Exendin-4 (Exenatide), a long-acting agonist of the glucagon-like peptide 1 receptor (GLP-1R), has been confirmed to protect the cardiovascular system from atherosclerosis in type 2 diabetes. However, the detailed mechanism of this process is not clear. Activation of endothelial nitric oxide synthase (eNOS) to produce nitric oxide (NO) plays an important role in endothelial homeostasis. Previous study shows that HDL activates eNOS via its receptor scavenger receptor type B class I (SR-BI). In this study, we checked the effect of exendin-4 on HDL/SR-BI-mediated eNOS activation in HUVECs. Firstly, we demonstrated the expression of GLP-1R in HUVECs and exendin-4 significantly induced HDL-mediated eNOS activation. Next, we found exendin-4 increased the expression and promoter activity of SR-BI, and then blocking of PKA or AMPK by its specific inhibitor cancelled this effect. Consistently, cAMP enhanced SR-BI promoter activity while domain negative AMPK inhibited the effect of exendin-4 on SR-BI promoter activity. Blocking of GLP-1R by exendin 9-39 cancelled exendin-4-induced SR-BI promoter activity and AMPK phosphorylation. As a downstream of AMPK, a transcription factor FoxO1 was confirmed to directly bind to the SR-BI promoter region by Chromatin Immunoprecipitation (ChIP) assay and overexpression of FoxO1 enhanced SR-BI promoter activity. Moreover, exendin-4 markedly increased the expression and nuclear recruitment of FoxO1 by decreasing its phosphorylation. As well as, mutation of FoxO1-binding site in the SR-BI promoter region or silence of FoxO1 cancelled exendin-4-induced SR-BI expression.
In summary, our results show that exendin-4 upregulates the expression and transcription of SR-BI via PKA/AMPK/FoxO1 pathway, which contributes to HDL-mediated eNOS activation and NO generation in human endothelial cells.
J. Lyu: None. H. Imachi: None. K. Fukunaga: None. S. Sato: None. T. Dong: None. T. Ibata: None. T. Kobayashi: None. M. Matsumoto: None. K. Murao: None.