Epithelial Cell Apoptosis by Fas Ligand–Positive Myofibroblasts in Lung Fibrosis

Abstract

The Fas/Fas ligand (FasL) apoptotic pathway has been shown to be involved in bleomycin-induced lung fibrosis. We examined the hypothesis that myofibroblasts from fibrotic lungs possess a cytotoxic phenotype that causes apoptosis of epithelial cells via the Fas/FasL pathway. We show in vivo epithelial cell apoptosis and associated upregulation of Fas and apoptotic Fas pathway genes in epithelial cells of lungs with bleomycin-induced fibrosis. In addition, we show that FasL surface molecules are overexpressed on alpha-SMA-positive cells in mice with bleomycin-induced fibrosis, and in humans with idiopathic pulmonary fibrosis. This enables the molecules to kill Fas-positive epithelial cells. In contrast, FasL-deficient myofibroblasts lose this myofibroblast cytotoxic phenotype, both in vivo and in vitro. In vivo, there was no bleomycin-induced epithelial cell apoptosis, as assessed by specific M30 staining in chimeric FasL-deficient mice that lacked FasL-positive myofibroblasts. In vitro, FasL-positive, but not FasL-negative myofibroblasts, induce mouse lung epithelial cell apoptosis. Thus myofibroblast cytotoxicity may underlie the absence of re-epithelialization, resulting in persistent lung fibrosis.

Telomerase activity in bleomycin-induced epithelial cell apoptosis and lung fibrosis

“…The current authors have recently confirmed that bleomycin causes apoptosis of lung epithelial cells in vitro in a time-and dose-dependent manner [10], and also reported the specific induction of epithelial cell apoptosis by myofibroblasts from fibrotic lungs via the Fas/Fas ligand pathway [11]. The aim of the present study was to evaluate telomerase activity in bleomycintreated lung epithelial cells (LECs) and the resulting effect on apoptosis in bleomycin-treated mouse lung epithelial (MLE) cells.…”

“…It was also demonstrated that they induce apoptosis of lung epithelial cells in vivo, a possible mechanism for the prevention of lung tissue remodelling [11]. Apoptosis thus plays a role in the induction of fibrosis.…”

“…The current authors have recently shown that myofibroblasts, which are known to accumulate abundantly in the lungs of mice with bleomycin-induced fibrosis [3,34], are not only collagen producers, but also function as effector cells [11]. It was also demonstrated that they induce apoptosis of lung epithelial cells in vivo, a possible mechanism for the prevention of lung tissue remodelling [11].…”

“…LEC isolation for ex vivo culture LECs were isolated as has been previously reported [11]. Briefly, animals were sacrificed by aortic transection while under pentobarbitol 6% anaesthesia.…”

Increased Cell Surface Fas Expression Is Necessary and Sufficient To Sensitize Lung Fibroblasts to Fas Ligation-Induced Apoptosis: Implications for Fibroblast Accumulation in Idiopathic Pulmonary Fibrosis

“…Two recent studies have shown a similar sensitizing effect of PGE 2 on Fas-induced fibroblast apoptosis (14,21). Although the source(s) of Fas ligand (FasL) are not completely known, recent studies have suggested that myofibroblasts themselves may be an important source in the fibrotic lung (22,23). Taken together, these findings suggest that fibroblast and myofibroblast accumulation in the lungs of IPF patients could occur as a result of impaired sensitization to Fas-induced apoptosis.…”