Effects of Injury Severity on Regional and Temporal mRNA Expression Levels of Calpains and Caspases after Traumatic Brain Injury in Rats

Spatial Measurement and Inhibition of Calpain Activity in Traumatic Brain Injury with an Activity-Based Nanotheranostic Platform

Traumatic brain injury (TBI) is a major public health concern that can result in long-term neurological impairments. Calpain is a calcium-dependent cysteine protease that is activated within minutes after TBI, and sustained calpain activation is known to contribute to neurodegeneration and blood-brain barrier dysregulation. Based on its role in disease progression, calpain inhibition has been identified as a promising therapeutic target. Efforts to develop therapeutics for calpain inhibition would benefit from the ability to measure calpain activity with spatial precision within the injured tissue. In this work, we designed an activity-based nanotheranostic (ABNT) that can both sense and inhibit calpain activity in TBI. To sense calpain activity, we incorporated a peptide substrate of calpain flanked by a fluorophore/quencher pair. To inhibit calpain activity, we incorporated calpastatin peptide, an endogenous inhibitor of calpain. Both sensor and inhibitor peptides were scaffolded onto a polymeric nanoscaffold to create our ABNT. We show that in the presence of recombinant calpain, our ABNT construct is able to sense and inhibit calpain activity. In a mouse model of TBI, systemically administered ABNT can access perilesional brain tissue through passive accumulation and inhibit calpain activity in the cortex and hippocampus. In an analysis of cellular calpain activity, we observe the ABNT-mediated inhibition of calpain activity in neurons, endothelial cells, and microglia of the cortex. In a comparison of neuronal calpain activity by brain structure, we observe greater ABNT-mediated inhibition of calpain activity in cortical neurons compared to that in hippocampal neurons. Furthermore, we found that apoptosis was dependent on both calpain inhibition and brain structure. We present a theranostic platform that can be used to understand the regional and cell-specific therapeutic inhibition of calpain activity to help inform drug design for TBI.

The role of spectrin breakdown products in patients with traumatic brain injury: a systematic review and meta-analysis

BACKGROUND

Spectrin Breakdown Products (SBDPs) accumulate in the brain after traumatic brain injury (TBI) and are expected to become a potentially promising biomarker of TBI.

OBJECTIVE

This systematic review and meta-analysis were undertaken to evaluate the role of SBDPs in the diagnosis and prognosis of TBI.

METHODS

We systematically searched the following databases up to 31 October 2022: Ovid MEDLINE, PubMed, EMBASE, Cochrane Library, and Web of Science Database, and studies were only included if they had sufficient data on SBDP concentrations in TBI patients. We calculated the standardized mean differences (SMDs) and 95% confidence intervals (CIs) for continuous outcomes and assessed the potential publication bias by using Egger's test and funnel plots. The statistical analysis was conducted by RevMan 5.4 and Stata 17.

RESULTS

Of 1429 identified studies, 10 studies involving 417 participants were included in our systematic review and meta-analysis. The results demonstrated that serum and cerebrospinal fluid (CSF) SBDP concentrations were significantly increased in TBI compared to controls (SBDP120: SMD = 1.42, 95% CI = 0.71 ~ 2.12, P < 0.00001; SBDP145: SMD = 1.32, 95% CI = 0.78 ~ 1.86, P < 0.00001; SBDP150: SMD = 1.39, 95% CI = 0.97 ~ 1.80, P < 0.00001), and CSF SBDPs were significantly associated with poor functional outcomes (PFO) (SBDP145: SMD = 1.75, 95% CI = 1.37 ~ 2.13, P < 0.00001; SBDP150: SMD = 1.14, 95% CI = 0.75 ~ 1.52, P < 0.00001). In addition, CSF and serum SBDP145 are valuable in diagnosing TBI (AUC = 0.89, 95% CI = 0.80 ~ 0.99, P < 0.00001), and CSF SBDP145 also has diagnostic value for PFO (AUC = 0.80, 95% CI = 0.76 ~ 0.84, P < 0.00001).

CONCLUSIONS

The limited evidence supports that the SBDPs can be employed as potential biomarkers for the diagnosis and prognosis of TBI.

An Activity-Based Nanosensor for Traumatic Brain Injury

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

Protective Functions of PJ34, a Poly(ADP-ribose) Polymerase Inhibitor, Are Related to Down-Regulation of Calpain and Nuclear Factor-κB in a Mouse Model of Traumatic Brain Injury

OBJECTIVES

Poly(ADP-ribose) polymerase (PARP), calpain, and nuclear factor-κB (NF-κB) are reported to participate in inflammatory reactions in pathologic conditions and are involved in traumatic brain injury. The objective of this study was to investigate whether PARP participates in inflammation related to calpain and NF-κB in a mouse model of controlled cortical impact (CCI).

METHODS

PJ34 (10 mg/kg), a selective PARP inhibitor, was administered intraperitoneally 5 minutes and 8 hours after experimental CCI. We then performed a histopathologic analysis, and we measured calpain activity and protein levels in all animals. The cytosolic, mitochondria, and nuclear fractions were prepared and used to determine the levels of PARP, calpastatin, NF-κB p65, inhibitory-κB-α, tumor necrosis factor-α, interleukin-1β, intracellular adhesion molecule-1, inducible nitric oxide synthase, and cyclooxygenase-2. We then measured blood-brain barrier disruption using electron microscopy at 6 and 24 hours after CCI.

RESULTS

Treatment with PJ34 markedly reduced the extent of both cerebral contusion and edema, improved neurologic scores, and attenuated blood-brain barrier damage resulting from CCI. Our data showed that the cytosolic and nuclear fractions of calpain and NF-κB were up-regulated in the injured cortex and that these changes were reversed by PJ34. Moreover, PJ34 significantly enhanced the calpastatin and inhibitory-κB levels and decreased the levels of inflammatory mediators.

CONCLUSIONS

PARP inhibition by PJ34 suppresses the overactivation of calpain and the production of inflammatory factors that are caused by NF-κB activation and attenuates neuronal cell death in a mouse model of CCI.

Protective Effects of Calpain Inhibition on Neurovascular Unit Injury through Downregulating Nuclear Factor-κB-related Inflammation during Traumatic Brain Injury in Mice

Background:

In addition to neurons, all components of the neurovascular unit (NVU), such as glial, endothelial, and basal membranes, are destroyed during traumatic brain injury (TBI). Previous studies have shown that excessive stimulation of calpain is crucial for cerebral injury after traumatic insult. The objective of this study was to investigate whether calpain activation participated in NVU disruption and edema formation in a mouse model of controlled cortical impact (CCI).

Methods:

One hundred and eight mice were divided into three groups: the sham group, the control group, and the MDL28170 group. MDL28170 (20 mg/kg), an efficient calpain inhibitor, was administered intraperitoneally at 5 min, 3 h, and 6 h after experimental CCI. We then measured neurobehavioral deficits, calpain activity, inflammatory mediator levels, blood–brain barrier (BBB) disruption, and NVU deficits using electron microscopy and histopathological analysis at 6 h and 24 h after CCI.

Results:

The MDL28170 treatment significantly reduced the extent of both cerebral contusion (MDL28170 vs. vehicle group, 16.90 ± 1.01 mm³ and 17.20 ± 1.17 mm³ vs. 9.30 ± 1.05 mm³ and 9.90 ± 1.17 mm³, both P < 0.001) and edema (MDL28170 vs. vehicle group, 80.76 ± 1.25% and 82.00 ± 1.84% vs. 82.55 ± 1.32% and 83.64 ± 1.25%, both P < 0.05), improved neurological scores (MDL28170 vs. vehicle group, 7.50 ± 0.45 and 6.33 ± 0.38 vs. 12.33 ± 0.48 and 11.67 ± 0.48, both P < 0.001), and attenuated NVU damage resulting (including tight junction (TJ), basement membrane, BBB, and neuron) from CCI at 6 h and 24 h. Moreover, MDL28170 markedly downregulated nuclear factor-κB-related inflammation (tumor necrosis factor-α [TNF-α]: MDL28170 vs. vehicle group, 1.15 ± 0.07 and 1.62 ± 0.08 vs. 1.59 ± 0.10 and 2.18 ± 0.10, both P < 0.001; inducible nitric oxide synthase: MDL28170 vs. vehicle group, 4.51 ± 0.23 vs. 6.23 ± 0.12, P < 0.001 at 24 h; intracellular adhesion molecule-1: MDL28170 vs. vehicle group, 1.45 ± 0.13 vs. 1.70 ± 0.12, P < 0.01 at 24 h) and lessened both myeloperoxidase activity (MDL28170 vs. vehicle group, 0.016 ± 0.001 and 0.016 ± 0.001 vs. 0.024 ± 0.001 and 0.023 ± 0.001, P < 0.001 and 0.01, respectively) and matrix metalloproteinase-9 (MMP-9) levels (MDL28170 vs. vehicle group, 0.87 ± 0.13 and 1.10 ± 0.10 vs. 1.17 ± 0.13 and 1.25 ± 0.12, P < 0.001 and 0.05, respectively) at 6 h and 24 h after CCI.

Conclusions:

These findings demonstrate that MDL28170 can protect the structure of the NVU by inhibiting the inflammatory cascade, reducing the expression of MMP-9, and supporting the integrity of TJ during acute TBI.

Role of α-II-spectrin breakdown products in the prediction of the severity and clinical outcome of acute traumatic brain injury

αII-spectrin breakdown products are regarded as potential biomarkers for traumatic brain injury (TBI). The aim of the present study was to further evaluate these biomarkers by assessing their clinical utility in predicting the severity of injury and clinical outcome of patients with TBI. Eligible patients with acute TBI (n=17), defined by a Glasgow Coma Scale (GCS) score of ≤8, were enrolled. Ventricular cerebrospinal fluid (CSF) was sampled from each patient at 24, 72 and 120 h following TBI. An immunoblot assay was used to determine the concentrations of SBDPs in the CSF samples. The concentrations of SBDPs combined with the GCS score at 24 h after injury and the Glasgow Outcome Score (GOS) at 30 days after injury were compared and analyzed. The levels of SBDPs in CSF were markedly increased following acute TBI in comparison with those in the control group. In the early period after TBI, the levels of SBDPs were closely associated with GCS score. Comparisons of the SBDP levels with the severity of injury revealed significant differences between patients with the most severe brain injury and patients with severe brain injury in the first 24 h post-injury (P<0.05). The levels and dynamic changes of SBDPs in CSF exhibited a close association with GOS at 30 days after injury. The levels of SBDPs differed significantly between patients grouped according to prognosis (P<0.05). These results suggest that in the early period after TBI, the levels and dynamic changes of SBDPs in CSF can be useful in the prediction of the severity of injury and clinical outcome of patients.

Protective effects of PARP inhibitor, PJ34, is related to down-regulation of calpain and NF-κB in a mouse model of TBI

BACKGROUND

Poly(ADP-ribose) polymerase (PARP), calpain and nuclear factor-κB (NF-κB) are reported to participate in inflammatory reactions in pathological conditions and are involved in traumatic brain injury. The objective of this study was to investigate whether PARP participated in inflammation related to calpain and NF-κB in a mouse model of controlled cortical impact (CCI).

MATERIALS AND METHODS

PJ34 (10 mg kg-1), a selective PARP inhibitor, was administered intraperitoneally 5 minutes and 8 hours after experimental CCI. A neurobehavioural evaluation and a histopathological analysis were then performed and the contusion volume, calpain activity and protein levels were measured in all animals.

RESULTS

Treatment with PJ34 markedly reduced neurological deficits, decreased contusion volume and attenuated necrotic and apoptotic neuronal cell death 24 hours after CCI. The data showed that the cytosolic and nuclear fractions of calpain and NF-κB were up-regulated in the injured cortex and that these changes were reversed by PJ34. Moreover, PJ34 significantly enhanced the calpastatin and IκB levels and decreased the levels of inflammatory mediators.

CONCLUSIONS

PARP inhibition by PJ34 suppresses the over-activation of calpain and the production of inflammatory factors that are caused by NF-κB activation and it improves neurological functioning, decreases the contusion volume and attenuates neuronal cell death in a mouse model of CCI.

Role of Microvascular Disruption in Brain Damage from Traumatic Brain Injury

Traumatic brain injury (TBI) is acquired from an external force, which can inflict devastating effects to the brain vasculature and neighboring neuronal cells. Disruption of vasculature is a primary effect that can lead to a host of secondary injury cascades. The primary effects of TBI are rapidly occurring while secondary effects can be activated at later time points and may be more amenable to targeting. Primary effects of TBI include diffuse axonal shearing, changes in blood-brain barrier (BBB) permeability, and brain contusions. These mechanical events, especially changes to the BBB, can induce calcium perturbations within brain cells producing secondary effects, which include cellular stress, inflammation, and apoptosis. These secondary effects can be potentially targeted to preserve the tissue surviving the initial impact of TBI. In the past, TBI research had focused on neurons without any regard for glial cells and the cerebrovasculature. Now a greater emphasis is being placed on the vasculature and the neurovascular unit following TBI. A paradigm shift in the importance of the vascular response to injury has opened new avenues of drug-treatment strategies for TBI. However, a connection between the vascular response to TBI and the development of chronic disease has yet to be elucidated. Long-term cognitive deficits are common amongst those sustaining severe or multiple mild TBIs. Understanding the mechanisms of cellular responses following TBI is important to prevent the development of neuropsychiatric symptoms. With appropriate intervention following TBI, the vascular network can perhaps be maintained and the cellular repair process possibly improved to aid in the recovery of cellular homeostasis.

Calpastatin overexpression limits calpain-mediated proteolysis and behavioral deficits following traumatic brain injury

Traumatic brain injury (TBI) results in abrupt, initial cell damage leading to delayed neuronal death. The calcium-activated proteases, calpains, are known to contribute to this secondary neurodegenerative cascade. Although the specific inhibitor of calpains, calpastatin, is present within neurons, normal levels of calpastatin are unable to fully prevent the damaging proteolytic activity of calpains after injury. In this study, increased calpastatin expression was achieved using transgenic mice that overexpress the human calpastatin (hCAST) construct under control of a calcium-calmodulin-dependent kinase II α promoter. Naïve hCAST transgenic mice exhibited enhanced neuronal calpastatin expression and significantly reduced protease activity. Acute calpain-mediated spectrin proteolysis in the cortex and hippocampus induced by controlled cortical impact brain injury was significantly attenuated in calpastatin overexpressing mice. Aspects of posttraumatic motor and cognitive behavioral deficits were also lessened in hCAST transgenic mice compared to their wildtype littermates. However, volumetric analyses of neocortical contusion revealed no histological neuroprotection at either acute or long-term time points. Partial hippocampal neuroprotection observed at a moderate injury severity was lost after severe TBI. This study underscores the effectiveness of calpastatin overexpression in reducing calpain-mediated proteolysis and behavioral impairment after TBI, supporting the therapeutic potential for calpain inhibition. In addition, the reduction in spectrin proteolysis without accompanied neocortical neuroprotection suggests the involvement of other factors that are critical for neuronal survival after contusion brain injury.

Calpain as a therapeutic target in traumatic brain injury

The family of calcium-activated neutral proteases, calpains, appears to play a key role in neuropathologic events following traumatic brain injury (TBI). Neuronal calpain activation has been observed within minutes to hours after either contusive or diffuse brain trauma in animals, suggesting that calpains are an early mediator of neuronal damage. Whereas transient calpain activation triggers numerous cell signaling and remodeling events involved in normal physiological processes, the sustained calpain activation produced by trauma is associated with neuron death and axonal degeneration in multiple models of TBI. Nonetheless, the causal relationship between calpain activation and neuronal death is not fully understood. Much remains to be learned regarding the endogenous regulatory mechanisms for controlling calpain activity, the roles of different calpain isoforms, and the in vivo substrates affected by calpain. Detection of stable proteolytic fragments of the submembrane cytoskeletal protein alphaII-spectrin specific for cleavage by calpains has been the most widely used marker of calpain activation in models of TBI. More recently, these protein fragments have been detected in the cerebrospinal fluid after TBI, driving interest in their potential utility as TBI-associated biomarkers. Post-traumatic inhibition of calpains, either direct or indirect through targets related to intracellular calcium regulation, is associated with attenuation of functional and behavioral deficits, axonal pathology, and cell death in animal models of TBI. This review focuses on the current state of knowledge of the role of calpains in TBI-induced neuropathology and effectiveness of calpain as a therapeutic target in the acute post-traumatic period.

Cell death mechanisms and modulation in traumatic brain injury

Cell death after traumatic brain injury (TBI) is a major cause of neurological deficits and mortality. Understanding the mechanisms of delayed post-traumatic cell loss may lead to new therapies that improve outcome. Although TBI induces changes in multiple cell types, mechanisms of neuronal cell death have been the predominant focus. Recent work has emphasized the diversity of neuronal death phenotypes, which have generally been defined by either morphological or molecular changes. This diversity has led to confusing and at times contradictory nomenclature. Here we review the historical basis of proposed definitions of neuronal cell death, with the goal of clarifying critical research questions and implications for therapy in TBI. We believe that both morphological and molecular features must be used to clarify post-traumatic cell death and related therapeutic targets. Further, we underscore that the most effective neuroprotective strategies will need to target multiple pathways to reflect the regional and temporal changes underlying diverse neuronal cell death phenotypes.

Differences in cell death between high and low energy brain injury in adult rats

BACKGROUND

Traumatic brain damage is dependent on energy transfer to the brain at impact. Different injury mechanisms may cause different types of brain injury. It is, however, unknown if the relative distribution between apoptotic cell-death and necrotic cell- death in different populations of brain cells varies depending on energy transfer.

METHOD

Experimental contusions were produced with a modified weight drop onto the exposed dura of rats. Animals were divided into two groups. They received a weight drop from two different heights to vary energy transfer to be higher or lower. Animals were sacrificed at 24 hours post injury (1 DPI) or 6 days (6 DPI); brains were frozen and processed for TUNEL (TdT mediated dUTP nick end labelling), light microscopy and immunochemistry.

FINDINGS

The total number of TUNEL positive cells was higher in the higher energy group on the first day after the injury. At the same time point, relatively fewer cells were apoptotic than necrotic, while relatively more glial cells than neurons were TUNEL-positive in higher energy trauma. At 6 day after the injury fewer cells were TUNEL positive and there were no longer significant differences between the high and low energy groups.

CONCLUSIONS

Increasing energy transfer in a model for brain contusion demonstrated qualitative and quantitative changes in the pattern of cell death. This complexity must be considered when evaluating brain-protection as treatment results may vary depending on which cellular population and which mechanism of cell death is treated under the exact experimental and clinical conditions.

Housekeeping while brain's storming Validation of normalizing factors for gene expression studies in a murine model of traumatic brain injury

BACKGROUND

Traumatic brain injury models are widely studied, especially through gene expression, either to further understand implied biological mechanisms or to assess the efficiency of potential therapies. A large number of biological pathways are affected in brain trauma models, whose elucidation might greatly benefit from transcriptomic studies. However the suitability of reference genes needed for quantitative RT-PCR experiments is missing for these models.

RESULTS

We have compared five potential reference genes as well as total cDNA level monitored using Oligreen reagent in order to determine the best normalizing factors for quantitative RT-PCR expression studies in the early phase (0-48 h post-trauma (PT)) of a murine model of diffuse brain injury. The levels of 18S rRNA, and of transcripts of beta-actin, glyceraldehyde-3P-dehydrogenase (GAPDH), beta-microtubulin and S100beta were determined in the injured brain region of traumatized mice sacrificed at 30 min, 3 h, 6 h, 12 h, 24 h and 48 h post-trauma. The stability of the reference genes candidates and of total cDNA was evaluated by three different methods, leading to the following rankings as normalization factors, from the most suitable to the less: by using geNorm VBA applet, we obtained the following sequence: cDNA(Oligreen); GAPDH > 18S rRNA > S100beta > beta-microtubulin > beta-actin; by using NormFinder Excel Spreadsheet, we obtained the following sequence: GAPDH > cDNA(Oligreen) > S100beta > 18S rRNA > beta-actin > beta-microtubulin; by using a Confidence-Interval calculation, we obtained the following sequence: cDNA(Oligreen) > 18S rRNA; GAPDH > S100beta > beta-microtubulin > beta-actin.

CONCLUSION

This work suggests that Oligreen cDNA measurements, 18S rRNA and GAPDH or a combination of them may be used to efficiently normalize qRT-PCR gene expression in mouse brain trauma injury, and that beta-actin and beta-microtubulin should be avoided. The potential of total cDNA as measured by Oligreen as a first-intention normalizing factor with a broad field of applications is highlighted. Pros and cons of the three methods of normalization factors selection are discussed. A generic time- and cost-effective procedure for normalization factor validation is proposed.

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.

Neuroprotection targets after traumatic brain injury

PURPOSE OF REVIEW

The scarcity of pharmacological neuroprotective treatments for traumatic brain injury is a concern being targeted on various fronts. This review examines the latest treatments under investigation.

RECENT FINDINGS

In the last 12-18 months, no drug has completed phase III clinical trials as a clearly proven method to treat traumatic brain injury. While the drugs work in rodents, when they make it to clinical trial they have failed primarily due to negative side-effects. Those still in trial show promise, and even those rejected have undergone modifications and now show potential, e.g. second-generation N-methyl-D-aspartic acid and alpha-amino-3-hydroxy-methyl-4-isoxazolyl-propionic acid receptor antagonists, calpain inhibitors, and cyclosporine A analogues. Also, several drugs not previously given much attention, such as the antibiotic minocycline, estrogen and progesterone, and a drug already approved for other diseases, erythropoietin, are being examined. Finally, a treatment generating some controversy, but showing potential, is the application of hypothermia to the patients.

SUMMARY

Clearly, finding treatments for traumatic brain injury is not going to be easy and is evidently going to require numerous trials. The good news is that we are closer to finding one or more methods for treating traumatic brain injury patients.

Extensive degradation of myelin basic protein isoforms by calpain following traumatic brain injury

Axonal injury is one of the key features of traumatic brain injury (TBI), yet little is known about the integrity of the myelin sheath. We report that the 21.5 and 18.5-kDa myelin basic protein (MBP) isoforms degrade into N-terminal fragments (of 10 and 8 kDa) in the ipsilateral hippocampus and cortex between 2 h and 3 days after controlled cortical impact (in a rat model of TBI), but exhibit no degradation contralaterally. Using N-terminal microsequencing and mass spectrometry, we identified a novel in vivo MBP cleavage site between Phe114 and Lys115. A MBP C-terminal fragment-specific antibody was then raised and shown to specifically detect MBP fragments in affected brain regions following TBI. In vitro naive brain lysate and purified MBP digestion showed that MBP is sensitive to calpain, producing the characteristic MBP fragments observed in TBI. We hypothesize that TBI-mediated axonal injury causes secondary structural damage to the adjacent myelin membrane, instigating MBP degradation. This could initiate myelin sheath instability and demyelination, which might further promote axonal vulnerability.

Relative effects of mannitol and hypertonic saline on calpain activity, apoptosis and polymorphonuclear infiltration in traumatic focal brain injury

The purpose of this study was to compare the relative effects of mannitol and hypertonic saline (HTS) on calpain activity, apoptosis and neuroinflammatory response induced by experimental cortical contusion. Four groups of 5 Sprague-Dawley male rats were submitted to focal brain injury produced by exposing the parietal cortex to dynamic cortical deformation. Groups were defined by rescucitation fluids administered 30 min post-injury as follows: group 1-0.9% normal saline 2 ml/kg; group 2-mannitol 20% 0.5 g/kg; group 3-HTS 2 ml/kg; group 4-HTS 4 ml/kg. At 72 h, animals were sacrificed. Paraffin-mounted sections of were stained for mu-Calpain, TUNEL, active caspase 3 and myeloperoxidase. There was no difference in the lesion size between the different groups. In contrast, there was a significant reduction in calpain and apoptosis activity and in the neuroinflammatory response in animals receiving HTS. Although mannitol proved to significantly decrease the neuroinflammatory response and calpain activity, it did not affect apoptosis, and its effect was significantly less than that of HTS. Importantly, the effect of HTS was mostly independent from the infused volume. Our results show that HTS promotes cell survival and reduces secondary brain damage following TBI. This protective effect was evidenced at rather small infused volumes, proved to encompass several cellular and molecular mechanisms involved in secondary cell death and could not be related to relief of intracranial pressure. These findings suggest that the high osmolality of HTS may have protective effects besides its impact on brain edema.

Unfolded Protein Response after Neurotrauma

The endoplasmic reticulum (ER) lumen, which actively monitors the synthesis, folding, and modification of newly synthesized transmembrane and secretory proteins as well as lipids, is quite sensitive to homeostatic perturbations. The biochemical, molecular, and physiological events that elevate cellular ER stress levels and disrupt Ca2+ homeostasis trigger secondary reactions. These reactions are factors in the ongoing neurological pathology contributing to the continual tissue loss. However, the cells are not without defensive systems. One of the reactive mechanisms, the unfolded protein response (UPR), when evoked, provides some measure of protection, unless the stress conditions become prolonged or overwhelming. UPR activation occurs when key ER membrane-bound sensor proteins detect the excess accumulation of misfolded or unfolded proteins within the ER lumen. The activation of these sensors leads to a general protein translation shut-down, transcriptional induction, and translation of select proteins to deal with the difficult and miscreant protein or to encourage their degradation so they will do no harm. If the stress is prolonged, caspase-12, along with other apoptotic proteins, are activated, triggering programmed cell death. UPR, once considered to be a rather simple response, can now be characterized as a multifaceted labyrinth of reactions that continues expanding as research intensifies. This review will examine what has been learned to date about how this highly efficient and specific signaling pathway copes with ER stress, by centering on the basic components, their roles, and the complex interactions engendered. Finally, the UPR impact in various central nervous system injuries is summarized.

Caspase-mediated cell death predominates following engraftment of neural progenitor cells into traumatically injured rat brain

Neural progenitor cells (NPCs) have been shown to be a promising therapy for cell replacement and gene transfer in neurological diseases including traumatic brain injury (TBI). However, NPCs often survive poorly after transplantation despite immunosuppression, and the mechanisms of graft cell death are unknown. In this study, we evaluated caspase- and calpain-mediated mechanisms of cell death of neonatal mouse C17.2 progenitor cells, transplanted at 24 h following lateral fluid percussion brain injury (FP) in rats. Adult Male Sprague-Dawley rats (n = 30) were subjected to lateral FP injury (n = 18) or sham surgery (n = 12). C17.2 cells labeled with green fluorescent dye (CMFDA) were engrafted in the perilesional deep cortex, and animals were sacrificed at 24 h, 72 h and 1 week post-transplantation. Pro-apoptotic caspase-mediated cleavage products (Ab246) and calpain-mediated cleavage products (Ab38) were detected in the engrafted cells using immunohistochemistry. Only 2 to 4.5% of grafted NPCs were found to survive at 24 h post-transplantation, regardless of injury status of the host brain, although brain-injured animals had significantly fewer graft cells than sham-injured animals. Limited caspase and calpain-mediated graft cell death was observed in both sham- and brain-injured animals, and caspase-mediated graft cell death was significantly greater than calpain-mediated graft cell death in all animals. Brain-injured animals had significantly increased caspase-mediated graft cell death compared to sham-injured animals. These results suggest that both the caspase and calpain family of proteases are involved in graft cell death, and that caspase-mediated apoptotic graft cell death predominates in the acute post-traumatic period following TBI.

Spatial and temporal characteristics of neurodegeneration after controlled cortical impact in mice: more than a focal brain injury

The present study examined the neuropathology of the lateral controlled cortical impact (CCI) traumatic brain injury (TBI) model in mice utilizing the de Olmos silver staining method that selectively identifies degenerating neurons and their processes. The time course of ipsilateral and contralateral neurodegeneration was assessed at 6, 24, 48, 72, and 168 h after a severe (1.0 mm, 3.5 M/sec) injury in young adult CF-1 mice. At 6 hrs, neurodegeneration was apparent in all layers of the ipsilateral cortex at the epicenter of the injury. A low level of degeneration was also detected within the outer molecular layer of the underlying hippocampal dentate gyrus and to the mossy fiber projections in the CA3 pyramidal subregions. A time-dependent increase in cortical and hippocampal neurodegeneration was observed between 6 and 72 hrs post-injury. At 24 h, neurodegeneration was apparent in the CA1 and CA3 pyramidal and dentate gyral granule neurons and in the dorsolateral portions of the thalamus. Image analysis disclosed that the overall volume of ipsilateral silver staining was maximal at 48 h. In the case of the hippocampus, staining was generalized at 48 and 72 h, indicative of damage to all of the major afferent pathways: perforant path, mossy fibers and Schaffer collaterals as well as the efferent CA1 pyramidal axons. The hippocampal neurodegeneration was preceded by a significant increase in the levels of calpain-mediated breakdown products of the cytoskeletal protein alpha-spectrin that began at 6 h, and persisted out to 72 h post-injury. Damage to the corpus callosal fibers was observed as early as 24 h. An anterior to posterior examination of neurodegeneration showed that the cortical damage included the visual cortex. At 168 h (7 days), neurodegeneration in the ipsilateral cortex and hippocampus had largely abated except for ongoing staining in the cortical areas surrounding the contusion lesion and in hippocampal mossy fiber projections. Callosal and thalamic neurodegeneration was also very intense. This more complete neuropathological examination of the CCI model shows that the associated damage is much more widespread than previously appreciated. The extent of ipsilateral and contralateral neurodegeneration provides a more complete anatomical correlate for the cognitive and motor dysfunction seen in this paradigm and suggests that visual disturbances are also likely to be involved in the post-CCI neurological deficits.

A novel marker for traumatic brain injury: CSF alphaII-spectrin breakdown product levels

Currently, there is no definitive diagnostic test for traumatic brain injury (TBI) to help physicians determine the seriousness of injury or the extent of cellular pathology. Calpain cleaves alphaII-spectrin into breakdown products (SBDP) after TBI and ischemia. Mean levels of both ipsilateral cortex (IC) and cerebral spinal fluid (CSF) SBDP at 2, 6, and 24 h after two levels of controlled cortical impact (1.0 mm and 1.6 mm of cortical deformation) in rats were significantly elevated by injury. CSF and IC SBDP levels were significantly higher after severe (1.6 mm) injury than mild (1.0 mm) injury over time. The correlation between CSF SBDP levels and lesion size from T2-weighted magnetic resonance images 24 hours after TBI as well as correlation of tau and S100beta was assessed. Mean levels of CSF SBDP (r = 0.833) and tau (r = 0.693) significantly correlated with lesion size while levels of CSF S100beta did not (r = 0.188). Although levels of CSF and IC SBDP and lesion size are all significantly higher after 1.6 mm than 1.0 mm injury, the correlation between CSF SBDP and lesion size was not significant following the removal of controls from the analysis. This indicates CSF SBDP is a reliable marker of the presence or absence of injury. Furthermore, larger lesion sizes 24 h after TBI were negatively correlated with motor performance on days 1-5 after TBI (r = -0.708). Based on these data, evaluation of CSF SBDP levels as a biomarker of TBI is warranted in clinical studies.