αSMA+ Periodontal Stem Cell Characterization and the Role of BMP2

Objectives: To examine the ex vivo differentiation of alpha smooth muscle actin positive periodontal stem cells (αSMA+ PSCs) and the effect of bone morphogenetic protein 2 (Bmp2) on differentiation capability.
Methods: αSMA+ PSCs were isolated from Bmp2-floxed mice mandibles and implanted subcutaneously in mice using an absorbable gelatin sponge and a denuded molar after: no additional treatment (4 transplants), green fluorescent protein (GFP) labeling (6 transplants), or Bmp2 knockout (3 transplants). Mice were sacrificed at 4-8 weeks, and retrieved samples underwent selected staining and immunocytochemistry (H&E, Trichrome, Bsp-Ab, Postn-Ab, αSMA-Ab, Col12-Ab, Bmp2-Ab, EdU Click-iT).
Results: 8 of 13 transplants were successfully retrieved – 5 samples were not present upon re-entry. Teeth were lost in several samples due to migration from the sponge during implantation/healing. αSMA-Ab (untreated samples) and GFP labelling confirmed the presence of implanted αSMA+ PSCs in the retrieved samples. Strong bone sialoprotein (Bsp) signaling was observed in the acellular cementum region of several samples. Mineralized tissue consistent with bone was present and oriented adjacent to PDL-like fibroblasts in the 6-week GFP sample. Periostin (Postn) was seen in fibroblast cells adjacent to the root surface and throughout the sample when a tooth was not present. Bmp2 was present in untreated and GFP labelled samples.
Conclusions: αSMA+ PSCs can differentiate ex vivo to produce bone, PDL fibroblasts, and possibly acellular cementum. The tooth acts as a matrix for differentiation.