Cigarette Smoke Extract Promotes Human Lung Myofibroblast Differentiation by the Induction of Endoplasmic Reticulum...

Idiopathic pulmonary fibrosis (IPF) is a progressive and lethal fibrotic lung disease with an unknown aetiology. Persistent myofibroblast differentiation is a prominent feature of IPF. Cigarette smoking is a risk factor for IPF and an indicator of poor prognosis. Cigarette smoking induces endoplasmic reticulum (ER) stress, and it has been shown that ER stress promotes fibroblast-to-myofibroblast differentiation in lung fibrosis. In this study, we investigated whether cigarette smoke extract (CSE) promotes lung myofibroblast differentiation via the induction of ER stress.

Our study concentrates on exploring the relationship between smoking and ER stress in the differentiation of lung fibroblasts to myofibroblasts.

Human embryonic lung fibroblasts (MRC-5 fibroblasts) were stimulated with various doses of CSE. Levels of α-smooth muscle actin (α-SMA) protein were evaluated by immunofluorescence and western blot analyses. ER stress was induced by thapsigargin (TG) and inhibited by 4-phenyl butyric acid (4-PBA). Protein levels of glucose-regulated protein-78 (GRP78), inositol-requiring enzyme 1 (IRE1), X box-binding protein-1 (XBP-1) and activating transcription factor 6 (ATF6) were determined by western blotting. GRP78 siRNA was transfected into MRC-5 cells using Lipofectamine RNAiMAX Reagent.

CSE at a concentration of 1.0% significantly increased α-SMA expression in MRC-5 cells. There was no significant cell apoptosis after cells were exposed to CSE. CSE treatment significantly increased the expression of GRP78, IRE1, XBP-1 and ATF6 at the protein level at 48 h. Pretreatment with TG enhanced, whereas pretreatment with 4-PBA inhibited, the CSE-induced expression of α-SMA, GRP78 and XBP-1. Furthermore, knockdown of GRP78 blocked α-SMA expression in MRC-5 cells exposed to CSE.

Our data suggested that CSE promotes lung fibroblast-to-myofibroblast differentiation by the induction of ER stress.