The Effects of Hyperglycemia on Early Endothelial Activation and the Initiation of Atherosclerosis.

It is well established that patients with diabetes have an increased risk of developing atherosclerotic cardiovascular disease. The earliest detectable sign of atherosclerosis initiation is endothelial cell activation. Activated endothelial cells express adhesion proteins, P-selectin, E-selectin, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1, which function to recruit monocytes to the subendothelial layer. This study examines the effect of hyperglycemia on endothelial cell activation and the initiation and progression of atherosclerosis. In vitro studies revealed that exposure of human aortic endothelial cells to elevated (30 mmol/L) glucose concentrations significantly increased the expression of P-selectin, E-selectin, and vascular cell adhesion molecule-1. In vivo studies showed that, before lesion development, 5-week-old hyperglycemic ApoE-/-Ins2+/akita mice had significantly increased expression of these adhesion proteins in the aortic sinus and increased macrophage infiltration, compared with normoglycemic ApoE-/- controls. At 25 weeks of age, ApoE-/-Ins2+/akita mice had significantly larger atherosclerotic plaques than ApoE-/- controls (0.022 ± 0.004 versus 0.007± 0.001 mm3; P < 0.05). Similar endothelial activation was observed in heterozygous ApoE+/-Ins2+/akita mice; however, detectable atherosclerotic lesions did not develop in the absence of dyslipidemia. Lowering blood glucose levels (by 55%) using a sodium-glucose cotransporter 2 inhibitor reduced endothelial activation. Together, these findings support a causative role for hyperglycemia in atherogenesis and highlight the importance of blood glucose regulation in preventing atherosclerotic cardiovascular disease.

Investigating the Role of Endothelial Glycogen Synthase Kinase3α/ß in Atherogenesis in Low Density Lipoprotein Receptor Knockout Mice.

Risk factors for developing cardiovascular disease (CVD) are associated with inflammation and endothelial activation. Activated endothelial cells (ECs) express adhesion proteins that recruit monocytes to the subendothelial layer initiating plaque development. Understanding the mechanism(s) by which ECs increase adhesion protein expression will facilitate the development of therapies aimed at preventing CVD progression and mortality. Glycogen synthase kinase (GSK)3α/ß are constitutively active kinases which have been associated with many cellular pathways regulating cell viability and metabolism. While roles for myeloid GSK3α/ß in the development of atherosclerosis have been established, there is limited knowledge on the potential roles of endothelial GSK3α/ß. With the use of Cre recombinase technology, GSK3α/ß was knocked out of both ECs and macrophages (Tie2Cre GSK3α/ßfl/fl LDLR-/-). A bone marrow transplant was used to replenish GSK3α/ß in the myeloid lineage allowing the assessment of an endothelial-selective GSK3α/ß knockout (BMT Tie2Cre GSK3α/ßfl/fl LDLR-/-). In both models, adhesion protein expression, macrophage recruitment and plaque volume were reduced in GSK3α knockout mice. GSK3ß knockout had no significant effect. Results from this study are the first to suggest a pro-atherogenic role of endothelial GSK3α and support existing evidence for targeting GSK3α in the treatment of atherosclerotic CVD.

Deletion of Macrophage-Specific Glycogen Synthase Kinase (GSK)-3α Promotes Atherosclerotic Regression in Ldlr-/- Mice.

Recent evidence from our laboratory suggests that impeding ER stress-GSK3α/ß signaling attenuates the progression and development of atherosclerosis in mouse model systems. The objective of this study was to determine if the tissue-specific genetic ablation of GSK3α/ß could promote the regression of established atherosclerotic plaques. Five-week-old low-density lipoprotein receptor knockout (Ldlr-/-) mice were fed a high-fat diet for 16 weeks to promote atherosclerotic lesion formation. Mice were then injected with tamoxifen to induce macrophage-specific GSK3α/ß deletion, and switched to standard diet for 12 weeks. All mice were sacrificed at 33 weeks of age and atherosclerosis was quantified and characterized. Female mice with induced macrophage-specific GSK3α deficiency, but not GSK3ß deficiency, had reduced plaque volume (~25%) and necrosis (~40%) in the aortic sinus, compared to baseline mice. Atherosclerosis was also significantly reduced (~60%) in the descending aorta. Macrophage-specific GSK3α-deficient mice showed indications of increased plaque stability and reduced inflammation in plaques, as well as increased CCR7 and ABCA1 expression in lesional macrophages, consistent with regressive plaques. These results suggest that GSK3α ablation promotes atherosclerotic plaque regression and identify GSK3α as a potential target for the development of new therapies to treat existing atherosclerotic lesions in patients with cardiovascular disease.