The Skeletal Biology Section has continued to investigate the biochemical nature of stem cells that form hard tissues. In studies using FACS analysis, the types of integrins present on the surface of bone marrow stromal stem cells (BMSSCs) were determined, and by performing functional assays it was found that the beta1 containing integrins are the predominant class, and that their functionality is required for BMSSCs to differentiate into osteoblasts. By using techniques designed to isolate BMSSCs, it was discovered for the first time that adult dental pulp contains a population of stem cells, dental pulp stem cells (DPSCs) that have the ability to regenerate dentin upon in vivo transplantation. BMSSCs and DPSCs were compared by using commerically available mircoarrays, and were found to be quite similar in their pattern of gene expression. However, BMSCs had a higher level of IGFBP7 and Col1a2, whereas DPSCs had a higher level of IGF-2 and Col18a1. Considering the distinctly different mineralized matrices that each stem cell type produces, it is surprising that their patterns of gene expression are so similar. In addition to the isolation and identification of DPSCs, it was also found that peripheral blood contains cells that become adherent, and form fibroblastic and polygonal colonies in vitro. Certain of these blood borne-adherent cells had the ability to form bone upon in vivo transplantation. This study identified for the first time, the existence of a cell in the circulation that can be osteogenic.
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