Defining a visual marker of osteoprogenitor cells within the periodontium.
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 alpha-smooth muscle actin (alphaSMA) promoter directed green fluorescent protein (GFP) expression.


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 alphaSMA-positive cells.


RESULTS
alphaSMA-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. alphaSMA-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 alphaSMA-GFP-positive population in which 55-65% of cells expressed the cell-surface markers Thy1(+) and Sca1(+). The alphaSMA-GFP-positive population exhibited high proliferative and osteogenic potentials when compared with an alphaSMA-GFP-negative population.


CONCLUSIONS
Our data indicate that the alphaSMA 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.
San Miguel
S M
SM
Department of Reconstructive Sciences, University of Connecticut Health Center, Farmington, CT 06032, USA.
Fatahi
M R
MR
Li
H
H
Igwe
J C
JC
Aguila
H L
HL
Kalajzic
I
I
D000199:Actins / Q000032:analysis*; D000469:Alkaline Phosphatase / Q000032:analysis; D000539:Alveolar Process / Q000166:cytology*; D000818:Animals; D000950:Antigens, Ly / Q000032:analysis; D015415:Biomarkers / Q000032:analysis; D002113:Calcification, Physiologic / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D049109:Cell Proliferation; D003795:Dental Sac / Q000166:cytology; D016326:Extracellular Matrix Proteins / Q000032:analysis; D049452:Green Fluorescent Proteins; D058574:Integrin-Binding Sialoprotein; D049408:Luminescent Agents; D008565:Membrane Proteins / Q000032:analysis; D051379:Mice; D008822:Mice, Transgenic; D009804:Odontoblasts / Q000166:cytology; D015675:Osteocalcin / Q000032:analysis; D010011:Osteocytes / Q000166:cytology; D010012:Osteogenesis / Q000502:physiology; D010513:Periodontal Ligament / Q000166:cytology; D010519:Periodontium / Q000166:cytology*; D010641:Phenotype; D010750:Phosphoproteins / Q000032:analysis; D012313:RNA / Q000032:analysis; D012795:Sialoglycoproteins / Q000032:analysis; D013234:Stem Cells / Q000166:cytology*; D018800:Thy-1 Antigens / Q000032:analysis; D019227:Tooth Apex / Q000166:cytology
D000199:Actins; D000469:Alkaline Phosphatase; D000950:Antigens, Ly; D015415:Biomarkers; D016326:Extracellular Matrix Proteins; D049452:Green Fluorescent Proteins; D058574:Integrin-Binding Sialoprotein; D049408:Luminescent Agents; D008565:Membrane Proteins; D015675:Osteocalcin; D010750:Phosphoproteins; D012313:RNA; D012795:Sialoglycoproteins; D018800:Thy-1 Antigens; C081635:Dmp1 protein, rat; C546872:Ibsp protein, mouse; C546873:Ibsp protein, rat; C498862:Acta2 protein, rat