A new constitutively active mutant of AMP-activated protein kinase inhibits anoxia-induced apoptosis of vascular endothelial cell

Abstract

The inhibition of apoptotic changes in vascular endothelial cells is important for preventing vascular damage from hypoxia. AMP-activated protein kinase (AMPK) has recently been identified as playing a role in vascular protection. Although the chemical reagent 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) has been used to stimulate AMPK activity, AICAR has been associated with several nonspecific reactions. We therefore constructed a new constitutively active mutant of AMPKα1 (NcaAMPK), which lacks the autoinhibitory domain in AMPKα1 and in which threonine 172 has been replaced with aspartate. We investigated whether NcaAMPK has an anti-apoptotic effect in vascular endothelial cells under anoxic conditions. NcaAMPK, or green fluorescent protein (GFP) as a control, was overexpressed in human umbilical vein endothelial cells (HUVECs). After HUVECs were incubated for 40h under normoxic or anoxic conditions, we examined cell viability, caspase 3/7 activity, and expression and phosphorylation levels of apoptosis-related proteins. Cell viabilities under anoxic conditions were improved in NcaAMPK-overexpressing cells. Anoxia increased caspase 3/7 activity, but NcaAMPK reduced this increase significantly. NcaAMPK overexpression increased protein kinase B/Akt Ser473 and endothelial nitric oxide synthase Ser1177 phosphorylation, but pretreatment with the nitric oxide synthase inhibitor NG -nitro-L-arginine methyl ester (L-NAME) did not decrease the viability of NcaAMPK-overexpressing HUVECs. Furthermore, co-expression of a dominant-negative Akt reduced the improvement in cell viability and the suppression of poly (ADP-ribose) polymerase cleavage by NcaAMPK under anoxic conditions. In conclusion, NcaAMPK inhibited anoxia-induced apoptosis in vascular endothelial cells through Akt activation, suggesting that activation of AMPK might protect against ischemic vascular injury.