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Inorganic arsenic (As 3+ ), a well-known worldwide industrial and environmental pollutant, has been linked to neurodegenerative disorders (NDs). Autophagy plays an important role in controlling neuronal cell survival/death. However, limited information is available regarding the toxicological mechanism at the interplay between autophagy and As 3+ -induced neurotoxicity. The present study found that As 3+ exposure induced a concomitant activation of apoptosis and autophagy in Neuro-2a cells, which was accompanied with the increase of phosphatidylserine exposure on outer membrane leaflets and apoptotic cell population, and the activation of caspase-3, -7, and PARP as well as the elevation of protein expressions of LC3-II, Atg-5, and Beclin-1, and the accumulation of autophagosome. Pretreatment of cells with autophagy inhibitor 3-MA, but not that of Z-VAD-FMK (a pan-caspase inhibitor), effectively prevented the As 3+ -induced autophagic and apoptotic responses, indicating that As 3+ -triggered autophagy was contributing to neuronal cell apoptosis. Furthermore, As 3+ exposure evoked the dephosphorylation of Akt. Pretreatment with SC79, an Akt activator, could significantly attenuated As 3+ -induced Akt inactivation as well as autophagic and apoptotic events. Expectedly, inhibition of Akt signaling with LY294002 obviously enhanced As 3+ -triggered autophagy and apoptosis. Exposure to As 3+ also dramatically increased the phosphorylation level of AMPKα. Pretreatment of AMPK inhibitor (Compound C) could markedly abrogate the As 3+ -induced phosphorylated AMPKα expression, and autophagy and apoptosis activation. Taken together, these results indicated that As 3+ exerted its cytotoxicity in neuronal cells via the Akt inactivation/AMPK activation downstream-regulated autophagy-dependent apoptosis pathways, which ultimately lead to cell death. Our findings suggest that the regulation of Akt/AMPK signals may be a promising intervention to against As 3+ -induced neurotoxicity and NDs., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Bisphenol A (BPA) is recognized as a harmful pollutant in the worldwide. Growing studies have reported that BPA can cause adverse effects and diseases in human, and link to a potential risk factor for development of neurodegenerative diseases (NDs). 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), which generated in the mammalian liver after BPA exposure, is a major active metabolite of BPA. MBP has been suggested to exert greater toxicity than BPA. However, the molecular mechanism of MBP on the neuronal cytotoxicity remains unclear. In this study, MBP exposure significantly reduced Neuro-2a cell viability and induced apoptotic events that MBP (5-15 μM) exhibited greater neuronal cytotoxicity than BPA (50-100 μM). The mitochondria-dependent apoptotic signals including the decrease in mitochondrial membrane potential (MMP) and the increase in cytosolic apoptosis-induced factor (AIF), cytochrome c release, and Bax protein expression were involved in MBP (10 μM)-induced Neuro-2a cell death. Exposure of Neuro-2a cells to MBP (10 μM) also triggered endoplasmic reticulum (ER) stress through the induction of several key molecules including glucose-regulated protein (GRP)78, C/EBP homologous protein (CHOP), X-box binding protein (XBP)-1, protein kinase R-like ER kinase (PERK), eukaryotic initiation factor 2α (eIF2α), inositol-requiring enzyme(IRE)-1, activation transcription factor(AFT)4 and ATF6, and caspase-12. Pretreatment with 4-PBA (an ER stress inhibitor) and specific siRNAs for GRP78, CHOP, and XBP-1 significantly suppressed the expression of these ER stress-related proteins and the activation of caspase-12/-3/-7 in MBP-exposed Neuro-2a cells. Furthermore, MBP (10 μM) exposure dramatically increased the activation of extracellular regulated protein (ERK)1/2 and decreased Akt phosphorylation. Pretreatment with PD98059 (an ERK1/2 inhibitor) and transfection with the overexpression of activation of Akt1 (myr-Akt1) effectively suppressed MBP-induced apoptotic and ER stress-related signals. Collectively, these results demonstrate that MBP exposure exerts neuronal cytotoxicity via the interplay of ERK activation and Akt inactivation-regulated mitochondria-dependent and ER stress-triggered apoptotic pathway, which ultimately leads to neuronal cell death., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Hexavalent chromium (Cr(VI)), a well-known toxic industrial and environmental pollutant, has been shown to cause serious toxic and health effects. However, limited information is available on Cr(VI)-induced neurotoxic potential, with the underlying toxicological mechanisms remain mostly unclear. The present study demonstrated that the mitochondria-dependent apoptosis pathway was involved in Cr(VI)-induced SH-SY5Y cell (the human neuroblastoma cell line) death, which was accompanied by the appearance of cell shrinkage, increased mitochondrial membrane potential (MMP) depolarization and cytochrome c release, and the activation of caspase cascades and poly (ADP-ribose) polymerase (PARP). Cr(VI) treatment also increased the generation of intracellular reactive oxygen species (ROS). Pretreatment of SH-SY5Y cells with antioxidant N-acetylcysteine (NAC) effectively attenuated ROS production and reversed these Cr(VI)-induced cytotoxicity and apoptotic responses. Furthermore, exposure to Cr(VI) significantly increased the phosphorylation levels of Akt, extracellular regulated kinase (ERK)1/2, and AMP-activated protein kinase (AMPK)α. NAC and the pharmacological inhibitor of Akt (LY294002), ERK1/2 (PD980590), and AMPKα (Compound C) markedly abrogated the Cr(VI)-induced activation of Akt, ERK1/2, and AMPKα signal, respectively, with the concomitant inhibition of mitochondrial dysfunction and caspase activation. Additionally, all these inhibitors suppressed Cr(VI)-induced phosphorylation of Akt, ERK1/2, and AMPKα and of each other. Collectively, these results suggest that Cr(VI) exerts its cytotoxicity on neuronal cells by inducing mitochondria-dependent apoptosis through the interdependent activation of Akt, ERK1/2, and AMPKα, which are mainly mediated by ROS generation., Competing Interests: Declaration of Competing Interest All authors declare that they have no conflicts of interest with respect to the research, authorship, and/or publication of this article., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Human exposure to silica nanoparticles (SiNPs) has been widely applied as vehicles for drug delivery and cellular manipulations in nanoneuromedicine. SiNPs may cause adverse effects in the brain, but potential mechanisms underlying SiNPs-induced neurotoxicity are remained unclear. Here, we examined cytotoxic effects and the cellular mechanisms of SiNPs-induced neuronal cell death. In this study, the results showed that SiNPs significantly decreased cell viability and induced apoptosis in Neuro-2a cells as evidenced by the increase caspase-3 activity and the activation of caspase cascades and poly (ADP-ribose) polymerase (PARP). In addition, endoplasmic reticulum (ER) stress was triggered as indicated by several key molecules including glucose-regulated protein (GRP)78 and 94, C/EBP homologous protein (CHOP), activation transcription factor (ATF)-4, and caspase-12. Pretreatment of Neuro-2a cells with specific pharmacological inhibitor of ER stress (4-phenylbutyric acid (4-PBA)) effectively alleviated the SiNPs-induced ER stress and apoptotic related signals. Furthermore, 2',7'-Dichlorofluorescein fluorescence as an indicator of reactive oxygen species (ROS) formation after exposure of Neuro-2a cells to SiNPs significantly increased ROS levels. Antioxidant N-acetylcyseine (NAC) effectively reversed SiNPs-induced cellular responses. Taken together, these results suggest that SiNPs exposure exerts its neurotoxicity in cultured neuronal cells by inducing apoptosis via a ROS generation-activated downstream ER stress signaling pathway., (Copyright © 2019. Published by Elsevier Ltd.)

Chloroacetic acid (CA), a chlorinated analog of acetic acid and an environmental toxin that is more toxic than acetic, dichloroacetic, or trichloroacetic acids, is widely used in chemical industries. Furthermore, CA has been found to be the major disinfection by-products (DBPs) of drinking water. CA has been reported to be highly corrosive and to induce severe tissue injuries (including nervous system) that lead to death in mammals. However, the effects and underlying mechanisms of CA-induced neurotoxicity remain unknown. In the present study, we found that CA (0.5-2.0 mM) significantly increased LDH release, decreased the number of viable cells (cytotoxicity) and induced apoptotic events (including: increases in the numbers of apoptotic cells, the membrane externalization of phosphatidylserine (PS), and caspase-3/-7 activity) in Neuro-2a cells. CA (1.5 mM; the approximate to LD50) also triggered ER stress, which was identified by monitoring several key molecules that are involved in the unfolded protein responses (including the increase in the expressions of p-PERK, p-IRE-1, p-eIF2α, ATF-4, ATF-6, CHOP, XBP-1, GRP 78, GRP 94, and caspase-12) and calpain activity. Transfection of GRP 78- and GRP 94-specific si-RNA effectively abrogated CA-induced cytotoxicity, caspase-3/-7 and caspase-12 activity, and GRP 78 and GRP 94 expression in Neuro-2a cells. Additionally, pretreatment with 2.5 mM N-acetylcysteine (NAC; a glutathione (GSH) precursor) dramatically suppressed the increase in lipid peroxidation, cytotoxicity, apoptotic events, calpain and caspase-12 activity, and ER stress-related molecules in CA-exposed cells. Taken together, these results suggest that the higher concentration of CA exerts its cytotoxic effects in neuronal cells by triggering apoptosis via a ROS-induced ER stress signaling pathway., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

Using primary cultured cortical neurons from embryonic rat brains, we elucidated an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/kainic acid (KA) receptor-mediated neuroprotective mechanism through actions of nerve growth factor (NGF) in developing neurons. Neurotoxicity of KA in early days in vitro neurons was quite low compared with the mature neurons. However, pretreatment with anti-NGF antibody or TrkA inhibitor AG-879 profoundly raised KA toxicity. Furthermore, KA stimulation resulted in an increase of TrkA expression and phosphorylation, which was blocked not only by the AMPA/KA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione and AG-879, but also by the phospholipase C inhibitor U73122 and the intracellular calcium chelator BAPTA. A study of polyphosphoinositide turnover showed that KA-stimulated phospholipase C (PLC) activity was directly triggered by the AMPA/KA receptor activity, but not by the activity of TrkA or other excitatory amino acid receptor subtypes. Sources of KA-increased intracellular calcium levels were contributed by both extracellular calcium influx and intracellular calcium release and were partially sensitive to guanosine 5'-O-(2-thiodiphosphate). These results indicate that in developing cortical neurons, activation of AMPA/KA receptors by KA may induce expression, followed by activation of TrkA via PLC signaling and intracellular calcium elevation and hence increase reception of NGF on KA-challenged neurons. A G protein-coupled AMPA/KA receptor may be involved in these metabotropic events for neuronal protection.