Downregulation of Adrenomedullin Leads to the Inhibition of the Tumorigenesis via VEGF Pathway in Human and Nude Mice Osteosarcoma Models

Abstract

Osteosarcoma is one of the most pernicious primary bone tumor characterized by high malignancy and metastasis, however its pathogenesis remain largely unknown. Our previous study showed elevated expression of adrenomedullin (ADM) is correlated with prognosis and disease severity in osteosarcoma patients. In this research, we continue to study the mechanisms of ADM-induced osteosarcoma cells proliferation invitro and invivo osteosarcoma models. The Radioimmunoassay was used to test the correlations of ADM and vascular endothelial growth factor (VEGF) expressions in plasma of osteosarcoma patients. The MTT and flow cytometry analysis were accepted to monitor the proliferation of osteosarcoma cells, meanwhile the ADM and VEGF expression were detected by real-time PCR and western blot. Moreover, the relationship among ADM and VEGF expression was also assessed in the osteosarcoma nude mice models. In this study, a significant correlation was found between ADM and VEGF expression in the plasma of osteosarcoma patients. As important stimuli in osteosarcoma proliferation, hypoxia could stimulate ADM and VEGF expression in MG-63cells. The expressions of ADM and VEGF increased with the duration of hypoxia, which also identify the positive correlations between the expression of ADM and VEGF. The proliferation of MG-63cells decreased when ADM was inhibited. And the proliferation increased when adding exogenous ADM, while VEGF inhibition attenuated this effect. Furthermore, ADM reduction also inhibited VEGF, CD31 expression and tumor cells growth in osteosarcoma nude mice models. These results suggested inhibition of osteosarcoma cells proliferation might be influenced by ADM through VEGF pathway, which implied ADM-VEGF signal was a potential target for impeding the proliferation of malignant cells in osteosarcoma.