Asparaginyl endopeptidase may promote liver sinusoidal endothelial cell angiogenesis via PI3K/Akt pathway

Background and aims: pathological angiogenesis plays an important role in the progression of chronic liver diseases. Asparaginyl endopeptidase (AEP) participates in tumor angiogenesis and was recently shown to be associated with liver fibrosis. This study aimed to explore the effect of AEP on liver sinusoidal endothelial cell (LSECs) angiogenesis and determine the underlying mechanism. Methods: cultured LSECs were infected with lentiviruses in order to suppress AEP expression (AEP-KD1, AEP-KD2). The effect of AEP on LSECs proliferation, apoptosis and migration were subsequently determined by a CCK8 assay, flow cytometry and wound-healing and Transwell assays, respectively, in AEP knocked-down and control LSECs.The expression of the endothelial cell surface markers CD31, CD34 and von Willebrand factor (vWF) were detected by immunofluorescence assay and western blot.The angiogenic factors, vascular endothelial growth factor receptor 2 (VEG-FR2) and interleukin 8 (IL 8) were detected by real-time PCR and western blot.The effect of AEP on vessel tube formation by LSECs was examined by Matrigel (TM) tube-formation assay. Phosphoinositide 3-kinase (PI3K)/Akt expression and phosphorylation were detected by western blot. Results: AEP was effectively knocked down by lentivirus infection in LSECs. Down-regulation of AEP expression significantly decreased proliferation and migration and increased apoptosis of LSECs. Moreover, expression levels of the endothelial cell surface markers CD31, CD34 and vWF, as well as angiogenic factors VEGFR2 and IL 8, were also reduced after AEP was knocked-down.The vessel tube formation abilities of AEP-KD1 and AEP-KD2 LSECs were significantly inhibited compared with LSECs without AEP knocked-down. Down-regulation of AEP also inhibited the phosphorylation of PI3K and Akt. Conclusion: AEP promotes LSECs angiogenesis in vitro, possibly via the PI3K/Akt pathway. AEP may therefore be a potential therapeutic target for preventing the progression of liver fibrosis.