Proliferation of human alveolar epithelial cells down‐regulates ACE‐2 activity

Abstract

In pulmonary fibrosis, a profibrotic effect is mediated by angiotensin II (ANGII). The accumulation of ANGII is limited by its conversion to angiotensin 1‐7 (ANG1‐7) by angiotensin converting enzyme‐2 (ACE‐2). Previous work from this lab demonstrated that ACE‐2 is protective against fibrogenesis, but down‐regulated in human and experimental lung fibrosis. ACE‐2 is expressed primarily by alveolar epithelial cells (AECs), which are quiescent in normal lung but proliferate in lung fibrosis. On this basis, we hypothesized that ACE‐2 activity would be dependent on cell cycle progression. It was predicted that ACE‐2 activity would be greater in quiescent cultures of human AECs (A‐549) compared to their proliferating counterparts. ACE‐2 activity was measured by assay with an ACE‐2 fluorogenic substrate and normalized to protein concentration. A competitive inhibitor for ACE‐2, Dx600, was co‐administered to analyze the specificity. In A‐549s, ACE‐2 activity was five‐fold greater in quiescent cells than proliferating cells (p = 0.0008). Inhibition of ACE‐2 with Dx600 demonstrated high specificity of the fluorogenic substrate. A similar effect was also seen in mouse lung epithelial cells (MLE‐12) with similar statistical significance (p < 0.001). These data show that proliferation of AECs down‐regulates ACE‐2 activity as a normal but unfortunate consequence of AEC proliferation during fibrogenesis. This cell culture model can be used to investigate the molecular control of the down‐regulation.Support: PHS HL‐45136