Diesel Exhaust Particle Exposure Reduces Expression of the Epithelial Tight Junction Protein Tricellulin

Abstract

Background: While exposure to diesel exhaust particles has been linked to aberrant immune responses in allergic diseases such as asthma, little attention has been paid to their effects on the airway epithelium. In this study, we sought to determine the effect of diesel exhaust exposure on airway epithelial barrier function and composition using in vitro and in vivo model systems. Methods: 16HBE14o- human bronchial epithelial cells were grown on collagen coated Transwell inserts and exposed to 5 to 50 µg/cm2 SRM 2975 diesel particulate matter (DEP) suspended in cell culture medium or vehicle controls. Changes in barrier function were assessed by measuring transepithelial electrical resistance (TEER) and permeability to 4 kDa FITC Dextran. Neonatal BALB/c mice were exposed to aerosolized DEP (255 ± 89 µg/m3; 2 hours per day for 5 days) and changes in the tight junction protein Tricellulin were assessed two weeks post exposure. Results: A six-hour incubation of epithelial cells with diesel exhaust particles caused a significant concentration-dependent reduction in epithelial barrier integrity as measured by decreased TEER and increased permeability to 4 kDa FITC-Dextran. This reduction in epithelial barrier integrity corresponded to a significant reduction in expression of the tight junction protein Tricellulin. siRNA mediated knockdown of Tricellulin recapitulated changes in barrier function caused by DEP exposure. Neonatal exposure to aerosolized DEP caused a significant reduction in lung Tricellulin two weeks post exposure at both the protein and mRNA level. Conclusion: Short term exposure to DEP causes a significant reduction in epithelial barrier integrity through a reduction in the tight junction protein Tricellulin. Neonatal exposure to aerosolized DEP caused a significant and sustained reduction in Tricellulin protein and mRNA in the lung, suggesting that early life exposure to inhaled DEP may cause lasting changes in airway epithelial barrier function.

Liquid application dosing alters the physiology of air-liquid interface (ALI) primary human bronchial epithelial cell/lung fibroblast co-cultures and in vitro testing relevant endpoints

“…In its role as a barrier, the normal bronchial epithelium forms an electrically resistant tissue layer that is selectively permeable to small molecules that separates inhaled substances from underlying host tissue (Rezaee and Georas, 2014). While often affected by exposure to inhaled insults, loss of bronchial epithelial barrier integrity is also a hallmark of both acute and chronic respiratory disease (Peterson et al, 1993;Gerloff et al, 2017;Smyth et al, 2020;Carlier et al, 2021). Further, loss of epithelial barrier integrity also results in the loss of apical-basolateral polarization and is a key aspect of epithelial-to-mesenchymal transition (EMT), an early step in epithelial carcinogenesis (Saitoh, 2018).…”

“…In contrast, hypoxia is protective against oxidant-induced loss of barrier integrity (Olson et al, 2011); however, our observations indicate that the stabilization of HIF-1α protein alone (Figure 5) is not sufficient to prevent the loss of barrier integrity following liquid application. Epithelial barrier integrity is also adversely affected following exposure to a diverse range of inhaled substances including diesel exhaust particulates, ambient particulate matter, acrolein, asbestos, ozone, wood smoke particulates, and e-cigarette flavorings (Peterson et al, 1993;Yu et al, 1994;Olson et al, 2011;Gerloff et al, 2017;Xiong et al, 2018;Zeglinski et al, 2019;Smyth et al, 2020;Xian et al, 2020;Bowers et al, 2022). Thus, the observation that liquid application alone significantly reduces barrier integrity indicates the potential for this manner of dosing to limit the sensitivity of this approach to identify test substances that disrupt barrier function.…”

The Effect of Air Pollution on the Transcriptomics of the Immune Response to Respiratory Infection

“…The association between the inflammation caused by air pollution and disruption of the lung's innate immune system, including epithelial barrier disruption, macrophage function, and protein/cytokine response, is typically studied via in vitro human cell and in vivo rodent models [9][10][11][12][13][14][15][16][17][18][19]. Although the majority of studies suggest that different air pollution components might predispose patients to RVI or RBI by multiple mechanisms, laboratory-based studies are generally limited to inbred mouse strains and/or only a single pollutant or a single category of pollution (traffic pollution), and do not fully capitulate complex events occurring in naturally exposed humans.…”