Proteoglycans and glycosaminoglycan fine structure in the mouse tail tendon fascicle

The isolated mouse tail tendon fascicle, a functional and homogenous volume of tendon extracellular matrix, was utilized as an experimental system to examine the structure-function relationships in tendon. Our previous work u sing this model system demonstrated relationships between mean collagen fib ril diameter and fascicle mechanical properties in isolated tail tendon fas cicles from three different groups of mice (3-week and 8-week control and 8 -week Mov13 transgenic) K.A. Derwin, L.J. Soslowsky, J. Biomech. Eng. 121 ( 1999) 598-604. These groups of mice were chosen to obtain tendon tissues wi th varying collagen fibril structure and/or biochemistry, such that relatio nships with material properties could be investigated. To further investiga te the molecular details of matrix composition and organization underlying tendon function, we report now on the preparation, characterization, and qu antitation of fascicle PGs (proteoglycans) from these three groups, The cho ndroitin sulfate/dermatan sulfate (CS/DS)-substituted PGs, biglycan and dec orin, which are the abundant proteoglycans of whole tendons, were also show n to be the predominant PGs in isolated fascicles. Furthermore, similar to the postnatal maturation changes in matrix composition previously reported for whole tendons, isolated fascicles from 8-week mice had lower CS/DS PG c ontents (both decorin and biglycan) and a higher collagen content than 3-we ek mice, In addition, CS/DS chains substituted on PGs from S-week fascicles were shorter (based on a number average) and richer in disulfated disaccha ride residues than chains from 3-week mice. Fascicles from 8-week Mov13 tra nsgenic mice were found to contain similar amounts of total collagen and to tal CS/DS PG as age-matched controls, and CS/DS chain lengths and sulfation also appeared normal. However., both decorin and biglycan in Mov13 tissue migrated slightly faster on sodium dodecyl sulfate polyacrylamide gel elect orphoresis (SDS-PAGE) than the corresponding species from 8-week control, a nd biglycan from the 8-week Mov13 fascicles appeared to migrate as a more p olydisperse band, suggesting the presence of a unique PG population in the transgenic tissue. These observations, together with our biomechanical data [Derwin and Soslowsky, 1999] suggest that compensatory pathways of extrace llular matrix assembly and maturation may exist, and that tissue mechanical properties may not be simply determined by the contents of individual matr ix components or collagen fibril size. (C) 2001 Orthopaedic Research Societ y. Published by Elsevier Science Ltd. All rights reserved.