Developmental Changes in the Glycosylation of Glycoprotein Hormone Free α Subunit during Pregnancy

Abstract

Glycoprotein hormone ␣ subunit, in its free form (free ␣), is a major placental product. Its glycosylation was found to change dramatically during the advancement of pregnancy. In this study, we have analyzed these glycosylation changes in five normal pregnancies. Binding to Lens culinaris lectin increased dramatically in all subjects between weeks 14 and 17 from the last menstrual period, indicating more core fucosylation as well as possible changes in branching of glycans. Studies using Datura stramonium agglutinin confirmed that the type of triantennary branching changed in this period of pregnancy. The precise structural nature of these changes was determined by high-pH anion-exchange chromatography and electrospray ionization mass spectrometry. Amounts of core fucosylation and of triantennary glycans increased substantially from early to late second trimester, and a shift was observed from 134/ 133-toward predominantly 136/136-branched triantennary structures. The glycosylation changes occurred in all five individuals at the same time period in gestation, suggesting developmental regulation of N-acetylglucosaminyltransferases IV and V and ␣6-fucosyltransferase during normal pregnancy. These enzymatic activities also appear to be affected in malignant transformation of the trophoblast. Our findings have important implications for the proposed use of specific forms of glycosylation as markers for cancer, as the relative amounts of these glycans in normal pregnancy will be determined by gestational age.Glycoprotein hormone ␣ subunit is common to the heterodimeric hormones chorionic gonadotropin, luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone. However, in its free form (free ␣ subunit), it is an important placental (1, 2) and pituitary (3) product, and it has been shown to have functions that are independent of the dimeric hormones (4 -7). Glycosylation of free ␣ differs from glycosylation of the combined form (8, 9). The combination of ␣ and ␤ for heterodimer formation takes place in the endoplasmic reticulum prior to processing of the immature glycans. In ␣ subunits that have not combined with a ␤ subunit, enzymes from the post-translational glycosylation machinery have access to substrate sites that are normally protected by the ␤ subunit of the heterodimer. As a result, the free form of ␣ subunit generally contains more elaborate oligosaccharide branching as well as higher amounts of core fucosylation than ␣ subunit obtained from dissociated hormone (8, 9). These characteristic glycosylation patterns prevent secreted free ␣ subunits from combining with ␤ subunits that might be encountered extracellularly, thus ensuring a population of free ␣ molecules (9, 10).The structural diversity of complex-type N-linked glycans is initiated by GlcNAc branching of the trimannosyl core and continues with the action of different glycosyltransferases that further extend these antennae (11). Specifically, the activity of N-acetylglucosaminyltransferase IV initiates the 134/133-branch of c...

Relative amounts of sialic acid and fucose of amniotic fluid glycoconjugates in relation to pregnancy age

“…The increased expression of core fucose (α1-6 fucosylation) in pregnancy has been demonstrated for hCG and transferrin [5,27]. According to Nemansky et al [6] the increased core fucosylation of N-glycans may reflect the change from an invasive state to a more nurturing role for the placenta during pregnancy.…”

“…5 Significantly different from 3rd trimester, perinatal period and post date pregnancy. 6 Significantly different from delivery at term and post date pregnancy. 7 Significantly different from perinatal period and post date pregnancy.…”

Terminal monosaccharide expression on amniotic glycoproteins as biomarkers of fetus maturity

“…The increased expression of core fucose in pregnancy has been demonstrated for hCG and transferrin [27,30]. According to Nemansky et al [31] the increased core fucosylation of Nglycans may reflect the change from an invasive state to a more nurturing role of the placenta during pregnancy.…”

“…Nemanski et al [31] have claimed that the intensive α1,6-fucosylation of some pregnancy-associated hormones is due to the high activity of the developmentally regulated fucosyltransferase. It was shown that the activity of α1,6-fucosyltransferase increases during the 14th-17th week of pregnancy and stays at a high level throughout the early third trimester of pregnancy.…”

Differential expression of human chorionic gonadotropin (hCG) glycosylation isoforms in failing and continuing pregnancies: preliminary characterization of the hyperglycosylated hCG epitope

“…The existence of hCG glycoforms has been documented for some time (Fein et al 1980, Wide & Hobson 1987, Skarulis et al 1992, Nemansky et al 1998. Most of this work was either based on isoelectric focusing patterns which are not feasible for general measurements or else by carbohydrate analysis on a few specimens.…”