Thiol Depletion Induces Apoptosis in Cultured Lung Fibroblasts

Thiol antioxidants are implicated in the protection of cells from oxidative injury. We studied the role of thiols in the regulation of apoptosis in cultured lung fibroblasts. Thiol depletion by culturing fibroblasts in cystine-free medium or with thiol-depleting agents induced oxidant accumulation and cell death by apoptosis. The cell death was prevented by the antioxidants ascorbic acid (AA) and catalase. Thiol depletion also induced leukotriene (LT) C4, LTD4, and LTE4 production and selective phosphorylation of p38-mitogen-activated protein kinase (MAPK) and its nuclear substrate ATF2. LT production and p38-MAPK phosphorylation were required for induction of apoptosis because thiol depletion-induced apoptosis was completely blocked by the 5-lipoxygenase inhibitor AA861, the LT antagonists FPL55712 and ONO1078, and the p38-MAPK inhibitor SB203580. LT production was inhibited by AA and p38-MAPK phosphorylation was inhibited by AA, AA861, and FPL55712. In an in vitro scratch wound model, repopulating fibroblasts at the wound margin, but not quiescent cells at the intact site, selectively underwent thiol depletion- induced apoptosis that was completely blocked by AA861, FPL55712, and SB203580. Thus, thiol depletion induces apoptosis through an ordered pathway involving oxidant accumulation, LT production, and p38-MAPK activation. Apoptosis of wound fibroblasts may be responsible for impaired wound healing in various organs, including the lung.