Knockdown of GSK3β increases basal autophagy and AMPK signalling in nutrient-laden human aortic endothelial cells

High concentrations of glucose and palmitate increase endothelial cell inflammation and apoptosis, events that often precede atherogenesis. They may do so by decreasing basal autophagy and AMP-activated protein kinase (AMPK) activity, although the mechanisms by which this occurs are not clear. Decreased function of the lysosome, an organelle required for autophagy and AMPK, have been associated with hyperactivity of glycogen synthase kinase 3β (GSK3β). To determine whether GSK3β affects nutrient-induced changes in autophagy and AMPK activity, we used a primary human aortic endothelial cell (HAEC) model of type 2 diabetes that we had previously characterized with impaired AMPK activity and autophagy [Weikel et al. (2015) Am. J. Phys. Cell Physiol. 308: , C249-C263]. Presently, we found that incubation of HAECs with excess nutrients (25 mM glucose and 0.4 mM palmitate) increased GSK3β activity and impaired lysosome acidification. Suppression of GSK3β in these cells by treatment with a chemical inhibitor or overexpression of kinase-dead GSK3β attenuated these lysosomal changes. Under control and excess nutrient conditions, knockdown of GSK3β increased autophagosome formation, forkhead box protein O1 (FOXO1) activity and AMPK signalling and decreased Akt signalling. Similar changes in autophagy, AMPK and Akt signalling were observed in aortas from mice treated with the GSK3β inhibitor CHIR 99021. Thus, increasing basal autophagy and AMPK activity by inhibiting GSK3β may be an effective strategy in the setting of hyperglycaemia and dyslipidaemia for restoring endothelial cell health and reducing atherogenesis.