TEMPORAL AND SPATIAL EXPRESSIONS OF TYPE-XII COLLAGEN IN THE REMODELING PERIODONTAL-LIGAMENT DURING EXPERIMENTAL TOOTH MOVEMENT

This study tested the hypothesis that the remodeling processes of adul t periodontal ligament (PDL) reiterate the cellular and molecular even ts that occur sequentially during development. Type XII collagen has b een implicated in the three-dimensional organization of the PDL extrac ellular matrix, and its expression has been restricted to the terminal ly differentiated stages. This study focused on the examination of the temporal and spatial expression of type XII collagen during experimen tal PDL remodeling in the rat. The temporal expressions of types I and XII collagen mRNAs were examined by RNA transfer blot and RNase prote ction assays, respectively, and were found to be relatively stable in the control group throughout the experimental period. In the tooth mov ement group, the expression of type I collagen increased at 72 hours a nd sustained the high level of expression at one week, while an increa se in the expression of type XII collagen was first noted at the one-w eek period. The temporal activation of types I and XII collagen expres sion in the remodeling occurred in a pattern similar to that found dur ing the development of the PDL. The spatial expression of type XII col lagen mRNA was examined by in situ hybridization in the one-week-tooth -movement specimens. Labeled cells, which were more evident in the ten sion side, typically exhibited a spindle shape and were surrounded by the mature PDL matrix. Our data suggest that the type XII collagen exp ression may be closely associated with the functional regeneration of the PDL.