Defining a visual marker of osteoprogenitor cells within the periodontium


Ivo Kalajzic, Department of Reconstructive Sciences, MC 3705, University of Connecticut Health Center, 263 Farmington Ave., Farmington, CT 06032, USA
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San Miguel SM, Fatahi MR, Li H, Igwe JC, Aguila HL, Kalajzic I. Defining a visual marker of osteoprogenitor cell within the periodontium. J Periodont Res 2009;doi: 10.1111/j.1600-0765.2009.01201.x.©2009 John Wiley & Sons A/S

Background and Objective:  Cells with osteoprogenitor potential are present within periodontal tissues during development and in postnatal life. To identify an osteoprogenitor population, this study utilized a transgenic model in which an α-smooth muscle actin (αSMA) promoter directed green fluorescent protein (GFP) expression.

Material and Methods:  Observation of GFP expression was complemented with analysis of osteogenic differentiation by determining the expression of RNA of bone markers, by histochemical staining for alkaline phosphatase and by the detection of mineralized nodules using xylenol orange. Flow cytometry was utilized to determine the proliferative potential and cell-surface phenotype of cultured αSMA-positive cells.

Results:  αSMA–GFP expression was detected within the dental follicle and in the apical region of the root (i.e. areas rich in vascularization) but not in mature bone. αSMA–GFP expression was observed during the early stages of primary cultures derived from the dental follicle and periodontal ligament and was diminished in areas undergoing mineralization. Intense alkaline phosphatase activity and the presence of mineralized nodules was observed 2 wk after osteogenic induction. Consequently, the expression of bone sialoprotein, osteocalcin and dentin matrix protein-1 was increased. Flow cytometry revealed that in vitro expansion enriched for an αSMA–GFP-positive population in which 55–65% of cells expressed the cell-surface markers Thy1+ and Sca1+. The αSMA–GFP-positive population exhibited high proliferative and osteogenic potentials when compared with an αSMA–GFP-negative population.

Conclusion:  Our data indicate that the αSMA promoter can be used to identify a population of osteoprogenitor cells residing within the dental follicle and periodontal ligament that can differentiate into mature osteoblasts.