Calpain activation in apoptosis of motoneurons in cell culture models of experimental parkinsonism

Inhibition of Calpain Attenuates Degeneration of Substantia Nigra Neurons in the Rotenone Rat Model of Parkinson's Disease

In the central nervous system (CNS), calcium homeostasis is a critical determinant of neuronal survival. Calpain, a calcium-dependent neutral protease, is widely expressed in the brain, including substantia nigra (SN) dopaminergic (DA) neurons. Though calpain is implicated in human Parkinson's disease (PD) and corresponding animal models, the roles of specific ubiquitous calpain isoforms in PD, calpain-1 and calpain-2, remain poorly understood. In this study, we found that both isoforms are activated in a nigrostriatal pathway with increased phosphorylated synuclein following the administration of rotenone in Lewis rats, but calpain isoforms played different roles in neuronal survival. Although increased expression of calpain-1 and calpain-2 were detected in the SN of rotenone-administered rats, calpain-1 expression was not altered significantly after treatment with calpain inhibitor (calpeptin); this correlated with neuronal survival. By contrast, increased calpain-2 expression in the SN of rotenone rats correlated with neuronal death, and calpeptin treatment significantly attenuated calpain-2 and neuronal death. Calpain inhibition by calpeptin prevented glial (astroglia/microglia) activation in rotenone-treated rats in vivo, promoted M2-type microglia, and protected neurons. These data suggest that enhanced expression of calpain-1 and calpain-2 in PD models differentially affects glial activation and neuronal survival; thus, the attenuation of calpain-2 may be important in reducing SN neuronal loss in PD.

Time-Course Changes and Role of Autophagy in Primary Spinal Motor Neurons Subjected to Oxygen-Glucose Deprivation: Insights Into Autophagy Changes in a Cellular Model of Spinal Cord Ischemia

Spinal cord ischemia is a severe clinical complication induced by thoracoabdominal aortic surgery, severe trauma, or compression to the spinal column. As one of the most important functional cells in the spinal cord, spinal motor neurons (SMNs) suffer most during the process since they are vulnerable to ischemic injury due to high demands of energy. Previous researches have tried various animal models or organotypic tissue experiments to mimic the process and get to know the pathogenesis and mechanism. However, little work has been performed on the cellular model of spinal cord ischemia, which has been hampered by the inability to obtain a sufficient number of pure primary SMNs for in vitro study. By optimizing the isolation and culture of SMNs, our laboratory has developed an improved culture system of primary SMNs, which allows cellular models and thus mechanism studies. In the present study, by establishing an in vitro model of spinal cord ischemia, we intended to observe the dynamic time-course changes of SMNs and investigate the role of autophagy in SMNs during the process. It was found that oxygen-glucose deprivation (OGD) resulted in destruction of neural networks and decreased cell viability of primary SMNs, and the severity increased with the prolonging of the OGD time. The OGD treatment enhanced autophagy, which reached a peak at 5 h. Further investigation demonstrated that inhibition of autophagy exacerbated the injury, evidencing that autophagy plays a protective role during the process.

Effects of Novel Calpain Inhibitors in Transgenic Animal Model of Parkinson's disease/dementia with Lewy bodies

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are neurodegenerative disorders of the aging population characterized by the accumulation of α-synuclein (α-syn). The mechanisms triggering α-syn toxicity are not completely understood, however, c-terminus truncation of α-syn by proteases such as calpain may have a role. Therefore, inhibition of calpain may be of value. The main objective of this study was to evaluate the effects of systemically administered novel low molecular weight calpain inhibitors on α-syn pathology in a transgenic mouse model. For this purpose, non-tg and α-syn tg mice received the calpain inhibitors - Gabadur, Neurodur or a vehicle, twice a day for 30 days. Immunocytochemical analysis showed a 60% reduction in α-syn deposition using Gabadur and a 40% reduction using Neurodur with a concomitant reduction in c-terminus α-syn and improvements in neurodegeneration. Western blot analysis showed a 77% decrease in α-spectrin breakdown products (SBDPs) SBDPs with Gabadur and 63% reduction using Neurodur. There was a 65% reduction in the active calpain form with Gabadur and a 45% reduction with Neurodur. Moreover, treatment with calpain inhibitors improved activity performance of the α-syn tg mice. Taken together, this study suggests that calpain inhibition might be considered in the treatment of synucleinopathies.

Inhibition of Calpain Activation Protects MPTP-Induced Nigral and Spinal Cord Neurodegeneration, Reduces Inflammation, and Improves Gait Dynamics in Mice

Parkinson's disease (PD) is the most common neurodegenerative movement disorder, resulting in dopaminergic (DA) neuronal loss in the substantia nigra pars compacta (SNpc) and damage to the extranigral spinal cord neurons. Current therapies do not prevent the disease progression. Hence, developing efficacious therapeutic strategies for treatment of PD is of utmost importance. The goal of this study is to delineate the involvement of calpain-mediated inflammation and neurodegeneration in SN and spinal cord in MPTP-induced parkinsonian mice (C57BL/6 N), thereby elucidating potential therapeutic target(s). Increased calpain expression was found localized to tyrosine hydroxylase (TH(+)) neurons in SN with significantly increased TUNEL-positive neurons in SN and spinal cord neurons in MPTP mice. Inflammatory markers Cox-2, caspase-1, and NOS-2 were significantly upregulated in MPTP mouse spinal cord as compared to control. These parameters correlated with the activation of astrocytes, microglia, infiltration of CD4(+)/CD8(+) T cells, and macrophages. We found that subpopulations of CD4(+) cells (Th1 and Tregs) were differentially expanded in MPTP mice, which could be regulated by inhibition of calpain with the potent inhibitor calpeptin. Pretreatment with calpeptin (25 μg/kg, i.p.) attenuated glial activation, T cell infiltration, nigral dopaminergic degeneration in SN, and neuronal death in spinal cord. Importantly, calpeptin ameliorated MPTP-induced altered gait parameters (e.g., reduced stride length and increased stride frequency) as demonstrated by analyses of spatiotemporal gait indices using ventral plane videography. These findings suggest that calpain plays a pivotal role in MPTP-induced nigral and extranigral neurodegenerative processes and may be a valid therapeutic target in PD.

Melatonin attenuates dexamethasone toxicity-induced oxidative stress, calpain and caspase activation in human neuroblastoma SH-SY5Y cells

Glucocorticoids (GCs) have a significant role in the adaptive response of the brain to stress. Increasing evidence has demonstrated that an increase of GC levels may induce neuronal cell death via apoptotic pathways. There is a correlation between over-production of reactive oxygen species (ROS) and an elevation in cytosolic calcium that causes a subsequent increase in the calcium-dependent death-process activation in GC-induced toxicity. Consequently, melatonin, via its antioxidant activity, exhibits a neuroprotective effect against apoptosis induced by intracellular calcium overload. Therefore, in the present study, we explored the protective effect of melatonin in GC-induced toxicity in dopaminergic SH-SY5Y cells. Cellular treatment with the synthetic GCs, dexamethasone (DEX), resulted in a marked decrease in cell viability and in the level of the calpain-inhibitor protein, calpastatin. DEX-induced toxicity also caused an increase in ROS production and the activation of the calcium-dependent cysteine protease, calpain, along with an increase in caspase-3 activation. Pretreatment of the cells with melatonin substantially prevented the decrease in cell viability, over-production of ROS and the activation of calpain and caspase-3, and reversed the depletion in calpastatin levels. These results suggest that melatonin may exert its protective effects against the calpain- and caspase-dependent death process in DEX-induced neurotoxicity.

Mitochondrial complex I inhibitor rotenone-induced toxicity and its potential mechanisms in Parkinson's disease models

The etiology of Parkinson's disease (PD) is attributed to both environmental and genetic factors. The development of PD reportedly involves mitochondrial impairment, oxidative stress, α-synuclein aggregation, dysfunctional protein degradation, glutamate toxicity, calcium overloading, inflammation and loss of neurotrophic factors. Based on a link between mitochondrial dysfunction and pesticide exposure, many laboratories, including ours, have recently developed parkinsonian models by utilization of rotenone, a well-known mitochondrial complex I inhibitor. Rotenone models for PD appear to mimic most clinical features of idiopathic PD and recapitulate the slow and progressive loss of dopaminergic (DA) neurons and the Lewy body formation in the nigral-striatal system. Notably, potential human parkinsonian pathogenetic and pathophysiological mechanisms have been revealed through these models. In this review, we summarized various rotenone-based models for PD and discussed the implied etiology of and treatment for PD.

Elevated calpain activity in acute myelogenous leukemia correlates with decreased calpastatin expression

Calpains are intracellular cysteine proteases that have crucial roles in many physiological and pathological processes. Elevated calpain activity has been associated with many pathological states. Calpain inhibition can be protective or lethal depending on the context. Previous work has shown that c-myc transformation regulates calpain activity by suppressing calpastatin, the endogenous negative regulator of calpain. Here, we have investigated calpain activity in primary acute myelogenous leukemia (AML) blast cells. Calpain activity was heterogeneous and greatly elevated over a wide range in AML blast cells, with no correlation to FAB classification. Activity was particularly elevated in the CD34+CD38− enriched fraction compared with the CD34+CD38+ fraction. Treatment of the cells with the specific calpain inhibitor, PD150606, induced significant apoptosis in AML blast cells but not in normal equivalent cells. Sensitivity to calpain inhibition correlated with calpain activity and preferentially targeted CD34+CD38− cells. There was no correlation between calpain activity and p-ERK levels, suggesting the ras pathway may not be a major contributor to calpain activity in AML. A significant negative correlation existed between calpain activity and calpastatin, suggesting calpastatin is the major regulator of activity in these cells. Analysis of previously published microarray data from a variety of AML patients demonstrated a significant negative correlation between calpastatin and c-myc expression. Patients who achieved a complete remission had significantly lower calpain activity than those who had no response to treatment. Taken together, these results demonstrate elevated calpain activity in AML, anti-leukemic activity of calpain inhibition and prognostic potential of calpain activity measurement.

Calpain inhibition protected spinal cord motoneurons against 1-methyl-4-phenylpyridinium ion and rotenone

Parkinson's disease (PD), characterized by selective midbrain nigrostriatal dopaminergic degeneration, is consistently associated with moderate systemic mitochondrial dysfunction. Downstream degeneration of spinal cord has also been suggested in PD, although the mechanisms have not been much investigated. In the present study, two mitochondrial toxicants, 1-methyl-4-phenylpyridinium ion (MPP(+)) and rotenone were tested in ventral spinal cord (VSC 4.1) motoneuronal cells. Cell death was assessed by morphological and biochemical means to discern a lower apoptosis-inducing concentration and lethal concentration of 50% cell death (LC(50)), which were subsequently compared in further cytoprotection experiments. Mitochondrial toxicants dose-dependently induced increase in intracellular free Ca(2+) level, which was conducive for increased expression and activities of Ca(2+)-activated neutral protease calpain and downstream caspase-3. Thus, mitochondrial damage triggered apoptotic mechanisms in spinal cord motoneurons. Inhibition of calpain by calpeptin significantly attenuated damaging effects of MPP(+) and rotenone on motoneurons, especially at low apoptosis-inducing concentrations of toxicants and partly at their LC(50), as demonstrated by absence of DNA ladder formation and decrease in terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells. Cytoprotection by calpeptin was observed with marked decreases in Bax: Bcl-2 ratio and activities of calpain and caspase-3, which affirmed the role of mitochondrial dysfunction and involvement of intrinsic pathway in mediation of apoptosis. These findings strongly suggested that parkinsonian toxicants MPP(+) and rotenone at low doses induced cascade of cell-damaging effects in spinal cord motoneurons, thus, highlighting the possibility of induction of apoptotic mechanisms in these cells, when subjected to mitochondrial stress. Cytoprotection rendered by calpeptin further validated the involvement of calpain in apoptosis and suggested calpain inhibition as a potential neuroprotective strategy.

Tracking extranigral degeneration in animal models of Parkinson's disease: quest for effective therapeutic strategies

Sporadic Parkinson's disease (PD) is now interpreted as a complex nervous system disorder in which the projection neurons are predominantly damaged. Such an interpretation is based on mapping of Lewy body and Lewy neurite pathology. Symptoms of the human disease are much widespread, which span from pre-clinical non-motor symptoms and clinical motor symptoms to cognitive discrepancies often seen in advanced stages. Existing symptomatic treatments further complicate with overt drug-irresponsive symptoms. PD is better understood by assimilation of extranigral degenerative pathways with nigrostriatal degenerative mechanisms. The term 'extranigral' appeared first in the 1990s to more rigorously define the nigral pathology by process of elimination. However, as clinicians progressively identified PD symptoms unresponsive to the gold standard drug l-DOPA, definitions of PD symptoms were redefined. Non-motor symptoms prodromal to motor symptoms just as pre-clinical to clinical, and conjointly emerged the concept of nigral versus extranigral degeneration in PD. While nigrostriatal degeneration is responsible for the neurobiological substrates of extrapyramydal motor features, extranigral degeneration corroborates a vast majority of other changes in discrete central, peripheral, and enteric nervous system nuclei, which together account for global symptoms of the human disease. As an extranigral site, spinal cord degeneration has also been implicated in PD progression. Interconnected to the upper CNS structures with descending and ascending pathways, spinal neurons participate in movement and sensory circuits, controlling movement and reflexes. Several clinical and in vivo studies have demonstrated signs of parkinsonism-related degenerative processes in spinal cord, which led to recent consideration of spinal cord as an area of potential therapeutic target. In a nutshell, this review explores how the existing animal models can actually reflect the human disease in order to facilitate PD research. Evolution of extranigral degeneration studies has been succinctly revisited, followed by a survey on animal models in light of recent findings in clinical PD. Together, it may help to develop effective therapeutic strategies for PD.

The protective effect of melatonin on methamphetamine-induced calpain-dependent death pathway in human neuroblastoma SH-SY5Y cultured cells

Methamphetamine (METH) is a potent psychostimulant drug that may cause neuronal cell degeneration. The underlying mechanisms of METH-induced neuronal toxicity remains poorly understood. In this study, we investigated an important role of calpain-dependent cascades in methamphetamine-induced toxicity in human dopaminergic neuroblastoma SH-SY5Y cultured cell lines. In addition, the protective effect of melatonin against METH-induced calpain-dependent death pathway was also investigated. The results of this study show that METH significantly decreased cell viability and tyrosine hydroxylase phosphorylation in SH-SY5Y cultured cells. Melatonin reversed the toxic effect of METH by inducing cell viability. In addition, melatonin was able to restore the reduction in mitochondrial function and phosphorylation of tyrosine hydroxylase in SH-SY5Y treated cells. An induction of calpain expression and activity but a reduction of calpain inhibitor (calpastatin) protein levels were observed in SH-SY5Y cells treated with METH but these effects were diminished by melatonin. These results implicated calpain-dependent death pathways in the processes of METH-induced toxicity and also indicated that melatonin has the capacity to reverse this toxic effect in SH-SY5Y cultured cells.

Methamphetamine toxicity and messengers of death

Methamphetamine (METH) is an illicit psychostimulant that is widely abused in the world. Several lines of evidence suggest that chronic METH abuse leads to neurodegenerative changes in the human brain. These include damage to dopamine and serotonin axons, loss of gray matter accompanied by hypertrophy of the white matter and microgliosis in different brain areas. In the present review, we summarize data on the animal models of METH neurotoxicity which include degeneration of monoaminergic terminals and neuronal apoptosis. In addition, we discuss molecular and cellular bases of METH-induced neuropathologies. The accumulated evidence indicates that multiple events, including oxidative stress, excitotoxicity, hyperthermia, neuroinflammatory responses, mitochondrial dysfunction, and endoplasmic reticulum stress converge to mediate METH-induced terminal degeneration and neuronal apoptosis. When taken together, these findings suggest that pharmacological strategies geared towards the prevention and treatment of the deleterious effects of this drug will need to attack the various pathways that form the substrates of METH toxicity.

Molecular bases of methamphetamine-induced neurodegeneration

Methamphetamine (METH) is a highly addictive psychostimulant drug, whose abuse has reached epidemic proportions worldwide. The addiction to METH is a major public concern because its chronic abuse is associated with serious health complications including deficits in attention, memory, and executive functions in humans. These neuropsychiatric complications might, in part, be related to drug-induced neurotoxic effects, which include damage to dopaminergic and serotonergic terminals, neuronal apoptosis, as well as activated astroglial and microglial cells in the brain. Thus, the purpose of the present paper is to review cellular and molecular mechanisms that might be responsible for METH neurotoxicity. These include oxidative stress, activation of transcription factors, DNA damage, excitotoxicity, blood-brain barrier breakdown, microglial activation, and various apoptotic pathways. Several approaches that allow protection against METH-induced neurotoxic effects are also discussed. Better understanding of the cellular and molecular mechanisms involved in METH toxicity should help to generate modern therapeutic approaches to prevent or attenuate the long-term consequences of psychostimulant use disorders in humans.

Extranigral neurodegeneration in Parkinson's disease

It is widely known that the pathophysiology of idiopathic Parkinson's disease (PD) is associated with neurodegeneration and inflammatory responses in the midbrain substantia nigra. However, the possibility of neurodegeneration and inflammatory responses in other areas of the central nervous system (CNS) in course of the pathogenesis of PD remains to be explored. In this investigation, we provide evidence in support of the hypothesis that spinal cord, the final coordinator of movement, is also involved during parkinsonian degeneration using two distinct experimental parkinsonism models induced by the neurotoxin 1-methyl-4-phenyl 1,2,3,6-tetrahydropyridine (MPTP) and the environmental toxin rotenone. A key focus of our study is the role that calpain, a Ca(2+)-activated neutral protease, plays in disrupting the structural-functional integrity of the spinal cord in the context of spinal cord degeneration in experimental parkinsonism. We examined the mechanisms of calpain-mediated neuronal death in differentiated spinal cord motoneuron cultures following exposure to the active parkinsonian toxins 1-methyl-4-phenyl-pyridinium ion (MPP(+)) and rotenone and also tested the neuroprotective efficacy of calpeptin, a calpain inhibitor, in these cell culture models of experimental parkinsonism. Our results implied that spinal cord motoneurons could be a potential extranigral target of neurodegeneration during pathogenesis of PD in the CNS and that calpain inhibition could provide neuroprotection.

Calpain-mediated signaling mechanisms in neuronal injury and neurodegeneration

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

Chronic stress enhances methamphetamine-induced extracellular glutamate and excitotoxicity in the rat striatum

Striking parallels exist between the neurochemical and toxic effects of stress and methamphetamine. Despite these similarities, no studies have examined how stress may promote the toxic effects of methamphetamine (METH). The current study tested the hypothesis that chronic stress enhances METH toxicity by augmenting glutamate (GLU) release and excitotoxicity in response to METH administration. Adult male Sprague-Dawley rats were exposed to 10 days of unpredictable stress and then received either saline or METH (7.5 mg/kg, i.p., once every 2 h x four injections). Prior exposure to unpredictable stress acutely enhanced the striatal extracellular GLU concentrations in response to METH, and eventually caused proteolysis of the cytoskeleton protein spectrin. Administration of the corticosterone synthesis inhibitor, metyrapone (25 mg/kg, i.p., prior to each stressor), during unpredictable stress attenuated the enhanced striatal GLU release in response to METH, blocked spectrin proteolysis, and attenuated METH-associated toxicity measured by long-term depletions in the dopamine and serotonin tissue content as well as depletions in dopamine and serotonin transporter immunoreactivity of the striatum. In summary, prior exposure to unpredictable stress enhances METH-induced elevations of GLU in the striatum, resulting in long-term excitotoxic damage and an augmentation of damage to dopamine and serotonin terminals. These studies provide a neurochemical basis for how stress contributes to the deleterious effects of METH abuse.

Spinal cord degeneration in C57BL/6N mice following induction of experimental parkinsonism with MPTP

We examined neurodegeneration in spinal cord (SC) and role of such extra-nigral degeneration in MPTP-induced experimental parkinsonism in C57BL/6N mice. HPLC-photodiode array analysis confirmed presence of the active neurotoxin MPP+ in SC after single injection of MPTP (25 mg/kg, i.p.). Mitochondrial enzyme monoamine oxidase-B (MAO-B) responsible for in vivo conversion of MPTP to MPP+ was inhibited in SC by pre-treatment with l-deprenyl, a specific inhibitor of MAO-B. Besides in vitro conversion of MPTP to MPP+ occurred by SC mitochondrial preparation, which was inhibited by l-deprenyl implicating SC as a specific target of MPTP-neurotoxicity. Double immunofluorescent labeling and spectrofluorimetric assay via kynuramine oxidation showed MAO-B expression and activity in SC neurons. Localization of dopamine transporter immunoreactivity in SC along with specific uptake of (3)H-MPP+ by SC synaptosomal preparation further confirmed SC as target of MPTP-neurotoxicity. Compared with control, increased neuronal death on the seventh day in SC of mice injected with MPTP (2 x 25 mg/kg, at 6 h interval) strongly suggested SC degeneration in pre-symptomatic phase of MPTP-induced experimental parkinsonism. Such extra-nigral neurodegeneration in Parkinson's disease indicated novel molecular mechanism preceding nigrostriatal degeneration and suggested designing broad therapeutic intervention for this complex movement disorder.

The parkinsonian neurotoxin rotenone activates calpain and caspase-3 leading to motoneuron degeneration in spinal cord of Lewis rats

Exposure to environmental toxins increases the risk of neurodegenerative diseases including Parkinson's disease (PD). Rotenone is a neurotoxin that has been used to induce experimental Parkinsonism in rats. We used the rotenone model of experimental Parkinsonism to explore a novel aspect of extra-nigral degeneration, the neurodegeneration of spinal cord (SC), in PD. Rotenone administration to male Lewis rats caused significant neuronal cell death in cervical and lumbar SC as compared with control animals. Dying neurons were motoneurons as identified by double immunofluorescent labeling for terminal deoxynucleotidyl transferase, recombinant-mediated dUTP nick-end labeling-positive (TUNEL(+)) cells and choline acetyltransferase (ChAT)-immunoreactivity. Neuronal death was accompanied by abundant astrogliosis and microgliosis as evidenced from glial fibrillary acidic protein (GFAP)-immunoreactivity and OX-42-immunoreactivity, respectively, implicating an inflammatory component during neurodegeneration in SC. However, the integrity of the white matter in SC was not affected by rotenone administration as evidenced from the non co-localization of any TUNEL(+) cells with GFAP-immunoreactivity and myelin basic protein (MBP)-immunoreactivity, the selective markers for astrocytes and oligodendrocytes, respectively. Increased activities of 76 kD active m-calpain and 17/19 kD active caspase-3 further demonstrated involvement of these enzymes in cell death in SC. The finding of ChAT(+) cell death also suggested degeneration of SC motoneurons in rotenone-induced experimental Parkinsonism. Thus, this is the first report of its kind in which the selective vulnerability of a putative parkinsonian target outside of nigrostriatal system has been tested using an environmental toxin to understand the pathophysiology of PD. Moreover, rotenone-induced degeneration of SC motoneuron in this model of experimental Parkinsonism progressed with upregulation of calpain and caspase-3.