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Abstract: The mechanisms underlying the disruption of glutamate–glutamine cycle (Glu–Gln cycle) in manganism are still unknown. To approach the concrete mechanisms, the rats were i.p. injected with different doses of MnCl2 (0, 8, 40, and 200 μmol/kg), and the levels of Mn, Glu, and Gln, the morphological and ultrastructural changes, activities of Na+-K+-ATPase, GS, and PAG, mRNA and protein expression of GS, GLAST, and GLT-1 in the striatum were investigated. In addition, the effect of 21.35 μmol/kg riluzole (Na+ channel blocker) was studied at 200 μmol/kg MnCl2. It was observed that (1) Mn and Glu levels and PAG activity increased; (2) many pathological changes occurred; (3) Gln levels, Na+-K+-ATPase and GS activities, and GS, GLAST, and GLT-1 mRNA and protein expression inhibited, does dependently. Furthermore, the research indicated that pretreatment of riluzole reversed toxic effects of MnCl2 significantly. These results suggested that Glu–Gln cycle was disrupted by Mn exposure dose dependently; riluzole might antagonize Mn neurotoxicity. [Copyright &y& Elsevier]

[Display omitted] • Summarizes the molecular mechanisms of autophagy and apoptosis in MeHg neurotoxicity. • Analyzes the relationship between autophagy and apoptosis in MeHg neurotoxicity. • Autophagic pathway may mitigate MeHg neurotoxicity through modulation of apoptosis. Methylmercury (MeHg) is a bio-accumulative global environmental contaminant present in fish and seafood. MeHg accumulates in the aquatic environment and eventually reaches the human system via the food chain by bio-magnification. The central nervous system is the primary target of toxicity and is particularly vulnerable during development. It is well documented that developmental MeHg exposure can lead to neurological alterations, including cognitive and motor dysfunction. Apoptosis is a primary characteristic of MeHg-induced neurotoxicity, and may be regulated by autophagic activity. However, mechanisms mediating the interaction between apoptosis and autophagy remains to be explored. Autophagy is an adaptive response under stressful conditions, and the basal level of autophagy ensures the physiological turnover of old and damaged organelles. Autophagy can regulate cell fate through different crosstalk signaling pathways. A complex interplay between autophagy and apoptosis determines the degree of apoptosis and the progression of MeHg-induced neurotoxicity as demonstrated by pre-clinical models and clinical trials. This review summarizes recent advances in the roles of autophagy and apoptosis in MeHg neurotoxicity and thoroughly explores the relationship between them. The autophagic pathway may be a potential therapeutic target in MeHg neurotoxicity through modulation of apoptosis. [ABSTRACT FROM AUTHOR]

Methylmercury (MeHg) is one of the ubiquitous environmental toxicant that leads to long-lasting neurological deficits in animals and humans. The identification of the underlying mechanisms has been a main focus of research in the neurotoxicology field. Glutamate (Glu) dyshomeostasis and oxidative stress have been identified as two critical mechanisms mediating MeHg-induced neurotoxicity. However, little has been known of the interaction between these two mechanisms that play in MeHg poisoning in vivo. We, therefore, developed a rat model of MeHg subchronic poisoning to evaluate its neurotoxic effects and investigated the neuroprotective role of memantine, a low-affinity, noncompetitive N-methyl- d-aspartate receptors (NMDARs) antagonist, against MeHg-induced neurotoxicity. Ninety rats were randomly divided into five groups: control, memantine control, MeHg-treated (4 and 12 μmol/kg), and memantine pretreated. Administration of 12 μmol/kg MeHg for 4 weeks significantly elevated total Hg levels, disrupted Glu metabolism, overexcited NMDARs, and led to intracellular calcium overload, which might be critical to excessive reactive oxygen species (ROS) formation in cerebral cortex. Meanwhile, MeHg administration reduced non-enzymatic (non-protein sulfhydryl, NPSH) and enzymatic (superoxide dismutase, SOD and glutathione peroxidase, GSH-Px) antioxidants; caused lipid, protein, and DNA oxidative damage; and enhanced neurocyte apoptosis in cerebral cortex. Moreover, glutamate/aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1) appear to be inhibited by MeHg exposure. Pretreatment with memantine at a dose of 5 μmol/kg significantly prevented MeHg-induced alterations of Glu metabolism and oxidative stress, alleviated neurocyte apoptosis, and pathological injury. In conclusion, the results suggested that Glu dyshomeostasis and oxidative stress resulting from MeHg exposure contributed to neuronal injury. Memantine possesses the ability to attenuate MeHg-induced neurotoxicity through mechanisms involving its NMDARs-binding properties and indirect antioxidation. [ABSTRACT FROM AUTHOR]

Abstract: Methylmercury (MeHg) is one of the ubiquitous environmental toxicants, which can induce oxidative stress and an indirect excitotoxicity caused by altered glutamate (Glu) metabolism. However, little is known of the interaction between oxidative stress and Glu metabolism play in MeHg poisoning rats. We have investigated the neuroprotective role of MK-801, a non-competitive N-methyl-d-aspartate receptors (NMDAR) antagonist, against MeHg-induced neurotoxicity. Fifty rats were randomly divided into five groups of 10 animals in each group: control group, MK-801 control group, MeHg-treated group (4 and 12μmol/kg) and MK-801 pre-treated group. Administration of MeHg at a dose of 12μmol/kg for four weeks significantly increased in ROS and total Hg levels and that caused lipid, protein and DNA peroxidative damage in cerebral cortex. In addition, MeHg also reduced nonenzymic (reduced glutathione, GSH) and enzymic (glutathione peroxidase, GPx and superoxide dismutase, SOD) antioxidants and enhanced neurocyte apoptosis rate in cerebral cortex. MeHg-induced ROS production appears to inhibit the activity of the glutamine synthetase (GS), leading to Glu metabolism dysfunction. Pretreatment with MK-801 at a dose of 0.3μmol/kg prevented the alterations of the activities of PAG and GS and oxidative stress. In addition, pretreatment with MK-801 significantly alleviated the neurocyte apoptosis rate and histopathological damage. In conclusion, the results suggested ROS formation resulting from MeHg- and Glu-induced oxidative stress contributed to neuronal injury. MK-801 possesses the ability to attenuate MeHg-induced neurotoxicity in the cerebral cortex through mechanisms involving its NMDA receptor binding properties and antioxidation. [Copyright &y& Elsevier]

Chronic manganese (Mn) exposure can disturb mitochondrial homeostasis leading to mitochondrial dysfunction, which is involved in Mn‐induced neurodegenerative diseases. Resveratrol (RSV), as a promoter of mitochondrial biogenesis, plays a significant role against mitochondrial dysfunction. However, whether RSV can relieve Mn‐induced neuronal injury and mitochondrial dysfunction remains unknown. Sirtuin 3 (SIRT3), a main mitochondrial sirtuin, is an important regulator of mitochondria to maintain mitochondrial homeostasis. Therefore, this study investigated whether SIRT3 was required for RSV alleviating Mn‐induced mitochondrial dysfunction in primary cultured neurons from C57BL/6 mice. Here, we showed that Mn (100 and 200 μM) exposure for 24 hr caused significant neuronal damage and mitochondrial dysfunction through increasing mitochondrial ROS, reducing mitochondrial membrane potential and adenosine triphosphate level, and leading to mitochondrial network fragmentation, which could be ameliorated by RSV pretreatment in primary cultured neurons. Additionally, our results also indicated that RSV could activate the SIRT1/PGC‐1α signaling pathway and alleviate Mn‐induced disruption of mitochondrial biogenesis by increasing SIRT1 expression and activity, enhancing deacetylation of PGC‐1α. Furthermore, SIRT3 over‐expression increased deacetylation of mitochondrial transcription factor A and mitochondrial DNA (mtDNA) copy number. Oppositely, silencing SIRT3 increased acetylation of mitochondrial transcription factor A and decreased mtDNA copy number. Our results showed SIRT3 was required for the protective effect of RSV in mitochondrial biogenesis. In conclusion, our findings demonstrated that RSV could ameliorate Mn‐induced neuronal injury and mitochondrial dysfunction in primary cultured neurons through activating the SIRT1/ PGC‐1α signaling pathway, and that SIRT3 is required for promoting mitochondrial biogenesis and attenuating Mn‐induced mitochondrial dysfunction. [ABSTRACT FROM AUTHOR]

Methylmercury (MeHg) is a widely distributed environmental pollutant that can easily cross the blood-brain barrier and accumulate in the brain, thereby damaging the central nervous system. Studies have shown that MeHg-induced mitochondrial damage and apoptosis play a crucial role in its neurotoxic effects. Mitochondrial unfolded protein response (UPRmt) is indispensable to maintain mitochondrial protein homeostasis and ensure mitochondrial function, and the ATF4/CHOP axis is one of the signaling pathways to activate UPRmt. In this study, the role of the ATF4/CHOP axis-mediated UPRmt in the neurotoxicity of MeHg has been investigated by C57BL/6 mice and the HT22 cell line. We discovered that mice exposed to MeHg had abnormal neurobehavioral patterns. The pathological section showed a significant decrease in the number of neurons. MeHg also resulted in a reduction in mtDNA copy number and mitochondrial membrane potential (MMP). Additionally, the ATF4/CHOP axis and UPRmt were found to be significantly activated. Subsequently, we used siRNA to knock down ATF4 or CHOP and observed that the expression of UPRmt-related proteins and the apoptosis rate were significantly reduced. Our research showed that exposure to MeHg can over-activate the UPRmt through the ATF4/CHOP axis, leading to mitochondrial damage and ultimately inducing neuronal apoptosis. [ABSTRACT FROM AUTHOR]

Overexposure to manganese (Mn) is an important environmental risk factor for Parkinsonian-like symptoms referred to as manganism. Alpha-synuclein (α-Syn) oligomerization is a major cause in Mn-induced neurotoxicity. Autophagy, as an adjust response to control intracellular protein homeostasis, is involved in the degradation of α-Syn monomers or oligomers. Furthermore, autophagy dysregulation is also related to development of neurodegenerative disorders. Hence, we speculated that there was an interaction effect between α-Syn oligomerization and autophagy upon Mn exposure. In this study, we applied α-Syn gene knockout mice (α-Syn−/−) and wild-type mice (α-Syn+/+) treated with three different concentrations of MnCl2 (50, 100, and 200 μmol/kg) to elucidate the physiological role of α-Syn in Mn-induced autophagy dysregulation and neurocytes injury. We found that activation of chaperone-mediated autophagy (CMA) pathway by Mn was independent of α-Syn. Additionally, α-Syn could ameliorate excessive autophagy induced by high dose Mn (200 μmol/kg). Next, we used 5 mg/kg Rapamycin (Rap) or 3-methyladenine (3-MA) to regulate autophagy. The study revealed that autophagy is involved in Mn-induced α-Syn oligomerization and neurocytes injury. Taken together, these findings indicated that α-Syn oligomerization might be the major responsible for the Mn-induced autophagy dysregulation and neurocytes injury. [ABSTRACT FROM AUTHOR]

Abstract Manganese (Mn) has recently come into the limelight as an important environmental risk factor for neurodegenerative disorders. Although multiple neurotoxicity of Mn have been extensively studied, the exact mechanism of Mn-induced autophagic dysregulation is still poorly understood. The main aim of this study was to explore the role of cytosolic high-mobility group box 1 (HMGB1)-dependent autophagy in Mn-induced autophagic dysregulation and neurotoxicity. SH-SY5Y cells were treated with culture solution (control) and three different concentrations of Mn (50, 100, and 200 μM) for 24 h to detect the effect of Mn on HMGB1-dependent autophagy. We found Mn could increase the HMGB1 mRNA level and its cytosolic translocation and dysregulate autophagy, and Mn-induced alpha-synuclein overexpression interfered with the interaction of HMGB1 and Beclin1, to subsequently promote Beclin1 binding to Bcl2. Another important finding was the neuroprotective role of corynoxine B (Cory B) in Mn-induced autophagic dysregulation and neurotoxicity. We set up six experimental groups: control (culture solution); 200 μM Mn treatment; 100 μM Cory B-alone treatment; and three different pretreated concentrations of Cory B (25, 50, and 100 μM). Our results showed that Cory B ameliorated Mn-induced autophagic dysregulation and neurotoxicity partly by dissociating HMGB1 from alpha-synuclein and inhibiting mTOR signaling. Highlights • Mn-induced autophagy is related to HMGB1-Beclin1 binding. • Mn-induced α-SYN protein disturbs HMGB1-dependent autophagy. • Cory B dissociates HMGB1 from α-SYN to bind to Beclin1. • Cory B ameliorates Mn-induced autophagic dysregulation and neurotoxicity. [ABSTRACT FROM AUTHOR]

MeHg is one of the environmental pollutants that lead to oxidative stress and an indirect excitotoxicity caused by altered glutamate (Glu) concentration. However, little was known of the interaction. Therefore, we developed a rat model of MeHg poisoning to explore its neurotoxic effects, and whether LA could attenuate MeHg-induced neurotoxicity. Seventy-two rats were randomly divided into four groups: control group, MeHg-treated groups (4 and 12 μmol/kg), and LA pre-treatment group. Administration of the 12 μmol/kg MeHg for 4 weeks significantly increased ROS formation that might be critical to aggravate oxidative damages in cerebral cortex. Meanwhile, Glu metabolism as well as GLAST and GLT-1 appeared to be disrupted by MeHg exposure. Pre-treatment of the 35 μmol/kg LA significantly prevented MeHg-induced oxidative stress and Glu dyshomoestasis. In conclusion, findings indicated that MeHg could induce oxidative stress and Glu uptake/metabolism disorders in cerebral cortex, LA might antagonize these neurotoxic effects induced by MeHg. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mn could cause nerve cell damage in a time-dependent manner. [•] ER stress signaling was involved in Mn-induced neurotoxicity. [•] Mn induced the ER stress via activation of PERK and IRE1 signaling pathways. [ABSTRACT FROM AUTHOR]

Abstract: Overexposure to manganese (Mn) has been known to induce neuronal damage. However, little is known of the role that reactive oxygen species (ROS) play in protein aggregation resulting from Mn exposure. The current study investigated whether oxidative stress is involved in manganese-induced alpha-synuclein oligomerization in organotypic brain slices. After application of Mn (0–400μM) for 24h, there was a dose-dependent increase in average percentage of propidium iodide positive (PI+) nuclei in slices and levels of lactate dehydrogenase (LDH) in the culture medium. Moreover, the treatment with Mn resulted in a dose-dependent increase in neurocyte apoptosis, ROS level, and decrease in superoxide dismutase (SOD) activity. Mn also caused oxidative damage in cell lipid and protein. At the same time, the exposure of Mn leaded to significantly increase in the expression of alpha-synuclein mRNA and protein. Alpha-synuclein oligomerization occurred in Mn-treated slices, especially on membrane-bound form. It indicated that alpha-synuclein oligomers were more likely to combination cell membranes and resulting in membrane damage. Mn-induced neurocyte damage and alpha-synuclein oligomerization were also partially alleviated by the pretreatment with GSH and aggravated by H2O2 pretreatment. The findings revealed Mn might exert its neurotoxic effects by oxidative stress-mediated alpha-synuclein oligomerization in organotypic brain slices. [Copyright &y& Elsevier]

Chronic manganese (Mn) exposure is related to elevated risks of neurodegenerative diseases, and mitochondrial dysfunction is considered a critical pathophysiological feature of Mn neurotoxicity. Although previous research has demonstrated Mn-induced alpha-synuclein (α-Syn) overexpression, the role of α-Syn in mitochondrial dysfunction remains unclear. Here, we used Wistar rats and human neuroblastoma cells (SH-SY5Y cells) to elucidate the molecular mechanisms underlying how α-Syn overexpression induced by different doses of Mn (15, 30, and 60 mg/kg) results in mitochondrial dysfunction. We found that Mn-induced neural cell injury was associated with mitochondrial damage. Furthermore, Mn upregulated α-Syn protein levels and increased the interaction between α-Syn and mitochondria. We then used a lentivirus vector containing α-Syn shRNA to examine the effect of Mn-induced α-Syn protein on PINK1/Parkin-mediated mitophagy in SH-SY5Y cells. Our data demonstrated that the knockdown of α-Syn decreased the interaction between α-Syn and PINK1. The enhanced level of phosphorylated Parkin (p-Parkin) was due to the decrease of the interaction between α-Syn and PINK1. Moreover, the knockdown of α-Syn increased recruitment of p-Parkin to mitochondria. Collectively, these observations revealed that Mn-induced α-Syn overexpression repressed PINK1/Parkin-mediated mitophagy and exacerbated mitochondrial damage. [Display omitted] • Mn could induce mitochondria-mediated nerve cell injury. • Mn-induced over-expressed α-Syn protein was localized to mitochondria. • Over-expressed α-Syn interfered with the phosphorylation of Parkin by PINK1. • Overexpression of α-Syn disturbed PINK1/Parkin-mediated mitophagy. • Mn-induced over-expressed α-Syn protein aggravated mitochondrial damage. [ABSTRACT FROM AUTHOR]

• The exposure of BaP could cause neurobehavioral deficits in rats. • BaP induced nerve cells damage in hippocampus. • BaP induced disruption of mitochondrial biogenesis and mitophagy in hippocampus. • RSV could ameliorate BaP-induced the cell apoptosis and mitochondrial damage. • The protective effect of RSV was associated with activating AMPK/PGC-1α signals. Exposure to benzo(a)pyrene (BaP) is associated with poor neurodevelopment in children and memory impairment in adults. Previous research has demonstrated that mitochondrial damage plays an important role in BaP-induced neurotoxicity. Of interest, increasing evidence has suggested that resveratrol (RSV) can alleviate nerve cell damage, however the exact mechanisms of biological activity in mitochondria are not fully understood. In the current study, Wistar rats were exposed to BaP (1, 2, 4 mg/kg) and/or RSV (15, 30 mg/kg) during embryonic development and adolescence, and learning and memory ability, mitochondrial damage, and the expression of proteins associated with mitochondrial biogenesis and mitophagy were evaluated. These studies indicated that 2 and 4 mg/kg BaP could induce disorders of mitochondrial biogenesis and mitophagy, which leads to abnormal nerve cell development. However, pretreatment with 30 mg/kg RSV alleviated cell damage and the disorder of mitochondrial biogenesis by activating the AMPK/PGC-1α signaling pathway and promoting mitophagy. These findings suggested that RSV had utility in promoting mitochondrial homeostasis against BaP-induced nerve cell damage in the hippocampus of rats. [ABSTRACT FROM AUTHOR]

Overexposure to manganese (Mn) can result in neurotoxicity and is associated with manganism, a Parkinson's-like neurological disorder. In addition, Mn can induce endoplasmic reticulum (ER) stress and autophagy. In this study, we used C57BL/6 mice to establish a model of manganism and found that Mn could induce cell injury. Our results also showed that Mn could initiate the unfolded protein response (UPR) signaling and autophagy, via initiation of the UPR signaling occurring earlier than autophagy. We further investigated the intrinsic relationship between the endoplasmic reticulum to nucleus 1(ERN1, also known as inositol requiring enzyme 1, IRE1) signaling pathway and autophagy induction in SH-SY5Y cells exposed to Mn. Our results revealed that autophagy activation was a protective response in Mn-induced toxicity. Additionally, we found that Jun N-terminal kinase (JNK) inhibition downregulated autophagy and interaction of c-Jun with the Beclin1 promoter. In addition, knockdown of IRE1 with the LV-IRE1 shRNA suppressed the expression of IRE1, TRAF2, p-ASK1, and p-JNK in Mn-treated SH-SY5Y cells. Furthermore, the expression of proteins associated with ASK1-TRAF2 complex formation and autophagy activation were reversed by the LV-IRE1 shRNA. These findings suggest that IRE1 was involved in the activation of JNK through the formation of the ASK1-TRAF2 complex, and JNK activation led to the induction of autophagy, which required Beclin1 transcription by c-Jun. In this study, we demonstrated that the IRE1 signaling pathway mediated the activation of JNK signaling via the formation of the ASK1-TRAF2 complex which could initiate autophagy and the protein c-Jun which regulates Beclin1 transcription in Mn-induced neurotoxicity. Unlabelled Image • Mn could induce unfolded protein response (UPR) and autophagy. • Prolonged ER stress could induce cell-death program through apoptosis. • IRE1 signaling pathway triggered protective autophagy. • JNK signaling pathway participated in the regulation of Beclin1 transcription. [ABSTRACT FROM AUTHOR]

Exposure to excess levels of manganese (Mn) may lead to nitrosative stress and neurotoxic effects on the central nervous system (CNS). The dysfunction of autophagy correlates with Mn-induced nitrosative stress; however, the exact mechanism of Mn-mediated autophagy dysfunction is still unclear. Three S-nitrosylated target proteins, namely, JNK, Bcl-2, and IKKβ, were classified as the pivotal signaling pathway mediators that could play a role in the regulation of autophagy. To reveal whether these three proteins were involved in Mn-mediated autophagy dysregulation, we studied the effects of Mn on C57/BL6 mice and human neuroblastoma cells. Exposing the mice or cells, to 300 μmol/kg or 200 μM Mn, inhibited the degradation system of the autophagy-lysosome pathway. Additionally, in Mn-treated mice or cells, S-nitrosylated JNK, Bcl-2, and IKKβ increased while the level of their phosphorylation reduced. The interaction of Beclin1 and Bcl-2 significantly increased in response to 200 μM Mn, whereas the decrease in phosphorylation of AMPK activated the mTOR pathway. We then used 20 μM 1400 W, an iNOS-specific inhibitor, to neutralize the nitrosative stress induced by Mn. Our results show that 1400 W reduced the S-nitrosylated JNK, Bcl-2, and Ikkβ and relieved their downstream signaling molecular functions. Moreover, pretreatment with 20 μM 1400 W alleviated Mn-induced autophagic dysregulation and nerve cell injury. These findings revealed that S-nitrosylated JNK, Bcl-2, and IKKβ are crucial signaling molecules in the Mn-mediated autophagic dysfunction. Unlabelled Image • Mn-induced nitrosative stress resulted in autophagic dysregulation. • S-nitrosylated Bcl-2 increased the interaction of Beclin1 with Bcl-2. • S-nitrosylated Ikkβ disturbed autophagy by Ikkβ/AMPK/mTOR pathway. • 1400 W could relieve Mn-induced autophagic dysregulation and cell injury. [ABSTRACT FROM AUTHOR]

Synaptic vesicle fusion is mediated by an assembly of soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors (SNAREs), composed of syntaxin 1, soluble NSF-attachment protein (SNAP)-25, and synaptobrevin-2/VAMP-2. Previous studies have suggested that over-exposure to manganese (Mn) could disrupt synaptic vesicle fusion by influencing SNARE complex formation, both in vitro and in vivo. However, the mechanisms underlying this effect remain unclear. Here we employed calpeptin, an inhibitor of calpains, along with a lentivirus vector containing alpha-synuclein (α-Syn) shRNA, to examine whether specific SNAP-25 cleavage and the over-expression of α-Syn disturbed the formation of the SNARE complex in SH-SY5Y cells. After cells were treated with Mn for 24 h, fragments of SNAP-25-N-terminal protein began to appear; however, this effect was reduced in the group of cells which were pre-treated with calpeptin. FM1-43-labeled synaptic vesicle fusion decreased with Mn treatment, which was consistent with the formation of SNARE complexes. The interaction of VAMP-2 and α-Syn increased significantly in normal cells in response to 100 μM Mn treatment, but decreased in LV-α-Syn shRNA cells treated with 100 μM Mn; similar results were observed in terms of the formation of SNARE complexes and FM1-43-labeled synaptic vesicle fusion. Our data suggested that Mn treatment could increase [Ca2+]i, leading to abnormally excessive calpains activity, which disrupted the SNARE complex by cleaving SNAP-25. Our data also provided convincing evidence that Mn could induce the over-expression of α-Syn; when combined with VAMP-2, α-Syn prevented VAMP-2 from joining the SNARE complex cycle. [ABSTRACT FROM AUTHOR]