ACE2 Attenuates Epithelial-Mesenchymal Transition in MLE-12 Cells Induced by Silica

PURPOSE: The role of angiotensin-converting enzyme 2 (ACE2) in silicosis remains unknown, although previous studies have suggested that ACE2 may be beneficial. We, therefore, investigated the effect of ACE2 on silicosis, particularly with regard to its role in regulating the epithelial-mesenchymal transition (EMT) induced by silica, with the aim to uncover a new potential target for the treatment of pulmonary fibrosis. MATERIALS AND METHODS: We employed wild-type mice treated with diminazene aceturate (DIZE, an ACE2 activator, 15 mg/kg/day for 4 weeks), hACE2-transgenic mice (overexpress the ACE2 gene), and the mouse lung type II epithelial cell line treated with DIZE (10(−7) M for 48 h) or angiotensin-(1–7) [Ang-(1–7)] (10(−4) M for 48 h), following induced fibrotic responses to determine the protective potential of ACE2. Silicosis models were established by orotracheal instillation of SiO(2) (2.5 mg/mouse). Immunostaining was used to determine α-smooth muscle actin (α-SMA) expression. The activities of angiotensin-converting enzyme (ACE) and ACE2 and the levels of angiotensin II (Ang II) and Ang-(1-7) were detected by enzyme-linked immunosorbent assay. The mRNA expression of ACE and ACE2, and protein expression of the renin-angiotensin system (RAS) components and EMT indicators were studied by qRT-PCR and Western blot, respectively. RESULTS: DIZE treatment and overexpression of ACE2 markedly inhibited the formation of silica-induced lung fibrosis and increased the level of E-cadherin, with concomitant downregulation of pro-collagen, vimentin, and α-SMA via RAS signaling. Furthermore, DIZE and Ang-(1–7) attenuated the EMT and collagen deposition induced by silica in MLE-12 cells. Moreover, these effects were abrogated by MLN-4760 (a specific ACE2 inhibitor) and A779 (a specific Mas receptor blocker). CONCLUSION: The overexpression of ACE2 and treatment with DIZE can ameliorate EMT in silicotic mice via activation of the ACE2-Ang-(1–7)-Mas receptor axis, and these changes are accompanied by suppression of the ACE–Ang II–AT1 receptor axis.