Cerebrospinal Fluid Biomarkers Are Associated With Glial Fibrillary Acidic Protein and αII-spectrin Breakdown Products in Brain Tissues Following Penetrating Ballistic-Like Brain Injury in Rats.

Treatments to improve outcomes following severe traumatic brain injury (TBI) are limited but may benefit from understanding subacute-chronic brain protein profiles and identifying biomarkers suitable for use in this time. Acute alterations in the well-known TBI biomarkers glial fibrillary acidic protein (GFAP), αII-spectrin, and their breakdown products (BDPs) have been well established, but little is known about the subacute-chronic post-injury profiles of these biomarkers. Thus, the current study was designed to determine the extended profile of these TBI-specific biomarkers both in brain tissue and cerebral spinal fluid (CSF). Protein abundance was evaluated in brain tissue samples taken from regions of interest and in CSF at 24 h, 3 days, 7 days, 1 month, and 3 months following severe TBI in rats. Results showed increased full length GFAP (GFAP-FL) and GFAP-BDPs starting at 24 h that remained significantly elevated in most brain regions out to 3 months post-injury. However, in CSF, neither GFAP-FL nor GFAP-BDPs were elevated as a consequence of injury. Regional-specific reduction in αII-spectrin was evident in brain tissue samples from 24 h through 3 months. In contrast, SBDP-145/150 was robustly elevated in most brain regions and in CSF from 24 h through 7 days. Correlation analyses revealed numerous significant relationships between proteins in CSF and brain tissue or neurological deficits. This work indicates that TBI results in chronic changes in brain protein levels of well-known TBI biomarkers GFAP, αII-spectrin, and their BDPs and that SBDP-145/150 may have utility as an acute-chronic biomarker.

Acute and subacute microRNA dysregulation is associated with cytokine responses in the rodent model of penetrating ballistic-like brain injury.

BACKGROUND: MicroRNAs (miRNAs) are small stable RNAs that regulate translational degradation or repression of genes involved in brain trauma-mediated inflammation. More recently, miRNAs have emerged as potential novel TBI biomarkers. The aim of this study was to determine if a select set of miRNAs (miR-21, Let-7i, miR-124a, miR-146a, miR-107) that were previously associated with TBI models and clinical studies would be dysregulated and correlated to inflammatory cytokine abundance in the rat penetrating ballistic-like brain injury (PBBI) model. METHODS: Adult male Sprague-Dawley rats received a unilateral frontal 10% PBBI, which produces a temporary cavity. Sham animals received a craniotomy only. Ipsilateral brain tissue and serum were collected 4 hours to 7 days post-injury. Quantitation of miR-21, Let-7i, miR-124a, miR-146a, or miR-107 levels was conducted using Taqman PCR assays normalized to the endogenous reference, U6 snRNA. Brain tissue derived from matching cohorts was used to determine 1L-1beta and IL-6 levels by enzyme-linked immunosorbent assay. RESULTS: Brain tissue Let-7i and miR-21 increased at 4 hours and 1 day, whereas miR-124a and miR-107 were enhanced only 1 day post-injury. MiR-146a displayed a biphasic response and increased 1 day and 7 days, whereas elevation of miR-21 was sustained 1 day to 7 days after PBBI. Pathway analysis indicated that miRNAs were linked to inflammatory proteins, IL-6 and IL-1beta. Confirmation by enzyme-linked immunosorbent assay indicated that both cytokines were increased and peaked at 1 day, but fell at 3 days through 7 days after PBBI, indicating an inverse relationship with miRNA abundance. Serum Let-7i, alone, was differentially abundant 7 days after PBBI. CONCLUSION: Brain tissue-derived miRNAs linked to increased cytokine levels demonstrates a plausible therapeutic target of TBI-induced inflammation. Suppression of serum derived Let-7i may have utility as a biomarker of subacute injury progression or therapeutic responses.

Functional and Molecular Correlates after Single and Repeated Rat Closed-Head Concussion: Indices of Vulnerability after Brain Injury.

Closed-head concussive injury is one of the most common causes of traumatic brain injury (TBI). Isolated concussions frequently produce acute neurological impairments, and individuals typically recover spontaneously within a short time frame. In contrast, brain injuries resulting from multiple concussions can result in cumulative damage and elevated risk of developing chronic brain pathologies. Increased attention has focused on identification of diagnostic markers that can prognostically serve as indices of brain health after injury, revealing the temporal profile of vulnerability to a second insult. Such markers may demarcate adequate recovery periods before concussed patients can return to required activities. We developed a noninvasive closed-head impact model that captures the hallmark symptoms of concussion in the absence of gross tissue damage. Animals were subjected to single or repeated concussive impact and examined using a battery of neurological, vestibular, sensorimotor, and molecular metrics. A single concussion induced transient, but marked, acute neurological impairment, gait alterations, neuronal death, and increased glial fibrillary acidic protein (GFAP) expression in brain tissue. As expected, repeated concussions exacerbated sensorimotor dysfunction, prolonged gait abnormalities, induced neuroinflammation, and upregulated GFAP and tau. These animals also exhibited chronic functional neurological impairments with sustained astrogliosis and white matter thinning. Acute changes in molecular signatures correlated with behavioral impairments, whereas increased times to regaining consciousness and balance impairments were associated with higher GFAP and neuroinflammation. Overall, behavioral consequences of either single or repeated concussive impact injuries appeared to resolve more quickly than the underlying molecular, metabolic, and neuropathological abnormalities. This observation, which is supported by similar studies in other mTBI models, underscores the critical need to develop more objective prognostic measures for guiding return-to-play decisions.

Subacute Changes in Cleavage Processing of Amyloid Precursor Protein and Tau following Penetrating Traumatic Brain Injury.

Traumatic brain injury (TBI) is an established risk factor for the development of Alzheimer's disease (AD). Here the effects of severe penetrating TBI on APP and tau cleavage processing were investigated in a rodent model of penetrating ballistic-like brain injury (PBBI). PBBI was induced by stereotactically inserting a perforated steel probe through the right frontal cortex of the anesthetized rat and rapidly inflating/deflating the probe's elastic tubing into an elliptical shaped balloon to 10% of total rat brain volume causing temporary cavitation injury. Separate animals underwent probe injury (PrI) alone without balloon inflation. Shams underwent craniectomy. Brain tissue was collected acutely (4h, 24h, 3d) and subacutely (7d) post-injury and analyzed by immunoblot for full length APP (APP-FL) and APP beta c-terminal fragments (ßCTFs), full length tau (tau-FL) and tau truncation fragments and at 7d for cytotoxic Beta amyloid (Aß) peptides Aß40 and Aß42 analysis. APP-FL was significantly decreased at 3d and 7d following PBBI whereas APP ßCTFs were significantly elevated by 4h post-injury and remained elevated through 7d post-injury. Effects on ßCTFs were mirrored with PrI, albeit to a lesser extent. Aß40 and Aß42 were significantly elevated at 7d following PBBI and PrI. Tau-FL decreased substantially 3d and 7d post-PBBI and PrI. Importantly, a 22 kDa tau fragment (tau22), similar to that found in AD, was significantly elevated by 4h and remained elevated through 7d post-injury. Thus both APP and tau cleavage was dramatically altered in the acute and subacute periods post-injury. As cleavage of these proteins has also been implicated in AD, TBI pathology shown here may set the stage for the later development of AD or other tauopathies.

Temporal alterations in aquaporin and transcription factor HIF1α expression following penetrating ballistic-like brain injury (PBBI).

OBJECTIVES: Brain edema is a primary factor in the morbidity and mortality of traumatic brain injury (TBI). The various isoforms of aquaporin 4 (AQP4) and aquaporin 9 (AQP9) are important factors influencing edema following TBI. Others have reported that these AQPs are regulated by the transcription factor hypoxia inducible factor (HIF) 1α. Therefore, we examined the temporal alterations in the multiple isoforms of AQP4 and AQP9, and its possible upstream regulation by HIF1α, and evaluated whether different severities of penetrating injury influence these mechanisms. METHODS: In the penetrating ballistic-like brain injury (PBBI) model, a temporary cavity and resultant injury was formed by the rapid inflation/deflation (i.e. <40ms) of an elastic balloon attached to the end of the custom probe, injuring 10% of total rat brain volume. Tissue from the ipsilateral core and perilesional injury zones was collected. Total RNA was isolated at 4, 12, and 24h, 3 and 7days post-injury (sham and PBBI, n=6 per group). cDNA was synthesized using oligodT primers. Quantitative real time PCR was performed using Taqman expression assays for aqp4 (recognizing all isoforms), aqp9, and hif1α. Using separate animals, tissue lysate was collected at 4 and 24h, 3 and 7days post-injury and analyzed by immunoblot for protein expression of multiple isoforms of AQP4, the single known isoform of AQP9 and for expression of transcription factor HIF1α (sham, probe only control, and PBBI, n=8-10 per group). RESULTS: Global aqp4 mRNA was decreased at 24h (p<0.01) with PBBI. Three of the four known protein isoforms of AQP4 were detected, M1 (34kDa), M23 (32kDa) and isoform 3 (30kDa). AQP4 M1 decreased at 3 and 7days post-injury (p<0.001; p<0.01). AQP4 M23 levels were highly variable with no significant changes. AQP4 isoform 3 levels were decreased 3days post-PBBI (p<0.05). From 4, 12, and 24h aqp9 mRNA levels were decreased with injury (p<0.01, p<0.05, p<0.01) while AQP9 levels were decreased at 3 and 7days after PBBI (p<0.001, p<0.01). At 12 and 24h post-PBBI hif1α mRNA levels increased (p<0.05, p<0.01) but at 3 and 7days mRNA levels decreased (p<0.05, p<0.01). From 24h and 3 and 7days HIF1α protein levels were decreased (p<0.0001, p<0.0001, p<0.0001). In comparison to probe control, PBBI led to greater decreases in protein for AQP4 M1 (trend), AQP4 isoform 3 (trend), AQP9 (p<0.05) and HIF1α (p<0.05). CONCLUSION: PBBI is characterized by a loss of AQP4 M1, AQP4 isoform 3 and AQP9 at delayed time-points. The severity of the injury (PBBI versus probe control) increased these effects. Therefore, AQP9 and the AQP4 M1 isoform may be regulated by HIF1α, but not AQP4 isoform 3. This delayed loss of aquaporins may markedly reduce the ability of the brain to efflux water, contributing to the protracted edema that is a characteristic following severe penetrating TBI. Factors contributing to edema differ with different types and severities of TBI. For example, cellular based edema is more prominent in diffuse non-penetrating TBI whereas vasogenic edema is more prevalent with TBI involving hemorrhage. Molecular regulation leading to edema will likely also differ, such that treatments which have been suggested for non-hemorrhagic moderate TBI, such as the suppression of aquaporins, may be detrimental in more severe forms of TBI.

Correlations between blood-brain barrier disruption and neuroinflammation in an experimental model of penetrating ballistic-like brain injury.

Abstract Blood-brain barrier (BBB) disruption is a pathological hallmark of severe traumatic brain injury (TBI) and is associated with neuroinflammatory events contributing to brain edema and cell death. The goal of this study was to elucidate the profile of BBB disruption after penetrating ballistic-like brain injury (PBBI) in conjunction with changes in neuroinflammatory markers. Brain uptake of biotin-dextran amine (BDA; 3 kDa) and horseradish peroxidase (HRP; 44 kDa) was evaluated in rats at 4 h, 24 h, 48 h, 72 h, and 7 days post-PBBI and compared with the histopathologic and molecular profiles for inflammatory markers. BDA and HRP both displayed a uniphasic profile of extravasation, greatest at 24 h post-injury and which remained evident out to 48 h for HRP and 7 days for BDA. This profile was most closely associated with markers for adhesion (mRNA for intercellular adhesion molecule-1) and infiltration of peripheral granulocytes (mRNA for matrix metalloproteinase-9 [MMP-9] and myeloperoxidase staining). Improvement of BBB dysfunction coincided with increased expression of markers implicated in tissue remodeling and repair. The results of this study reveal a uniphasic and gradient opening of the BBB after PBBI and suggest MMP-9 and resident inflammatory cell activation as candidates for future neurotherapeutic intervention after PBBI.

Mechanism of action for NNZ-2566 anti-inflammatory effects following PBBI involves upregulation of immunomodulator ATF3.

The tripeptide glycine-proline-glutamate analogue NNZ-2566 (Neuren Pharmaceuticals) demonstrates neuroprotective efficacy in models of traumatic brain injury. In penetrating ballistic-like brain injury (PBBI), it significantly decreases injury-induced upregulation of inflammatory cytokines including TNF-α, IFN-γ, and IL-6. However, the mechanism by which NNZ-2566 acts has yet to be determined. The activating transcription factor-3 (ATF3) is known to repress expression of these inflammatory cytokines and was increased at the mRNA and protein level 24-h post-PBBI. This study investigated whether 12 h of NNZ-2566 treatment following PBBI alters atf3 expression. PBBI alone significantly increased atf3 mRNA levels by 13-fold at 12 h and these levels were increased by an additional fourfold with NNZ-2566 treatment. To confirm that changes in mRNA translated to changes in protein expression, ATF3 expression levels were determined in vivo in microglia/macrophages, T cells, natural killer cells (NKCs), astrocytes, and neurons. PBBI alone significantly increased ATF3 in microglia/macrophages (820%), NKCs (58%), and astrocytes (51%), but decreased levels in T cells (48%). NNZ-2566 treatment further increased ATF3 protein expression in microglia/macrophages (102%), NKCs (308%), and astrocytes (13%), while reversing ATF3 decreases in T cells. Finally, PBBI increased ATF3 levels by 55% in neurons and NNZ-2566 treatment further increased these levels an additional 33%. Since increased ATF3 may be an innate protective mechanism to limit inflammation following injury, these results demonstrating that the anti-inflammatory and neuroprotective drug NNZ-2566 increase both mRNA and protein levels of ATF3 in multiple cell types provide a cellular mechanism for NNZ-2566 modulation of neuroinflammation following PBBI.

Changes in apoptotic mechanisms following penetrating ballistic-like brain injury.

We investigated apoptotic pathways in a model of severe traumatic brain injury, penetrating ballistic-like brain injury (PBBI). TUNEL staining identified increasing apoptosis within 24 h. From targeted arrays, 11 genes were identified for temporal mRNA evaluation. In addition, mRNA levels and enzyme activity for caspases 3, 8, and 9 were examined. In the death receptor-mediated apoptosis pathway, the relative quantities (RQs) of mRNA for tnfr1, fas, and tnf were upregulated while trail mRNA was downregulated. In the anti-apoptotic TNF-R2 pathway, tnfr2 and flip were upregulated while xiap was downregulated. These findings indicate that increases in tnf levels following injury are not only pro-apoptotic but may also signal competing anti-apoptotic mechanisms. For the mitochondria-mediated apoptosis pathway, RQs of anti-apoptotic factors bcl2a1d and birc3 were upregulated while both bcl2 and bax were downregulated. RQs for casp 3 and casp 8 increased while casp9 decreased. Enzymatic activity increased for caspases 3, 8, and 9. While multiple mechanisms promoting and inhibiting apoptosis are at play during the first week after a PBBI, the cumulative result remains increased apoptosis. The ability to understand and dissect these events will assist in the development and evaluation of treatments targeting apoptosis following severe brain injury.

A role for interleukin-2 trans-presentation in dendritic cell-mediated T cell activation in humans, as revealed by daclizumab therapy.

Although previous studies have described CD25 expression and production of interleukin-2 (IL-2) by mature dendritic cells (mDCs), it remains unclear how these molecules participate in the activation of T cells. In search of the mechanisms by which daclizumab, a humanized monoclonal antibody against CD25, inhibits brain inflammation in multiple sclerosis, we observed that although the drug has limited effects on polyclonal T cell activation, it potently inhibits activation of antigen-specific T cells by mDCs. We show that mDCs (and antigen-experienced T cells) secrete IL-2 toward the mDC-T cell interface in an antigen-specific manner, and mDCs 'lend' their CD25 to primed T cells in trans to facilitate early high-affinity IL-2 signaling, which is crucial for subsequent T cell expansion and development of antigen-specific effectors. Our data reveal a previously unknown mechanism for the IL-2 receptor system in DC-mediated activation of T cells.

24S-hydroxycholesterol effects on lipid metabolism genes are modeled in traumatic brain injury.

Membrane damage during traumatic brain injury (TBI) alters the brain homeostasis of cholesterol and other lipids. Cholesterol 24S-hydroxylase (Cyp46) is a cholesterol metabolic enzyme that is increased after TBI. Here, we systematically examined the effects of the enzymatic product of Cyp46, 24S-hydroxycholesterol, on the cholesterol regulatory genes, SREBP-1 and 2, their posttranslational regulation, and their effects on gene transcription. 24S-hydroxycholesterol increased levels of SREBP-1 mRNA and full-length protein but did not change levels of cleaved SREBP-1, consistent with the role of 24-hydroxycholesterol as an LXR agonist. In contrast, 24S-hydroxycholesterol decreased levels of LXR-independent SREBP-2 mRNA, full-length protein, and SREBP-2 active cleavage product. We examined the downstream effects of changes to these lipid regulatory factors by studying cholesterol and fatty acid synthesis genes. In neuroblastoma cells, 24S-hydroxycholesterol decreased mRNA levels of the cholesterol synthesis genes HMG CoA reductase, squalene synthase, and FPP synthase but did not alter levels of the mRNA of fatty acid synthesis genes acetyl CoA carboxylase or fatty acid synthase. After TBI, as after 24S-hydroxycholesterol treatment in vitro, SREBP-1 mRNA levels were increased while SREBP-2 mRNA levels were decreased. Also similar to the in vitro results with 24S-hydroxycholesterol, HMG CoA reductase and squalene synthase mRNA levels were significantly decreased. Fatty acid synthase mRNA levels were not altered but acetyl CoA carboxylase mRNA levels were significantly decreased. Thus, changes to transcription of cholesterol synthesis genes after TBI were consistent with increases in Cyp46 activity, but changes to fatty acid synthesis genes must be regulated by other mechanisms.

Cortical injury increases cholesterol 24S hydroxylase (Cyp46) levels in the rat brain.

In traumatic brain injury (TBI), cellular loss from initial impact as well as secondary neurodegeneration leads to increased cholesterol and lipid debris at the site of injury. Cholesterol accumulation in the periphery can trigger inflammatory mechanisms while cholesterol clearance may be anti-inflammatory. Here we investigated whether TBI altered the regulation of cholesterol 24S-hydroxylase (Cyp46), an enzyme that converts cholesterol to the more hydrophilic 24S-hydroxycholesterol. We examined by Western blot and immunohistochemistry changes in Cyp46 expression following fluid percussion injury. Under normal conditions, most Cyp46 was present in neurons, with very little measurable in glia. Cyp46 levels were significantly increased at 7 days post-injury, and cell type specific analysis at 3 days post-injury showed a significant increase in levels of Cyp46 (84%) in microglia. Since 24-hydroxycholesterol induces activation of genes through the liver X receptor (LXR), we examined protein levels of ATP-binding cassette transporter A1 and apolipoprotein E, two LXR regulated cholesterol homeostasis proteins. Apolipoprotein E and ATP-binding cassette transporter A1 were increased at 7 days post-injury, indicating that increased LXR activity coincided with increased Cyp46 levels. We found that activation of primary rat microglia by LPS in vitro caused increased Cyp46 levels. These data suggest that increased microglial Cyp46 activity is part of a system for removal of damaged cell membranes post-injury, by conversion of cholesterol to 24-hydroxycholesterol and by activation of LXR-regulated gene transcription.

The metalloprotease inhibitor TIMP-3 regulates amyloid precursor protein and apolipoprotein E receptor proteolysis.

Cellular cholesterol levels alter the processing of the amyloid precursor protein (APP) to produce Abeta. Activation of liver X receptors (LXRs), one cellular mechanism to regulate cholesterol homeostasis, has been found to alter Abeta levels in vitro and in vivo. To identify genes regulated by LXR, we treated human neuroblastoma cells with an LXR agonist (TO-901317) and examined gene expression by microarray. As expected, TO-901317 upregulated several cholesterol metabolism genes, but it also decreased expression of a metalloprotease inhibitor, TIMP-3. We confirmed this finding using real-time PCR and by measuring TIMP-3 protein in glia, SY5Y cells, and COS7 cells. TIMP-3 is a member of a family of metalloproteinase inhibitors and blocks A disintegrin and metalloproteinase-10 (ADAM-10) and ADAM-17, two APP alpha-secretases. We found that TIMP-3 inhibited alpha-secretase cleavage of APP and an apolipoprotein E (apoE) receptor, ApoER2. TIMP-3 decreased surface levels of ADAM-10, APP, and ApoER2. These changes were accompanied by increased APP beta-C-terminal fragment and Abeta production. These data suggest that TIMP-3 preferentially routes APP and ApoER2 away from the cell surface and alpha-secretase cleavage and encourages endocytosis and beta-secretase cleavage. In vivo, TO-901317 decreased brain TIMP-3 levels. TIMP-3 protein levels were increased in human Alzheimer's disease (AD) brain and in APP transgenic mice, suggesting that increased levels of TIMP-3 in AD may contribute to higher levels of Abeta.