The role of human neuraminidases in LFA-1-ICAM-1 adhesion

Abstract

The N-acetyl neuraminic acid (sialic acid) residue is a crucial monosaccharide in mammalian glycosylation and commonly serves as the terminal residue on glycoproteins and glycolipids. As a key regulation site in glycosylation, it plays an essential role in modulating cell-cell interactions and signaling. Human neuraminidase (hNEU) enzyme modulates glycosylation by cleaving the terminal sialic acid residues from glycoconjugates and are involved in various biological processes. The hNEU family comprises four distinct isoenzyme members (NEU1, NEU2, NEU3, and NEU4) with diverse functions. For instance, NEU1 is primarily localized in lysosomes and degrades glycoconjugates, while NEU3 is mostly found on the plasma membrane and modifies glycolipid substrates.Cells of the immune system use glycoprotein receptor systems to engage in specific cell-cell interactions. Many immune receptors are heavily glycosylated, and the role of sialic acid in these interactions has not been well characterized. To test if hNEU has a role in regulation of leukocyte adhesion we investigated individual hNEU isoenzyme effects on a critical adhesion system of leukocytes. We implemented an in vitro assay for LFA-1–mediated cell adhesion using flow cytometry. We observed that cells pre-treated with selective inhibitors of hNEU had increased LFA-1 adhesion. Additional controls support that binding is specific, and that native hNEU isoenzymes act as negative regulators of LFA-1 adhesion in leukocytes during inflammation. While hNEU3 has a selective effect on static adhesion, hNEU1 and hNEU4 regulate both static and activated states. These results suggest that targeting specific hNEU isoenzymes could serve as a potential therapeutic strategy for anti-inflammation treatments.In Chapter III, we investigated development of an assay to detect the activity of individual hNEU isoenzymes in human blood. To achieve this, we developed a direct detection assay by using a standard 4MU-NANA assay with and without hNEU selective inhibitors, allowing for measurement of each isoenzyme activity.