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

• Published in: Environmental health perspectives 2019-12, Vol.127 (12), p.127006
• Main Authors: Chang, Jie, Yang, Bobo, Zhou, Yun, Yin, Changsheng, Liu, Tingting, Qian, Hai, Xing, Guangwei, Wang, Suhua, Li, Fang, Zhang, Yubin, Chen, Da, Aschner, Michael, Lu, Rongzhu
• Format: Article
• Language: English
• Subjects: Acetylcysteine; Acute toxicity; Adaptation; Angiogenesis; Animals; Antibodies; Antioxidants; Apoptosis; Astrocytes; Biocompatibility; Brain; Cell death; Cell growth; Cell Proliferation; Cell Survival; Cobalt; Cobalt chloride; Cytotoxicity; Dimethylmercury; Environmental Pollutants - toxicity; Erythropoiesis; Erythropoietin; Exploration; Exposure; Fluorescence; Gene expression; Gene Expression Regulation; Glucose; Glucose metabolism; Growth factors; Hypoxia; Hypoxia-Inducible Factor 1, alpha Subunit; Kinases; Laboratory animals; Lactate dehydrogenase; Levels; Mercury (metal); Methylmercury; Methylmercury Compounds - toxicity; Nervous system; Neurotoxicity; Organic chemicals; Oxidative stress; Pollutants; Pretreatment; Proline; Proteasomes; Protein biosynthesis; Protein synthesis; Proteins; Rats; Reactive oxygen species; Reactive Oxygen Species - metabolism; RNA, Messenger - metabolism; Scavenging; Signal Transduction; Time dependence; Toxicity; Toxicity Tests, Acute; Transcriptional Activation; Transportation services; Up-Regulation; Vascular endothelial growth factor; Vascular Endothelial Growth Factor A; Vitamin E
• ISSN: 0091-6765; 1552-9924
• DOI: 10.1289/EHP5139

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 ( ), 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. The aim of this study was to explore the role of 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. Primary rat astrocytes were treated with MeHg ( ) for . 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',7'-dichlorofluorescin diacetate (DCFH-DA) fluorescence. , 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 mRNA. Pretreatment with protein synthesis inhibitor (CHX), proteasome inhibitor (MG132), or proline hydroxylase inhibitor (DHB) were applied to explore the possible mechanisms of inhibition by MeHg. To investigate the role of in MeHg-induced neurotoxicity, cobalt chloride ( ), 2-methoxyestradiol (2-MeOE2), small interfering RNA (siRNA) transfection and adenovirus overexpression were used. Pretreatment with -acetyl-L-cysteine (NAC) and vitamin E (Trolox) were used to investigate the putative role of oxidative stress in MeHg-induced alterations in levels. The expression of and related downstream proteins was detected in adult rat brain exposed to MeHg ( ) for . 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 MeHg for significantly inhibited the expression of astrocytic , and the downstream genes GLUT-1, EPO, and VEGF-A ( ), in the absence of a significant decrease in mRNA levels. When protein synthesis was inhibited by CHX, MeHg promoted the degradatio