Background:
Evidence suggests a causative role for endoplasmic reticulum (ER) stress in the development of atherosclerosis. The molecular mechanisms by which conditions of ER stress promote pro-atherogenic processes are not understood. We have found that ER stress-inducing agents can activate glycogen synthase kinase (GSK)-3α/β, a protein involved in many metabolic pathways. The objective of this study is to investigate the role of GSK3α/β in pro-atherogenic ER stress signaling.
Methods and Results:
Thp1-derived macrophages were treated with the ER stress-inducing agents, glucosamine, thapsigargin or palmitate, in the presence or absence of the GSK3α/β inhibitor CT99021. GSK3α/β inhibition did not affect the adaptive unfolded protein response (UPR), but did block ER stress-induced lipid accumulation as well as the up regulation of genes associated with lipid biosynthesis and uptake. Using small molecule inhibitors of specific UPR pathways, we found that PERK, but not IRE1 or ATF6, is required for the activation of GSK3α/β by ER stress. GSK3α/β inhibition attenuated ER stress-induced expression of distal components of the PERK pathway, including CHOP and ATF4. Atherosclerotic plaques from ApoE-/- mice, fed a diet supplemented with the GSK3α/β inhibitor valproate, had reduced levels of CHOP within the macrophage foam cells. In primary mouse macrophages PERK inhibition blocked ER stress induced lipid accumulation whereas the overexpression of constitutively active S9A-GSK3β promoted foam cell formation and CHOP expression, even in cells treated with a PERK inhibitor.
Conclusions:
Pharmacological inhibition of GSK3α/β attenuates ER stress-induced lipid accumulation and macrophage foam cell formation. These findings indicate that GSK3α/β is an important factor in the ER stress-PERK signaling pathway and may play a central role in the pro-atherogenic dysregulation of lipid metabolism.
