Fibroblasts isolated after fibrotic lung injury induce apoptosis of alveolar epithelial cells in vitro

Abstract

Primary lung fibroblasts were isolated from patients with idiopathic pulmonary fibrosis (HIPF), from normal human lung tissue (NH), from rats treated with 75% oxygen and paraquat (PA), and from normal adult rats (NR). Serum-free media conditioned by each fibroblast strain were tested on the human A549 cell line (HIPF and NH media) or on primary alveolar epithelial cells (AEC) isolated from normal adult rats (PA or NR media). Over 20-h incubation, HIPF- or PA-conditioned media induced DNA fragmentation and significant decreases in total recoverable DNA and cell number of A549 or AEC, respectively; NH or NR media had no significant effect relative to serum-free unconditioned media. Apoptosis of A549 and AEC was detected by altered nuclear morphology and was confirmed by terminal deoxynucleotidyl transferase-mediated bio-dUTP nick end labeling. The endonuclease inhibitors 10 microM aurintricarboxylic acid and 50 microM zinc inhibited HIPF-induced apoptosis of A549 cells by 68 and 71%, respectively. Both apoptosis and necrosis were induced by HIPF and PA media in a concentration-dependent manner. These results suggest that altered fibroblasts emerging during fibrotic lung injury release a soluble factor(s) capable of inducing cell death and net loss of AEC.

Unscheduled apoptosis during acute inflammatory lung injury

“…Alternatively, a protective role for apoptosis might have been impaired by the failue to effectively remove the dead cells during ALI, leading to inflammation. Regardless of the role of apoptosis during the acute and inflammatory phase, during repair from injury apoptosis appears to have an important and protective role in the removal of injured cells from lung (Polunovsky, 1993;Uhal, 1995). However, the occurrence of apoptosis in the early and inflammatory phase seems to have substantially different biological consequences than during repair.…”

“…The presence of apoptosis in acutely injured lung could be part of a protective mechanism to limit the extent of injury or inflammation, as has been proposed during resolution of acute respiratory distress syndrome (Polunovsky, 1993;Uhal, 1995). If apoptosis is also protective during acute lung injury, animals that are relatively resistant to such injury might be predicted to exhibit apoptosis sooner than sensitive animals.…”

The Role of Angiopoietin 2 in Hyperoxia-Inuduced Acute Lung Injury

“…[35][36][37][38] It is possible that both cell death pathways co-exist or that another distinct mechanism may be induced in hyperoxia. 27,39,40 The dose and/or duration of hyperoxia exposure can cause different cell types in the lung to undergo death via distinct or overlapping mechanisms.…”

Wnt Signaling and Pulmonary Fibrosis

“…Several lines of evidence suggest that these myofibroblasts can induce apoptosis in neighboring epithelial cells in vitro and in vivo, probably through degradation of the extracellular matrix. [53][54][55] In addition, in IPF there appears to be either a lack of re-epithelialization or an increase in type 2 cells with little if any maturation of type 1 cells, leading to injured areas with exposed mesodermal components or re-epithelialized with immature type 2 cells. Since it has been demonstrated that type 2 cells express high levels of TGF-␤1, which is a profibrotic cytokine, in IPF either scenario would inhibit the proper re-epithelialization of these injured areas, causing more fibrosis.…”