Adrenomedullin promotes human endothelial cell proliferation via HIF-1α

Adrenomedullin (ADM) and hypoxia-inducible factor-1 alpha (HIF-1 alpha) are important pro-proliferation genes in response to hypoxic stress. Although it was reported that ADM is a target gene for HIF-1, recent studies also showed that ADM regulates HIF-1 expression and its activity; however, the mechanism of action remains unknown. Two stable human endothelial cell lines with HIF-1 alpha knockdown by hy926-siHIF-1 alpha or HMEC-siHIF-1 alpha were established. mRNA and protein expression of ADM and HIF-1 alpha in EA.hy926 and HMEC1 cells were examined under hypoxic stress. Upon ADM treatment, cell proliferation was investigated and the expression profiles of HIF-1 alpha and its target genes (VEGF, PFKP, PGK1, and AK1) were examined. Furthermore, the proline hydroxylase (PHD) mRNA level and its activity were investigated. We observed that mRNA and protein expression of ADM in hypoxia are earlier events than HIF-1 alpha in EA.hy926 and HMEC1 cells. ADM-promoted cell proliferation of endothelial cells, which was HIF-1 alpha dependent. We also found that ADM up-regulated the mRNA and protein expressions of HIF-1 alpha- and HIF-1-targeted genes, and ADM up-regulated the protein expressions of HIF-1 alpha through down-regulation of PHD mRNA expression and PHD activity.