Calpain activation and alpha-spectrin cleavage in rat brain by ethanol

Glutamate-Mediated Excitotoxicity in the Pathogenesis and Treatment of Neurodevelopmental and Adult Mental Disorders

Glutamate is the main excitatory neurotransmitter in the brain wherein it controls cognitive functional domains and mood. Indeed, brain areas involved in memory formation and consolidation as well as in fear and emotional processing, such as the hippocampus, prefrontal cortex, and amygdala, are predominantly glutamatergic. To ensure the physiological activity of the brain, glutamatergic transmission is finely tuned at synaptic sites. Disruption of the mechanisms responsible for glutamate homeostasis may result in the accumulation of excessive glutamate levels, which in turn leads to increased calcium levels, mitochondrial abnormalities, oxidative stress, and eventually cell atrophy and death. This condition is known as glutamate-induced excitotoxicity and is considered as a pathogenic mechanism in several diseases of the central nervous system, including neurodevelopmental, substance abuse, and psychiatric disorders. On the other hand, these disorders share neuroplasticity impairments in glutamatergic brain areas, which are accompanied by structural remodeling of glutamatergic neurons. In the current narrative review, we will summarize the role of glutamate-induced excitotoxicity in both the pathophysiology and therapeutic interventions of neurodevelopmental and adult mental diseases with a focus on autism spectrum disorders, substance abuse, and psychiatric disorders. Indeed, glutamatergic drugs are under preclinical and clinical development for the treatment of different mental diseases that share glutamatergic neuroplasticity dysfunctions. Although clinical evidence is still limited and more studies are required, the regulation of glutamate homeostasis is attracting attention as a potential crucial target for the control of brain diseases.

Genetic impairment of succinate metabolism disrupts bioenergetic sensing in adrenal neuroendocrine cancer

Metabolic dysfunction mutations can impair energy sensing and cause cancer. Loss of function of the mitochondrial tricarboxylic acid (TCA) cycle enzyme subunit succinate dehydrogenase B (SDHB) results in various forms of cancer typified by pheochromocytoma (PC). Here we delineate a signaling cascade where the loss of SDHB induces the Warburg effect, triggers dysregulation of [Ca²⁺]_i, and aberrantly activates calpain and protein kinase Cdk5, through conversion of its cofactor from p35 to p25. Consequently, aberrant Cdk5 initiates a phospho-signaling cascade where GSK3 inhibition inactivates energy sensing by AMP kinase through dephosphorylation of the AMP kinase γ subunit, PRKAG2. Overexpression of p25-GFP in mouse adrenal chromaffin cells also elicits this phosphorylation signaling and causes PC. A potent Cdk5 inhibitor, MRT3-007, reverses this phospho-cascade, invoking a senescence-like phenotype. This therapeutic approach halted tumor progression in vivo. Thus, we reveal an important mechanistic feature of metabolic sensing and demonstrate that its dysregulation underlies tumor progression in PC and likely other cancers.

Polysaccharides from Polygonatum cyrtonema Hua Reduce Depression-Like Behavior in Mice by Inhibiting Oxidative Stress-Calpain-1-NLRP3 Signaling Axis

Polysaccharides from Polygonatum cyrtonema Hua (PSP) exert antioxidant, anti-inflammatory, and antidepressant effects. Production of reactive oxygen species (ROS) and activation of the calpain system and the NOD-like receptor protein 3 (NLRP3) inflammasome are closely related to the pathogenesis of depression. However, the relationships among those pathways and the protective effects of PSP have not been characterized. In this study, lipopolysaccharide (LPS) and chronic unpredictable mild stress- (CUMS-) induced depression models were used to evaluate the protective mechanisms of PSP against depression. ROS levels were measured in HT-22 cells using flow cytometry. Brain tissues were collected to determine the levels of oxidation-related indicators and inflammatory cytokines. The protein levels of calpain-1, calpain-2, calpastatin, phosphatase and Tensin Homolog deleted on Chromosome 10 (PTEN), suprachiasmatic nucleus circadian oscillatory protein (SCOP), nuclear factor-erythroid factor 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), NLRP3, apoptosis-associated speck-like protein (ASC), caspase-1, cleaved-caspase-1, ionized calcium binding adapter molecule 1 (Iba1), phosphorylation of extracellular signal-regulated kinase (p-ERK), nuclear factor-kappa B (NF-κB), interleukin-1β (IL-1β), and glial fibrillary acidic protein (GFAP) were measured using western blotting or immunofluorescence. In cellular experiments, we showed that PSP attenuated LPS-induced production of ROS in HT-22 cells. In animal experiments, we found that LPS increased the expression of calpain-1, NLRP3, ASC, caspase-1, cleaved-caspase-1, Iba1, p-ERK, NF-κB, and GFAP and reduced the expression of calpastatin, PTEN, SCOP, and Nrf2. Administration of PSP reversed these changes. N-Acetyl-L-cysteine (NAC) administration also inhibited oxidative stress and activation of the calpain system and the NLRP3 inflammasome. Furthermore, PSP, calpeptin, MCC950 (a selective NLRP3 inflammasome inhibitor), and NAC reduced LPS-induced proinflammatory cytokine release. We also showed that PSP prevented CUMS-induced changes in the calpain system and the Nrf2 and NLRP3 signaling pathways and reduced depression-like behavior. These results indicate that PSP exerts antidepressant effects through regulation of the oxidative stress-calpain-1-NLRP3 signaling axis.

A genetic screen for Drosophila social isolation mutants and analysis of sex pistol

Prolonged periods of forced social isolation is detrimental to well-being, yet we know little about which genes regulate susceptibility to its effects. In the fruit fly, Drosophila melanogaster, social isolation induces stark changes in behavior including increased aggression, locomotor activity, and resistance to ethanol sedation. To identify genes regulating sensitivity to isolation, I screened a collection of sixteen hundred P-element insertion lines for mutants with abnormal levels of all three isolation-induced behaviors. The screen identified three mutants whose affected genes are likely central to regulating the effects of isolation in flies. One mutant, sex pistol (sxp), became extremely aggressive and resistant to ethanol sedation when socially isolated. sxp also had a high level of male–male courtship. The mutation in sxp reduced the expression of two minor isoforms of the actin regulator hts (adducin), as well as mildly reducing expression of CalpA, a calcium-dependent protease. As a consequence, sxp also had increased expression of the insulin-like peptide, dILP5. Analysis of the social behavior of sxp suggests that these minor hts isoforms function to limit isolation-induced aggression, while chronically high levels of dILP5 increase male–male courtship.

Alcohol Use Disorder, Neurodegeneration, Alzheimer's and Parkinson's Disease: Interplay Between Oxidative Stress, Neuroimmune Response and Excitotoxicity

Alcohol use disorder (AUD) has been associated with neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Prolonged excessive alcohol intake contributes to increased production of reactive oxygen species that triggers neuroimmune response and cellular apoptosis and necrosis via lipid peroxidation, mitochondrial, protein or DNA damage. Long term binge alcohol consumption also upregulates glutamate receptors, glucocorticoids and reduces reuptake of glutamate in the central nervous system, resulting in glutamate excitotoxicity, and eventually mitochondrial injury and cell death. In this review, we delineate the following principles in alcohol-induced neurodegeneration: (1) alcohol-induced oxidative stress, (2) neuroimmune response toward increased oxidants and lipopolysaccharide, (3) glutamate excitotoxicity and cell injury, and (4) interplay between oxidative stress, neuroimmune response and excitotoxicity leading to neurodegeneration and (5) potential chronic alcohol intake-induced development of neurodegenerative diseases, including Alzheimer's and Parkinson's disease.

Voluntary alcohol consumption exacerbated high fat diet-induced cognitive deficits by NF-κB-calpain dependent apoptotic cell death in rat hippocampus: Ameliorative effect of melatonin

Modern sedentary lifestyle with altered dietary habits imposes the risk of human health towards several metabolic disorders such as obesity. The metabolic insults negatively affect the mental health status and quality life of affected individuals. Melatonin is a potent antioxidant with anti-inflammatory and neuroprotective properties. The aim of the present study was to investigate the protective effect of melatonin on the cognitive and neurochemical deficits induced by the high-fat diet (HFD) and alcohol (ALC) alone or in combination (HFD + ALC) in rats. Male Wistar rats were given ALC (3-15% i.e. increased gradually) and HFD for 12 weeks in different experimental groups. After 12 weeks, we found that simultaneous consumption of HFD and ALC exacerbates cognitive dysfunction and neurochemical anomalies. However, melatonin (10 mg/kg/day, i.p.) treatment for four weeks significantly prevented memory deficits, oxidative stress and neuroinflammation in HFD, ALC and HFD + ALC groups. RT-PCR analysis showed down-regulation of nuclear factor erythroid 2-related factor 2 (Nrf-2) and heme oxygenase-1 (HO-1) in ALC and HFD + ALC groups. Moreover, caspase-3 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) mRNA expression level were found up-regulated in hippocampus of HFD, ALC and HFD + ALC groups. However, calpain expression was found up-regulated only in the hippocampus of HFD + ALC group. Chronic treatment with melatonin significantly restored the aberrant gene expression level in HFD, ALC and HFD + ALC group. In conclusion, our findings indicated that melatonin can mitigate the HFD and ALC-induced cognitive deficits via attenuation of oxidative stress and calpain-1 dependent as well as independent caspase-3 mediated neuronal cell death.

Prenatal alcohol-induced neuroapoptosis in rat brain cerebral cortex: protective effect of folic acid and betaine

PURPOSE

Alcohol consumption in pregnancy may cause fetal alcohol syndrome (FAS) in the infant. This study aims to investigate prenatal alcohol exposure related neuroapoptosis on the cerebral cortex tissues of newborn rats and possible neuroprotective effects of betaine, folic acid, and combined therapy.

METHODS

Pregnant rats were divided into five experimental groups: control, ethanol, ethanol + betaine, ethanol + folic acid, and ethanol + betaine + folic acid combined therapy groups. We measured cytochrome c release, caspase-3, calpain and cathepsin B and L. enzyme activities. In order to observe apoptotic cells in the early stages, TUNEL method was chosen together with histologic methods such as assessing the diameters of the apoptotic cells, their distribution in unit volume and volume proportion of cortical intact neuron nuclei.

RESULTS

Calpain, caspase-3 activities, and cytochrome c levels were significantly increased in alcohol group while cathepsin B and L. activities were also found to be elevated albeit not statistically significant. These increases were significantly reversed by folic acid and betaine + folic acid treatments. While ethanol increased the number of apoptotic cells, this increase was prevented in ethanol + betaine and ethanol + betaine + folic acid groups. Morphometric examination showed that the mean diameter of apoptotic cells was increased with ethanol administration while this increase was reduced by betaine and betaine + folic acid treatments.

CONCLUSION

We observed that ethanol is capable of triggering apoptotic cell death in the newborn rat brains. Furthermore, folic acid, betaine, and combined therapy of these supplements may reduce neuroapoptosis related to prenatal alcohol consumption, and might be effective on preventing fetal alcohol syndrome in infants.

The Calpain Inhibitor A-705253 Attenuates Alcohol-Seeking and Relapse with Low Side-Effect Profile

Preclinical studies revealed contribution of N-methyl-D-aspartate receptors (NMDARs) to a variety of neuropsychiatric diseases including alcoholism, but development of NMDAR antagonists for therapeutic use has been a challenge, in part due to severe side effects. One of the key intracellular events resulting from stimulation of NMDAR is activation of calpains-calcium-dependent cysteine proteases. Here we studied whether inhibition of calpains would produce therapeutic-like effects of NMDAR antagonists but without their NMDAR-mediated side-effect profile. The calpain inhibitor A-705253 (3-10 mg/kg) was tested in a model of cue-induced reinstatement of alcohol-seeking behavior in post-dependent Wistar rats and in an alcohol deprivation effect (ADE) model in long-term alcohol drinking Wistar rats, two behavioral models for alcohol-seeking and relapse, respectively. We also tested the effect of A-705253 on the saccharine deprivation effect (SDE) as a selectivity measure. Acute treatment with A-705253 dose-dependently reduced cue-induced reinstatement of alcohol-seeking behavior. Repeated administration of A-705253 caused significant reductions of relapse-like excessive alcohol intake during the post-abstinence drinking days, an effect that persisted during two more successive drug-free drinking weeks, which was selective for the ADE as the SDE was unaffected. However, A-705253 did not produce psychostimulant, cognition impairing (delayed-matching-to-position), or psychotomimetic effects (specifically, phencyclidine discriminative stimulus effects). Taken together, these results demonstrate the involvement of calpains in alcohol-seeking and relapse and present a rationale for a novel pharmacological intervention that may reduce craving and relapse with minimal side effects in alcohol-dependent patients.

The investigation of the prenatal and postnatal alcohol exposure-induced neurodegeneration in rat brain: protection by betaine and/or omega-3

PURPOSE

We aim to study the effect of neurodegeneration on the brain of rat pups caused by prenatal and postnatal ethanol exposure with modified liquid diet to elucidate protective effects of betaine and omega-3 supplementation. When ethanol is consumed during prenatal and postnatal periods, it may result in fetal alcohol syndrome (FAS) in the offspring.

METHODS

Rats were divided into control, ethanol, ethanol + betaine, ethanol + omega-3, ethanol + omega-3 + betaine groups. The effect of betaine and omega-3 in response to ethanol-induced changes on the brain, by biochemical analyses cytochrome c, caspase-3, calpain, cathepsin B and L, DNA fragmentation, histological and morfometric methods were evaluated.

RESULTS

Caspase-3, calpain, cathepsin B, and cytochrome c levels in ethanol group were significantly higher than control. Caspase-3, calpain levels were decreased in ethanol + betaine, ethanol + omega-3, and ethanol + omega-3 + betaine groups compared to ethanol group. Cathepsin B in ethanol + omega-3 + betaine group was decreased compared to ethanol, ethanol + betaine groups. Cathepsin L and DNA fragmentation were found not statistically significant. We found similar results in histological and morfometric parameters.

CONCLUSION

We found that pre- and postnatal ethanol exposure is capable of triggering necrotic cell death in rat brains, omega-3, and betaine reduce neurodegeneration. Omega-3 and betaine may prove beneficial for neurodegeneration, particularly in preventing FAS.

Calpain inhibition prevents ethanol-induced alterations in spinal motoneurons

Long-term exposure of ethanol (EtOH) alters the structure and function in brain and spinal cord. The present study addresses the mechanisms of EtOH-induced damaging effects on spinal motoneurons in vitro. Altered morphology and biochemical changes of such damage were demonstrated by in situ Wright staining and DNA ladder assay. EtOH at low to moderate (25-50 mM) concentrations induced damaging effects in the motoneuronal scaffold which involved activation of proteases like μ-calpain and caspase-3. Caspase-8 was seen only at higher (100 mM) EtOH concentration. Further, pretreatment with calpeptin, a potent calpain inhibitor, confirmed the involvement of active proteases in EtOH-induced damage to motoneurons. The lysosomal enzyme cathepsin D was also elevated in the motoneurons by EtOH, and this effect was significantly attenuated by inhibitor treatment. Overall, EtOH exposure rendered spinal motoneurons vulnerable to damage, and calpeptin provided protection, suggesting a critical role of calpain activation in EtOH-induced alterations in spinal motoneurons.

Cardiomyocyte ryanodine receptor degradation by chaperone-mediated autophagy

AIMS

Chaperone-mediated autophagy (CMA) is a selective mechanism for the degradation of soluble cytosolic proteins bearing the sequence KFERQ. These proteins are targeted by chaperones and delivered to lysosomes where they are translocated into the lysosomal lumen and degraded via the lysosome-associated membrane protein type 2A (LAMP-2A). Mutations in LAMP2 that inhibit autophagy result in Danon disease characterized by hypertrophic cardiomyopathy. The ryanodine receptor type 2 (RyR2) plays a key role in cardiomyocyte excitation-contraction and its dysfunction can lead to cardiac failure. Whether RyR2 is degraded by CMA is unknown.

METHODS AND RESULTS

To induce CMA, cultured neonatal rat cardiomyocytes were treated with geldanamycin (GA) to promote protein degradation through this pathway. GA increased LAMP-2A levels together with its redistribution and colocalization with Hsc70 in the perinuclear region, changes indicative of CMA activation. The inhibition of lysosomes but not proteasomes prevented the loss of RyR2. The recovery of RyR2 content after incubation with GA by siRNA targeting LAMP-2A suggests that RyR2 is degraded via CMA. In silico analysis also revealed that the RyR2 sequence harbours six KFERQ motifs which are required for the recognition Hsc70 and its degradation via CMA. Our data suggest that presenilins are involved in RyR2 degradation by CMA.

CONCLUSION

These findings are consistent with a model in which oxidative damage of the RyR2 targets it for turnover by presenilins and CMA, which could lead to removal of damaged or leaky RyR2 channels.

Allopregnanolone prevents dieldrin-induced NMDA receptor internalization and neurotoxicity by preserving GABA(A) receptor function

Dieldrin is an endocrine disruptor that accumulates in mammalian adipose tissue and brain. It induces convulsions due to its antagonism of the γ-aminobutyric acid A receptor (GABA(A)R). We have previously reported that long-term exposure to dieldrin causes the internalization of the N-methyl-D-aspartate receptor (NMDAR) as a result of persistent GABA(A)R inhibition. Because the neurosteroids 17β-estradiol (E2) and allopregnanolone are known to modulate the function and trafficking of GABA(A)R and NMDAR, we examined the effects of E2 and allopregnanolone on dieldrin-induced GABA(A)R inhibition, NMDAR internalization, and neuronal death in cortical neurons. We found that 1 nM E2 increased the membrane expression of NR1/NR2B receptors and postsynaptic density 95 but did not induce their physical association. In contrast, 10 nM E2 had no effect on these proteins but reduced NR2A membrane expression. We also found that exposure to 60 nM dieldrin for 6 d in vitro caused the internalization of NR1 and NR2B but not NR2A. Treatment with either 1 nM E2 or 10 μM allopregnanolone prevented the dieldrin-induced reduction in membrane levels of the NR1/NR2B receptors. Furthermore, prolonged exposure to 200 nM dieldrin down-regulated the expression of NR2A; this was inhibited only by allopregnanolone. Although both hormones restored NMDAR function, as measured by the NMDA-induced rise in intracellular calcium, allopregnanolone (but not E2) reversed the inhibition of GABA(A)R and neuronal death caused by prolonged exposure to dieldrin. Our results indicate that allopregnanolone protects cortical neurons against the neurotoxicity caused by long-term exposure to dieldrin by maintaining GABA(A)R and NMDAR functionality.

Calcium-activated calpain-2 is a mediator of beta cell dysfunction and apoptosis in type 2 diabetes

The islet in type 2 diabetes (T2DM) and the brain in neurodegenerative diseases share progressive cell dysfunction, increased apoptosis, and accumulation of locally expressed amyloidogenic proteins (islet amyloid polypeptide (IAPP) in T2DM). Excessive activation of the Ca(2+)-sensitive protease calpain-2 has been implicated as a mediator of oligomer-induced cell death and dysfunction in neurodegenerative diseases. To establish if human IAPP toxicity is mediated by a comparable mechanism, we overexpressed human IAPP in rat insulinoma cells and freshly isolated human islets. Pancreas was also obtained at autopsy from humans with T2DM and nondiabetic controls. We report that overexpression of human IAPP leads to the formation of toxic oligomers and increases beta cell apoptosis mediated by increased cytosolic Ca(2+) and hyperactivation of calpain-2. Cleavage of alpha-spectrin, a marker of calpain hyperactivation, is increased in beta cells in T2DM. We conclude that overactivation of Ca(2+)-calpain pathways contributes to beta cell dysfunction and apoptosis in T2DM.

Role of caspases, calpain and cdk5 in ammonia-induced cell death in developing brain cells

Hyperammonemia in neonates and infants causes irreversible damages in the developing CNS due to brain cell loss. Elucidating the mechanisms triggering ammonia-induced cell death in CNS is necessary for the development of neuroprotective strategies. We used reaggregated developing brain cell cultures derived from fetal rat telencephalon exposed to ammonia as an experimental model. Ammonia induced neuronal and oligodendroglial death, triggered apoptosis and activated caspases and calpain. Probably due to calpain activation, ammonia caused the cleavage of the cyclin-dependent kinase 5 activator, p35, to p25, the cdk5/p25 complex being known to lead to neurodegeneration. Roscovitine, a cdk5 inhibitor, protected neurons from ammonia-induced cell death. However, roscovitine also impaired axonal growth, probably through inhibition of the remaining cdk5/p35 activity, which is involved in neurite outgrowth. Thus, cdk5 appears as a promising therapeutic target for treating hyperammonemic newborns and infants, especially if one develops specific cdk5/p25 inhibitors.

Abnormal expression of truncated CRMP-1 protein in the brain cortex of MPSIIIB mice

Mucopolysaccharidosis IIIB is a lysosomal disease characterized by a severe neurological deterioration, the pathophysiological mechanisms of which are poorly understood. Recently FGF pathway was shown to be altered leading us to explore a downstream target involved in brain development: the collapsin response mediator protein-1 (CRMP-1). CRMP-1 transcript level was normal but a cleavage of CRMP-1 was observed with an abnormal expression of the truncated form until adult age. This truncated CRMP-1 protein could play a role in post-natal cortex maturation and be involved in neuronal alterations occurring in lysosomal diseases.

Cell death is associated with reduced base excision repair during chronic alcohol administration in adult rat brain

The cell death cascades in different brain regions namely hippocampus and frontal cortex of rats fed with 10% (v/v) ethanol for 12 weeks, was examined. After Western blotting, different cell death associated proteins displayed differential activation in the two regions observed. In hippocampus, activated caspase-3 and caspase-7 resulted in subsequent cleavage of poly(ADP-ribose) polymerase-1 (PARP-1). Cytochrome c release to cytosol and apoptosis inducing factor (AIF) translocation to nucleus was marginal. B-cell leukemia/lymphoma-2 (Bcl-2) translocation to cytosol was significant whereas Bcl-2-associated X protein (Bax) and Bcl-associated death protein (Bad) were largely located in cytosol. Further, upregulation of N-methyl D-aspartate receptor subunit 1 (NMDAR1), N-methyl D-aspartate receptor subunit 2B (NMDAR2B), N-methyl D-aspartate receptor subunit 2C (NMDAR2C) and activation of calpains were observed. In frontal cortex, caspase-3 activation, cleavage of PARP-1 and nuclear translocation of AIF were more pronounced. Moreover, cytochrome c release to cytosol, Bcl-2 translocation to cytosol was evident. However, levels of Bax, Bad, NMDA receptor subunits, and calpains were unaffected. Apoptosis was further substantiated by in situ staining for terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL). Results of the current study revealed that frontal cortex exhibits a higher level of ethanol-induced apoptosis relative to hippocampus. DNA polymerase beta assay and immunoblot showed significant loss in base excision repair in ethanol treated group.

Ketamine exposure in adult mice leads to increased cell death in C3H, DBA2 and FVB inbred mouse strains

BACKGROUND

Drug abuse is common among adolescents and young adults. Although the consequences of intoxication are known, sequelae of drugs emerging on campuses and in clubs nationwide are not. We previously demonstrated that ketamine exposure results in lasting physiological abnormalities in mice. However, the extent to which these deficits reflect neuropathologic changes is not known.

METHODS

The current study examines neuropathologic changes following sub-anesthetic ketamine administration (5mg/kg i.p. x 5) to three inbred mouse strains. Stereologic quantification of silver stained nuclear and linear profiles as well as activated caspase-3 labeling was used to address: (1) whether or not ketamine increases excitotoxic and apoptotic cell death in hippocampal CA3 and (2) whether or not ketamine-induced cell death varies by genetic background.

RESULTS

Ketamine increased cell death in hippocampal CA3 of adult C3H, DBA2 and FVB mice. Neither silver staining nor activated caspase-3 labeling varied by strain, nor was there an interaction between ketamine-induced cell death and strain.

CONCLUSIONS

Ketamine exposure among young adults, even in limited amounts, may lead to irreversible changes in both brain function and structure. Loss of CA3 hippocampal cells may underlie persistent ERP changes previously shown in mice and possibly contribute to lasting cognitive deficits among ketamine abusers.

A novel dual inhibitor of calpains and lipid peroxidation (BN82270) rescues the cochlea from sound trauma

Free radical and calcium buffering mechanisms are implicated in cochlear cell damage that has been induced by sound trauma. Thus in this study we evaluated the therapeutic effect of a novel dual inhibitor of calpains and of lipid peroxidation (BN 82270) on the permanent hearing and hair cell loss induced by sound trauma. Perfusion of BN 82270 into the scala tympani of the guinea pig cochlea prevented the formation of calpain-cleaved fodrin, translocation of cytochrome c, DNA fragmentation and hair cell degeneration caused by sound trauma. This was confirmed by functional tests in vivo, showing a clear dose-dependent reduction of permanent hearing loss (ED50 = 4.07 microM) with almost complete protection at 100 microM. Furthermore, BN82270 still remained effective even when applied onto the round window membrane after sound trauma had occurred, within a therapeutic window of 24 h. This indicates that BN 82270 may be of potential therapeutic value in treating the cochlea after sound trauma.

Activation of calpains, calpastatin and spectrin cleavage in the brain during the pathology of fatal murine cerebral malaria

Neuronal calpains appear to be activated uncontrollably by sustained elevation of cytosolic calcium levels under pathological conditions as well as neurodegenerative diseases. In the present study, we have characterized calpain activation in cytosolic extract of mice cerebral cortex and cerebellum using an experimental model of fatal murine cerebral malaria (FMCM). Pathology of FMCM resulted in the increase in activity of calpains in both cerebral cortex and cerebellum. Western blot analysis revealed an increase in the levels of mu-calpain (calpain-1) in the cytosolic fraction of infected cerebral cortex and cerebellum although a decrease in the level of m-calpain was observed in the cytosolic fraction of infected cerebellum and cerebral cortex. Calpain activation was further confirmed by monitoring the formation of calpain-specific spectrin breakdown products (SBDP). Protease-specific SBDP revealed the formation of calpain-generated 150kDa product in the infected cerebral cortex and cerebellum. The specific signature fragment of calpain activation and spectrin breakdown after Plasmodium berghei ANKA infection provide a strong evidence of the role of calpains during the cell death in cerebral cortex and cerebellum. Given the role of calpains in neurodegeneration and cell death, our results strongly suggest that calpains are important mediators of cell injury and neurological sequelae associated with FMCM.

Calpain-mediated truncation of dihydropyrimidinase-like 3 protein (DPYSL3) in response to NMDA and H2O2 toxicity

Dihydropyrimidinase-like protein 3 (DPYSL3), a member of TUC (TOAD-64/Ulip/CRMP), is believed to play a role in neuronal differentiation, axonal outgrowth and, possibly, neuronal regeneration. In primary cortical cultures, glutamate (NMDA) excitotoxicity and oxidative stress (H2O2) caused the cleavage of DPYSL3, resulting in the appearance of a doublet of 62 kDa and 60 kDa. Pre-treatment of cell cultures with calpain inhibitors, but not caspase 3 inhibitor, before exposure to NMDA or H2O2 completely blocked the appearance of the doublet, suggesting calpain-mediated truncation. Furthermore, in vitro digestion of DPYSL3 in cell lysate with purified calpain revealed a cleavage product identical to that observed in NMDA- and H2O2-treated cells, and its appearance was blocked by calpain inhibitors. Analysis of the DPYSL3 protein sequence revealed a possible cleavage site for calpain (Val-Arg-Ser) on the C-terminus of DPYSL3. Collectively, these studies demonstrate for the first time that DPYSL3 is a calpain substrate. The physiological relevance of the truncated DPYSL3 protein remains to be determined.

N-methyl-D-aspartate receptor subtypes: multiple roles in excitotoxicity and neurological disease

N-methyl-D-aspartate (NMDA) receptors are the major mediator of excitotoxicity. Although physiological activation of the NMDA receptor is necessary for cell survival, overactivation is a signal for cell death. Several pathways are activated through NMDA receptor stimulation, most of which can contribute to excitotoxicity. These include events leading to mitochondrial dysfunction, activation of calcium-dependent enzymes, and activation of mitogen-activated protein kinase pathways. Understanding the role of these mechanisms is important in developing agents that block excitotoxicity without inhibiting functions necessary for survival. NMDA receptor subtypes may be responsible for mediating separate pathways, and subtype-specific inhibition has shown promising results in some neurological models. This review examines the roles of NMDA receptor subtypes in excitotoxicity and neurological disorders.

Calpain activity in the amikacin-damaged rat cochlea

The principal aim of this study was to investigate the involvement of calpain in the degeneration of hair cells and ganglion neurons in the amikacin-poisoned rat cochlea. An antibody designed against fodrin-breakdown products (FBDP), which result exclusively from cleavage by calpain, was used. In addition, the involvement of both caspases and protein kinase C (PKC) was studied using, respectively, antibodies against activated caspase 3 and PKCgamma. The results demonstrate the accumulation of FBDP in the degenerating hair cells, in some supporting cells such as Deiters cells, and, later, in the affected ganglion neurons that had been deprived of their sensory targets. Activated caspase 3 was evidenced in a few dying hair cells and ganglion neurons. PKCgamma was highly expressed in all ganglion neurons, sometimes after the loss of hair cells. We conclude that calpain plays a role in the degradation of both the sensory cells and neurons after amikacin ototoxicity. In the poisoned hair cells, calpain and caspase 3 may have synergistic effects in the process of apoptosis. In the ganglion neurons deprived of their sensory elements, calpain may have a prominent role in cell degradation. By contrast, in these ganglion neurons PKCgamma may be implicated in a survival process. Finally, we suggest that calpain is involved in the remodeling of Deiters cells during the scarring process that follows hair cell loss.

Dysregulation of the calpain-calpastatin system plays a role in the development of cerulein-induced acute pancreatitis in the rat

Calpain, a calcium-dependent cytosolic cysteine protease, is implicated in a multitude of cellular functions but also plays a role in cell death. Recently, we have shown that two ubiquitous isoforms, termed micro-calpain and m-calpain, are expressed in rat pancreatic acinar cells and that calcium ionophore-induced calpain activation leads to acinar cell injury. On the basis of these observations, we have now investigated the role of both calpain forms and the endogenous calpain inhibitor calpastatin in acute pancreatitis. After treatment of rats either without or with calpain inhibitor Z-Val-Phe methyl ester (ZVP; 60 mg/kg i.p.), pancreatitis was induced by cerulein injections (10 microg/kg i.p.; 5 times at hourly intervals). Calpain activation and calpastatin expression in the pancreatic tissue were studied by Western blot analysis. Pancreatic injury was assessed by plasma amylase activity, pancreatic wet/dry weight ratio (edema), histological and electron-microscopic analyses, as well as fluorescence labeling of actin filaments. Cerulein caused an activation of both micro-calpain and m-calpain, accompanied by degradation of calpastatin. Prophylactic administration of ZVP reduced the cerulein-induced calpain activation but had no effect on calpastatin alterations. In correlation to the diminished calpain activity, the severity of pancreatitis decreased as indicated by a decline in amylase activity (P < 0.01), pancreatic edema formation (P < 0.05), histological score for eight parameters (P < 0.01), and actin filament alterations. Our findings support the hypothesis that dysregulation of the calpain-calpastatin system may play a role in the onset of acute pancreatitis.

Caspase-3 and calpain activities after acute and repeated ethanol administration during the rat brain growth spurt

Ethanol administration during the rat brain growth spurt triggers apoptotic neurodegeneration that appears to be mediated by caspase-3 activation. In order to gain more insight on the role of this caspase in ethanol-induced developmental neurotoxicity, we studied its expression and activity under different conditions of ethanol exposure during development. Furthermore, because of the cross-talk between caspase-3 and calpain we extended our study also at this protease. Ethanol was administered by gavage to rat pups as a single-day exposure on postnatal day (PN) 7 or from PN4 to PN10. Cleaved caspase-3 expression peaked in the cerebral cortex 12 h after ethanol treatment and returned to control values at 24 h. An identical pattern was found for caspase-3-like activity, that was increased only with the highest dose of ethanol tested (5 g/kg) and mostly in PN4. Repeated ethanol exposure, at a dose that was previously found to induce microencephaly, did not increase caspase-3 expression and activity although it decreased procaspase-3 expression and released mitochondrial cytochrome c. Repeated ethanol administration also increased calpain activity. These data show that acute and repeated ethanol administration differentially affect caspase-3 and calpain activity, suggesting that calpain activation may play a role in developmental neurotoxicity of ethanol.

Ethanol-induced alteration in N-methyl-D-aspartate receptor 2A C-terminus and protein kinase C activity in rat brain

Ethanol is a potent inhibitor of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. In the present study, expression of NR2A and its phosphorylation status were investigated in adult rat cerebral cortex and cerebellum, using an experimental paradigm of in vivo chronic ethanol exposure. In addition, PKC activity was measured in both cytosol and membrane fraction of cerebral cortex and cerebellum using Histone III S as substrate. Western blot analysis using NR2A antibody showed an increased immunoreactivity in cerebral cortex and no immunoreactivity in cerebellum of alcohol-treated rats. Furthermore, PKC activity was increased in both membrane and cytosolic fraction of alcohol-treated rat cerebellum, whereas PKC activity in cerebral cortex was found to be decreased in membrane fraction with no appreciable change in cytosolic fraction. In vitro phosphorylation study showed hypophosphorylation in ethanol-treated cerebral cortex and cerebellum. Our current findings imply that the truncation of NR2A subunit upon alcohol administration in cerebellum probably contributes to altered NMDA receptor function and cerebellar atrophy and motor incoordination in alcoholic rats.

CaM kinase II-alpha activity, levels and Ca/calmodulin dependent phosphorylation of substrate proteins in mice brain during fatal murine cerebral malaria

The activity and levels of CaM kinase II-alpha was investigated in the cytosolic and membrane fraction of mice cerebral cortex and cerebellum using an experimental model of fatal murine cerebral malaria (FMCM). In parallel, Ca(2+)/Calmodulin dependent phosphorylation of target substrate proteins was studied using syntide-2 as substrate. Pathology of FMCM resulted in decreased CaM kinase-II activity in both cortex and cerebellum though western analysis revealed no appreciable changes in the levels of CaM kinase-II alpha in cytosol and membrane fractions from control and cerebral malaria infected brain. Given the abundant expression of Cam kinase-II in neuronal tissue, its significance in neurotransmitter release and synthesis and signal transduction during apoptosis, decreased levels of enzyme activity and altered phosphorylation of substrate proteins by CaM kinase II may serve as important cues in understanding the CaM kinase signal transduction events central to neurological disorders during FMCM.