A calpain inhibitor attenuates cortical cytoskeletal protein loss after experimental traumatic brain injury in the rat

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.

Lyssavirus M protein degrades neuronal microtubules by reprogramming mitochondrial metabolism

Infection with neurotropic viruses may result in changes in host behavior, which are closely associated with degenerative changes in neurons. The lyssavirus genus comprises highly neurotropic viruses, including the rabies virus (RABV), which has been shown to induce degenerative changes in neurons, marked by the self-destruction of axons. The underlying mechanism by which the RABV degrades neuronal cytoskeletal proteins remains incomplete. In this study, we show that infection with RABV or overexpression of its M protein can disrupt mitochondrial metabolism by binding to Slc25a4. This leads to a reduction in NAD+ production and a subsequent influx of Ca2+ from the endoplasmic reticulum and mitochondria into the cytoplasm of neuronal cell lines, activating Ca2+-dependent proteinase calpains that degrade α-tubulin. We further screened the M proteins of different lyssaviruses and discovered that the M protein of the dog-derived RABV strain (DRV) does not degrade α-tubulin. Sequence analysis of the DRV M protein and that of the lab-attenuated RABV strain CVS revealed that the 57th amino acid is vital for M-induced microtubule degradation. We generated a recombinant RABV with a mutation at the 57th amino acid position in its M protein and showed that this mutation reduces α-tubulin degradation in vitro and axonal degeneration in vivo. This study elucidates the mechanism by which lyssavirus induces neuron degeneration.IMPORTANCEPrevious studies have suggested that RABV (rabies virus, the representative of lyssavirus) infection induces structural abnormalities in neurons. But there are few articles on the mechanism of lyssavirus' effect on neurons, and the mechanism of how RABV infection induces neurological dysfunction remains incomplete. The M protein of lyssavirus can downregulate cellular ATP levels by interacting with Slc25a4, and this decrease in ATP leads to a decrease in the level of NAD+ in the cytosol, which results in the release of Ca2+ from the intracellular calcium pool, the endoplasmic reticulum, and mitochondria. The presence of large amounts of Ca2+ in the cytoplasm activates Ca2+-dependent proteases and degrades microtubule proteins. The amino acid 57 of M protein is the key site determining its disruption of mitochondrial metabolism and subsequent neuron degeneration.

Innate immune response to SARS-CoV-2 infection contributes to neuronal damage in human iPSC-derived peripheral neurons

Severe acute respiratory coronavirus 2 (SARS-CoV-2) causes neurological disease in the peripheral and central nervous system (PNS and CNS, respectively) of some patients. It is not clear whether SARS-CoV-2 infection or the subsequent immune response are the key factors that cause neurological disease. Here, we addressed this question by infecting human induced pluripotent stem cell-derived CNS and PNS neurons with SARS-CoV-2. SARS-CoV-2 infected a low number of CNS neurons and did not elicit a robust innate immune response. On the contrary, SARS-CoV-2 infected a higher number of PNS neurons. This resulted in expression of interferon (IFN) λ1, several IFN-stimulated genes and proinflammatory cytokines. The PNS neurons also displayed alterations characteristic of neuronal damage, as increased levels of sterile alpha and Toll/interleukin receptor motif-containing protein 1, amyloid precursor protein and α-synuclein, and lower levels of cytoskeletal proteins. Interestingly, blockade of the Janus kinase and signal transducer and activator of transcription pathway by Ruxolitinib did not increase SARS-CoV-2 infection, but reduced neuronal damage, suggesting that an exacerbated neuronal innate immune response contributes to pathogenesis in the PNS. Our results provide a basis to study coronavirus disease 2019 (COVID-19) related neuronal pathology and to test future preventive or therapeutic strategies.

Colloidal therapeutics in the management of traumatic brain injury: Portray of biomarkers and drug-targets, preclinical and clinical pieces of evidence and future prospects

Complexity associated with the aberrant physiology of traumatic brain injury (TBI) makes its therapeutic targeting vulnerable. The underlying mechanisms of pathophysiology of TBI are yet to be completely illustrated. Primary injury in TBI is associated with contusions and axonal shearing whereas excitotoxicity, mitochondrial dysfunction, free radicals generation, and neuroinflammation are considered under secondary injury. MicroRNAs, proinflammatory cytokines, and Glial fibrillary acidic protein (GFAP) recently emerged as biomarkers in TBI. In addition, several approved therapeutic entities have been explored to target existing and newly identified drug-targets in TBI. However, drug delivery in TBI is hampered due to disruption of blood-brain barrier (BBB) in secondary TBI, as well as inadequate drug-targeting and retention effect. Colloidal therapeutics appeared helpful in providing enhanced drug availability to the brain owing to definite targeting strategies. Moreover, immense efforts have been put together to achieve increased bioavailability of therapeutics to TBI by devising effective targeting strategies. The potential of colloidal therapeutics to efficiently deliver drugs at the site of injury and down-regulate the mediators of TBI are serving as novel policies in the management of TBI. Therefore, in present manuscript, we have illuminated a myriad of molecular-targets currently identified and recognized in TBI. Moreover, particular emphasis is given to frame armamentarium of repurpose drugs which could be utilized to block molecular targets in TBI in addition to drug delivery barriers. The critical role of colloidal therapeutics such as liposomes, nanoparticles, dendrimers, and exosomes in drug delivery to TBI through invasive and non-invasive routes has also been highlighted.

The Node of Ranvier as an Interface for Axo-Glial Interactions: Perturbation of Axo-Glial Interactions in Various Neurological Disorders

The action potential conduction along the axon is highly dependent on the healthy interactions between the axon and myelin-producing glial cells. Myelin, which facilitates action potential, is the protective insulation around the axon formed by Schwann cells and oligodendrocytes in the peripheral (PNS) and central nervous system (CNS), respectively. Myelin is a continuous structure with intermittent gaps called nodes of Ranvier, which are the sites enriched with ion channels, transmembrane, scaffolding, and cytoskeletal proteins. Decades-long extensive research has identified a comprehensive proteome with strictly regularized localization at the node of Ranvier. Concurrently, axon-glia interactions at the node of Ranvier have gathered significant attention as the pathophysiological targets for various neurodegenerative disorders. Numerous studies have shown the alterations in the axon-glia interactions culminating in neurological diseases. In this review, we have provided an update on the molecular composition of the node of Ranvier. Further, we have discussed in detail the consequences of disruption of axon-glia interactions during the pathogenesis of various CNS and PNS disorders.

Drosophila melanogaster as a model to study age and sex differences in brain injury and neurodegeneration after mild head trauma

Repetitive physical insults to the head, including those that elicit mild traumatic brain injury (mTBI), are a known risk factor for a variety of neurodegenerative conditions including Alzheimer's disease (AD), Parkinson's disease (PD), and chronic traumatic encephalopathy (CTE). Although most individuals who sustain mTBI typically achieve a seemingly full recovery within a few weeks, a subset experience delayed-onset symptoms later in life. As most mTBI research has focused on the acute phase of injury, there is an incomplete understanding of mechanisms related to the late-life emergence of neurodegeneration after early exposure to mild head trauma. The recent adoption of Drosophila-based brain injury models provides several unique advantages over existing preclinical animal models, including a tractable framework amenable to high-throughput assays and short relative lifespan conducive to lifelong mechanistic investigation. The use of flies also provides an opportunity to investigate important risk factors associated with neurodegenerative conditions, specifically age and sex. In this review, we survey current literature that examines age and sex as contributing factors to head trauma-mediated neurodegeneration in humans and preclinical models, including mammalian and Drosophila models. We discuss similarities and disparities between human and fly in aging, sex differences, and pathophysiology. Finally, we highlight Drosophila as an effective tool for investigating mechanisms underlying head trauma-induced neurodegeneration and for identifying therapeutic targets for treatment and recovery.

Calpain Inhibitors as Potential Therapeutic Modulators in Neurodegenerative Diseases

It is considered a significant challenge to understand the neuronal cell death mechanisms with a suitable cure for neurodegenerative disorders in the coming years. Calpains are one of the best-considered "cysteine proteases activated" in brain disorders. Calpain is an important marker and mediator in the pathophysiology of neurodegeneration. Calpain activation being the essential neurodegenerative factor causing apoptotic machinery activation, it is crucial to develop reliable and effective approaches to prevent calpain-mediated apoptosis in degenerating neurons. It has been recently seen that the "inhibition of calpain activation" has appeared as a possible therapeutic target for managing neurodegenerative diseases. A systematic literature review of PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was conducted. The present article reviews the basic pathobiology and role of selective calpain inhibitors used in various neurodegenerative diseases as a therapeutic target.

The Cell Biology of LRRK2 in Parkinson's Disease

Point mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson's disease (PD) and are implicated in a significant proportion of apparently sporadic PD cases. Clinically, LRRK2-driven PD is indistinguishable from sporadic PD, making it an attractive genetic model for the much more common sporadic PD. In this review, we highlight recent advances in understanding LRRK2's subcellular functions using LRRK2-driven PD models, while also considering some of the limitations of these model systems. Recent developments of particular importance include new evidence of key LRRK2 functions in the endolysosomal system and LRRK2's regulation of and by Rab GTPases. Additionally, LRRK2's interaction with the cytoskeleton allowed elucidation of the LRRK2 structure and appears relevant to LRRK2 protein degradation and LRRK2 inhibitor therapies. We further discuss how LRRK2's interactions with other PD-driving genes, such as the VPS35, GBA1, and SNCA genes, may highlight cellular pathways more broadly disrupted in PD.

Extending the Calpain-Cathepsin Hypothesis to the Neurovasculature: Protection of Brain Endothelial Cells and Mice from Neurotrauma

The calpain-cathepsin hypothesis posits a key role for elevated calpain-1 and cathepsin-B activity in the neurodegeneration underlying neurotrauma and multiple disorders including Alzheimer's disease (AD). AD clinical trials were recently halted on alicapistat, a selective calpain-1 inhibitor, because of insufficient exposure of neurons to the drug. In contrast to neuroprotection, the ability of calpain-1 and cathepsin-B inhibitors to protect the blood-brain barrier (BBB), is understudied. Since cerebrovascular dysfunction underlies vascular dementia, is caused by ischemic stroke, and is emerging as an early feature in the progression of AD, we studied protection of brain endothelial cells (BECs) by selective and nonselective calpain-1 and cathepsin-B inhibitors. We show these inhibitors protect both neurons and murine BECs from ischemia-reperfusion injury. Cultures of primary BECs from ALDH2 -/- mice that manifest enhanced oxidative stress were sensitive to ischemia, leading to reduced cell viability and loss of tight junction proteins; this damage was rescued by calpain-1 and cathepsin-B inhibitors. In ALDH2 -/- mice 24 h after mild traumatic brain injury (mTBI), BBB damage was reflected by significantly increased fluorescein extravasation and perturbation of tight junction proteins, eNOS, MMP-9, and GFAP. Both calpain and cathepsin-B inhibitors alleviated BBB dysfunction caused by mTBI. No clear advantage was shown by selective versus nonselective calpain inhibitors in these studies. The lack of recognition of the ability of calpain inhibitors to protect the BBB may have led to the premature abandonment of this therapeutic approach in AD clinical trials and requires further mechanistic studies of cerebrovascular protection by calpain-1 inhibitors.

Calpain-1 and Calpain-2 in the Brain: New Evidence for a Critical Role of Calpain-2 in Neuronal Death

Calpains are a family of soluble calcium-dependent proteases that are involved in multiple regulatory pathways. Our laboratory has focused on the understanding of the functions of two ubiquitous calpain isoforms, calpain-1 and calpain-2, in the brain. Results obtained over the last 30 years led to the remarkable conclusion that these two calpain isoforms exhibit opposite functions in the brain. Calpain-1 activation is required for certain forms of synaptic plasticity and corresponding types of learning and memory, while calpain-2 activation limits the extent of plasticity and learning. Calpain-1 is neuroprotective both during postnatal development and in adulthood, while calpain-2 is neurodegenerative. Several key protein targets participating in these opposite functions have been identified and linked to known pathways involved in synaptic plasticity and neuroprotection/neurodegeneration. We have proposed the hypothesis that the existence of different PDZ (PSD-95, DLG and ZO-1) binding domains in the C-terminal of calpain-1 and calpain-2 is responsible for their association with different signaling pathways and thereby their different functions. Results with calpain-2 knock-out mice or with mice treated with a selective calpain-2 inhibitor indicate that calpain-2 is a potential therapeutic target in various forms of neurodegeneration, including traumatic brain injury and repeated concussions.

TRPM7 Mediates Neuronal Cell Death Upstream of Calcium/Calmodulin-Dependent Protein Kinase II and Calcineurin Mechanism in Neonatal Hypoxic-Ischemic Brain Injury

Transient receptor potential melastatin 7 (TRPM7), a calcium-permeable, ubiquitously expressed ion channel, is critical for axonal development, and mediates hypoxic and ischemic neuronal cell death in vitro and in vivo. However, the downstream mechanisms underlying the TRPM7-mediated processes in physiology and pathophysiology remain unclear. In this study, we employed a mouse model of hypoxic-ischemic brain cell death which mimics the pathophysiology of hypoxic-ischemic encephalopathy (HIE). HIE is a major public health issue and an important cause of neonatal deaths worldwide; however, the available treatments for HIE remain limited. Its survivors face life-long neurological challenges including mental retardation, cerebral palsy, epilepsy and seizure disorders, motor impairments, and visual and auditory impairments. Through a proteomic analysis, we identified calcium/calmodulin-dependent protein kinase II (CaMKII) and phosphatase calcineurin as potential mediators of cell death downstream from TRPM7 activation. Further analysis revealed that TRPM7 mediates cell death through CaMKII, calmodulin, calcineurin, p38, and cofilin cascade. In vivo, we found a significant reduction of brain injury and improvement of short- and long-term functional outcomes after HI after administration of specific TRPM7 blocker waixenicin A. Our data demonstrate a molecular mechanism of TRPM7-mediated cell death and identifies TRPM7 as a promising therapeutic and drug development target for HIE.

Novel role of SARM1 mediated axonal degeneration in the pathogenesis of rabies

Neurotropic viral infections continue to pose a serious threat to human and animal wellbeing. Host responses combatting the invading virus in these infections often cause irreversible damage to the nervous system, resulting in poor prognosis. Rabies is the most lethal neurotropic virus, which specifically infects neurons and spreads through the host nervous system by retrograde axonal transport. The key pathogenic mechanisms associated with rabies infection and axonal transmission in neurons remains unclear. Here we studied the pathogenesis of different field isolates of lyssavirus including rabies using ex-vivo model systems generated with mouse primary neurons derived from the peripheral and central nervous systems. In this study, we show that neurons activate selective and compartmentalized degeneration of their axons and dendrites in response to infection with different field strains of lyssavirus. We further show that this axonal degeneration is mediated by the loss of NAD and calpain-mediated digestion of key structural proteins such as MAP2 and neurofilament. We then analysed the role of SARM1 gene in rabies infection, which has been shown to mediate axonal self-destruction during injury. We show that SARM1 is required for the accelerated execution of rabies induced axonal degeneration and the deletion of SARM1 gene significantly delayed axonal degeneration in rabies infected neurons. Using a microfluidic-based ex-vivo neuronal model, we show that SARM1-mediated axonal degeneration impedes the spread of rabies virus among interconnected neurons. However, this neuronal defense mechanism also results in the pathological loss of axons and dendrites. This study therefore identifies a potential host-directed mechanism behind neurological dysfunction in rabies infection. This study also implicates a novel role of SARM1 mediated axonal degeneration in neurotropic viral infection.

Lyssaviruses including rabies, still causes devastating loss of human life every year and many victims are children under the age of 15. Rabies infection causes severe neurological dysfunction in the host resulting in paralysis, cognitive deficits and behavioural abnormalities. The mechanism of how rabies infection induces neurological dysfunction in the host remains unclear. This is because unlike other microbial infections, rabies infection rarely causes neuronal cell death and loss of neurons in the host nervous system. In this study, we show that neurons activate specific axonal self-destruction mechanism during rabies infection to prevent the spread of virus. However, this neuronal self-defense mechanism results in the loss of axons and dendrites, the structural components essential for the functioning of neurons. We further show that axonal degeneration in rabies infection is mediated by SARM1 gene, which has been previously shown to mediate defensive self-destruction of axons and dendrites in the event of neuronal injury. In summary, this study identifies a novel molecular mechanism behind neuronal dysfunction in rabies infection. This study also describes a novel intrinsic anti-viral defence mechanism in neurons, which could influence the pathogenesis of neurotropic viral infections.

The fate and function of oligodendrocyte progenitor cells after traumatic spinal cord injury

Oligodendrocyte progenitor cells (OPCs) are the most proliferative and dispersed population of progenitor cells in the adult central nervous system, which allows these cells to rapidly respond to damage. Oligodendrocytes and myelin are lost after traumatic spinal cord injury (SCI), compromising efficient conduction and, potentially, the long-term health of axons. In response, OPCs proliferate and then differentiate into new oligodendrocytes and Schwann cells to remyelinate axons. This culminates in highly efficient remyelination following experimental SCI in which nearly all intact demyelinated axons are remyelinated in rodent models. However, myelin regeneration comprises only one role of OPCs following SCI. OPCs contribute to scar formation after SCI and restrict the regeneration of injured axons. Moreover, OPCs alter their gene expression following demyelination, express cytokines and perpetuate the immune response. Here, we review the functional contribution of myelin regeneration and other recently uncovered roles of OPCs and their progeny to repair following SCI.

Calpain-2 as a therapeutic target for acute neuronal injury

INTRODUCTION

Calpains represent a family of neutral, calcium-dependent proteases, which modify the function of their target proteins by partial truncation. These proteases have been implicated in numerous cell functions, including cell division, proliferation, migration, and death. In the CNS, where calpain-1 and calpain-2 are the main calpain isoforms, their activation has been linked to synaptic plasticity as well as to neurodegeneration. This review will focus on the role of calpain-2 in acute neuronal injury and discuss the possibility of developing selective calpain-2 inhibitors for therapeutic purposes. Areas covered: This review covers the literature showing how calpain-2 is implicated in neuronal death in a number of pathological conditions. The possibility of developing new selective calpain-2 inhibitors for treating these conditions is discussed. Expert opinion: As evidence accumulates that calpain-2 activation participates in acute neuronal injury, there is interest in developing therapeutic approaches using selective calpain-2 inhibitors. Recent data indicate the potential use of such inhibitors in various pathologies associated with acute neuronal death. The possibility of extending the use of such inhibitors to more chronic forms of neurodegeneration is discussed.

Protection against TBI-Induced Neuronal Death with Post-Treatment with a Selective Calpain-2 Inhibitor in Mice

Traumatic Brain Injury (TBI) is a major cause of death and disability worldwide. The calcium-dependent protease, calpain, has been shown to be involved in TBI-induced neuronal death. However, whereas various calpain inhibitors have been tested in several animal models of TBI, there has not been any clinical trial testing the efficacy of calpain inhibitors in human TBI. One important reason for this could be the lack of knowledge regarding the differential functions of the two major calpain isoforms in the brain, calpain-1 and calpain-2. In this study, we used the controlled cortical impact (CCI) model in mice to test the roles of calpain-1 and calpain-2 in TBI-induced neuronal death. Immunohistochemistry (IHC) with calpain activity markers performed at different time-points after CCI in wild-type and calpain-1 knock-out (KO) mice showed that calpain-1 was activated early in cortical areas surrounding the impact, within 0-8 h after CCI, whereas calpain-2 activation was delayed and was predominant during 8-72 h after CCI. Calpain-1 KO enhanced cell death, whereas calpain-2 activity correlated with the extent of cell death, suggesting that calpain-1 activation suppresses and calpain-2 activation promotes cell death following TBI. Systemic injection(s) of a calpain-2 selective inhibitor, NA101, at 1 h or 4 h after CCI significantly reduced calpain-2 activity and cell death around the impact site, reduced the lesion volume, and promoted motor and learning function recovery after TBI. Our data indicate that calpain-1 activity is neuroprotective and calpain-2 activity is neurodegenerative after TBI, and that a selective calpain-2 inhibitor can reduce TBI-induced cell death.

Neurometabolic indicators of mitochondrial dysfunction in repetitive mild traumatic brain injury

Mild traumatic brain injury (mTBI) is a significant national health concern and there is growing evidence that repetitive mTBI (rmTBI) can cause long-term change in brain structure and function. The mitochondrion has been suggested to be involved in the mechanism of TBI. There are noninvasive methods of determining mitochondrial dysfunction through biomarkers and spectroscopy. Mitochondrial dysfunction has been implicated in a variety of neurological consequences secondary to rmTBI through activation of caspases and calpains. The purpose of this review is to examine the mechanism of mitochondrial dysfunction in rmTBI and its downstream effects on neuronal cell death, axonal injury and blood–brain barrier compromise.

Degradomics in Neurotrauma: Profiling Traumatic Brain Injury

Degradomics has recently emerged as a subdiscipline in the omics era with a focus on characterizing signature breakdown products implicated in various disease processes. Driven by promising experimental findings in cancer, neuroscience, and metabolomic disorders, degradomics has significantly promoted the notion of disease-specific "degradome." A degradome arises from the activation of several proteases that target specific substrates and generate signature protein fragments. Several proteases such as calpains, caspases, cathepsins, and matrix metalloproteinases (MMPs) are involved in the pathogenesis of numerous diseases that disturb the physiologic balance between protein synthesis and protein degradation. While regulated proteolytic activities are needed for development, growth, and regeneration, uncontrolled proteolysis initiated under pathological conditions ultimately culminates into apoptotic and necrotic processes. In this chapter, we aim to review the protease-substrate repertoires in neural injury concentrating on traumatic brain injury. A striking diversity of protease substrates, essential for neuronal and brain structural and functional integrity, namely, encryptic biomarker neoproteins, have been characterized in brain injury. These include cytoskeletal proteins, transcription factors, cell cycle regulatory proteins, synaptic proteins, and cell junction proteins. As these substrates are subject to proteolytic fragmentation, they are ceaselessly exposed to activated proteases. Characterization of these molecules allows for a surge of "possible" therapeutic approaches of intervention at various levels of the proteolytic cascade.

Calpain-dependent truncated form of TrkB-FL increases in neurodegenerative processes

Recent findings indicate that the mechanisms that drive reshaping of the nervous system are aberrantly activated in epilepsy and several neurodegenerative diseases. The recurrent seizures in epilepsy, particularly in the condition called status epilepticus, can cause permanent neurological damage, resulting in cognitive dysfunction and other serious neurological conditions. In this study, we used an in vitro model of status epilepticus to examine the role of calpain in the degeneration of hippocampal neurons. We grew neurons on a culture system that allowed studying the dendritic and axonal domains separately from the cell bodies. We found that a recently characterized calpain substrate, the neurotrophin receptor TrkB, is cleaved in the dendritic and axonal domain of neurons committed to die, and this constitutes an early step in the neuronal degeneration process. While the full-length TrkB (TrkB-FL) levels decreased, the truncated form of TrkB (Tc TrkB-FL) concurrently increased, leading to a TrkB-FL/Tc TrkB-FL imbalance, which is thought to be causally linked to neurodegeneration. We further show that the treatment with N-acetyl-Leu-Leu-norleucinal, a specific calpain activity blocker, fully protects the neuronal processes from degeneration, prevents the TrkB-FL/Tc TrkB-FL imbalance, and provides full neuroprotection. Moreover, the use of the TrkB antagonist ANA 12 at the time when the levels of TrkB-FL were significantly decreased, totally blocked neuronal death, suggesting that Tc TrkB-FL may have a role in neuronal death. These results indicate that the imbalance of these neurotrophins receptors plays a key role in neurite degeneration induced by seizures.

Axonal Damage in Traumatic Brain Injury

Axonal damage is one of the most common and important pathologic features of traumatic brain injury. Severe diffuse axonal injury, resulting from inertial forces applied to the head, is associated with prolonged unconsciousness and poor outcome. The susceptibility of axons to mechanical injury appears to be due to both their viscoelastic properties and their highly organized structure in white matter tracts. Although axons are supple under normal conditions, they become brittle when exposed to rapid deformations associated with brain trauma. Accordingly, rapid stretch of axons can damage the axonal cytoskeleton, resulting in a loss of elasticity and impairment of axoplasmic transport. Subsequent swelling of the axon occurs in discrete bulb formations or in elongated varicosities that accumulate organelles. Calcium entry into damaged axons is thought to initiate further damage by the activation of proteases and the induction of mitochondrial swelling and dysfunction. Ultimately, swollen axons may become disconnected and contribute to additional neuropathologic changes in brain tissue. However, promising new therapies that reduce proteolytic activity or maintain mitochondrial integrity may attenuate progressive damage of injured axons following experimental brain trauma. Future advancements in the prevention and treatment of traumatic axonal injury will depend on our collective understanding of the relationship between the biomechanics and pathophysiology of various phases of axonal trauma.

Traumatic Axonal Injury: Mechanisms and Translational Opportunities

Traumatic axonal injury (TAI) is an important pathoanatomical subgroup of traumatic brain injury (TBI) and a major driver of mortality and functional impairment. Experimental models have provided insights into the effects of mechanical deformation on the neuronal cytoskeleton and the subsequent processes that drive axonal injury. There is also increasing recognition that axonal or white matter loss may progress for years post-injury and represent one mechanistic framework for progressive neurodegeneration after TBI. Previous trials of novel therapies have failed to make an impact on clinical outcome, in both TBI in general and TAI in particular. Recent advances in understanding the cellular and molecular mechanisms of injury have the potential to translate into novel therapeutic targets.

Multiple therapeutic targets are emerging that offer the potential to reduce secondary brain injury at a cellular level. These include cytoskeletal and membrane stabilisation, control of calcium flux and calpain activation, optimisation of cellular energetics, and modulation of the inflammatory response.

Wallerian degeneration, as occurs following an axonal injury, is an active, cell-autonomous death pathway that involves failure of axonal transport to deliver key enzymes involved in NAD biosynthesis.

Chronic microglial activation occurs following traumatic brain injury (TBI) and may persist for decades afterwards. This ongoing response has been linked to long-term neurodegeneration, particularly of white matter tracts.

Phagoptosis is the process whereby physiologically stressed but otherwise viable neurons are phagocytosed by microglia in response to a range of eat-me signals induced by tissue injury.

Administration of low dose estrogen attenuates gliosis and protects neurons in acute spinal cord injury in rats

Spinal cord injury (SCI) is a debilitating condition with neurological deficits and loss of motor function that, depending on the severity, may lead to paralysis. The only treatment currently available is methylprednisolone, which is widely used and renders limited efficacy in SCI. Therefore, other therapeutic agents must be developed. The neuroprotective efficacy of estrogen in SCI was studied with a pre-clinical and pro-translational perspective. Acute SCI was induced in rats that were treated with low doses of estrogen (1, 5, 10, or 100 μg/kg) and compared with vehicle-treated injured rats or laminectomy control (sham) rats at 48 h post-SCI. Changes in gliosis and other pro-inflammatory responses, expression and activity of proteolytic enzymes (e.g., calpain, caspase-3), apoptosis of neurons in SCI, and cell death were monitored via Western blotting and immunohistochemistry. Negligible pro-inflammatory responses or proteolytic events and very low levels of neuronal death were found in sham rats. In contrast, vehicle-treated SCI rats showed profound pro-inflammatory responses with reactive gliosis, elevated expression and activity of calpain and caspase-3, elevated Bax:Bcl-2 ratio, and high levels of neuronal death in lesion and caudal regions of the injured spinal cord. Estrogen treatment at each dose reduced pro-inflammatory and proteolytic activities and protected neurons in the caudal penumbra in acute SCI. Estrogen treatment at 10 μg was found to be as effective as 100 μg in ameliorating the above parameters in injured animals. Results from this investigation indicated that estrogen at a low dose could be a promising therapeutic agent for treating acute SCI. Experimental studies with low dose estrogen therapy in acute spinal cord injury (SCI) demonstrated the potential for multi-active beneficial outcomes. Estrogen has been found to ameliorate several degenerative pathways following SCI. Thus, such early protective effects may even lead to functional recovery in long term injury. Studies are underway in chronic SCI in a follow up manuscript.

Cysteine proteases as therapeutic targets: does selectivity matter? A systematic review of calpain and cathepsin inhibitors

Cysteine proteases continue to provide validated targets for treatment of human diseases. In neurodegenerative disorders, multiple cysteine proteases provide targets for enzyme inhibitors, notably caspases, calpains, and cathepsins. The reactive, active-site cysteine provides specificity for many inhibitor designs over other families of proteases, such as aspartate and serine; however, a) inhibitor strategies often use covalent enzyme modification, and b) obtaining selectivity within families of cysteine proteases and their isozymes is problematic. This review provides a general update on strategies for cysteine protease inhibitor design and a focus on cathepsin B and calpain 1 as drug targets for neurodegenerative disorders; the latter focus providing an interesting query for the contemporary assumptions that irreversible, covalent protein modification and low selectivity are anathema to therapeutic safety and efficacy.

The effect of simvastatin treatment on proliferation and differentiation of neural stem cells after traumatic brain injury

OBJECTIVE

To study the effect of simvastatin on neurological functional recovery after traumatic brain injuries (TBI) and the possible molecular mechanisms, we evaluated simvastatin-induced proliferation and differentiation of neural stem cells (NSCs) in vitro and in vivo and possible involvement of Notch-1 signaling in this process.

METHODS

Adult Wistar rats were randomly divided into three groups (n=28 for each): sham group, saline-treated group and simvastatin-treated group. Simvastatin was given orally at a dose of 1mg/kg/day starting at day 1 after TBI. At 1, 3, 7, 14, 21, 28, and 35 days after simvastatin treatment, functional outcome was measured using modified neurological severity scores (mNSS). Immunofluorescence of nestin was used to identify neurogenesis of NSCs in injured area of TBI rats. Western blot was applied to detect the expression level of Notch-1 protein in TBI rats with simvastatin.

RESULTS

Immunostaining showed a significant increase in the number of nestin-positive cells in injured area of the simvastatin-treated group compared to that of the saline-treated group (p<0.05). In in vitro experiment, simvastatin induced enhanced proliferation and neurogenesis of cultured NSCs and elevated Notch-1 protein expression. Co-incubation of γ-secretase inhibitor, an inhibitor of Notch-1 pathway, with simvastatin abolished its neurorestoration effect. Most importantly, the simvastatin-treated group had significantly decreased mNSS at day 35 after TBI compared with the saline-treated group (p<0.05).

CONCLUSION

Simvastatin treatment enhanced neurological functional recovery after TBI possibly via activation of Notch signaling and increasing neurogenesis in the injured area.

The role of calpains in traumatic brain injury

AIM

This article attempts to provide a framework that will help to illustrate the roles of calpains in the process of traumatic brain injury (TBI).

METHOD

This review provides meaningful points about the essential role of calpains in the neuropathological changes that follow TBI, identifies useful biomarkers of calpain activation and states the important roles of calpain in the treatment of TBI.

RESULTS

Neuronal calpains can be activated within hours or even minutes following contusive or diffuse brain trauma in animals. It has been suggested that they are early mediators of neuronal damage. Trauma can produce sustained calpain activation. In turn, this may result in axonal degeneration and neuronal death in models of TBI. Calpains can cleave cytoskeletal proteins into stable proteolytic fragments that have been widely used as biomarkers of the activation of calpain. The inhibition of calpains can reduce the functional and behavioural deficits by ameliorating axonal pathology and reducing cell deaths in animal models of TBI.

CONCLUSION

This review concentrates on the current understanding of the role of calpains in neuropathology that has been induced by TBI and the significance of calpains as a therapeutic target for the treatment of primary and secondary injuries that are associated with brain trauma.

The cysteine protease cathepsin B is a key drug target and cysteine protease inhibitors are potential therapeutics for traumatic brain injury

There are currently no effective therapeutic agents for traumatic brain injury (TBI), but drug treatments for TBI can be developed by validation of new drug targets and demonstration that compounds directed to such targets are efficacious in TBI animal models using a clinically relevant route of drug administration. The cysteine protease, cathepsin B, has been implicated in mediating TBI, but it has not been validated by gene knockout (KO) studies. Therefore, this investigation evaluated mice with deletion of the cathepsin B gene receiving controlled cortical impact TBI trauma. Results indicated that KO of the cathepsin B gene resulted in amelioration of TBI, shown by significant improvement in motor dysfunction, reduced brain lesion volume, greater neuronal density in brain, and lack of increased proapoptotic Bax levels. Notably, oral administration of the small-molecule cysteine protease inhibitor, E64d, immediately after TBI resulted in recovery of TBI-mediated motor dysfunction and reduced the increase in cathepsin B activity induced by TBI. E64d outcomes were as effective as cathepsin B gene deletion for improving TBI. E64d treatment was effective even when administered 8 h after injury, indicating a clinically plausible time period for acute therapeutic intervention. These data demonstrate that a cysteine protease inhibitor can be orally efficacious in a TBI animal model when administered at a clinically relevant time point post-trauma, and that E64d-mediated improvement of TBI is primarily the result of inhibition of cathepsin B activity. These results validate cathepsin B as a new TBI therapeutic target.

Suppression of neurocan and enhancement of axonal density in rats after treatment of traumatic brain injury with scaffolds impregnated with bone marrow stromal cells

OBJECT

Neurocan is a major form of growth-inhibitory molecule (growth-IM) that suppresses axonal regeneration after neural injury. Bone marrow stromal cells (MSCs) have been shown to inhibit neurocan expression in vitro and in animal models of cerebral ischemia. Therefore, the present study was designed to investigate the effects of treatment of MSCs impregnated with collagen scaffolds on neurocan expression after traumatic brain injury (TBI).

METHODS

Adult male Wistar rats were injured with controlled cortical impact and treated with saline, human MSCs (hMSCs) (3 × 10(6)) alone, or hMSCs (3 × 10(6)) impregnated into collagen scaffolds (scaffold + hMSCs) transplanted into the lesion cavity 7 days after TBI (20 rats per group). Rats were sacrificed 14 days after TBI, and brain tissues were harvested for immunohistochemical studies, Western blot analyses, laser capture microdissections, and quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR) to evaluate neurocan protein and gene expressions after various treatments.

RESULTS

Animals treated with scaffold + hMSCs after TBI showed increased axonal and synaptic densities compared with the other groups. Scaffold + hMSC treatment was associated with reduced TBI-induced neurocan protein expression and upregulated growth-associated protein 43 (GAP-43) and synaptophysin expression in the lesion boundary zone. In addition, animals in the scaffold + hMSC group had decreased neurocan transcription in reactive astrocytes after TBI. Reduction of neurocan expression was significantly greater in the scaffold + hMSC group than in the group treated with hMSCs alone.

CONCLUSIONS

The results of this study show that transplanting hMSCs with scaffolds enhances the effect of hMSCs on axonal plasticity in TBI rats. This enhanced axonal plasticity may partially be attributed to the downregulation of neurocan expression by hMSC treatment after injury.

Role of calpains in the injury-induced dysfunction and degeneration of the mammalian axon

Axonal injury and degeneration, whether primary or secondary, contribute to the morbidity and mortality seen in many acquired and inherited central nervous system (CNS) and peripheral nervous system (PNS) disorders, such as traumatic brain injury, spinal cord injury, cerebral ischemia, neurodegenerative diseases, and peripheral neuropathies. The calpain family of proteases has been mechanistically linked to the dysfunction and degeneration of axons. While the direct mechanisms by which transection, mechanical strain, ischemia, or complement activation trigger intra-axonal calpain activity are likely different, the downstream effects of unregulated calpain activity may be similar in seemingly disparate diseases. In this review, a brief examination of axonal structure is followed by a focused overview of the calpain family. Finally, the mechanisms by which calpains may disrupt the axonal cytoskeleton, transport, and specialized domains (axon initial segment, nodes, and terminals) are discussed.

Down-regulation of Nogo-A by collagen scaffolds impregnated with bone marrow stromal cell treatment after traumatic brain injury promotes axonal regeneration in rats

Nogo-A is a major form of growth inhibitory molecule (growth-IM) which inhibits axonal regeneration and neurite regrowth after neural injury. Bone marrow stromal cells (MSCs) have been shown to inhibit Nogo-A expression in vitro and in cerebral ischemic animal models. The present study was designed to investigate the effects of treatment with human MSCs (hMSCs) impregnated into collagen scaffolds on the expression of Nogo-A and axonal plasticity after traumatic brain injury (TBI). Adult male Wistar rats were injured with controlled cortical impact and treated either with saline, hMSCs-alone or hMSCs impregnated into collagen scaffolds (scaffold+hMSC) transplanted into the lesion cavity 7 days after TBI. Rats were sacrificed 14 days after TBI and brain tissues were harvested for immunohistochemical studies, Western blot analysis, laser capture microdissections and qRT-PCR to evaluate axonal density and Nogo-A protein and gene expressions. Our data showed that treatment of TBI with scaffold+hMSC significantly decreased TBI-induced Nogo-A protein expression and increased axonal density compared to saline and hMSC-alone treatments. In addition, scaffold+hMSC transplantation decreased Nogo-A transcription in oligodendrocytes after TBI. Scaffold+hMSC treatment was superior to hMSC-alone treatment in suppressing Nogo-A expression and enhancing axonal regeneration after TBI. Our data suggest that transplanting hMSCs with scaffolds down-regulates Nogo-A transcription and protein expression which may partially contribute to the enhanced axonal regeneration after TBI.

Tracking induced pluripotent stem cells-derived neural stem cells in the central nervous system of rats and monkeys

Despite of the immense breakthroughs of induced pluripotent stem cells (iPSCs), clinical application of iPSCs and their derivates remains hampered by a lack of definitive in vivo studies. Here, we attempted to track iPSCs-derived neural stem cells (NSCs) in the rodent and primate central nervous system (CNS) and explore their therapeutic viability for stem cell replacement in traumatic brain injury (TBI) rats and monkeys with spinal cord injury (SCI). Superparamagnetic iron oxide (SPIO) particles were used to label iPSCs-derived NSCs in vitro. Labeled NSCs were implanted into TBI rats and SCI monkeys 1 week after injury, and then imaged using gradient reflection echo (GRE) sequence by 3.0T magnetic resonance imaging (MRI) scanner. MRI analysis was performed at 1, 7, 14, 21, and 30 days, respectively, following cell transplantation. Pronounced hypointense signals were initially detected at the cell injection sites in rats and monkeys and were later found to extend progressively to the lesion regions, demonstrating that iPSCs-derived NSCs could migrate to the lesion area from the primary sites. The therapeutic efficacy of iPSCs-derived NSCs was examined concomitantly through functional recovery tests of the animals. In this study, we tracked iPSCs-derived NSCs migration in the CNS of TBI rats and SCI monkeys in vivo for the first time. Functional recovery tests showed obvious motor function improvement in transplanted animals. These data provide the necessary foundation for future clinical application of iPSCs for CNS injury.

Molecular mechanisms of cognitive dysfunction following traumatic brain injury

Traumatic brain injury (TBI) results in significant disability due to cognitive deficits particularly in attention, learning and memory, and higher-order executive functions. The role of TBI in chronic neurodegeneration and the development of neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic Lateral Sclerosis (ALS) and most recently chronic traumatic encephalopathy (CTE) is of particular importance. However, despite significant effort very few therapeutic options exist to prevent or reverse cognitive impairment following TBI. In this review, we present experimental evidence of the known secondary injury mechanisms which contribute to neuronal cell loss, axonal injury, and synaptic dysfunction and hence cognitive impairment both acutely and chronically following TBI. In particular we focus on the mechanisms linking TBI to the development of two forms of dementia: AD and CTE. We provide evidence of potential molecular mechanisms involved in modulating Aβ and Tau following TBI and provide evidence of the role of these mechanisms in AD pathology. Additionally we propose a mechanism by which Aβ generated as a direct result of TBI is capable of exacerbating secondary injury mechanisms thereby establishing a neurotoxic cascade that leads to chronic neurodegeneration.

Brain injury-induced proteolysis is reduced in a novel calpastatin-overexpressing transgenic mouse

The calpain family of calcium-dependent proteases has been implicated in a variety of diseases and neurodegenerative pathologies. Prolonged activation of calpains results in proteolysis of numerous cellular substrates including cytoskeletal components and membrane receptors, contributing to cell demise despite coincident expression of calpastatin, the specific inhibitor of calpains. Pharmacological and gene-knockout strategies have targeted calpains to determine their contribution to neurodegenerative pathology; however, limitations associated with treatment paradigms, drug specificity, and genetic disruptions have produced inconsistent results and complicated interpretation. Specific, targeted calpain inhibition achieved by enhancing endogenous calpastatin levels offers unique advantages in studying pathological calpain activation. We have characterized a novel calpastatin-overexpressing transgenic mouse model, demonstrating a substantial increase in calpastatin expression within nervous system and peripheral tissues and associated reduction in protease activity. Experimental activation of calpains via traumatic brain injury resulted in cleavage of α-spectrin, collapsin response mediator protein-2, and voltage-gated sodium channel, critical proteins for the maintenance of neuronal structure and function. Calpastatin overexpression significantly attenuated calpain-mediated proteolysis of these selected substrates acutely following severe controlled cortical impact injury, but with no effect on acute hippocampal neurodegeneration. Augmenting calpastatin levels may be an effective method for calpain inhibition in traumatic brain injury and neurodegenerative disorders.

Pharmacological analysis of the cortical neuronal cytoskeletal protective efficacy of the calpain inhibitor SNJ-1945 in a mouse traumatic brain injury model

The efficacy of the amphipathic ketoamide calpain inhibitor SNJ-1945 in attenuating calpain-mediated degradation of the neuronal cytoskeletal protein α-spectrin was examined in the controlled cortical impact (CCI) traumatic brain injury (TBI) model in male CF-1 mice. Using a single early (15 min after CCI-TBI) i.p. bolus administration of SNJ-1945 (6.25, 12.5, 25, or 50-mg/kg), we identified the most effective dose on α-spectrin degradation in the cortical tissue of mice at its 24 h peak after severe CCI-TBI. We then investigated the effects of a pharmacokinetically optimized regimen by examining multiple treatment paradigms that varied in dose and duration of treatment. Finally, using the most effective treatment regimen, the therapeutic window of α-spectrin degradation attenuation was assessed by delaying treatment from 15 min to 1 or 3 h post-injury. The effect of SNJ-1945 on α-spectrin degradation exhibited a U-shaped dose-response curve when treatment was initiated 15 min post-TBI. The most effective 12.5 mg/kg dose of SNJ-1945 significantly reduced α-spectrin degradation by ~60% in cortical tissue. Repeated dosing of SNJ-1945 beginning with a 12.5 mg/kg dose did not achieve a more robust effect compared with a single bolus treatment, and the required treatment initiation was less than 1 h. Although calpain has been firmly established to play a major role in post-traumatic secondary neurodegeneration, these data suggest that even brain and cell-permeable calpain inhibitors, when administered alone, do not show sufficient cytoskeletal protective efficacy or a practical therapeutic window in a mouse model of severe TBI. Such conclusions need to be verified in the human clinical situation.

Effects of treating traumatic brain injury with collagen scaffolds and human bone marrow stromal cells on sprouting of corticospinal tract axons into the denervated side of the spinal cord

OBJECT

This study was designed to investigate how transplantation into injured brain of human bone marrow stromal cells (hMSCs) impregnated in collagen scaffolds affects axonal sprouting in the spinal cord after traumatic brain injury (TBI) in rats. Also investigated was the relationship of axonal sprouting to sensorimotor functional recovery after treatment.

METHODS

Adult male Wistar rats (n = 24) underwent a controlled cortical impact injury and were divided into three equal groups (8 rats/group). The two treatment groups received either hMSCs (3 × 10(6)) alone or hMSC (3 × 10(6))-impregnated collagen scaffolds transplanted into the lesion cavity. In the control group, saline was injected into the lesion cavity. All treatments were performed 7 days after TBI. On Day 21 after TBI, a 10% solution of biotinylated dextran amine (10,000 MW) was stereotactically injected into the contralateral motor cortex to label the corticospinal tract (CST) originating from this area. Sensorimotor function was tested using the modified neurological severity score (mNSS) and foot-fault tests performed on Days 1, 7, 14, 21, 28, and 35 after TBI. Spatial learning was tested with Morris water maze test on Days 31-35 after TBI. All rats were sacrificed on Day 35 after TBI, and brain and spinal cord (cervical and lumbar) sections were stained immunohistochemically for histological analysis.

RESULTS

Few biotinylated dextran amine-labeled CST fibers crossing over the midline were found in the contralateral spinal cord transverse sections at both cervical and lumbar levels in saline-treated (control) rats. However, hMSC-alone treatment significantly increased axonal sprouting from the intact CST into the denervated side of the gray matter of both cervical and lumbar levels of the spinal cord (p < 0.05). Also, this axonal sprouting was significantly more in the scaffold+hMSC group compared with the hMSC-alone group (p < 0.05). Sensorimotor functional analysis showed significant improvement of mNSS (p < 0.05) and foot-fault tests (p < 0.05) in hMSC-alone and scaffold+hMSC-treated rats compared with controls (p < 0.05). Functional improvement, however, was significantly greater in the scaffold+hMSC group compared with the hMSC-alone group (p < 0.05). Morris water maze testing also showed significant improvement in spatial learning in scaffold+hMSC and hMSC-alone groups compared with the control group (p < 0.05), with rats in the scaffold+hMSC group performing significantly better than those in the hMSC-alone group (p < 0.05). Pearson correlation data showed significant correlation between the number of crossing CST fibers detected and sensorimotor recovery (p < 0.05).

CONCLUSIONS

Axonal plasticity plays an important role in neurorestoration after TBI. Transplanting hMSCs with scaffolds enhances the effect of hMSCs on axonal sprouting of CST fibers from the contralateral intact cortex into the denervated side of spinal cord after TBI. This enhanced axonal regeneration may at least partially contribute to the therapeutic benefits of treating TBI with hMSCs.

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.

Targeted gene inactivation of calpain-1 suppresses cortical degeneration due to traumatic brain injury and neuronal apoptosis induced by oxidative stress

Calpains are calcium-regulated cysteine proteases that have been implicated in the regulation of cell death pathways. Here, we used our calpain-1 null mouse model to evaluate the function of calpain-1 in neural degeneration following a rodent model of traumatic brain injury. In vivo, calpain-1 null mice show significantly less neural degeneration and apoptosis and a smaller contusion 3 days post-injury than wild type littermates. Protection from traumatic brain injury corroborated with the resistance of calpain-1 neurons to apoptosis induced by oxidative stress. Biochemical analysis revealed that caspase-3 activation, extracellular calcium entry, mitochondrial membrane permeability, and release of apoptosis-inducing factor from mitochondria are partially blocked in the calpain-1 null neurons. These findings suggest that the calpain-1 knock-out mice may serve as a useful model system for neuronal protection and apoptosis in traumatic brain injury and other neurodegenerative disorders in which oxidative stress plays a role.

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.

Mild traumatic brain injury (MTBI) leads to spatial learning deficits

PRIMARY OBJECTIVE

The aim of this study was to investigate the effect of mild and severe TBI on young male Wistar rats' spatial learning.

RESEARCH DESIGN

Randomized repeated measure experimental design was used to examine spatial learning in three independent animal groups.

METHODS AND PROCEDURES

Twenty-four (severe n = 9, mild n = 8, sham n = 7) male rats were included in the study. Animals received controlled mild (1.5 mm), severe (2.5 mm) cortical impact injury or sham surgery. Spatial learning was assessed daily using a modified Morris water maze test, 20 days post-trauma, for 5 consecutive days. Percentage time travelled within each quadrant and escape latency were calculated. All animals' hippocampal brain regions were examined post-injury using neuron (MAP2) and pre-synaptic protein (Synaptophysin) biomarkers.

MAIN OUTCOMES AND RESULTS

It took the animals with mild injury until day 3 to reach the platform; and animals with mild and severe injury spent significantly less time in the target quadrant than the sham. The hippocampal neuron numbers differed proportionately between animals with severe and mild injury, but the percentage of synaptophysin density was significantly less in the dentate gyrus of both animals with mild and severe injury than sham group.

CONCLUSION

Persistent spatial learning deficits exist after mild TBI; these deficits appear equivalent to deficits exhibited after a more severe injury.

An in situ method for the examination of calcium-dependent proteolysis

Proteases are involved in a multitude of cellular processes that are critical for the maintenance of normal cell function, and their aberrant activity has been linked to a large number of diseases. Calcium-dependent proteases (calpains) are found in cells distributed throughout the brain, and their activity contributes to normal and abnormal brain function. A limitation with common approaches to studying the activity of calpain is the requirement for homogenization of tissue samples, which limits the ability to resolve the spatial location of protease activity, and which also introduces the possibility of interaction with endogenous inhibitors that would have otherwise been kept spatially separated in vivo. We present a simple method for the investigation of protease activity that provides better spatial resolution than alternatives, and that alleviates the concern of protein interactions in homogenate. We examined calcium-dependent proteolysis in tissue sections by observation of a fluorescence signal produced by fragmentation of a casein substrate embedded in an agarose gel solution that covered the section. This technique preserved the anatomical characteristics of the tissue, and provided spatial resolution sufficient for ready examination of protease activity in cells and in blood vessels within a single tissue section.

Pharmacological inhibition of lipid peroxidation attenuates calpain-mediated cytoskeletal degradation after traumatic brain injury

Free radical-induced lipid peroxidation (LP) is critical in the evolution of secondary injury following traumatic brain injury (TBI). Previous studies in our laboratory demonstrated that U-83836E, a potent LP inhibitor, can reduce post-TBI LP along with an improved maintenance of mouse cortical mitochondrial bioenergetics and calcium (Ca(2+)) buffering following severe (1.0 mm; 3.5 m/s) controlled cortical impact TBI (CCI-TBI). Based upon this preservation of a major Ca(2+) homeostatic mechanism, we have now performed dose-response and therapeutic window analyses of the ability of U-83836E to reduce post-traumatic calpain-mediated cytoskeletal (α-spectrin) proteolysis in ipsilateral cortical homogenates at its 24 h post-TBI peak. In the dose-response analysis, mice were treated with a single i.v. dose of vehicle or U-83836E (0.1, 0.3, 1.3, 3.0, 10.0 or 30.0 mg/kg) at 15 min after injury. U-83836E produced a dose-related attenuation of α-spectrin degradation with the maximal decrease being achieved at 3.0 mg/kg. Next, the therapeutic window was tested by delaying the single 3 mg/kg i.v. dose from 15 min post-injury out to 1, 3, 6 or 12 h. No reduction in α-spectrin degradation was observed when the treatment delay was 1 h or longer. However, in a third experiment, we re-examined the window with repeated U-83836E dosing (3.0 mg/kg i.v. followed by 10 mg/kg i.p. maintenance doses at 1 and 3 h after the initial i.v. dose) which significantly reduced 24 h α-α-spectrin degradation even when treatment initiation was withheld until 12 h post-TBI. These results demonstrate the relationship between post-TBI LP, disruptions in neuronal Ca(2+) homeostasis and calpain-mediated cytoskeletal damage.

A pharmacological analysis of the neuroprotective efficacy of the brain- and cell-permeable calpain inhibitor MDL-28170 in the mouse controlled cortical impact traumatic brain injury model

The cytoskeletal and neuronal protective effects of early treatment with the blood-brain barrier- and cell-permeable calpain inhibitor MDL-28170 was examined in the controlled cortical impact (CCI) traumatic brain injury (TBI) model in male CF-1 mice. This was preceded by a dose-response and pharmacodynamic evaluation of IV or IP doses of MDL-28170 with regard to ex vivo inhibition of calpain 2 activity in harvested brain homogenates. From these data, we tested the effects of an optimized MDL-28170 dosing regimen on calpain-mediated degradation of the neuronal cytoskeletal protein α-spectrin in cortical or hippocampal tissue of mice 24 h after CCI-TBI (1.0 mm depth, 3.5 m/sec velocity). With treatment initiated at 15 min post-TBI, α-spectrin degradation was significantly reduced by 40% in hippocampus and 44% in cortex. This effect was still observed with a 1-h but not a 3-h post-TBI delay. The cytoskeletal protection is most likely taking place in neurons surrounding the area of mainly necrotic degeneration, since MDL-28170 did not reduce hemispheric lesion volume as measured by the aminocupric silver staining method. This lack of effect on lesion volume has been seen with other calpain inhibitors, which suggests that pharmacological calpain inhibition by itself, while able to reduce axonal injury, may not be able to produce a measurable reduction in lesion volume. This is in contrast to certain other neuroprotective mechanistic approaches such as the mitochondrial protectant cyclosporine A, which produces at least a partial decrease in lesion volume in the same model. Accordingly, the combination of a calpain inhibitor with a compound such as cyclosporine A may be needed to achieve the optimal degree of post-TBI neuroprotection.

Dual vulnerability of tau to calpains and caspase-3 proteolysis under neurotoxic and neurodegenerative conditions

Axonally specific microtubule-associated protein tau is an important component of neurofibrillary tangles found in AD (Alzheimer's disease) and other tauopathy diseases such as CTE (chronic traumatic encephalopathy). Such tau aggregate is found to be hyperphosphorylated and often proteolytically fragmented. Similarly, tau is degraded following TBI (traumatic brain injury). In the present study, we examined the dual vulnerability of tau to calpain and caspase-3 under neurotoxic and neurodegenerative conditions. We first identified three novel calpain cleavage sites in rat tau (four-repeat isoform) as Ser130↓Lys131, Gly157↓Ala158 and Arg380↓Glu381. Fragment-specific antibodies to target the major calpain-mediated TauBDP-35K (35 kDa tau-breakdown product) and the caspase-mediated TauBDP-45K respectively were developed. In rat cerebrocortical cultures treated with excitotoxin [NMDA (N-methyl-D-aspartate)], tau is significantly degraded into multiple fragments, including a dominant signal of calpain-mediated TauBDP-35K with minimal caspase-mediated TauBDP-45K. Following apoptosis-inducing EDTA treatment, tau was truncated only to TauBDP-48K/45K-exclusively by caspase. Cultures treated with another apoptosis inducer STS (staurosporine), dual fragmentation by calpain (TauBDP-35K) and caspase-3 (TauBDP-45K) was observed. Tau was also fragmented in injured rat cortex following TBI in vivo to BDPs of 45-42 kDa (minor), 35 kDa and 15 kDa, followed by TauBDP-25K. Calpain-mediated TauBDP-35K-specific antibody confirmed robust signals in the injured cortex, while caspase-mediated TauBDP-45K-specific antibody only detected faint signals. Furthermore, intravenous administration of a calpain-specific inhibitor SNJ-1945 strongly suppressed the TauBDP-35K formation. Taken together, these results suggest that tau protein is dually vulnerable to calpain and caspase-3 proteolysis under different neurotoxic and injury conditions.

Postinjury estrogen treatment of chronic spinal cord injury improves locomotor function in rats

Spinal cord injury (SCI) causes loss of neurological function and, depending on serverity, may cause paralysis. The only recommended pharmacotherapy for the treatment of SCI is high-dose methylprednisolone, and its use is controversial. We have previously shown that estrogen treatment attenuated cell death, axonal and myelin damage, calpain and caspase activities, and inflammation in acute SCI. The aim of this study was to examine whether posttreatment of SCI with estrogen would improve locomotor function by protecting cells and axons and reducing inflammation during the chronic phase following injury. Moderately severe injury (40 g . cm force) was induced in male Sprague-Dawley rats following laminectomy at T10. Three groups of animals were used: sham (laminectomy only), vehicle (dimethyl sulfoxide; DMSO)-treated injury group, and estrogen-treated injury group. Animals were treated with 4 mg/kg estrogen at 15 min and 24 hr postnjury, followed by 2 mg/kg estrogen daily for the next 5 days. After treatment, animals were sacrificed at the end of 6 weeks following injury, and 1-cm segments of spinal cord (lesion, rostral to lesion, and caudal to lesion) were removed for biochemical analyses. Estrogen treatment reduced COX-2 activity, blocked nuclear factor-kappaB translocation, prevented glial reactivity, attenuated neuron death, inhibited activation and activity of calpain and caspase-3, decreased axonal damage, reduced myelin loss in the lesion and penumbra, and improved locomotor function compared with vehicle-treated animals. These findings suggest that estrogen may be useful as a promising therapeutic agent for prevention of damage and improvement of locomotor function in chronic SCI. (c) 2010 Wiley-Liss, Inc.

Dendritic alterations after dynamic axonal stretch injury in vitro

Traumatic axonal injury (TAI) is the most common and important pathology of traumatic brain injury (TBI). However, little is known about potential indirect effects of TAI on dendrites. In this study, we used a well-established in vitro model of axonal stretch injury to investigate TAI-induced changes in dendrite morphology. Axons bridging two separated rat cortical neuron populations plated on a deformable substrate were used to create a zone of isolated stretch injury to axons. Following injury, we observed the formation of dendritic alterations or beading along the dendrite shaft. Dendritic beading formed within minutes after stretch then subsided over time. Pharmacological experiments revealed a sodium-dependent mechanism, while removing extracellular calcium exacerbated TAI's effect on dendrites. In addition, blocking ionotropic glutamate receptors with the N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 prevented dendritic beading. These results demonstrate that axon mechanical injury directly affects dendrite morphology, highlighting an important bystander effect of TAI. The data also imply that TAI may alter dendrite structure and plasticity in vivo. An understanding of TAI's effect on dendrites is important since proper dendrite function is crucial for normal brain function and recovery after 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.

Calpain inhibition reduces axolemmal leakage in traumatic axonal injury

Calcium-induced, calpain-mediated proteolysis (CMSP) has recently been implicated to the pathogenesis of diffuse (traumatic) axonal injury (TAI). Some studies suggested that subaxolemmal CMSP may contribute to axolemmal permeability (AP) alterations observed in TAI. Seeking direct evidence for this premise we investigated whether subaxolemmal CMSP may contribute to axolemmal permeability alterations (APA) and pre-injury calpain-inhibition could reduce AP in a rat model of TAI. Horseradish peroxidase (HRP, a tracer that accumulates in axons with APA) was administered one hour prior to injury into the lateral ventricle; 30 min preinjury a single tail vein bolus injection of 30 mg/kg MDL-28170 (a calpain inhibitor) or its vehicle was applied in Wistar rats exposed to impact acceleration brain injury. Histological detection of traumatically injured axonal segments accumulating HRP and statistical analysis revealed that pre-injury administration of the calpain inhibitor MDL-28170 significantly reduced the average length of HRP-labeled axonal segments. The axono-protective effect of pre-injury calpain inhibition recently demonstrated with classical immunohistochemical markers of TAI was further corroborated in this experiment; significant reduction of the length of labeled axons in the drug-treated rats implicate CMSP in the progression of altered AP in TAI.

Long-term benefits after treatment of traumatic brain injury with simvastatin in rats

OBJECTIVE

This study was designed to investigate the long-term effects of simvastatin treatment after traumatic brain injury (TBI) in rats.

METHODS

Adult female Wistar rats (n = 24) were injured with controlled cortical impact and divided into 3 groups. The first 2 groups were treated with simvastatin (0.5 or 1.0 mg/kg) administered orally for 14 days starting 1 day after TBI. The third group (control) received phosphate-buffered saline orally for 14 days. Neurological functional outcome was measured with modified neurological severity scores performed 1 day before TBI; on days 1, 4, 7, 14 after TBI; and biweekly thereafter. All animals were sacrificed 3 months after TBI. Brain tissues of half of the animals were processed for preparation of paraffin-embedded sections for immunohistological studies. The remaining half were frozen for enzyme-linked immunosorbent assay studies for quantification of brain-derived neurotrophic factor (BDNF) in the hippocampus and cortex.

RESULTS

The results showed that both doses of simvastatin significantly improved functional outcome compared with the control, with no difference between the 2 doses. Simvastatin treatment of 1.0 mg/kg increased the number of morphologically intact neurons in the hippocampus, but treatment of 0.5 mg/kg had no significant effect. Enzyme-linked immunosorbent assay studies showed that 0.5 mg/kg simvastatin significantly increased BDNF levels within the hippocampus, but 1.0 mg/kg had no significant effect. Neither dose had any effect on BDNF levels within the cortex.

CONCLUSION

Simvastatin treatment provides long-lasting functional improvement after TBI in rats. It also enhances neuronal survival in the hippocampus and increases BDNF levels in the hippocampus secondary to simvastatin treatment.

Long-lasting benefits after treatment of traumatic brain injury (TBI) in rats with combination therapy of marrow stromal cells (MSCs) and simvastatin

This study was designed to investigate the beneficial effects of combination therapy of simvastatin and marrow stromal cells (MSCs) in improving functional outcome after traumatic brain injury (TBI) in rats. Adult female Wistar rats (n=72 and 8, per group) were injured with controlled cortical impact and treated either with monotherapy of MSCs or simvastatin or a combination therapy of these two agents. Different combination doses were tested, and nine groups of animals were studied. Neurological function was evaluated using Modified Neurological Severity Score (MNSS), and animals were sacrificed 3 months after injury. Coronal brain sections were stained with standard hematoxylin and eosin immunohistochemistry. Our results showed that, though functional improvement was seen with monotherapies of MSCs and simvastatin, the combination therapy when used in optimal doses was significantly better in improving functional outcome. This improvement was long lasting and persisted until the end of the trial (3 months). The optimum combination dose was 0.5mg of simvastatin combined with 2 x 10(6) MSCs. Post mortem analysis showed the presence of donor MSCs within the injured cortex. Endogenous cellular proliferation induced by the neurorestorative treatments was also observed in the lesion boundary zone. Our data show that MSCs and simvastatin have a synergistic effect in improving functional outcome after TBI.

Stimulating neuroregeneration as a therapeutic drug approach for traumatic brain injury

Traumatic brain injury, a silent epidemic of modern societies, is a largely neglected area in drug development and no drug is currently available for the treatment of patients suffering from brain trauma. Despite this grim situation, much progress has been made over the last two decades in closely related medical indications, such as spinal cord injury, giving rise to a more optimistic approach to drug development in brain trauma. Fundamental insights have been gained with animal models of central nervous system (CNS) trauma and spinal cord injury. Neuroregenerative drug candidates have been identified and two of these have progressed to clinical development for spinal cord injury patients. If successful, these drug candidates may be used to treat brain trauma patients. Significant progress has also been made in understanding the fundamental molecular mechanism underlying irreversible axonal growth arrest in the injured CNS of higher mammals. From these studies, we have learned that the axonal retraction bulb, previously regarded as a marker for failure of regenerative growth, is not static but dynamic and, therefore, amenable to pharmacotherapeutic approaches. With the development of modified magnetic resonance imaging methods, fibre tracts can be visualised in the living human brain and such imaging methods will soon be used to evaluate the neuroregenerative potential of drug candidates. These significant advances are expected to fundamentally change the often hopeless situation of brain trauma patients and will be the first step towards overcoming the silent epidemic of brain injury.