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

The Role of Nanotechnology in Understanding the Pathophysiology of Traumatic Brain Injury

Recently, traumatic brain injury (TBI) has been a growing disorder due to frequent brain dysfunction. The Glasgow Coma Scale expresses TBI as classified as having mild, moderate, or severe brain effects, according to the effects on the brain. Brain receptors undergo various modifications in their pathology through chemical synaptic pathways, leading to depression, Alzheimer's, and Parkinson's disease. These brain disorders can be controlled using central receptors such as dopamine, glutamate, and γ-aminobutyric acid, which are clearly explained in this review. Furthermore, there are many complications in TBI's clinical trials and diagnostics, leading to insignificant treatment, causing permanent neuro-damage, physical disability, and even death. Bio-screening and conventional molecular-based therapies are inappropriate due to poor preclinical testing and delayed recovery. Hence, modern nanotechnology utilizing nanopulsed laser therapy and advanced nanoparticle insertion will be suitable for TBI's diagnostics and treatment. In recent days, nanotechnology has an important role in TBI control and provides a higher success rate than conventional therapies. This review highlights the pathophysiology of TBI by comprising the drawbacks of conventional techniques and supports suitable modern alternates for treating TBI.

Neuroinflammation after Traumatic Brain Injury Is Enhanced in Activating Transcription Factor 3 Mutant Mice

Traumatic brain injury (TBI) induces a neuroinflammatory response resulting in astrocyte and microglia activation at the lesion site. This involves upregulation of neuroinflammatory genes, including chemokines and interleukins. However, so far, there is lack of knowledge on transcription factors (TFs) modulating this TBI-associated gene expression response. Herein, we analyzed activating transcription factor 3 (ATF3), a TF encoding a regeneration-associated gene (RAG) predominantly studied in peripheral nervous system (PNS) injury. ATF3 contributes to PNS axon regeneration and was shown before to regulate inflammatory processes in other injury models. In contrast to PNS injury, data on ATF3 in central nervous system (CNS) injury are sparse. We used Atf3 mouse mutants and a closed-head weight-drop-based TBI model in adult mice to target the rostrolateral cortex resulting in moderate injury severity. Post-TBI, ATF3 was upregulated already at early time points (i.e,. 1-4 h) post-injury in the brain. Mortality and weight loss upon TBI were slightly elevated in Atf3 mutants. ATF3 deficiency enhanced TBI-induced paresis and hematoma formation, suggesting that ATF3 limits these injury outcomes in wild-type mice. Next, we analyzed TBI-associated RAG and inflammatory gene expression in the cortical impact area. In contrast to the PNS, only some RAGs (Atf3, Timp1, and Sprr1a) were induced by TBI, and, surprisingly, some RAG encoding neuropeptides were downregulated. Notably, we identified ATF3 as TF-regulating proneuroinflammatory gene expression, including CCL and CXCL chemokines (Ccl2, Ccl3, Ccl4, and Cxcl1) and lipocalin. In Atf3 mutant mice, mRNA abundance was further enhanced upon TBI compared to wild-type mice, suggesting immune gene repression by wild-type ATF3. In accord, more immune cells were present in the lesion area of ATF3-deficient mice. Overall, we identified ATF3 as a new TF-mediating TBI-associated CNS inflammatory responses.

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.

Acute death of astrocytes in blast-exposed rat organotypic hippocampal slice cultures

Blast traumatic brain injury (bTBI) affects civilians, soldiers, and veterans worldwide and presents significant health concerns. The mechanisms of neurodegeneration following bTBI remain elusive and current therapies are largely ineffective. It is important to better characterize blast-evoked cellular changes and underlying mechanisms in order to develop more effective therapies. In the present study, our group utilized rat organotypic hippocampal slice cultures (OHCs) as an in vitro system to model bTBI. OHCs were exposed to either 138 ± 22 kPa (low) or 273 ± 23 kPa (high) overpressures using an open-ended helium-driven shock tube, or were assigned to sham control group. At 2 hours (h) following injury, we have characterized the astrocytic response to a blast overpressure. Immunostaining against the astrocytic marker glial fibrillary acidic protein (GFAP) revealed acute shearing and morphological changes in astrocytes, including clasmatodendrosis. Moreover, overlap of GFAP immunostaining and propidium iodide (PI) indicated astrocytic death. Quantification of the number of dead astrocytes per counting area in the hippocampal cornu Ammonis 1 region (CA1), demonstrated a significant increase in dead astrocytes in the low- and high-blast, compared to sham control OHCs. However only a small number of GFAP-expressing astrocytes were co-labeled with the apoptotic marker Annexin V, suggesting necrosis as the primary type of cell death in the acute phase following blast exposure. Moreover, western blot analyses revealed calpain mediated breakdown of GFAP. The dextran exclusion additionally indicated membrane disruption as a potential mechanism of acute astrocytic death. Furthermore, although blast exposure did not evoke significant changes in glutamate transporter 1 (GLT-1) expression, loss of GLT-1-expressing astrocytes suggests dysregulation of glutamate uptake following injury. Our data illustrate the profound effect of blast overpressure on astrocytes in OHCs at 2 h following injury and suggest increased calpain activity and membrane disruption as potential underlying mechanisms.

Loss of PAFR prevents neuroinflammation and brain dysfunction after traumatic brain injury

Traumatic brain injury (TBI) is a principal cause of death and disability worldwide, which is a major public health problem. Death caused by TBI accounts for a third of all damage related illnesses, which 75% TBI occurred in low and middle income countries. With the increasing use of motor vehicles, the incidence of TBI has been at a high level. The abnormal brain functions of TBI patients often show the acute and long-term neurological dysfunction, which mainly associated with the pathological process of malignant brain edema and neuroinflammation in the brain. Owing to the neuroinflammation lasts for months or even years after TBI, which is a pivotal causative factor that give rise to neurodegenerative disease at late stage of TBI. Studies have shown that platelet activating factor (PAF) inducing inflammatory reaction after TBI could not be ignored. The morphological and behavioral abnormalities after TBI in wild type mice are rescued by general knockout of PAFR gene that neuroinflammation responses and cognitive ability are improved. Our results thus define a key inflammatory molecule PAF that participates in the neuroinflammation and helps bring about cerebral dysfunction during the TBI acute phase.

Analysis of the Role of CX3CL1 (Fractalkine) and Its Receptor CX3CR1 in Traumatic Brain and Spinal Cord Injury: Insight into Recent Advances in Actions of Neurochemokine Agents

CX3CL1 (fractalkine) is the only member of the CX3C (delta) subfamily of chemokines which is unique and combines the properties of both chemoattractant and adhesion molecules. The two-form ligand can exist either in a soluble form, like all other chemokines, and as a membrane-anchored molecule. CX3CL1 discloses its biological properties through interaction with one dedicated CX3CR1 receptor which belongs to a family of G protein-coupled receptors (GPCR). The CX3CL1/CX3CR1 axis acts in many physiological phenomena including those occurring in the central nervous system (CNS), by regulating the interactions between neurons, microglia, and immune cells. Apart from the role under physiological conditions, the CX3CL1/CX3CR1 axis was implied to have a role in different neuropathologies such as traumatic brain injury (TBI) and spinal cord injury (SCI). CNS injuries represent a serious public health problem, despite improvements in therapeutic management. To date, no effective treatment has been determined, so they constitute a leading cause of death and severe disability. The course of TBI and SCI has two consecutive poorly demarcated phases: the initial, primary injury and secondary injury. Recent evidence has implicated the role of the CX3CL1/CX3CR1 axis in neuroinflammatory processes occurring after CNS injuries. The importance of the CX3CL1/CX3CR1 axis in the pathophysiology of TBI and SCI in the context of systemic and direct local immune response is still under investigation. This paper, based on a review of the literature, updates and summarizes the current knowledge about CX3CL1/CX3CR1 axis involvement in TBI and SCI pathogenesis, indicating possible molecular and cellular mechanisms with a potential target for therapeutic intervention.

Bilateral gene interaction hierarchy analysis of the cell death gene response emphasizes the significance of cell cycle genes following unilateral traumatic brain injury

BACKGROUND

Delayed or secondary cell death that is caused by a cascade of cellular and molecular processes initiated by traumatic brain injury (TBI) may be reduced or prevented if an effective neuroprotective strategy is employed. Microarray and subsequent bioinformatic analyses were used to determine which genes, pathways and networks were significantly altered 24 h after unilateral TBI in the rat. Ipsilateral hemi-brain, the corresponding contralateral hemi-brain, and naïve (control) brain tissue were used for microarray analysis.

RESULTS

Ingenuity Pathway Analysis showed cell death and survival (CD) to be a top molecular and cellular function associated with TBI on both sides of the brain. One major finding was that the overall gene expression pattern suggested an increase in CD genes in ipsilateral brain tissue and suppression of CD genes contralateral to the injury which may indicate an endogenous protective mechanism. We created networks of genes of interest (GOI) and ranked the genes by the number of direct connections each had in the GOI networks, creating gene interaction hierarchies (GIHs). Cell cycle was determined from the resultant GIHs to be a significant molecular and cellular function in post-TBI CD gene response.

CONCLUSIONS

Cell cycle and apoptosis signalling genes that were highly ranked in the GIHs and exhibited either the inverse ipsilateral/contralateral expression pattern or contralateral suppression were identified and included STAT3, CCND1, CCND2, and BAX. Additional exploration into the remote suppression of CD genes may provide insight into neuroprotective mechanisms that could be used to develop therapies to prevent cell death following TBI.

Acute Response of the Hippocampal Transcriptome Following Mild Traumatic Brain Injury After Controlled Cortical Impact in the Rat

We have previously demonstrated that mild controlled cortical impact (mCCI) injury to rat cortex causes indirect, concussive injury to underlying hippocampus and other brain regions, providing a reproducible model for mild traumatic brain injury (mTBI) and its neurochemical, synaptic, and behavioral sequelae. Here, we extend a preliminary gene expression study of the hippocampus-specific events occurring after mCCI and identify 193 transcripts significantly upregulated, and 21 transcripts significantly downregulated, 24 h after mCCI. Fifty-three percent of genes altered by mCCI within 24 h of injury are predicted to be expressed only in the non-neuronal/glial cellular compartment, with only 13% predicted to be expressed only in neurons. The set of upregulated genes following mCCI was interrogated using Ingenuity Pathway Analysis (IPA) augmented with manual curation of the literature (190 transcripts accepted for analysis), revealing a core group of 15 first messengers, mostly inflammatory cytokines, predicted to account for >99% of the transcript upregulation occurring 24 h after mCCI. Convergent analysis of predicted transcription factors (TFs) regulating the mCCI target genes, carried out in IPA relative to the entire Affymetrix-curated transcriptome, revealed a high concordance with TFs regulated by the cohort of 15 cytokines/cytokine-like messengers independently accounting for upregulation of the mCCI transcript cohort. TFs predicted to regulate transcription of the 193-gene mCCI cohort also displayed a high degree of overlap with TFs predicted to regulate glia-, rather than neuron-specific genes in cortical tissue. We conclude that mCCI predominantly affects transcription of non-neuronal genes within the first 24 h after insult. This finding suggests that early non-neuronal events trigger later permanent neuronal changes after mTBI, and that early intervention after mTBI could potentially affect the neurochemical cascade leading to later reported synaptic and behavioral dysfunction.

What's New in Traumatic Brain Injury: Update on Tracking, Monitoring and Treatment

Traumatic brain injury (TBI), defined as an alteration in brain functions caused by an external force, is responsible for high morbidity and mortality around the world. It is important to identify and treat TBI victims as early as possible. Tracking and monitoring TBI with neuroimaging technologies, including functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), positron emission tomography (PET), and high definition fiber tracking (HDFT) show increasing sensitivity and specificity. Classical electrophysiological monitoring, together with newly established brain-on-chip, cerebral microdialysis techniques, both benefit TBI. First generation molecular biomarkers, based on genomic and proteomic changes following TBI, have proven effective and economical. It is conceivable that TBI-specific biomarkers will be developed with the combination of systems biology and bioinformation strategies. Advances in treatment of TBI include stem cell-based and nanotechnology-based therapy, physical and pharmaceutical interventions and also new use in TBI for approved drugs which all present favorable promise in preventing and reversing TBI.

Effects of blast overpressure on neurons and glial cells in rat organotypic hippocampal slice cultures

Due to recent involvement in military conflicts, and an increase in the use of explosives, there has been an escalation in the incidence of blast-induced traumatic brain injury (bTBI) among US military personnel. Having a better understanding of the cellular and molecular cascade of events in bTBI is prerequisite for the development of an effective therapy that currently is unavailable. The present study utilized organotypic hippocampal slice cultures (OHCs) exposed to blast overpressures of 150 kPa (low) and 280 kPa (high) as an in vitro bTBI model. Using this model, we further characterized the cellular effects of the blast injury. Blast-evoked cell death was visualized by a propidium iodide (PI) uptake assay as early as 2 h post-injury. Quantification of PI staining in the cornu Ammonis 1 and 3 (CA1 and CA3) and the dentate gyrus regions of the hippocampus at 2, 24, 48, and 72 h following blast exposure revealed significant time dependent effects. OHCs exposed to 150 kPa demonstrated a slow increase in cell death plateauing between 24 and 48 h, while OHCs from the high-blast group exhibited a rapid increase in cell death already at 2 h, peaking at ~24 h post-injury. Measurements of lactate dehydrogenase release into the culture medium also revealed a significant increase in cell lysis in both low- and high-blast groups compared to sham controls. OHCs were fixed at 72 h post-injury and immunostained for markers against neurons, astrocytes, and microglia. Labeling OHCs with PI, neuronal, and glial markers revealed that the blast-evoked extensive neuronal death and to a lesser extent loss of glial cells. Furthermore, our data demonstrated activation of astrocytes and microglial cells in low- and high-blasted OHCs, which reached a statistically significant difference in the high-blast group. These data confirmed that our in vitro bTBI model is a useful tool for studying cellular and molecular changes after blast exposure.

Regulation of brain microglia by female gonadal steroids

Microglial cells are the primary mediators of the CNS immune defense system and crucial for shaping inflammatory responses. They represent a highly dynamic cell population which is constantly moving and surveying their environment. Acute brain damage causes a local attraction and activation of this immune cell type which involves neuron-to-glia and glia-to-glia interactions. The prevailing view attributes microglia a "negative" role such as defense and debris elimination. More topical studies also suggest a protective and "positive" regulatory function. Estrogens and progestins exert anti-inflammatory and neuroprotective effects in the CNS in acute and chronic brain diseases. Recent work revealed that microglial cells express subsets of classical and non-classical estrogen and progesterone receptors in a highly dynamic way. In this review article, we would like to stress the importance of microglia for the spreading of neural damage during hypoxia, their susceptibility to functional modulation by sex steroids, the potency of sex hormones to switch microglia from a pro-inflammatory M1 to neuroprotective M2 phenotype, and the regulation of pro- and anti-inflammatory properties including the inflammasome. We will further discuss the possibility that the neuroprotective action of sex steroids in the brain involves an early and direct modulation of local microglia cell function. This article is part of a Special Issue entitled 'Sex steroids and brain disorders'.

A systems biology strategy to identify molecular mechanisms of action and protein indicators of traumatic brain injury

The multifactorial nature of traumatic brain injury (TBI), especially the complex secondary tissue injury involving intertwined networks of molecular pathways that mediate cellular behavior, has confounded attempts to elucidate the pathology underlying the progression of TBI. Here, systems biology strategies are exploited to identify novel molecular mechanisms and protein indicators of brain injury. To this end, we performed a meta-analysis of four distinct high-throughput gene expression studies involving different animal models of TBI. By using canonical pathways and a large human protein-interaction network as a scaffold, we separately overlaid the gene expression data from each study to identify molecular signatures that were conserved across the different studies. At 24 hr after injury, the significantly activated molecular signatures were nonspecific to TBI, whereas the significantly suppressed molecular signatures were specific to the nervous system. In particular, we identified a suppressed subnetwork consisting of 58 highly interacting, coregulated proteins associated with synaptic function. We selected three proteins from this subnetwork, postsynaptic density protein 95, nitric oxide synthase 1, and disrupted in schizophrenia 1, and hypothesized that their abundance would be significantly reduced after TBI. In a penetrating ballistic-like brain injury rat model of severe TBI, Western blot analysis confirmed our hypothesis. In addition, our analysis recovered 12 previously identified protein biomarkers of TBI. The results suggest that systems biology may provide an efficient, high-yield approach to generate testable hypotheses that can be experimentally validated to identify novel mechanisms of action and molecular indicators of TBI.

Neuroprotection by gonadal steroid hormones in acute brain damage requires cooperation with astroglia and microglia

The neuroactive steroids 17β-estradiol and progesterone control a broad spectrum of neural functions. Besides their roles in the regulation of classical neuroendocrine loops, they strongly influence motor and cognitive systems, behavior, and modulate brain performance at almost every level. Such a statement is underpinned by the widespread and lifelong expression pattern of all types of classical and non-classical estrogen and progesterone receptors in the CNS. The life-sustaining power of neurosteroids for tattered or seriously damaged neurons aroused interest in the scientific community in the past years to study their ability for therapeutic use under neuropathological challenges. Documented by excellent studies either performed in vitro or in adequate animal models mimicking acute toxic or chronic neurodegenerative brain disorders, both hormones revealed a high potency to protect neurons from damage and saved neural systems from collapse. Unfortunately, neurons, astroglia, microglia, and oligodendrocytes are comparably target cells for both steroid hormones. This hampers the precise assignment and understanding of neuroprotective cellular mechanisms activated by both steroids. In this article, we strive for a better comprehension of the mutual reaction between these steroid hormones and the two major glial cell types involved in the maintenance of brain homeostasis, astroglia and microglia, during acute traumatic brain injuries such as stroke and hypoxia. In particular, we attempt to summarize steroid-activated cellular signaling pathways and molecular responses in these cells and their contribution to dampening neuroinflammation and neural destruction. This article is part of a Special Issue entitled 'CSR 2013'.

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.

Gene expression patterns following unilateral traumatic brain injury reveals a local pro-inflammatory and remote anti-inflammatory response

Background

Traumatic brain injury (TBI) results in irreversible damage at the site of impact and initiates cellular and molecular processes that lead to secondary neural injury in the surrounding tissue. We used microarray analysis to determine which genes, pathways and networks were significantly altered using a rat model of TBI. Adult rats received a unilateral controlled cortical impact (CCI) and were sacrificed 24 h post-injury. The ipsilateral hemi-brain tissue at the site of the injury, the corresponding contralateral hemi-brain tissue, and naïve (control) brain tissue were used for microarray analysis. Ingenuity Pathway Analysis (IPA) software was used to identify molecular pathways and networks that were associated with the altered gene expression in brain tissues following TBI.

Results

Inspection of the top fifteen biological functions in IPA associated with TBI in the ipsilateral tissues revealed that all had an inflammatory component. IPA analysis also indicated that inflammatory genes were altered on the contralateral side, but many of the genes were inversely expressed compared to the ipsilateral side. The contralateral gene expression pattern suggests a remote anti-inflammatory molecular response. We created a network of the inversely expressed common (i.e., same gene changed on both sides of the brain) inflammatory response (IR) genes and those IR genes included in pathways and networks identified by IPA that changed on only one side. We ranked the genes by the number of direct connections each had in the network, creating a gene interaction hierarchy (GIH). Two well characterized signaling pathways, toll-like receptor/NF-kappaB signaling and JAK/STAT signaling, were prominent in our GIH.

Conclusions

Bioinformatic analysis of microarray data following TBI identified key molecular pathways and networks associated with neural injury following TBI. The GIH created here provides a starting point for investigating therapeutic targets in a ranked order that is somewhat different than what has been presented previously. In addition to being a vehicle for identifying potential targets for post-TBI therapeutic strategies, our findings can also provide a context for evaluating the potential of therapeutic agents currently in development.

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.

Genomic, transcriptomic, and epigenomic approaches to recovery after acquired brain injury

Genomics and its related fields have expanded rapidly, primarily because of the potential utility for clinical decision making and improving our understanding of the pathophysiology of complex conditions. The state of the science and technology associated with this field is such that current and future health care providers, when consulting with new patients about their acquired brain injury and options for rehabilitation, will use genetic information as a routine part of the process, which may include information received from a laboratory report that uses transcriptomic data, informs regarding patient prognosis, and makes recommendations for individualized therapeutic approaches to optimize recovery. This may sound like science fiction, but, in the field of oncology, it is the norm for breast cancer and, more recently, for colon cancer, with expansion to other types of cancer on the horizon as research data continue to contribute to the understanding of the pathophysiology of these conditions. Something similar for rehabilitation after acquired brain injury is much further off on the horizon. However, it is a possibility that will never be realized if the community of scientists and health care providers who work with these patients do not have the knowledge or expertise to embrace genomics and related approaches. This article discusses these approaches, some practical considerations for using such approaches, and what is currently published in this area with regard to brain injury.