CD300f immunoreceptor is associated with major depressive disorder and decreased microglial metabolic fitness.

A role for microglia in neuropsychiatric diseases, including major depressive disorder (MDD), has been postulated. Regulation of microglial phenotype by immune receptors has become a central topic in many neurological conditions. We explored preclinical and clinical evidence for the role of the CD300f immune receptor in the fine regulation of microglial phenotype and its contribution to MDD. We found that a prevalent nonsynonymous single-nucleotide polymorphism (C/T, rs2034310) of the human CD300f receptor cytoplasmic tail inhibits the protein kinase C phosphorylation of a threonine and is associated with protection against MDD, mainly in women. Interestingly, CD300f-/- mice displayed several characteristic MDD traits such as augmented microglial numbers, increased interleukin 6 and interleukin 1 receptor antagonist messenger RNA, alterations in synaptic strength, and noradrenaline-dependent and persistent depressive-like and anhedonic behaviors in females. This behavioral phenotype could be potentiated inducing the lipopolysaccharide depression model. RNA sequencing and biochemical studies revealed an association with impaired microglial metabolic fitness. In conclusion, we report a clear association that links the function of the CD300f immune receptor with MDD in humans, depressive-like and anhedonic behaviors in female mice, and altered microglial metabolic reprogramming.

Administration of Maresin-1 ameliorates the physiopathology of experimental autoimmune encephalomyelitis.

BACKGROUND: Resolution of inflammation is an active and regulated process that leads to the clearance of cell debris and immune cells from the challenged tissue, facilitating the recovery of homeostasis. This physiological response is coordinated by endogenous bioactive lipids known as specialized pro-resolving mediators (SPMs). When resolution fails, inflammation becomes uncontrolled leading chronic inflammation and tissue damage, as occurs in multiple sclerosis (MS). METHODS: SPMs and the key biosynthetic enzymes involved in SPM production were analysed by metabololipidomics and qPCR in active brain lesions, serum and peripheral blood mononuclear cells (PBMC) of MS patients as well as in the spinal cord of mice with experimental autoimmune encephalomyelitis (EAE). We also tested the therapeutic actions of the SPM coined Maresin-1 (MaR1) in EAE mice and studied its impact on inflammation by doing luminex and flow cytometry analysis. RESULTS: We show that levels of MaR1 and other SPMs were below the limit of detection or not increased in the spinal cord of EAE mice, whereas the production of pro-inflammatory eicosanoids was induced during disease progression. Similarly, we reveal that SPMs were undetected in serum and active brain lesion samples of MS patients, which was linked to impaired expression of the enzymes involved in the biosynthetic pathways of SPMs. We demonstrate that exogenous administration of MaR1 in EAE mice suppressed the protein levels of various pro-inflammatory cytokines and reduced immune cells counts in the spinal cord and blood. MaR1 also decreased the numbers of Th1 cells but increased the accumulation of regulatory T cells and drove macrophage polarization towards an anti-inflammatory phenotype. Importantly, we provide clear evidence that administration of MaR1 in mice with clinical signs of EAE enhanced neurological outcomes and protected from demyelination. CONCLUSIONS: This study reveals that there is an imbalance in the production of SPMs in MS patients and in EAE mice, and that increasing the bioavailability of SPMs, such as MaR1, minimizes inflammation and mediates therapeutic actions. Thus, these data suggest that immunoresolvent therapies, such as MaR1, could be a novel avenue for the treatment of MS.

Role for nuclear interleukin-37 in the suppression of innate immunity.

The IL-1 family member IL-37 broadly suppresses innate inflammation and acquired immunity. Similar to IL-1α and IL-33, IL-37 is a dual-function cytokine in that IL-37 translocates to the nucleus but also transmits a signal via surface membrane receptors. The role of nuclear IL-37 remains unknown on the ability of this cytokine to inhibit innate inflammation. Here, we compared suppression of innate inflammation in transgenic mice expressing native human IL-37 (IL-37Tg) with those of transgenic mice carrying the mutation of aspartic acid (D) to alanine (A) at amino acid 20 (IL-37D20ATg). The mutation D20A prevents cleavage of caspase-1, a step required for IL-37 nuclear translocation. In vitro, peritoneal macrophages from IL-37Tg mice reduced LPS-induced IL-1ß, IL-6, TNFα and IFNγ by 40-50% whereas in macrophages from IL-37D20ATg mice this suppression was not observed, consistent with loss of nuclear function. Compared with macrophages from IL-37Tg mice, significantly less or no suppression of LPS-induced MAP kinase and NFκB activation was also observed in macrophages from IL-37D20ATg mice. In vivo, levels of IL-1ß, IL-6, and TNFα in the lungs and liver were markedly reduced during endotoxemia in IL-37Tg mice but not observed in IL-37D20ATg mice. However, suppression of innate inflammation remains intact in the IL-37D20A mice once the cytokine is released from the cell and binds to its receptor. These studies reveal a nuclear function for suppression of innate inflammation and are consistent with the dual function of IL-37 and a role for caspase-1 in limiting inflammation.

Extracellular and nuclear roles of IL-37 after spinal cord injury.

Interleukin 37 (IL-37) is an anti-inflammatory cytokine of the interleukin 1 family. Transgenic mice expressing the human form of the IL37 gene (hIL-37Tg) display protective effects in several animal models of disease. Previous data from our group revealed that IL-37 limits inflammation after spinal cord injury (SCI) and ameliorates tissue damage and functional deficits. IL-37 can exert its anti-inflammatory effects by translocating to the nucleus or acting as an extracellular cytokine. However, whether this protection after SCI is mediated by translocating to the nucleus, activating of extracellular receptors, or both, is currently unknown. In the present study, we used different transgenic animals to answer this question. We demonstrated that the beneficial effects of IL-37 on functional and histological outcomes after SCI were lost in the lack of the extracellular receptor IL-1R8, indicating that IL-37 induces protection as an extracellular cytokine. On the other hand, transgenic mice with the nuclear function of IL-37 abolished (hIL-37D20ATg) showed significant improvement in locomotor skills and myelin sparing after SCI, indicating that nuclear pathway is not required for the protective actions of IL-37. Moreover, we also showed that the therapeutic effects of the recombinant IL-37 protein are produced only in the presence of the extracellular receptor IL-1R8, further highlighting the importance of the extracellular function of this cytokine after SCI. Finally, we revealed that the administration of recombinant IL-37 protein exerted therapeutic actions when administered in the lesion site but not systemically. This work demonstrated for the first time that translocation of IL-37 to the nucleus is not required for the beneficial actions of this cytokine after SCI and highlights the importance of the extracellular signaling of IL-37 to mediate neuroprotective actions.

Gene therapy for overexpressing Neuregulin 1 type I in skeletal muscles promotes functional improvement in the SOD1G93A ALS mice.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder affecting motoneurons (MNs), with no effective treatment currently available. The molecular mechanisms that are involved in MN death are complex and not fully understood, with partial contributions of surrounding glial cells and skeletal muscle to the disease. Neuregulin 1 (NRG1) is a trophic factor highly expressed in MNs and neuromuscular junctions. Recent studies have suggested a crucial role of the isoform I (NRG1-I) in the collateral reinnervation process in skeletal muscle, and NRG1-III in the preservation of MNs in the spinal cord, opening a window for developing novel therapies for neuromuscular diseases like ALS. In this study, we overexpressed NRG1-I widely in the skeletal muscles of the SOD1G93A transgenic mouse. The results show that NRG1 gene therapy activated the survival pathways in muscle and spinal cord, increasing the number of surviving MNs and neuromuscular junctions and reducing the astroglial reactivity in the spinal cord of the treated SOD1G93A mice. Furthermore, NRG1-I overexpression preserved motor function and delayed the onset of clinical disease. In summary, our data indicates that NRG1 plays an important role on MN survival and muscle innervation in ALS, and that viral-mediated overexpression of NRG1 isoforms may be considered as a promising approach for ALS treatment.

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

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

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.

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.

Maresin 1 Promotes Inflammatory Resolution, Neuroprotection, and Functional Neurological Recovery After Spinal Cord Injury.

Resolution of inflammation is defective after spinal cord injury (SCI), which impairs tissue integrity and remodeling and leads to functional deficits. Effective pharmacological treatments for SCI are not currently available. Maresin 1 (MaR1) is a highly conserved specialized proresolving mediator (SPM) hosting potent anti-inflammatory and proresolving properties with potent tissue regenerative actions. Here, we provide evidence that the inappropriate biosynthesis of SPM in the lesioned spinal cord hampers the resolution of inflammation and leads to deleterious consequences on neurological outcome in adult female mice. We report that, after spinal cord contusion injury in adult female mice, the biosynthesis of SPM is not induced in the lesion site up to 2 weeks after injury. Exogenous administration of MaR1, a highly conserved SPM, propagated inflammatory resolution after SCI, as revealed by accelerated clearance of neutrophils and a reduction in macrophage accumulation at the lesion site. In the search of mechanisms underlying the proresolving actions of MaR1 in SCI, we found that this SPM facilitated several hallmarks of resolution of inflammation, including reduction of proinflammatory cytokines (CXCL1, CXCL2, CCL3, CCL4, IL6, and CSF3), silencing of major inflammatory intracellular signaling cascades (STAT1, STAT3, STAT5, p38, and ERK1/2), redirection of macrophage activation toward a prorepair phenotype, and increase of the phagocytic engulfment of neutrophils by macrophages. Interestingly, MaR1 administration improved locomotor recovery significantly and mitigated secondary injury progression in a clinical relevant model of SCI. These findings suggest that proresolution, immunoresolvent therapies constitute a novel approach to improving neurological recovery after acute SCI.SIGNIFICANCE STATEMENT Inflammation is a protective response to injury or infection. To result in tissue homeostasis, inflammation has to resolve over time. Incomplete or delayed resolution leads to detrimental effects, including propagated tissue damage and impaired wound healing, as occurs after spinal cord injury (SCI). We report that inflammation after SCI is dysregulated in part due to inappropriate synthesis of proresolving lipid mediators. We demonstrate that the administration of the resolution agonist referred to as maresin 1 (MaR1) after SCI actively propagates resolution processes at the lesion site and improves neurological outcome. MaR1 is identified as an interventional candidate to attenuate dysregulated lesional inflammation and to restore functional recovery after SCI.

CD200 modulates spinal cord injury neuroinflammation and outcome through CD200R1.

The interaction between CD200 and its receptor CD200R1 is among the central regulators of microglia and macrophage phenotype. However, it remains to be established whether, in the context of a traumatic CNS injury, CD200R1 act as a negative regulator of these particular innate immune cells, and if the exogenous delivery of CD200 may ameliorate neurological deficits. In the present study, we first evaluated whether preventing the local interaction between the pair CD200-CD200R1, by using a selective blocking antibody against CD200R1, has a role on functional and inflammatory outcome after contusion-induced spinal cord injury (SCI) in mice. The injection of the αCD200R1, but not control IgG1, into the lesioned spinal cord immediately after the SCI worsened locomotor performance and exacerbated neuronal loss and demyelination. At the neuroimmunological level, we observed that microglial cells and macrophages showed increased levels of iNOS and Ly6C upon CD200R1 blockade, indicating that the disruption of CD200R1 drove these cells towards a more pro-inflammatory phenotype. Moreover, although CD200R1 blockade had no effect in the initial infiltration of neutrophils into the lesioned spinal cord, it significantly impaired their clearance, which is a key sign of excessive inflammation. Interestingly, intraparenchymal injection of recombinant CD200-His immediately after the injury induced neuroprotection and robust and long-lasting locomotor recovery. In conclusion, this study reveals that interaction of CD200-CD200R1 plays a crucial role in limiting inflammation and lesion progression after SCI, and that boosting the stimulation of this pathway may constitute a new therapeutic approach.

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.

IL-4 drives microglia and macrophages toward a phenotype conducive for tissue repair and functional recovery after spinal cord injury.

Macrophages and microglia play a key role in the maintenance of nervous system homeostasis. However, upon different challenges, they can adopt several phenotypes, which may lead to divergent effects on tissue repair. After spinal cord injury (SCI), microglia and macrophages show predominantly pro-inflammatory activation and contribute to tissue damage. However, the factors that hamper their conversion to an anti-inflammatory state after SCI, or to other protective phenotypes, are poorly understood. Here, we show that IL-4 protein levels are undetectable in the spinal cord after contusion injury, which likely favors microglia and macrophages to remain in a pro-inflammatory state. We also demonstrate that a single delayed intraspinal injection of IL-4, 48 hours after SCI, induces increased expression of M2 marker in microglia and macrophages. We also show that delayed injection of IL-4 leads to the appearance of resolution-phase macrophages, and that IL-4 enhances resolution of inflammation after SCI. Interestingly, we provide clear evidence that delayed administration of IL-4 markedly improves functional outcomes and reduces tissue damage after contusion injury. It is possible that these improvements are mediated by the presence of macrophages with M2 markers and resolution-phase macrophages. These data suggest that therapies aimed at increasing IL-4 levels could be valuable for the treatment of acute SCI, for which there are currently no effective treatments. GLIA 2016;64:2079-2092.

CD300f immunoreceptor contributes to peripheral nerve regeneration by the modulation of macrophage inflammatory phenotype.

BACKGROUND: It has recently become evident that activating/inhibitory cell surface immune receptors play a critical role in regulating immune and inflammatory processes in the central nervous system (CNS). The immunoreceptor CD300f expressed on monocytes, neutrophils, and mast cells modulates inflammation, phagocytosis, and outcome in models of autoimmune demyelination, allergy, and systemic lupus erythematosus. On the other hand, a finely regulated inflammatory response is essential to induce regeneration after injury to peripheral nerves since hematogenous macrophages, together with resident macrophages and de-differentiated Schwann cells, phagocyte distal axonal and myelin debris in a well-orchestrated inflammatory response. The possible roles and expression of CD300f and its ligands have not been reported under these conditions. METHODS: By using quantitative PCR (QPCR) and CD300f-IgG2a fusion protein, we show the expression of CD300f and its ligands in the normal and crush injured sciatic nerve. The putative role of CD300f in peripheral nerve regeneration was analyzed by blocking receptor-ligand interaction with the same CD300f-IgG2a soluble receptor fusion protein in sciatic nerves of Thy1-YFP-H mice injected at the time of injury. Macrophage M1/M2 polarization phenotype was also analyzed by CD206 and iNOS expression. RESULTS: We found an upregulation of CD300f mRNA and protein expression after injury. Moreover, the ligands are present in restricted membrane patches of Schwann cells, which remain stable after the lesion. The lesioned sciatic nerves of Thy1-YFP-H mice injected with a single dose of CD300f-IgG2a show long lasting effects on nerve regeneration characterized by a lower number of YFP-positive fibres growing into the tibial nerve after 10 days post lesion (dpl) and a delayed functional recovery when compared to PBS- or IgG2a-administered control groups. Animals treated with CD300f-IgG2a show at 10 dpl higher numbers of macrophages and CD206-positive cells and lower levels of iNOS expression than both control groups. At later time points (28 dpl), increased numbers of macrophages and iNOS expression occur. CONCLUSIONS: Taken together, these results show that the pair CD300f ligand is implicated in Wallerian degeneration and nerve regeneration by modulating both the influx and phenotype of macrophages.

Metabolic reprogramming of the inflammatory response in the nervous system: the crossover between inflammation and metabolism.

Metabolism is a fundamental process by which biochemicals are broken down to produce energy (catabolism) or used to build macromolecules (anabolism). Metabolism has received renewed attention as a mechanism that generates molecules that modulate multiple cellular responses. This was first identified in cancer cells as the Warburg effect, but it is also present in immunocompetent cells. Studies have revealed a bidirectional influence of cellular metabolism and immune cell function, highlighting the significance of metabolic reprogramming in immune cell activation and effector functions. Metabolic processes such as glycolysis, oxidative phosphorylation, and fatty acid oxidation have been shown to undergo dynamic changes during immune cell response, facilitating the energetic and biosynthetic demands. This review aims to provide a better understanding of the metabolic reprogramming that occurs in different immune cells upon activation, with a special focus on central nervous system disorders. Understanding the metabolic changes of the immune response not only provides insights into the fundamental mechanisms that regulate immune cell function but also opens new approaches for therapeutic strategies aimed at manipulating the immune system.

Beneficial effects of αB-crystallin in spinal cord contusion injury.

αB-crystallin is a member of the heat shock protein family that exerts cell protection under several stress-related conditions. Recent studies have revealed that αB-crystallin plays a beneficial role in a mouse model of multiple sclerosis, brain ischemia, and Alexander disease. Whether αB-crystallin plays a role in modulating the secondary damage after CNS trauma is not known. We report here that αB-crystallin mediates protective effects after spinal cord injury. The levels of αB-crystallin are reduced in spinal cord tissue following contusion lesion. In addition, administration of recombinant human αB-crystallin for the first week after contusion injury leads to sustained improvement in locomotor skills and amelioration of secondary tissue damage. We also provide evidence that recombinant human αB-crystallin modulates the inflammatory response in the injured spinal cord, leading to increased infiltration of granulocytes and reduced recruitment of inflammatory macrophages. Furthermore, the delivery of recombinant human αB-crystallin promotes greater locomotor recovery even when the treatment is initiated 6 h after spinal cord injury. Our findings suggest that administration of recombinant human αB-crystallin may be a good therapeutic approach for treating acute spinal cord injury, for which there is currently no effective treatment.

Lipocalin 2 plays an immunomodulatory role and has detrimental effects after spinal cord injury.

Lipocalin 2 (Lcn2) plays an important role in defense against bacterial infection by interfering with bacterial iron acquisition. Although Lcn2 is expressed in a number of aseptic inflammatory conditions, its role in these conditions remains unclear. We examined the expression and role of Lcn2 after spinal cord injury (SCI) in adult mice by using a contusion injury model. Lcn2 expression at the protein level is rapidly increased 12-fold at 1 d after SCI and decreases gradually thereafter, being three times as high as control levels at 21 d after injury. Lcn2 expression is strongly induced after contusion injury in astrocytes, neurons, and neutrophils. The Lcn2 receptor (Lcn2R), which has been shown to influence cell survival, is also expressed after SCI in the same cell types. Lcn2-deficient (Lcn2⁻/⁻) mice showed significantly better locomotor recovery after spinal cord contusion injury than wild-type (Lcn2⁺/⁺) mice. Histological assessments indicate improved neuronal and tissue survival and greater sparing of myelin in Lcn2⁻/⁻ mice after contusion injury. Flow cytometry showed a decrease in neutrophil influx and a small increase in the monocyte population in Lcn2⁻/⁻ injured spinal cords. This change was accompanied by a reduction in the expression of several pro-inflammatory chemokines and cytokines as well as inducible nitric oxide synthase early after SCI in Lcn2⁻/⁻ mice compared with wild-type animals. Our results, therefore, suggest a role for Lcn2 in regulating inflammation in the injured spinal cord and that lack of Lcn2 reduces secondary damage and improves locomotor recovery after spinal cord contusion injury.

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.

Role of Ninjurin-1 in the migration of myeloid cells to central nervous system inflammatory lesions.

OBJECTIVE: Blood-derived myeloid antigen-presenting cells (APCs) account for a significant proportion of the leukocytes found within lesions of multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE). These APCs along with activated microglia are thought to be pivotal in the initiation of the central nervous system (CNS)-targeted immune response in MS and EAE. However, the exact molecules that direct the migration of myeloid cells from the periphery across the blood-brain barrier (BBB) remain largely unknown. METHODS: We identified Ninjurin-1 in a proteomic screen of human BBB endothelial cells (ECs). We assessed the expression of Ninjurin-1 by BBB-ECs and immune cells, and we determined the role of Ninjurin-1 in immune cell migration to the CNS in vivo in EAE mice. RESULTS: Ninjurin-1 was found to be weakly expressed in the healthy human and mouse CNS but upregulated on BBB-ECs and on infiltrating APCs during the course of EAE and in active MS lesions. In human peripheral blood, Ninjurin-1 was predominantly expressed by monocytes, whereas it was barely detectable on T and B lymphocytes. Moreover, Ninjurin-1 neutralization specifically abrogated the adhesion and migration of human monocytes across BBB-ECs, without affecting lymphocyte recruitment. Finally, Ninjurin-1 blockade reduced clinical disease activity and histopathological indices of EAE and decreased infiltration of macrophages, dendritic cells, and APCs into the CNS. INTERPRETATION: Our study uncovers an important cell-specific role for Ninjurin-1 in the transmigration of inflammatory APCs across the BBB and further emphasizes the importance of myeloid cell recruitment during the development of neuroinflammatory lesions.

Phospholipase A2 superfamily members play divergent roles after spinal cord injury.

Spinal cord injury (SCI) results in permanent loss of motor functions. A significant aspect of the tissue damage and functional loss may be preventable as it occurs, secondary to the trauma. We show that the phospholipase A(2) (PLA(2)) superfamily plays important roles in SCI. PLA(2) enzymes hydrolyze membrane glycerophospholipids to yield a free fatty acid and lysophospholipid. Some free fatty acids (arachidonic acid) give rise to eicosanoids that promote inflammation, while some lysophospholipids (lysophosphatidylcholine) cause demyelination. We show in a mouse model of SCI that two cytosolic forms [calcium-dependent PLA(2) group IVA (cPLA(2) GIVA) and calcium-independent PLA(2) group VIA (iPLA(2) GVIA)], and a secreted form [secreted PLA(2) group IIA (sPLA(2) GIIA)] are up-regulated. Using selective inhibitors and null mice, we show that these PLA(2)s play differing roles. cPLA(2) GIVA mediates protection, whereas sPLA(2) GIIA and, to a lesser extent, iPLA(2) GVIA are detrimental. Furthermore, completely blocking all three PLA(2)s worsens outcome, while the most beneficial effects are seen by partial inhibition of all three. The partial inhibitor enhances expression of cPLA(2) and mediates its beneficial effects via the prostaglandin EP1 receptor. These findings indicate that drugs that inhibit detrimental forms of PLA(2) (sPLA(2) and iPLA2) and up-regulate the protective form (cPLA2) may be useful for the treatment of SCI.

CD200R1 Contributes to Successful Functional Reinnervation after a Sciatic Nerve Injury.

Activating and inhibitory immune receptors play a critical role in regulating systemic and central nervous system (CNS) immune and inflammatory processes. The CD200R1 immunoreceptor induces a restraining signal modulating inflammation and phagocytosis in the CNS under different inflammatory conditions. However, it remains unknown whether CD200R1 has a role in modulating the inflammatory response after a peripheral nerve injury, an essential component of the successful regeneration. Expression of CD200R1 and its ligand CD200 was analyzed during homeostasis and after a sciatic nerve crush injury in C57Bl/6 mice. The role of CD200R1 in Wallerian Degeneration (WD) and nerve regeneration was studied using a specific antibody against CD200R1 injected into the nerve at the time of injury. We found an upregulation of CD200R1 mRNA after injury whereas CD200 was downregulated acutely after nerve injury. Blockade of CD200R1 significantly reduced the acute entrance of both neutrophils and monocytes from blood after nerve injury. When long term regeneration and functional recovery were evaluated, we found that blockade of CD200R1 had a significant effect impairing the spontaneous functional recovery. Taken together, these results show that CD200R1 has a role in mounting a successful acute inflammatory reaction after injury, and contributes to an effective functional recovery.