Neuroprotection with a calpain inhibitor in a model of focal cerebral ischemia

The Role of Necroptosis in Cerebral Ischemic Stroke

Cerebral ischemia, also known as ischemic stroke, accounts for nearly 85% of all strokes and is the leading cause of disability worldwide. Due to disrupted blood supply to the brain, cerebral ischemic injury is trigged by a series of complex pathophysiological events including excitotoxicity, oxidative stress, inflammation, and cell death. Currently, there are few treatments for cerebral ischemia owing to an incomplete understanding of the molecular and cellular mechanisms. Accumulated evidence indicates that various types of programmed cell death contribute to cerebral ischemic injury, including apoptosis, ferroptosis, pyroptosis and necroptosis. Among these, necroptosis is morphologically similar to necrosis and is mediated by receptor-interacting serine/threonine protein kinase-1 and -3 and mixed lineage kinase domain-like protein. Necroptosis inhibitors have been shown to exert inhibitory effects on cerebral ischemic injury and neuroinflammation. In this review, we will discuss the current research progress regarding necroptosis in cerebral ischemia as well as the application of necroptosis inhibitors for potential therapeutic intervention in ischemic stroke.

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.

PACAP-derived mutant peptide MPAPO protects trigeminal ganglion cell and the retina from hypoxic injury through anti-oxidative stress, anti-apoptosis, and promoting axon regeneration

The purpose of this study was to determine whether the MPAPO, derived peptide of pituitary adenylate cyclase-activating polypeptide (PACAP), would protect trigeminal ganglion cells (TGCs) and the mice retinas from a hypoxic insult. The nerve endings of the ophthalmic nerve of the trigeminal nerve are widely distributed in eye tissues. In TGCs after hypoxia exposure, we discovered that reactive oxygen species level, the contents of cytosolic cytochrome c and cleaved-caspase-3 were significantly increased, in the meanwhile, m-Calpain was activated and cytoskeleton proteins (αII-spectrin and Synapsin) were degraded, neurites of TGCs disappeared, but these effects were reversed in TGCs treated with MPAPO. The structure of the mice retinas after hypoxic exposure was disordered. Increased lipid peroxidation (LPO), decreased glutathione (GSH) levels, and decreased superoxide dismutase (SOD) activity, positive cells of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), the disintegration of nerve fibers was examined in the retinas following a hypoxic insult. Disordered retina was attenuated with MPAPO eye drops, as well as hypoxia-induced apoptosis in the developing retina, increase in LPO, and decrease in GSH levels and SOD activity of the retina. Moreover, the disintegrated retinal nerve fibers were reassembled after MPAPO treatment. These results suggest that hypoxia induces oxidative stress, apoptosis, and neurites disruption, while MPAPO is remarkably protective against these adverse effects of hypoxia in TGCs and the developing retinas by specifically activating PAC1 receptor.

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.

Dietary docosahexaenoic acid inhibits neurodegeneration and prevents stroke

Stroke severely impairs quality of life and has a high mortality rate. On the other hand, dietary docosahexaenoic acid (DHA) prevents neuronal damage. In this review, we describe the effects of dietary DHA on ischemic stroke-associated neuronal damage and its role in stroke prevention. Recent epidemiological studies have been conducted to analyze stroke prevention through DHA intake. The effects of dietary intake and supply of DHA to neuronal cells, DHA-mediated inhibition of neuronal damage, and its mechanism, including the effects of the DHA metabolite, neuroprotectin D1 (NPD1), were investigated. These studies revealed that DHA intake was associated with a reduced risk of stroke. Moreover, studies have shown that DHA intake may reduce stroke mortality rates. DHA, which is abundant in fish oil, passes through the blood-brain barrier to accumulate as a constituent of phospholipids in the cell membranes of neuronal cells and astrocytes. Astrocytes supply DHA to neuronal cells, and neuronal DHA, in turn, activates Akt and Raf-1 to prevent neuronal death or damage. Therefore, DHA indirectly prevents neuronal damage. Furthermore, NDP1 blocks neuronal apoptosis. DHA, together with NPD1, may block neuronal damage and prevent stroke. The inhibitory effect on neuronal damage is achieved through the antioxidant (via inducing the Nrf2/HO-1 system) and anti-inflammatory effects (via promoting JNK/AP-1 signaling) of DHA.

Calpain-mediated cleavage of Fbxw7 during excitotoxicity

Neuronal cell death induced by ischemic injury has been attributed to glutamate receptor-mediated excitotoxicity, which is known to be accompanied by Ca²⁺ overload in the cytoplasm with concomitant activation of calcium-dependent mechanisms. More specifically, the overactivation of calpains, calcium-dependent cysteine proteases, have been associated with neuronal cell death following glutamate treatment. Previously, we observed decreased expression levels of F-box/WD repeat domain-containing protein 7 (Fbxw7) after the hyperactivation of cyclin-dependent kinase 5 (Cdk5) in cortical neurons challenged with glutamate. As determined using in vitro calpain cleavage assays, we demonstrated that the cleavage of Fbxw7 was mediated by activated calpain and attenuated in the presence of the calpain inhibitor, calpeptin. Using the rat middle cerebral artery occlusion model, we confirmed that Fbxw7 was indeed cleaved by activated calpain in the ipsilateral cortex. Based on our data, we hypothesize that the negative regulation of Fbxw7 by calpain may contribute to neuronal cell death and that the preservation of Fbxw7 by the inhibition of calpain, Cdk5, or both composes a novel protective mechanism following excitotoxicity.

Structural Insights into the Unique Activation Mechanisms of a Non-classical Calpain and Its Disease-Causing Variants

Increased calpain activity is linked to neuroinflammation including a heritable retinal disease caused by hyper-activating mutations in the calcium-activated calpain-5 (CAPN5) protease. Although structures for classical calpains are known, the structure of CAPN5, a non-classical calpain, remains undetermined. Here we report the 2.8 Å crystal structure of the human CAPN5 protease core (CAPN5-PC). Compared to classical calpains, CAPN5-PC requires high calcium concentrations for maximal activity. Structure-based phylogenetic analysis and multiple sequence alignment reveal that CAPN5-PC contains three elongated flexible loops compared to its classical counterparts. The presence of a disease-causing mutation (c.799G>A, p.Gly267Ser) on the unique PC2L2 loop reveals a function in this region for regulating enzymatic activity. This mechanism could be transferred to distant calpains, using synthetic calpain hybrids, suggesting an evolutionary mechanism for fine-tuning calpain function by modifying flexible loops. Further, the open (inactive) conformation of CAPN5-PC provides structural insight into CAPN5-specific residues that can guide inhibitor design.

Zinc induces CDK5 activation and neuronal death through CDK5-Tyr15 phosphorylation in ischemic stroke

CDK5 activation promotes ischemic neuronal death in stroke, with the recognized activation mechanism being calpain-dependent p35 cleavage to p25. Here we reported that CDK5-Tyr15 phosphorylation by zinc induced CDK5 activation in brain ischemic injury. CDK5 activation and CDK5-Tyr15 phosphorylation were observed in the hippocampus of the rats that had been subjected to middle cerebral artery occlusion, both of which were reversed by pretreatment with zinc chelator; while p35 cleavage and calpain activation in ischemia were not reversed. Zinc incubation resulted in CDK5-Tyr15 phosphorylation and CDK5 activation, without increasing p35 cleavage in cultured cells. Site mutation experiment confirmed that zinc-induced CDK5 activation was dependent on Tyr15 phosphorylation. Further exploration showed that Src kinase contributed to zinc-induced Tyr15 phosphorylation and CDK5 activation. Src kinase inhibition or expression of an unphosphorylable mutant Y15F-CDK5 abolished Tyr15 phosphorylation, prevented CDK5 activation and protected hippocampal neurons from ischemic insult in rats. We conclude that zinc-induced CDK5-Tyr15 phosphorylation underlies CDK5 activation and promotes ischemic neuronal death in stroke.

Newer pharmacological approaches for antioxidant neuroprotection in traumatic brain injury

Reactive oxygen species-induced oxidative damage remains an extensively validated secondary injury mechanism in traumatic brain injury (TBI) as demonstrated by the efficacy of various pharmacological antioxidants agents in decreasing post-traumatic free radical-induced lipid peroxidation (LP) and protein oxidative damage in preclinical TBI models. Based upon strong preclinical efficacy results, two antioxidant agents, the superoxide radical scavenger polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) and the 21-aminosteroid LP inhibitor tirilazad, which inhibits lipid peroxidation, (LP) were evaluated in large phase III trials in moderately- and severely-injured TBI patients. Both failed to improve 6 month survival and neurological recovery. However, in the case of tirilazad, a post hoc analysis revealed that the drug significantly improved survival of male TBI patients who exhibited traumatic subarachnoid hemorrhage (tSAH) that occurs in half of severe TBIs. In addition to reviewing the clinical trial results with PEG-SOD and tirilazad, newer antioxidant approaches which appear to improve neuroprotective efficacy and provide a longer therapeutic window in rodent TBI models will be presented. The first approach involves pharmacological enhancement of the multi-mechanistic Nrf2-antioxidant response element (ARE) pathway. The second involves scavenging of the neurotoxic LP-derived carbonyl compounds 4-hydroxynonenal (4-HNE) and acrolein which are highly damaging to neural protein and stimulate additional free radical generation. A third approach combines mechanistically complimentary antioxidants to interrupt post-TBI oxidative neurodegeneration at multiple points in the secondary injury cascade. These newer strategies appear to decrease variability in the neuroprotective effect which should improve the feasibility of achieving successful translation of antioxidant therapy to TBI patients.

Neuronal Cell Death

Neuronal cell death occurs extensively during development and pathology, where it is especially important because of the limited capacity of adult neurons to proliferate or be replaced. The concept of cell death used to be simple as there were just two or three types, so we just had to work out which type was involved in our particular pathology and then block it. However, we now know that there are at least a dozen ways for neurons to die, that blocking a particular mechanism of cell death may not prevent the cell from dying, and that non-neuronal cells also contribute to neuronal death. We review here the mechanisms of neuronal death by intrinsic and extrinsic apoptosis, oncosis, necroptosis, parthanatos, ferroptosis, sarmoptosis, autophagic cell death, autosis, autolysis, paraptosis, pyroptosis, phagoptosis, and mitochondrial permeability transition. We next explore the mechanisms of neuronal death during development, and those induced by axotomy, aberrant cell-cycle reentry, glutamate (excitoxicity and oxytosis), loss of connected neurons, aggregated proteins and the unfolded protein response, oxidants, inflammation, and microglia. We then reassess which forms of cell death occur in stroke and Alzheimer's disease, two of the most important pathologies involving neuronal cell death. We also discuss why it has been so difficult to pinpoint the type of neuronal death involved, if and why the mechanism of neuronal death matters, the molecular overlap and interplay between death subroutines, and the therapeutic implications of these multiple overlapping forms of neuronal death.

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.

Cerebral ischemic damage in diabetes: an inflammatory perspective

Stroke is one of the leading causes of death worldwide. A strong inflammatory response characterized by activation and release of cytokines, chemokines, adhesion molecules, and proteolytic enzymes contributes to brain damage following stroke. Stroke outcomes are worse among diabetics, resulting in increased mortality and disabilities. Diabetes involves chronic inflammation manifested by reactive oxygen species generation, expression of proinflammatory cytokines, and activation/expression of other inflammatory mediators. It appears that increased proinflammatory processes due to diabetes are further accelerated after cerebral ischemia, leading to increased ischemic damage. Hypoglycemia is an intrinsic side effect owing to glucose-lowering therapy in diabetics, and is known to induce proinflammatory changes as well as exacerbate cerebral damage in experimental stroke. Here, we present a review of available literature on the contribution of neuroinflammation to increased cerebral ischemic damage in diabetics. We also describe the role of hypoglycemia in neuroinflammation and cerebral ischemic damage in diabetics. Understanding the role of neuroinflammatory mechanisms in worsening stroke outcome in diabetics may help limit ischemic brain injury and improve clinical outcomes.

Gonadal steroids block the calpain-1-dependent intrinsic pathway of apoptosis in an experimental rat stroke model

OBJECTIVES

Apoptosis plays an important role in the progression of the ischemic penumbra after reperfusion. Estrogen and progesterone have neuroprotective effects against ischemic brain damage, however the exact mechanisms of neuroprotection and signaling pathways is not completely understood. In this study, we investigated the possible regulatory effects of a combined steroid treatment on extrinsic and intrinsic apoptotic signaling pathways after cerebral ischemia.

METHODS

Adult male Wistar rats were subjected to transient middle cerebral artery occlusion (tMCAO) using an intraluminal filament technique for 1 h followed by 23 h reperfusion. Estrogen and progesterone were immediately injected after tMCAO subcutaneously. Sensorimotor functional tests and the infarct volume were evaluated 24 h after ischemia. Protein expression of calpain-1 and Fas receptor (FasR), key members of intrinsic and extrinsic apoptosis, were determined in the penumbra region of the ischemic brain using western blot analysis, immunohistochemistry, and TUNEL staining.

RESULTS

Neurological deficits and infarct volume were significantly reduced following hormone therapy. Calpain-1 up-regulation and caspase-3 activation were apparent 24 h after ischemia in the peri-infarct area of the cerebral cortex. Steroid hormone treatment reduced infarct pathology and attenuated the induction of both proteases. FasR protein levels were not affected by ischemia and hormone application.

CONCLUSION

We conclude that a combined steroid treatment inhibits ischemia-induced neuronal apoptosis through the regulation of intrinsic pathways.

Effects of calpain on sevoflurane-induced aged rats hippocampal neuronal apoptosis

BACKGROUND

Sevoflurane is one of the most commonly used volatile anesthetics and it has been shown to induce widespread apoptotic neurodegeneration in aged rat. Calpain is also activated during apoptosis in several types of cells. We hypothesized that calpain resulted in apoptosis under long time sevoflurane exposure, and it might play a role in the sevoflurane-induced memory impairment in aged rats.

METHODS

Seventy-two 18-month-old male Sprague-Dawley rats were randomly divided into three groups (n = 24): Control group rats were exposed to simply humid 50 % O2 balanced by N2 for 3 h; While M group rats received calpain inhibitor 10 mg/kg via the tail vein intravenously at 30 min before the animals inhaled 3 % sevoflurane for 3 h, subsequently received MDL 28170 3.33 mg/kg/h for 3 h. Sev group rats were only exposed to 3 % sevoflurane for 3 h without calpain inhibitor. Morris Water Maze was used to test the ability of learning and memory. Cytosolic calcium concentration was measured by using flow cytometry. Annexin-V labeled with a fluorophore or biotin can identify apoptotic cells by binding to PS. The expression of calpain in the hippocampus of rats was tested by Western blots.

RESULTS

The results showed that the M group had a shorter latency and had a larger number of times crossing over the previous platform site than that of the Sev group. Compared with Sev group, apoptosis rate and 76/80 kDa ratio of μ-calpain were significantly decreased in M group on the 1st day.

CONCLUSIONS

Sevoflurane might induce apoptosis through increasing [Ca(2+)]c and the activity of μ-calpain, which might be identified at least partially the molecular mechanism by which sevoflurane induces apoptosis.

Review : Neuroprotection in Brain Ischemia: An Update (Part II

Ischemic brain injury produced by stroke or cardiac arrest is a major cause of human neurological disability. Steady advances in the neurosciences have elucidated the pathophysiological mechanisms of brain ischemia and have suggested many therapeutic approaches to achieve neuroprotection of the acutely ischemic brain that are directed at specific injury mechanisms. In the second portion of this two-part review, the following potential therapeutic approaches to acute ischemic injury are considered: 1) modulation of nonglutamatergic neurotransmission, including monoaminergic systems (dopamine, norepinephrine, serotonin), γ-aminobutyric acid, and adenosine; 2) mild-to-moderate therapeutic hypothermia; 3) calcium channel antagonism; 4) an tagonism of oxygen free radicals; 5) modulation of the nitric oxide system; 6) antagonism of cytoskeletal proteolysis; 7) growth factor administration; 8) therapy directed at cellular mediators of injury; and 9) the rationale for combination pharmacotherapy. The Neuroscientist 1:164-175, 1995

Involvement of calpains in adult neurogenesis: implications for stroke

Calpains are ubiquitous proteases involved in cell proliferation, adhesion and motility. In the brain, calpains have been associated with neuronal damage in both acute and neurodegenerative disorders, but their physiological function in the nervous system remains elusive. During brain ischemia, there is a large increase in the levels of intracellular calcium, leading to the activation of calpains. Inhibition of these proteases has been shown to reduce neuronal death in a variety of stroke models. On the other hand, after stroke, neural stem cells (NSC) increase their proliferation and newly formed neuroblasts migrate towards the site of injury. However, the process of forming new neurons after injury is not efficient and finding ways to improve it may help with recovery after lesion. Understanding the role of calpains in the process of neurogenesis may therefore open a new window for the treatment of stroke. We investigated the involvement of calpains in NSC proliferation and neuroblast migration in two highly neurogenic regions in the mouse brain, the dentate gyrus (DG) and the subventricular zone (SVZ). We used mice that lack calpastatin, the endogenous calpain inhibitor, and calpains were also modulated directly, using calpeptin, a pharmacological calpain inhibitor. Calpastatin deletion impaired both NSC proliferation and neuroblast migration. Calpain inhibition increased NSC proliferation, migration speed and migration distance in cells from the SVZ. Overall, our work suggests that calpains are important for neurogenesis and encourages further research on their neurogenic role. Prospective therapies targeting calpain activity may improve the formation of new neurons following stroke, in addition to affording neuroprotection.

Protective effect of grape seed and skin extract on cerebral ischemia in rat: implication of transition metals

Ischemic stroke is a leading cause of long lasting disability in humans and oxidative stress an important underlying cause. The present study aims to determine the effect of short term (seven-days) administration of high dosage grape seed and skin extract (GSSE 2.5 g/kg) on ischemia/reperfusion (I/R) injury in a rat model of global ischemia. Ischemia was induced by occlusion of the common carotid arteries for 30 min followed by one-hour reperfusion on control or GSSE treated animals. I/R induced a drastic oxidative stress characterized by high lipid and protein oxidation, a drop in antioxidant enzyme defenses, disturbed transition metals as free iron overload and depletion of copper, zinc and manganese as well as of associated brain enzyme activities as glutamine synthetase and lactate dehydrogenase. I/R also induced NO and calcium disruption and an increase in calpain activity, a calcium-sensitive cysteine protease. Interestingly, almost all I/R-induced disturbances were prevented by GSSE pretreatment as oxidative stress, transition metals associated enzyme activities, brain damage size and histology. Owing to its antioxidant potential, high dosage GSSE protected efficiently the brain against ischemic stroke and should be translated to humans.

Beneficial effects of antecedent exercise training on limb motor function and calpain expression in a rat model of stroke

[Purpose] In the present study, we investigated the effects of antecedent exercise on functional recovery and calpain protein expression following focal cerebral ischemia injury. [Subjects and Methods] The rat middle cerebral artery occlusion model was employed. Adult male Sprague-Dawley rats were randomly divided into 4 groups. Group I comprised untreated normal rats (n=10); Group II comprised untreated rats with focal cerebral ischemia (n=10); Group III comprised rats that performed treadmill exercise (20 m/min) training after focal cerebral ischemia (n=10); and Group IV comprised rats that performed antecedent treadmill exercise (20 m/min) training before focal cerebral ischemia (n=10). At different time points (1, 7, 14, and 21 days), limb placement test score and the levels of calpain protein in the hippocampus were examined. [Results] In the antecedent exercise group, improvements in the motor behavior index (limb placement test) were observed and hippocampal calpain protein levels were decreased. [Conclusion] These results indicated that antecedent treadmill exercise prior to focal cerebral ischemia exerted neuroprotective effects against ischemic brain injury by improving motor performance and decreasing the levels of calpain expression. Furthermore, these results suggest that antecedent treadmill exercise of an appropriate intensity is critical for post-stroke rehabilitation.

Design, synthesis, and optimization of novel epoxide incorporating peptidomimetics as selective calpain inhibitors

Hyperactivation of the calcium-dependent cysteine protease calpain 1 (Cal1) is implicated as a primary or secondary pathological event in a wide range of illnesses and in neurodegenerative states, including Alzheimer's disease (AD). E-64 is an epoxide-containing natural product identified as a potent nonselective, calpain inhibitor, with demonstrated efficacy in animal models of AD. By use of E-64 as a lead, three successive generations of calpain inhibitors were developed using computationally assisted design to increase selectivity for Cal1. First generation analogues were potent inhibitors, effecting covalent modification of recombinant Cal1 catalytic domain (Cal1cat), demonstrated using LC-MS/MS. Refinement yielded second generation inhibitors with improved selectivity. Further library expansion and ligand refinement gave three Cal1 inhibitors, one of which was designed as an activity-based protein profiling probe. These were determined to be irreversible and selective inhibitors by kinetics studies comparing full length Cal1 with the general cysteine protease papain.

Conditional disruption of calpain in the CNS alters dendrite morphology, impairs LTP, and promotes neuronal survival following injury

Ubiquitous classical (typical) calpains, calpain-1 and calpain-2, are Ca(+2)-dependent cysteine proteases, which have been associated with numerous physiological and pathological cellular functions. However, a clear understanding of the role of calpains in the CNS has been hampered by the lack of appropriate deletion paradigms in the brain. In this study, we describe a unique model of conditional deletion of both calpain-1 and calpain-2 activities in mouse brain, which more definitively assesses the role of these ubiquitous proteases in brain development/function and pathology. Surprisingly, we show that these calpains are not critical for gross CNS development. However, calpain-1/calpain-2 loss leads to reduced dendritic branching complexity and spine density deficits associated with major deterioration in hippocampal long-term potentiation and spatial memory. Moreover, calpain-1/calpain-2-deficient neurons were significantly resistant to injury induced by excitotoxic stress or mitochondrial toxicity. Examination of downstream target showed that the conversion of the Cdk5 activator, p35, to pathogenic p25 form, occurred only in the presence of calpain and that it played a major role in calpain-mediated neuronal death. These findings unequivocally establish two central roles of calpain-1/calpain-2 in CNS function in plasticity and neuronal death.

Hyperforin attenuates brain damage induced by transient middle cerebral artery occlusion (MCAO) in rats via inhibition of TRPC6 channels degradation

Hyperforin, a lipophilic constituent of medicinal herb St John's wort, has been identified as the main active ingredient of St John's wort extract for antidepressant action by experimental and clinical studies. Hyperforin is currently known to activate transient receptor potential canonical (subtype) 6 (TRPC6) channel, increase the phosphorylated CREB (p-CREB), and has N-methyl-D-aspartate receptor-antagonistic effect that convert potential neuroprotective effects in vitro. However, the protective effects of hyperforin on ischemic stroke in vivo remain controversial and its neuroprotective mechanisms are still unclear. This study was designed to examine the effects of intracerebroventricular (i.c.v.) injection of hyperforin on transient focal cerebral ischemia in rats. Hyperforin, when applied immediately after middle cerebral artery occlusion (MCAO) onset, significantly reduced infarct volumes and apoptotic cells, and also increased neurologic scores at 24 hours after reperfusion accompanied by elevated TRPC6 and p-CREB activity and decreased SBDP145 activity. When MEK or CaMKIV activity was specifically inhibited, the neuroprotective effect of hyperforin was attenuated, and we observed a correlated decrease in CREB activity. In conclusion, our results clearly showed that i.c.v. injection of hyperforin immediately after MCAO onset blocked calpain-mediated TRPC6 channels degradation, and then to stimulate the Ras/MEK/ERK and CaMKIV pathways that converge on CREB activation, contributed to neuroprotection.

Guanosine protects against reperfusion injury in rat brains after ischemic stroke

After ischemic stroke, early thrombolytic therapy to reestablish tissue perfusion improves outcome but triggers a cascade of deleterious cellular and molecular events. Using a collaborative approach, our groups examined the effects of guanosine (Guo) in response to ischemic reperfusion injury in vitro and in vivo. In a transient middle cerebral artery occlusion (MCAO) in rats, Guo significantly reduced infarct volume in a dose-dependent manner when given systemically either immediately before or 30 min, but not 60 min, after the onset of the 5.5-hr reperfusion period. In a separate experiment, Guo significantly reduced infarct volume after 24 hr of reperfusion when administered 5 min before reperfusion. Western blot analysis did not reveal any significant changes either in endoplasmic reticulum (ER) stress proteins (GRP 78 and 94) or HSP 70 or in levels of m-calpain. In vitro oxygen and glucose deprivation (OGD) significantly increased production of both reactive oxygen species (ROS) and interleukin-8 (IL-8) in the primary astrocytes. Guo did not alter ROS or IL-8 production when given to the astrocytes before OGD. However, Guo when added to the cells prior to or 30 min after reperfusion significantly reduced IL-8 release but not ROS formation. Our study revealed a dose- and time-dependent protective effect of Guo on reperfusion injury in vitro and vivo. The mechanisms by which Guo exerts its effect are independent of unfolded proteins in ER or the level of intracellular calcium or ROS formation. However, the effect may be induced, at least partially, by inhibiting IL-8, a marker of reperfusion-triggered proinflammatory events.

Proteases inhibition assessment on PC12 and NGF treated cells after oxygen and glucose deprivation reveals a distinct role for aspartyl proteases

Hypoxia is a severe stressful condition and induces cell death leading to neuronal loss both to the developing and adult nervous system. Central theme to cellular death is the activation of different classes of proteases such as caspases calpains and cathepsins. In the present study we investigated the involvement of these proteases, in the hypoxia-induced PC12 cell death. Rat PC12 is a model cell line for experimentation relevant to the nervous system and several protocols have been developed for either lethal hypoxia (oxygen and glucose deprivation OGD) or ischemic preconditioning (IPS). Nerve Growth Factor (NGF) treated PC12 differentiate to a sympathetic phenotype, expressing neurites and excitability. Lethal hypoxia was established by exposing undifferentiated and NGF-treated PC12 cells to a mixture of N₂/CO₂ (93:5%) in DMEM depleted of glucose and sodium pyruvate for 16 h. The involvement of caspases, calpains and lysosomal cathepsins D and E to the cell death induced by lethal OGD was investigated employing protease specific inhibitors such as z-VAD-fmk for the caspases, MDL28170 for the calpains and pepstatin A for the cathepsins D and E. Our findings show that pepstatin A provides statistically significant protection from cell death of both naive and NGF treated PC12 cells exposed to lethal OGD. We propose that apart from the established processes of apoptosis and necrosis that are integral components of lethal OGD, the activation of cathepsins D and E launches additional cell death pathways in which these proteases are key partners.

Systemic administration of guanosine promotes functional and histological improvement following an ischemic stroke in rats

Previously we have found that extracellular guanosine (Guo) has neuroprotective properties in in vitro and in vivo. Moreover, extracellular Guo significantly increased in the ipsilateral hemisphere within 2h following focal stroke in rats, and remained elevated for one week. Therefore, we hypothesized that Guo could be a potential candidate for a non-toxic neuroprotective agent. In the present study, we examined the effects of Guo on rats following permanent middle cerebral artery occlusion (MCAO). We also determined whether Guo can precondition neurons by modulating endoplasmic reticulum (ER) stress proteins. As most therapies employ a combination treatment regimen, we optimized the neuroprotection by combining pre- and post-MCAO treatments with Guo, attempting to reduce both ischemic cell death and improve functional recovery. A combination of 4mg/kg Guo given 30min pre-stroke and 8mg/kg Guo given 3, 24 and 48h post-stroke exerted the most significant decrease in infarct volume and sustainable improvement in neurological function. Moreover, these effects are not attributable to Guo metabolites. Measurements taken 6h post-MCAO from animals pre-treated with Guo did not reveal any significant changes in ER stress proteins (GRP 78 and 94) or HSP 70, but did reveal significantly increased levels of m-calpain. Thus, our data indicate that there is a treatment regimen for Guo as a neuroprotectant following ischemic stroke. The mechanism by which Guo confers neuroprotection may involve an increase in m-calpain, possibly resulting from a mild increase in intracellular calcium. M-calpain may be involved in the preconditioning response to ischemia by upregulating endogenous pro-survival mechanisms in neurons.

Control of AIF-mediated cell death by antagonistic functions of CHIP ubiquitin E3 ligase and USP2 deubiquitinating enzyme

Apoptosis inducing factor (AIF) is a mitochondrial oxidoreductase that scavenges reactive oxygen species under normal conditions. Under certain stresses, such as exposure to N-methyl-N'-nitro-N'-nitrosoguanidine (MNNG), AIF is truncated and released from the mitochondria and translocated into the nucleus, where the truncated AIF (tAIF) induces caspase-independent cell death. However, it is unknown how cells decide to kill themselves or operate ways to survive when they encounter stresses that induce the release of tAIF. Here, we demonstrated that USP2 and CHIP contribute to the control of tAIF stability. USP2 deubiquitinated and stabilized tAIF, thus promoting AIF-mediated cell death. In contrast, CHIP ubiquitinated and destabilized tAIF, thus preventing the cell death. Consistently, CHIP-deficient cells showed an increased sensitivity to MNNG. On the other hand, knockdown of USP2 attenuated MNNG-induced cell death. Moreover, exposure to MNNG caused a dramatic decrease in CHIP level, but not that of USP2, concurrent with cell shrinkage and chromatin condensation. These findings indicate that CHIP and USP2 show antagonistic functions in the control of AIF-mediated cell death, and implicate the role of the enzymes as a switch for cells to live or die under stresses that cause tAIF release.

Glutamate receptors, neurotoxicity and neurodegeneration

Glutamate excitotoxicity is a hypothesis that states excessive glutamate causes neuronal dysfunction and degeneration. As glutamate is a major excitatory neurotransmitter in the central nervous system (CNS), the implications of glutamate excitotoxicity are many and far-reaching. Acute CNS insults such as ischaemia and traumatic brain injury have traditionally been the focus of excitotoxicity research. However, glutamate excitotoxicity has also been linked to chronic neurodegenerative disorders such as amyotrophic lateral sclerosis, multiple sclerosis, Parkinson's disease and others. Despite the continued research into the mechanisms of excitotoxicity, there are currently no pharmacological interventions capable of providing significant neuroprotection in the clinical setting of brain ischaemia or injury. This review addresses the current state of excitotoxic research, focusing on the structure and physiology of glutamate receptors; molecular mechanisms underlying excitotoxic cell death pathways and their interactions with each other; the evidence for glutamate excitotoxicity in acute neurologic diseases; laboratory and clinical attempts at modulating excitotoxicity; and emerging targets for excitotoxicity research.

Resveratrol preconditioning induces cellular stress proteins and is mediated via NMDA and estrogen receptors

Resveratrol pretreatment has been shown to provide neuroprotection in models of cerebral ischemia. This phenomenon, commonly termed preconditioning, promotes ischemic tolerance and may involve mild activation of endoplasmic reticulum stress pathways in the affected tissue. Systemic injection of resveratrol (2 x 10(-3), 2 x 10(-4), 1 x 10(-4) mg/kg) 30 min prior to a 4 h period of right middle cerebral artery occlusion significantly reduced infarct area in the insular region of rat prefrontal cortex. This affect was blocked when resveratrol treatment was combined with a non-selective estrogen receptor antagonist, or preceded by intracortical injection of an NMDA receptor antagonist. The neuroprotective effect of resveratrol was associated with reduced renal sympathetic nerve activity as well as induction of resident endoplasmic reticulum chaperone proteins, glucose-regulated proteins 78 and 94. The calcium-sensitive chaperone heat shock protein 70 and the cysteine protease m calpain did not respond to resveratrol pretreatment. However, a significant induction of heat shock protein 70 was observed in the contralateral cortex of resveratrol pretreated rats following 4 h of right middle cerebral artery occlusion. These data suggest that resveratrol preconditioning promotes ischemic tolerance in the short term, in part via effects mediated through activation of estrogen and NMDA receptors, as well as through mild activation of cellular stress proteins.

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.

Folding transitions in calpain activator peptides studied by solution NMR spectroscopy

Calpastatin, the endogenous inhibitor of calpain, a cysteine protease in eukaryotic cells, is an intrinsically unstructured protein, which upon binding to the enzyme goes through a conformational change. Peptides calpA (SGKSGMDAALDDLIDTLGG) and calpC (SKPIGPDDAIDALSSDFTS), corresponding to the two conserved subdomains of calpastatin, are known to activate calpain and increase the Ca(2+) sensitivity of the enzyme. Using solution NMR spectroscopy, here we show that calpA and calpC are disordered in water but assume an alpha-helical conformation in 50% CD(3)OH. The position and length of the helices are in agreement with those described in the literature for the bound state of the corresponding segments of calpastatin suggesting that the latter might be structurally primed for the interaction with its target. According to our data, the presence of Ca(2+) induces a backbone rearrangement in the peptides, an effect that may contribute to setting the fine conformational balance required for the interaction of the peptides with calpain.

Neuroprotective strategies targeting apoptotic and necrotic cell death for stroke

It has been a major challenge to develop effective therapeutics for stroke, a leading cause of death and serious debilitation. Intensive research in the past 15 years have implicated many regulators and the related mechanisms by which neuronal cell death is regulated. It is now clear that even a brief ischemic stroke may trigger complex cellular events that lead to both apoptotic and necrotic neuronal cell death in a progressive manner. Although efforts at developing specific chemical inhibitors for validated targets have been successful for in vitro enzymatic assays, the development of some of such inhibitors into human therapy has been often hindered by their in vivo bioavailability profile. Considerations for the ability to chemically target a cellular mechanism in manner compatible with disease targets in vivo might be emphasized early in the development process by putting a priority on identifying key targets that can be effectively targeted chemically. Thorough interrogation of cellular pathways by saturation chemical genetics may provide a novel strategy to identify multiple key molecular entities that can be targeted chemically in order to select a target suitable for the treatment of intended human diseases such as stroke.

Neuroprotection with delayed calpain inhibition after transient forebrain ischemia

OBJECTIVE

Delayed neurodegeneration after transient global brain ischemia offers a therapeutic window for inhibiting molecular injury mechanisms. One such mechanism is calpain-mediated proteolysis, which peaks 24 to 48 hrs after transient forebrain ischemia in rats. This study tests the hypothesis that delayed calpain inhibitor therapy can reduce brain calpain activity and neurodegeneration after transient forebrain ischemia.

DESIGN

Prospective randomized placebo-controlled animal trial.

SETTING

University research laboratory.

SUBJECTS

Adult male Long-Evans rats.

INTERVENTIONS

Rats subjected to 10-min transient forebrain ischemia were randomized to intravenous infusion of calpain inhibitor CEP-3453 or vehicle beginning 22 hrs after injury.

MEASUREMENTS AND MAIN RESULTS

In a dose-response study, a 60 mg/kg bolus followed by 30 mg/kg infusion was required to reduce postischemic brain calpain activity measured by Western blot of hippocampal homogenates at 48 hrs after injury. The same dosing protocol decreased degeneration of CA1 pyramidal neurons measured at 72 hrs after injury.

CONCLUSIONS

These results suggest a causal role for calpains in delayed postischemic neurodegeneration, and demonstrate a broad therapeutic window for calpain inhibition in this model.

Calpain-mediated signaling mechanisms in neuronal injury and neurodegeneration

Calpain is a ubiquitous calcium-sensitive protease that is essential for normal physiologic neuronal function. However, alterations in calcium homeostasis lead to persistent, pathologic activation of calpain in a number of neurodegenerative diseases. Pathologic activation of calpain results in the cleavage of a number of neuronal substrates that negatively affect neuronal structure and function, leading to inhibition of essential neuronal survival mechanisms. In this review, we examine the mechanistic underpinnings of calcium dysregulation resulting in calpain activation in the acute neurodegenerative diseases such as cerebral ischemia and in the chronic neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, prion-related encephalopathy, and amylotrophic lateral sclerosis. The premise of this paper is that analysis of the signaling and transcriptional consequences of calpain-mediated cleavage of its various substrates for any neurodegenerative disease can be extrapolated to all of the neurodegenerative diseases vulnerable to calcium dysregulation.

Lysosomal release of cathepsins causes ischemic damage in the rat hippocampal slice and depends on NMDA-mediated calcium influx, arachidonic acid metabolism, and free radical production

NMDA-mediated calcium entry and reactive oxygen species (ROS) production are well-recognized perpetrators of ischemic neuronal damage. The current studies show that these events lead to the release of the protein hydrolase, cathepsin B, from lysosomes 2 h following 5-min oxygen-glucose deprivation in the rat hippocampal slice. This release reflects a lysosomal membrane permeabilization (LMP) and was measured as the appearance of diffuse immunolabeled cathepsin B in the cytosol of CA1 pyramidal neurons. Necrotic neuronal damage begins after the release of cathepsins and is prevented by inhibitors of either cathepsin B or D indicating that the release of cathepsins is an important mediator of severe damage. There was an increase in superoxide levels, measured by dihydroethidium fluorescence, at the same time as LMP and reducing ROS levels with antioxidants, Trolox or N-tert-butyl-alpha-phenyl nitrone, blocked LMP. Both LMP and ROS production were blocked by an NMDA channel blocker (MK-801) and by inhibitors of mitogen-activated protein kinase kinase (U0126), calcium-dependent/independent phospholipases A2 (methyl arachidonyl fluorophosphonate) but not calcium-independent phospholipases A2 (bromoenol lactone) and cyclooxygenase-2 (NS398). A cell-permeant specific inhibitor of calpain (PD150606) prevented LMP, but not ROS production. It is concluded that LMP results in part from calcium-initiated and extracellular signal-regulated kinase-initiated arachidonic acid metabolism, which produces free radicals; it also requires the action of calpain.

Excitotoxicity and focal cerebral ischemia induce truncation of the NR2A and NR2B subunits of the NMDA receptor and cleavage of the scaffolding protein PSD-95

The N-methyl-D-aspartate receptor (NMDAR) is central to physiological and pathological functioning of neurons. Although promising results are beginning to be obtained in the treatment of dementias, clinical trials with NMDAR antagonists for stroke, trauma and neurodegenerative disorders, such as Hungtinton's disease, have failed before. In order to design effective therapies to prevent excitotoxic neuronal death, it is critical to characterize the consequences of excessive NMDAR activation on its expression and function. Previous data have reported partial downregulation of the NR1 and NR2B receptor subunits in response to excitotoxicity and cerebral ischemia. However, the effect of NMDAR overactivation on NR2A, a subunit fundamental to synaptic transmission and neuronal survival, is still elusive. In this study, we report the rapid and extensive proteolytic processing of NR2A, together with the scaffolding protein postsynaptic density-95 (PSD-95), induced by excitotoxic stimulation of cortical neurons in vitro and by transient focal cerebral ischemia. Processing of the C terminus of NR2A is irreversibly induced by brief agonist exposure of NR2B-containing receptors, and requires calcium influx and the activity of calpain, also responsible for PSD-95 cleavage. The outcome is a truncated NR2A subunit that is stable and capable to interact with NR1 at the surface of neurons, but lacking the structural domains required for association with scaffolding, downstream signaling and cytoskeletal proteins. Therefore, a rapid and significant uncoupling of synaptic NMDARs from downstream survival pathways is expected to occur during ischemia. This novel mechanism induced by excitotoxicity helps to explain the failure of most therapies based on NMDAR antagonists.

Calcium and neurodegeneration

When properly controlled, Ca2+ fluxes across the plasma membrane and between intracellular compartments play critical roles in fundamental functions of neurons, including the regulation of neurite outgrowth and synaptogenesis, synaptic transmission and plasticity, and cell survival. During aging, and particularly in neurodegenerative disorders, cellular Ca2+-regulating systems are compromised resulting in synaptic dysfunction, impaired plasticity and neuronal degeneration. Oxidative stress, perturbed energy metabolism and aggregation of disease-related proteins (amyloid beta-peptide, alpha-synuclein, huntingtin, etc.) adversely affect Ca2+ homeostasis by mechanisms that have been elucidated recently. Alterations of Ca2+-regulating proteins in the plasma membrane (ligand- and voltage-gated Ca2+ channels, ion-motive ATPases, and glucose and glutamate transporters), endoplasmic reticulum (presenilin-1, Herp, and ryanodine and inositol triphosphate receptors), and mitochondria (electron transport chain proteins, Bcl-2 family members, and uncoupling proteins) are implicated in age-related neuronal dysfunction and disease. The adverse effects of aging on neuronal Ca2+ regulation are subject to modification by genetic (mutations in presenilins, alpha-synuclein, huntingtin, or Cu/Zn-superoxide dismutase; apolipoprotein E isotype, etc.) and environmental (dietary energy intake, exercise, exposure to toxins, etc.) factors that may cause or affect the risk of neurodegenerative disease. A better understanding of the cellular and molecular mechanisms that promote or prevent disturbances in cellular Ca2+ homeostasis during aging may lead to novel approaches for therapeutic intervention in neurological disorders such as Alzheimer's and Parkinson's diseases and stroke.

Development of Calpain-specific Inactivators by Screening of Positional Scanning Epoxide Libraries

Calpains are calcium-dependent proteases that are required for numerous intracellular processes but also play an important role in the development of pathologies such as ischemic injury and neurodegeneration. Many current small molecule calpain inhibitors also inhibit other cysteine proteases, including cathepsins, and need improved selectivity. The specificity of inhibition of several calpains and papain was profiled using synthetic positional scanning libraries of epoxide-based compounds that target the active-site cysteine. These peptidomimetic libraries probe the P4, P3, and P2 positions, display (S,S)- or (R,R)-epoxide stereochemistries, and incorporate both natural and non-natural amino acids. To facilitate library screening, an SDS-PAGE assay that measures the extent of hydrolysis of an inactive recombinant m-calpain was developed. Individual epoxide inhibitors were synthesized guided by calpain-specific preferences observed from the profiles and tested for inhibition against calpain. The most potent compounds were assayed for specificity against cathepsins B, L, and K. Several compounds demonstrated high inhibition specificity for calpains over cathepsins. The best of these inhibitors, WRH(R,R), irreversibly inactivates m- and mu-calpain rapidly (k(2)/K(i) = 131,000 and 16,500 m(-1) s(-1), respectively) but behaves exclusively as a reversible and less potent inhibitor toward the cathepsins. X-ray crystallography of the proteolytic core of rat mu-calpain inactivated by the epoxide compounds WR gamma-cyano-alpha-aminobutyric acid (S,S) and WR allylglycine (R,R) reveals that the stereochemistry of the epoxide influences positioning and orientation of the P2 residue, facilitating alternate interactions within the S2 pocket. Moreover, the WR gamma-cyano-alpha-aminobutyric acid (S,S)-complexed structure defines a novel hydrogen-bonding site within the S2 pocket of calpains.

Retinal Penetration of Calpain Inhibitors in Rats After Oral Administration

Calpain-mediated proteolysis has been involved in neuronal cell death of retinal neurological degeneration. An aldehyde-based calpain inhibitor, SJA6017 (1), was effective following oral administration in a rat retinal ischemia model but had low oral bioavailability. The aim of this study was to identify calpain inhibitors with good retinal penetration after oral dosing. The orally bioavailable inhibitors, hemiacetal 3 (SNJ-1715), amphipathic ketoamide 5 (SNJ-1945), and pyridine ketoamide 6 (SNJ-2008), were evaluated for their retinal pharmacokinetic (PK) profiles. The retinal drug exposure of these inhibitors was more than tenfold higher than 1. Among these compounds, 5 exhibited the most favorable retinal PK properties, such as good penetration and long half-life. Comparisons of 5 and the structurally related ketoamide 6 suggested that the presence of a methoxy diethylene glycol moiety resulted in the inhibitor with high penetration into the retina and the sustained high retinal levels. Ketoamide 5 was selected as the development candidate for the treatment of retinal diseases.

Identification and characterization of PEBP as a calpain substrate

Calpains are calcium- and thiol-dependent proteases whose dysregulation has been implicated in a number of diseases and conditions such as cardiovascular dysfunction, ischemic stroke, and Alzheimer's disease (AD). While the effects of calpain activity are evident, the precise mechanism(s) by which dysregulated calpain activity results in cellular degeneration are less clear. In order to determine the impact of calpain activity, there is a need to identify the range of specific calpain substrates. Using an in vitro proteomics approach we confirmed that phosphatidylethanolamine-binding protein (PEBP) as a novel in vitro and in situ calpain substrate. We also observed PEBP proteolysis in a model of brain injury in which calpain is clearly activated. In addition, with evidence of calpain dysregulation in AD, we quantitated protein levels of PEBP in postmortem brain samples from the hippocampus of AD and age-matched controls and found that PEBP levels were approximately 20% greater in AD. Finally, with previous evidence that PEBP may act as a serine protease inhibitor, we tested PEBP as an inhibitor of the proteasome and found that PEBP inhibited the chymostrypsin-like activity of the proteasome by approximately 30%. Together these data identify PEBP as a potential in vivo calpain substrate and indicate that increased PEBP levels may contribute to impaired proteasome function.

Postinjury administration of pituitary adenylate cyclase activating polypeptide (PACAP) attenuates traumatically induced axonal injury in rats

Pituitary adenylate cyclase activating polypeptide (PACAP) has several different actions in the nervous system. Numerous studies have shown its neuroprotective effects both in vitro and in vivo. Previously, it has been demonstrated that PACAP reduces brain damage in rat models of global and focal cerebral ischemia. Based on the protective effects of PACAP in cerebral ischemia and the presence of common pathogenic mechanisms in cerebral ischemia and traumatic brain injury (TBI), the aim of the present study was to investigate the possible protective effect of PACAP administered 30 min or 1 h postinjury in a rat model of diffuse axonal injury. Adult Wistar male rats were subjected to impact acceleration, and PACAP was administered intracerebroventricularly 30 min (n = 4), and 1 h after the injury (n = 5). Control animals received the same volume of vehicle at both time-points (n = 5). Two hours after the injury, brains were processed for immunohistochemical localization of damaged axonal profiles displaying either beta-amyloid precursor protein (beta-APP) or RMO-14 immunoreactivity, both considered markers of specific features of traumatic axonal injury. Our results show that treatment with PACAP (100 microg) 30 min or 1 h after the induction of TBI resulted in a significant reduction of the density of beta-APP-immunopositive axon profiles in the corticospinal tract (CSpT). There was no significant difference between the density of beta-APP-immunopositive axons in the medial longitudinal fascicle (MLF). PACAP treatment did not result in significantly different number of RMO-14-immunopositive axonal profiles in either brain areas 2 hours post-injury compared to normal animals. While the results of this study highlighted the complexity of the pathogenesis and manifestation of diffuse axonal injury, they also indicate that PACAP should be considered a potential therapeutic agent in TBI.

Intraventricular ascorbic acid administration decreases hypoxic-ischemic brain injury in newborn rats

Neuronal cell damage following hypoxic-ischemic (HI) brain injury is partly caused by production of free radicals and reactive oxygen species (ROS). Ascorbic acid (AA) is a potent antioxidant, which scavenges various types of ROS. Some studies have shown that it is neuroprotective, however, the issue is still controversial. In this study, we examined the effect of intraventricular AA administration on immature HI brain using the Rice-Vannucci model. After unilateral carotid artery ligation under isoflurane anesthesia, 7-day-old rat pups received varying concentrations of AA (0.04, 0.2, 1 and 5 mg/kg) by intraventricular injection and were exposed to 8% oxygen for 90 min. Vehicle controls received an equal volume of phosphate saline buffer. We assessed the neuroprotective effect of AA at 7 days post-HI. The percent brain damage measured by comparing the wet weight of the ligated side of hemisphere with that of contralateral one was reduced in both 1 and 5 mg/kg groups but not in either 0.04 or 0.2 mg/kg groups compared to vehicle controls (5 mg/kg 16.0 +/- 4.3%, 1 mg/kg 10.9 +/- 5.0%, vs. controls 36.7 +/- 3.6%, P < 0.05). Macroscopic evaluation of brain injury revealed the neuroprotective effect of AA in both 1 and 5 mg/kg groups (5 mg/kg 1.1 +/- 0.4, 1 mg/kg 0.4 +/- 0.3, vs. controls 2.9 +/- 0.3, P < 0.05). Western blots of fodrin on the ligated side also showed that AA significantly suppressed 150/145-kDa bands of fodrin breakdown products, which suggested that AA suppressed activation of calpain. Neuropathological quantitative analysis of cell death revealed that 1 mg/kg of AA injection significantly reduced the number of necrotic cells in cortex, caudate putamen, thalamus and hippocampus CA1, whereas that of apoptotic cells was only reduced in cortex. These findings show that intraventricular AA injection is neuroprotective after HI in immature rats.

Oestrogen receptor subtype-specific repression of calpain expression and calpain enzymatic activity in neuronal cells--implications for neuroprotection against Ca-mediated excitotoxicity

Calpains represent a superfamily of Ca2+-activated cysteine-proteases, which are important mediators of apoptosis and necrosis. In the brain, m-calpain and micro-calpain, the two ubiquitous calpain-isoforms, are strongly activated in neurones after an excitotoxic Ca2+ influx occurring, for example, during cerebral ischemia. Because oestrogen and its receptors (ERalpha/ERbeta) can exert neuroprotective activity, we investigated their influence on expression of calpains and their endogenous inhibitor, calpastatin. We found that ectopic expression of ERalpha in human neuroblastoma SK-N-MC cells led to a ligand-independent constitutive down-regulation of m-calpain accompanied by an up-regulation of micro-calpain expression. Up-regulation of micro-calpain was reversed in the presence of oestrogen, which, in turn, could be blocked by co-treatment with the oestrogen-receptor antagonist ICI 182,780. Expression of calpastatin was not altered, either in the absence or in the presence of oestrogen. Additional studies revealed that ERalpha-expressing cells exhibited decreased calpain enzymatic activity and increased survival when cells were exposed to the Ca2+ ionophore, ionomycin. Since all investigated effects could be observed exclusively in the presence of ERalpha, but not ERbeta, and since the effects are reduced when ERalpha and ERbeta are co-expressed, our data suggest a novel ER subtype-specific neuroprotective action by repressing calpain expression and calpain activity under conditions of a massive Ca2+ influx.

All roads lead to disconnection?--Traumatic axonal injury revisited

Traumatic brain injury (TBI) evokes widespread/diffuse axonal injury (TAI) significantly contributing to its morbidity and mortality. While classic theories suggest that traumatically injured axons are mechanically torn at the moment of injury, studies in the last two decades have not supported this premise in the majority of injured axons. Rather, current thought considers TAI a progressive process evoked by the tensile forces of injury, gradually evolving from focal axonal alteration to ultimate disconnection. Recent observations have demonstrated that traumatically induced focal axolemmal permeability leads to local influx of Ca2+ with the subsequent activation of the cysteine proteases, calpain and caspase, that then play a pivotal role in the ensuing pathogenesis of TAI via proteolytic digestion of brain spectrin, a major constituent of the subaxolemmal cytoskeletal network, the "membrane skeleton". In this pathological progression this local Ca2+ overloading with the activation of calpains also initiates mitochondrial injury that results in the release of cytochrome-c, with the activation of caspase. Both the activated calpain and caspases then participate in the degradation of the local axonal cytoskeleton causing local axonal failure and disconnection. In this review, we summarize contemporary thought on the pathogenesis of TAI, while discussing the potential diversity of pathological processes observed within various injured fiber types. The anterograde and retrograde consequences of TAI are also considered together with a discussion of various experimental therapeutic approaches capable of attenuating TAI.

Chlortetracycline and Demeclocycline Inhibit Calpains and Protect Mouse Neurons against Glutamate Toxicity and Cerebral Ischemia

Minocycline is a potent neuroprotective tetracycline in animal models of cerebral ischemia. We examined the protective properties of chlortetracycline (CTC) and demeclocycline (DMC) and showed that these two tetracyclines were also potent neuroprotective against glutamate-induced neuronal death in vitro and cerebral ischemia in vivo. However, CTC and DMC appeared to confer neuroprotection through a unique mechanism compared with minocycline. Rather than inhibiting microglial activation and caspase, CTC and DMC suppressed calpain activities. In addition, CTC and DMC only weakly antagonized N-methyl-D-aspartate (NMDA) receptor activities causing 16 and 14%, respectively, inhibition of NMDA-induced whole cell currents and partially blocked NMDA-induced Ca2+ influx, commonly regarded as the major trigger of neuronal death. In vitro and in vivo experiments demonstrated that the two compounds selectively inhibited the activities of calpain I and II activated following glutamate treatment and cerebral ischemia. In contrast, minocycline did not significantly inhibit calpain activity. Taken together, these results suggested that CTC and DMC provide neuroprotection through suppression of a rise in intracellular Ca2+ and inhibition of calpains.

Calpain inhibitor A-558693 in experimental focal cerebral ischemia in rats

OBJECTIVES

Calpains are intracellular proteases, which are activated in various cerebral injuries. We studied the expression of mu-calpain in a model of focal cerebral ischemia/reperfusion and the efficacy of the calpain inhibitor A-558693.

METHODS

A transient occlusion of the middle cerebral artery was produced in male Wistar rats by using the suture model with 3 hours of ischemia and 24 hours of reperfusion. Six animals were given the calpain inhibitor and six animals were treated with placebo. The infarct size was determined by the loss of the calpain substrate microtubule-associated protein-2 (MAP-2) immunohistochemistry using volumetry in serial slices of the brains. Furthermore mu-calpain positive-stained cells were detected by immunohistochemistry and western blotting.

RESULTS

In placebo-treated animals the mu-calpain expression was significantly increased in the ischemic hemisphere compared with the contralateral non-ischemic hemisphere (88.6 versus 10.5% in the basal ganglia, 60.7 versus 10.7% in the cortex, p < 0.001, respectively) with a subsequent loss its substrate MAP-2. However, the use of the calpain inhibitor A-558693 did not significantly change the mu-calpain expression, nor significantly reduce the infarct volume.

DISCUSSION

The present data indicate that mu-calpain proteolysis plays an important role in the chain of events following cerebral ischemia. However, the calpain inhibitor A-558693 failed to prevent these changes.

Identification of a novel calpain inhibitor using phage display

Calpains are calcium- and thiol-dependent proteases that cleave a variety of intracellular substrates. Overactivation of the calpains has been implicated in a number of diseases and conditions such as ischemic stroke indicating a need for the development of calpain inhibitors. A major problem with current calpain inhibitors has been specific targeting to calpain. To identify highly specific calpain interacting peptides, we developed a peptide-phage library screening method based on the calcium-dependent conformation change associated with calpain activation. A phage-peptide library representing greater than 2 billion expressed 12-mers was incubated with calpain I in the presence of calcium. The calcium-dependent bound phage was then eluted by addition of EGTA. After four rounds of selection we found a conserved 5-mer sequence represented by LSEAL. Synthetic LSEAL inhibited tau-calpain interaction and in vitro proteolysis of tau- and alpha-synuclein by calpains. Deletion of the portion of the tau protein containing a homologous sequence to LSEAL resulted in decreased calpain-mediated tau degradation. These data suggest that these peptides may represent novel calpastatin mimetics.

Oxidative stress in the brain: novel cellular targets that govern survival during neurodegenerative disease

Despite our present knowledge of some of the cellular pathways that modulate central nervous system injury, complete therapeutic prevention or reversal of acute or chronic neuronal injury has not been achieved. The cellular mechanisms that precipitate these diseases are more involved than initially believed. As a result, identification of novel therapeutic targets for the treatment of cellular injury would be extremely beneficial to reduce or eliminate disability from nervous system disorders. Current studies have begun to focus on pathways of oxidative stress that involve a variety of cellular pathways. Here we discuss novel pathways that involve the generation of reactive oxygen species and oxidative stress, apoptotic injury that leads to nuclear degradation in both neuronal and vascular populations, and the early loss of cellular membrane asymmetry that mitigates inflammation and vascular occlusion. Current work has identified exciting pathways, such as the Wnt pathway and the serine-threonine kinase Akt, as central modulators that oversee cellular apoptosis and their downstream substrates that include Forkhead transcription factors, glycogen synthase kinase-3beta, mitochondrial dysfunction, Bad, and Bcl-x(L). Other closely integrated pathways control microglial activation, release of inflammatory cytokines, and caspase and calpain activation. New therapeutic avenues that are just open to exploration, such as with brain temperature regulation, nicotinamide adenine dinucleotide modulation, metabotropic glutamate system modulation, and erythropoietin targeted expression, may provide both attractive and viable alternatives to treat a variety of disorders that include stroke, Alzheimer's disease, and traumatic brain injury.

Ischemic neuronal cell death and organellae damage

The brain is an organ that consumes much energy. This is partially due to the character of neurons; they possess excitable plasma membrane and a large amount of ATP is indispensable for maintaining ion gradient. Once neurons experience energy failure, calcium accumulates in the intracellular space as a result of disturbed ion homeostasis. This, in turn, activates many cellular processes, which culminate in cell death. In this cellular catastrophic cascade, many organelles play important roles. In addition to the plasma membrane, cytosol is the 'organelle' that first becomes exposed to the increased level of calcium. Many proteases, kinases and lipases are localized here, and are activated directly or indirectly by the ischemic insult. Some enzymes are pro-apoptotic ones, while others are anti-apoptotic. It was reported that neurons that would die later showed activated pro-apoptotic enzymes, but ones that would survive possessed activated anti-apoptotic molecules. Mitochondria is the organelle that plays the central role for intrinsic pathways of apoptosis. The release of cytochrome c from this organelle is the key step in apoptotic cascade in the ischemic neurons. However, the exact molecular mechanism of cytochrome c release remains uncertain. In addition, expression of genes essential for mitochondrial function changes in neurons after ischemia, which further indicates the crucial role of this organelle in cell death. Endoplasmic reticulum (ER) not only mediates proteins processing, but also regulates intracellular calcium homeostasis and cell death signal activation. Recent reports indicate that dysfunction of this organelle occurs at an early stage after ischemia and might be the initial step of apoptotic cascades in neurons. Golgi apparatus and lysosomes are organelles that are involved in apoptotic cell death in some situations. There have been no reports that demonstrated active role of these organelles in ischemic neuronal cell death. Further investigation would be desired about this issue. Nucleus is the organelle that contains genomic DNA. Many studies demonstrated DNA breakage in the neurons that would die later, but whether this is the cause or merely the result of the insult remains uncertain. If the more precise role of each organelle in neuronal cell death are disclosed, we should be able to think about new means of therapy for ischemic stroke.