Angiotensin II is mitogenic for human lung fibroblasts via activation of the type 1 receptor

The expression of renin-angiotensin system components and the elevation of angiotensin-converting enzyme (ACE) in a number of fibrotic lung diseases s uggests angiotensin II (All) could play a role in the pathogenesis of pulmo nary fibrosis. However, the effect of All on lung fibroblasts has not previ ously been assessed and the mechanisms by which All induces cell proliferat ion in mesenchymal cells are not fully understood. We have examined the abi lity of All to stimulate fetal and adult human lung fibroblast proliferatio n in vitro. In particular, we have assessed the receptor subtypes involved and the possible autocrine role of transforming growth factor beta (IGF-bet a) and platelet-derived growth factor (PDGF), two recognized fibroblast mit ogens. Angiotensin type 1 (AT1), but not type 2, receptors were identified on fetal and adult human lung fibroblasts by immunocytochemistry. Ail (1 mu M) increased DNA synthesis (determined by [H-3]thymidine incorporation) in fetal and adult cells by 211 +/- 18% and 150 +/- 14%, respectively (p < 0. 01), and was inhibited by a specific AT1 receptor antagonist, Losartan (74 1 14%). A proliferative response to All was confirmed by direct cell counts . Subsequently, fibroblasts were incubated with neutralizing antibodies to TGF-beta and PDGF. Anti-TGF-beta antibodies inhibited All-induced DNA synth esis by 73 +/- 13%. However, no effect was seen with anti-PDGF antibodies. In conclusion, we have shown that angiotensin II induces human lung fibrobl ast proliferation in vitro via activation of the AT1 receptor and involves the autocrine action of TGF-beta.