Inhibition of proteolysis protects hippocampal neurons from ischemia

Neuronal recovery after moderate hypoxia is improved by the calpain inhibitor MDL28170

The role of calcium-activated proteolysis in hypoxic neuronal injury was investigated using an in vitro slice model of moderate hypoxia that mimics many features of an ischemic penumbra. The calpain inhibitor, MDL28170, significantly improved the recovery of synaptic responses in hippocampal slices following prolonged, moderate hypoxia without hypoxic depolarization. This finding further implicates calpain-mediated proteolysis in the development of neuronal injury following moderate metabolic challenge such as occurs in regions of partial ischemia.

DNA fragmentation follows delayed neuronal death in CA1 neurons exposed to transient global ischemia in the rat

Apoptosis is an active, gene-directed process of cell death in which early fragmentation of nuclear DNA precedes morphological changes in the nucleus and, later, in the cytoplasm. In ischemia, biochemical studies have detected oligonucleosomes of apoptosis whereas sequential morphological studies show changes consistent with necrosis rather than apoptosis. To resolve this apparent discrepancy, we subjected rats to 10 minutes of transient forebrain ischemia followed by 1 to 14 days of reperfusion. Parameters evaluated in the CA1 region of the hippocampus included morphology, in situ end labeling (ISEL) of fragmented DNA, and expression of p53. Neurons were indistinguishable from controls at postischemic day 1 but displayed cytoplasmic basophilia or focal condensations at day 2; some neurons were slightly swollen and a few appeared normal. In situ end labeling was absent. At days 3 and 5, approximately 40 to 60% of CA1 neurons had shrunken eosinophilic cytoplasm and pyknotic nuclei, but only half of these were ISEL. By day 14, many of the necrotic neurons had been removed by phagocytes; those remaining retained mild ISEL. Neither p53 protein nor mRNA were identified in control or postischemic brain by in situ hybridization with riboprobes or by northern blot analysis. These results show that DNA fragmentation occurs after the development of delayed neuronal death in CA1 neurons subjected to 10 minutes of global ischemia. They suggest that mechanisms other than apoptosis may mediate the irreversible changes in the CA1 neurons in this model.

The Calpain Hypothesis of Neurodegeneration: Evidence for a Common Cytotoxic Pathway

Calpain's general function and pathogenic role in the CNS are reviewed. Collectively, the literature indicates that calpain proteolysis plays a common and important role in a variety of acute neurodegenerative conditions, including focal ischemia (stroke), global ischemia, traumatic brain injury, and spinal cord injury. This evidence indicates that 1) calpain is activated in an abnormally sustained fashion during cellular events commonly associated with neurodegeneration (e.g., excessive interstitial glutamate and cytosolic calcium); 2) many of calpain's preferred substrates are degraded as important components in these neurodegenerative conditions; 3) calpain activation occurs early in the pathogenic cascade of each, prior to onset of substantial cell death; and 4) calpain inhibitors can effectively reduce the severity of neuronal damage and loss of function normally associated with these acute neurodegenerative perturbations. Calpain proteolysis is also implicated in chronic neurodegenerative diseases, with the strength of current evidence varying among specific diseases. The evidence accumulated for a plausible role in Alzheimer's disease (AD) is currently the strongest. For example, empirical links have been established between abnormal calpain proteolysis and 1) the cellular formation of classic Alzheimer's pathology, such as β-amyloid plaques, neurofibrillary tangles, and Alz-50 immunoreactivity; 2) the brain regions with greatest concentrations of AD-related pathology; and 3) the degeneration of key brain pathways vulnerable in the early stages of the disease. Similar, though less extensive, evidence exists for a potential role of abnormal calpain proteolysis in Parkinson's disease. Finally, for several other chronic neurodegenerative conditions (e.g., Huntington's disease and amyotrophic lateral sclerosis), early evidence is emerging that calpain may also play some pathogenic role. Thus, these data support the possibility that uncontrolled calpain proteolysis may contribute to and/or accelerate the loss of neurons associated with a wide range of neurodegenerative conditions and may, therefore, represent an important, final common cytotoxic pathway for many diverse forms of neurodegeneration. NEUROSCIENTIST 3:314–327, 1997

Calpain is a mediator of preservation-reperfusion injury in rat liver transplantation

Proteases as well as alterations in intracellular calcium have important roles in hepatic preservation-reperfusion injury, and increased calpain activity recently has been demonstrated in liver allografts. Experiments were designed to evaluate (i) hepatic cytosolic calpain activity during different periods of cold ischemia (CI), rewarming, or reperfusion, and (ii) effects of inhibition of calpain on liver graft function using the isolated perfused rat liver and arterialized orthotopic liver transplantation models. Calpain activity was assayed using the fluorogenic substrate Suc-Leu-Leu-Val-Tyr-7-amino-4-methyl coumarin (AMC) and expressed as mean +/- SD pmol AMC released/min per mg of cytosolic protein. Calpain activity rose significantly after 24 hr of CI in University of Wisconsin solution and further increased with longer preservation. Activity also increased within 30 min of rewarming, peaking at 120 min. Increased durations of CI preceding rewarming resulted in significantly higher activity (P < 0.01). Calpain activity increased rapidly upon reperfusion and was significantly enhanced by previous CI (P < 0.01). Calpain inhibition with Cbz-Val-Phe methyl ester significantly decreased aspartate aminotransferase released in the isolated perfused rat liver perfusate (P < 0.05). Duration of survival after orthotopic liver transplantation using livers cold-preserved for 40 hr was also significantly increased (P < 0.05) with calpain inhibitor. In conclusion, calpain proteases are activated during each phase of transplantation and are likely to play an important role in the mechanisms of preservation-reperfusion injury.

Central nervous system resuscitation

Traumatic injury to the central nervous system induces delayed neuronal death, which may be mediated by acute and chronic neurochemical changes. Experimental identification of these injury mechanisms and elucidation of the neurochemical cascade following trauma may provide enhanced opportunities for treatment with novel neuroprotective strategies.

Identification of mu-, m-calpains and calpastatin and capture of mu-calpain activation in endothelial cells

The presence of the calpain-calpastatin system in human umbilical vein endothelial cells (HUVEC) was investigated by means of ion exchange chromatography, Western blot analysis, and Northern blot analysis. On DEAE anion exchange chromatography, calpain and calpastatin activities were eluted at approximately 0.30 M and 0.15-0.25 M NaCl, respectively. For half-maximal activity, the protease required 800 microM Ca2+, comparable to the Ca2+ requirement of m-calpain. By Western blot analysis, the large subunit of mu-calpain (80 kDa) was found to be eluted with calpastatin (110 kDa). Both the large subunit of m-calpain (80 kDa) and calpastatin were detected in the respective active fractions. By Northern blot analysis, mRNAs for large subunits of mu- and m-calpains were detected in single bands, each corresponding to approximately 3.5 Kb. Calpastatin mRNA was observed in two bands corresponding to approximately 3.8 and 2.6 Kb. Furthermore, the activation of mu-calpain in HUVEC by a calcium ionophore was examined, using an antibody specifically recognizing an autolytic intermediate form of mu-calpain large subunit (78 kDa). Both talin and filamin of HUVEC were proteolyzed in a calcium-dependent manner, and the reactions were inhibited by calpeptin, a cell-permeable calpain specific inhibitor. Proteolysis of the cytoskeleton was preceded by the appearance of the autolytic intermediate form of mu-calpain, while the fully autolyzed postautolysis form of mu-calpain (76 kDa) remained below detectable levels at all time points examined. These results indicate that the calpain-calpastatin system is present in human endothelial cells and that mu-calpain may be involved in endothelial cell function mediated by Ca2+ via the limited proteolysis of various proteins.

Crystal structure of calcium bound domain VI of calpain at 1.9 A resolution and its role in enzyme assembly, regulation, and inhibitor binding

The three dimensional structure of calcium-bound domain VI of porcine calpain has been determined to 1.9 A resolution. The crystal structure reveals five EF-hands, one more than previously suggested. There are two EF-hand pairs, one pair (EF1-EF2) displays an 'open' conformation and the other (EF3-EF4) a 'closed' conformation. Unusually, a calcium atom is found at the C-terminal end of the calcium binding loop of EF4. With two additional residues in the calcium binding loop, the fifth EF-hand (EF5) is in a 'closed' conformation. EF5 pairs up with the corresponding fifth EF-hand of a non-crystallographically related molecule. Considering the EF5's role in a homodimer formation of domain VI, we suggest a model for the assembly of heterodimeric calpain. The crystal structure of a Ca2+ bound domain VI-inhibitor (PD150606) complex has been refined to 2.1 A resolution. A possible mode for calpain inhibition is discussed.

Tissue inhibitor of metalloproteinases-1 (TIMP-1) is differentially induced in neurons and astrocytes after seizures: evidence for developmental, immediate early gene, and lesion response

We investigated in vivo the expression of the tissue inhibitor of metalloproteinases-1 (TIMP-1) in the rat CNS after kainate (KA)-induced excitotoxic seizures. In situ hybridization revealed that TIMP-1 mRNA is induced rapidly and massively in most regions of the adult forebrain after KA treatment. Neuronal activity seems to be necessary but not sufficient to trigger TIMP-1 induction, because it is not observed in seizing 10-d-old pups, unlike what is observed in 21- and 35-d-old animals after seizures. The rapid induction of TIMP-1 is not prevented by the inhibitor of protein synthesis cycloheximide, suggesting that, after seizures, TIMP-1 is induced in neurons as an immediate early gene (IEG). The initial neuronal upregulation is followed by enhanced expression in astrocytes, as assessed by double-labeling experiments. In the hippocampus rapid increases in mRNA are followed by relatively delayed (8 hr after KA) increases in TIMP-1 immunoreactivity in the perisomatic and dendro-axonic areas, suggesting secretion of the protein. At 3 d after KA treatment, strong immunoreactivity is found in astrocytes and in the cell bodies and dendro-axonic projections of resistant neurons such as the dentate granule cells. Taken together, the results suggest that TIMP-1 may be instrumental for neurons and astrocytes in coupling early cellular events triggered by seizures with the regulation of long-lasting changes involved in tissue reorganization and/or neuroprotection.

Suppression of cathepsins B and L causes a proliferation of lysosomes and the formation of meganeurites in hippocampus

Cultured hippocampal slices exhibited prominent ultrastructural features of brain aging after exposure to an inhibitor of cathepsins B and L. Six days of treatment with N-CBZ-L-phenylalanyl-L-alanine-diazomethylketone (ZPAD) resulted in a dramatic increase in the number of lysosomes in the perikarya of neurons and glial cells throughout the slices. Furthermore, lysosomes in CA1 and CA3 pyramidal cells were not restricted to the soma but instead were located throughout dendritic processes. Clusters of lysosomes were commonly found within bulging segments of proximal dendrites that were notable for an absence of microtubules and neurofilaments. Although pyknotic nuclei were sometimes encountered, most of the cells in slices exposed to ZPAD for 6 d appeared relatively normal. Slices given 7 d of recovery contained several unique features, compared with those processed immediately after incubation with the inhibitor. Cell bodies of CA1 neurons were largely cleared of the excess lysosomes but had gained fusiform, somatic extensions that were filled with fused lysosomes and related complex, dense bodies. These appendages, similar in form and content to structures previously referred to as "meganeurites," were not observed in CA3 neurons or granule cells. Because meganeurites were often interposed between cell body and axon, they have the potential to interfere with processes requiring axonal transport. It is suggested that inactivation of cathepsins B and L results in a proliferation of lysosomes and that meganeurite generation provides a means of storing residual catabolic organelles. The accumulated material could be eliminated by pinching off the meganeurite but, at least in some cases, this action would result in axotomy. Reduced cathepsin L activity, increased numbers of lysosomes, and the formation of meganeurites are all reported to occur during brain aging; thus, it is possible that the infusion of ZPAD into cultured slices sets in motion a greatly accelerated gerontological sequence.

Suppression of cathepsins B and L causes a proliferation of lysosomes and the formation of meganeurites in hippocampus

Cultured hippocampal slices exhibited prominent ultrastructural features of brain aging after exposure to an inhibitor of cathepsins B and L. Six days of treatment with N-CBZ-L-phenylalanyl-L-alanine-diazomethylketone (ZPAD) resulted in a dramatic increase in the number of lysosomes in the perikarya of neurons and glial cells throughout the slices. Furthermore, lysosomes in CA1 and CA3 pyramidal cells were not restricted to the soma but instead were located throughout dendritic processes. Clusters of lysosomes were commonly found within bulging segments of proximal dendrites that were notable for an absence of microtubules and neurofilaments. Although pyknotic nuclei were sometimes encountered, most of the cells in slices exposed to ZPAD for 6 d appeared relatively normal. Slices given 7 d of recovery contained several unique features, compared with those processed immediately after incubation with the inhibitor. Cell bodies of CA1 neurons were largely cleared of the excess lysosomes but had gained fusiform, somatic extensions that were filled with fused lysosomes and related complex, dense bodies. These appendages, similar in form and content to structures previously referred to as "meganeurites," were not observed in CA3 neurons or granule cells. Because meganeurites were often interposed between cell body and axon, they have the potential to interfere with processes requiring axonal transport. It is suggested that inactivation of cathepsins B and L results in a proliferation of lysosomes and that meganeurite generation provides a means of storing residual catabolic organelles. The accumulated material could be eliminated by pinching off the meganeurite but, at least in some cases, this action would result in axotomy. Reduced cathepsin L activity, increased numbers of lysosomes, and the formation of meganeurites are all reported to occur during brain aging; thus, it is possible that the infusion of ZPAD into cultured slices sets in motion a greatly accelerated gerontological sequence.

Immunohistochemical study of calpain-mediated breakdown products to alpha-spectrin following controlled cortical impact injury in the rat

This study examined the effect of unilateral controlled cortical impact on the appearance of calpain-mediated alpha-spectrin breakdown products (BDPs) in the rat cortex and hippocampus at various times following injury. Coronal sections were taken from animals at 15 min, 1 h, 3 h, 6 h, and 24 h after injury and immunolabeled with an antibody that recognizes calpain-mediated BDPs to alpha-spectrin (Roberts-Lewis et al., 1994). Sections from a separate group of rats were also taken at the same times and stained with hematoxylin and eosin. Analyses of early time points (15 min, 1 h, 3 h, and 6 h following injury) revealed alpha-spectrin BDPs in structurally intact neuronal soma and dendrites in cortex ipsilateral to site of injury that was not present in tissue from sham-injured control rats. By 24 h after injury labeling was not restricted to clearly defined neuronal structures in ipsilateral cortex, although there was an increased extent of diffuse labeling. BDPs to alpha-spectrin in axons were not detected until 24 h after injury, in contrast to the more rapid accumulation of BDPs observed in neuronal soma and dendrites. The presence of BDPs to alpha-spectrin in the cortex at the site of impact, and in the rostral and contralateral cortex, coincided with morphopathology detected by hematoxylin and eosin. alpha-Spectrin BDPs were also observed in the hippocampus ipsilateral to the injury in the absence of overt cell death. This investigation provides further evidence that calpain is activated after controlled cortical impact and could contribute to necrosis at the site of injury. The appearance of calpain-mediated BDPs at sites distal to the contusion site and in the hippocampus also suggests that calpain activation may precede and/or occur in the absence of extensive morphopathological changes.

Tissue inhibitor of metalloproteinases-1 (TIMP-1) is differentially induced in neurons and astrocytes after seizures: evidence for developmental, immediate early gene, and lesion response

We investigated in vivo the expression of the tissue inhibitor of metalloproteinases-1 (TIMP-1) in the rat CNS after kainate (KA)-induced excitotoxic seizures. In situ hybridization revealed that TIMP-1 mRNA is induced rapidly and massively in most regions of the adult forebrain after KA treatment. Neuronal activity seems to be necessary but not sufficient to trigger TIMP-1 induction, because it is not observed in seizing 10-d-old pups, unlike what is observed in 21- and 35-d-old animals after seizures. The rapid induction of TIMP-1 is not prevented by the inhibitor of protein synthesis cycloheximide, suggesting that, after seizures, TIMP-1 is induced in neurons as an immediate early gene (IEG). The initial neuronal upregulation is followed by enhanced expression in astrocytes, as assessed by double-labeling experiments. In the hippocampus rapid increases in mRNA are followed by relatively delayed (8 hr after KA) increases in TIMP-1 immunoreactivity in the perisomatic and dendro-axonic areas, suggesting secretion of the protein. At 3 d after KA treatment, strong immunoreactivity is found in astrocytes and in the cell bodies and dendro-axonic projections of resistant neurons such as the dentate granule cells. Taken together, the results suggest that TIMP-1 may be instrumental for neurons and astrocytes in coupling early cellular events triggered by seizures with the regulation of long-lasting changes involved in tissue reorganization and/or neuroprotection.

The nature of renal cell injury

The main functional change in patients with acute renal failure (ARF) is a decrease in glomerular filtration rate (GFR). The virtual complete recovery of renal function in those patients who survive ARF, as well as the minimal renal histological abnormalities during ARF when the GFR is less than 10 ml/min, suggest that a major component of the renal tubular cell injury is sublethal or reversible. Experimental models of acute tubular necrosis frequently have placed the emphasis on irreversible proximal tubular cell death. The nature of the renal tubular cell injury in ischemic acute renal failure, however, includes not only cell death (necrosis or apoptosis) but also sublethal injury causing cell dysfunction. The role of intracellular calcium, the calcium-dependent enzymes calpain, phospholipase A2 and nitric oxide synthase (NOS), in the pathophophysiology of this renal tubular cell injury during hypoxia/ischemia is described. The effects of calpain and nitric oxide (NO) on the cytoskeleton and cell adhesion are discussed. Potential mechanisms whereby tubular injury leads to a profound fall in GFR, including increased tubuloglomerular feedback and increased distal tubular obstruction, in ischemic acute renal failure are proposed.

Up-regulation of the Nedd2 gene encoding an ICE/Ced-3-like cysteine protease in the gerbil brain after transient global ischemia

We assessed the expression of several genes encoding pro-apoptotic cysteine proteases similar to interleukin-1 beta converting enzyme (ICE) and nematode Ced-3 in association with delayed neuronal death (DND) after transient forebrain ischemia in Mongolian gerbil. The levels of the two species of Nedd2 mRNA concomitantly increased about two-fold in the whole forebrain at 3-6 h after 10-min ischemia and declined to the basal level by 24 h. In situ hybridization revealed that the Nedd2 gene was up-regulated in some neuronal populations in CA1 and CA3 regions of the hippocampus. In contrast, expression of ICE, CPP32/Yama/Apopain, and TX/ICErelll did not change within 48 h. These observations raise the possibility that up-regulation of Nedd2 in the vulnerable neurons may contribute to the proteolytic processes preceding the manifestation of apoptosis and/or necrosis after ischemic insult.

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

The capacity of a calpain inhibitor to reduce losses of neurofilament 200-, neurofilament 68- and calpain 1-mediated spectrin breakdown products was examined following traumatic brain injury in the rat. Twenty-four hours after unilateral cortical impact injury, western blot analyses detected neurofilament 200 losses of 65% (ipsilateral) and 36% (contralateral) of levels observed in naive, uninjured rat cortices. Neurofilament 68 protein levels decreased only in the ipsilateral cortex by 35% relative to naive protein levels. Calpain inhibitor 2, administered 10 min after injury via continuous arterial infusion into the right external carotid artery for 24 h, significantly reduced neurofilament 200 losses to 17% and 3% relative to naive neurofilament 200 protein levels in the ipsilateral and contralateral cortices, respectively. Calpain inhibitor administration abolished neurofilament 68 loss in the ipsilateral cortex and was accompanied by a reduction of putative calpain-mediated neurofilament 68 breakdown products. Spectrin breakdown products mediated by calpain 1 activation were detectable in both hemispheres 24 h after traumatic brain injury and were substantially reduced in animals treated with calpain inhibitor 2 both ipsilaterally and contralaterally to the site of injury. Qualitative immunofluorescence studies of neurofilament 200 and neurofilament 68 confirmed western blot data, demonstrating morphological protection of neuronal structure throughout cortical regions of the traumatically injured brain. Morphological protection included preservation of dendritic structure and reduction of axonal retraction balls. In addition, histopathological studies employing hematoxylin and eosin staining indicated reduced extent of contusion at the injury site. These data indicate that calpain inhibitors could represent a viable strategy for preserving the cytoskeletal structure of injured neurons after experimental traumatic brain injury in vivo.

Calpain activation contributes to dendritic remodeling after brief excitotoxic injury in vitro

The calcium-dependent protease calpain may contribute to neuronal death in acute neurological insults and may be activated very early in the neuronal injury cascade. We assessed the role of calpain in a model of rapid, reversible dendritic injury in murine cortical cultures. Brief sublethal NMDA exposure (10-30 microM for 10 min) resulted in focal swellings, or varicosities, along the length of neuronal dendrites as visualized with the lipophilic membrane tracer Dil or with immunostaining using antibodies to the somatodendritic protein MAP2. These varicosities appeared within minutes of NMDA exposure and recovered spontaneously within 2 hr after NMDA removal. Addition of the calpain inhibitors MDL28,170, calpain inhibitors I and II, and leupeptin (all 1-100 microM) had little effect on the development of NMDA-induced dendrite injury. However, the resolution of varicosities was substantially delayed by addition of calpain inhibitors after sublethal excitotoxic exposure. Using Western blots and immunocytochemistry, we observed reactivity for a calpain-specific spectrin proteolytic fragment during the period of recovery from dendritic swelling, but not during its formation. Spectrin breakdown product immunoreactivity could be blocked by the calpain inhibitor MDL28,170 and appeared in neuronal cell bodies and neurites in a time course that paralleled dendritic recovery. These observations suggest that calcium-dependent proteolysis contributes to recovery of dendritic structure after NMDA exposure. Calpain activation is not necessarily detrimental and may play a role in dendritic remodeling after neuronal injury.

Mechanisms of calpain proteolysis following traumatic brain injury: implications for pathology and therapy: implications for pathology and therapy: a review and update

Much recent research has focused on the pathological significance of calcium accumulation in the central nervous system (CNS) following cerebral ischemia, spinal cord injury (SCI), and traumatic brain injury (TBI). Disturbances in neuronal calcium homeostasis may result in the activation of several calcium-sensitive enzymes, including lipases, kinases, phosphatases, and proteases. One potential pathogenic event in a number of acute CNS insults, including TBI, is the activation of the calpains, calcium-activated intracellular proteases. This article reviews new evidence indicating that overactivation of calpains plays a major role in the neurodegenerative cascade following TBI in vivo. Further, this article presents an overview from in vivo and in vitro models of CNS injuries suggesting that administration of calpain inhibitors during the initial 24-h period following injury can attenuate injury-induced derangements of neuronal structure and function. Lastly, this review addresses the potential contribution of other proteases to neuronal damage following TBI.

A new mechanism of methylprednisolone and other corticosteroids action demonstrated in vitro: inhibition of a proteinase (calpain) prevents myelin and cytoskeletal protein degradation

The affect of methylprednisolone (MP), an anti-inflammatory drug upon purified calpain and the Ca2+-mediated degradation of endogenous proteins of spinal cord homogenate in vitro has been examined. Activity of calpain purified from rabbit muscle was greatly inhibited in a dose-dependent fashion by MP. A 50% inhibition was obtained with 3.2 mM MP concentration and the activity was inhibited further (80%) at 8.1 mM. More potent inhibition of the purified enzyme (70-80%) was produced by dexamethasone (3.9 mM) and prednisolone (4.1 mM). Calpain-mediated degradation of myelin basic protein (MBP) was also inhibited by MP as was cathepsin B-mediated MBP breakdown. The effect of MP and other steroids upon calcium-mediated degradation of spinal cord homogenate was also evaluated. SDS-PAGE analysis revealed significant inhibition of neurofilament protein breakdown by MP and other corticosteroids. This inhibitory effect was much less than that exerted by the calpain inhibitors calpeptin and/or E64-d. These results indicate that MP acts as a proteinase (calpain) inhibitor and define a new mechanism for its actions.

Calpain activation contributes to dendritic remodeling after brief excitotoxic injury in vitro

The calcium-dependent protease calpain may contribute to neuronal death in acute neurological insults and may be activated very early in the neuronal injury cascade. We assessed the role of calpain in a model of rapid, reversible dendritic injury in murine cortical cultures. Brief sublethal NMDA exposure (10-30 microM for 10 min) resulted in focal swellings, or varicosities, along the length of neuronal dendrites as visualized with the lipophilic membrane tracer Dil or with immunostaining using antibodies to the somatodendritic protein MAP2. These varicosities appeared within minutes of NMDA exposure and recovered spontaneously within 2 hr after NMDA removal. Addition of the calpain inhibitors MDL28,170, calpain inhibitors I and II, and leupeptin (all 1-100 microM) had little effect on the development of NMDA-induced dendrite injury. However, the resolution of varicosities was substantially delayed by addition of calpain inhibitors after sublethal excitotoxic exposure. Using Western blots and immunocytochemistry, we observed reactivity for a calpain-specific spectrin proteolytic fragment during the period of recovery from dendritic swelling, but not during its formation. Spectrin breakdown product immunoreactivity could be blocked by the calpain inhibitor MDL28,170 and appeared in neuronal cell bodies and neurites in a time course that paralleled dendritic recovery. These observations suggest that calcium-dependent proteolysis contributes to recovery of dendritic structure after NMDA exposure. Calpain activation is not necessarily detrimental and may play a role in dendritic remodeling after neuronal injury.

Hyperthermia enhances spectrin breakdown in transient focal cerebral ischemia

Calpain-mediated spectrin degradation is triggered by cerebral ischemia and, when persistent, is thought to signal irreversible neuronal injury. Hyperthermia superimposed upon cerebral ischemia may exacerbate the injury process. In this study, we compared the extent of spectrin degradation in the brains of rats subjected to 1 h of transient proximal middle cerebral artery (MCA) clip-occlusion performed under conditions of cranial normothermia (37 degrees C) or mild cranial hyperthermia (39 degrees C). Immunocytochemical localization of spectrin breakdown products was achieved by the use of a rabbit polyclonal antibody which reacted selectively with calpain-generated fragments of brain spectrin. The perfusion times studied were 1, 4 or 24 h. Following normothermic MCA occlusion, spectrin immunoreactivity was present only occasionally and only in scattered cortical neurons immediately upon reperfusion and 1 h later; all normothermic brains showed space immunoreactivity at 4 h of reperfusion; and no immunoreactivity was detected at 24 h. By contrast, following hyperthermic MCA occlusion, moderate-to-intense immunostaining was present in cortical pyramidal neurons even immediately upon reperfusion and persisted at 1 h of reperfusion. At 4 and 24 h, most brains exhibited dense immunoreactivity associated with morphologically shrunken neurons. Following 24 h survival, semi-thick plastic sections revealed intact neuropil and only selective neuronal necrosis in normothermic rats. By contrast, pan-necrosis was evident 24 h after the hyperthermic ischemic insult. These results indicate that mild cranial hyperthermia superimposed upon transient focal ischemia markedly enhances calpain activation and spectrin degradation; this process appears to be an important mechanism by which hyperthermia exacerbates ischemic injury.

An immunocytochemical study of calpain II in the hippocampus of rats injected with kainate

The distributions of the kainate/DL-alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (KA/ AMPA) receptors GluR1 and calcium-activated neutral protease II (calpain II) in the hippocampus of normal and kainate-lesioned rats were studied by immunocytochemistry. There was a reduction in GluR1 immunoreactivity and a slight increase in calpain II immunoreactivity on the dendrites of pyramidal neurons in CA fields affected by the kainate at 18 h postinjection. Calpain II immunore-activity was associated with amyloid fibrils at electron microscopy. These fibrils were most often intracellular, in membrane-bound profiles, some of which were contacted by axon terminals and were identified as degenerating dendrites. There was extensive destruction of mitochondrial membranes in degenerating profiles, and accumulations of amyloid fibrils were often localised in mitochondria in a calpain-positive profile. This was unlike other, calpain-negative degenerating profiles, that contained tubulovesicular profiles or multilamellar bodies, where mitochondrial membranes were preserved. Many more calpain-positive profiles were observed at electron microscopy 6 days after kainate injection. The enzyme was present in macrophages and astrocytes in lesioned areas.

AMPA neurotoxicity in cultured cerebellar granule neurons: mode of cell death

Various forms of cell death induced by the glutamate receptor agonist, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), were analyzed by determining the capacity of cultured cerebellar granule cells to metabolize 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) into formazan, by measuring the leakage of lactate dehydrogenase (LDH), by using confocal microscopy to visualize propidium iodide staining of apoptotic nuclei, and by using field inversion gel electrophoresis (FIGE) for the detection of AMPA-produced cleavage of DNA into high molecular-weight fragments (50 kbp). All these measures indicated that stimulation of AMPA receptors may be involved in the neurotoxic effects of glutamate, and that AMPA-induced neurotoxicity in cerebellar granule cells display morphologically distinct features of both necrotic and apoptotic modes of cell death. In agreement with previous observations, a blockade of AMPA receptor desensitization was necessary to unmask AMPA-induced functional responses in cultured cerebellar granule neurons in vitro. Microfluorimetric measurements of free cytoplasmic calcium concentrations ([Ca2+]i) in single cerebellar neurons revealed that AMPA neurotoxicity was accompanied by a pronounced elevation of [Ca2+]i. Our current results add further evidence to the notion that glutamate-induced neurotoxicity in cerebellar granule cells is mediated not only through NMDA receptors but also through a direct activation of AMPA receptor-regulated cation channels.

Neuronal vulnerability in Parkinson's disease

Although Parkinson's disease is characterized by a loss of dopaminergic neurons in the substantia nigra not all dopaminergic neurons degenerate in this disease. This suggests that some specific factors make subpopulations of dopaminergic neurons more susceptible to the disease. Here, we show that the most vulnerable neurons are particularly sensitive to oxidative stress and rise in intracellular calcium concentrations. Because both events seem to occur in Parkinson's disease this may explain why some dopaminergic neurons degenerate and other do not.

Blockade of calpain proteolytic activity rescues neurons from glutamate excitotoxicity

The potential of protease inhibitors E-64, calpain inhibitor I (CPI-I) and MDL28170 to protect hippocampal neurons in an in vitro model of neurotoxicity was investigated. Hippocampal cultures were treated with glutamate, and neurotoxicity was quantified. Glutamate treated cultures exhibited damage to approximately 50% of neurons. In contrast only 20-30% of neurons were damaged in cultures treated with glutamate and calpain inhibitors. E-64 and CPI-I are capable of protecting neurons from injury only in pre-treatment schedule. MDL28170 exhibits a neuroprotective effect in the pre-treatment schedule and also even when given immediately after the cultures had been switched to the glutamate-containing medium. Although the neuroprotective effect of MDL28170 in the postreatment schedule was modest, this supports a strick link between the ability of protease inhibitors to penetrate cellular membranes and their potency of neuroprotection. These data provide evidence that calpain-induced proteolysis is an important pathogenic factor in brain injury and suggest that calpain inhibitors may be considered as a powerful mean to counteract the sequelea of neurotoxicity.

Specific cleavage of alpha-fodrin during Fas- and tumor necrosis factor-induced apoptosis is mediated by an interleukin-1beta-converting enzyme/Ced-3 protease distinct from the poly(ADP-ribose) polymerase protease

Interleukin-1beta-converting enzyme (ICE)/Ced-3 proteases play a critical role in apoptosis. One well characterized substrate of these proteases is the DNA repair enzyme poly(ADP-ribose) polymerase. We report here that alpha-fodrin, an abundant membrane-associated cytoskeletal protein, is cleaved rapidly and specifically during Fas- and tumor necrosis factor-induced apoptosis; this cleavage is mediated by an ICE/Ced-3 protease distinct from the poly(ADP-ribose) polymerase protease. Studies in cells treated with these apoptotic stimuli reveal that both fodrin and poly(ADP-ribose) polymerase proteolysis are inhibited by acetyl-Tyr-Val-Ala-Asp chloromethyl ketone and CrmA, specific inhibitors of ICE/Ced-3 proteases. However, fodrin proteolysis can be distinguished from poly(ADP-ribose) polymerase proteolysis by its relative insensitivity to acetyl-Asp-Glu-Val-Asp aldehyde (DEVD-CHO), a selective inhibitor of a subset of ICE/Ced-3 proteases that includes CPP32. DEVD-CHO protects cells from Fas-induced apoptosis but does not prevent fodrin proteolysis, indicating that cleavage of this protein can be uncoupled from apoptotic cell death. Moreover, purified fodrin is cleaved in vitro by CPP32 (but not by ICE) into fragments of the same size observed in vivo during apoptosis. These findings suggest that fodrin proteolysis in vivo may reflect the activity of multiple ICE/Ced-3 proteases whose partial sensitivity to DEVD-CHO reflects a limited contribution from CPP32, or an ICE/Ced-3 protease less sensitive than CPP32 to DEVD-CHO inhibition.

Immunohistochemical distribution and electron microscopic subcellular localization of the proteasome in the rat CNS

The proteasome multicatalytic proteinase (MCP) is a 20S complex that plays a major role in nonlysosomal pathways of intracellular protein degradation. A polyclonal antibody against rat liver MCP was used to investigate the distribution of MCP in the CNS of the rat and its subcellular localization within the neurons. As expected, MCP immunoreactivity (MCP-IR) was distributed ubiquitously in the rat CNS but not homogeneously. The most intensely stained neurons were the pyramidal cortical neurons of layer 5 and the motor neurons of the ventral horn in the spinal cord, which show an intense nuclear and cytoplasmatic MCP-IR and clearly stained processes. Additionally, some populations of large neurons in the mesencephalon and brainstem also displayed a moderate MCP-IR in their perikarya. The vast majority of neurons in the remaining structures did not show a strong cytoplasmatic MCP-IR, but their nuclei displayed an intense MCP-IR. The subcellular localization also was studied by immunoelectron microscopy. MCP-IR was intense in the neuronal nuclei, and significant staining also was found in the cytoplasm, dendritic, and axonic processes (including some myelinated axons) and in synaptic boutons, as illustrated in the cerebellar cortex. The distribution of MCP in the rat CNS and its subcellular localization are discussed in relation to (1) the distribution of calpain, the other major nonlysosomal cellular protease, and (2) the possible role of MCP in the degradation of regulatory proteins and key transcription factors that are essential in many neuronal responses.

Microtubular proteolysis in focal cerebral ischemia

Calpain, a neutral protease activated by calcium, may promote microtubular proteolysis in ischemic brain. We tested this hypothesis in an animal model of focal cerebral ischemia without reperfusion. The earliest sign of tissue injury was observed after no more than 15 min of ischemia, with coiling of apical dendrites immunolabeled to show microtubule-associated protein 2 (MAP2). After 6 h of ischemia, MAP2 immunoreactivity was markedly diminished in the infarct zone. Quantitative Western analysis demonstrated that MAP2 was almost unmeasurable after 24 h of ischemia. An increase in calpain activity, shown by an antibody recognizing calpain-cleaved spectrin fragments, paralleled the loss of MAP2 immunostaining. Double-labeled immunofluorescent studies showed that intraneuronal calpain activity preceded evidence of MAP2 proteolysis. Perikaryal immunolabeling of tau protein became increasingly prominent between 1 and 6 h in neurons located within the transition zone between ischemic and unaffected tissue. Western blot experiments confirmed that dephosphorylation of tau protein occurred during 24 h of ischemia, but was not associated with significant loss of tau antigen. We conclude that focal cerebral ischemia is associated with early microtubular proteolysis caused by calpain.

Immunohistochemical distribution and electron microscopic subcellular localization of the proteasome in the rat CNS

The proteasome multicatalytic proteinase (MCP) is a 20S complex that plays a major role in nonlysosomal pathways of intracellular protein degradation. A polyclonal antibody against rat liver MCP was used to investigate the distribution of MCP in the CNS of the rat and its subcellular localization within the neurons. As expected, MCP immunoreactivity (MCP-IR) was distributed ubiquitously in the rat CNS but not homogeneously. The most intensely stained neurons were the pyramidal cortical neurons of layer 5 and the motor neurons of the ventral horn in the spinal cord, which show an intense nuclear and cytoplasmatic MCP-IR and clearly stained processes. Additionally, some populations of large neurons in the mesencephalon and brainstem also displayed a moderate MCP-IR in their perikarya. The vast majority of neurons in the remaining structures did not show a strong cytoplasmatic MCP-IR, but their nuclei displayed an intense MCP-IR. The subcellular localization also was studied by immunoelectron microscopy. MCP-IR was intense in the neuronal nuclei, and significant staining also was found in the cytoplasm, dendritic, and axonic processes (including some myelinated axons) and in synaptic boutons, as illustrated in the cerebellar cortex. The distribution of MCP in the rat CNS and its subcellular localization are discussed in relation to (1) the distribution of calpain, the other major nonlysosomal cellular protease, and (2) the possible role of MCP in the degradation of regulatory proteins and key transcription factors that are essential in many neuronal responses.

Modulation of hypoxia-induced calpain activity in rat renal proximal tubules

The effect of the newly developed, nonpeptide, calpain inhibitor, PD 150606, on hypoxia and ionomycin-induced increases in calpain activity in rat proximal tubules (PT) was determined. PD150606 inhibited both hypoxia and ionomycin-induced calpain activity as determined by the fluorescent substrate N-succinyl-Leu-Leu-Val-Tyr-7-amido-4-methyl coumarin (N-succinyl-Leu-Leu-Val-Tyr-AMC). This decrease in calpain activity was accompanied by dose-dependent cytoprotection against hypoxia and ionomycin-induced cell membrane damage. PD150606 had no effect on cathepsin B and L activity in PT as measured by the fluorescent substrate, benzyloxycarbonyl-L-phenylalanyl-L-arginine-7-amido-4-methyl coumarin (Z-Phe-Arg-AMC). The effects of low intracellular pH (pHi) or low free cytosolic calcium [Ca2+]i on this hypoxia-induced calpain activity were also determined. Both low pHi and low [Ca2+]i attenuated the hypoxia-induced increase in calpain activity. This attenuation of calpain activity was observed early before hypoxia-induced membrane damage and was associated with marked reduction in the typical pattern of hypoxia-induced cell membrane damage observed in this model. To identify the isoform of calpain activated in rat proximal tubules, normoxic, hypoxic and ionomycin treated tubules were fractionated by MONO-Q anion exchange chromatography and the fractions were assayed for calpain activity. A single peak of calpain activity characteristic of mu-calpain was found. The calcium dependency of the calpain activity was in the nanomolar range, further confirming that the activity was the low Ca(2+)-sensitive mu-calpain. The present study suggests that in rat proximal tubules: (1) PD 150606 is a specific inhibitor of calpain and not cathepsins B and L; (2) the cytoprotective effects of low pHi and low [Ca2+]i are mediated, at least in part, by inhibition of calpain activity; and (3) the predominant active form of calpain is the isoenzyme mu-calpain.

Transient brain ischaemia provokes Ca2+, PIP2 and calpain responses prior to delayed neuronal death in monkeys

To clarify the mechanism of postischaemic delayed cornu Ammonis (CA)-1 neuronal death, we studied correlations among calpain activation and its subcellular localization, the immunoreactivity of phosphatidylinositol 4,5-bisphosphate (PIP2) and Ca2+ mobilization in the monkey hippocampus by two independent experimental approaches: in vivo transient brain ischaemia and in vitro hypoxia-hypoglycaemia of hippocampal acute slices. The CA-1 sector undergoing 20 min of ischaemia in vivo showed microscopically a small number of neuronal deaths on day 1 and almost global neuronal loss on day 5 after ischaemia. Immediately after ischaemia, CA-1 neurons ultrastructurally showed vacuolation and/or disruption of the lysosomes. Western blotting using antibodies against inactivated or activated mu-calpain demonstrated mu-calpain activation specifically in the CA-1 sector immediately after ischaemia. This finding was confirmed in the perikarya of CA-1 neurons by immunohistochemistry. CA-1 neurons on day 1 showed sustained activation of mu-calpain, and increased immunostaining for inactivated and activated forms of mu- and m-calpains and for PIP2. Activated mu-calpain and PIP2 were found to be localized at the vacuolated lysosomal membrane or endoplasmic reticulum and mitochondrial membrane respectively, by immunoelectron microscopy. Calcium imaging data using hippocampal acute slices showed that hypoxia-hypoglycaemia in vitro provoked intense Ca2+ mobilization with increased PIP2 immunostaining specifically in CA-1 neurons. These data suggest that transient brain ischaemia increases intracellular Ca2+ and PIP2 breakdown, which will activate calpain proteolytic activity. Therefore, we suggest that activated calpain at the lysosomal membrane, with the possible release of biodegrading enzyme, will cause postischaemic CA-1 neuronal death.

Evidence for mediation of L-2-chloropropionic acid-induced delayed neuronal cell death by activation of a constitutive nitric oxide synthase

1. Delayed neuronal cell death elicited by excess excitatory amino acid concentrations has been strongly implicated in many neurological disorders including head trauma, stroke, motor neurone disease and Huntington's disease. We have used the neurotoxin, L-2-chloropropionic acid (L-CPA) to model cellular events in vivo leading to delayed neuronal cell loss which is confined to the cerebellar cortex and can be prevented by inhibitors of nitric oxide synthase such as NG-nitro-L-arginine methyl ester. 2. Experiments were performed to determine whether the constitutive nitric oxide synthase (NOS) or inducible form of NOS (iNOS) was responsible for the neuronal cell death. Activation of NOS was confirmed by a 39% increase in cerebellar total nitrate and nitrite concentrations in L-CPA-treated brains, as compared to controls (controls = 2.53 +/- 0.10; L-CPA treated = 3.51 +/- 0.31 nmol mg-1 protein, P < 0.01 Student's t tests, n = 6, mean +/- s.e.mean). Biochemical measurements of total NOS activity were made in homogenates of cerebellum 6 h and 48 h following L-CPA administration, times at which L-CPA concentrations are maximal in brain and a time when there is a high proportion of cerebellar granule cell death, respectively. NOS activity as measured by the amount of [3H]-arginine converted to [3H]-citrulline, did not reveal any difference between controls (rats dosed with water) and animals dosed with L-CPA at either 6 or 48 h following dosing. Furthermore the ability of three NOS inhibitors, NG-nitro-L-arginine, 7-bromo-3-nitroindazole and S-methylisothiourea to block the conversion of [3H]-citrulline to [3H]-arginine was identical at 6 and 48 h time points in control and L-CPA treated rats. 3. Quantitative autoradiography using [3H]-NG-nitro-L-arginine was used to measure the relative anatomical distribution and amount of NOS enzyme in the cerebellum of controls and L-CPA-treated rats 48 h following dosing. There was no significant alteration in the binding of [3H]-NG-nitro-L-arginine to granular and molecular layers of the cerebellum of control and L-CPA-treated rat brains. 4. Western blotting using antibodies against the inducible NOS enzyme failed to detect the protein in cerebellums of L-CPA-treated rats when measured 48 h after L-CPA dosing. 5. In conclusion, the increase in cerebellar nitrate/nitrite concentrations in L-CPA-treated rats provides further evidence for activation of NOS in the cerebellum following administration of L-CPA. The failure to demonstrate an increase in NOS activity at 6 or 48 h in L-CPA-treated rats as compared to controls suggests that the source of nitric oxide responsible for the granule cell death must originate from the constitutive NOS enzyme, probably the neuronal form which is highly enriched in the cerebellum. This hypothesis was further substantiated by Western blotting and quantitative autoradiography.

An alpha-mercaptoacrylic acid derivative is a selective nonpeptide cell-permeable calpain inhibitor and is neuroprotective

Overactivation of calcium-activated neutral protease (calpain) has been implicated in the pathophysiology of several degenerative conditions, including stroke, myocardial ischemia, neuromuscular degeneration, and cataract formation. Alpha-mercaptoacrylate derivatives (exemplified by PD150606), with potent and selective inhibitory actions against calpain, have been identified. PD150606 exhibits the following characteristics: (i) Ki values for mu- and m-calpains of 0.21 microM and 0.37 microM, respectively, (ii) high specificity for calpains relative to other proteases, (iii) uncompetitive inhibition with respect to substrate, and (iv) it does not shield calpain against inactivation by the active-site inhibitor trans-(epoxysuccinyl)-L-leucyl-amido-3-methylbutane, suggesting a nonactive site action for PD150606. The recombinant calcium-binding domain from each of the large or small subunits of mu-calpain was found to interact with PD150606. In low micromolar range, PD15O6O6 inhibited calpain activity in two intact cell systems. The neuroprotective effects of this class of compound were also demonstrated by the ability of PD150606 to attenuate hypoxic/hypoglycemic injury to cerebrocortical neurons in culture and excitotoxic injury to Purkinje cells in cerebellar slices.

Hepatocellular carcinoma cells resist necrosis during anoxia by preventing phospholipase-mediated calpain activation

Although hepatocellular carcinoma (HCC) cells are more resistant to anoxic injury than normal hepatocytes, the mechanisms responsible for this differential sensitivity remain obscure. Because enhanced calpain protease activity contributes to hepatocyte necrosis, we tested the hypothesis that HCC cells resist anoxia by preventing calpain activation. Cell viability in two rat HCC cell lines (N1S1 and McA-RH7777 cells) was fourfold greater compared to rat hepatocytes after 4 h of anoxia. Although calpain activity increased twofold in rat hepatocytes during anoxia, no increase in calpain activity occurred in HCC cells. Western and Northern blot analysis revealed greater or equivalent expression of calpains and calpastatin in HCC cells compared to hepatocytes. Because increases in cytosolic free Ca++ (Cai++) and phospholipid degradation products regulate calpains in vitro, we measured Cai++ and phospholipid degradation. Ca++i did not change in any cell types during 60 min of anoxia. In contrast, phospholipid degradation was fourfold greater in hepatocytes compared to HCC cells. Melittin, a phospholipase A2 activator, increased calpain activity and cell necrosis in all cell types; melittin-induced cell necrosis was ameliorated by a calpain protease inhibitor. In summary, these data demonstrate for the first time 1) calpain activation without a measureable increase in Ca++i, 2) phospholipase-mediated calpain activation in hepatocytes and HCC cells, and 3) the adaptive mechanism responsible for the resistance of HCC cells to anoxia-an inhibition of phospholipid-mediated calpain activation. Interruption of phospholipase-mediated calpain activation may be a therapeutic strategy for preventing anoxic cell injury.

Effects of brain ischemia on intermediate filaments of rat hippocampus

Neurofilaments subunits (NF-H, NF-M, NF-L) and glial fibrillary acidic protein (GFAP) were investigated in the hippocampus of rats after distinct periods of reperfusion (1 to 15 days) following 20 min of transient global forebrain ischemia in the rat. In vitro [14Ca]leucine incorporation was not altered until 48 h after the ischemic insult, however concentration of intermediate filament subunits significantly decreased in this period. Three days after the insult, leucine incorporation significantly increased while the concentration NF-H, NF-M, and NF-L were still diminished after 15 days of reperfusion. In vitro incorporation of 32P into NF-M and NF-L suffered immediately after ischemia, but returned to control values after two days of reperfusion. GFAP levels decreased immediately after ischemia but quickly recovered and significantly peaked from 7 to 10 days after the insult. These results suggest that transient ischemia followed by reperfusion causes proteolysis of intermediate filaments in the hippocampus, and the proteolysis could be facilitated by diminished phosphorylation levels of NF-M and NF-L.

Calpain inhibitor AK295 attenuates motor and cognitive deficits following experimental brain injury in the rat

Marked increases in intracellular calcium may play a role in mediating cellular dysfunction and death following central nervous system trauma, in part through the activation of the calcium-dependent neutral protease calpain. In this study, we evaluated the effect of the calpain inhibitor AK295 [Z-Leu-aminobutyric acid-CONH(CH2)3-morpholine] on cognitive and motor deficits following lateral fluid percussion brain injury in rats. Before injury, male Sprague-Dawley rats (350-425 g) were trained to perform a beam-walking task and to learn a cognitive test using a Morris water maze paradigm. Animals were subjected to fluid percussion injury (2.2-2.4 atm; 1 atm = 101.3 kPa) and, beginning at 15 min postinjury, received a continuous intraarterial infusion of AK295 (120-140 mg/kg, n = 15) or vehicle (n= 16) for 48 hr. Sham (uninjured) animals received either drug (n = 5) or vehicle (n = 10). Animals were evaluated for neurobehavioral motor function at 48 hr and 7 days postinjury and were tested in the Morris water maze to evaluate memory retention at 7 days postinjury. At 48 hr, both vehicle- and AK295-treated injured animals showed significant neuromotor deficits (P< 0.005). At 7 days, injured animals that received vehicle continued to exhibit significant motor dysfunction (P< 0.01). However, brain-injured, AK295-treated animals showed markedly improved motor scores (P<0.02), which were not significantly different from sham (uninjured) animals. Vehicle-treated, injured animals demonstrated a profound cognitive deficit (P< 0.001), which was significantly attenuated by AK295 treatment (P< 0.05). To our knowledge, this study is the first to use a calpain inhibitor following brain trauma and suggests that calpain plays a role in the posttraumatic events underlying memory and neuromotor dysfunction.

Role of calpain in spinal cord injury: increased calpain immunoreactivity in rat spinal cord after impact trauma

Impact spinal cord injury (20 g-cm) was induced in rat by weight drop. The immunoreactivity of mcalpain was examined in the lesion and adjacent areas of the cord following trauma. Increased calpain immunoreactivity was evident in the lesion compared to control and the immunostaining intensity progressively increased after injury. The calpain immunoreactivity was also increased increased in tissue adjacent to the lesion. mCalpain immunoreactivity was significantly stronger in glial and endothelial cells, motor neurons and nerve fibers in the lesion. The calpain immunoreactivity also increased in astrocytes and microglial cells in the adjacent areas. Proliferation of microglia and astrocytes identified by GSA histochemical staining and GFAP immunostaining, respectively, was seen at one and three days after injury. Many motor neurons in the ventral horn showed increased calpain immunoreactivity and were shrunken in the lesion. These studies indicate a pivotal role for calpain and the involvement of glial cells in the tissue destruction in spinal cord injury.

Biologically active monomeric and heterodimeric recombinant human calpain I produced using the baculovirus expression system

Calpain I is a heterodimeric protein that is part of a family of calcium-activated intracellular cysteine proteases presumed to play a role in mediating signals transduced by calcium. Expression of bioactive recombinant human calpain I has been achieved using the baculovirus expression system, by either co-infection with two viruses, each expressing one of the subunits, or infection with a single virus containing both subunits. The approximately 80 kDa catalytic subunit exhibited calcium-dependent proteolytic activity when expressed alone or with the approximately 30 kDa regulatory subunit. Baculoviral recombinant calpain I appeared fully active in that the catalytic subunit in unpurified cell extracts exhibited calcium-dependent autocatalytic cleavage at the correct locus. The amount of approximately 80 kDa subunit accumulated at steady state was greatly increased by co-expression of the approximately 30 kDa subunit, suggesting a possible role for enzyme stabilization by the latter subunit. The recombinant human calpain I was purified to near homogeneity and compared with purified native human erythrocyte calpain I. The recombinant and native enzymes had equivalent inhibition constants for structurally diverse calpain inhibitors, identical calcium activation profiles, and similar specific activities, demonstrating the suitability of using the recombinant protein for studies of the native enzyme.

Dopamine-stimulated changes in activated calpain I in rat hippocampal slices

Activated calpain I immunoreactivity (76 kDa band) was detected in membranes prepared from rat brain hippocampal slices using a polyclonal antiserum raised against an N-terminus peptide of the cleaved subunit of calpain I. While basal levels of activated calpain I were stable over incubation times, 1 nM dopamine (DA) produced an initial 32% increase (5 min) in the 76 kDa protein followed by a 53% decrease in this band at 20 min of incubation. The DA-induced changes in activated calpain I immunoreactivity were blocked by the calpain inhibitor peptide, N-acetyl-Leu-Leu-norleucinal(100 microM) or by EGTA. Basal levels of the 76 kDa band were not affected by the calpain inhibitor. These changes in activated calpain I, elicited by DA, are in accord with the DA-induced decreases in the levels of the calpain substrate, gamma PKC (Yurko-Mauro and Friedman; J Cell Biochem [Abstr] 180:80, 1994; J Neurochem 65: 1622-1630, 1995) and suggest that DA activates this Ca(++)-dependent protease in its regulation of neuronal signal transduction.

Calpain inhibitors protect against depolarization-induced neurofilament protein loss of septo-hippocampal neurons in culture

We examined the effect of a 6 min depolarization with 60 mM KCl and 1.8, 2.8 or 5.8 mM extracellular CaCl2 on neurofilament proteins of high (NF-H), medium (NF-M) and low (NF-L) molecular weight in primary septohippocampal cultures. One day after depolarization, Western blot analyses revealed losses of all three neurofilament proteins. Increasing the extracellular calcium concentration from 1.8 to 5.8 mM CaCl2 in the presence of 60 mM KCl produced increased losses of all three neurofilament proteins to approximately 80% of control values in the absence of cell death. Calcium-dependent losses of the neurofilament proteins correlated with calcium-dependent increases in calpain 1-mediated breakdown products of alpha-spectrin. Calpain inhibitors 1 and 2, applied immediately after depolarization and made available to cultures for 24 h, reduced losses of all three neurofilament proteins to approximately 14% of control values. The protective effects of calpain inhibitors 1 and 2 were influenced by different levels of extracellular calcium. Qualitative immunohistochemical evaluations confirmed semiquantitative Western blot data on neurofilament loss and protection by calpain inhibitors 1 and 2. We propose that brief depolarization causes loss of neurofilament proteins, possibly due to calpain activation. Thus, calpain inhibitors could represent a viable strategy for preserving the cytoskeletal structure of injured neurons.

Degradation of nuclear matrix and DNA cleavage in apoptotic thymocytes

In dexamethasone-treated thymocyte cultures an increase in nuclear proteolytic activity paralleled chromatin fragmentation and the appearance of small apoptotic cells. The elevation of nuclear proteolytic activity was accompanied by site-specific degradation of nuclear mitotic apparatus protein and lamin B, two essential components of the nuclear matrix. Nuclear mitotic apparatus protein phosphorylation and cleavage into 200 and 48 kDa fragments occurred within 30 minutes of dexamethasone treatment. Cleavage of lamin B, which generated a fragment of 46 kDa consistent with the central rod domain of the protein, was also detected after 30 minutes of exposure to the steroid hormone. The level of lamin B phosphorylation did not change as a result of the dexamethasone treatment and the lamina did not solubilize until the later stages of apoptosis. Initial DNA breaks, detected by the terminal transferase-mediated dUTP-biotin nick end labeling assay, occurred throughout the nuclei and solubilization of lamina was not required for this process to commence. The data presented in this paper support a model of apoptotic nuclear destruction brought about by the site-specific proteolysis of key structural proteins. Both the nuclear mitotic apparatus protein and lamin B were specifically targeted by protease(s) at early stages of the cell death pathway, which possibly initiate the cascade of degradative events in apoptosis.

Time-related neuronal changes following middle cerebral artery occlusion: implications for therapeutic intervention and the role of calpain

Changes in neocortex and striatum were characterized over time following focal ischemia to the brain. Rats were subjected to permanent middle cerebral artery occlusion (MCA-O) and sacrificed 1, 3, 6, 12, or 24 h later. The affected tissue was processed for tetrazolium chloride (TTC) and cresyl violet staining, as well as for Western blots to detect calpain-induced spectrin proteolysis. Significant changes in cell size and spectrin breakdown occurred within the first hour of occlusion, with further, dramatic changes in these two early markers continuing over time. Initial evidence of cell loss was noted at 1 h postocclusion in the striatum and at 3 h in the neocortex. However, even in the center of the most affected portion of the neocortex, the majority of cells appeared to be intact through 6 h. By this time, a significant TTC-defined infarct also emerged. These quantitative data indicate that calpain-induced proteolysis occurs very soon after the ischemic insult, is correlated with earliest changes in cell hypotrophy, and precedes or occurs in tandem with evidence of significant cell loss. They also demonstrate that, while some cell loss occurs earlier than previously believed, the majority of cells remains morphologically intact well beyond what is typically thought to be the window of opportunity for intervention. The results thus raise the question of how long after the ischemic event pharmaceutic intervention might be employed to salvage substantial numbers of neurons.

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.