reperfusion and ultimately disrupts vascular permeability, resulting in adverse stroke outcomes.

Identification of immune associated potential molecular targets in proliferative diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes and causes of blindness in developed countries. Our study was designed to identify immune-related genes involved in the progression of proliferative diabetic retinopathy (PDR).

METHODS

The "GSE102485" dataset of neovascular membrane samples (NVMs) from type 1 and 2 diabetes mellitus patients was downloaded from the Gene Expression Omnibus database. Functional enrichment analyses, protein-protein interaction network (PPI) construction, and module analysis of immune pathways in NVMs and controls were conducted via Gene Set Enrichment Analysis and Metascape.

RESULTS

The significantly upregulated hallmark gene sets in DR2 and DR1 groups were involved in five immune pathways. Only CCR4, CXCR6, C3AR1, LPAR1, C5AR1, and P2RY14 were not previously reported in the context of PDR molecular pathophysiology. Except for P2RY14, all of the above were upregulated in retinal samples from experimental diabetes mouse models and human retina microvascular endothelial cells (HRMECs) treated with high glucose (HG) by quantitative Real Time Polymerase Chain Reaction (qRT-PCR).

CONCLUSION

The genes identified herein provide insight into immune-related differential gene expression during DR progression.

Correlation between Lpa, APO-A, APO-B, and Stenosis of Middle Cerebral Artery in Patients with Cerebral Ischemic Stroke

Ischemic stroke (CIS) is characterized by a high incidence, disability, and mortality. Numerous studies have demonstrated that intracranial arterial stenosis is an important pathological basis of CIS, and its main cause is atherosclerosis. Dyslipidemia is an important risk factor for atherosclerosis. Lysophosphatidic acid (Lpa), apolipoprotein -A(APO-A), and apolipoprotein -B(APO-B) proved to be significantly correlated with the severity of coronary artery disease. This study retrospectively collected the case data of 186 patients with CIS treated from May 2020 to May 2022 and explored the correlation between Lpa, APO-A, APO-B, and middle cerebral artery (MCA) stenosis in CIS patients.

Lysophosphatidic acid production from lysophosphatidylcholine by lysophospholipase D activity of autotaxin in plasma of women with normal and adverse pregnancies

To identify biomarker lipids causing preterm delivery, we focused on lysophosphatidylcholine (LPC) and lysophosphatidic acid (LPA). The results of liquid chromatography-tandem mass spectrometry revealed that plasma levels of LPCs and LPAs were higher in the first and third (T3) trimesters of human normal and adverse pregnancies than in the second trimester, suggesting the direct metabolic conversion of LPC to LPA by lysophospholipase D (lysoPLD) activity of autotaxin. The elevated LPC and LPA levels in women with preterm deliveries in T3 were higher than in women with term deliveries under normal pregnancy in T3. We measured lysoPLD activity of diluted sera of pregnant women by quantification of choline released from exogenous LPC, and found progressive increases of lysoPLD activities in women with normal and adverse pregnancies. Ratios of lysoPLD activities for linoleoyl LPC to that for palmitoyl LPC were found to be decreased in pregnant women compared to that in non-pregnant women. These results may be due to the altered patterns of endogenous modulators for autotaxin and the profiles of the bound metal ion.

Low Efficacy of Genetic Tests for the Diagnosis of Primary Lymphedema Prompts Novel Insights into the Underlying Molecular Pathways

Lymphedema is a chronic inflammatory disorder caused by ineffective fluid uptake by the lymphatic system, with effects mainly on the lower limbs. Lymphedema is either primary, when caused by genetic mutations, or secondary, when it follows injury, infection, or surgery. In this study, we aim to assess to what extent the current genetic tests detect genetic variants of lymphedema, and to identify the major molecular pathways that underlie this rather unknown disease. We recruited 147 individuals with a clinical diagnosis of primary lymphedema and used established genetic tests on their blood or saliva specimens. Only 11 of these were positive, while other probands were either negative (63) or inconclusive (73). The low efficacy of such tests calls for greater insight into the underlying mechanisms to increase accuracy. For this purpose, we built a molecular pathways diagram based on a literature analysis (OMIM, Kegg, PubMed, Scopus) of candidate and diagnostic genes. The PI3K/AKT and the RAS/MAPK pathways emerged as primary candidates responsible for lymphedema diagnosis, while the Rho/ROCK pathway appeared less critical. The results of this study suggest the most important pathways involved in the pathogenesis of lymphedema, and outline the most promising diagnostic and candidate genes to diagnose this disease.

Sesamol protects against liver fibrosis induced in rats by modulating lysophosphatidic acid receptor expression and TGF-β/Smad3 signaling pathway

The present study aimed to investigate the hepatoprotective effect of sesamol (SML), a nutritional phenolic compound obtained from sesame seeds, in liver fibrosis induced by thioacetamide (TAA) in rats and to explore the underlying mechanisms. Thirty-two male Sprague–Dawley rats were equally divided into four groups: control, TAA, TAA + SML 50 mg/kg, and TAA + SML 100 mg/kg groups. Liver functions and hepatic contents of glutathione (GSH) and malondialdehyde (MDA) were measured colorimetrically. Gene expressions of lysophosphatidic acid receptor (LPAR)-1 and -3, connective tissue growth factor (CTGF), transforming growth factor (TGF)-β1, small mothers against decapentaplegic (Smad)-3 and -7, α-smooth muscle actin (α-SMA), and cytokeratin 19 (CK19) were analyzed by qRT-PCR. Moreover, phosphorylated Smad3 (pSmad3) was quantified by ELISA. Additionally, TGF-β1, α-SMA, CK19, and vascular endothelial growth factor (VEGF) protein concentrations were semi-quantitatively analyzed by immunostaining of liver sections. SML treatment markedly improved liver index and liver functions. Moreover, SML protected against liver fibrosis in a dose-dependent manner as indicated by down-regulation of LPAR1, LPAR3, CTGF, TGF-β1/Smad3, and α-SMA expressions and a decrease in pSmad3 level, as well as an up-regulation of Smad7 expression. In addition, SML suppressed ductular reaction hinted by the decrease in CK19 expression. These results reveal the anti-fibrotic effect of SML against liver fibrosis that might be attributed to down-regulation of LPAR1/3 expressions, inhibition of TGF-β1/Smad3 pathway, and ductular reaction.

Recent Advancements in Antifibrotic Therapies for Regression of Liver Fibrosis

Cirrhosis is a severe form of liver fibrosis that results in the irreversible replacement of liver tissue with scar tissue in the liver. Environmental toxicity, infections, metabolic causes, or other genetic factors including autoimmune hepatitis can lead to chronic liver injury and can result in inflammation and fibrosis. This activates myofibroblasts to secrete ECM proteins, resulting in the formation of fibrous scars on the liver. Fibrosis regression is possible through the removal of pathophysiological causes as well as the elimination of activated myofibroblasts, resulting in the reabsorption of the scar tissue. To date, a wide range of antifibrotic therapies has been tried and tested, with varying degrees of success. These therapies include the use of growth factors, cytokines, miRNAs, monoclonal antibodies, stem-cell-based approaches, and other approaches that target the ECM. The positive results of preclinical and clinical studies raise the prospect of a viable alternative to liver transplantation in the near future. The present review provides a synopsis of recent antifibrotic treatment modalities for the treatment of liver cirrhosis, as well as a brief summary of clinical trials that have been conducted to date.

The ATX-LPA Axis Regulates Vascular Permeability during Cerebral Ischemic-Reperfusion

Endothelial permeability is a major complication that must be addressed during stroke treatment. Study of the mechanisms underlying blood−brain barrier (BBB) disruption and management of the hypoxic stress-induced permeability of the endothelium following reperfusion are both urgently needed for stroke management. Lysophosphatidic acid (LPA), a bioactive lipid essential for basic cellular functions, causes unfavorable outcomes during stroke progression. LPA-producing enzyme autotaxin (ATX) is regulated in ischemic stroke. We used an electrical cell-substrate impedance sensor (ECIS) to measure endothelial permeability. Mitochondrial bioenergetics were obtained using a Seahorse analyzer. AR-2 probe fluorescence assay was used to measure ATX activity. LPA increased endothelial permeability and reduced junctional protein expression in mouse brain microvascular endothelial cells (MBMEC). LPA receptor inhibitors Ki16425 and AM095 attenuated the LPA-induced changes in the endothelial permeability and junctional proteins. LPA significantly diminished mitochondrial function in MBMEC. ATX was upregulated (p < 0.05) in brain microvascular endothelial cells under hypoxic reperfusion. ATX activity and permeability were attenuated with the use of an ATX inhibitor in a mouse stroke model. The upregulation of ATX with hypoxic reperfusion leads to LPA production in brain endothelial cells favoring permeability. Inhibition of the ATX−LPA−LPAR axis could be therapeutically targeted in stroke to achieve better outcomes.

Influence of the autotaxin-lysophosphatidic acid axis on cellular function and cytokine expression in different breast cancer cell lines

Previous studies provide high evidence that autotaxin (ATX)-lysophosphatidic acid (LPA) signaling through LPA receptors (LPAR) plays an important role in breast cancer initiation, progression, and invasion. However, its specific role in different breast cancer cell lines remains to be fully elucidated to offer improvements in targeted therapies. Within this study, we analyzed in vitro the effect of LPA 18:1 and the LPAR1, LPAR3 (and LPAR2) inhibitor Ki16425 on cellular functions of different human breast cancer cell lines (MDA-MB-231, MDA-MB-468, MCF-7, BT-474, SKBR-3) and the human breast epithelial cell line MCF-10A, as well as Interleukin 8 (IL-8), Interleukin 6 (IL-6) and tumor necrosis factor (TNF)-alpha cytokine secretion after LPA-incubation. ATX-LPA signaling showed a dose-dependent stimulatory effect especially on cellular functions of triple-negative and luminal A breast cancer cell lines. Ki16425 inhibited the LPA-induced stimulation of triple-negative breast cancer and luminal A cell lines in variable intensity depending on the functional assay, indicating the interplay of different LPAR in those assays. IL-8, IL-6 and TNF-alpha secretion was induced by LPA in MDA-MB-468 cells. This study provides further evidence about the role of the ATX-LPA axis in different breast cancer cell lines and might contribute to identify subtypes suitable for a future targeted therapy of the ATX-LPA axis.

Membrane lipid raft homeostasis is directly linked to neurodegeneration

Age-associated neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD) and Alzheimer's disease (AD) are an unmet health need, with significant economic and societal implications, and an ever-increasing prevalence. Membrane lipid rafts (MLRs) are specialised plasma membrane microdomains that provide a platform for intracellular trafficking and signal transduction, particularly within neurons. Dysregulation of MLRs leads to disruption of neurotrophic signalling and excessive apoptosis which mirrors the final common pathway for neuronal death in ALS, PD and AD. Sphingomyelinase (SMase) and phospholipase (PL) enzymes process components of MLRs and therefore play central roles in MLR homeostasis and in neurotrophic signalling. We review the literature linking SMase and PL enzymes to ALS, AD and PD with particular attention to attractive therapeutic targets, where functional manipulation has been successful in preclinical studies. We propose that dysfunction of these enzymes is upstream in the pathogenesis of neurodegenerative diseases and to support this we provide new evidence that ALS risk genes are enriched with genes involved in ceramide metabolism (P=0.019, OR = 2.54, Fisher exact test). Ceramide is a product of SMase action upon sphingomyelin within MLRs, and it also has a role as a second messenger in intracellular signalling pathways important for neuronal survival. Genetic risk is necessarily upstream in a late age of onset disease such as ALS. We propose that manipulation of MLR structure and function should be a focus of future translational research seeking to ameliorate neurodegenerative disorders.

The development of modulators for lysophosphatidic acid receptors: A comprehensive review

Lysophosphatidic acids (LPAs) are bioactive phospholipids implicated in a wide range of cellular activities that regulate a diverse array of biological functions. They recognize two types of G protein-coupled receptors (LPARs): LPA_1-3 receptors and LPA_4-6 receptors that belong to the endothelial gene (EDG) family and non-endothelial gene family, respectively. In recent years, the LPA signaling pathway has captured an increasing amount of attention because of its involvement in various diseases, such as idiopathic pulmonary fibrosis, cancers, cardiovascular diseases and neuropathic pain, making it a promising target for drug development. While no drugs targeting LPARs have been approved by the FDA thus far, at least three antagonists have entered phase Ⅱ clinical trials for idiopathic pulmonary fibrosis (BMS-986020 and BMS-986278) and systemic sclerosis (SAR100842), and one radioligand (BMT-136088/¹⁸F-BMS-986327) has entered phase Ⅰ clinical trials for positron emission tomography (PET) imaging of idiopathic pulmonary fibrosis. This article provides an extensive review on the current status of ligand development targeting LPA receptors to modulate LPA signaling and their therapeutic potential in various diseases.

Lysophosphatidic acid receptor 6 regulated by miR-27a-3p attenuates tumor proliferation in breast cancer

Purpose

Lysophosphatidic acid (LPA) is a bioactive molecule which participates in many physical and pathological processes. Although LPA receptor 6 (LPAR6), the last identified LPA receptor, has been reported to have diverse effects in multiple cancers, including breast cancer, its effects and functioning mechanisms are not fully known.

Methods

Multiple public databases were used to investigate the mRNA expression of LPAR6, its prognostic value, and potential mechanisms in breast cancer. Western blotting was performed to validate the differential expression of LPAR6 in breast cancer tissues and their adjacent tissues. Furthermore, in vitro experiments were used to explore the effects of LPAR6 on breast cancer. Additionally, TargetScan and miRWalk were used to identify potential upstream regulating miRNAs and validated the relationship between miR-27a-3p and LPAR6 via real-time polymerase chain reaction and an in vitro rescue assay.

Results

LPAR6 was significantly downregulated in breast cancer at transcriptional and translational levels. Decreased LPAR6 expression in breast cancer is significantly correlated with poor overall survival, disease-free survival, and distal metastasis-free survival, particularly for hormone receptor-positive patients, regardless of lymph node metastatic status. In vitro gain and loss-of-function assays indicated that LPAR6 attenuated breast cancer cell proliferation. The analyses of TCGA and METABRIC datasets revealed that LPAR6 may regulate the cell cycle signal pathway. Furthermore, the expression of LPAR6 could be positively regulated by miR-27a-3p. The knockdown of miR-27a-3p increased cell proliferation, and ectopic expression of LPAR6 could partly rescue this phenotype.

Conclusion

LPAR6 acts as a tumor suppressor in breast cancer and is positively regulated by miR-27a-3p.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12094-021-02704-8.

Driving fibrosis in neuromuscular diseases: Role and regulation of Connective tissue growth factor (CCN2/CTGF)

Connective tissue growth factor or cellular communication network 2 (CCN2/CTGF) is a matricellular protein member of the CCN family involved in several crucial biological processes. In skeletal muscle, CCN2/CTGF abundance is elevated in human muscle biopsies and/or animal models for diverse neuromuscular pathologies, including muscular dystrophies, neurodegenerative disorders, muscle denervation, and muscle overuse. In this context, CCN2/CTGF is deeply involved in extracellular matrix (ECM) modulation, acting as a strong pro-fibrotic factor that promotes excessive ECM accumulation. Reducing CCN2/CTGF levels or biological activity in pathological conditions can decrease fibrosis, improve muscle architecture and function. In this work, we summarize information about the role of CCN2/CTGF in fibrosis associated with neuromuscular pathologies and the mechanisms and signaling pathways that regulate their expression in skeletal muscle.

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.

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.

Solution NMR Structure of the SH3 Domain of Human Caskin1 Validates the Lack of a Typical Peptide Binding Groove and Supports a Role in Lipid Mediator Binding

SH3 domains constitute an important class of protein modules involved in a variety of cellular functions. They participate in protein-protein interactions via their canonical ligand binding interfaces composed of several evolutionarily conserved aromatic residues forming binding grooves for typical (PxxP) and atypical (PxxxPR, RxxK, RKxxY) binding motifs. The calcium/calmodulin-dependent serine protein kinase (CASK)-interacting protein 1, or Caskin1, a multidomain scaffold protein regulating the cortical actin filaments, is enriched in neural synapses in mammals. Based on its known interaction partners and knock-out animal studies, Caskin1 may play various roles in neural function and it is thought to participate in several pathological processes of the brain. Caskin1 has a single, atypical SH3 domain in which key aromatic residues are missing from the canonical binding groove. No protein interacting partner for this SH3 domain has been identified yet. Nevertheless, we have recently demonstrated the specific binding of this SH3 domain to the signaling lipid mediator lysophospatidic acid (LPA) in vitro. Here we report the solution NMR structure of the human Caskin1 SH3 domain and analyze its structural features in comparison with other SH3 domains exemplifying different strategies in target selectivity. The key differences revealed by our structural study show that the canonical binding groove found in typical SH3 domains accommodating proline-rich motifs is missing in Caskin1 SH3, most likely excluding a bona fide protein target for the domain. The LPA binding site is distinct from the altered protein binding groove. We conclude that the SH3 domain of Caskin1 might mediate the association of Caskin1 with membrane surfaces with locally elevated LPA content.

Platelet-derived lysophosphatidic acid mediated LPAR1 activation as a therapeutic target for osteosarcoma metastasis

Osteosarcoma is the most common primary malignant bone cancer, with high rates of pulmonary metastasis. Osteosarcoma patients with pulmonary metastasis have worse prognosis than those with localized disease, leading to dramatically reduced survival rates. Therefore, understanding the biological characteristics of metastatic osteosarcoma and the molecular mechanisms of invasion and metastasis of osteosarcoma cells will lead to the development of innovative therapeutic intervention for advanced osteosarcoma. Here, we identified that osteosarcoma cells commonly exhibit high platelet activation-inducing characteristics, and molecules released from activated platelets promote the invasiveness of osteosarcoma cells. Given that heat-denatured platelet releasate maintained the ability to promote osteosarcoma invasion, we focused on heat-tolerant molecules, such as lipid mediators in the platelet releasate. Osteosarcoma-induced platelet activation leads to abundant lysophosphatidic acid (LPA) release. Exposure to LPA or platelet releasate induced morphological changes and increased invasiveness of osteosarcoma cells. By analyzing publicly available transcriptome datasets and our in-house osteosarcoma patient-derived xenograft tumors, we found that LPA receptor 1 (LPAR1) is notably upregulated in osteosarcoma. LPAR1 gene KO in osteosarcoma cells abolished the platelet-mediated osteosarcoma invasion in vitro and the formation of early pulmonary metastatic foci in experimental pulmonary metastasis models. Of note, the pharmacological inhibition of LPAR1 by the orally available LPAR1 antagonist, ONO-7300243, prevented pulmonary metastasis of osteosarcoma in the mouse models. These results indicate that the LPA-LPAR1 axis is essential for the osteosarcoma invasion and metastasis, and targeting LPAR1 would be a promising therapeutic intervention for advanced osteosarcoma.

Alteration of circRNA and lncRNA expression profile in exosomes derived from periodontal ligament stem cells undergoing osteogenic differentiation

OBJECTIVE

This study investigated circRNA and lncRNA expression profile in exosomes derived from periodontal ligament stem cell (PDLSC) before and after its osteogenic differentiation.

DESIGN

Exosomes derived from PDLSCs before (EX0) and after osteogenic induction for 5 (EX5) and 7 (EX7) days were harvested and exosomal circRNAs and lncRNAs were analyzed by RNA sequencing. Certain RNAs showing significantly altered expression were selected for qRT-PCR verification. The circRNA-miRNA-mRNA network and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed.

RESULTS

All groups of exosomes showed typical characteristics under nanoparticle tracking analysis, flow cytometry assay and transmission electron microscopy. 69-557 circRNAs and 2907-11581 lncRNAs were found in EX0, EX5 and EX7, which were broadly distributed across the 24 pairs of human chromosomes. Compared with EX0, 3 circRNAs and 2 lncRNAs were up-regulated and 39 circRNAs and 5 lncRNAs down-regulated consistently through out of EX5 and EX7, p < 0.05. qRT-PCR confirmed certain those consistently expressed RNAs, such as circ lysophosphatidic acid receptor 1 (LPAR1). KEGG analysis showed that those consistent expressed RNAs closely related to TGF-beta pathway, MAPK pathway, mTOR pathway and FoxO signaling pathways regulating pluripotency of stem cells.

CONCLUSIONS

Exosomal circRNAs and lncRNAs had significant expression changes during the early phase of osteogenic differentiation of PDLSCs. Further study would be taken for understanding the roles of exosomal circRNAs and lncRNAs playing in osteogenic differentiation of PDLSCs.

Immune and Metabolic Interactions of Human Erythrocytes: A Molecular Perspective

Apart from their main function as oxygen carriers in vertebrates, erythrocytes are also involved in immune regulation. By circulating throughout the body, the erythrocytes are exposed and interact with tissues that are damaged as a result of a disease. In this study, we summarize the literature regarding the contribution of erythrocytes to immune regulation and metabolism. Under the circumstances of a disease state, the erythrocytes may lose their antioxidant capacity and release Damage Associated Molecular Patterns, resulting in the regulation of innate and adaptive immunity. In addition, the erythrocytes scavenge and affect the levels of chemokines, circulating cell-free mtDNA, and C3b attached immune complexes. Furthermore, through surface molecules, erythrocytes control the function of T lymphocytes, macrophages, and dendritic cells. Through an array of enzymes, red blood cells contribute to the pool of blood's bioactive lipids. Finally, the erythrocytes contribute to reverse cholesterol transport through various mechanisms. Our study is highlighting overlooked molecular interactions between erythrocytes and immunity and metabolism, which could lead to the discovery of potent therapeutic targets for immunometabolic diseases.