Expression profiling following traumatic brain injury: a review

Clinical Theragnostic Signature of Extracellular Vesicles in Traumatic Brain Injury (TBI)

Traumatic brain injury (TBI) is a common cause of disability and fatality worldwide. Depending on the clinical presentation, it is a type of acquired brain damage that can be mild, moderate, or severe. The degree of patient's discomfort, prognosis, therapeutic approach, survival rates, and recurrence can all be strongly impacted by an accurate diagnosis made early on. The Glasgow Coma Scale (GCS), along with neuroimaging (MRI (Magnetic Resonance Imaging) and CT scan), is a neurological assessment tools used to evaluate and categorize the severity of TBI based on the patient's level of consciousness, eye opening, and motor response. Extracellular vesicles (EVs) are a growing domain, explaining neurological complications in a more detailed manner. EVs, in general, play a role in cellular communication. Its molecular signature such as DNA, RNA, protein, etc. contributes to the status (health or pathological stage) of the parental cell. Brain-derived EVs support more specific screening (diagnostic and prognostic) in TBI research. Therapeutic impact of EVs are more promising for aiding in TBI healing. It is nontoxic, biocompatible, and capable of crossing the blood-brain barrier (BBB) to transport therapeutic molecules. This review has highlighted the relationships between EVs and TBI theranostics, EVs and TBI-related clinical trials, and related research domain-associated challenges and solutions. This review motivates further exploration of associations between EVs and TBI and develops a better approach to TBI management.

Traumatic brain injury induced by exposure to blast overpressure via ear canal

Exposure to explosive shockwave often leads to blast-induced traumatic brain injury in military and civilian populations. Unprotected ears are most often damaged following exposure to blasts. Although there is an association between tympanic membrane perforation and TBI in blast exposure victims, little is known about how and to what extent blast energy is transmitted to the central nervous system via the external ear canal. The present study investigated whether exposure to blasts directed through the ear canal causes brain injury in Long-Evans rats. Animals were exposed to a single blast (0-30 pounds per square inch (psi)) through the ear canal, and brain injury was evaluated by histological and behavioral outcomes at multiple time-points. Blast exposure not only caused tympanic membrane perforation but also produced substantial neuropathological changes in the brain, including increased expression of c-Fos, induction of a profound chronic neuroinflammatory response, and apoptosis of neurons. The blast-induced injury was not limited only to the brainstem most proximal to the source of the blast, but also affected the forebrain including the hippocampus, amygdala and the habenula, which are all involved in cognitive functions. Indeed, the animals exhibited long-term neurological deficits, including signs of anxiety in open field tests 2 months following blast exposure, and impaired learning and memory in an 8-arm maze 12 months following blast exposure. These results suggest that the unprotected ear canal provides a locus for blast waves to cause TBI. This study was approved by the Institutional Animal Care and Use Committee at the University of Mississippi Medical Center (Animal protocol# 0932E, approval date: September 30, 2016 and 0932F, approval date: September 27, 2019).

Elevation of Pro-inflammatory and Anti-inflammatory Cytokines in Rat Serum after Acute Methamphetamine Treatment and Traumatic Brain Injury

The use of methamphetamine (METH) is a growing worldwide epidemic that bears grave societal implications. METH is known to exert its neurotoxic effects on the dopaminergic and serotonergic systems of the brain. In addition to this classical studied mechanism of damage, findings from our laboratory and others have shown that acute METH treatment and mechanical injury, i.e. traumatic brain injury (TBI), share common cell injury mechanism(s). Since neuro-inflammation is a signature event in TBI, we hypothesize that certain cytokine levels might also be altered in rat brain exposed to an acute METH insult. In this study, using a cytokine antibody array chip, we evaluated the serum levels of 19 cytokines in rats 24 h after exposure to a 40 mg/kg acute regimen of METH. Data were compared to rats subjected to experimental TBI using the controlled cortical impact (CCI) injury model and saline controls. Sandwich ELISA method was used to further validate some of the findings obtained from the antibody cytokine array. We confirmed that three major inflammatory-linked cytokines (IL-1β, IL-6, and IL-10) were elevated in the METH and TBI groups compared to the saline group. Such finding suggests the involvement of an inflammatory process in these brain insults, indicating that METH use is, in fact, a stressor to the immune system where systemic involvement of an altered cytokine profile may play a major role in mediating chemical brain injury after METH use.

Chronic traumatic encephalopathy and the nucleus basalis of Meynert

Due to the growing number of chronic traumatic encephalopathy (CTE) cases in the military and contact sports, defining the cellular and molecular substrate of this disorder is crucial. Most classic neuropathological investigations describe cortical tau and, to a lesser extent, amyloid lesions, which may underlie the clinical sequela associated with CTE. The application of modern molecular biologic technology to postmortem human brain tissue has made it possible to evaluate the genetic signature of specific neuronal phenotypes at different stages of CTE pathology. Most recently, molecular pathobiology has been used in the field of CTE, with an emphasis on the cholinergic neurons located within the nucleus basalis of Meynert, which develop tau pathology and are associated with cognitive dysfunction similar to that found in Alzheimer's disease (AD). Quantitative findings derived from single-cell transcript investigations provide clues to our understanding of the selective vulnerability of neurons containing AD-like tau pathology at different stages of CTE. Since human tissue-based studies provide a gold standard for the field of CTE, continued molecular pathological studies are needed to reveal novel drug targets for the treatment of this disorder.

Microglia and Macrophages in the Pathological Central and Peripheral Nervous Systems

Microglia, the immunocompetent cells in the central nervous system (CNS), have long been studied as pathologically deteriorating players in various CNS diseases. However, microglia exert ameliorating neuroprotective effects, which prompted us to reconsider their roles in CNS and peripheral nervous system (PNS) pathophysiology. Moreover, recent findings showed that microglia play critical roles even in the healthy CNS. The microglial functions that normally contribute to the maintenance of homeostasis in the CNS are modified by other cells, such as astrocytes and infiltrated myeloid cells; thus, the microglial actions on neurons are extremely complex. For a deeper understanding of the pathophysiology of various diseases, including those of the PNS, it is important to understand microglial functioning. In this review, we discuss both the favorable and unfavorable roles of microglia in neuronal survival in various CNS and PNS disorders. We also discuss the roles of blood-borne macrophages in the pathogenesis of CNS and PNS injuries because they cooperatively modify the pathological processes of resident microglia. Finally, metabolic changes in glycolysis and oxidative phosphorylation, with special reference to the pro-/anti-inflammatory activation of microglia, are intensively addressed, because they are profoundly correlated with the generation of reactive oxygen species and changes in pro-/anti-inflammatory phenotypes.

Estrogen as a Neuroprotectant in Both Sexes: Stories From the Bird Brain

Estrogens such as estradiol (E2) are potent effectors of neural structure and function via peripheral and central synthesis. In the zebra finch (Taeniopygia guttata), neural E2 synthesis is among the highest reported in homeotherms due to the abundant constitutive expression of aromatase (E-synthase) in discrete neuronal pools across the forebrain. Following penetrating or concussive trauma, E2 synthesis increases even further via the induced expression of aromatase in reactive astrocytes around the site of damage. Injury-associated astrocytic aromatization occurs in the brains of both sexes regardless of the site of injury and can remain elevated for weeks following trauma. Interestingly, penetrating injury induces astrocytic aromatase more rapidly in females compared to males, but this sex difference is not detectable 24 h posttrauma. Indeed, unilateral penetrating injury can increase E2 content 4-fold relative to the contralateral uninjured hemisphere, suggesting that glial aromatization may be a powerful source of neural E2 available to circuits. Glial aromatization is neuroprotective as inhibition of injury-induced aromatase increases neuroinflammation, gliosis, necrosis, apoptosis, and infarct size. These effects are ameliorated upon replacement with E2, suggesting that the songbird may have evolved a rapidly responsive neurosteroidogenic system to protect vulnerable brain circuits. The precise signals that induce aromatase expression in astrocytes include elements of the inflammatory cascade and underscore the sentinel role of the innate immune system as a crucial effector of trauma-associated E2 provision in the vertebrate brain. This review will describe the inductive signals of astroglial aromatase and the neuroprotective role for glial E2 synthesis in the adult songbird brains of both sexes.

Central aromatization: A dramatic and responsive defense against threat and trauma to the vertebrate brain

Aromatase is the requisite and limiting enzyme in the production of estrogens from androgens. Estrogens synthesized centrally have more recently emerged as potent neuroprotectants in the vertebrate brain. Studies in rodents and songbirds have identified key mechanisms that underlie both; the injury-dependent induction of central aromatization, and the protective effects of centrally synthesized estrogens. Injury-induced aromatase expression in astrocytes occurs following a broad range of traumatic brain damage including excitotoxic, penetrating, and concussive injury. Responses to neural insult such as edema and inflammation involve signaling pathways the components of which are excellent candidates as inducers of this astrocytic response. Finally, estradiol from astrocytes exerts a paracrine neuroprotective influence via the potent inhibition of inflammatory pathways. Taken together, these data suggest a novel role for neural aromatization as a protective mechanism against the threat of inflammation and suggests that central estrogen provision is a wide-ranging neuroprotectant in the vertebrate brain.

BDNF Val66Met Genetic Polymorphism Results in Poor Recovery Following Repeated Mild Traumatic Brain Injury in a Mouse Model and Treatment With AAV-BDNF Improves Outcomes

Clinicians have long noticed that some Traumatic Brain Injury (TBI) patients have worse symptoms and take a longer time to recover than others, for reasons unexplained by known factors. Identifying what makes some individuals more susceptible is critical to understanding the underlying mechanisms through which TBI causes deleterious effects. We have sought to determine the effect of a single nucleotide polymorphism (SNP) in Brain-derived neurotrophic factor (BDNF) at amino acid 66 (rs6265) on recovery after TBI. There is controversy from human studies as to whether the BDNF Val66Val or Val66Met allele is the risk factor for worse outcomes after brain trauma. We therefore investigated cellular and behavioral outcomes in genetically engineered mice following repeated mild TBI (rmTBI) using a lateral fluid percussion (LFP) injury model. We found that relative to injured Val66Val carriers, injured Val66Met carriers had a larger inflammation volume and increased levels of neurodegeneration, apoptosis, p-tau, activated microglia, and gliosis in the cortex and/or hippocampus at 1 and/or 21 days post-injury (DPI). We therefore concluded that the Val66Met genetic polymorphism is a risk factor for poor outcomes after rmTBI. In order to determine the mechanism for these differences, we investigated levels of the apoptotic-inducing pro BDNF and survival-inducing mature BDNF isoforms and found that Met carriers had less total BDNF in the cortex and a higher pro/mature ratio of BDNF in the hippocampus. We then developed a personalized approach to treating genetically susceptible individuals by overexpressing wildtype BDNF in injured Val66Met mice using an AAV-BDNF virus. This intervention improved cellular, motor, and cognitive behavior outcomes at 21 DPI and increased levels of mature BDNF and phosphorylation of mature BDNF's receptor trkB. This study lays the groundwork for further investigation into the genetics that play a role in the extent of injury after rmTBI and highlights how personalized therapeutics may be targeted for recovery in susceptible individuals.

Gene Profiling of Nucleus Basalis Tau Containing Neurons in Chronic Traumatic Encephalopathy: A Chronic Effects of Neurotrauma Consortium Study

Military personnel and athletes exposed to traumatic brain injury may develop chronic traumatic encephalopathy (CTE). Brain pathology in CTE includes intracellular accumulation of abnormally phosphorylated tau proteins (p-tau), the main constituent of neurofibrillary tangles (NFTs). Recently, we found that cholinergic basal forebrain (CBF) neurons within the nucleus basalis of Meynert (nbM), which provide the major cholinergic innervation to the cortex, display an increased number of NFTs across the pathological stages of CTE. However, molecular mechanisms underlying nbM neurodegeneration in the context of CTE pathology remain unknown. Here, we assessed the genetic signature of nbM neurons containing the p-tau pretangle maker pS422 from CTE subjects who came to autopsy and received a neuropathological CTE staging assessment (Stages II, III, and IV) using laser capture microdissection and custom-designed microarray analysis. Quantitative analysis revealed dysregulation of key genes in several gene ontology groups between CTE stages. Specifically, downregulation of the nicotinic cholinergic receptor subunit β-2 gene (CHRNB2), monoaminergic enzymes catechol-O-methyltransferase (COMT) and dopa decarboxylase (DDC), chloride channels CLCN4 and CLCN5, scaffolding protein caveolin 1 (CAV1), cortical development/cytoskeleton element lissencephaly 1 (LIS1), and intracellular signaling cascade member adenylate cyclase 3 (ADCY3) was observed in pS422-immunreactive nbM neurons in CTE patients. By contrast, upregulation of calpain 2 (CAPN2) and microtubule-associated protein 2 (MAP2) transcript levels was found in Stage IV CTE patients. These single-population data in vulnerable neurons indicate alterations in gene expression associated with neurotransmission, signal transduction, the cytoskeleton, cell survival/death signaling, and microtubule dynamics, suggesting novel molecular pathways to target for drug discovery in CTE.

Staying in the game: a pilot study examining the efficacy of protective headgear in an animal model of mild traumatic brain injury (mTBI)

PRIMARY OBJECTIVE

Rugby is one of the few contact sports that do not mandate protective headgear, possibly because studies have shown poor efficacy for protection related to concussion pathology with existing headguards.

RESEARCH DESIGN

Following innovative material technology utilization to produce headgear believed to have protective capabilities, this study examined the effects of a soft-shell headgear constructed from a novel viscoelastic material, on both behaviour and serum biomarkers after high and average impact force mild traumatic brain injuries (mTBI).

METHODS AND PROCEDURES

Seventy-five male Sprague Dawley rats were divided into five groups: control, average - 37G impact, with and without headgear, and high - 106G impact, with and without headgear. Rats were sacrificed at 3 or 48 hours and serum samples were analyzed for levels of TNF-α, NEF-L, and GFAP. Animals sacrificed at 48 hours also underwent testing for balance and motor coordination, and exploratory/locomotor behaviour.

MAIN OUTCOMES AND RESULTS

The novel headgear offered significant protection against mTBI symptomology and biomarkers in the group that experienced an average impact force, but only moderated protection for the animals in the high impact group.

CONCLUSIONS

This innovative headgear may prevent some of the negative sequel associated with concussion pathology.

Activation of the peripheral immune system regulates neuronal aromatase in the adult zebra finch brain

Estradiol provision via neural aromatization decreases neuro-inflammation and –degeneration, but almost nothing is known about the interactions between the peripheral immune system and brain aromatase. Given the vulnerability of the CNS we reasoned that brain aromatization may protect circuits from the threats of peripheral infection; perhaps shielding cells that are less resilient from the degeneration associated with peripheral infection or trauma. Lipopolysaccharide (LPS) or vehicle was administered peripherally to adult zebra finches and sickness behavior was recorded 2 or 24 hours later. The central transcription of cytokines and aromatase was measured, as were telencephalic aromatase activity and immunoreactive aromatase (24 hour time point only). Two hours post LPS, sickness-like behaviors increased, the transcription of IL-1β was higher in both sexes, and TNFα was elevated in females. 24 hours post-LPS, the behavior of LPS birds was similar to controls, and cytokines had returned to baseline, but aromatase mRNA and activity were elevated in both sexes. Immunocytochemistry revealed greater numbers of aromatase-expressing neurons in LPS birds. These data suggest that the activation of the immune system via peripheral endotoxin increases neuronal aromatase; a mechanism that may rapidly generate a potent anti-neuroinflammatory steroid in response to peripheral activation of the immune system.

Central Administration of Indomethacin Mitigates the Injury-Induced Upregulation of Aromatase Expression and Estradiol Content in the Zebra Finch Brain

Injury to the vertebrate brain causes neuroinflammation, characterized in part by increases in prostaglandins. In rodents and songbirds, brain injury also induces the transcription and translation of aromatase in reactive astrocytes around the site of damage. Interestingly, this induction is more rapid in female zebra finches relative to males. Induced aromatization is neuroprotective, as inhibition of aromatase and estrogen replacement, increases and decreases the extent of damage, respectively. Although the consequences of induced astrocytic aromatization are intensely studied, little is known about what factors induce aromatase. Inflammation is sufficient to induce astrocytic aromatase suggesting that the link between inflammation and aromatase expression may be causal. To test this hypothesis, adult male and female zebra finches received bilateral mechanical injuries through which either the cyclooxygenase (COX)-1/2 inhibitor indomethacin or vehicle was administered into contralateral hemispheres. Subjects were killed either 6 or 24 hours after injury. In both sexes, an enzyme immunoassay for prostaglandin E2 (PGE2) revealed that indomethacin decreased PGE2 relative to the contralateral hemisphere at both time points, suggesting that the dose and mode of administration used were successful in affecting neuroinflammation locally. Indomethacin reduced aromatase expression and 17β-estradiol (E2) content at 6 hours but not 24 hours following injury in females. However, in males, the inhibitory effect of indomethacin on aromatase and E2 was apparent at 24 but not 6 hours after treatment. These data suggest that COX activity, perhaps via consequent prostaglandin secretion, may induce aromatase expression and central E2, an effect that is detectable in temporally distinct patterns between sexes.

Centrally Synthesized Estradiol Is a Potent Anti-Inflammatory in the Injured Zebra Finch Brain

In homeotherms, injury to the brain, such as a penetrating wound, increases microglial cytokine expression and astroglial aromatase (estrogen synthase). In songbirds, injury-induced synthesis of estrogens is neuroprotective as aromatase inhibition and replacement with estradiol (E2) exacerbates and mitigates the extent of damage, respectively. The influence of induced aromatization on inflammation, however, remains unstudied. We hypothesized that injury-induced aromatization, via E2 synthesis, may affect neuroinflammation after a penetrating brain injury. Using adult zebra finches, we first documented an increase in the transcription of cytokines but not aromatase, 2 hours after the injury. Twenty-four hours after the injury, however, aromatase was dramatically elevated and cytokine expression had returned to baseline, suggesting that aromatization may be involved in the decrease of cytokines and neuroinflammation. In two subsequent experiments, we tested the influence of the inhibition of induced aromatization and aromatase inhibition with concomitant central E2 replacement on the transcription of the cytokines TNF-α, IL-1β, and IL-6, the enzyme cyclooxygenase-2 (cox-2), and its product prostaglandin E2 (PGE2). Administration of fadrozole, an aromatase inhibitor, caused a sustained elevation of IL-1β in females and TNF-α, cox-2, and PGE2 in both sexes. This prolonged neuroinflammation appears to be due to a failure to synthesize E2 locally because intracranial E2 replacement lowered IL-1β in females, TNF-α in males, and cox-2 and PGE2 in both sexes. IL-6 was not affected by injury, aromatase inhibition, or E2 replacement in either sex. These data suggest that E2 synthesis after a penetrating brain injury is a potent and inducible anti-inflammatory signal, with specific modulation of discrete cytokine signaling.

Genetic and pharmacological intervention of the p75NTR pathway alters morphological and behavioural recovery following traumatic brain injury in mice

PRIMARY OBJECTIVE

Neurotrophin levels are elevated after TBI, yet there is minimal regeneration. It was hypothesized that the pro-neurotrophin/p75NTR pathway is induced more than the mature neurotrophin/Trk pathway and that interfering with p75 signalling improves recovery following TBI.

RESEARCH DESIGN

Lateral Fluid Percussion (LFP) injury was performed on wildtype and p75 mutant mice. In addition, TrkB agonist 7,8 Dihydroxyflavone or p75 antagonist TAT-Pep5 were tested. Western blot and immunohistochemistry revealed biochemical and cellular changes. Morris Water Maze and Rotarod tests demonstrated cognitive and vestibulomotor function.

MAIN OUTCOMES AND RESULTS

p75 was up-regulated and TrkB was down-regulated 1 day post-LFP. p75 mutant mice as well as mice treated with the p75 antagonist or the TrkB agonist exhibited reduced neuronal death and degeneration and less astrocytosis. The cells undergoing apoptosis appear to be neurons rather than glia. There was improved motor function and spatial learning in p75 mutant mice and mice treated with the p75 antagonist.

CONCLUSIONS

Many of the pathological and behavioural consequences of TBI might be due to activation of the pro-neurotrophin/p75 toxic pathway overriding the protective mechanisms of the mature neurotrophin/Trk pathway. Targeting p75 can be a novel strategy to counteract the damaging effects of TBI.

Influence of Age on Cerebral Housekeeping Gene Expression for Normalization of Quantitative Polymerase Chain Reaction after Acute Brain Injury in Mice

To prevent methodological errors of quantitative PCR (qPCR) normalization with reference genes is obligatory. Although known to influence gene expression, impact of age on housekeeping gene expression has not been determined after acute brain lesions such as traumatic brain injury (TBI). Therefore, expression of eight common control genes was investigated at 15 min, 24 h, and 72 h after experimental TBI in 2- and 21-month-old C57Bl6 mice. Expression of β2-microglobulin (B2M), β-actin (ActB), and porphobilinogen deaminase (PBGD) increased after TBI in both ages. β2M demonstrated age-dependent differences and highest inter- and intragroup variations. Expression of cyclophilin A, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), hypoxanthine ribosyltransferase (HPRT), S100B, and 18SrRNA remained stable. Cyclophilin A and HPRT demonstrated strongest inter- and intragroup stability. The data indicate that the expression of most but not all control genes is stable during aging. The correct choice of housekeeping genes is of key importance to ensure adequate normalization of qPCR data. With respect to insult and age, normalization strategies should consider cyclophilin A as a single normalizer. Normalization with two reference genes is recommended with cyclophilin A and HPRT in young mice and in mixed age studies and with cyclophilin A and GAPDH in old mice. In addition, the present study suggests not to use β2-microglobulin, β-actin or PBGD as single control genes because of strong regulation after CCI in 2- and 21-month-old mice.

VGF (TLQP-62)-induced neurogenesis targets early phase neural progenitor cells in the adult hippocampus and requires glutamate and BDNF signaling

The neuropeptide VGF (non-acronymic), which has antidepressant-like effects, enhances adult hippocampal neurogenesis as well as synaptic activity and plasticity in the hippocampus, however the interaction between these processes and the mechanism underlying this regulation remain unclear. In this study, we demonstrate that VGF-derived peptide TLQP-62 specifically enhances the generation of early progenitor cells in nestin-GFP mice. Specifically, TLQP-62 significantly increases the number of Type 2a neural progenitor cells (NPCs) while reducing the number of more differentiated Type 3 cells. The effect of TLQP-62 on proliferation rather than differentiation was confirmed using NPCs in vitro; TLQP-62 but not scrambled peptide PEHN-62 increases proliferation in a cell line as well as in primary progenitors from adult hippocampus. Moreover, TLQP-62 but not scrambled peptide increases Cyclin D mRNA expression. The proliferation of NPCs induced by TLQP-62 requires synaptic activity, in particular through NMDA and metabotropic glutamate receptors. The activation of glutamate receptors by TLQP-62 activation induces phosphorylation of CaMKII through NMDA receptors and protein kinase D through metabotropic glutamate receptor 5 (mGluR5). Furthermore, pharmacological antagonists to CaMKII and PKD inhibit TLQP-62-induced proliferation of NPCs indicating that these signaling molecules downstream of glutamate receptors are essential for the actions of TLQP-62 on neurogenesis. We also show that TLQP-62 gradually activates Brain-Derived Neurotrophic Factor (BDNF)-receptor TrkB in vitro and that Trk signaling is required for TLQP-62-induced proliferation of NPCs. Understanding the precise molecular mechanism of how TLQP-62 influences neurogenesis may reveal mechanisms by which VGF-derived peptides act as antidepressant-like agents.

Injury-induced expression of glial androgen receptor in the zebra finch brain

Astrogliosis occurs following injury to the zebra finch brain. To date, only estrogen synthase (aromatase) has been identified in injury-induced astrocytes. The expression of other steroidogenic enzymes or their receptors remains unknown in the avian brain. However, in mammals, an upregulation of androgen receptors has been identified in glial cells. The aim of this study was to determine if the androgen receptor is upregulated following injury in adult zebra finches. Finches were given a single penetrating injury and brain tissue was collected 24 or 72 h later. Expression of androgen receptor was examined using immunohistochemistry and quantified using quantitative polymerase chain reaction (qPCR) analysis. Androgen receptors were localized to astrocytes versus neurons, further solidifying the role for astrocytes in neural recovery.

The effect of environmental enrichment on substantia nigra gene expression after traumatic brain injury in rats

Experimental investigations into the effects of traumatic brain injury (TBI) have demonstrated significant alterations in dopaminergic systems. Dopaminergic fibers originating within the substantia nigra and ventral tegmental area (VTA) are important for reward learning, addiction, movement, and behavior. However, little is known about the effect of TBI on substantia nigra and VTA function. Environmental enrichment (EE) has been shown to improve functional outcome after TBI, and a number of studies suggest that it may exert some benefits via dopaminergic signaling. To better understand the role of dopamine in chronic TBI pathophysiology and the effect of EE, we examined the mRNA expression profile within the substantia nigra and VTA at 4 weeks post-injury. Specifically, three comparisons were made: 1) TBI versus sham, 2) sham+EE versus sham+standard (STD) housing, and 3) TBI+EE versus TBI+STD. There were differential expressions of 25, 4, and 40 genes in these comparisons, respectively. Chronic alterations in genes post-injury within the substantia nigra and VTA included genes important for cellular membrane homeostasis and transcription. EE-induced gene alterations after TBI included genes important for signal transduction, in particular calcium signaling pathways, membrane homeostasis, and metabolism. Elucidation of these alterations in gene expression within the substantia nigra and VTA provides new insights into chronic changes in dopamine signaling post-TBI, and the potential role of EE in TBI rehabilitation.

The effect of progesterone dose on gene expression after traumatic brain injury

Microarray-based transcriptional profiling was used to determine the effect of progesterone in the cortical contusion (CCI) model. Gene ontology (GO) analysis then evaluated the effect of dose on relevant biological pathways. Treatment (vehicle, progesterone 10 mg/kg or 20 mg/kg given i.p.) was started 4 h post-injury and administered every 12 h post-injury for up to 72 h, with the last injection 12 hr prior to death for the 24 h and 72 h groups. In the CCI-injured vehicle group compared to non-injured animals, expression of 1,114, 4,229, and 291 distinct genes changed >1.5-fold (p<0.05) at 24 h, 72 h, and 7 days, respectively. At 24 h, the effect of low-dose progesterone on differentially expressed genes was <20% the effect of higher dose compared to vehicle. GO analysis identified a significant effect of low- and high-dose progesterone treatment compared to vehicle on DNA damage response. At 72 h, high-dose progesterone treatment compared to vehicle affected expression of almost twice as many genes as did low-dose progesterone. Both low- and high-dose progesterone resulted in expression of genes regulating inflammatory response and apoptosis. At 7 days, there was only a modest difference in high-dose progesterone compared to vehicle, with only 14 differentially expressed genes. In contrast, low-dose progesterone resulted in 551 differentially expressed genes compared to vehicle. GO analysis identified genes for the low-dose treatment involved in positive regulation of cell proliferation, innate immune response, positive regulation of anti-apoptosis, and blood vessel remodeling.

Neuroinflammation induces glial aromatase expression in the uninjured songbird brain

Background

Estrogens from peripheral sources as well as central aromatization are neuroprotective in the vertebrate brain. Under normal conditions, aromatase is only expressed in neurons, however following anoxic/ischemic or mechanical brain injury; aromatase is also found in astroglia. This increased glial aromatization and the consequent estrogen synthesis is neuroprotective and may promote neuronal survival and repair. While the effects of estradiol on neuroprotection are well studied, what induces glial aromatase expression remains unknown.

Methods

Adult male zebra finches (Taeniopygia guttata) were given a penetrating injury to the entopallium. At several timepoints later, expression of aromatase, IL-1β-like, and IL-6-like were examined using immunohisotchemistry. A second set of zebra birds were exposed to phytohemagglutinin (PHA), an inflammatory agent, directly on the dorsal surface of the telencephalon without creating a penetrating injury. Expression of aromatase, IL-1β-like, and IL-6-like were examined using both quantitative real-time polymerase chain reaction to examine mRNA expression and immunohistochemistry to determine cellular expression. Statistical significance was determined using t-test or one-way analysis of variance followed by the Tukey Kramers post hoc test.

Results

Following injury in the zebra finch brain, cytokine expression occurs prior to aromatase expression. This temporal pattern suggests that cytokines may induce aromatase expression in the damaged zebra finch brain. Furthermore, evoking a neuroinflammatory response characterized by an increase in cytokine expression in the uninjured brain is sufficient to induce glial aromatase expression.

Conclusions

These studies are among the first to examine a neuroinflammatory response in the songbird brain following mechanical brain injury and to describe a novel neuroimmune signal to initiate aromatase expression in glia.

Gene expression profiling for discovery of novel targets in human traumatic brain injury

Several clinical trials have failed to demonstrate a significant effect on outcome following human traumatic brain injury (TBI) despite promising results obtained in preclinical animal studies. These failures may be due in part to a misinterpretation of the findings obtained in preclinical animal models of TBI, a misunderstanding of the complexity of the human response to TBI, limited knowledge about the biological pathways that interact to contribute to good and bad outcomes after brain injury, and the effects of genomic variability and environment on individual recovery. Recent publications suggest that data obtained from gene expression profiling studies of complex neurological diseases such as stroke, multiple sclerosis (MS), Alzheimer's and Parkinson's may contribute to a more informed understanding of what affects outcome following TBI. These data may help to bridge the gap between successful preclinical studies and negative clinical trials in humans to reveal novel targets for therapy. Gene expression profiling has the capability to identify biomarkers associated with response to TBI, elucidate complex genetic interactions that may play a role in outcome following TBI, and reveal biological pathways related to brain health. This review highlights the current state of the literature on gene expression profiling for neurological disease and discusses its ability to aid in unraveling the variable human response to TBI and the potential for it to offer treatment strategies in an area where we currently have limited therapeutic options primarily based on supportive care.

Dosing and safety of cyclosporine in patients with severe brain injury

OBJECT

Cyclosporine neuroprotection has been reported in brain injury models but safety and dosing guidelines have not been determined in humans with severe traumatic brain injury (TBI). The purpose of this investigation was to establish the safety of cyclosporine using 4 clinically relevant dosing schemes.

METHODS

The authors performed a prospective, blinded, placebo-controlled, randomized, dose-escalation trial of cyclosporine administration initiated within 8 hours of TBI (Glasgow Coma Scale score range 4-8; motor score range 2-5). Four dosing cohorts (8 patients treated with cyclosporine and 2 receiving placebo treatment per cohort) received cyclosporine (1.25-5 mg/kg/day) or placebo in 2 divided doses (Cohorts I-III) or continuous infusion (Cohort IV) over 72 hours. Adverse events and outcome were monitored for 6 months.

RESULTS

Forty patients were enrolled over 3 years (cyclosporine cohorts, 24 male and 8 female patients; placebo group, 8 male patients). Systemic trough concentrations were below 250 ng/ml during intermittent doses. Higher blood concentrations were observed in Cohorts III and IV. There was no significant difference in immunological effects, adverse events, infection, renal dysfunction, or seizures. Mortality rate was not affected by cyclosporine administration, independent of dose, compared with placebo (6 of 32 patients receiving cyclosporine and 2 of 8 receiving placebo died, p>0.05). At 6 months, a dose-related improvement in favorable outcome was observed in cyclosporine-treated patients (p<0.05).

CONCLUSIONS

In patients with acute TBI who received cyclosporine at doses up to 5 mg/kg/day, administered intravenously, with treatment initiated within 8 hours of injury, the rate of mortality or other adverse events was not significantly different from that of the placebo group.

The effect of traumatic brain injury upon the concentration and expression of interleukin-1beta and interleukin-10 in the rat

BACKGROUND

Using a model of traumatic brain injury (TBI) in the rat, this study was undertaken to characterize the short-term biochemical changes of IL-1beta, IL-10, and tumor necrosis factor TNF-alpha to determine whether injury in the brain elicits a systemic cytokine response.

METHODS

Sprague-Dawley rats were subjected to a TBI using a weight-drop model and then killed at various time points after injury. Samples of blood, brain, and liver were recovered and analyzed for concentrations of IL-1beta, IL-10, and TNF-alpha as well as IL-1beta and IL-10 mRNA expression in liver and brain.

RESULTS

In brain, IL-1beta increased in the first hour after injury, peaked at 8 hours, and declined during the final 16 hours. IL-10 quickly increased during the first 4 hours and then gradually rose over the last 20 hours. Analysis of liver showed no upregulation of these markers and plasma IL-1beta and IL-10 were unchanged compared with controls. Although not upregulated in brain, TNF-alpha showed a statistically significant (p < 0.05) rise in plasma from 14 +/- 16 pg/mL at 20 minutes to 91 +/- 28 pg/mL at 24 hours.

CONCLUSION

Using a model of TBI, we have demonstrated that there is a rise in both IL-1beta and IL-10 in the injured rat brain within the first 24 hours after injury without a corresponding rise in either plasma or liver. Therefore, it appears as if two strong indicators of brain injury severity are expressed and possibly carry out their actions solely in the brain.

Activation of Rho after traumatic brain injury and seizure in rats

Traumatic brain injury (TBI) is characterized by a progressive cell loss and a lack of axonal regeneration. In the central nervous system (CNS), the Rho signaling pathway regulates the neuronal response to growth inhibitory proteins and regeneration of damaged axons, and Rho activation is also correlated with an increased susceptibility to apoptosis. To evaluate whether traumatic brain injury (TBI) results in changes in Rho activation in vulnerable regions of the brain, GTP-RhoA pull down assays were performed on rat cortical and hippocampal tissue homogenates obtained from 24 h to 3 days following lateral fluid percussion brain injury (FPI). Following FPI, a significantly increased RhoA activation was observed from 24 h to 3 days post-injury in the cortex and by 3 days in the hippocampus ipsilateral to the injury. We also detected activated RhoA in the cortex and hippocampus contralateral to the injury, without concomitant changes in total RhoA levels. To determine if immediate post-traumatic events such as seizures may activate Rho, we examined RhoA activation in the brains of rats with kainic acid-induced seizures. Severe seizures resulted in bilateral RhoA activation in the cortex and hippocampus. Together, these results indicate that RhoA is activated in vulnerable brain regions following traumatic and epileptic insults to the CNS.

Functional genomic methodologies

The ability to form tenable hypotheses regarding the neurobiological basis of normative functions as well as mechanisms underlying neurodegenerative and neuropsychiatric disorders is often limited by the highly complex brain circuitry and the cellular and molecular mosaics therein. The brain is an intricate structure with heterogeneous neuronal and nonneuronal cell populations dispersed throughout the central nervous system. Varied and diverse brain functions are mediated through gene expression, and ultimately protein expression, within these cell types and interconnected circuits. Large-scale high-throughput analysis of gene expression in brain regions and individual cell populations using modern functional genomics technologies has enabled the simultaneous quantitative assessment of dozens to hundreds to thousands of genes. Technical and experimental advances in the accession of tissues, RNA amplification technologies, and the refinement of downstream genetic methodologies including microarray analysis and real-time quantitative PCR have generated a wellspring of informative studies pertinent to understanding brain structure and function. In this review, we outline the advantages as well as some of the potential challenges of applying high throughput functional genomics technologies toward a better understanding of brain tissues and diseases using animal models as well as human postmortem tissues.

The effect of therapeutic hypothermia on the expression of inflammatory response genes following moderate traumatic brain injury in the rat

Traumatic brain injury (TBI) initiates a cascade of cellular and molecular responses including both pro- and anti-inflammatory. Although post-traumatic hypothermia has been shown to improve outcome in various models of brain injury, the underlying mechanisms responsible for these effects have not been clarified. In this study, inflammation cDNA arrays and semi-quantitative RT-PCR were used to detect genes that are differentially regulated after TBI. In addition, the effect of post-traumatic hypothermia on the expression of selective genes was also studied. Rats (n = 6-8 per group) underwent moderate fluid-percussion (F-P) brain injury with and without hypothermic treatment (33 degrees C/3 h). RNA from 3-h or 24-h survival was analyzed for the expression of IL1-beta, IL2, IL6, TGF-beta2, growth-regulated oncogene (GRO), migration inhibitory factor (MIF), and MCP (a transcription factor). The interleukins IL-1beta, IL-2, and IL-6 and TGF-beta and GRO were strongly upregulated early and transiently from 2- to 30-fold over sham at 3 h, with normalization by 24 h. In contrast, the expressions of MIF and MCP were both reduced by TBI compared to sham. Post-traumatic hypothermia had no significant effect on the acute expression of the majority of genes investigated. However, the expression of TGF-beta2 at 24 h was significantly reduced by temperature manipulation. The mechanism by which post-traumatic hypothermia is protective may not involve a general genetic response of the inflammatory genes. However, specific genes, including TGF-beta2, may be altered and effect cell death mechanisms after TBI. Hypothermia differentially regulates certain genes and may target more delayed responses underlying the secondary damage following TBI.

Expression profiling in the aging brain: a perspective

To evaluate molecular events associated with the aging process in animal models and human tissues, microarray analysis is performed at the regional and cellular levels to define transcriptional patterns or mosaics that may lead to better understanding of the mechanism(s) that drive senescence. In this review, we outline the experimental and analytical issues associated with high-throughput genomic analyses in aging brain and other tissues for a comprehensive evaluation of the current state of microarray analysis in aging paradigms. Ultimately, the goal of these studies is to apply functional genomics and proteomics approaches to aging research to develop new tools to assess age in cell- and tissue-specific manners in order to develop aging biomarkers for pharmacotherapeutic interventions and disease prevention.

Microarrays and expression profiling in microglia research and in inflammatory brain disorders

Expression profiling by using microarrays is a powerful tool for investigating transcriptional changes in a variety of diseases. In this survey, microarray data selected from the literature from in vivo and in vitro studies are scrutinized to find differentially expressed genes in common within specific inflammatory conditions in brain or microglial cell cultures, if there are at least two independent investigations available. Viral encephalitis, multiple sclerosis, epileptic seizures, ischemic lesions, and traumatic brain injury are the disorders covered. Moreover, by taking into account expression data obtained from cultured microglia, two examples are presented of how one can deal (or should not deal) with lists of candidate genes showing up in these kinds of studies without sophisticated software programs. Finally, some general remarks are made about pivotal issues when beginning to use microarray technology.

Expression profile analysis within the human hippocampus: Comparison of CA1 and CA3 pyramidal neurons

The hippocampus contains several distinct cell types that are interconnected by a well-characterized series of synaptic circuits. To evaluate molecular and cellular signatures of individual cell types within the normal adult human hippocampal formation, expression profile analysis was performed on individual CA1 and CA3 pyramidal neurons using a novel single cell RNA amplification methodology coupled with custom-designed cDNA array analysis. Populations of CA1 and CA3 neurons were also compared with regional dissections of the hippocampus from the same tissue sections. Molecular fingerprint comparison of cresyl violet-stained CA1 and CA3 pyramidal neurons microaspirated from the hippocampus of normal control subjects indicated significant differences in relative expression levels for approximately 16% (20 of 125) genes evaluated on the custom-designed cDNA array platform. Significant differences were observed for several transcripts relevant to the structure and function of hippocampal neurons, including specific glutamate receptors, gamma-aminobutyric acid (GABA) A receptors, cytoskeletal elements, dopamine receptors, and immediate-early genes. Compared with the regional assessment of gene expression, both CA1 and CA3 neurons displayed a relative enrichment of classes of transcripts that included glutamate receptors, transporters, and interacting proteins, GABA receptors and transporters, synaptic-related markers, and catecholamine receptors and transporters. In contrast, the regional hippocampal dissection had an increased level of gene expression for cytoskeletal elements as well as glial-associated markers. Expression profile analysis illustrates the importance of evaluating individual cellular populations within a functional circuit and may help define elements that confer unique properties to individual populations of hippocampal neurons under normal and diseased conditions.

Differential gene expression in hippocampus following experimental brain trauma reveals distinct features of moderate and severe injuries

Microarray technology was employed to determine the differential pattern of gene expression within the hippocampus as a result of traumatic brain injury (TBI). The validity of the microarray data was confirmed using real-time RT-PCR. Following either moderate or severe lateral fluid percussion injury, rats were studied 0.5, 4, and 24 h after injury. In general, animals exhibited mRNA up or down regulation of approximately 10% of the genes studied. However, it was clear that the pattern of gene expression was influenced by both the severity of injury and the time after injury at which animals were studied. For example, genes encoding molecules for cellular signaling, synaptic plasticity, metabolism, ion channels and transporters were up regulated following severe injury, but down regulated following moderate injury. Furthermore, moderate injury was associated with an increasing number of responsive genes as a function of time post-injury. However, animals sustaining a severe level of injury exhibited decreasing number of responsive genes during the same post-injury period. The different patterns of gene expression between injury severity and across time after the insult suggests that the pathophysiological cascade induced by TBI is accompanied by a molecular response which, like the other aspects of the cellular response for survival, may indicate a "molecular window" that may offer an opportunity for therapeutic interventions involving gene therapy. Our results also suggest that fundamentally different pathophysiological processes or cascades may be induced by different severities of injury.

Gene Expression Profile Changes Are Commonly Modulated across Models and Species after Traumatic Brain Injury

Brain trauma is a major cause of morbidity and mortality, both in adult and pediatric populations. Much of the functional deficit derives from delayed cell death resulting from induction of neurotoxic factors that overwhelm endogenous neuroprotective responses. To identify the potential molecular mechanisms underlying such delayed responses, we compared gene expression patterns using high-density oligonucleotide arrays at 4, 8, 24, and 72 h after moderate levels of lateral fluid percussion-induced brain injury in rats and lateral controlled cortical impact injury in mice (a total of 47 profiles). Expression of 82 genes in 12 functional categories was significantly changed in both species after trauma. The largest number of gene expression changes were found in the functional groups related to inflammation (17%), transcription regulation (16%), and cell adhesion/extracellular matrix (15%). Fifty percent of genes similarly altered across models had not been previously implicated in traumatic brain injury. Of particular interest were expression changes in genes linked to neurodegeneration, such as ATF3 and lysosomal membrane glycoprotein 2, and to neuroprotection including lipocortin 1, calponin 3, gelsolin, Id-1, and p45 NF-E2. Gene expression profiling across species and models may help identify candidate molecular pathways induced by brain injury, some of which may provide novel targets for therapeutic intervention.