Immunoexpression of aquaporin-1 in the rat periodontal ligament during experimental tooth movement

This study examined the immunoexpression pattern of aquaporin-1 (AQP1), first identified as a water channel protein, in the periodontal ligament of rat molars during experimental tooth movement to clarify its role in periodontal responses in an overloaded model by the insertion of a piece of elastic band. In the control group without any treatment, the cementoblasts and osteogenic cells as well as the vascular endothelial cells showed AQP1 immunoreaction. In the experimental group, hyalinized tissue and intensely AQP1 positive amorphous structures which were identified as degenerated endothelial cells by immunoelectron microscopy, occurred at the compression side on Days 1 and 3. AQP1 immunoreaction came to be stronger in the intact endothelial cells around the hyalinized tissue. The hyalinized tissue had almost disappeared by Day 5 when many macrophages reactive to acid phosphatase activity appeared. The periodontal width on Day 7 became almost the same as that in the control group. These findings indicate that the hyalinized tissue and damaged AQP1 positive endothelial cells are phagocytized by macrophages which have temporally migrated, and suggest that the surviving endothelial cells with intense AQP1 reaction are involved in periodontal regeneration by capillary sprouting.