Airway Epithelial Expression of TLR5 Is Downregulated in Healthy Smokers and Smokers with Chronic Obstructive Pulmonary Disease

Abstract

The toll-like receptors (TLRs) are important components of the respiratory epithelium host innate defense, enabling the airway surface to recognize and respond to a variety of insults in inhaled air. Based on the knowledge that smokers are more susceptible to pulmonary infection and that the airway epithelium of smokers with chronic obstructive pulmonary disease (COPD) is characterized by bacterial colonization and acute exacerbation of airway infections, we assessed whether smoking alters expression of TLRs in human small airway epithelium, the primary site of smoking-induced disease. Microarrays were used to survey the TLR family gene expression in small airway (10th–12th order) epithelium from healthy nonsmokers (n=60), healthy smokers (n=73) and smokers with COPD (n=36). Using the criteria of detection call of present in ≥50%, 6 of 10 TLRs (1, 2, 3, 4, 5 and 8) were expressed. Compared to nonsmokers, the most striking change was for TLR5, which was down-regulated in healthy smokers (1.4-fold, p<10−10) and smokers with COPD (1.6-fold, p<10−11). TaqMan RT-PCR confirmed these observations. Bronchial biopsy immunofluorescence studies showed that TLR5 was expressed mainly on the apical side of the epithelium and was decreased in healthy smokers and smokers with COPD. In vitro, the level of TLR5 downstream genes, IL-6 and IL-8, were highly induced by flagellin in TLR5 high-expressing cells compared to TLR5 low-expressing cells. In the context that TLR5 functions to recognize pathogens and activate innate immune responses, the smoking-induced down-regulation of TLR5 may contribute to smoking-related susceptibility to airway infection, at least for flagellated bacteria.

Early Events in the Pathogenesis of Chronic Obstructive Pulmonary Disease. Smoking-induced Reprogramming of Airway Epithelial Basal Progenitor Cells

“…These observations suggest that smoking-induced changes in the airway epithelium occur early during the pathogenesis of COPD and before decline in lung functon. Surprisingly, however, in contrast to the well-established role of inflammation in progression of alreadyestablished COPD (14,25,26,31,32), genome-wide studies revealed that the overall expression of genes related to inflammation and immunity are downregulated in both the large and small airway epithelia of smokers (19,27,28,33). These observations suggest that the early events in the pathogenesis of COPD in smokers may involve noninflammatory mechanisms.…”

Are healthy smokers really healthy?

“…Moreover, Wang with his team [66] demonstrated the toll-like receptor(TLR)5, expressed mainly on the apical side of the epithelium, was down-regulated in healthy smokers and smokers with COPD, compared to nonsmokers. The toll-like receptors are important components of the respiratory epithelium host innate defense and TLR-deficient mice develop exhibit impaired CD4 + T cell response to a flagellated pathogen [67], suggesting suppression of airway epithelial TLR5 may contribute to the increased susceptibility of smokers and smokers with COPD to airway flagellated bacterial infection.…”

“…The activated MUC5AC-core gene expression in smokers may lead to mucus hypersecretion. Down regulation of TLR5 and physiological apical junctional complex(AJC) gene in healthy smokers may be involved in smoking-related susceptibility to airway infection [66, 87]. Overexpression of ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) which is used as a marker of lung cancer in chronic smokers may represent an early event in the complex transformation from normal epithelium to overt malignancy [88].…”

TLR7 agonist attenuates acetylcholine‐induced, Ca2+‐dependent ionic currents in swine tracheal submucosal gland cells

“…In immunohistochemical staining for human airways using anti-TLR7 antibody, far fewer TLR7-immunopositive cells were observed in both SMG and AEP in subjects with COPD as compared to those without COPD AUC 120-600s from baseline 340/380 ratio (n = 10 for each experiment). It was also reported that TLR5 expression in AEP is significantly reduced in healthy smokers and smokers with COPD compared to that in healthy non-smokers (Wang et al, 2012). Ten reliable intracellular calcium assays were from more than 15 different swine airways.…”