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 mid-section of the ligament was powdered and extracted with 4 M guanidinium hydrochloride, and the residue was digested with pepsin to solubilize the collagens. Type I collagen was the major fibril collagen recovered in the pepsin solubilized fraction, with types III and V each representing about 5% and 2%, respectively. Type VI collagen was the major collagen present in the guanidinium hydrochloride extract, and it accounted for about 40% of the proteins in the extract or 4% of the tissue dry weight. Type XII and XIV collagens were also detected in the guanadinium hydrochloride extract as minor components. Immunofluorescence 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 high mechanical stresses that exist at the ligament-bone interface, presence of type XIV collagen in high concentration at this junction may contribute to the modulation of the biomechanical properties of this tissue.