E-64-d prevents both calpain upregulation and apoptosis in the lesion and penumbra following spinal cord injury in rats

TUNEL-n-DIFL Method for Detection and Estimation of Apoptosis Specifically in Neurons and Glial Cells in Mixed Culture and Animal Models of Central Nervous System Diseases and Injuries

Detection of merely apoptosis does not reveal the type of central nervous system (CNS) cells that are dying in the CNS diseases and injuries. In situ detection and estimation of amount of apoptosis specifically in neurons or glial cells (astrocytes, oligodendrocytes, and microglia) can unveil valuable information for designing therapeutics for protection of the CNS cells and functional recovery. A method was first developed and reported from our laboratory for in situ detection and estimation of amount of apoptosis precisely in neurons and glial cells using in vitro and in vivo models of CNS diseases and injuries. This is a combination of terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and double immunofluorescent labeling (DIFL) or simply TUNEL-n-DIFL method for in situ detection and estimation of amount of apoptosis in a specific CNS cell type. An anti-digoxigenin (DIG) IgG antibody conjugated with 7-amino-4-methylcoumarin-3-acetic acid (AMCA) for blue fluorescence, fluorescein isothiocyanate (FITC) for green fluorescence, or Texas Red (TR) for red fluorescence can be used for in situ detection of apoptotic cell DNA, which is earlier labeled with TUNEL using alkali-stable DIG-11-dUTP. A primary anti-NeuN (neurons), anti-GFAP (astrocytes), anti-MBP (oligodendrocytes), or anti-OX-42 (microglia) IgG antibody and a secondary IgG antibody conjugated with one of the above fluorophores (other than that of ani-DIG antibody) are used for in situ detection of apoptosis in a specific CNS cell type in the mixed culture and animal models of the CNS diseases and injuries.

Oxidative DNA Damage in the Pathophysiology of Spinal Cord Injury: Seems Obvious, but Where Is the Evidence?

Oxidative stress occurs at various phases of spinal cord injury (SCI), promoting detrimental processes such as free radical injury of proteins, nucleic acids, lipids, cytoskeleton, and organelles. Oxidative DNA damage is likely a major contributor to the pathogenesis of SCI, as a damaged genome cannot be simply turned over to avert detrimental molecular and cellular outcomes, most notably cell death. Surprisingly, the evidence to support this hypothesis is limited. There is some evidence that oxidative DNA damage is increased following SCI, mainly using comet assays and immunohistochemistry. However, there is great variability in the timing and magnitude of its appearance, likely due to differences in experimental models, measurement techniques, and the rigor of the approach. Evidence indicates that 8-oxodG is most abundant at 1 and 7 days post-injury (dpi), while DNA strand breaks peak at 7 and 28 dpi. The DNA damage response seems to be characterized by upregulation of PCNA and PARP1 but downregulation of APEX1. Significant improvements in the analysis of oxidative DNA damage and repair after SCI, including single-cell analysis at time points representative for each phase post-injury using new methodologies and better reporting, will uncover the role of DNA damage and repair in SCI.

Premarin Reduces Neurodegeneration and Promotes Improvement of Function in an Animal Model of Spinal Cord Injury

Spinal cord injury (SCI) causes significant mortality and morbidity. Currently, no FDA-approved pharmacotherapy is available for treating SCI. Previously, low doses of estrogen (17β-estradiol, E2) were shown to improve the post-injury outcome in a rat SCI model. However, the range of associated side effects makes advocating its therapeutic use difficult. Therefore, this study aimed at investigating the therapeutic efficacy of Premarin (PRM) in SCI. PRM is an FDA-approved E2 (10%) formulation, which is used for hormone replacement therapy with minimal risk of serious side effects. The effects of PRM on SCI were examined by magnetic resonance imaging, immunofluorescent staining, and western blot analysis in a rat model. SCI animals treated with vehicle alone, PRM, E2 receptor antagonist (ICI), or PRM + ICI were graded in a blinded way for locomotor function by using the Basso–Beattie–Bresnahan (BBB) locomotor scale. PRM treatment for 7 days decreased post-SCI lesion volume and attenuated neuronal cell death, inflammation, and axonal damage. PRM also altered the balance of pro- and anti-apoptotic proteins in favor of cell survival and improved angiogenesis and microvascular growth. Increased expression of estrogen receptors (ERs) ERα and ERβ following PRM treatment and their inhibition by ER inhibitor indicated that the neuroprotection associated with PRM treatment might be E2-receptor mediated. The attenuation of glial activation with decreased inflammation and cell death, and increased angiogenesis by PRM led to improved functional outcome as determined by the BBB locomotor scale. These results suggest that PRM treatment has significant therapeutic implications for the improvement of post-SCI outcome.

Nanoparticle-Based Estrogen Delivery to Spinal Cord Injury Site Reduces Local Parenchymal Destruction and Improves Functional Recovery

Spinal cord injury (SCI) patients sustain significant functional impairments; this is causally related to restricted neuronal regeneration after injury. The ensuing reactive gliosis, inflammatory cascade, and glial scar formation impede axonal regrowth. Although systemic anti-inflammatory agents (steroids) have been previously administered to counteract this, no current therapeutic is approved for post-injury neuronal regeneration, in part because of related side effects. Likewise, therapeutic systemic estrogen levels exhibit neuroprotective properties, but dose-dependent side effects are prohibitive. The current study thus uses low-dose estrogen delivery to the spinal cord injury (SCI) site using an agarose gel patch embedded with estrogen-loaded nanoparticles. Compared to controls, spinal cords from rodents treated with nanoparticle site-directed estrogen demonstrated significantly decreased post-injury lesion size, reactive gliosis, and glial scar formation. However, axonal regeneration, vascular endothelial growth factor production, and glial-cell-derived neurotrophic factor levels were increased with estrogen administration. Concomitantly improved locomotor and bladder functional recovery were observed with estrogen administration after injury. Therefore, low-dose site-directed estrogen may provide a future approach for enhanced neuronal repair and functional recovery in SCI patients.

Overexpression of HIPK2 attenuates spinal cord injury in rats by modulating apoptosis, oxidative stress, and inflammation

HIPK2 is considered to be a tumor suppressor. It also has been implicated in several functions such as apoptosis and inflammation that are linked to spinal cord injury (SCI). However, whether HIPK2 ameliorates the neurological pain of SCI remains unclear. Here, we investigated the effects of HIPK2 on neurological function, oxidative stress, levels of inflammatory cytokines and expression of Bcl-2/Bax in an SCI model. Firstly, we evaluated the therapeutic effects of HIPK2 on neurological pain in the SCI rat using the Basso, Beattie and Bresnahan scores and H & E staining. Overexpression of HIPK2 significantly elevated the levels of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF), and reduced the mRNA expression of Nogo-A and RhoA in SCI rats. Furthermore, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assays showed that overexpression of HIPK2 significantly reduced the number of apoptotic cells. Overexpression of HIPK2 also decreased expression of Bax and Caspase-3 and elevated expression of Bcl-2 in the SCI model, indicating that HIPK2 exhibited its protective activity by inhibiting SCI-induced apoptosis. Then, we measured the serum concentrations of malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-PX). We also determined the mRNA and protein levels of nuclear factor-κB p65 unit, tumor necrosis factor-α (TNF-α), and interleukin (IL)-1β. HIPK2 overexpression reduced oxidative stress and the levels of inflammatory cytokines compared with SCI control animals. Additionally, acetylation of HIPK2 was reduced in SCI rats. Overexpression of HIPK2 could enhance autophagy by elevating the expression of Beclin-1 and LC3-II while autophagy is regarded as a beneficial regulator to improve spinal cord injury. Together, overexpression of HIPK2 improved contusive SCI induced pain by modulating oxidative stress, Bcl‑2 and Bax signaling, and inflammation, and also regulating autophagy.

Calpain inhibitors ameliorate muscle wasting in a cachectic mouse model bearing CT26 colorectal adenocarcinoma

Cancer-related cachexia involves increased protein breakdown through various proteolytic pathways, including the ubiquitin-proteasome pathway (UPP). We hypothesized that a calcium- and calpain-dependent pathway might play a crucial role during the proteolytic procedure, and that pathway interventions would ameliorate cancer cachexia in vivo. After being inoculated with CT26 adenocarcinoma cell culture subcutaneously, BALB/c mice developed cachexia in 12 days. They were then administered with different types of calpain inhibitors individually or in combination for 7 consecutive days. Eighteen healthy mice were also assessed as a control group. Changes in body weight, gastrocnemius muscle mass, tumor volume, food intake, survival time, and serum nutritional markers were monitored. Also measured were the levels of calpains, E3 ubiquitin ligases, and apoptosis-associated markers in gastrocnemius muscle. Our study showed that the intraperitoneal administration of calpain inhibitors significantly improved tumor-free body weight and gastrocnemius muscle mass in all treatment groups. Treatment with calpain inhibitors also ameliorated cachexia-associated negative effects in metabolic profiles and increased survival time in most of the tumor-bearing mice compared with the cachexia controls. Furthermore, calpain inhibitors reduced the calpain activity and the expression of MuRF-1 and atrogin-1 in all treatment groups, while increasing the level of cleaved caspase-3 and BAX and lowering the level of BCL-2 in some groups. These results justify further evaluation of calpain inhibitors both alone and in combination with other candidate agents as a potential new therapeutic strategy for treating cancer cachexia.

Long-term expression of zinc transporters in hippocampus following penicillin-induced developmental seizures and its regulation by E-64d

Autophagy has been shown to be involved in the pathophysiology of developmental seizure-induced brain damage. The present study aimed to examine whether E-64d, an autophagy inhibitor, was able to facilitate developmental seizure-induced hippocampal mossy fiber sprouting, in particular sprouting-associated zinc transporter signals. Recurrent seizures were induced by penicillin every other day in Sprague-Dawley rats from postnatal day 21 (P21). Rats were randomly assigned into the control group (CONT), recurrent seizure group (RS) and the seizure plus E-64d group (E64D). The expression levels of beclin-1 and B-cell lymphoma 2 were analyzed at 1.5, 3, 6 and 24 h after the last seizures using western blot analysis. At P51, mossy fiber sprouting and the mRNA expression levels of zinc transporter 2 (ZnT-2), ZnT-4, ZnT-5, ZnT-6, ZnT-7, divalent cation transporter 1, Zrt-Irt-like protein 6 (ZIP-6), ZIP-7, cathepsin D and cathepsin L in the rat hippocampus were assessed using Timm staining and reverse transcription-quantitative polymerase chain reaction analysis, respectively. Reduced hippocampal mossy fiber sprouting were detected in the E-64d-treated rats compared with the non-treated control. In parallel with these observations, there was a marked reduction in the mRNA expression levels of ZnT-4 at P51 in the E-64d-treated rat hippocampus compared with the non-treated seizure group. Linear correlation analysis showed significant inter-relationship among ZIP-7, ZnT-4, ZnT-5, ZnT-7, cathepsin D and cathepsin L. These results indicate that the ZnT-4/ZIP-7/cathepsin signaling pathway serves a crucial function in the neuroprotective effects of E-64d. Thus, E-64d may offer a novel strategy for the development of therapeutic interventions for developmental seizure-induced brain damage.

Cathepsin B is a New Drug Target for Traumatic Brain Injury Therapeutics: Evidence for E64d as a Promising Lead Drug Candidate

There is currently no therapeutic drug treatment for traumatic brain injury (TBI) despite decades of experimental clinical trials. This may be because the mechanistic pathways for improving TBI outcomes have yet to be identified and exploited. As such, there remains a need to seek out new molecular targets and their drug candidates to find new treatments for TBI. This review presents supporting evidence for cathepsin B, a cysteine protease, as a potentially important drug target for TBI. Cathepsin B expression is greatly up-regulated in TBI animal models, as well as in trauma patients. Importantly, knockout of the cathepsin B gene in TBI mice results in substantial improvements of TBI-caused deficits in behavior, pathology, and biomarkers, as well as improvements in related injury models. During the process of TBI-induced injury, cathepsin B likely escapes the lysosome, its normal subcellular location, into the cytoplasm or extracellular matrix (ECM) where the unleashed proteolytic power causes destruction via necrotic, apoptotic, autophagic, and activated glia-induced cell death, together with ECM breakdown and inflammation. Significantly, chemical inhibitors of cathepsin B are effective for improving deficits in TBI and related injuries including ischemia, cerebral bleeding, cerebral aneurysm, edema, pain, infection, rheumatoid arthritis, epilepsy, Huntington's disease, multiple sclerosis, and Alzheimer's disease. The inhibitor E64d is unique among cathepsin B inhibitors in being the only compound to have demonstrated oral efficacy in a TBI model and prior safe use in man and as such it is an excellent tool compound for preclinical testing and clinical compound development. These data support the conclusion that drug development of cathepsin B inhibitors for TBI treatment should be accelerated.

Therapeutic Efficacy of E-64-d, a Selective Calpain Inhibitor, in Experimental Acute Spinal Cord Injury

This study aims to investigate the therapeutic effect of calpain inhibitor E-64-d on SCI and to find a new approach to treat SCI. When an SCI rat model was established, it was immediately administered with E-64-d. RT-PCR and Western blotting were used to determine the protein and mRNA levels of calpain 1 and 68-kD NFP. TUNEL staining and NeuN labeling were performed to analyze neuronal apoptosis in the lesion. Immunohistochemistry assay was carried out to observe the expressions of calpain 1 and GFAP. Cyclooxygenase-2 activity was measured to show the immune response status. Locomotor function was evaluated by inclined plane test and Basso, Beattie, and Bresnahan locomotor rating scale. The results showed that calpain 1 was activated after SCI occurred. Treatment with E-64-d decreased expressions of calpain 1 and GFAP, alleviated neuronal apoptosis, inhibited cyclooxygenase-2 activity, and resulted in the promoted locomotor function. Furthermore, combination of E-64-d and MP had better efficacy than did E-64-d or MP alone. E-64-d is expected to be applied to treat SCI, and its alliance with MP may provide a valid strategy for SCI therapy.

Involvement of calpains in adult neurogenesis: implications for stroke

Calpains are ubiquitous proteases involved in cell proliferation, adhesion and motility. In the brain, calpains have been associated with neuronal damage in both acute and neurodegenerative disorders, but their physiological function in the nervous system remains elusive. During brain ischemia, there is a large increase in the levels of intracellular calcium, leading to the activation of calpains. Inhibition of these proteases has been shown to reduce neuronal death in a variety of stroke models. On the other hand, after stroke, neural stem cells (NSC) increase their proliferation and newly formed neuroblasts migrate towards the site of injury. However, the process of forming new neurons after injury is not efficient and finding ways to improve it may help with recovery after lesion. Understanding the role of calpains in the process of neurogenesis may therefore open a new window for the treatment of stroke. We investigated the involvement of calpains in NSC proliferation and neuroblast migration in two highly neurogenic regions in the mouse brain, the dentate gyrus (DG) and the subventricular zone (SVZ). We used mice that lack calpastatin, the endogenous calpain inhibitor, and calpains were also modulated directly, using calpeptin, a pharmacological calpain inhibitor. Calpastatin deletion impaired both NSC proliferation and neuroblast migration. Calpain inhibition increased NSC proliferation, migration speed and migration distance in cells from the SVZ. Overall, our work suggests that calpains are important for neurogenesis and encourages further research on their neurogenic role. Prospective therapies targeting calpain activity may improve the formation of new neurons following stroke, in addition to affording neuroprotection.

Cold ischemia-induced autophagy in rat lung tissue

Autophagy is a highly conserved pathway that permits recycling of nutrients within the cell and is rapidly upregulated during starvation or cell stress. Autophagy has been implicated in the pathophysiological process of warm ischemia-reperfusion injury in the rat lung. Cold ischemia (CI) preservation for lung transplantation also exhibits cell stress and nutrient deprivation, however, little is known with regard to the involvement of autophagy in this process. In the present study, CI preservation-induced autophagy and apoptosis was investigated in the lungs of Sprague Dawley rats. Sprague Dawley rat lungs were flushed and preserved at 4°C (i.e. CI) for various durations (0, 3, 6, 12 and 24 h). The levels of autophagy, autophagic cell death and apoptosis were measured at each time point following CI. The results revealed that autophagy was induced by CI preservation, which was initiated at 3 h, peaked at 6 h after CI and declined thereafter. Additionally, a coexistence of autophagic cell death and apoptosis was observed in rat lung tissues following prolonged CI. These findings demonstrate that autophagy is involved in the pathophysiological process of lung CI. Furthermore, autophagic cell death in addition to necrosis and apoptosis occurs following CI in the lung. CI preservation may therefore be a potential mechanism of lung injury during organ preservation prior to lung transplantation.

Reconsider Alzheimer's disease by the 'calpain-cathepsin hypothesis'--a perspective review

Alzheimer's disease (AD) is characterized by slowly progressive neuronal death, but its molecular cascade remains elusive for over 100 years. Since accumulation of autophagic vacuoles (also called granulo-vacuolar degenerations) represents one of the pathologic hallmarks of degenerating neurons in AD, a causative connection between autophagy failure and neuronal death should be present. The aim of this perspective review is at considering such underlying mechanism of AD that age-dependent oxidative stresses may affect the autophagic-lysosomal system via carbonylation and cleavage of heat-shock protein 70.1 (Hsp70.1). AD brains exhibit gradual but continual ischemic insults that cause perturbed Ca(2+) homeostasis, calpain activation, amyloid β deposition, and oxidative stresses. Membrane lipids such as linoleic and arachidonic acids are vulnerable to the cumulative oxidative stresses, generating a toxic peroxidation product 'hydroxynonenal' that can carbonylate Hsp70.1. Recent data advocate for dual roles of Hsp70.1 as a molecular chaperone for damaged proteins and a guardian of lysosomal integrity. Accordingly, impairments of lysosomal autophagy and stabilization may be driven by the calpain-mediated cleavage of carbonylated Hsp70.1, and this causes lysosomal permeabilization and/or rupture with the resultant release of the cell degradation enzyme, cathepsins (calpain-cathepsin hypothesis). Here, the author discusses three topics; (1) how age-related decrease in lysosomal and autophagic activities has a causal connection to programmed neuronal necrosis in sporadic AD, (2) how genetic factors such as apolipoprotein E and presenilin 1 can facilitate lysosomal destabilization in the sequential molecular events, and (3) whether a single cascade can simultaneously account for implications of all players previously reported. In conclusion, Alzheimer neuronal death conceivably occurs by the similar 'calpain-hydroxynonenal-Hsp70.1-cathepsin cascade' with ischemic neuronal death. Blockade of calpain and/or extra-lysosomal cathepsins as well as scavenging of hydroxynonenal would become effective AD therapeutic approaches.

Expression profiles of hippocampal regenerative sprouting-related genes and their regulation by E-64d in a developmental rat model of penicillin-induced recurrent epilepticus

E-64d (a calpain and autophagy inhibitor) has previously been shown safe for the treatment of Alzheimer's disease in humans. In the present study, the potential protective mechanism of E-64d on hippocampal aberrant mossy fiber sprouting was examined in a developmental rat model of penicillin-induced recurrent epilepticus. A seizure was induced by penicillin every other day in Sprague-Dawley rats from postnatal day 21 (P21). The rats were randomly assigned into the control group (CONT1), the control plus E-64d (CONT2), the seizure group (EXP1) and the seizure plus E-64d (EXP2). On P51, mossy fiber sprouting and related gene expression in hippocampus were assessed by Timm staining and real-time RT-PCR methods, respectively. To validate the RT-PCR results, western blot analysis was performed on selected genes. E-64d obviously suppressed the aberrant mossy fiber sprouting in the supragranular region of dentate gyrus and CA3 subfield of hippocampus. Among the total twelve genes, six genes were strongly up- (MT-3, ACAT1, clusterin and ApoE) or down- (ZnT-1 and PRG-3) regulated by developmental seizures (EXP1) compared with that in the CONT1. Up-regulation of ApoE and Clusterin was blocked by pretreatment with E-64d both in mRNA and protein levels. Further, E-64d-pretreated seizure rats (EXP2) showed a significant downregulation of mRNA expression of PRG-1, PRG-3 and PRG-5, cathepsin B and ApoE, as well as up-regulated nSMase and ANX7 in hippocampus when compared with EXP1 rats. The results of the present study suggest that E-64d, an elective inhibitor of calpain and autophagy, is potentially useful in the treatment of developmental seizure-induced brain damage both by regulating abnormal zinc signal transduction and through the modulation of altered lipid metabolism via ApoE/clusterin pathway in hippocampus.

Effects of mechanical force on cytoskeleton structure and calpain-induced apoptosis in rat dorsal root ganglion neurons in vitro

BACKGROUND

A sudden mechanical insult to the spinal cord is usually caused by changing pressure on the surface of the spinal cord. Most of these insults are mechanical force injuries, and their mechanism of injury to the spinal cord is largely unknown.

METHODS

Using a compression-driven instrument to simulate mechanical force, we applied mechanical pressure of 0.5 MPa to rat dorsal root ganglion (DRG) neurons for 10 min to investigate cytoskeletal alterations and calpain-induced apoptosis after the mechanical force injury.

RESULTS

The results indicated that mechanical forces affect the structure of the cytoskeleton and cell viability, induce early apoptosis, and affect the cell cycle of DRG neurons. In addition, the calpain inhibitor PD150606 reduced cytoskeletal degradation and the rate of apoptosis after mechanical force injury.

CONCLUSION

Thus, calpain may play an important role in DRG neurons in the regulation of apoptosis and cytoskeletal alterations induced by mechanical force. Moreover, cytoskeletal alterations may be substantially involved in the mechanotransduction process in DRG neurons after mechanical injury and may be induced by activated calpain. To our knowledge, this is the first report to demonstrate a relationship between cytoskeletal degradation and apoptosis in DRG neurons.

A calpain inhibitor enhances the survival of Schwann cells in vitro and after transplantation into the injured spinal cord

Despite the diversity of cells available for transplantation into sites of spinal cord injury (SCI), and the known ability of transplanted cells to integrate into host tissue, functional improvement associated with cellular transplantation has been limited. One factor potentially limiting the efficacy of transplanted cells is poor cell survival. Recently we demonstrated rapid and early death of Schwann cells (SCs) within the first 24 h after transplantation, by both necrosis and apoptosis, which results in fewer than 20% of the cells surviving beyond 1 week. To enhance SC transplant survival, in vitro and in vivo models to rapidly screen compounds for their ability to promote SC survival are needed. The current study utilized in vitro models of apoptosis and necrosis, and based on withdrawal of serum and mitogens and the application of hydrogen peroxide, we screened several inhibitors of apoptosis and necrosis. Of the compounds tested, the calpain inhibitor MDL28170 enhanced SC survival both in vitro in response to oxidative stress induced by application of H2O2, and in vivo following delayed transplantation into the moderately contused spinal cord. The results support the use of calpain inhibitors as a promising new treatment for promoting the survival of transplanted cells. They also suggest that in vitro assays for cell survival may be useful for establishing new compounds that can then be tested in vivo for their ability to promote transplanted SC survival.

Inhibition of cysteine proteases in acute and chronic spinal cord injury

Spinal cord injury (SCI) is a serious neurological disorder that debilitates mostly young people. Unfortunately, we still do not have suitable therapeutic agents for treatment of SCI and prevention of its devastating consequences. However, we have gained a good understanding of pathological mechanisms that cause neurodegeneration leading to paralysis or even death following SCI. Primary injury to the spinal cord initiates the secondary injury process that includes various deleterious factors for ultimate activation of different cysteine proteases for degradation of cellular key cytoskeleton and other crucial proteins for delayed death of neurons and glial cells at the site of SCI and its penumbra in different animal models. An important aspect of SCI is the increase in intracellular free Ca(2+) concentration within a short time of primary injury. Various studies in different laboratories demonstrate that the most important cysteine protease for neurodegeneration in SCI is calpain, which absolutely requires intracellular free Ca(2+) for its activation. Furthermore, other cysteine proteases, such as caspases and cathepsin B also make a contribution to neurodegeneration in SCI. Therefore, inhibition of cysteine proteases is an important goal in prevention of neurodegeneration in SCI. Studies showed that individual inhibitors of cysteine proteases provided significant neuroprotection in animal models of SCI. Recent studies suggest that physiological hormones, such as estrogen and melatonin, can be successfully used for prevention of neurodegeneration and preservation of motor function in acute SCI as well as in chronic SCI in rats.

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.

Sustained calpain inhibition improves locomotor function and tissue sparing following contusive spinal cord injury

Following contusive spinal cord injury (SCI), calpain activity is dramatically increased and remains elevated for days to weeks. Although calpain inhibition has previously been demonstrated to be neuroprotective following spinal cord injury, most studies administered the calpain inhibitor at a single time point. We hypothesized that sustained calpain inhibition would improve functional and pathological outcomes, as compared to the results obtained with a single postinjury administration of the calpain inhibitor. Contusion SCI was produced in female Long-Evans rats using the Infinite Horizon spinal cord injury impactor at the 200 kdyn force setting. Open-field locomotor function was evaluated until 6 weeks postinjury. Histological assessment of lesion volume and tissue sparing was performed at 6 weeks after SCI. Calpain inhibitor MDL28170 administered as a single postinjury i.v. bolus (20 mg/kg) or as a daily i.p. dose (1 mg/kg) improved locomotor function, but did not increase tissue sparing. Combined i.v. and daily i.p. MDL28170 administration resulted in significant improvement in both functional and pathological outcome measures, supporting the calpain theory of SCI proposed by Dr. Banik and colleagues.

Glutamate receptor activation evokes calpain-mediated degradation of Sp3 and Sp4, the prominent Sp-family transcription factors in neurons

Sp-family transcription factors (Sp1, Sp3 and Sp4) contain a zinc-finger domain that binds to DNA sequences rich in G-C/T. As assayed by RT-PCR analysis of mRNA, western-blot analysis, immunofluorescence, and antibody-dependent "supershift" of DNA-binding assays, the prominent Sp-family factors in cerebral neurons were identified as Sp3 and Sp4. By contrast, glial cells were found to express Sp1 and Sp3. We previously showed that the pattern of G-C/T binding activity of Sp-family factors is rapidly and specifically altered by the calcium influx accompanying activation of glutamate receptors. Here, we demonstrate that Sp-factor activity is also lost after a cerebral ischemia/reperfusion injury in vivo. Consistent with its calcium-dependent nature, we found that glutamate's effect on Sp-family factors could be blocked by inhibitors of calpains, neutral cysteine proteases activated by calcium. Purified calpain I cleaved Sp3 and Sp4 into products that retained G-C/T-binding activity, consistent with species observed in glutamate-treated neurons. These data provide details of an impact of glutamate-receptor activation on molecular events connected to gene expression.

Cerebral calpain in fatal falciparum malaria

Disruption of axonal transport may represent a final common pathway leading to neurological dysfunction in cerebral malaria (CM). Calpains are calcium (Ca2+)-activated cysteine proteases which have been implicated in axonal injury in neurological diseases of various aetiologies. In this study we examined the association between mu- and m-calpain, the specific inhibitor calpastatin, and axonal injury in post mortem brain tissue from patients who died from severe malaria. Calpains were associated with axons labelled for the beta-amyloid precursor protein that detects impaired axonal transport. Elevated levels of calpastatin were rarely observed in injured axons. There were increased numbers of neurones with mu-calpain in the nuclear compartment in severe malaria cases compared with non-neurological controls, and increased numbers of glia with nuclear mu-calpain in CM patients compared with non-CM malaria cases and non-neurological controls. There was marked redistribution of calpastatin in the sequestered Plasmodium falciparum-infected erythrocytes. Responses specific to malaria infection were ascertained following analysis of brain samples from fatal cases with acute axonal injury, HIV encephalitis, and progressive multifocal leucoencephalopathy. Our findings implicate a role for calpains in the modulation of disease progression in CM.

Temporal profiles of cytoskeletal protein loss following traumatic axonal injury in mice

To examine the time course and relative extent of proteolysis of neurofilament and tubulin proteins after traumatic axonal injury (TAI), anesthetized mice were subjected to optic nerve stretch injury. Immunohistochemistry confirmed neurofilament accumulation within axonal swellings at 4, 24, and 72 h postinjury (n = 4 injured and 2 sham per time point). Immunoblotting of optic nerve homogenates (n = 5 injured and 1 sham at 0.5, 4, 24 or 72 h) revealed calpain-mediated spectrin proteolytic fragments after injury. Protein levels for NF68 progressively decreased from 0.5 h to 24 h postinjury, while NF200 and alpha-tubulin levels decreased acutely (0.5-4 h), with a secondary decline at 72 h postinjury. These data demonstrate that diffusely distributed TAI is associated not only with a localized accumulation of neurofilament proteins, but also significant decreases in total cytoskeletal protein levels which may be mediated, in part, by calpains. Protection of the axonal cytoskeleton represents a potential therapeutic target for axonal damage associated with injury or neurodegenerative diseases.

Calpeptin provides functional neuroprotection to rat retinal ganglion cells following Ca2+ influx

Apoptosis of retinal ganglion cells (RGCs) impairs vision in glaucoma patients. RGCs are also degenerated in multiple sclerosis (MS), resulting in loss of visual perception in MS patients. We examined the involvement of calpain and caspase cascades in apoptosis of the rat retinal ganglion cell line RGC-5 following 24 h of exposure to 250 nM ionomycin (IMN) or 300 units/ml interferon-gamma (IFN-gamma) and then evaluated functional neuroprotection with 2 microM calpeptin (CP, a calpain-specific inhibitor). Morphological and biochemical features of apoptosis were detected in RGC-5 cells following exposure to IMN or IFN-gamma. Fura-2 assay determined significant increases in intracellular free [Ca2+] following exposure to IMN or IFN-gamma. Pretreatment with CP for 1 h prevented Ca2+ influx, proteolytic activities, and apoptosis in RGC-5 cells. Western blot analyses showed an increase in activities of calpain and caspase-12, upregulation of Bax:Bcl-2 ratio, release of cytochrome c from mitochondria, and increase in caspase-9 and caspase-3 activities during apoptosis. Increased caspase-3 activity was also confirmed by a colorimetric assay. Activation of caspase-8 and cleavage of Bid to tBid in RGC-5 cells following exposure to IFN-gamma indicated co-operation between extrinsic and intrinsic pathways of apoptosis. Patch-clamp recordings showed that pretreatment with CP attenuated apoptosis and maintained normal whole-cell membrane potential, indicating functional neuroprotection. Taken together, our results demonstrated that Ca2+ overload could be responsible for activation of calpain and caspase cascades leading to apoptotic death of RGC-5 cells and CP provided functional neuroprotection.

The calpain inhibitor VI prevents apoptosis of adult motor neurons

Motor neuron cell death was studied in organotypic cultures of adult spinal cord slices from the mouse. Six hours after excision, many motor neuron nuclei displayed apoptotic features including nuclear and chromatin condensation. At this time point, many motor neurons also exhibited immunoreactivity to calpain II. Both the calpain inhibitor VI and ethyleneglycol-bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) prevented the appearance of apoptotic nuclei whereas the pan caspase inhibitor Z-VAD.fmk had no effect. The results suggest that calpain is required for apoptosis of motor neurons and that this type of apoptosis is independent of caspase activation.

Upregulation of calpain correlates with increased neurodegeneration in acute experimental auto-immune encephalomyelitis

Although calpain up-regulation is well established in experimental auto-immune encephalomyelitis (EAE), a link between increased calpain expression and activity and neurodegeneration has not been examined. Therefore, spinal cord tissue from Lewis rats with EAE was examined to test the hypothesis that increased calpain expression in neurons would correlate with increased cell death and axonal damage in a time-dependent manner following EAE induction. We found that increased calpain expression in EAE corresponded to increased TUNEL-positive neurons and to increased expression of dephosphorylated neurofilament protein, markers of cell death and axonal degeneration, respectively. An increase in internucleosomal DNA fragmentation in EAE spinal cord suggested that cell death was, at least partially, due to apoptosis. Axonal damage was further demonstrated in EAE spinal cord compared with control via morphological analysis, revealing granular degeneration of filament and microtubule integrity, loss of myelin, and mitochondrial damage. Calcium (Ca2+) influx, which is required for calpain activation, was also increased in EAE spinal cord. From these findings, we conclude that increases in Ca2+-induced calpain activity may play a crucial role in neurodegeneration in acute EAE.

Calpain activation in apoptosis of ventral spinal cord 4.1 (VSC4.1) motoneurons exposed to glutamate: calpain inhibition provides functional neuroprotection

Glutamate toxicity has been implicated in cell death in neurodegenerative diseases and injuries. Glutamate-induced Ca2+ influx may mediate activation of calpain, a Ca2+-dependent cysteine protease, which in turn may degrade key cytoskeletal proteins. We investigated glutamate-mediated apoptosis of VSC4.1 motoneurons and functional neuroprotection by calpain inhibition. Exposure of VSC4.1 cells to 10 microM glutamate for 24 hr caused significant increases in intracellular free [Ca2+], as determined by fura-2 assay. Pretreatment of cells with 10 or 25 microM calpeptin (a cell-permeable calpain-specific inhibitor) for 1 hr prevented glutamate-induced Ca2+ influx. Western blot analyses showed an increase in Bax:Bcl-2 ratio, release of cytochrome c from mitochondria, and calpain and caspase-3 activities during apoptosis. Cell morphology, as evaluated by Wright staining, indicated predominantly apoptotic features following glutamate exposure. ApopTag assay further substantiated apoptotic features morphologically as well as biochemically. Our data showed that calpeptin mainly prevented calpain-mediated proteolysis and apoptosis and maintained whole-cell membrane potential, indicating functional neuroprotection. The results imply that calpeptin may serve as a therapeutic agent for preventing motoneuron degeneration, which occurs in amyotrophic lateral sclerosis and spinal cord injury. In this investigation, we also examined glutamate receptor subtypes involved in the initiation of apoptosis in VSC4.1 cells following exposure to glutamate. Our results indicated that the N-methyl-D-aspartate (NMDA) receptors contributed more than alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) receptors to glutamate-mediated Ca2+ influx and cell death mechanism. Inhibition of the activities of both NMDA and AMPA receptors protected VSC4.1 cells from glutamate toxicity and preserved whole-cell membrane potential.

FAS deficiency reduces apoptosis, spares axons and improves function after spinal cord injury

After spinal cord injury (SCI), apoptosis of neurons and oligodendrocytes is associated with axonal degeneration and loss of neurological function. Recent data have suggested a potential role for FAS death receptor-mediated apoptosis in the pathophysiology of SCI. In this study, we examined the effect of FAS deficiency on SCI in vitro and in vivo. FAS(Lpr/lpr) mutant mice and wildtype background-matched mice were subjected to a T5-6 clip compression SCI, and complementary studies were done in an organotypic slice culture model of SCI. Post-traumatic apoptosis in the spinal cord, which was seen in neurons and oligodendrocytes, was decreased in the FAS-deficient mice both in vivo and in vitro particularly in oligodendrocytes. FAS deficiency was also associated with improved locomotor recovery, axonal sparing and preservation of oligodendrocytes and myelin. However, FAS deficiency did not result in a significant increase in surviving neurons in the spinal cord at 6 weeks after injury, likely reflecting the importance of other cell death mechanisms for neurons. We conclude that inhibition of the FAS pathway may be a clinically attractive neuroprotective strategy directed towards oligodendroglial and axonal preservation in the treatment of SCI and neurotrauma.

Amelioration of experimental arthritis by a calpain-inhibitory compound: regulation of cytokine production by E-64-d in vivo and in vitro

Calpain, a calcium-dependent cysteine proteinase, has been reported to participate in the pathophysiology of rheumatoid arthritis (RA). The aim of this study is to investigate the therapeutic efficacy of calpain-inhibitory compounds in an animal model of RA and to clarify the underlying mechanisms in vivo and in vitro. Arthritis was induced in BALB/c mice with anti-type II collagen mAbs and LPS, and the mice were treated intra-peritoneally with a high dose (9 mg kg(-1) per day) or low dose (3 mg kg(-1) per day) of E-64-d (a membrane-permeable cysteine proteinase inhibitor) or control diluent. As a result, a high dose of E-64-d significantly alleviated the clinical arthritis and the histopathological findings, compared with the control diluent, although a low dose of E-64-d did not have a significant effect. Next, we evaluated the effects of E-64-d on cytokine mRNA expression at the inflamed joints by quantitative reverse transcription-PCR. High dose of E-64-d significantly decreased IL-6 and IL-1beta mRNA levels at the inflamed joints. The regulatory effects of E-64-d on cytokine production were also confirmed in vitro, using a synovial cell line (E11) and crude synoviocytes derived from RA patients. These results suggest the key roles of calpain in the pathophysiology of arthritis and that calpain-inhibitory compounds might be applicable to the treatment of arthritic diseases such as RA.

BimEL up‐regulation potentiates AIF translocation and cell death in response to MPTP

This study attempted to elucidate the signaling mechanism underlying dopaminergic cell death in the MPP+ model for Parkinson's disease. In neuronal-differentiated PC12 cells, through the regulation by activated JNK and c-jun, BimEL expression was markedly increased in response to MPP+ treatment, which led to the cell degeneration. In lieu of Smac translocation as seen in other paradigms, up-regulation of BimEL effected an increase in calpain I activity that, in turn, mediated AIF release from the mitochondria. In support, we found that knocking down BimEL expression resulted in a decrease in calpain I activity, as well as AIF release from the mitochondria and cell death. Finally, inhibition of calpain activity mitigated AIF release from the mitochondria and cell death. Under cell-free conditions, activated purified calpain I could induce the release of AIF from isolated mitochondria without the participation of BimEL or activated JNK, suggesting that AIF release is a direct consequence of calpain I activity. In concert, the results suggest a novel signaling pathway for dopaminergic cell degeneration, in which MPP+ induces the up-regulation of BimEL, which in turn potentiates an elevation in calpain I activity that mediates AIF release and cell death in a caspase-independent manner.

Calpain inhibitors prevent neuronal cell death and ameliorate motor disturbances after compression-induced spinal cord injury in rats

Traumatic spinal cord injury (SCI) results in widespread neuronal cell death. Recent studies have suggested that activated calpain mediates neuronal cell death in the central nervous system. We conducted a study to determine whether calpain mediates neuronal cell death in the motor neurons of the spinal cord after SCI, and whether postinjury administration of the calpain inhibitors N-acetyl- Leu-Leu-Met-CHO (ALLM) and calpain inhibitor III (CI III) (MDL28170) reduces the motor disturbances in rats with a model of SCI. Adult male Wistar rats were subjected to SCI by application of a 20-g weight impactor probe to the spinal cord at T12 for 20 min. The rats were divided into three groups according to whether they were injected intravenously with 0.05-2.5 mg/kg ALLM, 10 mg/kg CI III, or 0.1% DMSO as a control every 24 h for 1 week after SCI. Calpain was activated in the spinal cord at 8 h, 24 h, and 5 days after SCI, and administration of ALLM inhibited its activation. ALLM, as compared to the DMSO vehicle alone, also significantly reduced the number of motor neurons in spinal-cord lesions that were positively labeled at 24 h after SCI with the terminal deoxynucleotidyl transferase-uridine nucleotide end-labeling (TUNEL) technique. Additionally, both the inclined plane test and footprint analysis showed markedly better motor activity after 4 weeks in rats injected with ALLM or CI III than in rats given vehicle only. These results suggest that activation of calpain plays a critical role in the neuronal cell death that follows SCI, and that calpain inhibitors may have benefit in treating the motor disturbances that follow SCI.

Dexamethasone protected human glioblastoma U87MG cells from temozolomide induced apoptosis by maintaining Bax:Bcl-2 ratio and preventing proteolytic activities

Background

Glioblastoma is the deadliest and most prevalent brain tumor. Dexamethasone (DXM) is a commonly used steroid for treating glioblastoma patients for alleviation of vasogenic edema and pain prior to treatment with chemotherapeutic drugs. Temozolomide (TMZ), an alkylating agent, has recently been introduced in clinical trials for treating glioblastoma. Here, we evaluated the modulatory effect of DXM on TMZ induced apoptosis in human glioblastoma U87MG cells.

Results

Freshly grown cells were treated with different doses of DXM or TMZ for 6 h followed by incubation in a drug-free medium for 48 h. Wright staining and ApopTag assay showed no apoptosis in cells treated with 40 μM DXM but considerable amounts of apoptosis in cells treated with 100 μM TMZ. Apoptosis in TMZ treated cells was associated with an increase in intracellular free [Ca²⁺], as determined by fura-2 assay. Western blot analyses showed alternations in the levels of Bax (pro-apoptotic) and Bcl-2 (anti-apoptotic) proteins resulting in increased Bax:Bcl-2 ratio in TMZ treated cells. Western blot analyses also detected overexpression of calpain and caspase-3, which cleaved 270 kD α-spectrin at specific sites for generation of 145 and 120 kD spectrin break down products (SBDPs), respectively. However, 1-h pretreatment of cells with 40 μM DXM dramatically decreased TMZ induced apoptosis, decreasing Bax:Bcl-2 ratio and SBDPs.

Conclusion

Our results revealed an antagonistic effect of DXM on TMZ induced apoptosis in human glioblastoma U87MG cells, implying that treatment of glioblastoma patients with DXM prior to chemotherapy with TMZ might result in an undesirable clinical outcome.

The calpain inhibitor MDL 28170 prevents inflammation-induced neurofilament light chain breakdown in the spinal cord and reduces thermal hyperalgesia

Since long-term hyperexcitability of nociceptive neurons in the spinal cord has been suggested to be caused and maintained by changes of protein expression we assessed protein patterns in lumbar spinal cord during a zymosan induced paw inflammation employing two-dimensional (2D) gel electrophoresis. 2D PAGE revealed a time-dependent breakdown of scaffolding proteins one of which was neurofilament light chain (NFL) protein, which has been previously found to be important for axonal architecture and transport. Nociception induced breakdown of NFL in the spinal cord and dorsal root ganglias was prevented by pretreatment of the animals with a single dose of the specific inhibitor of the protease calpain (MDL-28170) which has been shown to be the primary protease involved in neurofilament degradation in neurodegenerative diseases. Treatment with the calpain inhibitor also provided anti-inflammatory and anti-hyperalgesic effects in the zymosan-induced paw inflammation model irrespective of whether the drug was administered systemically (i.p.) or delivered onto the lumbar spinal cord. This suggests that the activation of calpain is involved in the sensitization of nociceptive neurons what is partly due to neurofilament breakdown but cleavage of other calpain substrates may also be involved. Our results indicate that inhibition of pathological calpain activity may present an interesting novel drug target in the treatment of pain and inflammation.

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 in the pathophysiology of spinal cord injury: neuroprotection with calpain inhibitors

Spinal cord injury (SCI) evokes an increase in intracellular free Ca(2+) level resulting in activation of calpain, a Ca(2+)-dependent cysteine protease, which cleaves many cytoskeletal and myelin proteins. Calpain is widely expressed in the central nervous system (CNS) and regulated by calpastatin, an endogenous calpain-specific inhibitor. Calpastatin degraded by overactivation of calpain after SCI may lose its regulatory efficiency. Evidence accumulated over the years indicates that uncontrolled calpain activity mediates the degradation of many cytoskeletal and membrane proteins in the course of neuronal death and contributes to the pathophysiology of SCI. Cleavage of the key cytoskeletal and membrane proteins by calpain is an irreversible process that perturbs the integrity and stability of CNS cells leading to cell death. Calpain in conjunction with caspases, most notably caspase-3, can cause apoptosis of the CNS cells following trauma. Aberrant Ca(2+) homeostasis following SCI inevitably activates calpain, which has been shown to play a crucial role in the pathophysiology of SCI. Therefore, calpain appears to be a potential therapeutic target in SCI. Substantial research effort has been focused upon the development of highly specific inhibitors of calpain and caspase-3 for therapeutic applications. Administration of cell permeable and specific inhibitors of calpain and caspase-3 in experimental animal models of SCI has provided significant neuroprotection, raising the hope that humans suffering from SCI may be treated with these inhibitors in the near future.

Evaluation of conditions for calpain inhibition in the rat spinal cord: effective postinjury inhibition with intraspinal MDL28170 microinjection

Calpains (calcium-activated cysteine proteases) are strongly implicated in the secondary damage that follows contusion injury to the spinal cord. Calpains are activated within a few minutes following injury and their elevated activity persists for 24 h, thereby providing a reasonable window of opportunity for postinjury inhibition. Previous studies demonstrated decreased axonal damage and neurofilament proteolysis with postinjury intravenous administration of relatively low concentrations of the calpain inhibitors leupeptin, E-64-D, and calpeptin. We sought to determine if conditions under which calpain inhibitors were administered in previous studies resulted in effective calpain inhibition, and to identify conditions that result in significant calpain inhibition following spinal cord injury. Contusive spinal cord injury was produced in female Long-Evans rats using the NYU impactor at the 12.5-25-mm height setting. The results demonstrate that intravenous administration of 1 mg/kg E-64-D or 250 micro g/kg calpeptin does not inhibit total calpain activity in the rat spinal cord, measured using a BODIPY-FL labeled casein assay. Intravenous administration of MDL28170 (20 mg/kg) resulted in mild calpain inhibition and a modest decrease in the proteolysis of calpain substrates alpha-spectrin and MAP2. Intraspinal microinjection of 50 nmoles/19 micro g MDL28170, either 30 min prior to or 20 min following contusion injury, resulted in a more robust inhibition of total calpain activity and greater attenuation of alpha-spectrin breakdown and MAP2 proteolysis. The decreased proteolysis persisted 24 h postinjury. Together, the results demonstrate that direct microinjection of the calpain inhibitor MDL28170 is more effective than intravenous infusion in reducing calpain activity and decreasing the injury-induced proteolysis of calpain substrates.

Calpain-dependent neurofilament breakdown in anoxic and ischemic rat central axons

Neurofilaments are key structural components of white matter axons. The effect of in vitro anoxia or oxygen-glucose deprivation (OGD) on the integrity of the 160 and 200 kDa neurofilament isoforms was studied by immunoblot, and correlated with physiological function. Adult rat optic nerves were exposed to 60 min of either anoxia or OGD. Compound action potential area recovered to 22+/-6% of control after 60 min of anoxia, and to 4+/-1% after 60 min of OGD. Ca(2+)-free (+EGTA) perfusate allowed complete recovery after OGD (108+/-42%). Tetrodotoxin (TTX, 1 microM) was less protective (45+/-6%). Both anoxia and OGD induced breakdown of neurofilament 160 (NF160) and NF200 revealed by the appearance of multiple lower molecular weight bands mainly in the 75-100 kDa range. Zero-Ca(2+)/EGTA completely prevented NF breakdown. TTX only partially reduced NF160 degradation. Non-phosphorylated NF200 appeared after reperfusion post-anoxia or OGD, and was also greatly reduced by zero-Ca(2+) or TTX. Calpain inhibitors (10 microM calpain inhibitor I or 50 microM MDL 28,170) significantly reduced NF160 and NF200 breakdown/dephosphorylation, but did not improve electrophysiological recovery. Significant calpain-mediated breakdown of NF160 and NF200 indicates structural damage to the axonal cytoskeleton, which was completely Ca(2+)-dependent. While pharmacological inhibition of calpain alone greatly reduced NF proteolysis, there was no concomitant improvement in function. These results imply that calpain inhibition is necessary but not sufficient for white matter protection, and emphasize the existence of multiple Ca(2+)-dependent degradative pathways activated in injured white matter.

Brain-derived neurotrophic factor suppresses delayed apoptosis of oligodendrocytes after spinal cord injury in rats

We evaluated the effect of brain-derived neurotrophic factor (BDNF) on cell death after spinal cord injury. A rat spinal cord injury model was produced by static load, and continuous intrathecal BDNF or vehicle infusion was carried out either immediately or 3 days after the injury. Cell death was examined by nuclear staining and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). After injury, typical apoptotic cells were observed. Double staining with TUNEL and specific cell markers revealed that, soon after the injury, the apoptotic or necrotic cells at the injury site were neurons and microglia. One week after the injury, apoptotic oligodendrocytes, but not apoptotic astrocytes, were observed in the white matter rostral and caudal to the injury site, whereas few apoptotic cells were found in the gray matter. The immediate BDNF treatment significantly reduced the number of TUNEL-positive cells in the adjacent rostral site 1 and 2 weeks after the injury, and in the adjacent caudal site 3 days and 1 week after the injury, even though there was no significant difference between BDNF-treated and control rats at the injury site itself. In addition, similar antiapoptotic effects were observed in these regions 1 week after injury in rats that received BDNF treatment from the third day after injury. These findings suggest that BDNF suppresses delayed apoptosis of oligodendrocytes after spinal cord injury, for which even delayed injections are effective. BDNF administration may therefore be useful for the clinical treatment of spinal cord injury through the suppression of secondary events.

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.

Cell death in spinal cord injury (SCI) requires de novo protein synthesis. Calpain inhibitor E-64-d provides neuroprotection in SCI lesion and penumbra

Degradation of cytoskeletal proteins by calpain, a Ca(2+)-dependent cysteine protease, may promote neuronal apoptosis in the lesion and surrounding areas following spinal cord injury (SCI). Clinically relevant moderate (40 g-cm force) SCI in rats was induced at T12 by a standardized weight-drop method. Internucleosomal DNA fragmentation or apoptosis in the lesion was inhibited by 24-h treatment of SCI rats with cycloheximide (1 mg/kg), indicating a requirement for de novo protein synthesis in this process. To prove an involvement of calpain activity in mediation of apoptosis in SCI, we treated SCI rats with a cell-permeable calpain inhibitor E-64-d (1 mg/kg). Following 24-h treatment, a 5-cm-long spinal cord section centered at the lesion was collected, and divided equally into five segments (1 cm each) to determine calpain activity, as shown by degradation of the 68-kD neurofilament protein (NFP), and apoptosis as indicated by internucleosomal DNA fragmentation. Neurodegeneration propagated from the site of injury to neighboring rostral and caudal regions. Both calpain activity and apoptosis were readily detectable in the lesion, and moderately so in neighboring areas of untreated SCI rats, whereas these were almost undetectable in E-64-d-treated SCI rats, and absent in sham animals. Results indicate that apoptosis in the SCI lesion and penumbra is prominently associated with calpain activity and is inhibited by the calpain inhibitor E-64-d providing neuroprotective benefit.