Activation, EGFR leads to Occurrence, Transdifferentiation of ciliated epithelial cells

It is not well-known how ciliated cell transdifferentiation occurs in humans. Under normal conditions, lung epithelial cells (except basal cells) are terminally differentiated (Donnelly et al., 1982; Breuer et al., 1990; Rawlins and Hogan, 2008), and which signals initiate the dedifferentiation/redifferentiation process is not well-understood. The available evidence is indirect or correlative. It also is not in agreement with other studies, which showed that ciliated cells do not give rise to goblet cells during airway remodeling in rodents and humans and with studies that provide evidence for increased goblet cell proliferation and goblet cell hyperplasia (Pardo-Sargenta et al., 2013; Hays et al., 2006; Lawson et al., 2002; Tesfaigzi et al., 2004; Taniguchi et al., 2011; Park et al., 2006; Turner et al., 2011).

Daily 30-minute treatment of primary human bronchial epithelial cells at the air-liquid interface with 0.6 mM xanthine and 0.5 units xanthine oxidase for 3 days resulted in goblet cell metaplasia as evidenced by an increase in the numbers of MUC5AC-positive cells from 3.3 ± 1.2%to 21.6 ± 3.4% and a decrease in ciliated cell numbers. This effect could be inhibited by EGFR blockade with neutralizing antibodies (Casalino-Matsuda et al., 2006).

Cigarette smoke exposure at 8 cigarettes per day for 5 days markedly increased AB-PAS staining in airway epithelia and goblet cell numbers from 40 ± 19 to 167 ± 19 cells/mm of epithelium, while decreasing the number of ciliated cells (not quantified). Treatment with the EGFR inhibitor BIBX1522 during exposure dose-dependently decreased goblet cell numbers, with a maximal decrease seen for 3 mg/kg inhibitor (51 ± 19 cells/mm epithelium) (Takeyama et al., 2001).

Induction of airway inflammation with 50 µg house dust mite (1.27 endotoxin units/mg) for 5 days/week for 3 weeks resulted in a 3-fold increase of pEGFR-positive cells in the bronchiolar epithelium of C57Bl/6 mice. Six-week treatment led to goblet cell metaplasia as evidenced by extensive AB staining and an approx. 10-fold increase in Clca3-positive cells in the animals' airways. Concomitant treatment with 100 mg/kg erlotinib six times a week for 6 weeks reduced the number of Clca3-positive cells by ca. 5-fold (Le Cras et al., 2011). Using the same model with a 3-week treatment demonstrated goblet cell metaplasia as judged by increased PAS staining in the airway epithelium and ca. 10-, 5-, and 4-fold increases in expression of goblet cell metaplasia-related genes Muc5ac, Clca1, and Postn, respectively (Habibovic et al., 2016).

Pyocyanin, a redox-active exotoxin of Pseudomonas aeruginosa, caused goblet cell metaplasia in C57Bl/6 mice after 3-week treatment (25 µg/day). PAS staining increased by ca. 30%; the percentage of Muc5ab-positive cell in bronchial epithelium increased 6.4-fold and in bronchiolar epithelium 11.4-fold. This was accompanied by increased EGFR phosphorylation coincident with AB/PAS staining. Moreover, 24-h pyocyanin treatment of H292 lung cancer cells and immortlaized human bronchial epithelial 16-HBE cells with physiologically relevant concentrations from 1.3 to 25 µg/mL pyocyanin significantly increased MUC5B mRNA expression 3.8- to 13.4-fold and increased levels of pEGFR 11.8- to 18.3-fold (1.6 to 12.5 µg/mL pyocyanin) (Hao et al., 2012).

Induction of airway inflammation with 50 µg house dust mite (1.27 endotoxin units/mg) for 5 days/week for 3 weeks resulted in a 3-fold increase of pEGFR-positive cells in the bronchiolar epithelium of C57Bl/6 mice. Six-week treatment led to goblet cell metaplasia as evidenced by extensive AB staining and an approx. 10-fold increase in Clca3-positive cells in the animals' airways. Concomitant treatment with 100 mg/kg erlotinib six times a week for 6 weeks reduced the number of Clca3-positive cells by ca. 5-fold (Le Cras et al., 2011). Using the same model with a 3-week treatment demonstrated goblet cell metaplasia as judged by increased PAS staining in the airway epithelium and ca. 10-, 5-, and 4-fold increases in expression of goblet cell metaplasia-related genes Muc5ac, Clca1, and Postn, respectively (Habibovic et al., 2016).

Instillation of agarose plugs (0.7-0.8 mm diameter, 4% agarose II) in Fischer rats caused a time-dependent increase in goblet cell area (by AB/PAS staining), which was detectable as early as 24 h and was greatest 72 h post-instillation. The AB/PAS-stained area increased from 0.1 ± 0.1% in control animals to 4.7 ± 1.4, 13.3 ± 0.7, and to 19.1 ± 0.7% at 24, 48, and 72 h post-instillation, respectively. Goblet cell numbers increased from 0 to 13.1 ± 5.6, 25.7 ± 15.0, and 51.5 ± 9.0 cells/mm basal lamina at 24, 48, and 72 h post-instillation, respectively. Treatment of the animals prior and after instillation with 80 mg/kg/day BIBX1522 resulted in a marked decrease in the AB/PAS-stained area (<5% at 72 h). Of note, the AB/PAS staining in the airway epithelia coincided with EGFR staining  (Lee et al., 2000).

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