IPF, the most severe subtype of interstitial lung disease, is characterized by chronic inflammatory, deposition of extracellular matrix (ECM), dysfunction of epithelial–mesenchymal transition (EMT), and remodeling of abnormal lung tissue structure.32 There is no accepted effective therapeutic approach currently. Therefore, a novel, effective and safe therapeutic method for IPF is urgently needed. Natural products have increasingly been one of the most important resources for pharmaceutical research and development due to their unique biological functions. AM and RPR are two main ingredients of Buyang Huanwu Decoction (BYHWD), a well-known Chinese formula for supplementing Qi and activating blood circulation. Recent study has demonstrated the protective effect of BYHWD in pulmonary fibrosis model in vitro and its mechanism is related to inhibit pulmonary inflammation, collagen deposition, and EMT by suppressing the TGF-β1 signaling pathway.33 AM extract injection has been reported to ameliorate pathological lung fibrotic damage caused by BLM in rats and improve lung function by reducing the expression levels of TGF-β1 and collagens I and III whereas elevating those of MMP-3, MMP-9, TIMP-1, CXCL12, and CD90.34
Therefore, we used network pharmacology analysis to investigate the common transcription factor regulatory network in IPF and identified AM and RPR as candidate drugs for IPF. The therapeutic effect and mechanism of AM and RPR were verified in vivo, and the network pharmacology analysis revealed their molecular functions and pharmacological targets for treating IPF.
The diverse and heterogeneous etiology and pathogenesis of IPF make it suitable to identify pathways and targets by comparing samples from IPF patients and control tissues based on microarray screening. First, 171 overlapped targets were screened out from targets of AM, RPR and DEGs in GSE110147, GSE101286, and GSE24206. Based on the 171 targets, we revealed a regulatory network and key targets in regulating IPF. Afterward, the GO and KEGG enrichment analysis were preformed, and the results indicated a combination of multiple biological processes and pathways involved in the anti-IPF effect of AM and RPR. Multiple pathways are associated with inflammation, autophagy, apoptosis, and cell survival, including PI3K/AKT pathway, MicroRNAs in cancer and apoptosis etc. The PI3K/AKT pathway is involved in multiple pathological changes of IPF, including alveolar epithelial cells damage, ECM overproduction, EMT and apoptosis.35–38 Targeting PI3K/AKT pathway has already shown benefits in the treatment of IPF.39 However, numerous crosstalk and interactions of PI3K/AKT with multiple pathways including TGF, VEGF, WNT and Notch pathway suggest a complex network of pathogenesis of IPF.40 Blocking a single node in this network will not be sufficient or effective.
Astragaloside III, (R)-Isomucronulatol, Astragaloside I, Paeoniflorin and β-sitosterol were selected as the main active components according to the CTP network and Sankey diagram. Many metabolites of AM and RPR have already been proven to be promising drugs to alleviate fibrosis progression in multiple organs. Astragaloside IV could significantly inhibited BLM-induced EMT in BLM-induced pulmonary fibrosis via targeting PI3K/AKT pathway.41 Quercetin could resist ROS damage and inflammation in the process of IPF.42 Paeoniflorin could inbihiy the early stages of TGF-β mediated EMT in alveolar epithelial cells by decreasing the expression of the transcription factors Snail via the up-regulation of Smad7.43
Molecular docking validation was performed and revealed that all main active components had good binding affinity with key targets. Based on the above results, we further investigated the therapeutic effect of AM and RPR on IPF. The results showed that AM and RPR treatment significantly reversed the rise of the expression of AKT1, HSP90AA1, CASP3, MAPK3 and VEGFA caused by BLM in vivo.
Mitophagy and apoptosis manifest a cell type specific feature in the progress of pulmonary fibrosis. Apoptosis and mitophagy-induced type II alveolar epithelial cells and apoptosis resistant and mitophagy- impaired macrophages promote the development of pulmonary fibrosis synergistically. Several transcription factors contribute to this. AKT1 activation plays a vital role in the regulation of pulmonary fibrosis as it is strongly associated with regulating survival and differentiation of myofibroblasts. The function of AKT1 in the progression of pulmonary fibrosis is strongly related to TGF-β. In alveolar macrophages, TGF-β induces AKT1 activation, which promotes mitochondrial reactive oxygen species (ROS) and mitophagy. This AKT1-mediated mitophagy leads to apoptosis resistance and prolonged survival of macrophages and is required for pulmonary fibrosis progression.44 However, apoptosis acts oppositely in alveolar epithelial cells. Apoptosis of alveolar cells contributes to early fibrosis and lung injury. Increased levels of pro-apoptotic factors Caspases-3, Bax, PARP have been observed in lipopolysaccharide-induced pulmonary fibrosis model and induction of alveolar cell apoptosis can exacerbate pulmonary fibrosis.45 In addition, activation of non-Smad signalling pathways including MAPK and AKT by TGF-β1 also promotes aspects of EMT.46 The activation of PI3K/AKT pathway has been identified to inhibit the function of FOXO3 and the repressed expression of FOXO3 in normal fibroblasts contributes to IPF fibroblast phenotype.47 HSP90, a member of stress-inducible proteins, is composed of two isoforms, HSP90A and HSP90B, and participate in the regulation of TGF-β1 by inhibiting the activity of CHIP (carboxyl terminus of Hsc70-interacting protein) to ubiquitinate and degrade Smad3.48 HSP90 inhibition has been proven to abrogate TGF-β-induced fibroblast activation and ECM production.49 Several MAPKs including ERK, JNK and p38 have been proven to activate activation protein 1 (AP-1), which is involved in the phenotypic transformation of human lung fibroblasts into myofibroblasts induced by TGF-β. VEGFA is a permeability and angiogenic factor. A recent study has demonstrated that the level of VEGFA correlated with TGF-β level and can be raised by BLM which was consistent with our result.50
Matrix metalloproteinases (MMPs) are metalloendopeptidases that can degrade components of the ECM and non-matrix proteins. Most MMPs have been demonstrated to promote the development of IPF and are up-regulated in IPF blood and/or lung samples. MMP7 is not the key target predicted by the PPI network though, it is the DEG of three series and potential target of AM and RPR. The role of MMP7 in IPF includes promoting EMT and increasing lung levels or activity of profibrotic mediators or reducing lung levels of antifibrotic mediators.
qPCR revealed an escalation of AKT1, HSP90AA1, CASP3, MAPK3, VEGFA and MMP7 after BML treatment, which was consistent with results of other studies. The downward trend of these factors after treatment implies a multi-target and multi-pathway characteristic of AM and RPR in the treatment of anti-IPF. Thus, we speculate that AM and RPR suppressed TGF-β1/PI3K/Akt, MAPK, VEGF signaling pathways by targeting these pharmacological targets, subsequently ameliorating ECM deposition and inflammation in IPF.
Some limitations lie in this study. Some of the active components of Chinese medicine will also change during the decoction process, while some other compounds with therapeutic effects that may be generated during the decoction process cannot be included in this study. In addition, we investigated several nodes in the complex network of multiple targets and pathways and further studies could link the upstream and downstream transcription factors of key targets to reveal more clearly the regulatory role of AM and RPR in the signaling pathway in IPF. It is expected that in the future, researchers will be able to overcome challenges and convert the extensive recognition of the pathogenetic mechanisms of IPF into effective therapeutic approaches.