BACKGROUND: Pulmonary fibrosis is a severe respiratory condition marked by the formation of scar tissue in the lungs, which makes it distinguishable from atypical fibrosis. The specific mechanisms of angiotensin-converting enzyme 2 (ACE2) in pulmonary fibrosis are still unclear, although it has been demonstrated to have a significant role in this condition. The objective of this study was to examine the impact of ACE2 on lung fibrosis.
METHODS: Both in vivo and in vitro experimental approaches were employed in this study to evaluate the function of ACE2. In the in vivo experiments, an animal model of pulmonary fibrosis was established by injecting 0.1 mL of bleomycin solution into C57BL/6 male mice, and the effects of ACE2 overexpression on pulmonary fibrosis were observed, for the animal group overexpressing ACE2 (Model+ACE2 group), treatments with SB505124 (transforming growth factor-β type I receptor (TGF-βRI) (ALK5) inhibitor) and XAV939 (Wnt Family Member 3a (Wnt3a) inhibitor) were administered, to evaluate the effects of these pathway inhibitors on ACE2 overexpression in the treatment of pulmonary fibrosis. Lung tissue samples were collected from the animals and subjected to pathological examination (hematoxylin and eosin (HE) and Masson's trichrome staining) to assess the degree of pathological inflammation and fibrosis. Concurrently, the expression levels of proteins and genes related to the ACE2, Wnt/glycogen synthase kinase (GSK)-3β/β-catenin, and TGF-β1/Smad2 signaling pathways were measured using Western blotting and quantitative reverse-transcription polymerase chain reaction (qRT-PCR) techniques. In the in vitro experiments, pulmonary fibrosis was simulated in human lung fibroblasts (HLFs), which were stimulated with TGF-β1. The correlation of ACE2 overexpression to attenuate pulmonary fibrosis with Wnt/GSK-3β/β-catenin and TGF-β1/Smad2 signaling pathways was explored.
RESULTS: The ACE2 overexpression could effectively reduce pulmonary fibrosis and inflammation in mice and HLFs by modulating signaling pathways (p < 0.01). In mice, ACE2 reduced inflammation and collagen accumulation, decreasing levels of α-smooth muscle actin (α-SMA) and fibronectin (p < 0.01). Compared to the Model+ACE2 group, the Model+ACE2+SB505124 underwent a greater reduction in inflammation and fibrosis, as well as decreased levels of α-SMA and fibronectin (p < 0.05). Overexpression of ACE2, XAV939, and SB505124 all significantly reduced the expression levels of Wnt3a, β-catenin, p-GSK-3β, TGF-β1, and p-Smad2 proteins in mice with pulmonary fibrosis (p < 0.05). In HLFs, ACE2 counteracted TGF-β1 effects, reducing cell proliferation and levels of fibrosis markers such as collagen, α-SMA and fibronectin (p < 0.01). It also inhibited the TGF-β1-induced epithelial-mesenchymal transition (EMT), showcasing its therapeutic potential against lung fibrosis and inflammation by regulating key signaling pathways and EMT processes (p < 0.01).
CONCLUSION: The desirable effects of ACE2 in alleviating pulmonary fibrosis are associated with the regulation of the Wnt/GSK-3β/β-catenin and TGF-β1/Smad2 signaling pathway. These results offer significant evidence for further investigation into the potential use of ACE2 in treating pulmonary fibrosis and provide new avenues for the advancement of innovative therapeutic approaches.