Changes in Liver Lipidomic Profile in G2019S-LRRK2 Mouse Model of Parkinson's Disease

The identification of Parkinson's disease (PD) biomarkers has become a main goal for the diagnosis of this neurodegenerative disorder. PD has not only been intrinsically related to neurological problems, but also to a series of alterations in peripheral metabolism. The purpose of this study was to identify metabolic changes in the liver in mouse models of PD with the scope of finding new peripheral biomarkers for PD diagnosis. To achieve this goal, we used mass spectrometry technology to determine the complete metabolomic profile of liver and striatal tissue samples from WT mice, 6-hydroxydopamine-treated mice (idiopathic model) and mice affected by the G2019S-LRRK2 mutation in LRRK2/PARK8 gene (genetic model). This analysis revealed that the metabolism of carbohydrates, nucleotides and nucleosides was similarly altered in the liver from the two PD mouse models. However, long-chain fatty acids, phosphatidylcholine and other related lipid metabolites were only altered in hepatocytes from G2019S-LRRK2 mice. In summary, these results reveal specific differences, mainly in lipid metabolism, between idiopathic and genetic PD models in peripheral tissues and open up new possibilities to better understand the etiology of this neurological disorder.

Biological effects of olive oil phenolic compounds on mitochondria

Phenolic compounds derived from olive oil have beneficial health properties against cancer, neurodegenerative, and metabolic diseases. Therefore, there are discrepancies in their impact on mitochondrial function that result in changes in oxidative capacity, mitochondrial respiration, and energetic demands. This review focuses on the versatile role of oleuropein, a potent antioxidant that regulates the AMPK/SIRT1/mTOR pathway to modulate autophagy/mitophagy and maintain metabolic homeostasis.

The parkinsonian LRRK2 R1441G mutation shows macroautophagy-mitophagy dysregulation concomitant with endoplasmic reticulum stress

Autophagy is a mechanism responsible for the degradation of cellular components to maintain their homeostasis. However, autophagy is commonly altered and compromised in several diseases, including neurodegenerative disorders. Parkinson's disease (PD) can be considered a multifactorial disease because environmental factors, genetic factors, and aging are involved. Several genes are involved in PD pathology, among which the LRRK2 gene and its mutations, inherited in an autosomal dominant manner, are responsible for most genetic PD cases. The R1441G LRRK2 mutation is, after G2019S, the most important in PD pathogenesis. Our results demonstrate a relationship between the R1441G LRRK2 mutation and a mechanistic dysregulation of autophagy that compromises cell viability. This altered autophagy mechanism is associated with organellar stress including mitochondrial (which induces mitophagy) and endoplasmic reticulum (ER) stress, consistent with the fact that patients with this mutation are more vulnerable to toxins related to PD, such as MPP⁺.

Metabolic alterations in plasma from patients with familial and idiopathic Parkinson's disease

The research of new biomarkers for Parkinson's disease is essential for accurate and precocious diagnosis, as well as for the discovery of new potential disease mechanisms and drug targets. The main objective of this work was to identify metabolic changes that might serve as biomarkers for the diagnosis of this neurodegenerative disorder. For this, we profiled the plasma metabolome from mice with neurotoxin-induced Parkinson's disease as well as from patients with familial or sporadic Parkinson's disease. By using mass spectrometry technology, we analyzed the complete metabolome from healthy volunteers compared to patients with idiopathic or familial (carrying the G2019S or R1441G mutations in the LRRK2 gene) Parkinson's disease, as well as, from mice treated with 6-hydroxydopamine to induce Parkinson disease. Both human and murine Parkinson was accompanied by an increase in plasma levels of unconjugated bile acids (cholic acid, deoxycholic acid and lithocholic acid) and purine base intermediary metabolites, in particular hypoxanthine. The comprehensive metabolomic analysis of plasma from Parkinsonian patients underscores the importance of bile acids and purine metabolism in the pathophysiology of this disease. Therefore, plasma measurements of certain metabolites related to these pathways might contribute to the diagnosis of Parkinson's Disease.

Impaired Mitophagy and Protein Acetylation Levels in Fibroblasts from Parkinson's Disease Patients

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder. While most PD cases are idiopathic, the known genetic causes of PD are useful to understand common disease mechanisms. Recent data suggests that autophagy is regulated by protein acetylation mediated by histone acetyltransferase (HAT) and histone deacetylase (HDAC) activities. The changes in histone acetylation reported to be involved in PD pathogenesis have prompted this investigation of protein acetylation and HAT and HDAC activities in both idiopathic PD and G2019S leucine-rich repeat kinase 2 (LRRK2) cell cultures. Fibroblasts from PD patients (with or without the G2019S LRRK2 mutation) and control subjects were used to assess the different phenotypes between idiopathic and genetic PD. G2019S LRRK2 mutation displays increased mitophagy due to the activation of class III HDACs whereas idiopathic PD exhibits downregulation of clearance of defective mitochondria. This reduction of mitophagy is accompanied by more reactive oxygen species (ROS). In parallel, the acetylation protein levels of idiopathic and genetic individuals are different due to an upregulation in class I and II HDACs. Despite this upregulation, the total HDAC activity is decreased in idiopathic PD and the total HAT activity does not significantly vary. Mitophagy upregulation is beneficial for reducing the ROS-induced harm in genetic PD. The defective mitophagy in idiopathic PD is inherent to the decrease in class III HDACs. Thus, there is an imbalance between total HATs and HDACs activities in idiopathic PD, which increases cell death. The inhibition of HATs in idiopathic PD cells displays a cytoprotective effect.

Acetylome in Human Fibroblasts From Parkinson's Disease Patients

Parkinson's disease (PD) is a multifactorial neurodegenerative disorder. The pathogenesis of this disease is associated with gene and environmental factors. Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most frequent genetic cause of familial and sporadic PD. Moreover, posttranslational modifications, including protein acetylation, are involved in the molecular mechanism of PD. Acetylation of lysine proteins is a dynamic process that is modulated in PD. In this descriptive study, we characterized the acetylated proteins and peptides in primary fibroblasts from idiopathic PD (IPD) and genetic PD harboring G2019S or R1441G LRRK2 mutations. Identified acetylated peptides are modulated between individuals' groups. Although acetylated nuclear proteins are the most represented in cells, they are hypoacetylated in IPD. Results display that the level of hyperacetylated and hypoacetylated peptides are, respectively, enhanced in genetic PD and in IPD cells.

ER-mitochondria signaling in Parkinson's disease

Mitochondria form close physical contacts with a specialized domain of the endoplasmic reticulum (ER), known as the mitochondria-associated membrane (MAM). This association constitutes a key signaling hub to regulate several fundamental cellular processes. Alterations in ER-mitochondria signaling have pleiotropic effects on a variety of intracellular events resulting in mitochondrial damage, Ca2+ dyshomeostasis, ER stress and defects in lipid metabolism and autophagy. Intriguingly, many of these cellular processes are perturbed in neurodegenerative diseases. Furthermore, increasing evidence highlights that ER-mitochondria signaling contributes to these diseases, including Parkinson's disease (PD). PD is the second most common neurodegenerative disorder, for which effective mechanism-based treatments remain elusive. Several PD-related proteins localize at mitochondria or MAM and have been shown to participate in ER-mitochondria signaling regulation. Likewise, PD-related mutations have been shown to damage this signaling. Could ER-mitochondria associations be the link between pathogenic mechanisms involved in PD, providing a common mechanism? Would this provide a pharmacological target for treating this devastating disease? In this review, we aim to summarize the current knowledge of ER-mitochondria signaling and the recent evidence concerning damage to this signaling in PD.

N370S-GBA1 mutation causes lysosomal cholesterol accumulation in Parkinson's disease

BACKGROUND

Heterozygous mutations in the GBA1 gene, which encodes the lysosomal enzyme β-glucocerebrosidase-1, increase the risk of developing Parkinson's disease, although the underlying mechanisms remain unclear. The aim of this study was to explore the impact of the N370S-GBA1 mutation on cellular homeostasis and vulnerability in a patient-specific cellular model of PD.

METHODS

We isolated fibroblasts from 4 PD patients carrying the N370S/wild type GBA1 mutation and 6 controls to study the autophagy-lysosome pathway, endoplasmic reticulum stress, and Golgi apparatus structure by Western blot, immunofluorescence, LysoTracker and Filipin stainings, mRNA analysis, and electron microscopy. We evaluated cell vulnerability by apoptosis, reactive oxygen species and mitochondrial membrane potential with flow cytometry.

RESULTS

The N370S mutation produced a significant reduction in β-glucocerebrosidase-1 protein and enzyme activity and β-glucocerebrosidase-1 retention within the endoplasmic reticulum, which interrupted its traffic to the lysosome. This led to endoplasmic reticulum stress activation and triggered unfolded protein response and Golgi apparatus fragmentation. Furthermore, these alterations resulted in autophagosome and p62/SQSTM1 accumulation. This impaired autophagy was a result of dysfunctional lysosomes, indicated by multilamellar body accumulation probably caused by increased cholesterol, enlarged lysosomal mass, and reduced enzyme activity. This phenotype impaired the removal of damaged mitochondria and reactive oxygen species production and enhanced cell death.

CONCLUSIONS

Our results support a connection between the loss of β-glucocerebrosidase-1 function, cholesterol accumulation, and the disruption of cellular homeostasis in GBA1-PD. Our work reveals new insights into the cellular pathways underlying PD pathogenesis, providing evidence that GBA1-PD shares common features with lipid-storage diseases. © 2017 International Parkinson and Movement Disorder Society.

Pompe Disease and Autophagy: Partners in Crime, or Cause and Consequence?

Pompe disease or glycogen storage disease type II (OMIM: 232300) is a lysosomal storage disorder resulting from a partial or total lack of acid alphaglucosidase, which may produce muscle weakness, gait abnormalities, or even death by respiratory failure. In the last decade, autophagy has been proposed as a mechanism involved in the severity of symptoms related to this disorder and as a potential therapeutic target to alleviate disease progression. This review summarizes the relationship between autophagy and Pompe disease, including what information has been recently discovered and what remains unclear.

Mitochondria-Associated Membranes (MAMs): Overview and Its Role in Parkinson's Disease

Mitochondria-associated membranes (MAMs) are structures that regulate physiological functions between endoplasmic reticulum (ER) and mitochondria in order to maintain calcium signaling and mitochondrial biogenesis. Several proteins located in MAMs, including those encoded by PARK genes and some of neurodegeneration-related proteins (huntingtin, presenilin, etc.), ensure this regulation. In this regard, MAM alteration is associated with neurodegenerative diseases such as Parkinson's (PD), Alzheimer's (AD), and Huntington's diseases (HD) and contributes to the appearance of the pathogenesis features, i.e., autophagy dysregulation, mitochondrial dysfunction, oxidative stress, and lately, neuronal death. Moreover,, ER stress and/or damaged mitochondria can be the cause of these disruptions. Therefore, ER-mitochondria contact structure and function are crucial to multiple cellular processes. This review is focused on the molecular interaction between ER and mitochondria indispensable to MAM formation and on MAM alteration-induced etiology of neurodegenerative diseases.

mRNA and protein dataset of autophagy markers (LC3 and p62) in several cell lines

We characterized the dynamics of autophagy in vitro using four different cell systems and analyzing markers widely used in this field, i.e. LC3 (microtubule-associated protein 1 light chain 3; protein recruited from the cytosol (LC3-I) to the autophagosomal membrane where it is lipidated (LC3-II)) and p62/SQSTM1 (adaptor protein that serves as a link between LC3 and ubiquitinated substrates), (Klionsky et al., 2016) [1]. Data provided include analyses of protein levels of LC3 and p62 by Western-blotting and endogenous immunofluorescence experiments, but also p62 mRNA levels obtained by quantitative PCR (qPCR). To monitor the turnover of these autophagy markers and, thus, measure the flux of this pathway, cells were under starvation conditions and/or treated with bafilomycin A1 (Baf. A1) to block fusion of autophagosomes with lysosomes.

IFDOTMETER: A New Software Application for Automated Immunofluorescence Analysis

Most laboratories interested in autophagy use different imaging software for managing and analyzing heterogeneous parameters in immunofluorescence experiments (e.g., LC3-puncta quantification and determination of the number and size of lysosomes). One solution would be software that works on a user's laptop or workstation that can access all image settings and provide quick and easy-to-use analysis of data. Thus, we have designed and implemented an application called IFDOTMETER, which can run on all major operating systems because it has been programmed using JAVA (Sun Microsystems). Briefly, IFDOTMETER software has been created to quantify a variety of biological hallmarks, including mitochondrial morphology and nuclear condensation. The program interface is intuitive and user-friendly, making it useful for users not familiar with computer handling. By setting previously defined parameters, the software can automatically analyze a large number of images without the supervision of the researcher. Once analysis is complete, the results are stored in a spreadsheet. Using software for high-throughput cell image analysis offers researchers the possibility of performing comprehensive and precise analysis of a high number of images in an automated manner, making this routine task easier.

PINK1 deficiency enhances autophagy and mitophagy induction

Parkinson's disease (PD) is a neurodegenerative disorder with poorly understood etiology. Increasing evidence suggests that age-dependent compromise of the maintenance of mitochondrial function is a key risk factor. Several proteins encoded by PD-related genes are associated with mitochondria including PTEN-induced putative kinase 1 (PINK1), which was first identified as a gene that is upregulated by PTEN. Loss-of-function PINK1 mutations induce mitochondrial dysfunction and, ultimately, neuronal cell death. To mitigate the negative effects of altered cellular functions cells possess a degradation mechanism called autophagy for recycling damaged components; selective elimination of dysfunctional mitochondria by autophagy is termed mitophagy. Our study indicates that autophagy and mitophagy are upregulated in PINK1-deficient cells, and is the first report to demonstrate efficient fluxes by one-step analysis. We propose that autophagy is induced to maintain cellular homeostasis under conditions of non-regulated mitochondrial quality control.

Autophagy, mitochondria and 3-nitropropionic acid joined in the same model

Huntington's disease (HD) is a neurodegenerative disorder caused by a mutation in the gene encoding the huntingtin protein. Although the precise mechanism by which neuronal degeneration occurs is still unclear, several elements are important to its development: (1) altered gene expression and protein synthesis, (2) mitochondrial damage and (3) improper regulation of the autophagy programme. In this issue of British Journal of Pharmacology, Galindo and co-workers provide the first evidence for a role of the mitochondrial permeability transition pore (mPTP) in mitochondrial fragmentation and autophagy activation. In a model of cell death induced by 3-nitropropionic acid (3-NP) in human neural cells, the authors describe clear functions for mPTP and Bax, but not the mitochondrial fusion/fission machinery, mitochondrial fragmentation and autophagy (mitophagy). This commentary summarises the significance of this relationship and suggests several points for future development.

The MAPK1/3 pathway is essential for the deregulation of autophagy observed in G2019S LRRK2 mutant fibroblasts

The link between the deregulation of autophagy and cell death processes can be essential in the development of several neurodegenerative diseases, such as Parkinson disease (PD). However, the molecular mechanism of deregulation of this degradative process in PD patients is unknown. The leucine-rich repeat kinase 2 (LRRK2) gene is related to PD and its implication in autophagy regulation has been described. Our recent work shows that the presence of the G2019S LRRK2 mutation, one of the most prevalent in LRRK2, is accompanied by a deregulation of autophagy basal levels dependent on the MAPK1/3 (ERK2/1) pathway.

Fipronil is a powerful uncoupler of oxidative phosphorylation that triggers apoptosis in human neuronal cell line SHSY5Y

Fipronil is a phenylpyrazole insecticide known to elicit neurotoxicity via an interaction with ionotropic receptors, namely GABA and glutamate receptors. Recently, we showed that fipronil and other phenylpyrazole compounds trigger cell death in Caco-2 cells. In this study, we investigated the mode of action and the type of cell death induced by fipronil in SH-SY5Y human neuroblastoma cells. Flow cytometric and western blot analyses demonstrated that fipronil induces cellular events belonging to the apoptosis process, such as mitochondrial potential collapse, cytochrome c release, caspase-3 activation, nuclear condensation and phosphatidylserine externalization. In addition, fipronil induces a rapid ATP depletion with concomitant activation of anaerobic glycolysis. This cellular response is characteristic of mitochondrial injury associated with a defect of the respiration process. Therefore, we also investigated the effect of fipronil on the oxygen consumption in isolated mitochondria. Interestingly, we show for the first time that fipronil is a strong uncoupler of oxidative phosphorylation at relative low concentrations. Thus in this study, we report a new mode of action by which the insecticide fipronil could triggers apoptosis.

DJ-1 as a modulator of autophagy: an hypothesis

The etiology of Parkinson's disease (PD) is not completely defined, although environmental factors (for example, exposure to the herbicide paraquat [PQ]) and genetic susceptibility (such as DJ-1 mutations that have been associated with an autosomal-recessive form of early-onset PD) have been demonstrated to contribute. Alterations in macroautophagy have been described in the pathogenesis of this neurodegenerative disease. We have established a model system to study the involvement of the DJ-1 protein in PQ-induced autophagy. When we transfected cells exposed to PQ with DJ-1–specific siRNA, we observed an inhibition of the autophagic events induced by the herbicide, as well as sensitization additive with PQ-induced apoptotic cell death and exacerbation of this cell death in the presence of the autophagy inhibitor 3-methyladenine. These results suggest, for the first time, an active role for DJ-1 in the autophagic response produced by PQ, opening the door to new strategies for PD therapy.

The neuroprotective effect of talipexole from paraquat-induced cell death in dopaminergic neuronal cells

Talipexole is a non-ergot dopamine (DA) agonist that has been used in the treatment of Parkinson's disease. In the present study, we examined the effect of talipexole on paraquat (PQ)-induced N27 cell death and the intracellular pathways involved in this effect. Pretreatment of N27 cells with talipexole (1mM) resulted in significant protection against paraquat-induced cell death. In N27 cells, talipexole inhibited paraquat-induced apoptotic hallmarks such as cytochrome c release, caspase-3 activation, chromatin condensation and externalization of phosphatidilserine. Talipexole pretreatment prevents the reduction in the anti-apoptotic Bcl-x(L) protein and increases in the pro-apoptotic form of Bak and p-Bad, both induced by PQ. Finally, we also observed that talipexole abrogates the activation of cell death pathways JNK1/2 and p38 produced by PQ, and increases the phosphorylated (active) forms of the pro-survival pathways ERK1/2 and Akt. These results reveal that talipexole exerts a neuroprotective effect in a mesencephalic cell line exposed to the neurotoxin PQ, which is related to the etiology of Parkinson's disease.

[Genetic screening for the LRRK2, G2019S and R1441 codon mutations in Parkinson's disease patients from Extremadura, Spain]

INTRODUCTION

LRRK2 mutations have been described as a common cause of Parkinson's disease (PD) in patients from northern Spain. Here we investigated the prevalence of these mutations in a cohort of Spanish PD patients (n = 96) from Extremadura, a region in southwestern Spain.

SUBJECTS AND METHODS

To evaluate the rate of the G2019S and R1441G/C/H LRKK2 mutations in PD patients and healthy controls (n = 163).

RESULTS

Here we show that the G2019S mutation is present at a low prevalence in our Spanish cohort, while the R1441G/C/H mutation, which has been reported to be common in northern Spain, was not observed in the PD patients or in the controls.

CONCLUSION

LRRK2 mutations do not appear to be a common cause of Parkinson's disease in Extremadura, Spain.

Activation of apoptosis signal-regulating kinase 1 is a key factor in paraquat-induced cell death: modulation by the Nrf2/Trx axis

Although oxidative stress is fundamental to the etiopathology of Parkinson disease, the signaling molecules involved in transduction after oxidant exposure to cell death are ill-defined, thus making it difficult to identify molecular targets of therapeutic relevance. We have addressed this question in human dopaminergic neuroblastoma SH-SY5Y cells exposed to the parkinsonian toxin paraquat (PQ). This toxin elicited a dose-dependent increase in reactive oxygen species and cell death that correlated with activation of ASK1 and the stress kinases p38 and JNK. The relevance of these kinases in channeling PQ neurotoxicity was demonstrated with the use of interference RNA for ASK1 and two well-established pharmaceutical inhibitors for JNK and p38. The toxic effect of PQ was substantially attenuated by preincubation with vitamin E, blocking ASK1 pathways and preventing oxidative stress and cell death. In a search for a physiological pathway that might counterbalance PQ-induced ASK1 activation, we analyzed the role of the transcription factor Nrf2, master regulator of redox homeostasis, and its target thioredoxin (Trx), which binds and inhibits ASK1. Trx levels were undetectable in Nrf2-deficient mouse embryo fibroblasts (MEFs), whereas they were constitutively high in Keap1-deficient MEFs as well as in SH-SY5Y cells treated with sulforaphane (SFN). Consistent with these data, Nrf2-deficient MEFs were more sensitive and Keap1-deficient MEFs and SH-SY5Y cells incubated with SFN were more resistant to PQ-induced cell death. This study identifies ASK1/JNK and ASK1/p38 as two critical pathways involved in the activation of cell death under oxidative stress conditions and identifies the Nrf2/Trx axis as a new target to block these pathways and protect from oxidant exposure such as that found in Parkinson and other neurodegenerative diseases.

Curcumin enhances paraquat-induced apoptosis of N27 mesencephalic cells via the generation of reactive oxygen species

Curcumin, the active compound of the rhizome of Curcuma longa has anti-inflammatory, antioxidant and antiproliferative activities. This agent has been shown to regulate numerous transcription factors, cytokines, protein kinases, adhesion molecules, redox status and enzymes that have been linked to inflammation. While curcumin has been identified as an activator of apoptosis in several cell lines, the mechanism by which it initiates apoptosis, however, remains poorly understood. We considered curcumin from the point of view of its ability to protect against oxidative stress, the latter being one factor strongly implicated in the development of Parkinson's disease. Although the etiology of Parkinson's disease remains unknown, epidemiological studies have linked exposure to pesticides such paraquat to an increased risk of developing the condition. Analysis of the neurotoxic properties of these pesticide compounds has been focused on their ability to induce oxidative stress in neural cells. Given curcumin's capacity to protect against oxidative stress, it has been considered as a potential therapeutic agent for neurodegenerative diseases such as Parkinson's disease that involve an oxidative stress component. In the present report we describe the effect of curcumin in paraquat-mediated apoptosis of N27 mesencepahlic cells. We show that subtoxic concentrations of curcumin sensitize N27 mesencephalic cells to paraquat-mediated apoptosis.

Relationship between autophagy and apoptotic cell death in human neuroblastoma cells treated with paraquat: could autophagy be a "brake" in paraquat-induced apoptotic death?

Paraquat (PQ) (1, 1'-dimethyl-4, 4'-bipyridinium dichloride), a widely used herbicide, has been suggested as a potential etiologic factor for the development of Parkinson's disease (PD). In neurons from patients with PD display characteristics of autophagy, a degradative mechanism involved in the recycling and turnover of cytoplasmic constituents from eukaryotic cells. Low concentrations of paraquat have been recently found to induce autophagy in human neuroblastoma cells, and ultimately the neurons succumb to apoptotic death. Whereas caspase inhibition retarded cell death, autophagy inhibition accelerated the apoptotic cell death induced by paraquat. These findings suggest a relationship between autophagy and apoptotic cell death in human neuroblastoma cells treated with paraquat and open a new line of investigation to advance our knowledge regarding the origin of PD.

Inhibition of paraquat-induced autophagy accelerates the apoptotic cell death in neuroblastoma SH-SY5Y cells

Autophagy is a degradative mechanism involved in the recycling and turnover of cytoplasmic constituents from eukaryotic cells. This phenomenon of autophagy has been observed in neurons from patients with Parkinson's disease (PD), suggesting a functional role for autophagy in neuronal cell death. On the other hand, it has been demonstrated that exposure to pesticides can be a risk factor in the incidence of PD. In this sense, paraquat (PQ) (1,1'-dimethyl-4,4'-bipyridinium dichloride), a widely used herbicide that is structurally similar to the known dopaminergic neurotoxicant MPP(+) (1-methyl-4-phenyl-pyridine), has been suggested as a potential etiologic factor for the development of PD. The current study shows, for the first time, that low concentrations of PQ induce several characteristics of autophagy in human neuroblastoma SH-SY5Y cells. In this way, PQ induced the accumulation of autophagic vacuoles (AVs) in the cytoplasm and the recruitment of a LC3-GFP fusion protein to AVs. Furthermore, the cells treated with PQ showed an increase of the long-lived protein degradation which is blocked in the presence of the autophagy inhibitor 3-methyladenine and regulated by the mammalian target of rapamycin (mTOR) signaling. Finally, the cells succumbed to cell death with hallmarks of apoptosis such as phosphatidylserine exposure, caspase activation, and chromatin condensation. While caspase inhibition retarded cell death, autophagy inhibition accelerated the apoptotic cell death induced by PQ. Altogether, these findings show the relationship between autophagy and apoptotic cell death in human neuroblastoma cells treated with PQ.

Low concentrations of paraquat induces early activation of extracellular signal-regulated kinase 1/2, protein kinase B, and c-Jun N-terminal kinase 1/2 pathways: role of c-Jun N-terminal kinase in paraquat-induced cell death

Paraquat is a herbicide with a potential risk to induce parkinsonism due to its demonstrated neurotoxicity and its strong structural similarity to 1-methyl-4-phenylpyridinium (MPP(+)), a well-known neurotoxin which causes a clinical syndrome similar to Parkinson's disease (PD). However, at present very little is known about the signaling pathways activated by paraquat in any cell system. In this study, we have investigated the effect of paraquat on extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun N-terminal kinase (JNK), and protein kinase B (PKB) activation in E18 cells. Low concentrations of paraquat stimulated very early increases in ERK1/2, JNK1/2, and PKB phosphorylation. The phosphatidylinositol 3-kinase (PI-3K) inhibitors wortmannin and LY 294002 (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one) inhibited early paraquat-induced increases in PKB phosphorylation. Furthermore, early paraquat-mediated increases in ERK1/2 activation were sensitive to the mitogen-activated protein kinase kinase 1 (MEK1) inhibitor PD 98059 (2'-amino-3'-methoxyflavone), whereas JNK1/2 responses were blocked by the JNK1/2 inhibitor SP 600125 (anthra[1-9-cd]pyrazol-6(2H)-one). Pretreatment with wortmannin, LY 294002, or PD 98059 had no effect on paraquat cell death in E18 cells. In contrast, SP 600125 significantly decreased paraquat-induced cell death in E18 cells. In conclusion, we have shown that low concentrations of paraquat stimulate robust very early increases in ERK1/2, JNK1/2, and PKB phosphorylation in E18 cells. Furthermore, the data presented clearly suggest that inhibition of the JNK1/2 pathway protects E18 cells from paraquat-induced cell death and support the fact that inhibition of early activation of JNK1/2 can constitute a potential strategy in PD treatment.

TH1/TH2 cytokines: an easy model to study gene expression in immune cells

This report describes a laboratory exercise that was incorporated into a Cell Biology and Molecular Biology advanced course. The exercise was made for a class size with eight students and was designed to reinforce the understanding of basic molecular biology techniques. Students used the techniques of reverse transcription and arginase activity measurement as well as nitric oxide determination to discover whether two specific genes were expressed by cytokine-stimulated dendritic cells. The experiment served as the basis for discussing the importance of differential gene expression inside the eukaryotic cell and the importance of cytokines in the immune system.

Heat shock proteins protect both MPP+ and paraquat neurotoxicity

The exposure of immortalized rat neuroblast cells to MPP(+) and paraquat results in cell death. Heat shock pre-treatment prior to the addition of MPP(+) and paraquat significantly reduced cell death and led to an increase in the synthesis of Hsp 27 and Hsp70 proteins. Quercetin inhibits the synthesis of heat shock proteins (Hsp) and prevents their protective effect, which suggests that this protection was dependent on the Hsps synthesis. These data indicate that heat shock protects cells from the toxic effect of MPP(+) and paraquat. These results and the structural similarity between paraquat and MPP(+) support the role of paraquat as a putative risk factor in the etiology of Parkinson's disease.

Paraquat-induced apoptotic cell death in cerebellar granule cells

We examined the toxicity of paraquat, a possible environmental risk factor for neurodegenerative disorders like Parkinson's disease (PD). Paraquat is structurally similar to the neurotoxin MPP+ that can induce Parkinsonian-like features in rodents, non-human primates and human. Exposure of cerebellar granule cells to relatively low concentrations of paraquat (5 microM) produces apoptotic cell death with a reduction in mitochondrial cytochrome c content, proteolytic activation and caspase-3 activity increase and DNA fragmentation. Paraquat-induced apoptosis was significantly attenuated by co-treatment of cerebellar granule cells with the radical scavenger vitamin E, suggesting that paraquat-induced free radicals serve as important signal in initiation of cell death. As a decrease in mitochondrial cytochrome c content is also prevented by allopurinol, we suggest that xanthine oxidase plays an important role in the free radical production that precedes the apoptotic cascade and cell death after paraquat exposition.

Protection against MPP+ neurotoxicity in cerebellar granule cells by antioxidants

The neuropathology associated with Parkinson's disease (PD) is thought to involve excessive production of free radicals, dopamine autoxidation, defects in glutathione peroxidase expression, attenuated levels of reduced glutathione, altered calcium homeostasis, excitotoxicity and genetic defects in mitochondrial complex I activity. While the neurotoxic mechanisms are vastly different for excitotoxins and 1-methyl-4-phenylpyridinium ion (MPP(+)), both are thought to involve free radical production, compromised mitochondrial activity and excessive lipid peroxidation. We show here that the levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS) increased significantly after treatment of cultured cerebellar granule cells (CGCs) with 50 microM MPP(+). Co-treatment with antioxidants such as ascorbate (ASC), catalase, alpha-tocopherol (alpha-TOH), coenzyme Q(10) (CoQ(10)) or superoxide dismutase (SOD) rescued the cells from MPP(+)-induced death. MPP(+)-induced cell death was also abolished by co-treatment with nitric oxide synthase (NOS) inhibitors such as 7-nitroindazole (7-NI), 2-ethyl-2-thiopseudourea hydrobromide (EPTU) or S-methylisothiourea sulphate (MPTU). We also tested the protective effects of an iron chelator (deferoxamine mesylate, DFx) and a peroxynitrite scavenger (FeTTPS) and the results lend further support to the view that the free radical cytotoxicity plays an essential role in MPP(+)-induced death in primary cultures of CGC.

MPP+: Mechanism for Its Toxicity in Cerebellar Granule Cells

Cerebellar granule cells constitute the largest homogeneous neuronal population of the mammalian brain. However, they are not often used in studies that involve MPP+-neurotoxicity. Currently, it is known that the toxicity of MPP+ in cerebellar granule cells as well as in other models, including dopaminergic cells, results from activation of the apoptotic machinery after an initial oxidative burst with mitochondrial damage and energetic failure. Therefore, cerebellar granule cells serve as a good model to investigate the MPP+ effects and to study in vitro the molecular mechanism implicated in the genesis of Parkinson's disease.

MPP(+) causes inhibition of cellular energy supply in cerebellar granule cells

A significant loss in ATP levels was found in cerebellar granule cells with 1-methyl-4-phenylpyridinium. Exposure of cerebellar granule cells to low concentrations of 1-methyl-4-phenylpyridinium (100 microM) resulted in a time and dose-dependent decreases in ATP levels and cell death. This neurotoxin caused inhibition of the enzymatic activity of NADH-dehydrogenase of mitochondrial complex I and consequent impairment of mitochondrial electronic transport with a reduction in the depletion of cytosolic NAD(+) levels. Activation of lactate dehydrogenase activity (detected by the increase of the lactate in the culture medium) partially reduced this depletion. Addition of glucose but not pyruvate to the culture medium protected 1-methyl-4-phenylpyridinium-induced cell death. These results suggest the 1-methyl-4-phenylpyridinium causes impairment of cellular energy metabolism with a major dependence on glycolysis as a source of energy. This fact could also explain the partial neuroprotection observed by glucose.

Vitamin E blocks early events induced by 1-methyl-4-phenylpyridinium (MPP+) in cerebellar granule cells

Exposure of cerebellar granule cells (CGCs) to 1-methyl-4-phenylpyridinium (MPP+) results in apoptotic cell death, which is markedly attenuated by co-treatment of CGCs with the radical scavenger vitamin E. Analysis of free radical production and mitochondrial transmembrane potential (DeltaPsim), using specific fluorescent probes, showed that MPP+ mediates early radical oxygen species (ROS) production without a loss of DeltaPsim. Exposure to MPP+ also produces an early increase in Bad dephosphorylation and translocation of Bax to the mitochondria. These events are accompanied by cytochrome c release from mitochondria to cytosol, which is followed by caspase 3 activation. Exposure of the neurons to vitamin E maintains Bad phosphorylation and attenuates Bax translocation, inhibiting cytochrome c release and caspase activation. MPP+-mediated cytochrome c release is also prevented by allopurinol, suggesting the participation of xanthine oxidase in the process. Our results indicate that free radicals play an active role in the MPP+-induced early events that culminate with cell death.

Diagnostic performance of arginase activity in colorectal cancer

Arginase activity was measured in serum and biopsy from healthy individuals and colorectal cancer patients. Arginase activity in tumor samples (87 +/- 7.7 U/g tissue) was significantly higher than in controls (40.7 +/- 3.3 U/g tissue). However, serum arginase activity did not show any significant change in both groups. Finally, the micromethod used to quantify arginase activity in this study is superior to other methods because it has increased sensitivity, requires less sample, and is less time-consuming. Arginase differences are significant, according to the t-test (P<0.05)

Mechanisms of MPP(+) incorporation into cerebellar granule cells

Exposure of cerebellar granule cells to 1-methyl-4-phenylpiridinium (MPP(+)) results in cell death. We have studied the implication of various membrane transporter systems on MPP(+) neurotoxicity, including the dopamine transporter system (DAT) and cationic amino acid transporters (CAT). We have showed a partial protection against MPP(+) toxicity when the dopamine transporter is inhibited by 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]4-(3-phenylpropyl)piperazinedihydrochloride (GBR-12909). However, almost full protection is only achieved by the simultaneous addition of GBR-12909 and cationic amino acids. These results suggest two ways system of MPP(+) entrance into cerebellar granule cells: the DAT with high activity and the CAT with low activity. We also demonstrated that 5,7-dichlorokynurenic acid (MK-801) failed to protect against MPP(+) exposure, evidencing that N-methyl-D-aspartate (NMDA) receptor is not involved in the MPP(+)-induced cell death.

Lithium inhibits caspase 3 activation and dephosphorylation of PKB and GSK3 induced by K+ deprivation in cerebellar granule cells

Lithium protects cerebellar granule cells from apoptosis induced by low potassium, and also from other apoptotic stimuli. However, the precise mechanism by which this occurs is not understood. When cerebellar granule cells were switched to low potassium medium, the activation of caspase 3 was detected within 6 h, suggesting a role of caspase 3 in mediating apoptosis under conditions of low potassium. In the same conditions, lithium (5 mM) inhibited the activation of caspase 3 induced by low potassium. As lithium did not inhibit caspase 3 activity in vitro, these results suggest that this ion inhibits an upstream component that is required for caspase 3 activation. Lithium is known to inhibit a kinase termed glycogen sythase kinase 3 (GSK3), which is implicated in the survival pathway of phosphatidylinositol 3-kinase/protein kinase B (PI3K/PKB). Here we demonstrate that low potassium in the absence of lithium induces the dephosphorylation, and therefore the activation, of GSK3. However, when lithium was present, GSK3 remained phosphorylated at the same level as observed under conditions of high potassium. Low potassium induced the dephosphorylation and inactivation of PKB, whereas when lithium was present PKB was not dephosphorylated. Our results allow us to propose a new hypothesis about the action mechanism of lithium, this ion could inhibit a serine-threonine phosphatase induced by potassium deprivation.

Different mechanisms of protection against apoptosis by valproate and Li+

Acute treatment with valproate and Li+ was found to protect cultured cerebellar granule cells against apoptosis induced by low K+ (5 mM). Because the protection was unaffected by MK801 (N-methyl-D-aspartate receptor inhibitor), an increase in glutamate release cannot be responsible for the observed neuroprotection. Insulin also protects against low-K+-induced apoptosis of cerebellar granule cells. This protection is totally dependent on LY294002 (a phosphatidylinositol 3-kinase inhibitor). These results suggest a role for phosphatidylinositol 3-kinase in the neuroprotection induced by insulin. Likewise, and in contrast with the results observed with Li+, the protection induced by valproate is also dependent on insulin and LY294002. Moreover, valproate (a branched-chain fatty acid) does not change the plasma membrane microviscosity under physiological conditions. These results suggest that valproate protects against low-K+-induced apoptosis by acting in the phosphatidylinositol 3-kinase/protein kinase B pathway. The protection by Li+ is independent of this transduction pathway.