PINK1 Overexpression Protects Against C2-ceramide-Induced CAD Cell Death Through the PI3K/AKT Pathway

Scutellaria incarnata Vent. root extract and isolated phenylethanoid glycosides are neuroprotective against C2-ceramide toxicity

ETHNOPHARMACOLOGICAL RELEVANCE

Neuronal death is a central process in neurodegenerative diseases and represents a therapeutic challenge for their prevention and treatment. Scutellaria incarnata Vent. roots are used traditionally in Colombia for central nervous system conditions including those affecting cognitive functions, but their chemistry and neuroprotective action remain to be explored to understand the scientific basis for their medicinal uses. In this study, S. incarnata roots are investigated to assess whether they have neuroprotective effects that could provide some explanation for their traditional use in neurodegenerative diseases.

AIM OF THE STUDY

To evaluate the neuroprotective effect of S. incarnata roots and its chemical constituents against C₂-ceramide-induced cell death in Cath.-a-differentiated (CAD) cells.

MATERIALS AND METHODS

S. incarnata root ethanol extract was fractionated and compounds were isolated by column chromatography; their structures were elucidated by nuclear magnetic resonance spectroscopy, mass spectrometry and infrared spectroscopy. The cytotoxic and neuroprotective effects against C₂-ceramide of S. incarnata root extract, fractions and isolated compounds were assessed in CAD cells.

RESULTS

S. incarnata root extract and its n-butanol fraction were not cytotoxic but showed neuroprotective effects against C₂-ceramide toxicity in CAD cells. The phenylethanoid glycosides incarnatoside (isolated for the first time) and stachysoside C (12.5, 25 and 50 μg/mL) from S. incarnata roots also protected CAD cells against C₂-ceramide without inducing cytotoxic effects.

CONCLUSION

The observed neuroprotective effects of S. incarnata root extract and isolated phenylethanoid glycosides in CAD cells provide an ethnopharmacological basis for the traditional use of this species in Colombia for central nervous system disorders.

Depletion of ALMS1 affects TGF-β signalling pathway and downstream processes such as cell migration and adhesion capacity

Background: ALMS1 is a ubiquitous gene associated with Alström syndrome (ALMS). The main symptoms of ALMS affect multiple organs and tissues, generating at last, multi-organic fibrosis in the lungs, kidneys and liver. TGF-β is one of the main pathways implicated in fibrosis, controlling the cell cycle, apoptosis, cell migration, cell adhesion and epithelial-mesenchymal transition (EMT). Nevertheless, the role of ALMS1 gene in fibrosis generation and other implicated processes such as cell migration or cell adhesion via the TGF- β pathway has not been elucidated yet. Methods: Initially, we evaluated how depletion of ALMS1 affects different processes like apoptosis, cell cycle and mitochondrial activity in HeLa cells. Then, we performed proteomic profiling with TGF-β stimuli in HeLa ALMS1 -/- cells and validated the results by examining different EMT biomarkers using qPCR. The expression of these EMT biomarkers were also studied in hTERT-BJ-5ta ALMS1 -/-. Finally, we evaluated the SMAD3 and SMAD2 phosphorylation and cell migration capacity in both models. Results: Depletion of ALMS1 generated apoptosis resistance to thapsigargin (THAP) and C2-Ceramide (C2-C), and G2/M cell cycle arrest in HeLa cells. For mitochondrial activity, results did not show significant differences between ALMS1 +/+ and ALMS1 -/-. Proteomic results showed inhibition of downstream pathways regulated by TGF-β. The protein-coding genes (PCG) were associated with processes like focal adhesion or cell-substrate adherens junction in HeLa. SNAI1 showed an opposite pattern to what would be expected when activating the EMT in HeLa and BJ-5ta. Finally, in BJ-5ta model a reduced activation of SMAD3 but not SMAD2 were also observed. In HeLa model no alterations in the canonical TGF-β pathway were observed but both cell lines showed a reduction in migration capacity. Conclusion: ALMS1 has a role in controlling the cell cycle and the apoptosis processes. Moreover, the depletion of ALMS1 affects the signal transduction through the TGF-β and other processes like the cell migration and adhesion capacity.

Bioactive lipids and their metabolism: new therapeutic opportunities for Parkinson's disease

Parkinson's disease (PD) is a neurological disorder characterized by motor dysfunction, which can also be associated with non-motor symptoms. Its pathogenesis is thought to stem from a loss of dopaminergic neurons in the substantia nigra pars compacta and the formation of Lewy bodies containing aggregated α-synuclein. Recent works suggested that lipids might play a pivotal role in the pathophysiology of PD. In particular, the so-called "bioactive" lipids whose changes in the concentration may lead to functional consequences and affect many pathophysiological processes, including neuroinflammation, are closely related to PD in terms of symptoms, disease progression, and incidence. This study aimed to explore the molecular metabolism and physiological functions of bioactive lipids, such as fatty acids (mainly unsaturated fatty acids), eicosanoids, endocannabinoids, oxysterols, representative sphingolipids, diacylglycerols, and lysophosphatidic acid, in the development of PD. The knowledge of bioactive lipids in PD gained through preclinical and clinical studies is expected to improve the understanding of disease pathogenesis and provide novel therapeutic avenues.

Labeling and measuring stressed mitochondria using a PINK1-based ratiometric fluorescent sensor

Mitochondria are essential organelles that carry out a number of pivotal metabolic processes and maintain cellular homeostasis. Mitochondrial dysfunction caused by various stresses is associated with many diseases such as type 2 diabetes, obesity, cancer, heart failure, neurodegenerative disorders, and aging. Therefore, it is important to understand the stimuli that induce mitochondrial stress. However, broad analysis of mitochondrial stress has not been carried out to date. Here, we present a set of fluorescent tools, called mito-Pain (mitochondrial PINK1 accumulation index), which enable the labeling of stressed mitochondria. Mito-Pain uses PTEN-induced putative kinase 1 (PINK1) stabilization on mitochondria and quantifies mitochondrial stress levels by comparison with PINK1-GFP, which is stabilized under mitochondrial stress, and RFP-Omp25, which is constitutively localized on mitochondria. To identify compounds that induce mitochondrial stress, we screened a library of 3374 compounds using mito-Pain and identified 57 compounds as mitochondrial stress inducers. Furthermore, we classified each compound into several categories based on mitochondrial response: depolarization, mitochondrial morphology, or Parkin recruitment. Parkin recruitment to mitochondria was often associated with mitochondrial depolarization and aggregation, suggesting that Parkin is recruited to heavily damaged mitochondria. In addition, many of the compounds led to various mitochondrial morphological changes, including fragmentation, aggregation, elongation, and swelling, with or without Parkin recruitment or mitochondrial depolarization. We also found that several compounds induced an ectopic response of Parkin, leading to the formation of cytosolic puncta dependent on PINK1. Thus, mito-Pain enables the detection of stressed mitochondria under a wide variety of conditions and provides insights into mitochondrial quality control systems.

The Parkinson's disease gene PINK1 activates Akt via PINK1 kinase-dependent regulation of the phospholipid PI(3,4,5)P3

Akt signalling is central to cell survival, metabolism, protein and lipid homeostasis, and is impaired in Parkinson's disease (PD). Akt activation is reduced in the brain in PD, and by many PD-causing genes, including PINK1 This study investigated the mechanisms by which PINK1 regulates Akt signalling. Our results reveal for the first time that PINK1 constitutively activates Akt in a PINK1-kinase dependent manner in the absence of growth factors, and enhances Akt activation in normal growth medium. In PINK1-modified MEFs, agonist-induced Akt signalling failed in the absence of PINK1, due to PINK1 kinase-dependent increases in PI(3,4,5)P₃ at both plasma membrane and Golgi being significantly impaired. In the absence of PINK1, PI(3,4,5)P₃ levels did not increase in the Golgi, and there was significant Golgi fragmentation, a recognised characteristic of PD neuropathology. PINK1 kinase activity protected the Golgi from fragmentation in an Akt-dependent fashion. This study demonstrates a new role for PINK1 as a primary upstream activator of Akt via PINK1 kinase-dependent regulation of its primary activator PI(3,4,5)P₃, providing novel mechanistic information on how loss of PINK1 impairs Akt signalling in PD.This article has an associated First Person interview with the first author of the paper.

Ceramides in Parkinson's Disease: From Recent Evidence to New Hypotheses

Ceramides (Cer) constitute a class of lipids present in the cell membranes where they act as structural components, but they can also work as signaling molecules. Increasing genetic and biochemical evidence supports a link between deregulation of ceramide metabolism in the brain and neurodegeneration. Here, we provide an overview of the genes and cellular pathways that link Cer with Parkinson’s disease and discuss how ceramide pathobiology is gaining increasing interest in the understanding of the pathological mechanisms that contribute to the disease and in the clinical and therapeutic side.

The Role of Lipids in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disease characterized by a progressive loss of dopaminergic neurons from the nigrostriatal pathway, formation of Lewy bodies, and microgliosis. During the past decades multiple cellular pathways have been associated with PD pathology (i.e., oxidative stress, endosomal-lysosomal dysfunction, endoplasmic reticulum stress, and immune response), yet disease-modifying treatments are not available. We have recently used genetic data from familial and sporadic cases in an unbiased approach to build a molecular landscape for PD, revealing lipids as central players in this disease. Here we extensively review the current knowledge concerning the involvement of various subclasses of fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, and lipoproteins in PD pathogenesis. Our review corroborates a central role for most lipid classes, but the available information is fragmented, not always reproducible, and sometimes differs by sex, age or PD etiology of the patients. This hinders drawing firm conclusions about causal or associative effects of dietary lipids or defects in specific steps of lipid metabolism in PD. Future technological advances in lipidomics and additional systematic studies on lipid species from PD patient material may improve this situation and lead to a better appreciation of the significance of lipids for this devastating disease.

δ-Opioid Receptor Activation Attenuates Hypoxia/MPP+-Induced Downregulation of PINK1: a Novel Mechanism of Neuroprotection Against Parkinsonian Injury

There is emerging evidence suggesting that neurotoxic insults and hypoxic/ischemic injury are underlying causes of Parkinson's disease (PD). Since PTEN-induced kinase 1 (PINK1) dysfunction is involved in the molecular genesis of PD and since our recent studies have demonstrated that the δ-opioid receptor (DOR) induced neuroprotection against hypoxic and 1-methyl-4-phenyl-pyridimium (MPP⁺) insults, we sought to explore whether DOR protects neuronal cells from hypoxic and/or MPP⁺ injury via the regulation of PINK1-related pathways. Using highly differentiated rat PC12 cells exposed to either severe hypoxia (0.5-1% O₂) for 24-48 h or varying concentrations of MPP⁺, we found that both hypoxic and MPP⁺ stress reduced the level of PINK1 expression, while incubation with the specific DOR agonist UFP-512 reversed this reduction and protected the cells from hypoxia and/or MPP⁺-induced injury. However, the DOR-mediated cytoprotection largely disappeared after knocking down PINK1 by PINK1 small interfering RNA. Moreover, we examined several important signaling molecules related to cell survival and apoptosis and found that DOR activation attenuated the hypoxic and/or MPP⁺-induced reduction in phosphorylated Akt and inhibited the activation of cleaved caspase-3, whereas PINK1 knockdown largely deprived the cell of the DOR-induced effects. Our novel data suggests a unique mechanism underlying DOR-mediated cytoprotection against hypoxic and MPP⁺ stress via a PINK1-mediated regulation of signaling.

Pink1 attenuates propofol-induced apoptosis and oxidative stress in developing neurons

BACKGROUND

The underlying mechanisms of propofol-induced neurotoxicity in developing neurons are still not completely understood. We examined the role of PTEN-induced kinase 1 (Pink1), an antioxidant protein, in propofol-induced apoptosis in developing neurons.

MATERIALS AND METHODS

Primary hippocampal neurons isolated from neonatal Sprague-Dawley rats were exposed to propofol 20 μM for 2, 4, 6 and 12 h. Subsequently, neurons underwent overexpression and knockdown of Pink1, followed by propofol exposure (20 μM, 6 h). Neuron apoptosis was detected by terminal transferase deoxyuridine triphosphate-biotin nick-end labeling (TUNEL). Reactive oxygen species (ROS) production in neurons was detected by using a 2,7-dichlorodihydro-fluorescein diacetate probe and target protein or mRNA levels were analyzed by Western blotting or real-time polymerase chain reaction.

RESULTS

Propofol treatment time-dependently increased the number of TUNEL-positive neurons and the expression levels of cleaved caspase-3 and B-cell lymphoma 2 (BcL-2) associated X protein, but decreased expression levels of BcL-2. Furthermore, propofol treatment time-dependently reduced the expression levels of Pink1 mRNA and protein. ROS production and the markers of oxidative stress, 2,4-dinitrophenol and 4-hydroxynonenal, were increased by propofol treatment. However, these propofol-induced changes were significantly restored by Pink1 overexpression.

CONCLUSIONS

Pink1 plays an important role in neuronal apoptosis induced by propofol. Our results may provide some new insights in propofol-induced neurotoxicity in developing neurons.

Effect of Temperature Downshift on the Transcriptomic Responses of Chinese Hamster Ovary Cells Using Recombinant Human Tissue Plasminogen Activator Production Culture

Recombinant proteins are widely used as biopharmaceuticals, but their production by mammalian cell culture is expensive. Hence, improvement of bioprocess productivity is greatly needed. A temperature downshift (TDS) from 37°C to 28–34°C is an effective strategy to expand the productive life period of cells and increase their productivity (q_p). Here, TDS in Chinese hamster ovary (CHO) cell cultures, initially grown at 37°C and switched to 30°C during the exponential growth phase, resulted in a 1.6-fold increase in the q_p of recombinant human tissue plasminogen activator (rh-tPA). The transcriptomic response using next-generation sequencing (NGS) was assessed to characterize the cellular behavior associated with TDS. A total of 416 (q > 0.8) and 3,472 (q > 0.9) differentially expressed transcripts, with more than a 1.6-fold change at 24 and 48 h post TDS, respectively, were observed in cultures with TDS compared to those at constant 37°C. In agreement with the extended cell survival resulting from TDS, transcripts related to cell growth arrest that controlled cell proliferation without the activation of the DNA damage response, were differentially expressed. Most upregulated genes were related to energy metabolism in mitochondria, mitochondrial biogenesis, central metabolism, and avoidance of apoptotic cell death. The gene coding for rh-tPA was not differentially expressed, but fluctuations were detected in the transcripts encoding proteins involved in the secretory machinery, particularly in glycosylation. Through NGS the dynamic processes caused by TDS were assessed in this biological system.

SGK-1 protects kidney cells against apoptosis induced by ceramide and TNF-α

Ceramide regulates several different cellular responses including mechanisms leading to apoptosis. Serum- and glucocorticoid-inducible protein kinase (SGK)-1 is a serine threonine kinase, which activates survival pathways in response to stress stimuli. Recently, we demonstrated an anti-apoptotic role of SGK-1 in human umbilical endothelial cells treated with high glucose. In the present study, since ceramide induces apoptosis by multiple mechanisms in diabetes and its complication such as nephropathy, we aimed to investigate whether SGK-1 may protect even against apoptosis induced by ceramide in kidney cells. Human embryonic kidney (HEK)-293 cells stable transfected with SGK-1 wild type (SGK-1wt) and its dominant negative gene (SGK-1dn) have been used in this study. Apoptotic stimuli were induced by C₂-ceramide and TNF-α to increase endogenous synthesis of ceramide. Upon activation with these stimuli, SGK-1wt transfected cells have a statistically significant reduction of apoptosis compared with SGK-1dn cells (P<0.001). This protection was dependent on activation of caspase-3 and Poly-ADP-ribose-polymerase-1 (PARP-1) cleavage. SGK-1 and AKT-1 two highly homologous kinases differently reacted to ceramide treatment, since SGK-1 increases in response to apoptotic stimulus while AKT-1 decreases. This enhancement of SGK-1 was dependent on p38-mitogen-activated-protein kinases (p38MAPK), cyclic-adenosine-monophosphate/protein kinase A (cAMP/PKA) and phosphoinositide-3-kinase (PI3K) pathways. Especially, by using selective LY294002 inhibitor, we demonstrated that the most involved pathway in the SGK-1 mediated process of protection was PI3K. Treatment with inhibitor of SGK-1 (GSK650394) significantly enhanced TNF-α-dependent apoptosis in HEK-293 cells overexpressing SGK-1wt. Caspase-3, -8 and -9 selective inhibitors confirmed that SGK-1 reduced the activation of caspase-dependent apoptosis, probably by both intrinsic and extrinsic pathways. In conclusion, we demonstrated that in kidney cells, overexpression of SGK-1 is protective against ceramide-induced apoptosis and the role of SGK-1 can be potentially explored as a therapeutic target in conditions like diabetes, where ceramide levels are increased.

Overexpression of DJ-1 protects against C2-ceramide-induced neuronal death through activation of the PI3K/AKT pathway and inhibition of autophagy

Parkinson's disease (PD) is the second most frequent neurodegenerative disorder. It is characterized by selective degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Early-onset familial forms of PD are associated with mutations in several genes, including parkin, pink1 and dj-1. DJ-1 encodes a protein whose neuroprotective function has not been completely clarified yet. We aim to understand the neuroprotective mechanisms of DJ-1, in particular, DJ-1's involvement in the regulation of the PI3K/PTEN/AKT/mTOR pathway and neuronal autophagy in a neurotoxic context induced by C2-ceramide, by using CAD cells, a murine cathecolaminergic cell line. We demonstrated that C2-ceramide induces CAD cell death associated with decreased phosphorylation of PTEN at Ser380, AKT at Ser473, and mTOR at Ser2448; and increased of autophagic flux (increased LC3-II and autophagosome formation). Additionally, we showed that overexpression of DJ-1 protects against C2-ceramide-induced neuronal death and it is not associated with change in the phosphorylation of mTOR at Ser2448. In conclusion, these data suggest that DJ-1 reinforces the PI3K/AKT survival pathway and inhibits autophagy, probably by a mechanism independent from mTOR.

Parkinson's disease-associated PINK1 G309D mutation increases abnormal phosphorylation of Tau

Mutations in PINK1 gene have been considered the second most common cause of Autosomal Recessive Parkinsonism (ARP). So far, different homozygous PINK1 mutations have been identified in different ARP patients. Abnormal hyperphosphorylation of tau leads to the loss of its biological activity. Multiple lines of evidence have demonstrated that hyperphosphorylated tau is associated with Alzheimer's disease and Parkinson's disease (PD). However, the effects of PD associated PINK1 mutations in tau phosphorylation are unknown. In this study, we investigated the effect of G309D PINK1 mutation in tau phosphorylation. Cells transfected with mutant G309D PINK1 exhibited a significant increase in the phosphorylation of tau protein at the PHF-1 (ser396/404) site. The levels of CDK5, an important activator of tau phosphorylation, did not change in mutant G309D PINK1 transfected cells, suggesting that CDK5 is not involved in tau phosphorylation induced by mutant G309D PINK1. Notably, we found that mutant G309D PINK1 significantly reduced phosphorylation of GSK3β at serine 9, suggesting that alterations in GSK3β activity play an essential role in mutant G309D PINK1-induced tau phosphorylation at the PHF-1 site. PP2A activity maintained consistent in mutant G309D PINK1 transfected cells, suggesting that the increased tau hyperphosphorylation is not ascribed to reduction in PP2A activity.

Silencing of PINK1 inhibits insulin-like growth factor-1-mediated receptor activation and neuronal survival

The etiology of Parkinson's disease remains unknown. Mutations in PINK1 have provided an understanding of the molecular mechanisms of this pathology. PINK1 and Parkin are important in the dismissal of dysfunctional mitochondria. However, the role of PINK1 in the control of neuronal survival pathways is not clear. To determine the role of PINK1 in the control of the phosphatidyl inositol 3-kinase (PI3K)/Akt pathway mediated by insulin-like grow factor type 1 (IGF-1), we use a model of mesencephalic neurons (CAD cells), which were transfected with lentiviral PINK1 shRNA or control shRNA constructs. Silencing of PINK1 was determined by RT-PCR and immunoblotting; cell viability was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays; proteins of the PI3K/Akt signaling pathway were tested by immunoblotting and IGF-1 receptor, and mitochondria were examined using fluorescence microscopy. PINK1 shRNA-transfected cells showed a reduction in cell survival compared to control shRNA cells. Exposure to IGF-1 induced a rapid and high increase in the phosphorylation level of IGF-1 receptor in control shRNA-transfected cells; however, silencing of PINK1 decreases phosphorylation level of IGF-1 receptor and downstream target proteins such as Akt, GSK3-beta, IRS-1, and hexokinase. Our results further suggest that PINK1 may be regulating the PI3K/Akt neuronal survival pathway through tyrosine kinase receptors such as IGF-1 receptor.

PINK1 signalling in cancer biology

PTEN-induced kinase 1 (PINK1) was identified initially in cancer cells as a gene up-regulated by overexpression of the major tumor suppressor, PTEN. Loss-of-function mutations in PINK1 were discovered subsequently to cause autosomal recessive Parkinson's disease. Substantial work during the past decade has revealed that PINK1 regulates several primary cellular processes of significance in cancer cell biology, including cell survival, stress resistance, mitochondrial homeostasis and the cell cycle. Mechanistically, PINK1 has been shown to interact on a number of levels with the pivotal oncogenic PI3-kinase/Akt/mTOR signalling axis and to control critical mitochondrial and metabolic functions that regulate cancer survival, growth, stress resistance and the cell cycle. A cytoprotective and chemoresistant function for PINK1 has been highlighted by some studies, supporting PINK1 as a target in cancer therapeutics. This article reviews the function of PINK1 in cancer cell biology, with an emphasis on the mechanisms by which PINK1 interacts with PI3-kinase/Akt signalling, mitochondrial homeostasis, and the potential context-dependent pro- and anti-tumorigenic functions of PINK1.

Upregulation of human PINK1 gene expression by NFκB signalling

Parkinson’s disease (PD) is one of the major neurodegenerative disorders. Mitochondrial malfunction is implicated in PD pathogenesis. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN)-induced putative kinase 1 (PINK1), a serine/threonine kinase, plays an important role in the quality control of mitochondria and more than 70 PINK1 mutations have been identified to cause early-onset PD. However, the regulation of PINK1 gene expression remains elusive. In the present study, we identified the transcription start site (TSS) of the human PINK1 gene using switching mechanism at 5’end of RNA transcription (SMART RACE) assay. The TSS is located at 91 bp upstream of the translation start site ATG. The region with 104 bp was identified as the minimal promoter region by deletion analysis followed by dual luciferase assay. Four functional cis-acting nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB)-binding sites within the PINK1 promoter were identified. NFκB overexpression led to the up-regulation of PINK1 expression in both HEK293 cells and SH-SY5Y cells. Consistently, lipopolysaccharide (LPS), a strong activator of NFκB, significantly increased PINK1 expression in SH-SY5Y cells. Taken together, our results clearly suggested that PINK1 expression is tightly regulated at its transcription level and NFκB is a positive regulator for PINK1 expression.

Downregulation of Pink1 influences mitochondrial fusion-fission machinery and sensitizes to neurotoxins in dopaminergic cells

It is now well established that mitochondria are organelles that, far from being static, are subject to a constant process of change. This process, which has been called mitochondrial dynamics, includes processes of both fusion and fission. Loss of Pink1 (PTEN-induced putative kinase 1) function is associated with early onset recessive Parkinson's disease and it has been proposed that mitochondrial dynamics might be affected by loss of the mitochondrial kinase. Here, we report the effects of silencing Pink1 on mitochondrial fusion and fission events in dopaminergic neuron cell lines. Cells lacking Pink1 were more sensitive to cell death induced by C2-Ceramide, which inhibits proliferation and induces apoptosis. In the same cell lines, mitochondrial morphology was fragmented and this was enhanced by application of forskolin, which stimulates the cAMP pathway that phosphorylates Drp1 and thereby inactivates it. Cells lacking Pink1 had lower Drp1 and Mfn2 expression. Based on these data, we propose that Pink1 may exert a neuroprotective role in part by limiting mitochondrial fission.

The neurodegenerative effects of selenium are inhibited by FOXO and PINK1/PTEN regulation of insulin/insulin-like growth factor signaling in Caenorhabditis elegans

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Insulin/insulin-like signaling reduction alters selenium-induced neurodegeneration.

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Selenium induces nuclear translocation of DAF-16/FOXO3a.

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DAF-16 overexpression decreases GABAergic and cholinergic motor neuron degeneration.

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Loss of DAF-18/PTEN increases sensitivity to selenium-induced movement deficits.

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Glutathione requires DAF-18/PINK-1 to improve selenium-induced movement deficits.

Exposures to high levels of environmental selenium have been associated with motor neuron disease in both animals and humans and high levels of selenite have been identified in the cerebrospinal fluid of patients with amyotrophic lateral sclerosis (ALS). We have shown previously that exposures to high levels of sodium selenite in the environment of Caenorhabditis elegans adult animals can induce neurodegeneration and cell loss resulting in motor deficits and death and that this is at least partially caused by a reduction in cholinergic signaling across the neuromuscular junction. Here we provide evidence that reduction in insulin/insulin-like (IIS) signaling alters response to high dose levels of environmental selenium which in turn can regulate the IIS pathway. Most specifically we show that nuclear localization and thus activation of the DAF-16/forkhead box transcription factor occurs in response to selenium exposure although this was not observed in motor neurons of the ventral cord. Yet, tissue specific expression and generalized overexpression of DAF-16 can partially rescue the neurodegenerative and behavioral deficits observed with high dose selenium exposures in not only the cholinergic, but also the GABAergic motor neurons. In addition, two modifiers of IIS signaling, PTEN (phosphatase and tensin homolog, deleted on chromosome 10) and PINK1 (PTEN-induced putative kinase 1) are required for the cellular antioxidant reduced glutathione to mitigate the selenium-induced movement deficits. Studies have suggested that environmental exposures can lead to ALS or other neurological diseases and this model of selenium-induced neurodegeneration developed in a genetically tractable organism provides a tool for examining the combined roles of genetics and environment in the neuro-pathologic disease process.

PINK1 and its familial Parkinson's disease-associated mutation regulate brain vascular endothelial inflammation

Parkinson's disease (PD) is a debilitating disorder that affects movement. Inflammation-mediated endothelial dysfunction has been found to be involved in neurodegenerative diseases, including PD. More than 40 PTEN-induced putative kinase 1 (PINK1) mutations have been found in PD patients. The effects of PINK1 in vascular inflammation are as yet unknown. In this study, our findings revealed that PINK1 can be increased by the inflammatory cytokine tumor necrosis factor-α in primary human brain microvascular endothelial cells (HBMECs). We found that wild-type PINK1 prevents expression of the adhesion molecule vascular cell adhesion molecule-1 (VCAM-1), thus inhibiting the attachment of monocytes to brain endothelial cells. However, PINK1G309D, the loss-of-function mutation associated with early-onset familial PD, promotes expression of VCAM-1 and exacerbates attachment of monocytes to brain endothelial cells. Mechanism studies revealed that overexpression of wild-type PINK1 inhibits the VCAM-1 promoter by inhibiting the transcriptional activity of interferon regulatory factor 1 (IRF-1). However, PINK1G309D promotes the VCAM-1 promoter by increasing the transcriptional activity of IRF-1.

Kinases and kinase signaling pathways: potential therapeutic targets in Parkinson's disease

Complex molecular mechanisms underlying the pathogenesis of Parkinson's disease (PD) are gradually being elucidated. Accumulating genetic evidence implicates dysfunction of kinase activities and phosphorylation pathways in the pathogenesis of PD. Causative and risk gene products associated with PD include protein kinases (such as PINK1, LRRK2 and GAK) and proteins related phosphorylation signaling pathways (such as SNCA, DJ-1). PINK1, LRRK2 and several PD gene products have been associated with mitogen-activated protein (MAP) and protein kinase B (AKT) kinase signaling pathways. C-Jun N-terminal kinase (JNK), extracellular signal-regulated kinases (ERK) and p38, signaling pathways downstream of MAP, are particularly important in PD. JNK and p38 play an integral role in neuronal death. Targeting JNK or p38 signaling may offer an effective therapy for PD. Inhibitors of the ERK signaling pathway, which plays an important role in the development of l-DOPA-induced dyskinesia (LID), have been shown to attenuate this condition in animal models. In this review, we summarize experimental evidence gathered over the last decade on the role of PINK1, LRRK2 and GAK and their related phosphorylation signaling pathways (JNK, ERK, p38 and PI3K/AKT) in PD. It is speculated that improvement or modulation of these signaling pathways will reveal potential therapeutic targets for attenuation of the cardinal symptoms and motor complications in patients with PD in the future.