Stephen F. Larner

Neuroprotection targets after traumatic brain injury.

Purpose of reviewThe 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 findingsIn 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 α-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. SummaryClearly, 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.

Ubiquitin C-terminal hydrolase-L1 as a biomarker for ischemic and traumatic brain injury in rats

Ubiquitin C‐terminal hydrolase‐L1 (UCH‐L1), also called neuronal‐specific protein gene product 9.5, is a highly abundant protein in the neuronal cell body and has been identified as a possible biomarker on the basis of a recent proteomic study. In this study, we examined whether UCH‐L1 was significantly elevated in cerebrospinal fluid (CSF) following controlled cortical impact (CCI) and middle cerebral artery occlusion (MCAO; model of ischemic stroke) in rats. Quantitative immunoblots of rat CSF revealed a dramatic elevation of UCH‐L1 protein 48 h after severe CCI and as early as 6 h after mild (30 min) and severe (2 h) MCAO. A sandwich enzyme‐linked immunosorbent assay constructed to measure UCH‐L1 sensitively and quantitatively showed that CSF UCH‐L1 levels were significantly elevated as early as 2 h and up to 48 h after CCI. Similarly, UCH‐L1 levels were also significantly elevated in CSF from 6 to 72 h after 30 min of MCAO and from 6 to 120 h after 2 h of MCAO. These data are comparable to the profile of the calpain‐produced αII‐spectrin breakdown product of 145 kDa biomarker. Importantly, serum UCH‐L1 biomarker levels were also significantly elevated after CCI. Similarly, serum UCH‐L1 levels in the 2‐h MCAO group were significantly higher than those in the 30‐min group. Taken together, these data from two rat models of acute brain injury strongly suggest that UCH‐L1 is a candidate brain injury biomarker detectable in biofluid compartments (CSF and serum).

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.

Increased expression and processing of caspase‐12 after traumatic brain injury in rats

Traumatic brain injury (TBI) disrupts tissue homeostasis resulting in pathological apoptotic activation. Recently, caspase‐12 was reported to be induced and activated by the unfolded protein response following excess endoplasmic reticulum (ER) stress. This study examined rat caspase‐12 expression using the controlled cortical impact TBI model. Immunoblots of fractionalized cell lysates found elevated caspase‐12 proform (∼60 kDa) and processed form (∼12 kDa), with peak induction observed within 24 h post‐injury in the cortex (418% and 503%, respectively). Hippocampus caspase‐12 proform induction peaked at 24 h post‐injury (641%), while processed form induction peaked at 6 h (620%). Semi‐quantitative reverse transcriptase‐polymerase chain reaction (RT‐PCR) analysis confirmed elevated caspase‐12 mRNA levels after TBI. Injury severity (1.0, 1.2 or 1.6 mm compression) was associated with increased caspase‐12 mRNA expression, peaking at 5 days in the cortex (657%, 651% and 1259%, respectively) and 6 h in the hippocampus (435%, 451% and 460%, respectively). Immunohistochemical analysis revealed caspase‐12 induction in neurons in both the cortex and hippocampus as well as in astrocytes at the contusion site. This is the first report of increased expression of caspase‐12 following TBI. Our results suggest that the caspase‐12‐mediated ER apoptotic pathway may play a role in rat TBI pathology independent of the receptor‐ or mitochondria‐mediated apoptotic pathways.

Biomarkers of blast-induced neurotrauma: profiling molecular and cellular mechanisms of blast brain injury.

The nature of warfare in the 21st century has led to a significant increase in primary blast or over-pressurization injuries to the whole body and head, which manifest as a complex of neuro-somatic damage, including traumatic brain injury (TBI). Identifying relevant pathogenic pathways in reproducible experimental models of primary blast wave exposure is therefore vital to the development of biomarkers for diagnostics of blast brain injury. Comparative analysis of mechanisms and putative biomarkers of blast brain injury is complicated by a deficiency of experimental studies. In this article, we present an overview of current TBI biomarkers, as well as outline experimental strategies to investigate molecular signatures of blast neurotrauma and to develop a pathway network map for novel biomarker discovery. These biomarkers will be effective for triaging and managing both combat and civilian casualities.

Acute NMDA toxicity in cultured rat cerebellar granule neurons is accompanied by autophagy induction and late onset autophagic cell death phenotype

BackgroundAutophagy, an intracellular response to stress, is characterized by double membrane cytosolic vesicles called autophagosomes. Prolonged autophagy is known to result in autophagic (Type II) cell death. This study examined the potential role of an autophagic response in cultured cerebellar granule neurons challenged with excitotoxin N-methyl-D-aspartate (NMDA).ResultsNMDA exposure induced light chain-3 (LC-3)-immunopositive and monodansylcadaverine (MDC) fluorescent dye-labeled autophagosome formation in both cell bodies and neurites as early as 3 hours post-treatment. Elevated levels of Beclin-1 and the autophagosome-targeting LC3-II were also observed following NMDA exposure. Prolonged exposure of the cultures to NMDA (8-24 h) generated MDC-, LC3-positive autophagosomal bodies, concomitant with the neurodegenerative phase of NMDA challenge. Lysosomal inhibition studies also suggest that NMDA-treatment diverted the autophagosome-associated LC3-II from the normal lysosomal degradation pathway. Autophagy inhibitor 3-methyladenine significantly reduced NMDA-induced LC3-II/LC3-I ratio increase, accumulation of autophagosomes, and suppressed NMDA-mediated neuronal death. ATG7 siRNA studies also showed neuroprotective effects following NMDA treatment.ConclusionsCollectively, this study shows that autophagy machinery is robustly induced in cultured neurons subjected to prolonged exposure to excitotoxin, while autophagosome clearance by lysosomal pathway might be impaired. Our data further show that prolonged autophagy contributes to cell death in NMDA-mediated excitotoxicity.

Neuroproteomics and systems biology-based discovery of protein biomarkers for traumatic brain injury and clinical validation

The rapidly growing field of neuroproteomics has expanded to track global proteomic changes underlying various neurological conditions such as traumatic brain injury (TBI), stroke, and Alzheimers disease. TBI remains a major health problem with approximately 2 million incidents occurring annually in the United States, yet no affective treatment is available despite several clinical trials. The absence of brain injury diagnostic biomarkers was identified as a significant road‐block to therapeutic development for brain injury. Recently, the field of neuroproteomics has undertaken major advances in the area of neurotrauma research, where several candidate markers have been identified and are being evaluated for their efficacy as biological biomarkers in the field of TBI. One scope of this review is to evaluate the current status of TBI biomarker discovery using neuroproteomics techniques, and at what stage we are at in their clinical validation. In addition, we will discuss the need for strengthening the role of systems biology and its application to the field of neuroproteomics due to its integral role in establishing a comprehensive understanding of specific brain disorder and brain function in general. Finally, to achieve true clinical input of these neuroproteomic findings, these putative biomarkers should be validated using preclinical and clinical samples and linked to clinical diagnostic assays including ELISA or other high‐throughput assays.

Caspase 7: increased expression and activation after traumatic brain injury in rats

Caspases, a cysteine proteinase family, are required for the initiation and execution phases of apoptosis. It has been suggested that caspase 7, an apoptosis executioner implicated in cell death proteolysis, is redundant to the main executioner caspase 3 and it is generally believed that it is not present in the brain or present in only minute amounts with highly restricted activity. Here we report evidence that caspase 7 is up‐regulated and activated after traumatic brain injury (TBI) in rats. TBI disrupts homeostasis resulting in pathological apoptotic activation. After controlled cortical impact TBI of adult male rats we observed, by semiquantitative real‐time PCR, increased mRNA levels within the traumatized cortex and hippocampus peaking in the former about 5 days post‐injury and in the latter within 6–24 h of trauma. The activation of caspase 7 protein after TBI, demonstrated by immunoblot by the increase of the active form of caspase 7 peaking 5 days post‐injury in the cortex and hippocampus, was found to be up‐regulated in both neurons and astrocytes by immunohistochemistry. These findings, the first to document the up‐regulation of caspase 7 in the brain after acute brain injury in rats, suggest that caspase 7 activation could contribute to neuronal cell death on a scale not previously recognized.

Calpain-and caspase-mediated αII-spectrin and tau proteolysis in rat cerebrocortical neuronal cultures after ecstasy or methamphetamine exposure

Abuse of 3,4-methylenedioxymethamphetamine (MDMA or Ecstasy) and methamphetamine (Meth or Speed) is a growing international problem with an estimated 250 million users of psychoactive drugs worldwide. It is important to demonstrate and understand the mechanism of neurotoxicity so potential prevention and treatment therapies can be designed. In this study rat primary cerebrocortical neuron cultures were challenged with MDMA and Meth (1 or 2 mM) for 24 and 48 h and compared to the excitotoxin N-methyl-D-aspartate (NMDA). The neurotoxicity of these drugs, as assessed by microscopy, lactate dehydrogenase release and immunoblot, was shown to be both dose- and time-dependent. Immunoblot analysis using biomarkers of cell death showed significant proteolysis of both alphaII-spectrin and tau proteins. Breakdown products of alphaII-spectrin (SBDPs) of 150, 145, and 120 kDa and tau breakdown products (TBDPs) of 45, 32, 26, and 14 kDa were observed. The use of the protease inhibitors calpain inhibitor SJA6017 and caspase inhibitors z-VAD-fmk and Z-D-DCB, attenuated drug-induced alphaII-spectrin and tau proteolysis. The calpain inhibitor reduced the calpain-induced breakdown products SBDP145 and TBDP14, but there was an offset increase in the caspase-mediated breakdown products SBDP120 and TBDP45. The caspase inhibitors, on the other hand, decreased SBDP120 and TBDP45. These data suggest that both MDMA and Meth trigger concerted proteolytic attacks of the structural proteins by both calpain and caspase family of proteases. The ability of the protease inhibitors to reduce the damage caused by these drugs suggests that the treatment arsenal could include similar drugs as possible tools to combat the drug-induced neurotoxicity in vivo.

Direct Rho-associated kinase inhibiton induces cofilin dephosphorylation and neurite outgrowth in PC-12 cells

Axons fail to regenerate in the adult central nervous system (CNS) following injury. Developing strategies to promote axonal regeneration is therapeutically attractive for various CNS pathologies such as traumatic brain injury, stroke and Alzheimer’s disease. Because the RhoA pathway is involved in neurite outgrowth, Rho-associated kinases (ROCKs), downstream effectors of GTP-bound Rho, are potentially important targets for axonal repair strategies in CNS injuries. We investigated the effects and downstream mechanisms of ROCK inhibition in promoting neurite outgrowth in a PC-12 cell model. Robust neurite outgrowth (NOG) was induced by ROCK inhibitors Y-27632 and H-1152 in a time-and dose-dependent manner. Dramatic cytoskeletal reorganization was noticed upon ROCK inhibition. NOG initiated within 5 to 30 minutes followed by neurite extension between 6 and 10 hours. Neurite processes were then sustained for over 24 hours. Rapid cofilin dephosphorylation was observed within 5 minutes of Y-27632 and H-1152 treatment. Re-phosphorylation was observed by 6 hours after Y-27632 treatment, while H-1152 treatment produced sustained cofilin dephosphorylation for over 24 hours. The results suggest that ROCK-mediated dephosphorylation of cofilin plays a role in the initiation of NOG in PC-12 cells.