Astrocyte-derived exosomes protect hippocampal neurons after traumatic brain injury by suppressing mitochondrial oxidative stress and apoptosis.

In this study, we investigated the mechanisms through which astrocyte-derived exosomes (AS-Exos) alleviate traumatic brain injury (TBI)-induced neuronal defects in TBI model rats and mice. Treatment with AS-Exos alleviated neurobehavioral deficits, cognitive impairment, and brain edema in TBI rats. AS-Exos also significantly reduced neuronal cell loss and atrophy in the TBI rats. AS-Exos significantly reduced oxidative stress and mitochondrial H2O2 levels by increasing the activity of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) in the hippocampal neurons of TBI rats. TUNEL-staining assays showed that AS-Exos significantly reduced TBI-induced neuronal apoptosis. Mechanistically, AS-Exos ameliorated oxidative stress by activating Nrf2/HO-1 signaling in the hippocampus of TBI rats. In addition, the neuroprotective effects of AS-Exos were abrogated in brain-specific Nrf2-knockout mice subjected to TBI. These findings demonstrate that AS-Exos protects against TBI-induced oxidative stress and neuronal apoptosis by activating Nrf2 signaling in both rat and mouse models.

Admission Features Associated With Paroxysmal Sympathetic Hyperactivity After Traumatic Brain Injury: A Case-Control Study.

OBJECTIVES: Paroxysmal sympathetic hyperactivity occurs in a subset of critically ill traumatic brain injury patients and has been associated with worse outcomes after traumatic brain injury. The goal of this study was to identify admission risk factors for the development of paroxysmal sympathetic hyperactivity in traumatic brain injury patients. DESIGN: Retrospective case-control study of age- and Glasgow Coma Scale-matched traumatic brain injury patients. SETTING: Neurotrauma ICU at the R. Adams Cowley Shock Trauma Center of the University of Maryland Medical System, January 2016 to July 2018. PATIENTS: Critically ill adult traumatic brain injury patients who underwent inpatient monitoring for at least 14 days were included. Cases were identified based on treatment for paroxysmal sympathetic hyperactivity with institutional first-line therapies and were confirmed by retrospective tabulation of established paroxysmal sympathetic hyperactivity diagnostic and severity criteria. Cases were matched 1:1 by age and Glasgow Coma Scale to nonparoxysmal sympathetic hyperactivity traumatic brain injury controls, yielding 77 patients in each group. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Admission characteristics independently predictive of paroxysmal sympathetic hyperactivity included male sex, higher admission systolic blood pressure, and initial CT evidence of diffuse axonal injury, intraventricular hemorrhage/subarachnoid hemorrhage, complete cisternal effacement, and absence of contusion. Paroxysmal sympathetic hyperactivity cases demonstrated significantly worse neurologic outcomes upon hospital discharge despite being matched for injury severity at admission. CONCLUSIONS: Several anatomical, epidemiologic, and physiologic risk factors for clinically relevant paroxysmal sympathetic hyperactivity can be identified on ICU admission. These features help characterize paroxysmal sympathetic hyperactivity as a clinical-pathophysiologic phenotype associated with worse outcomes after traumatic brain injury.

AMPK induces regulatory innate lymphoid cells after traumatic brain injury.

The CNS is regarded as an immunoprivileged organ, evading routine immune surveillance; however, the coordinated development of immune responses profoundly influences outcomes after brain injury. Innate lymphoid cells (ILCs) are cytokine-producing cells that are critical for the initiation, modulation, and resolution of inflammation, but the functional relevance and mechanistic regulation of ILCs are unexplored after acute brain injury. We demonstrate increased proliferation of all ILC subtypes within the meninges for up to 1 year after experimental traumatic brain injury (TBI) while ILCs were present within resected dura and elevated within cerebrospinal fluid (CSF) of moderate-to-severe TBI patients. In line with energetic derangements after TBI, inhibition of the metabolic regulator, AMPK, increased meningeal ILC expansion, whereas AMPK activation suppressed proinflammatory ILC1/ILC3 and increased the frequency of IL-10-expressing ILC2 after TBI. Moreover, intracisternal administration of IL-33 activated AMPK, expanded ILC2, and suppressed ILC1 and ILC3 within the meninges of WT and Rag1-/- mice, but not Rag1-/- IL2rg-/- mice. Taken together, we identify AMPK as a brake on the expansion of proinflammatory, CNS-resident ILCs after brain injury. These findings establish a mechanistic framework whereby immunometabolic modulation of ILCs may direct the specificity, timing, and magnitude of cerebral immunity.

MMP-9 Inhibitor GM6001 Prevents the Development of ssTBI-Induced Parkinson's Disease via the Autophagy Pathway.

Concussion is a widely recognized environmental risk factor for neurodegenerative diseases, including Parkinson's disease (PD). Small-vessel disease of the brain has been reported to contribute to neurodegenerative diseases. In this study, we observed BBB disruption in wild-type (WT) mice, but not in matrix metalloproteinase 9 (MMP-9) knockout mice, subjected to single severe traumatic brain injury (ssTBI). Furthermore, treating ssTBI mice with the MMP-9 inhibitor GM6001 effectively maintained BBB integrity, promoted the elimination of damaged mitochondria via mitophagy, and then prevented neuronal death and progressive neurodegeneration. However, we did not observe this neuroprotective effect of MMP-9 inhibition in beclin-1-/+ mice. Collectively, these findings revealed that concussion led to BBB disruption via MMP-9, and that GM6001 prevented the development of PD via the autophagy pathway.

Nrf2/HO-1 mediates the neuroprotective effects of pramipexole by attenuating oxidative damage and mitochondrial perturbation after traumatic brain injury in rats.

Pramipexole (PPX), a D2-like receptor agonist, is generally used in the treatment of Parkinson's disease and restless leg syndrome. Its neuroprotective effects have been shown against various neurological disorders. Recent research work has demonstrated that PPX exerts neuroprotection through mitochondria. However, the neuromodulator-related effects of PPX against traumatic brain injury (TBI) remain unexplored. The present study, therefore, investigated the mechanism of neuroprotection by PPX against oxidative stress, mitochondrial dysfunction and neuronal damage following TBI in rats. We hypothesized that the neuroprotection by PPX in TBI-subjected rats might involve activation of the Nrf2/HO-1 (also known as Nfe2l2/Hmox1) signaling pathway. PPX was injected intraperitoneally (0.25 mg/kg body weight and 1.0 mg/kg body weight) at different time intervals post-TBI. Several neurobehavioral parameters were assessed at 48 h post-TBI, and the brain was isolated for molecular and biochemical analysis. The results demonstrated that PPX treatment significantly improved the behavioral deficits, decreased the lipid peroxidation rate, increased glutathione levels and decreased 4-hydroxynonenal levels in TBI-subjected rats. PPX also increased the activities of glutathione peroxidase and superoxide dismutase enzymes. In addition, PPX treatment inhibited mitochondrial reactive oxygen species production, restored mitochondrial membrane potential and increased ATP levels after a TBI. Further, PPX treatment reduced the Bax/Bcl2 ratio and translocation of Bax to mitochondria and cytochrome-c to the cytosol. Finally, PPX treatment greatly accelerated the translocation of Nrf2 to the nucleus and upregulated HO-1 protein expression. We conclude that the neuroprotective effects of PPX are mediated by activation of the Nrf2/HO-1 signaling pathway following TBI.This article has an associated First Person interview with the first author of the paper.

Levels of caspase-1 in cerebrospinal fluid of patients with traumatic brain injury: correlation with intracranial pressure and outcome.

OBJECTIVE: The objectives of this study were to evaluate levels of inflammasome-signaling proteins in serum and CSF of patients with traumatic brain injury (TBI), and to correlate these protein levels with intracranial pressure (ICP) and clinical outcomes at 6 months after injury. METHODS: This is a prospective and observational study in patients with moderate and severe TBI who required an external ventricular drain as part of their treatment. Serum and CSF samples were collected 3 times a day for the first 5 days after TBI. The authors have determined the protein concentration of caspase-1 in the CSF and serum of patients with TBI by using commercially available enzyme-linked immunosorbent assays. The ICP value was recorded hourly. The 6-month outcome was assessed using the Glasgow Outcome Scale-Extended. RESULTS: A total of 21 patients were included in this study, and a total of 234 paired serum-CSF samples were analyzed. The area under the curve (AUC) value of caspase-1 in CSF during the 5-day period was 2452.9 pg/mL·hr in the group of patients with high ICP vs 617.6 pg/mL·hr in the patients with low ICP. The differences were mainly on day 2 (19.7 pg/mL vs 1.8 pg/mL; p = 0.06) and day 3 (13.9 pg/mL vs 1 pg/mL; p = 0.05). The AUC value of caspase in CSF during the 5-day period was 1918.9 pg/mL·hr in the group of patients with poor outcome versus 924.5 pg/mL·hr in the patients with good outcome. The protein levels of caspase-1 in CSF were higher in patients with unfavorable outcomes during the first 96 hours after TBI. CONCLUSIONS: In this cohort of patients with TBI who were admitted to the neurosurgical ICU, the inflammasome protein caspase-1 is increased in the CSF of patients with high ICP, especially on days 2 and 3 after TBI. Also the protein levels of caspase-1 in CSF were higher in patients with poor outcome during the first 96 hours after TBI. Moreover, not only the absolute value of caspase-1 in CSF but also its trend is associated with poor outcomes.

Cathepsin B in neurodegeneration of Alzheimer's disease, traumatic brain injury, and related brain disorders.

Investigations of Alzheimer's disease (AD), traumatic brain injury (TBI), and related brain disorders have provided extensive evidence for involvement of cathepsin B, a lysosomal cysteine protease, in mediating the behavioral deficits and neuropathology of these neurodegenerative diseases. This review integrates findings of cathepsin B regulation in clinical biomarker studies, animal model genetic and inhibitor evaluations, structural studies, and lysosomal cell biological mechanisms in AD, TBI, and related brain disorders. The results together indicate the role of cathepsin B in the behavioral deficits and neuropathology of these disorders. Lysosomal leakage occurs in AD and TBI, and related neurodegeneration, which leads to the hypothesis that cathepsin B is redistributed from the lysosome to the cytosol where it initiates cell death and inflammation processes associated with neurodegeneration. These results together implicate cathepsin B as a major contributor to these neuropathological changes and behavioral deficits. These findings support the investigation of cathepsin B as a potential drug target for therapeutic discovery and treatment of AD, TBI, and TBI-related brain disorders.

Manual acupuncture relieves microglia-mediated neuroinflammation in a rat model of traumatic brain injury by inhibiting the RhoA/ROCK2 pathway.

OBJECTIVE: To investigate the regulatory mechanism of manual acupuncture (MA) on microglial polarization-mediated neuroinflammation after traumatic brain injury (TBI), focusing on the RhoA/Rho-associated coiled coil-forming protein kinase (ROCK2) pathway. METHODS: Sprague Dawley (SD) rats were used to generate a TBI model using Feeney's freefall epidural impact method. MA was performed on half of the TBI model rats, while the others remained untreated. Acupuncture was administered at GV15, GV16, GV20, GV26, and LI4. At the end of the intervention, rat brain tissue samples were collected, and the microglial M1 polarization status was observed by immunofluorescence labeling of CD86, an M1 microglia-specific protein. RhoA/ROCK2 signaling components were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting. An enzyme-linked immunosorbent assay (ELISA) was used to detect the expression levels of inflammatory factors. RESULTS: Compared with normal rats, the CD86 expression density in the untreated TBI model rats was high and showed an aggregated expression pattern. The genes and proteins of the RhoA/ROCK2 signaling pathway were highly expressed, and inflammatory factors were significantly increased. The CD86 expression density in TBI rats after MA was reduced compared to that in untreated TBI rats and showed a scattered distribution. The expression of RhoA/ROCK2 signaling pathway genes and proteins was also significantly reduced, and inflammatory factors were decreased. CONCLUSION: These results show that MA may inhibit M1 polarization of microglia by regulating the RhoA/ROCK2 signaling pathway, thereby reducing neuroinflammation in TBI.

Acid Sphingomyelinase Inhibition Mitigates Histopathological and Behavioral Changes in a Murine Model of Traumatic Brain Injury.

Traumatic brain injury (TBI) can lead to the development of chronic traumatic encephalopathy as a result of neuronal phosphorylated tau (p-tau) protein aggregation and neuroinflammation. Acid sphingomyelinase (Asm) may also contribute to post-TBI neurodegenerative disorders. We hypothesized that Asm inhibition would ameliorate p-tau aggregation, neuroinflammation, and behavioral changes after TBI in a murine model. TBI was generated using a weight-drop method. Asm inhibition in wild-type mice was achieved with a single injection of amitriptyline 1 h after TBI. Genetic Asm ablation was achieved using Asm-deficient mice (Asm-/-). Thirty days after TBI, mice underwent behavioral testing with the forced swim test for symptoms of depression or were euthanized for neurohistological analysis. Neuroinflammation was quantified using the microglial markers, ionized calcium-binding adaptor molecule 1 and transmembrane protein 119. Compared to sham mice, TBI mice demonstrated increased hippocampal p-tau. Mice that received amitriptyline after TBI demonstrated decreased p-tau compared to mice that received a saline control. Further, post-TBI Asm-/- mice demonstrated lower levels of p-tau compared to wild-type mice. Though a decrease in neuroinflammation was observed at 1 month post-TBI, no change was demonstrated with mice treated with amitriptyline. Similarly, TBI mice were more likely to show depression compared to mice that received amitriptyline after TBI. Utilizing a weight-drop method to induce moderate TBI, we have shown that genetic deficiency or pharmacological inhibition of Asm prevented hippocampal p-tau aggregation 1 month after injury as well as decreased symptoms of depression. These findings highlight an opportunity to potentially reduce the long-term consequences of TBI.

An Effective NADPH Oxidase 2 Inhibitor Provides Neuroprotection and Improves Functional Outcomes in Animal Model of Traumatic Brain Injury.

Traumatic brain injury (TBI) has become a leading cause of death and disability all over the world. Pharmacological suppression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2) can inhibit oxidative stress which is implicated in the pathology of TBI. GSK2795039 was reported to target NOX2 to inhibit [Formula: see text] and ROS production. The present study aimed to investigate the effect of GSK2795039 on NOX2 activity and neurological deficits in a TBI mouse model. TBI mouse model was established by a weight-drop to mouse skull. GSK2795039 at a dose of 100 mg/kg was administrated to mice 30 min before TBI. NOX2 expression and activity were detected by Western blot and biochemical method. Neurological damage and apoptosis were detected by behavioral test and terminal deoxynucleotidyl transferase dUTP nick end labeling staining. GSK2795039 significantly inhibited NOX2 expression and activity in the TBI mouse model. It also attenuated TBI-induced neurological deficits, apoptosis, and neurological recovery. The results indicate that GSK2795039 can be used as a potential drug for TBI treatment.

Basic Fibroblast Growth Factor (bFGF) Protects the Blood-Brain Barrier by Binding of FGFR1 and Activating the ERK Signaling Pathway After Intra-Abdominal Hypertension and Traumatic Brain Injury.

BACKGROUND Intra-abdominal hypertension (IAH) is associated with high morbidity and mortality. IAH leads to intra-abdominal tissue damage and causes dysfunction in distal organs such as the brain. The effect of a combined injury due to IAH and traumatic brain injury (TBI) on the integrity of the blood-brain barrier (BBB) has not been investigated. MATERIAL AND METHODS Intracranial pressure (ICP) monitoring, brain water content, EB permeability detection, immunofluorescence staining, real-time PCR, and Western blot analysis were used to examine the effects of IAH and TBI on the BBB in rats, and to characterize the protective effects of basic fibroblast growth factor (bFGF) on combined injury-induced BBB damage. RESULTS Combined injury from IAH and TBI to the BBB resulted in brain edema and increased intracranial pressure. The effects of bFGF on alleviating the rat BBB injuries were determined, indicating that bFGF regulated the expression levels of the tight junction (TJ), adhesion junction (AJ), matrix metalloproteinase (MMP), and IL-1ß, as well as reduced BBB permeability, brain edema, and intracranial pressure. Moreover, the FGFR1 antagonist PD 173074 and the ERK antagonist PD 98059 decreased the protective effects of bFGF. CONCLUSIONS bFGF effectively protected the BBB from damage caused by combined injury from IAH and TBI, and binding of FGFR1 and activation of the ERK signaling pathway was involved in these effects.

An Activity-Based Nanosensor for Traumatic Brain Injury.

Currently, traumatic brain injury (TBI) is detected by medical imaging; however, medical imaging requires expensive capital equipment, is time- and resource-intensive, and is poor at predicting patient prognosis. To date, direct measurement of elevated protease activity has yet to be utilized to detect TBI. In this work, we engineered an activity-based nanosensor for TBI (TBI-ABN) that responds to increased protease activity initiated after brain injury. We establish that a calcium-sensitive protease, calpain-1, is active in the injured brain hours within injury. We then optimize the molecular weight of a nanoscale polymeric carrier to infiltrate into the injured brain tissue with minimal renal filtration. A calpain-1 substrate that generates a fluorescent signal upon cleavage was attached to this nanoscale polymeric carrier to generate an engineered TBI-ABN. When applied intravenously to a mouse model of TBI, our engineered sensor is observed to locally activate in the injured brain tissue. This TBI-ABN is the first demonstration of a sensor that responds to protease activity to detect TBI.

(-)-Epigallocatechin-3-gallate provides neuroprotection via AMPK activation against traumatic brain injury in a mouse model.

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. (-)-Epigallocatechin-3-gallate (EGCG) has shown robust neuroprotective effects on various brain injury models in rodents. Herein, we aimed to investigate if EGCG protects against TBI and unravel the underlying mechanisms. A total of 102 mice were used for this study. TBI was induced by controlled cortical impact (CCI). EGCG was given immediately after TBI injury. Neurological functions were accessed by corner test, paw placement, modified neurological severity score, rotarod test, and Morris water maze test. AMPK inhibitor and AMPKα1-knockout mice were used to further study the signaling pathways involved in the observed effects. Our results show that EGCG significantly ameliorated CCI-induced neurological impairment, including spatial learning and memory. EGCG suppressed CCI-induced inflammation and oxidative stress. Furthermore, EGCG downregulated the phosphorylation of IKKα/ß, IκBα, and nuclear translocation of NF-κB p65; upregulated AMPK phosphorylation; and altered corresponding changes in the phosphorylation of the downstream target's ribosomal protein S6, AS160, and CaMKKß. Our data demonstrate that EGCG protects against CCI-induced TBI through the activation of the AMPK pathway in mice, suggesting that EGCG might be a promising therapeutic intervention preventing locomotor and cognitive impairments after TBI.

Histone Deacetylase 4 Downregulation Elicits Post-Traumatic Psychiatric Disorders through Impairment of Neurogenesis.

An enduring deficit in neurogenesis largely contributes to the development of severe post-traumatic psychiatric disorders such as anxiety, depression, and memory impairment following traumatic brain injury (TBI); however, the mechanism remains obscure. Here we have shown that an imbalance in the generation of γ-aminobutyric acid (GABA)ergic and glutamatergic neurons due to aberrant induction of vesicular glutamate transporter 1 (vGlut1)-positive glutamatergic cells is responsible for impaired neuronal differentiation in the hippocampus following TBI. To elucidate the molecular mechanism, we found that TBI activates a transcription factor, Pax3, by increasing its acetylation status, and subsequently induces Ngn2 transcription. This event, in turn, augments the vGlut1-expressing glutamatergic neurons and accumulation of excess glutamate in the hippocampus that can affect neuronal differentiation. In our study the acetylation of Pax3 was increased due to loss of its interaction with a deacetylase, histone deacetylase 4 (HDAC4), which was downregulated after TBI. TBI-induced activation of GSK3ß was responsible for the degradation of HDAC4. We also showed that overexpression of HDAC4 before TBI reduces Pax3 acetylation by restoring an interaction between HDAC4 and Pax3 in the hippocampus. This event prevents the aberrant induction of vGlut1-positive glutamatergic neurons by decreasing the Ngn2 level and subsequently reinforces the balance between GABAergic and glutamatergic neurons following TBI. Further, we found that overexpression of HDAC4 in the hippocampus improves anxiety, depressive-like behavior, and memory functions following TBI.

Senescence-associated-ß-galactosidase staining following traumatic brain injury in the mouse cerebrum.

Primary and secondary traumatic brain injury (TBI) can cause tissue damage by inducing cell death pathways including apoptosis, necroptosis, and autophagy. However, similar pathways can also lead to senescence. Senescent cells secrete senescence-associated secretory phenotype proteins following persistent DNA damage response signaling, leading to cell disorders. TBI initially activates the cell cycle followed by the subsequent triggering of senescence. This study aims to clarify how the mRNA and protein expression of different markers of cell cycle and senescence are modulated and switched over time after TBI. We performed senescence-associated-ß-galactosidase (SA-ß-gal) staining, immunohistochemical analysis, and real-time PCR to examine the time-dependent changes in expression levels of proteins and mRNA, related to cell cycle and cellular senescence markers, in the cerebrum during the initial 14 days after TBI using a mouse model of controlled cortical impact (CCI). Within the area adjacent to the cerebral contusion after TBI, the protein and/or mRNA expression levels of cell cycle markers were increased significantly until 4 days after injury and senescence markers were significantly increased at 4, 7, and 14 days after injury. Our findings suggested that TBI initially activated the cell cycle in neurons, astrocytes, and microglia within the area adjacent to the hemicerebrum contusion in TBI, whereas after 4 days, such cells could undergo senescence in a cell-type-dependent manner.

Inhibition of Glycogen Synthase Kinase 3ß as a Treatment for the Prevention of Cognitive Deficits after a Traumatic Brain Injury.

Traumatic brain injury (TBI) has many long-term consequences, including impairment in memory and changes in mood. Glycogen synthase kinase 3ß (GSK-3ß) in its phosphorylated form (p-GSK-3ß) is considered to be a major contributor to memory problems that occur post-TBI. We have developed an antisense that targets the GSK-3ß (GAO) gene. Using a model of closed-head concussive TBI, we subjected mice to TBI and injected GAO or a random antisense (RAO) 15 min post-injury. One week post-injury, mice were tested in object recognition with 24 h delay. At 4 weeks post- injury, mice were tested with a T-maze foot shock avoidance memory test and a second object recognition test with 24 h delay using different objects. Mice that received GAO show improved memory in both object recognition and T-maze compared with RAO- treated mice that were subjected to TBI. Next, we verified that GAO blocked the surge in phosphorylated GSK-3ß post-TBI. Mice were subjected to TBI and injected with antisense 15 min post-TBI with GAO or RAO. Mice were euthanized at 4 and 72 h post-TBI. Analysis of p-ser9GSK-3ß, p-tyr216GSK-3ß, and phospho-tau (p-tau)404 showed that mice that received a TBI+RAO had significantly higher p-ser9GSK-3ß, p-tyr216GSK-3ß, and p-tau404 levels than the mice that received TBI+GAO and the Sham+RAO mice. The current finding suggests that inhibiting GSK-3ß increase after TBI with an antisense directed at GSK-3ß prevents learning and memory impairments.

Baicalin provides neuroprotection in traumatic brain injury mice model through Akt/Nrf2 pathway.

BACKGROUND: The neuroprotective effects of Baicalin have been confirmed in several central nervous system (CNS) diseases. However, its possible effect on traumatic brain injury (TBI) model is still not clear. The present study is aimed to investigate the role and the underling mechanisms of 7-D-glucuronic acid-5,6-dihydroxyflavone (Baicalin) on TBI model. METHODS: The weight-drop model of TBI in Institute of Cancer Research mice was treated with Baicalin intraperitoneally at 30 minutes after TBI. LY294002 (LY) (a commonly used PI3K/Akt pathway inhibitor) was injected into the left ventricle at 30 minutes before TBI. All mice were euthanized at 24 hours after TBI to collect the brain tissue for a series of tests except for neurological function, which was measured at 2 hours and 1 and 3 days post-TBI. RESULTS: Baicalin administration significantly improved neurobehavioral function, alleviated brain edema, and reduced apoptosis-positive cells by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay accompanied with the upregulation of B-cell lymphoma 2 (Bcl-2) and downregulation of Bcl-2-associated X protein (Bax) and cleaved-caspase 3 by Western blot. Besides, TBI-induced oxidant stress status was also restored in the Baicalin group by measuring malondialdehyde (MDA) content, glutathione peroxidase (GPx), and superoxide dismutase (SOD) levels in the injured brain cortex. Furthermore, translocation of Nrf2 to the nucleus was dramatically enhanced by Baicalin verified by immunofluorescence and Western blot analyses. Accordingly, its downstream antioxidative enzymes nicotinamide adenine dinucleotide phosphate:quinine oxidoreductase 1 (NQO-1) and heme oxygenase 1 (HO-1) were also activated by Baicalin confirmed by quantitative reverse transcription polymerase chain reaction (RT-qPCR) and Western blot. However, cotreatment with Baicalin and LY could partly abolish Baicalin-induced activation of Nrf2 and its neuroprotective effects in TBI. CONCLUSION: This study demonstrates that Baicalin provides a neuroprotective effect in TBI mice model via activating the Akt/Nrf2 pathway.

Dietary Zinc Modulates Matrix Metalloproteinases in Traumatic Brain Injury.

Animal models of mild traumatic brain injury (mTBI) provide opportunity to examine the extent to which dietary interventions can be used to improve recovery after injury. Animal studies also suggest that matrix metalloproteinases (MMPs) play a role in tissue remodeling post-TBI. Because dietary zinc (Zn) improved recovery in nonblast mTBI models, and the MMPs are Zn-requiring enzymes, we evaluated the effects of low- (LoZn) and adequate-Zn (AdZn) diets on MMP expression and behavioral responses, subsequent to exposure to a single blast. MMP messenger RNA expression in soleus muscle and frontal cortex tissues were quantified at 48 h and 14 days post-blast. In muscle, blast resulted in significant upregulation of membrane-type (MT)-MMP, MMP-2, tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 at 48 h post-injury in rats consuming AdZn. At 14 days post-blast, there were no blast or dietary effects observed on MMP levels in muscle, supporting the existence of a Zn-responsive, functional repair and remodeling mechanism. In contrast, blast resulted in a significant downregulation of MT-MMP, TIMP-1, and TIMP-2 and a significant upregulation of MMP-3 levels at 48 h post-injury in cortex tissue, whereas at 14 days post-blast, MT-MMP, MMP-2, and TIMP-2 were all downregulated in response to blast, independent of diet, and TIMP-1 were significantly increased in rats fed AdZn diets despite the absence of elevated MMPs. Because the blast injuries occurred while animals were under general anesthesia, the increased immobility observed post-injury in rats consuming LoZn diets suggest that blast mTBI can, in the absence of any psychological stressor, induce post-traumatic stress disorder-related traits that are chronic, but responsive to diet. Taken together, our results support a relationship between marginally Zn-deficient status and a compromised regenerative response post-injury in muscle, likely through the MMP pathway. However, in neuronal tissue, changes in MMP/TIMP levels after blast indicate a variable response to marginally Zn-deficient diets that may help explain compromised repair mechanism(s) previously associated with the systemic hypozincemia that develops in patients with TBI.

NADPH oxidase 2 deletion enhances neurogenesis following traumatic brain injury.

The NADPH oxidase (NOX) enzyme family is a major source of reactive oxygen species (ROS) and contributor to the secondary pathology underlying traumatic brain injury (TBI). However, little is known about how NOX-derived ROS influences the proliferation and cell-fate determination of neural stem/progenitor cells (NSCs/NPCs) following TBI. In the current study, we found that deletion of NOX2 (NOX2-KO) significantly decreases the population of radial glia-like NSCs and neuroblasts but maintains the population of non-radial Sox2 expressing stem cells under physiological (non-injury) conditions. Surprisingly, the brains of NOX2-KO mice demonstrated a robust increase in the number of neuroblasts during the first week after TBI, as compared to the wild-type group. This increase may result from an enhanced proliferation of NPCs in a lower ROS environment after brain injury, as further examination revealed a significant increase of dividing neuroblasts in both NOX2-KO and NOX inhibitor-treated mouse brain during the first week following TBI. Finally, 5-Bromo-2'-deoxyuridine (BrdU) lineage tracing demonstrated a significantly increased number of newborn neurons were present in the perilesional cortex of NOX2-KO mice at 5 weeks post TBI, indicating that deletion of NOX2 promotes long-term neurogenesis in the injured brain following TBI. Altogether, these findings suggest that targeting NOX through genetic deletion or inhibition enhances post-injury neurogenesis, which may be beneficial for recovery following TBI.

Elevation of MMP-9 Levels Promotes Epileptogenesis After Traumatic Brain Injury.

Posttraumatic epilepsy (PTE) is a recurrent seizure disorder that often develops secondary to traumatic brain injury (TBI) that is caused by an external mechanical force. Recent evidence shows that the brain extracellular matrix plays a major role in the remodeling of neuronal connections after injury. One of the proteases that is presumably responsible for this process is matrix metalloproteinase-9 (MMP-9). The levels of MMP-9 are elevated in rodent brain tissue and human blood samples after TBI. However, no studies have described the influence of MMP-9 on the development of PTE. The present study used controlled cortical impact (CCI) as a mouse model of TBI. We examined the detailed kinetics of MMP-9 levels for 1 month after TBI and observed two peaks after injury (30 min and 6 h after injury). We tested the hypothesis that high levels of MMP-9 predispose individuals to the development of PTE, and MMP-9 inhibition would protect against PTE. We used transgenic animals with either MMP-9 knockout or MMP-9 overexpression. MMP-9 overexpression increased the number of mice that exhibited TBI-induced spontaneous seizures, and MMP-9 knockout decreased the appearance of seizures. We also evaluated changes in responsiveness to a single dose of the chemoconvulsant pentylenetetrazol. MMP-9-overexpressing mice exhibited a significantly shorter latency between pentylenetetrazol administration and the first epileptiform spike. MMP-9 knockout mice exhibited the opposite response profile. Finally, we found that the occurrence of PTE was correlated with the size of the lesion after injury. Overall, our data emphasize the contribution of MMP-9 to TBI-induced structural and physiological alterations in brain circuitry that may lead to the development of PTE.