Lysophosphatidic acid effects on atherosclerosis and thrombosis

Large-scale, comprehensive plasma metabolomic analyses reveal potential biomarkers for the diagnosis of early-stage coronary atherosclerosis

BACKGROUND

Coronary atherosclerosis (CAS) is a prevalent and chronic life-threatening disease. However, the detection of CAS at an early stage is difficult because of the lack of effective noninvasive diagnostic methods. The present study aimed to characterize the plasma metabolome of early-stage CAS patients to discover metabolomic biomarkers, develop a novel metabolite-based model for accurate noninvasive diagnosis of early-stage CAS, and explore the underlying metabolic mechanisms involved.

METHODS

A total of 100 patients with early-stage CAS and 120 age- and sex-matched control subjects were recruited from the Chinese Han population and further randomly divided into training (n = 120) and test sets (n = 100). The metabolomic profiles of the plasma samples were analyzed by an integrated untargeted liquid chromatography-mass spectrometry approach, including two separation modes and two ionization modes. Univariate and multivariate statistical analyses were employed to identify potential biomarkers and construct an early-stage CAS diagnostic model.

RESULTS

The integrated analytical method established herein improved metabolite coverage compared with single chromatographic separation and MS ionization mode. A total of 80 metabolites were identified as potential biomarkers of early-stage CAS, and these metabolites were mainly involved in glycerophospholipid, fatty acid, sphingolipid, and amino acid metabolism. An effective diagnostic model for early-stage CAS was established, incorporating 11 metabolites and achieving areas under the receiver operating characteristic curve (AUCs) of 0.984 and 0.908 in the training and test sets, respectively.

CONCLUSIONS

Our study not only successfully developed an effective noninvasive diagnostic model for identifying early-stage CAS but also provided novel insights into the pathogenesis of CAS.

Spatial Metabolomics Identifies LPC(18:0) and LPA(18:1) in Advanced Atheroma With Translation to Plasma for Cardiovascular Risk Estimation

BACKGROUND

The metabolic alterations occurring within the arterial architecture during atherosclerosis development remain poorly understood, let alone those particular to each arterial tunica. We aimed first to identify, in a spatially resolved manner, the specific metabolic changes in plaque, media, adventitia, and cardiac tissue between control and atherosclerotic murine aortas. Second, we assessed their translatability to human tissue and plasma for cardiovascular risk estimation.

METHODS

In this observational study, mass spectrometry imaging (MSI) was applied to identify region-specific metabolic differences between atherosclerotic (n=11) and control (n=11) aortas from low-density lipoprotein receptor-deficient mice, via histology-guided virtual microdissection. Early and advanced plaques were compared within the same atherosclerotic animals. Progression metabolites were further analyzed by MSI in 9 human atherosclerotic carotids and by targeted mass spectrometry in human plasma from subjects with elective coronary artery bypass grafting (cardiovascular risk group, n=27) and a control group (n=27).

RESULTS

MSI identified 362 local metabolic alterations in atherosclerotic mice (log2 fold-change ≥1.5; P≤0.05). The lipid composition of cardiac tissue is altered during atherosclerosis development and presents a generalized accumulation of glycerophospholipids, except for lysolipids. Lysolipids (among other glycerophospholipids) were found at elevated levels in all 3 arterial layers of atherosclerotic aortas. LPC(18:0) (lysophosphatidylcholine; P=0.024) and LPA(18:1) (lysophosphatidic acid; P=0.025) were found to be significantly elevated in advanced plaques as compared with mouse-matched early plaques. Higher levels of both lipid species were also observed in fibrosis-rich areas of advanced- versus early-stage human samples. They were found to be significantly reduced in human plasma from subjects with elective coronary artery bypass grafting (P<0.001 and P=0.031, respectively), with LPC(18:0) showing significant association with cardiovascular risk (odds ratio, 0.479 [95% CI, 0.225-0.883]; P=0.032) and diagnostic potential (area under the curve, 0.778 [95% CI, 0.638-0.917]).

CONCLUSIONS

An altered phospholipid metabolism occurs in atherosclerosis, affecting both the aorta and the adjacent heart tissue. Plaque-progression lipids LPC(18:0) and LPA(18:1), as identified by MSI on tissue, reflect cardiovascular risk in human plasma.

Melatonin and TGF-β-Mediated Release of Extracellular Vesicles

The immune system, unlike other systems, must be flexible and able to "adapt" to fully cope with lurking dangers. The transition from intracorporeal balance to homeostasis disruption is associated with activation of inflammatory signaling pathways, which causes modulation of the immunology response. Chemotactic cytokines, signaling molecules, and extracellular vesicles act as critical mediators of inflammation and participate in intercellular communication, conditioning the immune system's proper response. Among the well-known cytokines allowing for the development and proper functioning of the immune system by mediating cell survival and cell-death-inducing signaling, the tumor necrosis factor α (TNF-α) and transforming growth factor β (TGF-β) are noteworthy. The high bloodstream concentration of those pleiotropic cytokines can be characterized by anti- and pro-inflammatory activity, considering the powerful anti-inflammatory and anti-oxidative stress capabilities of TGF-β known from the literature. Together with the chemokines, the immune system response is also influenced by biologically active chemicals, such as melatonin. The enhanced cellular communication shows the relationship between the TGF-β signaling pathway and the extracellular vesicles (EVs) secreted under the influence of melatonin. This review outlines the findings on melatonin activity on TGF-β-dependent inflammatory response regulation in cell-to-cell communication leading to secretion of the different EV populations.

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.

Lysophosphatidic Acid Promotes Epithelial-Mesenchymal Transition in Kidney Epithelial Cells via the LPAR1/MAPK-AKT/KLF5 Signaling Pathway in Diabetic Nephropathy

The epithelial–mesenchymal transition (EMT) is a differentiation process associated with fibrogenesis in diabetic nephropathy (DN). Lysophosphatidic acid (LPA) is a small, naturally occurring glycerophospholipid implicated in the pathogenesis of DN. In this study, we investigated the role of LPA/LPAR1 signaling in the EMT of tubular cells as well as the underlying mechanisms. We observed a decrease in E-cadherin and an increase in vimentin expression levels in the kidney tubules of diabetic db/db mice, and treatment with ki16425 (LPAR1/3 inhibitor) inhibited the expression of these EMT markers. Ki16425 treatment also decreased the expression levels of the fibrotic factors fibronectin and alpha-smooth muscle actin (α-SMA) in db/db mice. Similarly, we found that LPA decreased E-cadherin expression and increased vimentin expression in HK-2 cells, which was reversed by treatment with ki16425 or AM095 (LPAR1 inhibitor). In addition, the expression levels of fibronectin and α-SMA were increased by LPA, and this effect was reversed by treatment with ki16425 and AM095 or by LPAR1 knockdown. Moreover, LPA induced the expression of the transcription factor, Krüppel-like factor 5 (KLF5), which was decreased by AM095 treatment or LPAR1 knockdown. The expression levels of EMT markers and fibrotic factors induced by LPA were decreased upon KLF5 knockdown in HK-2 cells. Inhibition of the extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and serine-threonine kinase (AKT) pathways decreased LPA-induced expression of KLF5 and EMT markers. In conclusion, these data suggest that LPA contributes to the pathogenesis of diabetic nephropathy by inducing EMT and renal tubular fibrosis via regulation of KLF5 through the LPAR1.

Autotaxin Activity in Chronic Subdural Hematoma: A Prospective Clinical Study

Autotaxin (ATX) is the ectoenzyme producing the bulk of lysophosphatidic acid (LPA) in circulation. ATX and LPA-mediated signaling (the ATX-LPA axis) play critical roles in the vascular and nervous system development. In adults, this axis contributes to diverse processes, including coagulation, inflammation, fibroproliferation and angiogenesis under physiological and/or pathophysiological conditions. Given evidence implicating several of these processes in chronic subdural hematoma (CSDH) pathogenesis and development, we assessed ATX activity in CSDH patients. Twenty-eight patients were recruited. Blood and hematoma fluid were collected. Enzymatic assays were used to establish serum and hematoma ATX activity. Enzyme-linked immunosorbent assays were used to establish hematoma beta trace (BT) levels, a cerebrospinal fluid (CSF) marker, in a hematoma. ATX activity was nearly three folds higher in hematoma compared to serum (P < 0.001). There was no significant correlation between BT levels and ATX activity in a hematoma. The present results show, for the first time, that ATX is catalytically active in the hematoma fluid of CSDH patients. Moreover, our findings of significantly elevated ATX activity in hematoma compared to serum, implicate the ATX-LPA axis in CSDH pathophysiology. The CSF origin of ATX could not be inferred with the present results. Additional research is warranted to establish the significance of the ATX-LPA axis in CSDH and its potential as a biomarker and/or therapeutic target.

Crocin ameliorates atherosclerosis by promoting the reverse cholesterol transport and inhibiting the foam cell formation via regulating PPARγ/LXR-α

Crocin (CRO) is feasible in alleviating atherosclerosis (AS), the mechanism of which was therefore explored in the study. High-fat diet (HFD)-induced apolipoprotein E-deficient (ApoE^−/−) mice and lysophosphatidic acid (LPA)-treated macrophages received CRO treatment. Treated macrophage viability was determined via MTT assay. In both murine and macrophage, the lipid level and total Cholesterol/Cholesteryl l Ester (TC/CE) levels were quantified by oil-red-O staining and ELISA, respectively. Lipid droplet, aortic plaque formation and collagen deposition were detected via Oil-red-O staining, hematoxylin–eosin staining and Masson staining, respectively. Liver X Receptor-α (LXR-α), Peroxisome Proliferator-Activated Receptor γ (PPARγ), CD68, PCSK9, CD36, ATP Binding Cassette Subfamily A Member 1 (ABCA1), phosphorylated (p)-AKT, and AKT expressions were detected via Western blot, the former three also being detected using Immunohistochemistry and the first being measured by qRT-PCR. CRO decreased HFD-induced weight gain, ameliorated the abnormal serum lipid levels of HFD-treated mice, and inhibited aortic plaque formation and lipid deposition, and increased collagen fibers, with upregulated high-density lipoprotein-cholesterol (HDL-C) and downregulated TC and low-density lipoprotein-cholesterol (LDL-C). CRO alleviated the HFD-induced upregulations of CD68, PCSK9 and CD36 as well as downregulations of PPARγ/LXR-α, ABCA1 and AKT phosphorylation. In LPA-treated macrophages, CRO alone exerted no effect on the viability yet inhibited the lipid droplets formation and downregulated TC/CE levels. Silent LXR-α reversed the effect of CRO on the lipid droplets formation and levels of lipid metabolism-related factors. CRO ameliorated AS by inhibiting foam cells formation and promoting reverse cholesterol transport via PPARγ/LXR-α.

Preventing the Increase in Lysophosphatidic Acids: A New Therapeutic Target in Pulmonary Hypertension?

Cardiovascular diseases (CVD) are the leading cause of premature death and disability in humans that are closely related to lipid metabolism and signaling. This study aimed to assess whether circulating lysophospholipids (LPL), lysophosphatidic acids (LPA) and monoacylglycerols (MAG) may be considered as potential therapeutic targets in CVD. For this objective, plasma levels of 22 compounds (13 LPL, 6 LPA and 3 MAG) were monitored by liquid chromatography coupled with tandem mass spectrometry (HPLC/MS²) in different rat models of CVD, i.e., angiotensin-II-induced hypertension (HTN), ischemic chronic heart failure (CHF) and sugen/hypoxia(SuHx)-induced pulmonary hypertension (PH). On one hand, there were modest changes on the monitored compounds in HTN (LPA 16:0, 18:1 and 20:4, LPC 16:1) and CHF (LPA 16:0, LPC 18:1 and LPE 16:0 and 18:0) models compared to control rats but these changes were no longer significant after multiple testing corrections. On the other hand, PH was associated with important changes in plasma LPA with a significant increase in LPA 16:0, 18:1, 18:2, 20:4 and 22:6 species. A deleterious impact of LPA was confirmed on cultured human pulmonary smooth muscle cells (PA-SMCs) with an increase in their proliferation. Finally, plasma level of LPA(16:0) was positively associated with the increase in pulmonary artery systolic pressure in patients with cardiac dysfunction. This study demonstrates that circulating LPA may contribute to the pathophysiology of PH. Additional experiments are needed to assess whether the modulation of LPA signaling in PH may be of interest.

Lysophosphatidic acid species are associated with exacerbation in chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) exacerbations are heterogenous and profoundly impact the disease trajectory. Bioactive lipid lysophosphatidic acid (LPA) has been implicated in airway inflammation but the significance of LPA in COPD exacerbation is not known. The aim of the study was to investigate the utility of serum LPA species (LPA16:0, 18:0, 18:1, 18:2, 20:4) as biomarkers of COPD exacerbation.

PATIENTS AND METHODS

LPA species were measured in the baseline placebo sera of a COPD randomized controlled trial. Tertile levels of each LPA were used to assign patients into biomarker high, medium, and low subgroups. Exacerbation rate and risk were compared among the LPA subgroups.

RESULTS

The levels of LPA species were intercorrelated (rho 0.29-0.91). Patients with low and medium levels of LPA (LPA16:0, 20:4) had significantly higher exacerbation rate compared to the respective LPA-high patients [estimated rate per patient per year (95% CI)]: LPA16:0-low = 1.2 (0.8-1.9) (p = 0.019), LPA16:0-medium = 1.3 (0.8-2.0) (p = 0.013), LPA16:0-high = 0.5 (0.2-0.9); LPA20:4-low = 1.4 (0.9-2.1) (p = 0.0033), LPA20:4-medium = 1.2 (0.8-1.8) (p = 0.0089), LPA20:4-high = 0.4 (0.2-0.8). These patients also had earlier time to first exacerbation (hazard ratio (95% CI): LPA16:0-low = 2.6 (1.1-6.0) (p = 0.028), LPA16:0-medium = 2.7 (1.2-6.3) (p = 0.020); LPA20.4-low = 2.8 (1.2-6.6) (p = 0.017), LPA20:4-medium = 2.7 (1.2-6.4) (p = 0.021). Accordingly, these patients had a significant increased exacerbation risk compared to the respective LPA-high subgroups [odd ratio (95% CI)]: LPA16:0-low = 3.1 (1.1-8.8) (p = 0.030), LPA16:0-medium = 3.0 (1.1-8.3) (p = 0.031); LPA20:4-low = 3.8 (1.3-10.9) (p = 0.012), LPA20:4-medium = 3.3 (1.2-9.5) (p = 0.025). For the other LPA species (LPA18:0, 18:1, 18:2), the results were mixed; patients with low and medium levels of LPA18:0 and 18:2 had increased exacerbation rate, but only LPA18:0-low patients had significant increase in exacerbation risk and earlier time to first exacerbation compared to the LPA18:0-high subgroup.

CONCLUSIONS

The study provided evidence of association between systemic LPA levels and exacerbation in COPD. Patients with low and medium levels of specific LPA species (LPA16:0, 20:4) had increased exacerbation rate, risk, and earlier time to first exacerbation. These non-invasive biomarkers may aid in identifying high risk patients with dysregulated LPA pathway to inform risk management and drug development.

Disrupted Blood-Brain Barrier and Mitochondrial Impairment by Autotaxin-Lysophosphatidic Acid Axis in Postischemic Stroke

Background The loss of endothelial integrity increases the risk of intracerebral hemorrhage during ischemic stroke. Adjunct therapeutic targets for reperfusion in ischemic stroke are in need to prevent blood-brain barrier disruption. Recently, we have shown that endothelial permeability is mediated by lysophosphatidic acid (LPA), but the role of autotaxin, which produces LPA, remains unclear in stroke. We investigate whether autotaxin/LPA axis regulates blood-brain barrier integrity after cerebral ischemia. Methods and Results Ischemic stroke was induced in mice by middle cerebral artery occlusion for 90 minutes, followed by 24-hour reperfusion. The therapeutic efficacy of autotaxin/LPA receptor blockade was evaluated using triphenyl tetrazolium chloride staining, Evans blue permeability, infrared imaging, mass spectrometry, and XF24 analyzer to evaluate blood-brain barrier integrity, autotaxin activity, and mitochondrial bioenergetics. In our mouse model of ischemic stroke, the mRNA levels of autotaxin were elevated 1.7-fold following the cerebral ischemia and reperfusion (I/R) group compared with the sham. The enzymatic activity of autotaxin was augmented by 4-fold in the I/R group compared with the sham. Plasma and brain tissues in I/R group showed elevated LPA levels. The I/R group also demonstrated mitochondrial dysfunction, as evidenced by decreased (P<0.01) basal oxygen consumption rate, mitochondrial ATP production, and spare respiratory capacity. Treatment with autotaxin inhibitors (HA130 or PF8380) or autotaxin/LPA receptor inhibitor (BrP-LPA) rescued endothelial permeability and mitochondrial dysfunction in I/R group. Conclusions Autotaxin-LPA signaling blockade attenuates blood-brain barrier disruption and mitochondrial function following I/R, suggesting targeting this axis could be a new therapeutic approach toward treating ischemic stroke.

Hypercholesterolemia and Lymphatic Defects: The Chicken or the Egg?

Lymphatic vessels are necessary for maintaining tissue fluid balance, trafficking of immune cells, and transport of dietary lipids. Growing evidence suggest that lymphatic functions are limited under hypercholesterolemic conditions, which is closely related to atherosclerotic development involving the coronary and other large arteries. Indeed, ablation of lymphatic systems by Chy-mutation as well as depletion of lymphangiogenic factors, including vascular endothelial growth factor-C and -D, in mice perturbs lipoprotein composition to augment hypercholesterolemia. Several investigations have reported that periarterial microlymphatics were attracted by atheroma-derived lymphangiogenic factors, which facilitated lymphatic invasion into the intima of atherosclerotic lesions, thereby modifying immune cell trafficking. In contrast to the lipomodulatory and immunomodulatory roles of the lymphatic systems, the critical drivers of lymphangiogenesis and the details of lymphatic insults under hypercholesterolemic conditions have not been fully elucidated. Interestingly, cholesterol-lowering trials enable hypercholesterolemic prevention of lymphatic drainage in mice; however, a causal relationship between hypercholesterolemia and lymphatic defects remains elusive. In this review, the contribution of aberrant lymphangiogenesis and lymphatic cholesterol transport to hypercholesterolemic atherosclerosis was highlighted. The causal relationship between hypercholesterolemia and lymphatic insults as well as the current achievements in the field were discussed.

TRPV1 Ion Channel: Structural Features, Activity Modulators, and Therapeutic Potential

Although TRPV1 ion channel has been attracting researchers' attention for many years, its functions in animal organisms, the principles of regulation, and the involvement in pathological processes have not yet been fully clarified. Mutagenesis experiments and structural studies have identified the structural features of the channel and binding sites for its numerous ligands; however, these studies are far from conclusion. This review summarizes recent achievements in the TRPV1 research with special focus on structural and functional studies of the channel and on its ligands, which are extremely diverse in their nature and interaction specificity to TRPV1. Particular attention was given to the effects of numerous endogenous agonists and antagonists that can fine-tune the channel sensitivity to its usual activators, such as capsaicin, heat, acids, or their combination. In addition to the pain sensing not covered in this review, the TRPV1 channel was found to be involved in the regulation of many important physiological and pathological processes and, therefore, can be considered as a promising therapeutic target in the treatment of various diseases, such as pneumonia, ischemia, diabetes, epilepsy, schizophrenia, psoriasis, etc.

The lysophosphatidic acid axis in fibrosis: Implications for glaucoma

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

Mechanosensitive smooth muscle cell phenotypic plasticity emerging from a null state and the balance between Rac and Rho

Reversible differentiation of vascular smooth muscle cells (VSMCs) plays a critical role in vascular biology and disease. Changes in VSMC differentiation correlate with stiffness of the arterial extracellular matrix (ECM), but causal relationships remain unclear. We show that VSMC plasticity is mechanosensitive and that both the de-differentiated and differentiated fates are promoted by the same ECM stiffness. Differential equations developed to model this behavior predicted that a null VSMC state generates the dual fates in response to ECM stiffness. Direct measurements of cellular forces, proliferation, and contractile gene expression validated these predictions and showed that fate outcome is mediated by Rac-Rho homeostasis. Rac, through distinct effects on YAP and TAZ, is required for both fates. Rho drives the contractile state alone, so its level of activity, relative to Rac, drives phenotypic choice. Our results show how the cellular response to a single ECM stiffness generates bi-stability and VSMC plasticity.

Reversible differentiation/de-differentiation of smooth muscle cells plays a critical role in vascular biology and disease. Talwar et al. show that these differentiated and de-differentiated phenotypes emerge from a null state that is regulated by ECM stiffness and bidirectional effects of Rac on YAP and TAZ transcriptional coregulators.

"Modeling-Prediction" Strategy for Deep Profiling of Lysophosphatidic Acids by Liquid Chromatography-Mass Spectrometry: Exploration Biomarkers of Breast Cancer

Lysophosphatidic acids (LPAs) are important bioactive phospholipids consisting of various species involved in a wide array of physiological and pathological processes. However, LPAs were rarely identified in untargeted lipidomics studies because of the incompatibility with analytical methods. Moreover, in targeted studies, the coverages of LPAs remained unsatisfactorily low due to the limitation of reference standards. Herein, a "modeling-prediction" workflow for deep profiling of LPAs by liquid chromatography-mass spectrometry was developed. Multiple linear regression models of qualitative and quantitative parameters were established according to features of fatty acyl tails of the commercial standards to predict the corresponding parameters for unknown LPAs. Then 72 multiple reaction monitoring (MRM) transitions were monitored simultaneously and species of LPA 14:0, LPA 16:1, LPA 18:3, LPA 20:3 and LPA 20:5 were firstly characterized and quantified in plasma. Finally, the workflow was applied to explore the changes of LPAs in plasma of breast cancer patients compared with healthy volunteers. Multi-LPAs indexes with strong diagnostic ability for breast cancer were identified successfully using Student's t- test, orthogona partial least-squares discrimination analysis (OPLS-DA) and logistic regression- receiver operating characteristic (ROC) curve analysis. The proposed workflow with high sensitivity, high accuracy, high coverage and reliable identification would be a powerful complement to untargeted lipidomics and shed a light on the analysis of other lipids.

TRPV1 expressed throughout the arterial circulation regulates vasoconstriction and blood pressure

KEY POINTS

The functional roles of the capsaicin receptor, TRPV1, outside of sensory nerves are unclear. We mapped TRPV1 in the mouse circulation, revealing extensive expression in the smooth muscle of resistance arterioles supplying skeletal muscle, heart and adipose tissue.  Activation of TRPV1 in vascular myocytes constricted arteries, reduced coronary flow in isolated hearts and increased systemic blood pressure. These functional effects were retained after sensory nerve ablation, indicating specific signalling by arterial TRPV1.  TRPV1 mediated the vasoconstrictive and blood pressure responses to the endogenous inflammatory lipid lysophosphatidic acid.  These results show that TRPV1 in arteriolar myocytes modulates regional blood flow and systemic blood pressure, and suggest that TRPV1 may be a target of vasoactive inflammatory mediators.

ABSTRACT

The capsaicin receptor, TRPV1, is a key ion channel involved in inflammatory pain signalling. Although mainly studied in sensory nerves, there are reports of TRPV1 expression in isolated segments of the vasculature, but whether the channel localizes to vascular endothelium or smooth muscle is controversial and the distribution and functional roles of TRPV1 in arteries remain unknown. We mapped functional TRPV1 expression throughout the mouse arterial circulation. Analysis of reporter mouse lines TRPV1^PLAP-nlacZ and TRPV1-Cre:tdTomato combined with Ca²⁺ imaging revealed specific localization of TRPV1 to smooth muscle of terminal arterioles in the heart, adipose tissue and skeletal muscle. Capsaicin evoked inward currents (current density ∼10% of sensory neurons) and raised intracellular Ca²⁺ levels in arterial smooth muscle cells, constricted arterioles ex vivo and in vivo and increased systemic blood pressure in mice and rats. Further, capsaicin markedly and dose-dependently reduced coronary flow. Pharmacological and/or genetic disruption of TRPV1 abolished all these effects of capsaicin as well as vasoconstriction triggered by lysophosphatidic acid, a bioactive lipid generated by platelets and atherogenic plaques. Notably, ablation of sensory nerves did not affect the responses to capsaicin revealing a vascular smooth muscle-restricted signalling mechanism. Moreover, unlike in sensory nerves, TRPV1 function in arteries was resistant to activity-induced desensitization. Thus, TRPV1 activation in vascular myocytes enables a persistent depolarizing current, leading to constriction of coronary, skeletal muscle and adipose arterioles and a sustained increase in systemic blood pressure.

Lysophosphatidic acid promotes thrombus stability by inducing rapid formation of neutrophil extracellular traps: A new mechanism of thrombosis

BACKGROUND

Lysophosphatidic acid (LPA), a bioactive phospholipid released by activated platelets, can induce platelet shape changes and aggregation, which may play an important role in thrombosis. In contrast, the interaction of LPA with neutrophils in thrombosis has not been studied. Recently, neutrophil extracellular traps (NETs) have been shown to bind plasma proteins and activate platelets, which promotes thrombosis.

OBJECTIVES

To investigate whether LPA could activate neutrophils to release NETs, predisposing to thrombosis and promoting thrombus stability.

METHODS

Levels of neutrophils, NETs, and LPA were detected in 56 participants. Immunofluorescence of NETs and autotaxin, the LPA-producing ectoenzyme, were performed. Induction of NETs and signaling pathways were explored in vitro.

RESULTS

Patients with acute pulmonary embolism showed elevated levels of neutrophils, NETs (dsDNA, MPO-DNA, citrullinated histone H3, and nucleosomes), LPA18:1, and LPA20:4. NETs were present in human intrapulmonary thrombi and were surrounded by autotaxin. LPA18:1 induced rapid release of NETs from human neutrophils via a peptidylarginine deiminase 4-dependent pathway. LPA-induced NETs provided a scaffolding for plasma protein binding and generated a tissue plasminogen activator (tPA)-resistant blood clot. Addition of deoxyribonuclease I to tPA significantly accelerated the lysis of clots and human intrapulmonary thrombi. Furthermore, LPA-induced NETs could activate platelets to release LPA.

CONCLUSION

This is the first study to implicate LPA in regulating the stability of thrombi by inducing rapid release of NETs in vitro and ex vivo, which could be a new mechanism of thrombosis. These findings provide new insight into the prevention and therapy of venous thromboembolic disease by targeting the LPA-NET signaling pathway.

Lysophosphatidic acid-induced pro-thrombotic phosphatidylserine exposure and ionophore-induced microvesiculation is mediated by the scramblase TMEM16F in erythrocytes

Recent studies indicate that erythrocytes actively modulate blood clotting and thrombus formation. The lipid mediator lysophosphatidic acid (LPA) is produced by activated platelets, and triggers a signaling process in erythrocytes. This results in cellular calcium uptake and exposure of phosphatidylserine (PS) at the cell surface, thereby generating activated membrane binding sites for factors of the clotting cascade. Moreover, erythrocytes of patients with a bleeding disorder and mutations in the scramblase TMEM16F show impaired PS exposure and microvesiculation upon treatment with calcium ionophore. We report that TMEM16F inhibitors tannic acid (TA) and epigallocatechin-3-gallate (EGCG) inhibit LPA-induced PS exposure and calcium uptake at low micromolar concentrations; fluoxetine, an antidepressant and a known activator of TMEM16F, enhances these processes. These effectors likewise modulate erythrocyte PS exposure and microvesicle shedding induced by calcium ionophore treatment. Further, LPA-treated erythrocytes triggered thrombin generation in platelet-free plasma which was partially impaired in the presence of TA and EGCG. Thus, this study suggests that LPA activates the scramblase TMEM16F in erythrocytes, thereby possibly mediating a pro-thrombotic function in these cells. EGCG as well as fluoxetine, substances with potentially high plasma concentrations due to alimentation or medical treatment, should be considered as potential effectors of systemic hemostatic regulation.

Bioactive Lipid Signaling in Cardiovascular Disease, Development, and Regeneration

Cardiovascular disease (CVD) remains a leading cause of death globally. Understanding and characterizing the biochemical context of the cardiovascular system in health and disease is a necessary preliminary step for developing novel therapeutic strategies aimed at restoring cardiovascular function. Bioactive lipids are a class of dietary-dependent, chemically heterogeneous lipids with potent biological signaling functions. They have been intensively studied for their roles in immunity, inflammation, and reproduction, among others. Recent advances in liquid chromatography-mass spectrometry techniques have revealed a staggering number of novel bioactive lipids, most of them unknown or very poorly characterized in a biological context. Some of these new bioactive lipids play important roles in cardiovascular biology, including development, inflammation, regeneration, stem cell differentiation, and regulation of cell proliferation. Identifying the lipid signaling pathways underlying these effects and uncovering their novel biological functions could pave the way for new therapeutic strategies aimed at CVD and cardiovascular regeneration.

Lysophosphatidic acid decreased macrophage foam cell migration correlated with downregulation of fucosyltransferase 8 via HNF1α

BACKGROUND AND AIMS

Aberrant fucosylation, such as α-1,6 fucosylation catalyzed by fucosyltransferase 8 (Fut8), is associated with reduced cell migration and is responsible for cholesterol-enriched foam cell accumulation in the intima in the early stage of atherosclerosis. The current study evaluated the impact of glycosyltransferases on foam cell migration induced by lysophosphatidic acid (LPA) and its potential mechanism.

METHODS

The mobility of foam cells was evaluated via transwell and scratch assays. The expression of Fut8 and α-1,6 fucosylation of proteins were assessed by RT-PCR, Western blotting, etc. Overexpression of Fut8 was used to explore the direct relationship between Fut8 and foam cell migration. Dual luciferase reporter assay was performed to determine whether the regulation of Fut8 by LPA occurred at the transcriptional level. Binding of hepatocyte nuclear factor 1-alpha (HNF1α) to the Fut8 promoter was assessed by electrophoretic mobility shift assay and chromatin immunoprecipitation assay.

RESULTS

We found that the migration capacity of foam cells induced by LPA was significantly decreased. Fut8 and α-1,6 fucosylation showed the most obvious decline after treatment with 200 μM LPA for 24 h. Overexpression of Fut8 was able to restore the foam cell migration capacity. Another important finding was that the LPA₁ and LPA₃ (LPA_1,3) receptors were involved in the regulation of Fut8. It is interesting to note that LPA led to a decrease in Fut8 gene transcription activity, and HNF1α transcription factor played a positive role in downregulation of Fut8 promoter activity.

CONCLUSIONS

Our results strongly indicated that the LPA-LPA_{1, 3} receptor-HNF1α pathway is involved in the downregulation of Fut8, leading to diminished foam cell migration.

Lysophospholipid profiles of apolipoprotein E-deficient mice reveal potential lipid biomarkers associated with atherosclerosis progression using validated UPLC-QTRAP-MS/MS-based lipidomics approach

Lysophospholipids (Lyso-PLs) are lipid-derived signaling molecules which were demonstrated to have a strong correlation with the progression of atherosclerosis. In this study, we investigated the influence of high-fat diet on Lyso-PL profiles of atherosclerosis-prone apolipoprotein E-deficient (ApoE^-/-) mice and wild type C57BL/6 J mice to find out the potential biomarkers associated with atherosclerosis. Firstly, the quantitative profiling method for Lyso-PLs based on ultra-performance liquid chromatography-quadrupole linear ion trap mass spectrometry (UPLC-QTRAP-MS/MS) was established and validated. Secondly, this method was utilized to quantify 169 targeted Lyso-PLs in plasma samples of ApoE^-/- mice and wild type C57BL/6 J mice collected at different time points. Finally, 12 of 37 differential Lyso-PLs were identified as more reliable biomarkers by integrating static metabolomics and time-dependent analyses, among which Lyso-PC/15:0, 18:1/Lyso-PI, 22:5/Lyso-PI and 22:4/Lyso-PI were highly correlated with TCand LDL-C levels. Meanwhile, we found that the Lyso-PL profiles of ApoE^-/- mice and C57BL/6 J mice were distinguished by altered metabolism of different Lyso-PLs classes, while C57BL/6 J mice fed with high-fat diet and normal diet were discriminated by the content differences of Lyso-PLs with same fatty acid composition. In conclusion, these results provided detailed changes of Lyso-PL profiles associated with atherosclerosis and the differential Lyso-PLs with reasonable change trends may serve as promising biomarkers for atherosclerosis progression.

Lysophosphatidic acid acts on LPA1 receptor to increase H2 O2 during flow-induced dilation in human adipose arterioles

BACKGROUND AND PURPOSE

NO produces arteriolar flow-induced dilation (FID) in healthy subjects but is replaced by mitochondria-derived hydrogen peroxide (mtH2 O2 ) in patients with coronary artery disease (CAD). Lysophosphatidic acid (LPA) is elevated in patients with risk factors for CAD, but its functional effect in arterioles is unknown. We tested whether elevated LPA changes the mediator of FID from NO to mtH2 O2 in human visceral and subcutaneous adipose arterioles.

EXPERIMENTAL APPROACH

Arterioles were cannulated on glass micropipettes and pressurized to 60 mmHg. We recorded lumen diameter after graded increases in flow in the presence of either NOS inhibition (L-NAME) or H2 O2 scavenging (Peg-Cat) ± LPA (10 μM, 30 min), ±LPA1 /LPA3 receptor antagonist (Ki16425) or LPA2 receptor antagonist (H2L5186303). We analysed LPA receptor RNA and protein levels in human arterioles and human cultured endothelial cells.

KEY RESULTS

FID was inhibited by L-NAME but not Peg-Cat in untreated vessels. In vessels treated with LPA, FID was of similar magnitude but inhibited by Peg-Cat while L-NAME had no effect. Rotenone attenuated FID in vessels treated with LPA indicating mitochondria as a source of ROS. RNA transcripts from LPA1 and LPA2 but not LPA3 receptors were detected in arterioles. LPA1 but not LPA3 receptor protein was detected by Western blot. Pretreatment of vessels with an LPA1 /LPA3 , but not LPA2 , receptor antagonist prior to LPA preserved NO-mediated dilation.

CONCLUSIONS AND IMPLICATIONS

These findings suggest an LPA1 receptor-dependent pathway by which LPA increases arteriolar release of mtH2 O2 as a mediator of FMD.

The interaction of β2-glycoprotein I with lysophosphatidic acid in platelet aggregation and blood clotting

β₂-Glycoprotein I (β₂-GPI) is a plasma protein that binds to oxidized low-density lipoprotein (LDL) and negatively charged substances, and inhibits platelet activation and blood coagulation. In this study, we investigated the interaction of β₂-GPI with a negatively charged lysophosphatidic acid (LPA) in platelet aggregation and blood clotting. Two negatively charged lysophospholipids, LPA and lysophosphatidylserine, specifically inhibited the binding of β₂-GPI to oxidized LDL in a concentration-dependent manner. Intrinsic tryptophan fluorescence studies demonstrated that emission intensity of β₂-GPI decreases in an LPA-concentration-dependent manner without a shift in wavelength maxima. LPA specifically induced the aggregation of β₂-GPI in phosphate-buffered saline, and in incubated plasma and serum, both of which are known to accumulate LPA by the action of lecithin-cholesterol acyltransferase and lysophospholipase D/autotaxin. β₂-GPI aggregated by LPA did not inhibit activated von Willebrand factor-induced aggregation, and did not prolong the activated partial thromboplastin time in blood plasma, in contrast to non-aggregated β₂-GPI. These results suggest that β₂-GPI aggregated by the binding to LPA fails to inhibit platelet aggregation and blood clotting in contrast to non-aggregated β₂-GPI.

The AGP-PPARγ axis promotes oxidative stress and diabetic endothelial cell dysfunction

Alkyl-glycerophosphate (AGP) accumulates in atherogenic oxidized-LDL and human atherosclerotic plaques and is a potent agonist of peroxisome-proliferator-activated receptor-gamma (PPARγ). Recent studies suggest a potential regulatory role for PPARγ in endothelial nitric oxide synthase (eNOS) expression/activation and nitrogen oxide (NO) generation in the vascular endothelium. Importantly, eNOS-induced NO and advanced glycation end-products (AGEs) are involved in blood-vessel damage, and diabetic patients exhibit high serum NO and AGE levels; however, the effect of AGP on NO- and AGE-mediated endothelium dysfunction remains unknown. Investigation of the AGP-specific effects on NO- and AGE-mediated dysfunction and the underlying molecular mechanisms revealed that AGP upregulated eNOS expression and NO production, and that eNOS silencing and PPARγ antagonism inhibited AGP-mediated eNOS upregulation and NO production. Moreover, AGP-PPARγ-axis-mediated NO production promoted the generation of reactive oxygen species and AGE formation. These results suggested that AGP plays a significant role in the initiation/progression of diabetes-related atherosclerosis through PPARγ activation.

Lysophosphatidic Acid Promotes Expression and Activation of Matrix Metalloproteinase 9 (MMP9) in THP-1 Cells via Toll-Like Receptor 4/Nuclear Factor-κB (TLR4/NF-κB) Signaling Pathway

BACKGROUND Lysophosphatidic acid (LPA) is an active compound of oxidized low-density lipoprotein that serves as an endogenous TLR4 ligand. Ligand activation of TLR4 activates nuclear factor-kappaB (NF-κB) and the transcription of NF-κB-regulated inflammatory cytokines, which are involved in the development of atherosclerosis. MMP9 is a member of the MMP family and can affect plaque stability. However, the mechanism responsible for the effect of LPA on the expression and activation of MMP9 has not been fully elucidated. In the present study we examined the effect of LPA on MMP9 expression and activity in THP-1 cells and the involvement of Toll-like receptor 4/nuclear factor-κB (TLR4/NF-κB) signaling pathway in this effect. MATERIAL AND METHODS Human THP-1 cells were treated with 0-10 μM LPA for 4 h, or treated with 1 μM LPA for 0-8 h, and were then transfected with TLR4-specific siRNA or treated with 20 μg/ml cafestol acid phenethyl ester (CAPE, an NF-κB inhibitor). MMP9 mRNA and protein levels were measured by quantitative RT-PCR and Western blot analysis, respectively, and MMP9 activity was measured by zymography. RESULTS LPA upregulated MMP9 mRNA and protein levels and MMP9 activity in THP-1 cells in both concentration- and time-dependent manners. Transfection of cells with TLR4-siRNA-2 or treatment with CAPE significantly inhibited the upregulated MMP9 expression and activation. This inhibition was further enhanced by combining the TLR4-siRNA-2 transfection and CAPE pretreatment. CONCLUSIONS LPA can promote MMP9 expression and enhance MMP9 activity in THP-1 cells, in part via the TLR4/NF-kB signaling pathway.

Targeting the RhoA-ROCK pathway to regulate T-cell homeostasis in hypoxia-induced pulmonary arterial hypertension

BACKGROUND

Hypoxic pulmonary arterial hypertension (PAH) is a crippling disease with limited therapeutic methods. The imbalance of T helper 17 cell (Th17)/regulatory T cell (Treg) plays an important role in the development of Hypoxic PAH. However, whether targeting the ras homolog family member A-Rho kinase (RhoA-ROCK) pathway (activation and inhibition) by lysophosphatidic acid (LPA) and fasudil (FSD) regulate T-cell homeostasis in Hypoxic PAH remain unknown.

OBJECTIVE

To examine the effects of LPA and FSD on hypoxic pulmonary vascular remodeling and homeostasis of Th17/Treg cells in Hypoxic PAH.

METHODS

Rats were exposed to hypoxia (10 ± 0.5% O₂) to induce Hypoxic PAH. The experiments consists of two parts. Forty rats were randomly divided into four groups (n = 10): normoxia group, normoxia + LPA group, hypoxia group and hypoxia + LPA group. Thirty rats were randomly divided into another three groups (n = 10): normoxia group, hypoxia group, and hypoxia + FSD group. Rats in normoxia + LPA group and hypoxia + LPA group were intraperitoneally injected 40 μg/kg LPA daily. Rats in hypoxia + FSD group were intraperitoneally injected 30 mg/kg fasudil daily. The effects of LPA and FSD on the development of hypoxic PAH and right ventricle (RV) hypertrophy, on pulmonary vascular remodeling, and on changes of Th17/Treg cells and levels of interleukin-17 (IL-17) and IL-10 were examined.

RESULTS

PAH and RV hypertrophy occurred in rats exposed to hypoxia. LPA exacerbated hypoxic pulmonary vascular remodeling and FSD inhibited it. LPA increased Th17/Treg imbalance in peripheral blood and spleen. However, after treatment with FSD, hypoxic PAH rats showed an obvious reduction of Th17 cells as well as an increase of Treg cells. LPA increased the expression of phosphorylated-signal transducer and activator of transcription 3 (p-STAT3) and reduced the p-STAT5 in peripheral blood and spleen in hypoxic PAH rats. The expression of p-STAT3 and p-STAT5 in hypoxic PAH rats treated with FSD showed opposite changes. LPA increased the expression of IL-17 and reduced the IL-10 in small intrapulmonary arteries and serum in hypoxic PAH. However, the expression of IL-17 and IL-10 in hypoxic PAH rats treated with FSD showed opposite changes.

CONCLUSIONS

Activation and inhibition of RhoA-ROCK pathway by LPA and FSD modulated the homeostasis of Th17/Treg cells via regulating STAT3/STAT5 phosphorylation in hypoxic PAH. Thus, Apart from influence of pulmonary vascular remodeling, regulation of Th17/Treg homeostasis by RhoA-ROCK pathway play a key role in hypoxic PAH.

Study of the metabolomics characteristics of patients with metabolic syndrome based on liquid chromatography quadrupole time-of-flight mass spectrometry

BACKGROUND

Metabolic syndrome (MS) is a disease with complex pathophysiology and pathogenesis involving multiple systems of the human body. This study aimed to identify serum metabolites that are relevant to MS.

MATERIAL AND METHODS

This study involved 40 patients with MS and 28 healthy adults, and the following data were statistically analyzed: basic clinical data, blood lipids, fasting blood glucose, blood pressure, waist circumference, and visceral fat coefficient. Serum samples from both groups were collected and analyzed by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF/MS); multivariate and univariate statistical methods were used to identify potential MS biomarkers and MS-related metabolic pathways. In addition, leucine and valine levels in serum from MS patients and normal subjects were measured using enzyme-linked immunosorbent assays (ELISAs).

RESULTS

In this study, 23 potential biomarkers were identified in the plasma of MS patients. These biomarkers were mainly related to metabolism; the tricarboxylic acid cycle; galactose metabolism; arachidonic acid metabolism; valine, leucine, and isoleucine degradation; and valine, leucine, and isoleucine biosynthesis. ELISAs were utilized to verify serum leucine and valine levels, and the results supported the experimental metabolomics results.

CONCLUSIONS

In total, 23 MS-related metabolites were identified in the serum; these differential metabolites were mainly associated with lipid metabolism, amino acid metabolism, glucose metabolism, purine metabolism, and other related metabolic pathways. This study shows that LC/MS-based metabolomics methods can be used to investigate the pathological changes in MS patients and identify biomarkers for the early diagnosis of MS.

mTOR signaling promotes foam cell formation and inhibits foam cell egress through suppressing the SIRT1 signaling pathway

Atherosclerosis (AS) is a chronic immuno‑inflammatory disease accompanied by dyslipidemia. The authors previously demonstrated that sirtuin 1 (SIRT1) may prevent atherogenesis through influencing the liver X receptor/C‑C chemokine receptor type 7/nuclear factor‑κB (LXR‑CCR7/NF‑κB) signaling pathway. Previous studies have suggested a role for mammalian target of rapamycin (mTOR) signaling in the pathogenesis of cardiovascular diseases. The present study investigated the potential association between mTOR signaling and SIRT1‑LXR‑CCR7/NF‑κB signaling (SIRT1 signaling) in AS pathogenesis. To induce foam cell formation, U937 cells were differentiated into macrophages by exposure to phorbol 12‑myristate 13‑acetate (PMA) for 24 h, followed by treatment with palmitate and oxidized low density lipoprotein for a further 24 h. Oil red O staining revealed a large accumulation of lipid droplets present in foam cells. Western blot analysis demonstrated increased protein levels of phosphorylated (p)‑mTOR and its downstream factor p‑ribosomal protein S6 kinase (p70S6K). Reverse transcription‑quantitative polymerase chain reaction and western blot analyses additionally revealed decreased expression of SIRT1, LXRα and CCR7 and increased expression of NF‑κB and its downstream factor tumor necrosis factor‑α (TNF‑α) in an atherogenetic condition induced by lysophosphatidic acid (LPA). In addition, abundant lipid droplets accumulated in U937‑LPA‑treated foam cells. Rapamycin, an mTOR inhibitor, suppressed the expression and activity of mTOR and p70S6K, however enhanced expression of SIRT1, LXRα, and CCR7. Conversely, rapamycin deceased TNF‑α and NF‑κB activity, the latter of which was further confirmed by immunofluorescence analysis demonstrating increased levels of NF‑κB present in the cytoplasm compared with the nucleus. The findings of the present study suggest that mTOR signaling promotes foam cell formation and inhibits foam cell egress via suppression of SIRT1 signaling.

Lysophosphatidic acid directly induces macrophage-derived foam cell formation by blocking the expression of SRBI

The leading cause of morbidity and mortality is the result of cardiovascular disease, mainly atherosclerosis. The formation of macrophage foam cells by ingesting ox-LDL and focal retention in the subendothelial space are the hallmarks of the early atherosclerotic lesion. Lysophosphatidic acid (LPA), which is a low-molecular weight lysophospholipid enriched in oxidized LDL, exerts a range of effects on the cardiovascular system. Previous reports show that LPA increases the uptake of ox-LDL to promote the formation of foam cells. However, as the most active component of ox-LDL, there is no report showing whether LPA directly affects foam cell formation. The aim of this study was to investigate the effects of LPA on foam cell formation, as well as to elucidate the underlying mechanism. Oil red O staining and a Cholesterol/cholesteryl ester quantitation assay were used to evaluate foam cell formation in Raw264.7 macrophage cells. We utilized a Western blot and RT-PCR to investigate the relationship between LPA receptors and lipid transport related proteins. We found that LPA promoted foam cell formation, using 200 μM for 24 h. Meanwhile, the expression of the Scavenger receptor BI (SRBI), which promotes the efflux of free cholesterol, was decreased. Furthermore, the LPA_1/3 receptor antagonist Ki16425 significantly abolished the LPA effects, indicating that LPA_1/3 was involved in the foam cell formation and SRBI expression induced by LPA. Additionally, the LPA-induced foam cell formation was blocked with an AKT inhibitor. Our results suggest that LPA-enhanced foam cell formation is mediated by LPA_1/3 -AKT activation and subsequent SRBI expression.

CD14 is a key mediator of both lysophosphatidic acid and lipopolysaccharide induction of foam cell formation

Macrophage uptake of oxidized low-density lipoprotein (oxLDL) plays an important role in foam cell formation and the pathogenesis of atherosclerosis. We report here that lysophosphatidic acid (LPA) enhances lipopolysaccharide (LPS)-induced oxLDL uptake in macrophages. Our data revealed that both LPA and LPS highly induce the CD14 expression at messenger RNA and protein levels in macrophages. The role of CD14, one component of the LPS receptor cluster, in LPA-induced biological functions has been unknown. We took several steps to examine the role of CD14 in LPA signaling pathways. Knockdown of CD14 expression nearly completely blocked LPA/LPS-induced oxLDL uptake in macrophages, demonstrating for the first time that CD14 is a key mediator responsible for both LPA- and LPS-induced oxLDL uptake/foam cell formation. To determine the molecular mechanism mediating CD14 function, we demonstrated that both LPA and LPS significantly induce the expression of scavenger receptor class A type I (SR-AI), which has been implicated in lipid uptake process, and depletion of CD14 levels blocked LPA/LPS-induced SR-AI expression. We further showed that the SR-AI-specific antibody, which quenches SR-AI function, blocked LPA- and LPS-induced foam cell formation. Thus, SR-AI is the downstream mediator of CD14 in regulating LPA-, LPS-, and LPA/LPS-induced foam cell formation. Taken together, our results provide the first experimental evidence that CD14 is a novel connecting molecule linking both LPA and LPS pathways and is a key mediator responsible for LPA/LPS-induced foam cell formation. The LPA/LPS-CD14-SR-AI nexus might be the new convergent pathway, contributing to the worsening of atherosclerosis.

CRE and SRE mediate LPA-induced CCN1 transcription in mouse aortic smooth muscle cells

Lysophosphatidic acid (LPA), one component of oxidized low-density lipoprotein (ox-LDL), is a potent bioactive phospholipid. Our recent data reveal that LPA induces matricellular protein CCN1 (also known as Cyr61) expression in aortic smooth muscle cells (SMCs) and that CCN1 bridges LPA and integrin signaling pathways leading to SMC migration. Whether and how LPA regulates the transcriptional machinery of the CCN1 gene are unknown. In this study, we found that LPA markedly induces CCN1 mRNA expression in SMCs. Using deleting mutation and reporter gene strategies, we demonstrated regions from -2038 to -1787 and from -101 to +63 of the CCN1 promoter contain the essential regulatory elements. The serum response element (SRE) and cyclic AMP-response element (CRE) are located in these regions. LPA induced time-dependent phosphorylation of serum response factor (SRF) and CRE-binding protein (CREB) in mouse SMCs. Luciferase assays of a series of deleted, mutated CCN1 promoter-reporter gene constructs and dominant negative construct revealed the distal SRE and the proximal CRE in the CCN1 promoter are required for LPA-induced CCN1 gene expression. Our results imply that elevated LPA levels may trigger SMC migration and exacerbate restenosis and atherosclerotic lesions through the induced CCN1, which communicates with a set of plasma membrane proteins and intracellular kinases.

Lysophospholipids and their G protein-coupled receptors in atherosclerosis

Lysophospholipids (LPLs) are bioactive lipid-derived signaling molecules generated by the enzymatic and chemical processes of regiospecific phospholipases on substrates such as membrane phospholipids (PLs) and sphingolipids (SLs). They play a major role as extracellular mediators by activating G-protein coupled receptors (GPCRs) and stimulating diverse cellular responses from their signaling pathways. LPLs are involved in various pathologies of the vasculature system including coronary heart disease and hypertension. Many studies suggest the importance of LPLs in their association with the development of atherosclerosis, a chronic and severe vascular disease. This paper focuses on the pathophysiological effects of different lysophospholipids on atherosclerosis, which may promote the pathogenesis of myocardial infarction and strokes. Their atherogenic biological activities take place in vascular endothelial cells, vascular smooth muscle cells, fibroblasts, monocytes and macrophages, dendritic cells, T-lymphocytes, platelets, etc.

Identification of total reversible cysteine oxidation in an atherosclerosis model using a modified biotin switch assay

Oxidative stress due to the imbalance of reactive oxygen species (ROS) and the resulting reversible cysteine oxidation (CysOX) are involved in the early proatherogenic aspect of atherosclerosis. Given that the corresponding redox signaling pathways are still unclear, a modified biotin switch assay was developed to quantify the reversible CysOX in an atherosclerosis model established by using a monocytic cell line treated with platelet releasate. The accumulation of ROS was observed in the model system and validated in human primary monocytes. Through the application of the modified biotin switch assay, we obtained the first reversible CysOX proteome for this model. A total of 75 peptides, corresponding to 53 proteins, were quantified with oxidative modification. The bioinformatics analysis of these CysOX-containing proteins highlighted biological processes including glycolysis, cytoskeleton arrangement, and redox regulation. Moreover, the reversible oxidation of three glycolysis enzymes was observed using this method, and the regulation influence was verified by an enzyme activity assay. NADPH oxidase (NOX) inhibition treatment, in conjunction with the modified biotin switch method, was used to evaluate the global CysOX status. In conclusion, this versatile modified biotin switch assay provides an approach for the quantification of all reversible CysOX and for the study of redox signaling in atherosclerosis as well as in diseases in other biological systems.

Lysophosphatidylserine has Bilateral Effects on Macrophages in the Pathogenesis of Atherosclerosis

AIM

Lysophospholipids, particularly sphingosine 1-phosphate and lysophosphatidic acid, are known to be involved in the pathogenesis of atherosclerosis; however, the role of lysophosphatidylserine (LysoPS) in the onset of atherosclerotic diseases remains uncertain.

METHODS

We investigated the effects of LysoPS on the uptake of oxidized low-density lipoprotein (oxLDL) and the modulation of inflammatory mediators and ER stress utilizing RAW264.7 cells and mouse peritoneal macrophages (MPMs).

RESULTS

We found that LysoPS augmented cholesterol accumulation in both models. Consistent with these findings, LysoPS increased the expression of scavenger receptors (CD36, MSR1, LOX1 and TLR4). Regarding the involvement of these lipids in inflammation, LysoPS significantly decreased the expression of inflammatory mediators in lipopolysaccharide (LPS)-treated RAW264.7 cells and MPMs. LysoPS also attenuated ER stress in LPS-untreated RAW264.7 cells. The expression patterns of LysoPS receptors differed considerably among the LPS-untreated RAW264.7 cells, LPS-treated RAW264.7 cells and MPMs.

CONCLUSIONS

LysoPS may have proatherosclerotic properties in the setting of foam cell formation as well as antiatherosclerotic effects on inflammation in macrophages.

Lysophosphatidic acid induces integrin activation in vascular smooth muscle and alters arteriolar myogenic vasoconstriction

In vascular smooth muscle cells (VSMC) increased integrin adhesion to extracellular matrix (ECM) proteins, as well as the production of reactive oxygen species (ROS) are strongly stimulated by lysophosphatidic acid (LPA). We hypothesized that LPA-induced generation of ROS increases integrin adhesion to the ECM. Using atomic force microscopy (AFM) we determined the effects of LPA on integrin adhesion to fibronectin (FN) in VSMC isolated from rat (Sprague-Dawley) skeletal muscle arterioles. In VSMC, exposure to LPA (2 μM) doubled integrin-FN adhesion compared to control cells (P < 0.05). LPA-induced integrin-FN adhesion was reduced by pre-incubation with antibodies against β1 and β3 integrins (50 μg/ml) by 66% (P < 0.05). Inhibition of LPA signaling via blockade of the LPA G-protein coupled receptors LPAR1 and LPAR3 with 10 μM Ki16425 reduced the LPA-enhanced adhesion of VSCM to FN by 40% (P < 0.05). Suppression of ROS with tempol (250 μM) or apocynin (300 μM) also reduced the LPA-induced FN adhesion by 47% (P < 0.05) and 59% (P < 0.05), respectively. Using confocal microscopy, we observed that blockade of LPA signaling, with Ki16425, reduced ROS by 45% (P < 0.05), to levels similar to control VSMC unexposed to LPA. In intact isolated arterioles, LPA (2 μM) exposure augmented the myogenic constriction response to step increases in intraluminal pressure (between 40 and 100 mm Hg) by 71% (P < 0.05). The blockade of LPA signaling, with Ki16425, decreased the LPA-enhanced myogenic constriction by 58% (P < 0.05). Similarly, blockade of LPA-induced ROS release with tempol or gp91 ds-tat decreased the LPA-enhanced myogenic constriction by 56% (P < 0.05) and 55% (P < 0.05), respectively. These results indicate that, in VSMC, LPA-induced integrin activation involves the G-protein coupled receptors LPAR1 and LPAR3, and the production of ROS, and that LPA may play an important role in the control of myogenic behavior in resistance vessels through ROS modulation of integrin activity.

Regulation of T cell motility in vitro and in vivo by LPA and LPA2

Lysophosphatidic acid (LPA) and the LPA-generating enzyme autotaxin (ATX) have been implicated in lymphocyte trafficking and the regulation of lymphocyte entry into lymph nodes. High local concentrations of LPA are thought to be present in lymph node high endothelial venules, suggesting a direct influence of LPA on cell migration. However, little is known about the mechanism of action of LPA, and more work is needed to define the expression and function of the six known G protein-coupled receptors (LPA 1-6) in T cells. We studied the effects of 18∶1 and 16∶0 LPA on naïve CD4+ T cell migration and show that LPA induces CD4+ T cell chemorepulsion in a Transwell system, and also improves the quality of non-directed migration on ICAM-1 and CCL21 coated plates. Using intravital two-photon microscopy, lpa2-/- CD4+ T cells display a striking defect in early migratory behavior at HEVs and in lymph nodes. However, later homeostatic recirculation and LPA-directed migration in vitro were unaffected by loss of lpa2. Taken together, these data highlight a previously unsuspected and non-redundant role for LPA2 in intranodal T cell motility, and suggest that specific functions of LPA may be manipulated by targeting T cell LPA receptors.

Lysophosphatidic acid (LPA) signaling in human and ruminant reproductive tract

Lysophosphatidic acid (LPA) through activating its G protein-coupled receptors (LPAR 1–6) exerts diverse cellular effects that in turn influence several physiological processes including reproductive function of the female. Studies in various species of animals and also in humans have identified important roles for the receptor-mediated LPA signaling in multiple aspects of human and animal reproductive tract function. These aspects range from ovarian and uterine function, estrous cycle regulation, early embryo development, embryo implantation, decidualization to pregnancy maintenance and parturition. LPA signaling can also have pathological consequences, influencing aspects of endometriosis and reproductive tissue associated tumors. The review describes recent progress in LPA signaling research relevant to human and ruminant reproduction, pointing at the cow as a relevant model to study LPA influence on the human reproductive performance.

Methods for quantifying lysophosphatidic acid in body fluids: a review

Lysophosphatidic acid (LPA) is a bioactive lipid involved in cellular signal transduction. LPA plays a role in both physiological and pathological processes. Elevated levels of LPA are observed in the plasma of patients with epithelial ovarian cancer, indicating its potential as a diagnostic marker. Quantification of total LPA can be performed by radioenzymatic, fluorometric, colorimetric, or immunoezymatic assay. Determination of individual LPA molecular species requires the use of capillary electrophoresis, gas chromatography, thin layer chromatography, liquid chromatography, or a matrix-assisted laser desorption/ionization time-of-flight method connected to an appropriate detection system.

Matricellular protein Cyr61 bridges lysophosphatidic acid and integrin pathways leading to cell migration

Lysophosphatidic acid (LPA), a potent bioactive lipid found in atherosclerotic lesions, markedly induces smooth muscle cell (SMC) migration, which is an important process in atherogenesis. Therefore, understanding the mechanism of LPA-induced SMC migration is important. Several microarray databases suggest that the matricellular protein Cyr61 is highly induced by LPA. We hypothesized that Cyr61 mediates LPA-induced cell migration. Our data show that LPA induced temporal and spatial expression of Cyr61, which promptly accumulated in the cellular Golgi apparatus and then translocated to the extracellular matrix. Cyr61 antibody blockade and siRNA inhibition both diminished LPA-induced SMC migration, indicating a novel regulatory role of Cyr61. SMCs derived from LPA receptor 1 (LPA1) knock-out mice lack the ability of Cyr61 induction and cell migration, supporting the concept that LPA1 is required for Cyr61 expression and migration. By contrast, PPARγ was not found to be involved in LPA-mediated effects. Furthermore, focal adhesion kinase (FAK), a nonreceptor tyrosine kinase important for regulating cell migration, was activated by LPA at a late time frame coinciding with Cyr61 accumulation. Interestingly, knockdown of Cyr61 blocked LPA-induced FAK activation, indicating that an LPA-Cyr61-FAK axis leads to SMC migration. Our results further demonstrate that plasma membrane integrins α6β1 and ανβ3 transduced the LPA-Cyr61 signal toward FAK activation and migration. Taken together, these data reveal that de novo Cyr61 in the extracellular matrix bridges LPA and integrin pathways, which in turn, activate FAK, leading to cell migration. The current study provides new insights into mechanisms underlying cell migration-related disorders, including atherosclerosis, restenosis, and cancers.

Inhibition of lysophosphatidic acid increase by prestorage whole blood leukoreduction in autologous CPDA-1 whole blood

BACKGROUND

Lysophosphatidylcholine (LPC) has been implicated in the onset of transfusion-related acute lung injury (TRALI). In plasma, LPC is converted to lysophosphatidic acid (LPA) by autotaxin (ATX). The effect of leukoreduction in the accumulation of these bioactive lipids and ATX in human autologous blood has not been fully investigated.

STUDY DESIGN AND METHODS

The accumulation of choline-containing phospholipids (LPC, sphingomyelin [SM], and phosphatidylcholine [PC]), LPA, and ATX during the storage of autologous blood and the changes caused by leukoreduction were investigated. A total of 26 orthopedic patients were enrolled. Autologous blood was collected as whole blood and, after leukoreduction, preserved refrigerated until use. Prestorage leukoreduced (LR) and non-LR autologous blood samples were analyzed. The time-dependent changes and the effect of the filtration were compared.

RESULTS

A time-dependent and significant increase in the levels of LPA was observed in both non-LR and LR samples. The concentration of LPA was significantly reduced in LR compared to non-LR samples. The concentration of LPC was higher in LR compared to non-LR samples. The levels of PC, SM, and ATX were not affected by either the storage period or the leukoreduction.

CONCLUSIONS

Leukoreduction of autologous whole blood effectively reduced the accumulation of LPA. On the other hand, prestorage leukoreduction resulted in an increased concentration of LPC, without significantly affecting ATX. Further studies are necessary to confirm the role of LPA in the pathogenesis of adverse effects of blood transfusion, especially TRALI.

Lysophosphatidic acid triggers mast cell-driven atherosclerotic plaque destabilization by increasing vascular inflammation

Lysophosphatidic acid (LPA), a bioactive lysophospholipid, accumulates in the atherosclerotic plaque. It has the capacity to activate mast cells, which potentially exacerbates plaque progression. In this study, we thus aimed to investigate whether LPA contributes to plaque destabilization by modulating mast cell function. We here show by an imaging mass spectrometry approach that several LPA species are present in atherosclerotic plaques. Subsequently, we demonstrate that LPA is a potent mast cell activator which, unlike other triggers, favors release of tryptase. Local perivascular administration of LPA to an atherosclerotic carotid artery segment increases the activation status of perivascular mast cells and promotes intraplaque hemorrhage and macrophage recruitment without impacting plaque cell apoptosis. The mast cell stabilizer cromolyn could prevent intraplaque hemorrhage elicited by LPA-mediated mast cell activation. Finally, the involvement of mast cells in these events was further emphasized by the lack of effect of perivascular LPA administration in mast cell deficient animals. We demonstrate that increased accumulation of LPA in plaques induces perivascular mast cell activation and in this way contributes to plaque destabilization in vivo. This study points to local LPA availability as an important factor in atherosclerotic plaque stability.

Lipid phosphate phosphatase (LPP3) and vascular development

Lipid phosphate phosphatases (LPP) are integral membrane proteins with broad substrate specificity that dephosphorylate lipid substrates including phosphatidic acid, lysophosphatidic acid, ceramide 1-phosphate, sphingosine 1-phosphate, and diacylglycerol pyrophosphate. Although the three mammalian enzymes (LPP1-3) demonstrate overlapping catalytic activities and substrate preferences in vitro, the phenotypes of mice with targeted inactivation of the Ppap2 genes encoding the LPP enzymes reveal nonredundant functions. A specific role for LPP3 in vascular development has emerged from studies of mice lacking Ppap2b. A meta-analysis of multiple, large genome-wide association studies identified a single nucleotide polymorphism in PPAP2B as a novel predictor of coronary artery disease. In this review, we will discuss the evidence that links LPP3 to vascular development and disease and evaluate potential molecular mechanisms. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Lysophosphatidic acid induces increased BACE1 expression and Aβ formation

The abnormal production and accumulation of β-amyloid peptide (Aβ), which is produced from amyloid precursor protein (APP) by the sequential actions of β-secretase and γ-secretase, are thought to be the initial causative events in the development of Alzheimer's disease (AD). Accumulating evidence suggests that vascular factors play an important role in the pathogenesis of AD. Specifically, studies have suggested that one vascular factor in particular, oxidized low density lipoprotein (oxLDL), may play an important role in regulating Aβ formation in AD. However, the mechanism by which oxLDL modulates Aβ formation remains elusive. In this study, we report several new findings that provide biochemical evidence suggesting that the cardiovascular risk factor oxLDL may contribute to Alzheimer's disease by increasing Aβ production. First, we found that lysophosphatidic acid (LPA), the most bioactive component of oxLDL induces increased production of Aβ. Second, our data strongly indicate that LPA induces increased Aβ production via upregulating β-secretase expression. Third, our data strongly support the notion that different isoforms of protein kinase C (PKC) may play different roles in regulating APP processing. Specifically, most PKC members, such as PKCα, PKCβ, and PKCε, are implicated in regulating α-secretase-mediated APP processing; however, PKCδ, a member of the novel PKC subfamily, is involved in LPA-induced upregulation of β-secretase expression and Aβ production. These findings may contribute to a better understanding of the mechanisms by which the cardiovascular risk factor oxLDL is involved in Alzheimer's disease.

Alteration of the platelet transcriptome in chronic kidney disease

Bleeding and thrombotic disorders are major complications affecting patients with chronic kidney disease (CKD). Exposure of circulating platelets to uraemic toxins and contact with artificial surfaces during dialysis induce platelet abnormalities and alter the platelet proteome. We hypothesised that these changes may be subsequent to changes in the composition and/or regulation of the platelet transcriptome. In this study, we investigated the circulating platelets of 10 CKD patients (i.e. five chronic haemodialysis patients and five stage 4 CKD uraemic patients) and five age- and sex-matched healthy subjects. We observed an alteration of the platelet messenger RNA (mRNA) and microRNA transcriptome in CKD patients. Impaired in uraemic platelets, the levels of some mRNAs and of most microRNAs appeared to be corrected by dialysis, which is consistent with a beneficial effect of dialysis and a mRNA regulatory role of platelet microRNAs. Reduced in platelets of uraemic patients, phosphatidylcholine transfer protein (PCTP) and WD repeat-containing protein 1 (WDR1) were found to be regulated by microRNAs, the latter of which involving hsa-miR-19b, a microRNA increased in platelets of uraemic patients and involved in platelet reactivity. These results suggest that an alteration of microRNA-based mRNA regulatory mechanisms may underlie the platelet response to uremia and entail the development of platelet-related complications in CKD.

Lysophosphatidic acid induces early growth response-1 (Egr-1) protein expression via protein kinase Cδ-regulated extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) activation in vascular smooth muscle cells

Lysophosphatidic acid (LPA) modulates vascular cell function in vitro and in vivo via regulating the expression of specific genes. Previously, we reported that a transcriptional mechanism controls LPA-induced expression of Egr-1 in vascular smooth muscle cells. Egr-1 is a master transcription factor mediating the expression of various genes that have been implied to modulate a broad spectrum of vascular pathologies. In this study, we determined the essential intracellular signaling pathway leading to LPA-induced Egr-1 expression. Our data demonstrate that activation of ERK1/2 and JNK, but not p38 MAPK, is required for LPA-induced Egr-1 expression in smooth muscle cells. We provide the first evidence that MEK-mediated JNK activation leads to LPA-induced gene expression. JNK2 is required for Egr-1 induction. Examining the upstream kinases that mediate ERK and JNK activation, leading to Egr-1 expression, we found that LPA-induced activation of MAPKs and expression of Egr-1 are dependent on PKC activation. We observed that LPA rapidly activates PKCδ and PKCθ. Overexpression of dominant-negative PKCδ, but not dominant-negative PKCθ, diminished activation of ERK and JNK and blocked LPA-induced expression of Egr-1 mRNA and protein. We also evaluated LPA receptor involvement. Our data reveal an intracellular regulatory mechanism: LPA induction of Egr-1 expression is via LPA cognate receptor (LPA receptor 1)-dependent and PKCδ-mediated ERK and JNK activation. This study provides the first evidence that PKCδ mediates ERK and JNK activation in the LPA signaling pathway and that this pathway is required for LPA-induced gene regulation as evidenced by Egr-1 expression.