Common patterns of bcl-2 family gene expression in two traumatic brain injury models

Evaluation of Progesterone Receptor Antagonist and Maxi-K Channel Agonist as Neuroprotective in Feeney's Weight Drop Model of TBI

Background

Neuroprotection in traumatic brain injury (TBI) is an unmet medical need.

Objective

We evaluated two agents, aglepristone (progesterone receptor antagonist) and N-salicyloyltryptamine (STP) (activator of Maxi-K channel in GH3 cells), for neuroprotection in Feeney's weight drop model of TBI.

Material and Methods

Forty-eight male Wistar rats were divided into six groups (n = 8 per group). A battery of six neurobehavioral tests was evaluated at the end of the first week (EO1W), second week (EO2W), and third week (EO3W). In addition, histopathological and immunohistochemistry (BAX, Bcl-2, and M30 Cytodeath) tests were performed at EO3W.

Results

Aglepristone at 10 mg/kg showed significant neuroprotection compared to control as assessed by Rota-rod test at EO1W, VEFP right paw and 28-point neurobehavioral test at EO2W, MWM test at EO3W, and positive histopathological and IHC findings. Aglepristone at 20 mg/kg showed negative results as assessed by BAX expression, downregulation of Bcl-2, and positive M30 Cytodeath, thereby suggesting toxicity at higher doses. STP 100 mg/kg showed modest neuroprotective activity but failed to show a dose-response relationship at a dose of 50 mg/kg.

Conclusion

The study shows that progesterone receptor antagonists have neuroprotection at lower doses and toxicity at higher doses.

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.

Late starting treadmill exercise improves spatial leaning ability through suppressing CREP/BDNF/TrkB signaling pathway following traumatic brain injury in rats

Traumatic brain injury (TBI) causes deficit in spatial learning and memory function. Physical activity ameliorates neurological dysfunction after TBI. We investigated the effect of late starting treadmill exercise on spatial learning ability in relation with cAMP-response element binding protein (CREB)/brain-derived neurotrophic factor (BDNF) signaling pathway using TBI rats. For this study, radial 8-arm maze test, TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) staining, caspase-3 immunohistochemistry, and western blot for Bax, Bcl-2, BDNF, tyrosine kinase B (TrkB), CREB, and phosphorylated CREP (p-CREB) were performed. TBI was induced by an electromagnetic-controlled cortical impact. The rats in the exercise groups were scheduled to run on a treadmill for 30 min once a day for 8 weeks starting 3 weeks after TBI. TBI impaired spatial learning ability and increased caspase-3 expression in the hippocampal dentate gyrus. TBI enhanced Bax expression and suppressed Bcl-2 expression in the hip-pocampus. TBI increased BDNF and TrkB expressions, resulted in the enhancement of p-CREB/CREB ratio in the hippocampus. However, treadmill exercise improved spatial learning ability, decreased caspase-3 expression, suppressed Bax expression, and increased Bcl-2 expression. Treadmill exercise alleviated TBI-induced over-expression of BDNF and TrkB, which suppressed phosphorylation of CREB in the hippocampus. In the present study, late starting treadmill exercise improved spatial learning ability through suppressing TBI-induced activation of CREB/BDNF/TrkB signaling pathway after TBI.

Sinomenine Provides Neuroprotection in Model of Traumatic Brain Injury via the Nrf2-ARE Pathway

The neuroprotective effect of sinomenine (SIN) has been demonstrated in several brain injury models. However, its role and molecular mechanism in traumatic brain injury (TBI) remain unknown. In this study, we investigated the neuroprotective effects of SIN in the weight-drop model of TBI in male ICR mice. Mice were randomly divided into the sham and TBI groups, SIN (10 mg/kg, 30 mg/kg and 50 mg/kg, administered intraperitoneally) or equal volume of vehicle was given at 30 min after TBI. Treatment with 30 mg/kg SIN significantly improved motor performance and alleviated cerebral edema. However, treatment with 10 mg/kg or 50 mg/kg SIN did not exhibit a better outcome. Therefore, we chose 30 mg/kg SIN for our subsequent experiments. SIN significantly increased the expression of Bcl-2 and decreased that of cleaved caspase-3, indicating that SIN is anti-apoptotic. This was confirmed by the observation that SIN-treated animals had fewer apoptotic neurons. Cortical malondialdehyde content, glutathione peroxidase (GPx) activity and superoxide dismutase (SOD) activity were restored in the group that received SIN. Furthermore, Western blot and immunofluorescence experiments showed that SIN enhanced the translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) to the nucleus. SIN administration also significantly upregulated the expression of the downstream factors heme oxygenase 1 and NAD(P)H:quinone oxidoreductase 1 at pre- and post-transcriptional levels. Together, these data demonstrate that SIN exerts a neuroprotective effect in a model of TBI, possibly by activating the Nrf2–antioxidant response element (ARE) pathway.

The Fas Ligand/Fas Death Receptor Pathways Contribute to Propofol-Induced Apoptosis and Neuroinflammation in the Brain of Neonatal Rats

A number of experimental studies have reported that exposure to common, clinically used anesthetics induce extensive neuroapoptosis and cognitive impairment when applied to young rodents, up to 2 weeks old, in phase of rapid synaptogenesis. Propofol is the most used general anesthetic in clinical practice whose mechanisms of neurotoxicity on the developing brain remains to be examined in depth. This study investigated effects of different exposures to propofol anesthesia on Fas receptor and Fas ligand expressions, which mediate proapoptotic and proinflammation signaling in the brain. Propofol (20 mg/kg) was administered to 7-day-old rats in multiple doses sufficient to maintain 2-, 4- and 6-h duration of anesthesia. Animals were sacrificed at 0, 4, 16 and 24 h after termination of anesthesia. It was found that propofol anesthesia induced Fas/FasL and downstream caspase-8 expression more prominently in the thalamus than in the cortex. Opposite, Bcl-2 and caspase-9, markers of intrinsic pathway activation, were shown to be more influenced by propofol treatment in the cortex. Further, we have established upregulation of caspase-1 and IL-1β cytokine transcription as well as subsequent activation of microglia that is potentially associated with brain inflammation. Behavioral analyses revealed that P35 and P60 animals, neonatally exposed to propofol, had significantly higher motor activity during three consecutive days of testing in the open field, though formation of the intersession habituation was not prevented. This data, together with our previous results, contributes to elucidation of complex mechanisms of propofol toxicity in developing brain.

Serum levels of caspase-cleaved cytokeratin-18 in patients with severe traumatic brain injury are associated with mortality: a pilot study

OBJECTIVE

There have been found apoptotic changes in brain tissue samples from animals and humans after a traumatic brain injury (TBI). The protein cytokeratin 18 (CK-18), present in epithelial cells, is cleaved by the action of caspases during apoptosis, and the resulting fragments are released into the blood as caspase-cleaved CK (CCCK)-18. Circulating levels of CCCK-18, as biomarker of apoptosis, have been determined in patients with different processes; however, it has not been explored in TBI patients. Thus, the objective of this study was to determine whether there is an association between serum CCCK-18 levels and mortality and whether such levels could be used as a biomarker to predict outcomes in TBI patients.

METHODS

A prospective, observational, multicenter study carried out in six Spanish Intensive Care Units. We included patients with severe TBI defined as Glasgow Coma Scale (GCS) lower than 9; and were excluded those patients with Injury Severity Score (ISS) in non-cranial aspects higher than 9. We measured serum CCCK-18 levels at admission. The end-point of the study was 30-day mortality.

RESULTS

Surviving patients (n = 73) showed lower serum CCCK-18 levels (P = 0.003) than non-survivors (n = 27). On ROC analysis, the area under the curve (AUC) for serum CCCK-18 levels as predictor of 30-day mortality was 0.69 (95% CI = 0.59-0.78; P = 0.006). We found in survival analysis that patients with serum CCCK-18 higher than 201 u/L had higher 30-day mortality than patients with lower levels (Hazard ratio = 3.9; 95% CI = 1.81-8.34; P<0.001). Regression analyses showed that serum CCCK-18 levels higher than 201 u/L were associated with 30-day mortality (OR = 8.476; 95% CI = 2.087-34.434; P = 0.003) after controlling for age and GCS.

CONCLUSIONS

The novel finding of our study was that serum CCCK-18 levels are associated with 30-day mortality and could be used as a prognostic biomarker in patients with severe TBI.

Transcriptome profiling of hippocampal CA1 after early-life seizure-induced preconditioning may elucidate new genetic therapies for epilepsy

Injury of the CA1 subregion induced by a single injection of kainic acid (1 × KA) in juvenile animals (P20) is attenuated in animals with two prior sustained neonatal seizures on P6 and P9. To identify gene candidates involved in the spatially protective effects produced by early-life conditioning seizures we profiled and compared the transcriptomes of CA1 subregions from control, 1 × KA- and 3 × KA-treated animals. More genes were regulated following 3 × KA (9.6%) than after 1 × KA (7.1%). Following 1 × KA, genes supporting oxidative stress, growth, development, inflammation and neurotransmission were upregulated (e.g. Cacng1, Nadsyn1, Kcng1, Aven, S100a4, GFAP, Vim, Hrsp12 and Grik1). After 3 × KA, protective genes were differentially over-expressed [e.g. Cat, Gpx7, Gad1, Hspa12A, Foxn1, adenosine A1 receptor, Ca(2+) adaptor and homeostasis proteins, Cacnb4, Atp2b2, anti-apoptotic Bcl-2 gene members, intracellular trafficking protein, Grasp and suppressor of cytokine signaling (Socs3)]. Distinct anti-inflammatory interleukins (ILs) not observed in adult tissues [e.g. IL-6 transducer, IL-23 and IL-33 or their receptors (IL-F2 )] were also over-expressed. Several transcripts were validated by real-time polymerase chain reaction (QPCR) and immunohistochemistry. QPCR showed that casp 6 was increased after 1 × KA but reduced after 3 × KA; the pro-inflammatory gene Cox1 was either upregulated or unchanged after 1 × KA but reduced by ~70% after 3 × KA. Enhanced GFAP immunostaining following 1 × KA was selectively attenuated in the CA1 subregion after 3 × KA. The observed differential transcriptional responses may contribute to early-life seizure-induced pre-conditioning and neuroprotection by reducing glutamate receptor-mediated Ca(2+) permeability of the hippocampus and redirecting inflammatory and apoptotic pathways. These changes could lead to new genetic therapies for epilepsy.

Effect of resveratrol on Bcl-2 and VEGF expression in oxygen-induced retinopathy of prematurity

PURPOSE

To explore the effect of resveratrol on B-cell leukemia/lymphoma-2 (Bcl-2) and vascular endothelial growth factor (VEGF) expression in rats with oxygen-induced retinopathy of prematurity (ROP).

METHODS

Seven-day-old Sprague-Dawley rats (N = 60) were randomly assigned to five groups. Group A received normal partial oxygen pressure and groups B, C, D, and E received 75% ± 2% oxygen for 5 days to induce ROP. The rats in groups C, D, and E were intragastrically treated with resveratrol (10, 30, and 60 mg/kg/d, respectively) once daily for 5 days. Rats were killed at 17 days of age and the retina was collected.

RESULTS

Western blot analysis revealed increased Bcl-2 protein expression in group B versus group A. Levels of Bcl-2 decreased with the increase of resveratrol concentration in groups C, D, and E. The optical density of Bcl-2 protein expression in group B was four times higher than that in group A (P < .01). When compared with group B, expression of Bcl-2 and VEGF in groups C, D, and E decreased in a dose-dependent manner. Significant differences in expression of Bcl-2 and VEGF were also noted among the three treatment groups with resveratrol (P < .01). After treatment with resveratrol at 10, 30, and 60 mg/kg/d, the inhibition rate of Bcl-2 expression was 11.1%, 38.1%, and 69.8% and that of VEGF expression was 3.4%, 23.0%, and 43.7%, respectively.

CONCLUSION

Resveratrol can significantly inhibit expression of Bcl-2 and VEGF in the retina of neonatal rats with oxygen-induced ROP. It may provide a protective effect on retinal neovascular diseases, including ROP.

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.

Recent findings on neuroprotection against excitotoxicity in the hippocampus of female rats

Newborn mammals are totally dependent on maternal milk and care for survival. The mother's brain undergoes different behavioural, physiological and emotional adaptations that make the mother more likely to satisfy the demands of the offspring. Recent reports from our group show that, compared to nulliparous rats, lactation diminishes cell damage induced by excitotoxicity in the dorsal hippocampus of the dam after systemic or i.c. administration of kainic acid (KA) and the resulting motor seizures. Elevated levels of prolactin (PRL), oxytocin, progesterone and glucocorticoids are characteristics of lactation, and the pronounced fluctuation of these hormones occurring in this phase may play a role protecting the hippocampus. Indeed, PRL administration to ovariectomised rats significantly diminishes the deleterious effects of KA in the dorsal hippocampus and reduces the progression of KA-induced seizures. Thus, lactation is a natural model for neuroprotection because it effectively prevents acute and chronic cell damage of the hippocampus induced by excitotoxicity.

The role of crocetin in protection following cerebral contusion and in the enhancement of angiogenesis in rats

The protective role of crocetin following cerebral contusion and its effects on the enhancement of angiogenesis in rats was investigated. A total of 60 Sprague-Dawley rats were divided into three groups (n = 20 each): crocetin therapy group (cerebral contusion treated with crocetin), cerebral trauma control group (without treatment), sham operation control group. The effect of crocetin was examined by modified Neurological Severity Scores (mNSS), electron microscopy, terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) procedure, western blotting analysis of Bcl-2 protein expression, microvessel count (MVC), endothelial cell culture and immunocyto-chemistry. The mNSS results indicated that neurological function of therapy group was significantly recovered seven days and fifteen days after the trauma. The TUNEL staining and electron microscopy revealed that crocetin treatment led to an inhibition of neuronal apoptosis 72 h following treatment; this finding was confirmed by western blot analysis of B cell lymphoma/leukemia-2 (Bcl-2) protein expression. Expression levels of vascular endothelial growth factor receptor-2 (VEGFR-2) and serum response factor (SRF) were higher in the crocetin therapy group in comparison to the two other experimental groups. Our results demonstrate that the protective effects of crocetin upon brain injury may be related to its ability to inhibit apoptosis at early stages of the injury and its ability to promote angiogenesis at the sub-acute stage.

Strain-based regional traumatic brain injury intensity in controlled cortical impact: a systematic numerical analysis

Regional strain-based brain injury intensity during controlled cortical impact (CCI) was studied using a three-dimensional numerical rat brain model. A full factorial design of CCI computer experiments was performed using two typical impactor shapes (flat or hemispherical) at a fixed impact velocity of 4?m/s with various impact depths (1, 1.5, 1.6, 2, 2.5, 2.7, and 3?mm) and various impactor diameters (4, 5, 6, 8, and 9.5?mm). In total, 70 CCI cases were simulated numerically. Two injury assessment measures, the cumulative strain damage measure (CSDM), which accounts for the volume of brain tissue with elevated strains, and cumulative strain damage percentage measure (CSDPM), which is a strain-based estimate of the neuronal cell loss percentage, were used to evaluate the risk of brain injury. Results demonstrated positive nonlinear relationships between impact depth and these injury assessment measures in six regions of interest: ipsilateral cortex, ipsilateral corpus callosum, ipsilateral hippocampus, ipsilateral thalamus, cerebellum, and brainstem. However, the impactor diameter was not always positively correlated with regional tissue strains. For the flat impactor group, the 5?mm diameter impactor induced more tissue strain in the corpus callosum/hippocampus, and a smaller impactor induced more strain in the thalamus. For the hemispherical impactor group, a larger impactor tended to induce more tissue strain in subcortical regions, with the exception of the 6?mm diameter impactor. This study systematically predicts regional intensity of primary brain injury according to tissue strain distributions in the hope that strain distribution maps may become a common platform to compare CCI severities with different configurations.

Erythropoietin improves histological and functional outcomes after traumatic brain injury in mice in the absence of the neural erythropoietin receptor

Erythropoietin (EPO), essential for erythropoiesis, provides neuroprotection. The EPO receptor (EPOR) is expressed in both neural and non-neural cells in the brain. This study was designed to test the hypothesis that EPO provides beneficial therapeutic effects, even in the absence of the neural EPOR. In this study, EPOR-null mice were rescued with selective EpoR expression driven by the endogenous EpoR promoter in hematopoietic tissue, but not in the neural cells. Anesthetized young adult female EPOR-null and wild-type mice were subjected to traumatic brain injury (TBI) induced by controlled cortical impact. EPO (5000 U/kg) or saline was intraperitoneally administered at 6 h and 3 and 7 days post-injury. Sensorimotor and spatial learning functions were assessed. Expression of EPOR and its downstream signal proteins were evaluated by Western blot analysis. Our data demonstrated that EPO treatment significantly reduced cortical tissue damage and hippocampal cell loss, and improved spatial learning following TBI in both the wild-type and EPOR-null mice. EPO treatment significantly improved sensorimotor functional recovery, with better outcomes in the wild-type mice. EPO treatment upregulated anti-apoptotic proteins (p-Akt and Bcl-XL) in the ipsilateral hippocampus and cortex of the injured wild-type and EPOR-null mice. These data demonstrate that EPO significantly provides neuroprotection following TBI, even in the absence of EPOR in the neural cells, suggesting that its therapeutic benefits may be mediated through vascular protection.

Estrogen receptors increased expression during hippocampal neuroprotection in lactating rats

Estrogen receptor (ER)-mediated neuroprotection has been demonstrated in both in vitro and in vivo model systems. Two types of estrogen receptors, ERalpha and ERbeta, are the major mediators of the biological functions of estrogens. In the hippocampus, ERbeta is prevalent over ERalpha. Recently, we reported that during the final phase of lactation there is a neuroprotective mechanism in the hippocampus of the adult female rat against neuronal damage induced by systemic kainic acid administration vs. virgin (metestrus) rats. In this study, we assessed differential ER expression and localization in CA1, CA3 and dentate gyrus regions of dorsal hippocampus of metestrus and lactating adult rats at day 19 of lactation, during basal conditions (metestrus and L19, respectively) and 24h after systemic kainate administration. ERs were assessed by western blot and immunohistochemistry. We found a significant increase in the expression of ERs in the hippocampus during lactation as compared with metestrus. ERbeta was significantly increased in the CA1 and CA3 of lactating rats after the kainic acid insult. In addition, we observed a relocalization of ERbeta from the cytoplasm to the nucleus of neuronal cells. Our results suggest that there is a strong correlation between expression of ERs, especially ERbeta, in lactating CA1 and CA3 hippocampus regions in response to kainate administration, and neuroprotection observed during this reproductive period. This may be one of the mechanisms involved in the protection of the maternal brain to ensure offspring survival.

Neuroprotective effects of lactation against kainic acid treatment in the dorsal hippocampus of the rat

Marked hippocampal changes in response to excitatory amino acid agonists occur during pregnancy (e.g. decreased frequency in spontaneous recurrent seizures in rats with KA lesions of the hippocampus) and lactation (e.g. reduced c-Fos expression in response to N-methyl-d,l-aspartic acid but not to kainic acid). In this study, the possibility that lactation protects against the excitotoxic damage induced by KA in hippocampal areas was explored. We compared cell damage induced 24 h after a single systemic administration of KA (5 or 7.5 mg/kg bw) in regions CA1, CA3, and CA4 of the dorsal hippocampus of rats in the final week of lactation to that in diestrus phase. To determine cellular damage in a rostro-caudal segment of the dorsal hippocampus, we used NISSL and Fluorojade staining, immunohistochemistry for active caspase-3 and TUNEL, and we observed that the KA treatment provoked a significant loss of neurons in diestrus rats, principally in the pyramidal cells of CA1 region. In contrast, in lactating rats, pyramidal neurons from CA1, CA3, and CA4 in the dorsal hippocampus were significantly protected against KA-induced neuronal damage, indicating that lactation may be a natural model of neuroprotection.

Expression of apoptosis-related genes in the organ of Corti, modiolus and stria vascularis of newborn rats

Cell death in the inner ear tissues is an important mechanism leading to hearing impairment. Here, using microarrays and real-time RT-PCR we analyzed expression of selected apoptosis-related genes in rat's inner ear. We determined the gene expression in tissues freshly isolated from neonatal rats (3-5 days old) and compared it to that of explants cultured for 24 h under normoxic or hypoxic conditions. For the analyses, we used pooled samples of the organ of Corti (OC), modiolus (MOD) and stria vascularis (SV), respectively. We observed region-specific changes in gene expression between the fresh tissues and the normoxic culture. In the OC, expression of the proapoptotic genes caspase-2, caspase-3, caspase-6 and calpain-1 was downregulated. In the MOD, the antioxidative defense SOD-2 and SOD-3 were upregulated. In the SV, caspase-2, caspase-6, calpain-1 and SOD-3 were downregulated and SOD-2 upregulated. We speculate that these changes could reflect survival shift in transcriptome of inner ear explants tissues under in vitro conditions. With the exception of SOD-2, hypoxic culture conditions induced the same changes in gene expression as the normoxic conditions indicating that culture preparation is likely the dominating factor, which modifies the gene expression pattern. We conclude that various culture conditions induce different expression pattern of apoptosis-related genes in the organotypic cochlear cultures, as compared to fresh tissues. This transcriptional pattern may reflect the survival ability of specific tissues and could become a tempting target for a pharmacological intervention in inner ear diseases.

Neurotoxins and neurotoxicity mechanisms. an overview

Neurotoxins represent unique chemical tools, providing a means to 1) gain insight into cellular mechanisms of apopotosis and necrosis, 2) achieve a morphological template for studies otherwise unattainable, 3) specifically produce a singular phenotype of denervation, and 4) provide the starting point to delve into processes and mechanisms of nerve regeneration and sprouting. There are many other notable uses of neurotoxins in neuroscience research, and ever more being discovered each year. The objective of this review paper is to highlight the broad areas of neuroscience in which neurotoxins and neurotoxicity mechanism come into play. This shifts the focus away from neurotoxins per se, and onto the major problems under study today. Neurotoxins broadly defined are used to explore neurodegenerative disorders, psychiatric disorders and substance use disorders. Neurotoxic mechanisms relating to protein aggregates are indigenous to Alzheimer disease, Parkinson's disease. NeuroAIDS is a disorder in which microglia and macrophages have enormous import. The gap between the immune system and nervous system has been bridged, as neuroinflammation is now considered to be part of the neurodegenerative process. Related mechanisms now arise in the process of neurogenesis. Accordingly, the entire spectrum of neuroscience is within the purview of neurotoxins and neurotoxicity mechanisms. Highlights on discoveries in the areas noted, and on selective neurotoxins, are included, mainly from the past 2 to 3 years.

Reduced neuronal cell death after experimental brain injury in mice lacking a functional alternative pathway of complement activation

Background

Neuroprotective strategies for prevention of the neuropathological sequelae of traumatic brain injury (TBI) have largely failed in translation to clinical treatment. Thus, there is a substantial need for further understanding the molecular mechanisms and pathways which lead to secondary neuronal cell death in the injured brain. The intracerebral activation of the complement cascade was shown to mediate inflammation and tissue destruction after TBI. However, the exact pathways of complement activation involved in the induction of posttraumatic neurodegeneration have not yet been assessed. In the present study, we investigated the role of the alternative complement activation pathway in contributing to neuronal cell death, based on a standardized TBI model in mice with targeted deletion of the factor B gene (fB-/-), a "key" component required for activation of the alternative complement pathway.

Results

After experimental TBI in wild-type (fB+/+) mice, there was a massive time-dependent systemic complement activation, as determined by enhanced C5a serum levels for up to 7 days. In contrast, the extent of systemic complement activation was significantly attenuated in fB-/- mice (P < 0.05,fB-/- vs. fB+/+; t = 4 h, 24 h, and 7 days after TBI). TUNEL histochemistry experiments revealed that posttraumatic neuronal cell death was clearly reduced for up to 7 days in the injured brain hemispheres of fB-/- mice, compared to fB+/+ littermates. Furthermore, a strong upregulation of the anti-apoptotic mediator Bcl-2 and downregulation of the pro-apoptotic Fas receptor was detected in brain homogenates of head-injured fB-/- vs. fB+/+ mice by Western blot analysis.

Conclusion

The alternative pathway of complement activation appears to play a more crucial role in the pathophysiology of TBI than previously appreciated. This notion is based on the findings of (a) the significant attenuation of overall complement activation in head-injured fB-/- mice, as determined by a reduction of serum C5a concentrations to constitutive levels in normal mice, and (b) by a dramatic reduction of TUNEL-positive neurons in conjunction with an upregulation of Bcl-2 and downregulation of the Fas receptor in head-injured fB-/- mice, compared to fB+/+ littermates. Pharmacological targeting of the alternative complement pathway during the "time-window of opportunity" after TBI may represent a promising new strategy to be pursued in future studies.

Pharmacological complement inhibition at the C3 convertase level promotes neuronal survival, neuroprotective intracerebral gene expression, and neurological outcome after traumatic brain injury

The complement system represents an important mediator of neuroinflammation in traumatic brain injury. We have previously shown that transgenic mice with central nervous system-targeted overexpression of Crry, a potent murine complement inhibitor at the level of C3 convertases, are protected from complement-mediated neuropathological sequelae in brain-injured mice. This knowledge was expanded in the present study to a pharmacological approach by the use of a recombinant Crry molecule (termed Crry-Ig) which was recently made available in a chimeric form fused to the non-complement fixing mouse IgG1 Fc region. In a standardized model of closed head injury in mice, the systemic injection of 1 mg Crry-Ig at 1 h and 24 h after trauma resulted in a significant neurological improvement for up to 7 days, as compared to vehicle-injected control mice (P < 0.05, repeated measures ANOVA). Furthermore, the extensive neuronal destruction seen in the hippocampal CA3/CA4 sublayers in head-injured mice with vehicle injection only was shown to be preserved - to a similar extent as in "sham"-operated mice - by the posttraumatic injection of Crry-Ig. Real-time RT-PCR analysis revealed that the post-treatment with Crry-Ig resulted in a significant up-regulation of candidate neuroprotective genes in the injured hemisphere (Bcl-2, C1-Inh, CD55, CD59), as compared to the vehicle control group (P < 0.01, unpaired Student's t test). Increased intracerebral Bcl-2 expression by Crry-Ig treatment was furthermore confirmed at the protein level by Western blot analysis. These data suggest that pharmacological complement inhibition represents a promising approach for attenuation of neuroinflammation and secondary neurodegeneration after head injury.