Different glycoforms of alpha-1-acid glycoprotein contribute to its functional alterations in platelets and neutrophils

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 12-20 different glycoforms. We isolated a glycoform secreted from platelet-activating factor (PAF)-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 behavior, electrophoretic mobility, and pattern of glycosylation. The function of these 2 glycoforms also differed. sAGP-1 activated neutrophil adhesion, migration, and neutrophil extracellular traps (NETosis) involving myeloperoxidase, peptidylarginine deiminase 4, and phosphorylation of ERK in a dose-dependent fashion, whereas nAGP-1 was ineffective as an agonist for these events. Furthermore, sAGP-1, but not nAGP-1, inhibited LPS-stimulated NETosis. Interestingly, 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 PAF or ADP, but not by thrombin. These functional effects of sAGP-1 correlated with intracellular cAMP accumulation and phosphorylation of the protein kinase A substrate vasodilator-stimulated phosphoprotein and reduction of Akt, ERK, and p38 phosphorylation. Thus, the sAGP-1 glycoform limits platelet reactivity, whereas nAGP-1 glycoform also limits proinflammatory 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 2 critical cells of acute inflammation.

A diagnostic biomarker of acid glycoprotein 1 for distinguishing malignant from benign pulmonary lesions

“…17 Moreover, different glycoforms of AGP1 affect the activity of platelets and neutrophils in acute inflammation. 18 The abnormal expression of AGP1 was found to be associated with cardiovascular diseases, 19 primary aldosteronism, 20 and tumorigenesis of cancers. 21 Recently, more evidence has demonstrated that AGP1 could be a diagnostic or prognostic biomarker in tumors such as laryngeal 17 and pancreatic cancer.…”

N-Glycosylation and Inflammation; the Not-So-Sweet Relation

“…Furthermore, in addition to the liver, AGP-1 is expressed by activated neutrophils. In contrast to the N-glycans expressed on hepatic AGP-1 (hAGP-1), neutrophil-expressed AGP-1 (nAGP-1) carries mainly high-mannose, nonsialylated, and mono-sialylated N-glycans ( 76 ). Taken together, these data may indicate that chronic inflammation in some cases attenuates neutrophil recruitment and activation in favor of other, more potent leukocytes.…”

The role of N-glycosylation modification in the pathogenesis of liver cancer

“…At present, it has been confirmed that there are five N-glycosylation sites in AGP, which is a complex N-glycan and can form various types of branched conformations of sugar chains, with approximately 11% of the N-glycan chains undergoing sialylation [ 136 ]. It has been documented that the glycan conformation of AGP and other modification types on its N-glycan chain are highly correlated with the disease stage, and the level of N-glycan modification of AGP varies among different cancer types [ 137 ]. AGP can be used together with other marker proteins for the clinical diagnosis of liver cancer.…”