Cell transplants promote restoration of cell and tissue domains in healing rat periodontium

As the majority of periodontal ligament (PL) cells do not undergo renewal (>70%), transplantation of PL cells enriched for progenitors could be used therapeutically to compensate for the loss of specialized cell types caused by trauma or periodontitis. Objectives: To determine the fate of transplanted cells and assess their contribution to healing of periodontal tissues, we have isolated cells from the PL and the surrounding bone in homozygous Lac-Z mice (constitutive B-galactosidase expression). Methods: Prior to transplantation into B-galactosidase-negative rats, separating elastics were placed between lower first and second mandibular molars to initiate tooth movement, in an attempt to stimulate regeneration of PL. Following initiation of tooth movement, cells were transplanted into the PL of one group of rats using the periodontal window wound. In the control group, tooth movement was the only treatment. Animals were killed at days 1, 4 and 7 following initiation of tooth movement. Assessments included: migration of transplanted cells (X-Gal-staining), cell death (TUNEL), periodontal homeostasis (PL width) and cell repopulation (cell density). Results: There was massive cell death in the middle zone of the compression side of the PL, at day 1, for both groups (>90% of cells). At day 4, cell density was only 45% of unstimulated levels in control animals, whereas in rats with transplanted cells, cell density was >95% of unstimulated levels and there were very large numbers of X-Gal-stained cells that had migrated into the nascent PL. By day 4, PL width was restored to >60% of normal widths in rats treated with cell transplants compared to only 47% in controls (p>0.05). Conclusion: We conclude that cell transplants promote restoration of connective cell and tissue domains in orthodontically stimulated rat periodontium. This research was supported by CIHR Operating Grant MT-14904.