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Acute effect of cigarette smoke on TNF-α and proteases released by macrophages Demirjian, Loutfig

Abstract

Pulmonary emphysema is a major cause of mortality and morbidity in chronic obstructive pulmonary disease (COPD). Cigarette smoking is a major risk factor in the development of pulmonary emphysema. In this study we investigated the acute effect of cigarette smoke in vitro on the production of tumour necrosis factor-α (TNF- α) using differentiated U937 cells, a human monocyte cell line used as a macrophage model system and human alveolar macrophages (AM). We found that stimulation of the macrophages with cigarette smoke media (CSM) leads to a rapid activation of extracellular-regulated kinases 1 and 2 (ERK1/2), p90RSK, and a transient decrease in phosphorylation of PKB/akt in differentiated U937 cells and alveolar macrophages. The CSM also caused the subsequent induction of TNF- α release in U937 differentiated macrophages, whereas alveolar macrophages showed no consistent change in TNF- α release. Our studies revealed that U0126, an inhibitor of the ERK1/2 pathway, markedly suppressed CSM-induced TNF- α release in U937 differentiated macrophages. Consistent with this finding, U0126 blocked CSM-stimulated ERK1/2 phosphorylation, as well as phosphorylation of the downstream kinase, p90RSK. On the other hand, the PI3-K inhibitor, LY294002 and epidermal growth factor receptor (EGFR)-specific inhibitor, AG1478 did not suppress the release of TNF- α by U937 differentiated macrophages. Thus, CSM induction of TNF- α production by U937 differentiated macrophages is regulated primarily via the ERK1/2 pathway. In contrast, CSM suppressed or had no effect on TNF- α release by alveolar macrophages, even though CSM induced the phosphorylation of ERK1/2. This suggests that alveolar macrophages may utilize adifferent signaling pathway for TNF- α production. In addition, this study also investigated the acute effect of cigarette smoke solution in vitro on the release of Cathepsin L, Matrix Metalloprotease-1, 7, 9 and 12 by AM , from which only Cathepsin L showed a slight but statistically significant increase after smoke exposure.

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