The temporal expression, cellular localization, and inhibition of the chemokines MIP-2 and MCP-1 after traumatic brain injury in the rat

A One-Stone-Two-Birds Strategy of Targeting Microbubbles with "Dual" Anti-Inflammatory and Blood-Brain Barrier "Switch" Function for Ischemic Stroke Treatment

Inflammation is considered to be the main target of the development of new stroke therapies. There are three key issues in the treatment of stroke inflammation: the first one is how to overcome the blood-brain barrier (BBB) to achieve drug delivery, the second one is how to select drugs to treat stroke inflammation, and the third one is how to achieve targeted drug delivery. In this study, we constructed hydrocortisone-phosphatidylserine microbubbles and combined them with ultrasound (US)-targeted microbubble destruction technology to successfully open the BBB to achieve targeted drug delivery. Phosphatidylserine on the microbubbles was used for its "eat me" effect to increase the targeting of the microvesicles. In addition, we found that hydrocortisone can accelerate the closure of the BBB, achieving efficient drug delivery while reducing the entry of peripheral toxins into the brain. In the treatment of stroke inflammation, it was found that hydrocortisone itself has anti-inflammatory effects and can also change the polarization of microglia from the harmful pro-inflammatory M1 phenotype to the beneficial anti-inflammatory M2 phenotype, thus achieving dual anti-inflammatory effects and enhancing the anti-inflammatory effects in ischemic areas after stroke, well reducing the cerebellar infarction volume by inhibiting the inflammatory response after cerebral ischemia. A confocal microendoscope was used to directly observe the polarization of microglial cells in living animal models for dynamic microscopic visualization detection showing the advantage of being closer to clinical work. Taken together, this study constructed a multifunctional targeted US contrast agent with the function of "one-stone-two-birds", which can not only "on-off" the BBB but also have "two" anti-inflammatory functions, providing a new strategy of integrated anti-inflammatory targeted delivery and imaging monitoring for ischemic stroke treatment.

Neuroprotective Effects of CXCR2 Antagonist SB332235 on Traumatic Brain Injury Through Suppressing NLRP3 Inflammasome

The inflammatory process mediated by nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain comprising 3 (NLRP3) inflammasome plays a predominant role in the neurological dysfunction following traumatic brain injury (TBI). SB332235, a highly selective antagonist of chemokine receptor 2 (CXCR2), has been demonstrated to exhibit anti-inflammatory properties and improve neurological outcomes in the central nervous system. We aimed to determine the neuroprotective effects of SB332235 in the acute phase after TBI in mice and to elucidate its underlying mechanisms. Male C57BL/6J animals were exposed to a controlled cortical impact, then received 4 doses of SB332235, with the first dose administered at 30 min after TBI, followed by additional doses at 6, 24, and 30 h. Neurological defects were assessed by the modified neurological severity score, while the motor function was evaluated using the beam balance and open field tests. Cognitive performance was evaluated using the novel object recognition test. Brain tissues were collected for pathological, Western blot, and immunohistochemical analyses. The results showed that SB332235 significantly ameliorated TBI-induced deficits, including motor and cognitive impairments. SB332235 administration suppressed expression of both CXCL1 and CXCR2 in TBI. Moreover, SB332235 substantially mitigated the augmented expression levels and activation of the NLRP3 inflammasome within the peri-contusional cortex induced by TBI. This was accompanied by the blocking of subsequent production of pro-inflammatory cytokines. Additionally, SB332235 hindered microglial activity induced by TBI. These findings confirmed the neuroprotective effects of SB332235 against TBI, and the involved mechanisms were in part due to the suppression of NLRP3 inflammasome activity. This study suggests that SB332235 may act as an anti-inflammatory agent to improve functional outcomes in brain injury when applied clinically.

Inherent Susceptibility to Acquired Epilepsy in Selectively Bred Rats Influences the Acute Response to Traumatic Brain Injury

Traumatic brain injury (TBI) often causes seizures associated with a neuroinflammatory response and neurodegeneration. TBI responses may be influenced by differences between individuals at a genetic level, yet this concept remains understudied. Here, we asked whether inherent differences in one's vulnerability to acquired epilepsy would determine acute physiological and neuroinflammatory responses acutely after experimental TBI, by comparing selectively bred "seizure-prone" (FAST) rats with "seizure-resistant" (SLOW) rats, as well as control parental strains (Long Evans and Wistar rats). Eleven-week-old male rats received a moderate-to-severe lateral fluid percussion injury (LFPI) or sham surgery. Rats were assessed for acute injury indicators and neuromotor performance, and blood was serially collected. At 7 days post-injury, brains were collected for quantification of tissue atrophy by cresyl violet (CV) histology, and immunofluorescent staining of activated inflammatory cells. FAST rats showed an exacerbated physiological response acutely post-injury, with a 100% seizure rate and mortality within 24 h. Conversely, SLOW rats showed no acute seizures and a more rapid neuromotor recovery compared with controls. Brains from SLOW rats also showed only modest immunoreactivity for microglia/macrophages and astrocytes in the injured hemisphere compared with controls. Further, group differences were apparent between the control strains, with greater neuromotor deficits observed in Long Evans rats compared with Wistars post-TBI. Brain-injured Long Evans rats also showed the most pronounced inflammatory response to TBI across multiple brain regions, whereas Wistar rats showed the greatest extent of regional brain atrophy. These findings indicate that differential genetic predisposition to develop acquired epilepsy (i.e., FAST vs. SLOW rat strains) determines acute responses after experimental TBI. Differences in the neuropathological response to TBI between commonly used control rat strains is also a novel finding, and an important consideration for future study design. Our results support further investigation into whether genetic predisposition to acute seizures predicts the chronic outcomes after TBI, including the development of post-traumatic epilepsy.

Neuroinflammation Profiling of Brain Cytokines Following Repeated Blast Exposure

Due to use of explosive devices and heavy weapons systems in modern conflicts, the effect of BW on the brain and body is of increasing concern. These exposures have been commonly linked with neurodegenerative diseases and psychiatric disorders in veteran populations. A likely neurobiological link between exposure to blasts and the development of neurobehavioral disorders, such as depression and PTSD, could be neuroinflammation triggered by the blast wave. In this study, we exposed rats to single or repeated BW (up to four exposures-one per day) at varied intensities (13, 16, and 19 psi) to mimic the types of blast exposures that service members may experience in training and combat. We then measured a panel of neuroinflammatory markers in the brain tissue with a multiplex cytokine/chemokine assay to understand the pathophysiological process(es) associated with single and repeated blast exposures. We found that single and repeated blast exposures promoted neuroinflammatory changes in the brain that are similar to those characterized in several neurological disorders; these effects were most robust after 13 and 16 psi single and repeated blast exposures, and they exceeded those recorded after 19 psi repeated blast exposures. Tumor necrosis factor-alpha and IL-10 were changed by 13 and 16 psi single and repeated blast exposures. In conclusion, based upon the growing prominence of negative psychological health outcomes in veterans and soldiers with a history of blast exposures, identifying the molecular etiology of these disorders, such as blast-induced neuroinflammation, is necessary for rationally establishing countermeasures and treatment regimens.

Sex-stratified RNA-seq analysis reveals traumatic brain injury-induced transcriptional changes in the female hippocampus conducive to dementia

Introduction

Traumatic brain injury (TBI), resulting from a violent force that causes functional changes in the brain, is the foremost environmental risk factor for developing dementia. While previous studies have identified specific candidate genes that may instigate worse outcomes following TBI when mutated, TBI-induced changes in gene expression conducive to dementia are critically understudied. Additionally, biological sex seemingly influences TBI outcomes, but the discrepancies in post-TBI gene expression leading to progressive neurodegeneration between the sexes have yet to be investigated.

Methods

We conducted a whole-genome RNA sequencing analysis of post-mortem brain tissue from the parietal neocortex, temporal neocortex, frontal white matter, and hippocampus of 107 donors characterized by the Aging, Dementia, and Traumatic Brain Injury Project. Our analysis was sex-stratified and compared gene expression patterns between TBI donors and controls, a subset of which presented with dementia.

Results

We report three candidate gene modules from the female hippocampus whose expression correlated with dementia in female TBI donors. Enrichment analyses revealed that the candidate modules were notably enriched in cardiac processes and the immune-inflammatory response, among other biological processes. In addition, multiple candidate module genes showed a significant positive correlation with hippocampal concentrations of monocyte chemoattractant protein-1 in females with post-TBI dementia, which has been previously described as a potential biomarker for TBI and susceptibility to post-injury dementia. We concurrently examined the expression profiles of these candidate modules in the hippocampus of males with TBI and found no apparent indicator that the identified candidate modules contribute to post-TBI dementia in males.

Discussion

Herein, we present the first sex-stratified RNA sequencing analysis of TBI-induced changes within the transcriptome that may be conducive to dementia. This work contributes to our current understanding of the pathophysiological link between TBI and dementia and emphasizes the growing interest in sex as a biological variable affecting TBI outcomes.

The Role of Atypical Chemokine Receptor D6 (ACKR2) in Physiological and Pathological Conditions; Friend, Foe, or Both?

Chemokines exert crucial roles in inducing immune responses through ligation to their canonical receptors. Besides these receptors, there are other atypical chemokine receptors (ACKR1–4) that can bind to a wide range of chemokines and carry out various functions in the body. ACKR2, due to its ability to bind various CC chemokines, has attracted much attention during the past few years. ACKR2 has been shown to be expressed in different cells, including trophoblasts, myeloid cells, and especially lymphoid endothelial cells. In terms of molecular functions, ACKR2 scavenges various inflammatory chemokines and affects inflammatory microenvironments. In the period of pregnancy and fetal development, ACKR2 plays a pivotal role in maintaining the fetus from inflammatory reactions and inhibiting subsequent abortion. In adults, ACKR2 is thought to be a resolving agent in the body because it scavenges chemokines. This leads to the alleviation of inflammation in different situations, including cardiovascular diseases, autoimmune diseases, neurological disorders, and infections. In cancer, ACKR2 exerts conflicting roles, either tumor-promoting or tumor-suppressing. On the one hand, ACKR2 inhibits the recruitment of tumor-promoting cells and suppresses tumor-promoting inflammation to blockade inflammatory responses that are favorable for tumor growth. In contrast, scavenging chemokines in the tumor microenvironment might lead to disruption in NK cell recruitment to the tumor microenvironment. Other than its involvement in diseases, analyzing the expression of ACKR2 in body fluids and tissues can be used as a biomarker for diseases. In conclusion, this review study has tried to shed more light on the various effects of ACKR2 on different inflammatory conditions.

Chemokine C-C motif ligand 2 suppressed the growth of human brain astrocytes under Ischemic/hypoxic conditions via regulating ERK1/2 pathway

PRIMARY OBJECTIVE

Chemokine C-C motif ligand 2 (CCL2) plays a critical role in inflammation-related diseases in the central nervous system (CNS). However, the role of CCL2 in ischemic stroke remains unclear.

RESEARCH DESIGN

To investigate the role of CCL2 in ischemic stroke, we performed oxygen-glucose deprivation (OGD) on human brain astrocytes.

METHODS AND PROCEDURES

To assess cell proliferation, the CCK-8 assay was performed. Cell apoptosis was determined using flow cytometry. qRT-PCR and western blotting were utilized to measure gene expression.

MAIN OUTCOMES AND RESULTS

Our results suggest that CCL2 and its receptor CCR2 are upregulated in OGD cells. Moreover, a CCL2 antibody significantly alleviated the ischemic/hypoxic-induced suppression of growth in human brain astrocytes. Human recombinant protein, CCL2, inhibited the growth of human brain astrocytes under normoxia conditions. These results demonstrate that CCL2 upregulation suppresses the recovery of human brain astrocytes under ischemic/hypoxic conditions. This effect was abolished by the ERK inhibitor PD98059. Therefore, CCL2/CCR2 activation may suppress the growth of human brain astrocytes through enhancing the activity of ERK1/2.

CONCLUSIONS

Our results not only developed a deeper understanding of the role of CCL2 in human brain astrocytes but also provided novel insight into potential treatments for ischemic stroke.

Can Mesenchymal Stem Cells Act Multipotential in Traumatic Brain Injury?

Traumatic brain injury (TBI), a leading cause of morbidity and mortality throughout the world, will probably become the third cause of death in the world by the year 2020. Lack of effective treatments approved for TBI is a major health problem. TBI is a heterogeneous disease due to the different mechanisms of injury. Therefore, it requires combination therapies or multipotential therapy that can affect multiple targets. In recent years, mesenchymal stem cells (MSCs) transplantation has considered one of the most promising therapeutic strategies to repair of brain injuries including TBI. In these studies, it has been shown that MSCs can migrate to the site of injury and differentiate into the cells secreting growth factors and anti-inflammatory cytokines. The reduction in brain edema, neuroinflammation, microglia accumulation, apoptosis, ischemia, the improvement of motor and cognitive function, and the enhancement in neurogenesis, angiogenesis, and neural stem cells survival, proliferation, and differentiation have been indicated in these studies. However, translation of MSCs research in TBI into a clinical setting will require additional preclinical trials.

Investigating the effects of dexamethasone on blood-brain barrier permeability and inflammatory response following focused ultrasound and microbubble exposure

Rationale: Clinical trials are currently underway to test the safety and efficacy of delivering therapeutic agents across the blood-brain barrier (BBB) using focused ultrasound and microbubbles (FUS+MBs). While acoustic feedback control strategies have largely minimized the risk of overt tissue damage, transient induction of inflammatory processes have been observed following sonication in preclinical studies. The goal of this work was to explore the potential of post-sonication dexamethasone (DEX) administration as a means to mitigate treatment risk. Vascular permeability, inflammatory protein expression, blood vessel growth, and astrocyte activation were assessed. Methods: A single-element focused transducer (transmit frequency = 580 kHz) and Definity^TM microbubbles were used to increase BBB permeability unilaterally in the dorsal hippocampi of adult male rats. Sonicating pressure was calibrated based on ultraharmonic emissions. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was used to quantitatively assess BBB permeability at 15 min (baseline) and 2 hrs following sonication. DEX was administered following baseline imaging and at 24 hrs post-FUS+MB exposure. Expression of key inflammatory proteins were assessed at 2 days, and astrocyte activation and blood vessel growth were assessed at 10 days post-FUS+MB exposure. Results: Compared to saline-treated control animals, DEX administration expedited the restoration of BBB integrity at 2 hrs, and significantly limited the production of key inflammation-related proteins at 2 days, following sonication. Indications of FUS+MB-induced astrocyte activation and vascular growth were diminished at 10 days in DEX-treated animals, compared to controls. Conclusions: These results suggest that DEX provides a means of modulating the duration of BBB permeability enhancement and may reduce the risk of inflammation-induced tissue damage, increasing the safety profile of this drug-delivery strategy. This effect may be especially relevant in scenarios for which the goal of treatment is to restore or preserve neural function and multiple sonications are required.

Monocyte mobilisation, microbiota & mental illness

The gastrointestinal microbiome has emerged as a key player in regulating brain and behaviour. This has led to the strategy of targeting the gut microbiota to ameliorate disorders of the central nervous system. Understanding the underlying signalling pathways in which the microbiota impacts these disorders is crucial for the development of future therapeutics for improving CNS functionality. One of the major pathways through which the microbiota influences the brain is the immune system, where there is an increasing appreciation for the role of monocyte trafficking in regulating brain homeostasis. In this review, we will shed light on the role of monocyte trafficking as a relay of microbiota signals in conditions where the central nervous system is in disorder, such as stress, peripheral inflammation, ageing, traumatic brain injury, stroke, multiple sclerosis, Alzheimer's disease and Parkinson's disease. We also cover how the gastrointestinal microbiota is implicated in these mental illnesses. In addition, we aim to discuss how the monocyte system can be modulated by the gut microbiota to mitigate disorders of the central nervous system, which will lead to novel microbiota-targeted strategies.

CXCL1 and CXCL2 Inhibit the Axon Outgrowth in a Time- and Cell-Type-Dependent Manner in Adult Rat Dorsal Root Ganglia Neurons

The ability to regrow their axons after an injury is a hallmark of neurons in peripheral nervous system which distinguish them from central nervous system neurons. This ability is influenced by their intrinsic capacity to regrow and by the extracellular environment which needs to be supportive of regrowth. CXCL1 [Chemokine (C-X-C motif) Ligand 1] and CXCL2 [Chemokine (C-X-C motif) Ligand 2] are two low-molecular-weight chemokines which can influence neuronal proliferation, differentiation and neurogenesis, but which are also upregulated by injury or inflammation. In this study we investigated the effects of long-term incubation (24, 48 and 72 h) with different concentrations of CXCL1 (0.4, 4 or 40 nM) or CXCL2 (0.36, 3.6 or 36 nM) on the axon outgrowth of adult rat dorsal root ganglia neurons in culture. The results showed that both chemokines significantly inhibited the axon outgrowth, with large and medium NF200 (NeuroFilament 200) (+) dorsal root ganglia neurons affected quicker, compared to small IB4 (Isolectin B4) (+) dorsal root ganglia neurons which were affected after longer exposure. Blocking CXCR2 (C-X-C motif chemokine receptor 2) which mediates the effects of CXCL1 and CXCL2 prevented these effects, suggesting that CXCR2 may represent a new therapeutic target for promoting the axon outgrowth after a peripheral nerve injury.

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.

Neutrophils in traumatic brain injury (TBI): friend or foe?

Our knowledge of the pathophysiology about traumatic brain injury (TBI) is still limited. Neutrophils, as the most abundant leukocytes in circulation and the first-line transmigrated immune cells at the sites of injury, are highly involved in the initiation, development, and recovery of TBI. Nonetheless, our understanding about neutrophils in TBI is obsolete, and mounting evidences from recent studies have challenged the conventional views. This review summarizes what is known about the relationships between neutrophils and pathophysiology of TBI. In addition, discussions are made on the complex roles as well as the controversial views of neutrophils in TBI.

Diffuse Axonal Injury and Oxidative Stress: A Comprehensive Review

Traumatic brain injury (TBI) is one of the world’s leading causes of morbidity and mortality among young individuals. TBI applies powerful rotational and translational forces to the brain parenchyma, which results in a traumatic diffuse axonal injury (DAI) responsible for brain swelling and neuronal death. Following TBI, axonal degeneration has been identified as a progressive process that starts with disrupted axonal transport causing axonal swelling, followed by secondary axonal disconnection and Wallerian degeneration. These modifications in the axonal cytoskeleton interrupt the axoplasmic transport mechanisms, causing the gradual gathering of transport products so as to generate axonal swellings and modifications in neuronal homeostasis. Oxidative stress with consequent impairment of endogenous antioxidant defense mechanisms plays a significant role in the secondary events leading to neuronal death. Studies support the role of an altered axonal calcium homeostasis as a mechanism in the secondary damage of axon, and suggest that calcium channel blocker can alleviate the secondary damage, as well as other mechanisms implied in the secondary injury, and could be targeted as a candidate for therapeutic approaches. Reactive oxygen species (ROS)-mediated axonal degeneration is mainly caused by extracellular Ca²⁺. Increases in the defense mechanisms through the use of exogenous antioxidants may be neuroprotective, particularly if they are given within the neuroprotective time window. A promising potential therapeutic target for DAI is to directly address mitochondria-related injury or to modulate energetic axonal energy failure.

The scavenging chemokine receptor ACKR2 has a significant impact on acute mortality rate and early lesion development after traumatic brain injury

The atypical chemokine receptor ACKR2 promotes resolution of acute inflammation by operating as a scavenger receptor for inflammatory CC chemokines in several experimental models of inflammatory disorders, however its role in the brain remains unclear. Based on our previous reports of increased expression of inflammatory chemokines and their corresponding receptors following traumatic brain injury (TBI), we hypothesised that ACKR2 modulates neuroinflammation following brain trauma and that its deletion exacerbates cellular inflammation and chemokine production. We demonstrate increased CCL2 and ACKR2 mRNA expression in post-mortem human brain, whereby ACKR2 mRNA levels correlated with later times post-TBI. This data is consistent with the transient upregulation of ACKR2 observed in mouse brain after closed head injury (CHI). As compared to WT animals, ACKR2^-/- mice showed a higher mortality rate after CHI, while the neurological outcome in surviving mice was similar. At day 1 post-injury, ACKR2^-/- mice displayed aggravated lesion volume and no differences in CCL2 expression and macrophage recruitment relative to WT mice. Reciprocal regulation of ACKR2 and CCL2 expression was explored in cultured astrocytes, which are recognized as the major source of CCL2 and also express ACKR2. ACKR2 mRNA increased as early as 2 hours after an inflammatory challenge in WT astrocytes. As expected, CCL2 expression also dramatically increased at 4 hours in WT astrocytes but was significantly lower in ACKR2^-/- astrocytes, possibly indicating a co-regulation of CCL2 and ACKR2 in these cells. Conversely, in vivo, CCL2 mRNA/protein levels were increased similarly in ACKR2^-/- and WT brains at 4 and 12 hours after CHI, in line with the lack of differences in cerebral macrophage recruitment and neurological recovery. In conclusion, ACKR2 is induced after TBI and has a significant impact on mortality and lesion development acutely following CHI, while its role in chemokine expression, macrophage activation, brain pathology, and neurological recovery at later time-points is minor. Concordant to evidence in multiple sclerosis experimental models, our data corroborate a distinct role for ACKR2 in cerebral inflammatory processes compared to its reported functions in peripheral tissues.

S100A4 contributes to colitis development by increasing the adherence of Citrobacter rodentium in intestinal epithelial cells

S100A4 has been implicated in cancer and several inflammatory diseases, but its role in inflammatory bowel disease has not been well investigated. Here, upon infection with Citrobacter rodentium, a model for enteropathogenic Escherichia coli infection in humans, induced the infiltration of a large number of S100A4⁺ cells into the colon in wild type (WT) mice. Deficiency of S100A4 reduced weight loss, bacterial colonization and colonic pathology. Furthermore, the expression of inflammatory cytokines and the recruitment of macrophages and neutrophils also decreased significantly in S100A4 knock out (S100A4 ^-/-) mice. In vitro, soluble S100A4 directly up-regulated expression of integrin β-1 in intestinal epithelial cells and significantly increased the adherence of C. rodentium to intestinal epithelial cells. Additionally, the effects of S100A4 on the adherence of C. rodentium to epithelial cells could be abolished by a receptor for advanced glycation end products (RAGE)-specific inhibitor (FPS-ZM1). Therefore, these data indicate a novel mechanism for S100A4 that promotes colitis development by enhancing host adhesion and colonization of Citrobacter rodentium through the S100A4-mediated host inflammatory responses.

Effects of an Inhibitor of Monocyte Recruitment on Recovery from Traumatic Brain Injury in Mice Treated with Granulocyte Colony-Stimulating Factor

Administration of the hematopoietic growth factor granulocyte-colony stimulating Factor (G-CSF) has been reported to enhance recovery from controlled cortical impact (CCI) in rodent models. G-CSF exerts actions in both the periphery (stimulation of hematopoiesis) and in the brain, where it serves as a neurotrophic factor, promoting neuronal survival and stimulating neural stem/progenitor cell proliferation in the hippocampus. In order to distinguish the direct CNS actions of G-CSF from its peripheral actions, experiments were designed to block the recruitment of peripheral monocytes to the site of the lesion produced by CCI. The selective C-C motif receptor 2 (CCR2) antagonist (RS504303) was co-administered with G-CSF for three days after CCI in a chimeric mouse previously transplanted with GFP-expressing (GFP+) blood stem-progenitor cells. Results: The drug significantly impaired infiltration of GFP+ bone marrow-derived cells to the frontal cortex and striatum without impeding recovery performance and hippocampal neurogenesis in the behavioral test, the Radial Arm Water Maze (RAWM). Administration of the CCR2 antagonist alone, without G-CSF, was effective in promoting recovery in RAWM. These results support the hypothesis that the direct action of G-CSF on neural cells, independent of its hematopoietic effects, is primarily responsible for enhanced recovery from CCI. In addition, this study confirms the importance of CCR2 and its ligand, monocyte chemotactic protein-1 (MCP-1), in mediating the inflammatory response following CCI.

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.

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.

Anti-inflammatory effects of thymoquinone in activated BV-2 microglial cells

Thymoquinone (TQ), the main pharmacological active ingredient within the black cumin seed (Nigella sativa) is believed to be responsible for the therapeutic effects on chronic inflammatory conditions such as arthritis, asthma and neurodegeneration. In this study, we evaluated the potential anti-inflammatory role of TQ in lipopolysaccharide (LPS)-stimulated BV-2 murine microglia cells. The results obtained indicate that TQ was effective in reducing NO2(-) with an IC50 of 5.04μM, relative to selective iNOS inhibitor LNIL-l-N6-(1-iminoethyl)lysine (IC50 4.09μM). TQ mediated reduction in NO2(-) was found to parallel the decline of iNOS protein expression as confirmed by immunocytochemistry. In addition, we evaluated the anti-inflammatory effects of TQ on ninety-six (96) cytokines using a RayBio AAM-CYT-3 and 4 cytokine antibody protein array. Data obtained establish a baseline protein expression profile characteristic of resting BV-2 cells in the order of osteopontin>MIP-1alpha>MIP-1g>IGF-1 and MCP-I. In the presence of LPS [1ug/ml], activated BV-2 cells produced a sharp rise in specific pro-inflammatory cytokines/chemokine's IL-6, IL-12p40/70, CCL12 /MCP-5, CCL2/MCP-1, and G-CSF which were attenuated by the addition of TQ (10μM). The TQ mediated attenuation of MCP-5, MCP-1 and IL-6 protein in supernatants from activated BV-2 cells were corroborated by independent ELISA. Moreover, the data obtained from the RT(2) PCR demonstrated a similar pattern where the LPS mediated elevation of mRNA for IL-6, CCL12/MCP-5, CCL2/MCP-1 were significantly attenuated by TQ (10μM). Also, in this study, consistent data were obtained for both protein antibody array densitometry and ELISA assays. In addition, TQ was found to reduce LPS mediated elevation in gene expression of Cxcl10 and a number of other cytokines in the panel. These findings demonstrate the significant anti-inflammatory properties of TQ in LPS activated microglial cells. Therefore, the obtained results might indicate the usefulness of TQ in delaying the onset of inflammation-mediated neurodegenerative disorders involving activated microglia cells.

Blood Biomarkers in Moderate-To-Severe Traumatic Brain Injury: Potential Utility of a Multi-Marker Approach in Characterizing Outcome

BACKGROUND

Blood biomarkers are valuable tools for elucidating complex cellular and molecular mechanisms underlying traumatic brain injury (TBI). Profiling distinct classes of biomarkers could aid in the identification and characterization of initial injury and secondary pathological processes. This study characterized the prognostic performance of a recently developed multi-marker panel of circulating biomarkers that reflect specific pathogenic mechanisms including neuroinflammation, oxidative damage, and neuroregeneration, in moderate-to-severe TBI patients.

MATERIALS AND METHODS

Peripheral blood was drawn from 85 isolated TBI patients (n = 60 severe, n = 25 moderate) at hospital admission, 6-, 12-, and 24-h post-injury. Mortality and neurological outcome were assessed using the extended Glasgow Outcome Scale. A multiplex platform was designed on MULTI-SPOT(®) plates to simultaneously analyze human plasma levels of s100 calcium binding protein beta (s100B), glial fibrillary acidic protein (GFAP), neuron specific enolase (NSE), brain-derived neurotrophic factor (BDNF), monocyte chemoattractant protein (MCP)-1, intercellular adhesion molecule (ICAM)-5, and peroxiredoxin (PRDX)-6. Multivariable logistic regression and area under the receiver-operating characteristic curve (AUC) were used to evaluate both individual and combined predictive abilities of these markers for 6-month neurological outcome and mortality after TBI.

RESULTS

Unfavorable neurological outcome was associated with elevations in s100B, GFAP, and MCP-1. Mortality was related to differences in six of the seven markers analyzed. Combined admission concentrations of s100B, GFAP, and MCP-1 were able to discriminate favorable versus unfavorable outcome (AUC = 0.83), and survival versus death (AUC = 0.87), although not significantly better than s100B alone (AUC = 0.82 and 0.86, respectively).

CONCLUSION

The multi-marker panel of TBI-related biomarkers performed well in discriminating unfavorable and favorable outcomes in the acute period after moderate-to-severe TBI. However, the combination of these biomarkers did not outperform s100B alone.

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.

Hemorrhagic shock shifts the serum cytokine profile from pro- to anti-inflammatory after experimental traumatic brain injury in mice

Secondary insults, such as hemorrhagic shock (HS), worsen outcome from traumatic brain injury (TBI). Both TBI and HS modulate levels of inflammatory mediators. We evaluated the addition of HS on the inflammatory response to TBI. Adult male C57BL6J mice were randomized into five groups (n=4 [naïve] or 8/group): naïve; sham; TBI (through mild-to-moderate controlled cortical impact [CCI] at 5 m/sec, 1-mm depth), HS; and CCI+HS. All non-naïve mice underwent identical monitoring and anesthesia. HS and CCI+HS underwent a 35-min period of pressure-controlled hemorrhage (target mean arterial pressure, 25-27 mm Hg) and a 90-min resuscitation with lactated Ringer's injection and autologous blood transfusion. Mice were sacrificed at 2 or 24 h after injury. Levels of 13 cytokines, six chemokines, and three growth factors were measured in serum and in five brain tissue regions. Serum levels of several proinflammatory mediators (eotaxin, interferon-inducible protein 10 [IP-10], keratinocyte chemoattractant [KC], monocyte chemoattractant protein 1 [MCP-1], macrophage inflammatory protein 1alpha [MIP-1α], interleukin [IL]-5, IL-6, tumor necrosis factor alpha, and granulocyte colony-stimulating factor [G-CSF]) were increased after CCI alone. Serum levels of fewer proinflammatory mediators (IL-5, IL-6, regulated upon activation, normal T-cell expressed, and secreted, and G-CSF) were increased after CCI+HS. Serum level of anti-inflammatory IL-10 was significantly increased after CCI+HS versus CCI alone. Brain tissue levels of eotaxin, IP-10, KC, MCP-1, MIP-1α, IL-6, and G-CSF were increased after both CCI and CCI+HS. There were no significant differences between levels after CCI alone and CCI+HS in any mediator. Addition of HS to experimental TBI led to a shift toward an anti-inflammatory serum profile--specifically, a marked increase in IL-10 levels. The brain cytokine and chemokine profile after TBI was minimally affected by the addition of HS.

Pharmacotherapy of traumatic brain injury: state of the science and the road forward: report of the Department of Defense Neurotrauma Pharmacology Workgroup

Despite substantial investments by government, philanthropic, and commercial sources over the past several decades, traumatic brain injury (TBI) remains an unmet medical need and a major source of disability and mortality in both developed and developing societies. The U.S. Department of Defense neurotrauma research portfolio contains more than 500 research projects funded at more than $700 million and is aimed at developing interventions that mitigate the effects of trauma to the nervous system and lead to improved quality of life outcomes. A key area of this portfolio focuses on the need for effective pharmacological approaches for treating patients with TBI and its associated symptoms. The Neurotrauma Pharmacology Workgroup was established by the U.S. Army Medical Research and Materiel Command (USAMRMC) with the overarching goal of providing a strategic research plan for developing pharmacological treatments that improve clinical outcomes after TBI. To inform this plan, the Workgroup (a) assessed the current state of the science and ongoing research and (b) identified research gaps to inform future development of research priorities for the neurotrauma research portfolio. The Workgroup identified the six most critical research priority areas in the field of pharmacological treatment for persons with TBI. The priority areas represent parallel efforts needed to advance clinical care; each requires independent effort and sufficient investment. These priority areas will help the USAMRMC and other funding agencies strategically guide their research portfolios to ensure the development of effective pharmacological approaches for treating patients with TBI.

Endotoxin-induced lung alveolar cell injury causes brain cell damage

Sepsis is the most common cause of acute respiratory distress syndrome, a severe lung inflammatory disorder with an elevated morbidity and mortality. Sepsis and acute respiratory distress syndrome involve the release of inflammatory mediators to the systemic circulation, propagating the cellular and molecular response and affecting distal organs, including the brain. Since it has been reported that sepsis and acute respiratory distress syndrome contribute to brain dysfunction, we investigated the brain-lung crosstalk using a combined experimental in vitro airway epithelial and brain cell injury model. Conditioned medium collected from an in vitro lipopolysaccharide-induced airway epithelial cell injury model using human A549 alveolar cells was subsequently added at increasing concentrations (no conditioned, 2%, 5%, 10%, 15%, 25%, and 50%) to a rat mixed brain cell culture containing both astrocytes and neurons. Samples from culture media and cells from mixed brain cultures were collected before treatment, and at 6 and 24 h for analysis. Conditioned medium at 15% significantly increased apoptosis in brain cell cultures 24 h after treatment, whereas 25% and 50% significantly increased both necrosis and apoptosis. Levels of brain damage markers S100 calcium binding protein B and neuron-specific enolase, interleukin-6, macrophage inflammatory protein-2, as well as matrix metalloproteinase-9 increased significantly after treating brain cells with ≥2% conditioned medium. Our findings demonstrated that human epithelial pulmonary cells stimulated with bacterial lipopolysaccharide release inflammatory mediators that are able to induce a translational clinically relevant and harmful response in brain cells. These results support a brain-lung crosstalk during sepsis and sepsis-induced acute respiratory distress syndrome.

Neuronal CCL2 is upregulated during hepatic encephalopathy and contributes to microglia activation and neurological decline

Background

Acute liver failure leads to systemic complications with one of the most dangerous being a decline in neurological function, termed hepatic encephalopathy. Neurological dysfunction is exacerbated by an increase of toxic metabolites in the brain that lead to neuroinflammation. Following various liver diseases, hepatic and circulating chemokines, such as chemokine ligand 2 (CCL2), are elevated, though their effects on the brain following acute liver injury and subsequent hepatic encephalopathy are unknown. CCL2 is known to activate microglia in other neuropathies, leading to a proinflammatory response. However, the effects of CCL2 on microglia activation and the pathogenesis of hepatic encephalopathy following acute liver injury remain to be determined.

Methods

Hepatic encephalopathy was induced in mice via injection of azoxymethane (AOM) in the presence or absence of INCB 3284 dimesylate (INCB), a chemokine receptor 2 inhibitor, or C 021 dihydrochloride (C021), a chemokine receptor 4 inhibitor. Mice were monitored for neurological decline and time to coma (loss of all reflexes) was recorded. Tissue was collected at coma and used for real-time PCR, immunoblots, ELISA, or immunostaining analyses to assess the activation of microglia and consequences on pro-inflammatory cytokine expression.

Results

Following AOM administration, microglia activation was significantly increased in AOM-treated mice compared to controls. Concentrations of CCL2 in the liver, serum, and cortex were significantly elevated in AOM-treated mice compared to controls. Systemic administration of INCB or C021 reduced liver damage as assessed by serum liver enzyme biochemistry. Administration of INCB or C021 significantly improved the neurological outcomes of AOM-treated mice, reduced microglia activation, reduced phosphorylation of ERK1/2, and alleviated AOM-induced cytokine upregulation.

Conclusions

These findings suggest that CCL2 is elevated systemically following acute liver injury and that CCL2 is involved in both the microglia activation and neurological decline associated with hepatic encephalopathy. Methods used to modulate CCL2 levels and/or reduce CCR2/CCR4 activity may be potential therapeutic targets for the management of hepatic encephalopathy due to acute liver injury.

Temporal course of changes in gene expression suggests a cytokine-related mechanism for long-term hippocampal alteration after controlled cortical impact

Mild traumatic brain injury (mTBI) often has long-term effects on cognitive function and social behavior. Altered gene expression may be predictive of long-term psychological effects of mTBI, even when acute clinical effects are minimal or transient. Controlled cortical impact (CCI), which causes concussive, but nonpenetrant, trauma to underlying (non-cortical) brain, resulting in persistent changes in hippocampal synaptic function, was used as a model of mTBI. The hippocampal transcriptomes of sham-operated or injured male rats at 1, 7, and 30 days postinjury were examined using microarrays comprising a comprehensive set of expressed genes, subsequently confirmed by quantitative reverse-transcriptase polymerase chain reaction. Transcripts encoding the chemokines, chemokine (C-C motif) ligand (Ccl)2 and Ccl7, inflammatory mediators lipocalin-2 (Lcn2) and tissue inhibitor of metalloproteinase 1 (Timp1), immunocyte activators C-C chemokine receptor type 5 (Ccr5) and Fc fragment of IgG, low affinity IIb, receptor (CD32) (Fcgr2b), the major histocompatibility complex II immune response-related genes, Cd74 and RT1 class II, locus Da (RT1-Da), the complement component, C3, and the transcription factor, Kruppel-like factor 4 (Klf4), were identified as early (Ccl2, Ccl7, Lcn2, and Timp1), intermediate (Ccr5, Fcgr2b, Cd74, RT1-Da, and C3), and late (Klf4) markers for bilateral hippocampal response to CCI. Ccl2 and Ccl7 transcripts were up-regulated within 24 h after CCI, and their elevation subsided within 1 week of injury. Other transcriptional changes occurred later and were more stable, some persisting for at least 1 month, suggesting that short-term inflammatory responses trigger longer-term alteration in the expression of genes previously associated with injury, aging, and neuronal function in the brain. These transcriptional responses to mTBI may underlie long-term changes in excitatory and inhibitory neuronal imbalance in hippocampus, leading to long-term behavioral consequences of mTBI.

Phenoxybenzamine is neuroprotective in a rat model of severe traumatic brain injury

Phenoxybenzamine (PBZ) is an FDA approved α-1 adrenergic receptor antagonist that is currently used to treat symptoms of pheochromocytoma. However, it has not been studied as a neuroprotective agent for traumatic brain injury (TBI). While screening neuroprotective candidates, we found that phenoxybenzamine reduced neuronal death in rat hippocampal slice cultures following exposure to oxygen glucose deprivation (OGD). Using this system, we found that phenoxybenzamine reduced neuronal death over a broad dose range (0.1 μM–1 mM) and provided efficacy when delivered up to 16 h post-OGD. We further tested phenoxybenzamine in the rat lateral fluid percussion model of TBI. When administered 8 h after TBI, phenoxybenzamine improved neurological severity scoring and foot fault assessments. At 25 days post injury, phenoxybenzamine treated TBI animals also showed a significant improvement in both learning and memory compared to saline treated controls. We further examined gene expression changes within the cortex following TBI. At 32 h post-TBI phenoxybenzamine treated animals had significantly lower expression of pro-inflammatory signaling proteins CCL2, IL1β, and MyD88, suggesting that phenoxybenzamine may exert a neuroprotective effect by reducing neuroinflammation after TBI. These data suggest that phenonxybenzamine may have application in the treatment of TBI.

Chemokine ligand 2 in the trigeminal ganglion regulates pain induced by experimental tooth movement

OBJECTIVE

To test the hypothesis that the chemokine ligand 2/chemokine receptor 2 (CCL2/CCR2) signaling pathway plays an important role in pain induced by experimental tooth movement.

MATERIALS AND METHODS

Expression of CCL2/CCR2 in the trigeminal ganglion (TG) was determined by Western blotting 0 hours, 4 hours, 1 day, 3 days, 5 days, and 7 days after tooth movement. CCL2 localization and cell size distribution were revealed by immunohistochemistry. The effects of increasing force on CCL2 expression and behavioral changes were investigated. Furthermore, the effects of CCL2/CCR2 antagonists on these changes in pain behaviors were all evaluated. Exogenous CCL2 was injected into periodontal tissues and cultured TG neurons with different concentrations, and then the pain responses or c-fos expression were assessed.

RESULTS

Experimental tooth movement led to a statistically significant increase in CCL2/CCR2 expression from day 3 to day 7, especially in small to medium-sized TG neurons. It also triggered an increase in the time spent on directed face-grooming behaviors in a force magnitude-dependent and CCL2 dose-dependent manner. Pain induced by experimental tooth movement was effectively blocked by a CCR2 antagonist and by CCL2 neutralizing antibody. Also, exogenous CCL2 led to an increase in c-fos expression in cultured TG neurons, which was blocked by CCL2 neutralizing antibody.

CONCLUSIONS

The peripheral CCL2/CCR2 axis is modulated by experimental tooth movement and involved in the development of tooth movement pain.

Preinjury alcohol exposure attenuates the neuroinflammatory response to traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) initiates a neuroinflammatory response that increases the risk of TBI-related mortality. Acute alcohol intoxication at the time of TBI is associated with improved survival. Ethanol is recognized as a systemic immunomodulator that may also impart neuroprotection. The effects of alcohol on TBI-induced neuroinflammation, however, are unknown. We hypothesized that ethanol treatment prior to TBI may provide neuroprotection by diminishing the neuroinflammatory response to injury.

MATERIALS AND METHODS

Mice underwent gavage with ethanol (EtOH) or water (H2O) prior to TBI. Animals were subjected to blunt TBI or sham injury (Sham). Posttraumatic rapid righting reflex (RRR) and apnea times were assessed. Cerebral and serum samples were analyzed by ELISA for inflammatory cytokine levels. Serum neuron-specific enolase (NSE), a biomarker of injury severity, was also measured.

RESULTS

Neurologic recovery from TBI was more rapid in H2O-treated mice compared with EtOH-treated mice. However, EtOH/TBI mice had a 4-fold increase in RRR time compared with EtOH/Sham, whereas H2O/TBI mice had a 15-fold increase in RRR time compared with H2O/Sham. Ethanol intoxication at the time of TBI significantly increased posttraumatic apnea time. Preinjury EtOH treatment was associated with reduced levels of proinflammatory cytokines IL-6, KC, MCP-1, and MIP-1α post TBI. NSE was significantly increased post injury in the H2O/TBI group compared with H2O/Sham but was not significantly reduced by EtOH pretreatment.

CONCLUSIONS

Alcohol treatment prior to TBI reduces the local neuroinflammatory response to injury. The decreased neurologic and inflammatory impact of TBI in acutely intoxicated patients may be responsible for improved clinical outcomes.

Anti-inflammatory and immunomodulatory mechanisms of mesenchymal stem cell transplantation in experimental traumatic brain injury

Background

Previous studies have shown beneficial effects of mesenchymal stem cell (MSC) transplantation in central nervous system (CNS) injuries, including traumatic brain injury (TBI). Potential repair mechanisms involve transdifferentiation to replace damaged neural cells and production of growth factors by MSCs. However, few studies have simultaneously focused on the effects of MSCs on immune cells and inflammation-associated cytokines in CNS injury, especially in an experimental TBI model. In this study, we investigated the anti-inflammatory and immunomodulatory properties of MSCs in TBI-induced neuroinflammation by systemic transplantation of MSCs into a rat TBI model.

Methods/results

MSCs were transplanted intravenously into rats 2 h after TBI. Modified neurologic severity score (mNSS) tests were performed to measure behavioral outcomes. The effect of MSC treatment on neuroinflammation was analyzed by immunohistochemical analysis of astrocytes, microglia/macrophages, neutrophils and T lymphocytes and by measuring cytokine levels [interleukin (IL)-1α, IL-1β, IL-4, IL-6, IL-10, IL-17, tumor necrosis factor-α, interferon-γ, RANTES, macrophage chemotactic protein-1, macrophage inflammatory protein 2 and transforming growth factor-β1] in brain homogenates. The immunosuppression-related factors TNF-α stimulated gene/protein 6 (TSG-6) and nuclear factor-κB (NF-κB) were examined by reverse transcription-polymerase chain reaction and Western blotting. Intravenous MSC transplantation after TBI was associated with a lower density of microglia/macrophages and peripheral infiltrating leukocytes at the injury site, reduced levels of proinflammatory cytokines and increased anti-inflammatory cytokines, possibly mediated by enhanced expression of TSG-6, which may suppress activation of the NF-κB signaling pathway.

Conclusions

The results of this study suggest that MSCs have the ability to modulate inflammation-associated immune cells and cytokines in TBI-induced cerebral inflammatory responses. This study thus offers a new insight into the mechanisms responsible for the immunomodulatory effect of MSC transplantation, with implications for functional neurological recovery after TBI.

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.

Elevated plasma MCP-1 concentration following traumatic brain injury as a potential "predisposition" factor associated with an increased risk for subsequent development of Alzheimer's disease

We explored whether changes in the expression profile of peripheral blood plasma proteins may provide a clinical, readily accessible "window" into the brain, reflecting molecular alterations following traumatic brain injury (TBI) that might contribute to TBI complications. We recruited fourteen TBI and ten control civilian participants for the study, and also analyzed banked plasma specimens from 20 veterans with TBI and 20 control cases. Using antibody arrays and ELISA assays, we explored differentially-regulated protein species in the plasma of TBI compared to healthy controls from the two independent cohorts. We found three protein biomarker species, monocyte chemotactic protein-1 (MCP-1), insulin-like growth factor-binding protein-3, and epidermal growth factor receptor, that are differentially regulated in plasma specimens of the TBI cases. A three-biomarker panel using all three proteins provides the best potential criterion for separating TBI and control cases. Plasma MCP-1 contents are correlated with the severity of TBI and the index of compromised axonal fiber integrity in the frontal cortex. Based on these findings, we evaluated postmortem brain specimens from 7 mild cognitive impairment (MCI) and 7 neurologically normal cases. We found elevated MCP-1 expression in the frontal cortex of MCI cases that are at high risk for developing Alzheimer's disease. Our findings suggest that additional application of the three-biomarker panel to current diagnostic criteria may lead to improved TBI detection and more sensitive outcome measures for clinical trials. Induction of MCP-1 in response to TBI might be a potential predisposing factor that may increase the risk for development of Alzheimer's disease.

An overview of the basic science of concussion and subconcussion: where we are and where we are going

There has been a growing interest in the diagnosis and management of mild traumatic brain injury (TBI), or concussion. Repetitive concussion and subconcussion have been linked to a spectrum of neurological sequelae, including postconcussion syndrome, chronic traumatic encephalopathy, mild cognitive impairment, and dementia pugilistica. A more common risk than chronic traumatic encephalopathy is the season-ending or career-ending effects of concussion or its mismanagement. To effectively prevent and treat the sequelae of concussion, it will be important to understand the basic processes involved. Reviewed in this paper are the forces behind the primary phase of injury in mild TBI, as well as the immediate and delayed cellular events responsible for the secondary phase of injury leading to neuronal dysfunction and possible cell death. Advanced neuroimaging sequences have recently been developed that have the potential to increase the sensitivity of standard MRI to detect both structural and functional abnormalities associated with concussion, and have provided further insight into the potential underlying pathophysiology. Also discussed are the potential long-term effects of repetitive mild TBI, particularly chronic traumatic encephalopathy. Much of the data regarding this syndrome is limited to postmortem analyses, and at present there is no animal model of chronic traumatic encephalopathy described in the literature. As this arena of TBI research continues to evolve, it will be imperative to appropriately model concussive and even subconcussive injuries in an attempt to understand, prevent, and treat the associated chronic neurodegenerative sequelae.

Inflammatory response following diffuse axonal injury

DAI is a leading cause of the patient's death or lasting vegetable state following severe TBI, and up to now the detailed mechanism of axonal injury after head trauma is still unclear. Inflammatory responses have been proved to be an important mechanism of neural injury after TBI. However, most of these studies are concerned with focal cerebral injury following head trauma. In contrast to focal injury, studies on the inflammatory reaction following DAI are only beginning. And in this article, we aimed to review such studies. From the studies reviewed, immune response cells would become reactive around the sites of axonal injury after DAI. Besides, the concentrations of several important inflammatory factors, such as IL-1 family, IL-6 and TNF-ɑ, increased after DAI as well, which implies the participation of inflammatory responses. It can be concluded that inflammatory responses probably participate in the neural injury in DAI, but at present the study of inflammatory responses following DAI is still limited and the clear effects of inflammatory response on axonal injury remain to be more explored.

Controlled cortical impact and craniotomy induce strikingly similar profiles of inflammatory gene expression, but with distinct kinetics

An immediate consequence of traumatic brain injury (TBI) is the induction of an inflammatory response. Mounting data suggest that inflammation is a major contributor to TBI-induced brain damage. However, much remains unknown regarding the induction and regulation of the inflammatory response to TBI. In this study we compared the TBI-induced inflammatory response to severe parenchymal injury (controlled cortical impact) vs. mild brain injury (craniotomy) over a 21-day period. Our data show that both severe and mild brain injury induce a qualitatively similar inflammatory response, involving highly overlapping sets of effector molecules. However, kinetic analysis revealed that the inflammatory response to mild brain injury is of much shorter duration than the response to severe TBI. Specifically, the inflammatory response to severe brain injury persists for at least 21 days, whereas the response to mild brain injury returns to near baseline values within 10 days post-injury. Our data therefore imply that the development of accurate diagnostic tests of TBI severity that are based on imaging or biomarker analysis of the inflammatory response may require repeated measures over at least a 10-day period, post-injury.

Guilty molecules, guilty minds? The conflicting roles of the innate immune response to traumatic brain injury

Traumatic brain injury (TBI) is a complex disease in the most complex organ of the body, whose victims endure lifelong debilitating physical, emotional, and psychosocial consequences. Despite advances in clinical care, there is no effective neuroprotective therapy for TBI, with almost every compound showing promise experimentally having disappointing results in the clinic. The complex and highly interrelated innate immune responses govern both the beneficial and deleterious molecular consequences of TBI and are present as an attractive therapeutic target. This paper discusses the positive, negative, and often conflicting roles of the innate immune response to TBI in both an experimental and clinical settings and highlights recent advances in the search for therapeutic candidates for the treatment of TBI.

Inflammatory regulators of redirected neural migration in the injured brain

Brain injury following stroke or trauma induces the migration of neuroblasts derived from subventricular zone neural precursor cells (NPCs) towards the damaged tissue, where they then have the potential to contribute to repair. Enhancing the recruitment of new cells thus presents an enticing prospect for the development of new therapeutic approaches to treat brain injury; to this end, an understanding of the factors regulating this process is required. During the neuroinflammatory response to ischemic and traumatic brain injuries, a plethora of pro- and anti-inflammatory cytokines, chemokines and growth factors are released in the damaged tissue, and recent work indicates that a variety of these are able to influence injury-induced migration. In this review, we will discuss the contribution of specific chemokines and growth factors towards stimulating NPC migration in the injured brain.

Tumor necrosis factor-α-mediated threonine 435 phosphorylation of p65 nuclear factor-κB subunit in endothelial cells induces vasogenic edema and neutrophil infiltration in the rat piriform cortex following status epilepticus

BACKGROUND

Status epilepticus (SE) induces severe vasogenic edema in the piriform cortex (PC) accompanied by neuronal and astroglial damages. To elucidate the mechanism of SE-induced vasogenic edema, we investigated the roles of tumor necrosis factor (TNF)-α in blood-brain barrier (BBB) disruption during vasogenic edema and its related events in rat epilepsy models provoked by pilocarpine-induced SE.

METHODS

SE was induced by pilocarpine in rats that were intracerebroventricularly infused with saline-, and soluble TNF p55 receptor (sTNFp55R) prior to SE induction. Thereafter, we performed Fluoro-Jade B staining and immunohistochemical studies for TNF-α and NF-κB subunits.

RESULTS

Following SE, most activated microglia showed strong TNF-α immunoreactivity. In addition, TNF p75 receptor expression was detected in endothelial cells as well as astrocytes. In addition, only p65-Thr435 phosphorylation was increased in endothelial cells accompanied by SMI-71 expression (an endothelial barrier antigen). Neutralization of TNF-α by soluble TNF p55 receptor (sTNFp55R) infusion attenuated SE-induced vasogenic edema and neuronal damages via inhibition of p65-Thr435 phosphorylation in endothelial cells. Furthermore, sTNFp55R infusion reduced SE-induced neutrophil infiltration in the PC.

CONCLUSION

These findings suggest that impairments of endothelial cell functions via TNF-α-mediated p65-Thr 485 NF-κB phosphorylation may be involved in SE-induced vasogenic edema. Subsequently, vasogenic edema results in extensive neutrophil infiltration and neuronal-astroglial loss.

Immunoexcitotoxicity as a central mechanism in chronic traumatic encephalopathy-A unifying hypothesis

Some individuals suffering from mild traumatic brain injuries, especially repetitive mild concussions, are thought to develop a slowly progressive encephalopathy characterized by a number of the neuropathological elements shared with various neurodegenerative diseases. A central pathological mechanism explaining the development of progressive neurodegeneration in this subset of individuals has not been elucidated. Yet, a large number of studies indicate that a process called immunoexcitotoxicity may be playing a central role in many neurodegenerative diseases including chronic traumatic encephalopathy (CTE). The term immunoexcitotoxicity was first coined by the lead author to explain the evolving pathological and neurodevelopmental changes in autism and the Gulf War Syndrome, but it can be applied to a number of neurodegenerative disorders. The interaction between immune receptors within the central nervous system (CNS) and excitatory glutamate receptors trigger a series of events, such as extensive reactive oxygen species/reactive nitrogen species generation, accumulation of lipid peroxidation products, and prostaglandin activation, which then leads to dendritic retraction, synaptic injury, damage to microtubules, and mitochondrial suppression. In this paper, we discuss the mechanism of immunoexcitotoxicity and its link to each of the pathophysiological and neurochemical events previously described with CTE, with special emphasis on the observed accumulation of hyperphosphorylated tau.

Peripheral immune cells in the pathology of traumatic brain injury?

PURPOSE OF REVIEW

This review will consider the reasons why the inhibition of leucocyte recruitment after traumatic brain injury has not been demonstrated but should remain an area of active interest.

RECENT FINDINGS

Focal lesions to the brain display a characteristic inflammatory response with infiltration of peripheral immune cells after injury. These cells are believed to be important because they contain and release a multitude of inflammatory mediators associated with increased tissue injury. Furthermore a large body of evidence from ischaemic injuries suggests that inhibition of leucocyte recruitment can reduce injury and improve outcome. However, therapeutic efficacy has not been demonstrated in clinical trials and for traumatic injuries the results are less convincing.

SUMMARY

A greater appreciation of the timing of assessment, leucocyte subsets and the extended inflammatory response will be discussed.

Stem cells decreased neuronal cell death after hypoxic stress in primary fetal rat neurons in vitro

To explore stem cell-mediated neuronal protection through extracellular signaling pathways by transplanted stem cells, we sought to identify potential candidate molecules responsible for neuronal protection using an in vitro coculture system. Primary fetal rat hippocampal neurons underwent hypoxia (≤1% oxygen) for 96 h nad then were returned to a normoxic condition. The study group then received rat umbilical cord matrix-derived stem cells, while the control group received fresh media only. The experimental group showed decreased neuronal apoptosis compared to the control group [44.5 ± 1.6% vs. 71.0 ± 4.2% (mean ± SD, p = 0.0005) on day 5] and higher neuronal survival (4.9 ± 1.2 cells/100× field vs. 2.2 ± 0.3, p = 0.02 on day 5). Among 90 proteins evaluated using a protein array, stem cell coculture media showed increased protein secretion of TIMP-1 (5.61-fold), TIMP-2 (4.88), CNTF-Rα (3.42), activin A (2.20), fractalkine (2.04), CCR4 (2.02), and decreased secretion in MIP-2 (0.30-fold), AMPK α1 (0.43), TROY (0.48), and TIMP-3 (0.50). This study demonstrated that coculturing stem cells with primary neurons in vitro decreased neuronal cell death after hypoxia with significantly altered protein secretion. The results suggest that stem cells may offer neuronal protection through extracellular signaling.

Altered hippocampal synaptic transmission in transgenic mice with astrocyte-targeted enhanced CCL2 expression

Elevated expression of neuroinflammatory factors in the central nervous system (CNS) contributes to the cognitive impairment in CNS disorders such as injury, disease and neurodegenerative disorders. However, information on the role of specific neuroimmune factors in normal and abnormal CNS function is limited. In this study, we investigated the effects of chronic exposure to the chemokine CCL2 on hippocampal synaptic function at the Schaffer collateral-CA1 synapse, a synapse that is known to play an important role in cognitive functions such as memory and learning. Synaptic function was measured in vitro using hippocampal slices obtained from transgenic mice that express elevated levels of CCL2 in the CNS through astrocyte expression and their non-transgenic littermate controls. Extracellular field potential electrophysiological recordings showed a significant reduction in the magnitude of synaptic responses in hippocampal slices from the CCL2 transgenic mice compared with slices from non-transgenic littermate controls. Two forms of short-term synaptic plasticity (post-tetanic potentiation and short-term potentiation) thought to be important cellular mechanisms of short-term memory were enhanced in hippocampal slices from CCL2 transgenic mice compared to non-transgenic hippocampal slices, whereas long-term synaptic plasticity (LTP), which is critical to long-term memory formation, was not altered. Western blot analysis of hippocampus from the CCL2 transgenic mice and non-transgenic mice showed no change in level of neuronal specific enolase, a neuronal specific protein, GFAP, an astrocyte specific protein, and several synaptic proteins compared with non-transgenic littermate controls. These results show that CCL2, which is known to be chronically produced at elevated levels within the CNS in a number of CNS disorders, can significantly alter hippocampal function and implicate a role for CCL2 in the cognitive dysfunction associated with these CNS disorders.

Neuroprotective effect of neuroserpin in rat primary cortical cultures after oxygen and glucose deprivation and tPA

Besides its role as a thrombolytic agent, tissue plasminogen activator (tPA) triggers harmful effects in the brain parenchyma after stroke, such as inflammation, excitotoxicity and basal lamina degradation. Neuroserpin, a natural inhibitor of tPA, has shown neuroprotective effects in animal models of brain infarct. However, the molecular mechanisms of neuroserpin-mediated neuroprotection after brain ischemia remain to be well characterized. Then, our aim was to investigate such mechanisms in primary mixed cortical cell cultures after oxygen and glucose deprivation (OGD). Primary rat mixed cortical cultures containing both astrocytes and neurons were subjected to OGD for 150min and subsequently treated with either tPA (5μg/mL), neuroserpin (0.125, 0.25, 0.5 or 1μM), and tPA together with neuroserpin at the mentioned doses. Twenty-four hours after treatment, LDH release, caspase-3 activity, MCP-1, MIP-2, active MMP-9, GRO/KC and COX-2 were measured. Statistical differences were analyzed using Student's t-test or one-way ANOVA as appropriate. Treatment with tPA after OGD increased LDH release, active MMP-9, MCP-1 and MIP-2 (all p≤0.05), but not caspase-3, GRO/KC or COX-2 compared to control. Treatment with neuroserpin after OGD decreased LDH release and active MMP-9 (all p≤0.05). It had no effect on caspase-3 activity, or on MCP-1, MIP-2, GRO/KC or COX-2 expression compared to control. Administration of tPA together with neuroserpin decreased LDH release, active MMP-9 and MIP-2 (all p≤0.05) and showed no effect on MCP-1, GRO/KC or COX-2 compared to control. Our results suggest that neuroprotective activity of neuroserpin involves attenuation on tPA-mediated mechanisms of inflammation and BBB disruption after brain ischemia.

Identification of potentially neuroprotective genes upregulated by neurotrophin treatment of CA3 neurons in the injured brain

Specific neurotrophic factors mediate histological and/or functional improvement in animal models of traumatic brain injury (TBI). In previous work, several lines of evidence indicated that the mammalian neurotrophin NT-4/5 is neuroprotective for hippocampal CA3 pyramidal neurons after experimental TBI. We hypothesized that NT-4/5 neuroprotection is mediated by changes in the expression of specific sets of genes, and that NT-4/5-regulated genes are potential therapeutic targets for blocking delayed neuronal death after TBI. In this study, we performed transcription profiling analysis of CA3 neurons to identify genes regulated by lateral fluid percussion injury, or by treatment with the trkB ligands NT-4/5 or brain-derived neurotrophic factor (BDNF). The results indicate extensive overlap between genes upregulated by neurotrophins and genes upregulated by injury, suggesting that the mechanism behind neurotrophin neuroprotection may mimic the brain's endogenous protective response. A subset of genes selected for further study in vitro exhibited neuroprotection against glutamate excitotoxicity. The neuroprotective genes identified in this study were upregulated at 30 h post-injury, and are thus expected to act during a clinically useful time frame of hours to days after injury. Modulation of these factors and pathways by genetic manipulation or small molecules may confer hippocampal neuroprotection in vivo in preclinical models of TBI.

Expression analysis of the early chemokine response 4 h after in vitro traumatic brain injury

OBJECTIVE AND DESIGN

The importance of cytokine- and chemokine-mediated neuroinflammation in the progress of brain injury is becoming increasingly evident. We investigated the early local cytokine and chemokine expression and the development of tissue injury after moderate mechanical hippocampus trauma.

MATERIAL OR SUBJECTS

Mouse organotypic hippocampal slice cultures.

TREATMENT

Drop-weight trauma in the CA1 region of the hippocampus.

METHODS

Staining of necrotic tissue, PCR array and evaluation, real-time PCR, statistical analysis with a two-tailed, independent t test.

RESULTS

At 12 and 24 h after trauma, the tissue injury spread from the primary mechanical lesion to the entire hippocampal formation. A pronounced up-regulation of distinct chemokine transcripts was found 4 h after in vitro traumatic brain injury which preceded the development of the secondary injury.

CONCLUSIONS

The enhanced expression of inflammatory genes might contribute to the development of the secondary trauma and could pinpoint future neuroinflammatory and neuroprotective targets for research and treatment.

P2X7 receptor regulates leukocyte infiltrations in rat frontoparietal cortex following status epilepticus

BACKGROUND

In the present study, we investigated the roles of P2X7 receptor in recruitment and infiltration of neutrophil during epileptogenesis in rat epilepsy models.

METHODS

Status epilepticus (SE) was induced by pilocarpine in rats that were intracerebroventricularly infused with either saline, 2',3'-O-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP), adenosine 5'-triphosphate-2',3'-dialdehyde (OxATP), or IL-1Ra (interleukin 1 receptor antagonist) prior to SE induction. Thereafter, we performed immunohistochemical studies for myeloperoxidase (MPO), CD68, interleukin-1β (IL-1β), monocyte chemotactic protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2).

RESULTS

In saline-infused animals, neutrophils and monocytes were observed in frontoparietal cortex (FPC) at 1 day and 2 days after SE, respectively. In BzATP-infused animals, infiltrations of neutrophils and monocytes into the FPC were detected at 12 hr and 1 day after SE, respectively. In OxATP-infused animals, neutrophils and monocytes infiltrated into the FPC at 1 day and 2 days after SE, respectively. However, the numbers of both classes of leukocytes were significantly lower than those observed in the saline-infused group. In piriform cortex (PC), massive leukocyte infiltration was detected in layers III/IV of saline-infused animals at 1-4 days after induction of SE. BzATP or OxATP infusion did not affect neutrophil infiltration in the PC. In addition, P2X7 receptor-mediated MCP-1 (released from microglia)/MIP-2 (released from astrocytes) regulation was related to SE-induced leukocyte infiltration in an IL-1β-independent manner.

CONCLUSIONS

Our findings suggest that selective regulation of P2X7 receptor-mediated neutrophil infiltration may provide new therapeutic approaches to SE or epilepsy.

Deficiency of the chemokine receptor CXCR2 attenuates neutrophil infiltration and cortical damage following closed head injury

The contribution of infiltrated neutrophils to secondary damage following traumatic brain injury remains controversial. Chemokines that regulate neutrophil migration by signaling through the CXCR2 receptor are markedly elevated by brain injury and are associated with the propagation of secondary damage. This study thus investigated the function of CXCR2 in posttraumatic inflammation and secondary degeneration by examining Cxcr2-deficient (Cxcr2(-/-)) mice over 14 days following closed head injury (CHI). We demonstrate a significant attenuation of neutrophil infiltration in Cxcr2(-/-) mice at 12 hours and 7 days after CHI, despite increased levels of CXC neutrophil-attracting chemokines in the lesioned cortex. This coincides with reduced tissue damage, neuronal loss, and cell death in Cxcr2(-/-) mice compared to wild-type controls, with heterozygotes showing intermediate responses. In contrast, blood-brain barrier permeability and functional recovery did not appear to be affected by Cxcr2 deletion. This study highlights the deleterious contribution of neutrophils to posttraumatic neurodegeneration and demonstrates the importance of CXC chemokine signaling in this process. Therefore, CXCR2 antagonistic therapeutics currently in development for other inflammatory conditions may also be of benefit in posttraumatic neuroinflammation.