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

Cell type-specific and subcellular expression of phospholipid phosphatase-related proteins to modulate lyso-phosphatidic acid synaptic signaling in the developing and adult CNS

Lysophosphatidic acid (LPA) is a bioactive phospholipid that participates in critical processes in neural development and adult brain function and is implicated in various pathophysiological conditions. Along with its six well-characterized receptors, atypical regulators of LPA signaling have also been suggested, including phospholipid phosphatase-related proteins (PLPPRs). PLPPRs have been mostly studied in the developing brain where they control LPA-dependent axon guidance, cortical network hyperexcitability, and glutamatergic neurotransmission. PLPPR4 and PLPPR3 represent two closely related proteins reported to localize predominantly in dendrites and axons, respectively, and differ in their developmental expression patterns. Herein, we have revised the expression patterns of PLPPRs in the cerebellum, dorsal and ventral hippocampus, prefrontal cortex (PFC), nucleus accumbens, and striatum during development and in the adult using quantitative PCR. Expression patterns of Plppr2,4 and 5 were consistent with previous studies, whereas Plppr3 and Plppr1 exhibited a unique expression profile in nucleus accumbens (NAc) and striatum in later developmental and adult stages, which we verified at the protein level for PLPPR3. To investigate neuron type-specific expression at the single cell level, we developed a bioinformatic tool to analyze recent single-cell RNA-sequencing data in the cerebral cortex and hippocampus of adult mice. Our analysis revealed a widespread but also selective adult neuron-type expression with higher expression levels of Plppr3, Plppr1, and Plppr5 in GABAergic and Plppr4 and Plppr2 in glutamatergic neurons. PLPPR4 has been identified as a post-synaptic modulator of LPA levels in glutamatergic synapses operating via an uptake mechanism, to control LPA-dependent cortical network hyperexcitability. Using subcellular fractionation experiments, we found that both PLPPR4 and PLPPR3 are co-expressed in adult synaptosomal membranes. Furthermore, flow cytometry experiments in HEK293 cells showed comparable LPA uptake by PLPPR4 and PLPPR3, whereas PLPRR3, but not PLPPR4, induced also uptake of monoacylglycerol, the dephosphorylation product of LPA. We propose that synaptic LPA may be subject to both pre-synaptic and post-synaptic mechanisms of regulation by PLPPRs in addition to LPARs in developing and adult synapses.

Complanatuside A improves functional recovery after spinal cord injury through inhibiting JNK signaling-mediated microglial activation

BACKGROUND AND AIMS

Complanatuside A (ComA) is a flavonoid-rich compound in Astragalus membranaceus that has anti-inflammatory and neuroprotective effects. In this study, we focused on the effect of ComA on spinal cord injury (SCI) in mice and explored its possible mechanisms.

METHODS

The SCI model was constructed using C57BL/6J mice, and the effect of ComA on motor function recovery in SCI mice was evaluated through the BMS (Basso Mouse Scale) and footprint test. The histological effects of ComA on SCI mice were evaluated by hematoxylin-eosin (H&E) staining, Luxol-fast blue (LFB) staining, and Nissl staining. In both in vivo and in vitro experiments, we detected the activation of microglia and the release of inflammatory factors through molecular experiments. Immunofluorescence and Western blotting confirmed that ComA can prevent neuronal apoptosis caused by activated microglia through the c-Jun N-terminal kinase (JNK) pathway.

RESULTS

Our research results confirm that ComA can improve motor function in mice after SCI. Our in vitro results indicate that ComA can inhibit the activation of BV2 cells and the release of proinflammatory mediators. In addition, ComA can prevent neuronal cell apoptosis caused by activated BV2 cells. Finally, we found that ComA works through the JNK signaling pathway.

CONCLUSIONS

ComA can accelerate the restoration of motor function in mice after SCI, possibly by reducing neuronal apoptosis via inhibition of JNK-related signaling pathways, a reduction in microglial activation, and inhibition of inflammatory factor release. Our data indicate that ComA is a promising drug candidate for improving functional recovery in patients with SCI.

Inhibition of lysophosphatidic acid receptor 1 relieves PMN recruitment in CNS via LPA1/TSP1/CXCR2 pathway and alleviates disruption on blood-brain barrier following intracerebral haemorrhage in mice

BACKGROUD

The frequencies of morbidity and impairment associated with spontaneous intracerebral haemorrhage (ICH) are comparatively high. Blood-brain barrier (BBB) integrity was compromised due to subsequent brain injury induced by ICH, which is crucial for a poor prognosis. Polymorphonuclear leukocyte (PMN) strongly modulate the disruption of BBB in the central nervous system (CNS). The lysophosphatidic acid receptor 1 (LPA1) mediated thrombospondin-1 (TSP1) regulation in astrocytes, which induce macrophage inflammatory protein 2(MIP2) secretion. MIP2 enhance PMN recruitment through CXC chemokine type 2 (CXCR2) activation. The purpose of this study was to investigate whether the LPA1-mediated inhibition of PMN recruitment and BBB protection after ICH is regulated by TSP1 and CXCR2 networks.

METHODS

ICH induction was performed in CD1 mice using collagenase administration. AM966, a targeted LPA1 antagonist, was orally administered 1 and 12 h following ICH. further identify possible LPA1-mediated BBB protection mechanisms, we intracerebroventricularly (ICV) administered a CXCR2 ligand MIP2, as well as TSP1 CRISPR activation (ACT) with AM966. Consequently, we performed neurobehavioral, brain water content (BWC), Evans blue staining (EBS), immunofluorescence (IF), and western blot (WB) analyses.

RESULTS

After ICH, astrocytes showed signs of LPA1, which peaked after 24 h, while PMN\ displayed evidence of CXCR2. The AM966-mediated LPA1 suppression relieved PMN recruitment, diminished brain oedema, demonstrated extravasation (as evidenced by EBS), protected BBB integrity, and enhanced neurologic activity following ICH. AM966 treatment strongly reduced TSP1, CXCR2, Occludin, and Claudin-5 expressions and PMN recruitment following ICH, and their expressions were restored by MIP2 and TSP1 CRISPR (ACT).

CONCLUSIONS

This study shows that LAP1 suppression reduced PMN recruitment after ICH in mice via TSP1/CXCR2 signalling, which minimized BBB disruption and improved the CNS's neurobehavioral functioning. Hence, LPA1 is a strong candidate for therapy to reduce PMN recruitment and offer protection of BBB integrity after ICH.

Molecular and cognitive signatures of ageing partially restored through synthetic delivery of IL2 to the brain

Cognitive decline is a common pathological outcome during aging, with an ill-defined molecular and cellular basis. In recent years, the concept of inflammaging, defined as a low-grade inflammation increasing with age, has emerged. Infiltrating T cells accumulate in the brain with age and may contribute to the amplification of inflammatory cascades and disruptions to the neurogenic niche observed with age. Recently, a small resident population of regulatory T cells has been identified in the brain, and the capacity of IL2-mediated expansion of this population to counter neuroinflammatory disease has been demonstrated. Here, we test a brain-specific IL2 delivery system for the prevention of neurological decline in aging mice. We identify the molecular hallmarks of aging in the brain glial compartments and identify partial restoration of this signature through IL2 treatment. At a behavioral level, brain IL2 delivery prevented the age-induced defect in spatial learning, without improving the general decline in motor skill or arousal. These results identify immune modulation as a potential path to preserving cognitive function for healthy aging.

Lysophosphatidic acid, a simple phospholipid with myriad functions

Lysophosphatidic acid (LPA) is a simple phospholipid consisting of a phosphate group, glycerol moiety, and only one hydrocarbon chain. Despite its simple chemical structure, LPA plays an important role as an essential bioactive signaling molecule via its specific six G protein-coupled receptors, LPA_1-6. Recent studies, especially those using genetic tools, have revealed diverse physiological and pathological roles of LPA and LPA receptors in almost every organ system. Furthermore, many studies are illuminating detailed mechanisms to orchestrate multiple LPA receptor signaling pathways and to facilitate their coordinated function. Importantly, these extensive "bench" works are now translated into the "bedside" as exemplified by approaches targeting LPA₁ signaling to combat fibrotic diseases. In this review, we discuss the physiological and pathological roles of LPA signaling and their implications for clinical application by focusing on findings revealed by in vivo studies utilizing genetic tools targeting LPA receptors.

Plasma membrane phospholipid phosphatase-related proteins as pleiotropic regulators of neuron growth and excitability

Neuronal plasma membrane proteins are essential for integrating cell extrinsic and cell intrinsic signals to orchestrate neuronal differentiation, growth and plasticity in the developing and adult nervous system. Here, we shed light on the family of plasma membrane proteins phospholipid phosphatase-related proteins (PLPPRs) (alternative name, PRGs; plasticity-related genes) that fine-tune neuronal growth and synaptic transmission in the central nervous system. Several studies uncovered essential functions of PLPPRs in filopodia formation, axon guidance and branching during nervous system development and regeneration, as well as in the control of dendritic spine number and excitability. Loss of PLPPR expression in knockout mice increases susceptibility to seizures, and results in defects in sensory information processing, development of psychiatric disorders, stress-related behaviors and abnormal social interaction. However, the exact function of PLPPRs in the context of neurological diseases is largely unclear. Although initially described as active lysophosphatidic acid (LPA) ecto-phosphatases that regulate the levels of this extracellular bioactive lipid, PLPPRs lack catalytic activity against LPA. Nevertheless, they emerge as atypical LPA modulators, by regulating LPA mediated signaling processes. In this review, we summarize the effects of this protein family on cellular morphology, generation and maintenance of cellular protrusions as well as highlight their known neuronal functions and phenotypes of KO mice. We discuss the molecular mechanisms of PLPPRs including the deployment of phospholipids, actin-cytoskeleton and small GTPase signaling pathways, with a focus on identifying gaps in our knowledge to stimulate interest in this understudied protein family.

Novel Antagonist of the Type 2 Lysophosphatidic Acid Receptor (LPA2), UCM-14216, Ameliorates Spinal Cord Injury in Mice

Spinal cord injuries (SCIs) irreversibly disrupt spinal connectivity, leading to permanent neurological disabilities. Current medical treatments for reducing the secondary damage that follows the initial injury are limited to surgical decompression and anti-inflammatory drugs, so there is a pressing need for new therapeutic strategies. Inhibition of the type 2 lysophosphatidic acid receptor (LPA₂) has recently emerged as a new potential pharmacological approach to decrease SCI-associated damage. Toward validating this receptor as a target in SCI, we have developed a new series of LPA₂ antagonists, among which compound 54 (UCM-14216) stands out as a potent and selective LPA₂ receptor antagonist (E_max = 90%, IC₅₀ = 1.9 μM, K_D = 1.3 nM; inactive at LPA_1,3–6 receptors). This compound shows efficacy in an in vivo mouse model of SCI in an LPA₂-dependent manner, confirming the potential of LPA₂ inhibition for providing a new alternative for treating SCI.

Corrigendum: Purinergic signaling systems across comparative models of spinal cord injury

[This corrects the article DOI: 10.4103/1673-5374.338993].

Sodium tanshinone IIA sulfonate promotes spinal cord injury repair by inhibiting blood spinal cord barrier disruption in vitro and in vivo

Spinal cord injury (SCI) leads to microvascular damage and the destruction of the blood spinal cord barrier (BSCB), which can progress into secondary injuries, such as apoptosis and necrosis of neurons and glia, culminating in permanent neurological deficits. BSCB restoration is the primary goal of SCI therapy, although very few drugs can repair damaged barrier structure and permeability. Sodium tanshinone IIA sulfonate (STS) is commonly used to treat cardiovascular disease. However, the therapeutic effects of STS on damaged BSCB during the early stage of SCI remain uncertain. Therefore, we exposed spinal cord microvascular endothelial cells to H₂ O₂ and treated them with different doses of STS. In addition to protecting the cells from H₂ O₂ -induced apoptosis, STS also reduced cellular permeability. In the in vivo model of SCI, STS reduced BSCB permeability, relieved tissue edema and hemorrhage, suppressed MMP activation and prevented the loss of tight junction and adherens junction proteins. Our findings indicate that STS treatment promotes SCI recovery, and should be investigated further as a drug candidate against traumatic SCI.

Inhibition of lysophosphatidic acid receptor 1-3 deteriorates experimental autoimmune encephalomyelitis by inducing oxidative stress

Background

Lysophosphatidic acid receptors (LPARs) are G-protein-coupled receptors involved in many physiological functions in the central nervous system. However, the role of the LPARs in multiple sclerosis (MS) has not been clearly defined yet.

Methods

Here, we investigated the roles of LPARs in myelin oligodendrocyte glycoprotein peptides-induced experimental autoimmune encephalomyelitis (EAE), an animal model of MS.

Results

Pre-inhibition with LPAR1–3 antagonist Ki16425 deteriorated motor disability of EAE^low. Specifically, LPAR1–3 antagonist (intraperitoneal) deteriorated symptoms of EAE^low associated with increased demyelination, chemokine expression, cellular infiltration, and immune cell activation (microglia and macrophage) in spinal cords of mice compared to the sham group. This LPAR1–3 antagonist also increased the infiltration of CD4⁺/IFN-γ⁺ (Th1) and CD4⁺/IL-17⁺ (Th17) cells into spinal cords of EAE^low mice along with upregulated mRNA expression of IFN-γ and IL-17 and impaired blood–brain barrier (BBB) in the spinal cord. The underlying mechanism for negative effects of LPAR1–3 antagonist was associated with the overproduction of reactive oxygen species (ROS)-generating nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) 2 and NOX3. Interestingly, LPAR1/2 agonist 1-oleoyl-LPA (LPA 18:1) (intraperitoneal) ameliorated symptoms of EAE^high and improved representative pathological features of spinal cords of EAE^high mice.

Conclusions

Our findings strongly suggest that some agents that can stimulate LPARs might have potential therapeutic implications for autoimmune demyelinating diseases such as MS.

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.

White matter injury in infants with intraventricular haemorrhage: mechanisms and therapies

Intraventricular haemorrhage (IVH) continues to be a major complication of prematurity that can result in cerebral palsy and cognitive impairment in survivors. No optimal therapy exists to prevent IVH or to treat its consequences. IVH varies in severity and can present as a bleed confined to the germinal matrix, small-to-large IVH or periventricular haemorrhagic infarction. Moderate-to-severe haemorrhage dilates the ventricle and damages the periventricular white matter. This white matter injury results from a constellation of blood-induced pathological reactions, including oxidative stress, glutamate excitotoxicity, inflammation, perturbed signalling pathways and remodelling of the extracellular matrix. Potential therapies for IVH are currently undergoing investigation in preclinical models and evidence from clinical trials suggests that stem cell treatment and/or endoscopic removal of clots from the cerebral ventricles could transform the outcome of infants with IVH. This Review presents an integrated view of new insights into the mechanisms underlying white matter injury in premature infants with IVH and highlights the importance of early detection of disability and immediate intervention in optimizing the outcomes of IVH survivors.

Dual Role of Lysophosphatidic Acid Receptor 2 (LPA2) in Amyotrophic Lateral Sclerosis

Lysophosphatidic acid (LPA) is a pleiotropic extracellular lipid mediator with many physiological functions that signal through six known G protein-coupled receptors (LPA1-6). In the central nervous system (CNS), LPA mediates a wide range of effects including neural progenitor cell physiology, neuronal cell death, axonal retraction, and inflammation. Since inflammation is a hallmark of most neurological conditions, we hypothesized that LPA could be involved in the physiopathology of amyotrophic lateral sclerosis (ALS). We found that LPA2 RNA was upregulated in post-mortem spinal cord samples of ALS patients and in the sciatic nerve and skeletal muscle of SOD1G93A mouse, the most widely used ALS mouse model. To assess the contribution of LPA2 to ALS, we generated a SOD1G93A mouse that was deficient in Lpar2. This animal revealed that LPA2 signaling accelerates disease onset and neurological decline but, unexpectedly, extended the lifespan. To gain insights into the early harmful actions of LPA2 in ALS, we studied the effects of this receptor in the spinal cord, peripheral nerve, and skeletal muscle of ALS mice. We found that LPA2 gene deletion increased microglial activation but did not contribute to motoneuron death, astrogliosis, degeneration, and demyelination of motor axons. However, we observed that Lpar2 deficiency protected against muscle atrophy. Moreover, we also found the deletion of Lpar2 reduced the invasion of macrophages into the skeletal muscle of SOD1G93A mice, linking LPA2 signaling with muscle inflammation and atrophy in ALS. Overall, these results suggest for the first time that LPA2 contributes to ALS, and its genetic deletion results in protective actions at the early stages of the disease but shortens survival thereafter.

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.

Autotaxin stimulates LPA2 receptor in macrophages and exacerbates dextran sulfate sodium-induced acute colitis

Autotaxin (ATX) is a secreted enzyme that hydrolyzes lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA) and choline. ATX has been implicated in multiple chronic inflammatory diseases, but little is known about its role in the development of inflammatory bowel disease (IBD). Here, we investigated how ATX contributed to intestinal inflammation during colitis. We found that ATX expression levels were upregulated in the intestines of ulcerative colitis (UC) patients in acute state as well as in the intestines of dextran sulfate sodium (DSS)-induced colitis mice, which is likely due to increased infiltration of inflammatory cells including macrophages. Intriguingly, the inhibition of ATX activity led to reduced production of inflammatory cytokines, as well as attenuated colitis. These findings suggest that ATX may display strong pro-inflammatory properties. Supporting this, treatment with recombinant mouse ATX (rmATX) increased the production of inflammatory cytokines and enzymes in mouse macrophage cell line RAW264.7 and bone marrow-derived macrophages (BMDM), whereas silencing ATX by siRNA reduced LPS-stimulated production of pro-inflammatory factors. Notably, we found that the levels of LPA2 (an LPA receptor) were dramatically upregulated in rmATX-treated RAW264.7 cells and DSS-treated mice. Gene silencing of lpa2 in RAW264.7 cells by siRNA led to reduced production of inflammatory cytokines. Moreover, adenovirus-mediated delivery of lpa2 short hairpin RNA into DSS-treated mice ameliorated colitis. Collectively, our research suggests that ATX may exacerbate DSS-induced colitis by activating LPA2 receptor in macrophages and represent a promising target for the treatment of IBD. KEY MESSAGES: Increased ATX expression and secretion in colitic colons are likely due to increased infiltration of inflammatory cells including macrophages. Recombinant ATX promotes, but ATX silencing inhibits, the production of inflammatory cytokines in LPS-stimulated RAW264.7 cells and BMDM. •LPA2 mediates the pro-inflammatory effects of ATX on macrophages. Inhibition of ATX and downregulation of LPA2 ameliorate DSS-induced colitis.

Microglia Require CD4 T Cells to Complete the Fetal-to-Adult Transition

The brain is a site of relative immune privilege. Although CD4 T cells have been reported in the central nervous system, their presence in the healthy brain remains controversial, and their function remains largely unknown. We used a combination of imaging, single cell, and surgical approaches to identify a CD69⁺ CD4 T cell population in both the mouse and human brain, distinct from circulating CD4 T cells. The brain-resident population was derived through in situ differentiation from activated circulatory cells and was shaped by self-antigen and the peripheral microbiome. Single-cell sequencing revealed that in the absence of murine CD4 T cells, resident microglia remained suspended between the fetal and adult states. This maturation defect resulted in excess immature neuronal synapses and behavioral abnormalities. These results illuminate a role for CD4 T cells in brain development and a potential interconnected dynamic between the evolution of the immunological and neurological systems.

Video Abstract

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Residential CD4 T cells are present in the healthy mouse and human brain

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Brain residency is a transient program initiated in situ and lasting weeks

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CD4 T cell entry around birth drives a transcriptional maturation step in microglia

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Absence of CD4 T cells results in defective synaptic pruning and behavior

Lysophosphatidic Acid Receptor 5 Plays a Pathogenic Role in Brain Damage after Focal Cerebral Ischemia by Modulating Neuroinflammatory Responses

Receptor-mediated lysophosphatidic acid (LPA) signaling has come to be considered an important event for various diseases. In cerebral ischemia, LPA₁ has recently been identified as a receptor subtype that mediates brain injury, but the roles of other LPA receptor subtypes remain unknown. Here, we investigated the potential role of LPA₅ as a novel pathogenic factor for cerebral ischemia using a mouse model of transient middle cerebral artery occlusion (tMCAO). LPA₅ was upregulated in the ischemic core region after tMCAO challenge, particularly in activated microglia. When TCLPA5, a selective LPA₅ antagonist, was given to tMCAO-challenged mice immediately after reperfusion, brain damage, including brain infarction, functional neurological deficit, and neuronal and non-neuronal apoptosis, was reduced in mice. Similarly, delayed TCLPA5 administration (at three hours after reperfusion) reduced brain infarction and neurological deficit. The histological results demonstrated that TCLPA5 administration attenuated microglial activation, as evidenced by the decreased Iba1 immunoreactivities, the number of amoeboid cells, and proliferation in an injured brain. TCLPA5 administration also attenuated the upregulation of the expression of pro-inflammatory cytokines at mRNA levels in post-ischemic brain, which was also observed in lipopolysaccharide-stimulated BV2 microglia upon LPA₅ knockdown. Overall, this study identifies LPA₅ as a novel pathogenic factor for cerebral ischemia, further implicating it as a promising target for drug development to treat this disease.

Autotaxin inhibition attenuates endothelial permeability after ischemia-reperfusion injury

BACKGROUND

Autotaxin (ATX-secretory lysophospholipase D) is the primary lysophosphatidic acid (LPA) producing enzyme. LPA promotes endothelial hyper-permeability and microvascular dysfunction following cellular stress.

OBJECTIVE

We sought to assess whether ATX inhibition would attenuate endothelial monolayer permeability after anoxia-reoxygenation (A-R) in vitro and attenuate the increase in hydraulic permeability observed after ischemia-reperfusion injury (IRI) in vivo.

METHODS

A permeability assay assessed bovine endothelial monolayer permeability during anoxia-reoxygenation with/without administration of pipedimic acid, a specific inhibitor of ATX, administered either pre-anoxia or post-anoxia. Hydraulic permeability (Lp) of rat mesenteric post-capillary venules was evaluated after IRI, with and without ATX inhibition. Lastly, Lp was evaluated after the administration of ATX alone.

RESULTS

Anoxia-reoxygenation increased monolayer permeability 4-fold (p < 0.01). Monolayer permeability was reduced to baseline similarly in both the pre-anoxia and post-anoxia ATX inhibition groups (each p < 0.01, respectively). Lp was attenuated by 24% with ATX inhibition (p < 0.01). ATX increased Lp from baseline in a dose dependent manner (p < 0.05).

CONCLUSIONS

Autotaxin inhibition attenuated increases in endothelial monolayer permeability during A-R in vitro and hydraulic permeability during IRI in vivo. Targeting ATX may be especially beneficial by limiting its downstream mediators that contribute to mechanisms associated with endothelial permeability. ATX inhibitors may therefore have potential for pharmacotherapy during IRI.

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.

Melatonin exerts neuroprotective effects by attenuating astro- and microgliosis and suppressing inflammatory response following spinal cord injury

Reactive gliosis and inflammatory reaction are common pathological change to spinal cord injury (SCI). Whereas, the effects of melatonin (MT) on the astro- and microgliosis and their related inflammatory response in the injured spinal cord are not fully understood. In this study, MT's effects on the accumulation and proliferation of microglia and astrocytes and their related inflammatory response were investigated in an acute SCI model. The effects of MT on oxidative stress, neuronal survival and behavioral performance were also tested. It was found that MT treatment significantly suppressed the accumulation and the proliferation of microglia and astrocytes. Quantitative PCR data showed that MT significantly down-regulated the pro-inflammatory markers iNOS, IL-1β and TNF-α expressions. The data showed that MT led to the rise in SOD, CAT and GSH-Px contents and the decrease in MDA content. Western blotting analysis verified that MT significantly down-regulated caspase-3, Bax and GFAP expressions, up-regulated Bcl-2 expression. Compared with the SCI vehicle-treated group, the SCI MT-treated group exhibited a greater Basso Mouse Scale (BMS) locomotor rating score. On the whole, these findings implied that MT exerts its neuroprotective effects by suppressing the accumulation and the proliferation of microglia and astrocytes and reducing the release of pro-inflammatory cytokines, which might be one of the underlying mechanisms of the MT's neuroprotective effect after SCI. Accordingly, MT may be a promising therapeutic candidate for acute SCI.

TMEM16F inhibition limits pain-associated behavior and improves motor function by promoting microglia M2 polarization in mice

Spinal cord injury (SCI) leads to sensorimotor deficits and autonomic changes. Macrophages and microglia could be polarized into the classically activated pro-inflammatory M1 phenotype or the alternatively activated anti-inflammatory M2 phenotype. Transmembrane protein with unknown function 16F (TMEM16F) exhibits functional diversity and may contribute to microglial function. However, the effects of TMEM16F on the modulation of macrophage/microglial polarization are still not fully understood. In the study, TMEM16F up-regulation was detected after SCI in mice, and TMEM16F protein was found in macrophages/microglia in injured spinal cord sections. Depletion of TMEM16F improved motor function in male mice with SCI. M1-type macrophages/microglia accumulated in lower numbers in the injured spinal cord of TMEM16F-knockout (KO) mice. M2 polarization inhibited by SCI was improved in mice with TMEM16F deficiency. TMEM16F deletion also attenuated microglial/macrophage pro-inflammatory response. Furthermore, significant down-regulation of A disintegrin and metalloprotease 17 (ADAM17) was observed in TMEM16F-KO mice. Importantly, TMEM16F-promoted M1 polarization and -inhibited M1 polarization were largely associated with the suppression of ADAM17. Overall, our findings provided new insights into the regulatory mechanisms of macrophage/microglial polarization, thereby possibly facilitating the development of new therapeutic strategies for SCI through the regulation of TMEM16F/ADAM17 signaling.

Purinergic receptors and the inflammatory response mediated by lipids

The inflammatory response is regulated by the production of different extracellular mediators, including lipids and extracellular nucleotides. In the extracellular environment, intermediate lipids activate specific G-protein-coupled receptors (GPCRs) in target cells and promote cell recruitment and activation. Extracellular nucleotides activate two types of receptors, the ionotropic purinergic P2X and the metabotropic purinergic P2Y receptors, inducing the release of cytokines and promoting cell recruitment. Several P2X receptors are associated with an increase in the production of immunoactive lipids mediators, which in turn are able to interfere with the activation of different P2Y receptors, establishing a tight signalling link between purinergic receptors and lipid mediators. In this review, we summarise recent studies indicating signalling crosstalk between purinergic P2X and P2Y receptor activation and lipid mediators with a focus on inflammatory diseases. Novel concepts arising from this crosstalk would result in the development of combinatorial therapies targeting lipid synthesis together with individual P2 receptors for the management of inflammatory diseases.