New in vitro model of traumatic neuronal injury: evaluation of secondary injury and glutamate receptor-mediated neurotoxicity

Preso enhances mGluR1-mediated excitotoxicity by modulating the phosphorylation of mGluR1-Homer1 complex and facilitating an ER stress after traumatic brain injury

Glutamate receptor (GluR)-mediated excitotoxicity is an important mechanism causing delayed neuronal injury after traumatic brain injury (TBI). Preso, as a core scaffolding protein of postsynaptic density (PSD), is considered an important regulator during excitotoxicity and TBI and combines with glutamate receptors to form functional units for excitatory glutamatergic neurotransmission, and elucidating the mechanisms of these functional units will provide new targets for the treatment of TBI. As a multidomain scaffolding protein, Preso directly interacts with metabotropic GluR (mGluR) and another scaffold protein, Homer. Because the mGluR-Homer complex plays a crucial role in TBI, modulation of this complex by Preso may be an important mechanism affecting the excitotoxic damage to neurons after TBI. Here, we demonstrate that Preso facilitates the interaction between metabotropic mGluR1 and Homer1 to activate mGluR1 signaling and cause excitotoxic neuronal injury and endoplasmic reticulum (ER) stress after TBI. The regulatory effect of Preso on the mGluR1-Homer1 complex is dependent on the direct association between Preso and this complex and also involves the phosphorylation of the interactive binding sites of mGluR1 and Homer1 by Preso. Further studies confirmed that Preso, as an adaptor of cyclin-dependent kinase 5 (CDK5), promotes the phosphorylation of the Homer1-binding site on mGluR1 by CDK5 and thereby enhances the interaction between mGluR1 and Homer1. Preso can also promote the formation of the mGluR1-Homer1 complex by inhibiting the phosphorylation of the Homer1 hinge region by Ca2+/calmodulin-dependent protein kinase IIα (CaMKIIα). Based on these molecular mechanisms, we designed several blocking peptides targeting the interaction between Preso and the mGluR1-Homer1 complex and found that directly disrupting the association between mGluR1 and scaffolding proteins significantly promotes the recovery of motor function after TBI.

Simulating traumatic brain injury in vitro: developing high throughput models to test biomaterial based therapies

Traumatic brain injuries are serious clinical incidents associated with some of the poorest outcomes in neurological practice. Coupled with the limited regenerative capacity of the brain, this has significant implications for patients, carers, and healthcare systems, and the requirement for life-long care in some cases. Clinical treatment currently focuses on limiting the initial neural damage with long-term care/support from multidisciplinary teams. Therapies targeting neuroprotection and neural regeneration are not currently available but are the focus of intensive research. Biomaterial-based interventions are gaining popularity for a range of applications including biomolecule and drug delivery, and to function as cellular scaffolds. Experimental investigations into the development of such novel therapeutics for traumatic brain injury will be critically underpinned by the availability of appropriate high throughput, facile, ethically viable, and pathomimetic biological model systems. This represents a significant challenge for researchers given the pathological complexity of traumatic brain injury. Specifically, there is a concerted post-injury response mounted by multiple neural cell types which includes microglial activation and astroglial scarring with the expression of a range of growth inhibitory molecules and cytokines in the lesion environment. Here, we review common models used for the study of traumatic brain injury (ranging from live animal models to in vitro systems), focusing on penetrating traumatic brain injury models. We discuss their relative advantages and drawbacks for the developmental testing of biomaterial-based therapies.

Targeting NMDA Receptors at the Neurovascular Unit: Past and Future Treatments for Central Nervous System Diseases

The excitatory neurotransmission of the central nervous system (CNS) mainly involves glutamate and its receptors, especially N-methyl-D-Aspartate receptors (NMDARs). These receptors have been extensively described on neurons and, more recently, also on other cell types. Nowadays, the study of their differential expression and function is taking a growing place in preclinical and clinical research. The diversity of NMDAR subtypes and their signaling pathways give rise to pleiotropic functions such as brain development, neuronal plasticity, maturation along with excitotoxicity, blood-brain barrier integrity, and inflammation. NMDARs have thus emerged as key targets for the treatment of neurological disorders. By their large extracellular regions and complex intracellular structures, NMDARs are modulated by a variety of endogenous and pharmacological compounds. Here, we will present an overview of NMDAR functions on neurons and other important cell types involved in the pathophysiology of neurodegenerative, neurovascular, mental, autoimmune, and neurodevelopmental diseases. We will then discuss past and future development of NMDAR targeting drugs, including innovative and promising new approaches.

A Novel In Vitro Platform Development in the Lab for Modeling Blast Injury to Microglia

Traumatic brain injury (TBI), which is mainly caused by impact, often results in chronic neurological abnormalities. Since the pathological changes in vivo during primary biomechanical injury are quite complicated, the in-depth understanding of the pathophysiology and mechanism of TBI depends on the establishment of an effective experimental in vitro model. Usually, a bomb explosive blast was employed to establish the in vitro model, while the process is complex and unsuitable in the lab. Based on water-hammer, we have developed a device system to provide a single dynamic compression stress on living cells. A series of amplitude (∼5.3, ∼9.8, ∼13.5 MPa) were generated to explore the effects of dynamic compression loading on primary microglia within 48 h. Apoptosis experiments indicated that primary microglia had strong tolerance to blast waves. In addition, the generation of intercellular reactive oxygen species and secretory nitric oxide was getting strongly enhanced and recovered within 48 h. In addition, there is a notable release of pro-inflammatory cytokine by microglia. Our work provides a reproducible and peaceable method of loading single dynamic compression forces to cells in vitro. Microglia showed an acute inflammatory response to dynamic loadings, while no significant cell death was observed. This insight delivers a new technological approach that could open new areas to a better understanding of the mechanism of cell blast injuries.

Acute and Delayed Effects of Mechanical Injury on Calcium Homeostasis and Mitochondrial Potential of Primary Neuroglial Cell Culture: Potential Causal Contributions to Post-Traumatic Syndrome

In vitro models of traumatic brain injury (TBI) help to elucidate the pathological mechanisms responsible for cell dysfunction and death. To simulate in vitro the mechanical brain trauma, primary neuroglial cultures were scratched during different periods of network formation. Fluorescence microscopy was used to measure changes in intracellular free Ca²⁺ concentration ([Ca²⁺]_i) and mitochondrial potential (ΔΨm) a few minutes later and on days 3 and 7 after scratching. An increase in [Ca²⁺]_i and a decrease in ΔΨm were observed ~10 s after the injury in cells located no further than 150–200 µm from the scratch border. Ca²⁺ entry into cells during mechanical damage of the primary neuroglial culture occurred predominantly through the NMDA-type glutamate ionotropic channels. MK801, an inhibitor of this type of glutamate receptor, prevented an acute increase in [Ca²⁺]_i in 99% of neurons. Pathological changes in calcium homeostasis persisted in the primary neuroglial culture for one week after injury. Active cell migration in the scratch area occurred on day 11 after neurotrauma and was accompanied by a decrease in the ratio of live to dead cells in the areas adjacent to the injury. Immunohistochemical staining of glial fibrillary acidic protein and β-III tubulin showed that neuronal cells migrated to the injured area earlier than glial cells, but their repair potential was insufficient for survival. Mitochondrial Ca²⁺ overload and a drop in ΔΨm may cause delayed neuronal death and thus play a key role in the development of the post-traumatic syndrome. Preventing prolonged ΔΨm depolarization may be a promising therapeutic approach to improve neuronal survival after traumatic brain injury.

The Emergence of Model Systems to Investigate the Link Between Traumatic Brain Injury and Alzheimer’s Disease

Numerous epidemiological studies have demonstrated that individuals who have sustained a traumatic brain injury (TBI) have an elevated risk for developing Alzheimer’s disease and Alzheimer’s-related dementias (AD/ADRD). Despite these connections, the underlying mechanisms by which TBI induces AD-related pathology, neuronal dysfunction, and cognitive decline have yet to be elucidated. In this review, we will discuss the various in vivo and in vitro models that are being employed to provide more definite mechanistic relationships between TBI-induced mechanical injury and AD-related phenotypes. In particular, we will highlight the strengths and weaknesses of each of these model systems as it relates to advancing the understanding of the mechanisms that lead to TBI-induced AD onset and progression as well as providing platforms to evaluate potential therapies. Finally, we will discuss how emerging methods including the use of human induced pluripotent stem cell (hiPSC)-derived cultures and genome engineering technologies can be employed to generate better models of TBI-induced AD.

Regional Neurodegeneration in vitro: The Protective Role of Neural Activity

Traumatic brain injury is a devastating public health problem, the eighth leading cause of death across the world. To improve our understanding of how injury at the cellular scale affects neural circuit function, we developed a protocol to precisely injure individual neurons within an in vitro neural network. We used high speed calcium imaging to estimate alterations in neural activity and connectivity that occur followed targeted microtrauma. Our studies show that mechanically injured neurons inactivate following microtrauma and eventually re-integrate into the network. Single neuron re-integration is dependent on its activity prior to injury and initial connections in the network: more active and integrated neurons are more resistant to microtrauma and more likely to re-integrate into the network. Micromechanical injury leads to neuronal death 6 h post-injury in a subset of both injured and uninjured neurons. Interestingly, neural activity and network participation after injury were associated with survival in linear discriminate analysis (77.3% correct prediction, Wilks' Lambda = 0.838). Based on this observation, we modulated neuronal activity to rescue neurons after microtrauma. Inhibition of neuronal activity provided much greater survivability than did activation of neurons (ANOVA, p < 0.01 with post-hoc Tukey HSD, p < 0.01). Rescue of neurons by blocking activity in the post-acute period is partially mediated by mitochondrial energetics, as we observed silencing neurons after micromechanical injury led to a significant reduction in mitochondrial calcium accumulation. Overall, the present study provides deeper insight into the propagation of injury within networks, demonstrating that together the initial activity, network structure, and post-injury activity levels contribute to the progressive changes in a neural circuit after mechanical trauma.

Glycyrrhizin Blocks the Detrimental Effects of HMGB1 on Cortical Neurogenesis After Traumatic Neuronal Injury

Despite medical advances, neurological recovery after severe traumatic brain injury (TBI) remains poor. Elevated levels of high mobility group box protein-1 (HMGB1) are associated with poor outcomes; likely via interaction with receptors for advanced-glycation-end-products (RAGE). We examined the hypothesis that HMGB1 post-TBI is anti-neurogenic and whether this is pharmacologically reversible. Post-natal rat cortical mixed neuro-glial cell cultures were subjected to needle-scratch injury and examined for HMGB1-activation/neuroinflammation. HMGB1-related genes/networks were examined using genome-wide RNA-seq studies in cortical perilesional tissue samples from adult mice. Post-natal rat cortical neural stem/progenitor cell cultures were generated to quantify effects of injury-condition medium (ICM) on neurogenesis with/without RAGE antagonist glycyrrhizin. Needle-injury upregulated TNF-α/NOS-2 mRNA-expressions at 6 h, increased proportions of activated microglia, and caused neuronal loss at 24 h. Transcriptome analysis revealed activation of HMGB1 pathway genes/canonical pathways in vivo at 24 h. A 50% increase in HMGB1 protein expression, and nuclear-to-cytoplasmic translocation of HMGB1 in neurons and microglia at 24 h post-injury was demonstrated in vitro. ICM reduced total numbers/proportions of neuronal cells, but reversed by 0.5 μM glycyrrhizin. HMGB1 is activated following in vivo post mechanical injury, and glycyrrhizin alleviates detrimental effects of ICM on cortical neurogenesis. Our findings highlight glycyrrhizin as a potential therapeutic agent post-TBI.

Modeling traumatic brain injury with human brain organoids

Traumatic brain injury (TBI) remains a prominent public health concern despite several decades of attempts to develop therapies for the associated neurological and cognitive deficits. Effective models of this condition are imperative for better defining its pathophysiology and testing therapeutics. Human brain organoids are stem cell-derived neural tissues that recapitulate many of the steps of normal neurodevelopment, resulting in the reproduction of a substantial degree of brain architecture. Organoids are highly relevant to clinical conditions because of their human nature and three-dimensional tissue structure, yet they are easier to manipulate and interrogate experimentally than animals. Thus, they have the potential to serve as a novel platform for studying TBI. In this article, we discuss available in vitro models of TBI, active areas of inquiry on brain organoids, and how these two concepts could be merged.

Why Does Brain Trauma Research Fail?

Traumatic brain injury (TBI) represents a major health care problem and a significant social and economic issue worldwide. Considering the generalized failure in introducing effective drugs and clinical protocols, there is an urgent need for efficient treatment modalities, able to improve devastating posttraumatic morbidity and mortality. In this work, the status of brain trauma research is analyzed in all its aspects, including basic and translational science and clinical trials. Implicit and explicit challenges to different lines of research are discussed and clinical trial structures and outcomes are scrutinized, along with possible explanations for systematic therapeutic failures and their implications for future development of drug and clinical trials. Despite significant advances in basic and clinical research in recent years, no specific therapeutic protocols for TBI have been shown to be effective. New potential therapeutic targets have been identified, following a better understanding of pathophysiologic mechanisms underlying TBI, although with disappointing results. Several reasons can be pinpointed at different levels, from inaccurate animal models of disease to faulty preclinical and clinical trials, with poor design and subjective outcome measures. Distinct strategies can be delineated to overcome specific shortcomings of research studies. Identifying and contextualizing the failures that have dominated TBI research is mandatory. This review analyzes current approaches and discusses possible strategies for improving outcomes.

Advances in ex vivo models and lab-on-a-chip devices for neural tissue engineering

The technologies related to ex vivo models and lab-on-a-chip devices for studying the regeneration of brain, spinal cord, and peripheral nerve tissues are essential tools for neural tissue engineering and regenerative medicine research. The need for ex vivo systems, lab-on-a-chip technologies and disease models for neural tissue engineering applications are emerging to overcome the shortages and drawbacks of traditional in vitro systems and animal models. Ex vivo models have evolved from traditional 2D cell culture models to 3D tissue-engineered scaffold systems, bioreactors, and recently organoid test beds. In addition to ex vivo model systems, we discuss lab-on-a-chip devices and technologies specifically for neural tissue engineering applications. Finally, we review current commercial products that mimic diseased and normal neural tissues, and discuss the future directions in this field.

In Vitro Models as a Platform to Investigate Traumatic Brain Injury

Traumatic Brain Injury (TBI) remains a significant cause of mortality and morbidity, affecting individuals of all age groups. Much remains to be learned about its complex pathophysiology, with a view to designing effective neuroprotective strategies to protect sublethally injured brain tissue that would otherwise die in secondary injury processes. Experimental in vivo models offer the potential to study TBI in the laboratory, however, treatments that were neuroprotective in animals have, thus far, largely failed to translate in human clinical studies. In vitro models of neurotrauma can be used to study specific pathophysiological cascades — individually and without confounding factors — and to test potential neuroprotective strategies. These in vitro models include transection, compression, barotrauma, acceleration, hydrodynamic, chemical injury and cell-stretch methodologies. Various cell culture systems can also be utilised, including brain-on-a-chip, immortalised cell lines, primary cultures, acute preparations and organotypic cultures. Potential positive outcomes of the increased use of in vitro platforms to study TBI would be the refinement of in vivo experiments, as well as enhanced translation of the results into clinically meaningful neuroprotective strategies for the future. In addition, the replacement of in vivo experiments by suitable in vitro studies would lead to a welcome reduction in the numbers of animal procedures in this ethically-challenging field.

The Anti-Inflammatory Effects of Interferon Tau by Suppressing NF-κB/MMP9 in Macrophages Stimulated with Staphylococcus aureus

Previous studies have reported that interferon tau (IFNT) significantly mitigates tissue inflammation. However, this effect and its regulating pathways have not been reported for Staphylococcus aureus-induced inflammation. In this study, RAW 264.7 cells stimulated with S. aureus were used to identify the anti-inflammatory effects and mechanism of IFNT. First, IFNT was found to be noncytotoxic to macrophages treated with the high dose of 200 ng/mL IFNT. ELISA and qPCR revealed that IFNT decreased the expression of proinflammatory cytokines such as TNF-α, IL-1β, and IL-6. TLR2, which is involved in the immune response during S. aureus infection, directly affected NF-κB pathway activation and was also downregulated by IFNT. Subsequent Western blotting showed that the phosphorylation of IκBα and NF-κB p65 was inhibited by IFNT. Therefore, although the MMP9 levels were significantly downregulated in a dose-dependent manner by IFNT, little change in MMP2 was observed in S. aureus-stimulated RAW 264.7 cells. Furthermore, PDTC, an inhibitor of NF-κB, also significantly decreased MMP9 levels by inhibiting NF-κB p65 activation. All of these findings strongly suggested that IFNT suppresses the NF-κB/MMP9 signal transduction pathway and subsequently exerts its anti-inflammatory effects in S. aureus-stimulated RAW 264.7 cells.

Inhibition of Na(+)-K(+)-2Cl(-) Cotransporter-1 attenuates traumatic brain injury-induced neuronal apoptosis via regulation of Erk signaling

Traumatic brain injury (TBI) is the leading cause of mortality and morbidity worldwide and is characterized by immediate brain damage and secondary injuries, such as brain edema and ischemia. However, the exact pathological mechanisms that comprise these associated secondary injuries have not been fully elucidated. This study aimed to investigate the role of the Na(+)-K(+)-2Cl(-) cotransporter-1 (NKCC1) in the disruption of ion homeostasis and neuronal apoptosis in TBI. Using a traumatic neuron injury (TNI) model in vitro and a controlled cortex injury (CCI) model in vivo, the present study investigated changes in the expression and effects of NKCC1 in TBI using western blot, RNA interference, a lactate dehydrogenase (LDH) release assay, TdT-mediated dUTP Nick end-labeling (TUNEL) analysis, sodium imaging, brain water content, and neurological severity scoring. TBI induced the expression of NKCC1 to be significantly upregulated in the cortex, both in vitro and in vivo. Pharmacological inhibitor bumetanide (Bume) or NKCC1 RNA interference significantly attenuated TBI-induced intracellular Na(+) increase, inhibited neuronal apoptosis, and improved brain edema and neurological function. Furthermore, NKCC1 inhibition also significantly inhibited TBI-induced extracellular signal-regulated kinase (Erk) activation. Erk inhibition significantly protected neurons from TBI injury; however, Erk inhibition had no effect on NKCC1 expression or the neuroprotective effect of NKCC1 inhibition against TBI. This study demonstrates the role of NKCC1 in TBI-induced brain cortex injury, establishing that NKCC1 may play a neurotoxic role in TBI and that the inhibition of NKCC1 may protect neurons from TBI via the regulation of Erk signaling.

Downregulation of STIM2 improves neuronal survival after traumatic brain injury by alleviating calcium overload and mitochondrial dysfunction

Although store-operated calcium entry (SOCE) has been implicated in several neurological disorders, the exact mechanism for its role in traumatic brain injury (TBI) has not been elucidated. In this study, we found that TBI upregulated the expression of a calcium sensor protein called stromal interactive molecule 2 (STIM2); however, the levels of its homologue, STIM1, were unaffected. Both STIM1 and STIM2 are crucial components of SOCE, both in vivo and in vitro. Using shRNA, we discovered that downregulation of STIM2, but not STIM1, significantly improved neuronal survival in both an in vitro and in vivo model of TBI, decreasing neuronal apoptosis, and preserving neurological function. This neuroprotection was associated with alleviating TBI-induced calcium overload and preserving mitochondrial function. Additionally, downregulation of STIM2 not only inhibited Ca(2+) release from the endoplasmic reticulum (ER), but also reduced SOCE-mediated Ca(2+) influx, decreased mitochondrial Ca(2+), restored mitochondrial morphology and improved mitochondrial function, including MMP maintenance, ROS production and ATP synthesis. These results indicate that inhibition of STIM2 can protect neurons from TBI by inhibiting calcium overload and preserving mitochondrial function. This suggests that STIM2 might be an effective interventional target for TBI.

APOEε4 increases trauma induced early apoptosis via reducing delayed rectifier K(+) currents in neuronal/glial co-cultures model

Traumatic brain injury (TBI) is a commonly encountered emergency and severe neurosurgical injury. Previous studies have shown that the presence of the apolipoprotein E (APOE) ε4 allele has adverse outcomes across the spectrum of TBI severity. Our objective was to evaluate the effects of APOE alleles on trauma induced early apoptosis via modification of delayed rectifier K(+) current (Ik(DR)) in neuronal/glial co-cultures model. An ex vivo neuronal/glial co-cultures model carrying individual APOE alleles (ε2, ε3, ε4) of mechanical injury was developed. Flow cytometry and patch clamp recording were performed to analyze the correlations among APOE genotypes, early apoptosis and Ik(DR). We found that APOEε4 increased early apoptosis at 24h (p<0.05) compared to the ones transfected with APOEε3 and APOEε2. Noticeably, APOEε4 significantly reduced the amplitude of the Ik(DR) at 24h compared to the APOEε3 and APOEε2 (p<0.05) which exacerbate Ca(2+) influx. This indicates a possible effect of APOEε4 on early apoptosis via inhibiting Ik(DR) following injury which may adversely affect the outcome of TBI.

Postsynaptic scaffold protein Homer 1a protects against traumatic brain injury via regulating group I metabotropic glutamate receptors

Traumatic brain injury (TBI) produces excessive glutamate, leading to excitotoxicity via the activation of glutamate receptors. Postsynaptic density scaffold proteins have crucial roles in mediating signal transduction from glutamate receptors to their downstream mediators. Therefore, studies on the mechanisms underlying regulation of excitotoxicity by scaffold proteins can uncover new treatments for TBI. Here, we demonstrated that the postsynaptic scaffold protein Homer 1a was neuroprotective against TBI in vitro and in vivo, and this neuroprotection was associated with its effects on group I metabotropic glutamate receptors (mGluRs). Upon further study, we found that Homer 1a mainly affected neuronal injury induced by mGluR1 activation after TBI and also influenced mGluR5 function when its activity was restored. The ability of Homer 1a to disrupt mGluR-ERK signaling contributed to its ability to regulate the functions of mGluR1 and mGluR5 after traumatic injury. Intracellular Ca(2+) and PKC were two important factors involved in the mediation of mGluR-ERK signaling by Homer 1a. These results define Homer 1a as a novel endogenous neuroprotective agent against TBI.

Mechanical injured neurons stimulate astrocytes to express apolipoprotein E through ERK pathway

To explore the possible cellular source and mechanism of apolipoprotein E (apoE) expression in mechanical injured neuronal cultures. Primary cultured mouse cortical neurons were subjected into mechanical injury by needle scratching. The conditioned medium of wild type (WT) primary mouse astrocytes was collected and added into cultured injured apoE knockout (KO) neurons. Separately, the conditioned medium of injured apoE KO neurons was collected and added into cultured WT astrocytes. We used a specific inhibitor of extracellular signal-regulated kinase (ERK) to block the possible apoE-associated pathway between injured neurons and astrocytes. The apoE expression levels of the cells and secreted into medium were measured by Western blot, respectively. The apoE expression was increased in neurons after mechanically injury, and the injured neurons uptook the astrocyte-secreted apoE, as well. Furthermore, the injured neurons stimulated astrocytes to express more apoE through the ERK signaling pathway. Mechanical injury triggered the neurons to increasingly synthesized apoE and uptook exogenous apoE, while stimulators released from injured neurons elevated astrocytes in apoE expression and secretion.

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.

A new in vitro injury model of mouse neurons induced by mechanical scratching

The mixed culture of neurons and glial cells has been widely used as a mechanical insult model for the study of neuron injury in vitro. However, a better model is desirable to eliminate the interference of glial cells during the study. Here we report a new model with exclusive cerebellar granule neurons (CGNs), which can be used for the study of in vitro neuron injury without involvement of glial cells. We found that after scratching insult, there was a decrease in both the survival rate and vitality of injured CGNs. Meanwhile, pathological changes were observed by electron microscopy. With this new model, we also tested the effects of neurotrophin-3 (NT-3) on neuroprotection. The result showed that the vitality of injured CGNs was enhanced by the administration of NT-3. These findings demonstrate that this new model is useful for investigation of the precise effect of mechanical damage on neurons excluding other factors, and to detect the neuroprotective effect of certain factors on mechanically injured neurons.

Dynamic changes in neural circuit topology following mild mechanical injury in vitro

Despite its enormous incidence, mild traumatic brain injury is not well understood. One aspect that needs more definition is how the mechanical energy during injury affects neural circuit function. Recent developments in cellular imaging probes provide an opportunity to assess the dynamic state of neural networks with single-cell resolution. In this article, we developed imaging methods to assess the state of dissociated cortical networks exposed to mild injury. We estimated the imaging conditions needed to achieve accurate measures of network properties, and applied these methodologies to evaluate if mild mechanical injury to cortical neurons produces graded changes to either spontaneous network activity or altered network topology. We found that modest injury produced a transient increase in calcium activity that dissipated within 1 h after injury. Alternatively, moderate mechanical injury produced immediate disruption in network synchrony, loss in excitatory tone, and increased modular topology. A calcium-activated neutral protease (calpain) was a key intermediary in these changes; blocking calpain activation restored the network nearly completely to its pre-injury state. Together, these findings show a more complex change in neural circuit behavior than previously reported for mild mechanical injury, and highlight at least one important early mechanism responsible for these changes.

Ketamine inhibits tumor necrosis factor secretion by RAW264.7 murine macrophages stimulated with antibiotic-exposed strains of community-associated, methicillin-resistant Staphylococcus aureus

Background

Infections caused by community-associated strains of methicillin-resistant Staphylococcus aureus (CA-MRSA) are associated with a marked and prolonged host inflammatory response. In a sepsis simulation model, we tested whether the anesthetic ketamine inhibits the macrophage TNF response to antibiotic-exposed CA-MRSA bacteria via its antagonism of N-methyl-D-aspartate (NMDA) receptors. RAW264.7 cells were stimulated for 18 hrs with 10⁵ to 10⁷ CFU/mL inocula of either of two prototypical CA-MRSA isolates, USA300 strain LAC and USA400 strain MW2, in the presence of either vancomycin or daptomycin. One hour before bacterial stimulation, ketamine was added with or without MK-801 (dizocilpine, a chemically unrelated non-competitive NMDA receptor antagonist), APV (D-2-amino-5-phosphono-valerate, a competitive NMDA receptor antagonist), NMDA, or combinations of these agents. Supernatants were collected and assayed for TNF concentration by ELISA.

Results

RAW264.7 cells exposed to either LAC or MW2 in the presence of daptomycin secreted less TNF than in the presence of vancomycin. The addition of ketamine inhibited macrophage TNF secretion after stimulation with either of the CA-MRSA isolates (LAC, MW2) in the presence of either antibiotic. The NMDA inhibitors, MK-801 and APV, also suppressed macrophage TNF secretion after stimulation with either of the antibiotic-exposed CA-MRSA isolates, and the effect was not additive or synergistic with ketamine. The addition of NMDA substrate augmented TNF secretion in response to the CA-MRSA bacteria, and the addition of APV suppressed the effect of NMDA in a dose-dependent fashion.

Conclusions

Ketamine inhibits TNF secretion by MRSA-stimulated RAW264.7 macrophages and the mechanism likely involves NMDA receptor antagonism. These findings may have therapeutic significance in MRSA sepsis.

Effects of C3 deficiency on inflammation and regeneration following spinal cord injury in mice

Inflammation can activate the complement system, which in turn enhances inflammation and aggravates secondary injury after spinal cord injury (SCI). As the three complement activation pathways converge at the cleavage of C3, we investigated whether inhibiting complement activation in C3-deficient mice would reduce secondary injury after SCI and improve axon regeneration. Weight-drop contusion injury (5g, 6cm) was created in wild-type or C3-deficient mice. Astrocytes (ASTs) activation, TNF-α expression, and axon regeneration were investigated in vivo. In other studies, dorsal root ganglia (DRGs) were co-cultured with mechanically injured ASTs in vitro to evaluate effects on neurite outgrowth. Our results show that, after injury, C3-deficient mice exhibit higher BBB scores than wild-type mice. In addition, ASTs activation was inhibited, TNF-α expression process was delayed in vivo and inhibited in vitro, and nerve fiber regeneration was improved in C3-deficient mice. DRGs co-cultured with mechanically injured ASTs from C3-deficient mice also showed improved neurite outgrowth. We conclude that C3 deficiency can inhibit inflammation through suppressing ASTs activation and TNF-α expression, thereby reducing secondary injury and improving neural regeneration and functional recovery after SCI. The above results suggest that complement inhibition may be a potential therapy to promote central nervous system regeneration by targeting C3.

Examination of axonal injury and regeneration in micropatterned neuronal culture using pulsed laser microbeam dissection

We describe the integrated use of pulsed laser microbeam irradiation and microfluidic cell culture methods to examine the dynamics of axonal injury and regeneration in vitro. Microfabrication methods are used to place high purity dissociated central nervous system neurons in specific regions that allow the axons to interact with permissive and inhibitory substrates. Acute injury to neuron bundles is produced via the delivery of single 180 ps duration, lambda = 532 nm laser pulses. Laser pulse energies of 400 nJ and 800 nJ produce partial and complete transection of the axons, respectively, resulting in elliptical lesions 25 mum and 50 mum in size. The dynamics of the resulting degeneration and regrowth of proximal and distal axonal segments are examined for up to 8 h using time-lapse microscopy. We find the proximal and distal dieback distances from the site of laser microbeam irradiation to be roughly equal for both partial and complete transection of the axons. In addition, distinct growth cones emerge from the proximal neurite segments within 1-2 h post-injury, followed by a uniform front of regenerating axons that originate from the proximal segment and traverse the injury site within 8 h. We also examine the use of EGTA to chelate the extracellular calcium and potentially reduce the severity of the axonal degeneration following injury. While we find the addition of EGTA to reduce the severity of the initial dieback, it also hampers neurite repair and interferes with the formation of neuronal growth cones to traverse the injury site. This integrated use of laser microbeam dissection within a micropatterned cell culture system to produce precise zones of neuronal injury shows potential for high-throughput screening of agents to promote neuronal regeneration.

In-vitro approaches for studying blast-induced traumatic brain injury

Traumatic brain injury caused by explosive or blast events is currently divided into four phases: primary, secondary, tertiary, and quaternary blast injury. These phases of blast-induced traumatic brain injury (bTBI) are biomechanically distinct, and can be modeled in both in-vivo and in-vitro systems. The purpose of this review is to consider the mechanical phases of bTBI, how these phases are reproduced with in-vitro models, and to review findings from these models to assess how each phase of bTBI can be examined in more detail. Highlighted are some important gaps in the literature that may be addressed in the future to better identify the exact contributing mechanisms for bTBI. These in-vitro models, viewed in combination with in-vivo models and clinical studies, can be used to assess both the mechanisms and possible treatments for this type of trauma.

Combination therapies for traumatic brain injury: prospective considerations

Traumatic brain injury (TBI) initiates a cascade of numerous pathophysiological events that evolve over time.Despite the complexity of TBI, research aimed at therapy development has almost exclusively focused on single therapies, all of which have failed in multicenter clinical trials. Therefore, in February 2008 the National Institute of Neurological Disorders and Stroke, with support from the National Institute of Child Health and Development, the National Heart, Lung, and Blood Institute, and the Department of Veterans Affairs, convened a workshop to discuss the opportunities and challenges of testing combination therapies for TBI. Workshop participants included clinicians and scientists from a variety of disciplines, institutions, and agencies. The objectives of the workshop were to: (1) identify the most promising combinations of therapies for TBI; (2) identify challenges of testing combination therapies in clinical and pre-clinical studies; and (3) propose research methodologies and study designs to overcome these challenges. Several promising combination therapies were discussed, but no one combination was identified as being the most promising. Rather, the general recommendation was to combine agents with complementary targets and effects (e.g., mechanisms and time-points), rather than focusing on a single target with multiple agents. In addition, it was recommended that clinical management guidelines be carefully considered when designing pre-clinical studies for therapeutic development.To overcome the challenges of testing combination therapies it was recommended that statisticians and the U.S. Food and Drug Administration be included in early discussions of experimental design. Furthermore, it was agreed that an efficient and validated screening platform for candidate therapeutics, sensitive and clinically relevant biomarkers and outcome measures, and standardization and data sharing across centers would greatly facilitate the development of successful combination therapies for TBI. Overall there was great enthusiasm for working collaboratively to act on these recommendations.

Targeting cell death in vivo in experimental traumatic brain injury by a novel molecular probe

Traumatic brain injury (TBI) remains a frequent and major challenge in neurological and neurosurgical practice. Apoptosis may play a role in cerebral tissue damage induced by the traumatic insult, and thus its detection and inhibition may advance patient care. DDC (N,N'-didansyl-L-cystine) is a novel fluorescent probe for detection of apoptotic cells. We now report on the performance of DDC in experimental TBI. Closed head injury was induced in mice by weight-drop. DDC was administered intravenously in vivo. Two hours later, animals were sacrificed, and brain tissue was subjected to fluorescent microcopy, for assessment of DDC uptake, in correlation with histopathological assessment of apoptosis by TUNEL and caspase substrates, and also in correlation with the neurological deficits, as assessed by Neurological Severity Score (NSS). Selective uptake of DDC was observed at the primary site of injury, and also at remote sites. Uptake was at the cellular level, with accumulation of DDC in the cytoplasm. Cells manifesting DDC uptake were confirmed as apoptotic cells by detection of the characteristic apoptotic DNA fragmentation (positive TUNEL staining) and detection of activated caspases. The damaged region stained by DDC fluorescence correlated with the severity of neuronal deficits. Our study confirms the role of apoptosis in TBI, and proposes DDC as a useful tool for its selective targeting and detection in vivo. Such imaging of apoptosis, following future radiolabeling of DDC, may advance care for patients with head injury, by allowing real-time evaluation of the extent of tissue damage, assessment of novel therapeutic strategies, and optimization of treatment for the individual patient.

Linking impact to cellular and molecular sequelae of CNS injury: modeling in vivo complexity with in vitro simplicity

Traumatic brain injury (TBI) represents one of most common disorders to the central nervous system (CNS). Despite significant efforts, though, an effective clinical treatment for TBI is not yet available. The complexity of human TBI is modeled with a broad group of experimental models, with each model matching some aspect of the human condition. In the past 15 years, these in vivo models were complemented with a group of in vitro models, with these in vitro models allowing investigators to more precisely identify the mechanism(s) of TBI, the different intracellular events that occur in acute period following injury, and the possible treatment of this injury in vitro. In this paper, we review the available in vitro models to study TBI, discuss their biomechanical basis for human TBI, and review the findings from these in vitro models. Finally, we synthesize the current knowledge and point out possible future directions for this group of models, especially in the effort toward developing new therapies for the traumatically brain injured patient.

Modeling neural injury in organotypic cultures by application of inertia-driven shear strain

In vitro models of traumatic brain injury (TBI) are indispensable to explore the effects of mechanotrauma on neurological injury cascades and injury thresholds. This study characterizes a novel in vitro model of neural shear injury, which for the first time subjects organotypic cultures to inertia-driven shear strain. In this model, organotypic cultures preserved a high level of biological heterogeneity and spatial cytoarchitecture, while inertia-driven shear strain represented a tissue-level insult typical for closed head TBI in vivo. For neural injury simulation, organotypic hippocampal cultures derived from rats were inserted in an inertial loading module, which was subjected to impacts at five graded impact velocities ranging from 2 to 10 m/sec. The mechanical insult was quantified by measuring the transient shear deformation of the culture surface during impact with a high-speed camera. The resultant cell death was quantified with propidium iodide (PI) staining 24 hours following shear injury. Increasing impact velocities of 2, 4.6, 6.6, 8.1, and 10.4 m/sec caused graded peak shear elongation of 2.0 +/- 0.9%, 5.4 +/- 3.8%, 15.1 +/- 14.6%, 25.4 +/- 14.7%, and 56.3 +/- 51.3%, respectively. Cell death in response to impact velocities of 6.6 m/sec or less was not significantly higher than baseline cell death in sham cultures (4.4 +/- 1.5%). Higher impact velocities of 8.1 and 10.4 m/sec resulted in a significant increase in cell death to 19.9 +/- 12.9% and 36.7 +/- 14.2%, respectively (p < 0.001). The neural shear injury model delivered a gradable, defined mechanotrauma and thereby provides a novel tool for investigation of biological injury cascades in organotypic cultures.

Efficient Synthesis of the 3-Benzazepine Framework via Intramolecular Heck Reductive Cyclization

A microwave-assisted protocol based on reductive Heck reaction was developed for regio- and stereoselective construction of the 3-benzazepine core.

Identification of novel neuroprotective agents using pharmacophore modeling

In addition to its endocrine function, for which it was named, thyrotropin-releasing hormone (TRH) has substantial neuroprotective actions as well as other physiological effects. We have developed a number of modified TRH analogues as well as cyclic dipeptides structurally related to a major metabolic product of TRH, which have enhanced neuroprotective activity but none of the other major physiological effects of TRH. The extensive structure-activity data developed with these compounds were used to develop a pharmacophore model. Subsequently, a web-based pharmacophore searching program was used to query several large three-dimensional databases. Of the 219 compounds identified whose structures met the pharmacophore model, 15 were chosen for study in a classical model of neuronal cell death in vitro; five of these, 2-6, showed neuroprotective activity. Thus, pharmacophore modeling developed from neuroprotective small peptides can be used to identify novel lead compounds as neuroprotective agents.

Neuroprotective effects of selective group II mGluR activation in brain trauma and traumatic neuronal injury

The effects of group II mGluR activation by selective agonist (-)-2-oxa-4-aminobicyclo[3.1. 0]hexane-4,6-dicarboxylate (LY379268) were examined in a mouse model of controlled cortical impact (CCI)-induced brain injury and in primary neuronal/glial and neuronal cultures subjected to mechanical trauma. Systemic administration of LY379268 to mice at 30 min after CCI significantly improved both motor and cognitive recovery as compared with vehicle-treated control animals. LY379268 also significantly reduced cell death induced by mechanical injury in rat neuronal/glial and neuronal cultures, as measured by lactate dehydrogenase (LDH) release assay. The neuroprotective effect of LY379268 in vitro was abolished by co-administration of the mGluR2/3 antagonist (s)-alpha-ethylglutamic acid (EGLU); however, co-application of selective mGluR3 antagonist beta-N-acetyl-aspartyl-glutamate (NAAG) had no significant influence in the same system. Together, these findings demonstrate the neuroprotective activity of group II mGluR activation and underscore the role of the mGluR2 subtype for this effect.

The effect of poloxamer-188 on neuronal cell recovery from mechanical injury

Neuronal injury resulting from mechanical deformation is poorly characterized at the cellular level. The immediate structural consequences of the mechanical loading lead to a variety of inter- and intra-cellular signaling events that interact on multiple time and length scales. Thus, it is often difficult to establish cause-and-effect relationships such that appropriate treatment strategies can be devised. In this report, we showed that treating mechanically injured neuronal cells with an agent that promotes the resealing of disrupted plasma membranes rescues them from death at 24 h post-injury. A new in vitro model was developed to allow uniform mechanical loading conditions with precisely controlled magnitude and onset rate of loading. Injury severity increased monotonically with increasing peak shear stress and was strongly dependent on the rate of loading as assessed with the MTT cell viability assay, 24 h post-injury. Mechanical injury produced an immediate disruption of membrane integrity as indicated by a rapid and transient release of LDH. For the most severe injury, cell viability decreased approximately 40% with mechanical trauma compared to sham controls. Treatment of cells with Poloxamer 188 at 15 min post-injury restored long-term viability to control values. These data establish membrane integrity as a novel therapeutic target in the treatment of neuronal injury.

Glutamate receptor subunit expression after spinal cord injury in young rats

To investigate the possibility that glutamate receptor levels in the spinal cord are altered following injury to young rats, we used a previously characterized model of spinal cord contusion that produces a reliable injury in rats at postnatal day 14-15. Quantitative Western blot analysis was used to measure relative amounts of protein for several glutamate receptor subunits acutely (24 h) and chronically (28 days) after spinal cord injury (SCI). Acutely after injury significant decreases were observed in the GluR1, GluR2, and GluR4 subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionate (AMPA) receptor, and the NR2A and NR2B subunits, but not the NR1 subunit, of the N-methyl-d-aspartate (NMDA) receptor. However, 28 days after injury only one subunit (GluR4) was shown to be altered. These widespread changes that occur acutely in receptor subunit expression may be an attempt to protect cells from glutamate-induced death. The injured spinal cord in these young animals, however, appears to have the capacity to regulate receptor subunit levels to normal within a month of injury.

The "dark side" of endocannabinoids: a neurotoxic role for anandamide

Endocannabinoids, including 2-arachidonoylglycerol and anandamide (N-arachidonoylethanolamine; AEA), have neuroprotective effects in the brain through actions at CB1 receptors. However, AEA also binds to vanilloid (VR1) receptors and induces cell death in several cell lines. Here we show that anandamide causes neuronal cell death in vitro and exacerbates cell loss caused by stretch-induced axonal injury or trophic withdrawal in rat primary neuronal cultures. Administered intracerebroventricularly, AEA causes sustained cerebral edema, as reflected by diffusion-weighted magnetic resonance imaging, regional cell loss, and impairment in long-term cognitive function. These effects are mediated, in part, through VR1 as well as through calpain-dependent mechanisms, but not through CB1 receptors or caspases. Central administration of AEA also significantly upregulates genes involved in pro-inflammatory/microglial-related responses. Thus, anandamide produces neurotoxic effects both in vitro and in vivo through multiple mechanisms independent of the CB1 receptor.

Noncompetitive metabotropic glutamate5 receptor antagonist (E)-2-methyl-6-styryl-pyridine (SIB1893) depresses glutamate release through inhibition of voltage-dependent Ca2+ entry in rat cerebrocortical nerve terminals (synaptosomes)

The effect of (E)-2-methyl-6-styryl-pyridine (SIB1893), a selective metabotropic glutamate (subtype 5) receptor (mGlu(5)R) antagonist, on glutamate release from isolated nerve terminals (synaptosomes) was examined. SIB1893 caused a potent inhibition of the Ca(2+)-dependent release of glutamate evoked by 4-aminopyridine (4AP). That the implied mGlu(5)R-mediated modulation was contingent on diacylglycerol stimulation of protein kinase C (PKC) was indicated by PKC activator phorbol dibutyrate and PKC inhibitor Ro 32-0432 (bisindolylmaleimide XI), respectively, superceding or suppressing the inhibitory effect of SIB1893. The inhibitory action of SIB1893 was not due to it decreasing synaptosomal excitability or directly interfering with the release process at some point subsequent to Ca(2+) influx, because SIB1893 did not alter the 4AP-evoked depolarization of the synaptosomal plasma membrane potential or Ca(2+) ionophore ionomycin-induced glutamate release. Rather, examination of the effect of SIB1893 on cytosolic [Ca(2+)] revealed that the diminution of glutamate release could be attributed to a reduction in voltage-dependent Ca(2+) influx. Consistent with this, the SIB1893-mediated inhibition of glutamate release was completely prevented in synaptosomes pretreated with a combination of the N- and P/Q-type Ca(2+) channel blockers, omega-conotoxin GVIA, and omega-agatoxin IVA. Together, these results suggest that noncompetitive antagonism of mGlu(5)Rs using SIB1893 effects a decrease in PKC activation, which subsequently attenuates the Ca(2+) entry through voltage-dependent N- and P/Q-type Ca(2+) channels to cause a decrease in evoked glutamate release. These actions of SIB1893 and related agents may contribute to their neuroprotective effects in excitotoxic injury.

Susceptibility of hippocampal neurons to mechanically induced injury

Experimental models of traumatic cortical brain injury in rodents reveal that specific regions of the hippocampus (e.g., CA3 and hilar subfields) are severely injured despite their distance from the initial insult. Hippocampal neurons may be intrinsically more vulnerable to mechanical insult than cortical neurons due to increased NMDA receptor densities and lower energy capacities, as evidenced by increased susceptibility to ischemic insults. The selective vulnerability of hippocampal neurons was evaluated using an in vitro model of TBI in which either primary rat cortical or hippocampal neurons (E17) seeded onto silicone substrates were subjected to graded levels of mechanical stretch. Although cortical neurons exhibited significantly longer increases in stretch-induced membrane permeability, injury of hippocampal neurons resulted in larger increases in intracellular free calcium concentration [Ca(2+)](i) and cell death. [ATP](i) deficits due to stretch were apparent by 60 min after injury in cortical neurons but recovered by 24 h, whereas significant deficits in [ATP](i) were not observed in hippocampal neurons until 24 h after injury. MK801 pretreatment decreased the stretch-induced [Ca(2+)](i) transients in both hippocampal and cortical cultures, thereby negating the regional specificity. However, MK801 pretreatment did not improve hippocampal viability and paradoxically, significantly increased cell death among cortical neurons. As the hippocampus is the primary brain region responsible for the memory deficits and epileptic seizures associated with TBI, understanding why this region is selectively damaged could lead to the development of more accurate mechanical tolerances as well as effective pharmaceutical agents.

Ceramide-induced neuronal apoptosis is associated with dephosphorylation of Akt, BAD, FKHR, GSK-3beta, and induction of the mitochondrial-dependent intrinsic caspase pathway

Neuronal apoptosis has been implicated as an important mechanism of cell death in acute and chronic neurodegenerative disorders. Ceramide is a product of sphingolipid metabolism which induces neuronal apoptosis in culture, and ceramide levels increase in neurons during various conditions associated with cell death. In this study we investigate the mechanism of ceramide-induced apoptosis in primary cortical neuronal cells. We show that ceramide treatment initiates a cascade of biochemical alterations associated with cell death: earliest signal transduction changes involve Akt dephosphorylation and inactivation followed by dephosphorylation of proapoptotic regulators such as BAD (proapoptotic Bcl-2 family member), Forkhead family transcription factors, glycogen synthase kinase 3-beta, mitochondrial depolarization and permeabilization, release of cytochrome c into the cytosol, and caspase-3 activation. Bongkrekic acid, an agent that inhibits mitochondrial depolarization, significantly reduces ceramide-induced cell death and correlated caspase-3 activation. Together, these data demonstrate the importance of the mitochondrial-dependent intrinsic pathway of caspase activation for ceramide-induced neuronal apoptosis.