Downregulation of the Wnt/β-catenin signaling pathway is involved in manganese-induced neurotoxicity in rat striatum and PC12 cells

The protective role of sesame oil against Parkinson's-like disease induced by manganese in rats

Chronic exposure to manganese (Mn) results in motor dysfunction, biochemical and pathological alterations in the brain. Oxidative stress, inflammation, and dysfunction of dopaminergic and GABAergic systems stimulate activating transcription factor-6 (ATF-6) and protein kinase RNA-like ER kinase (PERK) leading to apoptosis. This study aimed to investigate the protective effect of sesame oil (SO) against Mn-induced neurotoxicity. Rats received 25 mg/kg MnCl2 and were concomitantly treated with 2.5, 5, or 8 ml/kg of SO for 5 weeks. Mn-induced motor dysfunction was indicated by significant decreases in the time taken by rats to fall during the rotarod test and in the number of movements observed during the open field test. Also, Mn resulted in neuronal degeneration as observed by histological staining. The striatal levels of lipid peroxides and reduced glutathione (oxidative stress markers), interleukin-6 and tumor necrosis factor-α (inflammatory markers) were significantly elevated. Mn significantly reduced the levels of dopamine and Bcl-2, while GABA, PERK, ATF-6, Bax, and caspase-3 were increased. Interestingly, all SO doses, especially at 8 ml/kg, significantly improved locomotor activity, biochemical deviations and reduced neuronal degeneration. In conclusion, SO may provide potential therapeutic benefits in enhancing motor performance and promoting neuronal survival in individuals highly exposed to Mn.

CYP1B1 affects the integrity of the blood-brain barrier and oxidative stress in the striatum: An investigation of manganese-induced neurotoxicity

AIMS

Excessive influx of manganese (Mn) into the brain across the blood-brain barrier induces neurodegeneration. CYP1B1 is involved in the metabolism of arachidonic acid (AA) that affects vascular homeostasis. We aimed to investigate the effect of brain CYP1B1 on Mn-induced neurotoxicity.

METHOD

Brain Mn concentrations and α-synuclein accumulation were measured in wild-type and CYP1B1 knockout mice treated with MnCl2 (30 mg/kg) and biotin (0.2 g/kg) for 21 continuous days. Tight junctions and oxidative stress were analyzed in hCMEC/D3 and SH-SY5Y cells after the treatment with MnCl2 (200 μM) and CYP1B1-derived AA metabolites (HETEs and EETs).

RESULTS

Mn exposure inhibited brain CYP1B1, and CYP1B1 deficiency increased brain Mn concentrations and accelerated α-synuclein deposition in the striatum. CYP1B1 deficiency disrupted the integrity of the blood-brain barrier (BBB) and increased the ratio of 3, 4-dihydroxyphenylacetic acid (DOPAC) to dopamine in the striatum. HETEs attenuated Mn-induced inhibition of tight junctions by activating PPARγ in endothelial cells. Additionally, EETs attenuated Mn-induced up-regulation of the KLF/MAO-B axis and down-regulation of NRF2 in neuronal cells. Biotin up-regulated brain CYP1B1 and reduced Mn-induced neurotoxicity in mice.

CONCLUSIONS

Brain CYP1B1 plays a critical role in both cerebrovascular and dopamine homeostasis, which might serve as a novel therapeutic target for the prevention of Mn-induced neurotoxicity.

Melatonin modulates the differentiation of neural stem cells exposed to manganese via SIRT1/β-catenin signaling

Excessive exposure of children to manganese (Mn) in the environment has a bearing on developmental neurotoxicity. Although melatonin (Mel) can play a neuroprotective role by modulating the differentiation of neural stem cells (NSCs) in the developing brain, its specific mechanism under Mn overexposure remains to be explored. Here, we cultured primary NSCs as an available model to investigate the relevant molecular mechanism of Mel mitigation on Mn-induced disorder of NSCs differentiation through sirtuin 1 (SIRT1)/β-catenin pathway. It was found that Mel could facilitate the differentiation of Mn-treated NSCs into neurons. Further, our results uncovered that the pro-differentiation mechanism of Mel depended upon ascending the activity of SIRT1, thereby weakening β-catenin acetylation and increasing phosphorylation of β-catenin ser675 in the cytoplasm, which facilitates the nuclear translocation of β-catenin. Furthermore, the role of SIRT1 in Mel-mediated signal transduction was investigated through the pretreatment of NSCs using a highly specific SIRT1 inhibitor, EX527. After EX527 pretreatment, Mel could not maintain its protective effect. Overall, our results revealed that Mel could alleviate Mn-induced disorder of NSCs differentiation through the activation of the SIRT1/β-catenin pathway.

Evaluating the neuroprotective activities of vinpocetine, punicalagin, niacin and vitamin E against behavioural and motor disabilities of manganese-induced Parkinson's disease in Sprague Dawley rats

The current study investigated the neuroprotective activity of some drugs and nutriceuticals with antioxidant and anti-inflammatory potential on the pathogenesis of Parkinson's disease (PD). Rats were categorized into seven groups: Rats received tween80 daily for 5 weeks as a control group, MnCl₂ (10 mg/kg, i.p) either alone (group II) or in combination with vinpocetine (VIN) (20 mg/kg) (group III), punicalagin (PUN) (30 mg/kg) (group IV), niacin (85 mg/kg) (group V), vitamin E (Vit E) (100 mg/kg) (group VI) or their combination (group VII). Motor activities was examined using open-field and catalepsy. Striatal monamines, acetylcholinesterase, excitatory/inhibitory neurotransmitters, redox status, pro-oxidant content, brain inflammatory, apoptotic and antioxidant biomarkers levels were assessed. Besides, histopathological investigations of different brain regions were determined. Groups (IV -GVII) showed improved motor functions of PD rats. Applied drugs significantly increased the brain levels of monoamines with the strongest effect to PUN. Meanwhile, they significantly decreased levels of acetylcholinesterase with a strongest effect to PUN. Moreover, they exhibited significant neuronal protection and anti-inflammatory abilities through significant reduction of the brain levels of COX2, TNF-α and Il-1β with a strongest effect to the PUN. Interestingly; groups (IV - GVII) showed restored glutamate/GABA balance and exhibited a pronounced decrease in caspase-3 content and GSK-3β protein expression levels. In addition, they significantly increased Bcl2 mRNA expression levels with a strongest effect for PUN. All these findings were further confirmed by the histopathological examinations. As a conclusion, we propose VIN and PUN to mitigate the progression of PD via their antioxidant, anti-inflammatory, anti-apoptotic, neurotrophic and neurogenic activities.

Cholinergic Receptor Modulation as a Target for Preventing Dementia in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative condition characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) in the midbrain resulting in progressive impairment in cognitive and motor abilities. The physiological and molecular mechanisms triggering dopaminergic neuronal loss are not entirely defined. PD occurrence is associated with various genetic and environmental factors causing inflammation and mitochondrial dysfunction in the brain, leading to oxidative stress, proteinopathy, and reduced viability of dopaminergic neurons. Oxidative stress affects the conformation and function of ions, proteins, and lipids, provoking mitochondrial DNA (mtDNA) mutation and dysfunction. The disruption of protein homeostasis induces the aggregation of alpha-synuclein (α-SYN) and parkin and a deficit in proteasome degradation. Also, oxidative stress affects dopamine release by activating ATP-sensitive potassium channels. The cholinergic system is essential in modulating the striatal cells regulating cognitive and motor functions. Several muscarinic acetylcholine receptors (mAChR) and nicotinic acetylcholine receptors (nAChRs) are expressed in the striatum. The nAChRs signaling reduces neuroinflammation and facilitates neuronal survival, neurotransmitter release, and synaptic plasticity. Since there is a deficit in the nAChRs in PD, inhibiting nAChRs loss in the striatum may help prevent dopaminergic neurons loss in the striatum and its pathological consequences. The nAChRs can also stimulate other brain cells supporting cognitive and motor functions. This review discusses the cholinergic system as a therapeutic target of cotinine to prevent cognitive symptoms and transition to dementia in PD.

Behavioral and neurochemical effects in mice after one-generation exposure to low doses of manganese: Focus on offspring development

The risk of exposure to toxic metals is a known concern to human populations. The overexposure to Mn can lead to a pathological condition, with symptoms similar to Parkinson's disease. Although toxicity of Mn has been reported, studies in neonates are scarce but necessary, as Mn can cross biological barriers. The present study evaluated if chronic perinatal exposure to Mn at low doses lead to neurotoxic effects in mice, after direct and indirect exposure. Couples of mice were exposed to Mn (0.013, 0.13, and 1.3 mg kg^-1.day^-1) for 60 days prior to mating, as well as during gestation and lactation. The offspring was distributed into two groups: animals that were not exposed after weaning - parental exposure only (PE); and animals subject to additional 60-day exposure through gavages after weaning - parental and direct exposure (PDE). Neurological effects were evaluated by Mn quantification, behavior tests and biochemical markers in the brain. PDE animals had alterations in short/long-term memory and increased anxiety-like behavior. Exposure to Mn triggered a decrease of glutathione-s-transferase and increase of cholinesterase activity in different regions of the brain. These findings highlight the risk of exposure to low doses of Mn over a generation and at early stages of development.

Molecular Targets of Manganese-Induced Neurotoxicity: A Five-Year Update

Understanding of the immediate mechanisms of Mn-induced neurotoxicity is rapidly evolving. We seek to provide a summary of recent findings in the field, with an emphasis to clarify existing gaps and future research directions. We provide, here, a brief review of pertinent discoveries related to Mn-induced neurotoxicity research from the last five years. Significant progress was achieved in understanding the role of Mn transporters, such as SLC39A14, SLC39A8, and SLC30A10, in the regulation of systemic and brain manganese handling. Genetic analysis identified multiple metabolic pathways that could be considered as Mn neurotoxicity targets, including oxidative stress, endoplasmic reticulum stress, apoptosis, neuroinflammation, cell signaling pathways, and interference with neurotransmitter metabolism, to name a few. Recent findings have also demonstrated the impact of Mn exposure on transcriptional regulation of these pathways. There is a significant role of autophagy as a protective mechanism against cytotoxic Mn neurotoxicity, yet also a role for Mn to induce autophagic flux itself and autophagic dysfunction under conditions of decreased Mn bioavailability. This ambivalent role may be at the crossroad of mitochondrial dysfunction, endoplasmic reticulum stress, and apoptosis. Yet very recent evidence suggests Mn can have toxic impacts below the no observed adverse effect of Mn-induced mitochondrial dysfunction. The impact of Mn exposure on supramolecular complexes SNARE and NLRP3 inflammasome greatly contributes to Mn-induced synaptic dysfunction and neuroinflammation, respectively. The aforementioned effects might be at least partially mediated by the impact of Mn on α-synuclein accumulation. In addition to Mn-induced synaptic dysfunction, impaired neurotransmission is shown to be mediated by the effects of Mn on neurotransmitter systems and their complex interplay. Although multiple novel mechanisms have been highlighted, additional studies are required to identify the critical targets of Mn-induced neurotoxicity.

Mechanisms of VPS35-Mediated Neurodegeneration in Parkinson's Disease

Parkinson's disease is a sporadic and common neurodegenerative movement disorder resulting from the complex interplay between genetic risk, aging and environmental exposure. Familial forms of PD account for ~10% of cases and are known to result from the inheritance of mutations in at least 15 genes. Mutations in the vacuolar protein sorting 35 ortholog (VPS35) gene cause late-onset, autosomal dominant familial PD. VPS35 is a key suunit of the pentameric retromer complex that plays a role in the retrograde sorting and recycling of transmembrane cargo proteins from endosomes to the plasma membrane and trans-Golgi network. A single heterozygous Asp620Asn (D620N) mutation in VPS35 has been identified in multiple families that segregates with PD, and a number of experimental cellular and animal models have been developed to understand its pathogenic effects. At the molecular level, the D620N mutation has been shown to impair the interaction of VPS35 with the WASH complex, that plays an accessory function in retromer-dependent sorting. In addition, the D620N mutation has been linked to the abnormal sorting of retromer cargo, including CI-M6PR, AMPA receptor subunits, MUL1, LAMP2a and ATG9A, as well as to LRRK2 hyperactivation. At the cellular level, data support an impact of D620N VPS35 on mitochondrial function, the autophagy-lysosomal pathway, Wnt signaling and neurotransmission via altered endosomal sorting. The relevance of abnormal retromer sorting and cellular pathways to PD-related neurodegenerative phenotypes induced by D620N VPS35 in rodent models is not yet clear. There is also uncertainty regarding the mechanism-of-action of the D620N mutation and whether it manifests pathogenic effects in animal models and PD through a gain-of-function and/or a partial dominant-negative mechanism. Here, we discuss the emerging molecular and cellular mechanisms underlying PD induced by familial VPS35 mutations, going from structure to cellular function to neuropathology. We further discuss studies linking reduced retromer function to other neurodegenerative diseases and potential therapeutic strategies to normalize retromer function to mitigate disease.

(D620N) VPS35 causes the impairment of Wnt/β-catenin signaling cascade and mitochondrial dysfunction in a PARK17 knockin mouse model

Patients with familial type 17 of Parkinson’s disease (PARK17) manifest autosomal dominant pattern and late-onset parkinsonian syndromes. Heterozygous (D620N) mutation of vacuolar protein sorting 35 (VPS35) is genetic cause of PARK17. We prepared heterozygous VPS35^D620N/+ knockin mouse, which is an ideal animal model of (D620N) VPS35-induced autosomal dominant PARK17. Late-onset loss of substantia nigra pars compacta (SNpc) dopaminergic (DAergic) neurons and motor deficits of Parkinson’s disease were found in 16-month-old VPS35^D620N/+ mice. Normal function of VPS35-containing retromer is needed for activity of Wnt/β-catenin cascade, which participates in protection and survival of SNpc DAergic neurons. It was hypothesized that (D620N) VPS35 mutation causes the malfunction of VPS35 and resulting impaired activity of Wnt/β-catenin pathway. Protein levels of Wnt1 and nuclear β-catenin were reduced in SN of 16-month-old VPS35^D620N/+ knockin mice. Downregulated protein expression of survivin, which is a target gene of nuclear β-catenin, and upregulated protein levels of active caspase-8 and active caspase-9 were observed in SN of VPS35^D620N/+ mice at age of 16 months. VPS35 is involved in controlling morphology and function of mitochondria. Impaired function of VPS35 caused by (D620N) mutation could lead to abnormal morphology and malfunction of mitochondria. A significant decrease in mitochondrial size and resulting mitochondrial fragmentation was found in tyrosine hydroxylase-positive and neuromelanin-positive SNpc DAergic neurons of 16-month-old VPS35^D620N/+ mice. Mitochondrial complex I activity or complex IV activity was reduced in SN of 16-month-old VPS35^D620N/+ mice. Increased level of mitochondrial ROS and oxidative stress were found in SN of 16-month-old VPS35^D620N/+ mice. Levels of cytosolic cytochrome c and active caspase-3 were increased in SN of VPS35^D620N/+ mice aged 16 months. Our results suggest that PARK17 mutant (D620N) VPS35 impairs activity of Wnt/β-catenin signaling pathway and causes abnormal morphology and dysfunction of mitochondria, which could lead to neurodegeneration of SNpc DAergic cells.

Knockdown of PDIA6 Inhibits Cell Proliferation and Enhances the Chemosensitivity in Gastric Cancer Cells

Background

Protein disulfide isomerase A6 (PDIA6), a member of the disulfide isomerase (PDI) family, has been reported to be closely associated with progression of various cancers. However, the specific effects of PDIA6 on gastric cancer (GC) remain unclear. In this study, we investigated the expression pattern and biological functions of PDIA6 in GC.

Materials and Methods

The CCK-8 assay was carried out to examine cell proliferation and cisplatin cytotoxicity. The Western blot analysis was used to measure the protein expression of PDIA6, Wnt3a and β-catenin. The xenograft tumor assay was performed to evaluate the in vivo effect of PDIA6 on GC cell proliferation and chemoresistance.

Results

PDIA6 was significantly elevated in GC tissues and cell lines. Down-regulation of PDIA6 inhibited GC cell proliferation and chemoresistance to cisplatin while up-regulation of PDIA6 promoted the proliferation and chemoresistance of GC cells. Besides, PDIA6 regulated the chemosensitivity of GC cells to cisplatin in vivo. Mechanically, PDIA6 served as a regulator of the Wnt/β-catenin signaling pathway by affecting the protein expression of Wnt3a and β-catenin in GC cells. Additionally, Wnt activator reversed the inhibitory effect of PDIA6 knockdown on cisplatin resistance in GC cells.

Conclusion

These findings provided new insight into the potential role of PDIA6 as a promising target for drug resistance in GC chemotherapy.

Akt inhibition-dependent downregulation of the Wnt/β-Catenin Signaling pathway contributes to antimony-induced neurotoxicity

Antimony (Sb), as a newly identified nerve poison, can lead to neuronal apoptosis. However, its neurotoxicological mechanisms remain largely unclear. Here, we evaluated the role and regulation of Wnt/β-catenin pathway in Sb-mediated neurotoxicity. Under Sb treatment, β-catenin was dramatically downregulated in vivo and in vitro. Moreover, overexpression of β-catenin effectively attenuated Sb-induced survivin gene expression suppression and subsequent apoptosis in PC12 cells. In addition, Sb stimualted glycogen synthase kinase-3β (GSK-3β) activation, shown as decreased phosphorylation levels at Ser 9 both in PC12 cells and mice brain. Paramacological inhibition of GSK-3β using lithium chloride (LiCl) significantly rescued β-catenin expression. For upstream pathway analysis, we found Sb treatment decreased protein kinase B (Akt) phosphorylation, and Akt activator protected PC12 cells from GSK-3β activation and subsequent β-catenin suppression. In summary, our data provided a novel molecular mechanism of Sb-associated neurotoxicity, namely that Sb induces Wnt/β-catenin pathway suppression through Akt inhibition, thus resulted in neuronal apoptosis.

Protective effect of vinpocetine against neurotoxicity of manganese in adult male rats

Manganese (Mn) is required for many essential biological processes as well as in the development and functioning of the brain. Extensive accumulation of Mn in the brain may cause central nervous system dysfunction known as manganism, a motor disorder associated with cognitive and neuropsychiatric deficits similar to parkinsonism. Vinpocetine, a synthetic derivative of the alkaloid vincamine, is used to improve the cognitive function in cerebrovascular diseases. It possesses antioxidant and antiinflammatory properties. The present work was designed to explore the potential neuroprotective mechanisms exerted by vinpocetine in the Mn-induced neurotoxicity in rats. Rats were allocated into four groups. First group was given saline. The other three groups were given MnCl₂; two of them were treated with either L-dopa, the gold standard antiparkinsonian drug, or vinpocetine. Rats receiving MnCl₂ exhibited lengthened catalepsy duration in the grid and bar tests, motor impairment in the open-field test and short-term memory deficit in the Y-maze test. Additionally, histological examination revealed structural alterations and degeneration in different brain regions. Besides, striatal monoamines and mitochondrial complex I contents were declined, apoptotic biomarker caspase-3 expression and acetylcholinesterase activity were elevated. Moreover, oxidative stress and inflammation were detected in the striata. L-dopa or vinpocetine exerted protective effects against MnCl₂-induced neurotoxicity. It could be hypothesized that modulation of monoamines, upregulation of mitochondrial complex I, antioxidant, antiinflammatory, and antiapoptotic activities are significant mechanisms underlying the neuroprotective effect of vinpocetine in the Mn-induced neurotoxicity model in rats.

Magnetic resonance imaging patterns of treatment-related toxicity in the pediatric brain: an update and review of the literature

Treatment-related neurotoxicity is a potentially life-threatening clinical condition that can represent a diagnostic challenge. Differentiating diagnoses between therapy-associated brain injury and recurrent disease can be difficult, and the immediate recognition of neurotoxicity is crucial to providing correct therapeutic management, ensuring damage reversibility. For these purposes, the knowledge of clinical timing and specific treatment protocols is extremely important for interpreting MRI patterns. Neuroradiologic findings are heterogeneous and sometimes overlapping, representing the compounding effect of the different treatments. Moreover, MRI patterns can be acute, subacute or delayed and involve different brain regions, depending on (1) the mechanism of action of the specific medication and (2) which brain regions are selectively vulnerable to specific toxic effects. This review illustrates the most common radiologic appearance of radiotherapy, chemotherapy and medication-associated brain injury in children, with special focus on the application of advanced MRI techniques (diffusion, perfusion and proton spectroscopy) in the diagnosis of the underlying processes leading to brain toxicity.

Enhancing Beta-Catenin Activity via GSK3beta Inhibition Protects PC12 Cells against Rotenone Toxicity through Nurr1 Induction

Parkinson’s disease (PD) is characterized by progressive degeneration of dopaminergic (DA) neurons in the substantial nigra pars compacta. Increasing evidence showed that Wnt/β-catenin pathway and the orphan nuclear receptor Nurr1 play crucial roles in the survival and functional maintenance of DA neurons in the midbrain and GSK-3β antagonists LiCl and SB216763 were used to activate Wnt/β-catenin pathway experimentally. However, the detail mechanism underlying the neuroprotection against apoptosis on DA neuron is still unclear and the interaction between Wnt/β-catenin and Nurr1 remains undisclosed. In this study, using cell biological assay we investigated the function of Wnt/β-catenin and its crosstalk with Nurr1 on the course of PC12 cell degeneration in vitro. Our data showed that PC12 cell viability was inhibited by rotenone, but attenuated by GSK-3β antagonists LiCl or SB216763. The activity of Wnt/β-catenin pathway was deregulated on exposure of rotenone in a concentration-dependent manner. After the interference of β-catenin with siRNA, LiCl or SB216763 failed to protect PC12 cells from apoptosis by the rotenone toxicity. Our data confirmed that Wnt/β-catenin signaling activated by LiCl or SB216763 enhanced Nurr1 expression to 2.75 ± 0.55 and 4.06 ± 0.41 folds respectively compared with control detected by real-time PCR and the interaction of β-catenin with Nurr1 was identified by co-immunoprecipitate analysis. In conclusion, the data suggested that Wnt/β-catenin and Nurr1 are crucial factors in the survival of DA neurons, and the activation of Wnt/β-catenin pathway exerts protective effects on DA neurons partly by mean of a co-active pattern with Nurr1. This finding may shed a light on the potential treatment of Parkinson disease.

Involvement of dysregulated Wip1 in manganese-induced p53 signaling and neuronal apoptosis

Overexposure to manganese (Mn) has been known to induce neuronal death and neurodegenerative symptoms. However, the precise mechanisms underlying Mn neurotoxicity remain incompletely understood. In the present study, we established a Mn-exposed rat model and found that downregulation of wild type p53-induced phosphatase 1 (Wip1) might contribute to p53 activation and resultant neuronal apoptosis following Mn exposure. Western blot and immunohistochemical analyses revealed that the expression of Wip1 was markedly decreased following Mn exposure. In addition, immunofluorescence assay demonstrated that Mn exposure led to significant reduction in the number of Wip1-positive neurons. Accordingly, the expression of Mdm2 was progressively decreased, which was accompanied with markedly increased expression of p53, as well as the ratio of Bax/Bcl-xl. Furthermore, we showed that Mn exposure decreased the viability and induced apparent apoptosis in NFG-differentiated neuron-like PC12 cells. Importantly, the expression of Wip1 decreased progressively, whereas the level of cellular p53 and the ratio of Bax/Bcl-xl were elevated, which resembled the expression of the proteins in animal model studies. Depletion of p53 significantly ameliorated Mn-mediated cytotoxic effect in PC12 cells. In addition, ectopic expression of Wip1 attenuated Mn-induced p53 signaling as well as apoptosis in PC12 cells. Finally, we observed that depletion of Wip1 augmented Mn-induced apoptosis in PC12 cells. Collectively, these findings suggest that downregulated Wip1 expression plays an important role in Mn-induced neuronal death in the brain striatum via the modulation of p53 signaling.

Inhibitory Effects of Bisphenol-A on Neural Stem Cells Proliferation and Differentiation in the Rat Brain Are Dependent on Wnt/β-Catenin Pathway

Neurogenesis, a process of generation of new neurons, occurs throughout the life in the hippocampus and sub-ventricular zone (SVZ). Bisphenol-A (BPA), an endocrine disrupter used as surface coating for packaged food cans, injures the developing and adult brain. However, the effects of BPA on neurogenesis and underlying cellular and molecular mechanism(s) are still unknown. Herein, we studied the effect(s) of prenatal and early postnatal exposure of low dose BPA on Wnt/β-catenin signaling pathway that controls different steps of neurogenesis such as neural stem cell (NSC) proliferation and neuronal differentiation. Pregnant rats were treated with 4, 40, and 400 μg BPA/kg body weight orally daily from gestational day 6 to postnatal day 21. Both in vivo and in vitro studies showed that BPA alters NSC proliferation and differentiation. BPA impaired NSC proliferation (5'-bromo-2'-deoxyuridine (BrdU(+)) and nestin(+) cells) and neuronal differentiation (BrdU/doublecortin(+) and BrdU/neuronal nuclei (NeuN(+)) cells) in the hippocampus and SVZ as compared to control. It significantly altered expression/protein levels of neurogenic genes and the Wnt pathway genes in the hippocampus. BPA reduced cellular β-catenin and p-GSK-3β levels and decreased β-catenin nuclear translocation, and cyclin-D1 and TCF/LEF promoter luciferase activity. Specific activation and blockage of the Wnt pathway suggested involvement of this pathway in BPA-mediated inhibition of neurogenesis. Further, blockage of GSK-3β activity by SB415286 and GSK-3β small interfering RNA (siRNA) attenuated BPA-induced downregulation of neurogenesis. Overall, these results suggest significant inhibitory effects of BPA on NSC proliferation and differentiation in the rat via the Wnt/β-catenin signaling pathway.

Pivotal roles of p53 transcription-dependent and -independent pathways in manganese-induced mitochondrial dysfunction and neuronal apoptosis

Chronic exposure to excessive manganese (Mn) has been known to lead to neuronal loss and a clinical syndrome resembling idiopathic Parkinson's disease (IPD). p53 plays an integral role in the development of various human diseases, including neurodegenerative disorders. However, the role of p53 in Mn-induced neuronal apoptosis and neurological deficits remains obscure. In the present study, we showed that p53 was critically involved in Mn-induced neuronal apoptosis in rat striatum through both transcription-dependent and -independent mechanisms. Western blot and immunohistochemistrical analyses revealed that p53 was remarkably upregulated in the striatum of rats following Mn exposure. Coincidentally, increased level of cleaved PARP, a hallmark of apoptosis, was observed. Furthermore, using nerve growth factor (NGF)-differentiated PC12 cells as a neuronal cell model, we showed that Mn exposure decreased cell viability and induced apparent apoptosis. Importantly, p53 was progressively upregulated, and accumulated in both the nucleus and the cytoplasm. The cytoplasmic p53 had a remarkable distribution in mitochondria, suggesting an involvement of p53 mitochondrial translocation in Mn-induced neuronal apoptosis. In addition, Mn-induced impairment of mitochondrial membrane potential (ΔΨm) could be partially rescued by pretreatment with inhibitors of p53 transcriptional activity and p53 mitochondrial translocation, Pifithrin-α (PFT-α) and Pifithrin-μ (PFT-μ), respectively. Moreover, blockage of p53 activities with PFT-α and PFT-μ significantly attenuated Mn-induced reactive oxidative stress (ROS) generation and mitochondrial H₂O₂ production. Finally, we observed that pretreatment with PFT-α and PFT-μ ameliorated Mn-induced apoptosis in PC12 cells. Collectively, these findings implicate that p53 transcription-dependent and -independent pathways may play crucial roles in the regulation of Mn-induced neuronal death.

KHSRP participates in manganese-induced neurotoxicity in rat striatum and PC12 cells

Manganese (Mn) is an essential micronutrient. However, exposure to high doses of Mn may lead to a neurological disease known as manganism, which is characterized by marked brain neuronal loss. K-homology splicing regulator protein (KHSRP) is a multifunctional RNA-binding protein and has been implicated in the regulation of multiple cellular signaling associated with neuronal apoptosis and survival, such as p38 mitogen-activated protein kinase (MAPK), nuclear factor kappaB (NF-κB), and Wnt/β-catenin pathways. In the present study, the role of KHSRP in Mn-induced neurotoxicity was investigated in vivo using a rat model of chronic Mn exposure and in vitro using differentiated PC12 cell cultures. Western blot and immunohistochemical analyses showed a significant upregulation of KHSRP in rat striatum following Mn exposure. Immunofluorescent labeling indicated that KHSRP was localized mainly in neurons. Terminal deoxynucleotidyl transferase-mediated biotinylated-dUTP nick end labeling (TUNEL) assay showed that KHSRP was mainly distributed in apoptotic neurons. Increased KHSRP expression was positively correlated with the upregulation of several apoptosis-related proteins, such as p53, bax, and active caspase-3. In addition, significant co-localization of KHSRP and active caspase-3 in neurons after Mn exposure was also observed, suggesting a potential involvement of KHSRP in the regulation of Mn-induced striatal neuronal apoptosis. Importantly, interference with KHSRP apparently decreased the level of p53 and attenuated Mn-induced neuronal apoptosis. Taken together, these results indicate that upregulation of KHSRP may be involved in the pathological process underlying Mn neurotoxicity via the modulation of p53 signaling.