Estrogen Activates AMP-Activated Protein Kinase in Human Endothelial Cells via ERβ/Ca2+/Calmodulin-Dependent Protein Kinase Kinase β Pathway

Our previous studies suggested that Estrogen inhibits cytokine-induced expression of VCAM-1 and ICAM-1 in cultured human endothelial cells via AMP-activated protein kinase (AMPK) activation. Here, we sought to delineate the mechanisms underlying estrogen activation of AMPK. AMPK can be considered a ‘fuel gauge’ of cellular energy status in response to metabolic stress. It is controlled by upstream kinases such as Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ) or LKB1. The present study of human endothelial cells demonstrates that AMPK is activated by estradiol (E2) through a Ca2+-dependent mechanism involving the estrogen receptor-β (ERβ) activation. Inhibition of CaMKK with STO-609, a specific inhibitor of CaMKKα and CaMKKβ, attenuated E2-induced AMPK activation, suggesting that CaMKKβ was the responsible AMPK kinase. Conversely, down-regulation of LKB1 did not affect E2-induced AMPK activation. E2 stimulation caused phosphorylation of acetyl coenzyme A carboxylase (ACC) and endothelial nitric oxide synthase (eNOS), two main targets of AMPK. Inhibition or down-regulation of CaMKKβ eliminated phosphorylation of ACC and eNOS in response to E2. Together, our data highlight the role of Ca2+ as a regulator of AMPK activation in response to E2 stimulation. We demonstrate that E2 activates AMPK via an ERβ/Ca2+/CaMKKβ-dependent pathway in endothelial cells.