Anti-lysophosphatidic acid antibodies improve traumatic brain injury outcomes

Glycerophospholipid dysregulation after traumatic brain injury

Brain tissue is highly enriched in lipids, the majority of which are glycerophospholipids. Glycerophospholipids are the major constituents of cellular membranes and play an important role in maintaining integrity and function of cellular and subcellular structures. Any changes in glycerophospholipid homeostasis can adversely affect brain functions. Traumatic brain injury (TBI), an acquired injury caused by the impact of external forces to the brain, triggers activation of secondary biochemical events that include perturbation of lipid homeostasis. Several studies have demonstrated glycerophospholipid dysregulation in the brain and circulation after TBI. This includes spatial and temporal changes in abundance and distribution of glycerophospholipids in the injured brain. This is at least in part mediated by TBI-induced oxidative stress and by activation of lipid metabolism pathways involved in tissue repairing. In this review, we discuss current advances in understanding of the mechanisms and implications of glycerophospholipid dysregulation following TBI.

Neurological Improvement via Lysophosphatidic Acid Administration in a Rodent Model of Cardiac Arrest-Induced Brain Injury

Lysophosphatidic acid (LPA) serves as a fundamental constituent of phospholipids. While prior studies have shown detrimental effects of LPA in a range of pathological conditions, including brain ischemia, no studies have explored the impact of LPA in the context of cardiac arrest (CA). The aim of this study is to evaluate the effects of the intravenous administration of an LPA species containing oleic acid, LPA (18:1) on the neurological function of rats (male, Sprague Dawley) following 8 min of asphyxial CA. Baseline characteristics, including body weight, surgical procedure time, and vital signs before cardiac arrest, were similar between LPA (18:1)-treated (n = 10) and vehicle-treated (n = 10) groups. There was no statistically significant difference in 24 h survival between the two groups. However, LPA (18:1)-treated rats exhibited significantly improved neurological function at 24 h examination (LPA (18:1), 85.4% ± 3.1 vs. vehicle, 74.0% ± 3.3, p = 0.045). This difference was most apparent in the retention of coordination ability in the LPA (18:1) group (LPA (18:1), 71.9% ± 7.4 vs. vehicle, 25.0% ± 9.1, p < 0.001). Overall, LPA (18:1) administration in post-cardiac arrest rats significantly improved neurological function, especially coordination ability at 24 h after cardiac arrest. LPA (18:1) has the potential to serve as a novel therapeutic in cardiac arrest.

CSF hypersecretion versus impaired CSF absorption in posthemorrhagic hydrocephalus: a systematic review

BACKGROUND

The molecular mechanisms underlying development of posthemorrhagic hydrocephalus (PHH) remain elusive. The aim of this systematic review was to evaluate existing literature on increased CSF secretion and impaired CSF absorption as pathogenic contributors to CSF accumulation in neonatal and adult PHH.

METHODS

The systematic review was conducted in accordance with the PRISMA guidelines. Relevant studies published before March 11th, 2023, were identified from PubMed and reference lists. Studies were screened for eligibility using predefined inclusion and exclusion criteria. Data from eligible studies were extracted and potential sources of bias were evaluated.

RESULTS

Nineteen studies quantified CSF production rates and/or CSF absorption capacity in human patients with PHH or animals with experimentally induced PHH. Increased CSF production was reported as early as 24 h and as late as 28 days post ictus in six out of eight studies quantifying CSF production rates in animals with experimentally induced PHH. Impaired CSF absorption was reported in all four studies quantifying CSF absorption capacity in human patients with PHH and in seven out of nine studies quantifying CSF absorption capacity in animals with experimentally induced PHH. Impaired CSF absorption was reported as early as 30 min and as late as 10 months post ictus.

CONCLUSIONS

The pathological CSF accumulation in PHH likely arises from a combination of increased CSF secretion and impaired CSF absorption, which may manifest at different time scales following a hemorrhagic event. Emergent evidence on increased CSF secretion by the choroid plexus may herald a paradigm shift in our understanding of PHH.

Distinct Cerebrospinal Fluid Lipid Signature in Patients with Subarachnoid Hemorrhage-Induced Hydrocephalus

Patients with subarachnoid hemorrhage (SAH) may develop posthemorrhagic hydrocephalus (PHH), which is treated with surgical cerebrospinal fluid (CSF) diversion. This diversion is associated with risk of infection and shunt failure. Biomarkers for PHH etiology, CSF dynamics disturbances, and potentially subsequent shunt dependency are therefore in demand. With the recent demonstration of lipid-mediated CSF hypersecretion contributing to PHH, exploration of the CSF lipid signature in relation to brain pathology is of interest. Despite being a relatively new addition to the omic's landscape, lipidomics are increasingly recognized as a tool for biomarker identification, as they provide a comprehensive overview of lipid profiles in biological systems. We here employ an untargeted mass spectroscopy-based platform and reveal the complete lipid profile of cisternal CSF from healthy control subjects and demonstrate its bimodal fluctuation with age. Various classes of lipids, in addition to select individual lipids, were elevated in the ventricular CSF obtained from patients with SAH during placement of an external ventricular drain. The lipidomic signature of the CSF in the patients with SAH suggests dysregulation of the lipids in the CSF in this patient group. Our data thereby reveal possible biomarkers present in a brain pathology with a hemorrhagic event, some of which could be potential future biomarkers for hypersecretion contributing to ventriculomegaly and thus pharmacological targets for pathologies involving disturbed CSF dynamics.

Cerebrospinal Fluid Levels of Lysophosphatidic Acids Can Provide Suitable Biomarkers of Blast-Induced Traumatic Brain Injury

Blast-induced traumatic brain injury (bTBI) has been identified as the signature injury of Operation Iraqi Freedom and Operation Enduring Freedom. Although the incidence of bTBI increased significantly after the introduction of improvised explosive devices, the mechanism of the injury is still uncertain, which is negatively impacting the development of suitable countermeasures. Identification of suitable biomarkers that could aid in the proper diagnosis of and prognosis for both acute and chronic bTBI is essential since bTBI frequently is occult and may not be associated with overtly detectable injuries to the head. Lysophosphatidic acid (LPA) is a bioactive phospholipid generated by activated platelets, astrocytes, choroidal plexus cells and microglia and is reported to play major roles in stimulating inflammatory processes. The levels of LPA in the cerebrospinal fluid (CSF) have been reported to increase acutely after non-blast related brain injuries. In the present study, we have evaluated the utility of LPA levels measured in the CSF and plasma of laboratory rats as an acute and chronic biomarker of brain injury resulting from single and tightly coupled repeated blast overpressure exposures. In the CSF, many LPA species increased at acute time-points, returned to normal levels at 1 month, and increased again at 6 months and 1 year post-blast overpressure exposures. In the plasma, several LPA species increased acutely, returned to normal levels by 24 h, and were significantly decreased at 1 year post-blast overpressure exposures. These decreases in LPA species in the plasma were associated with decreased levels of lysophosphatidyl choline, suggesting a defective upstream biosynthetic pathway of LPAs in the plasma. Notably, the changes in LPA levels in the CSF (but not plasma) negatively correlated with neurobehavioral functions in these rats, suggesting that CSF levels of LPAs may provide a suitable biomarker of bTBI that reflects severity of injury.

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

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

2-carba-cyclic phosphatidic acid modulates astrocyte-to-microglia communication and influences microglial polarization towards an anti-inflammatory phenotype

2-carba-cyclic phosphatidic acid (2ccPA) suppresses microglial and astrocyte inflammation for neuronal survival following traumatic brain injury. However, it remains unknown how 2ccPA regulates microglial activation. In this study, to elucidate the 2ccPA behavior in glial communication, we collected the astrocyte conditioned media (ACM) from primary astrocyte cultures that were treated by lipopolysaccharide (LPS) and 2ccPA and analyzed the alteration of microglial inflammation caused by the ACM treatment. The addition of the ACM derived from LPS- and 2ccPA-double treated astrocytes to microglia decreased the CD86⁺ pro-inflammatory M1 microglia, which were upregulated with the ACM collected from astrocytes treated by LPS without 2ccPA, while the direct addition of LPS and 2ccPA to microglia failed to decrease the CD86⁺ microglia to the basal level. We confirmed that the ACM from LPS- and 2ccPA-treated astrocytes increased the ratio of CD206⁺ anti-inflammatory M2 microglia to total microglia, whereas direct treatment of microglia with LPS and 2ccPA had no effect on the CD206⁺ microglia ratio, demonstrating the importance of astrocyte intervention in microglial polarization. In addition, we examined whether astrocytes modulate the 2ccPA-regulated proinflammatory cytokine production derived from microglia. The addition of the ACM from LPS- and 2ccPA-treated astrocytes to microglia remarkably canceled the LPS-induced upregulation of IL-1β, IL-6, and TNF-α secreted from microglia, while the direct addition of LPS and 2ccPA to microglia showed no affect. Therefore, our results indicate that astrocytes mediate the 2ccPA function to shift microglia towards the M2 phenotype by interfering with the polarization of M1 microglia and to suppress cytokine production.

Astrocytic Neuroimmunological Roles Interacting with Microglial Cells in Neurodegenerative Diseases

Both astrocytic and microglial functions have been extensively investigated in healthy subjects and neurodegenerative diseases. For astrocytes, not only various sub-types were identified but phagocytic activity was also clarified recently and is making dramatic progress. In this review paper, we mostly focus on the functional role of astrocytes in the extracellular matrix and on interactions between reactive astrocytes and reactive microglia in normal states and in neurodegenerative diseases, because the authors feel it is necessary to elucidate the mechanisms among activated glial cells in the pathology of neurological diseases in order to pave the way for drug discovery. Finally, we will review cyclic phosphatidic acid (cPA), a naturally occurring phospholipid mediator that induces a variety of biological activities in the brain both in vivo and in vitro. We propose that cPA may serve as a novel therapeutic molecule for the treatment of brain injury and neuroinflammation.

Inhibition of Autotaxin Ameliorates LPA-Mediated Neuroinflammation and Alleviates Neurological Dysfunction in Acute Hepatic Encephalopathy

Growing evidence suggests an essential role of neuroinflammation in behavioral abnormalities associated with hepatic encephalopathy (HE). Here, we report the involvement of autotaxin-lysophosphatidic acid (LPA) signaling in HE's pathogenesis. We demonstrate that the autotaxin (ATX) inhibitor PF-8380 attenuates neuroinflammation and improves neurological dysfunction in the mouse model of HE. In the thioacetamide (TAA)-induced model of HE, we found a twofold increase in the levels of ammonia in the brain and in plasma along with a significant change in HE-related behavioral parameters. Mice with HE show an increased brain weight, increased levels of tumor necrosis factor-α (TNF-α), IL-1β (interleukin-1β), interleukin-6 (IL-6), and LPA 18:0 in the cerebral cortex and hippocampus, and increased levels of LPA 18:0 in plasma. Treatment with the autotaxin inhibitor (ATXi) did not affect liver injury, as we observed no change in liver function markers including aspartate aminotransferase (AST), alanine aminotransferase (ALT), and total bilirubin (TBIL) and no change in ammonia levels in the brain and plasma. However, ATXi treatment significantly ameliorated the neuroinflammation, reduced the levels of LPA 18:0 in the cerebral cortex and hippocampus in the brain and plasma, and reduced brain edema and the levels of IL1β, IL-6, and TNF-α. The neurobehavioral symptoms for HE such as the cognitive and motor function deficit and overall clinical grading score were significantly improved in ATXi-treated mice. Mouse astrocytes and microglia stimulated with NH₄CL with or without ATXi showed significant attenuation of oxidative stress and the neuroinflammatory effect of NH4CL in ATXi-treated cells.

Lysophosphatidic acid as a CSF lipid in posthemorrhagic hydrocephalus that drives CSF accumulation via TRPV4-induced hyperactivation of NKCC1

Background

A range of neurological pathologies may lead to secondary hydrocephalus. Treatment has largely been limited to surgical cerebrospinal fluid (CSF) diversion, as specific and efficient pharmacological options are lacking, partly due to the elusive molecular nature of the CSF secretion apparatus and its regulatory properties in physiology and pathophysiology.

Methods

CSF obtained from patients with subarachnoid hemorrhage (SAH) and rats with experimentally inflicted intraventricular hemorrhage (IVH) was analyzed for lysophosphatidic acid (LPA) by alpha-LISA. We employed the in vivo rat model to determine the effect of LPA on ventricular size and brain water content, and to reveal the effect of activation and inhibition of the transient receptor potential vanilloid 4 (TRPV4) ion channel on intracranial pressure and CSF secretion rate. LPA-mediated modulation of TRPV4 was determined with electrophysiology and an ex vivo radio-isotope assay was employed to determine the effect of these modulators on choroid plexus transport.

Results

Elevated levels of LPA were observed in CSF obtained from patients with subarachnoid hemorrhage (SAH) and from rats with experimentally-inflicted intraventricular hemorrhage (IVH). Intraventricular administration of LPA caused elevated brain water content and ventriculomegaly in experimental rats, via its action as an agonist of the choroidal transient receptor potential vanilloid 4 (TRPV4) channel. TRPV4 was revealed as a novel regulator of ICP in experimental rats via its ability to modulate the CSF secretion rate through its direct activation of the Na⁺/K⁺/2Cl⁻ cotransporter (NKCC1) implicated in CSF secretion.

Conclusions

Together, our data reveal that a serum lipid present in brain pathologies with hemorrhagic events promotes CSF hypersecretion and ensuing brain water accumulation via its direct action on TRPV4 and its downstream regulation of NKCC1. TRPV4 may therefore be a promising future pharmacological target for pathologies involving brain water accumulation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00361-9.

KAI1/CD82 gene and autotaxin-lysophosphatidic acid axis in gastrointestinal cancers

The KAI1/CD82 gene inhibits the metastasis of most tumors and is remarkably correlated with tumor invasion and prognosis. Cell metabolism dysregulation is an important cause of tumor occurrence, development, and metastasis. As one of the important characteristics of tumors, cell metabolism dysregulation is attracting increasing research attention. Phospholipids are an indispensable substance in the metabolism in various tumor cells. Phospholipid metabolites have become important cell signaling molecules. The pathological role of lysophosphatidic acid (LPA) in tumors was identified in the early 1990s. Currently, LPA inhibitors have entered clinical trials but are not yet used in clinical treatment. Autotaxin (ATX) has lysophospholipase D (lysoPLD) activity and can regulate LPA levels in vivo. The LPA receptor family and ATX/lysoPLD are abnormally expressed in various gastrointestinal tumors. According to our recent pre-experimental results, KAI1/CD82 might inhibit the migration and metastasis of cancer cells by regulating the ATX-LPA axis. However, no relevant research has been reported. Clarifying the mechanism of ATX-LPA in the inhibition of cancer metastasis by KAI1/CD82 will provide an important theoretical basis for targeted cancer therapy. In this paper, the molecular compositions of the KAI1/CD82 gene and the ATX-LPA axis, their physiological functions in tumors, and their roles in gastrointestinal cancers and target therapy are reviewed.

Sex Differences in Plasma Lysophosphatidic Acid Species in Patients with Alcohol and Cocaine Use Disorders

Preclinical evidence suggests a main role of lysophosphatidic acid (LPA) signaling in drug addiction. Recently, we reported alterations in the plasma concentrations of LPA species in patients with alcohol use disorder (AUD). As there are sex differences in drug addiction, the main aim of the present study was to investigate whether relevant LPA species (16:0-LPA, 18:0-LPA, 18:1-LPA, 18:2-LPA and 20:4-LPA) were associated with sex and/or substance use disorder (SUD). This exploratory study was conducted in 214 abstinent patients with lifetime SUD, and 91 healthy control subjects. The SUD group was divided according to the diagnosis of AUD and/or cocaine use disorder (CUD). Participants were clinically assessed, and plasma samples were collected to determine LPA species and total LPA. We found that LPA concentrations were significantly affected by sex, and women showed higher concentrations than men. In addition, there were significantly lower 16:0-LPA, 18:2-LPA and total LPA concentrations in patients with SUD than in controls. Namely, patients with CUD and AUD + CUD showed lower LPA concentrations than controls or patients with AUD. In conclusion, our data suggest that LPA species could be potential biomarkers for SUD in women and men, which could contribute to a better stratification of these patients in treatment programs.

Inhibition of the enzyme autotaxin reduces cortical excitability and ameliorates the outcome in stroke

Stroke penumbra injury caused by excess glutamate is an important factor in determining stroke outcome; however, several therapeutic approaches aiming to rescue the penumbra have failed, likely due to unspecific targeting and persistent excitotoxicity, which continued far beyond the primary stroke event. Synaptic lipid signaling can modulate glutamatergic transmission via presynaptic lysophosphatidic acid (LPA) 2 receptors modulated by the LPA-synthesizing molecule autotaxin (ATX) present in astrocytic perisynaptic processes. Here, we detected long-lasting increases in brain ATX concentrations after experimental stroke. In humans, cerebrospinal fluid ATX concentration was increased up to 14 days after stroke. Using astrocyte-specific deletion and pharmacological inhibition of ATX at different time points after experimental stroke, we showed that inhibition of LPA-related cortical excitability improved stroke outcome. In transgenic mice and in individuals expressing a single-nucleotide polymorphism that increased LPA-related glutamatergic transmission, we found dysregulated synaptic LPA signaling and subsequent negative stroke outcome. Moreover, ATX inhibition in the animal model ameliorated stroke outcome, suggesting that this approach might have translational potential for improving the outcome after stroke.

Pain-like behavior in the collagen antibody-induced arthritis model is regulated by lysophosphatidic acid and activation of satellite glia cells

Inflammatory and neuropathic-like components underlie rheumatoid arthritis (RA)-associated pain, and lysophosphatidic acid (LPA) is linked to both joint inflammation in RA patients and to neuropathic pain. Thus, we investigated a role for LPA signalling using the collagen antibody-induced arthritis (CAIA) model. Pain-like behavior during the inflammatory phase and the late, neuropathic-like phase of CAIA was reversed by a neutralizing antibody generated against LPA and by an LPA_1/3 receptor inhibitor, but joint inflammation was not affected. Autotaxin, an LPA synthesizing enzyme was upregulated in dorsal root ganglia (DRG) neurons during both CAIA phases, but not in joints or spinal cord. Late-phase pronociceptive neurochemical changes in the DRG were blocked in Lpar1 receptor deficient mice and reversed by LPA neutralization. In vitro and in vivo studies indicated that LPA regulates pain-like behavior via the LPA₁ receptor on satellite glia cells (SGCs), which is expressed by both human and mouse SGCs in the DRG. Furthermore, CAIA-induced SGC activity is reversed by phospholipid neutralization and blocked in Lpar1 deficient mice. Our findings suggest that the regulation of CAIA-induced pain-like behavior by LPA signalling is a peripheral event, associated with the DRGs and involving increased pronociceptive activity of SGCs, which in turn act on sensory neurons.

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.

Inhibition of Autotaxin and Lysophosphatidic Acid Receptor 5 Attenuates Neuroinflammation in LPS-Activated BV-2 Microglia and a Mouse Endotoxemia Model

Increasing evidence suggests that systemic inflammation triggers a neuroinflammatory response that involves sustained microglia activation. This response has deleterious consequences on memory and learning capability in experimental animal models and in patients. However, the mechanisms connecting systemic inflammation and microglia activation remain poorly understood. Here, we identify the autotaxin (ATX)/lysophosphatidic acid (LPA)/LPA-receptor axis as a potential pharmacological target to modulate the LPS-mediated neuroinflammatory response in vitro (the murine BV-2 microglia cell line) and in vivo (C57BL/6J mice receiving a single i.p. LPS injection). In LPS-stimulated (20 ng/mL) BV-2 cells, we observed increased phosphorylation of transcription factors (STAT1, p65, and c-Jun) that are known to induce a proinflammatory microglia phenotype. LPS upregulated ATX, TLR4, and COX2 expression, amplified NO production, increased neurotoxicity of microglia conditioned medium, and augmented cyto-/chemokine concentrations in the cellular supernatants. PF8380 (a type I ATX inhibitor, used at 10 and 1 µM) and AS2717638 (an LPA5 antagonist, used at 1 and 0.1 µM) attenuated these proinflammatory responses, at non-toxic concentrations, in BV-2 cells. In vivo, we demonstrate accumulation of PF8380 in the mouse brain and an accompanying decrease in LPA concentrations. In vivo, co-injection of LPS (5 mg/kg body weight) and PF8380 (30 mg/kg body weight), or LPS/AS2717638 (10 mg/kg body weight), significantly attenuated LPS-induced iNOS, TNFα, IL-1β, IL-6, and CXCL2 mRNA expression in the mouse brain. On the protein level, PF8380 and AS2717638 significantly reduced TLR4, Iba1, GFAP and COX2 expression, as compared to LPS-only injected animals. In terms of the communication between systemic inflammation and neuroinflammation, both inhibitors significantly attenuated LPS-mediated systemic TNFα and IL-6 synthesis, while IL-1β was only reduced by PF8380. Inhibition of ATX and LPA5 may thus provide an opportunity to protect the brain from the toxic effects that are provoked by systemic endotoxemia.

Critical Roles of Lysophospholipid Receptors in Activation of Neuroglia and Their Neuroinflammatory Responses

Activation of microglia and/or astrocytes often releases proinflammatory molecules as critical pathogenic mediators that can promote neuroinflammation and secondary brain damages in diverse diseases of the central nervous system (CNS). Therefore, controlling the activation of glial cells and their neuroinflammatory responses has been considered as a potential therapeutic strategy for treating neuroinflammatory diseases. Recently, receptor-mediated lysophospholipid signaling, sphingosine 1-phosphate (S1P) receptor- and lysophosphatidic acid (LPA) receptor-mediated signaling in particular, has drawn scientific interest because of its critical roles in pathogenies of diverse neurological diseases such as neuropathic pain, systemic sclerosis, spinal cord injury, multiple sclerosis, cerebral ischemia, traumatic brain injury, hypoxia, hydrocephalus, and neuropsychiatric disorders. Activation of microglia and/or astrocytes is a common pathogenic event shared by most of these CNS disorders, indicating that lysophospholipid receptors could influence glial activation. In fact, many studies have reported that several S1P and LPA receptors can influence glial activation during the pathogenesis of cerebral ischemia and multiple sclerosis. This review aims to provide a comprehensive framework about the roles of S1P and LPA receptors in the activation of microglia and/or astrocytes and their neuroinflammatory responses in CNS diseases.

Bioactive Lipid Mediators in the Initiation and Resolution of Inflammation after Spinal Cord Injury

Neuroinflammation is a prominent feature of the response to CNS trauma. It is also an important hallmark of various neurodegenerative diseases in which inflammation contributes to the progression of pathology. Inflammation in the CNS can contribute to secondary damage and is therefore an excellent therapeutic target for a range of neurological conditions. Inflammation in the nervous system is complex and varies in its fine details in different conditions. It involves a wide variety of secreted factors such as chemokines and cytokines, cell adhesion molecules, and different cell types that include resident cell of the CNS, as well as immune cells recruited from the peripheral circulation. Added to this complexity is the fact that some aspects of inflammation are beneficial, while other aspects can induce secondary damage in the acute, subacute and chronic phases. Understanding these aspects of the inflammatory profile is essential for developing effective therapies. Bioactive lipids constitute a large group of molecules that modulate the initiation and the resolution of inflammation. Dysregulation of these bioactive lipid pathways can lead to excessive acute inflammation, and failure to resolve this by specialized pro-resolution lipid mediators can lead to the development of chronic inflammation. The focus of this review is to discuss the effects of bioactive lipids in spinal cord trauma and their potential for therapies.

Lysophosphatidic acid (LPA)-antibody (504B3) engagement detected by interferometry identifies off-target binding

Background

Lysophosphatidic acid (LPA) is a bioactive lysophospholipid that acts through its six cognate G protein-coupled receptors. As a family, lysophospholipids have already produced medicines (e.g., sphingosine 1-phosphate) as is being pursued for LPA through the use of specific antibodies that reduce ligand availability.

Methods

The binding properties of a commercially available, reportedly specific, monoclonal LPA antibody named 504B3 that is related to the clinical candidate Lpathomab/LT3015 were reexamined using a free solution assay (FSA) measured in a compensated interferometric reader (CIR).

Results

Measurement of 504B3 binding properties with an FSA-CIR approach revealed similar binding affinities for 504B3 against LPA as well as the non-LPA lipids, phosphatidic acid (PA) and lysophosphatidylcholine (LPC).

Conclusions

Antibody binding specificity and sensitivity, particularly involving lipid ligands, can be assessed in solution and without labels using FSA-CIR. These findings could affect interpretations of both current and past basic and clinical studies employing 504B3 and related anti-LPA antibodies.

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.

Microglial Metabolism After Pediatric Traumatic Brain Injury - Overlooked Bystanders or Active Participants?

Microglia play an integral role in brain development but are also crucial for repair and recovery after traumatic brain injury (TBI). TBI induces an intense innate immune response in the immature, developing brain that is associated with acute and chronic changes in microglial function. These changes contribute to long-lasting consequences on development, neurologic function, and behavior. Although alterations in glucose metabolism are well-described after TBI, the bulk of the data is focused on metabolic alterations in astrocytes and neurons. To date, the interplay between alterations in intracellular metabolic pathways in microglia and the innate immune response in the brain following an injury is not well-studied. In this review, we broadly discuss the microglial responses after TBI. In addition, we highlight reported metabolic alterations in microglia and macrophages, and provide perspective on how changes in glucose, fatty acid, and amino acid metabolism can influence and modulate the microglial phenotype and response to injury.

Strategies for Oligodendrocyte and Myelin Repair in Traumatic CNS Injury

A major consequence of traumatic brain and spinal cord injury is the loss of the myelin sheath, a cholesterol-rich layer of insulation that wraps around axons of the nervous system. In the central nervous system (CNS), myelin is produced and maintained by oligodendrocytes. Damage to the CNS may result in oligodendrocyte cell death and subsequent loss of myelin, which can have serious consequences for functional recovery. Demyelination impairs neuronal function by decelerating signal transmission along the axon and has been implicated in many neurodegenerative diseases. After a traumatic injury, mechanisms of endogenous remyelination in the CNS are limited and often fail, for reasons that remain poorly understood. One area of research focuses on enhancing this endogenous response. Existing techniques include the use of small molecules, RNA interference (RNAi), and monoclonal antibodies that target specific signaling components of myelination for recovery. Cell-based replacement strategies geared towards replenishing oligodendrocytes and their progenitors have been utilized by several groups in the last decade as well. In this review article, we discuss the effects of traumatic injury on oligodendrocytes in the CNS, the lack of endogenous remyelination, translational studies in rodent models promoting remyelination, and finally human clinical studies on remyelination in the CNS after injury.

Antibodies Against Lysophosphatidic Acid Protect Against Blast-Induced Ocular Injuries

Exposure to blast overpressure waves is implicated as the major cause of ocular injuries and resultant visual dysfunction in veterans involved in recent combat operations. No effective therapeutic strategies have been developed so far for blast-induced ocular dysfunction. Lysophosphatidic acid (LPA) is a bioactive phospholipid generated by activated platelets, astrocytes, choroidal plexus cells, and microglia and is reported to play major roles in stimulating inflammatory processes. The levels of LPA in the cerebrospinal fluid have been reported to increase acutely in patients with traumatic brain injury (TBI) as well as in a controlled cortical impact (CCI) TBI model in mice. In the present study, we have evaluated the efficacy of a single intravenous administration of a monoclonal LPA antibody (25 mg/kg) given at 1 h post-blast for protection against injuries to the retina and associated ocular dysfunctions. Our results show that a single 19 psi blast exposure significantly increased the levels of several species of LPA in blood plasma at 1 and 4 h post-blast. The anti-LPA antibody treatment significantly decreased glial cell activation and preserved neuronal cell morphology in the retina on day 8 after blast exposure. Optokinetic measurements indicated that anti-LPA antibody treatment significantly improved visual acuity in both eyes on days 2 and 6 post-blast exposure. Anti-LPA antibody treatment significantly increased rod photoreceptor and bipolar neuronal cell signaling in both eyes on day 7 post-blast exposure. These results suggest that blast exposure triggers release of LPAs, which play a major role promoting blast-induced ocular injuries, and that a single early administration of anti-LPA antibodies provides significant protection.

Altered cleavage plane orientation with increased genomic aneuploidy produced by receptor-mediated lysophosphatidic acid (LPA) signaling in mouse cerebral cortical neural progenitor cells

The brain is composed of cells having distinct genomic DNA sequences that arise post-zygotically, known as somatic genomic mosaicism (SGM). One form of SGM is aneuploidy-the gain and/or loss of chromosomes-which is associated with mitotic spindle defects. The mitotic spindle orientation determines cleavage plane positioning and, therefore, neural progenitor cell (NPC) fate during cerebral cortical development. Here we report receptor-mediated signaling by lysophosphatidic acid (LPA) as a novel extracellular signal that influences cleavage plane orientation and produces alterations in SGM by inducing aneuploidy during murine cortical neurogenesis. LPA is a bioactive lipid whose actions are mediated by six G protein-coupled receptors, LPA₁-LPA₆. RNAscope and qPCR assessment of all six LPA receptor genes, and exogenous LPA exposure in LPA receptor (Lpar)-null mice, revealed involvement of Lpar1 and Lpar2 in the orientation of the mitotic spindle. Lpar1 signaling increased non-vertical cleavage in vivo by disrupting cell-cell adhesion, leading to breakdown of the ependymal cell layer. In addition, genomic alterations were significantly increased after LPA exposure, through production of chromosomal aneuploidy in NPCs. These results identify LPA as a receptor-mediated signal that alters both NPC fate and genomes during cortical neurogenesis, thus representing an extracellular signaling mechanism that can produce stable genomic changes in NPCs and their progeny. Normal LPA signaling in early life could therefore influence both the developing and adult brain, whereas its pathological disruption could contribute to a range of neurological and psychiatric diseases, via long-lasting somatic genomic alterations.

Lysophosphatidic Acid Signalling in Nervous System Development and Function

One class of molecules that are now coming to be recognized as essential for our understanding of the nervous system are the lysophospholipids. One of the major signaling lysophospholipids is lysophosphatidic acid, also known as LPA. LPA activates a variety of G protein-coupled receptors (GPCRs) leading to a multitude of physiological responses. In this review, I describe our current understanding of the role of LPA and LPA receptor signaling in the development and function of the nervous system, especially the central nervous system (CNS). In addition, I highlight how aberrant LPA receptor signaling may underlie neuropathological conditions, with important clinical application.

Lysophosphatidic acid increased infarct size in the early stage of cerebral ischemia-reperfusion with increased BBB permeability

BACKGROUND

We investigated whether exogenous lysophosphatidic acid (LPA), a phospholipid extracellular signaling molecule, would increase infarct size and blood-brain barrier (BBB) disruption during the early stage of cerebral ischemia-reperfusion, and whether it works through Akt-mTOR-S6K1 intracellular signaling.

MATERIAL AND METHODS

Rats were given either vehicle or LPA 1 mg/kg iv three times during reperfusion after one hour of middle cerebral artery (MCA) occlusion. In another group, prior to administration of LPA, 30 mg/kg of PF-4708671, an S6K1 inhibitor, was injected. After one hour of MCA occlusion and two hours of reperfusion the transfer coefficient (K_i) of ¹⁴C-α-aminoisobutyric acid and the volume of ³H-dextran distribution were determined to measure the degree of BBB disruption. At the same time, the size of infarct was determined and western blot analysis was performed to determine the levels of phosphorylated Akt (p-Akt) and phosphorylated S6 (pS6).

RESULTS

LPA increased the K_i in the ischemic-reperfused cortex (+43%) when compared with Control rats and PF-4708671 pretreatment prevented the increase of K_i by LPA. LPA increased the percentage of cortical infarct out of total cortical area (+36%) and PF-4708671 pretreatment prevented the increase of the infarct size. Exogenous LPA did not significantly change the levels of p-Akt as well as pS6 in the ischemic-reperfused cortex.

CONCLUSION

Our data demonstrate that the increase in BBB disruption could be one of the reasons of the increased infarct size by LPA. S6K1 may not be the major target of LPA. A decrease of LPA during early cerebral ischemia-reperfusion might be beneficial for neuronal survival.

MAPK signaling determines lysophosphatidic acid (LPA)-induced inflammation in microglia

Background

In the extracellular environment, lysophosphatidic acid (LPA) species are generated via autotaxin (ATX)-mediated hydrolysis of lysophospholipid precursors. Members of the LPA family are potent lipid mediators transmitting signals via six different G protein-coupled LPA receptors (LPAR1-6). The LPA signaling axis is indispensable for brain development and function of the nervous system; however, during damage of the central nervous system, LPA levels can increase and aberrant signaling events counteract brain function. Here, we investigated regulation of the ATX/LPA/LPAR axis in response to lipopolysaccharide-induced systemic inflammation in mice and potential neurotoxic polarization programs in LPA-activated primary murine microglia.

Methods

In vivo, LPAR1-6 expression was established by qPCR in whole murine brain homogenates and in FACS-sorted microglia. ELISAs were used to quantitate LPA concentrations in the brain and cyto-/chemokine secretion from primary microglia in vitro. Transcription factor phosphorylation was analyzed by immunoblotting, and plasma membrane markers were analyzed by flow cytometry. We used MAPK inhibitors to study signal integration by the JNK, p38, and ERK1/2 branches in response to LPA-mediated activation of primary microglia.

Results

Under acute and chronic inflammatory conditions, we observed a significant increase in LPA concentrations and differential regulation of LPAR, ATX (encoded by ENPP2), and cytosolic phospholipase A2 (encoded by PLA2G4A) gene expression in the brain and FACS-sorted microglia. During pathway analyses in vitro, the use of specific MAPK antagonists (SP600125, SB203580, and PD98059) revealed that JNK and p38 inhibition most efficiently attenuated LPA-induced phosphorylation of proinflammatory transcription factors (STAT1 and -3, p65, and c-Jun) and secretion of IL-6 and TNFα. All three inhibitors decreased LPA-mediated secretion of IL-1β, CXCL10, CXCL2, and CCL5. The plasma membrane marker CD40 was solely inhibited by SP600125 while all three inhibitors affected expression of CD86 and CD206. All MAPK antagonists reduced intracellular COX-2 and Arg1 as well as ROS and NO formation, and neurotoxicity of microglia-conditioned media.

Conclusion

In the present study, we show that systemic inflammation induces aberrant ATX/LPA/LPAR homeostasis in the murine brain. LPA-mediated polarization of primary microglia via MAPK-dependent pathways induces features reminiscent of a neurotoxic phenotype.

Manual acupuncture relieves microglia-mediated neuroinflammation in a rat model of traumatic brain injury by inhibiting the RhoA/ROCK2 pathway

Objective:

To investigate the regulatory mechanism of manual acupuncture (MA) on microglial polarization–mediated neuroinflammation after traumatic brain injury (TBI), focusing on the RhoA/Rho-associated coiled coil-forming protein kinase (ROCK2) pathway.

Methods:

Sprague Dawley (SD) rats were used to generate a TBI model using Feeney’s freefall epidural impact method. MA was performed on half of the TBI model rats, while the others remained untreated. Acupuncture was administered at GV15, GV16, GV20, GV26, and LI4. At the end of the intervention, rat brain tissue samples were collected, and the microglial M1 polarization status was observed by immunofluorescence labeling of CD86, an M1 microglia-specific protein. RhoA/ROCK2 signaling components were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting. An enzyme-linked immunosorbent assay (ELISA) was used to detect the expression levels of inflammatory factors.

Results:

Compared with normal rats, the CD86 expression density in the untreated TBI model rats was high and showed an aggregated expression pattern. The genes and proteins of the RhoA/ROCK2 signaling pathway were highly expressed, and inflammatory factors were significantly increased. The CD86 expression density in TBI rats after MA was reduced compared to that in untreated TBI rats and showed a scattered distribution. The expression of RhoA/ROCK2 signaling pathway genes and proteins was also significantly reduced, and inflammatory factors were decreased.

Conclusion:

These results show that MA may inhibit M1 polarization of microglia by regulating the RhoA/ROCK2 signaling pathway, thereby reducing neuroinflammation in TBI.

Lysophosphatidic Acid Induces Apoptosis of PC12 Cells Through LPA1 Receptor/LPA2 Receptor/MAPK Signaling Pathway

Lysophosphatidic acid is a small extracellular signaling molecule, which is elevated in pathological conditions such as ischemic stroke and traumatic brain injury (TBI). LPA regulates the survival of neurons in various diseases. However, the molecular mechanisms underlying LPA-induced neuronal death remain unclear. Here we report that LPA activates LPA1 and LPA2 receptors, and the downstream MAPK pathway to induce the apoptosis of PC12 cells through mitochondrial dysfunction. LPA elicits the activation of ERK1/2, p38, and JNK pathways, decreases the expression of Bcl2, promotes the translocation of Bax, and enhances the activation of caspase-3, resulting in mitochondrial dysfunction and cell apoptosis. This process can be blocked by LPA1 receptor antagonist and LPA2 receptor antagonist and MAPK pathway inhibitors. Our results indicate that LPA1 receptor, LPA2 receptor and MAPK pathway play a critical role in LPA-induced neuronal injury. LPA receptors and MAPK pathways may be novel therapeutic targets for ischemic stroke and TBI, where excessive LPA signaling exist.

Small-Molecule Lysophosphatidic Acid Receptor 5 (LPAR5) Antagonists: Versatile Pharmacological Tools to Regulate Inflammatory Signaling in BV-2 Microglia Cells

Lysophosphatidic acid (LPA) species in the extracellular environment induce downstream signaling via six different G protein-coupled receptors (LPAR1–6). These signaling cascades are essential for normal brain development and function of the nervous system. However, in response to acute or chronic central nervous system (CNS) damage, LPA levels increase and aberrant signaling events can counteract brain function. Under neuro-inflammatory conditions signaling along the LPA/LPAR5 axis induces a potentially neurotoxic microglia phenotype indicating the need for new pharmacological intervention strategies. Therefore, we compared the effects of two novel small-molecule LPAR5 antagonists on LPA-induced polarization parameters of the BV-2 microglia cell line. AS2717638 is a selective piperidine-based LPAR5 antagonist (IC₅₀ 0.038 μM) while compound 3 is a diphenylpyrazole derivative with an IC₅₀ concentration of 0.7 μM in BV-2 cells. Both antagonists compromised cell viability, however, at concentrations above their IC₅₀ concentrations. Both inhibitors blunted LPA-induced phosphorylation of STAT1 and STAT3, p65, and c-Jun and consequently reduced the secretion of pro-inflammatory cyto-/chemokines (IL-6, TNFα, IL-1β, CXCL10, CXCL2, and CCL5) at non-toxic concentrations. Both compounds modulated the expression of intracellular (COX-2 and Arg1) and plasma membrane-located (CD40, CD86, and CD206) polarization markers yet only AS2717638 attenuated the neurotoxic potential of LPA-activated BV-2 cell-conditioned medium towards CATH.a neurons. Our findings from the present in vitro study suggest that the two LPAR5 antagonists represent valuable pharmacological tools to interfere with LPA-induced pro-inflammatory signaling cascades in microglia.

Metabolomics and Biomarker Discovery in Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the leading causes of disability and mortality worldwide. The TBI pathogenesis can induce broad pathophysiological consequences and clinical outcomes attributed to the complexity of the brain. Thus, the diagnosis and prognosis are important issues for the management of mild, moderate, and severe forms of TBI. Metabolomics of readily accessible biofluids is a promising tool for establishing more useful and reliable biomarkers of TBI than using clinical findings alone. Metabolites are an integral part of all biochemical and pathophysiological pathways. Metabolomic processes respond to the internal and external stimuli resulting in an alteration of metabolite concentrations. Current high-throughput and highly sensitive analytical tools are capable of detecting and quantifying small concentrations of metabolites, allowing one to measure metabolite alterations after a pathological event when compared to a normal state or a different pathological process. Further, these metabolic biomarkers could be used for the assessment of injury severity, discovery of mechanisms of injury, and defining structural damage in the brain in TBI. Metabolic biomarkers can also be used for the prediction of outcome, monitoring treatment response, in the assessment of or prognosis of post-injury recovery, and potentially in the use of neuroplasticity procedures. Metabolomics can also enhance our understanding of the pathophysiological mechanisms of TBI, both in primary and secondary injury. Thus, this review presents the promising application of metabolomics for the assessment of TBI as a stand-alone platform or in association with proteomics in the clinical setting.

Pleotropic Roles of Autotaxin in the Nervous System Present Opportunities for the Development of Novel Therapeutics for Neurological Diseases

Autotaxin (ATX) is a soluble extracellular enzyme that is abundant in mammalian plasma and cerebrospinal fluid (CSF). It has two known enzymatic activities, acting as both a phosphodiesterase and a phospholipase. The majority of its biological effects have been associated with its ability to liberate lysophosphatidic acid (LPA) from its substrate, lysophosphatidylcholine (LPC). LPA has diverse pleiotropic effects in the central nervous system (CNS) and other tissues via the activation of a family of six cognate G protein-coupled receptors. These LPA receptors (LPARs) are expressed in some combination in all known cell types in the CNS where they mediate such fundamental cellular processes as proliferation, differentiation, migration, chronic inflammation, and cytoskeletal organization. As a result, dysregulation of LPA content may contribute to many CNS and PNS disorders such as chronic inflammatory or neuropathic pain, glioblastoma multiforme (GBM), hemorrhagic hydrocephalus, schizophrenia, multiple sclerosis, Alzheimer's disease, metabolic syndrome-induced brain damage, traumatic brain injury, hepatic encephalopathy-induced cerebral edema, macular edema, major depressive disorder, stress-induced psychiatric disorder, alcohol-induced brain damage, HIV-induced brain injury, pruritus, and peripheral nerve injury. ATX activity is now known to be the primary biological source of this bioactive signaling lipid, and as such, represents a potentially high-value drug target. There is currently one ATX inhibitor entering phase III clinical trials, with several additional preclinical compounds under investigation. This review discusses the physiological and pathological significance of the ATX-LPA-LPA receptor signaling axis and summarizes the evidence for targeting this pathway for the treatment of CNS diseases.

Metabolic perturbations after pediatric TBI: It's not just about glucose

Improved patient survival following pediatric traumatic brain injury (TBI) has uncovered a currently limited understanding of both the adaptive and maladaptive metabolic perturbations that occur during the acute and long-term phases of recovery. While much is known about the redundancy of metabolic pathways that provide adequate energy and substrates for normal brain growth and development, the field is only beginning to characterize perturbations in these metabolic pathways after pediatric TBI. To date, the majority of studies have focused on dysregulated oxidative glucose metabolism after injury; however, the immature brain is well-equipped to use alternative substrates to fuel energy production, growth, and development. A comprehensive understanding of metabolic changes associated with pediatric TBI cannot be limited to investigations of glucose metabolism alone. All energy substrates used by the brain should be considered in developing nutritional and pharmacological interventions for pediatric head trauma. This review summarizes post-injury changes in brain metabolism of glucose, lipids, ketone bodies, and amino acids with discussion of the therapeutic potential of altering substrate utilization to improve pediatric TBI outcomes.

LPA1 , LPA2 , LPA4 , and LPA6 receptor expression during mouse brain development

Background

LPA is a small bioactive phospholipid that acts as an extracellular signaling molecule and is involved in cellular processes, including cell proliferation, migration, and differentiation. LPA acts by binding and activating at least six known G protein–coupled receptors: LPA_1–6. In recent years, LPA has been suggested to play an important role both in normal neuronal development and under pathological conditions in the nervous system.

Results

We show the expression pattern of LPA receptors during mouse brain development by using qRT‐PCR, in situ hybridization, and immunocytochemistry. Only LPA₁, LPA_2,LPA_4, and LPA₆ mRNA transcripts were detected throughout development stages from embryonic day 16 until postnatal day 30 of hippocampus, neocortex, cerebellum, and bulbus olfactorius in our experiments, while expression of LPA₃ and LPA₅ genes was below detection level. In addition to our qRT‐PCR results, we also analyzed the cellular protein expression of endogenous LPA receptors, with focus on LPA₁ and LPA₂ within postnatal brain slices and primary neuron differentiation with and without cytoskeleton stabilization and destabilization.

Conclusions

The expression of LPA receptors changes depends on the developmental stage in mouse brain and in cultured hippocampal primary neurons. Interestingly, we found that commercially available antibodies for LPA receptors are largely unspecific.

LPA1, ‐2, ‐4, and ‐6 genes are dynamically expressed during postnatal brain development.

LPA1, ‐2, ‐4, and ‐6 genes are differently expressed in the hippocampus, neocortex, cerebellum, and bulbus olfactorius.

LPA1 and ‐2 gene expression alters during neuronal differentiation.

LPA1, ‐2, ‐3, ‐4, and ‐6 genes are expressed in glia cells, but differed in gene expression levels.

Targeting the autotaxin - Lysophosphatidic acid receptor axis in cardiovascular diseases

Lysophosphatidic acid (LPA) is a well-characterized bioactive lipid mediator, which is involved in development, physiology, and pathological processes of the cardiovascular system. LPA can be produced both inside cells and in biological fluids. The majority of extracellularLPAis produced locally by the secreted lysophospholipase D, autotaxin (ATX), through its binding to various β integrins or heparin sulfate on cell surface and hydrolyzing various lysophospholipids. LPA initiates cellular signalling pathways upon binding to and activation of its G protein-coupled receptors (LPA1-6). LPA has potent effects on various blood cells and vascular cells involved in the development of cardiovascular diseases such as atherosclerosis and aortic valve sclerosis. LPA signalling drives cell migration and proliferation, cytokine production, thrombosis, fibrosis, as well as angiogenesis. For instance, LPA promotes activation and aggregation of platelets through LPA5, increases expression of adhesion molecules in endothelial cells, and enhances expression of tissue factor in vascular smooth muscle cells. Furthermore, LPA induces differentiation of monocytes into macrophages and stimulates oxidized low-density lipoproteins (oxLDLs) uptake by macrophages to form foam cells during formation of atherosclerotic lesions through LPA1-3. This review summarizes recent findings of the roles played by ATX, LPA and LPA receptors (LPARs) in atherosclerosis and calcific aortic valve disease. Targeting the ATX-LPAR axis may have potential applications for treatment of patients suffering from various cardiovascular diseases.

Lysophosphatidic acid receptor type 2 activation contributes to secondary damage after spinal cord injury in mice

Lysophosphatidic acid (LPA) is an extracellular lipid mediator involved in many physiological functions by signaling through six known G-protein-coupled receptors (LPA₁-LPA₆). In the central nervous system (CNS), LPA mediates a wide range of effects, including neural progenitor cell physiology, astrocyte and microglia activation, neuronal cell death, axonal retraction, and contributions to pain, schizophrenia and hydrocephalus. We recently reported that LPA-LPA₁ signaling mediates functional deficits and myelin loss after spinal cord injury (SCI). Here, we provide clear evidence on the deleterious contribution of another LPA receptor, LPA₂, to myelin loss after SCI. We found that LPA₂ is constitutively expressed in the spinal cord parenchyma and its transcripts were up-regulated after contusion injury, in part, by microglial cells. We also found that the demyelinating lesion triggered by intraspinal injection of LPA into the undamaged spinal cord was markedly reduced in the lack of LPA₂. Similarly, LPA₂ deficient mice showed enhanced motor skills and myelin sparing after SCI. To gain insights into the detrimental actions of LPA₂ in spinal cord we performed cell culture studies. These experiments revealed that, similar to LPA₁, activation of microglia LPA₂ led to oligodendrocyte cell death. Moreover, we also found that the cytotoxic effects underlaying microglial LPA-LPA₂ axis were mediated by the release of purines by microglia and the activation of P₂X₇ receptor on oligodendrocytes. Overall, this study provides new mechanistic insights into how LPA contributes to SCI physiopathology, and suggest that targeting LPA₂ could be a novel therapeutic approach for the treatment of acute SCI.

Roles of lysophosphatidic acid and sphingosine-1-phosphate in stem cell biology

Stem cells are unique in their ability to self-renew and differentiate into various cell types. Because of these features, stem cells are key to the formation of organisms and play fundamental roles in tissue regeneration and repair. Mechanisms controlling their fate are thus fundamental to the development and homeostasis of tissues and organs. Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are bioactive phospholipids that play a wide range of roles in multiple cell types, during developmental and pathophysiological events. Considerable evidence now demonstrates the potent roles of LPA and S1P in the biology of pluripotent and adult stem cells, from maintenance to repair. Here we review their roles for each main category of stem cells and explore how those effects impact development and physiopathology.

Matrix-Assisted Laser Desorption Ionization Mapping of Lysophosphatidic Acid Changes after Traumatic Brain Injury and the Relationship to Cellular Pathology

Lysophosphatidic acid (LPA) levels increase in the cerebrospinal fluid and blood within 24 hours after traumatic brain injury (TBI), indicating it may be a biomarker for subsequent cellular pathology. However, no data exist that document this association after TBI. We, therefore, acquired matrix-assisted laser desorption ionization imaging mass spectrometry data of LPA, major LPA metabolites, and hemoglobin from adult rat brains at 1 and 3 hours after controlled cortical impact injury. Data were semiquantitatively assessed by signal intensity analysis normalized to naïve rat brains acquired concurrently. Gray and white matter pathology was assessed on adjacent sections using immunohistochemistry for cell death, axonal injury, and intracellular LPA, to determine the spatiotemporal patterning of LPA corresponding to pathology. The results revealed significant increases in LPA and LPA precursors at 1 hour after injury and robust enhancement in LPA diffusively throughout the brain at 3 hours after injury. Voxel-wise analysis of LPA by matrix-assisted laser desorption ionization and β-amyloid precursor protein by immunohistochemistry in adjacent sections showed significant association, raising the possibility that LPA is linked to secondary axonal injury. Total LPA and metabolites were also present in remotely injured areas, including cerebellum and brain stem, and in particular thalamus, where intracellular LPA is associated with cell death. LPA may be a useful biomarker of cellular pathology after TBI.

2-carba cyclic phosphatidic acid suppresses inflammation via regulation of microglial polarisation in the stab-wounded mouse cerebral cortex

Traumatic brain injury (TBI) is caused by physical damage to the brain and it induces blood-brain barrier (BBB) breakdown and inflammation. To diminish the sequelae of TBI, it is important to decrease haemorrhage and alleviate inflammation. In this study, we aimed to determine the effects of 2-carba-cyclic phosphatidic acid (2ccPA) on the repair mechanisms after a stab wound injury as a murine TBI model. The administration of 2ccPA suppressed serum immunoglobulin extravasation after the injury. To elucidate the effects of 2ccPA on inflammation resulting from TBI, we analysed the mRNA expression of inflammatory cytokines. We found that 2ccPA prevents a TBI-induced increase in the mRNA expression of Il-1β, Il-6, Tnf-α and Tgf-β1. In addition, 2ccPA reduces the elevation of Iba1 levels. These data suggest that 2ccPA attenuates the inflammation after a stab wound injury via the modulation of pro-inflammatory cytokines release from microglial cells. Therefore, we focused on the function of 2ccPA in microglial polarisation towards M1 or M2 phenotypes. The administration of 2ccPA decreased the number of M1 and increased the number of M2 type microglial cells, indicating that 2ccPA modulates the microglial polarisation and shifts them towards M2 phenotype. These data suggest that 2ccPA treatment suppresses the extent of BBB breakdown and inflammation after TBI.

Autotaxin⁻Lysophosphatidic Acid Signaling in Alzheimer's Disease

The brain contains various forms of lipids that are important for maintaining its structural integrity and regulating various signaling cascades. Autotaxin (ATX) is an ecto-nucleotide pyrophosphatase/phosphodiesterase-2 enzyme that hydrolyzes extracellular lysophospholipids into the lipid mediator lysophosphatidic acid (LPA). LPA is a major bioactive lipid which acts through G protein-coupled receptors (GPCRs) and plays an important role in mediating cellular signaling processes. The majority of synthesized LPA is derived from membrane phospholipids through the action of the secreted enzyme ATX. Both ATX and LPA are highly expressed in the central nervous system. Dysfunctional expression and activity of ATX with associated changes in LPA signaling have recently been implicated in the pathogenesis of Alzheimer’s disease (AD). This review focuses on the current understanding of LPA signaling, with emphasis on the importance of the autotaxin–lysophosphatidic acid (ATX–LPA) pathway and its alterations in AD and a brief note on future therapeutic applications based on ATX–LPA signaling.

Nervous system delivery of antilysophosphatidic acid antibody by nasal application attenuates mechanical allodynia after traumatic brain injury in rats

Lysophosphatidic acid (LPA) is a bioactive lipid that impacts neurological outcomes after neurotrauma by inhibiting neuroregeneration, promoting inflammation, and contributing to behavioral deficits. Blocking LPA signaling with a novel anti-LPA monoclonal antibody (mAb) is neuroprotective after traumatic brain injury (TBI) if given to injured animals whose blood-brain barrier (BBB) has been compromised. It is hypothesized that the anti-LPA mAb could improve chronic pain initiated by TBI. However, poor brain penetration after systemic application of the antibody makes access to the central nervous system (CNS) problematic in situations where the BBB is intact. Our experiments investigated whether intranasal delivery of the anti-LPA mAb could bypass the BBB, allowing for direct entry of the antibody to certain areas of the CNS. When the humanized anti-LPA mAb, LT3114, was intranasally applied to injured rats within 30 minutes after mild TBI using the central lateral percussion model, enzyme-linked immunospecific assay and immunohistochemistry demonstrated antibody uptake to several areas in the CNS, including the area of cortical injury, the corpus callosum, cerebellum, and the subventricular region. Compared with control rats that received LT3114 but no TBI, TBI rats demonstrated significantly higher concentrations of intranasally administered LT3114 antibody in some tissues. In behavioral studies, a significant attenuation of mechanical allodynia after TBI was observed in the anti-LPA treatment group (P = 0.0079), when compared with vehicle controls within 14 days after TBI. These results suggest that intranasal application of the anti-LPA antibody directly accesses CNS sites involved in TBI-related pain and that this access attenuates pain sequelae to the neurotrauma.

Multi-Target Protective Effects of Gintonin in 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-Mediated Model of Parkinson's Disease via Lysophosphatidic Acid Receptors

Gintonin is a ginseng-derived lysophosphatidic acid receptor (LPAR) ligand. Although previous in vitro and in vivo studies demonstrated the therapeutic role of gintonin against Alzheimer's disease, the neuroprotective effects of gintonin in Parkinson's disease (PD) are still unknown. We investigated whether gintonin (50 and 100 mg/kg/day, p.o., daily for 12 days) had neuroprotective activities against neurotoxicity in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD. Pre-administration of 100 mg/kg gintonin displayed significantly ameliorating effects in neurological disorders (motor and welfare) as measuring using pole, rotarod, and nest building tests, and in the survival rate. These effects were associated to the reduction of the loss of tyrosine hydroxylase-positive neurons, microglial activation, activation of inflammatory mediators (interleukin-6, tumor necrosis factor, and cyclooxygenase-2), and alteration of blood-brain barrier (BBB) integrity in the substantia nigra pars compacta and/or striatum following MPTP injection. The benefits of gintonin treatment against MPTP also included the activation of the nuclear factor erythroid 2-related factor 2 pathways and the inhibition of phosphorylation of the mitogen-activated protein kinases and nuclear factor-kappa B signaling pathways. Interestingly, these neuroprotective effects of gintonin were blocked by LPAR1/3 antagonist, Ki16425. Overall, the present study shows that gintonin attenuates MPTP-induced neurotoxicity via multiple targets. Gintonin combats neuronal death, and acts as an anti-inflammatory and an anti-oxidant agent. It maintains BBB integrity. LPA receptors play a key role in gintonin-mediated anti-PD mechanisms. Finally, gintonin is a key agent for prevention and/or treatment of PD.

Coming of Age for Autotaxin and Lysophosphatidate Signaling: Clinical Applications for Preventing, Detecting and Targeting Tumor-Promoting Inflammation

A quarter-century after the discovery of autotaxin in cell culture, the autotaxin-lysophosphatidate (LPA)-lipid phosphate phosphatase axis is now a promising clinical target for treating chronic inflammatory conditions, mitigating fibrosis progression, and improving the efficacy of existing cancer chemotherapies and radiotherapy. Nearly half of the literature on this axis has been published during the last five years. In cancer biology, LPA signaling is increasingly being recognized as a central mediator of the progression of chronic inflammation in the establishment of a tumor microenvironment which promotes cancer growth, immune evasion, metastasis, and treatment resistance. In this review, we will summarize recent advances made in understanding LPA signaling with respect to chronic inflammation and cancer. We will also provide perspectives on the applications of inhibitors of LPA signaling in preventing cancer initiation, as adjuncts extending the efficacy of current cancer treatments by blocking inflammation caused by either the cancer or the cancer therapy itself, and by disruption of the tumor microenvironment. Overall, LPA, a simple molecule that mediates a plethora of biological effects, can be targeted at its levels of production by autotaxin, LPA receptors or through LPA degradation by lipid phosphate phosphatases. Drugs for these applications will soon be entering clinical practice.

Systemic blockade of LPA1/3 lysophosphatidic acid receptors by ki16425 modulates the effects of ethanol on the brain and behavior

The systemic administration of lysophosphatidic acid (LPA) LPA_1/3 receptor antagonists is a promising clinical tool for cancer, sclerosis and fibrosis-related diseases. Since LPA₁ receptor-null mice engage in increased ethanol consumption, we evaluated the effects of systemic administration of an LPA_1/3 receptor antagonist (intraperitoneal ki16425, 20 mg/kg) on ethanol-related behaviors as well as on brain and plasma correlates. Acute administration of ki16425 reduced motivation for ethanol but not for saccharine in ethanol self-administering Wistar rats. Mouse experiments were conducted in two different strains. In Swiss mice, ki16425 treatment reduced both ethanol-induced sedation (loss of righting reflex, LORR) and ethanol reward (escalation in ethanol consumption and ethanol-induced conditioned place preference, CPP). Furthermore, in the CPP-trained Swiss mice, ki16425 prevented the effects of ethanol on basal c-Fos expression in the medial prefrontal cortex and on adult neurogenesis in the hippocampus. In the c57BL6/J mouse strain, however, no effects of ki16425 on LORR or voluntary drinking were observed. The c57BL6/J mouse strain was then evaluated for ethanol withdrawal symptoms, which were attenuated when ethanol was preceded by ki16425 administration. In these animals, ki16425 modulated the expression of glutamate-related genes in brain limbic regions after ethanol exposure; and peripheral LPA signaling was dysregulated by either ki16425 or ethanol. Overall, these results suggest that LPA_1/3 receptor antagonists might be a potential new class of drugs that are suitable for treating or preventing alcohol use disorders. A pharmacokinetic study revealed that systemic ki16425 showed poor brain penetration, suggesting the involvement of peripheral events to explain its effects.

Lysophosphatidic acid via LPA-receptor 5/protein kinase D-dependent pathways induces a motile and pro-inflammatory microglial phenotype

BACKGROUND

Extracellular lysophosphatidic acid (LPA) species transmit signals via six different G protein-coupled receptors (LPAR1-6) and are indispensible for brain development and function of the nervous system. However, under neuroinflammatory conditions or brain damage, LPA levels increase, thereby inducing signaling cascades that counteract brain function. We describe a critical role for 1-oleyl-2-hydroxy-sn-glycero-3-phosphate (termed "LPA" throughout our study) in mediating a motile and pro-inflammatory microglial phenotype via LPAR5 that couples to protein kinase D (PKD)-mediated pathways.

METHODS

Using the xCELLigence system and time-lapse microscopy, we investigated the migrational response of microglial cells. Different M1 and M2 markers were analyzed by confocal microscopy, flow cytometry, and immunoblotting. Using qPCR and ELISA, we studied the expression of migratory genes and quantitated the secretion of pro-inflammatory cytokines and chemokines, respectively. Different transcription factors that promote the regulation of pro-inflammatory genes were analyzed by western blot. Reactive oxygen species (ROS) and nitric oxide (NO) production, phagocytosis, and microglial cytotoxicity were determined using commercially available assay kits.

RESULTS

LPA induces MAPK family and AKT activation and pro-inflammatory transcription factors' phosphorylation (NF-κB, c-Jun, STAT1, and STAT3) that were inhibited by both LPAR5 and PKD family antagonists. LPA increases migratory capacity, induces secretion of pro-inflammatory cytokines and chemokines and expression of M1 markers, enhances production of ROS and NO by microglia, and augments cytotoxicity of microglial cell-conditioned medium towards neurons. The PKD family inhibitor blunted all of these effects. We propose that interference with this signaling axis could aid in the development of new therapeutic approaches to control neuroinflammation under conditions of overshooting LPA production.

CONCLUSIONS

In the present study, we show that inflammatory LPA levels increased the migratory response of microglia and promoted a pro-inflammatory phenotype via the LPAR5/PKD axis. Interference with this signaling axis reduced microglial migration, blunted microglial cytotoxicity, and abrogated the expression and secretion of pro-inflammatory mediators.

Plasma metabolomics profiles in rats with acute traumatic brain injury

Traumatic brain injury (TBI) is a major cause of mortality and disability worldwide. We validated the utility of plasma metabolomics analysis in the clinical diagnosis of acute TBI in a rat model of controlled cortical impact (CCI) using gas chromatography/mass spectrometry (GC/MS). Thirty Sprague-Dawley rats were randomly divided into two groups of 15 rats each: the CCI group and sham group. Blood samples were obtained from the rats within the first 24 h after TBI injury. GC/MS measurements were performed to evaluate the profile of acute TBI-induced metabolic changes, resulting in the identification of 45 metabolites in plasma. Principal component analysis, partial least squares-discriminant analysis, orthogonal partial least square discriminant analysis using hierarchical clustering and univariate/multivariate analyses revealed clear differences in the plasma metabolome between the acute CCI group and the sham group. CCI induced distinctive changes in metabolites including linoleic acid metabolism, amino acid metabolism, galactose metabolism, and arachidonic acid metabolism. Specifically, the acute CCI group exhibited significant alterations in proline, phosphoric acid, β-hydroxybutyric acid, galactose, creatinine, L-valine, linoleic acid and arachidonic acid. A receiver operating characteristic curve analysis showed that the above 8 metabolites in plasma could be used as the potential biomarkers for the diagnosis of acute TBI. Furthermore, this study is the first time to identify the galactose as a biomarker candidate for acute TBI. This comprehensive metabolic analysis complements target screening for potential diagnostic biomarkers of acute TBI and enhances predictive value for the therapeutic intervention of acute TBI.