p38alpha antagonizes p38gamma activity through c-Jun-dependent ubiquitin-proteasome pathways in regulating Ras transformation and stress response

p38 MAPK family consists of four isoform proteins (alpha, beta, gamma, and delta) that are activated by the same stimuli, but the information about how these proteins act together to yield a biological response is missing. Here we show a feed-forward mechanism by which p38alpha may regulate Ras transformation and stress response through depleting its family member p38gamma protein via c-Jun-dependent ubiquitin-proteasome pathways. Analyses of MAPK kinase 6 (MKK6)-p38 fusion proteins showed that constitutively active p38alpha (MKK6-p38alpha) and p38gamma (MKK6-p38gamma) stimulates and inhibits c-Jun phosphorylation respectively, leading to a distinct AP-1 regulation. Depending on cell type and/or stimuli, p38alpha phosphorylation results in either Ras-transformation inhibition or a cell-death escalation that invariably couples with a decrease in p38gamma protein expression. p38gamma, on the other hand, increases Ras-dependent growth or inhibits stress induced cell-death independent of phosphorylation. In cells expressing both proteins, p38alpha phosphorylation decreases p38gamma protein expression, whereas its inhibition increases cellular p38gamma concentrations, indicating an active role of p38alpha phosphorylation in negatively regulating p38gamma protein expression. Mechanistic analyses show that p38alpha requires c-Jun activation to deplete p38gamma proteins by ubiquitin-proteasome pathways. These results suggest that p38alpha may, upon phosphorylation, act as a gatekeeper of the p38 MAPK family to yield a coordinative biological response through disrupting its antagonistic p38gamma family protein.     

6-OHDA generated ROS induces DNA damage and p53- and PUMA-dependent cell death

Background

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic neurons in the substantia nigra (SN), resulting in tremor, rigidity, and bradykinesia. Although the etiology is unknown, insight into the disease process comes from the dopamine (DA) derivative, 6-hydroxydopamine (6-OHDA), which produces PD-like symptoms. Studies show that 6-OHDA activates stress pathways, such as the unfolded protein response (UPR), triggers mitochondrial release of cytochrome-c, and activates caspases, such as caspase-3. Because the BH3-only protein, Puma (p53-upregulated mediator of apoptosis), is activated in response to UPR, it is thought to be a link between cell stress and apoptosis.

Results

To test the hypothesis that Puma serves such a role in 6-OHDA-mediated cell death, we compared the response of dopaminergic neurons from wild-type and Puma-null mice to 6-OHDA. Results indicate that Puma is required for 6-OHDA-induced cell death, in primary dissociated midbrain cultures as well as in vivo. In these cultures, 6-OHDA-induced DNA damage and p53 were required for 6-OHDA-induced cell death. In contrast, while 6-OHDA led to upregulation of UPR markers, loss of ATF3 did not protect against 6-OHDA.

Conclusions

Together, our results indicate that 6-OHDA-induced upregulation of Puma and cell death are independent of UPR. Instead, p53 and DNA damage repair pathways mediate 6-OHDA-induced toxicity.     

Alterations in bioenergetic function induced by Parkinson's disease mimetic compounds: lack of correlation with superoxide generation

J. Neurochem. (2012) 122, 941-951. ABSTRACT: In vitro and in vivo models of Parkinson's disease (PD) suggest that increased oxidant production leads to mitochondrial dysfunction in dopaminergic neurons and subsequent cell death. However, it remains unclear if cell death in these models is caused by inhibition of mitochondrial function or oxidant production. The objective of this study was to determine the relationship between mitochondrial dysfunction and oxidant production in response to multiple PD neurotoxicant mimetics. MPP(+) caused a dose-dependent decrease in the basal oxygen consumption rate in dopaminergic N27 cells, indicating a loss of mitochondrial function. In parallel, we found that MPP(+) only modestly increased oxidation of hydroethidine as a diagnostic marker of superoxide production in these cells. Similar results were found using rotenone as a mitochondrial inhibitor, or 6-hydroxydopamine (6-OHDA) as a mechanistically distinct PD neurotoxicant, but not with exposure to paraquat. In addition, the extracellular acidification rate, used as a marker of glycolysis, was stimulated to compensate for oxygen consumption rate inhibition after exposure to MPP(+) , rotenone, or 6-OHDA, but not paraquat. Together these data indicate that MPP(+) , rotenone, and 6-OHDA dramatically shift bioenergetic function away from the mitochondria and towards glycolysis in N27 cells.     

Endoplasmic reticulum: the unfolded protein response is tangled in neurodegeneration

The endoplasmic reticulum (ER) is involved in the folding and maturation of membrane-bound and secreted proteins. Disturbed homeostasis in the ER can lead to accumulation of misfolded proteins, which trigger a stress response called the unfolded protein response (UPR). In neurodegenerative diseases that are classified as tauopathies, activation of the UPR coincides with the pathogenic accumulation of the microtubule associated protein tau. Several lines of evidence indicate that UPR activation contributes to increased levels of phosphorylated tau, a prerequisite for the formation of tau aggregates. Increased understanding of the crosstalk between signaling pathways involved in protein quality control in the ER and tau phosphorylation will support the development of new therapeutic targets that promote neuronal survival.     

Protein Kinase D1 (PKD1) Phosphorylation Promotes Dopaminergic Neuronal Survival during 6-OHDA-Induced Oxidative Stress

Oxidative stress is a major pathophysiological mediator of degenerative processes in many neurodegenerative diseases including Parkinson’s disease (PD). Aberrant cell signaling governed by protein phosphorylation has been linked to oxidative damage of dopaminergic neurons in PD. Although several studies have associated activation of certain protein kinases with apoptotic cell death in PD, very little is known about protein kinase regulation of cell survival and protection against oxidative damage and degeneration in dopaminergic neurons. Here, we characterized the PKD1-mediated protective pathway against oxidative damage in cell culture models of PD. Dopaminergic neurotoxicant 6-hydroxy dopamine (6-OHDA) was used to induce oxidative stress in the N27 dopaminergic cell model and in primary mesencephalic neurons. Our results indicated that 6-OHDA induced the PKD1 activation loop (PKD1S744/S748) phosphorylation during early stages of oxidative stress and that PKD1 activation preceded cell death. We also found that 6-OHDA rapidly increased phosphorylation of the C-terminal S916 in PKD1, which is required for PKD1 activation loop (PKD1S744/748) phosphorylation. Interestingly, negative modulation of PKD1 activation by RNAi knockdown or by the pharmacological inhibition of PKD1 by kbNB-14270 augmented 6-OHDA-induced apoptosis, while positive modulation of PKD1 by the overexpression of full length PKD1 (PKD1^WT) or constitutively active PKD1 (PKD1^S744E/S748E) attenuated 6-OHDA-induced apoptosis, suggesting an anti-apoptotic role for PKD1 during oxidative neuronal injury. Collectively, our results demonstrate that PKD1 signaling plays a cell survival role during early stages of oxidative stress in dopaminergic neurons and therefore, positive modulation of the PKD1-mediated signal transduction pathway can provide a novel neuroprotective strategy against PD.     

内质网应激响应在脂肪组织中的代谢调节作用

在真核细胞中,内质网是蛋白合成、加工及质量监控的关键细胞器,也是Ca2+储存及脂质合成的重要场所.细胞通过未折叠蛋白响应(unfolded protein response,UPR)感应外界不同刺激引发的内质网应激,在维持细胞功能稳态中发挥至关重要的作用.在哺乳动物中,三个位于内质网的跨膜蛋白——肌醇依赖酶la(ino...     

Phosphorylation of p66shc mediates 6-hydroxydopamine cytotoxicity

6-Hydroxydopamine (6-OHDA) is a neurotoxin that has been widely used to generate Parkinson's disease (PD) models. Increased oxidative stress is suggested to play an important role in 6-OHDA-induced cell death. Given the lessened susceptibility to oxidative stress exhibited by mice lacking p66shc, this study investigated the role of p66shc in the cytotoxicity of 6-OHDA. 6-OHDA induced cell death and p66shc phosphorylation at Ser36 in SH-SY5Y cells. Pre-treatment with the protein kinase C β (PKCβ) inhibitor hispidin suppressed 6-OHDA-induced p66shc phosphorylation. Elimination of H(2)O(2) by catalase reduced cell death and p66shc phosphorylation induced by 6-OHDA. Cells deficient in p66shc were more resistant to 6-OHDA-induced cell death than wild-type cells. Furthermore, reconstitution of wild-type p66shc, but not the S36A mutant, in p66shc-deficient cells increased susceptibility to 6-OHDA. These results indicate that H(2)O(2) derived from 6-OHDA is an important mediator of cell death and p66shc phosphorylation induced by 6-OHDA and that p66shc phosphorylation at Ser36 is indispensable for the cytotoxicity of 6-OHDA.     

1-Methyl-4-phenyl-pyridinium ion-induced oxidative stress, c-Jun phosphorylation and DNA fragmentation factor-45 cleavage in SK-N-SH cells are averted by selegiline

Parkinson's disease is a progressive neurodegenerative disorder, associated with the selective loss of dopaminergic neurons in the substantia nigra pars compacta. Recent studies have shown that c-Jun-N terminal kinase pathways might be involved in the oxidative stress-induced neuronal demise. In addition, there are several studies demonstrating that selegiline protects neural cell degeneration. In view of the above, the toxic effects of MPP(+) and the protective roles of selegiline were studied in cultures of human neuroblastoma (SK-N-SH) cell lines in the present study. MPP(+) significantly decreased cell viability but increased reactive oxygen species formation and lipid peroxidation, and the said effects were attenuated by selegiline. MPP(+) did not change the total levels of c-Jun but enhanced phosphorylation of c-Jun at Ser73 and cleavage of DNA fragmentation factor 45, which were diminished by selegiline. MPP(+)-treated SK-N-SH cells exhibited an irregularly shaped nuclear chromatin or DNA fragmentation, which was abolished by selegiline. These data suggest that c-Jun-N terminal kinase pathways are involved in oxidative stress-induced dopaminergic neuronal degeneration and pretreatment with selegiline affords neuroprotection by inhibiting these cell death-signaling pathways.     

ER stress and UPR in familial amyotrophic lateral sclerosis

The primary mechanism by which mutations in Cu, Zn-superoxide dismutase (SOD1) contribute to progressive motor neuron loss in familial amyotrophic lateral sclerosis (FALS) remains unknown. Misfolded protein aggregates, ubiquitin-proteasome system impairment and neuronal apoptosis mediated by death receptor or mitochondrial-dependent pathways are implicated in mutant SOD1-induced toxicity. Recent evidence from cellular and transgenic rodent models of FALS proposes activation of a third apoptotic pathway linked to sustained endoplasmic reticulum (ER) stress. Here, we review the emerging role of ER stress and the unfolded protein response (UPR) in the pathogenesis of mutant SOD1-linked FALS. The UPR observed in FALS rodents is described which encompasses induction of key ER-resident chaperones during presymptomatic disease, leading to activation of stress transducers and pro-apoptotic molecules by late stage disease. Importantly, mutant SOD1 co-aggregates with UPR components and recruits to the ER, suggesting a direct adverse effect on ER function. By contrast, the opposing neuroprotective effects of wild-type SOD1 overexpression on UPR signalling are also highlighted. In addition, the potential impact of neuronal Golgi apparatus (GA) fragmentation and subsequent disturbances in intracellular protein trafficking on motor neuron survival in FALS is also discussed. We propose that ER stress and UPR may be coupled to GA dysfunction in mutant SOD1-mediated toxicity, promoting ER-initiated cell death signalling in FALS.     

Dietary oxyresveratrol prevents parkinsonian mimetic 6-hydroxydopamine neurotoxicity

Oxyresveratrol (OXY) is a polyhydroxylated stilbene existing in mulberry. Increasing lines of evidence have shown its neuroprotective effects against Alzheimer disease and stroke. However, little is known about its neuroprotective effect in Parkinson disease (PD). Owing to its antioxidant activity, blood-brain barrier permeativity, and water solubility, we hypothesized that OXY may exert neuroprotective effects against parkinsonian mimetic 6-hydroxydopamine (6-OHDA) neurotoxicity. Neuroblastoma SH-SY5Y cells have long been used as dopaminergic neurons in PD research. We found that both pretreatment and posttreatment with OXY on SH-SY5Y cells significantly reduced the release of lactate dehydrogenase, the activity of caspase-3, and the generation of intracellular reactive oxygen species triggered by 6-OHDA. Compared to resveratrol, OXY exhibited a wider effective dosage range. We proved that OXY could penetrate the cell membrane by HPLC analysis of cell extracts. These results suggest that OXY may act as an intracellular antioxidant to reduce oxidative stress induced by 6-OHDA. Western blot analysis demonstrated that OXY markedly attenuated 6-OHDA-induced phosphorylation of JNK and c-Jun. Furthermore, we proved that OXY increased the basal levels of SIRT1, which may disclose new pathways accounting for the neuroprotective effects of OXY. Taken together, our results suggest OXY, a dietary phenolic compound, as a potential nutritional candidate for protection against neurodegeneration in PD.     

Prednisolone-induced beta cell dysfunction is associated with impaired endoplasmic reticulum homeostasis in INS-1E cells

Glucocorticoids (GCs), such as prednisolone (PRED), are widely prescribed anti-inflammatory drugs, but their use may induce glucose intolerance and diabetes. GC-induced beta cell dysfunction contributes to these diabetogenic effects through mechanisms that remain to be elucidated. In this study, we hypothesized that activation of the unfolded protein response (UPR) following endoplasmic reticulum (ER) stress could be one of the underlying mechanisms involved in GC-induced beta cell dysfunction. We report here that PRED did not affect basal insulin release but time-dependently inhibited glucose-stimulated insulin secretion in INS-1E cells. PRED treatment also decreased both PDX1 and insulin expression, leading to a marked reduction in cellular insulin content. These PRED-induced detrimental effects were found to be prevented by prior treatment with the glucocorticoid receptor (GR) antagonist RU486 and associated with activation of two of the three branches of the UPR. Indeed, PRED induced a GR-mediated activation of both ATF6 and IRE1/XBP1 pathways but was found to reduce the phosphorylation of PERK and its downstream substrate eIF2α. These modulations of ER stress pathways were accompanied by upregulation of calpain 10 and increased cleaved caspase 3, indicating that long term exposure to PRED ultimately promotes apoptosis. Taken together, our data suggest that the inhibition of insulin biosynthesis by PRED in the insulin-secreting INS-1E cells results, at least in part, from a GR-mediated impairment in ER homeostasis which may lead to apoptotic cell death.     

Signal transduction pathways leading to increased eIF4E phosphorylation caused by oxidative stress

Phosphorylation of eIF4E is associated with increased activity of the translational machinery. Oxidative stress of resident vascular cells and macrophages potently enhances eIF4E phosphorylation. Oxidative stress activates numerous intracellular signaling pathways, including MAP-family kinase pathways and pathways leading to S6 kinase activation. The activation of MAP-family kinase pathways leads to the activation of Mnk and hence eIF4E phosphorylation, whereas the S6 kinase pathway is not involved, based on insensitivity to its inhibitors rapamycin and wortmannin. Ca-dependent pathways have been implicated in eIF4E phosphorylation, but the oxidative stress response pathway targeting eIF4E does not appear to require their participation. The results suggest that the potent activation of ERK and p38 protein kinases is sufficient to account for the enhanced eIF4E phosphorylation. Either is independently sufficient to effect the change, as neither PD098059 (Erk pathway inhibitor) nor SB202190 (p38 pathway inhibitor) alone can block the response, but when combined the response is almost completely abrogated. Mnk activation by oxidative stress leading to enhanced eIF4E phosphorylation may play a role in promoting stress-induced hyperproliferative diseases, such as smooth muscle cell proliferation and hypertrophy in cardiovascular disease, as the synthesis of several key regulators of cell growth has been shown to be held in check by moderation of eIF4E activity.     

The Endoplasmic Reticulum Stress Response in Neuroprogressive Diseases: Emerging Pathophysiological Role and Translational Implications

The endoplasmic reticulum (ER) is the main cellular organelle involved in protein synthesis, assembly and secretion. Accumulating evidence shows that across several neurodegenerative and neuroprogressive diseases, ER stress ensues, which is accompanied by over-activation of the unfolded protein response (UPR). Although the UPR could initially serve adaptive purposes in conditions associated with higher cellular demands and after exposure to a range of pathophysiological insults, over time the UPR may become detrimental, thus contributing to neuroprogression. Herein, we propose that immune-inflammatory, neuro-oxidative, neuro-nitrosative, as well as mitochondrial pathways may reciprocally interact with aberrations in UPR pathways. Furthermore, ER stress may contribute to a deregulation in calcium homoeostasis. The common denominator of these pathways is a decrease in neuronal resilience, synaptic dysfunction and even cell death. This review also discusses how mechanisms related to ER stress could be explored as a source for novel therapeutic targets for neurodegenerative and neuroprogressive diseases. The design of randomised controlled trials testing compounds that target aberrant UPR-related pathways within the emerging framework of precision psychiatry is warranted.     

Intracellular signaling pathways involved in post-mitotic dopaminergic PC12 cell death induced by 6-hydroxydopamine

Oxidative stress has been shown to mediate neuron damage in Parkinson's disease (PD). In the present report, we intend to clarify the intracellular pathways mediating dopaminergic neuron death after oxidative stress production using post-mitotic PC12 cells treated with the neurotoxin 6-hydroxydopamine (6-OHDA). The use of post-mitotic cells is crucial, because one of the suggested intracellular pathways implicated in neuron death relates to the re-entry of neurons (post-mitotic cells) in the cell cycle. We find that 6-OHDA sequentially increases intracellular oxidants, functional cell damage and caspase-3 activation, leading to cell death after 12 h of incubation. Prevention of cell damage by different antioxidants supports the implication of oxidative stress in the observed neurotoxicity. Oxidative stress-dependent phosphorylation of the MAPK JNK and oxidative stress-independent PKB/Akt dephosphorylation are involved in 6-OHDA neurotoxicity. Decrease in p21(WAF1/CIP1) and cyclin-D1 expression, disappearance of the non-phosphorylated band of retinoblastoma protein (pRb), and expression of proliferating cell nuclear antigen, not present in PC12 post-mitotic cells, suggest a re-entry of differentiated cells into cell cycle. Our results indicate that such a re-entry is mediated by oxidative stress and is involved in 6-OHDA-induced cell death. We conclude that at least three intracellular pathways are involved in 6-OHDA-induced cell death in differentiated PC12 cells: JNK activation, cell cycle progression (both oxidative stress-dependent), and Akt dephosphorylation (not related to the increase of oxidants); the three pathways are necessary for the cells to die, since blocking one of them is sufficient to keep the cells alive.     

Protective effect of (+/-) isoborneol against 6-OHDA-induced apoptosis in SH-SY5Y cells.

Oxidative stress caused by dopamine (DA) may play an important role in the pathogenesis of Parkinson's disease (PD). (+/-) Isoborneol is a monoterpenoid alcohol present in the essential oils of numerous medicinal plants and is a known antioxidant. In this study, we investigated the neuroprotective effect of isoborneol against 6-hydroxydopamine (6-OHDA)-induced cell death in human neuroblastoma SH-SY5Y cells. Pretreatment of SH-SY5Y cells with isoborneol significantly reduced 6-OHDA-induced generation of reactive oxygen species (ROS) and 6-OHDA-induced increases in intracellular calcium. Furthermore, apoptosis induced by 6-OHDA was reversed by isoborneol treatment. Isoborneol protected against 6-OHDA-induced increases in caspase-3 activity and cytochrome C translocation into the cytosol from mitochondria. Isoborneol prevented 6-OHDA from decreasing the Bax/Bcl-2 ratio. We also observed that isoborneol decreased the activation of c-Jun N-terminal kinase and induced activation of protein kinase C (PKC) which had been suppressed by 6-OHDA. Our results indicate that the protective function of isoborneol is dependent upon its antioxidant potential and strongly suggest that isoborneol may be an effective treatment for neurodegenerative diseases associated with oxidative stress.     

Unfolding protein response signaling is involved in development,maintenance, and regression of the corpus luteum during the bovine estrous cycle

The corpus luteum (CL) is a transient endocrine organ. Development, maintenance, and regression of CL are effectively controlled by dynamic changes in gene expression. However, it is unknown what types of gene are affected during the CL life span of the estrous cycle in bovine. Here, we determined whether unfolded protein response (UPR) signaling via eIF2α/ATF4/GADD34, p90ATF6/p50ATF6, and IRE1/XBP1, which is a cellular stress response associated with the endoplasmic reticulum (ER), is involved in the bovine CL life span. Our results indicated that expression of Grp78/Bip, the master UPR regulator, was increased during the maintenance stage and rapidly decreased at the regression stage. Additionally, UPR signaling pathways genes were found to be involved in luteal phase progression during the estrous cycle. Our findings suggested that Grp78/Bip, ATF6, and XBP1 act as ER chaperones for initiating CL development and maintaining the CL. In addition, we investigated whether ER stress-mediated apoptosis is occurred through three UPR signaling pathways in CL regression stage. Interestingly, pIRE1 and CHOP were found to be involved in both the adaptive response and ER stress-mediated apoptosis. During the CL regression stage, increased expression of pJNK and CHOP, two components of ER stress-mediated apoptotic cascades, occurred before increased level of cleaved caspase 3 were observed. The present investigation was performed to identify a functional link between UPR signaling and CL life span during the bovine estrous cycle. Taken together, results from this study demonstrated that UPR protein/gene expression levels were different at various stages of the bovine CL life span. Variations in the expression of these protein/genes may play important roles in luteal stage progression during the estrous cycle.     

Activation of the unfolded protein response in Parkinson's disease

Parkinson's disease (PD) is, at the neuropathological level, characterized by the accumulation of misfolded proteins. The presence of misfolded proteins can trigger a cellular stress response in the endoplasmic reticulum (ER) called the Unfolded Protein Response (UPR). The UPR has been shown to be involved in cellular models for PD. In this study, we investigated UPR activation in the substantia nigra of control and PD patients. Immunoreactivity for the UPR activation markers phosphorylated pancreatic ER kinase (pPERK) and phosphorylated eukaryotic initiation factor 2alpha (peIF2alpha) is detected in neuromelanin containing dopaminergic neurons in the substantia nigra of PD cases but not in control cases. In addition, pPERK immunoreactivity is colocalized with increased alpha-synuclein immunoreactivity in dopaminergic neurons. These data show that the UPR is activated in PD and that UPR activation is closely associated with the accumulation and aggregation of alpha-synuclein.