Mechanism for nicotine-induced up-regulation of Wnt signaling in human alveolar interstitial fibroblasts (original) (raw)

2011, Experimental Lung Research

Nicotine exposure alters normal homeostatic pulmonary epithelial-mesenchymal paracrine signaling pathways, resulting in alveolar interstitial fibroblast (AIF)-to-myofibroblast (MYF) transdifferentiation. Since the AIF vs MYF phenotype is determined by the expression of Peroxisome Proliferator-Activated Receptor (PPAR)γ and Wingless/Int (Wnt) signaling, respectively, we hypothesized that nicotine-induced AIF-to-MYF transdifferentiation is characterized by the down-regulation of PPARγ, and the up-regulation of the Wnt signaling pathway. As nicotine is known to activate PKC signaling, we also hypothesized that in AIFs, nicotine-induced up-regulation of Wnt signaling might be due to PKC activation. Embryonic human lung fibroblasts (WI38 cells) were treated with nicotine (1 × 10 −6 M) for either 30 minutes or 24 hours, with or without 30 minute pretreatment with calphostin C (1 × 10 −7 ), a pan-PKC inhibitor. Then we examined the activation of PKC (p-PKC) and Wnt signaling (p-GSK-3β, βcatenin, LEF-1, and fibronectin). Furthermore, activation of nicotinic acetylcholine receptors (nAChR)-α3 and −α7, and whether a PPARγ agonist, Rosiglitazone, blocks nicotine-mediated Wnt activation were examined. Following nicotine stimulation, there was clear evidence for nAChR-α3 and −α7 up-regulation, accompanied by the activation of PKC and Wnt signaling, which was further accompanied by significant changes in the expression of the down-stream targets of Wnt signaling at 24h. Nicotine-mediated Wnt activation was almost completely blocked by pretreatment with either calphostin C or RGZ, indicating the central involvement of PKC activation and Wnt/PPARγ interaction in nicotine-induced up-regulation of Wnt signaling, and hence AIF-to-MYF transdifferentiation, providing novel preventive/therapeutic targets for nicotine-induced lung injury.