Carbon Black and Titanium Dioxide Particulates Differentially Activate ER Stress and Apoptosis in Alveolar Epithelial Cells
Mentor:Jay Brewster, Associate Provost and Professor of Biology, Pepperdine University
Recent findings have shown that particulate matter of many kinds have adverse effects on cells and living tissues. Carbon black and titanium dioxide are two such particulates that make up a significant portion of particulate air pollution and exist in the air as nanoparticles on the scale of <100 nm. The objective of this study was to characterize the effect of carbon black (CB) and titanium dioxide (TiO2) particulates on molecular stress signaling pathways in A549 human alveolar epithelial cells. CB and TiO2 powders were broken into the smallest pieces possible through bath sonication or bead beater homogenization and mixed with the cell culture media. We hypothesize these two methods result in larger and smaller particulates, respectively. Death assays with DAPI nuclear fluorescent staining revealed that both particulate types exhibit toxicity to cells and induce apoptosis but on a smaller scale than known ER stress poisons such as Brefeldin A. Fluorescent microscope imaging of live cells showed perinuclear localization of both CB and TiO2 particulates. Western blotting analysis revealed that TiO2 causes moderate induction of the PERK unfolded protein response (UPR) pathway, but RT-PCR analysis showed no induction of the XBP1 pathway by TiO2. Bead beaten CB shows a small trend toward induction of PERK and RT-PCR analysis revealed that sonicated CB does show a trend toward modest reduction of tunicamycin induced XBP1 splicing, while bead beaten CB shows a trend toward increased splicing. Further research is required to characterize the effects of bead beaten versus sonicated CB on A549 cells and to definitively determine through which apoptotic signaling pathway CB causes cell death.