The cytokine temporal profile in rat cortex after controlled cortical impact

PKC Mediates LPS-Induced IL-1β Expression and Participates in the Pro-inflammatory Effect of A2AR Under High Glutamate Concentrations in Mouse Microglia

Pathogens such as bacterial lipopolysaccharide (LPS) play an important role in promoting the production of the inflammatory cytokines interleukin-1 beta (IL-1β) and tumour necrosis factor-α (TNF-α) in response to infection or damage in microglia. However, whether different signalling pathways regulate these two inflammatory factors remains unclear. The protein kinase C (PKC) family is involved in the regulation of inflammation, and our previous research showed that the activation of the PKC pathway played a key role in the LPS-induced transformation of the adenosine A_2A receptor (A_2AR) from anti-inflammatory activity to pro-inflammatory activity under high glutamate concentrations. Therefore, in the current study, we investigated the role of PKC in the LPS-induced production of these inflammatory cytokines in mouse primary microglia. GF109203X, a specific PKC inhibitor, inhibited the LPS-induced expression of IL-1β messenger ribonucleic acid and intracellular protein in a dose-dependent manner. Moreover, 5 µM GF109203X prevented LPS-induced IL-1β expression but did not significantly affect LPS-induced TNF-α expression. PKC promoted IL-1β expression by regulating the activity of NF-κB but did not significantly impact the activity of ERK1/2. A_2AR activation by CGS21680, an A_2AR agonist, facilitated LPS-induced IL-1β expression through the PKC pathway at high glutamate concentrations but did not significantly affect LPS-induced TNF-α expression. Taken together, these results suggest a new direction for specific intervention with LPS-induced inflammatory factors in response to specific signalling pathways and provide a mechanism for A_2AR targeting, especially after brain injury, to influence inflammation by interfering with A_2AR.

CCL20-CCR6 axis modulated traumatic brain injury-induced visual pathologies

BACKGROUND

Traumatic brain injury (TBI) is a major cause of death and disability in the USA and the world; it constitutes 30% of injury-related deaths (Taylor et al., MMWR Surveill Summ 66:1-16, 2017). Contact sports athletes often experience repetitive TBI (rTBI), which exerts a cumulative effect later in life. Visual impairment is a common after-effect of TBI. Previously, we have shown that C-C chemokine 20 (CCL20) plays a critical role in neurodegeneration and inflammation following TBI (Das et al., J Neuroinflammation 8:148, 2011). C-C chemokine receptor 6 (CCR6) is the only receptor that CCL20 interacts with. The objective of the present study was to investigate the role of CCL20-CCR6 axis in mediating rTBI-induced visual dysfunction (TVD).

METHODS

Wild type (WT) or CCR6 knock out (CCR6-/-) mice were subjected to closed head rTBI. Pioglitazone (PG) is a peroxisome proliferator-activated receptor γ (PPARγ) agonist which downregulates CCL20 production. Subsets of WT mice were treated with PG following final rTBI. A subset of mice was also treated with anti-CCL20 antibody to neutralize the CCL20 produced after rTBI. Histopathological assessments were performed to show cerebral pathologies, retinal pathologies, and inflammatory changes induced by rTBI.

RESULTS

rTBI induced cerebral neurodegeneration, retinal degeneration, microgliosis, astrogliosis, and CCL20 expression. CCR6-/- mice showed reduced retinal degeneration, microgliosis, and inflammation. Treatment with CCL20 neutralization antibody or PG showed reduced CCL20 expression along with reduced retinal degeneration and inflammation. rTBI-induced GFAP-positive glial activation in the optic nerve was not affected by knocking out CCR6.

CONCLUSION

The present data indicate that rTBI-induced retinal pathology is mediated at least in part by CCL20 in a CCR6-dependent manner.

The complexity of neuroinflammation consequent to traumatic brain injury: from research evidence to potential treatments

This review recounts the definitions and research evidence supporting the multifaceted roles of neuroinflammation in the injured brain following trauma. We summarise the literature fluctuating from the protective and detrimental properties that cytokines, leukocytes and glial cells play in the acute and chronic stages of TBI, including the intrinsic factors that influence cytokine responses and microglial functions relative to genetics, sex, and age. We elaborate on the pros and cons that cytokines, chemokines, and microglia play in brain repair, specifically neurogenesis, and how such conflicting roles may be harnessed therapeutically to sustain the survival of new neurons. With a brief review of the clinical and experimental findings demonstrating early and chronic inflammation impacts on outcomes, we focus on the clinical conditions that may be amplified by neuroinflammation, ranging from acute seizures to chronic epilepsy, neuroendocrine dysfunction, dementia, depression, post-traumatic stress disorder and chronic traumatic encephalopathy. Finally, we provide an overview of the therapeutic agents that have been tested to reduce inflammation-driven secondary pathological cascades and speculate the future promise of alternative drugs.

Dissemination of brain inflammation in traumatic brain injury

Traumatic brain injury (TBI) is recognized as a global health problem due to its increasing occurrence, challenging treatment, and persistent impacts on brain pathophysiology. Neural cell death in patients with TBI swiftly causes inflammation in the injured brain areas, which is recognized as focal brain inflammation. Focal brain inflammation causes secondary brain injury by exacerbating brain edema and neuronal death, while also exerting divergent beneficial effects, such as sealing the damaged limitans and removing cellular debris. Recent evidence from patients with TBI and studies on animal models suggest that brain inflammation after TBI is not only restricted to the focal lesion but also disseminates to remote areas of the brain. The dissemination of inflammation has been detected within days after the primary injury and persists chronically. This state of inflammation may be related to remote complications of TBI in patients, such as hyperthermia and hypopituitarism, and may lead to progressive neurodegeneration, such as chronic traumatic encephalopathy. Future studies should focus on understanding the mechanisms that govern the initiation and propagation of brain inflammation after TBI and its impacts on post-trauma brain pathology.

Protection Before Impact: the Potential Neuroprotective Role of Nutritional Supplementation in Sports-Related Head Trauma

Even in the presence of underreporting, sports-related concussions/mild traumatic brain injuries (mTBI) are on the rise. In the absence of proper diagnosis, an athlete may return to play prior to full recovery, increasing the risk of second-impact syndrome or protracted symptoms. Recent evidence has demonstrated that sub-concussive impacts, those sustained routinely in practice and competition, result in a quantifiable pathophysiological response and the accumulation of both concussive and sub-concussive impacts sustained over a lifetime of sports participation may lead to long-term neurological impairments and an increased risk of developing neurodegenerative diseases. The pathophysiological, neurometabolic, and neurochemical cascade that initiates subsequent to the injury is complex and involves multiple mechanisms. While pharmaceutical treatments may target one mechanism, specific nutrients and nutraceuticals have been discovered to impact several pathways, presenting a broader approach. Several studies have demonstrated the neuroprotective effect of nutritional supplementation in the treatment of mTBI. However, given that many concussions go unreported and sub-concussive impacts result in a pathophysiological response that, too, may contribute to long-term brain health, protection prior to impact is warranted. This review discusses the current literature regarding the role of nutritional supplements that, when provided before mTBI and traumatic brain injury, may provide neurological protection.

Traumatic Injury Leads to Inflammation and Altered Tryptophan Metabolism in the Juvenile Rabbit Brain

Neuroinflammation after traumatic brain injury (TBI) contributes to widespread cell death and tissue loss. Here, we evaluated sequential inflammatory response in the brain, as well as inflammation-induced changes in brain tryptophan metabolism over time, in a rabbit pediatric TBI model. On post-natal days 5-7 (P5-P7), New Zealand white rabbit littermates were randomized into three groups: naïve (no injury), sham (craniotomy alone), and TBI (controlled cortical impact). Animals were sacrificed at 6 h and 1, 3, 7, and 21 days post-injury for evaluating levels of pro- and anti-inflammatory cytokines, as well as the major components in the tryptophan-kynurenine pathway. We found that 1) pro- and anti-inflammatory cytokine levels in the brain injury area were differentially regulated in a time-dependent manner post-injury; 2) indoleamine 2,3 dioxygeenase 1 (IDO1) was upregulated around the injury area in TBI kits that persisted at 21 days post-injury; 3) mean length of serotonin-staining fibers was significantly reduced in the injured brain region in TBI kits for at least 21 days post-injury; and 4) kynurenine level significantly increased at 7 days post-injury. A significant decrease in serotonin/tryptophan ratio and melatonin/tryptophan ratio at 21 days post-injury was noted, suggesting that tryptophan metabolism is altered after TBI. A better understanding of the temporal evolution of immune responses and tryptophan metabolism during injury and repair after TBI is crucial for the development of novel therapeutic strategies targeting these pathways.

Acute Inflammatory Biomarker Responses to Diffuse Traumatic Brain Injury in the Rat Monitored by a Novel Microdialysis Technique

Neuroinflammation is a major contributor to the progressive brain injury process induced by traumatic brain injury (TBI), and may play an important role in the pathophysiology of axonal injury. The immediate neuroinflammatory cascade cannot be characterized in the human setting. Therefore, we used the midline fluid percussion injury model of diffuse TBI in rats and a novel microdialysis (MD) method providing stable diffusion-driven biomarker sampling. Immediately post-injury, bilateral amphiphilic tri-block polymer coated MD probes (100 kDa cut off membrane) were inserted and perfused with Dextran 500 kDa-supplemented artificial cerebrospinal fluid (CSF) to optimize protein capture. Six hourly samples were analyzed for 27 inflammatory biomarkers (9 chemokines, 13 cytokines, and 5 growth factors) using a commercial multiplex biomarker kit. TBI (n = 6) resulted in a significant increase compared with sham-injured controls (n = 6) for five chemokines (eotaxin/CCL11, fractalkine/CX3CL1, LIX/CXCL5, monocyte chemoattractant protein [MCP]1α/CCL2, macrophage inflammatory protein [MIP]1α /CCL3), 10 cytokines (interleukin [IL]-1α, IL-1β, IL-4, IL-6, IL-10, IL-13, IL-17α, IL-18, interferon [IFN]-γ, tumor necrosis factor [TNF]-α), and four growth factors (epidermal growth factor [EGF], granulocyte-macrophage colony-stimulating factor [GM-CSF], leptin, vascular endothelial growth factor [VEGF]). Therefore, diffuse TBI was associated with an increased level of 18 of the 27 inflammatory biomarkers at one through six time points, during the observation period whereas the remaining 9 biomarkers were unaltered. The study shows that diffuse TBI induces an acute increase in a number of inflammatory biomarkers. The novel MD technique provides stable MD sampling suitable for further studies on the early neuroinflammatory cascade in TBI.

Interferons in Traumatic Brain and Spinal Cord Injury: Current Evidence for Translational Application

This review article provides a general perspective of the experimental and clinical work surrounding the role of type-I, type-II, and type-III interferons (IFNs) in the pathophysiology of brain and spinal cord injury. Since IFNs are themselves well-known therapeutic targets (as well as pharmacological agents), and anti-IFNs monoclonal antibodies are being tested in clinical trials, it is timely to review the basis for the repurposing of these agents for the treatment of brain and spinal cord traumatic injury. Experimental evidence suggests that IFN-α may play a detrimental role in brain trauma, enhancing the pro-inflammatory response while keeping in check astrocyte proliferation; converging evidence from genetic models and neutralization by monoclonal antibodies suggests that limiting IFN-α actions in acute trauma may be a suitable therapeutic strategy. Effects of IFN-β administration in spinal cord and brain trauma have been reported but remain unclear or limited in effect. Despite the involvement in the inflammatory response, the role of IFN-γ remains controversial: although IFN-γ appears to improve the outcome of traumatic spinal cord injury, genetic models have produced either beneficial or detrimental results. IFNs may display opposing actions on the injured CNS relative to the concentration at which they are released and strictly dependent on whether the IFN or their receptors are targeted either via administration of neutralizing antibodies or through genetic deletion of either the mediator or its receptor. To date, IFN-α appears to most promising target for drug repurposing, and monoclonal antibodies anti IFN-α or its receptor may find appropriate use in the treatment of acute brain or spinal cord injury.

Broad spectrum proteomics analysis of the inferior colliculus following acute hydrogen sulfide exposure

Acute exposure to high concentrations of H₂S causes severe brain injury and long-term neurological disorders, but the mechanisms involved are not known. To better understand the cellular and molecular mechanisms involved in acute H₂S-induced neurodegeneration we used a broad-spectrum proteomic analysis approach to identify key molecules and molecular pathways involved in the pathogenesis of acute H₂S-induced neurotoxicity and neurodegeneration. Mice were subjected to acute inhalation exposure of up to750 ppm of H₂S. H₂S induced behavioral deficits and severe lesions including hemorrhage in the inferior colliculus (IC). The IC was microdissected for proteomic analysis. Tandem mass tags (TMT) liquid chromatography mass spectrometry (LC-MS/MS)-based quantitative proteomics was applied for protein identification and quantitation. LC-MS/MS identified 598, 562, and 546 altered proteomic changes at 2 h, and on days 2 and 4 post-H₂S exposure, respectively. Of these, 77 proteomic changes were statistically significant at any of the 3 time points. Mass spectrometry data were subjected to Perseus 1.5.5.3 statistical analysis, and gene ontology heat map clustering. Expressions of several key molecules were verified to confirm H₂S-dependent proteomics changes. Webgestalt pathway overrepresentation enrichment analysis with Panther engine revealed H₂S exposure disrupted several biological processes including metabotropic glutamate receptor group 1 and inflammation mediated by chemokine and cytokine signaling pathways among others. Further analysis showed that energy metabolism, integrity of blood-brain barrier, hypoxic, and oxidative stress signaling pathways were also implicated. Collectively, this broad-spectrum proteomics data has provided important clues to follow up in future studies to further elucidate mechanisms of H₂S-induced neurotoxicity.

Therapeutic time window of multipotent adult progenitor therapy after traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is a major cause of death and disability. TBI results in a prolonged secondary central neuro-inflammatory response. Previously, we have demonstrated that multiple doses (2 and 24 h after TBI) of multipotent adult progenitor cells (MAPC) delivered intravenously preserve the blood-brain barrier (BBB), improve spatial learning, and decrease activated microglia/macrophages in the dentate gyrus of the hippocampus. In order to determine if there is an optimum treatment window to preserve the BBB, improve cognitive behavior, and attenuate the activated microglia/macrophages, we administered MAPC at various clinically relevant intervals.

METHODS

We administered two injections intravenously of MAPC treatment at hours 2 and 24 (2/24), 6 and 24 (6/24), 12 and 36 (12/36), or 36 and 72 (36/72) post cortical contusion injury (CCI) at a concentration of 10 million/kg. For BBB experiments, animals that received MAPC at 2/24, 6/24, and 12/36 were euthanized 72 h post injury. The 36/72 treated group was harvested at 96 h post injury.

RESULTS

Administration of MAPC resulted in a significant decrease in BBB permeability when administered at 2/24 h after TBI only. For behavior experiments, animals were harvested post behavior paradigm. There was a significant improvement in spatial learning (120 days post injury) when compared to cortical contusion injury (CCI) in groups when MAPC was administered at or before 24 h. In addition, there was a significant decrease in activated microglia/macrophages in the dentate gyrus of hippocampus of the treated group (2/24) only when compared to CCI.

CONCLUSIONS

Intravenous injections of MAPC at or before 24 h after CCI resulted in improvement of the BBB, improved cognitive behavior, and attenuated activated microglia/macrophages in the dentate gyrus.

Effects of Female Sex Steroids Administration on Pathophysiologic Mechanisms in Traumatic Brain Injury

Secondary brain damage following initial brain damage in traumatic brain injury (TBI) is a major cause of adverse outcomes. There are many gaps in TBI research and a lack of therapy to limit debilitating outcomes in TBI or enhance the neurogenesis, despite pre-clinical and clinical research performed in TBI. Females show harmful outcomes against brain damage including TBI less than males, independent of different TBI occurrence. A significant reduction in secondary brain damage and improvement in neurologic outcome post-TBI has been reported following the use of progesterone and estrogen in many experimental studies. Although useful features of sex steroids including progesterone have been identified in TBI clinical trials I and II, clinical trials III have been unsuccessful. This review article focuses on evidence of secondary injury mechanisms and neuroprotective effects of estrogen and progesterone in TBI. Understanding these mechanisms may enable researchers to achieve greater success in TBI clinical studies. It seems that the design of clinical studies should be revised due to translation loss of animal studies to clinical studies. The heterogeneous and complex nature of TBI, the endogenous levels of sex hormones at the time of taking these hormones, the therapeutic window of the drug, the dosage of the drug, the selection of appropriate targets in evaluation, the determination of responsive population, gender and age based on animal studies should be considered in the design of TBI human studies in future.

YKL-40 in the brain and cerebrospinal fluid of neurodegenerative dementias

BACKGROUND

YKL-40 (also known as Chitinase 3-like 1) is a glycoprotein produced by inflammatory, cancer and stem cells. Its physiological role is not completely understood but YKL-40 is elevated in the brain and cerebrospinal fluid (CSF) in several neurological and neurodegenerative diseases associated with inflammatory processes. Yet the precise characterization of YKL-40 in dementia cases is missing.

METHODS

In the present study, we comparatively analysed YKL-40 levels in the brain and CSF samples from neurodegenerative dementias of different aetiologies characterized by the presence of cortical pathology and disease-specific neuroinflammatory signatures.

RESULTS

YKL-40 was normally expressed in fibrillar astrocytes in the white matter. Additionally YKL-40 was highly and widely expressed in reactive protoplasmic cortical and perivascular astrocytes, and fibrillar astrocytes in sporadic Creutzfeldt-Jakob disease (sCJD). Elevated YKL-40 levels were also detected in Alzheimer's disease (AD) but not in dementia with Lewy bodies (DLB). In AD, YKL-40-positive astrocytes were commonly found in clusters, often around β-amyloid plaques, and surrounding vessels with β-amyloid angiopathy; they were also distributed randomly in the cerebral cortex and white matter. YKL-40 overexpression appeared as a pre-clinical event as demonstrated in experimental models of prion diseases and AD pathology. CSF YKL-40 levels were measured in a cohort of 288 individuals, including neurological controls (NC) and patients diagnosed with different types of dementia. Compared to NC, increased YKL-40 levels were detected in sCJD (p < 0.001, AUC = 0.92) and AD (p < 0.001, AUC = 0.77) but not in vascular dementia (VaD) (p > 0.05, AUC = 0.71) or in DLB/Parkinson's disease dementia (PDD) (p > 0.05, AUC = 0.70). Further, two independent patient cohorts were used to validate the increased CSF YKL-40 levels in sCJD. Additionally, increased YKL-40 levels were found in genetic prion diseases associated with the PRNP-D178N (Fatal Familial Insomnia) and PRNP-E200K mutations.

CONCLUSIONS

Our results unequivocally demonstrate that in neurodegenerative dementias, YKL-40 is a disease-specific marker of neuroinflammation showing its highest levels in prion diseases. Therefore, YKL-40 quantification might have a potential for application in the evaluation of therapeutic intervention in dementias with a neuroinflammatory component.

Gene co-expression networks identify Trem2 and Tyrobp as major hubs in human APOE expressing mice following traumatic brain injury

Traumatic brain injury (TBI) is strongly linked to an increased risk of developing dementia, including chronic traumatic encephalopathy and possibly Alzheimer's disease (AD). APOEε4 allele of human Apolipoprotein E (APOE) gene is the major genetic risk factor for late onset AD and has been associated with chronic traumatic encephalopathy and unfavorable outcome following TBI. To determine if there is an APOE isoform-specific response to TBI we performed controlled cortical impact on 3-month-old mice expressing human APOE3 or APOE4 isoforms. Following injury, we used several behavior paradigms to test for anxiety and learning and found that APOE3 and APOE4 targeted replacement mice demonstrate cognitive impairments following moderate TBI. Transcriptional profiling 14days following injury revealed a significant effect of TBI, which was similar in both genotypes. Significantly upregulated by injury in both genotypes were mRNA expression and protein level of ABCA1 transporter and APOJ, but not APOE. To identify gene-networks correlated to injury and APOE isoform, we performed Weighted Gene Co-expression Network Analysis. We determined that the network mostly correlated to TBI in animals expressing both isoforms is immune response with major hub genes including Trem2, Tyrobp, Clec7a and Cd68. We also found a significant increase of TREM2, IBA-1 and GFAP protein levels in the brains of injured mice. We identified a network representing myelination that correlated significantly with APOE isoform in both injury groups. This network was significantly enriched in oligodendrocyte signature genes, such as Mbp and Plp1. Our results demonstrate unique and distinct gene networks at this acute time point for injury and APOE isoform, as well as a network driven by APOE isoform across TBI groups.

Pathological vascular and inflammatory biomarkers of acute- and chronic-phase traumatic brain injury

Given the demand for developing objective methods for characterizing traumatic brain injury (TBI), research dedicated to evaluating putative biomarkers has burgeoned over the past decade. Since it is critical to elucidate the underlying pathological processes that underlie the higher diverse outcomes that follow neurotrauma, considerable efforts have been aimed at identifying biomarkers of both the acute- and chronic-phase TBI. Such information is not only critical for helping to elucidate the pathological changes that lead to poor long-term outcomes following TBI but it may also assist in the identification of possible prevention and interventions for individuals who sustain head trauma. In the current review, we discuss the potential role of vascular dysfunction and chronic inflammation in both acute- and chronic-phase TBI, and we also highlight existing studies that have investigated inflammation biomarkers associated with poorer injury outcome.

Sports-related concussions: diagnosis, complications, and current management strategies

Sports-related concussions (SRCs) are traumatic events that affect up to 3.8 million athletes per year. The initial diagnosis and management is often instituted on the field of play by coaches, athletic trainers, and team physicians. SRCs are usually transient episodes of neurological dysfunction following a traumatic impact, with most symptoms resolving in 7-10 days; however, a small percentage of patients will suffer protracted symptoms for years after the event and may develop chronic neurodegenerative disease. Rarely, SRCs are associated with complications, such as skull fractures, epidural or subdural hematomas, and edema requiring neurosurgical evaluation. Current standards of care are based on a paradigm of rest and gradual return to play, with decisions driven by subjective and objective information gleaned from a detailed history and physical examination. Advanced imaging techniques such as functional MRI, and detailed understanding of the complex pathophysiological process underlying SRCs and how they affect the athletes acutely and long-term, may change the way physicians treat athletes who suffer a concussion. It is hoped that these advances will allow a more accurate assessment of when an athlete is truly safe to return to play, decreasing the risk of secondary impact injuries, and provide avenues for therapeutic strategies targeting the complex biochemical cascade that results from a traumatic injury to the brain.

Neuroinflammation in animal models of traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity worldwide. Neuroinflammation is prominent in the short and long-term consequences of neuronal injuries that occur after TBI. Neuroinflammation involves the activation of glia, including microglia and astrocytes, to release inflammatory mediators within the brain, and the subsequent recruitment of peripheral immune cells. Various animal models of TBI have been developed that have proved valuable to elucidate the pathophysiology of the disorder and to assess the safety and efficacy of novel therapies prior to clinical trials. These models provide an excellent platform to delineate key injury mechanisms that associate with types of injury (concussion, contusion, and penetration injuries) that occur clinically for the investigation of mild, moderate, and severe forms of TBI. Additionally, TBI modeling in genetically engineered mice, in particular, has aided the identification of key molecules and pathways for putative injury mechanisms, as targets for development of novel therapies for human TBI. This Review details the evidence showing that neuroinflammation, characterized by the activation of microglia and astrocytes and elevated production of inflammatory mediators, is a critical process occurring in various TBI animal models, provides a broad overview of commonly used animal models of TBI, and overviews representative techniques to quantify markers of the brain inflammatory process. A better understanding of neuroinflammation could open therapeutic avenues for abrogation of secondary cell death and behavioral symptoms that may mediate the progression of TBI.

Cerebrospinal Fluid Chemokine (C-C Motif) Ligand 2 Is an Early-Response Biomarker for Blast-Overpressure-Wave-Induced Neurotrauma in Rats

Chemokines and their receptors are of great interest within the milieu of immune responses elicited in the central nervous system in response to trauma. Chemokine (C-C motif)) ligand 2 (CCL2), which is also known as monocyte chemotactic protein-1, has been implicated in the pathogenesis of traumatic brain injury (TBI), brain ischemia, Alzheimer's disease, and other neurodegenerative diseases. In this study, we investigated the time course of CCL2 accumulation in cerebrospinal fluid (CSF) after exposures to single and repeated blast overpressures of varied intensities along with the neuropathological changes and motor deficits resulting from these blast conditions. Significantly increased concentrations of CCL2 in CSF were evident by 1 h of blast exposure and persisted over 24 h with peak levels measured at 6 h post-injury. The increased levels of CCL2 in CSF corresponded with both the number and intensities of blast overpressure and were also commensurate with the extent of neuromotor impairment and neuropathological abnormalities resulting from these exposures. CCL2 levels in CSF and plasma were tightly correlated with levels of CCL2 messenger RNA in cerebellum, the brain region most consistently neuropathologically disrupted by blast. In view of the roles of CCL2 that have been implicated in multiple neurodegenerative disorders, it is likely that the sustained high levels of CCL2 and the increased expression of its main receptor, CCR2, in the brain after blast may similarly contribute to neurodegenerative processes after blast exposure. In addition, the markedly elevated concentration of CCL2 in CSF might be a candidate early-response biomarker for diagnosis and prognosis of blast-induced TBI.

Etifoxine improves sensorimotor deficits and reduces glial activation, neuronal degeneration, and neuroinflammation in a rat model of traumatic brain injury

Background

Traumatic brain injury (TBI) results in important neurological impairments which occur through a cascade of deleterious physiological events over time. There are currently no effective treatments to prevent these consequences. TBI is followed not only by an inflammatory response but also by a profound reorganization of the GABAergic system and a dysregulation of translocator protein 18 kDa (TSPO). Etifoxine is an anxiolytic compound that belongs to the benzoxazine family. It potentiates GABAergic neurotransmission, either through a positive allosteric effect or indirectly, involving the activation of TSPO that leads to an increase in neurosteroids synthesis. In several models of peripheral nerve injury, etifoxine has been demonstrated to display potent regenerative and anti-inflammatory properties and to promote functional recovery. Prior study also showed etifoxine efficacy in reducing brain edema in rats. In light of these positive results, we used a rat model of TBI to explore etifoxine treatment effects in a central nervous system injury, from functional outcomes to the underlying mechanisms.

Methods

Male Sprague-Dawley rats received contusion (n = 18) or sham (n = 19) injuries centered laterally to bregma over the left sensorimotor cortex. They were treated with etifoxine (50 mg/kg, i.p.) or its vehicle 30 min following injury and every day during 7 days. Rats underwent behavioral testing to assess sensorimotor function. In another experiment, injured rats (n = 10) or sham rats (n = 10) received etifoxine (EFX) (50 mg/kg, i.p.) or its vehicle 30 min post-surgery. Brains were then dissected for analysis of neuroinflammation markers, glial activation, and neuronal degeneration.

Results

Brain-injured rats exhibited significant sensorimotor function deficits compared to sham-injured rats in the bilateral tactile adhesive removal test, the beam walking test, and the limb-use asymmetry test. After 2 days of etifoxine treatment, behavioral impairments were significantly reduced. Etifoxine treatment reduced pro-inflammatory cytokines levels without affecting anti-inflammatory cytokines levels in injured rats, reduced macrophages and glial activation, and reduced neuronal degeneration.

Conclusions

Our results showed that post-injury treatment with etifoxine improved functional recovery and reduced neuroinflammation in a rat model of TBI. These findings suggest that etifoxine may have a therapeutic potential in the treatment of TBI.

Investigation of the mechanisms of neuroprotection mediated by Ro5-4864 in brain injury

Increasing evidence has established the involvement of the 18-kDa translocator protein (TSPO) in the process of mitochondrial membrane permeabilization and subsequent apoptosis through modulation of the mitochondrial permeability transition pore. Recent studies have shown that treatment with Ro5-4864, a TSPO ligand, resulted in a neuroprotective effect in traumatic brain injury. Yet, the nature of this effect remained uncertain as mature neurons are considered to be lacking the TSPO protein. In order to investigate the mechanism of Ro5-4864-mediated neuroprotection, the neuro-inflammatory and neurosteroid response to cortical injury was tested in sham-operated, vehicle, cyclosporine A (CsA) and Ro5-4864-treated rats. As anticipated, the levels of interleukin 1β and tumor necrosis factor α, as well as the astrocyte and microglia cellular density in the injured area were all decreased by CsA in comparison with the vehicle group. By contrast, no visible effect could be observed in Ro5-4864-treated animals. None of the groups showed any significant difference with any other in respect with the expression of brain-derived neurotrophic factor. Double immunofluorescence staining with NeuN and TSPO confirmed the absence of TSPO in native neurons though showed clear evidence of co-localization of TSPO in the cytoplasm of NeuN-stained injured neurons. Altogether, this study shows that the neuronal protection mediated by Ro5-4864 in brain injury cannot be solely attributed to an indirect effect of the ligand on glial TSPO but may also represent the consequence of the modulation of upregulated TSPO in injured neurons. This observation may be of importance for future pharmacological research in neurotrauma.

Beneficial Effect of Erythropoietin Short Peptide on Acute Traumatic Brain Injury

There is currently no effective medical treatment for traumatic brain injury (TBI). Beyond the immediate physical damage caused by the initial impact, additional damage evolves due to the inflammatory response that follows brain injury. Here we show that therapy with JM4, a low molecular weight 19-amino acid nonhematopoietic erythropoietin (EPO) peptidyl fragment, containing amino acids 28-46 derived from the first loop of EPO, markedly reduces acute brain injury. Mice underwent controlled cortical injury and received either whole molecule EPO, JM4, or sham-treatment with phosphate-buffered saline. Animals treated with JM4 peptide exhibited a large decrease in number of dead neural cells and a marked reduction in lesion size at both 3 and 8 days postinjury. Therapy with JM4 also led to improved functional recovery and we observed a treatment window for JM4 peptide that remained open for at least 9 h postinjury. The full-length EPO molecule was divided into a series of 6 contiguous peptide segments; the JM4-containing segment and the adjoining downstream region contained the bulk of the death attenuating effects seen with intact EPO molecule following TBI. These findings indicate that the JM4 molecule substantially blocks cell death and brain injury following acute brain trauma and, as such, presents an excellent opportunity to explore the therapeutic potential of a small-peptide EPO derivative in the medical treatment of TBI.

Call Off the Dog(ma): M1/M2 Polarization Is Concurrent following Traumatic Brain Injury

Following the primary mechanical impact, traumatic brain injury (TBI) induces the simultaneous production of a variety of pro- and anti-inflammatory molecular mediators. Given the variety of cell types and their requisite expression of cognate receptors this creates a highly complex inflammatory milieu. Increasingly in neurotrauma research there has been an effort to define injury-induced inflammatory responses within the context of in vitro defined macrophage polarization phenotypes, known as “M1” and “M2”. Herein, we expand upon our previous work in a rodent model of TBI to show that the categorization of inflammatory response cannot be so easily delineated using this nomenclature. Specifically, we show that TBI elicited a wide spectrum of concurrent expression responses within both pro- and anti-inflammatory arms. Moreover, we show that the cells principally responsible for the production of these inflammatory mediators, microglia/macrophages, simultaneously express both “M1” and “M2” phenotypic markers. Overall, these data align with recent reports suggesting that microglia/macrophages cannot adequately switch to a polarized “M1-only” or “M2-only” phenotype, but display a mixed phenotype due to the complex signaling events surrounding them.

Brain Region-Specific Histopathological Effects of Varying Trajectories of Controlled Cortical Impact Injury Model of Traumatic Brain Injury

AIMS

Traumatic brain injury (TBI) occurs when the head is impacted by an external force causing either a closed or penetrating head injury through a direct or accelerating impact. In laboratory research, most of the TBI animal models focus on a specific region to cause brain injury, but traumatic injuries in patients do not always impact the same brain regions. The aim of this study was to examine the histopathological effects of different angles of mechanical injury by manipulating the trajectory of the controlled cortical impact injury (CCI) model in adult Sprague-Dawley rats.

METHODS

The CCI model was manipulated as follows: conventional targeting of the frontal cortex, farthest right angle targeting the frontal cortex, closest right angle targeting the frontal cortex, olfactory bulb injury, and cerebellar injury. Three days after TBI, brains were harvested to analyze cortical and hippocampal cell loss, neuroinflammatory response, and neurogenesis via immunohistochemistry.

RESULTS

Results revealed cell death in the M1 region of the cortex across all groups, and in the CA3 area from olfactory bulb injury group. This observed cell death involved upregulation of inflammation as evidenced by rampant MHCII overexpression in cortex, but largely spared Ki-67/nestin neurogenesis in the hippocampus during this acute phase of TBI.

CONCLUSION

These results indicate a trajectory-dependent injury characterized by exacerbation of inflammation and different levels of impaired cell proliferation and neurogenesis. Such multiple brain areas showing varying levels of cell death after region-specific CCI model may closely mimic the clinical manifestations of TBI.

The immune system in traumatic brain injury

Traumatic brain injury (TBI) is the major cause of death in children and young adults and one of the major reasons for long-term disability worldwide, however, no specific clinical treatment option could be established so far. This is surprising since it is well known that following the initial mechanical damage to the brain a plethora of delayed processes are activated which ultimately result in additional brain damage. Among these secondary mechanisms, acute and chronic activation of the innate and adaptive immune system is increasingly believed to play an important role for the pathogenesis of TBI. Understanding these processes may results in new, clinically applicable therapeutic options for TBI patients.

Microglia in the TBI brain: The good, the bad, and the dysregulated

As the major cellular component of the innate immune system in the central nervous system (CNS) and the first line of defense whenever injury or disease occurs, microglia play a critical role in neuroinflammation following a traumatic brain injury (TBI). In the injured brain microglia can produce neuroprotective factors, clear cellular debris and orchestrate neurorestorative processes that are beneficial for neurological recovery after TBI. However, microglia can also become dysregulated and can produce high levels of pro-inflammatory and cytotoxic mediators that hinder CNS repair and contribute to neuronal dysfunction and cell death. The dual role of microglial activation in promoting beneficial and detrimental effects on neurons may be accounted for by their polarization state and functional responses after injury. In this review article we discuss emerging research on microglial activation phenotypes in the context of acute brain injury, and the potential role of microglia in phenotype-specific neurorestorative processes such as neurogenesis, angiogenesis, oligodendrogenesis and regeneration. We also describe some of the known molecular mechanisms that regulate phenotype switching, and highlight new therapeutic approaches that alter microglial activation state balance to enhance long-term functional recovery after TBI. An improved understanding of the regulatory mechanisms that control microglial phenotypic shifts may advance our knowledge of post-injury recovery and repair, and provide opportunities for the development of novel therapeutic strategies for TBI.

Inflammatory cytokine receptor blockade in a rodent model of mild traumatic brain injury

In rodent models of traumatic brain injury (TBI), both Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNFα) levels increase early after injury to return later to basal levels. We have developed and characterized a rat mild fluid percussion model of TBI (mLFP injury) that results in righting reflex response times (RRRTs) that are less than those characteristic of moderate to severe LFP injury and yet increase IL-1α/β and TNFα levels. Here we report that blockade of IL-1α/β and TNFα binding to IL-1R and TNFR1, respectively, reduced neuropathology in parietal cortex, hippocampus, and thalamus and improved outcome. IL-1β binding to the type I IL-1 receptor (IL-1R1) can be blocked by a recombinant form of the endogenous IL-1R antagonist IL-1Ra (Kineret). TNFα binding to the TNF receptor (TNFR) can be blocked by the recombinant fusion protein etanercept, made up of a TNFR2 peptide fused to an Fc portion of human IgG1. There was no benefit from the combined blockades compared with individual blockades or after repeated treatments for 11 days after injury compared with one treatment at 1 hr after injury, when measured at 6 hr or 18 days, based on changes in neuropathology. There was also no further enhancement of blockade benefits after 18 days. Given that both Kineret and etanercept given singly or in combination showed similar beneficial effects and that TNFα also has a gliotransmitter role regulating AMPA receptor traffic, thus confounding effects of a TNFα blockade, we chose to focus on a single treatment with Kineret.

Temporal profile of M1 and M2 responses in the hippocampus following early 24h of neurotrauma

Traumatic brain injury (TBI) elicits complex inflammatory assets (M1 and M2 responses) in the brain that include the expression of various cytokines/chemokines and the recruitment of blood cells, contributing secondary injury cascades (SIC), and also recovery processes. The modulation of such inflammatory assets might be a therapeutic option following TBI. The present study assesses a temporal profile of various molecular markers of M1 and M2 response in the hippocampus after TBI. Following a unilateral controlled cortical impact (CCI) on young rats, hippocampal tissues of each brain were harvested at 2, 4, 6, 10, and 24h post trauma. Including shams (craniotomy only), half of the rats were assessed for gene expression and half for the protein of various markers for M1 [interferon-gamma (IFNγ), tumor necrosis factor-α (TNFα), interleukin (IL)-1-β (IL-1β), and IL-6] and M2 [IL-4, IL-10, IL-13, arginase 1 (Arg1), YM1, FIZZ1, and mannose receptor C-1 (MRC1)] responses. Analysis revealed that molecular markers of M1 and M2 responses have heterogeneous injury effects in the hippocampus and that "time-post-injury" is an important factor in determining inflammation status. With the heterogeneous gene expression of pro-inflammatory cytokines, M1 response was significantly elevated at 2h and declined at 24h after TBI, however, their levels remained higher than the sham rats. Except IFNγ, proteins of M1 cytokines were significantly elevated in the first 24h, and peaked between 2-6h [TNFα (2h), IL-1β (6h), and IL-6 (4-6h)]. With the heterogeneous relative gene expression of Arg1, YM1, FIZZ1, and MRC1, levels of M2 cytokines were peaked at 24h post TBI. IL-10 and IL-13 expression appeared biphasic in the first 24h. Protein values of IL-4 and IL-13 peaked at 24h and IL-10 at 6h post injury. Results suggest that the M1 response rises rapidly after injury and overpowers the initial, comparatively smaller, or transient M2 response. A treatment that can modulate inflammation, reduce SIC, and improve recovery should be initiated early (within 10h) after TBI.

Inflammatory reaction after traumatic brain injury: therapeutic potential of targeting cell-cell communication by chemokines

Traumatic brain injury (TBI) affects millions of people worldwide every year. The primary impact initiates the secretion of pro- and anti-inflammatory factors, subsequent recruitment of peripheral immune cells, and activation of brain-resident microglia and astrocytes. Chemokines are major mediators of peripheral blood cell recruitment to damaged tissue, including the TBI brain. Here we review the involvement of specific chemokine pathways in TBI pathology and attempts to modulate these pathways for therapeutic purposes. We focus on chemokine (C-C motif) ligand 2/chemokine (C-C motif) receptor 2 (CCL2/CCR2) and chemokine (C-X-C motif) ligand 12/chemokine (C-X-C motif) receptor 4 (CXCL12/CXCR4). Recent microarray and multiplex expression profiling have also implicated CXCL10 and CCL5 in TBI pathology. Chemokine (C-X3-C motif) ligand 1/chemokine (C-X3-C motif) receptor 1 (CX3CL1/CX3CR1) signaling in the context of TBI is also discussed. Current literature suggests that modulating chemokine signaling, especially CCL2/CCR2, may be beneficial in TBI treatment.

Improved fracture healing in patients with concomitant traumatic brain injury: proven or not?

Over the last 3 decades, scientific evidence advocates an association between traumatic brain injury (TBI) and accelerated fracture healing. Multiple clinical and preclinical studies have shown an enhanced callus formation and an increased callus volume in patients, respectively, rats with concomitant TBI. Over time, different substances (cytokines, hormones, etc.) were in focus to elucidate the relationship between TBI and fracture healing. Until now, the mechanism behind this relationship is not fully clarified and a consensus on which substance plays the key role could not be attained in the literature. In this review, we will give an overview of current concepts and opinions on this topic published in the last decade and both clinical and pathophysiological theories will be discussed.

Expression levels of tumor necrosis factor-α and the corresponding receptors are correlated with trauma severity

This study investigated the plasma levels of tumor necrosis factor α (TNF-α) and the expression levels of TNF receptors (TNFRs) in patients with multiple trauma, together with the association between the levels of this cytokine and these cytokine receptors with the severity of traumatic injury. Blood samples were obtained from 60 multiple trauma patients at hospital admission (within 2 h of injury), and 6–8 h and 1–5 days after admission. The plasma levels of TNF-α and TNFR1/TNFR2 were detected using enzyme immunoassay. TNFR1 and TNFR2 expression levels on leukocytes, including neutrophils, lymphocytes and monocytes, were determined by flow cytometry. Clinical parameters were determined by injury severity score (ISS). At hospital admission, the plasma TNF-α and soluble TNFR levels in the trauma patients were elevated compared with those of healthy controls. Increased expression levels of TNFR1 and TNFR2 were also detected on leukocytes, particularly on lymphocytes and monocytes. The expression levels of the cytokine and the corresponding receptors were correlated with the ISS. TNF-α and TNFR expression levels remained significantly elevated for up to the third to fifth day following the traumatic injury. In the trauma patients, increased levels of TNF-α and TNFRs were correlated with the severity of traumatic injury in the early post-injury period, supporting the hypothesis that trauma-provoked organ dysfunction may be caused by an overwhelming auto-destructive inflammatory response.

Nervous and immune systems signals and connections: cytokines in hippocampus physiology and pathology

Signaling through secretion of small molecules is a hallmark of both nervous and immune systems. The scope and influence of the intense message exchange between these two complex systems are only now becoming objects of scientific inquiry. Both neurotransmitters and cytokines affect their target cells through surface receptors and also by other molecular mechanisms. Cytokine receptors are present in neurons and glial cell populations in discrete brain regions. This review firstly focuses on the role of cytokines in hippocampal physiological processes, such as memory and learning, and secondly on the pathological involvement of cytokines in diseases like depression and epilepsy. Interleukin-1β is necessary for long-term potentiation (LTP) maintenance in the hippocampus. On the other hand, interleukin-6 has a negative regulatory role in long-term memory acquisition. Astrocyte-secreted tumor necrosis factor plays a role in synaptic strength by increasing surface translocation of glutamate AMPA receptors, and the chemokine CXCL12 can silence the tonic activity of Cajal-Retzius neurons in the hippocampus. Manifold increased concentrations of interleukin-10, interferon-γ, ICAM1, CCL2, and CCL4 are observed in the hippocampi of patients with temporal lobe epilepsy. A contemporary view of the role of cytokines as neuromodulators is emerging from studies in humans and manipulations of experimental animals. Despite the accumulating evidence of the role of cytokines on nervous system physiology and pathology, it is important not to exaggerate its relevance.

Propofol administration modulates AQP-4 expression and brain edema after traumatic brain injury

The increased intracranial pressure caused by brain edema following traumatic brain injury (TBI) always leads to poor patient prognosis. Aquaporin-4 (AQP-4) plays an important role in edema formation and resolution, which may provide a novel therapeutic target for edema treatment. In this present study, we found that propofol treatment, within a short time, after TBI significantly reduced brain edema in a controlled cortical injury rat model and suppressed in vivo expression of AQP-4. The ameliorating effect of propofol was associated with attenuated expression of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). In addition, the regulatory effect of propofol on AQP-4 expression was investigated in cultured astrocytes. Results showed that propofol could block the stimulatory effect of IL-1β and TNF-α on AQP-4 expression in cultured astrocytes. We also found that both NFκB and p38/MAPK pathways were involved in IL-1β and TNF-α-induced AQP-4 expression and that propofol functions as a dual inhibitor of NFκB and p38/MAPK pathways. In conclusion, treatment with propofol, within a short time, after TBI attenuates cerebral edema and reduces the expression of AQP-4. Propofol modulates acute AQP-4 expression by attenuating IL-1β and TNF-α expression and inhibiting IL-1β and TNF-α induced AQP-4 expression.

Macrophagic and microglial responses after focal traumatic brain injury in the female rat

BACKGROUND

After central nervous system injury, inflammatory macrophages (M1) predominate over anti-inflammatory macrophages (M2). The temporal profile of M1/M2 phenotypes in macrophages and microglia after traumatic brain injury (TBI) in rats is unknown. We subjected female rats to severe controlled cortical impact (CCI) and examined the postinjury M1/M2 time course in their brains.

METHODS

The motor cortex (2.5 mm left laterally and 1.0 mm anteriorly from the bregma) of anesthetized female Wistar rats (ages 8 to 10 weeks; N = 72) underwent histologically moderate to severe CCI with a 5-mm impactor tip. Separate cohorts of rats had their brains dissociated into cells for flow cytometry, perfusion-fixed for immunohistochemistry (IHC) and ex vivo magnetic resonance imaging or flash-frozen for RNA and protein analysis. For each analytical method used, separate postinjury times were included for 24 hours; 3 or 5 days; or 1, 2, 4 or 8 weeks.

RESULTS

By IHC, we found that the macrophagic and microglial responses peaked at 5 to 7 days post-TBI with characteristics of mixed populations of M1 and M2 phenotypes. Upon flow cytometry examination of immunological cells isolated from brain tissue, we observed that peak M2-associated staining occurred at 5 days post-TBI. Chemokine analysis by multiplex assay showed statistically significant increases in macrophage inflammatory protein 1α and keratinocyte chemoattractant/growth-related oncogene on the ipsilateral side within the first 24 hours after injury relative to controls and to the contralateral side. Quantitative RT-PCR analysis demonstrated expression of both M1- and M2-associated markers, which peaked at 5 days post-TBI.

CONCLUSIONS

The responses of macrophagic and microglial cells to histologically severe CCI in the female rat are maximal between days 3 and 7 postinjury. The response to injury is a mixture of M1 and M2 phenotypes.

Diffuse brain injury does not affect chronic sleep patterns in the mouse

PRIMARY OBJECTIVE

To test if the current model of diffuse brain injury produces chronic sleep disturbances similar to those reported by TBI patients.

METHODS AND PROCEDURES

Adult male C57BL/6 mice were subjected to moderate midline fluid percussion injury (n = 7; 1.4 atm; 6-10 minutes righting reflex time) or sham injury (n = 5). Sleep-wake activity was measured post-injury using a non-invasive, piezoelectric cage system. Chronic sleep patterns were analysed weekly for increases or decreases in percentage sleep (hypersomnia or insomnia) and changes in bout length (fragmentation).

MAIN OUTCOMES AND RESULTS

During the first week after diffuse TBI, brain-injured mice exhibited increased mean percentage sleep and mean bout length compared to sham-injured mice. Further analysis indicated the increase in mean percentage sleep occurred during the dark cycle. Injury-induced changes in sleep, however, did not extend beyond the first week post-injury and were not present in weeks 2-5 post-injury.

CONCLUSIONS

Previously, it has been shown that the midline fluid percussion model used in this study immediately increased post-traumatic sleep. The current study extended the timeline of investigation to show that sleep disturbances extended into the first week post-injury, but did not develop into chronic sleep disturbances. However, the clinical prevalence of TBI-related sleep-wake disturbances warrants further experimental investigation.

Taurine improves functional and histological outcomes and reduces inflammation in traumatic brain injury

We investigated the effect of taurine on inflammatory cytokine expression, on astrocyte activity and cerebral edema and functional outcomes, following traumatic brain injury (TBI) in rats. 72 rats were randomly divided into sham, TBI and Taurine groups. Rats subjected to moderate lateral fluid percussion injury were injected intravenously with taurine (200mg/kg) or saline immediately after injury or daily for 7days. Functional outcome was evaluated using Modified Neurological Severity Score (mNSS). Glial fibrillary acidic protein (GFAP) of the brain was measured using immunofluorescence. Concentration of 23 cytokines and chemokines in the injured cortex at 1 and 7days after TBI was assessed by Luminex xMAP technology. The results showed that taurine significantly improved functional recovery except 1day, reduced accumulation of GFAP and water content in the penumbral region at 7days after TBI. Compared with the TBI group, taurine significantly suppressed growth-related oncogene (GRO/KC) and interleukin (IL)-1β levels while elevating the levels of regulated on activation, normal T cell expressed and secreted (RANTES) at 1day. And taurine markedly decreased the level of 17 cytokine: eotaxin, Granulocyte colony-stimulating factor (G-CSF), Granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon-gamma (IFN-γ), IL-1α, IL-1β, IL-4, IL-5, IL-6, IL-10, IL-12p70, IL-13, IL-17, leptin, monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-α), vascular endothelial growth factor (VEGF), and only increased the level of MIP-1α in a week. The results suggest that taurine effectively mitigates the severity of brain damage in TBI by attenuating the increase of astrocyte activity and edema as well as pro-inflammatory cytokines.

Impaired cortical mitochondrial function following TBI precedes behavioral changes

Traumatic brain injury (TBI) pathophysiology can be attributed to either the immediate, primary physical injury, or the delayed, secondary injury which begins minutes to hours after the initial injury and can persist for several months or longer. Because these secondary cascades are delayed and last for a significant time period post-TBI, they are primary research targets for new therapeutics. To investigate changes in mitochondrial function after a brain injury, both the cortical impact site and ipsilateral hippocampus of adult male rats 7 and 17 days after a controlled cortical impact (CCI) injury were examined. State 3, state 4, and uncoupler-stimulated rates of oxygen consumption, respiratory control ratios (RCRs) were measured and membrane potential quantified, and all were significantly decreased in 7 day post-TBI cortical mitochondria. By contrast, hippocampal mitochondria at 7 days showed only non-significant decreases in rates of oxygen consumption and membrane potential. NADH oxidase activities measured in disrupted mitochondria were normal in both injured cortex and hippocampus at 7 days post-CCI. Respiratory and phosphorylation capacities at 17 days post-CCI were comparable to naïve animals for both cortical and hippocampus mitochondria. However, unlike oxidative phosphorylation, membrane potential of mitochondria in the cortical lining of the impact site did not recover at 17 days, suggesting that while diminished cortical membrane potential at 17 days does not adversely affect mitochondrial capacity to synthesize ATP, it may negatively impact other membrane potential-sensitive mitochondrial functions. Memory status, as assessed by a passive avoidance paradigm, was not significantly impaired until 17 days after injury. These results indicate pronounced disturbances in cortical mitochondrial function 7 days after CCI which precede the behavioral impairment observed at 17 days.

Bridge between neuroimmunity and traumatic brain injury

The pathophysiology of degenerative, infectious, inflammatory and traumatic diseases of the central nervous system includes a significant immune component. As to the latter, damage to the cerebral vasculature and neural cell bodies, caused by traumatic brain injury (TBI) activates innate immunity with concomitant infiltration of immunocytes into the damaged nervous system. This leads to proinflammatory cytokine and prostaglandin production and lost synaptic integrity and more generalized neurotoxicity. Engagement of adaptive immune responses follows including the production of antibodies and lymphocyte proliferation. These affect the tempo of disease along with tissue repair and as such provide a number of potential targets for pharmacological treatments for TBI. However, despite a large body of research, no such treatment intervention is currently available. In this review we will discuss the immune response initiated following brain injuries, drawing on knowledge gained from a broad array of experimental and clinical studies. Our discussion seeks to address potential therapeutic targets and propose ways in which the immune system can be controlled to promote neuroprotection.

Cellular and temporal expression of NADPH oxidase (NOX) isotypes after brain injury

BACKGROUND

Brain injury results in an increase in the activity of the reactive oxygen species generating NADPH oxidase (NOX) enzymes. Preliminary studies have shown that NOX2, NOX3, and NOX4 are the most prominently expressed NOX isotypes in the brain. However, the cellular and temporal expression profile of these isotypes in the injured and non-injured brain is currently unclear.

METHODS

Double immunofluorescence for NOX isotypes and brain cell types was performed at acute (24 hours), sub-acute (7 days), and chronic (28 days) time points after controlled cortical impact-induced brain injury or sham-injury in rats.

RESULTS

NOX2, NOX3, and NOX4 isotypes were found to be expressed in neurons, astrocytes, and microglia, and this expression was dependent on both cellular source and post-injury time. NOX4 was found in all cell types assessed, while NOX3 was positively identified in neurons only, and NOX2 was identified in microglia and neurons. NOX2 was the most responsive to injury, increasing primarily in microglia in response to injury. Quantitation of this isotype showed a significant increase in NOX2 expression at 24 hours, with reduced expression at 7 days and 28 days post-injury, although expression remained above sham levels at later time points. Cellular confirmation using purified primary or cell line culture demonstrated similar patterns in microglia, astrocytes, and neurons. Further, inhibition of NOX, and more specifically NOX2, reduced pro-inflammatory activity in microglia, demonstrating that NOX is not only up-regulated after stimulation, but may also play a significant role in post-injury neuroinflammation.

CONCLUSIONS

This study illustrates the expression profiles of NOX isotypes in the brain after injury, and demonstrates that NOX2, and to a lesser extent, NOX4, may be responsible for the majority of oxidative stress observed acutely after traumatic brain injury. These data may provide insight into the design of future therapeutic approaches.

Immunosuppression does not affect human bone marrow mesenchymal stromal cell efficacy after transplantation in traumatized mice brain

The need for immunosuppression after allo/xenogenic mesenchymal stromal cell (MSC) transplantation is debated. This study compared the long-term effects of human (h) bone marrow MSC transplant in immunocompetent or immunosuppressed traumatic brain injured (TBI) mice. C57Bl/6 male mice were subjected to TBI or sham surgery followed 24 h later by an intracerebroventricular infusion of phosphate buffer saline (PBS, control) or hMSC (150,000/5 μl). Immunocompetent and cyclosporin A immunosuppressed (CsA) mice were analyzed for gene expression at 72 h, functional deficits and histological analysis at five weeks. Gene expression analysis showed the effectiveness of immunosuppression (INFγ reduction in CsA treated groups), with no evidence of early rejection (no changes of MHCII and CD86 in all TBI groups) and selective induction of T-reg (increase of Foxp3) only in the TBI hMSC group. Five weeks after TBI, hMSC had comparable efficacy, with functional recovery (on both sensorimotor and cognitive deficits) and structural protection (contusion volume, vessel rescue effect, gliotic scar reduction, induction of neurogenesis) in immunosuppressed and immunocompetent mice. Therefore, long-term hMSC efficacy in TBI is not dependent on immunosuppressive treatment. These findings could have important clinical implication since immunosuppression in acute TBI patients may increase their risk of infection and not be tolerated.

Brain inflammation induces post-synaptic changes during early synapse formation in adult-born hippocampal neurons

An inflammatory reaction in the brain is primarily characterized by activation of parenchymal microglial cells. Microglia regulate several aspects of adult neurogenesis, i.e. the continuous production of new neurons in the adult brain. Hippocampal neurogenesis is thought to be important for memory formation, but its role in brain diseases is not clear. We have previously shown that brain inflammation modulates the functional integration of newly formed hippocampal neurons. Here, we explored whether there is a defined time period during synaptic development when new neurons are susceptible to brain inflammation. Newly formed hippocampal neurons, born in an intact environment in the adult mouse brain, were exposed to lipopolysaccharide (LPS)-induced inflammation during either early or late phases of excitatory and inhibitory synaptogenesis. We used intra-hippocampal injections of GFP-retroviral vector (RV-GFP) to label the new neurons and ipsilateral LPS injection at either 1 or 4weeks post-RV-GFP injection. A single intra-hippocampal LPS injection induced an inflammatory response for at least 3weeks, including an acute transient pro-inflammatory cytokine release as well as a sub-acute and sustained change in microglial morphology. The general cytoarchitecture of the hippocampal dentate gyrus, including granule cell layer (GCL) volume, and astrocytic glial fibrillary acidic protein expression was not different compared to vehicle controls, and no Fluoro-Jade-positive cell death was observed. New neurons encountering this inflammatory environment exhibited no changes in their gross morphology. However, when inflammation occurred during early stages of synapse formation, we found a region-specific increase in the number of thin dendritic spines and post-synaptic density-95 (PSD-95) cluster formation on spines, suggesting an enhanced excitatory synaptic connectivity in the newborn neurons. No changes were observed in the expression of N-cadherin, an adhesion molecule primarily associated with excitatory synapses. At the inhibitory synapses, alterations due to inflammation were also evident during early but not later stages of synaptic development. Gephyrin, an inhibitory scaffolding protein, was down-regulated in the somatic region, while the adhesion molecules neuroligin-2 (NL-2) and neurofascin were increased in the somatic region and/or on the dendrites. The GABAA receptor-α2 subunit (GABAAR-α2) was increased, while pre/peri-synaptic GABA clustering remained unaltered. The disproportional changes in post-synaptic adhesion molecules and GABAA receptor compared to scaffolding protein expression at the inhibitory synapses during brain inflammation are likely to cause an imbalance in GABAergic transmission. These changes were specific for the newborn neurons and were not observed when estimating the overall expression of gephyrin, NL-2, and GABAAR-α2 in the hippocampal GCL. The expression of interleukin-1-type 1 receptor (IL-1R1) on preferentially the somatic region of new neurons, often in close apposition to NL-2 clusters, may indicate a direct interaction between brain inflammation and synaptic proteins on newborn neurons. In summary, this study provides evidence that adult-born hippocampal neurons alter their inhibitory and excitatory synaptic integration when encountering an LPS-induced brain inflammation during the initial stages of synapse formation. Changes at this critical developmental period are likely to interfere with the physiological functions of new neurons within the hippocampus.

Chemokine CCL2 induces apoptosis in cortex following traumatic brain injury

The chemokine C-C motif ligand 2 (CCL2) is an important mediator of neuroinflammation. Released in response to acute injury, ischemia, and neurodegenerative disease, CCL2 binds primarily to the G-protein-coupled chemokine C-C motif receptor 2 (CCR2) to recruit inflammatory cells to sites of tissue damage. Inflammation is thought to have both beneficial and deleterious consequences following traumatic brain injury (TBI), so we investigated CCL2-CCR2 signaling during the post-TBI period to assess possible neurodegenerative and protective actions. Local TBI in adult rat cortex was induced by Feeney's weight-drop method, and the expression of CCL2 and CCR2 in the tissue around the contusion site was measured by real-time quantitative PCR. Both CCL2 and CCR2 mRNA levels were increased markedly for at least 10 days after injury, peaking on day 3. The CCL2 protein was mainly co-localized with the astroglial marker glial fibrillary acidic protein and CCR2 protein with the neuronal nuclear marker NeuN as revealed by double immunofluorescence staining. A selective CCR2 antagonist, RS504393, reduced TUNEL staining, a marker of apoptosis, and improved performance in the Morris water maze 3 days post-TBI, suggesting that CCL2-CCR2 signaling has deleterious effects on neuronal survival and learning. Targeting the CCL2-CCR2 pathway may provide a novel therapeutic approach for the treatment of TBI.

Maternal immune activation causes age- and region-specific changes in brain cytokines in offspring throughout development

Maternal infection is a risk factor for autism spectrum disorder (ASD) and schizophrenia (SZ). Indeed, modeling this risk factor in mice through maternal immune activation (MIA) causes ASD- and SZ-like neuropathologies and behaviors in the offspring. Although MIA upregulates pro-inflammatory cytokines in the fetal brain, whether MIA leads to long-lasting changes in brain cytokines during postnatal development remains unknown. Here, we tested this possibility by measuring protein levels of 23 cytokines in the blood and three brain regions from offspring of poly(I:C)- and saline-injected mice at five postnatal ages using multiplex arrays. Most cytokines examined are present in sera and brains throughout development. MIA induces changes in the levels of many cytokines in the brains and sera of offspring in a region- and age-specific manner. These MIA-induced changes follow a few, unexpected and distinct patterns. In frontal and cingulate cortices, several, mostly pro-inflammatory, cytokines are elevated at birth, followed by decreases during periods of synaptogenesis and plasticity, and increases again in the adult. Cytokines are also altered in postnatal hippocampus, but in a pattern distinct from the other regions. The MIA-induced changes in brain cytokines do not correlate with changes in serum cytokines from the same animals. Finally, these MIA-induced cytokine changes are not accompanied by breaches in the blood-brain barrier, immune cell infiltration or increases in microglial density. Together, these data indicate that MIA leads to long-lasting, region-specific changes in brain cytokines in offspring-similar to those reported for ASD and SZ-that may alter CNS development and behavior.

In vivo microdialysis sampling of cytokines from rat hippocampus: comparison of cannula implantation procedures

Cytokines are signaling proteins that have been of significant importance in the field of immunology, since these proteins affect different cells in the immune system. In addition to their immune system significance, these proteins have recently been referred to as a third chemical communication network within the CNS. The role that cytokines play in orchestrating the immune response within tissues after a mechanical injury leads to potential complications if the source of cytokines (i.e., trauma vs disease) is of interest. Microdialysis sampling has seen wide use in collection of many different solutes within the CNS. Yet, implantation of microdialysis guide cannulas and the probes creates tissue injury. In this study, we compared the differences in cytokine levels in dialysates from 4 mm, 100 kDa molecular weight cutoff (MWCO) polyethersulfone membrane microdialysis probes implanted in the hippocampus of male Sprague-Dawley rats. Comparisons were made between animals that were dialyzed immediately after cannula implantation (day 0), 7 days post cannula implantation (day 7), and repeatedly sampled on day 0 and day 7. Multiplexed bead-based immunoassays were used to quantify CCL2 (MCP-1), CCL3 (MIP-1α), CCL5 (RANTES), CXCL1 (KC/GRO), CXCL2 (MIP-2), IL-1β, IL-6, and IL-10 in dialysates. Differences in cytokine concentrations between the different treatment groups were observed with higher levels of inflammatory cytokines measured in day 7 cannulated animals. Only CCL3 (MIP-1α), CXCL1 (KC/GRO), CXCL2 (MIP-2), and IL-10 were measured above the assay limits of detection for a majority of the dialysates, and their concentrations were typically in the low to high (10-1000) picogram per milliliter range. The work described here lays the groundwork for additional basic research studies with microdialysis sampling of cytokines in rodent CNS.

The role of markers of inflammation in traumatic brain injury

Within minutes of a traumatic impact, a robust inflammatory response is elicited in the injured brain. The complexity of this post-traumatic squeal involves a cellular component, comprising the activation of resident glial cells, microglia, and astrocytes, and the infiltration of blood leukocytes. The second component regards the secretion immune mediators, which can be divided into the following sub-groups: the archetypal pro-inflammatory cytokines (Interleukin-1, Tumor Necrosis Factor, Interleukin-6), the anti-inflammatory cytokines (IL-4, Interleukin-10, and TGF-beta), and the chemotactic cytokines or chemokines, which specifically drive the accumulation of parenchymal and peripheral immune cells in the injured brain region. Such mechanisms have been demonstrated in animal models, mostly in rodents, as well as in human brain. Whilst the humoral immune response is particularly pronounced in the acute phase following Traumatic brain injury (TBI), the activation of glial cells seems to be a rather prolonged effect lasting for several months. The complex interaction of cytokines and cell types installs a network of events, which subsequently intersect with adjacent pathological cascades including oxidative stress, excitotoxicity, or reparative events including angiogenesis, scarring, and neurogenesis. It is well accepted that neuroinflammation is responsible of beneficial and detrimental effects, contributing to secondary brain damage but also facilitating neurorepair. Although such mediators are clear markers of immune activation, to what extent cytokines can be defined as diagnostic factors reflecting brain injury or as predictors of long term outcome needs to be further substantiated. In clinical studies some groups reported a proportional cytokine production in either the cerebrospinal fluid or intraparenchymal tissue with initial brain damage, mortality, or poor outcome scores. However, the validity of cytokines as biomarkers is not broadly accepted. This review article will discuss the evidence from both clinical and laboratory studies exploring the validity of immune markers as a correlate to classification and outcome following TBI.

Post-injury conditioning with lipopolysaccharide or lipooligosaccharide reduces inflammation in the brain

BACKGROUND

Traumatic brain injury (TBI) is a leading cause of mortality and disability in the Western world. The first stage of TBI results from the mechanical damage from an impact or blast. A second stage occurs as an inflammatory response to the primary injury and presents an opportunity for clinical intervention. In this study, we investigated the effect of pre- and post-injury treatment with lipopolysaccharide (LPS) from Escherichia coli and lipooligosaccharide (LOS) from Neisseria meningitidis on levels of cerebral inflammatory cells, circulating blood cells, and pro- and anti-inflammatory cytokine levels in a rat model of neuroinflammation induced by intrastriatal injection of IL-1β to mimic the second stage of TBI.

METHODS

LPS or LOS was administered intravenously (IV) or intranasally (IN) 2h pre- or post-injection of IL-1β. The rats were euthanized 12h following IL-1β injection. Brain sections were immunostained with antibody to ED-1, a microglia cell marker. Cells in whole blood were assessed with a VetScan HM2 analyzer, and cytokine levels in sera were analyzed with a Bio-Plex system.

RESULTS

Pre- and post-injury IV administration of LPS or LOS significantly reduced microglia in the brain, and IN pre-treatment with LPS or LOS showed a statistical trend towards reducing microglia. Pre- and post-treatment IV with LOS increased circulating levels of IL-2 and IL-4, whereas IN post-treatment with LPS reduced levels of the inflammatory cytokines, TNF-α and IFN-γ.

CONCLUSIONS

The findings strongly support continued investigation of post-conditioning with LPS or LOS as potential neuroprotective treatments for neuroinflammation from TBI.

The role of markers of inflammation in traumatic brain injury

Within minutes of a traumatic impact, a robust inflammatory response is elicited in the injured brain. The complexity of this post-traumatic squeal involves a cellular component, comprising the activation of resident glial cells, microglia, and astrocytes, and the infiltration of blood leukocytes. The second component regards the secretion immune mediators, which can be divided into the following sub-groups: the archetypal pro-inflammatory cytokines (Interleukin-1, Tumor Necrosis Factor, Interleukin-6), the anti-inflammatory cytokines (IL-4, Interleukin-10, and TGF-beta), and the chemotactic cytokines or chemokines, which specifically drive the accumulation of parenchymal and peripheral immune cells in the injured brain region. Such mechanisms have been demonstrated in animal models, mostly in rodents, as well as in human brain. Whilst the humoral immune response is particularly pronounced in the acute phase following Traumatic brain injury (TBI), the activation of glial cells seems to be a rather prolonged effect lasting for several months. The complex interaction of cytokines and cell types installs a network of events, which subsequently intersect with adjacent pathological cascades including oxidative stress, excitotoxicity, or reparative events including angiogenesis, scarring, and neurogenesis. It is well accepted that neuroinflammation is responsible of beneficial and detrimental effects, contributing to secondary brain damage but also facilitating neurorepair. Although such mediators are clear markers of immune activation, to what extent cytokines can be defined as diagnostic factors reflecting brain injury or as predictors of long term outcome needs to be further substantiated. In clinical studies some groups reported a proportional cytokine production in either the cerebrospinal fluid or intraparenchymal tissue with initial brain damage, mortality, or poor outcome scores. However, the validity of cytokines as biomarkers is not broadly accepted. This review article will discuss the evidence from both clinical and laboratory studies exploring the validity of immune markers as a correlate to classification and outcome following TBI.