Lysophosphatidic acid and renal fibrosis

Unveiling the bidirectional role of MMP9: A key player in kidney injury

Matrix metalloproteinases (MMPs) are a group of zinc-dependent proteolytic metalloenzymes that are involved in numerous pathological conditions, including nephropathy. MMP9, a member of the MMPs family, is categorized as a constituent of the gelatinase B subgroup, and its involvement in extracellular matrix (ECM) remodeling and renal fibrosis highlights its importance in the development and progression of renal diseases. The exact role of MMP9 in the development of kidney diseases is still controversial. This study investigated the dual role of MMP9 in kidney injury, discussing its implications in the pathogenesis of kidney diseases and investigating the design and mechanism of MMP9 inhibitors based on previous studies. This study provides an effective basis for the development of novel and selective MMP9 inhibitors for treating renal diseases.

MNK-driven eIF4E phosphorylation regulates the fibrogenic transformation of mesenchymal cells and chronic lung allograft dysfunction

Tissue fibrosis remains unamenable to meaningful therapeutic interventions and is the primary cause of chronic graft failure after organ transplantation. Eukaryotic translation initiation factor (eIF4E), a key translational regulator, serves as convergent target of multiple upstream profibrotic signaling pathways that contribute to mesenchymal cell (MC) activation. Here, we investigate the role of MAP kinase-interacting serine/threonine kinase-induced (MNK-induced) direct phosphorylation of eIF4E at serine 209 (Ser209) in maintaining fibrotic transformation of MCs and determine the contribution of the MNK/eIF4E pathway to the pathogenesis of chronic lung allograft dysfunction (CLAD). MCs from patients with CLAD demonstrated constitutively higher eIF4E phosphorylation at Ser209, and eIF4E phospho-Ser209 was found to be critical in regulating key fibrogenic protein autotaxin, leading to sustained β-catenin activation and profibrotic functions of CLAD MCs. MNK1 signaling was upregulated in CLAD MCs, and genetic or pharmacologic targeting of MNK1 activity inhibited eIF4E phospho-Ser209 and profibrotic functions of CLAD MCs in vitro. Treatment with an MNK1/2 inhibitor (eFT-508) abrogated allograft fibrosis in an orthotopic murine lung-transplant model. Together these studies identify what we believe is a previously unrecognized MNK/eIF4E/ATX/β-catenin signaling pathway of fibrotic transformation of MCs and present the first evidence, to our knowledge, for the utility of MNK inhibitors in fibrosis.

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

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

Extracellular and intracellular productions of lysophosphatidic acids and cyclic phosphatidic acids by lysophospholipase D from exogenously added lysophosphatidylcholines to cultured NRK52E cells

Lysophosphatidic acid (LPA) is a bioactive lysophospholipid that is a notable biomarker of kidney injury. However, it is not clear how LPA is produced in renal cells. In this study, we explored LPA generation and its enzymatic pathway in a rat kidney-derived cell, NRK52E cells. Culturing of NRK52E cells with acyl lysophosphatidylcholine (acyl LPC), or lyso-platelet activating factor (lysoPAF, alkyl LPC) was resulted in increased extracellular level of choline, co-product with LPA by lysophospholipase D (lysoPLD). Their activities were enhanced by addition of calcium ions to the cell culture medium, but failed to be inhibited by S32826, an autotaxin (ATX)-specific inhibitor. Liquid chromatography-tandem mass spectrometric analysis revealed the small, but significant extracellular production of acyl LPA/cyclic phosphatidic acid (cPA) and alkyl LPA/cPA. The mRNA expression of glycerophosphodiesterase (GDE) 7 with lysoPLD activity was elevated in confluent NRK52E cells cultured over 3 days. GDE7 plasmid-transfection of NRK52E cells augmented both extracellular and intracellular productions of LPAs (acyl and alkyl) as well as extracellular productions of cPAs (acyl and alkyl) from exogenous LPCs (acyl and alkyl). These results suggest that intact NRK52E cells are able to produce choline and LPA/cPA from exogenous LPCs through the enzymatic action of GDE7 that is located on the plasma membranes and intracellular membranes.

Hesperidin protects against aluminum-induced renal injury in rats via modulating MMP-9 and apoptosis: biochemical, histological, and ultrastructural study

Aluminum, one of the most abundant metallic elements, is known to be toxic to multiple organs including the kidneys. This study aimed to investigate the pleiotropic nephroprotective effects of Hesperidin in aluminum chloride (ALCL3)-induced renal injury, highlighting the potential molecular mechanisms underlying. Twenty-four male albino rats were divided into four groups: control, Hesperidin (80 mg/kg BW, orally), ALCL3 (10 mg/kg BW, IP), and ALCL3 + Hesperidin groups. By the end of the study, blood samples were collected, and tissue samples were harvested at sacrifice. ALCL3 rats showed dramatically declined renal function, enhanced intrarenal oxidative stress, inflammation, apoptosis, and extravagant renal histopathological damage with interstitial fibrosis as shown by a higher Endothelial, Glomerular, Tubular, and Interstitial (EGTI) score. Hesperidin significantly reversed all the aforementioned detrimental effects in ALCL3-treated rats. The study verified the nephroprotective effects of Hesperidin on ALCL3-induced renal damage and confirmed the critical role of extracellular matrix (ECM) remodeling and apoptosis inhibition.

Effect of BBT-877, a novel inhibitor of ATX, on a mouse model of type 1 diabetic nephropathy

Diabetic nephropathy (DN) is one of the common microvascular complications of diabetes. Autotaxin (ATX) is an enzyme with lysophospholipase D activity, producing lysophosphatidic acid (LPA). LPA signaling has been implicated in renal fibrosis, thereby inducing renal dysfunction. BBT-877 is an orally administered small molecule inhibitor of ATX. However, its effect on DN has not been studied so far. In this study, we investigated the effect of BBT-877, a novel inhibitor of ATX, on the pathogenesis of DN in a mouse model of streptozotocin (STZ)-induced diabetes. BBT-877 treatment significantly reduced albuminuria, albumin-to-creatinine ratio (ACR), neutrophil gelatinase-associated lipocalin (NGAL), and glomerular volume compared to the STZ-vehicle group. Interestingly, BBT-877 treatment attenuated hyperglycemia and dyslipidemia in STZ-induced diabetes mice. In the liver, the expression levels of β-oxidation-related genes such as PPAR α and CPT1 were significantly decreased in STZ-induced diabetic mice. However, this effect was reversed by BBT-877 treatment. BBT-877 treatment also suppressed mRNA levels of pro-inflammatory cytokines IL-6, MCP-1, and TNF-α and protein levels of fibrotic factors (TGF-β, fibronectin, CTGF, and collagen type Ι alpha Ι (COL1A1)) in the kidneys of STZ-induced diabetic mice. In conclusion, our results indicate that BBT-877 is effective in preventing the pathogenesis of DN by reducing systemic blood glucose levels and inhibiting inflammation and fibrosis in the renal tissue of diabetes mice. These novel findings suggest that inhibition of ATX may be a potential therapeutic target for DN.

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.

Imaging Autotaxin In Vivo with 18F-Labeled Positron Emission Tomography Ligands

Autotaxin (ATX) is a secreted phosphodiesterase that has been implicated in a remarkably wide array of pathologies, especially in fibrosis and cancer. While ATX inhibitors have entered the clinical arena, a validated probe for positron emission tomography (PET) is currently lacking. With the aim to develop a suitable ATX-targeted PET radioligand, we have synthesized a focused library of fluorinated imidazo[1,2-a]pyridine derivatives, determined their inhibition constants, and confirmed their binding mode by crystallographic analysis. Based on their promising in vitro properties, compounds 9c, 9f, 9h, and 9j were radiofluorinated. Also, a deuterated analog of [¹⁸F]9j, designated as [¹⁸F]ATX-1905 ([¹⁸F]20), was designed and proved to be highly stable against in vivo radiodefluorination compared with [¹⁸F]9c, [¹⁸F]9f, [¹⁸F]9h, and [¹⁸F]9j. These results along with in vitro and in vivo studies toward ATX in a mouse model of LPS-induced liver injury suggest that [¹⁸F]ATX-1905 is a suitable PET probe for the non-invasive quantification of ATX.

Establishment of a novel, cell-based autotaxin assay

Autotaxin (ATX) plays an important role in (patho-)physiological lysophosphatidic acid (LPA) signaling. Here we describe the establishment of novel cell-based ATX assay formats. ATX-mediated LPA generation is detected by using a stable LPA receptor reporter cell line. In a first assay variant, ATX-mediated LPA generation is started in the absence of cells and the reaction mix is transferred to the reporter cells after stopping the reaction (two-tube assay). In a second assay variant, ATX is added to the reporter cells expressing the known autotaxin binding partners integrin β1, integrin β3 and the LPA receptor 1. LPA generation is started in the presence of cells and is detected in real-time (one-tube assay). Structurally diverse ATX inhibitors with different binding modes were characterized in both cell-based assay variants and were also tested in the well-established biochemical choline release assay. ATX inhibitors displayed similar potencies, regardless if the assay was performed in the absence or presence of cells, and comparable results were obtained in all three assay formats. In summary, our novel cell-based ATX assay formats are well-suited for sensitive detection of enzyme activity as well as for the characterization of ATX inhibitors in the presence and absence of cells.

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.

Clinical Usefulness of Serum Autotaxin for Early Prediction of Relapse in Male Patients with Type 1 Autoimmune Pancreatitis

BACKGROUND

Serum IgG4 level is a useful diagnostic marker for autoimmune pancreatitis (AIP), but it is difficult to use to predict relapse.

AIMS

We investigated whether serum autotaxin (ATX) level is predictive of AIP relapse after steroid therapy.

METHODS

Fifty-six patients with type 1 AIP were investigated. We measured serum ATX at the time of diagnosis. We selected 24 males for whom serum samples during steroid therapy had been obtained and measured serum ATX at steroid therapy for induction of remission and at maintenance therapy. In the relapse group, we also measured ATX at the time of relapse.

RESULTS

ATX was significantly higher in female patients than in male patients. In order to clarify changes in ATX during steroid therapy, we focused on 24 male patients. We found that ATX decreased significantly during steroid therapy for induction of remission and at the time of maintenance therapy. In half of all patients who relapsed during maintenance therapy, ATX was significantly elevated at the time of relapse compared with that of induction therapy (P = 0.039). When we compared ATX at the time of maintenance therapy between patients with relapse and without, we observed significantly higher ATX in the former (P = 0.024). We found that the combination of ATX and elastase-1 could predict relapse with high accuracy (95%).

CONCLUSIONS

Preliminary evidence suggests that serum ATX might serve as a candidate biomarker to predict relapse of AIP as well as to monitor the effect of steroid therapy.

The linkage between inflammation and fibrosis in muscular dystrophies: The axis autotaxin-lysophosphatidic acid as a new therapeutic target?

Muscular dystrophies (MDs) are a diverse group of severe disorders characterized by increased skeletal muscle feebleness. In many cases, respiratory and cardiac muscles are also compromised. Skeletal muscle inflammation and fibrosis are hallmarks of several skeletal muscle diseases, including MDs. Until now, several keys signaling pathways and factors that regulate inflammation and fibrosis have been identified. However, no curative treatments are available. Therefore, it is necessary to find new therapeutic targets to fight these diseases and improve muscle performance. Lysophosphatidic acid (LPA) is an active glycerophospholipid mainly synthesized by the secreted enzyme autotaxin (ATX), which activates six different G protein-coupled receptors named LPA₁ to LPA₆ (LPARs). In conjunction, they are part of the ATX/LPA/LPARs axis, involved in the inflammatory and fibrotic response in several organs-tissues. This review recapitulates the most relevant aspects of inflammation and fibrosis in MDs. It analyzes experimental evidence of the effects of the ATX/LPA/LPARs axis on inflammatory and fibrotic responses. Finally, we speculate about its potential role as a new therapeutic pharmacological target to treat these diseases.

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.

Increased Levels of Renal Lysophosphatidic Acid in Rodent Models with Renal Disease

Lysophosphatidic acid (LPA) is a bioactive lipid mediator that has been implicated in the pathophysiology of kidney disease. However, few studies have attempted to measure changes in the levels of various LPA species in the kidney after the development of renal disease. The present study measured the renal LPA levels during the development of kidney disease in rat models of hypertension, diabetes, and obstructive nephropathy using liquid chromatography/mass spectrometry/mass spectrometry. LPA levels (sum of 16:0, 18:0, 18:1, 18:2, and 20:4 LPA) were higher in the renal cortex of hypertensive Dahl salt-sensitive (Dahl S) rats fed a high-salt diet than those in normotensive rats fed a low-salt diet (296.6 ± 22.9 vs. 196.3 ± 8.5 nmol/g protein). LPA levels were elevated in the outer medulla of the kidney of streptozotocin-induced type 1 diabetic Dahl S rats compared with control rats (624.6 ± 129.5 vs. 318.8 ± 17.1 nmol/g protein). LPA levels were also higher in the renal cortex of 18-month-old, type 2 diabetic nephropathy (T2DN) rats with more severe renal injury than in 6-month-old T2DN rats (184.9 ± 20.9 vs. 116.9 ± 6.0 nmol/g protein). LPA levels also paralleled the progression of renal fibrosis in the renal cortex of Sprague-Dawley rats after unilateral ureteral obstruction (UUO). Administration of an LPA receptor antagonist, Ki16425, reduced the degree of renal fibrosis in UUO rats. These results suggest that the production of renal LPA increases during the development of renal injury and contributes to renal fibrosis. SIGNIFICANCE STATEMENT: The present study reveals that the lysophosphatidic acid (LPA) levels increase in the kidney in rat models of hypertension, diabetes, and obstructive nephropathy, and administration of an LPA receptor antagonist attenuates renal fibrosis. Therapeutic approaches that target the formation or actions of renal LPA might be renoprotective and have therapeutic potential.

Radiation-Induced Lung Fibrosis: Preclinical Animal Models and Therapeutic Strategies

Radiation-induced lung injury (RILI), including acute radiation pneumonitis and chronic radiation-induced lung fibrosis, is the most common side effect of radiation therapy. RILI is a complicated process that causes the accumulation, proliferation, and differentiation of fibroblasts and, finally, results in excessive extracellular matrix deposition. Currently, there are no approved treatment options for patients with radiation-induced pulmonary fibrosis (RIPF) partly due to the absence of effective targets. Current research advances include the development of small animal models reflecting modern radiotherapy, an understanding of the molecular basis of RIPF, and the identification of candidate drugs for prevention and treatment. Insights provided by this research have resulted in increased interest in disease progression and prognosis, the development of novel anti-fibrotic agents, and a more targeted approach to the treatment of RIPF.

Lysophosphatidic Acid Receptors: Biochemical and Clinical Implications in Different Diseases

Lysophosphatidic acid (LPA, 1-acyl-2-hemolytic-sn-glycerol-3-phosphate) extracted from membrane phospholipid is a kind of simple bioactive glycophospholipid, which has many biological functions such as stimulating cell multiplication, cytoskeleton recombination, cell survival, drug-fast, synthesis of DNA and ion transport. Current studies have shown that six G-coupled protein receptors (LPAR1-6) can be activated by LPA. They stimulate a variety of signal transduction pathways through heterotrimeric G-proteins (such as Gα12/13, Gαq/11, Gαi/o and GαS). LPA and its receptors play vital roles in cancers, nervous system diseases, cardiovascular diseases, liver diseases, metabolic diseases, etc. In this article, we discussed the structure of LPA receptors and elucidated their functions in various diseases, in order to better understand them and point out new therapeutic schemes for them.

GPCR-induced YAP activation sensitizes fibroblasts to profibrotic activity of TGFβ1

Tissue fibrosis is a pathological condition characterized by uncontrolled fibroblast activation that ultimately leads to organ failure. The TGFβ1 pathway, one of the major players in establishment of the disease phenotype, is dependent on the transcriptional co-activators YAP/TAZ. We were interested whether fibroblasts can be sensitized to TGFβ1 by activation of the GPCR/YAP/TAZ axis and whether this mechanism explains the profibrotic properties of diverse GPCR ligands. We found that LPA, S1P and thrombin cooperate in human dermal fibroblasts with TGFβ1 to induce extracellular matrix synthesis, myofibroblast marker expression and cytokine secretion. Whole genome expression profiling identified a YAP/TAZ signature behind the synergistic profibrotic effects of LPA and TGFβ1. LPA, S1P and thrombin stimulation led to activation of the Rho-YAP axis, an increase of nuclear YAP-Smad2 complexes and enhanced expression of profibrotic YAP/Smad2-target genes. More generally, dermal, cardiac and lung fibroblast responses to TGFβ1 could be enhanced by increasing YAP nuclear levels (with GPCR ligands LPA, S1P, thrombin or Rho activator) and inhibited by decreasing nuclear YAP (with Rho inhibitor, forskolin, latrunculin B or 2-deoxy-glucose). Thus, we present here a conceptually interesting finding that fibroblast responses to TGFβ1 can be predicted based on the nuclear levels of YAP and modulated by stimuli/treatments that change YAP nuclear levels. Our study contributes to better understanding of fibrosis as a complex interplay of signalling pathways and proposes YAP/TAZ as promising targets in the treatment of fibrosis.

Lysophosphatidic Acid Signaling in Diabetic Nephropathy

Lysophosphatidic acid (LPA) is a bioactive phospholipid present in most tissues and body fluids. LPA acts through specific LPA receptors (LPAR1 to LPAR6) coupled with G protein. LPA binds to receptors and activates multiple cellular signaling pathways, subsequently exerting various biological functions, such as cell proliferation, migration, and apoptosis. LPA also induces cell damage through complex overlapping pathways, including the generation of reactive oxygen species, inflammatory cytokines, and fibrosis. Several reports indicate that the LPA–LPAR axis plays an important role in various diseases, including kidney disease, lung fibrosis, and cancer. Diabetic nephropathy (DN) is one of the most common diabetic complications and the main risk factor for chronic kidney diseases, which mostly progress to end-stage renal disease. There is also growing evidence indicating that the LPA–LPAR axis also plays an important role in inducing pathological alterations of cell structure and function in the kidneys. In this review, we will discuss key mediators or signaling pathways activated by LPA and summarize recent research findings associated with DN.

Associations between plasma lysophospholipids concentrations, chronic kidney disease and the type of renal replacement therapy

BACKGROUND

Lysophosphatidic acid (LPA) and lysophosphatidylcholine (LPC) are bioactive lysophospholipids involved in the pathogenesis of renal diseases, especially the renal fibrosis. Plasma LPC concentrations in chronic kidney disease (CKD) patients are lower or similar to those observed in control groups, but less is known about the LPA concentrations. The main aim of the study was the analysis of associations of chronic kidney disease and renal replacement therapy with the plasma LPA concentrations. We have also analyzed the relationship between the plasma concentrations of LPA and LPC.

MATERIAL AND METHODS

Study group consisted of 110 patients with CKD in stages G3-G5 according to the KDIGO guidelines and was divided into four subgroups: treated conservatively (CT, 30 patients), on hemodialysis (HD, 30 patients), on peritoneal dialysis (PD, 30 patients) and renal transplant recipients (RT, 20 patients). In HD the blood was collected immediately before (HD D1) and after the dialysis (HD D2). In RT the blood was collected immediately before (RT D1) and 3-14 days after the transplantation (RT D2). The control group (Con) consisted of 50 healthy volunteers. Plasma concentrations of LPA and LPC were measured using enzyme-linked immunosorbent assays.

RESULTS

In CT, PD and RT D2 plasma concentrations of LPA were significantly higher, compared to Con. In HD, LPA levels did not differ compared to Con and they were significantly lower compared to PD (HD D1 and HD D2), RT D2 (HD D1 and HD D2) and CT (HD D1). However, in most of patients concentrations of LPA were within the range of reference values established in healthy volunteers. Concentrations of LPC were significantly lower in almost all patients subgroups, compared to Con, except in PD. There were no significant correlations between plasma concentrations of LPA and LPC in any of patients subgroups.

CONCLUSIONS

Presence of CKD is associated with increased plasma LPA levels and the hemodialysis therapy reduces this influence. However, only in a small percentage of patients with CKD, LPA concentrations are out of the reference range, which makes LPA not useful as a diagnostic marker for CKD. Further studies are needed to confirm and explain observed relationships.

Development and therapeutic potential of autotaxin small molecule inhibitors: From bench to advanced clinical trials

Several years after its isolation from melanoma cells, an increasing body of experimental evidence has established the involvement of Autotaxin (ATX) in the pathogenesis of several diseases. ATX, an extracellular enzyme responsible for the hydrolysis of lysophosphatidylcholine (LPC) into the bioactive lipid lysophosphatidic acid (LPA), is overexpressed in a variety of human metastatic cancers and is strongly implicated in chronic inflammation and liver toxicity, fibrotic diseases, and thrombosis. Accordingly, the ATX-LPA signaling pathway is considered a tractable target for therapeutic intervention substantiated by the multitude of research campaigns that have been successful in identifying ATX inhibitors by both academia and industry. Furthermore, from a therapeutic standpoint, the entry and the so far promising results of the first ATX inhibitor in advanced clinical trials against idiopathic pulmonary fibrosis (IPF) lends support to the viability of this approach, bringing it to the forefront of drug discovery efforts. The present review article aims to provide a comprehensive overview of the most important series of ATX inhibitors developed so far. Special weight is lent to the design, structure activity relationship and mode of binding studies carried out, leading to the identification of advanced leads. The most significant in vitro and in vivo pharmacological results of these advanced leads are also summarized. Lastly, the development of the first ATX inhibitor entered in clinical trials accompanied by its phase 1 and 2a clinical trial data is disclosed.

Establishing a Cell-Based High-Content Screening Assay for TCM Compounds with Anti-Renal Fibrosis Effects

Renal fibrosis is thought to be the final common pathway leading to chronic kidney disease (CKD) and end-stage renal failure. Except for renal replacement therapy, no adequate treatment regimen is available; therefore studies on the treatment of renal fibrosis have attracted significant interest. In recent years, studies have shown that traditional Chinese medicine (TCM) may represent an attractive source to produce drugs with antifibrosis effects. The aim of this study was to establish a robust cell-based high-content screening (HCS) approach to identify TCM compounds with antifibrosis effects in NRK49F cells following TGF-β1 exposure. When designing the model, one of the most important steps involved the stability and reproducibility of this cell-based model. Therefore, we initially optimized the experimental parameters. Then, our HCS model was validated using SB525334, an inhibitor of the TGF-β1 receptor, and curcumin and emodin, two TCM compounds with well-documented anti-renal fibrosis activity. Subsequently, the proven reliable HCS model was used to screen a standard TCM compound library, which included 344 TCM molecules. Based on our HCS algorithm, a total of 16 compounds were identified to have prospective inhibitory activity. These compounds were further validated by verification experiments. Strikingly, eight compounds have been shown to inhibit renal fibrosis; six of them had rarely been described in the literature, namely, Ligustrazine, Glycyrrhizic acid, Astragaloside iv, Hydroxysafflor Yellow A, Crocin, and Gypenosides. To the best of our knowledge, this is the first study in which a HCS assay was performed to identify TCM compounds with anti-renal fibrosis effects. The HCS approach was successfully applied to screen active compounds and will be propitious to further anti-renal fibrosis drugs discovery research. Meanwhile, it may offer possibilities for identifying lead compounds for treating other diseases from registered Chinese herbal medicines.

Autotaxin in Pathophysiology and Pulmonary Fibrosis

Lysophospholipid signaling is emerging as a druggable regulator of pathophysiological responses, and especially fibrosis, exemplified by the relative ongoing clinical trials in idiopathic pulmonary fibrosis (IPF) patients. In this review, we focus on ectonucleotide pyrophosphatase-phosphodiesterase 2 (ENPP2), or as more widely known Autotaxin (ATX), a secreted lysophospholipase D (lysoPLD) largely responsible for extracellular lysophosphatidic acid (LPA) production. In turn, LPA is a bioactive phospholipid autacoid, forming locally upon increased ATX levels and acting also locally through its receptors, likely guided by ATX's structural conformation and cell surface associations. Increased ATX activity levels have been detected in many inflammatory and fibroproliferative conditions, while genetic and pharmacologic studies have confirmed a pleiotropic participation of ATX/LPA in different processes and disorders. In pulmonary fibrosis, ATX levels rise in the broncheoalveolar fluid (BALF) and stimulate LPA production. LPA engagement of its receptors activate multiple G-protein mediated signal transduction pathways leading to different responses from pulmonary cells including the production of pro-inflammatory signals from stressed epithelial cells, the modulation of endothelial physiology, the activation of TGF signaling and the stimulation of fibroblast accumulation. Genetic or pharmacologic targeting of the ATX/LPA axis attenuated disease development in animal models, thus providing the proof of principle for therapeutic interventions.

Microrna-139-5p inhibits epithelial-mesenchymal transition and fibrosis in post-menopausal women with interstitial cystitis by targeting LPAR4 via the PI3K/Akt signaling pathway

The study explores whether miR-139-5p targeting LPAR4 affects epithelial-mesenchymal transition (EMT) and fibrosis in post-menopausal women with interstitial cystitis (IC) via the PI3K/Akt signaling pathway. Bladder tissues of IC and normal bladder tissues were collected. The pathology of bladder tissues was observed by HE, Masson and Picrosirius red staining. LPAR4 positive expression rate were determined by IHC. ELISA was performed to detect the levels of IL-6, IL-8, IL-10, and TNF-α. Rat IC models were randomized into seven different groups. miR-139-5p, LPAR1, LPAR2, LPAR3, LPAR4, LPAR5, P13K, Akt, E-cadherin, N-cadherin, Vimentin, TGF-β1, and CTGF expression were determined by RT-qPCR and Western blotting. Dual luciferase reporter gene assay verified that LPAR4 is a target gene of miR-139-5p. Fibrosis was a pathological manifestation of IC. The IC group showed higher LPAR4, PI3K, Akt, p-PI3K, p-Akt, N-cadherin, Vimentin, TGF-β1, and CTGF expression but lower miR-139-5p and E-cadherin expression than the normal group. The levels of IL-6, IL-8, IL-10, and TNF-α expression decreased while HB-EGF increased in the IC group in comparison of the normal group. Compared with the blank and NC groups, E-cadherin expression was increased in the miR-139-5p mimic and siRNA-LPAR4 groups, while LPAR4, PI3K, Akt, p-P13K, p-Akt, N-cadherin, Vimentin, TGF-β1, and CTGF expression were decreased. An opposite trend was found in the miR-139-5p inhibitor group. The miR-139-5p decreased in the miR-139-5p inhibitor + siRNA-LPAR4 and miR-139-5p inhibitor + wortmannin groups. Conclusively, miR-139-5p targeting LPAR4 inhibits EMT and fibrosis in post-menopausal IC women through the PI3K/Akt signaling pathway.

Expression of CTGF/CCN2 in response to LPA is stimulated by fibrotic extracellular matrix via the integrin/FAK axis

Fibrosis is a common feature of several chronic diseases and is characterized by exacerbated accumulation of ECM. An understanding of the cellular and molecular mechanisms involved in the development of this condition is crucial for designing efficient treatments for those pathologies. Connective tissue growth factor (CTGF/CCN2) is a pleiotropic protein with strong profibrotic activity. In this report, we present experimental evidence showing that ECM stimulates the synthesis of CTGF in response to lysophosphatidic acid (LPA).The integrin/focal adhesion kinase (FAK) signaling pathway mediates this effect, since CTGF expression is abolished by the use of the Arg-Gly-Asp-Ser peptide and also by an inhibitor of FAK autophosphorylation at tyrosine 397. Cilengitide, a specific inhibitor of αv integrins, inhibits the expression of CTGF mediated by LPA or transforming growth factor β1. We show that ECM obtained from decellularized myofibroblast cultures or derived from activated fibroblasts from muscles of the Duchenne muscular dystrophy mouse model ( mdx) induces the expression of CTGF. This effect is dependent on FAK phosphorylation in response to its activation by integrin. We also found that the fibrotic ECM inhibits skeletal muscle differentiation. This novel regulatory mechanism of CTGF expression could be acting as a positive profibrotic feedback between the ECM and CTGF, revealing a novel concept in the control of fibrosis under chronic damage.

Role of lysophosphatidic acid and its receptors in the kidney

Lysophosphatidic acid (LPA) is a bioactive phospholipid that can exert diverse biological effects in various diseased states of the kidney by activating at least six cognate G protein-coupled receptors and its complex network of heterotrimeric G proteins. In many models of acute and chronic kidney injury, pathological elevations in LPA promotes abnormal changes in renal tubular epithelial cell architecture by activating apoptotic signaling, recruits immune cells to the site of injury, and stimulates profibrotic signaling by increasing gene transcription. In renal cancers, LPA can promote vascular cell proliferation and tumor cell invasion. In this review, a summary will be provided to describe the involvement of LPA, its synthetic enzymes, and its associated receptors in normal and diseased kidneys. Further elucidation of the LPA system may open new doors in developing a lipid-receptor therapeutic platform for kidney diseases.

Evaluation of the Lysophosphatidic Acid Receptor Type 1 Radioligand 11C-BMT-136088 for Lung Imaging in Rhesus Monkeys

The lysophosphatidic acid receptor type 1 (LPA1) is 1 of 6 known receptors of the extracellular signaling molecule lysophosphatidic acid. It mediates effects such as cell proliferation, migration, and differentiation. In the lung, LPA1 is involved in pathways leading, after lung tissue injury, to pulmonary fibrosis instead of normal healing, by mediating fibroblast recruitment and vascular leakage. Thus, a LPA1 PET radiotracer may be useful for studying lung fibrosis or for developing LPA1-targeting drugs. We developed and evaluated the radiotracer ¹¹C-BMT-136088 (1-(4'-(3-methyl-4-(((1(R)-(3-¹¹C-methylphenyl)ethoxy)carbonyl)amino)isoxazol-5-yl)-[1,1'-biphenyl]-4-yl)cyclopropane-1-carboxylic acid) in rhesus monkeys to image LPA1 in the lung in vivo with PET. Methods: The study consisted of 3 parts: test-retest scans; self-saturation to estimate the tracer's in vivo dissociation constant, nondisplaceable volume of distribution (V_ND), and nondisplaceable binding potential (BP_ND); and dosimetry. In the first 2 parts, the radiotracer was administered using a bolus-plus-infusion protocol, the arterial input function was measured, and the animals underwent 2 scans per day separated by about 4 h. Lung regions of interest were segmented, and the tissue density estimated, from CT images. A fixed blood volume correction was applied. The tracer volume of distribution (V_T) was estimated using multilinear analysis 1 (MA1) or equilibrium analysis (EA). Results:¹¹C-BMT-136088 baseline V_T was 1.83 ± 0.16 (MA1, n = 5) or 2.1 ± 0.55 (EA, n = 7) mL of plasma per gram of tissue in the left and right lung regions of interest, with a test-retest variability of -6% (MA1, n = 1) or -1% ± 14% (EA, n = 2). For the self-saturation study, ¹¹C-BMT-136088 V_ND and BP_ND were estimated to be 0.9 ± 0.08 mL of plasma per gram of tissue and 1.1 ± 0.14, respectively. The unlabeled drug dose and plasma concentration leading to a 50% reduction of ¹¹C-BMT-136088 specific binding were 73 ± 30 nmol/kg and 28 ± 12 nM, respectively. The average plasma free fraction was 0.2%; thus, the tracer's in vivo dissociation constant was estimated to be 55 pM. For the dosimetry study, the highest organ dose was in the liver (43.1 ± 4.9 and 68.9 ± 9.4 μSv/MBq in reference human male and female phantoms, respectively), and the effective dose equivalent was 6.9 ± 0.6 and 8.7 ± 0.6 μSv/MBq, respectively. Conclusion: Specific binding of ¹¹C-BMT-136088 can be reliably measured to quantify LPA1 in the lungs of rhesus monkeys in vivo.

Lysophosphatidic acid plasma concentrations in healthy subjects: circadian rhythm and associations with demographic, anthropometric and biochemical parameters

Background

Lysophosphatidic acid (LPA) is a bioactive lipid with a wide biological activity. Previous studies have shown its potential usefulness as a diagnostic marker for ovarian cancer. The aim of the study was to investigate which factors may influence plasma LPA concentrations in healthy subjects and to propose reference values.

Methods

The study group consisted of 100 healthy subjects. From all of them the blood samples were taken at 7 a.m. (fasting state). From 40 volunteers additional blood samples were taken at 2 p.m., at 8 p.m. and at 2 a.m. next morning. Concentrations of LPA were measured in plasma samples using enzyme-linked immunosorbent assay.

Results

Analysis of samples from 100 healthy volunteers showed significant influence of sex and age on plasma LPA. The reference range for the plasma LPA concentration corrected for age and sex, determined at 2.5–97.5 percentile interval is 0.14–1.64 μM. LPA correlates positively with BMI, serum total cholesterol, triacylglycerols, uric acid and negatively with estimated glomerular filtration rate and serum albumin. Concentration of LPA at 2 a.m. was lower than at 2 p.m. There were not any significant differences between plasma LPA at 7 a.m. and any other time of the day.

Conclusions

Plasma LPA is associated with demographic, anthropometric and biochemical parameters. It seems that LPA concentrations have no specific circadian rhythm and the time of donation and fasting state have marginal effect on plasma LPA. These findings may be helpful in future incorporation of LPA as a diagnostic marker.

Lysophosphatidic acid-induced RhoA signaling and prolonged macrophage infiltration worsens fibrosis and fatty infiltration following rotator cuff tears

Previous studies have suggested that macrophage-mediated chronic inflammation is involved in the development of rotator cuff muscle atrophy and degeneration following massive tendon tears. Increased RhoA signaling has been reported in chronic muscle degeneration, such as muscular dystrophy. However, the role of RhoA signaling in macrophage infiltration and rotator muscle degeneration remains unknown. Using a previously established rat model of massive rotator cuff tears, we found RhoA signaling is upregulated in rotator cuff muscle following a massive tendon-nerve injury. This increase in RhoA expression is greatly potentiated by the administration of a potent RhoA activator, lysophosphatidic acid (LPA), and is accompanied by increased TNFα and TGF-β1 expression in rotator cuff muscle. Boosting RhoA signaling with LPA significantly worsened rotator cuff muscle atrophy, fibrosis, and fatty infiltration, accompanied with massive monocytic infiltration of rotator cuff muscles. Co-staining of RhoA and the tissue macrophage marker CD68 showed that CD68+ tissue macrophages are the dominant cell source of increased RhoA signaling in rotator cuff muscles after tendon tears. Taken together, our findings suggest that LPA-mediated RhoA signaling in injured muscle worsens the outcomes of atrophy, fibrosis, and fatty infiltration by increasing macrophage infiltraion in rotator cuff muscle. Clinically, inhibiting RhoA signaling may represent a future direction for developing new treatments to improve muscle quality following massive rotator cuff tears. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1539-1547, 2017.

Lysophosphatidic Acid Signaling through the Lysophosphatidic Acid-1 Receptor Is Required for Alveolarization

Lysophosphatidic acid (LPA) signaling through one of its receptors, LPA1, contributes to both the development and the pathological remodeling after injury of many organs. Because we found previously that LPA-LPA1 signaling contributes to pulmonary fibrosis, here we investigated whether this pathway is also involved in lung development. Quantitative assessment of lung architecture of LPA1-deficient knock-out (KO) and wild-type (WT) mice at 3, 12, and 24 weeks of age using design-based stereology suggested the presence of an alveolarization defect in LPA1 KO mice at 3 weeks, which persisted as alveolar numbers increased in WT mice into adulthood. Across the ages examined, the lungs of LPA1 KO mice exhibited decreased alveolar numbers, septal tissue volumes, and surface areas, and increased volumes of the distal airspaces. Elastic fibers, critical to the development of alveolar septa, appeared less organized and condensed and more discontinuous in KO alveoli starting at P4. Tropoelastin messenger RNA expression was decreased in KO lungs, whereas expression of matrix metalloproteinases degrading elastic fibers was either decreased or unchanged. These results are consistent with the abnormal lung phenotype of LPA1 KO mice, being attributable to reduced alveolar septal formation during development, rather than to increased septal destruction as occurs in the emphysema of chronic obstructive pulmonary disease. Peripheral septal fibroblasts and myofibroblasts, which direct septation in late alveolarization, demonstrated reduced production of tropoelastin and matrix metalloproteinases, and diminished LPA-induced migration, when isolated from LPA1 KO mice. Taken together, our data suggest that LPA-LPA1 signaling is critically required for septation during alveolarization.

Autocrine lysophosphatidic acid signaling activates β-catenin and promotes lung allograft fibrosis

Tissue fibrosis is the primary cause of long-term graft failure after organ transplantation. In lung allografts, progressive terminal airway fibrosis leads to an irreversible decline in lung function termed bronchiolitis obliterans syndrome (BOS). Here, we have identified an autocrine pathway linking nuclear factor of activated T cells 2 (NFAT1), autotaxin (ATX), lysophosphatidic acid (LPA), and β-catenin that contributes to progression of fibrosis in lung allografts. Mesenchymal cells (MCs) derived from fibrotic lung allografts (BOS MCs) demonstrated constitutive nuclear β-catenin expression that was dependent on autocrine ATX secretion and LPA signaling. We found that NFAT1 upstream of ATX regulated expression of ATX as well as β-catenin. Silencing NFAT1 in BOS MCs suppressed ATX expression, and sustained overexpression of NFAT1 increased ATX expression and activity in non-fibrotic MCs. LPA signaling induced NFAT1 nuclear translocation, suggesting that autocrine LPA synthesis promotes NFAT1 transcriptional activation and ATX secretion in a positive feedback loop. In an in vivo mouse orthotopic lung transplant model of BOS, antagonism of the LPA receptor (LPA1) or ATX inhibition decreased allograft fibrosis and was associated with lower active β-catenin and dephosphorylated NFAT1 expression. Lung allografts from β-catenin reporter mice demonstrated reduced β-catenin transcriptional activation in the presence of LPA1 antagonist, confirming an in vivo role for LPA signaling in β-catenin activation.

Expression and function of lysophosphatidic acid receptors (LPARs) 1 and 3 in human hepatic cancer progenitor cells

Hepatocellular carcinoma (HCC) is the most common primary cancer of the liver and is characterized by rapid tumor expansion and metastasis. Lysophosphatidic acid (LPA) signaling, via LPA receptors 1–6 (LPARs1–6), regulates diverse cell functions including motility, migration, and proliferation, yet the role of LPARs in hepatic tumor pathology is poorly understood. We sought to determine the expression and function of endothelial differentiation gene (EDG) LPARs (LPAR1–3) in human HCC and complimentary in vitro models. Human HCC were characterized by significantly elevated LPAR1/LPAR3 expression in the microenvironment between the tumor and non-tumor liver (NTL), a finding mirrored in human SKHep1 cells. Analysis of human tissue and human hepatic tumor cells in vitro revealed cells that express LPAR3 (HCC-NTL margin in vivo and SKHep1 in vitro) also express cancer stem cell markers in the absence of hepatocyte markers. Treatment of SKHep1 cells with exogenous LPA led to significantly increased cell motility but not proliferation. Using pharmacological agents and cells transfected to knock-down LPAR1 or LPAR3 demonstrated LPA-dependent cell migration occurs via an LPAR3-Gi-ERK-pathway independent of LPAR1. These data suggest cells that stain positive for both LPAR3 and cancer stem cell markers are distinct from the tumor mass per se, and may mediate tumor invasiveness/expansion via LPA-LPAR3 signaling.

Synergistic induction of CTGF by cytochalasin D and TGFβ-1 in primary human renal epithelial cells: Role of transcriptional regulators MKL1, YAP/TAZ and Smad2/3

Changes in cell morphology that involve alterations of the actin cytoskeleton are a hallmark of diseased renal tubular epithelial cells. While the impact of actin remodeling on gene expression has been analyzed in many model systems based on cell lines, this study investigated human primary tubular epithelial cells isolated from healthy parts of tumor nephrectomies. Latrunculin B (LatB) and cytochalasin D (CytoD) were used to modulate G-actin levels in a receptor-independent manner. Both compounds (at 0.5μM) profoundly altered F-actin structures in a Rho kinase-dependent manner, but only CytoD strongly induced the pro-fibrotic factor CTGF (connective tissue growth factor). CTGF induction was dependent on YAP as shown by transient downregulation experiments. However, CytoD did not alter the nuclear localization of either YAP or TAZ, whereas LatB reduced nuclear levels particularly of TAZ. CytoD modified MKL1, a coactivator of serum response factor (SRF) regulating CTGF induction, and promoted its nuclear localization. TGFβ-1 is one of the major factors involved in tubulointerstitial disease and an inducer of CTGF. Preincubation with CytoD but not LatB synergistically enhanced the TGFβ-1-stimulated synthesis of CTGF, both in cells cultured on plastic dishes as well as in polarized epithelial cells. CytoD had no direct effect on the phosphorylation of Smad2/3, but facilitated their phosphorylation and thus activation by TGFβ-1. Our present findings provide evidence that morphological alterations have a strong impact on cellular signaling of one of the major pro-fibrotic factors, TGFβ-1. However, our data also indicate that changes in cell morphology per se cannot predict those interactions which are critically dependent on molecular fine tuning of actin reorganization.

Metabolomic Signatures of Chronic Kidney Disease of Diverse Etiologies in the Rats and Humans

Chronic kidney disease (CKD) has emerged as a major public health problem worldwide. It frequently progresses to end-stage renal disease, which is related to very high cost and mortality. Novel biomarkers can provide insight into the novel mechanism, facilitate early detection, and monitor progression of CKD and its response to therapeutic interventions. To identify potential biomarkers, we applied an UPLC-HDMS together with univariate and multivariate statistical analyses using plasma samples from patients with CKD of diverse etiologies (100 sera in discovery set and 120 sera in validation set) and two different rat models of CKD. Using comprehensive screening and validation workflow, we identified a panel of seven metabolites that were shared by all patients and animals regardless of the underlying cause of CKD. These included ricinoleic acid, stearic acid, cytosine, LPA(16:0), LPA(18:2), 3-methylhistidine, and argininic acid. The combination of these seven biomarkers enabled the discrimination of patients with CKD from healthy subjects with a sensitivity of 83.3% and a specificity of 96.7%. In addition, these biomarkers accurately reflected improvements in renal function in response to the therapeutic interventions. Our results indicated that the identified biomarkers may improve the diagnosis of CKD and provide a novel tool for monitoring of the progression of disease and response to treatment in CKD patients.

An integrated lipidomics and metabolomics reveal nephroprotective effect and biochemical mechanism of Rheum officinale in chronic renal failure

Chronic renal failure (CRF) is a major public health problem worldwide. Earlier studies have revealed salutary effects of rhubarb extracts in CRF. In this study, we employed lipidomic and metabolomic approaches to identify the plasma biomarkers and to determine the effect of treatment with petroleum ether, ethyl acetate and n-butanol extracts of rhubarb in a rat model of CRF with adenine-induced chronic tubulointerstitial nephropathy. In addition, clinical biochemistry, histological evaluation and pro-fibrotic protein expression were analyzed. Significant changes were found between the CRF and control groups representing characteristic phenotypes of rats with CRF. Treatment with the three rhubarb extracts improved renal injury and dysfunction, either fully or partially reversed the plasma metabolites abnormalities and attenuated upregulation of pro-fibrotic proteins including TGF-β1, α-SMA, PAI-1, CTGF, FN and collagen-1. The nephroprotective effect of ethyl acetate extract was better than other extracts. The differential metabolites were closely associated with glycerophospholipid, fatty acid and amino acid metabolisms. The results revealed a strong link between renal tubulointerstitial fibrosis and glycerophospholipid metabolism and L-carnitine metabolism in the development of CRF. Amelioration of CRF with the three rhubarb extracts was associated with the delayed development and/or reversal the disorders in key metabolites associated with adenine-induced CRF.

Serum Autotaxin Levels Are Associated with Proteinuria and Kidney Lesions in Japanese Type 2 Diabetic Patients with Biopsy-proven Diabetic Nephropathy

Objective We evaluated the relationships between the serum autotaxin (ATX) levels and the clinical and pathological parameters, as well as the long-term renal outcome, in type 2 diabetic patients with biopsy-proven diabetic nephropathy. Methods In this retrospective single-center cohort study, serum samples were collected from 38 Japanese type 2 diabetic patients with biopsy-proven diabetic nephropathy at the time of renal biopsy. The serum ATX levels were measured using a specific sandwich enzyme immunoassay. Results A multivariate linear regression analysis revealed the urinary protein excretion to be independently associated with the serum ATX levels. In addition, patients with serum ATX levels above the median showed more advanced diffuse lesions, nodular lesions and arteriolar hyalinosis compared to those with serum ATX levels below the median. However, high serum ATX levels were not associated with any increase in the number of renal composite events [a need for dialysis or a 50% decline in the estimated glomerular filtration rate (eGFR) from baseline]. Conclusion The serum ATX levels in type 2 diabetic patients with diabetic nephropathy were associated with proteinuria and diabetic kidney lesions, although the serum ATX levels were not identified to be a predictive indicator for the renal outcome.

Tubular cell phenotype in HIV-associated nephropathy: role of phospholipid lysophosphatidic acid

Collapsing glomerulopathy and microcysts are characteristic histological features of HIV-associated nephropathy (HIVAN). We have previously reported the role of epithelial mesenchymal transition (EMT) in the development of glomerular and tubular cell phenotypes in HIVAN. Since persistent tubular cell activation of NFκB has been reported in HIVAN, we now hypothesize that HIV may be contributing to tubular cell phenotype via lysophosphatidic acid (LPA) mediated downstream signaling. Interestingly, LPA and its receptors have also been implicated in the tubular interstitial cell fibrosis (TIF) and cyst formation in autosomal dominant polycystic kidney disease (PKD). Primary human proximal tubular cells (HRPTCs) were transduced with either empty vector (EV/HRPTCs), HIV (HIV/HRPTCs) or treated with LPA (LPA/HRPTC). Immunoelectrophoresis of HIV/HRPTCs and LPA/HRPTCs displayed enhanced expression of pro-fibrotic markers: a) fibronectin (2.25 fold), b) connective tissue growth factor (CTGF; 4.8 fold), c) α-smooth muscle actin (α-SMA; 12 fold), and d) collagen I (5.7 fold). HIV enhanced tubular cell phosphorylation of ILK-1, FAK, PI3K, Akt, ERKs and P38 MAPK. HIV increased tubular cell transcriptional binding activity of NF-κB; whereas, a LPA biosynthesis inhibitor (AACOCF3), a DAG kinase inhibitor, a LPA receptor blocker (Ki16425), a NF-κB inhibitor (PDTC) and NFκB-siRNA not only displayed downregulation of a NFκB activity but also showed attenuated expression of profibrotic/EMT genes in HIV milieu. These findings suggest that LPA could be contributing to HIV-induced tubular cell phenotype via NFκB activation in HIVAN.

Anti-fibrotic effect of natural toxin bee venom on animal model of unilateral ureteral obstruction

Progressive renal fibrosis is the final common pathway for all kidney diseases leading to chronic renal failure. Bee venom (BV) has been widely used as a traditional medicine for various diseases. However, the precise mechanism of BV in ameliorating the renal fibrosis is not fully understood. To investigate the therapeutic effects of BV against unilateral ureteral obstruction (UUO)-induced renal fibrosis, BV was given intraperitoneally after ureteral ligation. At seven days after UUO surgery, the kidney tissues were collected for protein analysis and histologic examination. Histological observation revealed that UUO induced a considerable increase in the number of infiltrated inflammatory cells. However, BV treatment markedly reduced these reactions compared with untreated UUO mice. The expression levels of TNF-α and IL-1β were significantly reduced in BV treated mice compared with UUO mice. In addition, treatment with BV significantly inhibited TGF-β1 and fibronectin expression in UUO mice. Moreover, the expression of α-SMA was markedly withdrawn after treatment with BV. These findings suggest that BV attenuates renal fibrosis and reduces inflammatory responses by suppression of multiple growth factor-mediated pro-fibrotic genes. In conclusion, BV may be a useful therapeutic agent for the prevention of fibrosis that characterizes progression of chronic kidney disease.

Evaluation of 11C-acetate and 18F-FDG PET/CT in mouse multidrug resistance gene-2 deficient mouse model of hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) remains a global health problem with unique diagnostic and therapeutic challenges, including difficulties in identifying the highest risk patients. Previous work from our lab has established the murine multidrug resistance-2 mouse (MDR2) model of HCC as a reasonable preclinical model that parallels the changes seen in human inflammatory associated HCC. The purpose of this study is to evaluate modalities of PET/CT in MDR2(-/-) mice in order to facilitate therapeutic translational studies from bench to bedside.

METHODS

18F-FDG and 11C-acetate PET/CT was performed on 12 m MDR2(-/-) mice (n = 3/tracer) with HCC and 12 m MDR2(-/+) control mice (n = 3/tracer) without HCC. To compare PET/CT to biological markers of HCC and cellular function, serum alpha-fetoprotein (AFP), lysophosphatidic acid (LPA), cAMP and hepatic tumor necrosis factor α (TNFα) were quantified in 3-12 m MDR2(-/-) (n = 10) mice using commercially available ELISA analysis. To translate results in mice to patients 11C-acetate PET/CT was also performed in 8 patents suspected of HCC recurrence following treatment and currently on the liver transplant wait list.

RESULTS

Hepatic18F-FDG metabolism was not significantly increased in MDR2(-/-) mice. In contrast, hepatic 11C-acetate metabolism was significantly elevated in MDR2(-/-) mice when compared to MDR2(-/+) controls. Serum AFP and LPA levels increased in MDR2(-/-) mice contemporaneous with the emergence of HCC. This was accompanied by a significant decrease in serum cAMP levels and an increase in hepatic TNFα. In patients suspected of HCC recurrence there were 5 true positives, 2 true negatives and 1 suspected false 11C-acetate negative.

CONCLUSIONS

Hepatic 11C-acetate PET/CT tracks well with HCC in MDR2(-/-) mice and patients with underlying liver disease. Consequently 11C-acetate PET/CT is well suited to study (1) HCC emergence/progression in patients and (2) reduce animal numbers required to study new chemotherapeutics in murine models of HCC.

Reduced kidney levels of lysophosphatidic acids in rats after chronic administration of aristolochic acid: Its possible protective role in renal fibrosis

Aristolochic acid (AA) is considered to be a causative agent for progressive interstitial renal fibrosis, leading to AA nephropathy. Lysophosphatidic acid (LPA) is a mediator in the onset of renal fibrosis. In this study, we analyzed the molecular species of LPA and its precursor lysophospholipids in kidney tissue from rats exposed to AA. Daily intraperitoneal injections of AA for 35 days to rats gave rise to fibrosis in kidney, decreased the kidney levels of LPA, lysophosphatidylserine and lysophosphatidylinositol. In rat renal cell lines (NRK52E and NRK49F), AA-induced cytotoxicity was potentiated by Ki16425, LPA_1,3 receptor antagonist. The level of mRNA encording α-smooth muscle actin was significantly increased by AA-treatment only in NRK52E cells, while the mRNA level of collagen III was decreased in both NRK52E and NRK49F cells. These results suggest that endogenous LPA in rat kidney prevents AA-induced renal fibrosis.

Lysophosphatidic acid mediates fibrosis in injured joints by regulating collagen type I biosynthesis

OBJECTIVE

Articular cartilage is a highly specialized tissue which forms the surfaces in synovial joints. Full-thickness cartilage defects caused by trauma or microfracture surgery heal via the formation of fibrotic tissue characterized by a high content of collagen I (COL I) and subsequent poor mechanical properties. The goal of this study is to investigate the molecular mechanisms underlying fibrosis after joint injury.

DESIGN

Rat knee joint models were used to mimic cartilage defects after acute injury. Immunohistochemistry was performed to detect proteins related to fibrosis. Human fetal chondrocytes and bone marrow stromal cells (BMSCs) were used to study the influence of the lipid lysophosphatidic acid (LPA) on COL I synthesis. Quantitative PCR, ELISA and immunohistochemistry were performed to evaluate the production of COL I. Chemical inhibitors were used to block LPA signaling both in vitro and in vivo.

RESULTS

After full-thickness cartilage injury in rat knee joints, stromal cells migrating to the injury expressed high levels of the LPA-producing enzyme autotaxin (ATX); intact articular cartilage in rat and humans expressed negligible levels of ATX despite expressing the LPA receptors LPAR1 and LPAR2. LPA-induced increases in COL I production by chondrocytes and BMSCs were mediated by the MAP kinase and PI3 Kinase signaling pathways. Inhibition of the ATX/LPA axis significantly reduced COL I-enriched fibrocartilage synthesis in full-thickness cartilage defects in rats in favor of the collagen II-enriched normal state.

CONCLUSION

Taken together, these results identify an attractive target for intervention in reducing the progression of post-traumatic fibrosis and osteoarthritis.

Possible role of lysophosphatidic acid in rat model of hypoxic pulmonary vascular remodeling

Pulmonary hypertension is characterized by cellular and structural changes in the vascular wall of pulmonary arteries. We hypothesized that lysophosphatidic acid (LPA), a bioactive lipid, is implicated in this vascular remodeling in a rat model of hypoxic pulmonary hypertension. Exposure of Wistar rats to 10% O2 for 3 weeks induced an increase in the mean serum levels of LPA, to 40.9 (log-detransformed standard deviations: 23.4-71.7) μM versus 21.6 (11.0-42.3) μM in a matched control animal group (P = 0.037). We also observed perivascular LPA immunohistochemical staining in lungs of hypoxic rats colocalized with the secreted lysophospholipase D autotaxin (ATX). Moreover, ATX colocalized with mast cell tryptase, suggesting implication of these cells in perivascular LPA production. Hypoxic rat lungs expressed more ATX transcripts (2.4-fold) and more transcripts of proteins implicated in cell migration: β2 integrin (1.74-fold), intracellular adhesion molecule 1 (ICAM-1; 1.84-fold), and αM integrin (2.70-fold). Serum from the hypoxic group of animals had significantly higher chemoattractant properties toward rat primary lung fibroblasts, and this increase in cell migration could be prevented by the LPA receptor 1 and 3 antagonists. LPA also increased adhesive properties of human pulmonary artery endothelial cells as well as those of human peripheral blood mononuclear cells, via the activation of LPA receptor 1 or 3 followed by the stimulation of gene expression of ICAM-1, β-1, E-selectin, and vascular cell adhesion molecule integrins. In conclusion, chronic hypoxia increases circulating and tissue levels of LPA, which might induce fibroblast migration and recruitment of mononuclear cells in pulmonary vasculature, both of which contribute to pulmonary vascular remodeling.

Lysophospholipid receptor nomenclature review: IUPHAR Review 8

Lysophospholipids encompass a diverse range of small, membrane-derived phospholipids that act as extracellular signals. The signalling properties are mediated by 7-transmembrane GPCRs, constituent members of which have continued to be identified after their initial discovery in the mid-1990s. Here we briefly review this class of receptors, with a particular emphasis on their protein and gene nomenclatures that reflect their cognate ligands. There are six lysophospholipid receptors that interact with lysophosphatidic acid (LPA): protein names LPA1 - LPA6 and italicized gene names LPAR1-LPAR6 (human) and Lpar1-Lpar6 (non-human). There are five sphingosine 1-phosphate (S1P) receptors: protein names S1P1 -S1P5 and italicized gene names S1PR1-S1PR5 (human) and S1pr1-S1pr5 (non-human). Recent additions to the lysophospholipid receptor family have resulted in the proposed names for a lysophosphatidyl inositol (LPI) receptor - protein name LPI1 and gene name LPIR1 (human) and Lpir1 (non-human) - and three lysophosphatidyl serine receptors - protein names LyPS1 , LyPS2 , LyPS3 and gene names LYPSR1-LYPSR3 (human) and Lypsr1-Lypsr3 (non-human) along with a variant form that does not appear to exist in humans that is provisionally named LyPS2L . This nomenclature incorporates previous recommendations from the International Union of Basic and Clinical Pharmacology, the Human Genome Organization, the Gene Nomenclature Committee, and the Mouse Genome Informatix.

Diabetic nephropathy induces alterations in the glomerular and tubule lipid profiles

Diabetic nephropathy (DN) is a major life-threatening complication of diabetes. Renal lesions affect glomeruli and tubules, but the pathogenesis is not completely understood. Phospholipids and glycolipids are molecules that carry out multiple cell functions in health and disease, and their role in DN pathogenesis is unknown. We employed high spatial resolution MALDI imaging MS to determine lipid changes in kidneys of eNOS(-/-) db/db mice, a robust model of DN. Phospholipid and glycolipid structures, localization patterns, and relative tissue levels were determined in individual renal glomeruli and tubules without disturbing tissue morphology. A significant increase in the levels of specific glomerular and tubular lipid species from four different classes, i.e., gangliosides, sulfoglycosphingolipids, lysophospholipids, and phosphatidylethanolamines, was detected in diabetic kidneys compared with nondiabetic controls. Inhibition of nonenzymatic oxidative and glycoxidative pathways attenuated the increase in lipid levels and ameliorated renal pathology, even though blood glucose levels remained unchanged. Our data demonstrate that the levels of specific phospho- and glycolipids in glomeruli and/or tubules are associated with diabetic renal pathology. We suggest that hyperglycemia-induced DN pathogenic mechanisms require intermediate oxidative steps that involve specific phospholipid and glycolipid species.

Lysophosphatidic acid receptor-2 deficiency confers protection against bleomycin-induced lung injury and fibrosis in mice

Idiopathic pulmonary fibrosis is a devastating disease characterized by alveolar epithelial cell injury, the accumulation of fibroblasts/myofibroblasts, and the deposition of extracellular matrix proteins. Lysophosphatidic acid (LPA) signaling through its G protein-coupled receptors is critical for its various biological functions. Recently, LPA and LPA receptor 1 were implicated in lung fibrogenesis. However, the role of other LPA receptors in fibrosis remains unclear. Here, we use a bleomycin-induced pulmonary fibrosis model to investigate the roles of LPA2 in pulmonary fibrogenesis. In the present study, we found that LPA2 knockout (Lpar2(-/-)) mice were protected against bleomycin-induced lung injury, fibrosis, and mortality, compared with wild-type control mice. Furthermore, LPA2 deficiency attenuated the bleomycin-induced expression of fibronectin (FN), α-smooth muscle actin (α-SMA), and collagen in lung tissue, as well as levels of IL-6, transforming growth factor-β (TGF-β), and total protein in bronchoalveolar lavage fluid. In human lung fibroblasts, the knockdown of LPA2 attenuated the LPA-induced expression of TGF-β1 and the differentiation of lung fibroblasts to myofibroblasts, resulting in the decreased expression of FN, α-SMA, and collagen, as well as decreased activation of extracellular regulated kinase 1/2, Akt, Smad3, and p38 mitogen-activated protein kinase. Moreover, the knockdown of LPA2 with small interfering RNA also mitigated the TGF-β1-induced differentiation of lung fibroblasts. In addition, LPA2 deficiency significantly attenuated the bleomycin-induced apoptosis of alveolar and bronchial epithelial cells in the mouse lung. Together, our data indicate that the knockdown of LPA2 attenuated bleomycin-induced lung injury and pulmonary fibrosis, and this may be related to an inhibition of the LPA-induced expression of TGF-β and the activation and differentiation of fibroblasts.