Culture Media Strongly Influences Primary Human Bronchial Epithelial Cells' Transcriptomic Response to Ozone Exposure
Exposure to the ambient air pollutant ozone induces acute and chronic respiratory health effects in part by causing inflammation of the airways. Several aspects of the inflammatory response to ozone can be modeled in vitro using primary human bronchial epithelial cells (HBECs) cultured at an air-liquid interface. We tested two commonly used HBEC culture media systems, one proprietary and one non-proprietary, to identify which system yielded the most in vivo-like pro-inflammatory response to acute ozone exposure as indicated by gene expression. Cells from six donors were grown in each culture system in parallel followed by examination of epithelial morphology and cell type proportions prior to ozone exposure. Cultures grown in the proprietary system were notably thicker and contained more ciliated and secretory cells, as well as internal cyst-like structures. The transcriptomic response to acute ozone exposure (0.5 parts per million ozone x 2 hours) was strongly affected by media. HBECs grown in the proprietary system exhibited minimal changes after ozone, with only  only 7 differentially expressed genes (DEGs). In contrast,  HBECs grown in the non-proprietary system exhibited a more dynamic response with 128 DEGs, including hallmark response genes indicative of inflammation (CXCL8) and oxidative stress (HMOX1). Gene set enrichment analysis using the 128 DEGs further corroborated upregulation of oxidative stress and inflammation pathways. In total, our results indicate that the choice of HBEC culture media should be carefully considered to best model the in vivo response to ozone. Overall design: RNA-seq profiling of well-differentiated primary human bronchial epithelial cells grown in PneumaCult or UNC media systems, collected 2hr after ozone or filtered air exposure.