Previous work suggests that a local extravascular angiotensin system plays an important role in the development of pulmonary fibrosis through stimulation of alveolar epithelial cell (AEC) apoptosis and collagen deposition. To demonstrate a causative role for the local tissue angiotensin (ANG) system in lung fibrosis, we hypothesize that overexpression of the angiotensinogen (AGT) gene or pharmacologic elevation of lung tissue ANG II levels might cause apoptosis of AECs and lung fibrosis. ANGII levels were elevated in rat or mouse lung tissue by intratracheal instillation of either purified ANGII or an adenovirus expressing AGT, or by ubiquitous overexpression of AGT in transgenic mice. Intratracheal instillation of purified ANGII caused significant collagen accumulation in lung tissue, both ex vivo and in vivo. Ubiquitous overexpression of AGT enhanced the profibrotic effect of bleomycin given at suboptimal doses. Intratracheal delivery of an adenoviral vector expressing mouse AGT (Ad-AGT) overexpressed AGT primarily in AECs and caused both apoptosis of AECs and pulmonary fibrosis. The lung collagen accumulation and AEC apoptosis caused by Ad-AGT was blocked by the caspase inhibitor ZVAD-fmk, by the ANG receptor AT1 antagonist Losartan or by the non-selective ANGII receptor antagonist Saralasin. Together, these data support the hypothesis that elevated pulmonary expression of AGT and its conversion to angiotensin II plays a causative role in the development of lung fibrosis through its induction of AEC apoptosis.
Keywords: alveolar epithelium; angiotensinogen; lung fibrogenesis.