COLLAGENS IN AN ADULT BOVINE MEDIAL COLLATERAL LIGAMENT - IMMUNOFLUORESCENCE LOCALIZATION BY CONFOCAL MICROSCOPY REVEALS THAT TYPE-XIV COLLAGEN PREDOMINATES AT THE LIGAMENT-BONE JUNCTION

To understand the structure and function of medial collateral ligament , collagens present in an adult bovine ligament were determined. The m id-section of the ligament was powdered and extracted with 4 M guanidi nium hydrochloride, and the residue was digested with pepsin to solubi lize the collagens. Type I collagen was the major fibril collagen reco vered in the pepsin solubilized fraction, with types III and V each re presenting about 5% and 2%, respectively. Type VI collagen was the maj or collagen present in the guanidinium hydrochloride extract, and it a ccounted for about 40% of the proteins in the extract or 4% of the tis sue dry weight. Type XII and XIV collagens were also detected in the g uanadinium hydrochloride extract as minor components. Immunofluorescen ce localization using confocal microscopy showed that type XII and XIV collagens are associated with the ligament fibrillar network and that type XIV collagen was prominent at the ligament-bone junction. These data reinforce the notion that these collagens are associated with the type I collagen fibrillar network in connective tissues. In view of h igh mechanical stresses that exist at the ligament-bone interface, pre sence of type XIV collagen in high concentration at this junction may contribute to the modulation of the biomechanical properties of this t issue.