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 adult periodontal ligament (PDL) reiterate the cellular and molecular events that occur sequentially during development. Type XII collagen has been implicated in the three-dimensional organization of the PDL extracellular matrix, and its expression has been restricted to the terminally differentiated stages. This study focused on the examination of the temporal and spatial expression of type XII collagen during experimental PDL remodeling in the rat. The temporal expressions of types I and XII collagen mRNAs were examined by RNA transfer blot and RNase protection assays, respectively, and were found to be relatively stable in the control group throughout the experimental period. In the tooth movement group, the expression of type I collagen increased at 72 hours and sustained the high level of expression at one week, while an increase in the expression of type XII collagen was first noted at the one-week period. The temporal activation of types I and XII collagen expression in the remodeling occurred in a pattern similar to that found during the development of the PDL. The spatial expression of type XII collagen mRNA was examined by in situ hybridization in the one-week-tooth-movement specimens. Labeled cells, which were more evident in the tension side, typically exhibited a spindle shape and were surrounded by the mature PDL matrix. Our data suggest that the type XII collagen expression may be closely associated with the functional regeneration of the PDL.