Immunohistochemical distribution of calcium-activated neutral proteinases and endogenous CANP inhibitor in the rabbit hippocampus

Ivleva, Irina M. Kotova, Dmitriy S. Traktirov, Marina N. Karpenko. Region-specific changes in expression and activity of calpains in the CNS of native rats

Introduction and Aim: It has been proposed that µ-calpain is responsible for neuronal survival, while m-calpain – for the degeneration. It can be assumed that the "susceptibility" to the damage factor for neurons in different CNS regions depends on the content/activity of calpain isoforms. We analyzed the mRNA levels and the activity of µ-and m-calpain in the different CNS structures of rats.   Materials and Methods: After decapitation intact male Wistar rats the prefrontal cortex, striatum, hippocampus, midbrain, brainstem, cerebellum, and spinal cord were removed. Each structure was divided into two parts: casein zymography was performed to determine the activity and real-time RT–PCR - to determine the level of expression mRNA of µ-and m-calpains.   Results: We have shown that m-calpain mRNA predominates in the striatum, midbrain and brainstem, while µ-calpain mRNA enrichment was noticed for the hippocampus and cerebellum. The highest µ-calpain activity was in the cervical spinal cord, the lowest - in the striatum. The m-calpain activity was relatively high in the midbrain, striatum, hippocampus and brainstem, while in the cervical spinal cord and cerebellum it was moderate.   Conclusion: The selective neuronal death observed during neurodegeneration can be partially determined by the initial level of calpains expression and/or activity.  

Calpains and neuronal damage in the ischemic brain: The swiss knife in synaptic injury

The excessive extracellular accumulation of glutamate in the ischemic brain leads to an overactivation of glutamate receptors with consequent excitotoxic neuronal death. Neuronal demise is largely due to a sustained activation of NMDA receptors for glutamate, with a consequent increase in the intracellular Ca(2+) concentration and activation of calcium- dependent mechanisms. Calpains are a group of Ca(2+)-dependent proteases that truncate specific proteins, and some of the cleavage products remain in the cell, although with a distinct function. Numerous studies have shown pre- and post-synaptic effects of calpains on glutamatergic and GABAergic synapses, targeting membrane- associated proteins as well as intracellular proteins. The resulting changes in the presynaptic proteome alter neurotransmitter release, while the cleavage of postsynaptic proteins affects directly or indirectly the activity of neurotransmitter receptors and downstream mechanisms. These alterations also disturb the balance between excitatory and inhibitory neurotransmission in the brain, with an impact in neuronal demise. In this review we discuss the evidence pointing to a role for calpains in the dysregulation of excitatory and inhibitory synapses in brain ischemia, at the pre- and post-synaptic levels, as well as the functional consequences. Although targeting calpain-dependent mechanisms may constitute a good therapeutic approach for stroke, specific strategies should be developed to avoid non-specific effects given the important regulatory role played by these proteases under normal physiological conditions.

Mechanistic role of calpains in postischemic neurodegeneration

The calpain family of proteases is causally linked to postischemic neurodegeneration. However, the precise mechanisms by which calpains contribute to postischemic neuronal death have not been fully elucidated. This review outlines the key features of the calpain system, and the evidence for its causal role in postischemic neuronal pathology. Furthermore, the consequences of specific calpain substrate cleavage at various subcellular locations are explored. Calpain substrates within synapses, plasma membrane, endoplasmic reticulum, lysosomes, mitochondria, and the nucleus, as well as the overall effect of postischemic calpain activity on calcium regulation and cell death signaling are considered. Finally, potential pathways for calpain-mediated neurodegeneration are outlined in an effort to guide future studies aimed at understanding the downstream pathology of postischemic calpain activity and identifying optimal therapeutic strategies.

Mu-calpain mediates hippocampal neuron death in rats after lithium-pilocarpine-induced status epilepticus

Status epilepticus (SE) is a severe clinical manifestation of epilepsy which causes brain damage. The pathological process and underlying mechanisms involved in the programmed cell death (PCD) are still not fully clear. In the current study, rats were induced SE by lithium-pilocarpine administration. Our data showed hippocampal neurons death appeared at 6h after SE and sustained for 7 days. By blotting the activation of mu-calpain and its specific cleavage of nonerythroid alpha-spectrin (alphaSpII) (145 kDa) was evident at 1 and 3 days after SE, which coincided with Bid activation, apoptosis inducing factor (AIF) translocation and cytochrome c release from mitochondria, whereas, activated caspase-3 and caspase-3-specific fragments of alphaSpII (120 kDa) predominantly appeared at 5 and 7 days after SE. Moreover, MDL-28170, a calpain inhibitor, partially rescued the neuron death and attenuated the expression of activated mu-calpain, cleavage of Bid (15 kDa), AIF translocation and cytochrome c release. Taken together, our study indicated that mu-calpain mediated hippocampal neuron PCD is prior to caspase-3 activation. It functioned via translocation of Bid, AIF and cytochrome c release.

Screening for motility-associated genes in malignant astrocytoma cell lines

The most characteristic feature of a malignant astrocytoma is its early and extensive infiltration into adjacent parenchymal structures. We focused on detecting the possible expression changes as the determining factors for malignant astrocytoma's motile ability. We confirmed that four of 39 genes showed different expression on DD-PCR by RT-PCR and Northern blot analysis. These findings suggest that the genes identified may be important for determining high motility in astrocytoma cell lines. These findings may help us understand the molecular invasion mechanism in astrocytomas.

Degradation of spectrin via calpains in the ventral horn after transient spinal cord ischemia in rabbits

In the present study, we investigated chronological changes of mu-calpain, m-calpain and cleaved spectrin alphaII immunoreactivity in the ventral horn after transient spinal cord ischemia to investigate relationship between calpains and vulnerability to ischemia using abdominal aorta occlusion model in rabbits. Spinal cord sections at the level of L(7) were immunostained with calpains and cleaved spectrin alphaII monoclonal antibodies. mu-Calpain and m-calpain immunoreactivity was significantly increased in the ischemic ventral horn at 30 min and 1 h after ischemia/reperfusion, respectively. Thereafter, they were decreased with time after ischemia/reperfusion: at 48 h after ischemia, their immunoreactivities nearly disappeared in the ischemic ventral horn. Cleaved spectrin alphaII immunoreactivity was significantly increased in the ventral horn of spinal cord at 12 h after ischemia/reperfusion, and thereafter, its immunoreactivity was decreased with time after ischemia/reperfusion. In addition, spectrin alphaII protein level (280 kDa) was decreased from 12 h after ischemia/reperfusion; in contrast, cleaved spectrin alphaII protein level (150 kDa) was significantly increased at 12 h after ischemia/reperfusion. In conclusion, our observations in this study indicate that calpain is associated with neuronal degeneration in the ventral horn at early time after transient spinal cord ischemia via the proteolysis of spectrin alphaII.

3-[2-[4-(3-Chloro-2-methylphenylmethyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole Dihydro-chloride 3.5 Hydrate (DY-9760e) Is Neuroprotective in Rat Microsphere Embolism: Role of the Cross-Talk between Calpain and Caspase-3 through Calpastatin

Microsphere embolism (ME)-induced cerebral ischemia can elicit various pathological events leading to neuronal death. Western blotting and immunohistochemical studies revealed that expression of calpastatin, an endogenous calpain inhibitor, decreased after ME induction. Calpain activation after ME was apparently due to, in part, a decrease in calpastatin in a late phase of neuronal injury. The time course of that decrease also paralleled caspase-3 activation. In vitro studies demonstrated that calpastatin was degraded by caspase-3 in a Ca(2+)/calmodulin (CaM)-dependent manner. Because CaM binds directly to calpastatin, we asked whether a novel CaM antagonist, 3-[2-[4-(3-chloro-2-methylphenylmethyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydro-chloride 3.5 hydrate (DY-9760e), inhibits caspase-3-induced calpastatin degradation during ME-induced neuronal damage. We also tested the effect of DY-9760e on degradation of fodrin, a calpain substrate. Consistent with our hypothesis, DY-9760e (25 or 50 mg/kg i.p.) treatment inhibited degradation of calpastatin and fodrin in a dose-dependent manner. Because DY-9760e showed powerful neuroprotective activity with concomitant inhibition of calpastatin degradation, cross-talk between calpain and caspase-3 through calpastatin possibly accounts for ME-induced neuronal injury. Taken together, both inhibition of caspase-3-induced calpastatin degradation and calpain-induced fodrin breakdown by DY-9760e in part mediate its neuroprotective action.

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.

Calretinin and calbindin D-28k, but not parvalbumin protect against glutamate-induced delayed excitotoxicity in transfected N18-RE 105 neuroblastoma-retina hybrid cells

Excitotoxic effects leading to neuronal cell degeneration are often accompanied by a prolonged increase in the intracellular level of Ca(2+) ions and L-glutamate-induced toxicity is assumed to be mediated via a Ca(2+)-dependent mechanism. Due to their buffering properties, EF-hand Ca(2+)-binding proteins (CaBPs) can affect intracellular Ca(2+) homeostasis and a neuroprotective role has been attributed to some of the family members including calretinin, calbindin D-28k and parvalbumin. We have stably transfected N18-RE 105 neuroblastoma-retina hybrid cells with the cDNAs for the three CaBPs and investigated the effect of these proteins on the L-glutamate-induced, Ca(2+)-dependent cytotoxicity. Several clones for each CaBP were selected according to immunocytochemical staining and characterization of the overexpressed proteins by Western blot analysis. In calretinin- and parvalbumin-expressing clones, expression levels were quantitatively determined by ELISA techniques. Cytotoxicity of transfected clones was quantified by measurement of the activity of lactate dehydrogenase (LDH) that was released into the medium after L-glutamate (10 mM) exposure as a result of necrotic cell death. In untransfected and parvalbumin-transfected cells, LDH released into the medium progressively increased (starting from the 20th hour) reaching maximum levels after 28-30 h of glutamate application. In contrast, LDH release in both, calretinin and calbindin D-28k-transfected clones, was not significantly different from unstimulated transfected or untransfected cells over the same period of time. The results indicate that the 'fast' Ca(2+)-buffers calretinin and calbindin D-28k, but not the 'slow' buffer parvalbumin can protect N18-RE 105 cells from this type of Ca(2+)-dependent L-glutamate-induced delayed cytotoxicity.

The purification and characterisation of m-calpain from ostrich brain

Calpains are intracellular cysteine proteases activated in a Ca(2+)-dependent manner. The purpose of the present study was to investigate the physico-chemical and kinetic properties of ostrich brain m-calpain. m-Calpain was purified by successive chromatographic steps on Toyopearl-Super Q 650s and Pharmacia Mono Q HR 5/5 columns. A Ca(2+) concentration of 5mM and a casein concentration of 5mg/ml were found to be necessary for optimum calpain activity. Ostrich m-calpain exhibited a M(r) of 84K using SDS-PAGE and a M(min) of 79.3K from amino acid analysis. The pH and temperature optima were found to be 7.5 and 37 degrees C, respectively. The amino acid composition of m-calpain revealed 700 residues. The N-terminal sequence of m-calpain showed sequence identity with chicken (27%), human (23%) and rabbit (18%) and Schistoma mansoni (9%).

Calretinin and calbindin D-28k delay the onset of cell death after excitotoxic stimulation in transfected P19 cells

In some neurological diseases, injury to neurones reflects an over-stimulation of their receptors for excitatory amino acids. This response may disturb the Ca(2+)-homeostasis and lead to a pronounced and sustained increase in the intracellular concentration of this ion. On the basis of data derived from correlative studies, calcium-binding proteins have been postulated to play a protective role in these pathologies. We tested, directly, the capacity of the three calcium-binding proteins calretinin (CR), calbindin D-28k (CB) and parvalbumin (PV) to buffer [Ca(2+)], and to protect cells against excitotoxic death. We used P19 murine embryonic carcinoma cells, which can be specifically induced (by retinoic acid) to transform into nerve-like ones. The differentiated cells express functional glutamate-receptors and are susceptible to excitotoxic shock. Undifferentiated P19-cells were stably transfected with the cDNA for CR, CB or PV, induced to differentiate, and then exposed to NMDA, a glutamate-receptor agonist. The survival rates of clones expressing CR, CB or PV were compared with those of untransfected P19-cells using the lactate-dehydrogenase assay. CR- and CB-expressing cells were protected from death during the first 2 h of exposure to NMDA. This protection was, however, transient, and did not suffice to rescue P19-cells after prolonged stimulation. Two of the three PV-transfected clones raised were vulnerable to NMDA-induced excitotoxicity; the third, which expressed the lowest level of PV, was protected to a similar degree as that found for the CR- and CB-transfected clones. Our results indicate that in the P19-cell model, CR and CB can help to delay the onset of cell death after excitotoxic stimulation.

Molecular mechanisms of ischemic neuronal injury

Brain ischemia triggers a complex cascade of molecular events that unfolds over hours to days. Identified mechanisms of postischemic neuronal injury include altered Ca(2+) homeostasis, free radical formation, mitochondrial dysfunction, protease activation, altered gene expression, and inflammation. Although many of these events are well characterized, our understanding of how they are integrated into the causal pathways of postischemic neuronal death remains incomplete. The primary goal of this review is to provide an overview of molecular injury mechanisms currently believed to be involved in postischemic neuronal death specifically highlighting their time course and potential interactions.

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.

Brain ischemia and reperfusion: molecular mechanisms of neuronal injury

Brain ischemia and reperfusion engage multiple independently-fatal terminal pathways involving loss of membrane integrity in partitioning ions, progressive proteolysis, and inability to check these processes because of loss of general translation competence and reduced survival signal-transduction. Ischemia results in rapid loss of high-energy phosphate compounds and generalized depolarization, which induces release of glutamate and, in selectively vulnerable neurons (SVNs), opening of both voltage-dependent and glutamate-regulated calcium channels. This allows a large increase in cytosolic Ca(2+) associated with activation of mu-calpain, calcineurin, and phospholipases with consequent proteolysis of calpain substrates (including spectrin and eIF4G), activation of NOS and potentially of Bad, and accumulation of free arachidonic acid, which can induce depletion of Ca(2+) from the ER lumen. A kinase that shuts off translation initiation by phosphorylating the alpha-subunit of eukaryotic initiation factor-2 (eIF2alpha) is activated either by adenosine degradation products or depletion of ER lumenal Ca(2+). Early during reperfusion, oxidative metabolism of arachidonate causes a burst of excess oxygen radicals, iron is released from storage proteins by superoxide-mediated reduction, and NO is generated. These events result in peroxynitrite generation, inappropriate protein nitrosylation, and lipid peroxidation, which ultrastructurally appears to principally damage the plasmalemma of SVNs. The initial recovery of ATP supports very rapid eIF2alpha phosphorylation that in SVNs is prolonged and associated with a major reduction in protein synthesis. High catecholamine levels induced by the ischemic episode itself and/or drug administration down-regulate insulin secretion and induce inhibition of growth-factor receptor tyrosine kinase activity, effects associated with down-regulation of survival signal-transduction through the Ras pathway. Caspase activation occurs during the early hours of reperfusion following mitochondrial release of caspase 9 and cytochrome c. The SVNs find themselves with substantial membrane damage, calpain-mediated proteolytic degradation of eIF4G and cytoskeletal proteins, altered translation initiation mechanisms that substantially reduce total protein synthesis and impose major alterations in message selection, down-regulated survival signal-transduction, and caspase activation. This picture argues powerfully that, for therapy of brain ischemia and reperfusion, the concept of single drug intervention (which has characterized the approaches of basic research, the pharmaceutical industry, and clinical trials) cannot be effective. Although rigorous study of multi-drug protocols is very demanding, effective therapy is likely to require (1) peptide growth factors for early activation of survival-signaling pathways and recovery of translation competence, (2) inhibition of lipid peroxidation, (3) inhibition of calpain, and (4) caspase inhibition. Examination of such protocols will require not only characterization of functional and histopathologic outcome, but also study of biochemical markers of the injury processes to establish the role of each drug.

Calpastatin immunoreactivity in the monkey and human brain of control subjects and patients with Parkinson's disease

Parkinson's disease is characterized by a selective loss of dopaminergic neurons in the nigrostriatal pathway. However, not all dopaminergic neurons degenerate in this disease, and calcium has been suspected of playing a role in this differential vulnerability. An overexpression of the calcium-dependent protease calpain II has recently been reported in the parkinsonian substantia nigra, suggesting that a rise in intracellular calcium concentrations may be involved in the mechanism leading to cell death. The proteasic activity of calpain is regulated by an endogenous inhibitory protein called calpastatin. Because little is known about the distribution of calpastatin in the primate brain, we first analyzed immunohistochemically the calpastatin expression in normal human and monkey brain. A ubiquitous distribution of calpastatin immunostaining was observed in both cases, but its expression was variable from one region to another. In the basal ganglia, staining was intense in the striatum, in the pallidal complex, and in some nuclei of the thalamus. The cerebellum was stained intensely, particularly in the granular and Purkinje cell layers. A dense, heterogeneous staining was observed in the hippocampal formation, mostly in the pyramidal and granular layers. The distribution of staining was similar in the different cerebral cortices studied, and it was most intense in layer V. In the brainstem, staining was particularly prominent in the substantia nigra pars reticulata and compacta, the central gray substance, the superior colliculus, and the cuneiform nucleus, and staining was moderate in the tegmenti pedonculopontinus nucleus and the griseum pontis. In the second part of the study, the authors compared calpastatin expression in the mesencephalon between patients with Parkinson's disease and control subjects. Sequential double staining revealed that some dopaminergic neurons coexpress calpastatin, the proportion of double-stained neurons ranging between 52% and 76% among the different dopaminergic cell groups. Quantitative analysis of the number of calpastatin-stained neurons evidenced a loss of both calpastatin-positive and calpastatin-negative neurons in the substantia nigra of patients with Parkinson's disease. These data suggest that calpain II overexpression in Parkinson's disease is not compensated for by a concomitant increase in calpastatin expression.

Cytoskeletal disruption following contusion injury to the rat spinal cord

Following experimental spinal cord injury (SCI), there is a delayed loss of neurofilament proteins but relatively little is known regarding the status of other cytoskeletal elements. The purpose of the present study was to compare the extent and time course of the MAP2 loss with that of neurofilament proteins, and to examine tau protein levels and distribution following SCI. Within 1 to 6 hours following SCI, there is rapid loss of MAP2, tau, and nonphosphorylated neurofilament proteins at the injury site. In contrast, the loss of phosphorylated neurofilament proteins was not significant until 1 week postinjury. In addition to the loss of MAP2 protein, there was extensive beading of MAP2-immunoreactive dendrites extending into the white matter. This was most pronounced 1 hour after injury and gradually resolved such that beading was no longer evident 2 weeks after SCI. The time course of beading resolution is similar to that of behavioral recovery following SCI, but the functional significance of the beading remains to be determined. Together, these results demonstrate that there are 2 phases of cytoskeletal disruption following SCI; a rapid loss of MAP2, tau, and nonphosphorylated neurofilament proteins, and a delayed loss of phosphorylated neurofilaments.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Calpain mediates eukaryotic initiation factor 4G degradation during global brain ischemia

Global brain ischemia and reperfusion result in the degradation of the eukaryotic initiation factor (eIF) 4G, which plays a critical role in the attachment of the mRNA to the ribosome. Because eIF-4G is a substrate of calpain, these studies were undertaken to examine whether calpain I activation during global brain ischemia contributes to the degradation of eIF-4G in vivo. Immunoblots with antibodies against calpain I and eIF-4G were prepared from rat brain postmitochondrial supernatant incubated at 37 degrees C with and without the addition of calcium and the calpain inhibitors calpastatin or MDL-28,170. Addition of calcium alone resulted in calpain I activation (as measured by autolysis of the 80-kDa subunit) and degradation of eIF-4G; this effect was blocked by either 1 micromol/L calpastatin or 10 micromol/L MDL-28,170. In rabbits subjected to 20 minutes of cardiac arrest, immunoblots of brain postmitochondrial supernatants showed that the percentage of autolyzed calpain I increased from 1.9% +/- 1.1% to 15.8% +/- 5.0% and that this was accompanied by a 68% loss of eIF-4G. MDL-28,170 pretreatment (30 mg/kg) decreased ischemia-induced calpain I autolysis 40% and almost completely blocked eIF-4G degradation. We conclude that calpain I degrades eIF-4G during global brain ischemia.

Active site-directed antibodies identify calpain II as an early-appearing and pervasive component of neurofibrillary pathology in Alzheimer's disease

Calpain proteases influence intracellular signaling pathways and regulate cytoskeleton organization, but the neuronal and pathological roles of individual isoenzymes are unknown. In Alzheimer's disease (AD), the activated form of calpain I is significantly increased while the fate of calpain II has been more difficult to address. Here, calpain II antibodies raised to different sequences within a cryptic region around the active site, which becomes exposed during protease activation, were shown immunohistochemically to bind extensively to neurofibrillary tangles (NFT), neuritic plaques, and neuropil threads in brains from individuals with AD. Additional 'pre-tangle' granular structures in neurons were also intensely immunostained, indicating calpain II mobilization at very early stages of NFT formation. Total levels of calpain II remained constant in the prefrontal cortex of AD patients but were increased 8-fold in purified NFT relative to levels of calpain I. These results implicate activated calpain II in neurofibrillary degeneration, provide further evidence for the involvement of the calpain system in AD pathogenesis, and imply that neuronal calcium homeostasis is altered in AD.

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.

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.

Increased M-calpain expression in the mesencephalon of patients with Parkinson's disease but not in other neurodegenerative disorders involving the mesencephalon: a role in nerve cell death?

Parkinson's disease is characterized by the loss of dopaminergic neurons in the substantia nigra and, to a lesser extent, the ventral tegmental area and catecholaminergic cell group A8. However, among these dopaminergic neurons, those expressing the calcium buffering protein calbindin are selectively preserved, suggesting that a rise in intracellular calcium concentrations may be involved in the cascade of events leading to nerve cell death in Parkinson's disease. We therefore analysed immunohistochemically the expression of the calcium-dependent protease calpain II (m-calpain) in the mesencephalon of patients with Parkinson's disease, progressive supranuclear palsy or striatonigral degeneration, where nigral dopaminergic neurons degenerate, and matched controls without nigral involvement. Calpain immunoreactivity was found in fibers and neuronal perikarya in the substantia nigra, the ventral tegmental area, catecholaminergic cell group A8 and the locus coeruleus. In patients with Parkinson's disease but not with the other neurodegenerative disorders, m-calpain immunoreactivity was detected in fibers with an abnormal morphology and in Lewy bodies. Sequential double staining revealed that most of these m-calpain-positive fibers and neuronal perikarya co-expressed tyrosine hydroxylase, indicating that most m-calpain neurons are catecholaminergic. Quantitative analysis of m-calpain staining in the substantia nigra and locus coeruleus revealed an increased density of fibers and neuronal perikarya in parkinsonian patients in both structures. These data suggest that increased calcium concentrations may be associated with nerve cell death in Parkinson's disease.

Regional differences in gene expression for calcium activated neutral proteases (calpains) and their endogenous inhibitor calpastatin in mouse brain and spinal cord

The family of calpains (CANP or calcium activated neutral proteases) and their endogenous inhibitor calpastatin have been implicated in many neural functions; however, functional distinctions between the major calpain isoforms, calpain I and II, have not been clearly established. In the present study we analyzed the gene expression patterns for calpain I and II and calpastatin in mouse brain and spinal cord by measuring both their mRNA and protein levels. Our results show that the overall mRNA level measured by competitive reverse transcription polymerase chain reaction for calpain II is 15-fold higher and for calpastatin is three-fold higher than that for calpain I. Overall, both mRNA and protein expression levels for the calpains and calpastatin showed no significant difference between the spinal cord and the brain. The cellular distributions of mRNA for calpain I or calpastatin, measured by in situ hybridization, are relatively uniform throughout the brain. In contrast, calpain II gene expression is selectively higher in certain neuron populations including pyramidal neurons of the hippocampus and the deep neocortical layers, Purkinje cells of cerebellum, and motor neurons of the spinal cord. The motor neurons were the most enriched in calpain message. Motor neurons possessed 10-fold more calpain II mRNA than any other spinal cord cell type. The differential distribution of the two proteases in the brain and the spinal cord at the mRNA level indicates that the two calpain genes are differentially regulated, suggesting that they play different physiological roles in neuronal activities and that they may participate in the pathogenesis of certain regional neurological degenerative diseases.

Distribution of mu-calpain proenzyme in the brain and other neural tissues in the rat

We raised antibodies against the acetyl N-terminal peptide of the human mu-calpain 80 kDa (80 K) subunit (N-acetyl SEETPVYCT-GVSAQVQKQRARELG) in the rabbit. A specific antibody was purified using N-acetyl SEEITPVYCTGVSAQVQKQ peptide-conjugated Sepharose 4B as an affinity gel support. Epitope analysis revealed that the purified antibody reacted only with mu-calpain N-terminal peptides containing N-acetyl SEETT structure but no reactions occurred with other analogous peptides. Western blot analysis showed that the antibody reacted with both human and rat mu-calpain proenzymes but not with the activated calpains lacking N-terminal peptide. Using this antibody we investigated immunohistochemically the distribution of mu-calpain proenzyme in central and peripheral nervous systems as well as other non-neural tissues in the rat. The proenzyme was detected mainly in neurons both in the central and peripheral nervous tissues, but not in non-neural tissues except for red blood cells. Immunoreaction was stronger in the perikarya and/or in the nuclei than in-the cytoplasm. Specificity of the antibody was verified by an absorption test. In summary, the mu-calpain proenzyme is mainly distributed in the perikarya and/or nuclei or neurons. Our present antibody specific to the N-terminus of the mu-calpain 80 K subunit could serve as a useful tool to detect various functions of mu-calpain as well as the damage in neurons caused by the enzyme.

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.

Relationship between astrocytic processes and "perineuronal nets" in rat neocortex

"Perineuronal nets" (PNs) ensheath a subtype of inhibitory neurons in the mammalian neocortex. In the light of the proposal that PNs consist of glial processes, we have analyzed the relationship between intracellularly injected glial cells and PNs in the rat neocortex. Glial cells were injected iontophoretically with Lucifer Yellow in lightly fixed tissue slices and PNs were visualized with the lectin from Vicia villosa. Using confocal laser scanning microscopy, glial processes and PNs were identified as distinct structures. Lectin labeling was consistently associated with the extracellular space interposed between LY-labeling was consistently associated with the extracellular space interposed between LY-labeled astrocyte processes and neurons. Of the different types of glial cells injected, only the densely-ramifying protoplasmic astrocytes extended processes which could be traced to contact PNs. These protoplasmic astrocytes also sent out processes to adjacent neurons not ensheathed by PNs, and to capillaries. The present data strongly suggests that PNs do not consist of glial processes but rather support the idea that PNs represent specialized extracellular material interposed between the surface of some inhibitory interneurons and astrocytic processes.

Three distinct phases of fodrin proteolysis induced in postischemic hippocampus. Involvement of calpain and unidentified protease

BACKGROUND AND PURPOSE

Fodrin, a neuronal cytoskeleton protein, is proteolyzed by calpain after ischemic insult. We examined proteolysis of fodrin induced by global forebrain ischemia in gerbil hippocampus in spatial terms by using the antibody specific to the calpain-proteolyzed form of fodrin.

METHODS

In gerbils, a 10-minute forebrain ischemia was produced by occlusion of both carotid arteries. After recirculation, the hippocampus was processed for immunohistochemical and immunoblot study with the antibody against the calpain-proteolyzed form of fodrin. Additionally, short-term ischemia was studied to find the threshold of fodrin proteolysis.

RESULTS

Three phases of fodrin proteolysis distinct in chronology and distribution arose: (1) an early predegeneration phase in the molecular layer and stratum oriens of the CA1 and CA3 sectors within the first 15 minutes, which lasted up to 4 hours; (2) a late predegeneration phase in the whole CA1 sector, except for the pyramidal cells, between 12 hours and 2 days; and (3) a postdegeneration phase in the cytoplasm of the CA1 neurons, which arose in 3 to 7 days. A 4-minute (not a 3-minute) forebrain ischemia induced the late predegeneration phase of fodrin proteolysis and delayed neuronal death in CA1. Immunoblotting showed that the primary product of calpain action was further proteolyzed by an unidentified protease.

CONCLUSIONS

Calpain induced proteolysis of fodrin in ischemic hippocampus, and the late predegeneration phase of the proteolysis was closely associated with the delayed neuronal death in the CA1 sector. Calpain and another protease may play a role in the development of neuronal death after transient forebrain ischemia.

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.

Calcium-activated neutral proteinase (calpain) system in aging and Alzheimer's disease

Calpains (CANPs) are a family of calcium-dependent cysteine proteases under complex cellular regulation. By making selective limited proteolytic cleavages, they activate or alter the regulation of certain enzymes, including key protein kinases and phosphatases, and induce specific cytoskeletal rearrangements, accounting for their suspected involvement in intracellular signaling, vesicular trafficking, and structural stabilization. Calpain activity has been implicated in various aging phenomena, including cataract formation and erythrocyte senescence. Abnormal activation of the large stores of latent calpain in neurons induces cell injury and is believed to underlie neurodegeneration in excitotoxicity, Wallerian degeneration, and certain other neuropathologic states involving abnormal calcium influx. In Alzheimer's disease, we found the ratio of activated calpain I to its latent precursor isoform in neocortex to be threefold higher than that in normal individuals and those with Huntington's or Parkinson's disease. Immunoreactivity toward calpastatin, the endogenous inhibitor of calpain, was also markedly reduced in layers II-V of the neocortex in Alzheimer's disease. The excessive calpain system activation suggested by these findings represents a potential molecular basis for synaptic loss and neuronal cell death in the brain in Alzheimer's disease given the known destructive actions of calpain I and its preferential neuronal and synaptic localization. In surviving cells, persistent calpain activation may also contribute to neurofibrillary pathology and abnormal amyloid precursor protein trafficking/processing through its known actions on protein kinases and the membrane skeleton. The degree of abnormal calpain activation in the brain in Alzheimer's disease strongly correlated with the extent of decline in levels of secreted amyloid precursor protein in brain. Cytoskeletal proteins that are normally good calpain substrates become relatively calpain resistant when they are hyperphosphorylated, which may contribute to their accumulation in neurofibrillary tangles. As a major effector of calcium signals, calpain activity may mirror disturbances in calcium homeostasis and mediate important pathologic consequences of such disturbances.

Calpain inhibitors block Ca(2+)-induced suppression of neurite outgrowth in isolated hippocampal pyramidal neurons

Ca2+ is an important regulator of neurite elongation and growth cone movements but the mechanism(s) mediating these Ca(2+)-dependent effects is unclear. Since cytoskeletal proteins are rapidly degraded by Ca(2+)-dependent proteinases (calpains) in vitro and in vivo, we investigated whether Ca(2+)-induced pruning or regression of neuronal processes is mediated by calpains. Isolated hippocampal pyramidal-like neurons were cultured and the ability of the membrane-permeable calpain inhibitors ethyl(+)-(2S,3S)-3-[(S)-methyl-1-(3-methylbutylcarbamoyl)-butyl carbamoyl]-2 - oxiranecarboxylate (EST) and carbobenzoxyl-valyl-phenylalanyl-H (MDL 28170) to block the Ca2+ ionophore A23187-induced suppression in neurite outgrowth was investigated. Addition of 100 nM A23187 to the culture medium resulted in a retraction of dendrites without altering axonal elongation. The addition of 300 nM A23187 to the culture medium resulted in a significant decrease in the rate of axonal elongation as well as a retraction of dendritic processes. Administration of EST (5 or 20 microM) to the culture medium completely blocked the pruning effect of 100 nM A23187 on dendrites and of 300 nM A23187 on axons, while EST alone did not significantly affect neurite outgrowth rate. MDL 28170 (20 microM) showed the same effect as EST in preventing ionophore-induced pruning of dendrites and axons at 100 and 300 nM concentrations, respectively, of A23187. EST (20 microM) did not block the A23187-induced rise of [Ca2+]i as measured with fura-2. These results suggest that calpains play a role in Ca(2+)-induced pruning of neurites in isolated hippocampal pyramidal neurons.

The calpain-calpastatin system is regulated differently during human neuroblastoma cell differentiation to Schwannian and neuronal cells

Changes in expression of calpains and calpastatin during differentiation in GOTO cells were examined using antibodies specific to calpains and calpastatin. Neuronal differentiation induced by dibutyryl cyclic AMP elicited a remarkable decrease in m-calpain. No marked changes in the levels of calpains were found in bromodeoxyuridine-induced Schwannian differentiation. Calpastatin was detected as a single band of 110k in undifferentiated and in neuronally differentiated cells by Western blot analysis. However, the appearance of a 120k species was detected in Schwannian differentiation associated with morphological change. The data show that marked changes in m-calpain and calpastatin occur in a differentiation-specific manner.

Localization of mRNAs for calpain and calpastatin in the adult rat brain by in situ hybridization histochemistry

The detailed localization of mRNAs for calpain II and calpastatin was examined in adult rat brain by in situ hybridization histochemistry. The expression patterns of the two mRNAs were similar to each other throughout the brain in terms of relative expression intensity, and almost all neurons expressed both mRNAs more or less. Among them, neurons in cranial nerve nuclei and some others in the brain stem expressed at relatively high levels, suggesting the high involvement of the non-lysosomal proteolytic system in the function of these neurons. On the other hand, the expression levels of the two mRNAs in non-neuronal cells including glia were basically low with the choroid plexuses expressing calpastatin mRNA relatively highly.

Immunohistochemical localization of calpains and calpastatin in the rabbit eye

The localization of the two Ca-activated extralysosomal proteases m-calpain and mu-calpain in the eye of the adult rabbit was examined by immunohistochemistry, using poly- and monoclonal antibodies against the corresponding rabbit antigens. Immunoreactivity against the two forms of calpains was observed in the epithelial cells on the external and internal surface of the cornea as well as in the epithelial cells covering the iris and ciliary body. The sclera and choroid layers showed a relatively weak immunoreactivity. Using anti m-calpain antibodies, the pigment epithelium in the retina was heavily labelled as well as the outer and inner plexiform layers. The other and inner borders of the Müller cells were clearly labelled. The outer segments of the receptor cells showed a strong immunoreactivity for both mu-calpain and m-calpain. Labelling was also observed in the retinal ganglion cells and in the nerve fiber layer. The immunohistochemical localization of calpastatin, an endogenous inhibitor of both m- and mu-calpain was also examined. A high level of calpastatin immunoreactivity was observed in the outer segments of the receptor cells. The results may be compatible with a role for calpains, especially m-calpain, in the secretory/phagocytic process and as modulators of the cytoskeleton in cell processes.

Protective effects of calpain inhibitors against neuronal damage caused by cytotoxic hypoxia in vitro and ischemia in vivo

The calpains are calcium-dependent intracellular proteases that are activated in a number of pathogenic conditions. We tested the capacities of protease inhibitors, calpain inhibitor I and leupeptin, to protect against the neuronal degeneration caused by cytotoxic hypoxia or transient global cerebral ischemia. Primary neuronal cultures were prepared from embryonic chick telencephalon, and cytotoxic hypoxia was induced by adding 1 mM NaCN to the culture medium for 30 min. Global ischemia was induced in rats by clamping both carotid arteries and lowering the arterial blood pressure to 40 mmHg for 10 min. Both calpain inhibitor I and leupeptin protected neurons against ischemic and hypoxic damage. Neuroprotection was indicated by increased cell viability and protein content in the cultures, and fewer damaged neurons in the hippocampal CA1-subfield. Thus, blockade of proteolysis can protect neurons against cytotoxic and ischemic damage.

Widespread activation of calcium-activated neutral proteinase (calpain) in the brain in Alzheimer disease: a potential molecular basis for neuronal degeneration

Calcium-activated neutral proteinases (CANPs or calpains) are believed to be key enzymes in intracellular signaling cascades and potential mediators of calcium-induced neuronal degeneration. To investigate their involvement in Alzheimer disease, we identified three isoforms of muCANP (calpain I) in human postmortem brain corresponding to an 80-kDa precursor and two autolytically activated isoforms (78 and 76 kDa). As an index of changes in the in vivo activity of muCANP in Alzheimer disease, the ratio of the 76-kDa activated isoform of muCANP to its 80-kDa precursor was measured by immunoassay in selected brain regions from 22 individuals with Alzheimer disease and 18 normal controls. This muCANP activation ratio was elevated 3-fold in the prefrontal cortex from patients with Alzheimer disease but not from patients with Huntington disease. The activation ratio was also significantly elevated, but to a lesser degree, in brain regions where Alzheimer pathology is milder and has not led to overt neuronal degeneration. These findings indicate that muCANP activation is not simply a consequence of cellular degeneration but may be associated with dysfunction in many neurons before gross structural changes occur. The known influences of CANPs on cytoskeleton and membrane dynamics imply that persistent CANP activation may contribute to neurofibrillary pathology and abnormal amyloid precursor protein processing prior to causing synapse loss or cell death in the most vulnerable neuronal populations. Pharmacological modulation of the CANP system may merit consideration as a potential therapeutic strategy in Alzheimer disease.

Persistent degenerative state of non-pyramidal neurons in the CA1 region of the gerbil hippocampus following transient forebrain ischemia

Morphological changes in the neurons of the gerbil hippocampus following 5 min of forebrain ischemia were examined using light and electron microscopy. Although non-pyramidal neurons in the CA1 region of the hippocampus survived through the full length of the observation period, up to six weeks after ischemia, they consistently demonstrated degenerative changes distinct from those of the well-known "delayed neuronal death" of CA1 pyramidal cells. When examined with the light microscope, CA1 non-pyramidal neurons were found to be shrunken and their nuclei and cytoplasm were hyperchromatic between seven days and six weeks after ischemia. When examined with the electron microscope, postischemic non-pyramidal neurons were found to have markedly electron-dense profiles; their cytoplasm contained numerous free ribosomes and heterogeneous smaller granular substances, the latter also filling the nuclei. However, there was no loss of ribosomes from the rough endoplasmic reticulum, and mitochondrial cristae were preserved, suggesting that these neurons were viable. CA1 non-pyramidal neurons were studied immunohistochemically using three types of monoclonal antibodies, one each against parvalbumin, a nonphosphorylated epitope on the 168,000 mol. wt and 200,000 mol. wt subunits of neurofilament proteins, and microtubule-associated protein 2. CA1 non-pyramidal neurons lost immunoreactivity to these neuron-specific substances six weeks after ischemia, suggesting that these degenerating cells lacked certain types of normal neuronal activity. We conclude that non-pyramidal neurons in the hippocampal CA1 region survive transient ischemia but undergo degenerative changes following complete loss of CA1 pyramidal cells. These changes may be due to depletion of presumptive target-derived trophic factors within the non-pyramidal neurons.

The distribution of cathepsin D activity in adult and aging human brain regions

We measured the activity of cathepsin D, the major cerebral protease, in 50 separate areas of the central nervous system of adult and aged humans, using hemoglobin as the substrate. The activity showed significant regional heterogeneity, with average differences of 50-100% between the lower and higher level areas, and a more than threefold difference between the lowest and highest levels. The forebrain, midbrain, and hindbrain each had areas of high and low activity; cerebellum and cord areas were among those with low activity. Cathepsin levels tended to increase with age in about half of the areas analyzed, and the increases were significant in 14. Statistically significant decreases with aging were observed in two areas. The increases varied between 30 and 60%, and the decreases were 20%. Enzyme activity in thalamus, hypothalamus, pons, medulla, and cerebellum increased with age. In the ventrolateral medulla, which contains the major portion of the cerebral noradrenergic cells, the cathepsin D levels increased with age; in the dorsal raphe area, which contains the major portion of the cerebral serotonergic cells, the enzyme levels decreased. The change with age in human brain seems to be less than what we observed in rat brain, where activity more than doubled in most areas. The changes in enzyme levels need to be tested at more ages to establish a pattern of changes in activity throughout life.

Calpain II in rat peripheral nerve

We used a polyclonal antiserum directed against calpain II to study the distribution of that enzyme in rat sciatic nerve. Western blot of nerve homogenate showed that the antibody reacted with a single protein band of 80 kDa, corresponding to the catalytic subunit of calpain II. By light microscopy, immunoreactivity appeared predominantly in Schwann cell cytoplasm. By electron microscopy, calpain II was especially dense along the plasmalemma of Schwann cells, and was also seen in axoplasm.