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Developing a gene biomarker at the tipping point of adaptive and adverse responses in human bronchial epithelial cells
Citation:
Currier, J., W. Cheng, D. Menendez, R. Conolly, AND B. Chorley. Developing a gene biomarker at the tipping point of adaptive and adverse responses in human bronchial epithelial cells. PLOS ONE . Public Library of Science, San Francisco, CA, 11(5):1-14, (2016).
Impact/Purpose:
Determining molecular biomarkers that differentiate adaptive and adverse cellular processes is critical to understanding the health effects of hazardous environmental exposures. As a case study, we focused on the adaptive and adverse responses of tracheobronchial airway cells to zinc (Zn) exposure. Zn is a ubiquitous contaminant of ambient air that presents an oxidant challenge to the human lung in environmental settings and has been linked to various adverse health effects. Saturation of intracellular Zn2+ increases free cytosolic Zn2+ which mediates the oxidative-linked effects of this heavy metal, including activation of stress signaling pathways and programmed cell death. Recent evidence indicates that crosstalk between the transcription factors p53 and NRF2 coordinate the p53-initiated cell survival response. However, mechanisms of the shift from p53-mediated cellular adaptation to programmed cell death are less understood. To delineate underlying molecular mechanisms mediating this switch in normal human bronchial epithelial cell culture (BEAS-2B), we utilized a systems biology approach to determine a gene expression biomarker comprised of NRF2 and p53 downstream targets that distinguishes the cellular adaptive and apoptotic/cytotoxic state before traditional apical measurements are detected. This biomarker will improve high-throughput in vitro and in silico-based screening models for predicting adverse effects on human health due to chemical and environmental-based exposure.
Description:
Determining mechanism-based biomarkers that distinguish adaptive and adverse cellular processes is critical to understanding the health effects of environmental exposures. Shifting from in vivo, low-throughput toxicity studies to high-throughput screening (HTS) paradigms and risk assessment based on in vitro and in silico testing requires utilizing toxicity pathway information to distinguish adverse outcomes from recoverable adaptive events. Little work has focused on oxidative stresses in human airway for the purposes of predicting adverse responses. We hypothesize that early gene expression-mediated molecular changes could be used to delineate adaptive and adverse responses to environmentally-based perturbations. Here, we examined cellular responses of the tracheobronchial airway to zinc (Zn) exposure, a model oxidant. Lung derived, BEAS-2B cells exposed to 2–10 µM Zn2+ elicited concentration- and time-dependent cytotoxicity. Normal, adaptive, and cytotoxic Zn2+ exposure conditions were determined with traditional apical endpoints, and differences in global gene expression around the tipping point of the responses were used to delineate underlying molecular mechanisms. Bioinformatic analyses of differentially expressed genes indicate early enrichment of stress signaling pathways, including those mediated by the transcription factors p53 and NRF2. After 4 h, 154 genes were differentially expressed (p<0.01) between the adaptive and cytotoxic Zn2+ concentrations. Nearly 40% of the biomarker genes were related to the p53 signaling pathway with 30 genes identified as likely direct targets using a database of p53 ChIP-seq studies. Despite similar p53 activation profiles, these data revealed widespread dampening of p53 and NRF2-related genes as early as 4 h after exposure at higher, unrecoverable Zn2+ exposures. Thus, in our model early increased activation of stress response pathways indicated a recoverable adaptive event. Overall, this study highlights the importance of characterizing molecular mechanisms around the tipping point of adverse responses to better inform HTS paradigms.
