Advisor(s)
Rakesh P Patel
Committee Member(s)
Scott Ballinger
Jarrod Barnes
Susan Bellis
Silvio Litovsky
Jan Novak
Document Type
Dissertation
Date of Award
2019
Abstract
Monocyte extravasation through the endothelial layer is a hallmark of atherosclerotic plaque development and is mediated by heavily glycosylated surface adhesion molecules, such as intercellular adhesion molecule-1 (ICAM-1). Human monocytes have been classified into three distinct groups: classical (anti-inflammatory; CD14+/CD16-), nonclassical (patrolling; CD14+/CD16++), and intermediate (pro-inflammatory; CD14++/CD16+). The CD16+ nonclassical / intermediate monocytes have been implicated in atherosclerosis progression and their levels positively associate with adverse cardiac events. However, there is a relative lack of understanding as to whether there are distinct mechanisms that regulate CD16+ vs. CD16- monocyte adhesion to the inflamed endothelium. Our previous data identified a high-mannose (HM) glycoform of ICAM-1 present during inflammation, but the function of different endothelial N-glycoforms is not yet known. Here, we test the hypothesis that distinct ICAM-1 N-glycoforms mediate recruitment of different monocyte subsets and specifically that endothelial HM-ICAM-1 promotes adhesion of CD16+ monocytes. We measured monocyte rolling and adhesion to i) TNFalpha-activated HUVEC, in which N-glycosylation was modulated by inhibiting alpha- mannosidase activity or by lectin-based blocking or ii) Cos-1 cells expressing HM- or complex ICAM-1. Expression of HM-ICAM-1 selectively enhanced CD16+ monocyte adhesion under flow with no effect on CD16- monocytes noted. This effect was dependent upon both HM epitopes and ICAM-1; adhesion was abrogated by blocking either. iv Further, using the proximity ligation assay (PLA) we show that HM-ICAM-1 is present in human and mouse atherosclerosis, increasing with disease severity and positively correlating with CD68 macrophage staining. Finally, we addressed the mechanism behind the formation of HM-ICAM-1 during inflammation by studying endothelial alpha-mannosidases, a class of enzymes responsible for early N-glycan processing. We show that TNFalpha decreases class I alpha-mannosidase activity in a time-dependent manner, resulting in formation of HM-ICAM-1 on the cell surface. We also show that this decrease in activity is independent of NF-kappaB, suggesting a parallel mechanism of N-glycan regulation distinct from up-regulation of adhesion molecule protein expression. Together, these data highlight a high-mannose ICAM-1 present in human and mouse atherosclerotic lesions as a key mediator of CD16+ monocyte recruitment to the endothelium, and identify alpha-mannosidases as a potential therapeutic target in atherosclerosis.
ProQuest Publication Number
ISBN
9781392661642
Recommended Citation
McDonald, Kellie Regal, "Endothelial N-Glycan Hypoglycosylation Enhances Cd16+ Monocyte Adhesion: A Role For Alpha-Mannosidases" (2019). All ETDs from UAB. 2431.
https://digitalcommons.library.uab.edu/etd-collection/2431
Comments
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