Phospholipase A2 superfamily members play divergent roles after spinal cord injury

Necroptosis pathway emerged as potential diagnosis markers in spinal cord injury

The present research focused on identifying necroptosis-related differentially expressed genes (NRDEGs) in spinal cord injury (SCI) to highlight potential therapeutic and prognostic target genes in clinical SCI. Three SCI-related datasets were downloaded, including GSE151371, GSE5296 and GSE47681. MSigDB and KEGG datasets were searched for necroptosis-related genes (NRGs). Differentially expressed genes (DEGs) and NRGs were intersected to obtain NRDEGs. The MCC algorithm was employed to select the first 10 genes as hub genes. A protein-protein interaction (PPI) network related to NRDEGs was developed utilizing STRING. Several databases were searched to predict interactions between hub genes and miRNAs, transcription factors, potential drugs, and small molecules. Immunoassays were performed to identify DEGs using CIBERSORTx. Additionally, qRT-PCR was carried out to verify NRDEGs in an animal model of SCI. Combined analysis of all datasets identified 15 co-expressed DEGs and NRGs. GO and KEGG pathway analyses highlighted DEGs mostly belonged to pathways associated with necroptosis and apoptosis. Hub gene expression analysis showed high accuracy in SCI diagnosis was associated with the expression of CHMP7 and FADD. A total of two hub genes, i.e. CHMP7, FADD, were considered potential targets for SCI therapy.

DADLE promotes motor function recovery by inhibiting cytosolic phospholipase A2 mediated lysosomal membrane permeabilization after spinal cord injury

BACKGROUND AND PURPOSE

Autophagy is a protective factor for controlling neuronal damage, while necroptosis promotes neuroinflammation after spinal cord injury (SCI). DADLE (D-Ala2 , D-Leu5 ]-enkephalin) is a selective agonist for delta (δ) opioid receptor and has been identified as a promising drug for neuroprotection. The aim of this study was to investigate the mechanism/s by which DADLE causes locomotor recovery following SCI.

EXPERIMENTAL APPROACH

Spinal cord contusion model was used and DADLE was given by i.p. (16 mg·kg-1 ) in mice for following experiments. Motor function was assessed by footprint and Basso mouse scale (BMS) score analysis. Western blotting used to evaluate related protein expression. Immunofluorescence showed the protein expression in each cell and its distribution. Network pharmacology analysis was used to find the related signalling pathways.

KEY RESULTS

DADLE promoted functional recovery after SCI. In SCI model of mice, DADLE significantly increased autophagic flux and inhibited necroptosis. Concurrently, DADLE restored autophagic flux by decreasing lysosomal membrane permeabilization (LMP). Additionally, chloroquine administration reversed the protective effect of DADLE to inhibit necroptosis. Further analysis showed that DADLE decreased phosphorylated cPLA2 , overexpression of cPLA2 partially reversed DADLE inhibitory effect on LMP and necroptosis, as well as the promotion autophagy. Finally, AMPK/SIRT1/p38 pathway regulating cPLA2 is involved in the action DADLE on SCI and naltrindole inhibited DADLE action on δ receptor and on AMPK signalling pathway.

CONCLUSION AND IMPLICATION

DADLE causes its neuroprotective effects on SCI by promoting autophagic flux and inhibiting necroptosis by decreasing LMP via activating δ receptor/AMPK/SIRT1/p38/cPLA2 pathway.

Tlr4 Deletion Modulates Cytokine and Extracellular Matrix Expression in Chronic Spinal Cord Injury, Leading to Improved Secondary Damage and Functional Recovery

Toll-like receptors (TLRs) play an important role in the innate immune response after CNS injury. Although TLR4 is one of the best characterized, its role in chronic stages after spinal cord injury (SCI) is not well understood. We examined the role of TLR4 signaling in injury-induced responses at 1 d, 7 d, and 8 weeks after spinal cord contusion injury in adult female TLR4 null and wild-type mice. Analyses include secondary damage, a range of transcriptome and protein analyses of inflammatory, cell death, and extracellular matrix (ECM) molecules, as well as immune cell infiltration and changes in axonal sprouting and locomotor recovery. Lack of TLR4 signaling results in reduced neuronal and myelin loss, reduced activation of NFκB, and decreased expression of inflammatory cytokines and necroptotic cell death pathway at a late time point (8 weeks) after injury. TLR4 null mice also showed reduction of scar-related ECM molecules at 8 weeks after SCI, accompanied by increase in ECM molecules associated with perineuronal nets, increased sprouting of serotonergic fibers, and improved locomotor recovery. These findings reveal novel effects of TLR4 signaling in chronic SCI. We show that TLR4 influences inflammation, cell death, and ECM deposition at late-stage post-injury when secondary injury processes are normally considered to be over. This highlights the potential for late-stage targeting of TLR4 as a potential therapy for chronic SCI.

Chondroitin Sulfate Proteoglycans Revisited: Its Mechanism of Generation and Action for Spinal Cord Injury

Reactive astrocytes (RAs) produce chondroitin sulfate proteoglycans (CSPGs) in large quantities after spinal cord injury (SCI) and inhibit axon regeneration through the Rho-associated protein kinase (ROCK) pathway. However, the mechanism of producing CSPGs by RAs and their roles in other aspects are often overlooked. In recent years, novel generation mechanisms and functions of CSPGs have gradually emerged. Extracellular traps (ETs), a new recently discovered phenomenon in SCI, can promote secondary injury. ETs are released by neutrophils and microglia, which activate astrocytes to produce CSPGs after SCI. CSPGs inhibit axon regeneration and play an important role in regulating inflammation as well as cell migration and differentiation; some of these regulations are beneficial. The current review summarized the process of ET-activated RAs to generate CSPGs at the cellular signaling pathway level. Moreover, the roles of CSPGs in inhibiting axon regeneration, regulating inflammation, and regulating cell migration and differentiation were discussed. Finally, based on the above process, novel potential therapeutic targets were proposed to eliminate the adverse effects of CSPGs.

Maresin-1 prevents blood-spinal cord barrier disruption associated with TRPV4 elevation in the experimental model of spinal cord injury

Recently, we reported the TRPV4 ion channel activation and its association with secondary damage after spinal cord injury (SCI). TRPV4 activation is linked with blood-spinal cord barrier (BSCB) disruption, endothelial damage, and inflammation after SCI. Specialized pro-resolving mediators (SPM) are endogenous lipid mediators released for inflammation resolution. Studies suggest that SPM could act as an endogenous antagonist of ion channels directly or indirectly at the plasma membrane. Herein, we studied the effect of maresin-1, a docosahexaenoic acid (DHA)-derived SPM, in SCI-induced TRPV4 expression and subsequent associated damage. First, employing a particular agonist (4αPDD) in endothelial and neuronal cell lines, we examined the potential of maresin-1 to block TRPV4 activation. Then we quantify the DHA levels in plasma and epicenter of the spinal cord in sham and at 1, 3, 7, 14, 21, and 28-days post-injury (DPI) using LC-MS. Then, we exogenously administered maresin-1 using two dosing regimens i.e., single-dose (1 μg) and multiple-dose (1 μg/day for seven days), to confirm its role in the TRPV4 inhibition and its linked damage. After SCI, DHA levels decrease in the spinal cord epicenter area as well as in the plasma. Treatment with maresin-1 attenuates TRPV4 expression, inflammatory cytokines, and chemokines and impedes neutrophil infiltration. Furthermore, treatment with maresin-1 prevents BSCB disruption, alleviates glial scar formation, and improves functional recovery. Thus, our results suggest that maresin-1 could modulate TRPV4 expression and could be a safe and promising approach to target inflammation and BSCB damage after SCI.

iPLA2 inhibition blocks LysoPC-induced TRPC6 externalization and promotes Re-endothelialization of carotid injuries in hypercholesterolemic mice

Lipid oxidation products, including lysophosphatidylcholine (lysoPC), accumulate at the site of arterial injury after vascular interventions and hinder re-endothelization. LysoPC activates calcium-permeable channels, specifically canonical transient receptor potential 6 (TRPC6) channels that induce a sustained increase in intracellular calcium ion concentration [Ca2+]i and contribute to dysregulation of the endothelial cell (EC) cytoskeleton. Activation of TRPC6 leads to inhibition of EC migration in vitro and delayed re-endothelization of arterial injuries in vivo. Previously, we demonstrated the role of phospholipase A2 (PLA2), specifically calcium-independent PLA2 (iPLA2), in lysoPC-induced TRPC6 externalization and inhibition of EC migration in vitro. The ability of FKGK11, an iPLA2-specific pharmacological inhibitor, to block TRPC6 externalization and preserve EC migration was assessed in vitro and in a mouse model of carotid injury. Our data suggest that FKGK11 prevents lysoPC-induced PLA2 activity, blocks TRPC6 externalization, attenuates calcium influx, and partially preserves EC migration in vitro. Furthermore, FKGK11 promotes re-endothelization of an electrocautery carotid injury in hypercholesterolemic mice. FKGK11 has similar arterial healing effects in male and female mice on a high-fat diet. This study suggests that iPLA2 is a potential therapeutic target to attenuate calcium influx through TRPC6 channels and promote EC healing in cardiovascular patients undergoing angioplasty.

Drug screening in zebrafish larvae reveals inflammation-related modulators of secondary damage after spinal cord injury in mice

Prolonged inflammation after spinal cord injury is detrimental to recovery. To find pharmacological modulators of the inflammation response, we designed a rapid drug screening paradigm in larval zebrafish followed by testing of hit compounds in a mouse spinal cord injury model. Methods: We used reduced il-1β linked green fluorescent protein (GFP) reporter gene expression as a read-out for reduced inflammation in a screen of 1081 compounds in larval zebrafish. Hit drugs were tested in a moderate contusion model in mice for cytokine regulation, and improved tissue preservation and locomotor recovery. Results: Three compounds robustly reduced il-1β expression in zebrafish. Cimetidine, an over-the-counter H2 receptor antagonist, also reduced the number of pro-inflammatory neutrophils and rescued recovery after injury in a zebrafish mutant with prolonged inflammation. Cimetidine action on il-1β expression levels was abolished by somatic mutation of H2 receptor hrh2b, suggesting specific action. In mice, systemic treatment with Cimetidine led to significantly improved recovery of locomotor behavior as compared to controls, accompanied by decreased neuronal tissue loss and a shift towards a pro-regenerative profile of cytokine gene expression. Conclusion: Our screen revealed H2 receptor signaling as a promising target for future therapeutic interventions in spinal cord injury. This work highlights the usefulness of the zebrafish model for rapid screening of drug libraries to identify therapeutics to treat mammalian spinal cord injury.

Progranulin inhibits phospholipase sPLA2-IIA to control neuroinflammation

Mutations in the granulin (GRN) gene, resulting in haploinsufficiency of the progranulin (PGRN) protein, are a leading cause of frontotemporal lobar degeneration (FTLD) and PGRN polymorphisms are associated with Alzheimer's disease (AD) and Parkinson's disease (PD). PGRN is a key regulator of microglia-mediated inflammation but the mechanism is still unknown. Here we report that PGRN interacts with sPLA2-IIA, a secreted phospholipase involved in inflammatory responses, to downregulate sPLA2-IIA activities and levels. sPLA2-IIA expression modifies PGRN deficiency phenotypes in mice and sPLA2-IIA inhibition rescues inflammation and lysosomal abnormalities in PGRN deficient mice. Furthermore, FTLD patients with GRN mutations show increased levels of sPLA2-IIA in astrocytes. Our data support sPLA2-IIA as a critical target for PGRN and a novel therapeutic target for FTLD-GRN.

LC-MS/MS-based arachidonic acid metabolomics in acute spinal cord injury reveals the upregulation of 5-LOX and COX-2 products

Arachidonic acid (AA) plays a critical role in inflammatory regulation and secondary injury after spinal cord injury (SCI). However, the overall AA metabolism profile in the acute phase of SCI remains elusive. Here we quantified AA metabolomics by High Performance Liquid Chromatography-Tandem Mass Spectrometry-Based Method (LC-MS/MS) using spinal cord tissue collected at 4 h, 24 h and 48 h after contusive SCI in rats. Remarkably, Prostaglandin E2 (PGE2) and Leukotriene B4 (LTB4) were significantly increased throughout the acute SCI. Cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX), the key enzymes involved in the production of PGE2 and LTB4, were elevated in the lesioned spinal cord tissue, validated by both western blot and immunofluorecnce. The spatial-temporal changes of COX-2 and 5-LOX mainly occurs in neurons both in epicenter and rostral and caudal spinal cord segments after SCI. Our study sheds light on the dynamic microenvironment changes in acute SCI by characterizing the profile of AA metabolism. The COX-2 and 5-LOX may be promising therapeutic target for SCI.

Promising Advances in Pharmacotherapy for Patients with Spinal Cord Injury-A Review of Studies Performed In Vivo with Modern Drugs

Spinal cord injury (SCI) is a pathological neurological condition that leads to significant motor dysfunction. It is a condition that occurs as a result of tragic accidents, violent acts, or as a consequence of chronic diseases or degenerative changes. The current treatments for patients with SCI have moderate efficacy. They improve the quality of life of patients, but they are still doomed to long-term disability. In response to the modern directions of research on possible therapeutic methods that allow for the recovery of patients with SCI, a scientific review publication is needed to summarize the recent developments in this topic. The following review is focused on the available pharmacological treatments for SCIs and the problems that patients face depending on the location of the injury. In the following review, the research team describes problems related to spasticity and neuropathic pain; possible therapeutic pathways are also described for neuroprotection and the improvement of neurotransmission within the injured spinal cord, and the review focuses on issues related to oxidative stress.

The design and discovery of phospholipase A2 inhibitors for the treatment of inflammatory diseases

AREAS COVERED

This review article summarizes the most important synthetic PLA₂ inhibitors developed to target each one of the four major types of human PLA₂ (cytosolic cPLA₂, calcium-independent iPLA₂, secreted sPLA₂, and lipoprotein-associated Lp-PLA₂), discussing their in vitro and in vivo activities as well as their recent applications and therapeutic properties. Recent findings on the role of PLA₂ in the pathobiology of COVID-19 are also discussed.

EXPERT OPINION

Although a number of PLA₂ inhibitors have entered clinical trials, none has reached the market yet. Lipoprotein-associated PLA₂ is now considered a biomarker of vascular inflammation rather than a therapeutic target for inhibitors like darapladib. Inhibitors of cytosolic PLA₂ may find topical applications for diseases like atopic dermatitis and psoriasis. Inhibitors of secreted PLA₂, varespladib and varespladib methyl, are under investigation for repositioning in snakebite envenoming. A deeper understanding of PLA₂ enzymes is needed for the development of novel selective inhibitors. Lipidomic technologies combined with medicinal chemistry approaches may be useful tools toward this goal.

Neutrophil, Extracellular Matrix Components, and Their Interlinked Action in Promoting Secondary Pathogenesis After Spinal Cord Injury

Secondary pathogenesis following primary mechanical damage to the spinal cord is believed to be the ultimate reason for the limitation of currently available therapies. Precisely, the complex cascade of secondary events-mediated scar formation is the sole hurdle in the recovery process due to its inhibitory effect on axonal regeneration, plasticity, and remyelination. Neutrophils initiate this secondary injury along with other extracellular matrix components such as matrix metalloproteinase (MMPs), and chondroitin sulfate proteoglycans (CSPGs). Together, they mediate inflammation, necrosis, apoptosis, lesion, and scar formation at the injury site. Activated neutrophil releases several proteases, cytokines, and chemokines that cause complete tissue destruction. Thus, neutrophil activation and infiltration in the acute phase of injury act as a roadmap for inducing tissue destruction. MMPs, are extracellular proteolytic enzymes that degrade the ECM proteins, increases vascular permeability, and are predominantly released by neutrophils. These MMPs, in turn, cleave NG2 proteoglycan, a subtype of CSPG, into the active form. This active or shed form is involved in both the fibrotic as well as glial scar formation. Since neutrophils and ECM components are closely associated with each other in pathological conditions. Herein, we emphasize the interaction of neutrophils and their influence on ECM protein expression during the acute and chronic phases to identify a promising targets for designing a therapeutic approach in spinal cord injury.

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.

The effects of myelin on macrophage activation are phenotypic specific via cPLA2 in the context of spinal cord injury inflammation

Spinal cord injury (SCI) produces chronic, pro-inflammatory macrophage activation that impairs recovery. The mechanisms driving this chronic inflammation are not well understood. Here, we detail the effects of myelin debris on macrophage physiology and demonstrate a novel, activation state-dependent role for cytosolic phospholipase-A2 (cPLA₂) in myelin-mediated potentiation of pro-inflammatory macrophage activation. We hypothesized that cPLA₂ and myelin debris are key mediators of persistent pro-inflammatory macrophage responses after SCI. To test this, we examined spinal cord tissue 28-days after thoracic contusion SCI in 3-month-old female mice and observed both cPLA₂ activation and intracellular accumulation of lipid-rich myelin debris in macrophages. In vitro, we utilized bone marrow-derived macrophages to determine myelin's effects across a spectrum of activation states. We observed phenotype-specific responses with myelin potentiating only pro-inflammatory (LPS + INF-γ; M1) macrophage activation, whereas myelin did not induce pro-inflammatory responses in unstimulated or anti-inflammatory (IL-4; M2) macrophages. Specifically, myelin increased levels of pro-inflammatory cytokines, reactive oxygen species, and nitric oxide production in M1 macrophages as well as M1-mediated neurotoxicity. PACOCF3 (cPLA₂ inhibitor) blocked myelin's detrimental effects. Collectively, we provide novel spatiotemporal evidence that myelin and cPLA₂ play an important role in the pathophysiology of SCI inflammation and the phenotype-specific response to myelin implicate diverse roles of myelin in neuroinflammatory conditions.

RNA-seq analysis and compound screening highlight multiple signalling pathways regulating secondary cell death after acute CNS injury in vivo

Understanding the molecular mechanisms that regulate secondary cell death after acute central nervous system (CNS) injury is critical for the development of effective neuroprotective drugs. Previous research has shown that neurotoxic processes including excitotoxicity, oxidative stress and neuroinflammation can cause secondary cell death. Nevertheless, clinical trials targeting these processes have been largely unsuccessful, suggesting that the signalling pathways underlying secondary cell death remain incompletely understood. Due to their suitability for live imaging and their amenability to genetic and pharmacological manipulation, larval zebrafish provide an ideal platform for studying the regulation of secondary cell death in vivo Here, we use RNA-seq gene expression profiling and compound screening to identify signalling pathways that regulate secondary cell death after acute neural injury in larval zebrafish. RNA-seq analysis of genes upregulated in cephalic mpeg1⁺ macrophage-lineage cells isolated from mpeg1:GFP transgenic larvae after neural injury suggested an involvement of cytokine and polyamine signalling in secondary cell death. Furthermore, screening a library of FDA approved compounds indicated roles for GABA, serotonin and dopamine signalling. Overall, our results highlight multiple signalling pathways that regulate secondary cell death in vivo, and thus provide a starting point for the development of novel neuroprotective treatments for patients with CNS injury.This article has an associated First Person interview with the two first authors of the paper.

Small-molecule inhibitors as potential therapeutics and as tools to understand the role of phospholipases A2

Phospholipase A2 (PLA2) enzymes are involved in various inflammatory pathological conditions including arthritis, cardiovascular and autoimmune diseases. The regulation of their catalytic activity is of high importance and a great effort has been devoted in developing synthetic inhibitors. We summarize the most important small-molecule synthetic PLA2 inhibitors developed to target each one of the four major types of human PLA2 (cytosolic cPLA2, calcium-independent iPLA2, secreted sPLA2, and lipoprotein-associated LpPLA2). We discuss recent applications of inhibitors to understand the role of each PLA2 type and their therapeutic potential. Potent and selective PLA2 inhibitors have been developed. Although some of them have been evaluated in clinical trials, none reached the market yet. Apart from their importance as potential medicinal agents, PLA2 inhibitors are excellent tools to unveil the role that each PLA2 type plays in cells and in vivo. Modern medicinal chemistry approaches are expected to generate improved PLA2 inhibitors as new agents to treat inflammatory diseases.

Bioactive Lipids in Inflammation After Central Nervous System Injury

Despite the progress made over the last decades to understand the mechanisms underlying tissue damage and neurological deficits after neurotrauma, there are currently no effective treatments in the clinic. It is well accepted that the inflammatory response in the CNS after injury exacerbates tissue loss and functional impairments. Unfortunately, the use of potent anti-inflammatory drugs, such as methylprednisolone, fails to promote therapeutic recovery and also gives rise to several undesirable side effects related to immunosuppression. The injury-induced inflammatory response is complex, and understanding the mechanisms that regulate this inflammation is therefore crucial in the quest to develop effective treatments. Bioactive lipids have emerged as potent molecules in controlling the initiation, coordination, and resolution of inflammation and in promoting tissue repair and recovery of homeostasis. These bioactive lipids are produced by cells involved in the inflammatory response, and their defective synthesis leads to persistent chronic inflammation, tissue damage, and fibrosis. The present chapter discusses recent evidence for the role of some of these bioactive lipids, in particular, eicosanoid and pro-resolving lipid mediators, in the regulation of inflammation after neurotrauma and highlights the therapeutic potential of some of these lipids in enhancing neurological outcomes after CNS injuries.

PLA2G6-Associated Neurodegeneration (PLAN): Review of Clinical Phenotypes and Genotypes

Phospholipase A2 group VI (PLA2G6)-associated neurodegeneration (PLAN) includes a series of neurodegenerative diseases that result from the mutations in PLA2G6. PLAN has genetic and clinical heterogeneity, with different mutation sites, mutation types and ethnicities and its clinical phenotype is different. The clinical phenotypes and genotypes of PLAN are closely intertwined and vary widely. PLA2G6 encodes a group of VIA calcium-independent phospholipase A2 proteins (iPLA₂β), an enzyme involved in lipid metabolism. According to the age of onset and progressive clinical features, PLAN can be classified into the following subtypes: infantile neuroaxonal dystrophy (INAD), atypical neuroaxonal dystrophy (ANAD) and parkinsonian syndrome which contains adult onset dystonia parkinsonism (DP) and autosomal recessive early-onset parkinsonism (AREP). In this review, we present an overview of PLA2G6-associated neurodegeneration in the context of current research.

cPLA2α-/- sympathetic neurons exhibit increased membrane excitability and loss of N-Type Ca2+ current inhibition by M1 muscarinic receptor signaling

Group IVa cytosolic phospholipase A₂ (cPLA₂α) mediates GPCR-stimulated arachidonic acid (AA) release from phosphatidylinositol 4,5-bisphosphate (PIP₂) located in plasma membranes. We previously found in superior cervical ganglion (SCG) neurons that PLA₂ activity is required for voltage-independent N-type Ca²⁺ (N-) current inhibition by M₁ muscarinic receptors (M₁Rs). These findings are at odds with an alternative model, previously observed for M-current inhibition, where PIP₂ dissociation from channels and subsequent metabolism by phospholipase C suffices for current inhibition. To resolve cPLA₂α’s importance, we have investigated its role in mediating voltage-independent N-current inhibition (~40%) that follows application of the muscarinic agonist oxotremorine-M (Oxo-M). Preincubation with different cPLA₂α antagonists or dialyzing cPLA₂α antibodies into cells minimized N-current inhibition by Oxo-M, whereas antibodies to Ca²⁺-independent PLA₂ had no effect. Taking a genetic approach, we found that SCG neurons from cPLA₂α^-/- mice exhibited little N-current inhibition by Oxo-M, confirming a role for cPLA₂α. In contrast, cPLA₂α antibodies or the absence of cPLA₂α had no effect on voltage-dependent N-current inhibition by M₂/M₄Rs or on M-current inhibition by M₁Rs. These findings document divergent M₁R signaling mediating M-current and voltage-independent N-current inhibition. Moreover, these differences suggest that cPLA₂α acts locally to metabolize PIP₂ intimately associated with N- but not M-channels. To determine cPLA₂α’s functional importance more globally, we examined action potential firing of cPLA₂α^+/+ and cPLA₂α^-/- SCG neurons, and found decreased latency to first firing and interspike interval resulting in a doubling of firing frequency in cPLA₂α^-/- neurons. These unanticipated findings identify cPLA₂α as a tonic regulator of neuronal membrane excitability.

Mechanisms of lysophosphatidylcholine-induced demyelination: A primary lipid disrupting myelinopathy

For decades lysophosphatidylcholine (LPC, lysolecithin) has been used to induce demyelination, without a clear understanding of its mechanisms. LPC is an endogenous lysophospholipid so it may cause demyelination in certain diseases. We investigated whether known receptor systems, inflammation or nonspecific lipid disruption mediates LPC-demyelination in mice. We found that LPC nonspecifically disrupted myelin lipids. LPC integrated into cellular membranes and rapidly induced cell membrane permeability; in mice, LPC injury was phenocopied by other lipid disrupting agents. Interestingly, following its injection into white matter, LPC was cleared within 24 hr but by five days there was an elevation of endogenous LPC that was not associated with damage. This elevation of LPC in the absence of injury raises the possibility that the brain has mechanisms to buffer LPC. In support, LPC injury in culture was significantly ameliorated by albumin buffering. These results shed light on the mechanisms of LPC injury and homeostasis.

Analyses of Calcium-Independent Phospholipase A2beta (iPLA2β) in Biological Systems

The Ca²⁺-independent phospholipases A₂ (iPLA₂s) are part of a diverse family of PLA₂s, manifest activity in the absence of Ca²⁺, are ubiquitous, and participate in a variety of biological processes. Among the iPLA₂s, the cytosolic iPLA₂β has received considerable attention and ongoing studies from various laboratories suggest that dysregulation of iPLA₂β can have a profound impact on the onset and/or progression of many diseases (e.g., cardiovascular, neurological, metabolic, autoimmune). Therefore, appropriate approaches are warranted to gain a better understanding of the role of iPLA₂β in vivo and its contribution to pathophysiology. Given that iPLA₂β is very labile, its basal expression is low in a number of cell systems, and that crystal structure of iPLA₂β is not yet available, careful and efficient protocols are needed to appropriately assess iPLA₂β biochemistry, dynamics, and membrane association. Here, step-by-step details are provided to (a) measure iPLA₂β-specific activity in cell lines or tissue preparations (using a simple radiolabel-based assay) and assess the impact of stimuli and inhibitors on resting- and disease-state iPLA₂β activity, (b) purify the iPLA₂β to near homogeneity (via sequential chromatography) from cell line or tissue preparations, enabling concentration of the enzyme for subsequent analyses (e.g., proteomics), and (c) employ hydrogen/deuterium exchange mass spectrometry analyses to probe both the structure of iPLA₂β and dynamics of its association with the membranes, substrates, and inhibitors.

Liberating Chiral Lipid Mediators, Inflammatory Enzymes, and LIPID MAPS from Biological Grease

In 1970, it was well accepted that the central role of lipids was in energy storage and metabolism, and it was assumed that amphipathic lipids simply served a passive structural role as the backbone of biological membranes. As a result, the scientific community was focused on nucleic acids, proteins, and carbohydrates as information-containing molecules. It took considerable effort until scientists accepted that lipids also "encode" specific and unique biological information and play a central role in cell signaling. Along with this realization came the recognition that the enzymes that act on lipid substrates residing in or on membranes and micelles must also have important signaling roles, spurring curiosity into their potentially unique modes of action differing from those acting on water-soluble substrates. This led to the creation of the concept of "surface dilution kinetics" for describing the mechanism of enzymes acting on lipid substrates, as well as the demonstration that lipid enzymes such as phospholipase A₂ (PLA₂) contain allosteric activator sites for specific phospholipids as well as for membranes. As our understanding of phospholipases advanced, so did the understanding that many of the lipids released by these enzymes are chiral information-containing signaling molecules; for example, PLA₂ regulates the generation of precursors for the biosynthesis of eicosanoids and other bioactive lipid mediators of inflammation and resolution underlying disease progression. The creation of the LIPID MAPS initiative in 2003 and the ensuing development of the lipidomics field have revealed that lipid metabolites are central to human metabolism. Today lipids are recognized as key mediators of health and disease as we enter a new era of biomarkers and personalized medicine. This article is my personal "reflection" on these scientific advances.

Arachidonic acid pathway alterations in cerebrospinal fluid of dogs with naturally occurring spinal cord injury

Background

Canine intervertebral disc πherniation causes a naturally-occurring spinal cord injury (SCI) that bears critical similarities to human SCI with respect to both injury pathomechanisms and treatment. As such, it has tremendous potential to enhance our understanding of injury biology and the preclinical evaluation of novel therapies. Currently, there is limited understanding of the role of arachidonic acid metabolites in canine SCI.

Results

The CSF concentrations of PLA2 and PGE2 were higher in SCI dogs compared to control dogs (p = 0.0370 and 0.0273, respectively), but CSF LCT4 concentration in SCI dogs was significantly lower than that in control dogs (p < 0.0001). Prostaglandin E2 concentration in the CSF was significantly and positively associated with increased severity of SCI at the time of sampling (p = 0.041) and recovery 42 days post-injury (p = 0.006), as measured by ordinal behavioral scores.

Conclusion

Arachidonic acid metabolism is altered in dogs with SCI, and these data suggest that these AA metabolites reflect injury severity and recovery, paralleling data from other model systems.

Beneficial effects of IL-37 after spinal cord injury in mice

IL-37, a member of the IL-1 family, broadly reduces innate inflammation as well as acquired immunity. Whether the antiinflammatory properties of IL-37 extend to the central nervous system remains unknown, however. In the present study, we subjected mice transgenic for human IL-37 (hIL-37tg) and wild-type (WT) mice to spinal cord contusion injury and then treated them with recombinant human IL-37 (rIL-37). In the hIL-37tg mice, the expression of IL-37 was barely detectable in the uninjured cords, but was strongly induced at 24 h and 72 h after the spinal cord injury (SCI). Compared with WT mice, hIL-37tg mice exhibited increased myelin and neuronal sparing and protection against locomotor deficits, including 2.5-fold greater speed in a forced treadmill challenge. Reduced levels of cytokines (e.g., an 80% reduction in IL-6) were observed in the injured cords of hIL-37tg mice, along with lower numbers of blood-borne neutrophils, macrophages, and activated microglia. We treated WT mice with a single intraspinal injection of either full-length or processed rIL-37 after the injury and found that the IL-37-treated mice had significantly enhanced locomotor skills in an open field using the Basso Mouse Scale, as well as supported faster speed on a mechanical treadmill. Treatment with both forms of rIL-37 led to similar beneficial effects on locomotor recovery after SCI. This study presents novel data indicating that IL-37 suppresses inflammation in a clinically relevant model of SCI, and suggests that rIL-37 may have therapeutic potential for the treatment of acute SCI.

Amniotic fluid levels of phospholipase A2 in fetal rats with retinoic acid induced myelomeningocele: the potential "second hit" in neurologic damage

OBJECTIVES

There is growing evidence of ongoing, in utero neurological damage in fetuses with myelomeningocele (MMC). Phospholipase A2 (PLA2) has known neurotoxic properties and is predominantly present in its secretory isoform (sPLA2) in meconium, the passage of which is increased in MMC fetuses. The objective of this study was to determine if amniotic fluid (AF) levels of PLA2 are elevated in a rat model of MMC.

METHODS

Timed pregnant Sprague-Dawley rats were gavage fed 60 mg/kg/bodyweight retinoic acid (RA) in olive oil at embryonic day 10 (E10). Amniocentesis was performed at multiple gestational time points on MMC fetuses, RA-exposed fetuses without MMC and control fetuses. AF PLA2 levels were analyzed by a fluorescent enzyme activity assay. PLA2 isoforms were determined by measuring activity in the presence of specific inhibitors.

RESULTS

There was no difference in AF PLA2 activity between groups on E15. PLA2 activity was significantly increased in MMC fetuses on E17, E19 and E21 (p < 0.001). Secretory PLA2 primarily accounted for the overall greater activity.

CONCLUSIONS

PLA2 levels are elevated in the AF of fetal rats with MMC and may contribute to ongoing neural injury. This pathway may be a useful drug target to limit ongoing damage and better preserve neurologic function.

Activation of Lysophosphatidic Acid Receptor Type 1 Contributes to Pathophysiology of Spinal Cord Injury

Lysophosphatidic acid (LPA) is an extracellular lipid mediator involved in many physiological functions that signals through six known G-protein-coupled receptors (LPA1-LPA6). A wide range of LPA effects have been identified in the CNS, including neural progenitor cell physiology, astrocyte and microglia activation, neuronal cell death, axonal retraction, and development of neuropathic pain. However, little is known about the involvement of LPA in CNS pathologies. Herein, we demonstrate for the first time that LPA signaling via LPA1 contributes to secondary damage after spinal cord injury. LPA levels increase in the contused spinal cord parenchyma during the first 14 d. To model this potential contribution of LPA in the spinal cord, we injected LPA into the normal spinal cord, revealing that LPA induces microglia/macrophage activation and demyelination. Use of a selective LPA1 antagonist or mice lacking LPA1 linked receptor-mediated signaling to demyelination, which was in part mediated by microglia. Finally, we demonstrate that selective blockade of LPA1 after spinal cord injury results in reduced demyelination and improvement in locomotor recovery. Overall, these results support LPA-LPA1 signaling as a novel pathway that contributes to secondary damage after spinal cord contusion in mice and suggest that LPA1 antagonism might be useful for the treatment of acute spinal cord injury.

SIGNIFICANCE STATEMENT

This study reveals that LPA signaling via LPA receptor type 1 activation causes demyelination and functional deficits after spinal cord injury.

Analgesic Effects of Bee Venom Derived Phospholipase A(2) in a Mouse Model of Oxaliplatin-Induced Neuropathic Pain

A single infusion of oxaliplatin, which is widely used to treat metastatic colorectal cancer, induces specific sensory neurotoxicity signs that are triggered or aggravated when exposed to cold or mechanical stimuli. Bee Venom (BV) has been traditionally used in Korea to treat various pain symptoms. Our recent study demonstrated that BV alleviates oxaliplatin-induced cold allodynia in rats, via noradrenergic and serotonergic analgesic pathways. In this study, we have further investigated whether BV derived phospholipase A₂ (bvPLA₂) attenuates oxaliplatin-induced cold and mechanical allodynia in mice and its mechanism. The behavioral signs of cold and mechanical allodynia were evaluated by acetone and a von Frey hair test on the hind paw, respectively. The significant allodynia signs were observed from one day after an oxaliplatin injection (6 mg/kg, i.p.). Daily administration of bvPLA₂ (0.2 mg/kg, i.p.) for five consecutive days markedly attenuated cold and mechanical allodynia, which was more potent than the effect of BV (1 mg/kg, i.p.). The depletion of noradrenaline by an injection of N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP4, 50 mg/kg, i.p.) blocked the analgesic effect of bvPLA₂, whereas the depletion of serotonin by injecting DL-p-chlorophenylalanine (PCPA, 150 mg/kg, i.p.) for three successive days did not. Furthermore, idazoxan (α2-adrenegic receptor antagonist, 1 mg/kg, i.p.) completely blocked bvPLA₂-induced anti-allodynic action, whereas prazosin (α1-adrenegic antagonist, 10 mg/kg, i.p.) did not. These results suggest that bvPLA₂ treatment strongly alleviates oxaliplatin-induced acute cold and mechanical allodynia in mice through the activation of the noradrenergic system, via α2-adrenegic receptors, but not via the serotonergic system.

Synthetic and natural inhibitors of phospholipases A2: their importance for understanding and treatment of neurological disorders

Phospholipases A2 (PLA2) are a diverse group of enzymes that hydrolyze membrane phospholipids into arachidonic acid and lysophospholipids. Arachidonic acid is metabolized to eicosanoids (prostaglandins, leukotrienes, thromboxanes), and lysophospholipids are converted to platelet-activating factors. These lipid mediators play critical roles in the initiation, maintenance, and modulation of neuroinflammation and oxidative stress. Neurological disorders including excitotoxicity; traumatic nerve and brain injury; cerebral ischemia; Alzheimer's disease; Parkinson's disease; multiple sclerosis; experimental allergic encephalitis; pain; depression; bipolar disorder; schizophrenia; and autism are characterized by oxidative stress, inflammatory reactions, alterations in phospholipid metabolism, accumulation of lipid peroxides, and increased activities of brain phospholipase A2 isoforms. Several old and new synthetic inhibitors of PLA2, including fatty acid trifluoromethyl ketones; methyl arachidonyl fluorophosphonate; bromoenol lactone; indole-based inhibitors; pyrrolidine-based inhibitors; amide inhibitors, 2-oxoamides; 1,3-disubstituted propan-2-ones and polyfluoroalkyl ketones as well as phytochemical based PLA2 inhibitors including curcumin, Ginkgo biloba and Centella asiatica extracts have been discovered and used for the treatment of neurological disorders in cell culture and animal model systems. The purpose of this review is to summarize information on selective and potent synthetic inhibitors of PLA2 as well as several PLA2 inhibitors from plants, for treatment of oxidative stress and neuroinflammation associated with the pathogenesis of neurological disorders.

Calcium-independent phospholipases A2 and their roles in biological processes and diseases

Among the family of phospholipases A2 (PLA2s) are the Ca(2+)-independent PLA2s (iPLA2s) and they are designated group VI iPLA2s. In relation to secretory and cytosolic PLA2s, the iPLA2s are more recently described and details of their expression and roles in biological functions are rapidly emerging. The iPLA2s or patatin-like phospholipases (PNPLAs) are intracellular enzymes that do not require Ca(2+) for activity, and contain lipase (GXSXG) and nucleotide-binding (GXGXXG) consensus sequences. Though nine PNPLAs have been recognized, PNPLA8 (membrane-associated iPLA2γ) and PNPLA9 (cytosol-associated iPLA2β) are the most widely studied and understood. The iPLA2s manifest a variety of activities in addition to phospholipase, are ubiquitously expressed, and participate in a multitude of biological processes, including fat catabolism, cell differentiation, maintenance of mitochondrial integrity, phospholipid remodeling, cell proliferation, signal transduction, and cell death. As might be expected, increased or decreased expression of iPLA2s can have profound effects on the metabolic state, CNS function, cardiovascular performance, and cell survival; therefore, dysregulation of iPLA2s can be a critical factor in the development of many diseases. This review is aimed at providing a general framework of the current understanding of the iPLA2s and discussion of the potential mechanisms of action of the iPLA2s and related involved lipid mediators.

Cytosolic phospholipase A₂: physiological function and role in disease

The group IV phospholipase A2 (PLA2) family is comprised of six intracellular enzymes (GIVA, -B, -C, -D, -E, and -F) commonly referred to as cytosolic PLA2 (cPLA2)α, -β, -γ, -δ, -ε, and -ζ. They contain a Ser-Asp catalytic dyad and all except cPLA2γ have a C2 domain, but differences in their catalytic activities and subcellular localization suggest unique regulation and function. With the exception of cPLA2α, the focus of this review, little is known about the in vivo function of group IV enzymes. cPLA2α catalyzes the hydrolysis of phospholipids to arachidonic acid and lysophospholipids that are precursors of numerous bioactive lipids. The regulation of cPLA2α is complex, involving transcriptional and posttranslational processes, particularly increases in calcium and phosphorylation. cPLA2α is a highly conserved widely expressed enzyme that promotes lipid mediator production in human and rodent cells from a variety of tissues. The diverse bioactive lipids produced as a result of cPLA2α activation regulate normal physiological processes and disease pathogenesis in many organ systems, as shown using cPLA2α KO mice. However, humans recently identified with cPLA2α deficiency exhibit more pronounced effects on health than observed in mice lacking cPLA2α, indicating that much remains to be learned about this interesting enzyme.

Inhibition of Ca2+-independent phospholipase A2β (iPLA2β) ameliorates islet infiltration and incidence of diabetes in NOD mice

Autoimmune β-cell death leads to type 1 diabetes, and with findings that Ca(2+)-independent phospholipase A2β (iPLA2β) activation contributes to β-cell death, we assessed the effects of iPLA2β inhibition on diabetes development. Administration of FKGK18, a reversible iPLA2β inhibitor, to NOD female mice significantly reduced diabetes incidence in association with 1) reduced insulitis, reflected by reductions in CD4(+) T cells and B cells; 2) improved glucose homeostasis; 3) higher circulating insulin; and 4) β-cell preservation. Furthermore, FKGK18 inhibited production of tumor necrosis factor-α (TNF-α) from CD4(+) T cells and antibodies from B cells, suggesting modulation of immune cell responses by iPLA2β-derived products. Consistent with this, 1) adoptive transfer of diabetes by CD4(+) T cells to immunodeficient and diabetes-resistant NOD.scid mice was mitigated by FKGK18 pretreatment and 2) TNF-α production from CD4(+) T cells was reduced by inhibitors of cyclooxygenase and 12-lipoxygenase, which metabolize arachidonic acid to generate bioactive inflammatory eicosanoids. However, adoptive transfer of diabetes was not prevented when mice were administered FKGK18-pretreated T cells or when FKGK18 administration was initiated with T-cell transfer. The present observations suggest that iPLA2β-derived lipid signals modulate immune cell responses, raising the possibility that early inhibition of iPLA2β may be beneficial in ameliorating autoimmune destruction of β-cells and mitigating type 1 diabetes development.

Bee venom phospholipase A2 protects against acetaminophen-induced acute liver injury by modulating regulatory T cells and IL-10 in mice

The aim of this study was to investigate the protective effects of phospholipase A2 (PLA2) from bee venom against acetaminophen-induced hepatotoxicity through CD4⁺CD25⁺Foxp3⁺ T cells (Treg) in mice. Acetaminophen (APAP) is a widely used antipyretic and analgesic, but an acute or cumulative overdose of acetaminophen can cause severe hepatic failure. Tregs have been reported to possess protective effects in various liver diseases and kidney toxicity. We previously found that bee venom strongly increased the Treg population in splenocytes and subsequently suppressed immune disorders. More recently, we found that the effective component of bee venom is PLA2. Thus, we hypothesized that PLA2 could protect against liver injury induced by acetaminophen. To evaluate the hepatoprotective effects of PLA2, C57BL/6 mice or interleukin-10-deficient (IL-10^−/−) mice were injected with PLA2 once a day for five days and sacrificed 24 h (h) after acetaminophen injection. The blood sera were collected 0, 6, and 24 h after acetaminophen injection for the analysis of aspartate aminotransferase (AST) and alanine aminotransferase (ALT). PLA2-injected mice showed reduced levels of serum AST, ALT, proinflammatory cytokines, and nitric oxide (NO) compared with the PBS-injected control mice. However, IL-10 was significantly increased in the PLA2-injected mice. These hepatic protective effects were abolished in Treg-depleted mice by antibody treatment and in IL-10^−/− mice. Based on these findings, it can be concluded that the protective effects of PLA2 against acetaminophen-induced hepatotoxicity can be mediated by modulating the Treg and IL-10 production.

Cytosolic phospholipase A2 protein as a novel therapeutic target for spinal cord injury

Objective

The objective of this study was to investigate whether cytosolic phospholipase A₂ (cPLA₂), an important isoform of PLA₂ that mediates the release of arachidonic acid, plays a role in the pathogenesis of spinal cord injury (SCI).

Methods

A combination of molecular, histological, immunohistochemical, and behavioral assessments were used to test whether blocking cPLA₂ activation pharmacologically or genetically reduced cell death, protected spinal cord tissue, and improved behavioral recovery after a contusive SCI performed at the 10th thoracic level in adult mice.

Results

SCI significantly increased cPLA₂ expression and activation. Activated cPLA₂ was localized mainly in neurons and oligodendrocytes. Notably, the SCI-induced cPLA₂ activation was mediated by the extracellular signal-regulated kinase signaling pathway. In vitro, activation of cPLA₂ by ceramide-1-phosphate or A23187 induced spinal neuronal death, which was substantially reversed by arachidonyl trifluoromethyl ketone, a cPLA₂ inhibitor. Remarkably, blocking cPLA₂ pharmacologically at 30 minutes postinjury or genetically deleting cPLA₂ in mice ameliorated motor deficits, and reduced cell loss and tissue damage after SCI.

Interpretation

cPLA₂ may play a key role in the pathogenesis of SCI, at least in the C57BL/6 mouse, and as such could be an attractive therapeutic target for ameliorating secondary tissue damage and promoting recovery of function after SCI.

Arachidonic acid closes innexin/pannexin channels and thereby inhibits microglia cell movement to a nerve injury

Pannexons are membrane channels formed by pannexins and are permeable to ATP. They have been implicated in various physiological and pathophysiological processes. Innexins, the invertebrate homologues of the pannexins, form innexons. Nerve injury induces calcium waves in glial cells, releasing ATP through glial pannexon/innexon channels. The ATP then activates microglia. More slowly, injury releases arachidonic acid (ArA). The present experiments show that ArA itself reduced the macroscopic membrane currents of innexin- and of pannexin-injected oocytes; ArA also blocked K(+) -induced release of ATP. In leeches, whose large glial cells have been favorable for studying control of microglia migration, ArA blocked glial dye-release and, evidently, ATP-release. A physiological consequence in the leech was block of microglial migration to nerve injuries. Exogenous ATP (100 µM) reversed the effect, for ATP causes activation and movement of microglia after nerve injury, but nitric oxide directs microglia to the lesion. It was not excluded that metabolites of ArA may also inhibit the channels. But for all these effects, ArA and its non-metabolizable analog eicosatetraynoic acid (ETYA) were indistinguishable. Therefore, ArA itself is an endogenous regulator of pannexons and innexons. ArA thus blocks release of ATP from glia after nerve injury and thereby, at least in leeches, stops microglia at lesions.

Dietary omega-3 polyunsaturated fatty acids improve the neurolipidome and restore the DHA status while promoting functional recovery after experimental spinal cord injury

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) confer multiple health benefits and decrease the risk of neurological disorders. Studies are needed, however, to identify promising cellular targets and to assess their prophylactic value against neurodegeneration. The present study (1) examined the efficacy of a preventive diet enriched with ω-3 PUFAs to reduce dysfunction in a well-established spinal cord injury (SCI) animal model and (2) used a novel metabolomics data analysis to identify potential neurolipidomic targets. Rats were fed with either control chow or chow enriched with ω-3 PUFAs (750 mg/kg/day) for 8 weeks before being subjected to a sham or a contusion SCI operation. We report new evidence showing that rats subjected to SCI after being pre-treated with a diet enriched with ω-3 PUFAs exhibit significantly better functional outcomes. Pre-treated animals exhibited lower sensory deficits, autonomic bladder recovery, and early improvements in locomotion that persisted for at least 8 weeks after trauma. We found that SCI triggers a robust alteration in the cord PUFA neurolipidome, which was characterized by a marked docosahexaenoic acid (DHA) deficiency. This DHA deficiency was associated with dysfunction and corrected with the ω-3 PUFA-enriched diet. Multivariate data analyses revealed that the spinal cord of animals consuming the ω-3 PUFA-enriched diet had a fundamentally distinct neurolipidome, particularly increasing the levels of essential and long chain ω-3 fatty acids and lysolipids at the expense of ω-6 fatty acids and its metabolites. Altogether, dietary ω-3 PUFAs prophylaxis confers resiliency to SCI mediated, at least in part, by generating a neuroprotective and restorative neurolipidome.

Potent and selective 2-oxoamide inhibitors of phospholipases A2 as novel medicinal agents for the treatment of inflammatory diseases

Phospholipases A2 (PLA2s) are enzymes that are capable of catalyzing the hydrolysis of the sn-2 ester bond of glycerophospholipids, releasing free fatty acids, including arachidonic acid (AA), and lysophospholipids. Both products are precursor signaling molecules involved in inflammation. Among the various PLA2s, cytosolic GIVA cPLA2 is considered a major target for inflammatory diseases, while secreted GIIA sPLA2 is involved in cardiovascular diseases. We have developed lipophilic 2-oxoamides based on (S)-γ- or δ-amino acids as potent and selective inhibitors of GIVA cPLA2, which present interesting in vivo anti-inflammatory activity. 2-Oxoamides based on natural α-amino acids are selective inhibitors of GIIA sPLA2. The mode of binding of 2-oxoamides with either GIVA cPLA2 or GIIA sPLA2 has been studied by various techniques.

Maintenance of synaptic stability requires calcium-independent phospholipase A₂ activity

Phospholipases A₂ (PLA₂s) represent one of the largest groups of lipid-modifying enzymes. Over the years, significant advances have been made in understanding their potential physiological and pathological functions. Depending on their calcium requirement for activation, PLA₂s are classified into calcium dependent and independent. This paper mainly focuses on brain calcium-independent PLA₂ (iPLA₂) and on the mechanisms by which they influence neuronal function and regulate synaptic plasticity. Particular attention will be given to the iPLA₂γ isoform and its role in the regulation of synaptic glutamate receptors. In particular, the paper discusses the possibility that brain iPLA₂γ deficiencies could destabilise normal synaptic operation and might contribute to the aetiology of some brain disorders. In this line, the paper presents new data indicating that iPLA₂γ deficiencies accentuate AMPA receptor destabilization and tau phosphorylation, which suggests that this iPLA₂ isoform should be considered as a potential target for the treatment of Tau-related disorders.

Role of phospholipase A2s and lipid mediators in secondary damage after spinal cord injury

Inflammation is considered to be an important contributor to secondary damage after spinal cord injury (SCI). This secondary damage leads to further exacerbation of tissue loss and functional impairments. The immune responses that are triggered by injury are complex and are mediated by a variety of factors that have both detrimental and beneficial effects. In this review, we focus on the diverse effects of the phospholipase A(2) (PLA(2)) superfamily and the downstream pathways that generate a large number of bioactive lipid mediators, some of which have pro-inflammatory and demyelinating effects, whereas others have anti-inflammatory and pro-resolution properties. For each of these lipid mediators, we provide an overview followed by a discussion of their expression and role in SCI. Where appropriate, we have compared the latter with their role in other neurological conditions. The PLA(2) pathway provides a number of targets for therapeutic intervention for the treatment of SCI and other neurological conditions.

Inflammatory pathways in spinal cord injury

Injury to the spinal cord results in direct damage to axons, neuronal cell bodies, and glia that cause functional loss below the site of injury. In addition, the injury also triggers an inflammatory response that contributes to secondary tissue damage that leads to further functional loss. Reducing inflammation after spinal cord injury (SCI) is therefore a worthy therapeutic goal. Inflammation in the injured spinal cord is a complex response that involves resident cells of the central nervous system as well as infiltrating immune cells, and is mediated by a variety of molecular pathways and signaling molecules. Here, we discuss approaches we have used to identify novel therapeutic targets to modulate the inflammatory response after SCI to reduce tissue damage and promote recovery. Effective treatments for SCI will likely require a combination of approaches to reduce inflammation and secondary damage with those that promote axon regeneration.

Harmful and beneficial effects of inflammation after spinal cord injury: potential therapeutic implications

Spinal cord injury (SCI) results in immediate damage followed by a secondary phase of tissue damage that occurs over a period of several weeks. The mechanisms underlying this secondary damage are multiple and not fully understood. A number of studies suggest that the local inflammatory response in the spinal cord that occurs after SCI contributes importantly to secondary damage. This response is mediated by cells normally found in the central nervous system (CNS) as well as infiltrating leukocytes. While the inflammatory response mediated by these cells is required for efficient clearance of tissue debris, and promotes wound healing and tissue repair, they also release various factors that can be detrimental to neurons, glia, axons, and myelin. In this chapter we provide an overview of the inflammatory response at the cell and molecular level after SCI, and review the current state of knowledge about its contribution to tissue damage and repair. Additionally, we discuss how some of this work is leading to the development and testing of drugs that modulate inflammation to treat acute SCI in humans.