Endoplasmic Reticulum Stress and Glycogen Synthase Kinase-3β Activation in Apolipoprotein E–Deficient Mouse Models of Accelerated Atherosclerosis
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OBJECTIVE: The goal of this study was to examine the role of endoplasmic reticulum (ER) stress signaling and the contribution of glycogen synthase kinase (GSK)-3β activation in hyperglycemic, hyperhomocysteinemic, and high-fat-fed apolipoprotein E-deficient (apoE(-/-)) mouse models of accelerated atherosclerosis. METHODS AND RESULTS: Female apoE(-/-) mice received multiple low-dose injections of streptozotocin (40 μg/kg) to induce hyperglycemia, methionine-supplemented drinking water (0.5% wt/vol) to induce hyperhomocysteinemia, or a high-fat (21% milk fat+0.2% cholesterol) diet to induce relative dyslipidemia. A subset of mice from each group was supplemented with sodium valproate (625 mg/kg), a compound with GSK3 inhibitory activity. At 15 and 24 weeks of age, markers of ER stress, lipid accumulation, GSK3β phosphorylation, and GSK3β activity were analyzed in liver and aorta. Atherosclerotic lesions were examined and quantified. Hyperglycemia, hyperhomocysteinemia, and high-fat diet significantly enhanced GSK3β activity and also increased hepatic steatosis and atherosclerotic lesion volume compared with controls. Valproate supplementation blocked GSK3β activation and attenuated the development of atherosclerosis and the accumulation of hepatic lipids in each of the models examined. The mechanism by which GSK3β activity is regulated in these models likely involves alterations in phosphorylation at serine 9 and tyrosine 216. CONCLUSIONS: These findings support the existence of a common mechanism of accelerated atherosclerosis involving ER stress signaling through activation of GSK3β. Furthermore, our results suggest that atherosclerosis can be attenuated by modulating GSK3β phosphorylation.
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