Arylhydrocarbon Receptor Activation in NCI-H441 Cells and C57BL/6 Mice

Abstract

The arylhydrocarbon receptor (AhR) is known for its ability to bind aromatic-containing compounds, which starts a molecular cascade involving the induction of cytochrome P450s and inflammatory cytokines. Our hypothesis is that many inhaled environmental toxicant components activate these inflammatory pathways via an initial binding to the AhR. To test this possibility, we treated Clara cell-derived NCI-H441 cells with the AhR agonist, 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD), and demonstrated that AhR activation increased the expression of both cytochrome P450 s and inflammatory markers. We also found increased mucin 5AC production with TCDD treatment. Similar results were observed in NCI-H441 cells treated with urban dust particles. Mucin 5AC expression was highly correlated with increased-expression cyclooxygenase-2 and IL-1b, thus implicating these two inflammatory markers as possible conduits for AhR-mediated mucin production. We hypothesize that this increase in mucin 5AC production is a result of inflammation-induced differentiation of our epithelial cell to a mucin-producing cell. This theory is supported by morphological changes observed in the cells, as well as decreased expression of Clara cell secretory protein (CC10). In an in vivo C57BL/6 mouse model, TCDD increased expression of inflammatory cytokines, mucin 5AC, and a number of matrix metalloproteases in whole-lung samples. These changes were not seen in mice in which AhR signaling was repressed. These markers from the whole-lung samples have been correlated to onset of bronchitis, asthma, small airways disease, and fibrosis, and their increased expression further implicates AhR activation in producing the molecular environment for the development of lung injury to occur.

A role for 12R-lipoxygenase in MUC5AC expression by respiratory epithelial cells

“…Regarding the mechanism through which 12(R)-HETE induces MUC5AC, 12(R)-HETE is a potent activator of the arylhydrocarbon receptor (AhR) [31], a ligand-regulated transcription factor related to environmental insults. Activation of AhR receptor results in upregulation of MUC5AC expression in mouse lungs and in NCI-H292 cells [32,33]. Therefore, 12R-LOX stimulating action could be explained by the capacity of 12R-LOX products (e.g.…”

The Aryl Hydrocarbon Receptor in Barrier Organ Physiology, Immunology, and Toxicology

“…AhR expression by lung epithelium allows detection and metabolic elimination of unwanted xenobiotic pollutants through induction of CYP1 enzymes. Another (mechanical) possibility is the regulation of mucus secretion; the genes for MUC5B and MUC5AC could be targeted by the activated AhR in a lung epithelial cell line (Wong et al, 2010;Chiba et al, 2011). In vivo mucus production enforces the physical protection of the lung epithelium.…”

Interaction of matrix metalloproteinases with pulmonary pollutants: Table 1–

“…In this context, WONG et al [47] examined the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in vitro in human airway epithelial cell lines and in vivo in mice in order to analyse whether activation of the arylhydrocarbon receptor (AhR) was involved. MMP expression was only analysed in mice.…”