Differential glycosylation of alpha-1-acid glycoprotein (AGP-1) contributes to its functional diversity

Abstract

Alpha-1-acid glycoprotein (AGP-1) is a positive acute phase glycoprotein with uncertain functions. Serum AGP-1 (sAGP-1) is primarily derived from hepatocytes and circulates as 12 to 20 different glycoforms. We isolated a glycoform secreted from stimulated human neutrophils (nAGP-1). Its peptide sequence was identical to hepatocyte-derived sAGP-1, but nAGP-1 differed from sAGP-1 in its chromatographic behaviour, electrophoretic mobility, and glycosylation. The function of these two glycoforms also differed. sAGP-1 activated neutrophil adhesion, migration and NETosis in a dose-dependent fashion, while nAGP-1 was ineffective as an agonist for these events. Furthermore, sAGP-1, but not nAGP-1, inhibited LPS-stimulated NETosis. However, nAGP-1 inhibited sAGP-1-stimulated neutrophil NETosis. The discordant effect of the differentially glycosylated AGP-1 glycoforms was also observed in platelets where neither of the AGP-1 glycoforms alone stimulated aggregation of washed human platelets, but sAGP-1, and not nAGP-1, inhibited aggregation induced by Platelet-activating Factor (PAF) or ADP, but not by thrombin. These functional effects of sAGP-1 correlated with intracellular cAMP accumulation and were accompanied by phosphorylation of the PKA substrate Vasodialator stimulated phosphoprotein (VASP) and reduction of Akt, ERK, and p38 phosphorylation. Thus, the sAGP-1 glycoform limits platelet reactivity while nAGP-1 glycoform also limits pro-inflammatory actions of sAGP-1. These studies identify new functions for this acute phase glycoprotein and demonstrate that the glycosylation of AGP-1 controls its effects on two critical cells of acute inflammation.

Sialoglyco-Conjugate Abnormalities, IL-6 Trans-Signaling and Anti-Ganglioside Immune Response—Potential Interferences in Lupus Nephritis Pathogenesis

“…Studies in literature showed that sialoglyco-conjugates are abundant in kidneys, and they could determine SLE organ determinations [ 11 , 12 , 13 , 14 , 15 ]. Seromucoids are released in the early stages of inflammation, act as acute phase reactants, modulate immunity, maintain the barrier function of the capillaries by mediating sphingolipids metabolism [ 12 ].…”

“…Aberrant expression of carbohydrates on cells surface are associated with malignant transformation, microbiome status, viral infections, altered immune response [ 1 , 7 , 8 , 9 , 10 ]. Circulant glyco-proteins (orosomucoids or alpha-1-acid glycoprotein) have important functions in immune and inflammatory response and could play a primary role in SLE disease activity and relapse [ 11 , 12 ]. Glycosphingolipids are involved in autoimmune diseases pathogenesis and renal disfunctions [ 13 , 14 , 15 ].…”

A Two-Dimensional Affinity Capture and Separation Mini-Platform for the Isolation, Enrichment, and Quantification of Biomarkers and Its Potential Use for Liquid Biopsy

“…There are many AGP isoforms or proteoforms of which about 10–20 glycoforms are detected in the serum. The variations of the AGP glycoforms are of interest to the study of the binding alteration of this protein with certain drugs, and of their usefulness as diagnostic biomarkers for some systemic inflammatory diseases [ 127 , 128 , 129 ]. The quantification of the immunoreactive exorphins derived from milk beta casein A1, casomorphins 5 and 7, is important as these exorphins are potential modulators of numerous regulatory processes in the body as well as potential biomarkers of several diseases.…”

Effect of Acute Phase Protein, Alpha – 1 – Acid Glycoprotein (AGP-1), On Platelet-Activating Factor (PAF) – Induced Pro-Inflammatory Responses

“…AGP-1 is often considered as one of the inflammatory biomarkers and its functions are not very well understood 3,5,6 . Although hepatocytes are the primary site of synthesis of AGP-1, extra hepatic cells like neutrophils, epithelial cells, monocytes and lymphocytes are known to secrete AGP-1 6,5,7 . However, AGP-1 demonstrates opposing effects on the isolated cells of the innate immune system, although its receptor is yet to be defined 8,7 .…”

“…Although hepatocytes are the primary site of synthesis of AGP-1, extra hepatic cells like neutrophils, epithelial cells, monocytes and lymphocytes are known to secrete AGP-1 6,5,7 . However, AGP-1 demonstrates opposing effects on the isolated cells of the innate immune system, although its receptor is yet to be defined 8,7 . Hence we need to understand how AGP-1 modulates the effects of PAF, for which receptor is well characterized on neutrophils.…”