Chronological gene expression of parathyroid hormone-related protein (PTHrP) in the stellate reticulum of the rat: implications for tooth eruption.
OBJECTIVE
Tooth eruption is a localized event that requires the expression of certain molecules at precise times to regulate bone resorption and bone formation. Parathyroid hormone-related protein (PTHrP) may be one of those molecules. Although PTHrP is produced in the stellate reticulum (SR) of the tooth and exerts its effect on the adjacent dental follicle, its expression pattern in the SR is unknown. Thus, it was the objectives of this study to determine the chronology of expression of PTHrP, and then to determine its effect on vascular endothelial growth factor (VEGF) expression for osteoclastogenesis and on bone morphogenetic protein-2 (BMP-2) for bone growth.


METHODS
Laser capture microdissection and RT-PCR were used to determine the chronological expression of PTHrP in vivo. In vitro, dental follicle cells were incubated with PTHrP and RT-PCR was conducted to determine its effect on VEGF and BMP-2 gene expression.


RESULTS
PTHrP was maximally expressed at day 7 postnatally in the SR with the level of expression still high at day 9. In vitro, PTHrP upregulated VEGF120 and VEGF164 expression after 4h of incubation with a maximum effect at 6h. PTHrP upregulated BMP-2 gene expression with a maximal effect at 2h.


CONCLUSIONS
Because the secondary burst of osteoclastogenesis needed for eruption occurs around day 10, it is possible that PTHrP is stimulating this osteoclastogenesis by upregulating VEGF. Concurrently, the upregulation of BMP-2 by PTHrP may stimulate bone growth at the base of the bony crypt to promote eruption.
Yao
Shaomian
S
Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
Pan
Fenghui
F
Wise
Gary E
GE
D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000235:genetics; D002478:Cells, Cultured; D003795:Dental Sac / Q000166:cytology; D015870:Gene Expression / Q000235:genetics*; D008334:Mandible / Q000254:growth & development; D008963:Molar; D010010:Osteoclasts / Q000502:physiology; D044162:Parathyroid Hormone-Related Protein / Q000235:genetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014078:Tooth Eruption / Q000235:genetics*; D016212:Transforming Growth Factor beta / Q000235:genetics; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics
C525720:Bmp2 protein, rat; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D044162:Parathyroid Hormone-Related Protein; D016212:Transforming Growth Factor beta; D042461:Vascular Endothelial Growth Factor A