Role of Endothelial N-Glycan Mannose Residues in Monocyte Recruitment During Atherogenesis

Abstract

Objective— Upregulated expression of endothelial adhesion molecules and subsequent binding to cognate monocytic receptors are established paradigms in atherosclerosis. However, these proteins are the scaffolds, with their posttranslational modification with sugars providing the actual ligands. We recently showed that tumor necrosis factor-α increased hypoglycosylated (mannose-rich) N-glycans on the endothelial surface. In the present study, our aim was to determine whether (1) hypoglycosylated N-glycans are upregulated by proatherogenic stimuli (oscillatory flow) in vitro and in vivo, and (2) mannose residues on hypoglycosylated endothelial N-glycans mediate monocyte rolling and adhesion. Methods and Results— Staining with the mannose-specific lectins concanavalin A and lens culinaris agglutinin was increased in human aortic endothelial cells exposed to oscillatory shear or tumor necrosis factor-α and at sites of plaque development and progression in both mice and human vessels. Increasing surface N-linked mannose by inhibiting N-glycan processing potentiated monocyte adhesion under flow during tumor necrosis factor-α stimulation. Conversely, enzymatic removal of high-mannose N-glycans, or masking mannose residues with lectins, significantly decreased monocyte adhesion under flow. These effects occurred without altering induced expression of adhesion molecule proteins. Conclusion— Hypoglycosylated (high mannose) N-glycans are present on the endothelial cell surface at sites of early human lesion development and are novel effectors of monocyte adhesion during atherogenesis.

Increased sensitivity of Apolipoprotein E knockout mice to swainsonine dependent immunomodulation

“…Moreover, emerging studies are demonstrating that N-glycosylation is dynamically controlled during inflammatory diseases including atherosclerosis. Specifically we have demonstrated that pro-atherogenic/inflammatory stressors inhibit endothelial α -mannosidase activity leading to hypoglycosylated structures on the cell surface that then mediate increased inflammatory cell adhesion (Scott et al, 2012, 2013; Chacko et al, 2011). Given that autoimmune diseases are risk factors for atherosclerosis, our objectives in this study were to determine the effect of pharmacological inhibition of α -mannosidases on atherosclerosis in vivo .…”

“…A common sequelae of these diseases is accelerated cardiovascular disease including atherosclerosis (Skaggs et al, 2012; Gerli et al, 2007; Karmon et al, 2012). While the genetic and environmental risk factors underlying development and onset of autoimmune diseases vary, most are characterized by changes in protein N-glycosylation with enrichment in mannose rich structures (van Kooyk and Rabinovich, 2008; Green et al, 2007; Chui et al, 2001), and recently it has been demonstrated that these same alterations on endothelial cells are associated with atherosclerosis development (Scott et al, 2012, 2013). …”

Macrophages

“…29 Disturbed flow and proinflammatory mediators increase hypoglycosylated, high-mannose and hybrid N-glycans on the endothelial cell surface at sites of early lesion development, which leads to increased monocyte adhesion. 30 However, sialyltransferase IV activity, which catalyzes the formation of a sialylated sLe x , seems to promote monocyte recruitment into inflamed arteries and promotes atherogenesis through its essential role in the generation of a functional Ccr5 (C-C chemokine receptor) receptor, 31 suggesting that selective targeting of these post-translational events may constitute an interesting therapeutic option. In addition to Ccr5, signaling events through Ccr2 and Cx3cr1 (CX3C chemokine receptor) play nonredundant roles in atherosclerosis.…”

Glycoconjugates and Related Molecules in Human Vascular Endothelial Cells

“…This β -1,6-GlcNAc branching glycan was demonstrated to initiate endothelial cell contraction and gap formation, and these events lead to subsequent biological events such as tumorigenesis. High-mannose-type N -glycans increase in HAECs exposed to oscillatory shear or TNF- α [8]. Increasing surface N-linked mannose by inhibiting N -glycan processing potentiated monocyte adhesion under flow during TNF- α stimulation.…”