Abstract: This study aims at investigating the alleviating effect of diazene aceturate (DIZE) on the development of mouse pulmonary fibrosis by endogenously activating Angiotensin-converting enzyme 2 (ACE2). Bleomycin induced pulmonary fibrosis injury model in mice was established for this aim. Twenty-four male ICR mice were randomly divided into control group (CON group), model group (MOD group) and DIZE group (DIZE group). Mice in the two groups other than CON group were injected with bleomycin (5 mg·kg ^-1) intratracheal only once to establish pulmonary fibrosis injury model. One day after establishing the model, mice in DIZE group were given DIZE (15 mg·(kg·d) ^-1) gavage, and mice in CON group and MOD group were given gavage with normal saline at the same dose. After continuous intragastric administration for 28 days, all mice were executed, serum and lung tissue were taken for the following tests: 1) Lung tissue was weighed and lung coefficient was calculated; HE and Masson staining were used to observe the pulmonary histological changes; the content of hydroxyproline in lung tissue was determined by alkaline hydrolysis; 2) The contents of Ang Ⅱ and Ang 1-7 in serum were determined by indirect ELISA; 3) The expression levels of fibrosis related factor genes and proteins in lung tissues were detected by qPCR and Western blot. Results showed that: 1) Compared with CON group, lung coefficient and hydroxyproline content in MOD group increased significantly (P<0.01 & P<0.05). The lung tissue showed obvious pathological changes, mainly manifested as alveolar collapse, inflammatory cell infiltration, alveolar septum congestion and thickening, and large amount of collagen fiber deposition. After DIZE treatment, the lung coefficient and hydroxyproline content decreased significantly (P<0.01 & P<0.05); The degree of pulmonary fibrosis reduced significantly; 2) Compared with CON group, the expression of ACE2 protein in lung tissue of MOD group was down-regulated, and the content of Ang Ⅱ in serum increased significantly (P<0.01), the content of Ang 1-7 decreased significantly (P<0.01); DIZE group showed a reverse on the changes happened in MOD group ; 3) Compared with CON group, the expressions of Col1a1 and Col3a1 genes in the lung tissues of MOD group were significantly up-regulated (P<0.01), α-SMA and TGF-β1 gene and protein expressions were significantly up-regulated (P<0.01), the expression of the characteristic protein E-cadherin in epithelial cells was significantly down-regulated (P<0.01); Compared with the MOD group, the DIZE group mitigated the above changes. After 28 days of one-time intratracheal injection of bleomycin, pulmonary fibrosis injury was successfully induced in mice. The production of Ang Ⅱ and the increased expression of TGF-β1 are the major factors of bleomycin-induced pulmonary fibrosis in mice. DIZE may reduce the high level of Ang Ⅱ by activating the expression of ACE2 and thus has a substantial relieving effect on pulmonary fibrosis in mice.

Key words: mice, diminazene aceturate, angiotensin converting enzyme, AngⅡ-TGF-β1 pathway, pulmonary fibrosis