Serum Xylosyltransferase: a New Biochemical Marker of the Sclerotic Process in Systemic Sclerosis

Abstract

UDP-D-xylose:proteoglycan core protein beta-D-xylosyltransferase (EC2.4.2.26) is the initial enzyme in the biosynthesis of chondroitin sulfate and dermatan sulfate proteoglycans in fibroblasts and chondrocytes. Secretion of xylosyltransferase into the extracellular space was determined in cultured human dermal fibroblasts. A more than 6-fold accumulation of xylosyltransferase activity in cell culture supernatant was observed (day 1, 0.6 microU per 106 cells; day 9, 4.1 microU per 106 cells); however, intracellular xylosyltransferase activity remained at a constant level (0.4 microU per 106 cells). Exposure of human chondrocytes to colchicine led to a 3-fold decreased level of xylosyltransferase and chondroitin-6-sulfate concentration in cell culture. Specific xylosyltransferase activity and chondroitin-6-sulfate concentration decreased in a concentration-dependent manner and in parallel in culture medium and accumulated 5-fold in cell lysates indicating that xylosyltransferase is secreted simultaneously into the extracellular space with chondroitin sulfate proteoglycans. Xylosyltransferase activities were determined in serum samples of 30 patients with systemic sclerosis. Xylosyltransferase activities in female (mean value 1.28 mU per liter, 90% range 1.10-1.55 mU per liter) and male patients (mean 1.39 mU per liter, 90% range 1.16-1. 57 mU per liter) with systemic sclerosis were significantly increased in comparison with blood donors of a corresponding age. Furthermore, xylosyltransferase activity was correlated with the clinical classification of systemic sclerosis. Female patients with diffuse cutaneous systemic sclerosis showed higher serum xylosyltransferase activities than patients with limited systemic sclerosis. These results confirm that the increase of proteoglycan biosynthesis in sclerotic processes of scleroderma is closely related to an elevated xylosyltransferase activity in blood and demonstrate the validity of xylosyltransferase as an additional diagnostic marker for determination of sclerotic activity in systemic sclerosis.

Cloning and Recombinant Expression of Active Full-length Xylosyltransferase I (XT-I) and Characterization of Subcellular Localization of XT-I and XT-II

“…XT-I activities in synovial fluid were found to be significantly increased in chronic inflammatory joint diseases (21). Furthermore, we detected elevated levels of XT-I in the sera of patients with systemic sclerosis and in the seminal plasma of infertile men (18,22,23). In previous studies, we could prove the existence of a gene encoding for XT-II in higher organisms.…”

“…Several investigations suggested that soluble glycosyltransferases were formed from membrane-bound enzymes by proteolytic cleavage between the catalytic and the transmembrane domain (37,38). We have shown that XT-I is secreted into the extracellular space together with proteoglycans (22,39), and that serum XT-I activity is a confirmed biochemical marker for the determination of fibrotic activity in systemic sclerosis (22,24).…”

“…XT-I catalyzes the transfer of D-xylose from UDP-D-xylose to specific serine residues of the core protein (17). We have shown that this enzyme is secreted to a great extent into the extracellular matrix, together with chondroitin sulfate proteoglycans (18). Therefore, XT-I activity was proposed to be a diagnostic marker for the determination of alterations in the proteoglycan metabolism (19).…”

Measurement of Fibrosis Marker Xylosyltransferase I Activity by HPLC Electrospray Ionization Tandem Mass Spectrometry

“…We describe the development of a selective LC-MS/MS method for quantification of XT-I activity, a new fibrosis marker (6,21,22 ). The test is based on the binding of D-xylose to the synthetic peptide Bio-BIK-F, which was used as an acceptor for XT-I to form Bio-BIK-F-Xyl.…”

“…Longitudinal studies found that XT-I activity remained increased in the serum of scleroderma and SSC patients (6 ), a finding that corresponds to an increase of proteoglycan metabolism in sclerotic organs and the theory that XT-I is secreted simultaneously into the extracellular matrix with chondroitin sulfate containing proteoglycans (6 -8 ). Increased glycosaminoglycans have been found in patients with SSC, and the increased chondroitin sulfate and dermatan sulfate content in affected skin correlates with the severity of sclerotic skin (9 -11 ).…”