Can the immune system be harnessed to repair the CNS?

Photobiomodulation Increases M2-Type Polarization of Macrophages by Inhibiting Versican Production After Spinal Cord Injury

Spinal cord injury (SCI) is a catastrophic accidence with little effective treatment, and inflammation played an important role in that. Previous studies showed photobiomodulation (PBM) could effectively downregulate the process of inflammation with modification of macrophage polarization after SCI; however, the potential mechanism behind that is still unclear. In the presented study, we aimed to investigate the effect of PBM on the expression level of versican, a matrix molecular believed to be associated with inflammation, and tried to find the mechanism on how that could regulate the inflammation process. Using immunofluorescence technique and western blot, we found the expression level of versican is increased after injury and markedly downregulated by irradiation treatment. Using virus intrathecal injection, we found the knock-down of versican could produce the effect similar to that of PBM and might have an effect on inflammation and macrophage polarization after SCI. To further verify the deduction, we peptide the supernatant of astrocytes to induce M0, M1, and M2 macrophages. We found that the versican produced by astrocytes might have a role on the promotion of M2 macrophages to inflammatory polarization. Finally, we investigated the potential pathway in the regulation of M2 polarization with the induction of versican. This study tried to give an interpretation on the mechanism of inflammation inhibition for PBM in the perspective of matrix regulation. Our results might provide light on the inflammation regulation after SCI.

Delayed administration of interleukin-4 coacervate alleviates the neurotoxic phenotype of astrocytes and promotes functional recovery after a contusion spinal cord injury

Objective. Macrophages and astrocytes play a crucial role in the aftermath of a traumatic spinal cord injury (SCI). Infiltrating macrophages adopt a pro-inflammatory phenotype while resident astrocytes adopt a neurotoxic phenotype at the injury site, both of which contribute to neuronal death and inhibit axonal regeneration. The cytokine interleukin-4 (IL-4) has shown significant promise in preclinical models of SCI by alleviating the macrophage-mediated inflammation and promoting functional recovery. However, its effect on neurotoxic reactive astrocytes remains to be elucidated, which we explored in this study. We also studied the beneficial effects of a sustained release of IL-4 from an injectable biomaterial compared to bolus administration of IL-4.Approach. We fabricated a heparin-based coacervate capable of anchoring and releasing bioactive IL-4 and tested its efficacyin vitroandin vivo. Main results. We show that IL-4 coacervate is biocompatible and drives a robust anti-inflammatory macrophage phenotype in culture. We also show that IL-4 and IL-4 coacervate can alleviate the reactive neurotoxic phenotype of astrocytes in culture. Finally, using a murine model of contusion SCI, we show that IL-4 and IL-4 coacervate, injected intraspinally 2 d post-injury, can reduce macrophage-mediated inflammation, and alleviate neurotoxic astrocyte phenotype, acutely and chronically, while also promoting neuroprotection with significant improvements in hindlimb locomotor recovery. We observed that IL-4 coacervate can promote a more robust regenerative macrophage phenotypein vitro, as well as match its efficacyin vivo,compared to bolus IL-4.Significance. Our work shows the promise of coacervate as a great choice for local and prolonged delivery of cytokines like IL-4. We support this by showing that the coacervate can release bioactive IL-4, which acts on macrophages and astrocytes to promote a pro-regenerative environment following a SCI leading to robust neuroprotective and functional outcomes.

Modulating amacrine cell-derived dopamine signaling promotes optic nerve regeneration and preserves visual function

As part of the central nervous system, the optic nerve, composed of axons from retinal ganglion cells (RGCs), generally fails to regenerate on its own when injured in adult mammals. An innovative approach to promoting optic nerve regeneration involves manipulating the interactions between amacrine cells (ACs) and RGCs. Here, we identified a unique AC subtype, dopaminergic ACs (DACs), that responded early after optic nerve crush by down-regulating neuronal activity and reducing retinal dopamine (DA) release. Activating DACs or augmenting DA release with levodopa demonstrated neuroprotective effects and modestly enhanced axon regeneration. Within this context, we pinpointed the DA receptor D1 (DRD1) as a critical mediator of DAC-derived DA and showed that RGC-specific Drd1 overexpression effectively overcame subtype-specific barriers to regeneration. This strategy markedly boosted RGC survival and axon regeneration after crush and preserved vision in a glaucoma model. This study unveils the crucial role of DAC-derived DA signaling in optic nerve regeneration, holding promise for therapeutic insights into neural repair.

Advances in gene therapy approaches targeting neuro-inflammation in neurodegenerative diseases

Over the last three decades, neurodegenerative diseases (NDs) have increased in frequency. About 15% of the world's population suffers from NDs in some capacity, which causes cognitive and physical impairment. Neurodegenerative diseases, including Amyotrophic Lateral Sclerosis, Parkinson's disease, Alzheimer's disease, and others represent a significant and growing global health challenge. Neuroinflammation is recognized to be related to all NDs, even though NDs are caused by a complex mix of genetic, environmental, and lifestyle factors. Numerous genes and pathways such as NFκB, p38 MAPK, Akt/mTOR, caspase, nitric oxide, and COX are involved in triggering brain immune cells like astrocytes and microglia to secrete inflammatory cytokines such as tumor necrosis factor-α, interleukin (IL)-1β, and IL-6. In AD, the binding of Aβ with CD36, TLR4, and TLR6 receptors results in activation of microglia which start to produce proinflammatory cytokines and chemokines. Consequently, the pro-inflammatory cytokines worsen and spread neuroinflammation, causing the deterioration of healthy neurons and the impairment of brain functions. Gene therapy has emerged as a promising therapeutic approach to modulate the inflammatory response in NDs, offering potential neuroprotective effects and disease-modifying benefits. This review article focuses on recent advances in gene therapy strategies targeting neuroinflammation pathways in NDs. We discussed the molecular pathways involved in neuroinflammation, highlighted key genes and proteins implicated in these processes, and reviewed the latest preclinical and clinical studies utilizing gene therapy to modulate neuroinflammatory responses. Additionally, this review addressed the prospects and challenges in translating gene therapy approaches into effective treatments for NDs.

Microglia in Glioblastomas: Molecular Insight and Immunotherapeutic Potential

Glioblastoma (GBM) is one of the most aggressive and devastating primary brain tumors, with a median survival of 15 months following diagnosis. Despite the intense treatment regimen which routinely includes maximal safe neurosurgical resection followed by adjuvant radio- and chemotherapy, the disease remains uniformly fatal. The poor prognosis associated with GBM is multifactorial owing to factors such as increased proliferation, angiogenesis, and metabolic switching to glycolytic pathways. Critically, GBM-mediated local and systemic immunosuppression result in inadequate immune surveillance and ultimately, tumor-immune escape. Microglia-the resident macrophages of the central nervous system (CNS)-play crucial roles in mediating the local immune response in the brain. Depending on the specific pathological cues, microglia are activated into either a pro-inflammatory, neurotoxic phenotype, known as M1, or an anti-inflammatory, regenerative phenotype, known as M2. In either case, microglia secrete corresponding pro- or anti-inflammatory cytokines and chemokines that either promote or hinder tumor growth. Herein, we review the interplay between GBM cells and resident microglia with a focus on contemporary studies highlighting the effect of GBM on the subtypes of microglia expressed, the associated cytokines/chemokines secreted, and ultimately, their impact on tumor pathogenesis. Finally, we explore how understanding the intricacies of the tumor-immune landscape can inform novel immunotherapeutic strategies against this devastating disease.

The good or the bad: an overview of autoantibodies in traumatic spinal cord injury

Infections remain the most common cause of death after traumatic spinal cord injury, likely due to a developing immune deficiency syndrome. This, together with a somewhat contradictory development of autoimmunity in many patients, are two major components of the maladaptive systemic immune response. Although the local non-resolving inflammation in the lesioned spinal cord may lead to an antibody formation against autoantigens of the injured spinal cord tissue, there are also natural (pre-existing) autoantibodies independent of the injury. The way in which these autoantibodies with different origins affect the neuronal and functional outcome of spinal cord-injured patients is still controversial.

Brief Electrical Stimulation Promotes Recovery after Surgical Repair of Injured Peripheral Nerves

Injured peripheral nerves regenerate their axons in contrast to those in the central nervous system. Yet, functional recovery after surgical repair is often disappointing. The basis for poor recovery is progressive deterioration with time and distance of the growth capacity of the neurons that lose their contact with targets (chronic axotomy) and the growth support of the chronically denervated Schwann cells (SC) in the distal nerve stumps. Nonetheless, chronically denervated atrophic muscle retains the capacity for reinnervation. Declining electrical activity of motoneurons accompanies the progressive fall in axotomized neuronal and denervated SC expression of regeneration-associated-genes and declining regenerative success. Reduced motoneuronal activity is due to the withdrawal of synaptic contacts from the soma. Exogenous neurotrophic factors that promote nerve regeneration can replace the endogenous factors whose expression declines with time. But the profuse axonal outgrowth they provoke and the difficulties in their delivery hinder their efficacy. Brief (1 h) low-frequency (20 Hz) electrical stimulation (ES) proximal to the injury site promotes the expression of endogenous growth factors and, in turn, dramatically accelerates axon outgrowth and target reinnervation. The latter ES effect has been demonstrated in both rats and humans. A conditioning ES of intact nerve days prior to nerve injury increases axonal outgrowth and regeneration rate. Thereby, this form of ES is amenable for nerve transfer surgeries and end-to-side neurorrhaphies. However, additional surgery for applying the required electrodes may be a hurdle. ES is applicable in all surgeries with excellent outcomes.

Inflammatory stimulation of astrocytes affects the expression of miRNA-22-3p within NSCs-EVs regulating remyelination by targeting KDM3A

BACKGROUND

Endogenous neural stem cells (NSCs) are critical for the remyelination of axons following spinal cord injury (SCI). Cell-cell communication plays a key role in the regulation of the differentiation of NSCs. Astrocytes act as immune cells that encounter early inflammation, forming a glial barrier to prevent the spread of destructive inflammation following SCI. In addition, the cytokines released from astrocytes participate in the regulation of the differentiation of NSCs. The aim of this study was to investigate the effects of cytokines released from inflammation-stimulated astrocytes on the differentiation of NSCs following SCI and to explore the influence of these cytokines on NSC-NSC communication.

RESULTS

Lipopolysaccharide stimulation of astrocytes increased bone morphogenetic protein 2 (BMP2) release, which not only promoted the differentiation of NSCs into astrocytes and inhibited axon remyelination in SCI lesions but also enriched miRNA-22-3p within extracellular vesicles derived from NSCs. These miRNA-22 molecules function as a feedback loop to promote NSC differentiation into oligodendrocytes and the remyelination of axons following SCI by targeting KDM3A.

CONCLUSIONS

This study revealed that by releasing BMP2, astrocytes were able to regulate the differentiation of NSCs and NSC-NSC communication by enriching miRNA-22 within NSC-EVs, which in turn promoted the regeneration and remyelination of axons by targeting the KDM3A/TGF-beta axis and the recovery of neurological outcomes following SCI.

Title: Immunotherapy; a ground-breaking remedy for spinal cord injury with stumbling blocks: An overview

Spinal cord injury (SCI) is a debilitating disorder with no known standard and effective treatment. Despite its ability to exacerbate SCI sequel by accelerating auto-reactive immune cells, an immune response is also considered essential to the healing process. Therefore, immunotherapeutic strategies targeting spinal cord injuries may benefit from the dual nature of immune responses. An increasing body of research suggests that immunization against myelin inhibitors can promote axon remyelination after SCI. However, despite advancements in our understanding of neuroimmune responses, immunoregulation-based therapeutic strategies have yet to receive widespread acceptance. Therefore, it is a prerequisite to enhance the understanding of immune regulation to ensure the safety and efficacy of immunotherapeutic treatments. The objective of the present study was to provide an overview of previous studies regarding the advantages and limitations of immunotherapeutic strategies for functional recovery after spinal cord injury, especially in light of limiting factors related to DNA and cell-based vaccination strategies by providing a novel prospect to lay the foundation for future studies that will help devise a safe and effective treatment for spinal cord injury.

Characterization of microglia/macrophage phenotypes in the spinal cord following intervertebral disc herniation

Dogs frequently suffer from traumatic spinal cord injury (SCI). Most cases of SCI have a favorable prognosis but 40-50% of dogs with paraplegia and absence of nociception do not regain ambulatory abilities, eventually leading to euthanasia. Microglia and infiltrating macrophages play a crucial role in inflammatory process after SCI. However, little is known about microglia/macrophage phenotypes representing a potential target for future therapeutic strategies. In the present study, the microglia/macrophage phenotype was characterized by immunohistochemistry in the morphologically unaltered canine spinal cord (10 control dogs) and during acute and subacute SCI (1-4 and 5-10 days post injury, 9 and 8 dogs, respectively) using antibodies directed against IBA1, MAC387, MHC-II, lysozyme, EGR2, myeloperoxidase, CD18, CD204 and lectin from Griffonia simplicifolia (BS-1). The expression of these markers was also analyzed in the spleen as reference for the phenotype of histiocytic cells. Histological lesions were absent in controls. In acute SCI, 4 dogs showed mild to moderate hemorrhages, 2 dogs bilateral gray matter necrosis and 6 dogs mild multifocal axonal swellings and myelin sheath dilation. One dog with acute SCI did not show histological alterations except for few dilated myelin sheaths. In subacute SCI, variable numbers of gitter cells, axonal changes and dilated myelin sheaths were present in all dogs and large areas of tissue necrosis in 2 dogs. Neuronal chromatolysis was found in 3 dogs with acute and subacute SCI, respectively. In control dogs, microglia/macrophage constitutively expressed IBA1 and rarely other markers. In acute SCI, a similar marker expression was found except for an increase in MAC387-positive cells in the spinal cord white matter due to an infiltration of few blood-borne macrophages. In subacute SCI, increased numbers of microglia/macrophages expressed CD18, CD204 and MHC-II in the gray matter SCI indicating enhanced antigen recognition, processing and presentation as well as cell migration and phagocytosis during this stage. Interestingly, only CD204-positive cells were upregulated in the white matter, which might be related to gray-white matter heterogeneity of microglia as previously described in humans. The present findings contribute to the understanding of the immunological processes during SCI in a large animal model for human SCI.

Oxytocin and microglia in the development of social behaviour

Oxytocin is a well-established regulator of social behaviour. Microglia, the resident immune cells of the central nervous system, regulate brain development and maintenance in health and disease. Oxytocin and microglia interact: microglia appear to regulate the oxytocin system and are, in turn, regulated by oxytocin, which appears to have anti-inflammatory effects. Both microglia and oxytocin are regulated in sex-specific ways. Oxytocin and microglia may work together to promote experience-dependent circuit refinement through multiple developmental-sensitive periods contributing to individual differences in social behaviour. This article is part of the theme issue 'Interplays between oxytocin and other neuromodulators in shaping complex social behaviours'.

Autologous Platelet-Rich Growth Factor Reduces M1 Macrophages and Modulates Inflammatory Microenvironments to Promote Sciatic Nerve Regeneration

The failure of peripheral nerve regeneration is often associated with the inability to generate a permissive molecular and cellular microenvironment for nerve repair. Autologous therapies, such as platelet-rich plasma (PRP) or its derivative platelet-rich growth factors (PRGF), may improve peripheral nerve regeneration via unknown mechanistic roles and actions in macrophage polarization. In the current study, we hypothesize that excessive and prolonged inflammation might result in the failure of pro-inflammatory M1 macrophage transit to anti-inflammatory M2 macrophages in large nerve defects. PRGF was used in vitro at the time the unpolarized macrophages (M0) macrophages were induced to M1 macrophages to observe if PRGF altered the secretion of cytokines and resulted in a phenotypic change. PRGF was also employed in the nerve conduit of a rat sciatic nerve transection model to identify alterations in macrophages that might influence excessive inflammation and nerve regeneration. PRGF administration reduced the mRNA expression of tumor necrosis factor-α (TNFα), interleukin-1β (IL-1β), and IL-6 in M0 macrophages. Increased CD206 substantiated the shift of pro-inflammatory cytokines to the M2 regenerative macrophage. Administration of PRGF in the nerve conduit after rat sciatic nerve transection promoted nerve regeneration by improving nerve gross morphology and its targeted gastrocnemius muscle mass. The regenerative markers were increased for regrown axons (protein gene product, PGP9.5), Schwann cells (S100β), and myelin basic protein (MBP) after 6 weeks of injury. The decreased expression of TNFα, IL-1β, IL-6, and CD68⁺ M1 macrophages indicated that the inflammatory microenvironments were reduced in the PRGF-treated nerve tissue. The increase in RECA-positive cells suggested the PRGF also promoted angiogenesis during nerve regeneration. Taken together, these results indicate the potential role and clinical implication of autologous PRGF in regulating inflammatory microenvironments via macrophage polarization after nerve transection.

Chondroitin sulfate proteoglycans prevent immune cell phenotypic conversion and inflammation resolution via TLR4 in rodent models of spinal cord injury

Chondroitin sulfate proteoglycans (CSPGs) act as potent inhibitors of axonal growth and neuroplasticity after spinal cord injury (SCI). Here we reveal that CSPGs also play a critical role in preventing inflammation resolution by blocking the conversion of pro-inflammatory immune cells to a pro-repair phenotype in rodent models of SCI. We demonstrate that enzymatic digestion of CSPG glycosaminoglycans enhances immune cell clearance and reduces pro-inflammatory protein and gene expression profiles at key resolution time points. Analysis of phenotypically distinct immune cell clusters revealed CSPG-mediated modulation of macrophage and microglial subtypes which, together with T lymphocyte infiltration and composition changes, suggests a role for CSPGs in modulating both innate and adaptive immune responses after SCI. Mechanistically, CSPG activation of a pro-inflammatory phenotype in pro-repair immune cells was found to be TLR4-dependent, identifying TLR4 signalling as a key driver of CSPG-mediated immune modulation. These findings establish CSPGs as critical mediators of inflammation resolution failure after SCI in rodents, which leads to prolonged inflammatory pathology and irreversible tissue destruction.

Synaptic or Non-synaptic? Different Intercellular Interactions with Retinal Ganglion Cells in Optic Nerve Regeneration

Axons of adult neurons in the mammalian central nervous system generally fail to regenerate by themselves, and few if any therapeutic options exist to reverse this situation. Due to a weak intrinsic potential for axon growth and the presence of strong extrinsic inhibitors, retinal ganglion cells (RGCs) cannot regenerate their axons spontaneously after optic nerve injury and eventually undergo apoptosis, resulting in permanent visual dysfunction. Regarding the extracellular environment, research to date has generally focused on glial cells and inflammatory cells, while few studies have discussed the potentially significant role of interneurons that make direct connections with RGCs as part of the complex retinal circuitry. In this study, we provide a novel angle to summarize these extracellular influences following optic nerve injury as "intercellular interactions" with RGCs and classify these interactions as synaptic and non-synaptic. By discussing current knowledge of non-synaptic (glial cells and inflammatory cells) and synaptic (mostly amacrine cells and bipolar cells) interactions, we hope to accentuate the previously neglected but significant effects of pre-synaptic interneurons and bring unique insights into future pursuit of optic nerve regeneration and visual function recovery.

Aldehyde-methacrylate-hyaluronan profited hydrogel system integrating aligned and viscoelastic cues for neurogenesis

Either oriented architecture or viscoelasticity is pivotal to neurogenesis, thus, native neural extracellular matrix derived-hyaluronan hydrogels with nano-orientation and viscoelasticity recapitulated might be instructive for neurogenesis, however it is still unexploited. Herein, based on aldehyde-methacrylate difunctionalized hyaluronan, by integrating imine kinetic modulation and microfluidic biofabrication, we construct a hydrogel system with orthogonal viscoelasticity and nano-topography. We then find the positive synergy effects of matrix nano-orientation and viscoelasticity not only on neurites outgrowth and elongation of neural cells, but also on neuronal differentiation of stem cells. Moreover, by implanting viscoelastic and nano-aligned hydrogels into lesion sites, we demonstrate the enhanced repair of spinal cord injury, including ameliorated pathological microenvironment, facilitated endogenous neurogenesis and functional axons regeneration as well as motor function restoration. This work supplies universal platform for preparing neuronal inducing hyaluronan-based hydrogels which might serve as promising therapeutic strategies for nerve injury.

Therapeutic promise of carotenoids as antioxidants and anti-inflammatory agents in neurodegenerative disorders

Neurodegenerative disorders (NDs) including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and multiple sclerosis have various disease-specific causal factors and pathological features. A very common characteristic of NDs is oxidative stress (OS), which takes place due to the elevated generation of reactive oxygen species during the progression of NDs. Furthermore, the pathological condition of NDs including an increased level of protein aggregates can further lead to chronic inflammation because of the microglial activation. Carotenoids (CTs) are naturally occurring pigments that play a significant role in averting brain disorders. More than 750 CTs are present in nature, and they are widely available in plants, microorganisms, and animals. CTs are accountable for the red, yellow, and orange pigments in several animals and plants, and these colors usually indicate various types of CTs. CTs exert various bioactive properties because of its characteristic structure, including anti-inflammatory and antioxidant properties. Due to the protective properties of CTs, levels of CTs in the human body have been markedly linked with the prevention and treatment of multiple diseases including NDs. In this review, we have summarized the relationship between OS, neuroinflammation, and NDs. In addition, we have also particularly focused on the antioxidants and anti-inflammatory properties of CTs in the management of NDs.

Central nervous system injury-induced immune suppression

Central nervous system trauma is a common cause of morbidity and mortality. Additionally, these injuries frequently occur in younger individuals, leading to lifetime expenses for patients and caregivers and the loss of opportunity for society. Despite this prevalence and multiple attempts to design a neuroprotectant, clinical trials for a pharmacological agent for the treatment of traumatic brain injury (TBI) or spinal cord injury (SCI) have provided disappointing results. Improvements in outcome from these disease processes in the past decades have been largely due to improvements in supportive care. Among the many challenges facing patients and caregivers following neurotrauma, posttraumatic nosocomial infection is a significant and potentially reversible risk factor. Multiple animal and clinical studies have provided evidence of posttraumatic systemic immune suppression, and injuries involving the CNS may be even more prone, leading to a higher risk for in-hospital infections following neurotrauma. Patients who have experienced neurotrauma with nosocomial infection have poorer recovery and higher risks of long-term morbidity and in-hospital mortality than patients without infection. As such, the etiology and reversal of postneurotrauma immune suppression is an important topic. There are multiple possible etiologies for these posttraumatic changes including the release of damage-associated molecular patterns, the activation of immunosuppressive myeloid-derived suppressor cells, and sympathetic nervous system activation. Postinjury systemic immunosuppression, particularly following neurotrauma, provides a challenge for clinicians but also an opportunity for improvement in outcome. In this review, the authors sought to outline the evidence of postinjury systemic immune suppression in both animal models and clinical research of TBI, TBI polytrauma, and SCI.

Circulating neutrophil activation in dogs with naturally occurring spinal cord injury secondary to intervertebral disk herniation

OBJECTIVE

To investigate the time course of circulating neutrophil priming and activity in dogs with spinal cord injury secondary to intervertebral disk herniation that undergo decompressive surgery.

ANIMALS

9 dogs with spinal cord injury and 9 healthy dogs (controls).

PROCEDURES

For dogs with spinal cord injury, blood samples were collected on the day of hospital admission and 3, 7, 30, and 90 days after injury and decompressive surgery. A single blood sample was collected from the control dogs. Flow cytometry analysis was performed on isolated neutrophils incubated with antibody against CD11b and nonfluorescent dihydrorhodamine 123, which was converted to fluorescent rhodamine 123 to measure oxidative burst activity.

RESULTS

Expression of CD11b was increased in dogs with spinal cord injury 3 days after injury and decompressive surgery, relative to day 7 expression. Neutrophils expressed high oxidative burst activity both 3 and 7 days after injury and decompressive surgery, compared with activity in healthy dogs.

CLINICAL RELEVANCE

For dogs with spinal cord injury, high CD11b expression 3 days after injury and decompressive surgery was consistent with findings for rodents with experimentally induced spinal cord injury. However, the high oxidative burst activity 3 and 7 days after injury and decompressive surgery was not consistent with data from other species, and additional studies on inflammatory events in dogs with naturally occurring spinal cord injury are needed.

Neuroinduction and neuroprotection co-enhanced spinal cord injury repair based on IL-4@ZIF-8-loaded hyaluronan-collagen hydrogels with nano-aligned and viscoelastic cues

Spontaneous recovery after spinal cord injury (SCI) is extremely limited since the severe inflammatory responses lead to secondary damage, and the diseased extracellular matrix (ECM) fails to provide inductive cues...

The Repertoire of Small-Molecule PET Probes for Neuroinflammation Imaging: Challenges and Opportunities beyond TSPO

Neuroinflammation is an adaptive response of the central nervous system to diverse potentially injurious stimuli, which is closely associated with neurodegeneration and typically characterized by activation of microglia and astrocytes. As a noninvasive and translational molecular imaging tool, positron emission tomography (PET) could provide a better understanding of neuroinflammation and its role in neurodegenerative diseases. Ligands to translator protein (TSPO), a putative marker of neuroinflammation, have been the most commonly studied in this context, but they suffer from serious limitations. Herein we present a repertoire of different structural chemotypes and novel PET ligand design for classical and emerging neuroinflammatory targets beyond TSPO. We believe that this Perspective will support multidisciplinary collaborations in academic and industrial institutions working on neuroinflammation and facilitate the progress of neuroinflammation PET probe development for clinical use.

Imaging immune responses in neuroinflammatory diseases

Innate and adaptive immune responses in the central nervous system (CNS) play critical roles in the pathogenesis of neurological diseases. In the first of a two-part special issue, leading researchers discuss how imaging modalities are used to monitor immune responses in several neurodegenerative diseases and glioblastoma and brain metastases. While comparative studies in humans between imaging and pathology are biased towards the end stage of disease, animal models can inform regarding how immune responses change with disease progression and as a result of treatment regimens. Magnetic resonance imaging (MRI) and positron emission tomography (PET) are frequently used to image disease progression, and the articles indicate how one or more of these modalities have been applied to specific neuroimmune diseases. In addition, advanced microscopical imaging using two-dimensional photon microscopy and in vitro live cell imaging have also been applied to animal models. In this special issue (Parts 1 and 2), as well as the imaging modalities mentioned, several articles discuss biomarkers of disease and microscopical studies that have enabled characterization of immune responses. Future developments of imaging modalities should enable tracking of specific subsets of immune cells during disease allowing longitudinal monitoring of immune responses. These new approaches will be critical to more effectively monitor and thus target specific cell subsets for therapeutic interventions which may be applicable to a range of neurological diseases.

Hepatitis C Virus-Related Central and Peripheral Nervous System Disorders

Hepatitis C Virus (HCV), despite being a hepatotropic virus, is the causative agent of many systemic disorders, such as vasculitis, autoimmune diseases, lymphoproliferative disorders, and a broad spectrum of neurological and psychiatric manifestations. Although symptoms have been misdiagnosed or underdiagnosed, only recently, evidence of direct (inflammatory) or indirect (immune-mediated) HCV-dependent cerebral effects has been established. HCV infection can promote acute inflammatory response, pro-coagulative status and ischemic disorders, and neurodegeneration. These effects rely on cerebral HCV replication, possibly mediated by blood-brain barrier alterations. Further study is needed to better understand the HCV-related mechanisms of brain damage.

Neural Stem Cells: Promoting Axonal Regeneration and Spinal Cord Connectivity

Spinal cord injury (SCI) leads to irreversible functional impairment caused by neuronal loss and the disruption of neuronal connections across the injury site. While several experimental strategies have been used to minimize tissue damage and to enhance axonal growth and regeneration, the corticospinal projection, which is the most important voluntary motor system in humans, remains largely refractory to regenerative therapeutic interventions. To date, one of the most promising pre-clinical therapeutic strategies has been neural stem cell (NSC) therapy for SCI. Over the last decade we have found that host axons regenerate into spinal NSC grafts placed into sites of SCI. These regenerating axons form synapses with the graft, and the graft in turn extends very large numbers of new axons from the injury site over long distances into the distal spinal cord. Here we discuss the pathophysiology of SCI that makes the spinal cord refractory to spontaneous regeneration, the most recent findings of neural stem cell therapy for SCI, how it has impacted motor systems including the corticospinal tract and the implications for sensory feedback.

An Overview of NO Signaling Pathways in Aging

Nitric Oxide (NO) is a potent signaling molecule involved in the regulation of various cellular mechanisms and pathways under normal and pathological conditions. NO production, its effects, and its efficacy, are extremely sensitive to aging-related changes in the cells. Herein, we review the mechanisms of NO signaling in the cardiovascular system, central nervous system (CNS), reproduction system, as well as its effects on skin, kidneys, thyroid, muscles, and on the immune system during aging. The aging-related decline in NO levels and bioavailability is also discussed in this review. The decreased NO production by endothelial nitric oxide synthase (eNOS) was revealed in the aged cardiovascular system. In the CNS, the decline of the neuronal (n)NOS production of NO was related to the impairment of memory, sleep, and cognition. NO played an important role in the aging of oocytes and aged-induced erectile dysfunction. Aging downregulated NO signaling pathways in endothelial cells resulting in skin, kidney, thyroid, and muscle disorders. Putative therapeutic agents (natural/synthetic) affecting NO signaling mechanisms in the aging process are discussed in the present study. In summary, all of the studies reviewed demonstrate that NO plays a crucial role in the cellular aging processes.

Cost-reducing traits for agonistic head collisions: a case for neurophysiology

Many animal species have evolved extreme behaviors requiring them to engage in repeated high-impact collisions. These behaviors include mating displays like headbutting in sheep and drumming in woodpeckers. To our knowledge, these taxa do not experience any notable acute head trauma, even though the deceleration forces would cause traumatic brain injury in most animals. Previous research has focused on skeletomuscular morphology, biomechanics, and material properties in an attempt to explain how animals moderate these high-impact forces. However, many of these behaviors are understudied, and most morphological or computational studies make assumptions about the behavior without accounting for the physiology of an organism. Studying neurophysiological and immune adaptations that co-vary with these behaviors can highlight unique or synergistic solutions to seemingly deleterious behavioral displays. Here, we argue that selection for repeated, high-impact head collisions may rely on a suite of coadaptations in intracranial physiology as a cost-reducing mechanism. We propose that there are three physiological systems that could mitigate the effects of repeated head trauma: (i) the innate neuroimmune response, (ii) the glymphatic system, and (iii) the choroid plexus. These systems are interconnected yet can evolve in an independent manner. We then briefly describe the function of these systems, their role in head trauma, and research that has examined how these systems may evolve to help reduce the cost of repeated, forceful head impacts. Ultimately, we note that little is known about cost-reducing intracranial mechanisms making it a novel field of comparative study that is ripe for exploration.

Blood-Spinal Cord Barrier in Spinal Cord Injury: A Review

The blood-spinal cord barrier (BSCB), a physical barrier between the blood and spinal cord parenchyma, prevents the toxins, blood cells, and pathogens from entering the spinal cord and maintains a tightly controlled chemical balance in the spinal environment, which is necessary for proper neural function. A BSCB disruption, however, plays an important role in primary and secondary injury processes related to spinal cord injury (SCI). After SCI, the structure of the BSCB is broken down, which leads directly to leakage of blood components. At the same time, the permeability of the BSCB is also increased. Repairing the disruption of the BSCB could alleviate the SCI pathology. We review the morphology and pathology of the BSCB and progression of therapeutic methods targeting BSCB in SCI.

Transcriptomic characterization of microglia activation in a rat model of ischemic stroke

Microglia are key regulators of inflammatory response after stroke and brain injury. To better understand activation of microglia as well as their phenotypic diversity after ischemic stroke, we profiled the transcriptome of microglia after 75 min transient focal cerebral ischemia in 3-month- and 12-month-old male spontaneously hypertensive rats. Microglia were isolated from the brains by FACS sorting on days 3 and 14 after cerebral ischemia. GeneChip Rat 1.0ST microarray was used to profile the whole transcriptome of sorted microglia. We identified an evolving and complex pattern of activation from 3 to 14 days after stroke onset. M2-like patterns were extensively and persistently upregulated over time. M1-like patterns were only mildly upregulated, mostly at day 14. Younger 3-month-old brains showed a larger microglial response in both pro- and anti-inflammatory pathways, compared to older 12-month-old brains. Importantly, our data revealed that after stroke, most microglia are activated towards a wide spectrum of novel polarization states beyond the standard M1/M2 dichotomy, especially in pathways related to TLR2 and dietary fatty acid signaling. Finally, classes of transcription factors that might potentially regulate microglial activation were identified. These findings should provide a comprehensive database for dissecting microglial mechanisms and pursuing neuroinflammation targets for acute ischemic stroke.

Effective Modulation of CNS Inhibitory Microenvironment using Bioinspired Hybrid-Nanoscaffold-Based Therapeutic Interventions

Central nervous system (CNS) injuries are often debilitating, and most currently have no cure. This is due to the formation of a neuroinhibitory microenvironment at injury sites, which includes neuroinflammatory signaling and non-permissive extracellular matrix (ECM) components. To address this challenge, a viscous interfacial self-assembly approach, to generate a bioinspired hybrid 3D porous nanoscaffold platform for delivering anti-inflammatory molecules and establish a favorable 3D-ECM environment for the effective suppression of the neuroinhibitory microenvironment, is developed. By tailoring the structural and biochemical properties of the 3D porous nanoscaffold, enhanced axonal growth from the dual-targeting therapeutic strategy in a human induced pluripotent stem cell (hiPSC)-based in vitro model of neuroinflammation is demonstrated. Moreover, nanoscaffold-based approaches promote significant axonal growth and functional recovery in vivo in a spinal cord injury model through a unique mechanism of anti-inflammation-based fibrotic scar reduction. Given the critical role of neuroinflammation and ECM microenvironments in neuroinhibitory signaling, the developed nanobiomaterial-based therapeutic intervention may pave a new road for treating CNS injuries.

Neuroinflammation after SCI: Current Insights and Therapeutic Potential of Intravenous Immunoglobulin

Traumatic spinal cord injury (SCI) elicits a complex cascade of cellular and molecular inflammatory events. Although certain aspects of the inflammatory response are essential to wound healing and repair, post-SCI inflammation is, on balance, thought to be detrimental to recovery by causing "bystander damage" and the spread of pathology into spared but vulnerable regions of the spinal cord. Much of the research to date has therefore focused on understanding the inflammatory drivers of secondary tissue loss after SCI, to define therapeutic targets and positively modulate this response. Numerous experimental studies have demonstrated that modulation of the inflammatory response to SCI can indeed lead to significant neuroprotection and improved recovery. However, it is now also recognized that broadscale immunosuppression is not necessarily beneficial and may even carry the risk of contributing to the development of serious adverse events. Immune modulation rather than suppression is therefore now considered a more promising approach to target harmful post-traumatic inflammation following a major neurotraumatic event such as SCI. One promising immunomodulatory agent is intravenous immunoglobulin (IVIG), a plasma product that contains mostly immunoglobulin G (IgG) from thousands of healthy donors. IVIG is currently already widely used to treat a range of autoimmune diseases, but recent studies have found that it also holds great promise for treating acute neurological conditions, including SCI. This review provides an overview of the inflammatory response to SCI, immunomodulatory approaches that are currently in clinical trials, proposed mechanisms of action for IVIG therapy, and the putative relevance of these in the context of neurotraumatic events.

Thrombomodulin facilitates peripheral nerve regeneration through regulating M1/M2 switching

Background

Excessive inflammation within damaged tissue usually leads to delayed or insufficient regeneration, and nerves in the peripheral nervous system (PNS) generally do not recover fully following damage. Consequently, there is growing interest in whether modulation of the inflammatory response could help to promote nerve regeneration in the PNS. However, to date, there are no practical therapeutic strategies for manipulating inflammation after nerve injury. Thrombomodulin (TM) is a transmembrane glycoprotein containing five domains. The lectin-like domain of TM has the ability to suppress the inflammatory response. However, whether TM can modulate inflammation in the PNS during nerve regeneration has yet to be elucidated.

Methods

We investigated the role of TM in switching proinflammatory type 1 macrophages (M1) to anti-inflammatory type 2 macrophages (M2) in a human monocytic cell line (THP-1) and evaluated the therapeutic application of TM in transected sciatic nerve injury in rats.

Results

The administration of TM during M1 induction significantly reduced the expression levels of inflammatory cytokines, including TNF-a (p < 0.05), IL-6 (p < 0.05), and CD86 (p < 0.05), in THP-1 cells. Simultaneously, the expression levels of M2 markers, including IL-10 (p < 0.05) and CD206 (p < 0.05), were significantly increased in TM-treated THP-1 cells. Inhibition of IL-4R-c-Myc-pSTAT6-PPARγ signaling abolished the expression levels of IL-10 (p < 0.05) and CD206 (p < 0.05). The conditioned medium (CM) collected from M1 cells triggered an inflammatory response in primary Schwann cells, while CM collected from M1 cells treated with TM resulted in a dose-dependent reduction in inflammation. TM treatment led to better nerve regeneration when tested 6 weeks after injury and preserved effector muscle function. In addition, TM treatment reduced macrophage infiltration at the site of injury and led to potent M1 to M2 transition, thus indicating the anti-inflammatory capacity of TM.

Conclusions

Collectively, our findings demonstrate the anti-inflammatory role of TM during nerve regeneration. Therefore, TM represents a potential drug for the promotion and modulation of functional recovery in peripheral nerves that acts by regulating the M1/M2 ratio.

Kynurenine pathway modulation reverses the experimental autoimmune encephalomyelitis mouse disease progression

BACKGROUND

Multiple sclerosis (MS) is a chronic immune-mediated disorder of the central nervous system characterized by demyelination, neuroinflammation, and neurodegeneration. Activation of the kynurenine pathway (KP) results from acute and chronic neuroinflammation leading to both immune suppression and neurotoxicity. However, the exact effects of KP metabolites and changes in neurodegenerative diseases over time are not fully understood. Studies, including those in MS models, have reported that short-term KP activation is beneficial through immune tolerance. However, the effects of long-term KP activation are poorly understood. We hypothesized that such chronic activation is responsible for the neurodegeneration in MS, and further, modulating the KP in EAE-induced mice could significantly decrease the EAE disease severity.

METHODS

We biochemically altered the KP at different stages of the disease in experimental allergic encephalomyelitis (EAE) mouse model of MS and at two different enzymatic levels of the KP (IDO-1 (indoleamine 2,3 dioxygenase)) and KMO (kynurenine monooxygenase). CNS tissue and blood samples were analyzed longitudinally using GCMS, HPLC, IHC, and RT-PCR.

RESULTS

We showed that the KP was steadily upregulated correlating with disease severity and associated with a shift towards increasing concentrations of the KP metabolite quinolinic acid, a neuro- and gliotoxin. KP modulation by inhibition of IDO-1 with 1-methyl tryptophan (1-MT) was dependent on the timing of treatment at various stages of EAE. IDO-1 inhibition at EAE score 2 led to significantly higher numbers of FoxP3 cells (p < 0.001) in the spleen than earlier IDO-1 inhibition (prophylactic 1-MT treatment group (p < 0.001)), 1-MT treatment after EAE induction (EAE score 0; p < 0.001), and 1-MT treatment at EAE score of 1 (p < 0.05). Significant improvement of disease severity was observed in EAE mice treated with 1-MT at EAE score 2 compared to the untreated group (p < 0.05). KP modulation by KMO inhibition with Ro 61-8048 led to significantly greater numbers of Foxp3 cells (p < 0.05) in Ro 61-8048 treated mice and even more significant amelioration of EAE disease compared to the 1-MT treatment groups.

CONCLUSIONS

These results provide a new mechanistic link between neuroinflammation and neurodegeneration and point to KP modulation at the KMO level to preserve immune tolerance and limit neurodegeneration in EAE. They provide the foundation for new clinical trials for MS.

SOCS3 Attenuates GM-CSF/IFN-γ-Mediated Inflammation During Spontaneous Spinal Cord Regeneration

SOCS3, a feedback inhibitor of the JAK/STAT signal pathway, negatively regulates axonal regrowth and inflammation in the central nervous system (CNS). Here, we demonstrated a distinct role of SOCS3 in the injured spinal cord of the gecko following tail amputation. Severing the gecko spinal cord did not evoke an inflammatory cascade except for an injury-stimulated elevation of the granulocyte/macrophage colony-stimulating factor (GM-CSF) and interferon gamma (IFN-γ) cytokines. Simultaneously, the expression of SOCS3 was upregulated in microglia, and unexpectedly not in neurons. Enforced expression of SOCS3 was sufficient to suppress the GM-CSF/IFN-γ-driven inflammatory responses through its KIR domain by attenuating the activities of JAK1 and JAK2. SOCS3 was also linked to GM-CSF/IFN-γ-induced cross-tolerance. Transfection of adenovirus overexpressing SOCS3 in the injured cord resulted in a significant decrease of inflammatory cytokines. These results reveal a distinct role of SOCS3 in the regenerating spinal cord, and provide new hints for CNS repair in mammals.

Antipruritic effects of electroacupuncture on morphine-induced pruritus model mice through the TLR2/4-MyD88-NF-κB pathway

Pruritus is one of the common side effects of intrathecal or epidural injection of opioids. The aim of this study was to test the antipruritic effect of acupuncture and its possible mechanism. We used electroacupuncture (EA), toll-like receptor (TLR)2/4 antagonist sparstolonin B (SsnB), and TLR2/4 agonist peptidoglycan (PGN) to precondition female wild-type BALB/c mice, and then prepared a morphine-induced pruritus model. The mRNA and protein expression levels of TLR2, TLR4, MyD88, and NF-κB were detected by RT-PCR and western blotting. The contents of interleukin (IL)-1, IL-6, IL-12, IL-10, and tumor necrosis factor-α in serum were measured by ELISA assays. Flow cytometry was performed to analyze the ratio of M1-phenotype to M2-phenotype macrophages. Our results showed that EA preconditioning improved pruritus; reduced the expressions of TLR2, TLR4, MyD88, and NF-κB both at the mRNA and protein levels (P<0.05); reduced the expression of proinflammatory cytokines IL-1, IL-6, IL-12, and tumor necrosis factor-α; and increased the expression of anti-inflammatory cytokine IL-10 (P<0.05). EA promoted M2-phenotype macrophage differentiation. Moreover, these results showed no significant difference between the SsnB group and the EA+SsnB group (P>0.05), but showed a significant difference between the PGN group and the EA+PGN group (P<0.05). Therefore, we propose that EA may be involved in the remission of pruritus in morphine-induced pruritus model mice through the TLR2/4-MyD88-NF-κB pathway. EA is a potential therapeutic treatment for pruritus.

Resolution of neuroinflammation: mechanisms and potential therapeutic option

The central nervous system (CNS) is comprised by an elaborate neural network that is under constant surveillance by tissue-intrinsic factors for maintenance of its homeostasis. Invading pathogens or sterile injuries might compromise vitally the CNS integrity and function. A prompt anti-inflammatory response is therefore essential to contain and repair the local tissue damage. Although the origin of the insults might be different, the principles of tissue backlashes, however, share striking similarities. CNS-resident cells, such as microglia and astrocytes, together with peripheral immune cells orchestrate an array of events that aim to functional restoration. If the acute inflammatory event remains unresolved, it becomes toxic leading to progressive CNS degeneration. Therefore, the cellular, molecular, and biochemical processes that regulate inflammation need to be on a fine balance with the intrinsic CNS repair mechanisms that influence tissue healing. The purpose of this review is to highlight aspects that facilitate the resolution of CNS inflammation, promote tissue repair, and functional recovery after acute injury and infection that could potentially contribute as therapeutic interventions.

Predicting Reactive Astrogliosis Propagation by Bayesian Computational Modeling: the Repeater Stations Model

Reactive astrogliosis occurs upon focal brain injury and in neurodegenerative diseases. The mechanisms that propagate reactive astrogliosis to distal parts of the brain, in a rapid wave that activates astrocytes and other cell types along the way, are not completely understood. It is proposed that damage-associated molecular patterns (DAMP) released by necrotic cells from the injury core have a major role in the reactive astrogliosis initiation but whether they also participate in reactive astrogliosis propagation remains to be determined. We here developed a Bayesian computational model to define the most probable model for reactive astrogliosis propagation. Starting with experimental data from GFAP-immunostained reactive astrocytes, we defined five types of astrocytes based on morphometrical cues and registered the position of each reactive astrocyte cell type in the hemisphere ipsilateral to the injured site after 3 and 7 days post-ischemia. We developed equations for the changes in DAMP concentration (due to diffusion, binding to receptors or degradation), soluble mediators secretion, and for the evolution reactive astrogliosis. We tested four predefined models based on abovementioned previous hypothesis and modifications to it. Our results showed that DAMP diffusion alone has not justified the reactive astrogliosis propagation as previously assumed. Only two models succeeded in accurately reproducing the experimentally measured data and they highlighted the role of microglia and the glial secretion of soluble mediators to sustain the reactive signal and activating neighboring astrocytes. Thus, our in silico analysis proposes that glial cells behave as repeater stations of the injury signal in order to propagate reactive astrogliosis.

Unbiased transcriptomic analyses reveal distinct effects of immune deficiency in CNS function with and without injury

The mammalian central nervous system (CNS) is considered an immune privileged system as it is separated from the periphery by the blood brain barrier (BBB). Yet, immune functions have been postulated to heavily influence the functional state of the CNS, especially after injury or during neurodegeneration. There is controversy regarding whether adaptive immune responses are beneficial or detrimental to CNS injury repair. In this study, we utilized immunocompromised SCID mice and subjected them to spinal cord injury (SCI). We analyzed motor function, electrophysiology, histochemistry, and performed unbiased RNA-sequencing. SCID mice displayed improved CNS functional recovery compared to WT mice after SCI. Weighted gene-coexpression network analysis (WGCNA) of spinal cord transcriptomes revealed that SCID mice had reduced expression of immune function-related genes and heightened expression of neural transmission-related genes after SCI, which was confirmed by immunohistochemical analysis and was consistent with better functional recovery. Transcriptomic analyses also indicated heightened expression of neurotransmission-related genes before injury in SCID mice, suggesting that a steady state of immune-deficiency potentially led to CNS hyper-connectivity. Consequently, SCID mice without injury demonstrated worse performance in Morris water maze test. Taken together, not only reduced inflammation after injury but also dampened steady-state immune function without injury heightened the neurotransmission program, resulting in better or worse behavioral outcomes respectively. This study revealed the intricate relationship between immune and nervous systems, raising the possibility for therapeutic manipulation of neural function via immune modulation.

Neuronal activity and microglial activation support corticospinal tract and proprioceptive afferent sprouting in spinal circuits after a corticospinal system lesion

Spared corticospinal tract (CST) and proprioceptive afferent (PA) axons sprout after injury and contribute to rewiring spinal circuits, affecting motor recovery. Loss of CST connections post-injury results in corticospinal signal loss and associated reduction in spinal activity. We investigated the role of activity loss and injury on CST and PA sprouting. To understand activity-dependence after injury, we compared CST and PA sprouting after motor cortex (MCX) inactivation, produced by chronic MCX muscimol microinfusion, with sprouting after a CST lesion produced by pyramidal tract section (PTx). Activity suppression, which does not produce a lesion, is sufficient to trigger CST axon outgrowth from the active side to cross the midline and to enter the inactivated side of the spinal cord, to the same extent as PTx. Activity loss was insufficient to drive significant CST gray matter axon elongation, an effect of PTx. Activity suppression triggered presynaptic site formation, but less than PTx. Activity loss triggered PA sprouting, as PTx. To understand injury-dependent sprouting further, we blocked microglial activation and associated inflammation after PTX by chronic minocycline administration after PTx. Minocycline inhibited myelin debris phagocytosis contralateral to PTx and abolished CST axon elongation, formation of presynaptic sites, and PA sprouting, but not CST axon outgrowth from the active side to cross the midline. Our findings suggest sprouting after injury has a strong activity dependence and that microglial activation after injury supports axonal elongation and presynaptic site formation. Combining spinal activity support and inflammation control is potentially more effective in promoting functional restoration than either alone.

Macrophage migration inhibitory factor facilitates prostaglandin E2 production of astrocytes to tune inflammatory milieu following spinal cord injury

Background

Astrocytes have been shown to produce several pro- and anti-inflammatory cytokines to maintain homeostasis of microenvironment in response to vast array of CNS insults. Some inflammation-related cytokines are responsible for regulating such cell events. Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that can be inducibly expressed in the lesioned spinal cord. Unknown is whether MIF can facilitate the production of immunosuppressive factors from astrocytes to tune milieu following spinal cord injury.

Methods

Following establishment of contusion SCI rat model, correlation of PGE₂ synthesis-related protein levels with that of MIF was assayed by Western blot. ELISA assay was used to detect production of PGE₂, TNF-α, IL-1β, and IL-6. Immunohistochemistry was performed to observe colocalization of COX2 with GFAP- and S100β-positive astrocytes. The primary astrocytes were treated by various inhibitors to validate relevant signal pathway.

Results

The protein levels of MIF and COX2, but not of COX1, synchronously increased following spinal cord injury. Treatment of MIF inhibitor 4-IPP to the lesion sites significantly reduced the expression of COX2, mPGES-1, and as a consequence, the production of PGE₂. Astrocytes responded robustly to the MIF interference, by which regulated MAPK/COX2/PGE₂ signal pathway through coupling with the CD74 membrane receptor. MIF-induced production of PGE₂ from astrocytes was able to suppress production of TNF-α, but boosted production of IL-1β and IL-6 in LPS-activated macrophages.

Conclusion

Collectively, these results reveal a novel function of MIF-mediated astrocytes, which fine-tune inflammatory microenvironment to maintain homeostasis. These suggest an alternative therapeutic strategy for CNS inflammation.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1468-6) contains supplementary material, which is available to authorized users.

Basic biomechanics of spinal cord injury - How injuries happen in people and how animal models have informed our understanding

The wide variability, or heterogeneity, in human spinal cord injury is due partially to biomechanical factors. This review summarizes our current knowledge surrounding the patterns of human spinal column injury and the biomechanical factors affecting injury. The biomechanics of human spinal injury is studied most frequently with human cadaveric models and the features of the two most common injury patterns, burst fracture and fracture dislocation, are outlined. The biology of spinal cord injury is typically studied with animal models and the effects of the most relevant biomechanical factors - injury mechanism, injury velocity, and residual compression, are described. Tissue damage patterns and behavioural outcomes following dislocation or distraction injury mechanisms differ from the more commonly used contusion mechanism. The velocity of injury affects spinal cord damage, principally in the white matter. Ongoing, or residual compression after the initial impact does affect spinal cord damage, but few models exist that replicate the clinical scenario. Future research should focus on the effects of these biomechanical factors in different preclinical animal models as recent data suggests that treatment outcomes may vary between models.

Traumatic Spinal Cord Injury: An Overview of Pathophysiology, Models and Acute Injury Mechanisms

Traumatic spinal cord injury (SCI) is a life changing neurological condition with substantial socioeconomic implications for patients and their care-givers. Recent advances in medical management of SCI has significantly improved diagnosis, stabilization, survival rate and well-being of SCI patients. However, there has been small progress on treatment options for improving the neurological outcomes of SCI patients. This incremental success mainly reflects the complexity of SCI pathophysiology and the diverse biochemical and physiological changes that occur in the injured spinal cord. Therefore, in the past few decades, considerable efforts have been made by SCI researchers to elucidate the pathophysiology of SCI and unravel the underlying cellular and molecular mechanisms of tissue degeneration and repair in the injured spinal cord. To this end, a number of preclinical animal and injury models have been developed to more closely recapitulate the primary and secondary injury processes of SCI. In this review, we will provide a comprehensive overview of the recent advances in our understanding of the pathophysiology of SCI. We will also discuss the neurological outcomes of human SCI and the available experimental model systems that have been employed to identify SCI mechanisms and develop therapeutic strategies for this condition.

Cerebrovascular inflammation: A critical trigger for neurovascular injury?

The cerebrovascular system is not only inert bystandard that support the metabolic demands of the brain but also elicit the barrier functions against risk factors mediated neurovascular injury. The onsets of cerebrovascular inflammation are considered as stimuli that can provoke the host defense system and trigger the development of neurological disorders. Homeostasis of the brain function is regulated by the movement of endothelial, glial, and neuronal cells within the neurovascular unit (NVU), which acts as a "platform" for the coordinated action of anti- and pro-inflammatory mechanisms. The cerebrovascular system plays an integral role in the inflammatory response by either producing or expressing a variety of cytokines, adhesion molecules, metalloproteinases, and serine proteases. Excessive inflammatory cytokine production can further be affecting the blood-brain barrier (BBB) integrity and lead to brain tissue damage. In this review, we summarize the more recent evidence highlighting the importance of cerebrovascular injury in terms of risk prediction, and the mechanisms mediating the upregulation of inflammatory mediators in cerebrovascular dysfunction and neurodegeneration.

Astrocytic mobilization of glutathione peroxidase-1 contributes to the protective potential against cocaine kindling behaviors in mice via activation of JAK2/STAT3 signaling

Compelling evidence indicates that oxidative stress contributes to cocaine neurotoxicity. The present study was performed to elucidate the role of the glutathione peroxidase-1 (GPx-1) in cocaine-induced kindling (convulsive) behaviors in mice. Cocaine-induced convulsive behaviors significantly increased GPx-1, p-IkB, and p-JAK2/STAT3 expression, and oxidative burdens in the hippocampus of mice. There was no significant difference in cocaine-induced p-IkB expression between non-transgenic (non-TG) and GPx-1 overexpressing transgenic (GPx-1 TG) mice, but significant differences were observed in cocaine-induced p-JAK2/STAT3 expression and oxidative stress between non-TG and GPx-1 TG mice. Cocaine-induced glial fibrillary acidic protein (GFAP)-labeled astrocytic level was significantly higher in the hippocampus of GPx-1 TG mice. Triple-labeling immunocytochemistry indicated that GPx-1-, p-STAT3-, and GFAP-immunoreactivities were co-localized in the same cells. AG490, a JAK2/STAT3 inhibitor, but not pyrrolidone dithiocarbamate, an NFκB inhibitor, significantly counteracted GPx-1-mediated protective potentials (i.e., anticonvulsant-, antioxidant-, antiapoptotic-effects). Genetic overexpression of GPx-1 significantly attenuated proliferation of Iba-1-labeled microglia induced by cocaine in mice. However, AG490 or astrocytic inhibition (by GFAP antisense oligonucleotide and α-aminoadipate) significantly increased Iba-1-labeled microglial activity and M1 phenotype microglial mRNA levels, reflecting that proinflammatory potentials were mediated by AG490 or astrocytic inhibition. This microglial activation was less pronounced in GPx-1 TG than in non-TG mice. Furthermore, either AG490 or astrocytic inhibition significantly counteracted GPx-1-mediated protective potentials. Therefore, our results suggest that astrocytic modulation between GPx-1 and JAK2/STAT3 might be one of the underlying mechanisms for protecting against convulsive neurotoxicity induced by cocaine.

Brain aging: A Ianus-faced player between health and neurodegeneration

Neurodegenerative diseases are incurable debilitating disorders characterized by structural and functional neuronal loss. Approximately 30 million people are affected worldwide, and this number is predicted to reach more than 150 million by 2050. Neurodegenerative disorders include Alzheimer's, Parkinson's, and prion diseases among others. These disorders are characterized by the accumulation of aggregating proteins forming amyloid, responsible for the disease-associated pathological lesions. The aggregation of amyloidogenic proteins can result either in gaining of toxic functions, derived from the damage provoked by these deposits in affected tissue, or in a loss of functions, due to the sequestration and the consequent inability of the aggregating protein to ensure its physiological role. While it is widely accepted that aging represents the main risk factor for neurodegeneration, there is still no clear cut-off line between the two conditions. Indeed, many of the pathways that are commonly altered in neurodegeneration-misfolded protein accumulation, chronic inflammation, mitochondrial dysfunction, impaired iron homeostasis, epigenetic modifications-have been often correlated also with healthy aging. This overlap could be explained by the fact that the continuous accumulation of cellular damages, together with a progressive decline in metabolic efficiency during aging, makes the neurons more vulnerable to toxic injuries. When a given threshold is exceeded, all these alterations might give rise to pathological phenotypes that ultimately lead to neurodegeneration.

The Biology of Regeneration Failure and Success After Spinal Cord Injury

Since no approved therapies to restore mobility and sensation following spinal cord injury (SCI) currently exist, a better understanding of the cellular and molecular mechanisms following SCI that compromise regeneration or neuroplasticity is needed to develop new strategies to promote axonal regrowth and restore function. Physical trauma to the spinal cord results in vascular disruption that, in turn, causes blood-spinal cord barrier rupture leading to hemorrhage and ischemia, followed by rampant local cell death. As subsequent edema and inflammation occur, neuronal and glial necrosis and apoptosis spread well beyond the initial site of impact, ultimately resolving into a cavity surrounded by glial/fibrotic scarring. The glial scar, which stabilizes the spread of secondary injury, also acts as a chronic, physical, and chemo-entrapping barrier that prevents axonal regeneration. Understanding the formative events in glial scarring helps guide strategies towards the development of potential therapies to enhance axon regeneration and functional recovery at both acute and chronic stages following SCI. This review will also discuss the perineuronal net and how chondroitin sulfate proteoglycans (CSPGs) deposited in both the glial scar and net impede axonal outgrowth at the level of the growth cone. We will end the review with a summary of current CSPG-targeting strategies that help to foster axonal regeneration, neuroplasticity/sprouting, and functional recovery following SCI.

Antibody biomarker for de novo Parkinson disease: attempted validation

Parkinson disease (PD) is a progressive neurodegenerative disease with motor symptoms that result from degeneration of midbrain dopaminergic neurons. Biomarker research seeks to identify the disease during the pre-symptomatic phase, which is a time when therapeutic intervention will be most helpful. Previously, we screened a combinatorial peptoid library to search for antibodies that are present at much higher levels in the serum of PD patients than in control subjects. One such compound, called the PD2 peptoid, was 84% accurate for the identification of de novo PD when employed as the capture agent in an enzyme-linked immunosorbent assay. This peptoid recognized an IgG3 antibody, and IgG3 levels were also found to be significantly higher in PD vs. control serum. In that study we used samples from the NINDS Parkinson's Disease Biomarker Program. The current study sought to validate that finding using serum samples from de novo and control subjects in the Parkinson's Progression Markers Initiative study. We found no difference in levels of antibodies captured by the PD2 peptoid in the de novo PD vs. control subjects, and no difference in IgG3 serum levels in the two groups. The failure to replicate our previous study appears to be due to the lack of difference in serum IgG3 levels between the PD and control subjects in the current study.

Early Targeting of L-Selectin on Leukocytes Promotes Recovery after Spinal Cord Injury, Implicating Novel Mechanisms of Pathogenesis

L-selectin, a lectin-like receptor on all leukocyte classes, functions in adhesive and signaling roles in the recruitment of myeloid cells from the blood to sites of inflammation. Here, we consider L-selectin as a determinant of neurological recovery in a murine model of spinal cord injury (SCI). Spinal cord-injured, L-selectin knock-out (KO) mice (male) showed improved long-term recovery with greater white matter sparing relative to wild-type (WT) mice and reduced oxidative stress in the injured cord at 72 h post-SCI. There was a partial and transient reduction in accumulation of neutrophils in the injured spinal cords of KOs at 24 h post-injury. To complement these findings with KO mice, we sought a pharmacologic means for lowering L-selectin levels. We found that diclofenac, a nonsteroidal anti-inflammatory drug (NSAID), induced the shedding of L-selectin from the cell surface of myeloid subsets, specifically neutrophils and non-classical monocytes, in the blood and the injured spinal cord. Diclofenac administration to injured WT mice enhanced neurological recovery to a level comparable to that of KOs but did not improve recovery in KOs. While diclofenac treatment had no effect on myeloid cell accumulation, there was a reduction in oxidative stress at 72 h post-SCI. These findings implicate L-selectin in secondary pathogenesis beyond a role in leukocyte recruitment and raise the possibility of repurposing diclofenac for the treatment of SCI.

CD93 regulates central nervous system inflammation in two mouse models of autoimmune encephalomyelitis

Microglia and non-professional immune cells (endothelial cells, neurons) participate in the recognition and removal of pathogens and tissue debris in the injured central nervous system through major pro-inflammatory processes. However, the mechanisms involved in regulating these responses remain ill-characterized. We herein show that CD93, also known as complement C1qRp/AA4 stem cell marker, has an important role in the regulation of inflammatory processes. The role of CD93 was evaluated in two models of neuroinflammation. We used the MOG-experimental autoimmune encephalomyelitis (EAE) model and the antibody-dependent EAE (ADEAE), which were induced in wild-type and CD93 knockout mice. We found that CD93 was highly expressed by neurons, endothelial cells and microglia (ramified >> amoeboid). Astrocytes and oligodendrocytes did not to express CD93. We further observed that CD93-deficient (CD93^-/- ) mice presented a more robust brain and spinal cord inflammation in EAE and ADEAE. Encephalitis in CD93^-/- was characterized by increased numbers of infiltrating M1 macrophages (CD11c⁺ CD206^- ) and amoeboid microglia exhibiting a more activated phenotype (Tomato Lectin^high Cox2^high ). Damage to and leakage through the blood-brain barrier was increased in CD93^-/- animals and was associated with a more robust neuronal injury when compared with wild-type EAE mice. We propose that CD93 is an important neuro-immune regulator to control central nervous system inflammation.