2, 3, 7, 8-Tetrachlorodibenzo-P-Dioxin (TCDD) Induces Premature Senescence in Human and Rodent Neuronal Cells via ROS-Dependent Mechanisms

8-Tetrachlorodibenzo-P-Dioxin (TCDD) Induces Premature Senescence in Human and Rodent Neuronal Cells via ROS-Dependent Mechanisms. PLoS ONE 9(2): e89811. doi:10.1371/journal.pone.0089811 2, 3, 7, 8-Tetrachlorodibenzo-P-Dioxin (TCDD) Induces Premature Senescence in Human and Rodent Neuronal Cells via ROS-Dependent Mechanisms Chunhua Wan. 0 Jiao Liu. 0 Xiaoke Nie 0 Jianya Zhao 0 Songlin Zhou 0 Zhiqing Duan 0 Cuiying Tang 0 Lingwei Liang 0 Guangfei Xu 0 Aamir Ahmad, Wayne State University School of Medicine, United States of America 0 Department of Nutrition and Food Hygiene, School of Public Health, Nantong University , Nantong, Jiangsu , People's Republic of China The widespread environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a potent toxicant that causes significant neurotoxicity. However, the biological events that participate in this process remain largely elusive. In the present study, we demonstrated that TCDD exposure triggered apparent premature senescence in rat pheochromocytoma (PC12) and human neuroblastoma SH-SY5Y cells. Senescence-associated b-galactosidase (SA-b-Gal) assay revealed that TCDD induced senescence in PC12 neuronal cells at doses as low as 10 nM. TCDD led to F-actin reorganization and the appearance of an alternative senescence marker, c-H2AX foci, both of which are important features of cellular senescence. In addition, TCDD exposure altered the expression of senescence marker proteins, such as p16, p21 and p-Rb, in both doseand time-dependent manners. Furthermore, we demonstrated that TCDD promotes mitochondrial dysfunction and the accumulation of cellular reactive oxygen species (ROS) in PC12 cells, leading to the activation of signaling pathways that are involved in ROS metabolism and senescence. TCDD-induced ROS generation promoted significant oxidative DNA damage and lipid peroxidation. Notably, treatment with the ROS scavenger N-acetylcysteine (NAC) markedly attenuated TCDDinduced ROS production, cellular oxidative damage and neuronal senescence. Moreover, we found that TCDD induced a similar ROS-mediated senescence response in human neuroblastoma SH-SY5Y cells. In sum, these results demonstrate for the first time that TCDD induces premature senescence in neuronal cells by promoting intracellular ROS production, supporting the idea that accelerating the onset of neuronal senescence may be an important mechanism underlying TCDDinduced neurotoxic effects. - Funding: This work was supported by the National Natural Science Foundation of China (No. 21077061). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. . These authors contributed equally to this work. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) represents one of the most notorious environmental toxicants and is known to accumulate in both the environment and the human body. One of the important public health concerns related to TCDD is its adverse effect on the neural system. Recent studies have demonstrated that TCDD causes significant neurodevelopmental and neurobehavioral deficits in rodents [1,2]. Consistent with these observations, epidemiological investigations have indicated that accidental exposure to high doses of PCB/TCDD mixtures results in delayed motor development and a higher incidence of hypotonicity in children [3]. In addition, the incidence of many neurological disorders, including sleep disturbances, neuralgia and headache, was markedly elevated in workers that had been accidentally exposed to TCDD [4]. These findings suggest that TCDD may lead to significant neurotoxicity in both humans and rodents. The majority of the toxic effects of TCDD are related to the role it plays in activating the aryl hydrocarbon receptor (AhR) [5]. The AhR is a ligand-activated transcription factor that normally exists in a quiescent state in the cytoplasm. Once it has bound to TCDD, the AhR will rapidly translocate into the nucleus and promote the transcription of dozens of target genes. The expression of these genes further activates downstream events that promote the toxic effects of TCDD. In the process, the production of reactive oxygen species (ROS) is regarded as one of the major features underlying TCDD-mediated AhR activation and is believed to be a key determinant of TCDD-induced neurotoxicity [6]. Thus, a better understanding of the role of ROS in mediating neurotoxicity may help clarify the mechanisms underlying TCDD-mediated adverse effects on the neural system. Decades ago, replicative senescence/permanent cell cycle arrest was identified to be an important mechanism controlling normal cell proliferation and organismal aging. Replicative senescence is a physiological state during which dividing cells gradually lose the ability to proliferate and is accompanied by distinctive morphological changes and the altered expression of sen (...truncated)