Endothelial-to-mesenchymal transition (EndMT) is an essential mechanism in myocardial
fibrosis (MF).
Tongxinluo (TXL) has been confirmed to protect the endothelium against
reperfusion injury after acute
myocardial infarction (AMI). However, whether TXL can inhibit MF after AMI via inhibiting EndMT remained unknown. This study aims to identify the role of EndMT in MF after AMI as well as the protective effects and underlying mechanisms of TXL on MF. The AMI model was established in rats by ligating left anterior descending coronary artery. Then, rats were administered with high- (0.8 g·kg-1·d-1), mid- (0.4 g·kg-1·d-1), and low- (0.2 g·kg-1·d-1) dose
Tongxinluo and
benazepril for 4 weeks, respectively. Cardiac function,
infarct size, MF, and related indicators of EndMT were measured. In vitro, human cardiac microvascular endothelial cells (HCMECs) were pretreated with TXL for 4 h and then incubated in
hypoxia conditions for 3 days to induce EndMT. Under this hypoxic condition,
neuregulin-1 (NRG-1)
siRNA were further applied to silence NRG-1 expression. Immunofluorescence microscopy was used to assess expression of endothelial marker of vWF and fibrotic marker of
Vimentin. Related factors of EndMT were determined by Western blot analysis. TXL treatment significantly improved cardiac function, ameliorated MF, reduced
collagen of
fibrosis area (types I and III
collagen) and limited excessive extracellular matrix deposition (mmp2 and mmp9). In addition, TXL inhibited EndMT in cardiac tissue and
hypoxia-induced HCMECs. In
hypoxia-induced HCMECs, TXL increased the expression of endothelial markers, whereas decreasing the expression of fibrotic markers, partially through enhanced expressions of NRG-1, phosphorylation of ErbB2, ErbB4, AKT, and downregulated expressions of
hypoxia inducible factor-1a and
transcription factor snail. After NRG-1 knockdown, the protective effect of TXL on HCMEC was partially abolished. In conclusion, TXL attenuates MF after AMI by inhibiting EndMT and through activating the NRG-1/ErbB- PI3K/AKT signalling cascade.