Modulation of collagen fibrillogenesis by dentinal proteoglycans

Studies have identified different pools of proteoglycan (PG) species present within the unmineralized matrix of the predentine, the transitional phase at the predentine-dentine interface and the mineralized dentine. These PGs alter with respect to the chemical nature of their glycosaminoglycan (GAG) chains and as a result of extracellular processing of the macromolecule in the matrix. The present study has examined the influence of the PGs isolated from these phases and the influence of the attached GAG chains, upon their ability to control collagen fibrillogenesis. PGs isolated from the three phases were characterized and determined to contain a mixture of decorin and biglycan. Results have indicated that predentine PGs, which are substituted with a higher proportion of dermatan sulfate, significantly delayed fibril formation while ultimately promoting the formation of thicker fibrils. Removal of the GAG chains further delayed fibrillogenesis, leading to the formation of thinner fibrils, compared with the collagen-only control. PGs isolated from predentine-dentine, which contained a higher proportion of chondroitin sulfate, also significantly delayed fibrillogenesis, resulting in thicker collagen fibrils. GAG chains attached to the predentine-dentine interface PGs played a role in the timing of fibrillogenesis with fibril formation initiated at the same time as the collagen control, but yielding thicker fibrils. Dentine PGs significantly inhibited fibrillogenesis and fibril thickness over concentrations of 50-25 microg/mL protein. In conclusion, the PGs isolated from the distinct phases have indicated differing roles in the orchestrated organization of the extracellular matrix during dentinogenesis, with roles for both the core protein and attached GAG chains indicated.