Calcium-activated neutral proteinase in rat brain myelin and subcellular fractions

Multi-targeted DATS prevents tumor progression and promotes apoptosis in ectopic glioblastoma xenografts in SCID mice via HDAC inhibition

Glioblastoma, the most lethal brain tumor, remains incurable despite aggressive chemotherapy and surgical interventions. New chemotherapeutics for glioblastoma have been explored in preclinical models and some agents have reached the clinical setting. However, success rates are not significant. Previous investigations involving diallyl trisulfide (DATS), a garlic compound, indicated significant anti-cancer effects in glioblastoma in vitro. DATS has also been shown to inhibit histone deacetylase activity and impede glioblastoma tumor progression. We hypothesized that DATS would block ectopic U87MG tumor by multiple pro-apoptotic pathways via inhibiting histone deacetylase (HDAC). To prove this, we developed ectopic U87MG tumors in SCID mice and treated them daily with intraperitoneal injections of DATS for 7 days. Results indicated that DATS (10 μg/kg-10 mg/kg) dose-dependently reduced tumor mass and number of mitotic cells within tumors. Histological and biochemical assays demonstrated that DATS reduced mitosis in tumors, decreased HDAC activity, increased acetylation of H3 and H4, inhibited cell cycle progression, decreased pro-tumor markers (e.g., survivin, Bcl-2, c-Myc, mTOR, EGFR, VEGF), promoted apoptotic factors (e.g., bax, mcalpian, active caspase-3), and induced DNA fragmentation. Our data also demonstrated an increase in p21Waf1 expression, which correlated with increased p53 expression and MDM2 degradation following DATS treatment. Finally, histological assessment and enzyme assays showed that even the highest dose of DATS did not negatively impact hepatic function. Collectively, our results clearly demonstrated that DATS could be an effective therapeutic agent in preventing tumor progression and inducing apoptosis in human glioblastoma in vivo, without impairing hepatic function.

Melatonin attenuates calpain upregulation, axonal damage and neuronal death in spinal cord injury in rats

Multiple investigations in vivo have shown that melatonin (MEL) has a neuroprotective effect in the treatment of spinal cord injury (SCI). This study investigates the role of MEL as an intervening agent for ameliorating Ca(2+)-mediated events, including activation of calpain, following its administration to rats sustaining experimental SCI. Calpain, a Ca(2+)-dependent neutral protease, is known to be involved in the pathogenesis of SCI. Rats were injured using a standard weight-drop method that induced a moderately severe injury (40 g.cm force) at T10. Sham controls received laminectomy only. Injured animals were given either 45 mg/kg MEL or vehicle at 15 min post-injury by intraperitoneal injection. At 48 hr post-injury, spinal cord (SC) samples were collected. Immunofluorescent labelings were used to identify calpain expression in specific cell types, such as neurons, glia, or macrophages. Combination of terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) and double immunofluorescent labelings was used to identify apoptosis in specific cells in the SC. The effect of MEL on axonal damage was also investigated using antibody specific for dephosphorylated neurofilament protein (dNFP). Treatment of SCI animals with MEL attenuated calpain expression, inflammation, axonal damage (dNFP), and neuronal death, indicating that MEL provided neuroprotective effect in SCI. Further, expression and activity of calpain and caspse-3 were examined by Western blotting. The results indicated a significant decrease in expression and activity of calpain and caspse-3 in SCI animals after treatment with MEL. Taken together, this study strongly suggested that MEL could be an effective neuroprotective agent for treatment of SCI.

N terminus of calpain 1 is a mitochondrial targeting sequence

The ubiquitous m- and mu-calpains are thought to be localized in the cytosolic compartment, as is their endogenous inhibitor calpastatin. Previously, mu-calpain was found to be enriched in mitochondrial fractions isolated from rat cerebral cortex and SH-SY5Y neuroblastoma cells, but the submitochondrial localization of mu-calpain was not determined. In the present study, submitochondrial fractionation and digitonin permeabilization studies indicated that both calpain 1 and calpain small subunit 1, which together form mu-calpain, are present in the mitochondrial intermembrane space. The N terminus of calpain 1 contains an amphipathic alpha-helical domain, and is distinct from the N terminus of calpain 2. Calpain 1, but not calpain 2, was imported into mitochondria. Removal of the N-terminal 22 amino acids of calpain 1 blocked the mitochondrial calpain import, while addition of this N-terminal region to calpain 2 or green fluorescent protein enabled mitochondrial import. The N terminus of calpain 1 was not processed following mitochondrial import, but was removed by autolysis following calpain activation. Calpain small subunit 1 was not directly imported into mitochondria, but was imported in the presence of calpain 1. The presence of a mitochondrial targeting sequence in the N-terminal region of calpain 1 is consistent with the localization of mu-calpain to the mitochondrial intermembrane space and provides new insight into the possible functions of this cysteine protease.

Direct evidence for calpain involvement in apoptotic death of neurons in spinal cord injury in rats and neuroprotection with calpain inhibitor

To demonstrate calpain involvement in neurodegeneration in rat spinal cord injury (SCI), we examined SCI segments for DNA fragmentation, neurons for calpain overexpression, neuronal death, and neuroprotection with calpain inhibitor (E-64-d). After the induction of SCI (40 g cm force) on T12, rats were treated within 15 min with vehicle (DMSO) or E-64-d. Sham animals underwent laminectomy only. Animals were sacrificed at 24 h, and five 1-cm long spinal cord segments were collected: two rostral (S1 and S2), one lesion (S3), and two caudal segments (S4 and S5). Agarose gel electrophoresis of DNA samples isolated from the SCI segments showed both random and internucleosomal DNA fragmentation indicating occurrence of necrosis as well as apoptosis mostly in the lesion, moderately in caudal, and slightly in rostral segments from SCI rats. Treatment of SCI rats with E-64-d (1 mg/kg) reduced DNA fragmentation in all segments. The lesion and adjacent caudal segments (S3 and S4) were further investigated by in situ double-immunofluorescent labelings that showed increase in calpain expression in neurons in SCI rats and decrease in calpain expression in SCI rats treated with E-64-d. In situ combined TUNEL and double-immunofluorescent labelings directly detected co-localization of neuronal death and calpain overexpressin in SCI rats treated with only vehicle while attenuation of neuronal death in SCI rats treated with E-64-d. Previous studies from our laboratory indirectly showed neuroprotective effect of E-64-d in SCI rats. Our current results provide direct in situ evidence for calpain involvement in neuronal death and neuroprotective efficacy of E-64-d in lesion and penumbra in SCI rats.

Molecular mechanism of inositol hexaphosphate-mediated apoptosis in human malignant glioblastoma T98G cells

Glioblastoma is the deadliest brain tumor in humans. Current therapies are mostly ineffective and new agents need to be explored for controlling this devastating disease. Inositol hexaphosphate (IP6) is a phytochemical that is widely found in corns, cereals, nuts, and high fiber-content foods. Previous studies demonstrated anti-cancer properties of IP6 in several in vitro and in vivo tumor models. However, therapeutic efficacy of IP6 has not yet been evaluated in glioblastoma. Here, we explored the molecular mechanism of action of IP6 in human malignant glioblastoma T98G cells. The viability of T98G cells decreased following treatment with increasing doses of IP6. T98G cells exposed to 0.25, 0.5, and 1 mM IP6 for 24 h showed morphological and biochemical features of apoptosis. Western blotting indicated changes in expression of Bax and Bcl-2 proteins resulting in an increase in Bax:Bcl-2 ratio and upregulation of cytosolic levels of cytochrome c and Smac/Diablo, suggesting involvement of mitochondria-dependent caspase cascade in apoptosis. IP6 downregulated cell survival factors such as baculovirus inhibitor-of-apoptosis repeat containing-2 (BIRC-2) protein and telomerase to promote apoptosis. Upregulation of calpain and caspase-9 occurred in course of apoptosis. Increased activities of calpain and caspase-3 cleaved 270 kD alpha-spectrin at specific sites generating 145 kD spectrin break down product (SBDP) and 120 kD SBDP, respectively. Increased caspase-3 activity also cleaved inhibitor of caspase-3-activated DNase and poly(ADP-ribose) polymerase. Collectively, our results demonstrated that IP6 down regulated the survival factors BIRC-2 and telomerase and upregulated calpain and caspase-3 activities for apoptosis in T98G cells.

Curcumin suppressed anti-apoptotic signals and activated cysteine proteases for apoptosis in human malignant glioblastoma U87MG cells

Glioblastoma is the most malignant human brain tumor that shows poor response to existing therapeutic agents. Search continues for an effective therapy for controlling this deadliest brain tumor. Curcumin (CCM), a polyphenolic compound from Curcuma longa, possesses anti-cancer properties in both in vitro and in vivo. In the present investigation, we evaluated the therapeutic efficacy of CCM against human malignant glioblastoma U87MG cells. Trypan blue dye exclusion test showed decreased viability of U87MG cells with increasing dose of CCM. Wright staining and ApopTag assay, respectively, showed the morphological and biochemical features of apoptosis in U87MG cells treated with 25 microM and 50 microM of CCM for 24 h. Western blotting showed activation of caspase-8, cleavage of Bid to tBid, increase in Bax:Bcl-2 ratio, and release of cytochrome c from mitochondria followed by activation of caspase-9 and caspase-3 for apoptosis. Also, CCM treatments increased cytosolic level of Smac/Diablo to suppress the inhibitor-of-apoptosis proteins and down regulated anti-apoptotic nuclear factor kappa B (NFkappaB), favoring the apoptosis. Increased activities of calpain and caspase-3 cleaved 270 kDa alpha-spectrin at specific sites generating 145 kDa spectrin break down product (SBDP) and 120 kDa SBDP, respectively, leading to apoptosis in U87MG cells. Results show that CCM is an effective therapeutic agent for suppression of anti-apoptotic factors and activation of calpain and caspase proteolytic cascades for apoptosis in human malignant glioblastoma cells.

Activation of multiple molecular mechanisms for apoptosis in human malignant glioblastoma T98G and U87MG cells treated with sulforaphane

Glioblastoma is the most malignant and prevalent brain tumor that still remains incurable. Recent studies reported anti-cancer effect of the broccoli-derived compound sulforaphane. We explored the mechanisms of sulforaphane-mediated apoptosis in human glioblastoma T98G and U87MG cells. Wright staining and ApopTag assay confirmed apoptosis in glioblastoma cells treated with sulforaphane. Increase in intracellular free Ca2+ was detected by fura-2 assay, suggesting activation of Ca2+-dependent pathways for apoptosis. Western blotting was used to detect changes in expression of Bax and Bcl-2 proteins resulting in increased Bax:Bcl-2 ratio that indicated a commitment of glioblastoma cells to apoptosis. Upregulation of calpain, a Ca2+-dependent cysteine protease, activated caspase-12 that in turn caused activation of caspase-9. With the increased Bax:Bcl-2 ratio, cytochrome c was released from mitochondria to cytosol for sequential activation of caspase-9 and caspase-3. Increased calpain and caspase-3 activities generated 145 kD spectrin breakdown product and 120 kD spectrin breakdown product, respectively. Activation of caspase-3 also cleaved the inhibitor-of-caspase-activated-DNase. Accumulation of apoptosis-inducing-factor in cytosol suggested caspase-independent pathway of apoptosis as well. Two of the inhibitor-of-apoptosis proteins were downregulated because of an increase in 'second mitochondrial activator of caspases/Direct inhibitor-of-apoptosis protein binding protein with low pI.' Decrease in nuclear factor kappa B and increase in inhibitor of nuclear factor kappa B alpha expression favored the process of apoptosis. Collectively, our results indicated activation of multiple molecular mechanisms for apoptosis in glioblastoma cells following treatment with sulforaphane.

Inhibition of calpain and caspase-3 prevented apoptosis and preserved electrophysiological properties of voltage-gated and ligand-gated ion channels in rat primary cortical neurons exposed to glutamate

Glutamate toxicity in traumatic brain injury, ischemia, and Huntington's disease causes cortical neuron death and dysfunction. We tested the efficacy of calpain and caspase-3 inhibitors alone and in combination to prevent neuronal death and preserve electrophysiological functions in rat primary cortical neurons following glutamate exposure. Cortical neurons exposed to 0.5 microM glutamate for 24 h committed mostly apoptotic death as determined by Wright staining and ApopTag assay. Levels of expression, formation of active forms, and activities of calpain and caspase-3 were increased following glutamate exposure. Also, in situ double labeling identified conformationally active caspase-3-p20 fragment and chromatin condensation in apoptotic neurons. Pretreatment of cortical neurons with 0.2 microM N-benzyloxylcarbonyl-Leu-Nle-aldehyde (calpain-specific inhibitor) and 100 microM N-benzyloxylcarbonyl-Asp(OCH3)-Glu(OCH3)-Val-Asp(OCH3)-fluoromethyl ketone (caspase-3-specific inhibitor) provided strong neuroprotection. Standard patch-clamp techniques were used to measure the whole-cell currents associated with Na+ channels, N-methyl-D-aspartate receptors, and kainate receptors. The lack of a change in capacitance indicated that neurons treated with inhibitor(s) plus glutamate did not undergo apoptotic shrinkage and maintained the same size as the control neurons. Whole-cell currents associated with Na+ channels, N-methyl-D-aspartate receptors, and kainate receptors were similar in amplitude and activation/inactivation kinetics for cells untreated and treated with inhibitor(s) and glutamate. Spontaneous synaptic activity as observed by miniature end-plate currents was also similar. Prevention of glutamate-induced apoptosis by calpain and caspase-3 inhibitors preserved normal activities of crucial ion channels such as Na+ channels, N-methyl-D-aspartate receptors, and kainate receptors in neurons. Our studies strongly imply that calpain and caspase-3 inhibitors may also provide functional neuroprotection in the animal models of traumatic brain injury and neurodegenerative diseases.

Mitochondrial localization of mu-calpain

Calcium-dependent cysteine proteases, calpains, have physiological roles in cell motility and differentiation but also play a pathological role following insult or disease. The ubiquitous calpains are widely considered to be cytosolic enzymes, although there has been speculation of a mitochondrial calpain. Within a highly enriched fraction of mitochondria obtained from rat cortex and SH-SY5Y human neuroblastoma cells, immunoblotting demonstrated enrichment of the 80kDa mu-calpain large subunit and 28kDa small subunit. In rat cortex, antibodies against domains II and III of the large mu-calpain subunit also detected a 40kDa fragment, similar to the autolytic fragment generated following incubation of human erythrocyte mu-calpain with Ca(2+). Mitochondrial proteins including apoptosis inducing factor and mitochondrial Bax are calpain substrates, but the mechanism by which calpains gain access to these proteins is uncertain. Mitochondrial localization of mu-calpain places the enzyme in proximity to its mitochondrial substrates and to Ca(2+) released from mitochondrial stores.

Higher calpastatin levels correlate with resistance to calpain-mediated proteolysis and neuronal apoptosis in juvenile rats after spinal cord injury

While the average age for patients admitted with spinal cord injury is 32 years, patients under the age of 16 account for 5% of spinal cord injured persons. For these younger patients, an increased mortality up to 24 h post-injury has been reported, however, survivors may regain more function than their adult counterparts, suggesting that age may play a role in injury tolerance. While the use of growth factors as a therapy for spinal cord injury is well researched, the response of the developing cord to secondary injury has not been thoroughly investigated. Following spinal cord injury, Ca(2+) influx can activate enzymes such as calpain, a Ca(2+)-dependent protease, which plays a role in the pathogenesis of spinal cord injury in rats. The present investigation revealed that following spinal cord injury, calpain upregulation was significantly less (15.3%) in the 21-day-old rats than in either 45-day-old (70%) or 90-day-old (99.6%) rats, as shown by Western blot and in situ immunofluorescent studies. Expression of the endogenous calpain inhibitor, calpastatin, was significantly higher in juvenile rats than adult rats. Juvenile rats with spinal cord injury also showed a reduced Bax:Bcl-2 ratio (4:1 vs. 6:1), reduced caspase-3 staining, reduced myelin loss (3% vs. 18%), and less neuronal DNA damage, as compared to older rats. These results suggest that increased calpastatin levels found in juvenile rats muted calpain activity and neuronal apoptosis, following spinal cord injury.

Early induction of secondary injury factors causing activation of calpain and mitochondria-mediated neuronal apoptosis following spinal cord injury in rats

To investigate a potential relationship between calpain and mitochondrial damage in spinal cord injury (SCI), a 40 gram-centimeter force (g-cm) injury was induced in rats by a weight-drop method and allowed to progress for 4 hr. One-centimeter segments of spinal cord tissue representing the adjacent rostral, lesion, and adjacent caudal areas were then removed for various analyses. Calcium green 2-AM staining of the lesion and penumbra sections showed an increase in intracellular free calcium (Ca(2+)) levels following injury, compared with corresponding tissue sections from sham-operated (control) animals. Western blot analysis showed increased calpain expression and activity in the lesion and penumbra segments following SCI. Double-immunofluorescent labeling indicated that increased calpain expression occurred in neurons in injured segments. Western blot analysis also showed an increased Bax:Bcl-2 ratio, indicating the induction of the mitochondria-mediated cell death pathway in the lesion and penumbra. The morphology of mitochondria was altered in lesion and penumbra following SCI: mostly hydropic change (swelling) in the lesion, with the penumbra shrunken or normal. At 4 hr after induction of injury, a substantial amount of cytochrome c had been released into the cytoplasm, suggesting a trigger for apoptosis through caspase 3 activation. Neuronal death after 4 hr of injury was detected by a combined TUNEL and double-immunofluoresence assay in the lesion and penumbra sections of injured cord, compared with sham controls. These results suggest that an early induction of secondary factors is involved in the pathogenesis of SCI. The increased Ca(2+) levels could activate calpain and mediate mitochondrial damage leading to neuronal death in lesion and penumbra following injury. Thus, secondary injury processes mediating cell death are induced as early as 4 hr after the injury, and calpain and caspase inhibitors may provide neuroprotection.

Calpain and calpastatin expression in primary oligodendrocyte culture: preferential localization of membrane calpain in cell processes

The cellular localization of calpain is important in understanding the roles that calpain may play in physiological function. We, therefore, examined calpain expression, activity, and immunofluorescent localization in primary cultures of rat oligodendrocytes. The mRNA expression of m-calpain was 64.8% (P = 0.0033) and 50.5% (P = 0.0254) higher than that of mu-calpain and calpastatin, respectively, in primary culture oligodendrocytes. The levels of mRNA expression of mu-calpain and calpastatin were not significantly different. As revealed by Western blotting, cultured oligodendrocytes contained a 70 kD major band identified by membrane m-calpain antibody, a 80 kD band recognized by cytosolic m-calpain antibody, and calpastatin bands ranging from 45 to 100 kD detected by a calpastatin antibody. Calpain activity in oligodendrocytes was determined by Ca(2+)-dependent 71.2% degradation of endogenous myelin basic protein compared with control; this activity was inhibited significantly (P = 0.0111) by EGTA and also substantially by calpeptin. Localization of calpain in cultured oligodendrocytes revealed strong membrane m-calpain immunofluorescence in the oligodendrocyte cell body and its processes. In contrast, the cytosolic antibody stained primarily the oligodendrocyte cell body, whereas the processes were stained very weakly or not at all. These results indicate that the major form of calpain in glial cells is myelin (membrane) m-calpain. The dissimilar localization of cytosolic and membrane m-calpain may indicate that each isoform has a unique role in oligodendrocyte function.

Molecular evidence of apoptotic death in malignant brain tumors including glioblastoma multiforme: upregulation of calpain and caspase-3

Cell death in the core of human brain tumors is triggered by hypoxia and lack of nutrients, but the mode of cell death whether necrosis or apoptosis is not clearly defined. To identify the role of apoptosis in brain tumor cell death, we investigated macromolecular (RNA and protein) synthesis and activity in the central to peripheral region of benign [desmoplastic infantile ganglioglioma (DIG) and transitional meningioma (TMG)] and malignant [ependymoma (END), anaplastic astrocytoma (APA), and glioblastoma multiforme (GBM)] brain tumors derived from five patients who had not received previously radiotherapy or chemotherapy. Normal brain tissue (NBT) served as control. RT-PCR analysis of tumor tissues covering central to peripheral regions detected mRNA overexpression of pro-apoptotic gene bax in malignant tumors, indicating a commitment to apoptosis. The mRNA expression of calpain (a Ca(2+)-dependent cysteine protease) and calpastatin (endogenous calpain inhibitor) was altered resulting in an elevated calpain/calpastatin ratio. Calpain content and activity were increased, suggesting a role for calpain in cell death. In the mitochondria-dependent death pathway, caspase-9 and caspase-3 were also overexpressed in tumors. The increased caspase-3 activity cleaved poly(ADP-ribose) polymerase (PARP). Agarose gel electrophoresis detected a mixture of random and internucleosomal DNA fragmentation in malignant brain tumors. Overexpression of pro-apoptotic bax, upregulation of calpain and caspase-3, and occurrence of internucleosomal DNA fragmentation are now presented indicating that one mechanism of cell death in malignant brain tumors is apoptosis, and that enhancement of this process therapeutically may promote decreased tumor growth.

Inhibition of calpain-mediated apoptosis by E-64 d-reduced immediate early gene (IEG) expression and reactive astrogliosis in the lesion and penumbra following spinal cord injury in rats

Upregulation of calpain, a Ca(2+)-activated cysteine protease, has been implicated in apoptosis and tissue degeneration in spinal cord injury (SCI) that over time spreads from the site of injury to the surrounding regions. We examined calpain content and activity, regulation of immediate early genes (IEGs) such as c-jun and c-fos, reactive astrogliosis as the expression of glial fibrillary acidic protein (GFAP), and apoptosis-related features such as caspase-3 mRNA expression and internucleosomal DNA fragmentation in 1-cm long spinal cord segments (S1, distant rostral; S2, adjacent rostral; S3, lesion or injury; S4, adjacent caudal; and S5, distant caudal) following SCI in rats. Calpain content and production of 150 kD calpain-cleaved alpha-fodrin fragment, expression of IEGs, reactive astrogliosis, and apoptotic features were highly increased in the lesion (S3), moderately in adjacent areas (S2 and S4), and slightly in distant areas (S1 and S5) in SCI rats when compared to sham animals. Administration of the calpain-specific inhibitor E-64-d (1 mg/kg) to SCI rats continuously for 24 h inhibited calpain activity and other factors contributing to apoptosis in the lesion and surrounding areas, indicating that calpain played a key role in the pathophysiology of SCI. The results obtained from this animal model of SCI suggest that calpain inhibitor can provide neuroprotection in patients with SCI.

Increased calpain expression is associated with apoptosis in rat spinal cord injury: calpain inhibitor provides neuroprotection

Calpain content was investigated in the lesion of rat spinal cord at 1, 4, 24, and 72 h following injury induced by the weight-drop (40 g-cm force) technique. Calpain content was increased in the lesion, and was highest at 24 h following injury. microCalpain mRNA level in the lesion was increased by 58.4% (p = 0.0135) at 24 h following trauma, compared to sham. Alterations in mRNA expression in the lesion increased bax/bcl-2 ratio by 20.8% (p = 0.0395) at this time point, indicating a commitment to apoptosis. Therapeutic effect of the calpain inhibitor E-64-d (1 mg/kg) was studied in SCI rats following administration for 24 h. Internucleosomal DNA fragmentation (apoptosis) was observed in SCI rats, but not in sham or E-64-d treated rats. These results indicate a new information that E-64-d has the therapeutic potential for inhibiting apoptosis in SCI.

Calpain activity and expression are increased in splenic inflammatory cells associated with experimental allergic encephalomyelitis

Since calcium-activated neutral proteinase (calpain) activity and expression are significantly increased in activated glial/inflammatory cells in the central nervous system of animals with autoimmune demyelinating diseases, this enzyme may also play a role in peripheral organ systems in these diseases. In this study, the activity and expression of calpain and the endogenous inhibitor, calpastatin, were evaluated at transcriptional and translational levels in spleens of Lewis rats with acute experimental allergic encephalomyelitis (EAE) prior to the onset of clinical symptoms. Calpain activity and translational expression were increased by 475.5% and 44.3% respectively, on day 4 post-induction in adjuvant controls and animals with EAE. These levels remained elevated compared to normal controls on days 8 and 12. Calpastatin translational expression was similarly increased at these time points although transcriptional expression was not significantly altered at any time following induction of EAE. Likewise, transcriptional expression of mu-calpain was unchanged following induction, while small increases in m-calpain transcriptional expression were observed on days 2 and 8. Most calpain expression was observed in activated splenic macrophages at day 8 post-induction even though activated T cells were also calpain positive. In spinal cords of animals with EAE, calpain expression was significantly increased in rats with severe disease compared to those exhibiting only mild symptoms at day 12 post-induction. Thus, prior to symptomatic EAE, increased calpain activity and expression in peripheral lymphoid organs may play an important role in T cell migration and subsequent disease progression.

Diverse stimuli induce calpain overexpression and apoptosis in C6 glioma cells

Calpain, a Ca2+-activated cysteine protease, has been implicated in apoptosis of immune cells. Since central nervous system (CNS) is abundant in calpain, the possible involvement of calpain in apoptosis of CNS cells needs to be investigated. We studied calpain expression in rat C6 glioma cells exposed to reactive hydroxyl radical (.OH) [formed via the Fenton reaction (Fe2++H2O2+H+-->Fe3++H2O+.OH)], interferon-gamma (IFN-gamma), and calcium ionophore (A23187). Cell death, cell cycle, calpain expression, and calpain activity were examined. Diverse stimuli induced apoptosis in C6 cells morphologically (chromatin condensation as detected by light microscopy) and biochemically [DNA fragmentation as detected by TdT-mediated dUTP Nick-End Labeling (TUNEL) assay]. Oxidative stress arrested a population of C6 cells at the G2/M phase of cell cycle. The levels of mRNA expression of six genes were analyzed by the reverse transcriptase-polymerase chain reaction (RT-PCR). Diverse stimuli did not alter beta-actin (internal control) expression, but increased calpain expression, and the upregulated bax (pro-apoptotic)/bcl-2 (anti-apoptotic) ratio. There was no significant increase in expression of calpastatin (endogenous calpain inhibitor). Western blot analysis showed an increase in calpain content and degradation of myelin-associated glycoprotein (MAG), a calpain substrate. Pretreatment of C6 cells with calpeptin (a cell-permeable calpain inhibitor) blocked calpain overexpression, MAG degradation, and DNA fragmentation. We conclude that calpain overexpression due to.OH stress, IFN-gamma stimulation, or Ca2+ influx is involved in C6 cell death, which is attenuated by a calpain-specific inhibitor.

Pathophysiological role of calpain in experimental demyelination

Calcium-activated neutral proteinase (calpain) has been extensively studied over the past three decades such that many enzymatic and structural properties of this enzyme are well understood. However, the pathophysiological roles of calpain remain poorly defined. In addition to recent studies delineating a role for calpain in various pathological conditions, this proteinase has been implicated in the degradation of myelin proteins in autoimmune demyelinating diseases such as multiple sclerosis and experimental allergic encephalomyelitis (EAE). In EAE, calpain translational expression is significantly increased in activated glial/inflammatory cells that participate in myelinolysis while calpain substrates (axonal and myelin proteins) are lost. Thus, since all major myelin proteins are calpain substrates, early studies suggest calpain may play an important role in demyelination of the central nervous system.

Calpain activity and translational expression increased in spinal cord injury

Calpain, a calcium-activated neutral proteinase, has been implicated in myelin and cytoskeletal protein degradation following spinal cord injury. In the present study, we examined the activity and transcriptional expression of calpain in spinal cord injury lesions via Western blotting analysis and RT-PCR, respectively. No increases in transcriptional expression of calpain or calpastatin, the endogenous inhibitor, were observed in the lesion at 1, 4, 24, and 72 h following injury. However, calpain activity (as measured by calpain-specific degradation of the endogenous substrate fodrin) was marginally increased at 4 h and significantly increased by 129.8% at 48 h compared to sham controls after injury. Calpain translational expression was localized in injured spinal cords using double immunofluorescent labeling which revealed increased calpain expression in astrocytes compared to sham controls. These results suggest that calpain produced by astrocytes located in or near spinal cord injury lesions may participate in myelin/axon degeneration following injury.

Putative role of calpain in the pathophysiology of experimental optic neuritis

Since myelin proteins are degraded in autoimmune demyelinating diseases such as optic neuritis, proteinases are believed to participate in myelinolysis. Calpain (calcium activated neutral proteinase) degrades myelin proteins at physiological pH and is found in glial and inflammatory cells involved in demyelination. To examine the putative role of calpain in myelinolysis, the activity and expression (translational and transcriptional) of this enzyme and endogenous inhibitor, calpastatin were examined in optic nerves of Lewis rats with experimental allergic encephalomyelitis (EAE), an animal model of optic neuritis. Calpain activity was examined via Western blotting by measuring the extent of myelin protein degradation and calpain-specific fodrin proteolysis in optic nerves from controls versus rats with experimental optic neuritis. RT-PCR studies demonstrated no significant change in millicalpain, microcalpain, or calpastatin expression at the mRNA level in optic nerves from animals with experimental optic neuritis compared to controls. However, myelin associated glycoprotein (MAG) levels were decreased by 25.5% while calpain translational expression and calpain-autolyzed fodrin levels were increased by 72.1% and 462.8% respectively, in experimental optic neuritis compared to controls. Translational expression of calpastatin isoforms (80, 68 and 55 KD) was not significantly different in rats with experimental optic neuritis compared to controls. Thus, increased activity and translational expression of calpain in experimental optic neuritis suggests this proteinase may participate in the degradation of myelin and cytoskeletal proteins in demyelinating diseases such as optic neuritis.

Weak binding and removal of extrinsic proteinase activities of myelin membranes

The concurrent release of myelin basic protein (MBP) and extrinsic proteinases from isolated myelin membranes by aqueous solvents of high ionic strength is considered circumstantial evidence of a presumptive mutual interaction in situ. The joint release of proteins and proteinases from myelin membranes of bovine brain, depending on the ionic strength of aqueous solvents, was therefore examined; 25 mM Tris buffer released an average 1.4% of total myelin protein. It was attributable to about 25 different electrophoretic bands, but no apparent MBP. However, the extract potently mediated the limited proteolysis of added MBP at pH 4.0, 5.6, and 9.0. Because of the pH and the effects of specific inhibitors, proteolysis appears to be owing to activities of cathepsin B and D, and an alkaline metalloproteinase. The subsequent extraction of myelin membranes with buffered 300 mM NaCl released an additional 20% of total myelin protein, mainly MBP. The extracts, unlike those of untreated myelin membranes, no longer cleaved MBP at pH 5.6 and 9.0, and did so only slightly at pH 4.0. The results indicate that the bulk of soluble myelin-associated proteinases is much less tightly bound than MBP. The weak binding of the former and the prevalence of lysosomal cathepsin B- and D-like activities suggest that during their isolation, myelin membranes may adsorb soluble cellular proteins of tissue homogenates. At any rate the washing of myelin membranes with dilute buffer was found to largely remove soluble proteinase activities that are otherwise associated with salt-soluble MBP of myelin.

Upregulation of calpain activity and expression in experimental allergic encephalomyelitis: a putative role for calpain in demyelination

The degradation of myelin proteins has been implicated in destabilization of the myelin sheath in autoimmune demyelinating diseases such as multiple sclerosis (MS). In order to investigate the role of calcium-activated neutral proteinase (calpain), which degrades myelin proteins, the activity and expression (translational and transcriptional) of this enzyme were examined in spinal cords of Lewis rats with experimental allergic encephalomyelitis (EAE), an animal model of MS. In addition to calpain, the translational expression of calpastatin (endogenous inhibitor of calpain) and extent of neurofilament (NFP) and myelin protein degradation were evaluated via Western blotting in controls and rats with EAE. The transcriptional expression of millicalpain, microcalpain, and calpastatin as examined by RT-PCR was not significantly increased in EAE. However, calpain translational expression was increased by 206. 5% while the levels of 68 kDa NFP and myelin-associated glycoprotein were decreased by 42.9 and 39.7%, respectively, in animals with EAE compared to controls. Calpastatin isoforms (180, 110, 80, and 68 kDa) were significantly increased in EAE as well. The findings of increased activity and translational expression of calpain in EAE suggest a major role for this enzyme in myelinolysis associated with autoimmune demyelinating diseases.

Increased calpain expression in activated glial and inflammatory cells in experimental allergic encephalomyelitis

In demyelinating diseases such as multiple sclerosis (MS), myelin membrane structure is destabilized as myelin proteins are lost. Calcium-activated neutral proteinase (calpain) is believed to participate in myelin protein degradation because known calpain substrates [myelin basic protein (MBP); myelin-associated glycoprotein] are degraded in this disease. In exploring the role of calpain in demyelinating diseases, we examined calpain expression in Lewis rats with acute experimental allergic encephalomyelitis (EAE), an animal model for MS. Using double-immunofluorescence labeling to identify cells expressing calpain, we labeled rat spinal cord sections for calpain with a polyclonal millicalpain antibody and with mAbs for glial (GFAP, OX42, GalC) and inflammatory (CD2, ED2, interferon gamma) cell-specific markers. Calpain expression was increased in activated microglia (OX42) and infiltrating macrophages (ED2) compared with controls. Oligodendrocytes (galactocerebroside) and astrocytes (GFAP) had constitutive calpain expression in normal spinal cords whereas reactive astrocytes in spinal cords from animals with EAE exhibited markedly increased calpain levels compared with astrocytes in adjuvant controls. Oligodendrocytes in spinal cords from rats with EAE expressed increased calpain levels in some areas, but overall the increases in calpain expression were small. Most T cells in grade 4 EAE expressed low levels of calpain, but interferon gamma-positive cells demonstrated markedly increased calpain expression. These findings suggest that increased levels of calpain in activated glial and inflammatory cells in EAE may contribute to myelin destruction in demyelinating diseases such as MS.

Dual response of calpain to rat brain postdecapitative ischemia

Calpains, Ca(2+)-dependent neutral proteinases (microM and mM Ca(2+)-sensitive), and their endogenous inhibitor calpastatin were examined in rat brain. Specific activity of m-calpain exceeded almost 10 times that of mu-calpain, and the both isoforms of calpain together with calpastatin were mainly located in the soluble fraction of homogenate. Acute postdecapitative ischemia of 15 min duration resulted in a gradual, time-dependent decrease of total mu-calpain activity (to 60% of control values) and in the moderate elevation of calpastatin activity (by 28%). The decrease of total mu-calpain activity coincided with its remarkable increase (above 300% of control values) in particulate fraction. In the case of m-calpain, the only observed effect of ischemia was its redistribution and, as a consequence, the elevation of activity in particulate fraction. The accumulation of breakdown products, resulting from calpain-catalyzed proteolysis of fodrin (as revealed by Western blotting) indicated activation of calpain under ischemia. The findings suggest that this rapid activation involves partial enzyme translocation toward membranes, and is followed (at least in acute phase) by mu-calpain downregulation and increased calpastatin activity.

Increased calpain expression in experimental demyelinating optic neuritis: an immunocytochemical study

Since calcium activated neutral proteinase (calpain) is present in the central nervous system (CNS) and degrades myelin proteins, this endopeptidase has been suggested to play a role in myelin destruction in demyelinating diseases such as multiple sclerosis (MS). In the present study, calpain immunocytochemical expression was examined in Lewis rats with acute experimental allergic encephalomyelitis (EAE), an animal model for MS and optic neuritis. To identify cells expressing calpain, we labeled rat optic nerve sections for calpain with a polyclonal myelin calpain antibody and with monoclonal antibodies for glial (GFAP, OX42) and inflammatory (CD2, ED2, ED1, IFN-gamma) cell-specific markers. The results showed increased calpain expression in microglia (OX42) and infiltrating macrophages (ED1,2) in EAE compared to normal controls. Astrocytes constitutively expressed calpain in controls and acute EAE. Reactive astrocytes in EAE located in or near inflammatory foci, exhibited markedly increased calpain expression. Most T cells in acute EAE showed low level calpain expression while activated IFN-gamma-producing lymphocytes in inflammatory foci exhibited elevated levels of calpain expression. Thus, our results demonstrate increased calpain expression (at transcriptional and/or translational levels) in a rat model of optic neuritis. A role for calpain in myelin destruction during optic neuritis may be relevant to the pathogenesis of this disorder.

Calcium-mediated neurofilament protein degradation in rat optic nerve in vitro: activity and autolysis of calpain proenzyme

In this study, we examined calcium-mediated degradation of a neurofilament protein (NFP), and autolytic activation of calpain in Lewis rat optic nerve in vitro. After incubation with calcium, homogenized optic nerve samples were analysed by SDS-PAGE in association with ECL immunoblot techniques. 68 kD NFP, calpain, and calpastatin antibodies were used for identification of the respective proteins. The extent of calcium-mediated 68 kD NFP degradation compared to EGTA controls, served to quantify calpain activity, while the extent of calpain autolysis measured the activation of the enzyme. A progressive loss of 68 kD NFP was observed at 15 min (42.1%), 1 hr (52.7%) and 6 hr (73.4%) incubation periods compared to EGTA controls. The immunoreactive calpain bands showed progressive autolysis after 15 min (26.6%), 1 hr (31.4%) and 6 hr (43.4%) incubations. We also found degradation of low molecular weight isoforms of calpastatin (43 kD and 27 kD) in the presence of calcium compared to controls. These results indicate that calpain is present in optic nerve in its inactive form but when calcium is added, it undergoes autolysis and becomes active. Thus, active calpain is capable of degrading endogenous substrates (e.g. cytoskeletal and myelin proteins) and may promote the degeneration of optic nerve in optic neuritis.

Regulation of brain m calpain Ca2+ sensitivity by mixtures of membrane lipids: activation at intracellular Ca2+ level

Combinations of certain phospholipids and gangliosides increase the specific activity of m calpain and can activate m calpain at 1 to 10 microM Ca2+ concentration. However, this level of calcium is still greater than the normal intracellular calcium level. We have used combinations of lipids to demonstrate the m calpain activity at the physiological Ca2+ level. GD1a (100 microM) and cerebroside (Cerb; 750 microM; 1:7.5) mixture was the most effective. At 0.5 microM to 1.0 microM Ca2+ concentrations, 15-20% of the maximal activity was detected for the purified myelin and cytosolic m calpains. Other combinations were GD1a (100 microM), GM1 (100 microM), Cerb (750 microM), sulfatide (Sulf; 750 microM), and phosphatidylinositol (PI; 300 microM) at a ratio of 1:1: 7.5:7.5:3, respectively. These lipid mixtures stimulated calpain activity at three- to tenfold less calcium concentration than control. The other mixtures, including GD1a:Sulf (1:9) > GD1a:PI (1:4) > PI:Sulf (1:5) > Cerb:Sulf (1:5) and PI:Cerb (1:2.5), also stimulated calpain activity at 1.0 microM Ca2+ concentration. Triton X-100, oxidized glutathione (GSSG), and calpain activator did not affect the Ca2+ requirement. Liposomes containing GD1a, Cerb, and m calpain also showed recognizable calpain activity at a significantly reduced Ca2+ concentration (0.4 microM), confirming the glycolipid-mediated enzyme modulation. These studies indicate that specific lipid mixtures can stimulate m calpain activity at an intracellular level of Ca2+.

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.

The localization of mcalpain in myelin: immunocytochemical evidence in different areas of rat brain and nerves

A major part of brain mcalpain activity has been found associated with myelin, but its presence in the myelin sheath has not been clearly demonstrated by microscopic (morphological) means. Using myelin mcalpain antisera the localization of mcalpain has been investigated in tissue of rat CNS and PNS by immunohistochemical methods. These experiments also have been carried out by double labeling studies using antibodies to myelin basic protein (MBP) and neurofilament protein (NFP). Our results indicate calpain/MBP immunoreactivity in the myelin sheath surrounding the axon while NFP antibody stained inside the axon in spinal cord; pons, cerebellum, trigeminal nerve, and sciatic nerve. Patches of light immunoreactivity of calpain were also seen in the axonal cytoplasm. The calpain immunostaining of myelin was similar to that of MBP staining indicating the presence of calpain in myelin. This finding supports the view that calpain is a constituent of myelin, may be involved in the normal turnover of myelin proteins. In pathological situations such as in demyelinating and other brain degenerative diseases, myelin may be autodigestive.

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.

Upregulation of calpain activity in neonatal rat brain after hypoxic-ischemia

Neonatal rats were subjected to transient cerebral hypoxic-ischemia (unilateral occlusion of the common carotid artery plus 7.7% O2 for 2 h) and allowed to recover for 0 min, 30 min or 20 h. The calpain and calpastatin activities were assayed in subcellular fractions of the ipsilateral, hypoxic-ischemic and the contralateral, hypoxic hemisphere. An upregulation of calpain activity occurred in the hypoxic hemisphere, both in the major, cytosolic fraction and in the hypotonic, membrane associated fraction (110% and 133% of controls, respectively). The hypoxic-ischemic hemisphere displayed a decrease in calpain activity in the cytosolic fraction but an increase in the hypotonic fraction (90% and 111% of controls, respectively). The changes in calpastatin activity were less pronounced. This indicates that an upregulation of calpain activity occurs in parallel with development of hypoxic-ischemic damage. However, this upregulation is not necessarily coupled to development of injury as lesions are not seen in the hypoxic hemisphere.

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.

Effects of detergents on Ca(2+)-activated neural proteinase activity (calpain) in neural and non-neural tissue: a comparative study

Calcium activated neutral proteinase (mcalpain) activity was determined in brain and other tissue of rat. More than 60% of the brain mcalpain activity was present in the particulate fraction while only 30% was in cytosol. In contrast, particulate fractions of liver, kidney, muscle, and heart contained about 8-12% of tissue mcalpain activity while 88% was present in cytosol. Removal of the endogenous inhibitor calpastatin increased the tissue mcalpain activity severalfold. Triton X-100 and deoxycholate (DOC) stimulated the neural calpain activity by ten-fold while activity in non-neural tissue was unaffected. Incubation with other detergents, e.g. Triton N-57 and thioglucopyranoside, stimulated brain calpain activity five-fold while Brij-35 did not have any effect. Sodiumdodecylsulphate (SDS), on the other hand, inhibited the enzyme activity. Brain contained the lowest calpain activity compared to non-neural tissue. The calpain activity in muscle, kidney and heart was three-fold greater than liver. Immunoblot identification of the enzyme revealed that calpain was predominantly in the particulate fraction and less in cytosol of brain while it was present mainly in cytosol and less in the pellet fractions of non-neural tissue.

Calcium-activated neutral protease (CANP) in normal and dysmyelinating mutant paralytic tremor rabbit myelin

Calcium-activated neutral protease (CANP) in normal and dysmyelinating mutant, paralytic tremor (PT) rabbit myelin and premyelin fractions was studied using immature (4-5 wk) or adult animals. The enzyme was estimated by determination of its catalytic activity as well as by using immunoblot analysis after SDS-PAGE separation. The presence of two forms of CANP--one activated by calcium in the micromolar concentration (mu CANP) range and the other exhibiting low calcium sensitivity in the millimolar concentration range (m-CANP)--was found in the myelin and premyelin fractions. The developmental pattern of the enzyme activity was different for each of these two enzyme isoforms depending on the fraction studied. The higher activity on CANP (both isoforms) found in PT myelin and premyelin could be related to delayed myelination and/or to the higher turnover rate of already formed myelin. These results suggest complex and specific roles for these isoenzymes during myelin formation as is discussed further in this article. Our results confirm the extensive degradation of myelin basic protein (MBP), proteolipid protein (PLP), and, to a lesser extent, the other myelin proteins by endo- and exogenous CANP. This degradation process was significantly elevated in PT rabbit myelin. Moreover as was shown by two-dimensional gel electrophoresis, calcium-controlled proteolysis in nonmutant rabbits affected the net-charge of MBP in a manner similar to that reported for PT myelin, suggesting the possible involvement of CANP in the generation of charge isomers of MBP.

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.

Calcium-activated neutral proteinase (calpain) activity in C6 cell line: compartmentation of mu and m calpain

Calcium-activated neutral proteinase (calpain) activity was determined, including in cytosol and membrane fractions, in rat glioma C6 cell line. The mu and m forms of calpain were separated by DEAE and phenylsepharose column chromatography and with removal of the endogenous inhibitor calpastatin. C6 cells contained more mcalpain than the mu isoform. More than 70% of mcalpain activity was membrane-associated and 20% was cytosolic. Isolated plasma membrane also contained 69% of the mcalpain activity. In contrast, approximately 80% of mucalpain activity was cytosolic and 16% was membranous. Half-maximal activity for mu and mcalpain was obtained at 1 microM and 0.2 mM CaCl2, respectively. Trypsin dissociation of cells reduced activity. Triton X-100 stimulated mcalpain activity of the whole homogenate and the membrane pellet but not of the cytosol. Activity of the myelin marker enzyme adenosine 2'3'-cyclic nucleotide 3'-phosphohydrolase (CNPase), was also found in C6 cells. The identification of calpain and CNPase in C6 cells is in keeping with an interpretation that C6 differentiation resembles, at least in part, that of the myelin-forming oligodendroglial cells.

Immunoassay and activity of calcium-activated neutral proteinase (mCANP): distribution in soluble and membrane-associated fractions in human and mouse brain

The millimolar form of calcium-activated neutral proteinase (mCANP) is generally regarded as a cytosolic enzyme in nonneuronal systems, although its subcellular localization in brain is less well established. To resolve conflicting reports on the localization of mCANP based on activity measurements, we developed an immunoassay for CANP and compared the content and activity of the molecule in soluble and membrane fractions of mouse and human brain. Western blot immunoassays, using two different antibodies specific for mCANP, demonstrated that mCANP content is 4.5 ng/g in human or mouse brain, about 0.0005% of the total protein. More than 95% of the total immunoreactive mCANP remained in the soluble fraction after 15,000 g centrifugation of the whole homogenate. mCANP activity was determined with [14C]azocasein as substrate after removing endogenous CANP inhibitor(s) by ion-exchange chromatography on DEAE-cellulose. Caseinolytic activity was detected only in fractions derived from the supernatant extract. The distribution of mCANP content and enzyme activity were unchanged when tissues were extracted with different concentrations of Triton X-100. These findings establish the usefulness and validity of the CANP immunoassay and demonstrate that mCANP in mouse and human brain is localized predominantly within the cytosol.

Calcium-activated neutral proteinase (CANP; calpain) activity in Schwann cells: immunofluorescence localization and compartmentation of mu- and mCANP

Calcium-activated neutral proteinase (CANP) activity was determined in cytosolic and membranous subcellular fractions of transformed Schwann cells (tSc). The muM and mM Ca(2+)-sensitive (mu- and mCANP) forms of CANP were separated by DEAE and phenyl Sepharose column chromatography, the latter step enabling removal of the endogenous inhibitor calpastatin. The tSc contained more muCANP than the mM isoform. More than 75% of mCANP activity was membrane-associated and 20% was cytosolic. In contrast, approximately 80% of muCANP was cytosolic and 15% was membranous. Triton X-100 stimulated activity of the whole homogenate and of the membrane pellet but did not stimulate CANP activity in the cytosolic fraction. Immunohistochemical distribution of mM enzyme was studied in both fixed and permeabilized tSc with cytosolic (anti-cyt-mCANP) and myelin (anti-my-mCANP) antibodies. Live cells (non-permeabilized) stained with anti-my-mCANP had a single filamentous ring circumscribing individual cells. Permeabilized cells treated with anti-my-mCANP had immunoreactive deposits throughout the intracellular space but sparing the perinuclear region. No immunohistochemical staining was detected when live cells were exposed to anti-cyt-mCANP whereas permeabilized cells had extensive intracellular staining with the most intense immunoreactivity in the perinuclear region. Our results indicate that both forms of CANP are present in tSc and that the activity of most of the muCANP is cytosolic while mCANP is particulate.

Changes in brain calpain activity as a result of in vitro ischemia and pH alterations

Calpains and calpastatin in the brain of the rabbit were examined in experimental situations that could mimic some features of brain ischemia. Incubations of bisected brains in saline at 39 degrees C for 0.5, 1, or 1.5 h resulted in a decreased calpain I activity in the cytosol and in an increased hydrophobicity of cytosolic calpain II activity. Incubation of brain homogenates at different pH levels demonstrated an almost-complete transfer of calpains from the cytoplasmic compartment to the membranes when pH was lowered from 6 to 5. At pH values lower than 5, the total calpain activity (soluble plus membrane-bound) markedly decreased. No significant changes of calpastatin activity or its subcellular distribution was found following incubation of the homogenates at different pH levels.

Ganglioside-modulated proteolysis by Ca2(+)-activated neutral proteinase (CANP): a role of glycoconjugates in CANP regulation

We examined ganglioside modulation of the activity of the millimolar Ca2(+)-sensitive form (mCANP) of calcium-activated neutral proteinase (CANP), which is enriched in myelin, from brain. GM1, GD1a, GT1a, GM2, and GM4 produced a concentration-dependent increase of mCANP activity. GD1a stimulated the greatest increase of enzyme activity (107%), followed by GT1a, whereas GD1b was inhibitory (56%). GM1, GM2, and GM4 stimulated but less so than GD1a and GT1a. Free N-acetylneuraminic acid, asialo-GM1, GM3, and a ganglioside mixture containing GM1, GD3, GD1a, and GD1b had no effect. The ganglioside-mediated modulation was not affected by trifluoperazine and chlorpromazine (phospholipid-binding antagonists). The mCANP Ca2+ requirement was significantly reduced in the presence of stimulatory gangliosides, and this increased sensitivity varied (10-50-fold) with ganglioside structure. Gangliosides may interact with membrane mCANP and modulate its proteolytic action.

Regulation of the calcium-activated neutral proteinase (CANP) of bovine brain by myelin lipids

Since calcium-activated neutral proteinase (CANP; calpain) activation occurs at the plasmalemma and the enzyme is found in myelin, we examined myelin lipid activation of brain CANP. Purified lipids were dried, sonicated and incubated with purified myelin CANP. The CANP was assayed using [14C]azocasein as substrate and the Ca2+ concentration ranged from 2 microM for muCANP to 5 mM for mCANP. Phosphatidylinositol (PI), phosphatidylserine (PS) and dioleoylglycerol stimulated the mCANP activity by 193, 89 and 78%, respectively. PI stimulated both m- and muCANP in a concentration-dependent manner, while phosphatidylcholine was least effective. Cerebroside and sulfatide at higher concentrations (750 microM) were stimulatory. The phospholipid (PL)-mediated activation was inhibited by the PL-binding drug trifluoperazine. PI reduced the Ca2+ requirement for CANPs significantly (20-fold). These results suggest that acidic lipids and particularly acidic phospholipids activate membrane CANP.

Purification of an endogenous 68 kD inhibitor of calcium-activated neutral proteinase (CANP) from bovine brain: immunoblot identification and characterization

A calcium-activated neutral proteinase (CANP)-specific endogenous inhibitor (calpastatin) was purified from bovine brain by successive column chromatography. The purified inhibitor exhibited a major band on sodium dodecylsulfate polyacrylamide gel electrophoresis with an approximate molecular weight of 68 kD. The polyclonal antisera raised to the inhibitor strongly reacted with the 68 kD protein band. Two lightly stained bands approximately 55-68 kD and 120-130 kD were also recognized by the inhibitor antiserum. The inhibitor specifically inhibited CANP activity and the half-maximal inhibition was found with 75 ng of calpastatin per 1 micrograms of CANP in a final volume of 125 microliters. Cathepsin B and papain were not inhibited by the inhibitor, while trypsin and chymotrypsin were inhibited to some extent. The inhibitor formed a complex with CANP and the inactive complex was dissociated into active fractions of enzyme and calpastatin in the presence of EGTA.

Developmental changes of calpain and calpastatin in rabbit brain

A major part of the Ca-activated proteolytic activity in the soluble fraction from rabbit brain could be due to the activity of the neutral thiol-proteases calpain I and II. The activity of calpains exceeded that of the endogenous inhibitor, calpastatin, at all developmental stages studied. The level of calpains increased rapidly from the prenatal stage to reach a peak 10-20 days postnatally. From this period the level of calpains decreased slowly to reach the adult levels. The level of calpastatin increased steadily from the prenatal stage to old age.