Pathophysiological role of calpain in experimental demyelination

Functions and distribution of calpain-calpastatin system components in brain during mammal ontogeny

Calpain and calpastatin are the key components of the calcium-dependent proteolytic system. Calpains are regulatory, calcium-dependent, cytoplasmic proteinases, and calpastatin is the endogenous inhibitor of calpains. Due to the correlation between changes in the activity of the calpain-calpastatin system in the brain and central nervous system (CNS) pathology states, this proteolytic system is a prime focus of research on CNS pathological processes, generally characterized by calpain activity upregulation. The present review aims to generalize existing data on cerebral calpain distribution and function through mammalian ontogenesis. Special attention is given to the most recent studies on the topic as more information on calpain-calpastatin system involvement in normal CNS development and functioning has become available. We also discuss data on calpain and calpastatin activity and production in different brain regions during ontogenesis as comparative analysis of these results in association with ontogeny processes can reveal brain regions and developmental stages with pronounced function of the calpain system.

Calpain in the cleavage of alpha-synuclein and the pathogenesis of Parkinson's disease

Parkinson's disease (PD) devastates 6.3 million people, ranking it as one of the most prevalent neurodegenerative motor disorders worldwide. PD patients may manifest symptoms of postural instability, bradykinesia, and resting tremors as a result of increasing α-synuclein aggregation and neuron death with disease progression. Therapy options are limited, and those available to patients may worsen their condition. Thus, investigations to understand disease progression may help develop therapeutic strategies for improvement of quality of life for patients suffering from PD. This review provides an overview of α-synuclein, a presynaptic neuronal protein whose function in the healthy brain and PD pathology remains a mystery. This review also focuses on calcium-induced activation of calpain, a neutral protease, and the subsequent cascade of cellular processing of α-synuclein and emerging defense responses observed in experimental models of PD: microglial activation, dysregulation of T cells, and inflammatory responses in the brain. In addition, this review discusses the events of cross presentation of synuclein peptides by professional antigen presenting cells and microglia, induction of inflammatory responses in the periphery and brain, and emerging calpain-targeted therapeutic strategies to attenuate neuronal death in PD.

Distinct Cytokine and Chemokine Expression in Plasma and Calpeptin-Treated PBMCs of a Relapsing-Remitting Multiple Sclerosis Patient: A Case Report

The cytokine/chemokine expression signature of a 60-year-old African American male with relapsing-remitting multiple sclerosis (RRMS) was analyzed using patient blood samples obtained from two separate visits to the clinic. Thirty-six different cytokines, chemokines, and growth factors were detected in the plasma of the RRMS patient using a multiplexed bead-based immunoassay. Results indicated that at least ten of these factors with a concentration of > 100 pg/mL are identified as pro-inflammatory. Calpain inhibition led to an anti-inflammatory effect, as indicated by a decrease in expression of pro-inflammatory cytokines/chemokines such as GM-CSF, IFNγ, and IL-17A, and a relative increase in two of the anti-inflammatory cytokines (IL-13 and IL-4) in the peripheral blood mononuclear cells activated with anti-CD3/CD28. Overall, these results suggest that the unique cytokine/chemokine pattern observed in the plasma of the RRMS patient can be used as a prognostic marker and calpain inhibition may be used as a novel therapeutic strategy for treating excessive inflammatory response specific to RRMS patients.

Formation and disruption of functional domains in myelinated CNS axons

Communication in the central nervous system (CNS) occurs through initiation and propagation of action potentials at excitable domains along axons. Action potentials generated at the axon initial segment (AIS) are regenerated at nodes of Ranvier through the process of saltatory conduction. Proper formation and maintenance of the molecular structure at the AIS and nodes are required for sustaining conduction fidelity. In myelinated CNS axons, paranodal junctions between the axolemma and myelinating oligodendrocytes delineate nodes of Ranvier and regulate the distribution and localization of specialized functional elements, such as voltage-gated sodium channels and mitochondria. Disruption of excitable domains and altered distribution of functional elements in CNS axons is associated with demyelinating diseases such as multiple sclerosis, and is likely a mechanism common to other neurological disorders. This review will provide a brief overview of the molecular structure of the AIS and nodes of Ranvier, as well as the distribution of mitochondria in myelinated axons. In addition, this review highlights important structural and functional changes within myelinated CNS axons that are associated with neurological dysfunction.

Acrolein detection: potential theranostic utility in multiple sclerosis and spinal cord injury

Oxidative stress has been implicated as a major pathological process underlying CNS disease and trauma. More specifically, acrolein, an unsaturated aldehyde, produced by way of lipid peroxidation, has been shown to play a crucial role in initiating and perpetuating detrimental effects associated with multiple sclerosis and spinal cord injury. In light of these findings, quantification of acrolein levels both systemically and locally could allow for the use of acrolein as a biomarker to aid in diagnosis and guide treatment regimens. The three main approaches currently available are acrolein derivatization followed by LC/GC-MS, application of an acrolein antibody and subsequent immunoblotting, and the 3-hydroxypropylmercapturic acid-based method. Of these three strategies, the 3-hydroxypropylmercapturic acid-based method is the least invasive allowing for rapid translation of acrolein detection into a clinical setting.

Effects of a novel orally administered calpain inhibitor SNJ-1945 on immunomodulation and neurodegeneration in a murine model of multiple sclerosis

Multiple sclerosis (MS) pathology is marked by the massive infiltration of myelin-specific T cells into the CNS. Hallmarks of T helper (Th) cells during active disease are pro-inflammatory Th1/Th17 cells that predominate over immunoregulatory Th2/Treg cells. Neurodegeneration, a major factor in progressive MS, is often overlooked when considering drug prescription. Here, we show that oral dosing with SNJ-1945, a novel water-soluble calpain inhibitor, reduces experimental autoimmune encephalomyelitis clinical scores in vivo and has a two pronged effect via anti-inflammation and protection against neurodegeneration. We also show that SNJ-1945 treatment down-regulates Th1/Th17 inflammatory responses, and promotes regulatory T cells (Tregs) and myeloid-derived suppressor cells in vivo, which are known to have the capacity to suppress helper as well as cytotoxic T cell functions. Through analysis of spinal cord samples, we show a reduction in calpain expression, decreased infiltration of inflammatory cells, and signs of inhibition of neurodegeneration. We also show a marked reduction in neuronal cell death in spinal cord (SC) sections. These results suggest that calpain inhibition attenuates experimental autoimmune encephalomyelitis pathology by reducing both inflammation and neurodegeneration, and could be used in clinical settings to augment the efficacy of standard immunomodulatory agents used to treat MS. Multiple sclerosis (MS) pathology is marked by inflammation and infiltration of myelin-specific T cells into the central nervous system. Inflammation leads to neurodegeneration in progressive MS which also leads to epitope spreading, feedback looping to more inflammation. Calpain can play a role in both arms of the disease. Here, oral dosing with SNJ-1945, a novel water-soluble calpain inhibitor, reduces experimental autoimmune encephalomyelitis clinical scores in vivo and has a two-pronged effect via anti-inflammation and protection against neurodegeneration.

Myelin recovery in multiple sclerosis: the challenge of remyelination

Multiple sclerosis (MS) is the most common demyelinating and an autoimmune disease of the central nervous system characterized by immune-mediated myelin and axonal damage, and chronic axonal loss attributable to the absence of myelin sheaths. T cell subsets (Th1, Th2, Th17, CD8⁺, NKT, CD4⁺CD25⁺ T regulatory cells) and B cells are involved in this disorder, thus new MS therapies seek damage prevention by resetting multiple components of the immune system. The currently approved therapies are immunoregulatory and reduce the number and rate of lesion formation but are only partially effective. This review summarizes current understanding of the processes at issue: myelination, demyelination and remyelination—with emphasis upon myelin composition/architecture and oligodendrocyte maturation and differentiation. The translational options target oligodendrocyte protection and myelin repair in animal models and assess their relevance in human. Remyelination may be enhanced by signals that promote myelin formation and repair. The crucial question of why remyelination fails is approached is several ways by examining the role in remyelination of available MS medications and avenues being actively pursued to promote remyelination including: (i) cytokine-based immune-intervention (targeting calpain inhibition), (ii) antigen-based immunomodulation (targeting glycolipid-reactive iNKT cells and sphingoid mediated inflammation) and (iii) recombinant monoclonal antibodies-induced remyelination.

Inhibition of myelin-cleaving poteolytic activities by interferon-beta in rat astrocyte cultures. Comparative analysis between gelatinases and calpain-II

Background

Proteolytic enzymes have been implicated in the pathogenesis of Multiple Sclerosis (MS) for both their ability to degrade myelin proteins and for their presence in MS plaques.In this study we investigated whether interferon-beta (IFN-β) could differently modulate the activity and the expression of proteolytic activities against myelin basic protein (MBP) present in lipopolysaccharide (LPS)-activated astrocytes.

Methodology/Principal Findings

Rat astrocyte cultures were activated with LPS and simultaneously treated with different doses of IFN-β. To assess the presence of MBP-cleaving proteolytic activity, culture supernatants and cellular extracts collected from astrocytes were incubated with exogenous MBP. A MBP-degrading activity was found in both lysates and supernatants from LPS-activated astrocytes and was dose-dependently inhibited by IFN-β. The use of protease inhibitors as well as the zymographic analysis indicated the presence of calpain II (CANP-2) in cell lysates and gelatinases A (MMP-2) and B (MMP-9) in cell supernatants. RT-PCR revealed that the expression of CANP-2 as well as of MMP-2 and MMP-9 was increased in LPS-activated astrocytes and was dose-dependently inhibited by IFN-β treatment. The expression of calpastatin, the natural inhibitor of CANPs, was not affected by IFN-β treatment. By contrast, decreased expression of TIMP-1 and TIMP-2, the natural inhibitors of MMP-9 and MMP-2, respectively, was observed in IFN-β-treated astrocytes compared to LPS-treated cells. The ratio enzyme/inhibitor indicated that the effect of IFN-β treatment is more relevant to CANP-2 than on MMPs.

Conclusions/ Significance

These results suggest that the neuroinflammatory damage during MS involves altered balance between multiple proteases and their inhibitors and indicate that IFN-β is effective in regulating different enzymatic systems involved in MS pathogenesis.

Immunoenrichment microwave and magnetic proteomics for quantifying CD47 in the experimental autoimmune encephalomyelitis model of multiple sclerosis

We hypothesized that quantitative MS/MS-based proteomics at multiple time points, incorporating immunoenrichment prior to rapid microwave and magnetic (IM(2) ) sample preparation, might enable correlation of the relative expression of CD47 and other low abundance proteins to disease progression in the experimental autoimmune encephalomyelitis (EAE) animal model of multiple sclerosis. To test our hypothesis, anti-CD47 antibodies were used to enrich for low abundance CD47 prior to microwave and magnetic proteomics in EAE. Decoding protein expression at each time point, with CD47-immunoenriched samples and targeted proteomic analysis, enabled peptides from the low abundance proteins to be precisely quantified throughout disease progression, including: CD47: 86-99, corresponding to the "marker of self" overexpressed by myelin that prevents phagocytosis, or "cellular devouring," by microglia and macrophages; myelin basic protein: 223-228, corresponding to myelin basic protein; and migration inhibitory factor: 79-87, corresponding to a proinflammatory cytokine that inhibits macrophage migration. While validation in a larger cohort is underway, we conclude that IM(2) proteomics is a rapid method to precisely quantify peptides from CD47 and other low abundance proteins throughout disease progression in EAE. This is likely due to improvements in selectivity and sensitivity, necessary to partially overcome masking of low abundance proteins by high abundance proteins and improve dynamic range.

Calpain inhibition attenuated morphological and molecular changes in skeletal muscle of experimental allergic encephalomyelitis rats

Muscle weakness and atrophy are important manifestations of multiple sclerosis (MS). To investigate the pathophysiological mechanisms of skeletal muscle change in MS, we induced experimental autoimmune encephalomyelitis (EAE) in Lewis male rats and examined morphological and molecular changes in skeletal muscle. We also treated EAE rats with calpepetin, a calpain inhibitor, to examine its beneficial effects on skeletal muscle damage. Morphological changes in muscle tissue of EAE rats included smaller and irregularly shaped muscle fibers and fibrosis. Western blot analysis demonstrated increased calpain:calpastatin ratio, inflammation-related transcription factors (nuclear factor-κB:inhibitor of κB α ratio), and proinflammatory enzymes (cyclooxygenase-2). TUNEL-positive myonuclei in skeletal muscle cells of EAE rats indicated cell death. In addition, markers of apoptotic cell death (Bax:Bcl-2 ratio and caspase-12 protein levels) were elevated. Expression of muscle-specific ubiquitin ligases (muscle atrophy F-box and muscle ring finger protein 1), was upregulated in muscle tissue of EAE-vehicle animals. Both prophylactic and therapeutic treatment with calpeptin partially attenuated muscle changes noted in EAE animals. These results indicate that morphological and molecular changes including apoptotic cell death and protein breakdown develop in skeletal muscle of EAE animals and that these changes can be reversed by calpain inhibition.

Anti-acrolein treatment improves behavioral outcome and alleviates myelin damage in experimental autoimmune encephalomyelitis mouse

Oxidative stress is considered a major contributor in the pathology of multiple sclerosis (MS). Acrolein, a highly reactive aldehyde byproduct of lipid peroxidation, is thought to perpetuate oxidative stress. In this study, we aimed to determine the role of acrolein in an animal model of MS, experimental autoimmune encephalomyelitis (EAE) mice. We have demonstrated a significant elevation of acrolein protein adduct levels in EAE mouse spinal cord. Hydralazine, a known acrolein scavenger, significantly improved behavioral outcomes and lessened myelin damage in spinal cord. We postulate that acrolein is an important pathological factor and likely a novel therapeutic target in MS.

Regulation of Th1/Th17 cytokines and IDO gene expression by inhibition of calpain in PBMCs from MS patients

Multiple sclerosis (MS) pathology is marked by the massive infiltration of myelin-specific T cells into the central nervous system (CNS). During active disease, pro-inflammatory Th1/Th17 cells predominate over immunoregulatory Th2/Treg cells. Here, we show that calpain inhibition downregulates Th1/Th17 inflammatory cytokines and mRNA in MS patient peripheral blood mononuclear cells (PBMCs) activated with anti-CD3/28 or MBP. Interestingly, calpain inhibition elevated IDO gene expression in MS PBMCs, which was markedly decreased in calpain expressing cells. Functional assay showed that incubation of MS patient PBMCs with calpain inhibitor or recombinant IDO attenuates T cell proliferation. These results suggest that calpain inhibition may attenuate MS pathology and augment the efficacy of standard immunomodulatory agents used to treat this disease.

Calpeptin attenuated inflammation, cell death, and axonal damage in animal model of multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is an animal model for studying multiple sclerosis (MS). Calpain has been implicated in many inflammatory and neurodegenerative events that lead to disability in EAE and MS. Thus, treating EAE animals with calpain inhibitors may block these events and ameliorate disability. To test this hypothesis, acute EAE Lewis rats were treated dose dependently with the calpain inhibitor calpeptin (50-250 microg/kg). Calpain activity, gliosis, loss of myelin, and axonal damage were attenuated by calpeptin therapy, leading to improved clinical scores. Neuronal and oligodendrocyte death were also decreased, with down-regulation of proapoptotic proteins, suggesting that decreases in cell death were due to decreases in the expression or activity of proapoptotic proteins. These results indicate that calpain inhibition may offer a novel therapeutic avenue for treating EAE and MS.

Calpain-mediated down-regulation of myelin-associated glycoprotein in lysophosphatidic acid-induced neuropathic pain

Lysophosphatidic acid receptor (LPA(1)) signaling initiates neuropathic pain through demyelination of the dorsal root (DR). Although LPA is found to cause down-regulation of myelin proteins underlying demyelination, the detailed mechanism remains to be determined. In the present study, we found that a single intrathecal injection of LPA evoked a dose- and time-dependent down-regulation of myelin-associated glycoprotein (MAG) in the DR through LPA(1) receptor. A similar event was also observed in ex vivo DR cultures. Interestingly, LPA-induced down-regulation of MAG was significantly inhibited by calpain inhibitors (calpain inhibitor X, E-64 and E-64d) and LPA markedly induced calpain activation in the DR. The pre-treatment with calpain inhibitors attenuated LPA-induced neuropathic pain behaviors such as hyperalgesia and allodynia. Moreover, we found that sciatic nerve injury activates calpain activity in the DR in a LPA(1) receptor-dependent manner. The E-64d treatments significantly blocked nerve injury-induced MAG down-regulation and neuropathic pain. However, there was no significant calpain activation in the DR by complete Freund's adjuvant treatment, and E-64d failed to show anti-hyperalgesic effects in this inflammation model. The present study provides strong evidence that LPA-induced calpain activation plays a crucial role in the manifestation of neuropathic pain through MAG down-regulation in the DR.

Inhibition of calpain attenuates encephalitogenicity of MBP-specific T cells

Multiple sclerosis (MS) is a T-cell mediated autoimmune disease of the CNS, possessing both immune and neurodegenerative events that lead to disability. Adoptive transfer (AT) of myelin basic protein (MBP)-specific T cells into naïve female SJL/J mice results in a relapsing-remitting (RR) form of experimental autoimmune encephalomyelitis (EAE). Blocking the mechanisms by which MBP-specific T cells are activated before AT may help characterize the immune arm of MS and offer novel targets for therapy. One such target is calpain, which is involved in activation of T cells, migration of immune cells into the CNS, degradation of axonal and myelin proteins, and neuronal apoptosis. Thus, the hypothesis that inhibiting calpain in MBP-specific T cells would diminish their encephalitogenicity in RR-EAE mice was tested. Incubating MBP-specific T cells with the calpain inhibitor SJA6017 before AT markedly suppressed the ability of these T cells to induce clinical symptoms of RR-EAE. These reductions correlated with decreases in demyelination, inflammation, axonal damage, and loss of oligodendrocytes and neurons. Also, calpain : calpastatin ratio, production of truncated Bid, and Bax : Bcl-2 ratio, and activities of calpain and caspases, and internucleosomal DNA fragmentation were attenuated. Thus, these data suggest calpain as a promising target for treating EAE and MS.

Time-dependent increases in protease activities for neuronal apoptosis in spinal cords of Lewis rats during development of acute experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is characterized by axonal demyelination and neurodegeneration, the latter having been inadequately explored in the MS animal model experimental autoimmune encephalomyelitis (EAE). The purpose of this study was to examine the time-dependent correlation between increased calpain and caspase activities and neurodegeneration in spinal cord tissues from Lewis rats with acute EAE. An increase in TUNEL-positive neurons and internucleosomal DNA fragmentation in EAE spinal cords suggested that neuronal death was a result of apoptosis on days 8-10 following induction of EAE. Increases in calpain expression in EAE correlated with activation of pro-apoptotic proteases, leading to apoptotic cell death beginning on day 8 of EAE, which occurred before the appearance of visible clinical symptoms. Increases in calcineurin expression and decreases in phospho-Bad (p-Bad) suggested Bad activation in apoptosis during acute EAE. Increases in the Bax:Bcl-2 ratio and activation of caspase-9 showed the involvement of mitochondria in apoptosis. Further, caspase-8 activation suggested induction of the death receptor-mediated pathway for apoptosis. Endoplasmic reticulum stress leading to caspase-3 activation was also observed, indicating that multiple apoptotic pathways were activated following EAE induction. In contrast, cell death was mostly a result of necrosis on the later day (day 11), when EAE entered a severe stage. From these findings, we conclude that increases in calpain and caspase activities play crucial roles in neuronal apoptosis during the development of acute EAE.

Calpain-mediated signaling mechanisms in neuronal injury and neurodegeneration

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

Mechanisms of neuronal damage in multiple sclerosis and its animal models: role of calcium pumps and exchangers

Multiple sclerosis is an inflammatory, demyelinating and neurodegenerative disorder of the central nervous system. Increasing evidence indicates that neuronal pathology and axonal injury are early hallmarks of multiple sclerosis and are major contributors to progressive and permanent disability. Yet, the mechanisms underlying neuronal dysfunction and damage are not well defined. Elucidation of such mechanisms is of critical importance for the development of therapeutic strategies that will prevent neurodegeneration and confer neuroprotection. PMCA2 (plasma-membrane Ca(2+)-ATPase 2) and the NCX (Na(+)/Ca(2+) exchanger) have been implicated in impairment of axonal and neuronal function in multiple sclerosis and its animal models. As PMCA2 and NCX play critical roles in calcium extrusion in cells, alterations in their expression or activity may affect calcium homoeostasis and thereby induce intracellular injury mechanisms. Interventions that restore normal PMCA2 and NCX activity may prevent or slow disease progression by averting neurodegeneration.

Increased calpain correlates with Th1 cytokine profile in PBMCs from MS patients

Multiple sclerosis (MS) is a devastating autoimmune demyelinating disease of the central nervous system (CNS). This study investigated whether expression and activity of the calcium-activated protease calpain correlated with Th1/Th2 dysregulation in MS patients during states of relapse and remission. Calpain expression and activity were significantly increased in peripheral blood mononuclear cells (PBMCs) from MS patients, compared to controls, with the highest expression and activity noted during relapse. Th1 cytokines were highest and Th2 cytokines were lowest in MS patients during relapse. Treatment with calpain inhibitor, calpeptin, decreased Th1 cytokines in PBMCs from MS patients. Calpain inhibitor also reduced degradation of myelin basic protein (MBP) by inhibiting the calpain secreted from MBP-specific T cells. Taken together, these results suggested calpain involvement in Th1/Th2 dysregulation in MS patients.

A novel calpain inhibitor for the treatment of acute experimental autoimmune encephalomyelitis

Aberrant activation of calpain plays a key role in the pathophysiology of several neurodegenerative disorders. Calpain is increasingly expressed in inflammatory cells in EAE and is significantly elevated in the white matter of patients with multiple sclerosis, thus calpain inhibition could be a target for therapeutic intervention. The experiments reported here employed a myelin oligodendrocyte glycoprotein-induced disease model in C57Bl/6 mice (EAE) and a novel calpain inhibitor, targeted to nervous tissue. CYLA was found to reduce clinical signs of EAE and prevent demyelination and inflammatory infiltration in a dose- and time-dependent manner. Oral administration of the diacetal prodrug was equally effective.

Calpain: a death protein that mediates progression of liver injury

Calpain is a Ca(2+)-regulated cytosolic cysteine protease that exists mainly in two isoforms and mediates crucial cellular functions, including rearrangement of cytoskeletal proteins, transport of the glucose transporter GLUT4, and protein cleavage to activate various receptors and pro-enzymes. Unintentional activation or functional loss of intracellular calpain has been implicated in several pathologies, including neurodegenerative diseases, traumatic brain and spinal cord injuries, cataracts and ischemia-associated injuries. Furthermore, polymorphism in the gene encoding calpain-10 has been associated with increased risk of type 2 diabetes. Recent studies have revealed a novel role for calpain in the progression of toxicant-induced liver damage. Evidence suggests that calpain leaking out of necrotic hepatocytes is highly activated in the extracellular milieu and hydrolyzes proteins in the plasma membrane of neighboring cells leading to progression of injury. Experimental intervention with calpain inhibitors substantially mitigates progression of liver injury initiated by toxicants, thereby preventing acute liver failure, and toxicant-induced animal death, pointing to a new potential therapeutic strategy against acute toxicities.

Hyperphosphorylation and Aggregation of Tau in Experimental Autoimmune Encephalomyelitis

Axonal damage is a major morphological correlate and cause of permanent neurological deficits in patients with multiple sclerosis (MS), a multifocal, inflammatory and demyelinating disease of the central nervous system. Hyperphosphorylation and pathological aggregation of microtubule-associated protein tau is a common feature of many neurodegenerative diseases with axonal degeneration including Alzheimer's disease. We have therefore analyzed tau phosphorylation, solubility and distribution in the brainstem of rats with experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Tau was hyperphosphorylated at several sites also phosphorylated in Alzheimer's disease and became partially detergent-insoluble in EAE brains. Morphological examination demonstrated accumulation of amorphous deposits of abnormally phosphorylated tau in the cell body and axons of neurons within demyelinating plaques. Hyperphosphorylation of tau was accompanied by up-regulation of p25, an activator of cyclin-dependent kinase 5. Phosphorylation of tau, activation of cdk5, and axonal pathology were significantly reduced when diseased rats were treated with prednisolone, a standard therapy of acute relapses in MS. Hyperphosphorylation of tau was not observed in a genetic or nutritional model of axonal degeneration or demyelination, suggesting that inflammation as detected in the brains of rats with EAE is the specific trigger of tau pathology. In summary, our data provide evidence that axonal damage in EAE and possibly MS is linked to tau pathology.

Nuclear calpain regulates Ca2+-dependent signaling via proteolysis of nuclear Ca2+/calmodulin-dependent protein kinase type IV in cultured neurons

Accumulating evidence indicates that calpains can reside in or translocate to the cell nucleus, but their functions in this compartment remain poorly understood. Dissociated cultures of cerebellar granule cells (GCs) demonstrate improved long-term survival when their growth medium is supplemented with depolarizing agents that stimulate Ca(2+) influx and activate calmodulin-dependent signaling cascades, notably 20 mm KCl. We previously observed Ca(2+)-dependent down-regulation of Ca(2+)/calmodulin-dependent protein kinase (CaMK) type IV, which was attenuated by calpain inhibitors, in GCs supplemented with 20 mm KCl (Tremper-Wells, B., Mathur, A., Beaman-Hall, C. M., and Vallano, M. L. (2002) J. Neurochem. 81, 314-324). CaMKIV is highly enriched in the nucleus and thought to be critical for improved survival. Here, we demonstrate by immunolocalization/confocal microscopy and subcellular fractionation that the regulatory and catalytic subunits of m-calpain are enriched in GC nuclei, including GCs grown in medium containing 5 mm KCl. Calpain-mediated proteolysis of CaMKIV is selective, as several other nuclear and non-nuclear calpain substrates were not degraded under chronic depolarizing culture conditions. Depolarization and Ca(2+)-dependent down-regulation of CaMKIV were associated with significant alterations in other components of the Ca(2+)-CaMKIV signaling cascade: the ratio of phosphorylated to total cAMP response element-binding protein (a downstream CaMKIV substrate) was reduced by approximately 10-fold, and the amount of CaMK kinase (an upstream activator of CaMKIV) protein and mRNA was significantly reduced. We hypothesize that calpain-mediated CaMKIV proteolysis is an autoregulatory feedback response to sustained activation of a Ca(2+)-CaMKIV signaling pathway, resulting from growth of cultures in medium containing 25 mm KCl. This study establishes nuclear m-calpain as a regulator of CaMKIV and associated signaling molecules under conditions of sustained Ca(2+) influx.

Immunofluorescent labeling of increased calpain expression and neuronal death in the spinal cord of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice

Parkinson's disease (PD) is a movement disorder characterized by rigidity, tremor, and bradykinesia, originating from degeneration of dopaminergic neurons in the substantia nigra (SN), retrorubral area, and locus ceoruleus (LC). Calpain has been implicated in the pathophysiology of neurodegenerative diseases. Since the spinal cord (SC) and brain are integrally connected and calpain is involved in cell death and mitochondrial dysfunction, we hypothesized that SC neurons are also affected in PD. In order to examine this hypothesis, we examined both brain and SC from mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). To identify cells expressing calpain, double immunofluorescent labeling was performed with antibodies specific for calpain and a cell type (OX-42, GFAP, or NeuN). Combined terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and double immunofluorescent labeling were used to identify death of specific cells in the central nervous system (CNS). There was an increase in calpain expression in microglia, astrocytes, and neurons in the SC of MPTP-treated mice at 1 and 7 days, as compared to controls. TUNEL-positive neurons in the SC and SN showed apoptotic characteristics. These results demonstrated that neuronal death occurred not only in SN but also in the SC of MPTP-treated mice and has provided evidence for a possible calpain-mediated SC neuronal death in MPTP-induced parkinsonism in mice.

Activation of calpain-1 in myelin and microglia in the white matter of the aged rhesus monkey

Ultrastructural disruption of myelin sheaths and a loss of myelin with age are well-documented phenomena in both the human and rhesus monkey. Age-dependent activation of calpain-1 (EC 3.4.22.52) has been suggested as a plausible mechanism for increased proteolysis in the white matter of the rhesus monkey. The present study documents activation of calpain-1 throughout brain white matter in aged animals, evidenced by immunodetection of the activated enzyme as well as a calpain-derived spectrin fragment in both tissue section and Triton X-100-soluble homogenate of subcortical white matter from the frontal, temporal, and parietal lobes. Separation of myelin fractions from brain stem tissue into intact and floating myelin confirmed previous reports of an age-related increase in activated calpain-1 in the floating fraction. Measurements of calpain-1 activity using a fluorescent substrate revealed an age-related increase in calpain-1 proteolytic activity in the floating myelin fraction consistent with immunodetection of the activated enzyme in this fraction. Double-immunofluorescence demonstrated co-localization of activated calpain-1 with human leukocyte antigen-DR (HLA-DR), a marker for activated microglia, suggesting that these cells represent the major source of the increase in activated calpain-1 in the aging brain. These data solidify the role of calpain-1 in myelin protein metabolism and further implicate activated microglia in the pathology of the aging brain.

Ischemic neuronal death in the rat hippocampus: the calpain-calpastatin-caspase hypothesis

Inappropriate imbalances between proteases and protease inhibitors are known to occur under cerebral ischemia and neurodegenerative processes, and could be contributors to various diseases that are characterized by excessive (ischemia, AIDS) or inadequate (cancer, autoimmunity) cell death. For instance, calpain is activated in various necrotic and apoptotic conditions, whereas caspase-3 is only activated in neuronal apoptosis. Caspases and calpains are cysteine proteases that require proteolytic cleavage for activation. The substrates cleaved by caspases include cytoskeletal and associated proteins, kinases, members of the Bcl-2 family of apoptosis-related proteins, presenilins, and DNA-modulating enzymes. Calpain substrates include cytoskeletal and associated proteins, kinases and phosphatases, membrane receptors and transporters, and steroid receptors. This article provides a review of the properties of caspases and calpains, their roles in cell death pathways following cerebral ischemia, and the substrates upon which they act. Because calpain inhibitors and caspase inhibitors appear to protect brain tissue by distinct mechanisms in cerebral ischemia, the possible therapeutic interactions between these drugs in a well-defined rodent model of global ischemia are briefly discussed and documented.

The calpain system

The calpain system originally comprised three molecules: two Ca2+-dependent proteases, mu-calpain and m-calpain, and a third polypeptide, calpastatin, whose only known function is to inhibit the two calpains. Both mu- and m-calpain are heterodimers containing an identical 28-kDa subunit and an 80-kDa subunit that shares 55-65% sequence homology between the two proteases. The crystallographic structure of m-calpain reveals six "domains" in the 80-kDa subunit: 1). a 19-amino acid NH2-terminal sequence; 2). and 3). two domains that constitute the active site, IIa and IIb; 4). domain III; 5). an 18-amino acid extended sequence linking domain III to domain IV; and 6). domain IV, which resembles the penta EF-hand family of polypeptides. The single calpastatin gene can produce eight or more calpastatin polypeptides ranging from 17 to 85 kDa by use of different promoters and alternative splicing events. The physiological significance of these different calpastatins is unclear, although all bind to three different places on the calpain molecule; binding to at least two of the sites is Ca2+ dependent. Since 1989, cDNA cloning has identified 12 additional mRNAs in mammals that encode polypeptides homologous to domains IIa and IIb of the 80-kDa subunit of mu- and m-calpain, and calpain-like mRNAs have been identified in other organisms. The molecules encoded by these mRNAs have not been isolated, so little is known about their properties. How calpain activity is regulated in cells is still unclear, but the calpains ostensibly participate in a variety of cellular processes including remodeling of cytoskeletal/membrane attachments, different signal transduction pathways, and apoptosis. Deregulated calpain activity following loss of Ca2+ homeostasis results in tissue damage in response to events such as myocardial infarcts, stroke, and brain trauma.

A 48-hour exposure of pancreatic islets to calpain inhibitors impairs mitochondrial fuel metabolism and the exocytosis of insulin

Genetic variation in the gene for a cytosolic cysteine protease, calpain-10, increases the susceptibility to type 2 diabetes apparently by altering levels of gene expression. In view of the importance of altered beta-cell function in the pathophysiology of type 2 diabetes, the present study was undertaken to define the effects on insulin secretion of exposing pancreatic islets to calpain inhibitors for 48 hours. Exposure of mouse islets to calpain inhibitors (ALLN, ALLM, E-64-d, MDL 18270, and PD147631) of different structure and mechanism of action for 48 hours reversibly suppresses glucose-induced insulin secretion by 40% to 80%. Exposure of islets to inhibitors of other proteases, ie, cathepsin B and proteasome, did not affect insulin secretion. The 48-hour incubation with calpain inhibitors also attenuates insulin secretory responses to the mitochondrial fuel alpha-ketoisocaproate (KIC). The same incubation also suppresses glucose metabolism and intracellular calcium ([Ca(2+)](i)) responses to glucose or KIC in islets. In summary, long-term inhibition of islet calpain activity attenuates insulin secretion possibly by limiting the rate of glucose metabolism. A reduction of calpain activity in islet could contribute to the development of beta-cell failure in type 2 diabetes thereby providing a link between genetic susceptibility to diabetes and the pathophysiologic manifestations of the disease.

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.

Diffusion-weighted MR findings of central pontine and extrapontine myelinolysis

Diffusion-weighted MR (DWI) can detect changes in water diffusion associated with cellular dysfunction, which enables the differentiation of cytotoxic edema from vasogenic edema. In this study on DWI findings in central pontine (CPM) and extrapontine myelinolysis (EPM), DWI showed high signal intensities in the bilateral pons, midbrain, and genu of the corpus callosum. The corresponding apparent diffusion coefficient values were rather low. This suggests that cytotoxic edema does in fact exist in CPM and EPM and that DWI can be useful in the rapid diagnosis and prediction of the various types of edema occurring in active demyelinating diseases.

The novel calpain inhibitor SJA6017 improves functional outcome after delayed administration in a mouse model of diffuse brain injury

A principal mechanism of calcium-mediated neuronal injury is the activation of neutral proteases known as calpains. Proteolytic substrates for calpain include receptor and cytoskeletal proteins, signal transduction enzymes and transcription factors. Recently, calpain inhibitors have been shown to provide benefit in rat models of focal head injury and focal cerebral ischemia. The present study sought to investigate, in experiment 1, the time course of calpain-mediated cytoskeletal injury in a mouse model of diffuse head injury by measuring the 150- and 145-kDa alpha-spectrin breakdown products (SBDP). Secondly, in experiment 2, we examined the effect of early (20 min postinjury) administration of the novel calpain inhibitor SJA6017 on functional outcome measured 24 h following injury and its effect on posttraumatic alpha-spectrin degradation. Lastly, in experiment 3, we examined the effect of delayed (4 or 6 h postinjury) administration of SJA6017 on 24-h postinjury functional outcome. In experiment 1, isoflurane-anesthetized male CF-1 mice (18-22 g) were subjected to a 750 g-cm weight drop-induced injury and were sacrificed for SBDP analysis at postinjury times of 30 min, and 1, 2, 6, 24 and 48 h (plus sham). In experiments 2 and 3, mice were injured as described, and delivered a single tail vein injection of either SJA6017 (0.3, 1, or 3 mg/kg) or vehicle (administered immediately, 4 or 6 h postinjury [3 mg/kg]). Functional outcome was evaluated in both studies, and, in experiment 2, 24-h postinjury assessment of SBDPs was determined. Following injury, the level of SBDP 145 was significantly different from sham at 24 and 48 h in cortical and at 24 h in the hippocampal tissues and at 48 h in the striatum. Immediate postinjury administration of SJA6017 resulted in a dose-related improvement in 24-h functional outcome (p < 0.05 at 3 mg/kg). Significance was maintained after a 4-h delay of the 3 mg/kg, but was lost after a 6-h delay. Despite improvement in functional outcome at 24 h, SJA6017 did not reduce spectrin breakdown in cortical or hippocampal tissues. These results support a role for calpain-mediated neuronal injury and the potential for a practical therapeutic window for calpain inhibition following traumatic brain injury. However, measurements of regional spectrin degradation may not be the most sensitive marker for determining the effects of calpain inhibition.

Mechanism of myelin breakdown in experimental demyelination: a putative role for calpain

Although calpain has been extensively studied, its physiological function is poorly understood. In contrast, its role in the pathophysiology of various diseases has been implicated, including that of experimental allergic encephalomyelitis (EAE), an animal model of the demyelinating disease multiple sclerosis (MS). In EAE, calpain degrades myelin proteins, including myelin basic protein (MBP), suggesting a role for calpain in the breakdown of myelin in this disease. Subsequent studies revealed increased calpain activity and expression in the glial and inflammatory cells concomitant with loss of axon and myelin proteins. This suggested a crucial role for calpain in demyelinating diseases.

Osmotic demyelination disorders: central pontine and extrapontine myelinolysis

Focal symmetric demyelination in the central nervous system may be precipitated by aggressive correction of a hyper- or hypo-osmolar state and until recently has been associated with a high rate of morbidity and mortality. Specific anatomical locations are more susceptible to demyelination than others, although the mechanism of injury is unknown. Classic clinical and anatomical descriptions associated with a central pontine location have been supplemented by descriptions of patients with unusual symptoms associated with demyelinating lesions in extrapontine locations. The separation of patients with myelinolysis in central pontine and extrapontine locations is possible on the basis of clinical symptoms, and may direct specific pharmacological treatment. Patients at risk of central myelinolysis who are subjected to aggressive osmolar correction may be rescued with appropriate fluid management before brain injury has occurred; once injury is suspected on the basis of neurological symptoms, additional forms of intervention may still improve the outcome. Recent investigation of the molecular basis of the demyelinating process and the adaptive responses of the brain to dysosmolar challenge has allowed for the refinement of standard treatments and has made the osmotic demyelination syndrome a treatable condition with a better than expected prognosis.

Acute multiple sclerosis characterized by extensive mononuclear phagocyte infiltration

In this study, we examine the clinical, neuroradiological, and immunohistochemical findings of a 51 year old white female who died 27 months after onset of acute multiple sclerosis despite treatment with interferon-beta, azathioprine, corticosteroids, and cyclophosphamide. Immunohistochemical studies revealed extensive gliosis and mononuclear phagocyte infiltration with corresponding upregulation of proinflammatory cytokines (eg. IFN-alpha, TNF-alpha). The significance of immunohistochemical findings with respect to clinical presentation is discussed.

Inhibition of proteolysis by a cyclooxygenase inhibitor, indomethacin

The effect of indomethacin, a non-steroidal anti-inflammatory drug upon purified calpain has been studied. Also, its effects upon Ca2+-mediated degradation of cytoskeletal proteins (neurofilament) in spinal cord homogenate has been investigated. A dose-dependent inhibition of purified calpain activity was observed. A 50% inhibition of 14C-caseinolytic activity was obtained with less than 1.1 mM of indomethacin while the activity was completely inhibited at 3.3 mM concentration. The inhibitory effect of ketorlac, another non-steroidal anti-inflammatory drug, upon calpain was weaker than that of indomethacin. The degradation of myelin basic protein (MBP) by cathepsin B, a lysosomal cysteine protease, was significantly inhibited by indomethacin. It also inhibited the Ca2+-mediated degradation of neurofilament protein (NFP) in spinal cord homogenate. The extent of NFP degradation was analyzed by SDS-PAGE and the inhibition shown by indomethacin was weaker than that observed with leupeptin and the calpain inhibitor E64-d. The inhibitory effect of indomethacin on the activity of multicatalytic proteinase complex was negligible. These results suggest that indomethacin, a non-steroidal anti-inflammatory drug and cyclooxygenase inhibitor also inhibits proteinases, including cathepsin B and calpain.

Association of tenascin-R with murine brain myelin membranes: involvement of divalent cations

In the central nervous system (CNS), tenascin-R (TN-R) is mainly expressed by oligodendrocytes and in white matter tracts. Here, we have examined the molecular association of TN-R with CNS myelin by incubation of myelin membranes (MM) purified from adult mouse brain under different ionic conditions. By Western blot analysis, the 160 kDa isoform was the main TN-R component detectable in MM as a dimer which became degraded to monomers of 160 kDa and major fragments of 125 and 80 kDa in the absence of protease inhibitors. In the presence of chelating agents, TN-R was completely extracted from MM. Calcium ions promoted the dissociation of TN-R while zinc or copper blocked it. TN-R release from MM was sensitive to heat suggesting the involvement of calcium-dependent myelin protease(s) in this process. In addition, 1,10-phenanthroline (a metalloprotease blocker) partially inhibited TN-R release in the presence of calcium ions. We conclude that divalent metal ions stabilize the association of TN-R with CNS myelin and upon damage, the protein can be released and degraded by endogenous proteases, suggesting the implication of myelin-derived TN-R in axon growth inhibition and demyelinating diseases.