AGR3 Regulates Airway Epithelial Junctions in Patients with Frequent Exacerbations of COPD

Abstract

Background: The mechanisms underlying differences in the susceptibility to chronic obstructive pulmonary disease (COPD) exacerbations between patients are not well understood. Recent studies have shown that the patients with frequent COPD exacerbations is related to specific protein expression in lung tissue. Anterior gradient 3 (AGR3) is expressed in airway epithelial cells in the lung and proteomic analysis revealed that its expression is decreased in patients with frequent COPD exacerbations. Moreover, the loss of epithelial integrity might facilitate trans-epithelial permeability of pathogens in such patients. This study was performed to determine that AGR3 protein play a role in COPD frequency exacerbators.Methods: Human lung tissues were collected from current-smoking patients (Control; n = 15) as well as patients with infrequent COPD exacerbations (IFCOPD; n = 18) and frequent COPD exacerbations (FCOPD; n = 8). While AGR3 protein expression was measured by immunohistochemistry and western blotting, AGR mRNA expression was determined by real time quantitative polymerase chain reaction (RT-qPCR). Furthermore, adherent junctions (AJs) and tight junctions (TJs) protein expression in human lung tissues were measured by immunohistochemistry. The effects of cigarette smoke extract (CSE) on AJ and TJ protein and mRNA expression in BEAS-2B cells were assessed by western blotting and RT-qPCR. In addition, the effect of AGR3 overexpression and knockdown on AJ and TJ protein expression was determined.Results: AGR3 was mainly expressed in the airway epithelium and AGR3-positive products were localized in the cytoplasm. Western blotting and RT-qPCR results showed that AGR3 protein (p = 0.009) and mRNA (p = 0.04) expression in the FCOPD group was significantly lower than that in the IFCOPD group. Moreover, E-cadherin, occludin, and zonula occludens-1 (ZO-1) expression was lower in the FCOPD group than in the IFCOPD group. The protein and mRNA expression of E-cadherin, occludin, and ZO-1 was decreased within 24 h post-CSE exposure. AGR3 overexpression rescued CSE-induced downregulation of E-cadherin, occludin, and ZO-1.Conclusion: Difference in AGR3 expression in the lung tissue might be correlated with increased susceptibility to COPD exacerbation. AGR3 can prevent CSE-induced downregulation of E-cadherin, occludin, and ZO-1 in airway epithelial cells. Loss of AGR3 might promote viral and bacterial infection and induce immune inflammation to increase COPD exacerbation.

Cleavage of Occludin by Cigarette Smoke-Elicited Cathepsin S Increases Permeability of Lung Epithelial Cells

“…A higher amount of occludin was found for the non-COPD patients compared to the COPD patients (see representative samples: Figure 1a). the present results corroborated an immunohistochemistry (IHC) study that assessed that the expression level of occludin was significantly decreased in COPD patients [55]. Next, we compared the expression levels of occludin in the lung tissue samples of the never-smokers and smokers.…”

Is the epithelial barrier hypothesis the key to understanding the higher incidence and excess mortality during COVID‐19 pandemic? The case of Northern Italy

“… 89 A recent study in human lung tissues showed that E‐cadherin, occludin and zonula occludens‐1 (ZO‐1) expression were lower in the frequently exacerbated COPD patients than in the infrequently exacerbated COPD group. 90 Overall, these results suggest a mechanism in COVID‐19 severity namely increased systemic inflammation due to the continuous epithelial barrier disruption.…”

“…Comorbid chronic obstructive pulmonary disease (COPD) was identified as a risk factor for mortality in COVID‐19 patients admitted in ICU with an HR of 1.68 (95% CI: 1.28–2.19) in multivariate analysis in Lombardy, Italy 89 . A recent study in human lung tissues showed that E‐cadherin, occludin and zonula occludens‐1 (ZO‐1) expression were lower in the frequently exacerbated COPD patients than in the infrequently exacerbated COPD group 90 . Overall, these results suggest a mechanism in COVID‐19 severity namely increased systemic inflammation due to the continuous epithelial barrier disruption.…”

The effects of epithelial–mesenchymal transitions in COPD induced by cigarette smoke: an update

“…E-cadherin is an adhesion molecule responsible for the organization of interepithelial junctions [72,73]. Numerous studies have shown that E-cadherin was markedly decreased in smokers and COPD [68,[74][75][76][77][78]. Particularly, the expression of E-cadherin was positively related to FEV1/VC ratio [74].…”