Temporal profile of serum metabolites and inflammation following closed head injury in rats is associated with HPA axis hyperactivity.

INTRODUCTION: Closed head injury (CHI) causes neurological disability along with systemic alterations that can activate neuro-endocrine response through hypothalamic-pituitary-adrenal (HPA) axis activation. A dysregulated HPA axis function can lead to relocation of energy substrates and alteration in metabolic pathways and inflammation at the systemic level. OBJECTIVES: Assessment of time-dependent changes in serum metabolites and inflammation after both mild and moderate CHI. Along with this, serum corticosterone levels and hypothalamic microglial response were observed. METHODS: Rats underwent mild and moderate weight-drop injury and their serum and hypothalamus were assessed at acute, sub-acute and chronic timepoints. Changes in serum metabolomics were determined using high resolution NMR spectroscopy. Serum inflammatory cytokine, corticosterone levels and hypothalamic microglia were assessed at all timepoints. RESULTS: Metabolites including lactate, choline and branched chain amino acids were found as the classifiers that helped distinguish between control and injured rats during acute, sub-acute and chronic timepoints. While, increased αglucose: ßglucose and TMAO: choline ratios after acute and sub-acute timepoints of mild injury differentiated from moderate injured rats. The injured rats also showed distinct inflammatory profile where IL-1ß and TNF-α levels were upregulated in moderate injured rats while IL-10 levels were downregulated in mild injured rats. Furthermore, injury specific alterations in serum metabolic and immunologic profile were found to be associated with hyperactive HPA axis, with consistent increase in serum corticosterone concentration post injury. The hypothalamic microglia showed a characteristic activated de-ramified cellular morphology in both mild and moderate injured rats. CONCLUSION: The study suggests that HPA axis hyperactivity along with hypothalamic microglial activation led to temporal changes in the systemic metabolism and inflammation. These time dependent changes in the metabolite profile of rats can further strengthen the knowledge of diagnostic markers and help distinguish injury related outcomes after TBI.

Sirt1 attenuates astrocyte activation via modulating Dnajb1 and chaperone-mediated autophagy after closed head injury.

Our previous study indicates that Silent information regulator 1 (Sirt1) is involved in macroautophagy by upregulating light chain 3 (LC3) expression in astrocyte to exert a neuroprotective effect. Chaperon-mediated autophagy (CMA), another form of autophagy, is also upregulated after brain injury. However, little is known about the role of Sirt1 in regulation of the CMA. In the present study, an in vivo model of closed head injury (CHI) and an in vitro model of primary cortical astrocyte stimulated with interleukin-1ß were employed to mimic the astrocyte activation induced by traumatic brain injury. Lentivirus carrying target complementary DNA (cDNA) or short hairpin RNA (shRNA) sequence was used to overexpress Sirt1 or knockdown DnaJ heat shock protein family member B1 (Dnajb1) (a molecular chaperone). We found that Sirt1 overexpression ameliorated neurological deficits, reduced tissue loss, and attenuated astrocyte activation after CHI, which was reversed by Dnajb1-shRNA administration. The upregulation of CMA activity induced by CHI in vivo and in vitro was inhibited after Dnajb1 knockdown. Sirt1 potently promoted CMA activity via upregulating Dnajb1 expression. Mechanically, Sirt1 could interact with Dnajb1 and modulate the deacetylation and ubiquitination of Dnajb1. These findings collectively suggest that Sirt1 plays a protective role against astrocyte activation, which may be associated with the regulation of the CMA activity via modulating the deacetylation and ubiquitination of Dnajb1 after CHI.

Assessment of the Effects of Altered Amyloid-Beta Clearance on Behavior following Repeat Closed-Head Brain Injury in Amyloid-Beta Precursor Protein Humanized Mice.

Traumatic brain injury (TBI) increases the risk for dementias including Alzheimer's disease (AD) and chronic traumatic encephalopathy. Further, both human and animal model data indicate that amyloid-beta (Aß) peptide accumulation and its production machinery are upregulated by TBI. Considering the clear link between chronic Aß elevation and AD as well as tau pathology, the role(s) of Aß in TBI is of high importance. Endopeptidases, including the neprilysin (NEP)-like enzymes, are key mediators of Aß clearance and may affect susceptibility to pathology post-TBI. Here, we use a "humanized" mouse model of Aß production, which expresses normal human amyloid-beta precursor protein (APP) under its natural transcriptional regulation and exposed them to a more clinically relevant repeated closed-head TBI paradigm. These transgenic mice also were crossed with mice deficient for the Aß degrading enzymes NEP or NEP2 to assess models of reduced cerebral Aß clearance in our TBI model. Our results show that the presence of the human form of Aß did not exacerbate motor (Rotarod) and spatial learning/memory deficits (Morris water maze) post-injuries, while potentially reduced anxiety (Open Field) was observed. NEP and NEP2 deficiency also did not exacerbate these deficits post-injuries and was associated with protection from motor (NEP and NEP2) and spatial learning/memory deficits (NEP only). These data suggest that normally regulated expression of wild-type human APP/Aß does not contribute to deficits acutely after TBI and may be protective at this stage of injury.

Interactions among Genetic Background, Anesthetic Agent, and Oxygen Concentration Shape Blunt Traumatic Brain Injury Outcomes in Drosophila melanogaster.

Following traumatic brain injury (TBI), the time window during which secondary injuries develop provides a window for therapeutic interventions. During this time, many TBI victims undergo exposure to hyperoxia and anesthetics. We investigated the effects of genetic background on the interaction of oxygen and volatile general anesthetics with brain pathophysiology after closed-head TBI in the fruit fly Drosophila melanogaster. To test whether sevoflurane shares genetic risk factors for mortality with isoflurane and whether locomotion is affected similarly to mortality, we used a device that generates acceleration-deceleration forces to induce TBI in ten inbred fly lines. After TBI, we exposed flies to hyperoxia alone or in combination with isoflurane or sevoflurane and quantified mortality and locomotion 24 and 48 h after TBI. Modulation of TBI-induced mortality and locomotor impairment by hyperoxia with or without anesthetics varied among fly strains and among combinations of agents. Resistance to increased mortality from hyperoxic isoflurane predicted resistance to increased mortality from hyperoxic sevoflurane but did not predict the degree of locomotion impairment under any condition. These findings are important because they demonstrate that, in the context of TBI, genetic background determines the latent toxic potentials of oxygen and anesthetics.

Sarm1 loss reduces axonal damage and improves cognitive outcome after repetitive mild closed head injury.

One of the consistent pathologies associated with both clinical and experimental traumatic brain injury is axonal injury, especially following mild traumatic brain injury (or concussive injury). Several lines of experimental evidence have demonstrated a role for NAD+ metabolism in axonal degeneration. One of the enzymes that metabolizes NAD+ in axons is Sarm1 (Sterile Alpha and TIR Motif Containing 1), and its activity is thought to play a key role in axonal degeneration. Using a Sarm1 knock-out mouse, we examined if loss of Sarm1 offers axonal injury protection and improves cognitive outcome after repeated mild closed head injury (rmCHI). Our results indicate that rmCHI caused white matter damage that can be observed in the corpus callosum, cingulum bundle, alveus of the hippocampus, and fimbria of the fornix of wild-type mice. These pathological changes were markedly reduced in injured Sarm1-/- mice. Interestingly, the activation of astrocytes and microglia was also attenuated in the areas with white matter damage, suggesting reduced inflammation. Associated with these improved pathological outcomes, injured Sarm1-/- mice performed significantly better in both motor and cognitive tasks. Taken together, our results suggest that strategies aimed at inhibiting Sarm1 and/or restoring NAD+ levels in injured axons may have therapeutic utility.

Pre-treatment with microRNA-181a Antagomir Prevents Loss of Parvalbumin Expression and Preserves Novel Object Recognition Following Mild Traumatic Brain Injury.

Mild traumatic brain injury (mTBI) can result in permanent impairment in memory and learning and may be a precursor to other neurological sequelae. Clinical treatments to ameliorate the effects of mTBI are lacking. Inhibition of microRNA-181a (miR-181a) is protective in several models of cerebral injury, but its role in mTBI has not been investigated. In the present study, miR-181a-5p antagomir was injected intracerebroventricularly 24 h prior to closed-skull cortical impact in young adult male mice. Paw withdrawal, open field, zero maze, Y maze, object location and novel object recognition tests were performed to assess neurocognitive dysfunction. Brains were assessed immunohistologically for the neuronal marker NeuN, the perineuronal net marker wisteria floribunda lectin (WFA), cFos, and the interneuron marker parvalbumin. Protein quantification was performed with immunoblots for synaptophysin and postsynaptic density 95 (PSD95). Fluorescent in situ hybridization was utilized to localize hippocampal miR-181a expression. MiR-181a antagomir treatment reduced neuronal miR-181a expression after mTBI, restored deficits in novel object recognition and increased hippocampal parvalbumin expression in the dentate gyrus. These changes were associated with decreased dentate gyrus hyperactivity indicated by a relative reduction in PSD95 and cFos expression. These results suggest that miR-181a inhibition may be a therapeutic approach to reduce hippocampal excitotoxicity and prevent cognitive dysfunction following mTBI.

PrPC expression and calpain activity independently mediate the effects of closed head injury in mice.

The normal cellular prion protein (PrPC) is a sialoglycoprotein with a glycophosphatidylinositol anchor and expressed in highest levels within the CNS particularly at neuronal synapses. This membrane-bound protein is involved with many cell functions including cell signaling and neuroprotection. Calpains are calcium-activated cysteine proteases that typically undergo controlled activation. PrPC is a calpain substrate and is neurotoxic if it undergoes aberrant processing with cytosol accumulation. Following traumatic brain injury (TBI), there is an abnormal influx of Ca+2 and overactivation of calpains resulting in neuronal dysfunction and cell death. We investigated whether PrPC expression and calpain activity have an effect on, or are affected by, TBI. PrPC expression in the hippocampus, cortex and cerebellum of WT and Tga20 (PrPC overexpression) mice were unchanged after closed head injury (CHI). Further, PrPC in WT and Tga20 mice was resistant to TBI-induced calpain proteolysis. CHI-induced calpain activation resulted in breakdown products (BDPs) of αII-spectrin (SBDPs) and GFAP (GBDP-44K) in all brain regions and mouse lines. CHI caused significant increases in SBDP145, GFAP and GBDP-44K when compared to sham. With few exceptions, the calpain inhibitor, SNJ-1945, reduced SBDP145 and GBDP-44K levels. Behavioral studies suggested that PrPC and calpain independently affect learning and memory. Overall, we conclude that: (i) there is SNJ-1945-sensitive calpain activation in both neuron and glial cells following CHI, (ii) closed head trauma is not affected by, nor does it have an influence on, PrPC expression, and (iii) PrPC expression plays a minor role, if any, in CHI-induced calpain activation in vivo.

Repeated Closed Head Injury in Mice Results in Sustained Motor and Memory Deficits and Chronic Cellular Changes.

Millions of mild traumatic brain injuries (TBIs) occur every year in the United States, with many people subject to multiple head injuries that can lead to chronic behavioral dysfunction. We previously reported that mild TBI induced using closed head injuries (CHI) repeated at 24h intervals produced more acute neuron death and glial reactivity than a single CHI, and increasing the length of time between injuries to 48h reduced the cumulative acute effects of repeated CHI. To determine whether repeated CHI is associated with behavioral dysfunction or persistent cellular damage, mice receiving either five CHI at 24h intervals, five CHI at 48h intervals, or five sham injuries at 24h intervals were evaluated across a 10 week period after injury. Animals with repeated CHI exhibited motor coordination and memory deficits, but not gait abnormalities when compared to sham animals. At 10wks post-injury, no notable neuron loss or glial reactivity was observed in the cortex, hippocampus, or corpus callosum. Argyrophilic axons were found in the pyramidal tract of some injured animals, but neither silver stain accumulation nor inflammatory responses in the injury groups were statistically different from the sham group in this region. However, argyrophilic axons, microgliosis and astrogliosis were significantly increased within the optic tract of injured animals. Repeated mild CHI also resulted in microgliosis and a loss of neurofilament protein 200 in the optic nerve. Lengthening the inter-injury interval from 24h to 48h did not effectively reduce these behavioral or cellular responses. These results suggest that repeated mild CHI results in persistent behavioral dysfunction and chronic pathological changes within the visual system, neither of which was significantly attenuated by lengthening the inter-injury interval from 24h to 48h.

Combined [(18)F]DPA-714 micro-positron emission tomography and autoradiography imaging of microglia activation after closed head injury in mice.

BACKGROUND: Traumatic brain injury (TBI) is a major cause of death and disability. Neuroinflammation contributes to acute damage after TBI and modulates long-term evolution of degenerative and regenerative responses to injury. The aim of the present study was to evaluate the relationship of microglia activation to trauma severity, brain energy metabolism, and cellular reactions to injury in a mouse closed head injury model using combined in vivo PET imaging, ex vivo autoradiography, and immunohistochemistry. METHODS: A weight-drop closed head injury model was used to produce a mixed diffuse and focal TBI or a purely diffuse mild TBI (mTBI) in C57BL6 mice. Lesion severity was determined by evaluating histological damage and functional outcome using a standardized neuroscore (NSS), gliosis, and axonal injury by immunohistochemistry. Repeated intra-individual in vivo µPET imaging with the specific 18-kDa translocator protein (TSPO) radioligand [(18)F]DPA-714 was performed on day 1, 7, and 16 and [(18)F]FDG-µPET imaging for energy metabolism on days 2-5 after trauma using freshly synthesized radiotracers. Immediately after [(18)F]DPA-714-µPET imaging on days 7 and 16, cellular identity of the [(18)F]DPA-714 uptake was confirmed by exposing freshly cut cryosections to film autoradiography and successive immunostaining with antibodies against the microglia/macrophage marker IBA-1. RESULTS: Functional outcome correlated with focal brain lesions, gliosis, and axonal injury. [(18)F]DPA-714-µPET showed increased radiotracer uptake in focal brain lesions on days 7 and 16 after TBI and correlated with reduced cerebral [(18)F]FDG uptake on days 2-5, with functional outcome and number of IBA-1 positive cells on day 7. In autoradiography, [(18)F]DPA-714 uptake co-localized with areas of IBA1-positive staining and correlated strongly with both NSS and the number of IBA1-positive cells, gliosis, and axonal injury. After mTBI, numbers of IBA-1 positive cells with microglial morphology increased in both brain hemispheres; however, uptake of [(18)F]DPA-714 was not increased in autoradiography or in µPET imaging. CONCLUSIONS: [(18)F]DPA-714 uptake in µPET/autoradiography correlates with trauma severity, brain metabolic deficits, and microglia activation after closed head TBI.

Interleukin (IL)-8 immunoreactivity of injured axons and surrounding oligodendrocytes in traumatic head injury.

Interleukin (IL)-8 has been suggested to be a positive regulator of myelination in the central nervous system, in addition to its principal role as a chemokine for neutrophils. Immunostaining for beta-amyloid precursor protein (AßPP) is an effective tool for detecting traumatic axonal injury, although AßPP immunoreactivity can also indicate axonal injury due to hypoxic causes. In this study, we examined IL-8 and AßPP immunoreactivity in sections of corpus callosum obtained from deceased patients with blunt head injury and from equivalent control tissue. AßPP immunoreactivity was detected in injured axons, such as axonal bulbs and varicose axons, in 24 of 44 head injury cases. These AßPP immunoreactive cases had survived for more than 3h. The AßPP immunostaining pattern can be classified into two types: traumatic (Pattern 1) and non-traumatic (Pattern 2) axonal injuries, which we described previously [Hayashi et al. Int. J. Legal Med. 129 (2015) 1085-1090]. Three of 44 control cases also showed AßPP immunoreactive injured axons as Pattern 2. In contrast, IL-8 immunoreactivity was detected in 7 AßPP immunoreactive and in 2 non-AßPP immunoreactive head injury cases, but was not detected in any of the 44 control cases, including the 3 AßPP immunoreactive control cases. The IL-8 immunoreactive cases had survived from 3 to 24 days, whereas those cases who survived less than 3 days (n=29) and who survived 90 days (n=1) were not IL-8 immunoreactive. Moreover, IL-8 was detected as Pattern 1 axons only. In addition, double immunofluorescence analysis showed that IL-8 is expressed by oligodendrocytes surrounding injured axons. In conclusion, our results suggest that immunohistochemical detection of IL-8 may be useful as a complementary diagnostic marker of traumatic axonal injury.

Site-targeted complement inhibition by a complement receptor 2-conjugated inhibitor (mTT30) ameliorates post-injury neuropathology in mouse brains.

Intracerebral complement activation after severe traumatic brain injury (TBI) leads to a cascade of neuroinflammatory pathological sequelae that propagate host-mediated secondary brain injury and adverse outcomes. There are currently no specific pharmacological agents on the market to prevent or mitigate the development of secondary cerebral insults after TBI. A novel chimeric CR2-fH compound (mTT30) provides targeted inhibition of the alternative complement pathway at the site of tissue injury. This experimental study was designed to test the neuroprotective effects of mTT30 in a mouse model of closed head injury. The administration of 500 µg mTT30 i.v. at 1 h, 4 h and 24 h after head injury attenuated complement C3 deposition in injured brains, reduced the extent of neuronal cell death, and decreased post-injury microglial activation, compared to vehicle-injected placebo controls. These data imply that site-targeted alternative pathway complement inhibition may represent a new promising therapeutic avenue for the future management of severe TBI.

Differential detection of impact site versus rotational site injury by magnetic resonance imaging and microglial morphology in an unrestrained mild closed head injury model.

Seventy-five percent of all traumatic brain injuries are mild and do not cause readily visible abnormalities on routine medical imaging making it difficult to predict which individuals will develop unwanted clinical sequelae. Microglia are brain-resident macrophages and early responders to brain insults. Their activation is associated with changes in morphology or expression of phenotypic markers including P2Y12 and major histocompatibility complex class II. Using a murine model of unrestrained mild closed head injury (mCHI), we used microglia as reporters of acute brain injury at sites of impact versus sites experiencing rotational stress 24 h post-mCHI. Consistent with mild injury, a modest 20% reduction in P2Y12 expression was detected by quantitative real-time PCR (qPCR) analysis but only in the impacted region of the cortex. Furthermore, neither an influx of blood-derived immune cells nor changes in microglial expression of CD45, TREM1, TREM2, major histocompatibility complex class II or CD40 were detected. Using magnetic resonance imaging (MRI), small reductions in T2 weighted values were observed but only near the area of impact and without overt tissue damage (blood deposition, edema). Microglial morphology was quantified without cryosectioning artifacts using ScaleA(2) clarified brains from CX3CR1-green fluorescence protein (GFP) mice. The cortex rostral to the mCHI impact site receives greater rotational stress but neither MRI nor molecular markers of microglial activation showed significant changes from shams in this region. However, microglia in this rostral region did display signs of morphologic activation equivalent to that observed in severe CHI. Thus, mCHI-triggered rotational stress is sufficient to cause injuries undetectable by routine MRI that could result in altered microglial surveillance of brain homeostasis. Acute changes in microglial morphology reveal brain responses to unrestrained mild traumatic brain injury In areas subjected to rotational stress distant from impact site In the absence of detectable changes in standard molecular indicators of brain damage, inflammation or microglial activation. That might result in decreased surveillance of brain function and increased susceptibility to subsequent brain insults.

Leukemia Inhibitory Factor Haplodeficiency Desynchronizes Glial Reactivity and Exacerbates Damage and Functional Deficits after a Concussive Brain Injury.

Reactions of both astrocytes and microglia to central nervous system injury can be beneficial or detrimental to recovery. To gain insights into the functional importance of gliosis, we developed a new model of adolescent closed-head injury (CHI) and interrogated the behavioral, physiological, and cellular outcomes after a concussive CHI in leukemia inhibitory factor (LIF) haplodeficient mice. These mice were chosen because LIF is important for astrocyte and microglial activation. Behaviorally, the LIF haplodeficient animals were equally impaired 4 h after the injury, but in the subsequent 2 weeks, the LIF haplodeficient mice acquired more severe motor and sensory deficits, compared with wild type mice. The prolonged accumulation of neurological impairment was accompanied by desynchronization of the gliotic response, increased cell death, axonal degeneration, diminished callosal compound action potential, and hypomyelination. Our results clearly show that LIF is an essential injury-induced cytokine that is required to prevent the propagation of secondary neurodegeneration.

Neuroprotective effect of carnosine and cyclosporine-A against inflammation, apoptosis, and oxidative brain damage after closed head injury in immature rats.

CONTEXT: Traumatic brain injury in the pediatric population can have a great economic and emotional impact on both the child's family and society. OBJECTIVE: The present study aimed to compare the effects of carnosine (CAR) and/or cyclosporine A (CyA) on oxidative brain damage after closed head injury (CHI) in immature rats. MATERIALS AND METHODS: Thirty-day-old rat pups were divided into five groups: non-traumatic control group, trauma group underwent CHI, trauma group injected with CAR (200 mg/kg, i.p.) following CHI for 7 d, trauma group injected with CyA (20 mg/kg, i.p.) given 15 min and 24 h after CHI, and trauma group treated with CAR and CyA. At the end of the treatment, rats were sacrificed; blood and brains were collected for assessing different biochemical parameters. RESULTS: Trauma significantly increased brain level of malondialdehyde, nitric oxide, glucose, calcium, inflammatory mediators. Brain DNA damage was confirmed by comet assay and the significant increase in brain caspase-3 activity. Moreover, the serum level of Fas ligand in traumatized animals was significantly elevated. Concomitant decrease in brain-reduced glutathione (GSH) and calcium-adenosine triphosphatase activity was observed in the traumatized-untreated group. Treatment of traumatized animals with CAR and/or CyA ameliorated all the biochemical changes induced by CHI with marked protective effect in the combination group. DISCUSSION AND CONCLUSION: CAR and CyA exerted a synergistic neuroprotective effect against CHI through blocking the induction of lipid peroxidation, reducing inflammatory, and oxidative stress biomarkers, preserving brain GSH content, and reducing the alterations in brain apoptotic biomarkers in traumatized animals.

Two different immunostaining patterns of beta-amyloid precursor protein (APP) may distinguish traumatic from nontraumatic axonal injury.

Immunostaining for beta-amyloid precursor protein (APP) is recognized as an effective tool for detecting traumatic axonal injury, but it also detects axonal injury due to ischemic or other metabolic causes. Previously, we reported two different patterns of APP staining: labeled axons oriented along with white matter bundles (pattern 1) and labeled axons scattered irregularly (pattern 2) (Hayashi et al. (Leg Med (Tokyo) 11:S171-173, 2009). In this study, we investigated whether these two patterns are consistent with patterns of trauma and hypoxic brain damage, respectively. Sections of the corpus callosum from 44 cases of blunt head injury and equivalent control tissue were immunostained for APP. APP was detected in injured axons such as axonal bulbs and varicose axons in 24 of the 44 cases of head injuries that also survived for three or more hours after injury. In 21 of the 24 APP-positive cases, pattern 1 alone was observed in 14 cases, pattern 2 alone was not observed in any cases, and both patterns 1 and 2 were detected in 7 cases. APP-labeled injured axons were detected in 3 of the 44 control cases, all of which were pattern 2. These results suggest that pattern 1 indicates traumatic axonal injury, while pattern 2 results from hypoxic insult. These patterns may be useful to differentiate between traumatic and nontraumatic axonal injuries.

Deletion of aquaporin-4 is neuroprotective during the acute stage of micro traumatic brain injury in mice.

Micro traumatic brain injury (TBI) is the most common type of brain injury, but the mechanisms underlying it are poorly understood. Aquaporin-4 (AQP4) is a water channel expressed in astrocyte end-feet, which plays an important role in brain edema. However, little is known about the role of AQP4 in micro TBI. Here, we examined the role of AQP4 in the pathogenesis of micro TBI in a closed-skull brain injury model, using two-photon microscopy. Our results indicate that AQP4 deletion reduced cell death, water content, astrocyte swelling and lesion volume during the acute stage of micro TBI. Our data revealed that astrocyte swelling is a decisive pathophysiological factor in the acute phase of this form of micro brain injury. Thus, treatments that inhibit AQP4 could be used as a neuroprotective strategy for micro TBI.

Taurine attenuates hippocampal and corpus callosum damage, and enhances neurological recovery after closed head injury in rats.

The protective effects of taurine against closed head injury (CHI) have been reported. This study was designed to investigate whether taurine reduced white matter damage and hippocampal neuronal death through suppressing calpain activation after CHI in rats. Taurine (50 mg/kg) was administered intravenously 30 min and 4 h again after CHI. It was found that taurine lessened the corpus callosum damage, attenuated the neuronal cell death in hippocampal CA1 and CA3 subfields and improved the neurological functions 7 days after CHI. Moreover, it suppressed the over-activation of calpain, enhanced the levels of calpastatin, and reduced the degradation of neurofilament heavy protein, myelin basic protein and αII-spectrin in traumatic tissue 24 h after CHI. These data confirm the protective effects of taurine against gray and white matter damage due to CHI, and suggest that down-regulating calpain activation could be one of the protective mechanisms of taurine against CHI.

Inhibition of monoacylglycerol lipase prevents chronic traumatic encephalopathy-like neuropathology in a mouse model of repetitive mild closed head injury.

Emerging evidence suggests that the risk of developing chronic traumatic encephalopathy (CTE), a progressive neurodegenerative disease, is significantly increased in military personnel and contact sports players who have been exposed to repetitive trauma brain injury (TBI). Unfortunately there are no effective medications currently available for prevention and treatment of CTE. Here we demonstrate that inhibition of monoacylglycerol lipase (MAGL), the key enzyme that metabolizes the endocannabinoid 2-arachidonoylglycerol (2-AG) in the brain, significantly reduced CTE-like neuropathologic changes in a mouse model of repetitive mild closed head injury (rmCHI). Inhibition of 2-AG metabolism promoted neurologic recovery following rmCHI and reduced proinflammatory cytokines, astroglial reactivity, expression of amyloid precursor protein and the enzymes that make Aß, as well as formation of Aß. Importantly, neurodegeneration, TDP-43 protein aggregation, and tau phosphorylation, which are the neuropathologic hallmarks of CTE, were significantly suppressed by MAGL inactivation. Furthermore, alterations in expression of glutamate receptor subunits and impairments in basal synaptic transmission, long-term synaptic plasticity, and spatial learning and memory were recovered by inhibition of 2-AG metabolism in animals exposed to rmCHI. Our results suggest that MAGL inhibition, which boosts 2-AG and reduces 2-AG metabolites prostaglandins in the brain, may lead to a new therapy for CTE.

Protective effects of taurine against closed head injury in rats.

Taurine, an abundant amino acid in the nervous system, is reported to reduce ischemic brain injury in a dose-dependent manner. This study was designed to investigate whether taurine protected the brain against closed head injury (CHI) in rats. Taurine was administered intravenously 30 min after CHI. It was found that taurine lessened body-weight loss and improved neurological functions at 7 days after CHI. Moreover, it lowered brain edema and blood-brain barrier permeability, enhanced activity of superoxide dismutase and the level of glutathione, and reduced levels of malondialdehyde and lactic acid in traumatic tissue 24 h after CHI. In addition, it attenuated neuronal cell death in hippocampal CA1 and CA3 subfields 7 days after CHI. All of these effects were dose dependent. These data demonstrated the dose-dependent protection of taurine against experimental CHI and suggest that taurine treatment might be beneficial in reducing trauma-induced oxidative damage to the brain, thus showing the potential for clinical implications.

Neuroprotection after traumatic brain injury in heat-acclimated mice involves induced neurogenesis and activation of angiotensin receptor type 2 signaling.

Long-term exposure of mice to mild heat (34°C±1°C) confers neuroprotection against traumatic brain injury (TBI); however, the underling mechanisms are not fully understood. Heat acclimation (HA) increases hypothalamic angiotensin II receptor type 2 (AT2) expression and hypothalamic neurogenesis. Accumulating data suggest that activation of the brain AT2 receptor confers protection against several types of brain pathologies, including ischemia, a hallmark of the secondary injury occurring following TBI. As AT2 activates the same pro-survival pathways involved in HA-mediated neuroprotection (e.g., Akt phosphorylation, hypoxia-inducible factor 1α (HIF-1α), and brain-derived neurotrophic factor (BDNF)), we examined the role of AT2 in HA-mediated neuroprotection after TBI. Using an AT2-specific antagonist PD123319, we found that the improvements in motor and cognitive recovery as well as reduced lesion volume and neurogenesis seen in HA mice were all diminished by AT2 inhibition, whereas no significant alternations were observed in control mice. We also found that nerve growth factor/tropomyosin-related kinase receptor A (TrkA), BDNF/TrkB, and HIF-1α pathways are upregulated by HA and inhibited on PD123319 administration, suggesting that these pathways play a role in AT2 signaling in HA mice. In conclusion, AT2 is involved in HA-mediated neuroprotection, and AT2 activation may be protective and should be considered a novel drug target in the treatment of TBI patients.