Involvement of reactive oxygen species derived from mitochondria in neuronal injury elicited by methylmercury

Ishihara, Yasuhiro; Tsuji, Mayumi; Kawamoto, Toshihiro; Yamazaki, Takeshi

doi:10.3164/jcbn.16-19

Cited by 31 publications

(25 citation statements)

References 38 publications

(45 reference statements)

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“…Moreover, we also found that MeHg inhibited the expression of HIF-1a in the SD rat brain, which better revealed the relationship between MeHg and the HIF-1a signaling pathway found in the in vitro and in vivo experiments. MeHg is an established neurotoxicant (Aschner and Syversen 2005;Clarkson and Magos 2006;Culbreth and Aschner, 2016;Farina et al 2011aFarina et al , 2011b, whose mechanism(s) of toxicity have yet to be fully understood; however, oxidative stress seems to play a role (Aschner et al 2007;Santos et al 2018;Ishihara et al 2016). Oxidative stress is one of the known mechanisms for the induction of HIF-1a.…”

Section: Discussionmentioning

confidence: 99%

Acute Methylmercury Exposure and the Hypoxia-Inducible Factor-1α Signaling Pathway under Normoxic Conditions in the Rat Brain and Astrocytes in Vitro

Chang

Yang

Zhou

et al. 2019

Environ Health Perspect

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BACKGROUND: As a ubiquitous environmental pollutant, methylmercury (MeHg) induces toxic effects in the nervous system, one of its main targets. However, the exact mechanisms of its neurotoxicity have not been fully elucidated. Hypoxia-inducible factor-1a (HIF-1a), a transcription factor, plays a crucial role in adaptive and cytoprotective responses in cells and is involved in cell survival, proliferation, apoptosis, inflammation, angiogenesis, glucose metabolism, erythropoiesis, and other physiological activities. OBJECTIVES: The aim of this study was to explore the role of HIF-1a in response to acute MeHg exposure in rat brain and primary cultured astrocytes to improve understanding of the mechanisms of MeHg-induced neurotoxicity and the development of effective neuroprotective strategies. METHODS: Primary rat astrocytes were treated with MeHg (0-10 lM) for 0:5 h. Cell proliferation and cytotoxicity were assessed with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl diphenyltetrazolium bromide (MTT) assay and a lactate dehydrogenase (LDH) release assay, respectively. Reactive oxygen species (ROS) levels were analyzed to assess the level of oxidative stress using 2 0 ,7 0-dichlorofluorescin diacetate (DCFH-DA) fluorescence. HIF-1a, and its downstream proteins, glucose transporter 1 (GLUT-1), erythropoietin (EPO), and vascular endothelial growth factor A (VEGF-A) were analyzed by means of Western blotting. Real-time PCR was used to detect the expression of HIF-1a mRNA. Pretreatment with protein synthesis inhibitor (CHX), proteasome inhibitor (MG132), or proline hydroxylase inhibitor (DHB) were applied to explore the possible mechanisms of HIF-1a inhibition by MeHg. To investigate the role of HIF-1a in MeHg-induced neurotoxicity, cobalt chloride (CoCl 2), 2-methoxyestradiol (2-MeOE2), small interfering RNA (siRNA) transfection and adenovirus overexpression were used. Pretreatment with N-acetyl-L-cysteine (NAC) and vitamin E (Trolox) were used to investigate the putative role of oxidative stress in MeHg-induced alterations in HIF-1a levels. The expression of HIF-1a and related downstream proteins was detected in adult rat brain exposed to MeHg (0-10 mg=kg) for 0:5 h in vivo. RESULTS: MeHg caused lower cell proliferation and higher cytotoxicity in primary rat astrocytes in a time-and concentration-dependent manner. In comparison with the control cells, exposure to 10 lM MeHg for 0:5 h significantly inhibited the expression of astrocytic HIF-1a, and the downstream genes GLUT-1, EPO, and VEGF-A (p < 0:05), in the absence of a significant decrease in HIF-1a mRNA levels. When protein synthesis was inhibited by CHX, MeHg promoted the degradation rate of HIF-1a. MG132 and DHB significantly blocked the MeHg-induced decrease in HIF-1a expression (p < 0:05). Overexpression of HIF-1a significantly attenuated the decline in MeHg-induced cell proliferation, whereas the inhibition of HIF-1a significantly increased the decline in cell proliferation (p < 0:05). NAC and Trolox, two established antioxidants, reversed the MeHg-induced decl...

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Section: Discussionmentioning

confidence: 99%

Acute Methylmercury Exposure and the Hypoxia-Inducible Factor-1α Signaling Pathway under Normoxic Conditions in the Rat Brain and Astrocytes in Vitro

Chang

Yang

Zhou

et al. 2019

Environ Health Perspect

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“…Methyl mercury. This neurotoxic compound was used as a reference compound since several results have already been published applying mono-culture approach, 14,[32][33][34][35] and few with co-culture approach. 6,7 Methyl mercury concentrations of 1 and 2.5 mM were applied based on its cytotoxicity to cerebellar granular cells after 1-hour exposure, causing a 50% reduction in cell viability, respectively, as evaluated by MTT test.…”

Section: Chemical Treatmentsmentioning

confidence: 99%

“…32 In SH-SY5Y neurons, the lethal concentration 50 (LC 50 ) of MeHg (evaluated by MTT) after 24-hour exposure was reported to be about 7 mM, 33 and in a more recent investigation, when SH-SY5Y cells were treated with MeHg for 24 hours, approximately 40% of cells died following 1 mM MeHg treatment and almost all cells died after 10 mM MeHg. 35 Methyl mercury stock solution (2.5 mM) was prepared by dissolving the powder in dimethyl sulfoxide (DMSO). From the stock solution, appropriate work dilutions were made in DMEM growth medium containing 10% FBS.…”

Section: Chemical Treatmentsmentioning

confidence: 99%

Human Co-culture Model of Neurons and Astrocytes to Test Acute Cytotoxicity of Neurotoxic Compounds

et al. 2017

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Alternative methods and their use in planning and conducting toxicology experiments have become essential for modern toxicologists, thus reducing or replacing living animals. Although in vitro human co-culture models allow the establishment of biologically relevant cell-cell interactions that recapitulate the tissue microenvironment and better mimic its physiology, the number of publications is limited specifically addressing this scientific area and utilizing this test method which could provide an additional valuable model in toxicological studies. In the present study, an in vitro model based on central nervous system (CNS) cell co-cultures was implemented using a transwell system combining human neuronal cells (SH-SY5Y cell line) and glial cells, namely astrocytes (D384 cell line), to investigate neuroprotection of D384 on SH-SY5Y and vice versa. The model was applied to test acute (24-48 hours) cytotoxicity of 3 different neurotoxicants: (1) methyl mercury (1-2.5 μM), (2) FeO nanoparticles (1-100 μg/mL), and (3) methylglyoxal (0.5-1 mM). Data were compared to mono-cultures evaluating the mitochondrial function and cell morphology. The results clearly showed that all compounds tested affected the mitochondrial activity and cell morphology in both mono-culture and co-culture conditions. However, astrocytes, when cultured together with neurons, diminish the neurotoxicant-induced cytotoxic effects that occurred in neurons cultured alone, and astrocytes become more resistant in the presence of neurons. This human CNS co-culture system seems a suitable cell model to feed high-throughput acute screening platforms and to evaluate both human neuronal and astrocytic toxicity and neuroprotective effects of new and emerging materials (eg, nanomaterials) and new products with improved sensitivity due to the functional neuron-astrocyte metabolic interactions.

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“…One of the main mechanisms of MeHg-induced neurotoxicity is oxidative stress. We have reported that mitochondrial ROS injures neurons under MeHg exposure 6 . Because treatment with an antioxidant, namely, vitamin E, at the same time as MeHg administration suppressed the delay of latency and increases in the threshold at the IC (data not shown), oxidative stress generated by MeHg exposure could induce IC dysfunction.…”

Section: Discussionmentioning

confidence: 97%

“…MeHg also inhibits the activity of glutathione reductase to attenuate the regeneration of reduced glutathione 5 . We previously reported that ROS generated inside cells by MeHg exposure are amplified in mitochondria to induce further neuronal damage 6 , suggesting that mitochondria play an important role in MeHg-induced neuronal injury. Some reports have suggested possible mechanisms of MeHg-induced neuronal damage other than oxidative stress, including disruption of microtubules 7 , decreases in intracellular ATP 8 and apoptosis 6 .…”

Section: Introductionmentioning

confidence: 99%

Neuroprotective activation of astrocytes by methylmercury exposure in the inferior colliculus

Ishihara

Itoh

Oguro

et al. 2019

Sci Rep

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Methylmercury (MeHg) is well known to induce auditory disorders such as dysarthria. When we performed a global analysis on the brains of mice exposed to MeHg by magnetic resonance imaging, an increase in the T1 signal in the inferior colliculus (IC), which is localized in the auditory pathway, was observed. Therefore, the purpose of this study is to examine the pathophysiology and auditory dysfunction induced by MeHg, focusing on the IC. Measurement of the auditory brainstem response revealed increases in latency and decreases in threshold in the IC of mice exposed to MeHg for 4 weeks compared with vehicle mice. Incoordination in MeHg-exposed mice was noted after 6 weeks of exposure, indicating that IC dysfunction occurs earlier than incoordination. There was no change in the number of neurons or microglial activity, while the expression of glial fibrillary acidic protein, a marker for astrocytic activity, was elevated in the IC of MeHg-exposed mice after 4 weeks of exposure, indicating that astrogliosis occurs in the IC. Suppression of astrogliosis by treatment with fluorocitrate exacerbated the latency and threshold in the IC evaluated by the auditory brainstem response. Therefore, astrocytes in the IC are considered to play a protective role in the auditory pathway. Astrocytes exposed to MeHg increased the expression of brain-derived neurotrophic factor in the IC, suggesting that astrocytic brain-derived neurotrophic factor is a potent protectant in the IC. This study showed that astrogliosis in the IC could be an adaptive response to MeHg toxicity. The overall toxicity of MeHg might be determined on the basis of the balance between MeHg-mediated injury to neurons and protective responses from astrocytes.

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Involvement of reactive oxygen species derived from mitochondria in neuronal injury elicited by methylmercury

Cited by 31 publications

References 38 publications

Acute Methylmercury Exposure and the Hypoxia-Inducible Factor-1α Signaling Pathway under Normoxic Conditions in the Rat Brain and Astrocytes in Vitro

Acute Methylmercury Exposure and the Hypoxia-Inducible Factor-1α Signaling Pathway under Normoxic Conditions in the Rat Brain and Astrocytes in Vitro

Human Co-culture Model of Neurons and Astrocytes to Test Acute Cytotoxicity of Neurotoxic Compounds

Neuroprotective activation of astrocytes by methylmercury exposure in the inferior colliculus

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