Abstract Rationale Chronic Obstructive Pulmonary Disease (COPD) is a progressive lung disorder mostly driven by prolonged exposure to cigarette smoke (CS). The airway epithelium, as the first line of defense, undergoes significant structural and functional changes upon CS exposure. This contributes to the muco-obstructive disease of COPD. Emerging evidence implicates dysregulation of WNT signaling in these processes. Specifically, CS exposure alters WNT responsiveness in epithelial cells leading to impaired epithelial repair and remodeling. This study investigates the effects of CS on WNT signaling and the potential therapeutic role of metformin in restoring epithelial regeneration and homeostasis. Methods Primary human bronchial epithelial cells of healthy smokers and smokers with COPD were cultured at the air-liquid interface (ALI) and differentiated for 3-4 weeks before CS exposure using the Vitrocell VC1 smoking robot. Some cultures were treated with metformin (1µM) starting on the day when cultures went to ALI and maintained throughout differentiation. One 3R4F cigarette was smoked once or once daily for 5 days and control cultures were exposed to room air using the same parameters. Experiments were done 24h and 20d after CS exposure. Real-time PCR for mRNA expression was used to assess WNT signaling target genes such as, but not limited to, WNT5A, WNT5B, WNT7A and GAPDH. Western blotting was used to determine WNT signaling secreted proteins such as DKK1 and DKK3. Results Cells from healthy smokers displayed higher mRNA levels of WNT5A, WNT5B and FOXJ1 and lower mRNA expression of WNT7A compared to smokers with COPD. Twenty-four hours after CS exposure, WNT5A and WNT5B were decreased in both groups. After 20 days, they recovered in cells from healthy smokers but levels remained significantly lower in COPD. WNT7A remained increased 20 days after CS exposure in COPD but recovered in healthy smokers. Metformin treatment prevented smoke-induced increases in WNT7A and decreases in WNT5B. Furthermore, metformin decreased WNT7A and increased WNT5B in cells exposed to air control. DKK1 and DKK3 protein levels were decreased in apical washes of cells from smokers with COPD 24h after 5 days of CS exposure. Loss of DKK3 protein was prevented by metformin treatment. Conclusion These findings suggest that CS-mediated disruption of WNT signaling contributes to defective epithelial regeneration and airway remodeling in COPD. Understanding the interplay between CS exposure and WNT pathway modulation in airway epithelial cells may offer novel therapeutic targets for COPD. Metformin show promises in maintaining WNT signaling homeostasis and epithelial regeneration. This abstract is funded by: James and Esther King and Flight Attendant Medical Research Institute
Baumlin et al. (Fri,) studied this question.