72-kDa heat shock protein and mRNA expression after controlled cortical impact injury with hypoxemia in rats

Experimental traumatic brain injury increases epichaperome formation

Under normal conditions, heat shock proteins work in unison through dynamic protein interactions collectively referred to as the "chaperome." Recent work revealed that during cellular stress, the functional interactions of the chaperome are modified to form the "epichaperome," which results in improper protein folding, degradation, aggregation, and transport. This study is the first to investigate this novel mechanism of protein dishomeostasis in traumatic brain injury (TBI). Male and female adult, Sprague-Dawley rats received a lateral controlled cortical impact (CCI) and the ipsilateral hippocampus was collected 24 h 1, 2, and 4 weeks after injury. The epichaperome complex was visualized by measuring HSP90, HSC70 and HOP expression in native-PAGE and normalized to monomeric protein expression. A two-way ANOVA examined the effect of injury and sex at each time-point. Native HSP90, HSC70 and HOP protein expression showed a significant effect of injury effect across all time-points. Additionally, HSC70 and HOP showed significant sex effects at 24 h and 4 weeks. Altogether, controlled cortical impact significantly increased formation of the epichaperome across all proteins measured. Further investigation of this pathological mechanism can lead to a greater understanding of the link between TBI and increased risk of neurodegenerative disease and targeting the epichaperome for therapeutics.

Synergistic effects of brain injury and aging: common mechanisms of proteostatic dysfunction

The aftermath of TBI is associated with an acute stress response and the accumulation of insoluble protein aggregates. Even after the symptoms of TBI are resolved, insidious molecular processes continue to develop, which often ultimately result in the development of age-associated neurodegenerative disorders. The precise molecular cascades that drive unhealthy brain aging are still largely unknown. In this review, we discuss proteostatic dysfunction as a converging mechanism contributing to accelerated brain aging after TBI. We examine evidence from human tissue and in vivo animal models, spanning both the aging and injury contexts. We conclude that TBI has a sustained debilitating effect on the proteostatic machinery, which may contribute to the accelerated pathological and cognitive hallmarks of aging that are observed following injury.

Diffuse Axonal Injury in the Rat Brain: Axonal Injury and Oligodendrocyte Activity Following Rotational Injury

Traumatic brain injury (TBI) commonly results in primary diffuse axonal injury (DAI) and associated secondary injuries that evolve through a cascade of pathological mechanisms. We aim at assessing how myelin and oligodendrocytes react to head angular-acceleration-induced TBI in a previously described model. This model induces axonal injuries visible by amyloid precursor protein (APP) expression, predominantly in the corpus callosum and its borders. Brain tissue from a total of 27 adult rats was collected at 24 h, 72 h and 7 d post-injury. Coronal sections were prepared for immunohistochemistry and RNAscope^® to investigate DAI and myelin changes (APP, MBP, Rip), oligodendrocyte lineage cell loss (Olig2), oligodendrocyte progenitor cells (OPCs) (NG2, PDGFRa) and neuronal stress (HSP70, ATF3). Oligodendrocytes and OPCs numbers (expressed as percentage of positive cells out of total number of cells) were measured in areas with high APP expression. Results showed non-statistically significant trends with a decrease in oligodendrocyte lineage cells and an increase in OPCs. Levels of myelination were mostly unaltered, although Rip expression differed significantly between sham and injured animals in the frontal brain. Neuronal stress markers were induced at the dorsal cortex and habenular nuclei. We conclude that rotational injury induces DAI and neuronal stress in specific areas. We noticed indications of oligodendrocyte death and regeneration without statistically significant changes at the timepoints measured, despite indications of axonal injuries and neuronal stress. This might suggest that oligodendrocytes are robust enough to withstand this kind of trauma, knowledge important for the understanding of thresholds for cell injury and post-traumatic recovery potential.

Alcohol protects the CNS by activating HSF1 and inducing the heat shock proteins

Although alcohol abuse and dependence have profound negative health consequences, emerging evidence suggests that exposure to low/moderate concentrations of ethanol protects multiple organs and systems. In the CNS, moderate drinking decreases the risk of dementia and Alzheimer's disease. This neuroprotection correlates with an increased expression of the heat shock proteins (HSPs). Multiple epidemiological studies revealed an inverse association between ethanol intoxication and traumatic brain injury mortality. In this case, ethanol-induced HSPs limit the inflammatory immune response diminishing cell death and improving the neurobehavioural outcome. Ethanol also protects the brain against ischemic injuries via the HSPs. In our laboratory, we demonstrated that ethanol increased the expression of several HSP genes in neurons and astrocytes by activating the transcription factor, heat shock factor 1 (HSF1). HSF1 induces HSPs that target misfolded proteins for refolding or degradation, increasing the survival chances of the cells. These data indicate that ethanol neuroprotection is mediated by the activation HSF1 and the induction of HSPs.

Exercise attenuates neurological deficits by stimulating a critical HSP70/NF-κB/IL-6/synapsin I axis in traumatic brain injury rats

Background

Despite previous evidence for a potent inflammatory response after a traumatic brain injury (TBI), it is unknown whether exercise preconditioning (EP) improves outcomes after a TBI by modulating inflammatory responses.

Methods

We performed quantitative real-time PCR (qPCR) to quantify the genes encoding 84 cytokines and chemokines in the peripheral blood and used ELISA to determine both the cerebral and blood levels of interleukin-6 (IL-6). We also performed the chromatin immunoprecipitation (ChIP) assay to evaluate the extent of nuclear factor kappa-B (NF-κB) binding to the DNA elements in the IL-6 promoter regions. Also, we adopted the Western blotting assay to measure the cerebral levels of heat shock protein (HSP) 70, synapsin I, and β-actin. Finally, we performed both histoimmunological and behavioral assessment to measure brain injury and neurological deficits, respectively.

Results

We first demonstrated that TBI upregulated nine pro-inflammatory and/or neurodegenerative messenger RNAs (mRNAs) in the peripheral blood such as CXCL10, IL-18, IL-16, Cd-70, Mif, Ppbp, Ltd, Tnfrsf 11b, and Faslg. In addition to causing neurological injuries, TBI also upregulated the following 14 anti-inflammatory and/or neuroregenerative mRNAs in the peripheral blood such as Ccl19, Ccl3, Cxcl19, IL-10, IL-22, IL-6, Bmp6, Ccl22, IL-7, Bmp7, Ccl2, Ccl17, IL-1rn, and Gpi. Second, we observed that EP inhibited both neurological injuries and six pro-inflammatory and/or neurodegenerative genes (Cxcl10, IL-18, IL-16, Cd70, Mif, and Faslg) but potentiated four anti-inflammatory and/or neuroregenerative genes (Bmp6, IL-10, IL-22, and IL-6). Prior depletion of cerebral HSP70 with gene silence significantly reversed the beneficial effects of EP in reducing neurological injuries and altered gene profiles after a TBI. A positive Pearson correlation exists between IL-6 and HSP70 in the peripheral blood or in the cerebral levels. In addition, gene silence of cerebral HSP70 significantly reduced the overexpression of NF-κB, IL-6, and synapsin I in the ipsilateral brain regions after an EP in rats.

Conclusions

TBI causes neurological deficits associated with stimulating several pro-inflammatory gene profiles but inhibiting several anti-inflammatory gene profiles of cytokines and chemokines. Exercise protects against neurological injuries via stimulating an anti-inflammatory HSP70/NF-κB/IL-6/synapsin I axis in the injured brains.

Improving on Laboratory Traumatic Brain Injury Models to Achieve Better Results

Experimental modeling of traumatic brain injury (TBI) in animals has identified several potential means and interventions that might have beneficial applications for treating traumatic brain injury clinically. Several of these interventions have been applied and tried with humans that are at different phases of testing (completed, prematurely terminated and others in progress). The promising results achieved in the laboratory with animal models have not been replicated with human trails as expected. This review will highlight some insights and significance attained via laboratory animal modeling of TBI as well as factors that require incorporation into the experimental studies that could help in translating results from laboratory to the bedside. Major progress has been made due to laboratory studies; in explaining the mechanisms as well as pathophysiological features of brain damage after TBI. Attempts to intervene in the cascade of events occurring after TBI all rely heavily on the knowledge from basic laboratory investigations. In looking to discover treatment, this review will endeavor to sight and state some central discrepancies between laboratory models and clinical scenarios.

Lesion Size Is Exacerbated in Hypoxic Rats Whereas Hypoxia-Inducible Factor-1 Alpha and Vascular Endothelial Growth Factor Increase in Injured Normoxic Rats: A Prospective Cohort Study of Secondary Hypoxia in Focal Traumatic Brain Injury

BACKGROUND

Hypoxia following traumatic brain injury (TBI) is a severe insult shown to exacerbate the pathophysiology, resulting in worse outcome. The aim of this study was to investigate the effects of a hypoxic insult in a focal TBI model by monitoring brain edema, lesion volume, serum biomarker levels, immune cell infiltration, as well as the expression of hypoxia-inducible factor-1 alpha (HIF-1α) and vascular endothelial growth factor (VEGF).

MATERIALS AND METHODS

Female Sprague-Dawley rats (n = 73, including sham and naive) were used. The rats were intubated and mechanically ventilated. A controlled cortical impact device created a 3-mm deep lesion in the right parietal hemisphere. Post-injury, rats inhaled either normoxic (22% O2) or hypoxic (11% O2) mixtures for 30 min. The rats were sacrificed at 1, 3, 7, 14, and 28 days post-injury. Serum was collected for S100B measurements using ELISA. Ex vivo magnetic resonance imaging (MRI) was performed to determine lesion size and edema volume. Immunofluorescence was employed to analyze neuronal death, changes in cerebral macrophage- and neutrophil infiltration, microglia proliferation, apoptosis, complement activation (C5b9), IgG extravasation, HIF-1α, and VEGF.

RESULTS

The hypoxic group had significantly increased blood levels of lactate and decreased pO2 (p < 0.0001). On MRI post-traumatic hypoxia resulted in larger lesion areas (p = 0.0173), and NeuN staining revealed greater neuronal loss (p = 0.0253). HIF-1α and VEGF expression was significantly increased in normoxic but not in hypoxic animals (p < 0.05). A trend was seen for serum levels of S100B to be higher in the hypoxic group at 1 day after trauma (p = 0.0868). No differences were observed between the groups in cytotoxic and vascular edema, IgG extravasation, neutrophils and macrophage aggregation, microglia proliferation, or C5b-9 expression.

CONCLUSION

Hypoxia following focal TBI exacerbated the lesion size and neuronal loss. Moreover, there was a tendency to higher levels of S100B in the hypoxic group early after injury, indicating a potential validity as a biomarker of injury severity. In the normoxic group, the expression of HIF-1α and VEGF was found elevated, possibly indicative of neuro-protective responses occurring in this less severely injured group. Further studies are warranted to better define the pathophysiology of post-TBI hypoxia.

Experimental Models Combining Traumatic Brain Injury and Hypoxia

Traumatic brain injury (TBI) is one of the most common causes of death and disability, and cerebral hypoxia is a frequently occurring harmful secondary event in TBI patients. The hypoxic conditions that occur on the scene of accident, where the airways are often obstructed or breathing is in other ways impaired, could be reproduced using animal TBI models where oxygen delivery is strictly controlled throughout the entire experimental procedure. Monitoring physiological parameters of the animal is of utmost importance in order to maintain an adequate quality of the experiment. Peripheral oxygen saturation, O2 pressure (pO2) in the blood, or fraction of inhaled O2 (FiO2) could be used as goals to validate the hypoxic conditions. Different models of traumatic brain injury could be used to inflict desired injury type, whereas effects then could be studied using radiological, physiological and functional tests. In order to confirm that the brain has been affected by a hypoxic injury, appropriate substances in the affected cerebral tissue, cerebrospinal fluid, or serum should be analyzed.

Neuroprotective effects of geranylgeranylacetone in experimental traumatic brain injury

Geranylgeranylacetone (GGA) is an inducer of heat-shock protein 70 (HSP70) that has been used clinically for many years as an antiulcer treatment. It is centrally active after oral administration and is neuroprotective in experimental brain ischemia/stroke models. We examined the effects of single oral GGA before treatment (800 mg/kg, 48 hours before trauma) or after treatment (800 mg/kg, 3 hours after trauma) on long-term functional recovery and histologic outcomes after moderate-level controlled cortical impact, an experimental traumatic brain injury (TBI) model in mice. The GGA pretreatment increased the number of HSP70(+) cells and attenuated posttraumatic α-fodrin cleavage, a marker of apoptotic cell death. It also improved sensorimotor performance on a beam walk task; enhanced recovery of cognitive/affective function in the Morris water maze, novel object recognition, and tail-suspension tests; and improved outcomes using a composite neuroscore. Furthermore, GGA pretreatment reduced the lesion size and neuronal loss in the hippocampus, cortex, and thalamus, and decreased microglial activation in the cortex when compared with vehicle-treated TBI controls. Notably, GGA was also effective in a posttreatment paradigm, showing significant improvements in sensorimotor function, and reducing cortical neuronal loss. Given these neuroprotective actions and considering its longstanding clinical use, GGA should be considered for the clinical treatment of TBI.

Brain endothelial HSP-70 stress response coincides with endothelial and pericyte death after brain trauma

OBJECTIVES

Our objective was to characterize the heat shock response (HSR) in a model of traumatic brain injury (TBI) and to determine the association of HSR to cell death.

METHODS

We used immunofluorescent detection of HSP-70 to characterize HSR and TUNEL labeling to determine the pattern of cell death.

RESULTS

HSP-70 immunofluorescence revealed a steady increase from 4 to 48 hours following TBI, culminating in a ubiquitous expression with the capillary bed 48 hours post-TBI. TUNEL labeling revealed a small subset of endothelial cell death and a most robust staining of putative pericyte cell death.

DISCUSSION

Our results show that while injury causes a detectable stress response, cell death is not a direct consequence of the HSR.

Low levels of mutant ubiquitin are degraded by the proteasome in vivo

The ubiquitin-proteasome system fulfills a pivotal role in regulating intracellular protein turnover. Impairment of this system is implicated in the pathogenesis of neurodegenerative diseases characterized by ubiquitin- containing proteinaceous deposits. UBB(+1), a mutant ubiquitin, is one of the proteins accumulating in the neuropathological hallmarks of tauopathies, including Alzheimer's disease, and polyglutamine diseases. In vitro, UBB(+1) properties shift from a proteasomal ubiquitin-fusion degradation substrate at low expression levels to a proteasome inhibitor at high expression levels. Here we report on a novel transgenic mouse line (line 6663) expressing low levels of neuronal UBB(+1). In these mice, UBB(+1) protein is scarcely detectable in the neuronal cell population. Accumulation of UBB(+1) commences only after intracranial infusion of the proteasome inhibitors lactacystin or MG262, showing that, at these low expression levels, the UBB(+1) protein is a substrate for proteasomal degradation in vivo. In addition, accumulation of the protein serves as a reporter for proteasome inhibition. These findings strengthen our proposition that, in healthy brain, UBB(+1) is continuously degraded and disease-related UBB(+1) accumulation serves as an endogenous marker for proteasomal dysfunction. This novel transgenic line can give more insight into the intrinsic properties of UBB(+1) and its role in neurodegenerative disease.

Neuroproteomics: a biochemical means to discriminate the extent and modality of brain injury

Diagnosis and treatment of stroke and traumatic brain injury remain significant health care challenges to society. Patient care stands to benefit from an improved understanding of the interactive biochemistry underlying neurotrauma pathobiology. In this study, we assessed the power of neuroproteomics to contrast biochemical responses following ischemic and traumatic brain injuries in the rat. A middle cerebral artery occlusion (MCAO) model was employed in groups of 30-min and 2-h focal neocortical ischemia with reperfusion. Neuroproteomes were assessed via tandem cation-anion exchange chromatography-gel electrophoresis, followed by reversed-phase liquid chromatography-tandem mass spectrometry. MCAO results were compared with those from a previous study of focal contusional brain injury employing the same methodology to characterize homologous neocortical tissues at 2 days post-injury. The 30-min MCAO neuroproteome depicted abridged energy production involving pentose phosphate, modulated synaptic function and plasticity, and increased chaperone activity and cell survival factors. The 2-h MCAO data indicated near complete loss of ATP production, synaptic dysfunction with degraded cytoarchitecture, more conservative chaperone activity, and additional cell survival factors than those seen in the 30-min MCAO model. The TBI group exhibited disrupted metabolism, but with retained malate shuttle functionality. Synaptic dysfunction and cytoarchitectural degradation resembled the 2-h MCAO group; however, chaperone and cell survival factors were more depressed following TBI. These results underscore the utility of neuroproteomics for characterizing interactive biochemistry for profiling and contrasting the molecular aspects underlying the pathobiological differences between types of brain injuries.

Heat shock proteins: cellular and molecular mechanisms in the central nervous system

Emerging evidence indicates that heat shock proteins (HSPs) are critical regulators in normal neural physiological function as well as in cell stress responses. The functions of HSPs represent an enormous and diverse range of cellular activities, far beyond the originally identified roles in protein folding and chaperoning. HSPs are now understood to be involved in processes such as synaptic transmission, autophagy, ER stress response, protein kinase and cell death signaling. In addition, manipulation of HSPs has robust effects on the fate of cells in neurological injury and disease states. The ongoing exploration of multiple HSP superfamilies has underscored the pluripotent nature of HSPs in the cellular context, and has demanded the recent revamping of the nomenclature referring to these families to reflect a re-organization based on structure and function. In keeping with this re-organization, we first discuss the HSP superfamilies in terms of protein structure, regulation, expression and distribution in the brain. We then explore major cellular functions of HSPs that are relevant to neural physiological states, and from there we discuss known and proposed HSP impacts on major neurological disease states. This review article presents a three-part discussion on the array of HSP families relevant to neuronal tissue, their cellular functions, and the exploration of therapeutic targets of these proteins in the context of neurological diseases.

Blast-induced brain injury and posttraumatic hypotension and hypoxemia

Explosive munitions account for more than 50% of all wounds sustained in military combat, and the proportion of civilian casualties due to explosives is increasing as well. But there has been only limited research on the pathophysiology of blast-induced brain injury, and the contributions of alterations in cerebral blood flow (CBF) or cerebral vascular reactivity to blast-induced brain injury have not been investigated. Although secondary hypotension and hypoxemia are associated with increased mortality and morbidity after closed head injury, the effects of secondary insults on outcome after blast injury are unknown. Hemorrhage accounted for approximately 50% of combat deaths, and the lungs are one of the primary organs damaged by blast overpressure. Thus, it is likely that blast-induced lung injury and/or hemorrhage leads to hypotensive and hypoxemic secondary injury in a significant number of combatants exposed to blast overpressure injury. Although the effects of blast injury on CBF and cerebral vascular reactivity are unknown, blast injury may be associated with impaired cerebral vascular function. Reactive oxygen species (ROS) such as the superoxide anion radical and other ROS, likely major contributors to traumatic cerebral vascular injury, are produced by traumatic brain injury (TBI). Superoxide radicals combine with nitric oxide (NO), another ROS produced by blast injury as well as other types of TBI, to form peroxynitrite, a powerful oxidant that impairs cerebral vascular responses to reduced intravascular pressure and other cerebral vascular responses. While current research suggests that blast injury impairs cerebral vascular compensatory responses, thereby leaving the brain vulnerable to secondary insults, the effects of blast injury on the cerebral vascular reactivity have not been investigated. It is clear that further research is necessary to address these critical concerns.

Heat shock proteins HSP70 and HSP27 in the cerebral spinal fluid of patients undergoing thoracic aneurysm repair correlate with the probability of postoperative paralysis

An understanding of the time course and correlation with injury of heat shock proteins (HSPs) released during brain and/or spinal cord cellular stress (ischemia) is critical in understanding the role of the HSPs in cellular survival, and may provide a clinically useful biomarker of severe cellular stress. We have analyzed the levels of HSPs in the cerebrospinal fluid (CSF) from patients who are undergoing thoracic aneurysm repair. Blood and CSF samples were collected at regular intervals, and CSF was analyzed by enzyme-linked immunosorbent assay for HSP70 and HSP27. These results were correlated with intraoperative somatosensory-evoked potentials measurements and postoperative paralysis. We find that the levels of these proteins in many patients are elevated and that the degree of elevation correlates with the risk of permanent paralysis. We hypothesize that sequential measurement intraoperatively of the levels of the heat shock proteins HSP70 and HSP27 in the CSF can predict those patients who are at greatest risk for paralysis during thoracic aneurysm surgery and will allow us to develop means of preventing or attenuating this severe and often fatal complication.

Heme oxygenase 1 in cerebrospinal fluid from infants and children after severe traumatic brain injury

Heme oxygenase 1 (HO-1) is an enzyme important in the catabolism of heme that is induced under conditions of oxidative stress. HO-1 degradation of heme yields biliverdin, bilirubin, carbon monoxide and iron. HO-1 is thought to serve a protective antioxidant function, and upregulation of HO-1 has been demonstrated in experimental models of neurodegeneration, subarachnoid hemorrhage, cerebral ischemia and traumatic brain injury (TBI). We measured HO-1 concentration in cerebral spinal fluid samples from 48 infants and children following TBI and 7 control patients by ELISA. Increased HO-1 was seen in TBI versus control patients--mean 2.75+/-0.63, peak 4.17+/-0.96 ng/ml versus control (<0.078 ng/ml, not detectable) (p<0.001). Increased HO-1 concentration was associated with increased injury severity and unfavorable neurological outcome (both p<0.05). Increased HO-1 concentration was independently associated with younger age; however, statistical analysis could not rule out the possibility that the effect of age was related to inflicted TBI from child abuse. HO-1 increases after TBI and appears to be more prominent in infants compared with older children after injury.

Animal models of head trauma

Animal models of traumatic brain injury (TBI) are used to elucidate primary and secondary sequelae underlying human head injury in an effort to identify potential neuroprotective therapies for developing and adult brains. The choice of experimental model depends upon both the research goal and underlying objectives. The intrinsic ability to study injury-induced changes in behavior, physiology, metabolism, the blood/tissue interface, the blood brain barrier, and/or inflammatory- and immune-mediated responses, makes in vivo TBI models essential for neurotrauma research. Whereas human TBI is a highly complex multifactorial disorder, animal trauma models tend to replicate only single factors involved in the pathobiology of head injury using genetically well-defined inbred animals of a single sex. Although such an experimental approach is helpful to delineate key injury mechanisms, the simplicity and hence inability of animal models to reflect the complexity of clinical head injury may underlie the discrepancy between preclinical and clinical trials of neuroprotective therapeutics. Thus, a search continues for new animal models, which would more closely mimic the highly heterogeneous nature of human TBI, and address key factors in treatment optimization.

Induction of the Stress Response after Inflicted and Non-Inflicted Traumatic Brain Injury in Infants and Children

Rapid induction of 72-kD heat shock protein (Hsp70) is a key component of the stress response and is seen after a variety of insults to the brain including experimental hyperthermia, ischemia, seizures, and traumatic brain injury (TBI). Little is known about the endogenous stress response in pediatric patients after brain injury. Accordingly, the concentration of Hsp70 was determined in 61 cerebrospinal fluid (CSF) samples from 20 infants and children after TBI. Peak Hsp70 level were increased in TBI patients vs. controls (4.60 [1.49-78.99] vs. 2.18 [1.38-4.25] ng/mL, respectively, median (range), p = 0.01) and occurred most often on day 1 after injury. Strikingly, CSF levels of Hsp70 were positively and independently associated with inflicted vs. non-inflicted TBI (7.03 [2.30-27.22] vs. 2.06 [1.06-78.99] ng/mL, respectively, p = 0.05). Endogenous Hsp70 expression was confirmed by Western blot and immunocytochemistry using brain tissue samples removed from patients who underwent decompressive craniotomy for refractory intracranial hypertension or at autopsy. These data suggest that the endogenous stress response, as measured and quantified by the Hsp70 concentration in CSF, occurs in infants and children after TBI. The endogenous stress response is more robust in victims of child abuse, compared with patients with accidental TBI, supporting age-dependence or a difference in either injury frequency, duration, severity, or mechanism in this subgroup of TBI patients. Further studies are needed to determine the role of Hsp70 in both non-inflicted and inflicted TBI in infants and children.

Hyperthermia following traumatic brain injury: a critical evaluation

Hyperthermia, frequently seen in patients following traumatic brain injury (TBI), may be due to posttraumatic cerebral inflammation, direct hypothalamic damage, or secondary infection resulting in fever. Regardless of the underlying cause, hyperthermia increases metabolic expenditure, glutamate release, and neutrophil activity to levels higher than those occurring in the normothermic brain-injured patient. This synergism may further compromise the injured brain, enhancing the vulnerability to secondary pathogenic events, thereby exacerbating neuronal damage. Although rigorous control of normal body temperature is the current standard of care for the brain-injured patient, patient management strategies currently available are often suboptimal and may be contraindicated. This article represents a compendium of published work regarding the state of knowledge of the relationship between hyperthermia and TBI, as well as a critical examination of current management strategies.

Alterations in inducible 72-kDa heat shock protein and the chaperone cofactor BAG-1 in human brain after head injury

The stress response in injured brain is well characterized after experimental ischemic and traumatic brain injury (TBI); however, the induction and regulation of the stress response in humans after TBI remains largely undefined. Accordingly, we examined injured brain tissue from adult patients (n = 8) that underwent emergent surgical decompression after TBI, for alterations in the inducible 72-kDa heat shock protein (Hsp70), the constitutive 73-kDa heat shock protein (Hsc70), and isoforms of the chaperone cofactor BAG-1. Control samples (n = 6) were obtained postmortem from patients dying of causes unrelated to CNS trauma. Western blot analysis showed that Hsp70, but not Hsc70, was increased in patients after TBI versus controls. Both Hsp70 and Hsc70 coimmunoprecipitated with the cofactor BAG-1. The 33 and 46, but not the 50-kDa BAG-1 isoforms were increased in patients after TBI versus controls. The ratio of the 46/33-kDa isoforms was increased in TBI versus controls, suggesting negative modulation of Hsp70/Hsc70 protein refolding activity in injured brain. These data implicate induction of the stress response and its modulation by the chaperone cofactor and Bcl-2 family member BAG-1, after TBI in humans.

Traumatic brain injury-induced acute gene expression changes in rat cerebral cortex identified by GeneChip analysis

Proper CNS function depends on concerted expression of thousands of genes in a controlled and timely manner. Traumatic brain injury (TBI) in mammals results in neuronal death and neurological dysfunction, which might be mediated by altered expression of several genes. By employing a CNS-specific GeneChip and real-time polymerase chain reaction (PCR), the present study analyzed the gene expression changes in adult rat cerebral cortex in the first 24 hr after a controlled cortical impact injury. Many functional families of genes not previously implicated in TBI-induced brain damage are altered in the injured cortex. These include up-regulated transcription factors (SOCS-3, JAK-2, STAT-3, CREM, IRF-1, SMN, silencer factor-B, ANIA-3, ANIA-4, and HES-1) and signal transduction pathways (cpg21, Narp, and CRBP) and down-regulated transmitter release mechanisms (CITRON, synaptojanin II, ras-related rab3, neurexin-1beta, and SNAP25A and -B), kinases (IP-3-kinase, Pak1, Ca(2+)/CaM-dependent protein kinases), and ion channels (K(+) channels TWIK, RK5, X62839, and Na(+) channel I). In addition, several genes previously shown to play a role in TBI pathophysiology, including proinflammatory genes, proapoptotic genes, heat shock proteins, immediate early genes, neuropeptides, and glutamate receptor subunits, were also observed to be altered in the injured cortex. Real-time PCR analysis confirmed the GeneChip data for many of these transcripts. The novel physiologically relevant gene expression changes observed here might explain some of the molecular mechanisms of TBI-induced neuronal damage.

Posttraumatic hypothermia is neuroprotective in a model of traumatic brain injury complicated by a secondary hypoxic insult

OBJECTIVE

Human traumatic brain injury frequently results in secondary complications, including hypoxia. In previous studies, we have reported that posttraumatic hypothermia is neuroprotective and that secondary hypoxia exacerbates histopathologic outcome after fluid-percussion brain injury. The purpose of this study was to assess the therapeutic effects of mild (33 degrees C) hypothermia after fluid-percussion injury combined with secondary hypoxia. In addition, the importance of the rewarming period on histopathologic outcome was investigated.

DESIGN

Prospective experimental study in rats.

SETTING

Experimental laboratory in a university teaching hospital.

INTERVENTION

Intubated, anesthetized rats underwent normothermic parasagittal fluid-percussion brain injury (1.8-2.1 atmospheres) followed by either 30 mins of normoxia (n = 6) or hypoxic (n = 6) gas levels and by 4 hrs of normothermia (37 degrees C). In hypothermic rats, brain temperature was reduced immediately after the 30-min hypoxic insult and maintained for 4 hrs. After hypothermia, brain temperature was either rapidly (n = 6) or slowly (n = 5) increased to normothermic levels. Rats were killed 3 days after traumatic brain injury, and contusion volumes were quantitatively assessed.

MEASUREMENTS AND MAIN RESULTS

As previously shown, posttraumatic hypoxia significantly increased contusion volume compared with traumatic brain injury-normoxic animals (p <.02). Importantly, although posttraumatic hypothermia followed by rapid rewarming (15 mins) failed to decrease contusion volume, those animals undergoing a slow rewarming period (120 mins) demonstrated significantly (p <.03) reduced contusion volumes, compared with hypoxic normothermic rats.

CONCLUSIONS

These data emphasize the beneficial effects of posttraumatic hypothermia in a traumatic brain injury model complicated by secondary hypoxia and stress the importance of the rewarming period in this therapeutic intervention.

Detection of single- and double-strand DNA breaks after traumatic brain injury in rats: comparison of in situ labeling techniques using DNA polymerase I, the Klenow fragment of DNA polymerase I, and terminal deoxynucleotidyl transferase

DNA damage is a common sequela of traumatic brain injury (TBI). Available techniques for the in situ identification of DNA damage include DNA polymerase I-mediated biotin-dATP nick-translation (PANT), the Klenow fragment of DNA polymerase I-mediated biotin-dATP nick-end labeling (Klenow), and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). While TUNEL has been widely utilized to detect primarily double-strand DNA breaks, the use of PANT to detect primarily single-strand DNA breaks and Klenow to detect both single- and double-strand DNA breaks has not been reported after TBI. Accordingly, coronal brain sections from naive rats and rats at 0, 0.5, 1, 2, 6, 24, and 72 h (n = 3-5/group) after controlled cortical impact with imposed secondary insult were processed using the PANT, Klenow, and TUNEL methods. Cells with DNA breaks were detected by PANT in the ipsilateral hemisphere as early as 0.5 h after injury and were maximal at 6 h (cortex = 66.3+/-15.8, dentate gyrus 58.6+/-12.8, CA1 = 15.8+/-5.9, CA3 = 12.8+/-4.2 cells/x 400 field, mean +/- SEM, all p < 0.05 versus naive). Cells with DNA breaks were detected by Klenow as early as 30 min and were maximal at 24 h (cortex = 56.3+/-14.3, dentate gyrus 78.0+/-16.7, CA1 = 25.8+/-4.7, CA3 = 29.3+/-15.1 cells/x 400 field, all p < 0.05 versus naive). Cells with DNA breaks were not detected by TUNEL until 2 h and were maximal at 24 h (cortex = 47.7+/-21.4, dentate gyrus 63.0+/-11.9, CA1 = 5.6+/-5.4, CA3 = 6.9+/-3.7 cells/x 400 field, cortex and dentate gyrus p < 0.05 versus naive). Dual-label immunofluorescence revealed that PANT-positive cells were predominately neurons. These data demonstrate that TBI results in extensive DNA damage, which includes both single- and double-strand breaks in injured cortex and hippocampus. The presence of multiple types of DNA breaks implicate several pathways in the evolution of DNA damage after TBI.

Caspase-3 mediated neuronal death after traumatic brain injury in rats

During programmed cell death, activation of caspase-3 leads to proteolysis of DNA repair proteins, cytoskeletal proteins, and the inhibitor of caspase-activated deoxyribonuclease, culminating in morphologic changes and DNA damage defining apoptosis. The participation of caspase-3 activation in the evolution of neuronal death after traumatic brain injury in rats was examined. Cleavage of pro-caspase-3 in cytosolic cellular fractions and an increase in caspase-3-like enzyme activity were seen in injured brain versus control. Cleavage of the caspase-3 substrates DNA-dependent protein kinase and inhibitor of caspase-activated deoxyribonuclease and co-localization of cytosolic caspase-3 in neurons with evidence of DNA fragmentation were also identified. Intracerebral administration of the caspase-3 inhibitor N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone (480 ng) after trauma reduced caspase-3-like activity and DNA fragmentation in injured brain versus vehicle at 24 h. Treatment with N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone for 72 h (480 ng/day) reduced contusion size and ipsilateral dorsal hippocampal tissue loss at 3 weeks but had no effect on functional outcome versus vehicle. These data demonstrate that caspase-3 activation contributes to brain tissue loss and downstream biochemical events that execute programmed cell death after traumatic brain injury. Caspase inhibition may prove efficacious in the treatment of certain types of brain injury where programmed cell death occurs.

Experimental models of brain trauma

A short review of the most widely used and popular experimental models of traumatic brain injury is presented. This review focuses on current animal models of traumatic brain injury that apply mechanical energy to the skull or, after trephination of the skull, to the intact dura. Recent experimental studies evaluating the pathobiology of traumatic brain injury using these models are also discussed. This article attempts to provide a broad overview of current knowledge and controversies in experimental animal research on brain trauma.

Secondary hypoxia following moderate fluid percussion brain injury in rats exacerbates sensorimotor and cognitive deficits

Human head trauma is frequently associated with respiratory problems resulting in secondary hypoxic insult. To document the behavioral consequences of secondary hypoxia in an established model of traumatic brain injury (TBI), intubated anesthetized animals were subjected to fluid percussion (FP) injury (1.87-2.17 atm) followed by 30 min of either normoxic (TBI-NO, n = 10) or hypoxic (TBI-HY, n = 11; pO2 = 30-40 mm Hg) gas levels. Sham animals (n = 19) underwent all manipulations except for the actual trauma. Animals were tested on various sensorimotor tasks beginning 3 days after FP injury along with cognitive testing on days 22 through 29 posttrauma. The secondary hypoxic insult exacerbated the sensorimotor deficits on beam-walking compared to those animals only receiving trauma. Cognitive impairments were also observed in the TBI-HY group in the hidden platform task compared to FP injury alone. These data indicate that a secondary hypoxic insult exacerbates both sensorimotor and cognitive deficits after TBI. This study provides direct evidence that incidences of hypoxia after brain trauma may potentially result in an increase in neurological deficits for the subpopulation of head injured patients undergoing hypoxic conditions further warranting strict monitoring of these events.

Exacerbation of cortical and hippocampal CA1 damage due to posttraumatic hypoxia following moderate fluid-percussion brain injury in rats

OBJECT

Patients with head injuries often experience respiratory distress that results in a secondary hypoxic insult. The present experiment was designed to assess the histopathological consequences of a secondary hypoxic insult by using an established rodent model of traumatic brain injury (TBI).

METHODS

Intubated anesthetized rats were subjected to moderate (1.94-2.18 atm) parasagittal fluid-percussion injury (FPI) to the brain. Following the TBI, the animals were maintained for 30 minutes by using either hypoxic (TBI-HY group, nine animals) or normoxic (TBI-NO, 10 animals) gas levels. Sham-operated animals also underwent all manipulations except for the FPI (sham-HY group, seven animals; and sham-NO group, seven animals). Three days after TBI the rats were killed, and quantitative histopathological evaluation was undertaken. Cortical contusion volumes were dramatically increased in the TBI-HY group compared with the TBI-NO group (p < 0.03). Qualitative assessment of cortical and subcortical structures demonstrated significant damage within the hippocampal areas, CA1 and CA2, of TBI-HY animals compared with the TBI-NO animals (both p < 0.03). There was also a significant increase in the frequency of damaged neuronal profiles within the middle and medial sectors of the CA1 hippocampus (p < 0.03) due to the hypoxic insult.

CONCLUSIONS

The results of this study demonstrate that a secondary hypoxic insult following parasagittal FPI exacerbates contusion and neuronal pathological conditions. These findings emphasize the need to control for secondary hypoxic insults after experimental and human head injury.