Failure of the ubiquitin-proteasome system in Parkinson's disease

Redox modulation of heat shock protein expression by acetylcarnitine in aging brain: relationship to antioxidant status and mitochondrial function

There is significant evidence to show that aging is characterized by a stochastic accumulation of molecular damage and by a progressive failure of maintenance and repair processes. Protective mechanisms exist in the brain which are controlled by vitagenes and include members of the heat shock system, heme oxygenase-I, and Hsp70 as critical determinants of brain stress tolerance. Given the broad cytoprotective properties of the heat shock response, molecules inducing this defense mechanism appear to be possible candidates for novel cytoprotective strategies. Acetyl-L-carnitine is proposed as a therapeutic agent for several neurodegenerative disorders, and the present study reports that treatment for 4 months of senescent rats with acetyl-L-carnitine induces heme oxygenase-1 as well as Hsp70 and SOD-2. This effect was associated with upregulation of GSH levels, prevention of age-related changes in mitochondrial respiratory chain complex expression, and decrease in protein carbonyls and HNE formation. We hypothesize that maintenance or recovery of the activity of vitagenes may delay the aging process and decrease the risk of age-related diseases. Particularly, modulation of endogenous cellular defense mechanisms via acetyl-L-carnitine may represent an innovative approach to therapeutic intervention in diseases causing tissue damage, such as neurodegeneration.

L-DOPA treatment from the viewpoint of neuroprotection. Possible mechanism of specific and progressive dopaminergic neuronal death in Parkinson's disease

With regard to the mechanism of selective dopaminergic neuronal death, experimental results of studies on the neurotoxicity of MPTP and rotenone indicate that degeneration of dopamine neurons is closely related to mitochondrial dysfunction, inflammatory process and oxidative stress, particularly with regard to the generation of quinones as dopamine neuron-specific oxidative stress. Thus, it is now clear that the presence of high levels of discompartmentalized free dopamine in dopaminergic neurons may explain the specific vulnerability of dopaminergic neurons through the generation of highly toxic quinones.

Neuroprotection of Parkin against apoptosis is independent of inclusion body formation

Loss-of-function mutations in the parkin gene are known to result in autosomal recessive juvenile parkinsonism, which causes selective degeneration of nigrostriatal dopaminergic neurons in the absence of Lewy bodies. Here, we show that overexpression of parkin protects PC12 cells from neurotoxin of the proteasome inhibitor lactacystin and increases the accumulation of ubiquitin-protein conjugates and the formation of ubiquitin-positive inclusions induced by lactacystin. However, the protective effect of parkin against lactacystin-induced apoptosis is not associated with its ability to promote the formation of ubiquitinated inclusions. It is likely that Lewy body formation may be only a compensatory mechanism of dopaminergic neurons attempting to counteract toxicity, and not the ultimate cause of neuronal death.

Ubiquitin–proteasome system and Parkinson's disease

Increasing genetic, pathological, and experimental evidence suggest that neurodegeneration in both familial and sporadic forms of Parkinson's disease (PD) may be related to a defect in the capacity of the ubiquitin-proteasome system (UPS) to clear unwanted proteins, resulting in protein accumulation, aggregation, and cytotoxicity. This concept is supported by in vitro and in vivo laboratory experiments which show that inhibition of UPS function can cause neurodegeneration coupled with the formation of Lewy body-like inclusions. This hypothesis could account for the presence of protein aggregates and Lewy bodies in PD, the other biochemical features seen in the disorder, and the age-related vulnerability of the substantia nigra pars compacta. It also suggests novel targets for putative neuroprotective therapies for PD.

Mitochondrial toxins in Basal Ganglia disorders: from animal models to therapeutic strategies

Current knowledge of the pathogenesis of basal ganglia disorders, such as Huntington's disease (HD) and Parkinson's disease (PD) appoints a central role to a dysfunction in mitochondrial metabolism. The development of animal models, based upon the use of mitochondrial toxins has been successfully introduced to reproduce human disease, leading to important acquisitions. Most notably, experimental evidence supports the existence, within basal ganglia, of a peculiar regional vulnerability to distinct mitochondrial toxins. MPTP and rotenone, both selective inhibitors of mitochondrial complex I have been extensively used to mimic PD. Accordingly, in human PD, a specific dysfunction of complex I activity was found in vulnerable dopaminergic neurons of the substantia nigra. Conversely, in HD a selective impairment of mitochondrial succinate dehydrogenase, key enzyme in complex II activity was found in medium spiny neurons of the caudate-putamen. The relevance of such finding is further demonstrated by the evidence that toxins able to primarily target mitochondrial complex II, such as malonic acid and 3-nitropropionic acid (3-NP), strikingly reproduce the main phenotypic and pathological features of HD.Despite the advances obtained from these experimental models, a deeper understanding of the molecular and cellular mechanisms underlying such neuronal vulnerability is lacking.The present review provides a brief survey of currently utilized animal models of mitochondrial intoxication, in attempt to address the cellular mechanisms triggered by energy metabolism failure and to identify potential therapeutic targets.

The proteasome in Alzheimer's disease and Parkinson's disease: lessons from ubiquitin B+1

Ubiquitin-containing cellular inclusions are characteristic of major neurodegenerative diseases and suggest an involvement of the ubiquitin-proteasome system. The frameshifted form of ubiquitin has proved to be a valuable tool for studying the role of the ubiquitin-proteasome system. It is an endogenous reporter for proteasome activity in human pathology but it is also capable of inhibiting proteasomal degradation. Current studies have revealed that the frameshifted form of ubiquitin accumulates in the brains of patients with Alzheimer's disease but not in those with Parkinson's disease.

Loss of Usp14 results in reduced levels of ubiquitin in ataxia mice

The ataxia (ax(J)) mutation is a spontaneous recessive mutation that results in reduced expression of ubiquitin-specific protease 14, Usp14. Mice homozygous for the ax(J) mutation are retarded for growth and exhibit several behavioral disorders, including a resting tremor and hindlimb paralysis. Although pathological defects appear to be limited to the central nervous system, reduction of Usp14 expression was widespread in the ax(J) mice. Usp14 co-fractionated with proteasomes isolated from livers and brains of wild-type mice. Proteasomes isolated from the ax(J) brains still possessed deubiquitinating activity and were functionally competent to hydrolyze 20S proteasomal substrates in vitro. However, the levels of monomeric ubiquitin were reduced approximately 35% in most of the ax(J) tissues examined. These results indicate that Usp14 functions to maintain the cellular levels of monomeric ubiquitin in mammalian cells, and that alterations in the levels of ubiquitin may contribute to neurological disease.

Neurotoxicity and behavioral deficits associated with Septin 5 accumulation in dopaminergic neurons

Septin 5, a parkin substrate, is a vesicle- and membrane-associated protein that plays a significant role in inhibiting exocytosis. The regulatory function of Septin 5 in dopaminergic (DAergic) neurons of substantia nigra (SN), maintained at relatively low levels, has not yet been delineated. As loss of function mutations of parkin are the principal cause of a familial Parkinson's disease, a prevailing hypothesis is that the loss of parkin activity results in accumulation of Septin 5 which confers neuron-specific toxicity in SN-DAergic neurons. In vitro and in vivo models were used to support this hypothesis. In our well-characterized DAergic SN4741 cell model, acute accumulation of elevated levels of Septin 5, but not synphilin-1 (another parkin substrate), resulted in cytotoxic cell death that was markedly reduced by parkin co-transfection. A transgenic mouse model expressing a dominant negative parkin mutant accumulated moderate levels of Septin 5 in SN-DAergic neurons. These mice acquired a progressive l-DOPA responsive motor dysfunction that developed despite a 25% higher than normal level of striatal dopamine (DA) and no apparent loss of DAergic neurons. The phenotype of this animal, increased striatal dopamine and reduced motor function, was similar to that observed in parkin knockout animals, suggesting a common DAergic alteration. These data suggest that a threshold level of Septin 5 accumulation is required for DAergic cell loss and that l-DOPA-responsive motor deficits can occur even in the presence of elevated DA.

p53 mediates cellular dysfunction and behavioral abnormalities in Huntington's disease

We present evidence for a specific role of p53 in the mitochondria-associated cellular dysfunction and behavioral abnormalities of Huntington's disease (HD). Mutant huntingtin (mHtt) with expanded polyglutamine (polyQ) binds to p53 and upregulates levels of nuclear p53 as well as p53 transcriptional activity in neuronal cultures. The augmentation is specific, as it occurs with mHtt but not mutant ataxin-1 with expanded polyQ. p53 levels are also increased in the brains of mHtt transgenic (mHtt-Tg) mice and HD patients. Perturbation of p53 by pifithrin-alpha, RNA interference, or genetic deletion prevents mitochondrial membrane depolarization and cytotoxicity in HD cells, as well as the decreased respiratory complex IV activity of mHtt-Tg mice. Genetic deletion of p53 suppresses neurodegeneration in mHtt-Tg flies and neurobehavioral abnormalities of mHtt-Tg mice. Our findings suggest that p53 links nuclear and mitochondrial pathologies characteristic of HD.

Neuroprotective therapy in Parkinson's disease and motor complications: a search for a pathogenesis-targeted, disease-modifying strategy

The introduction of levodopa in the late 1960s represented a landmark in the therapy of Parkinson's disease (PD). However, motor complications of chronic levodopa therapy have emerged as a major limitation of this otherwise effective therapy. Advancing medical and surgical treatment of these complications has been the main objective of clinical trials during the past few decades. In addition, basic research has focused on better understanding of the mechanisms of motor complications and how to prevent them. Slowing or delaying the progression of the disease delays the need for levodopa therapy; therefore, neuroprotective strategies may play an important role in preventing the onset and reducing the severity of levodopa-related adverse effects. In this introductory review, we present the rationale for current and experimental therapies designed to favorably modify the progression of PD. If implemented early in the course of the disease, such treatments, if found effective, may not only alter the natural progression of the disease but may also delay or minimize motor and nonmotor complications associated with levodopa.

Apoptosis and the conformational change of Bax induced by proteasomal inhibition of PC12 cells are inhibited by bcl-xL and bcl-2

The function of the proteasome has been linked to various pathologies, including cancer and neurodegeneration. Proteasomal inhibition can lead to death in a variety of cell types, however the manner in which this occurs is unclear, and may depend on the particular cell type. In this work we have extended previous findings pertaining to the effects of pharmacological proteasomal inhibitors on PC12 cells, by examining in more detail the induced death pathway. We find that cell death is apoptotic by ultrastructural criteria. Caspase 9 and 3 are processed, cytochrome c is released from the mitochondria and a dominant negative form of caspase 9 prevents death. Furthermore, Bax undergoes a conformational change and is translocated to the mitochondria in a caspase-independent fashion. Total cell levels of Bax however do not change, whereas levels of the BH3-only protein Bim increase with proteasomal inhibition. Transient overexpression of bcl-xL or, to a lesser extent, of bcl-2, significantly decreased apoptotic death and prevented Bax conformational change. We conclude that death elicited by proteasomal inhibition of PC12 cells follows a classical "intrinsic" pathway. Significantly, antiapoptotic bcl-2 family members prevent apoptosis by inhibiting Bax conformational change. Increased levels of Bim may contribute to cell death in this model.

α-Synuclein redistributes to neuromelanin lipid in the substantia nigra early in Parkinson's disease

The distribution and tempo of neuronal loss in Parkinson's disease correlates poorly with the characteristic and more widely spread intracellular changes associated with the disease process (Lewy bodies and Lewy neurites). To determine early intracellular changes in regions where cell loss is most marked (dopaminergic A9 substantia nigra) versus regions with Lewy bodies but where cell loss is limited, we assessed 13 patients with definite Parkinson's disease at various disease stages in comparison with controls. Using immunohistochemistry for alpha-synuclein, we confirmed the concentration of this protein in the soma of normal A9 neurons and in Lewy body pathology in brainstem catecholamine neurons in Parkinson's disease. Analysis of the degree of cell loss in brainstem catecholamine cell groups revealed that only the A9 substantia nigra had consistent significant cell loss early in the disease course with greater A9 cell loss correlating with increasing disease duration. To assess the earliest intracellular changes differentiating neurons more likely to degenerate, pigmented A9 and A10 neurons with and without obvious pathology were targeted, cell size and pigment density measured, and intracellular changes in alpha-synuclein location and lipid components analysed at both the light and electron microscope levels. There were no changes observed in healthy A10 neurons in Parkinson's disease compared with controls. Pigmented A9 neurons in later stages of degeneration with obvious Lewy body formation had a significant reduction in intracellular pigment, as previously described. In contrast, A9 neurons of normal morphological appearance and no characteristic pathology in Parkinson's disease exhibited significantly increased pigment density associated with a concentration of alpha-synuclein to the lipid component of the pigment and a loss of associated cholesterol. These changes in vulnerable but apparently healthy A9 neurons occurred without any change in cell size or in the amount of intracellular pigment compared with controls. The increase in pigment density is consistent with previously reported increases associated with oxidation and iron loading, reactions known to precipitate alpha-synuclein. The selectivity of the changes observed in A9 nigral neurons suggests that these early intracellular changes predispose these neurons to more rapid cell loss in Parkinson's disease. The increased concentration of neuronal alpha-synuclein and pigment in normal A9 neurons may already predispose these neurons to precipitate alpha-synuclein around pigment-associated lipid under oxidative conditions. Overall, these changes may trigger a cascade of events leading to larger intracellular aggregates of alpha-synuclein and the dispersement of protective pigment to precipitate cell death in Parkinson's disease.

Acute intranigral infusion of rotenone in rats causes progressive biochemical lesions in the striatum similar to Parkinson's disease

We examined in Sprague-Dawley rats whether intranigral administration of complex-I inhibitor, rotenone, produces biochemical lesions in the striatum similar to those observed in Parkinson's disease (PD). Unilateral stereotaxic infusion of rotenone (2-12 mug in 1 mul) into substantia nigra (SN) pars compacta caused significant inhibition of complex-I activity and increased production of hydroxyl radicals in vivo as measured employing spectrophotometric and HPLC-electrochemical procedures, respectively. It also caused a significant time- and dose-dependent reduction of dopamine level, but not serotonin, in the ipsilateral striatum when assayed using an HPLC electrochemical method. This effect was found to be progressive for 90 days. A dose-dependent decrease in nigral glutathione level, as measured fluorimetrically, was also observed to be progressive till 90th day. A significant decrease in tyrosine hydroxylase immunoreactivity in the striatum (73 +/- 8.4% as assessed by densitometric studies) or in SN ipsilateral to the side of infusion suggested nigrostriatal neuronal degeneration. A dose of rotenone (6 microg in 1 microl) that caused 55% striatal dopamine depletion when infused into the SN failed to affect serotonin levels in the terminal regions when infused into the nucleus raphe dorsalis, indicating rotenone's specificity of action towards dopaminergic neurons. Our findings suggest that unilateral infusion of rotenone reproduces neurochemical and neuropathological features of hemiparkinsonism in rats and indicate an active involvement of oxidative stress in rotenone-induced nigrostriatal neurodegeneration. The present study also demonstrates more sensitivity of dopaminergic neurons towards rotenone and establishes mitochondrial complex-I damage as one of the major contributory components of neurodegeneration in PD. The progressive nature of pathology in this model closely mimics idiopathic PD, and absence of mortality warrants the use of this model in drug discovery programs.

Oxidized SOD1 alters proteasome activities in vitro and in the cortex of SOD1 overexpressing mice

Premature ageing, one of the characteristics of Down syndrome (DS), may involve oxidative stress and impairment of proteasome activity. Transgenic mice overexpressing the human copper/zinc superoxide dismutase (SOD1) gene are one of the first murine models for DS and it has been shown that SOD1 overexpression might be either deleterious or beneficial. Here, we show a reduction in proteasome activities in the cortex of SOD1 transgenic mice and an associated increase in the content of oxidized SOD1 protein. As we demonstrate that in vitro oxidized SOD can inhibit purified proteasome peptidase activities, modified SOD1 might be partially responsible for proteasome inhibition shown in SOD1 transgenic mice.

Replaceable neurons and neurodegenerative disease share depressed UCHL1 levels

Might there be systematic differences in gene expression between neurons that undergo spontaneous replacement in the adult brain and those that do not? We first explored this possibility in the high vocal center (HVC) of male zebra finches by using a combination of neuronal tracers, laser capture microdissection, and RNA profiling. HVC has two kinds of projection neurons, one of which continues to be produced and replaced in adulthood. HVC neurons of the replaceable kind showed a consistent and robust underexpression of the deubiquitination gene ubiquitin carboxyl-terminal hydrolase (UCHL1) that is involved with protein degradation. Singing behavior, known to increase the survival of adult-born HVC neurons in birds, significantly up-regulated the levels of UCHL1 in the replaceable neurons but not in their equally active nonreplaceable counterparts. We then looked in the mouse brain and found relatively low UCHL1 expression in granule neurons of the hippocampus and olfactory bulb, two well characterized types of replaceable neurons in mammals. UCHL1 dysfunction has been associated with neurodegeneration in Parkinson's, Alzheimer's, and Huntington's disease patients. In all these instances, reduced UCHL1 function may jeopardize the survival of CNS neurons.

Treadmill training ameliorates dopamine loss but not behavioral deficits in hemi-parkinsonian rats

The purpose of this study was to investigate whether locomotor training could ameliorate neurochemical changes and behavioral deficits in the 6-hydroxydopamine (6-OHDA) rat model of Parkinson's disease. It has been recently demonstrated that forelimb motor training, or brief treadmill training, can attenuate dopamine loss and some deficits in forelimb usage in this animal model. Nevertheless, it is not known whether locomotor training could result in an amelioration of locomotor deficits. Rats were lesioned with 6-OHDA injected intracerebrally and randomly assigned to one of 3 groups: early treadmill trained, late treadmill trained and untrained. Animals in the early trained group underwent 2 x 20 min treadmill sessions daily for 30 days, beginning 24 h after 6-OHDA injection. Late trained animals underwent the same training regime beginning 7 days post-injection. All animals were assessed on their abilities to perform several behavioral tasks designed to test locomotor and forelimb movement abilities prior to 6-OHDA injection and at 3 and 6 weeks post-injection. Treadmill training resulted in the attenuation of dopamine depletion in the striatum compared to non-treadmill trained animals, as measured by in vivo apomorphine-induced rotations and post-mortem dopamine analysis. Nevertheless, treadmill training produced essentially no difference in behavioral deficits on most tests compared to untrained animals. We discuss the possible reasons for the discrepancies with previous studies, including differences in lesioning, training regimes and methods of behavioral assessment. We conclude that treadmill training does not ameliorate locomotor deficits in the 6-OHDA model of Parkinson's disease, even though this same training results in attenuation of dopamine loss in the striatum.

Nitric oxide-related species-induced protein oxidation: reversible, irreversible, and protective effects on enzyme function of papain

Protein oxidation, irreversible modification, and inactivation may play key roles in various neurodegenerative disorders. Therefore, we studied the effects of the potentially in vivo occurring nitric oxide-related species on two different markers of protein oxidation: protein carbonyl generation on bovine serum albumine (BSA) and loss of activity of a cysteine-dependent protease, papain, in vitro by using Angeli's salt, papanonoate, SIN-1, and S-nitrosoglutathione (GSNO) as donors of nitroxyl, nitric oxide, peroxynitrite, and nitrosonium ions, respectively. Angeli's salt, SIN-1, and papanonoate (0-1000 microM) all generated a concentration-dependent increase in carbonyl formation on BSA (107, 60, and 45%, respectively). GSNO did not affect carbonyl formation. Papain was inhibited by Angeli's salt, SIN-1, papanonoate, and GSNO with IC50 values of 0.62, 2.3, 54, and 80 microM, respectively. Angeli's salt (3.16 microM)-induced papain inactivation was only partially reversible, while the effects of GSNO (316 microM) and papanonoate (316 microM) were reversible upon addition of excess DTT. The Angeli's salt-mediated DTT-irreversible inhibition of papain was prevented by GSNO or papanonoate pretreatment, hypothetically through mixed disulfide formation or S-nitrosylation of the catalytically critical thiol group of papain. These results, for the first time, compare the generation of carbonyls in proteins by Angeli's salt, papanonoate, and SIN-1. Furthermore, these results suggest that S-nitrosothiols may have a novel function in protecting critical thiols from irreversible oxidative damage.

[Neurodegeneration caused by ER stress?--the pathogenetic mechanisms underlying AR-JP]

Mutations of the Parkin gene are responsible for autosomal recessive juvenile parkinsonism (AR-JP), the most common cause of early-onset familial Parkinson's disease. Parkin functions as an E3 ubiquitin ligase, thereby promoting ubiquitination and subsequent proteosomal degradation of its substrate(s). AR-JP is, therefore, thought to be caused by accumulation of an unknown toxic protein(s), which would normally be degraded by a molecular machinery involving Parkin. To date, ten different proteins are reported to be substrates of Parkin. Among these, a G protein-coupled orphan receptor called the Pael receptor (Pael-R), which is highly expressed in dopaminergic neurons, attracts particular attention. When over-expressed in cells, the Pael-R protein became improperly folded and insoluble. Excessive accumulation of insoluble Pael-R led to endoplasmic reticulum (ER) stress-induced cell death. Parkin was observed to ubiquitinate the misfolded Pael-R protein, thereby promoting its degradation and suppressing misfolded Pael-R-induced cell death. Moreover, selective dopaminergic neurodegeneration was observed when human Pael-R was ectopically expressed in Drosophila brain, further supporting the idea that Pael-R accumulation plays a major role in AR-JP. In contrast, neither dopaminergic neurodegeneration nor accumulation of any known Parkin substrates was detected in Parkin knockout mice. The role of Pael-R in AR-JP will be discussed based on recent data.

Neuronal inclusions in degenerative disorders

This brief paper analyzes a few degenerative diseases expressing as movement disorders and featuring at sub-cellular level the presence of neuronal inclusions in selective brain regions. We will first draw a short draft of representative neurological diseases featuring inclusion bodies by describing the type of inclusions occurring in various disorders and analyzing both common features and distinctive aspects. As a further step, we move from the bed to the bench side discussing recent developments obtained from experimental models of these disorders which shed new light into the cause and progression of neuronal inclusions, thus helping to understand the pathophysiology of neuronal degeneration underlying movement disorders. In line with this, we will focus on recent studies which led to reproduce neuronal inclusions in vivo and in vitro by manipulating selective cellular structures/enzymatic pathways. In this way, we will try to encompass the dynamics of inclusion formation based on their fine ultrastructure and the analysis of the molecular components as well as their subcellular compartmentalization trying to relate the dynamics of inclusion formation and the pathophysiology of the disease process. An emphasis will be made on the ubiquitin proteasome system and Parkinson's disease where the analysis of neuronal inclusions enlightened potential therapeutic strategies to occlude the progression of this neuronal degeneration featured by movement disorders.

Ubiquitin-proteasome system and Parkinson's diseases

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by nigrostriatal dopaminergic degeneration and development of cytoplasmic inclusions known as Lewy bodies. To date, the mechanisms involved in PD pathogenesis are not clearly understood. Clues from genetic studies including identification of mutations in genes for alpha-synuclein, parkin, and ubiquitin carboxy hydrolase L1 associated with familial PD and the presence of proteinaceous cytoplasmic inclusions in spared dopaminergic nigral neurons in sporadic cases of PD have suggested an important role for ubiquitin-proteasome system (UPS) and aberrant protein degradation. In vivo and in vitro studies have linked parkin, alpha-synuclein, and oxidative stress to a compromised UPS and PD pathogenesis suggesting novel therapeutic targets.

Proteasome inhibition and Tau proteolysis: an unexpected regulation

Increasing evidence suggests that an inhibition of the proteasome, as demonstrated in Parkinson's disease, might be involved in Alzheimer's disease. In this disease and other Tauopathies, Tau proteins are hyperphosphorylated and aggregated within degenerating neurons. In this state, Tau is also ubiquitinated, suggesting that the proteasome might be involved in Tau proteolysis. Thus, to investigate if proteasome inhibition leads to accumulation, hyperphosphorylation and aggregation of Tau, we used neuroblastoma cells overexpressing Tau proteins. Surprisingly, we showed that the inhibition of the proteasome led to a bidirectional degradation of Tau. Following this result, the cellular mechanisms that may degrade Tau were investigated.

Risk of cancer after the diagnosis of Parkinson's disease: A historical cohort study

We investigated the risk of cancer after the diagnosis of Parkinson's disease (PD) through a historical cohort study. We used the medical records-linkage system of the Rochester Epidemiology Project to identify all incident cases of PD in Olmsted County, Minnesota from 1976 through 1995. Patients with PD were matched by age (+/- 1 year) and gender to referent subjects from the same population. For 196 patients and 185 referent subjects, we ascertained the incidence of cancer through medical records abstraction between the date of diagnosis (or index date) and death, loss to follow-up, or end of study. The risk of cancer was higher among patients than in referent subjects (relative risk [RR] = 1.64; 95% confidence interval [CI] = 1.15-2.35; P = 0.007). The RR did not change noticeably after adjustment for smoking. The increased risk was significant for nonmelanoma skin cancer (RR = 1.76; 95% CI = 1.07-2.89; P = 0.03), but not for other more severe types of cancer; therefore, we cannot exclude the occurrence of a surveillance bias. Among PD patients, there was no relation between the risk of cancer and the cumulative dose of levodopa received or the use of other PD medications.

L-dopa and dopamine enhance the formation of aggregates under proteasome inhibition in PC12 cells

The formation of inclusion bodies in dopaminergic neurons is associated with the pathogenesis of Parkinson's disease. In order to clarify the role of dopamine/L-dopa in the formation of protein aggregates, we investigated dopamine/L-dopa-related aggregation using an experimental inclusion model. The inhibition of tyrosine hydroxylase (TH) by alpha-methyltyrosine dramatically decreased MG132-induced aggregate formation. In addition, the inhibition of TH caused the upregulation of proteasomes in cultured cells and the dopamine/L-dopa induced non-enzymatic polymerization of ubiquitin. This inhibition did not affect cell viability. These results suggest that dopamine/L-dopa might enhance aggregate formation, and that intracellular aggregates may not be toxic to cells.

The kinder side of killer proteases: caspase activation contributes to neuroprotection and CNS remodeling

Caspases are a family of cysteine proteases that are expressed as inactive zymogens and undergo proteolytic maturation in a sequential manner in which initiator caspases cleave and activate the effector caspases 3, 6 and 7. Effector caspases cleave structural proteins, signaling molecules, DNA repair enzymes and proteins which inhibit apoptosis. Activation of effector, or executioner, caspases has historically been viewed as a terminal event in the process of programmed cell death. Emerging evidence now suggests a broader role for activated caspases in cellular maturation, differentiation and other non-lethal events. The importance of activated caspases in normal cell development and signaling has recently been extended to the CNS where these proteases have been shown to contribute to axon guidance, synaptic plasticity and neuroprotection. This review will focus on the adaptive roles activated caspases in maintaining viability, the mechanisms by which caspases are held in check so as not produce apoptotic cell death and the ramifications of these observations in the treatment of neurological disorders.

Effect of overexpression of wild-type or mutant parkin on the cellular response induced by toxic insults

Mutations in parkin are involved in some cases of autosomal recessive juvenile parkinsonism (AR-JP), but it is not known how they result in nigral cell death. We examined the effect of parkin overexpression on the response of cells to various insults. Wild-type and AR-JP-associated mutant parkins (Del3-5, T240R, and Q311X) were overexpressed in NT-2 and SK-N-MC cells. Overexpressed wild-type parkin delayed cell death induced by serum withdrawal, H(2)O(2), 1-methyl-4-phenylpyridinium (MPP(+)), or 4-hydroxy-2-trans-nonenal (HNE) but did not delay cell death caused by the proteasome inhibitor lactacystin. Increases in damage to proteins (protein carbonyls and 3-nitrotyrosine) were attenuated by wild-type parkin after serum withdrawal or exposure to H(2)O(2), MPP(+), or HNE but not after exposure to lactacystin. The mutant parkins (of all types) markedly accelerated cell death in response to all the insults, accompanied by increased levels of 8-hydroxyguanine, protein carbonyls, lipid peroxidation, and 3-nitrotyrosine and decreased levels of GSH. The viability loss induced by all the insults showed apoptotic features. The presence of parkin mutations in substantia nigra in Parkinson's disease may increase neuronal vulnerability to a range of toxic insults.

Proteasome Inhibitors Protect Against Degeneration of Nigral Dopaminergic Neurons in Hemiparkinsonian Rats

Parkinson's disease is characterized by dopaminergic neuronal death and the presence of Lewy bodies in the substantia nigra pars compacta (SNpc). alpha-Synuclein and ubiquitin are components of Lewy bodies, but the process of Lewy body formation and the relationship between inclusion formation and dopaminergic neuronal death have not been resolved. In this study, unilateral intranigral microinjection of 6-hydroxydopamine caused a significant loss of tyrosine hydroxylase-immunopositive neurons in both the substantia nigra and striatum and apomorphine-induced contralateral rotation. The co-administration of proteasome inhibitors, such as lactacystin or carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG-132), significantly prevented both dopaminergic neurodegeneration and apomorphine-induced rotational asymmetry. Proteasome inhibitors markedly formed intracellular protein inclusions labeled by thioflavin-S in the SNpc. Inclusion-like immunoreactivities for alpha-synuclein and ubiquitin were detected after 4 weeks. These results suggest that proteasome plays an important role in both the early phase of dopaminergic neuronal death and inclusion body formation.

Intracellular dopamine oxidation mediates rotenone-induced apoptosis in PC12 cells

AIM

To study the role of dopamine (DA) in rotenone-induced neurotoxicity in PC12 cells.

METHODS

Cell viability was assessed by detecting the leakage of lactate dehydrogenase (LDH) into the medium. Apoptosis rate was measured by flow cytometry. Caspase-3-like activity was measured by fluorescence assay using the probe Ac-DEVD-AMC. The level of intracellular hydrogen peroxide and other peroxides in PC12 cells were quantified by loading cells with 2'-7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) in fluorescence assay. Lactic acid was measured spectrophotometrically. The DA levels in PC12 cells were determined by HPLC-ECD.

RESULTS

A 48-h incubation of PC12 cells with rotenone caused an apoptotic cell death and elevated intracellular reactive oxygen species (ROS) and lactic acid accumulation. Intracellular DA depletion with reserpine significantly attenuated rotenone-induced ROS accumulation and apoptotic cell death. No change was found in rotenone-induced ROS accumulation when cells were co-treated with deprenyl. Brief treatment with reserpine at the end of rotenone treatment had no effect on rotenone-induced neurotoxicity. However, when cells were first incubated with deprenyl, a monoamine oxidase-B inhibitor for 30 min then co-incubated with rotenone plus deprenyl, a brief treatment with reserpine enhanced cell injury.

CONCLUSION

Rotenone-induced apoptosis in PC12 cells was mediated by intracellular dopamine oxidation.

Upregulation of clusterin/apolipoprotein J in lactacystin-treated SH-SY5Y cells

Clusterin (apolipoprotein J) is a highly conserved, multifunctional, vertebrate glycoprotein. Several isoforms of clusterin have been described including the predominant secreted isoform (sCLU) and several nuclear isoforms (nCLU) associated with cell death. sCLU has been shown to bind a variety of partly unfolded, stressed proteins including those associated with Lewy bodies (LBs) in patients with Parkinson's disease (PD). The development of familial and sporadic PD has been associated with the ubiquitin-proteasome system (UPS) dysfunction and aberrant protein degradation. This suggests that failure of the UPS to degrade abnormal proteins may underlie nigral degeneration and LB formation in PD. The effects of toxin-mediated proteasomal impairment on changes in gene expression and cell viability were studied in differentiated SH-SY5Y cells. Clusterin expression was increased in cells exposed for 24 hr to the proteasomal inhibitor lactacystin (10 microM) as determined by gene microarray analysis. RT-PCR showed that sCLU, not nCLU, was the major clusterin isoform expressed in both control and lactacystin-treated cells. Western blot analysis identified statistically significant increases in sCLU in total cell lysates after 24 hr of lactacystin exposure and showed that sCLU fractionates with the endoplasmic reticulum. Time-course studies demonstrated that maximal decreases in proteasome activity (4 hr) preceded maximal increases in clusterin expression (24 hr). Together these data suggest that proteasome impairment results in the upregulation of sCLU in SH-SY5Y cells, supporting the hypothesis that the association of clusterin with LBs in PD may be related to UPS failure.

Proteasomal inhibition induced by manganese ethylene-bis-dithiocarbamate: relevance to Parkinson's disease

Maneb, a widely used fungicide, has been associated with Parkinsonism in humans. In experimental models, maneb and its major active element, manganese ethylene-bis-dithiocarbamate (Mn-EBDC) cause selective nigrostriatal neurodegeneration in mice and in rats, respectively. To investigate the mechanisms underlying this neurodegeneration, we studied the effects of Mn-EBDC on proteasomal function, which is decreased in patients with Parkinson's disease (PD), in a dopaminergic neuronal cell line (MES 23.5 or MES). The results demonstrated that exposure of MES cells to 6 microM Mn-EBDC for 7 days produced not only significant neurotoxicity but also inhibition of proteasomal chymotrypsin-like and postglutamyl peptidase activities. Proteasomal dysfunction was accompanied by formation of cytoplasmic inclusions that were positive for alpha-synuclein immunostaining and significantly increased sodium dodecyl sulfate-insoluble alpha-synuclein aggregation seen by Western blot analysis. In addition, there was a significant increase in oxidative stress, evidenced by elevated total protein carbonyl content, in cells treated with Mn-EBDC. Manipulation of intracellular reduced glutathione levels with N-acetyl-L-cysteine or L-buthionine sulfoximine pretreatment to modulate Mn-EBDC-mediated oxidative stress altered Mn-EBDC-mediated neurotoxicity, proteasomal dysfunction, and alpha-synuclein aggregation in these cells. These data suggest that neurotoxicity-induced by Mn-EBDC is at least partially attributable to Mn-EBDC-mediated proteasomal inhibition, and that the proteasome may be an important target by which environmental exposure modifies the risk for developing PD in vulnerable populations.

Involvement of macroautophagy in the dissolution of neuronal inclusions

Ubiquitinated inclusions are a common feature of many neurodegenerative conditions. We have proposed that, at least in part, such inclusions may be formed due to dysfunction of the proteasome. We have modeled such proteasomal dysfunction by applying pharmacological inhibitors to cultured embryonic rat cortical neurons. This treatment leads to neuronal death and formation of ubiquitin/alpha-synuclein-positive cytoplasmic inclusions. At late time points following proteasomal inhibition such inclusions are no longer discerned. Instead, many neurons accumulate small ubiquitinated aggregates, which may represent remnants of the inclusions. In this work we have examined a potential mechanism for inclusion dissolution. Electron microscopy images showed activation of macroautophagy at late time points after proteasomal inhibition. Labeling with LysoTracker Red, a dye that accumulates in acidic compartments, or immunostaining for the lysosomal enzyme Cathepsin D, showed an increase in globular staining. Cathepsin D co-localized partially with small ubiquitinated aggregates, but not inclusions. Application of an inhibitor of macroautophagy or of the vacuolar ATPase led to an increase in the number of inclusions and a decrease in small aggregates, whereas an activator of autophagy had the opposite effects. There was no significant change in apoptotic death following these manipulations. We conclude that, following proteasomal inhibition of cultured cortical neurons, there is activation of macroautophagy and of the lysosomal pathway. This activation results in dissolution of ubiquitinated inclusions into small aggregates, without directly impacting neuronal cell death. These data further support the idea that in this model inclusions and neuronal cell death are independent processes.

Redox regulation in neurodegeneration and longevity: role of the heme oxygenase and HSP70 systems in brain stress tolerance

Efficient functioning of maintenance and repair processes seems to be crucial for both survival and physical quality of life. This is accomplished by a complex network of the so-called longevity assurance processes, which are composed of several genes termed "vitagenes," among these, the heat shock system, a highly conserved mechanism responsible for the preservation and repair of cellular macromolecules, such as proteins, RNAs, and DNA. Recent studies have shown that the heat shock response contributes to establishing a cytoprotective state in a wide variety of human diseases, including ischemia and reperfusion damage, inflammation, cancer, as well as metabolic and neurodegenerative disorders. Recently, the involvement of the heme oxygenase (HO) pathway in antidegenerative mechanisms has received considerable attention, as it has been demonstrated that the expression of HO is closely related to that of amyloid precursor protein. HO induction occurs together with the induction of other heat shock proteins during various physiopathological conditions. The vasoactive molecule carbon monoxide and the potent antioxidant bilirubin, products of HO-catalyzed reaction, represent a protective system potentially active against brain oxidative injury. Given the broad cytoprotective properties of the heat shock response, molecules inducing this defense mechanism appear to be possible candidates for novel cytoprotective strategies. Particularly, manipulation of endogenous cellular defense mechanisms, via the heat shock response, through nutritional antioxidants or pharmacological compounds, may represent an innovative approach to therapeutic intervention in diseases causing tissue damage, such as neurodegeneration. Consistently, by maintaining or recovering the activity of vitagenes, it is feasible to delay the aging process and decrease the occurrence of age-related diseases with resulting prolongation of a healthy life span.

Similarities between Methamphetamine Toxicity and Proteasome Inhibition

The monoamine neurotoxin methamphetamine (METH) is commonly used as an experimental model for Parkinson's disease (PD). In fact, METH-induced striatal dopamine (DA) loss is accompanied by damage to striatal nerve endings arising from the substantia nigra. On the other hand, PD is characterized by neuronal inclusions within nigral DA neurons. These inclusions contain alpha-synuclein, ubiquitin, and various components of a metabolic pathway named the ubiquitin-proteasome (UP) system, while mutation of genes coding for various components of the UP system is responsible for inherited forms of PD. In this presentation we demonstrate for the first time the occurrence of neuronal inclusions in vivo in the nigrostriatal system of the mouse following administration of METH. We analyzed, in vivo and in vitro, the shape and the fine structure of these neuronal bodies by using transmission electron microscopy. Immunocytochemical investigation showed that these METH-induced cytosolic inclusions stain for ubiquitin, alpha-synuclein, and UP-related molecules, thus sharing similar components with Lewy bodies occurring in PD, with an emphasis on enzymes belonging to the UP system. In line with this, blockade of this multicatalytic pathway by the selective inhibitor epoxomycin produced cell inclusions with similar features. Moreover, using a multifaceted pharmacological approach, we could demonstrate the need for endogenous DA in order to form neuronal inclusions.

Identification of the human ubiquitin specific protease 31 (USP31) gene: structure, sequence and expression analysis

Parkinson's disease (PD) is a common neurodegenerative disorder with clinical features of bradykinesia, rigidity and resting tremor resulting from the deficiency of dopamine in the nigrostriatal system. Recently, PARK6 was identified as a novel locus associated with autosomal recessive PD. Here we report the identification and characterization of a novel human deubiquitylating gene (USP31), which maps to the critical PARK6 region. Database analysis and 5' RACE identified a 4070bp cDNA, encoded by 27 exons spanning approximately 105kbp of genomic sequence. The predicted protein of 1035 amino acids included a conserved ubiquitin hydrolase region (Prosite profile PS50235), a DUSP (domain in ubiquitin specific proteases-Smart00695) and a ubiquitin-like domain (Prosite pattern PS00299). Northern blot analysis revealed a single USP31 transcript of approximately 4 kb, which was primarily expressed in the testis and lung.

Role of the ubiquitin-proteasome pathway in the diagnosis of human diseases

The ubiquitin-proteasome pathway constitutes the major system for nuclear and extralysosomal cytosolic protein degradation in eukaryotic cells. A plethora of cell proteins implicated in the maintenance and regulation of essential cellular processes undergoes processing and functional modification by proteolytic degradation via the ubiquitin-proteasome pathway. Deregulations of the pathway have been shown to contribute to the pathogenesis of several human diseases, such as cancer, neurodegenerative, autoimmune, genetic and metabolic disorders, most of them exhibiting abnormal accumulation and altered composition of components of the pathway that is suitable for diagnostic proceedings. While the ubiquitin-proteasome pathway is currently exploited to develop novel therapeutic strategies, it is less regarded as a diagnostic area. Future research should lead to an improved understanding of the pathophysiology of the ubiquitin-proteasome pathway with the aim of allowing the development of subtle diagnostic strategies.

Neuronal pathology in Parkinson?s disease

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra leading to the major clinical and pharmacological abnormalities of PD. In order to establish causal or protective treatments for PD, it is necessary to identify the cascade of deleterious events that lead to the dysfunction and death of dopaminergic neurons. Based on genetic, neuropathological, and biochemical data in patients and experimental animal models, dysfunction of the ubiquitin-proteasome pathway, protein aggregation, mitochondrial dysfunction, oxidative stress, activation of the c-Jun N-terminal kinase pathway, and inflammation have all been identified as important pathways leading to excitotoxic and apoptotic death of dopaminergic neurons. Toxin-based and genetically engineered animal models allow (1) the study of the significance of these aspects and their interaction with each other and (2) the development of causal treatments to stop disease progression.

Generalized brain and skin proteasome inhibition in Huntington's disease

Mutated intracellular huntingtin is widely expressed in tissues of Huntington's disease (HD) patients. Intraneuronal nuclear protein aggregates of mutant huntingtin are present in HD brains, suggesting a dysfunction of the ubiquitin proteasome system (UPS). Because many cells and tissues can cope with the abnormal gene effects while others dysfunction and die, we determined gene-induced effects and considered the hypothesis that the gene causes multiple intracellular problems, but severe pathology is seen only in selected brain regions. In this study, we found inhibition of UPS function in both early (0-1, with no or little neuronal loss) and late (3-4, with more severe neuronal loss) stage HD patients' cerebellum, cortex, substantia nigra and caudate-putamen brain regions. Late HD stage increases in ubiquitin levels were unique to caudate-putamen. HD patients' skin fibroblasts also had UPS inhibition similar to brain despite increases in proteasome beta-subunit expression. Gene delivery and expression of proteasome activator PA28 increased UPS function in normal but not HD fibroblasts. These generalized UPS problems are associated with severe neuronal pathology only when coupled with decreases in brain-derived neurotrophic factor levels, mitochondrial complex II/III activity, and increases of ubiquitin levels particularly as seen in the caudate-putamen of HD patients.

Impaired degradation of mutant alpha-synuclein by chaperone-mediated autophagy

Aberrant alpha-synuclein degradation is implicated in Parkinson's disease pathogenesis because the protein accumulates in the Lewy inclusion bodies associated with the disease. Little is known, however, about the pathways by which wild-type alpha-synuclein is normally degraded. We found that wild-type alpha-synuclein was selectively translocated into lysosomes for degradation by the chaperone-mediated autophagy pathway. The pathogenic A53T and A30P alpha-synuclein mutants bound to the receptor for this pathway on the lysosomal membrane, but appeared to act as uptake blockers, inhibiting both their own degradation and that of other substrates. These findings may underlie the toxic gain-of-function by the mutants.

Inhibition of tyrosine hydroxylase expression in α-synuclein-transfected dopaminergic neuronal cells

Although the aberrant expression of alpha-synuclein (alpha-Syn) is toxic to dopaminergic neurons, little is known about the correlation between the abnormality of alpha-Syn and the expression of tyrosine hydroxylase (TH), a rate-limiting enzyme for the synthesis of dopamine neurotransmitter. In this study, the MES23.5 rat dopaminergic cell line transfected with wild-type human alpha-Syn cDNA (h alpha-Syn) construct was used to investigate the association between alpha-Syn and TH. Immunocytochemical staining and Western blot for TH showed that the TH expression was greatly decreased in h alpha-Syn-transfected cells. Northern blot confirmed that the TH mRNA level was also dramatically reduced. Reduction of TH protein levels did not affect the growth and proliferation of the transfected cells. No apparent cell injury or death was observed. These results suggest that an abnormal expression of alpha-Syn may inhibit TH synthesis in dopaminergic cells.

Focal dysfunction of the proteasome: a pathogenic factor in a mouse model of amyotrophic lateral sclerosis

Mutations in the Cu/Zn-superoxide dismutase (SOD-1) gene are responsible for a familial form of amyotrophic lateral sclerosis (fALS). The present study demonstrated impaired proteasomal function in the lumbar spinal cord of transgenic mice expressing human SOD-1 with the ALS-causing mutation G93A (SOD-1(G93A)) compared to non-transgenic littermates (LM) and SOD-1(WT) transgenic mice. Chymotrypsin-like activity was decreased as early as 45 days of age. By 75 days, chymotrypsin-, trypsin-, and caspase-like activities of the proteasome were impaired, at about 50% of control activity in lumbar spinal cord, but unchanged in thoracic spinal cord and liver. Both total and specific activities of the proteasome were reduced to a similar extent, indicating that a change in proteasome function, rather than a decrease in proteasome levels, had occurred. Similar decreases of total and specific activities of the proteasome were observed in NIH 3T3 cell lines expressing fALS mutants SOD-1(G93A) and SOD-1(G41S), but not in SOD-1(WT) controls. Although overall levels of proteasome were maintained in spinal cord of SOD-1(G93A) transgenic mice, the level of 20S proteasome was substantially reduced in lumbar spinal motor neurons relative to the surrounding neuropil. It is concluded that impairment of the proteasome is an early event and contributes to ALS pathogenesis.

Loss of an individual proteasome subunit alters motor function but not cognitive function or ambulation in mice

The proteasome is a large intracellular protease, composed of multiple subunits, that is present in all cells. In the present study we examined motor function, cognitive function, and ambulation in transgenic mice that lack the low molecular protein 2 (LMP2) proteasome subunit. Comparison of LMP2 knock out (LMP2 KO) mice and non-transgenic mice of the same background demonstrate that LMP2 KO mice exhibit a higher degree of motor function, but possess a similar level of cognitive function and ambulation, as compared to non-transgenic control mice. Interestingly, LMP2 KO mice also exhibited increased body weight as compared to non-transgenic mice. These data demonstrate for the first time that specific proteasome subunits may play a role in regulating both brain function and body weight.

Transcriptional activation of p62/A170/ZIP during the formation of the aggregates: possible mechanisms and the role in Lewy body formation in Parkinson's disease

Formation of intracellular inclusion bodies due to defects in the protein degradation machinery is associated with the pathogenesis of neurodegenerative diseases. Sequestosomal protein p62/A170/ZIP, which is an oxidative stress-related protein and a ubiquitin-binding protein, is a component protein of Lewy bodies that are observed in patients with Parkinson's disease. The association of p62 with poly-ubiquitinated proteins may be an important step in the formation of intracellular protein aggregates like Lewy bodies. To study the role of p62 in the formation of protein aggregates in PC12 cells, we monitored the intracellular localizations of p62 and ubiquitinated proteins and the levels of both components during treatment with MG132, a proteasome inhibitor. In the early stage of aggregate formation, p62 did not always co-localize with ubiquitin. In contrast, these proteins were always co-localized in later stages. After the treatment of the cells with MG132, we found that the expression level of p62 increased due to the transcriptional activation of the gene and that higher molecular sizes of p62, corresponding to mono- and di-ubiquitinated formes, were also formed. Both the transcriptional inhibitor actinomycin D and an antisense oligonucleotide of p62 inhibited the MG132-mediated increase of p62, the sequestration of ubiquitinated proteins, and the enlargement of the aggregates. Furthermore, p62-positive aggregates were observed primarily in surviving cells. Together, these results suggest that p62 plays an important role in the protection of cells from the toxicity of misfolded proteins by enhancing aggregate formation especially in the later stages.

A critical review of the development and importance of proteinaceous aggregates in animal models of Parkinson's disease: new insights into Lewy body formation

The pace of development of new animal models of Parkinson's disease (PD) has increased dramatically in the recent past, primarily because of the identification of the protein, alpha-synuclein, in Lewy bodies in both idiopathic and familial PD. This discovery has allowed the production of transgenic models that incorporate a form of human, mutant alpha-synuclein from rare familial cases, and has enabled the search for Lewy-body-like aggregations of this protein in toxin-induced models. Indeed, alpha-synuclein-positive inclusions, some of which bear strong resemblance to Lewy bodies, have now been recognized and their formation investigated in several different, environmentally-induced and transgenic models. Nevertheless, these data have yet to provide a uniform theory of inclusion pathogenesis for PD. The aim of this review is not only to summarize the findings to date on alpha-synuclein-immunopositive inclusion bodies, including some new information on Lewy bodies, but also provide a concise viewpoint on their origin and formation in animal models. We will provide evidence for a predicted series of intracellular events that underlie inclusion formation. Triggered by oxidative and metabolic stress, chronic, toxin-treated animals, rather than transgenic models transfected with human alpha-synuclein, eventually produce inclusion bodies that most closely resemble early stages of Lewy bodies. Elucidating the common mechanisms in animal models is a first step towards understanding the role of Lewy bodies and their formation in Parkinson's disease.

Parkinson's disease

Parkinson's disease is the most common serious movement disorder in the world, affecting about 1% of adults older than 60 years. The disease is attributed to selective loss of neurons in the substantia nigra, and its cause is enigmatic in most individuals. Symptoms of Parkinson's disease respond in varying degrees to drugs, and surgery offers hope for patients no longer adequately controlled in this manner. The high prevalence of the disease, and important advances in its management, mean that generalists need to have a working knowledge of this disorder. This Seminar covers the basics, from terminology to aspects of diagnosis, treatment, and pathogenesis.

Genetic ablation of tumor necrosis factor-alpha (TNF-alpha) and pharmacological inhibition of TNF-synthesis attenuates MPTP toxicity in mouse striatum

The impact of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) in the pathology of Parkinson's disease (PD) and in MPTP neurotoxicity remains unclear. Here, male TNF-alpha (-/-) deficient mice and C57bL/6 mice were treated with MPTP (4 x 15 mg/kg, 24 h intervals) and in one series, thalidomide was administered to inhibit TNF-alpha synthesis. Real-time RT-PCR revealed that the striatal mRNA levels of TNF-alpha, of the astrocytic marker glial fibrillary acidic protein (GFAP) and of the marker for activated microglia, macrophage antigen complex-1 (MAC-1), were significantly enhanced after MPTP administration. Thalidomide (50 mg/kg, p.o.) partly protected against the MPTP-induced dopamine (DA) depletion, and TNF-alpha (-/-) mice showed a significant attenuation of striatal DA and DA metabolite loss as well as striatal tyrosine hydroxylase (TH) fiber density, but no difference in nigral TH and DA transporter immunoreactivity. TNF-alpha deficient mice suffered a lower mortality (10%) compared to the high mortality (75%) seen in wild-type mice after acute MPTP treatment (4 x 20 mg/kg, 2 h interval). HPLC measurement of MPP(+) levels revealed no differences in TNF-alpha (-/-), wild-type and thalidomide treated mice. This study demonstrates that TNF-alpha is involved in MPTP toxicity and that inhibition of TNF-alpha response may be a promising target for extending beyond symptomatic treatment and developing anti-parkinsonian drugs for the treatment of the inflammatory processes in PD.

Pael-R is accumulated in Lewy bodies of Parkinson's disease

We examined the distribution of Pael-R, a newly identified substrate for Parkin, in Parkinson's disease (PD) and multiple system atrophy (MSA). Pael-R, Parkin, alpha-synuclein, and ubiquitin accumulated in Lewy bodies (LBs) and neurites. Pael-R was localized in the core of LBs. Parkin and alpha-synuclein accumulated in the halo, neuronal cell bodies, and processes. These findings potentially suggest the involvement of Pael-R in LB formation, and protection role of Parkin in Pael-R-mediated neurotoxicity in PD. The absence of Pael-R and Parkin in glial cytoplasmic inclusions (GCIs) in MSA implies a distinct pathway involved in the formation of LBs and GCIs.

Senescence-initiated Reversal of Drug Resistance

The present study was undertaken to verify whether induction of senescence could be sufficient to reverse drug resistance and, if so, to determine the underlying mechanism(s). Our findings indicated that cotreatment of drug-resistant neuroblastoma cells with doxorubicin, at sublethal concentrations, in combination with the pan-caspase inhibitor, Q-VD-OPH, elicited a strong reduction of cell viability that occurred in a caspase-independent manner. This was accompanied by the appearance of a senescence phenotype, as evidenced by increased p21/WAF1 expression and senescence-associated beta-galactosidase activity. Experiments using specific inhibitors of major cellular proteases other than caspases have shown that inhibition of cathepsin L, but not proteasome or cathepsin B, was responsible for the senescence-initiated reversal of drug resistance. This phenomenon appeared to be general because it was valid for other drugs and drug-resistant cell lines. A nonchemical approach, through cell transfection with cathepsin L small interfering RNA, also strongly reversed drug resistance. Further investigation of the underlying mechanism revealed that cathepsin L inhibition resulted in the alteration of intracellular drug distribution. In addition, in vitro experiments have demonstrated that p21/WAF1 is a substrate for cathepsin L, suggesting that inhibition of this enzyme may result in p21/WAF1 stabilization and its increased accumulation. All together, these findings suggest that cathepsin L inhibition in drug-resistant cells facilitates induction of senescence and reversal of drug resistance. This may represent the basis for a novel function of cathepsin L as a cell survival molecule responsible for initiation of resistance to chemotherapy.