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The aim of the present study was to evaluate the therapeutic effects of human umbilical cord mesenchymal stem cells (uMSCs) in the presence of angiotensin-converting enzyme 2 gene (ACE2; ACE2-uMSCs) on bleomycin (BLM)-induced lung injury and pulmonary fibrosis in mice. A total of 100 male C57BL/6 mice were divided at random into five groups (n=20) as follows: Control group, BLM group, ACE2 group, uMSC group and ACE2-uMSC group. At 7, 14 and 28 days post-treatment, the following parameters were evaluated in lung tissue: Oxidation indexes [malondialedehyde (MDA), superoxide dismutase (SOD), glutathione (GSH) and oxidized glutathione (GSSG)]; fibrosis factors [tumor necrosis factor (TNF)-α, interferon (IFN)-γ and transforming growth factor (TGF)-β]; inflammatory cytokines [Interleukin (IL)-1, IL-2, IL-6 and IL-10]; ACE2 gene expression; hydroxyproline and collagen type 1 messenger RNA (mRNA) concentration; as well as matrix metalloproteinase (MMPs; 2 and 9) and tissue inhibitor of metalloproteinase (TIMP)1–4 expression. ACE2-uMSC injection following bleomycin pretreatment significantly alleviated lung injury in mice. In addition, treatment with ACE2-uMSCs demonstrated a stronger therapeutic effect than ACE2- or uMSC treatment alone, indicated by decreased expression of MDA, GSSG, TNF-α, IFN-γ, TGF-β, IL-1, IL-2, IL-6, collagen type 1 mRNA, MMPs and TIMPs as well as hydroxyproline concentration, and upregulation of SOD, GSH and ACE2 and IL-10. In conclusion, the results of the present study demonstrated that ACE2 and uMSCs had a synergistic therapeutic effect on bleomycin-induced acute lung injury.

Summary Objective To investigate the role of angiotensin-converting enzyme 2 (ACE2) in hyperoxic lung injury. Methods Adult mice were exposed to 95% O2 for 72 h to induce hyperoxic lung injury, and simultaneously treated with ACE2 agonist diminazene aceturate (DIZE) or inhibitor MLN-4760. ACE2 expression/activity in lung tissue and angiotensin (Ang)-(1–7)/Ang II in bronchoalveolar lavage fluid (BALF), and the severity of hyperoxic lung injury were evaluated. The levels of inflammatory factors in BALF and lung tissue and the expression levels of phospho-p65, p65 and IkBα were measured. Oxidative parameter and antioxidant enzyme levels in lung tissue were measured to assess oxidative stress. Finally, the expression levels of nuclear factor-erythroid-2-related factor (Nrf2), NAD(P)H quinine oxidoreductase 1 (NQO1) and heme oxygenase-1 (HO-1) were measured using Western blotting. Results Hyperoxia treatment significantly decreased lung ACE2 expression/activity and increased the Ang II/Ang-(1–7) ratio, while co-treatment with hyperoxia and DIZE significantly increased lung ACE2 expression/activity and decreased the Ang II/Ang-(1–7) ratio. By contrast, co-treatment with hyperoxia and MLN-4760 significantly decreased lung ACE2 expression/activity and increased the Ang II/Ang-(1–7) ratio. Hyperoxia treatment induced significant lung injury, inflammatory response and oxidative stress, which were attenuated by DIZE but aggravated by MLN-4760. The NF-κB pathways were activated by hyperoxia and MLN-4760 but inhibited by DIZE. The Nrf2 pathway and its downstream proteins NQO1 and HO-1 were activated by DIZE but inhibited by MLN-4760. Conclusion Activation of ACE2 can reduce the severity of hyperoxic lung injury by inhibiting inflammatory response and oxidative stress. ACE2 can inhibit the NF-κB pathway and activate the Nrf2/HO-1/NQO1 pathway, which may be involved in the underlying mechanism.

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This is an Open Access article licensed under the terms of the Creative Commons AttributionNonCommercial 3.0 Unported license (CC BY-NC) (www.karger.com/OA-license), applicable to the online version of the article only. Distribution permitted for non-commercial purposes only. Abstract Background/Aims: Angiotensin converting enzyme 2 (ACE2) treatment suppresses the severity of acute lung injury (ALI). The effects of ACE2 in ALI have been shown to not only result from its antagonizing hydrolyzing angiotensin II (AngII), which is responsible for reduction in the vascular tension and pulmonary accumulation of inflammatory cells, but also result from a role of ACE2 in suppressing the ALI-induced apoptosis of pulmonary endothelial cells (PECs). Nevertheless, the underlying mechanisms of the role of ACE2 on PEC apoptosis are not completely understood. Methods: Here, we used a bleomycin-induced mouse model for ALI that has been published in our previous studies. We analyzed the mRNA and protein levels of an anti-apoptotic protein Bcl-2 in the ALI-mice that have been treated w/o ACE2. We analyzed miR-4262 levels in the mouse lung in these mice. Bcl-2-targeting miRNAs were predicted using bioinformatics algorithms and a luciferase reporter assay was applied to examine the effects of miR-4262 on the Bcl-2 protein translation upon their binding to 3'-UTR of Bcl-2 mRNA. Adeno-associated viruses carrying either miR-4262 mimics or antisense were injected into ALI-mice without ACE2, and their effects on the apoptosis in mouse lung cells were analyzed by Western blot. Results: ACE2 inhibited the ALI-induced apoptosis of pulmonary cells in vivo partially through upregulation of Bcl-2 protein, but not Bcl-2 mRNA. ACE2 appeared to significantly suppress the upregulation of miR-4262 in mouse lung after ALI. MiR-4262 was found to target 3'-UTR of Bcl-2 mRNA to inhibit its protein translation in PECs. In vivo administration of antisense of miR-4262 decreased apoptosis of pulmonary cells and severity of the ALI in mice. Conclusion: ACE2-induced suppression of miR-4262 partially contribute to the inhibition of the PEC apoptosis after ALI through Bcl-2. MiR-4262 may be a novel promising treatment target for ALI and ARDS.