Changes in leucine-rich repeat proteoglycans during maturation of the bovine growth plate

The primary growth plate of the fetal bovine tibia was studied in order to determine whether changes in the structure, abundance and expression of the leucine-rich repeat proteoglycans were occurring during tissue maturation from reserve cartilage to hypertrophic cartilage. The proteoglycans under study were decorin, biglycan, fibromodulin and lumican. Decorin was readily detectable in both the reserve and proliferating zones of the growth plate, but its abundance decreased markedly in the zones of maturation and hypertrophy where it could not be detected under the same conditions of analysis. In contrast to decorin, fibromodulin and biglycan could be detected throughout the growth plate, though their abundance was decreased in the proliferative and hypertrophic zones. Unlike the other proteoglycans, lumican could not be detected throughout the growth plate. At the message level, the expression of decorin shows a similar trend to that of protein abundance in the extracellular matrix, with its expression dropping markedly in the proliferative and hypertrophic zones. In the case of both biglycan and fibromodulin, message expression continued at a similar level throughout the growth plate. Thus, the leucine-rich repeat proteoglycans are different in the way they behave during growth plate maturation.