Calpain facilitates the neuron death induced by 3-nitropropionic acid and contributes to the necrotic morphology

Morin post-treatment surpassed calpeptin in ameliorating 3-NP-induced cortical neurotoxicity via modulation of glutamate/calpain axis, Kidins220, and BDNF/TrkB/AKT/CREB trajectory

The neuroprotective capacity of morin hydrate (MH), a potent antioxidant flavonoid, and calpeptin (CP), a calpain inhibitor, was documented against different insults but not Huntington's disease (HD). Accordingly, we aim to assess the neuroprotective potential of MH and/or CP in a 3-nitropropionic acid (3-NP)-induced HD model. The 3-NP-treated rats were post-treated with saline, MH, CP, or MH + CP for a week. Post-treatment with MH and/or CP amended motor function (beam walking test) and short-/ long-term spatial memory (novel object recognition test) and improved cortical microscopic architecture. On the molecular level, MH, and to a lesser extent CP, inhibited the cortical content/expression of glutamate, calpain, and Kidins220 and abated the inflammatory molecules, nuclear factor (NF)-κB, tumor necrosis factor-α, and interleukin-1β, as well as lipid peroxidation. However, MH, but barely CP, activated the molecules of the neuroprotective trajectory; viz., brain-derived neurotrophic factor (BDNF), tropomyosin-related kinase receptor B (TrkB), protein kinase B (AKT), and cAMP response element-binding protein (CREB). Compared to the single treatments, the combination regimen mediated further reductions in the cortical contents of glutamate, calpain, and Kidins220, effects that extended to entail the anti-inflammatory/anti-oxidant potentials of MH and to a greater extent CP. However, the combination of MH strengthened the fair effect of CP on the survival signaling pathway BDNF/TrkB/AKT/CREB. In conclusion, MH, CP, and especially their combination, afforded neuroprotection against HD through curbing the glutamate/calpain axis, Kidins220, as well as NF-κB-mediated neuroinflammation/oxidative stress, besides activating the BDNF/TrkB/AKT/CREB hub that was partly dependent on calpain inhibition.

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.

Inhibition of mitochondrial complex II in neuronal cells triggers unique pathways culminating in autophagy with implications for neurodegeneration

Mitochondrial dysfunction and neurodegeneration underlie movement disorders such as Parkinson’s disease, Huntington’s disease and Manganism among others. As a corollary, inhibition of mitochondrial complex I (CI) and complex II (CII) by toxins 1-methyl-4-phenylpyridinium (MPP⁺) and 3-nitropropionic acid (3-NPA) respectively, induced degenerative changes noted in such neurodegenerative diseases. We aimed to unravel the down-stream pathways associated with CII inhibition and compared with CI inhibition and the Manganese (Mn) neurotoxicity. Genome-wide transcriptomics of N27 neuronal cells exposed to 3-NPA, compared with MPP⁺ and Mn revealed varied transcriptomic profile. Along with mitochondrial and synaptic pathways, Autophagy was the predominant pathway differentially regulated in the 3-NPA model with implications for neuronal survival. This pathway was unique to 3-NPA, as substantiated by in silico modelling of the three toxins. Morphological and biochemical validation of autophagy markers in the cell model of 3-NPA revealed incomplete autophagy mediated by mechanistic Target of Rapamycin Complex 2 (mTORC2) pathway. Interestingly, Brain Derived Neurotrophic Factor (BDNF), which was elevated in the 3-NPA model could confer neuroprotection against 3-NPA. We propose that, different downstream events are activated upon neurotoxin-dependent CII inhibition compared to other neurotoxins, with implications for movement disorders and regulation of autophagy could potentially offer neuroprotection.

Estrogen receptor agonists for attenuation of neuroinflammation and neurodegeneration

Recent results from laboratory investigations and clinical trials indicate important roles for estrogen receptor (ER) agonists in protecting the central nervous system (CNS) from noxious consequences of neuroinflammation and neurodegeneration. Neurodegenerative processes in several CNS disorders including spinal cord injury (SCI), multiple sclerosis (MS), Parkinson's disease (PD), and Alzheimer's disease (AD) are associated with activation of microglia and astrocytes, which drive the resident neuroinflammatory response. During neurodegenerative processes, activated microglia and astrocytes cause deleterious effects on surrounding neurons. The inhibitory activity of ER agonists on microglia activation might be a beneficial therapeutic option for delaying the onset or progression of neurodegenerative injuries and diseases. Recent studies suggest that ER agonists can provide neuroprotection by modulation of cell survival mechanisms, synaptic reorganization, regenerative responses to axonal injury, and neurogenesis process. The anti-inflammatory and neuroprotective actions of ER agonists are mediated mainly via two ERs known as ERα and ERβ. Although some studies have suggested that ER agonists may be deleterious to some neuronal populations, the potential clinical benefits of ER agonists for augmenting cognitive function may triumph over the associated side effects. Also, understanding the modulatory activities of ER agonists on inflammatory pathways will possibly lead to the development of selective anti-inflammatory molecules with neuroprotective roles in different CNS disorders such as SCI, MS, PD, and AD in humans. Future studies should be concentrated on finding the most plausible molecular pathways for enhancing protective functions of ER agonists in treating neuroinflammatory and neurodegenerative injuries and diseases in the CNS.

Autophagy and neuronal cell death in neurological disorders

Autophagy is implicated in the pathogenesis of major neurodegenerative disorders although concepts about how it influences these diseases are still evolving. Once proposed to be mainly an alternative cell death pathway, autophagy is now widely viewed as both a vital homeostatic mechanism in healthy cells and as an important cytoprotective response mobilized in the face of aging- and disease-related metabolic challenges. In Alzheimer's, Parkinson's, Huntington's, amyotrophic lateral sclerosis, and other diseases, impairment at different stages of autophagy leads to the buildup of pathogenic proteins and damaged organelles, while defeating autophagy's crucial prosurvival and antiapoptotic effects on neurons. The differences in the location of defects within the autophagy pathway and their molecular basis influence the pattern and pace of neuronal cell death in the various neurological disorders. Future therapeutic strategies for these disorders will be guided in part by understanding the manifold impact of autophagy disruption on neurodegenerative diseases.

Expression pattern of ataxia telangiectasia mutated (ATM), p53, Akt, and glycogen synthase kinase-3β in the striatum of rats treated with 3-nitropropionic acid

3-Nitropropionic acid (3-NPA) is a mitochondrial toxin used in the laboratory to replicate neurodegenerative conditions that are accompanied by degeneration of the caudate-putamen. 3-NPA induces depletion in ATP production, reactive oxygen species production, and secondary excitotoxicity mediated by activation of N-methyl-D-aspartate receptors that culminates in the triggering of cell death mechanisms, including apoptosis. We here examined by immunohistochemical methods whether cellular expression of phospho(Ser1981) -ataxia telangiectasia mutated (ATM), phospho(Ser15) -p53, phospho(Ser473) -Akt, and phospho(Ser9) -glycogen synthase kinase-3β (GSK3β), which are key signal molecules that play a critical role in regulating cellular processes related to cell survival and demise, were involved in the striatal neurodegeneration in the brains of rats treated with 3-NPA. Our results indicate that the toxin induced the activation of ATM and p53 only in astrocytes, and a role for these proteins in neuronal degeneration was ruled out. On the other hand, striatal neurons lost the active form of Akt as soon as they began to appear pyknotic, indicating impairment of the PI3K/Akt/GSK3 pathway in their degenerative process. The inactive form of GSK3β was detected extensively, mainly in the rim of the striatal lesions around degenerating neurons, which could be attributed to a cell death or cell survival response.

Mechanisms to prevent caspase activation in rotenone-induced dopaminergic neurodegeneration: role of ATP depletion and procaspase-9 degradation

The evidence implicating a mode of cell death that either favors or argues against caspase-dependent apoptosis is available in studies that used experimental models of Parkinson's disease. We sought to investigate the mechanisms by which release of cytochrome c is not linked to caspase activation during rotenone-induced dopaminergic (DA) neurodegeneration. Unlike caspase activation in 6-hydroxydopamine-treated cells, both MN9D DA neuronal cells and primary cultures of mesencephalic neurons showed no obvious signs of caspase activation upon exposure to rotenone. We found that intracellular levels of ATP significantly decreased at the early phase of neurodegeneration (<~24 h) and therefore external addition of ATP to the lysates obtained at this stage reconstituted caspase-3 activity. At a later phase of cell death (>~24 h), both decreased levels of ATP and procaspase-9 contributed to the lack of caspase-3 activation. Under this condition, calpain and the proteasome system were responsible for the degradation of procaspase-9. Consequently, external addition of ATP and procaspase-9 to the lysates harvested at the later phase was required for activation of caspase-3. Similarly, caspase-3 activity was also reconstituted in the lysates harvested from cells co-treated with inhibitors of these proteases and incubated in the presence of external ATP. Taken together, our findings provided a sequential mechanism underlying how DA neurons may undergo caspase-independent cell death, even in the presence of cytoplasmic cytochrome c following inhibition of mitochondrial complex I.

Zinc pyrithione induces ERK- and PKC-dependent necrosis distinct from TPEN-induced apoptosis in prostate cancer cells

Zinc dyshomeostasis can induce cell death. However, the mechanisms involved have not been fully elucidated in prostate cancer (PCa) cells, which differ dramatically from normal cells in their zinc handling ability. Here, we studied the effects of the ionophore Zn-pyrithione (ZP) and the chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN). Both compounds induced cell death at micromolar concentrations when incubated with androgen-dependent (LNCaP), androgen-independent (PC3, DU145) and androgen-sensitive (C4-2) PCa cell-lines. Compared to PCa cells, RWPE1 prostate epithelial cells were less sensitive to ZP and more sensitive to TPEN, but total cellular zinc levels were changed similarly. ZnSO4 enhanced the toxicity of ZP, but inhibited the effects of TPEN as expected. The morphological/biochemical responses to ZP and TPEN differed. ZP decreased ATP levels and stimulated ERK, AKT and PKC phosphorylation. DNA laddering was observed only at low doses of ZP but all doses of TPEN. TPEN activated caspase 3/7 and induced PARP-cleavage, DNA-fragmentation, ROS-formation and apoptotic bodies. PKC and ERK-pathway inhibitors, and antioxidants protected against ZP-induced but not TPEN-induced death. Inhibitors of MPTP-opening protected both. Cell death in response to TPEN (but not ZP) was diminished by a calpain inhibitor and largely prevented by a caspase 3 inhibitor. Overall, the results indicated primarily a necrotic cell death for ZP and an apoptotic cell death for TPEN. The enhanced sensitivity of PCa cells to ZP and the apparent ability of ZP and TPEN to kill quiescent and rapidly dividing cells in a p53-independent manner suggest that ZP/TPEN might be used to develop adjunct treatments for PCa.

Low dose estrogen prevents neuronal degeneration and microglial reactivity in an acute model of spinal cord injury: effect of dosing, route of administration, and therapy delay

Spinal cord injury (SCI), depending on the severity of injury, leads to neurological dysfunction and paralysis. Methylprednisolone, the only currently available therapy renders limited protection in SCI. Therefore, other therapeutic agents must be tested to maximize neuroprotection and functional recovery. Previous data from our laboratory indicate that estrogen (17β-estradiol) at a high dose may attenuate multiple damaging pathways involved in SCI and improve locomotor outcome. Since use of high dose estrogen may have detrimental side effects and therefore may never be used in the clinic, the current study investigated the efficacy of this steroid hormone at very low doses in SCI. In particular, we tested the impact of dosing (1-10 μg/kg), mode of delivery (intravenous vs. osmotic pump), and delay in estrogen application (15 min-4 h post-SCI) on microgliosis and neuronal death in acute SCI in rats. Treatment with 17β-estradiol (1-10 μg/kg) significantly reduced microglial activation and also attenuated apoptosis of neurons compared to untreated SCI animals. The attenuation of cell death and inflammation by estrogen was observed regardless of mode and time of delivery following injury. These findings suggest estrogen as a potential agent for the treatment of individuals with SCI.

Regulation of GSK-3beta by calpain in the 3-nitropropionic acid model

Glycogen synthase kinase-3beta (GSK-3beta) is a crucial component in the cascade of events that culminate in a range of neurodegenerative diseases. It is controlled by several pathways, including calpain-mediated cleavage. Calpain mediates in cell death induced by 3-nitropropionic acid (3-NP), but GSK-3beta regulation has not been demonstrated. Here we studied changes in total GSK-3beta protein levels and GSK-3beta phosphorylation at Ser-9 in this model. The 3-NP treatment induced GSK-3beta truncation. This regulation was dependent on calpain activation, since addition of calpeptin to the medium prevented this cleavage. While calpain inhibition prevented 3-NP-induced neuronal loss, inhibition of GSK-3beta by SB-415286 did not. Furthermore, inhibition of cdk5, a known target of calpain involved in 3-NP-induced cell death, also failed to rescue neurons in our model. Our results point to a new target of calpain and indicate possible cross-talk between calpain and GSK-3beta in the 3-NP toxicity pathway. On the basis of our findings, we propose that calpain may modulate 3-NP-induced neuronal loss.

Androgens selectively protect against apoptosis in hippocampal neurones

Androgens can protect neurones from injury, although androgen neuroprotection is not well characterised in terms of either specificity or mechanism. In the present study, we compared the ability of androgens to protect neurones against a panel of insults, empirically determined to induce cell death by apoptotic or non-apoptotic mechanisms. Three criteria defining but not inclusive of apoptosis are: protection by caspase inhibition, protection by protein synthesis inhibition and the presence of pyknotic nuclei. According to these criteria, beta-amyloid, staurosporine, and Apoptosis Activator II induced cell death involving apoptosis, whereas hydrogen peroxide (H(2)O(2)), iron, calcium ionophore and 3-nitropropionic acid induced cell death featuring non-apoptotic characteristics. Pretreatment of hippocampal neurones with testosterone or dihydrotestosterone attenuated cell death induced by beta-amyloid, staurosporine and Apoptosis Activator II, but none of the other insults. The anti-oxidant Trolox did not reduce cell death induced by beta-amyloid, staurosporine and Apoptosis Activator II, but did protect against H(2)O(2) and iron. Similarly, a supra-physiological concentration of oestrogen reduced cell death induced by H(2)O(2) and iron, an effect not observed with androgens. We also show that activation of oestrogen pathways was not necessary for androgen neuroprotection. These data suggest that androgens directly activate a neuroprotective mechanism specific to inhibition of cell death involving apoptosis. Determining the specificity of androgen neuroprotection may enable the development of androgen compounds for the treatment of neurodegenerative disorders.

Postinjury estrogen treatment of chronic spinal cord injury improves locomotor function in rats

Spinal cord injury (SCI) causes loss of neurological function and, depending on serverity, may cause paralysis. The only recommended pharmacotherapy for the treatment of SCI is high-dose methylprednisolone, and its use is controversial. We have previously shown that estrogen treatment attenuated cell death, axonal and myelin damage, calpain and caspase activities, and inflammation in acute SCI. The aim of this study was to examine whether posttreatment of SCI with estrogen would improve locomotor function by protecting cells and axons and reducing inflammation during the chronic phase following injury. Moderately severe injury (40 g . cm force) was induced in male Sprague-Dawley rats following laminectomy at T10. Three groups of animals were used: sham (laminectomy only), vehicle (dimethyl sulfoxide; DMSO)-treated injury group, and estrogen-treated injury group. Animals were treated with 4 mg/kg estrogen at 15 min and 24 hr postnjury, followed by 2 mg/kg estrogen daily for the next 5 days. After treatment, animals were sacrificed at the end of 6 weeks following injury, and 1-cm segments of spinal cord (lesion, rostral to lesion, and caudal to lesion) were removed for biochemical analyses. Estrogen treatment reduced COX-2 activity, blocked nuclear factor-kappaB translocation, prevented glial reactivity, attenuated neuron death, inhibited activation and activity of calpain and caspase-3, decreased axonal damage, reduced myelin loss in the lesion and penumbra, and improved locomotor function compared with vehicle-treated animals. These findings suggest that estrogen may be useful as a promising therapeutic agent for prevention of damage and improvement of locomotor function in chronic SCI. (c) 2010 Wiley-Liss, Inc.

Calpain activation and Na+/Ca2+ exchanger degradation occur downstream of calcium deregulation in hippocampal neurons exposed to excitotoxic glutamate

Delayed calcium deregulation (DCD) plays an essential role in glutamate excitotoxicity, a major detrimental factor in stroke, traumatic brain injury, and various neurodegenerations. In the present study, we examined the role of calpain activation and Na(+)/Ca(2+) exchanger (NCX) degradation in DCD and excitotoxic cell death in cultured hippocampal neurons. Exposure of neurons to glutamate caused DCD accompanied by secondary mitochondrial depolarization. Activation of calpain was evidenced by detecting NCX isoform 3 (NCX3) degradation products. Degradation of NCX isoform 1 (NCX1) was below the detection limit of Western blotting. Degradation of NCX3 was detected only after 1 hr of incubation with glutamate, whereas DCD occurred on average within 15 min after glutamate application. Calpeptin, an inhibitor of calpain, significantly attenuated NCX3 degradation but failed to inhibit DCD and excitotoxic neuronal death. Calpain inhibitors I, III, and VI also failed to influence DCD and glutamate-induced neuronal death. On the other hand, MK801, an inhibitor of the NMDA subtype of glutamate receptors, added shortly after the initial glutamate-induced jump in cytosolic Ca(2+), completely prevented DCD and activation of calpain and strongly protected neurons against excitotoxicity. Taken together, our results suggest that, in glutamate-treated hippocampal neurons, the initial increase in cytosolic Ca(2+) that precedes DCD is insufficient for sustained calpain activation, which most likely occurs downstream of DCD.

Calpain 1 and Calpastatin expression is developmentally regulated in rat brain

Calpains and caspases are cysteine endopeptidases which share many similar substrates. Caspases are essential for caspase-dependent apoptotic death where calpains may play an augmentive role, while calpains are strongly implicated in necrotic cell death morphologies. Previous studies have demonstrated a down-regulation in the expression of many components of the caspase-dependent cell death pathway during CNS development. We therefore sought to determine if there is a corresponding upregulation of calpains. The major CNS calpains are the mu-and m-isoforms, composed of the unique 80 kDa calpain 1 and 2 subunits, respectively, and the shared 28 kDa small subunit. In rat brain, relative protein and mRNA levels of calpain 1, calpain 2, caspase 3, and the endogenous calpain inhibitor-calpastatin, were evaluated using western blot and real-time RT-PCR. The developmental time points examined ranged from embryonic day 18 until postnatal day 90. Calpain 1 and calpastatin protein and mRNA levels were low at early developmental time points and increased dramatically by P30. Conversely, caspase-3 expression was greatest at E18, and was rapidly downregulated by P30. Calpain 2 protein and mRNA levels were relatively constant throughout the E18-P90 age range examined. The inverse relationship of calpain 1 and caspase 3 levels during CNS development is consistent with the shift from caspase-dependent to caspase-independent cell death mechanisms following CNS injury in neonatal vs. adult rat brain.

CREB is a key regulator of striatal vulnerability in chemical and genetic models of Huntington's disease

Evidence of dysregulation of the CREB/CRE transcriptional pathway in animal models of Huntington's disease (HD) suggests that strategies designed to augment CRE-mediated transcription may be of therapeutic value. Here, we investigated the consequences of CREB activation and repression in chemical and transgenic mouse models of HD. In the 3-nitropropionic acid (3-NP) model, CREB phospho-activation in the striatum was potently repressed within the neurotoxic "core" region prior to cell death. Conversely, marked expression of phospho-CREB, as well the CREB-regulated cytoprotective gene Bcl-2, was detected in the "penumbral" region. To examine potential contributory roles for the CREB/CRE transcriptional pathway in striatal degeneration, we used both CREB loss- (A-CREB) and gain- (VP16-CREB) of-function transgenic mouse strains. 3-NP-induced striatal lesion size and motor dysfunction were significantly increased in A-CREB mice compared to controls. Conversely, striatal damage and motor deficits were diminished in VP16-CREB mice. Furthermore, transgenic A-CREB significantly accelerated motor impairment in the YAC128 mouse model of HD. Together, these results indicate that CREB functionality is lost during the early stages of striatal cell stress and that the repression of CREB-mediated transcription contributes to the pathogenic process.

Cell cycle activation in striatal neurons from Huntington's disease patients and rats treated with 3-nitropropionic acid

This study was undertaken to investigate the potential role of cell cycle re-entry in an experimental model of Huntington's disease and in human brain samples. We found that after treatment of rats with the mitochondrial neurotoxin 3-nitropropionic acid, the expression of cell cycle markers of G1 phase measured by immunohistochemistry was induced in the striatal brain region. Furthermore, we detected an increase in the nuclear and also cytoplasmatic E2F-1 expression, suggesting that this protein could activate the apoptotic cascade in rat brain. Western blot analysis of post-mortem brain samples from patients also showed an increase in the expression of E2F-1 and cyclin D1 in comparison with control samples. These results indicate that cell cycle re-entry is activated in Huntington's disease and may contribute to the neurodegenerative process.

Mild mitochondrial inhibition in vivo enhances glutamate-induced neuronal damage through calpain but not caspase activation: role of ionotropic glutamate receptors

Glutamate neurotoxicity is exacerbated when energy metabolism is impaired. In vitro studies show that neuronal death in these conditions is related to mitochondrial dysfunction, ATP depletion, and the loss of calcium homeostasis. We have recently observed that, in vivo, enhancement of glutamate toxicity elicited by previous mitochondrial inhibition does not involve severe ATP depletion, suggesting the involvement of other processes. Factors such as the activation of different proteases may determine the extent and type of cell death. Protease activation might be triggered by internal or external factors, such as mitochondrial damage or the activation of a particular glutamate receptor subtype. In the present study we aimed to investigate whether moderate inhibition of mitochondrial metabolism facilitates glutamate toxicity through caspase-3 or calpain activation, as well as the contribution of NMDA and non-NMDA glutamate ionotropic receptors to this activation. Rats were pre-treated with a subtoxic dose of 3-NP and 4 h later intrastriatally injected with glutamate. Results show that neither of these treatments alone (3-NP or Glu) or in combination (3-NP+Glu) activated caspase-3. Conversely, calpain activity is induced after glutamate injection both in intact and 3-NP pre-treated rats. Inhibition of calpain activity by MDL-28170 significantly prevented striatal damage. NMDA and non-NMDA receptors contributed equally to calpain activation and to the induction of neuronal death. Results suggest that enhancement of glutamate toxicity due to inhibition of mitochondrial metabolism in vivo, does not recruit caspase-dependent apoptosis but favors calpain activation through the stimulation of both subtypes of glutamate ionotropic receptors.

N terminus of calpain 1 is a mitochondrial targeting sequence

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

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

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

High cyclophilin D content of synaptic mitochondria results in increased vulnerability to permeability transition

Mitochondria isolated from synaptosomes are more sensitive to Ca2+ overload and the resultant opening of the mitochondrial permeability transition pore (mPTP) than nonsynaptic mitochondria. To identify the mechanisms underlying these differences in Ca2+ dynamics, we examined relative levels of mPTP components in synaptic versus nonsynaptic mitochondria. Synaptic mitochondria had higher levels of cyclophilin D when compared with nonsynaptic mitochondria, whereas levels of the voltage-dependent anion channel and the adenine nucleotide translocase were similar in the two mitochondrial fractions. These differences in Ca2+ handling between synaptic and nonsynaptic mitochondria were greatly reduced in cyclophilin D null [Ppif-/- (peptidylprolyl isomerase F)] mice. Higher concentrations of cyclosporine A, which interacts with cyclophilin D to delay mPTP opening, were necessary to increase the Ca2+ uptake capacity of synaptic versus nonsynaptic mitochondria. To determine whether the differences in Ca2+ handling might reflect the relative abundance of neuronal and glial mitochondria in the two mitochondrial fractions, we compared cyclophilin D levels in primary cortical neurons and astrocytes. Primary rat cortical neurons possess higher cyclophilin D levels than do primary astrocytes. In the adult rat brain, cyclophilin D immunoreactivity was abundant in neurons but sparse in astrocytes. Together, these results demonstrate that the Ca2+ handling differences observed in synaptic versus nonsynaptic mitochondria are primarily the result of the high levels of cyclophilin D in synaptic mitochondria, reflecting the greater proportion of neuronal mitochondria in this fraction. The high levels of cyclophilin D in neuronal mitochondria result in their greater vulnerability to mPT and in higher levels of cyclosporine A being required to inhibit mPTP opening.

3-Nitropropionic acid activates calpain/cdk5 pathway in rat striatum

3-Nitropropionic acid (3-NP) is a neurotoxin that inhibits mitochondrial complex II and is used in an experimental model of Huntington's disease. Treatment of rats with 3-NP 30mgkg(-1) i.p. once a day for 5 days induced an increase in calpain activation in rat striatum, measured by the formation of 145kDa fragment of alpha-spectrin breakdown and by an increase in enzymatic calpain activity. In this neurotoxic model, Western blot studies revealed that calpain activity increase was followed by changes in cyclin-dependent kinase 5 (cdk5) and its activator p25. Our results indicated, after 10 days of treatment with 3-NP, a decrease in myocyte enhancer factor phosphorylation, a neuronal prosurvival factor. Thus, a decrease in its expression indicates a new potential mechanism of neuronal cell death mediated by the neurotoxin 3-NP. Accordingly, in our study we demonstrated in rat striatum the activation of the calpain/cdk5/p25 pathway in the 3-NP model. Previous studies have linked the deregulation of cdk5 with neurodegenerative diseases, such as Alzheimer's and Parkinson's. We suggest that calpain/cdk5 activation could also be a common pathway activated in other neurodegenerative diseases, which is liable to be targeted.

Effect of testosterone on oxidative stress and cell damage induced by 3-nitropropionic acid in striatum of ovariectomized rats

This paper evaluates the effects of testosterone (0.5 mg/kg subcutaneously (s.c.) for 8 days) on oxidative stress and cell damage induced by 3-nitropropionic acid (20 mg/kg intraperitoneally (i.p.) for 4 days) in ovariectomized rats. Gonadectomy triggered oxidative damage and cell loss, evaluated by the detection of caspase-3, whereas 3-nitropropionic acid increased the levels of oxidative stress induced by ovariectomy and prompted cell damage characterized by enhanced levels of lactate dehydrogenase. These changes were blocked by testosterone administration. Our results support the following conclusions: i) ovariectomy triggers oxidative and cell damage via caspase-3 in the striatum; ii) 3-nitropropionic acid exacerbates oxidative stress induced by ovariectomy and leads to cell damage characterized by increased levels of lactate dehydrogenase; iii) testosterone administration decreases oxidative stress and cell damage. Additionally, these data support the hypothesis that testosterone might play an important role in the onset and development of neurodegenerative diseases.

Estrogen treatment of spinal cord injury attenuates calpain activation and apoptosis

Spinal cord injury (SCI) is a devastating neurologic injury, and currently, the only recommended pharmacotherapy is high-dose methylprednisolone, which has limited efficacy. Estrogen is a multi-active steroid with anti-oxidant and anti-apoptotic effects. Estrogen may modulate intracellular Ca2+ and prevent inflammation. For this study, male rats were divided into three groups. Sham-group animals received a laminectomy at T12. Injured rats received both laminectomy and 40 gram centimeter force SCI. Estrogen-group rats received 4 mg/kg 17beta-estradiol (estrogen) at 15 min and 24 hr post-injury, and vehicle-group rats received equal volumes of dimethyl sulfoxide. Animals were sacrificed at 48 hr post-injury, and 1-cm segments of the lesion, rostral penumbra, and caudal penumbra were excised. The degradation of 68 kD neurofilament protein (NFP) and estrogen receptors (ER) was examined by Western blot analysis. Protein levels of calpain and the activities of calpain and caspase-3 were also examined. Levels of cytochrome c were determined in both cytosolic and mitochondrial fractions. Cell death with DNA fragmentation was examined using the TUNEL assay. At the lesion, samples from both vehicle and estrogen treated animals showed increased levels of 68 kD NFP degradation, calpain content, calpain activity, cytochrome c release, and degradation of ERalpha and ERbeta, as compared to sham. In the caudal penumbra, estrogen treatment significantly attenuated 68 kD NFP degradation, calpain content, calpain activity, levels of cytosolic cytochrome c, and ERbeta degradation. At the lesion, vehicle-treated animals displayed more TUNEL+ cells, and estrogen treatment significantly attenuated this cell death marker. We conclude that estrogen may inhibit cell death in SCI through calpain inhibition.

Involvement of calpain activation in neurodegenerative processes

One of the challenges in the coming years will be to better understand the mechanisms of neuronal cell death with the objective of developing adequate drugs for the treatment of neurodegenerative disorders. Caspases and calpains are among the best-characterized cysteine proteases activated in brain disorders. Likewise, during the last decade, extensive research revealed that the deregulation of calpains activity is a key cytotoxic event in a variety of neurodegenerative disorders. Moreover, interest in the role of calpain in neurodegenerative processes is growing due to implication of the involvement of cdk5 in neurodegenerative diseases. Since calpain inhibitors appear to not only protect brain tissue from ischemia, but also to prevent neurotoxicity caused by such neurotoxins as beta-amyloid or 3-nitropropionic acid, the currently available data suggest that calpain and cdk5 play a key role in neuronal cell death. It seems clear that the inappropriate activation of cysteine proteases occurs not only during neuronal cell death, but may also contribute to brain pathology in ischemia and traumatic brain disorders. Pharmacological modulation of calpain activation may, therefore, be useful in the treatment of neurodegenerative disorders. It is possible, although difficult, to develop synthetic inhibitors of cysteine proteases, specifically calpains. The inhibition of calpain activation has recently emerged as a potential therapeutic target for the treatment of neurodegenerative diseases.

17 β-Estradiol may affect vulnerability of striatum in a 3-nitropropionic acid-induced experimental model of Huntington's disease in ovariectomized rats

The aim of present study was to clarify the role of female sex hormones in the development and course of neurodegenerative disease in an experimental model of Huntington's disease induced by 3-nitropropionic acid (NPA) (30 mg/kg intraperitoneally (i.p.)/day for 4 days) in ovariectomized rat. Gonadectomy prompted oxidative stress and cell death evaluated by the detection of caspase-3, whereas 3-nitropropionic acid enhanced the oxidative stress induced by ovariectomy and it triggered cell damage characterized by increases of LDH levels. These changes were prevented by administration of 17 beta-estradiol. Our findings suggested that: (i) ovariectomy induced oxidative stress and apoptosis in the brain; (ii) 3-nitropropionic acid exacerbated oxidative stress induced by ovariectomy and shifting cell to cell death; and (iii) 17 beta-estradiol administration decreased oxidative stress and cell death induced by ovariectomy and 3-nitropropionic acid. These results revealed that sex ovarian hormones play a important role in onset and development of neurodegenerative diseases, as well as neuroprotective effects of 17 beta-estradiol against the changes induced ovariectomy and ovariectomy plus 3-nitropropionic acid.

Extracellular signal-regulated kinase as an inducer of non-apoptotic neuronal death

Extracellular signal-regulated kinase (ERK) is a versatile protein kinase, which has been implicated in signaling numerous biological functions ranging from embryonic development to memory formation. Recent reports, including ours, indicate that ERK plays a central role in promoting neuronal degeneration in various neuronal systems including neurodegenerative diseases. Mechanisms involved in ERK-induced neuronal degeneration are beginning to emerge. In this review, we summarize evidence suggesting ERK to be a predominant inducer of a non-apoptotic mode of neuronal death. Further, we discuss the mechanisms and the putative molecular inter-players associated with ERK-mediated neuronal death.

Ester Derivatives of Tournefolic Acid B Attenuate N-Methyl-d-aspartate-Mediated Excitotoxicity in Rat Cortical Neurons

The effects of tournefolic acid B (TAB) and two ester derivatives, TAB methyl ester (TABM) and TAB ethyl ester (TABE), on N-methyl-D-aspartate (NMDA)-mediated excitotoxicity and the underlying mechanisms were investigated. Treatment with 50 microM NMDA elicited neuronal death by 48.7 +/- 5.1%, coinciding with the appearance of injured morphology. TABM (50 microM) attenuated the NMDA-induced cell death by 60.9 +/- 19.7%, and to a lesser extent by TABE. The NMDA-mediated activation of calpain was not affected by TABM and TABE, as determined by the cleavage of alpha-spectrin. NMDA increased the activity of caspases 2, 3, 6, 8, and 9 and reached the maximum after 8-h treatment. TABM and TABE abrogated NMDA-induced activation of caspases 2, 3, 6, and 8 by approximately 80 to 90% and 50 to 60%, respectively, and to a higher extent for caspase 9. TABM and TABE also blocked the NMDA-mediated activation of caspase 12. Furthermore, TABM and TABE eliminated the NMDA-induced accumulation of superoxide anion (O2-*). NMDA evoked significant depolarization of mitochondria, whereas TABM elicited a mild decrease of mitochondrial membrane potential as determined by tetramethylrhodamine methyl ester perchlorate. NMDA treatment induced elevation of Ca2+ levels in cytosol, endoplasmic reticulum (ER), and mitochondria. TABM (50 microM) significantly diminished the NMDA-induced elevation of Ca2+ levels in mitochondria and ER but not cytosol. Therefore, TABM decreased mitochondrial membrane potential and attenuated the NMDA-mediated Ca2+-loading in ER and mitochondria. These events subsequently eliminated the accumulation of O2-* and blocked the activation of caspase cascade, thereby conferring their neuroprotective effects on NMDA-mediated excitotoxicity.

3-Nitropropionic acid: a mitochondrial toxin to uncover physiopathological mechanisms underlying striatal degeneration in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder caused by a mutation in the gene encoding Huntingtin. The mechanisms underlying the preferential degeneration of the striatum, the most striking neuropathological change in HD, are unknown. Of those probably involved, mitochondrial defects might play an important role. The behavioural and anatomical similarities found between HD and models using the mitochondrial toxin 3-nitropropionic acid (3NP) in rats and primates support this hypothesis. Here, we discuss the recently identified mechanisms of 3NP-induced striatal degeneration. Two types of important factor have been identified. The first are the 'executioner' components that have direct roles in cell death, such as c-Jun N-terminal kinase and Ca2+-activated protease calpains. The second are 'environmental' factors, such as glutamate, dopamine and adenosine, which modulate the striatal degeneration induced by 3NP. Interestingly, these recent studies support the hypothesis that 3NP and mutated Huntingtin have certain mechanisms of toxicity in common, suggesting that the use of 3NP might give new insights into the pathogenesis of HD. Research on 3NP provides additional proof that the neurochemical environment of a given neurone can determine its preferential vulnerability in neurodegenerative diseases.

Caspase-mediated cell death predominates following engraftment of neural progenitor cells into traumatically injured rat brain

Neural progenitor cells (NPCs) have been shown to be a promising therapy for cell replacement and gene transfer in neurological diseases including traumatic brain injury (TBI). However, NPCs often survive poorly after transplantation despite immunosuppression, and the mechanisms of graft cell death are unknown. In this study, we evaluated caspase- and calpain-mediated mechanisms of cell death of neonatal mouse C17.2 progenitor cells, transplanted at 24 h following lateral fluid percussion brain injury (FP) in rats. Adult Male Sprague-Dawley rats (n = 30) were subjected to lateral FP injury (n = 18) or sham surgery (n = 12). C17.2 cells labeled with green fluorescent dye (CMFDA) were engrafted in the perilesional deep cortex, and animals were sacrificed at 24 h, 72 h and 1 week post-transplantation. Pro-apoptotic caspase-mediated cleavage products (Ab246) and calpain-mediated cleavage products (Ab38) were detected in the engrafted cells using immunohistochemistry. Only 2 to 4.5% of grafted NPCs were found to survive at 24 h post-transplantation, regardless of injury status of the host brain, although brain-injured animals had significantly fewer graft cells than sham-injured animals. Limited caspase and calpain-mediated graft cell death was observed in both sham- and brain-injured animals, and caspase-mediated graft cell death was significantly greater than calpain-mediated graft cell death in all animals. Brain-injured animals had significantly increased caspase-mediated graft cell death compared to sham-injured animals. These results suggest that both the caspase and calpain family of proteases are involved in graft cell death, and that caspase-mediated apoptotic graft cell death predominates in the acute post-traumatic period following TBI.

Estrogen prevents glutamate-induced apoptosis in C6 glioma cells by a receptor-mediated mechanism

Estrogen-mediated neuroprotection is well established; however, no single mechanism of action for this effect has yet been established. As glial cells are integral for both the intact and injured nervous system, we hypothesized that estrogen-mediated neuroprotection may partly be attributed to attenuation of glial cell apoptosis, allowing them to protect neurons following injury. To assess the protective effects of estrogen on glia, C6 rat glioma cells were treated for 24 h with 500 microM glutamate. Cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and apoptosis was confirmed by cell morphology and DNA fragmentation. Pretreatment with 10 nM 17beta-estradiol (estrogen) increased cell viability and attenuated apoptosis. Treatment with the stereoisomer 17alpha-estradiol, or estrogen plus estrogen receptor antagonist ICI 182,780, was significantly less effective, indicating that cytoprotection was receptor-mediated. Estrogen treatment upregulated expression of estrogen receptor alpha. Cell impermeable bovine serum albumin-conjugated estrogen was also protective, indicating activation of estrogen receptors on the cell membrane. Intracellular free [Ca2+] was increased after glutamate treatment. This increase was attenuated in cells pretreated with estrogen. Glutamate increased the activity of pro-apoptotic proteases, such as calpain and caspase-3, and these protease activities were significantly attenuated by estrogen. The mechanism by which estrogen decreased intracellular Ca2+ was examined by assaying cell viability after using inhibitors that either blocked extracellular Ca2+ influx or prevented the release of intracellular Ca2+ stores. While several inhibitors increased cell viability in glutamate-treated cells, none were as protective as estrogen, and estrogen co-treatment significantly increased cell viability. These findings indicate that estrogen-mediated cytoprotection may be related to effects on Ca2+ entry but that these effects are not limited to any one of these Ca2+ entry points alone.

Mitochondrial localization of mu-calpain

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

Calpain inhibitor inhibits p35-p25-Cdk5 activation, decreases tau hyperphosphorylation, and improves neurological function after spinal cord hemisection in rats

Aberrant calpain activation is a key mediator of neuron death. We examined the cell-permeable calpain inhibitor MDL28170 in the pathophysiological processes after spinal cord injury (SCI) including p35-p25- cyclin-dependent kinase-5 (Cdk5) activation, tau hyperphosphorylation, neuron cell death, calpain I activation, astrogliosis, and microglia activation. Our study showed that intrathecal administration of MDL28170 improved neurologic dysfunction, prevented neuron loss, decreased the number of apoptotic cells, and abated astrogliosis and microglia activation 7 days after spinal cord hemisection in rats. Reverse transcription polymerase chain reaction demonstrated calpain inhibition significantly attenuated the ratio of proapoptotic Bax/anti-apoptotic Bcl-2 mRNA in the lesion and penumbra after SCI. Calpain, the calcium-activated proteolytic enzyme, was found to digest p35 to its truncated product, p25. Moreover, abnormal Cdk5 activation by p25 and subsequent tau hyperphosphorylation triggers pathologic events leading to neurodegeneration and neurofibrillary tangles. We found p35-p25-Cdk5 activation and tau hyperphosphorylation in SCI, and then we showed that intrathecal MDL28170 treatment could diminish p35 truncation, and abrogate aberrant tau phosphorylation. Double labeling of calpain I and phosphorylated tau (AT8) in the same cells of spinal cord lesion further implicated pathogenesis of SCI. In conclusion, MDL28170 abated calpain I activation, inhibited apoptosis and neuron loss, quenched microglia and astrocyte activation, and significantly improved neurologic deficit one week after spinal cord hemisection. The neuroprotective mechanisms of calpain inhibitor in SCI could be attenuating upregulation of Bax/Bcl-2 ratio, preventing p35 truncation in the lesion and penumbra, and abrogating tau hyperphosphorylation.

Distinct mechanistic roles of calpain and caspase activation in neurodegeneration as revealed in mice overexpressing their specific inhibitors

Enzymatic proteolysis has been implicated in diverse neuropathological conditions, including acute/subacute ischemic brain injuries and chronic neurodegeneration such as Alzheimer disease and Parkinson disease. Calcium-dependent proteases, calpains, have been intensively analyzed in relation to these pathological conditions, but in vivo experiments have been hampered by the lack of appropriate experimental systems for a selective regulation of the calpain activity in animals. Here we have generated transgenic (Tg) mice that overexpress human calpastatin, a specific and the only natural inhibitor of calpains. In order to clarify the distinct roles of these cell death-associated cysteine proteases, we dissected neurodegenerative changes in these mice together with Tg mice overexpressing a viral inhibitor of caspases after intrahippocampal injection of kainic acid (KA), an inducer of neuronal excitotoxicity. Immunohistochemical analyses using endo-specific antibodies against calpain- and caspase-cleaved cytoskeletal components revealed that preclusion of KA-induced calpain activation can rescue the hippocampal neurons from disruption of the neuritic cytoskeletons, whereas caspase suppression has no overt effect on the neuritic pathologies. In addition, progressive neuronal loss between the acute and subacute phases of KA-induced injury was largely halted only in human calpastatin Tg mice. The animal models and experimental paradigm employed here unequivocally demonstrate their usefulness for clarifying the distinct contribution of calpain and caspase systems to molecular mechanisms governing neurodegeneration in adult brains, and our results indicate the potentials of specific calpain inhibitors in ameliorating excitotoxic neuronal damages.

The influence of age on apoptotic and other mechanisms of cell death after cerebral hypoxia-ischemia

Unilateral hypoxia-ischemia (HI) was induced in C57/BL6 male mice on postnatal day (P) 5, 9, 21 and 60, corresponding developmentally to premature, term, juvenile and adult human brains, respectively. HI duration was adjusted to obtain a similar extent of brain injury at all ages. Apoptotic mechanisms (nuclear translocation of apoptosis-inducing factor, cytochrome c release and caspase-3 activation) were several-fold more pronounced in immature than in juvenile and adult brains. Necrosis-related calpain activation was similar at all ages. The CA1 subfield shifted from apoptosis-related neuronal death at P5 and P9 to necrosis-related calpain activation at P21 and P60. Oxidative stress (nitrotyrosine formation) was also similar at all ages. Autophagy, as judged by the autophagosome-related marker LC-3 II, was more pronounced in adult brains. To our knowledge, this is the first report demonstrating developmental regulation of AIF-mediated cell death as well as involvement of autophagy in a model of brain injury.

Caspase inhibitor z-DEVD-fmk attenuates calpain and necrotic cell death in vitro and after traumatic brain injury

In studies designed to evaluate the therapeutic window for treatment of traumatic brain injury, the caspase 3 inhibitor z-DEVD-fmk improved neurologic function and reduced lesion volumes when administered at 1 but not at 4, 8, or 24 hours after injury. Moreover, neither caspase 3 nor PARP, a caspase 3 substrate, were cleaved in injured, untreated cortex from 1 to 72 hours after injury. Few cortical neurons expressed active caspase 3 or were TUNEL positive from 6 to 24 hours after injury, and TUNEL staining was primarily Type I (necrotic). Nissl staining revealed extensive neuronal necrosis in the injured cortex from 6 to 24 hours after impact. Considered together, these data suggested that z-DEVD-fmk may reduce neuronal necrosis, so we used an in vitro model of necrotic cell death induced by maitotoxin to test this further and explore the potential mechanism(s) involved. Z-DEVD-fmk (1 nM-100 microM) significantly attenuated maitotoxin induced neuronal cell death and markedly reduced expression of the 145 kD calpain-mediated alpha-spectrin breakdown product after maitotoxin injury. Neither the 120 kD caspase-mediated alpha-spectrin cleavage product nor cathepsin B were expressed after maitotoxin injury. In a cell free assay, z-DEVD-fmk reduced hydrolysis of casein by purified calpain I. Finally, z-DEVD-fmk reduced expression of the 145 kD calpain-mediated alpha-spectrin cleavage fragment after traumatic brain injury in vivo. These data suggest that neuroprotection by z-DEVD-fmk may, in part, reflect inhibition of calpain-related necrotic cell death.

Induction of corticostriatal LTP by 3-nitropropionic acid requires the activation of mGluR1/PKC pathway

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder typically affecting individuals in midlife. HD is characterized by the selective loss of striatal spiny neurons, while large cholinergic interneurons are spared. An impaired mitochondrial complex II (succinate dehydrogenase, SD) activity is known as a prominent metabolic alteration in HD. Accordingly, chronic treatment with 3-nitropropionic acid (3-NP), an irreversible SD inhibitor, mimics motor abnormalities and pathology of HD in several animal models. We have previously shown that in vitro application of 3-NP induces a long-term potentiation (LTP) of corticostriatal synaptic transmission through NMDA glutamate receptor. Since this 3-NP-induced LTP (3-NP-LTP) is shown by striatal spiny neurons, but not by cholinergic interneurons, it might play a role in the regional and cell type-specific neuronal death observed in HD. Here we investigate the role of group I metabotropic glutamate receptors (mGluRs) in the induction of 3-NP-LTP. We report that selectively blocking mGluR1, but not mGluR5, suppresses 3-NP-LTP induction. Moreover, we show that a PKC-mediated mechanism is involved in the formation of 3-NP-LTP. Characterizing the cellular mechanisms underlying 3-NP-LTP may provide new insights to better understand the processes leading to the selective neuronal loss observed in HD.

Reduction of excitotoxicity and associated leukocyte recruitment by a broad‐spectrum matrix metalloproteinase inhibitor

An important step in the cascade leading to neuronal cell death is degradation of laminin and other components of the brain extracellular matrix by microglia-derived proteases. Excitotoxic cell death of murine hippocampal neurones in vivo can be prevented by inhibitors of tissue plasminogen activator (tPA) or by inhibitors of plasmin. Plasmin is a potent activator of the matrix metalloproteinases (MMPs), which are made by resident and recruited leukocytes following CNS injury. In this study, we show, using Taqman RT-PCR, that MMP mRNAs, but not other calcium-dependent proteases such as calpain mRNAs, are acutely up-regulated after an excitotoxic challenge in vivo. alpha(2)-antiplasmin or BB-3103, a broad-spectrum inhibitor of the MMPs, co-injected with kainic acid into the striatum, inhibits excitotoxic cell death in the rat striatum, and reduces both the number of recruited macrophages and the size of the lesion. We also show that leukocyte populations differentially express MMPs, which may account, in part, for the expression profile we observe in the challenged brain. Our results show that inhibition of the MMPs in the rat will prevent kainic acid-induced cell death in the brain. These studies suggest that MMP inhibitors have therapeutic potential for use in stroke, and support the increasing evidence that microglial activation may contribute to neuronal cell death.

Sequential activation of individual caspases, and of alterations in Bcl-2 proapoptotic signals in a mouse model of Huntington's disease

Caspases play an important role in neurodegeneration in Huntington's disease (HD). Members of the Bcl-2 family are critical modulators of terminal cell death pathways. However, alterations of Bcl-2 family members and their functional role in an in vivo model of HD have not been documented. With the goal of gaining mechanistic insight, we used a transgenic mouse model of HD (R6/2) to investigate the chronology of caspase activation and functional alterations in members of the Bcl-2 family. In R6/2 mice caspase activation precedes proapoptotic changes in Bcl-2 family members. Of the caspases that we screened, caspase-1-like activation was the first to be detected in the disease process (7 weeks). Proapoptotic changes in members of the Bcl-2 family were first detected at 9 weeks. To demonstrate a potential functional/therapeutic role of Bcl-2 in HD, we crossed R6/2 mice with mice overexpressing Bcl-2 in neurons. Transgenic expression of Bcl-2 in R6/2 mice resulted in slight prolonged survival. Understanding the chronology of apoptotic events provides important information for appropriate therapeutic targeting in this devastating and untreatable disease.