Disruption of Bax protein prevents neuronal cell death but produces cognitive impairment in mice following traumatic brain injury

Directly targeting BAX for drug discovery: Therapeutic opportunities and challenges

For over two decades, the development of B-cell lymphoma-2 (Bcl-2) family therapeutics has primarily focused on anti-apoptotic proteins, resulting in the first-in-class drugs called BH3 mimetics, especially for Bcl-2 inhibitor Venetoclax. The pro-apoptotic protein Bcl-2-associated X protein (BAX) plays a crucial role as the executioner protein of the mitochondrial regulated cell death, contributing to organismal development, tissue homeostasis, and immunity. The dysregulation of BAX is closely associated with the onset and progression of diseases characterized by pathologic cell survival or death, such as cancer, neurodegeneration, and heart failure. In addition to conducting thorough investigations into the physiological modulation of BAX, research on the regulatory mechanisms of small molecules identified through biochemical screening approaches has prompted the identification of functional and potentially druggable binding sites on BAX, as well as diverse all-molecule BAX modulators. This review presents recent advancements in elucidating the physiological and pharmacological modulation of BAX and in identifying potentially druggable binding sites on BAX. Furthermore, it highlights the structural and mechanistic insights into small-molecule modulators targeting diverse binding surfaces or conformations of BAX, offering a promising avenue for developing next-generation apoptosis modulators to treat a wide range of diseases associated with dysregulated cell death by directly targeting BAX.

Radiotherapy-Induced Neurocognitive Impairment Is Driven by Heightened Apoptotic Priming in Early Life and Prevented by Blocking BAX

Although external beam radiotherapy (xRT) is commonly used to treat central nervous system (CNS) tumors in patients of all ages, young children treated with xRT frequently experience life-altering and dose-limiting neurocognitive impairment (NI) while adults do not. The lack of understanding of mechanisms responsible for these differences has impeded the development of neuroprotective treatments. Using a newly developed mouse model of xRT-induced NI, we found that neurocognitive function is impaired by ionizing radiation in a dose- and age-dependent manner, with the youngest animals being most affected. Histologic analysis revealed xRT-driven neuronal degeneration and cell death in neurogenic brain regions in young animals but not adults. BH3 profiling showed that neural stem and progenitor cells, neurons, and astrocytes in young mice are highly primed for apoptosis, rendering them hypersensitive to genotoxic damage. Analysis of single-cell RNA sequencing data revealed that neural cell vulnerability stems from heightened expression of proapoptotic genes including BAX, which is associated with developmental and mitogenic signaling by MYC. xRT induced apoptosis in primed neural cells by triggering a p53- and PUMA-initiated, proapoptotic feedback loop requiring cleavage of BID and culminating in BAX oligomerization and caspase activation. Notably, loss of BAX protected against apoptosis induced by proapoptotic signaling in vitro and prevented xRT-induced apoptosis in neural cells in vivo as well as neurocognitive sequelae. On the basis of these findings, preventing xRT-induced apoptosis specifically in immature neural cells by blocking BAX, BIM, or BID via direct or upstream mechanisms is expected to ameliorate NI in pediatric patients with CNS tumor.

SIGNIFICANCE

Age- and differentiation-dependent apoptotic priming plays a pivotal role in driving radiotherapy-induced neurocognitive impairment and can be targeted for neuroprotection in pediatric patients.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Endogenous Interleukin-17a Contributes to Normal Spatial Memory Retention but Does Not Affect Early Behavioral or Neuropathological Outcomes after Experimental Traumatic Brain Injury

Interleukin-17 (IL-17) is a proinflammatory cytokine primarily secreted in the brain by inflammatory T lymphocytes and glial cells. IL-17+ T-helper (Th17) cells are increased in the ipsilateral hemisphere after experimental traumatic brain injury (TBI), and IL-17 levels are increased in serum and brain tissue. We hypothesized that il17a and related gene expression would be increased in brain tissue after TBI in mice and il17a-/- mice would demonstrate neuroprotection versus wild type. The controlled cortical impact (CCI) model of TBI in adult male C57BL6/J mice was used for all experiments. Data were analyzed by analysis of variance (ANOVA) or repeated-measures two-way ANOVA with the Bonferroni correction. A value of p < 0.05 determined significance. Expression of il17a was significantly reduced in the ipsilateral cortex and hippocampus by day 3 after TBI, and expression remained low at 28 days. There were no differences between il17a-/- and il17a+/+ mice in beam balance, Morris water maze performance, or lesion volume after CCI. Surprisingly, naïve il17a -/- mice performed significantly (p = 0.02) worse than naïve il17a+/+ mice on the probe trial. In conclusion, sustained depression of il17a gene expression was observed in brains after TBI in adult mice. Genetic knockout of IL-17 was not neuroprotective after TBI. IL-17a may be important for memory retention in naïve mice.

Too much death can kill you: inhibiting intrinsic apoptosis to treat disease

Apoptotic cell death is implicated in both physiological and pathological processes. Since many types of cancerous cells intrinsically evade apoptotic elimination, induction of apoptosis has become an attractive and often necessary cancer therapeutic approach. Conversely, some cells are extremely sensitive to apoptotic stimuli leading to neurodegenerative disease and immune pathologies. However, due to several challenges, pharmacological inhibition of apoptosis is still only a recently emerging strategy to combat pathological cell loss. Here, we describe several key steps in the intrinsic (mitochondrial) apoptosis pathway that represent potential targets for inhibitors in disease contexts. We also discuss the mechanisms of action, advantages and limitations of small-molecule and peptide-based inhibitors that have been developed to date. These inhibitors serve as important research tools to dissect apoptotic signalling and may foster new treatments to reduce unwanted cell loss.

Fibrinogen Interaction with Astrocyte ICAM-1 and PrPC Results in the Generation of ROS and Neuronal Death

Many neuroinflammatory diseases, like traumatic brain injury (TBI), are associated with an elevated level of fibrinogen and short-term memory (STM) impairment. We found that during TBI, extravasated fibrinogen deposited in vasculo-astrocyte interfaces, which was associated with neurodegeneration and STM reduction. The mechanisms of this fibrinogen-astrocyte interaction and its functional role in neurodegeneration are still unclear. Cultured mouse brain astrocytes were treated with fibrinogen in the presence or absence of function-blocking antibody or peptide against its astrocyte receptors intercellular adhesion molecule-1 (ICAM-1) or cellular prion protein (PrP^C), respectively. Fibrinogen interactions with astrocytic ICAM-1 and PrP^C were characterized. The expression of pro-inflammatory markers, generations of reactive oxygen species (ROS) and nitric oxide (NO) in astrocytes, and neuronal death caused by astrocyte-conditioned medium were assessed. Data showed a strong association between fibrinogen and astrocytic ICAM-1 or PrP^C, overexpression of pro-inflammatory cytokines and overproduction of ROS and NO, resulting in neuronal apoptosis and death. These effects were reduced by blocking the function of astrocytic ICAM-1 and PrP^C, suggesting that fibrinogen association with its astrocytic receptors induce the release of pro-inflammatory cytokines, resulting in oxidative stress, and ultimately neuronal death. This can be a mechanism of neurodegeneration and the resultant STM reduction seen during TBI.

GABAergic neurons are susceptible to BAX-dependent apoptosis following isoflurane exposure in the neonatal period

Exposure to volatile anesthetics during the neonatal period results in acute neuron death. Prior work suggests that apoptosis is the dominant mechanism mediating neuron death. We show that Bax deficiency blocks neuronal death following exposure to isoflurane during the neonatal period. Blocking Bax-mediated neuron death attenuated the neuroinflammatory response of microglia following isoflurane exposure. We find that GABAergic interneurons are disproportionately overrepresented among dying neurons. Despite the increase in neuronal apoptosis induced by isoflurane exposure during the neonatal period, seizure susceptibility, spatial memory retention, and contextual fear memory were unaffected later in life. However, Bax deficiency alone led to mild deficiencies in spatial memory and contextual fear memory, suggesting that normal developmental apoptotic death is important for cognitive function. Collectively, these findings show that while GABAergic neurons in the neonatal brain undergo elevated Bax-dependent apoptotic cell death following exposure to isoflurane, this does not appear to have long-lasting consequences on overall neurological function later in life.

Neuronal cell life, death, and axonal degeneration as regulated by the BCL-2 family proteins

Axonal degeneration and neuronal cell death are fundamental processes in development and contribute to the pathology of neurological disease in adults. Both processes are regulated by BCL-2 family proteins which orchestrate the permeabilization of the mitochondrial outer membrane (MOM). MOM permeabilization (MOMP) results in the activation of pro-apoptotic molecules that commit neurons to either die or degenerate. With the success of small-molecule inhibitors targeting anti-apoptotic BCL-2 proteins for the treatment of lymphoma, we can now envision the use of inhibitors of apoptosis with exquisite selectivity for BCL-2 family protein regulation of neuronal apoptosis in the treatment of nervous system disease. Critical to this development is deciphering which subset of proteins is required for neuronal apoptosis and axon degeneration, and how these two different outcomes are separately regulated. Moreover, noncanonical BCL-2 family protein functions unrelated to the regulation of MOMP, including impacting necroptosis and other modes of cell death may reveal additional potential targets and/or confounders. This review highlights our current understanding of BCL-2 family mediated neuronal cell death and axon degeneration, while identifying future research questions to be resolved to enable regulating neuronal survival pharmacologically.

Isoliquiritigenin Attenuates Neuroinflammation in Traumatic Brain Injury in Young Rats

OBJECTIVES

Inflammation and apoptosis play a critical role in the pathological progress of traumatic brain injury (TBI). Isoliquiritigenin is a bioactive component extracted from licorice roots, which possesses anti-inflammatory and anti-apoptotic properties. This study aims to investigate the potential effects of isoliquiritigenin on neuroinflammation in a rat model of TBI.

METHODS

The SH-SY5Y cells were subjected to cell injury induced by shear stress and the effect of isoliquiritigenin on cell apoptosis was measured. Male rats received a controlled cortical impact to induce TBI and were then treated with isoliquiritigenin (20 mg/kg). Brain edema and contusion volume were measured to assess brain damage. Morris water maze, the beam-balance test, and the beam-walk test were performed to evaluate the cognitive and motor functions.

RESULTS

Levels of proinflammatory cytokines and apoptotic regulators were measured. Results showed that isoliquiritigenin reduced shear stress-induced cell apoptosis in vitro. In young rats subjected to TBI, treatment of isoliquiritigenin reduced brain damage and attenuated motor and cognitive impairments. Isoliquiritigenin also reduced the level of proinflammatory cytokines and Bax and increased Bcl-2 and Bcl-xL in TBI rats.

CONCLUSIONS

These findings suggest that isoliquiritigenin possesses beneficial effects in TBI by inhibiting inflammation and apoptosis.

Traumatic Brain Injury Altered Normal Brain Signaling Pathways: Implications for Novel Therapeutics Approaches

Traumatic brain injury (TBI) is the main reason of lifelong disability and casualty worldwide. In the United State alone, 1.7 million traumatic events occur yearly, out of which 50,000 results in deaths. Injury to the brain could alter various biological signaling pathways such as excitotoxicity, ionic imbalance, oxidative stress, inflammation, and apoptosis which can result in various neurological disorders such as Psychosis, Depression, Alzheimer disease, Parkinson disease, etc. In literature, various reports have indicated the alteration of these pathways after traumatic brain injury but the exact mechanism is still unclear. Thus, in the first part of this article, we have tried to summarize TBI as a modulator of various neuronal signaling pathways. Currently, very few drugs are available in the market for the treatment of TBI and these drugs only provide the supportive care. Thus, in the second part of the article, based on TBI altered signaling pathways, we have tried to find out potential targets and promising therapeutic approaches in the treatment of TBI.

Both oophorectomy and obesity impaired solely hippocampal-dependent memory via increased hippocampal dysfunction

Our previous study demonstrated that obesity aggravated peripheral insulin resistance and brain dysfunction in the ovariectomized condition. Conversely, the effect of obesity followed by oophorectomy on brain oxidative stress, brain apoptosis, synaptic function and cognitive function, particularly in hippocampal-dependent and hippocampal-independent memory, has not been investigated. Our hypothesis was that oophorectomy aggravated metabolic impairment, brain dysfunction and cognitive impairment in obese rats. Thirty-two female rats were fed with either a normal diet (ND, n = 16) or a high-fat diet (HFD, n = 16) for a total of 20 weeks. At week 13, rats in each group were subdivided into sham and ovariectomized subgroups (n = 8/subgroup). At week 20, all rats were tested for hippocampal-dependent and hippocampal-independent memory by using Morris water maze test (MWM) and Novel objective recognition (NOR) tests, respectively. We found that the obese-insulin resistant condition occurred in sham-HFD-fed rats (HFS), ovariectomized-ND-fed rats (NDO), and ovariectomized-HFD-fed rats (HFO). Increased hippocampal oxidative stress level, increased hippocampal apoptosis, increased hippocampal synaptic dysfunction, decreased hippocampal estrogen level and impaired hippocampal-dependent memory were observed in HFS, NDO, and HFO rats. However, the hippocampal-independent memory, cortical estrogen levels, cortical ROS production, and cortical apoptosis showed no significant difference between groups. These findings suggested that oophorectomy and obesity exclusively impaired hippocampal-dependent memory, possibly via increased hippocampal dysfunction. Nonetheless, oophorectomy did not aggravate these deleterious effects under conditions of obesity.

Neuronal Cell Death

Neuronal cell death occurs extensively during development and pathology, where it is especially important because of the limited capacity of adult neurons to proliferate or be replaced. The concept of cell death used to be simple as there were just two or three types, so we just had to work out which type was involved in our particular pathology and then block it. However, we now know that there are at least a dozen ways for neurons to die, that blocking a particular mechanism of cell death may not prevent the cell from dying, and that non-neuronal cells also contribute to neuronal death. We review here the mechanisms of neuronal death by intrinsic and extrinsic apoptosis, oncosis, necroptosis, parthanatos, ferroptosis, sarmoptosis, autophagic cell death, autosis, autolysis, paraptosis, pyroptosis, phagoptosis, and mitochondrial permeability transition. We next explore the mechanisms of neuronal death during development, and those induced by axotomy, aberrant cell-cycle reentry, glutamate (excitoxicity and oxytosis), loss of connected neurons, aggregated proteins and the unfolded protein response, oxidants, inflammation, and microglia. We then reassess which forms of cell death occur in stroke and Alzheimer's disease, two of the most important pathologies involving neuronal cell death. We also discuss why it has been so difficult to pinpoint the type of neuronal death involved, if and why the mechanism of neuronal death matters, the molecular overlap and interplay between death subroutines, and the therapeutic implications of these multiple overlapping forms of neuronal death.

Ginger and Propolis Exert Neuroprotective Effects against Monosodium Glutamate-Induced Neurotoxicity in Rats

Central nervous system cytotoxicity is linked to neurodegenerative disorders. The objective of the study was to investigate whether monosodium glutamate (MSG) neurotoxicity can be reversed by natural products, such as ginger or propolis, in male rats. Four different groups of Wistar rats were utilized in the study. Group A served as a normal control, whereas group B was orally administered with MSG (100 mg/kg body weight, via oral gavage). Two additional groups, C and D, were given MSG as group B along with oral dose (500 mg/kg body weight) of either ginger or propolis (600 mg/kg body weight) once a day for two months. At the end, the rats were sacrificed, and the brain tissue was excised and levels of neurotransmitters, ß-amyloid, and DNA oxidative marker 8-OHdG were estimated in the brain homogenates. Further, formalin-fixed and paraffin-embedded brain sections were used for histopathological evaluation. The results showed that MSG increased lipid peroxidation, nitric oxide, neurotransmitters, and 8-OHdG as well as registered an accumulation of ß-amyloid peptides compared to normal control rats. Moreover, significant depletions of glutathione, superoxide dismutase, and catalase as well as histopathological alterations in the brain tissue of MSG-treated rats were noticed in comparison with the normal control. In contrast, treatment with ginger greatly attenuated the neurotoxic effects of MSG through suppression of 8-OHdG and β-amyloid accumulation as well as alteration of neurotransmitter levels. Further improvements were also noticed based on histological alterations and reduction of neurodegeneration in the brain tissue. A modest inhibition of the neurodegenerative markers was observed by propolis. The study clearly indicates a neuroprotective effect of ginger and propolis against MSG-induced neurodegenerative disorders and these beneficial effects could be attributed to the polyphenolic compounds present in these natural products.

Hyperactivity and depression-like traits in Bax KO mice

The Bax gene is a member of the Bcl-2 gene family and its pro-apoptotic Bcl-associated X (Bax) protein is believed to be crucial in regulating apoptosis during neuronal development as well as following injury. With the advent of mouse genomics, mice lacking the pro-apoptotic Bax gene (Bax KO) have been extensively used to study how cell death helps to determine synaptic circuitry formation during neurodevelopment and disease. Surprisingly, in spite of its wide use and the association of programmed neuronal death with motor dysfunctions and depression, the effects of Bax deletion on mice spontaneous locomotor activity and depression-like traits are unknown. Here we examine the behavioral characteristics of Bax KO male mice using classical paradigms to evaluate spontaneous locomotor activity and depressive-like responses. In the open field, Bax KO animals exhibited greater locomotor activity than their control littermates. In the forced swimming test, Bax KO mice displayed greater immobility times, a behavior despair state, when compared to controls. Collectively, our findings corroborate the notion that a fine balance between cell survival and death early during development is critical for normal brain function later in life. Furthermore, it points out the importance of considering depressive-like and hyperactivity behavioral phenotypes when conducting neurodevelopmental and other studies using the Bax KO strain.

Influence of mild traumatic brain injury during pediatric stage on short-term memory and hippocampal apoptosis in adult rats

Traumatic brain injury (TBI) is a leading cause of neurological deficit in the brain, which induces short- and long-term brain damage, cognitive impairment with/without structural alteration, motor deficits, emotional problems, and death both in children and adults. In the present study, we evaluated whether mild TBI in childhood causes persisting memory impairment until adulthood. Moreover, we investigated the influence of mild TBI on memory impairment in relation with hippocampal apoptosis. For this, step-down avoidance task, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, and immunohistochemistry for caspase-3 were performed. Male Sprague-Dawley rats were used in the experiments. The animals were randomly divided into two groups: sham-operation group and TBI-induction group. The mild TBI model was created with an electromagnetic contusion device activated at a velocity of 3.0 m/sec. The results showed that mild TBI during the pediatric stage significantly decreased memory retention. The numbers of TUNEL-positive and caspase-3-positive cells were increased in the TBI-induction group compared to those in the sham-operation group. Defective memory retention and apoptosis sustained up to the adult stage. The present results shows that mild TBI induces long-lasting cognitive impairment from pediatric to adult stages in rats through the high level of apoptosis. The finding of this study suggests that children with mild TBI may need intensive treatments for the reduction of long-lasting cognitive impairment by secondary neuronal damage.

The effect of different intensities of treadmill exercise on cognitive function deficit following a severe controlled cortical impact in rats

Exercise has been proposed for the treatment of traumatic brain injury (TBI). However, the proper intensity of exercise in the early phase following a severe TBI is largely unknown. To compare two different treadmill exercise intensities on the cognitive function following a severe TBI in its early phase, rats experienced a controlled cortical impact (CCI) and were forced to treadmill exercise for 14 days. The results revealed that the rats in the low intensity exercise group had a shorter latency to locate a platform and a significantly better improvement in spatial memory in the Morris water maze (MWM) compared to the control group (p < 0.05). The high intensity exercise group showed a longer latency and a mild improvement in spatial memory compared to the control group rats in the MWM; however, this difference was not statistically significant (p > 0.05). The brain-derived neurotrophic factor (BDNF) and p-CREB protein levels in the contralateral hippocampus were increased significantly in the low intensity exercise group. Our results suggest that 2 weeks of low intensity of treadmill exercise is beneficial for improving cognitive function and increasing hippocampal BDNF expression after a severe TBI in its early phase.

Tumor necrosis factor in traumatic brain injury: effects of genetic deletion of p55 or p75 receptor

The role of tumor necrosis factor (TNF) and its receptors after traumatic brain injury (TBI) remains unclear. We evaluated the effects of genetic deletion of either p55 or p75 TNF receptor on neurobehavioral outcome, histopathology, DNA damage and apoptosis-related cell death/survival gene expression (bcl-2/bax), and microglia/macrophage (M/M) activation in wild-type (WT) and knockout mice after TBI. Injured p55 (-/-) mice showed a significant attenuation while p75 (-/-) mice showed a significant worsening of sensorimotor deficits compared with WT mice over 4 weeks postinjury. At the same time point, contusion volume in p55 (-/-) mice (11.1±3.3 mm(3)) was significantly reduced compared with WT (19.7±3.4 mm(3)) and p75 (-/-) mice (20.9±3.2 mm(3)). At 4 hours postinjury, bcl-2/bax ratio mRNA expression was increased in p55 (-/-) compared with p75 (-/-) mice and was associated with reduced DNA damage terminal deoxynucleotidyl transferaseYmediated dUTP nick end labeling (TUNEL-positivity), reduced CD11b expression and increased Ym1 expression at 24 hours postinjury in p55 (-/-) compared with p75 (-/-) mice, indicative of a protective M/M response. These data suggest that TNF may exacerbate neurobehavioral deficits and tissue damage via p55 TNF receptor whose inhibition may represent a specific therapeutic target after TBI.

Growth hormone and melatonin prevent age-related alteration in apoptosis processes in the dentate gyrus of male rats

It has been suggested that the age-related decrease in the number of neurons in the hippocampus that leads to alterations in brain function, may be associated with an increase in apoptosis due to the reduced secretion of growth hormone (GH) and/or melatonin in old animals. In order to investigate this possibility, male Wistar rats of 22 months of age were divided into three groups. One group remained untreated and acted as the control group. The second was treated with growth hormone (hGH) for 10 weeks (2 mg/kg/d sc) and the third was subjected to melatonin treatment (1 mg/kg/d) in the drinking water for the same time. A group of 2-months-old male rats was used as young controls. All rats were killed by decapitation at more than 24 month of age and dentate gyri of the hippocampi were collected. Aging in the dentate gyrus was associated with an increase in apoptosis promoting markers (Bax, Bad and AIF) and with the reduction of some anti-apoptotic ones (XIAP, NIAP, Mcl-1). Expressions of sirtuin 1 and 2 (SIRT1 and 2) as well as levels of HSP 70 were decreased in the dentate gyrus of old rats. GH treatment was able to reduce the pro/anti-apoptotic ratio to levels observed in young animals and also to increase SIRT2. Melatonin reduced also expression of pro-apoptotic genes and proteins (Bax, Bad and AIF), and increased levels of myeloid cell leukemia-1 proteins and SIRT1. Both treatments were able to reduce apoptosis and to enhance survival markers in this part of the hippocampus.

The expression of FBP1 after traumatic brain injury and its role in astrocyte proliferation

Far upstream element binding protein 1 (FBP1) has been identified as an upstream gene of p27kip1 (p27), which is a key regulator of mammalian cell cycle regulation and neurogenesis. To elucidate the expression and function of FBP1 in central nervous system lesion and repair, we performed a traumatic brain injury (TBI) model in adult rats. We observed that FBP1 protein level significantly reduced at day 3 after injury, and the downregulation of FBP1 was predominant in astrocytes, which were largely proliferated after injury. Furthermore, in vitro, overexpression of FBP1 was concomitant with the up-regulation of p27 and reduction of PCNA in LPS-induced astrocyte proliferation. These results suggest that a decreased level of FBP1 in brain is involved in the proliferation of glial cells after TBI.

Severe brief pressure-controlled hemorrhagic shock after traumatic brain injury exacerbates functional deficits and long-term neuropathological damage in mice

Hypotension after traumatic brain injury (TBI) worsens outcome. We published the first report of TBI plus hemorrhagic shock (HS) in mice using a volume-controlled approach and noted increased neuronal death. To rigorously control blood pressure during HS, a pressure-controlled HS model is required. Our hypothesis was that a brief, severe period of pressure-controlled HS after TBI in mice will exacerbate functional deficits and neuropathology versus TBI or HS alone. C57BL6 male mice were randomized into four groups (n=10/group): sham, HS, controlled cortical impact (CCI), and CCI+HS. We used a pressure-controlled shock phase (mean arterial pressure [MAP]=25-27 mm Hg for 35 min) and its treatment after mild to moderate CCI including, a 90 min pre-hospital phase, during which lactated Ringer's solution was given to maintain MAP >70 mm Hg, and a hospital phase, when the shed blood was re-infused. On days 14-20, the mice were evaluated in the Morris water maze (MWM, hidden platform paradigm). On day 21, the lesion and hemispheric volumes were quantified. Neuropathology and hippocampal neuron counts (hematoxylin and eosin [H&E], Fluoro-Jade B, and NeuN) were evaluated in the mice (n=60) at 24 h, 7 days, or 21 days (n=5/group/time point). HS reduced MAP during the shock phase in the HS and CCI+HS groups (p<0.05). Fluid requirements during the pre-hospital phase were greatest in the CCI+HS group (p<0.05), and were increased in HS versus sham and CCI animals (p<0.05). MWM latency was increased on days 14 and 15 after CCI+HS (p<0.05). Swim speed and visible platform latency were impaired in the CCI+HS group (p<0.05). CCI+HS animals had increased contusion volume versus the CCI group (p<0.05). Hemispheric volume loss was increased 33.3% in the CCI+HS versus CCI group (p<0.05). CA1 cell loss was seen in CCI+HS and CCI animals at 24 h and 7 days (p<0.05). CA3 cell loss was seen after CCI+HS (p<0.05 at 24 h and 7 days). CA1 cell loss at 21 days was seen only in CCI+HS animals (p<0.05). Brief, severe, pressure-controlled HS after CCI produces robust functional deficits and exacerbates neuropathology versus CCI or HS alone.

Nestin overexpression precedes caspase-3 upregulation in rats exposed to controlled cortical impact traumatic brain injury

Our understanding of biological mechanisms and treatment options for traumatic brain injury (TBI) is limited. Here, we employed quantitative real-time PCR (QRT-PCR) and immunohistochemical analyses to determine the dynamic expression of cell proliferation and apoptosis in an effort to provide insights into the therapeutic window for developing regenerative strategies for TBI. For this purpose, young adult Sprague-Dawley rats were subjected to experimental TBI using a controlled cortical impactor, then euthanized 1-48 hours after TBI for QRT-PCR and immunohistochemistry. QRT-PCR revealed that brains from TBI exposed rats initially displayed nestin mRNA expression that modestly increased as early as 1-hour post-TBI, then significantly peaked at 8 hours, but thereafter reverted to pre-TBI levels. On the other hand, caspase-3 mRNA expression was slightly elevated at 8 hours post-TBI, which did not become significantly upregulated until 48 hours. Immunofluorescent microscopy revealed a significant surge in nestin immunoreactive cells in the cortex, corpus callosum, and subventricular zone at 24 hours post-TBI, whereas a significant increase in the number of active caspase-3 immunoreactive cells was only found in the cortex and not until 48 hours. These results suggest that the injured brain attempts to repair itself via cell proliferation immediately after TBI, but that this endogenous regenerative mechanism is not sufficient to abrogate the secondary apoptotic cell death. Treatment strategies designed to amplify cell proliferation and to prevent apoptosis are likely to exert maximal benefits when initiated at the acute phase of TBI.

Increased cytochrome c in rat cerebrospinal fluid after cardiac arrest and its effects on hypoxic neuronal survival

Cerebrospinal fluid (CSF) proteins may be useful biomarkers of neuronal death and ultimate prognosis after hypoxic-ischemic brain injury. Cytochrome c has been identified in the CSF of children following traumatic brain injury. Cytochrome c is required for cellular respiration but it is also a central component of the intrinsic pathway of apoptosis. Thus, in addition to serving as a biomarker, cytochrome c release into CSF may have an effect upon survival of adjacent neurons. In this study, we use Western blot and ELISA to show that cytochrome c is elevated in CSF obtained from pediatric rats following resuscitation from cardiac arrest. Using biotinylated human cytochrome c in culture media we show that cytochrome c crosses the cell membrane and is incorporated into mitochondria of neurons exposed to anoxia. Lastly, we show that addition of human cytochrome c to primary neuronal culture exposed to anoxia improves survival. To our knowledge, this is the first study to show cytochrome c is elevated in CSF following hypoxic ischemic brain injury. Results from primary neuronal culture suggest that extracellular cytochrome c is able to cross the cell membrane of injured neurons, incorporate into mitochondria, and promote survival following anoxia.

Do β-defensins and other antimicrobial peptides play a role in neuroimmune function and neurodegeneration?

It is widely accepted that the brain responds to mechanical trauma and development of most neurodegenerative diseases with an inflammatory sequelae that was once thought exclusive to systemic immunity. Mostly cationic peptides, such as the β-defensins, originally assigned an antimicrobial function are now recognized as mediators of both innate and adaptive immunity. Herein supporting evidence is presented for the hypothesis that neuropathological changes associated with chronic disease conditions of the CNS involve abnormal expression and regulatory function of specific antimicrobial peptides. It is also proposed that these alterations exacerbate proinflammatory conditions within the brain that ultimately potentiate the neurodegenerative process.

Genetic manipulation of cell death and neuroplasticity pathways in traumatic brain injury

Traumatic brain injury (TBI) initiates a complex cascade of secondary neurodegenerative mechanisms contributing to cell dysfunction and necrotic and apoptotic cell death. The injured brain responds by activating endogenous reparative processes to counter the neurodegeneration or remodel the brain to enhance functional recovery. A vast array of genetically altered mice provide a unique opportunity to target single genes or proteins to better understand their role in cell death and endogenous repair after TBI. Among the earliest targets for transgenic and knockout studies in TBI have been programmed cell death mediators, such as the Bcl-2 family of proteins, caspases, and caspase-independent pathways. In addition, the role of cell cycle regulatory elements in the posttraumatic cell death pathway has been explored in mouse models. As interest grows in neuroplasticity in TBI, the use of transgenic and knockout mice in studies focused on gliogenesis, neurogenesis, and the balance of growth-promoting and growth-inhibiting molecules has increased in recent years. With proper consideration of potential effects of constitutive gene alteration, traditional transgenic and knockout models can provide valuable insights into TBI pathobiology. Through increasing sophistication of conditional and cell-type specific genetic manipulations, TBI studies in genetically altered mice will be increasingly useful for identification and validation of novel therapeutic targets.

In vitro models of traumatic brain injury

In vitro models of traumatic brain injury (TBI) are helping elucidate the pathobiological mechanisms responsible for dysfunction and delayed cell death after mechanical stimulation of the brain. Researchers have identified compounds that have the potential to break the chain of molecular events set in motion by traumatic injury. Ultimately, the utility of in vitro models in identifying novel therapeutics will be determined by how closely the in vitro cascades recapitulate the sequence of cellular events that play out in vivo after TBI. Herein, the major in vitro models are reviewed, and a discussion of the physical injury mechanisms and culture preparations is employed. A comparison between the efficacy of compounds tested in vitro and in vivo is presented as a critical evaluation of the fidelity of in vitro models to the complex pathobiology that is TBI. We conclude that in vitro models were greater than 88% predictive of in vivo results.

Protective effect of Bax ablation against cell loss in the retinal ganglion layer induced by optic nerve crush in transgenic mice

BACKGROUND

Bax expression is a prerequisite for retinal ganglion cell (RGC) apoptosis. Experimental studies have reported Bax protein upregulation following optic nerve transection. The stimuli that trigger apoptosis share a common executioner proteolysis cascade, including caspase-3 and poly-(adenosine diphosphate ribose) polymerase cleavage. This study sought to elucidate the role of the mitochondrial apoptotic pathway in RGCs using a Bax transgenic knockout mouse model.

METHODS

The right optic nerves of 26 C57BL mice, 7 Bax, 7 Bax, and 12 Bax, were subjected to crush injury and analyzed for apoptosis and neuronal cell loss on days 1, 3, and 21. Levels of Bax, Bcl-2, and caspase-3 messenger RNA expression were determined with real-time polymerase chain reaction.

RESULTS

Multiple apoptotic cells were detected in the retinas of the Bax and Bax mice at days 1 and 3, but not in the Bax mice. The Bax/Bcl-2 ratio was higher in the Bax than in the Bax mice on day 1 (1.33 and 0.83, respectively), with a trend toward an increase on day 3 (1.47 and 1.66, respectively); Bax/Bcl-X showed the same elevation on day 1 in the wild-type mice (1.34) but decreased on day 3 (0.8). Bax gene expression was undetectable in the Bax mice. Caspase-3 gene expression was higher in the Bax than in the Bax mice on day 1 and dropped toward baseline on day 3. The opposite trend was noted in the Bax mice.

CONCLUSION

The lack of apoptosis combined with the reduction in proapoptotic genes in the Bax mice after injury compared to the Bax and Bax mice suggests that Bax plays a crucial role in the induction of apoptosis. Suppression of Bax expression may reduce retinal cell loss.

Effect of growth hormone and melatonin on the brain: from molecular mechanisms to structural changes

Aging of the brain causes important reductions in quality of life and has wide socio-economic consequences. An increase in oxidative stress, and the associated inflammation and apoptosis, could be responsible for the pathogenesis of aging associated brain lesions. Melatonin has neuroprotective effects, by limiting the negative effects of oxygen and nitrogen free radicals. Growth hormone (GH) might exert additional neuro-protective and or neurogenic effects on the brain. The molecular mechanisms of the protective effects of GH and melatonin on the aging brain have been investigated in young and old Wistar rats. A reduction in the total number of neurons in the hilus of the dentate gyrus was evident at 24 months of age and was associated with a significant increase in inflammation markers as well as in pro-apoptotic parameters, confirming the role of apoptosis in its reduction. Melatonin treatment was able to enhance neurogenesis in old rats without modification of the total number of neurons, whereas GH treatment increased the total number of neurons without enhancing neurogenesis. Both GH and melatonin were able to reduce inflammation and apoptosis in the hippocampus. In conclusion, neuroprotective effects demonstrated by GH and melatonin in the hippocampus were exerted by decreasing inflammation and apoptosis.

Bax and calpain mediate excitotoxic oligodendrocyte death induced by activation of both AMPA and kainate receptors

Sustained activation of AMPA and kainate receptors in rat oligodendrocytes induces cytosolic calcium overload, mitochondrial depolarization, and an increase of reactive oxygen species, resulting in cell death. Here, we provide evidence that Bax, a proapoptotic member of the Bcl-2 protein family, is involved in excitotoxic apoptotic death of oligodendrocytes and that calpain mediates Bax activation. Cultured Bax(-/-) oligodendrocytes, obtained from the optic nerve of Bax knock-out mice, were resistant to AMPA and kainate receptor-mediated insults. In turn, both mitochondrial calcium uptake and mitochondrial alterations after excitotoxic insults were diminished in Bax-null oligodendrocytes. Moreover, pretreatment with furosemide, a blocker of Bax translocation to mitochondria, significantly protected rat and mouse oligodendrocytes from AMPA- and kainate-induced damage; in contrast, bongkrekic acid, a blocker of the mitochondrial permeability transition pore, had no effect. Finally, we analyzed the participation of calpain, which cleaves Bax and is activated by AMPA and kainate, in oligodendrocyte death. Pretreatment with 3-(4-iodophenyl)-2-mercapto-(Z)-2-propenoic acid (PD150606), a broad cell-permeable calpain inhibitor, and two additional calpain inhibitors diminished Bax activation, inhibited its translocation to mitochondria, and attenuated all apoptotic events resulting from excitotoxic insults to rat oligodendrocytes. Together, these results indicate that Bax and calpain are essential intermediaries of the mitochondria-dependent death pathway, triggered by AMPA and kainate receptor activation in oligodendrocytes.

Increased expression of transcription initiation factor IIB after rat traumatic brain injury

The protein TFIIB is a general transcription initiation factor that plays a pivotal role in the preinitiation complex (PIC) and selects the transcription initiation site. However, its distribution and function in the central nervous system (CNS) remains unclear. In the present study, we mainly investigated the expression and cellular localization of TFIIB during traumatic brain injury (TBI). Western blot analysis revealed that TFIIB was present in normal rat brain cortex. It gradually increased, reached a peak at the 5th day after TBI, and then decreased. Importantly, more TFIIB was colocalized with astrocytes and microglia, which are largely proliferated. In addition, Western blot detection showed that the 5th day post injury was also the proliferation peak indicated by the elevated expression of PCNA. Importantly, injury-induced expression of TFIIB was colabelled by proliferating cell nuclear antigen (proliferating cells marker). These data suggested that TFIIB may be implicated in the proliferation of astrocytes and microglia and the recovery of neurological outcomes. But the inherent mechanisms remained unknown. Further studies are needed to confirm the exact role of TFIIB after brain injury.

In vivo contributions of BH3-only proteins to neuronal death following seizures, ischemia, and traumatic brain injury

The Bcl-2 homology (BH) domain 3-only proteins are a proapoptotic subgroup of the Bcl-2 gene family, which regulate cell death via effects on mitochondria. The BH3-only proteins react to various cell stressors and promote cell death by binding and inactivating antiapoptotic Bcl-2 family members and direct activation of proapoptotic multi-BH domain proteins such as Bax. Here, we review the in vivo evidence for their involvement in the pathophysiology of status epilepticus and contrast it to ischemia and traumatic brain injury. Seizures in rodents activate three potent proapoptotic BH3-only proteins: Bid, Bim, and Puma. Analysis of damage after seizures in mice singly deficient for each BH3-only protein supports a causal role for Puma and to a lesser extent Bim but, surprisingly, not Bid. In ischemia and trauma, where core aspects of the pathophysiology of cell death overlap, multiple BH3-only proteins are also activated and Bid has been shown to be required for neuronal death. The findings suggest that while each neurologic insult activates multiple BH3-only proteins, there may be specificity in their functional contribution. Future challenges include evaluating the remaining BH3-only proteins, explaining different causal contributions, and, if possible, exploring neurologic outcomes in mouse models deficient for multiple BH3-only proteins.

Autophagy is involved in traumatic brain injury-induced cell death and contributes to functional outcome deficits in mice

Previous data demonstrate that traumatic brain injury (TBI) activates autophagy, and increases microtubule-associated protein 1 light chain 3 (LC3) immunostaining mainly in neurons. However, the role of autophagy in traumatic brain damage remains elusive. The aim of the present study was to investigate the autophagic mechanisms participating in traumatic brain injury. The autophagy inhibitors 3-methyladenine (3-MA) and bafliomycin A1 (BFA) were administered with a single i.c.v. injection before TBI. We first examined the protein levels of Beclin-1 and LC3 II, which have been found to promote autophagy previously. Immunoblotting analysis showed that 3-MA pretreatment reduced post-TBI Beclin-1 and LC3-II levels, and maintained p62/SQSTM1 (p62) levels. In addition, double immunolabeling showed that the increased punctate LC3-II dots colocalizing with Propidium Iodide (PI)-stained nuclei at 24 h after injury, were partially inhibited by 3-MA pretreatment. Furthermore, inhibition of autophagy could reduce TBI-induced cell injury assessed with i.p. injection of PI and lesion volume, and attenuate behavioral outcome evaluated by motor test and Morris water maze. The neuroprotective effects were associated with an inhibition on TBI-induced up-regulation of LC3, Beclin-1, cathepsin B, caspase-3 and the Beclin-1/Bcl-2 ratio. Taken together, these data imply that the autophagy pathway is involved in the pathophysiologic responses after TBI, and inhibition of this pathway may help attenuate traumatic damage and functional outcome deficits.

Regional calcineurin subunit B isoform expression in rat hippocampus following a traumatic brain injury

Calcineurin subunit isoforms are implicated in long term potentiation, long term depression, and structural plasticity. Calcineurin inhibitors benefit axonal damage, cellular dysfunction, and cognitive outcomes in animal models of traumatic brain injury (TBI). Distribution of the catalytic calcineurin A subunit is altered and calcineurin activity increased following fluid percussion injury. Alterations in calcineurin subunit A isoform distribution within the hippocampus also occur post controlled cortical impact (CCI) demonstrating a reduction in catalytic subunit distribution in CA1-2 dendritic fields. Furthermore the effect of TBI on the regulatory subunit, calcineurin B, is unknown. Understanding the role of both subunits is necessary to effectively target alterations in calcineurin signaling as current calcineurin inhibitors, such as cyclosporin A and FK-506, rely upon binding sites on both subunits for complete inhibition. The effect of moderate CCI on the expression and distribution of calcineurin B isoforms within the hippocampus was examined at 2h and 2weeks post injury. Calcineurin B isoforms showed increased expression throughout the CA1 and CA2 while there was a decrease in expression within the ipsilateral dentate gyrus. Alterations in CnB isoform expression within the CA1, CA1-2, and dentate gyrus have significant implications for persistent hippocampal dysfunction following TBI. Regional changes in regulatory subunit expression may alter the effect of calcineurin inhibitors regionally following a traumatic brain injury.

Simvastatin therapy prevents brain trauma-induced increases in beta-amyloid peptide levels

Elevations in beta-amyloid peptide (A beta) levels after traumatic brain injury (TBI) may confer risk for developing Alzheimer's disease in head trauma patients. We investigated the effects of simvastatin, a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor, on hippocampal A beta burden in a clinically relevant head injury/intervention model using mice expressing human A beta. Simvastatin therapy blunted TBI-induced increases in A beta, reduced hippocampal tissue damage and microglial activation, and improved behavioral outcome. The ability of statins to reduce post-injury A beta load and ameliorate pathological sequelae of brain injury makes them potentially effective in reducing the risk of developing Alzheimer's disease in TBI patients.

Quantitative analyses of matrix metalloproteinase activity after traumatic brain injury in adult rats

Recent laboratory evidence implicates matrix metalloproteinases (MMPs) as playing a pivotal role in ischemic and traumatic brain injuries (TBI). Here, quantitative real-time PCR analyses revealed that brains from TBI rats displayed significantly elevated MMP-9 expression at 24 h post-TBI, which remained upregulated at least until 48 h after injury. Immunohistochemical analyses similarly revealed significantly increased MMP-9 immunoreactivity at 24 and 48 h post-TBI. These results demonstrate that alterations in MMPs (i.e., MMP-9) commenced immediately after TBI, suggesting that treatment strategies designed to maintain MMP integrity should be initiated in the acute phase of injury.