Biological Functions Of Proteoglycans Research Articles

An essential glycobiology resource for developmental biologists

![Figure][1] Essentials of Glycobiology, Second Edition Edited by Ajit Varki, Richard D. Cummings, Jeffrey D. Esko, Hudson H. Freeze, Pamela Stanley, Carolyn R. Bertozzi, Gerald W. Hart and Marilynn E. Etzler Cold Spring Harbor Laboratory Press (2009) 784 pages, ISBN 978-087969770-9, $158

Recent Developments in Proteoglycan Purification and Analysis

Proteoglycans are ubiquitous biomolecules in the body located in the extracellular matrix, on the cell surface and also within the cells. They contain at least one glycosaminoglycan (GAG) chain covalently attached to a core protein and may also present N- or O-linked glycans. The high structural diversity and distribution relate to the various biological functions of proteoglycans. In recent years, new members have enlarged the proteoglycan family and advances in molecular biology and glycobiology contributed to elucidate more of the biological functions of proteoglycans. In order to study the structure of a proteoglycan molecule and relate it to its function (or dysfunction), its isolation and purification from cell culture or tissue extracts is necessary. Next to the widely used anion exchange chromatographic methods, techniques based on lectin affinity chromatography have created new possibilities to increase the degree of purity. Introduction of electrospray ionization (ESI) and matrix-assisted laser desorption-ionization (MALDI) sources, together with tandem mass spectrometry (MS/MS or MSn), mark a further important step towards the structural analysis of glycosaminoglycans. The aim of this review is to present the most recent advances in proteoglycan purification and analysis.

Decorin from different bovine tissues: Study of glycosaminoglycan chain by PAGEFS

The sulphation pattern of glycosaminoglycan (GAG) plays a critical role in biological functions of proteoglycans. In this study, we showed that decorins from different bovine tissues present specific sulphation pattern coupled with peculiar biological activity. In order to elucidate chemical structure of decorin glycosaminoglycan chains, we improved an electrophoretic method to analyse fluorescent disaccharides from dermatan/chondroitin sulphate GAG chains. The disaccharide separation is based on minigels, and this technique was able to define the polysaccharide chain composition in terms of sulphated and not sulphated disaccharides. This approach allowed not only the measurement of few picomoles of material, but it also permits a rapid qualitative analysis of the GAG chains. Data obtained by PAGEFS indicate that the sulphation pattern of GAG is tissue specific and this finding may explain the different binding properties to von Willebrand factor of decorins.

Occlusal hypofunction causes changes of proteoglycan content in the rat periodontal ligament.

The biological functions of proteoglycans and glycosaminoglycans are closely associated with mechanical stress on the tissue. In order to reveal the relationship between proteoglycans in the periodontal ligament and mechanical stress such as occlusal stimuli, occlusal hypofunction of rat unilateral mandibular molars was induced by extraction of the opposing first, second and third maxillary molars. Immunohistochemical analyses were performed using antibodies for chondroitin sulfate, decorin, biglycan, heparan sulfate and keratan sulfate, and hyaluronic acid-binding protein. Chondroitin sulfate, observed more strongly in the cervical side than in the apical side of the periodontal ligament of the unextracted sides of mandible, and uniformly present in the extracellular matrix of the periodontal ligament, decreased significantly from 1 wk post-extraction of the antagonists, with a decrease in thickness and disarrangement in fibrous components. Decorin core protein, uniformly present in the periodontal ligament of the unextracted sides, decreased as early on as 2 d post-extraction. Heparan sulfate, mainly localized on the cell surface of vascular endothelial cells and osteoclastic cells as well as in the extracellular matrix of the unextracted sides, decreased significantly in association with the decreased number of blood vessels and osteoclastic cells as early on as 2 d post-extraction. Biglycan, keratan sulfate and hyaluronic acid, uniformly distributed in the periodontal ligament of the unextracted sides, showed little change after the extraction. These results demonstrate that occlusal hypofunction causes tissue remodeling of the periodontal ligament, with a significant decrease of chondroitin sulfate, decorin and heparan sulfate.

Biological functions of proteoglycans: use of specific inhibitors of proteoglycan synthesis

The use of specific inhibitors of proteoglycan synthesis have demonstrated essential functions for these molecules. Proteoglycans do not appear to be essential for cell viability or proliferation but are necessary for stable assembly of ECM and functional cell-ECM interaction. Because of their ability to nearly completely abolish ECM assembly in cell culture systems, proteoglycan synthesis inhibitors are useful tools to examine effects of ECM on the phenotypic behavior of cells. Despite its usefulness, the use of proteoglycan synthesis inhibitors has some drawbacks. The most significant of these is the fact that synthesis of all proteoglycans is inhibited, making it difficult to assign a particular function to a specific proteoglycan type. For this reason, inhibition studies need to be done in conjunction with additional biochemical, immunological or molecular biological studies.