The influence of alpha1-acid glycoprotein (orosomucoid) and its glycoforms on the function of human thyrocytes and CHO cells transfected with the human TSH receptor

Abstract

Local immunological reactions might influence the structure of alpha1-acid glycoprotein (AGP, orosomucoid) leading to a pathological condition in e.g. the thyroid. The aim of this study was to investigate whether the AGP molecule had a direct effect on thyroid cell function in vitro. The influence of AGP and its three glycoforms, TSH (1.0 U/l), serum samples and several sugars (methyl-mannose, methyl-glycoside, N-acetyl- d-galactose, N-acetyl- d-glycoside, neuramidase) were studied with respect to their influence on the function of the Chinese Hamster Ovary (CHO) cell line transfected with the human TSH receptor (hTSHr) and on human thyroid follicular epithelial cells (TFEC) in secondary cultures. We found that low concentrations of AGP (0.001–0.05 μg/l) stimulated while high concentrations of AGP (0.25–1.0 μg/l) inhibited cAMP accumulation in both cell systems ( n=24, P<0.0002). In CHO cells (JP26) and TFEC glycoforms 1 ( n=9), 2 ( n=12) or 3 ( n=11) significantly inhibited the TSH stimulated cAMP production, respectively, compared to controls ( P<0.0001) and was partially reversed by mannose ( P<0.0004). Control CHO cells (JP02) without the hTSHr showed no response. The specificity of the reaction was further confirmed by binding of biotinylated glycoforms and streptavidin conjugated FITC to both cell systems. This is the first report demonstrating that AGP and/or its glycoforms affects thyroid cell function in vitro and that it does so by influencing the second messenger cAMP probably by interacting directly with the TSH receptor.