Background In utero nicotine exposure disrupts the critical homeostatic pulmonary epithelial-mesenchymal paracrine signaling pathway, resulting in the transdifferentiation of alveolar intersitial fibroblasts (AIFs) to myofibroblasts (MYFs). AIF-to-MYF transdifferentiation is characterized by down-regulation of the peroxisome proliferator-activated receptor γ (PPAR-γ) signaling pathway and up-regulation of the Wingless/Int (Wnt) signaling pathway. Although effects of in utero nicotine exposure on PPAR-γ signaling are known, there is no information regarding its effect on Wnt signaling. We hypothesize that in utero nicotine exposure up-regulates AIF Wnt signaling, and in utero nicotine-induced lung injury can be prevented by specific molecular targeting to down-regulate Wnt signaling and/or up-regulate PPAR-γ signaling.
Objectives To determine (1) how in utero nicotine exposure affects AIF Wnt signaling and (2) if Wnt signaling antagonists and/or PPAR-γ agonists can prevent in utero nicotine-induced AIF-to-MYF transdifferentiation.
Methods WI38 cells, a human embryonic pulmonary fibroblast cell line, were cultured using standard methods. At near-confluence, the cells were treated twith nicotine (10−9 M) with or without a Wnt pathway antagonist (Wnt inhibitory factor [WIF-1]), or a PPAR-γ agonist (rosiglitazone [RGZ] 10−5M) for 24 hours to 7 days. Then the expression of various intermediates in Wnt and PPAR-γ signaling was determined at the mRNA (RT-PCR) and protein (Western blot) levels.
Results Nicotine treatment up-regulated Wnt pathway signaling intermediates such as LEF-1, β-catenin, its downstream target α-smooth muscle actin (α-SMA), and down-regulated PPAR-γ pathway signaling intermediates such as PPAR-γ and adipocyte differentiation-related protein. Concomitant treatment with WIF-1 or RGZ completely inhibited the nicotine-induced up-regulation of the expression of LEF-1 and its downstream target α-SMA.
Conclusions By either down-regulating AIF Wnt signaling and/or by up- regulating AIF PPAR-γ signaling, prohomeostatic AIFs can be maintained, preventing MYF transdifferentiation, thereby potentially preventing in utero nicotine-induced lung injury.
Supported by grants from TRDRP ((14RT-0073 and 15IT-0250), Philip Morris USA Inc. and Philip Morris International, and NIH (HL55268 and HL075405).
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