Intrahippocampal colchicine injection results in spectrin proteolysis

Degradation of βII-Spectrin Protein by Calpain-2 and Caspase-3 Under Neurotoxic and Traumatic Brain Injury Conditions

A major consequence of traumatic brain injury (TBI) is the rapid proteolytic degradation of structural cytoskeletal proteins. This process is largely reflected by the interruption of axonal transport as a result of extensive axonal injury leading to neuronal cell injury. Previous work from our group has described the extensive degradation of the axonally enriched cytoskeletal αII-spectrin protein which results in molecular signature breakdown products (BDPs) indicative of injury mechanisms and to specific protease activation both in vitro and in vivo. In the current study, we investigated the integrity of βII-spectrin protein and its proteolytic profile both in primary rat cerebrocortical cell culture under apoptotic, necrotic, and excitotoxic challenge and extended to in vivo rat model of experimental TBI (controlled cortical impact model). Interestingly, our results revealed that the intact 260-kDa βII-spectrin is degraded into major fragments (βII-spectrin breakdown products (βsBDPs)) of 110, 108, 85, and 80 kDa in rat brain (hippocampus and cortex) 48 h post-injury. These βsBDP profiles were further characterized and compared to an in vitro βII-spectrin fragmentation pattern of naive rat cortex lysate digested by calpain-2 and caspase-3. Results revealed that βII-spectrin was degraded into major fragments of 110/85 kDa by calpain-2 activation and 108/80 kDa by caspase-3 activation. These data strongly support the hypothesis that in vivo activation of multiple protease system induces structural protein proteolysis involving βII-spectrin proteolysis via a specific calpain and/or caspase-mediated pathway resulting in a signature, protease-specific βsBDPs that are dependent upon the type of neural injury mechanism. This work extends on previous published work that discusses the interplay spectrin family (αII-spectrin and βII-spectrin) and their susceptibility to protease proteolysis and their implication to neuronal cell death mechanisms.

Behavioural effects of antidepressants are dependent and independent on the integrity of the dentate gyrus

The dentate gyrus (DG), a part of the hippocampal formation, is a candidate target of antidepressants and may play a role in the development of depressive syndrome; however, there is no direct neurobiological evidence supporting this theory. Here, we examined whether DG integrity is necessary for the behavioural effects of acute or chronic antidepressant treatment. Microinjection of colchicine into DG severely damaged the granule cells, as confirmed by morphological, electrophysiological, and behavioural analyses. Acute treatment with desipramine and fluoxetine decreased the immobility of saline-treated rats in the forced swimming test, whereas this decrease was inhibited in colchicine-treated rats. Chronic treatment with desipramine and fluoxetine also decreased the immobility of saline-treated rats; however, the extensive DG damage induced by colchicine had no effect on this decrease. In the novelty-suppressed feeding test, chronic treatment with desipramine and fluoxetine decreased the latency to feed in saline-treated rats while, once again, the extensive DG damage caused by colchicine had no effect on this decrease. Thus, we concluded that DG integrity was required for the behavioural effects of acute but not chronic antidepressant treatment; this disparity was not due to the time interval between surgery and behavioural tests. These findings indicate that treatment duration determines the influence of DG integrity on antidepressant effects.

Calpain induces proteolysis of neuronal cytoskeleton in ischemic gerbil forebrain

We investigated the relationship between the activity of calcium-dependent protease (calpain) and the ischemic neuronal damage. We also investigated the mechanism of ischemic resistance in astrocytes. In gerbil, a 10-min forebrain ischemia was induced by occlusion of both common carotid arteries. The calpain-induced proteolysis of cytoskeleton (fodrin) was examined by immunohistochemistry. Immunolocalization of micro and m-calpain was also examined. Intact fodrin was observed both in neurons and astrocytes, but proteolyzed fodrin was not observed in normal brain. Fifteen minutes after ischemia, proteolysis of fodrin took place in putamen, parietal cortex and hippocampal CA1. The proteolysis extended to thalamus 4 h after ischemia after which the immunoreactivity faded down in all areas except hippocampus. On day 7, the proteolysis was still observed only in hippocampus. Neurons with the proteolysis of soma resulted in neuronal death. Throughout the experiment, the proteolysis was not observed in astrocytes. micro -Calpain was observed only in neurons but m-calpain was observed both in neurons and astrocytes. The ischemia induced only micro -calpain activation, which resulted in fodrin proteolysis of neurons with differential spatial distribution and temporal course. The proteolysis was developed rapidly and was completed within 24 h in all vulnerable regions except hippocampal CA1. The proteolysis preceded the neuronal death. The mechanism of the proteolysis seemed to be involved by Ca(2+) influx via glutamate receptor and rapid neuronal death seemed reasonable. The reason why neuronal death in CA1 evolved slowly was not clarified. In astrocytes, fodrin was not proteolyzed by m-calpain. The low Ca(2+)-sensitivity of m-calpain may be the reason of ischemic resistance in astrocytes.

Effects of commercial antiglaucoma drugs to glutamate-induced [Ca2+)]i increase in cultured neuroblastoma cells

Over releasing of glutamate and cellular calcium influx always results in neuronal death. In the present study, we investigated various commercial antiglaucoma drugs including timolol (0.58 microM to 58 microM), betaxolol (1.62 microM to 162 microM), carteolol (6.8 microM to 680 microM), pilocarpine (4.08 microM to 408 microM), latanoprost (0.01 microM to 1.1 microM), dorzolamide (6.16 microM to 616 microM), brinzolamide (2.6 microM to 260 microM), brimonidine (0.68 microM to 68 microM), dipivefrin (0.28 microM to 28 microM) and preservative benzalkonium chloride on their effects to inhibit glutamate-induced intracellular free Ca(2+) ([Ca(2+)](i)) increase in cultured N1E-115 neuroblastoma cells. These drugs were diluted from original concentrations to 1/100, 1/1000 and 1/10000. The [Ca(2+)](i) mobility was studied after loading with fura-2-AM and analyzed by spectrofluorometry. It was found that betaxolol, dipivefrin and brimonidine have remarkable effects not only to inhibit the glutamate-induced [Ca(2+)](i) increase but also to decrease the basal [Ca(2+)](i). In the case of other drugs, only high concentration of timolol (58 microM) exhibited significant effect to completely prevent glutamate-induced [Ca(2+)](i) increase. Moreover, benzalkonium chloride did not exhibit any inhibitive effect. These results indicate that betaxolol, dipivefrin and brimonidine may have neuroprotective effects to inhibit the glutamate-induced over Ca(2+) influx damage.

Cyclosporin A prevents calpain activation despite increased intracellular calcium concentrations, as well as translocation of apoptosis-inducing factor, cytochrome c and caspase-3 activation in neurons exposed to transient hypoglycemia

Blockade of mitochondrial permeability transition protects against hypoglycemic brain damage. To study the mechanisms downstream from mitochondria that may cause neuronal death, we investigated the effects of cyclosporin A on subcellular localization of apoptosis-inducing factor and cytochrome c, activation of the cysteine proteases calpain and caspase-3, as well as its effect on brain extracellular calcium concentrations. Redistribution of cytochrome c occurred at 30 min of iso-electricity, whereas translocation of apoptosis-inducing factor to nuclei occurred at 30 min of recovery following 30 min of iso-electricity. Active caspase-3 and calpain-induced fodrin breakdown products were barely detectable in the dentate gyrus and CA1 region of the hippocampus of rat brain exposed to 30 or 60 min of insulin-induced hypoglycemia. However, 30 min or 3 h after recovery of blood glucose levels, fodrin breakdown products and active caspase-3 markedly increased, concomitant with a twofold increase in caspase-3-like enzymatic activity. When rats were treated with neuroprotective doses of cyclosporin A, but not with FK 506, the redistribution of apoptosis-inducing factor and cytochrome c was reduced and fodrin breakdown products and active caspase-3 immuno-reactivity was diminished whereas the extracellular calcium concentration was unaffected. We conclude that hypoglycemia leads to mitochondrial permeability transition which, upon recovery of energy metabolism, mediates the activation of caspase-3 and calpains, promoting cell death.

Discovery of a novel compound: insight into mechanisms for acrylamide-induced axonopathy and colchicine-induced apoptotic neuronal cell death

The exposure of humans and experimental animals to certain industrial toxins such as acrylamide is known to cause nerve damage classified as axonopathy, but the mechanisms involved are poorly understood. Here we show that acrylamide induces morphological changes and tyrosine phosphorylation of focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (Pyk2), a member of the FAK subfamily, in human differentiating neuroblastoma SH-SY5Y cells. Furthermore, we identified a novel molecule designated 'compound-1' that inhibits the morphological and biochemical events. Daily oral administrations of the compound also effectively alleviated behavioral deficits in animals elicited by acrylamide in inclined plane testing, landing foot spread testing and rota-rod performance testing. The compound also effectively inhibited the biological and biochemical responses caused by another axonopathy inducer, colchicine, including tyrosine phosphorylation of Pyk2, formation of an 85-kDa poly(ADP-ribose)polymerase (PARP) fragment and apoptosis-associated induction of the NAPOR gene as well as neuronal cell death. Our findings not only provide insight into FAK and Pyk2 functions in neuronal cells, but may also be important in the development of therapeutic agents for peripheral neuropathy and neurodegeneration.

The pathogenic activation of calpain: a marker and mediator of cellular toxicity and disease states

Over-activation of calpain, a ubiquitous calcium-sensitive protease, has been linked to a variety of degenerative conditions in the brain and several other tissues. Dozens of substrates for calpain have been identified and several of these have been used to measure activation of the protease in the context of experimentally induced and naturally occurring pathologies. Calpain-mediated cleavage of the cytoskeletal protein spectrin, in particular, results in a set of large breakdown products (BDPs) that are unique in that they are unusually stable. Over the last 15 years, measurements of BDPs in experimental models of stroke-type excitotoxicity, hypoxia/ischemia, vasospasm, epilepsy, toxin exposure, brain injury, kidney malfunction, and genetic defects, have established that calpain activation is an early and causal event in the degeneration that ensues from acute, definable insults. The BDPs also have been found to increase with normal ageing and in patients with Alzheimer's disease, and the calpain activity may be involved in related apoptotic processes in conjunction with the caspase family of proteases. Thus, it has become increasingly clear that regardless of the mode of disturbance in calcium homeostasis or the cell type involved, calpain is critical to the development of pathology and therefore a distinct and powerful therapeutic target. The recent development of antibodies that recognize the site at which spectrin is cleaved has greatly facilitated the temporal and spatial resolution of calpain activation in situ. Accordingly, sensitive spectrin breakdown assays now are utilized to identify potential toxic side-effects of compounds and to develop calpain inhibitors for a wide range of indications including stroke, cerebral vasospasm, and kidney failure.

Hippocampal microtubule-associated protein-2 alterations with contextual memory

Using immunohistochemistry and immunoblots, we show that alterations in hippocampal microtubule-associated protein-2 appear to be highly correlated with contextual memory as measured by significantly heightened fear responses. Compared to naive controls, rats trained in a novel context showed significantly increased immunostaining for the high molecular weight microtubule-associated protein-2a/b. This increase was observed 2 weeks after training and it was selective for hippocampal CA1 and CA2 pyramidal cells. Pre-exposure to the training context one month before training altered the hippocampal microtubule-associated protein-2 response; in these animals only the dentate gyrus showed significantly increased microtubule-associated protein-2a/b. Training-related increases in immunohistochemical staining for microtubule-associated protein-2 suggested that there was an increase in overall intact protein, an increase in immunoreactive breakdown products, or changes in protein compartmentalization. Immunoblots of hippocampal homogenates reacted with monoclonal antibodies to microtubule-associated protein-2a/b showed an increased presence of breakdown products in trained animals compared to untrained controls. Additional immunoblot studies demonstrated statistically significant decreases in the levels and/or phosphorylation state of the low molecular weight microtubule-associated protein-2c in the hippocampus of trained animals as compared to that of controls. These alterations in microtubule-associated protein-2 may reflect dendritic remodeling related to contextual memory storage.

Glutamate in neurologic diseases

Excitotoxicity has been implicated as a mechanism of neuronal death in acute and chronic neurologic diseases. Cerebral ischemia, head and spinal cord injury, and prolonged seizure activity are associated with excessive release of glutamate into the extracellular space and subsequent neurotoxicity. Accumulating evidence suggests that impairment of intracellular energy metabolism increases neuronal vulnerability to glutamate which, even when present at physiologic concentrations, can damage neurons. This mechanism of slow excitotoxicity may be involved in neuronal death in chronic neurodegenerative diseases such as the mitochondrial encephalomyopathies, Huntington's disease, spinocerebellar degeneration syndromes, and motor neuron diseases. If so, glutamate antagonists in combination with agents that selectively inhibit the multiple steps downstream of the excitotoxic cascade or help improve intracellular energy metabolism may slow the neurodegenerative process and offer a therapeutic approach to treat these disorders.

Regional distribution and time-course of calpain activation following kainate-induced seizure activity in adult rat brain

Systemic injection of kainic acid (KA) in adult rat elicits a pattern of neuronal pathology which exhibits several features of human temporal lobe epilepsy. KA-induced seizure activity is accompanied by the activation of the calcium-dependent protease calpain in limbic structures. In the present study, we evaluated the spatio-temporal activation of calpain after the onset of seizure activity by immunohistochemistry using an antibody for the spectrin breakdown product (sbdp) generated by calpain-mediated spectrin proteolysis. In addition, we compared the changes in sbdp immunoreactivity with those in immunoreactivity to subunits of the Glu/AMPA receptors (GluR1 and GluR2/3). One hour after seizure onset, sbdp accumulation was observed in selected interneurons in stratum oriens and in the hilus of the dentate gyrus. By 4 h, sbdp immunoreactivity was prominent in dendritic fields of the hippocampus as well as in neurons in thalamus and piriform cortex. By 8 h, sbdp immunoreactivity had disappeared from interneurons but was localized in pyramidal cell bodies in hippocampus. Intense labeling of cell bodies and dendritic fields persisted until 5 days following KA treatment. Changes in GluR subunit immunoreactivity were mirror images of those seen for sbdp. In general, increased sbdp immunoreactivity in dendritic fields was associated with decreased GluR1 immunoreactivity. However, increased sbdp immunoreactivity in neuronal perikarya was also associated with increased GluR immunoreactivity. These results indicate that calpain activation following seizure onset exhibits a specific spatio-temporal pattern, with activation in restricted interneurons preceding widespread activation in pyramidal neurons. Calpain activation also precedes neuronal pathology and could thus represent an initial trigger for neuronal pathology. Finally, the results suggest that calpain activation produces rapid alterations in GluR subunit properties which could be involved in the hyperexcitability observed following seizure activity.

Long-term hippocampal slices: a model system for investigating synaptic mechanisms and pathologic processes

Organotypic cultures provide a unique strategy with which to examine many aspects of brain physiology and pathology. Long-term slice cultures from the hippocampus, a region involved in memory encoding and one that exhibits early degeneration in Alzheimer's disease and ischemia, are particularly valuable in this regard due to their expression of synaptic plasticity mechanisms (e.g., long-term potentiation) and responsiveness to pathological insults (e.g., excitotoxicity). Long-term slices can be prepared from hippocampi at the second or third postnatal week of development and thus incorporate a number of relatively mature features; further signs of maturation and the preservation of adult-like characteristics occur over succeeding weeks. The stability of the cultured slice renders it an appropriate model for studying 1) prolonged regulation/stabilization events linked to synaptogenesis and certain forms of plasticity, 2) temporal patterns of cellular atrophy associated with pathogenic conditions such as ischemia and epilepsia, and 3) slow processes associated with aging and age-related pathologies.

Translational suppression of calpain I reduces NMDA-induced spectrin proteolysis and pathophysiology in cultured hippocampal slices

Transfection of cultured hippocampal slices for five days with antisense oligonucleotides directed against mRNA encoding calpain I resulted in an approximately 60% decrease in the amount of caseinolytic activity stimulated by 10 microM calcium. Increases in a single proteolytic fragment of spectrin produced by 10-20 min of NMDA receptor stimulation were substantially (approximately 50%) reduced in antisense treated slices; this effect was not obtained in slices exposed to NMDA for 45 min. Attenuation of NMDA receptor-induced spectrin proteolysis by the antisense oligonucleotides was confirmed in immunoassays using antibodies that recognize multiple spectrin breakdown products and in immunocytochemical experiments with an antibody that detects an individual calpain I-mediated fragment. Translational suppression of calpain I did not detectably affect evoked synaptic responses but markedly improved their recovery from a 15 min infusion of NMDA. These results indicate that spectrin breakdown products provide a useful index of in situ calpain I activity and support the hypothesis that the protease plays a significant role in excitotoxicity.

Proteolysis of spectrin by calpain accompanies theta-burst stimulation in cultured hippocampal slices

Tests were carried out to determine if repetitive bursts of afferent stimulation activate calpain, a calcium-dependent protease hypothesized to be involved in the production of long-term potentiation. Antibodies against a stable breakdown product that results from proteolysis of spectrin by calpain were used to identify sites of enzyme activation in cultured hippocampal slices. Slices in which theta-burst stimulation was applied to the Schaffer collateral fibers had pronounced accumulations of breakdown product that were restricted to field CA1, the zone innervated by the stimulated axons. Labelling occurred in the form of scattered puncta and was also present in dendritic processes. The extent of these effects was correlated (r = 0.73) with the amount of theta-burst stimulation delivered. Control slices or those receiving low frequency stimulation had variable, but uniformly lower, amounts of breakdown product and were clearly distinguishable from those given theta bursts. Statistical analyses using a six point rating scheme confirmed this point (P < 0.001). These results satisfy an essential prediction of the hypothesis that calpain plays an important role in the induction of long-term potentiation.

Calpain inhibitor AK295 protects neurons from focal brain ischemia. Effects of postocclusion intra-arterial administration

BACKGROUND AND PURPOSE

This research was performed to determine whether a selective inhibitor of the calcium-dependent protease, calpain, could reduce ischemia-associated brain damage when peripherally administered after a vascular occlusion.

METHODS

A variation of the rat middle cerebral artery occlusion model was used. A range of doses of AK295 (a novel calpain inhibitor synthesized for this purpose) was continuously infused through the internal carotid artery, beginning 1.25 hours from the initiation of the occlusion. Rats were killed at 21 hours, and the infarct volume was quantified.

RESULTS

Postocclusion (1.25-hour) infusion of the calpain inhibitor AK295 elicited a dose-dependent neuroprotective effect after focal ischemia. The highest dose tested (3 mg/kg per hour) afforded the maximum effect, illustrated by a 32% reduction in infarct volume 21 hours after the ischemia (vehicle, 81.7 +/- 4.7 mm3; AK295, 54.9 +/- 6.9 mm3; P < .007).

CONCLUSIONS

These data provide the first evidence that a peripherally administered calpain inhibitor can protect against ischemic brain damage. They offer further support for an important role of calpain proteolysis in the brain degeneration associated with cerebral ischemic events and suggest that selective calpain inhibitors provide a rational, novel, and viable means of treating such neurodegenerative problems.

Calcium-activated proteolysis in rat neocortex induced by transient focal ischemia

Ischemia-induced elevation of intracellular calcium triggers a cascade of events which is considered to play a major role in neuronal death. One candidate to participate in this process is the calcium-sensitive protease, calpain. This protease is activated by calcium, and is capable of degrading critical cytoskeletal and regulatory proteins. In order to further elucidate the role of calpain in focal ischemic damage, the present study investigated the proteolysis of spectrin, a preferred substrate for calpain, in response to transient focal ischemia. Ischemia was induced by occluding reversibly both carotid arteries and the left middle cerebral artery for three hours in Sprague-Dawley rats. Western blotting techniques were used to identify and quantify the amounts of spectrin breakdown products (BDPs) in neocortical samples from the area destined for infarction, the peri-infarct area, and the contralateral hemisphere. Substantial increases in spectrin proteolysis were observed within the first few hours of ischemia in the areas that will undergo infarction. The increase in spectrin BDPs in these areas reached a plateau around the end of the 3 h ischemic period. In the peri-infarct zone, the levels of spectrin BDPs increased in a biphasic manner. A small to moderate increase was observed by the second hour of ischemia, followed by a larger increase between the 6th and 24th hours post-ischemia. The contralateral neocortex showed a significant increase in BDPs at 2 h after the initiation of ischemia. A smaller increase in BDPs was observed thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)

Postischemic administration of AK275, a calpain inhibitor, provides substantial protection against focal ischemic brain damage

Experiments were conducted to determine whether a potent, reversible calpain inhibitor could reduce the cortical ischemic brain damage associated with focal ischemia in the rat. AK275 (Z-Leu-Abu-CONH-CH2CH3), the active isomer of the diastereomeric mixture, CX275, was employed in conjunction with a novel method of perfusing drug directly onto the infarcted cortical surface. This protocol reduced or eliminated numerous, nonspecific pharmacokinetic, hemodynamic, and other potentially confounding variables that might complicate interpretation of any drug effect. Focal ischemia was induced using a variation of the middle cerebral artery occlusion method. These studies demonstrated a reliable and robust neuroprotective effect of AK275 over the concentration range of 10 to 200 microM (perfused supracortically at 4 microliters/h for 21 h). Moreover, a 75% reduction in infarct volume was observed when initiation of drug treatment was delayed for 3 h postocclusion. Our data further support an important role of calpain in ischemia-induced neuropathology and suggest that calpain inhibitors may provide a unique and potentially powerful means of treating stroke and other ischemic brain incidents.

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

BACKGROUND AND PURPOSE

Excessive elevation of intracellular calcium and uncontrolled activation of calcium-sensitive events are believed to play a central role in ischemic neuronal damage. Calcium-activated proteolysis by calpain is a candidate to participate in this form of pathology because it is activated under ischemic conditions and its activation results in the degradation of crucial cytoskeletal and regulatory proteins. The present studies examined the effects of a cell-penetrating inhibitor of calpain on the pathological outcome after transient focal ischemia in the brain.

METHODS

Twenty-five male Sprague-Dawley rats were divided into four groups: a saline-treated group, a vehicle-treated group, and two calpain inhibitor-treated groups (Cbz-Val-Phe-H; 30-mg/kg and 60-mg/kg cumulative doses). Ischemia was induced by occluding the left middle cerebral artery and both common carotid arteries for 3 hours followed by reperfusion. Animals were killed 72 hours after surgery, and quantitative measurements of infarction volumes were performed using histological techniques. Eight additional rats were killed 30 minutes after ischemia and examined for the extent of proteolysis using immunoblot techniques. A final group of 12 animals was decapitated after injection of vehicle or calpain inhibitor, and the proteolytic response was measured after 60 minutes of total ischemia.

RESULTS

Rats treated with Cbz-Val-Phe-H exhibited significantly smaller volumes of cerebral infarction than saline-treated or vehicle-treated control animals. Intravenous injections of cumulative doses of 30 mg/kg or 60 mg/kg of Cbz-Val-Phe-H were effective in reducing infarction, edema, and calcium-activated proteolysis. The proteolytic response to postdecapitation ischemia was also reduced by the calpain inhibitor.

CONCLUSIONS

These results demonstrate the neuroprotective effect of a cell-penetrating calpain inhibitor when administered systemically. The findings suggest that targeting intracellular, calcium-activated mechanisms, such as proteolysis, represents a viable therapeutic strategy for limiting neurological damage after ischemia.

Effects of intrahippocampal colchicine administration on the levels and localization of microtubule-associated proteins, tau and MAP2

Colchicine, a microtubule disrupting agent, has been used to model several aspects of Alzheimer's disease-related neuropathology. The formation of neurofibrillary tangles, one of the pathological hallmarks of Alzheimer's disease, involves the loss of tau (a low mol. wt. microtubule-associated protein) from axons and accumulation of abnormally phosphorylated tau in somatodendritic compartments. Other cytoskeletal proteins, such as microtubule-associated protein 2 (MAP2), disappear as tau accumulates. The present study was directed at evaluating the effects of colchicine on tau and MAP2, to determine if changes in their levels or distribution might be similar to those which precede the formation of neurofibrillary tangles in Alzheimer's disease. Six hours following intrahippocampal colchicine injection (3.5 micrograms injected into two rostro-caudal locations) tau-1 immunostaining was enhanced in CA1 s. radiatum and decreased in the outer molecular layer of the dentate gyrus. In addition, a shift in the relative abundance of tau isoforms was observed in Western blots. Both the immunocytochemical and immunoblot results are consistent with a dephosphorylation of tau. Loss of MAP2 was evident 3 days postinjection which coincided with a loss of Cresyl violet staining in granule cell, CA3, subicular and entorhinal neurons. Accumulation of tau or MAP2 in neuronal perikarya was not observed at any postinjection time points. Thus, intrahippocampal colchicine administration does not model the shift in tau localization, excessive tau phosphorylation, or other cytoskeletal alterations that are suggested to precede or accompany the formation of neurofibrillary pathology in Alzheimer's disease.

Corticosterone exacerbates kainate-induced alterations in hippocampal tau immunoreactivity and spectrin proteolysis in vivo

Aberrant elevations in intracellular calcium levels, promoted by the excitatory amino acid glutamate, may be a final common mediator of the neuronal damage that occurs in hypoxic-ischemic and seizure disorders. Glutamate and altered neuronal calcium homeostasis have also been proposed to play roles in more chronic neurodegenerative disorders, including Alzheimer's disease. Any extrinsic factors that may augment calcium levels during such disorders may significantly exacerbate the resulting damage. Glucocorticoids (GCs), the adrenal steroid hormones released during stress, may represent one such extrinsic factor. GCs can exacerbate hippocampal damage induced by excitotoxic seizures and hypoxia-ischemia, and we have observed recently that GCs elevate intracellular calcium levels in hippocampal neurons. We now report that the excitotoxin kainic acid (KA) can elicit antigenic changes in the microtubule-associated protein tau similar to those seen in the neurofibrillary tangles of Alzheimer's disease. KA induced a transient increase in the immunoreactivity of hippocampal CA3 neurons towards antibodies that recognize aberrant forms of tau (5E2 and Alz-50). The tau immunoreactivity appeared within 3 h of KA injection, preceded extensive neuronal damage, and subsequently disappeared as neurons degenerated. KA also caused spectrin breakdown, indicating the involvement of calcium-dependent proteases. Physiological concentrations of corticosterone (the species-typical GC of rats) enhanced the neuronal damage induced by KA and, critically, enhanced the intensity of tau immunoreactivity and spectrin breakdown. Moreover, the GC enhancement of spectrin proteolysis was prevented by energy supplementation, supporting the hypothesis that GC disruption of calcium homeostasis in the hippocampus is energetic in nature. Taken together, these findings demonstrate that neurofibrillary tangle-like alterations in tau, and spectrin breakdown, can be induced by excitatory amino acids and exacerbated by GCs in vivo.

Amyloid precursor protein mRNA encoding the Kunitz protease inhibitor domain is increased by kainic acid-induced seizures in rat hippocampus

A 168-nucleotide exon, found in alternatively spliced amyloid precursor protein (APP) mRNAs, encodes a Kunitz protease inhibitor (KPI) domain. Kainic acid (ip) caused a selective increase of KPI mRNA in rat hippocampus. By in situ hybridization, KPI mRNA was induced in the neuronal layers of the hippocampus 11-12 h after the onset of kainate-induced seizures. The kainate-induced elevation of the KPI-containing APP-770 mRNA was blocked by pretreatment with the anticonvulsant pentobarbital. These data suggest that kainate-induced seizures cause alterations in APP RNA stability and/or processing in rat hippocampal neurons.

Seizure activity-induced changes in polyamine metabolism and neuronal pathology during the postnatal period in rat brain

Systemic injection of kainic acid (KA) does not cause neuronal pathology in limbic structures in rat brain prior to postnatal day (PND) 21. The present study tested if the development of the pathogenic response is associated with the maturation of a link between seizure activity and polyamine metabolism. Pathology was assessed with histological techniques and with the binding of [3H]Ro5-4864, a ligand for the peripheral type benzodiazepine binding sites (PTBBS), a marker of glial cell proliferation. In agreement with previous results, peripherally administered kainate at doses sufficient to induce intense behavioral seizures produced a loss of Nissl staining in hippocampus after PND 21 but not at earlier ages. The pattern of neuronal damage observed after PND 21 resembled that found in adult animals: extensive losses of Nissl staining in area CA3 of hippocampus and in piriform cortex, more modest effects in CA1 and sparing of the granule cells of the dentate gyrus. Similarly, no increase in [3H]Ro5-4864 binding as a result of KA administration was observed in hippocampus and piriform cortex until PND 21. Ornithine decarboxylase (ODC) activity and putrescine levels were high in the neonatal brain and decreased to reach adult values by PND 21. KA-induced seizure activity did not significantly alter both variables until PND 21. After PND 21, ODC activity and putrescine levels markedly increased 16 h after KA-induced seizure activity in hippocampus and piriform cortex. The magnitude of the effects increased between PND 21 and PND 30, at which point the changes in both parameters were comparable to those found in adults. Polyamines stimulate the activity of the calcium-dependent proteases calpain in brain fractions and may increase calpain-mediated proteolysis in situ. In accord with this, kainate-induced breakdown of spectrin, a preferred substrate of calpain, measured 16 h after KA injection followed a developmental curve parallel to that for kainate-induced increases in putrescine levels. These results indicate that the onset of vulnerability to seizure activity triggered by kainic acid is correlated with the development of an ODC/polyamine response to the seizures and further support a critical role for the ODC/polyamine pathway in neuronal pathology following a variety of insults.

Spectrin breakdown products increase with age in telencephalon of mouse brain

Calcium activated proteolysis of brain spectrin produces characteristic breakdown products (BDPs), the concentrations of which increase markedly in many instances of brain pathology. Results reported here indicate that levels of the BDPs rise with age (3-30 months) in the telencephalon but not in the hindbrain of Balb/c mice. These observations suggest that spectrin breakdown is a pathologic biochemical marker which increases with age in some but not all brain regions.

Effects of injected Alzheimer beta-amyloid cores in rat brain

Although amyloid deposits have long been known to accumulate in Alzheimer disease (AD) brain, their origin and significance remain speculative. Because of the lack of an in vivo model where amyloid deposits can be induced, the relationship of the extracellular beta-amyloid deposits to other AD pathology has never been directly investigated. Therefore, we injected SDS-isolated amyloid cores into rat cortex and hippocampus. Similarly isolated lipofuscin fractions from control human brains were injected on the contralateral side. Rats were perfused and brains were examined immunohistochemically at 2 days, 7 days, and 1 month after injection. Alz-50, a monoclonal antibody against abnormally phosphorylated tau proteins, stained neurons along the cortical needle track at 2 but not 7 days after injection of either amyloid or lipofuscin. At 1 month, however, ubiquitin, Alz-50 antigen, and silver-positive structures were observed only in response to amyloid. In 7 of 10 animals, there was considerable neuronal loss in the hippocampal layers. In each instance, these effects were in the immediate vicinity of beta-protein immunoreactive material. Marked neuronal loss was never observed at any time after lipofuscin injection. These results indicate a neuronal response to amyloid. When preparations of mature plaque amyloid isolated from the AD brain are injected into the rat brain, they exert neurotoxic effects and induce antigens found in the AD brain.

Complex interactions between polyamines and calpain-mediated proteolysis in rat brain

Polyamine synthesis is induced by various extracellular signals, and it is widely held that this biochemical response participates in cell growth and differentiation. Certain of the triggers for synthesis in brain tissues also increase the breakdown of high-molecular-weight structural proteins, apparently by activating calcium-dependent proteases (calpains). The present experiments tested the possibility that calpain activity is modulated by polyamines. Spermine, spermidine, and putrescine all increased calcium-dependent proteolysis of [14C]casein by soluble fractions of rat brain. The order of potency was spermine greater than spermidine greater than putrescine, with apparent affinities of 30, 300, and 6,000 microM, respectively. Each of the three polyamines at physiological concentrations also potentiated the calcium-dependent breakdown of two endogenous high-molecular-weight structural proteins known to be substrates of calpain, in both supernatant and membrane fractions. The thiol protease inhibitor leupeptin, a known calpain inhibitor, also inhibited calcium-dependent proteolysis in the presence and absence of polyamines. The polyamines did not increase the activity of purified calpain I or calpain II determined with either [14C]casein or purified spectrin as the substrate, nor did they interfere with the inhibitory effects of calpastatin, an endogenous inhibitor of calpain. However, polyamines potentiated the stimulation of endogenous but not purified calpain activity produced by an endogenous calpain activator. These results suggest a role for polyamines in protein degradation as well as protein synthesis.

Inhibition of proteolysis protects hippocampal neurons from ischemia

Intense proteolysis of cytoskeletal proteins occurs in brain within minutes of transient ischemia, possibly because of the activation of calcium-sensitive proteases (calpains). This proteolytic event precedes overt signs of neuronal degeneration, is most pronounced in regions of selective neuronal vulnerability, and could have significant consequences for the integrity of cellular function. The present studies demonstrate that (i) the early phase of enhanced proteolysis is a direct response to hypoxia rather than other actions of ischemia, (ii) it is possible to pharmacologically inhibit the in vivo proteolytic response to ischemia, (iii) inhibition of proteolysis is associated with a marked reduction in the extent of neuronal death, and (iv) protected neurons exhibit normal-appearing electrophysiological responses and retain their capacity for expressing long-term potentiation, a form of physiological plasticity thought to be involved in memory function. These observations indicate that calcium-activated proteolysis is an important component of the post-ischemic neurodegenerative response and that targeting this response may be a viable therapeutic strategy for preserving both the structure and function of vulnerable neurons.

A brief period of hypoxia causes proteolysis of cytoskeletal proteins in hippocampal slices

Breakdown products (BDPs) resulting from the partial proteolysis of spectrin were examined in hippocampal slices after periods of hypoxia lasting for 5 or 10 min. The concentration of a approximately 155 kDa BDP increased nearly twofold after 5 min of hypoxia; further increases were not seen with 10 min episodes or 10 min of hypoxia followed by reoxygenation. The hypoxia-induced proteolysis was blocked by prior infusion of a newly introduced inhibitor of calpain (calpain inhibitor I, 200 microM). Together with previously published data showing improved recovery of hippocampal slices from hypoxia in the presence of calpain inhibitors, these data suggest that activation of calpain may contribute significantly to the pathophysiology of ischemia.

Entorhinal cortex lesion or intrahippocampal colchicine injection increases peripheral type benzodiazepine binding sites in rat hippocampus

The peripheral type benzodiazepine binding site (PTBBS) has been proposed to be a good marker for reactive glial cells following brain insults. In the present study, homogenate binding of 3H-Ro5-4864 and quantitative autoradiography of 3H-PK-11195 binding (two ligands for the PTBBS) were used to assess the distribution, time-course and extent of reactive gliosis in the hippocampus following deafferentation by unilateral entorhinal cortex lesion or neuronal death produced by intrahippocampal colchicine injection. Intrahippocampal colchicine injections produced a 3-fold increase in 3H-Ro5-4864 binding in the dentate gyrus within 2 days. This effect was doubled in animals pretreated with the lysosomal inhibitor chloroquine. Quantitative autoradiography of 3H-PK-11195 binding 1 or 2 weeks after colchicine injection indicated that the increase in binding was restricted to the dorsal hippocampus both rostrally and caudally and was present in the dentate gyrus and CA1. Following a unilateral electrolytic lesion of the entorhinal cortex, the binding of 3H-Ro5-4864 to homogenates of the dentate gyrus was doubled 18 h after the lesion, reached a maximum at 4 days post-lesion, and returned to control values by 2 months after the lesion. A transient increase in binding was also observed 2 and 4 days post-lesion in the dentate gyrus contralateral to the lesion side. Autoradiography of 3H-PK-11195 binding indicated that the increase in PTBBS following entorhinal cortex lesion was restricted to the molecular layer of the dentate gyrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Degradation of microtubule-associated protein 2 and brain spectrin by calpain: a comparative study

The in vitro degradation of microtubule-associated protein 2 (MAP-2) and spectrin by the calcium-dependent neutral protease calpain was studied. Five major results are reported. First, MAP-2 isolated from twice-cycled microtubules (2 X MT MAP-2) was extremely sensitive to calpain-induced hydrolysis. Even at an enzyme-to-substrate ratio (wt/wt) of 1:200, 2 X MT MAP-2 was significantly degraded by calpain. Second, MAP-2 purified from the total brain heat-stable fraction (total MAP-2) was significantly more resistant to calpain-induced hydrolysis compared with 2 X MT MAP-2. Third, MAP-2a and MAP-2b were proteolyzed similarly by calpain, although some relative resistance of MAP-2b was observed. Fourth, the presence of calmodulin significantly increased the extent of calpain-induced hydrolysis of the alpha-subunit of spectrin. Fifth, the two neuronal isoforms of brain spectrin (240/235 and 240/235E, referred to as alpha/beta N and alpha/beta E, respectively) showed different sensitivities to calpain. alpha N-spectrin was significantly more sensitive to calpain-induced degradation compared to alpha E-spectrin. Among other things, these results suggest a role for the calpain-induced degradation of MAP-2, as well as spectrin, in such physiological processes as alterations in synaptic efficacy, dendritic remodeling, and in pathological processes associated with neurodegeneration.

Modulation of DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/quisqualate receptors by phospholipase A2: a necessary step in long-term potentiation?

The effects of kainate (KA)-induced epileptic seizures on the binding properties of hippocampal glutamate receptors, on the modulation of DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/quisqualate receptor by phospholipase A2 (PLA2), and on the formation of long-term potentiation (LTP) were studied in hippocampal membranes and hippocampal slices. Systemic administration of KA (10 mg/kg; 15 hr survival) produced specific changes in the binding properties of the AMPA/quisqualate receptors and its regulation. Whereas the binding of various ligands to the N-methyl-D-aspartate receptors was not modified by KA treatment, there was a significant decrease in the maximal number of binding sites for [3H]AMPA. In addition, the increase in [3H]AMPA binding elicited by PLA2 treatment of hippocampal, but not cerebellar, membranes was markedly decreased after KA injection. LTP was also substantially reduced in area CA1 of hippocampal slices from KA-treated animals. The loss of LTP was not due to changes in postsynaptic responses elicited by the bursts that trigger the potentiation effect, thus suggesting that KA treatment disrupts processes that follow N-methyl-D-aspartate receptor activation. Systemic administration of KA was associated with calpain activation as the amount of spectrin breakdown products was increased severalfold in hippocampus but not in cerebellum. Pretreatment of telencephalic membranes with calpain greatly reduced the PLA2-induced increase in [3H]AMPA binding. The results provide evidence in favor of an essential role of PLA2 in the development of LTP and suggest that the order of activation of different calcium-dependent processes is critical for producing the final changes underlying LTP.

Increased spectrin proteolysis in fibroblasts from aged and Alzheimer donors

Since calcium homeostasis is altered in cultured skin fibroblasts from aged and Alzheimer donors, the present study examined the degradation of spectrin, a substrate of the calcium dependent protease calpain. Spectrin proteolysis was estimated as the percentage of spectrin breakdown products (e.g., 150 + 155 kDa bands) per total spectrin immunoreactivity. In the baseline condition (e.g., unstimulated fibroblasts), spectrin breakdown was 53% greater in cells from aged donors when compared to cells from either young or Alzheimer donors. Compared to unstimulated cells, serum increased spectrin breakdown in cells from aged (22.4%) or Alzheimer (92.1%) donors but was ineffective in cells from young donors. Thus, when compared to young donors (100%), serum stimulation increased spectrin proteolysis by 183.9% (aged) or 231.7% (Alzheimer) after serum stimulation. Treatment of unstimulated cells with carbonyl cyanide 4-trifluoromethoxy-phenylhydrazone (FCCP), an uncoupler of mitochondrial function, increased spectrin degradation by 360.6% (young), 242.4% (aged) or 239.7% (Alzheimer) when compared to unstimulated cells of the same group. The combination of FCCP and serum stimulation enhanced spectrin breakdown in cells from aged (123.6%) and Alzheimer (154.0%) donors when compared to young cells (100%). Thus, changes in the regulation of calcium dependent proteases may contribute to decreased cell spreading and may play a role in the altered cytoskeletal dynamics characteristic of Alzheimer's disease.

Astrocytes: a possible primary site for colchicine-mediated neurotoxicity in the rat striatum

Ultrastructural changes in rat astrocytes including endfoot swelling and rupture of plasma membranes were seen as early as 1 h after injection of 6.0 micrograms colchicine (CO) into the striatum. Significant change in neuronal morphology was not seen by 24 h. Astrocytes may therefore be primary targets for CO-mediated damage, which then may have secondary neurotoxic consequences.

Calpain inhibitors improve the recovery of synaptic transmission from hypoxia in hippocampal slices

Two inhibitors of calcium activated proteases (calpains) were tested for their effects on hypoxia-induced synaptic dysfunction in hippocampal slices. Hypoxic episodes lasting for either one or two minutes beyond the point at which action potentials (fiber volleys) disappeared were used. Leupeptin and calpain inhibitor I had no reliable effects on the rate at which synaptic transmission declined during hypoxia or the time required for loss of action potentials, but both drugs did substantially improve the degree of recovery. Moreover, the percentage of slices meeting an arbitrary criterion for viability after hypoxic treatment was greatly increased by the drug treatment. These results point to the conclusion that proteolysis triggered by calcium influx during hypoxia contributes to pathophysiology.

The protease inhibitor leupeptin interferes with the development of LTP in hippocampal slices

The effect of leupeptin, an inhibitor of thiol-proteases, was tested on the induction of long-term potentiation (LTP) in field CA1 of hippocampal slices. Two h of drug application did not produce substantial changes while a greater than 3-h application caused a sizeable reduction in the degree of LTP induced. Leupeptin had no obvious effects on the facilitation of postsynaptic responses occurring within or between the short high frequency bursts used to induce LTP, suggesting that the drug acted on cellular chemistries occurring after the initial physiological events that normally trigger LTP. These results are consistent with the hypothesis that a calcium-activated thiol protease (calpain) is involved in the induction of LTP.

Ischemia triggers NMDA receptor-linked cytoskeletal proteolysis in hippocampus

Transient forebrain ischemia is followed within minutes by accelerated proteolysis of the cytoskeletal protein, spectrin. This effect is most pronounced in the selectively vulnerable CA1 region of hippocampus which also experiences a second proteolytic phase during the terminal stages of neuronal degeneration. Both proteolytic phases are suppressed by MK-801, an NMDA receptor antagonist. Cytoskeletal disruption, via NMDA receptor-linked proteolytic events, is suggested to predispose vulnerable neurons to delayed cell death.

Dissociation between changes in glutamate receptor binding sites and their coupling to phosphatidylinositol metabolism following intrahippocampal colchicine injection

Intrahippocampal colchicine injection produces a rapid death of granule cells and pyramidal neurons in the hippocampus in the rat. Under the appropriate assay conditions, [3H]glutamate labels the N-methyl-D-aspartate type of glutamate receptors while [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate labels the quisqualate type. Unilateral injection of colchicine (15 micrograms) in the dorsal hippocampus did not produce any change in [3H]glutamate and [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate binding in membrane fractions from the dentate gyrus or CA1 field contralateral to the injection side, at least up to 12 days after the injection. However, it produced a progressive decrease in the binding of both ligands in dentate gyrus and CA1 of the injected hippocampus. In the dentate gyrus the changes in binding as a function of time after the injection were biphasic with a rapid exponential decrease (t1/2 about 8 days for both [3H]glutamate and [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate) until 12 days after the injection followed by a much slower decrease afterwards. A similar pattern was observed in CA1 although the changes in binding were smaller and delayed by about three days as compared to the dentate gyrus. Kinetic analyses of the binding at equilibrium were performed seven days after the injection and indicated that the changes in [3H]glutamate binding were due to a change in the maximum number of sites but not in affinity for the ligand.(ABSTRACT TRUNCATED AT 250 WORDS)