Apoptosis of alveolar epithelial cells (AECs) is believed to be a critical event in the pathogenesis of lung fibrosis. It was previously shown that apoptosis of AECs requires autocrine generation of angiotensin (ANG) II. ANG II can also be degraded to ANG1-7 by angiotensin converting enzyme-2 (ACE-2). ACE2 was recently found to be protective but significantly downregulated in experimental lung fibrosis and patients with IPF. In other organ systems, ANG1-7 has been found to inhibit the actions of ANGII through the ANG1-7 receptor mas. Therefore, it was hypothesized that ANG1-7 in the lungs might antagonize the actions of ANG II in the regulation of AEC apoptosis. To test this theory, the AEC cell line MLE-12 and primary cultures of human AECs were stimulated by the profibrotic apoptosis inducers ANG II or bleomycin (BLEO). Caspase-3 activation and nuclear fragmentation were used as markers of apoptosis and were measured along with JNK phosphorylation. Exposure to ANG II or BLEO induced caspase-3 activation, nuclear fragmentation, and JNK phosphorylation in cultured AECs. Pretreatment with ANG1-7, at a concentration of 0.1μM, prevented JNK phosphorylation and apoptosis. In addition, pretreatment with A779, a specific blocker of the ANG 1-7 receptor mas, successfully prevented ANG1-7 induced blockade of JNK phosphorylation and nuclear fragmentation. These data indicate that ANG1-7 prevents AEC apoptosis, and its actions are mediated through the ANG1-7 mas receptor.
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