Composition changes in human tracheal cartilage in growth and aging, including changes in proteoglycan structure

High-buoyant-density proteoglycans were extracted and purified from tracheal cartilage obtained from nine individuals aged 1-58 yr. Cartilage from young individuals contained one major species of extractable aggregating proteoglycan and very little link protein. Link protein concentration relative to proteoglycan was observed to increase during the first 14 years of life, consistent with the increased formation of proteoglycan aggregates that are stabilized by link protein, as the process of tracheal cartilage growth and airway lumen widening ends. With increasing age after maturity, two further populations of proteoglycans became more abundant; these were characterized by higher mobility in composite agarose-polyacrylamide gel electrophoresis. The ability of the proteoglycans to associate with hyaluronan decreased with increasing age, although members of each of the three proteoglycan species contained functional hyaluronan-binding domains. Link proteins showed evidence of increasing proteolysis with age. Hydroxyproline content of the cartilage decreased with age; total tissue glycosaminoglycan and water contents showed no significant changes. Altered proteoglycan charge density, proteoglycan size, and aggregation properties, as well as changes in distribution of proteoglycans, may contribute to the changes in cartilage biomechanics that are associated with age-dependent changes in human lung function.