LOCALIZATION AND EXPRESSION OF CSF-1 RECEPTOR IN RAT DENTAL FOLLICLE CELLS

Colony-stimulating factor-1 (CSF-1) accelerates tooth eruption in rats and is localized in the dental follicle, a loose connective tissue sa c that is necessary for eruption to occur. CSF-1 enhances the cellular events that occur in the follicle prior to eruption-namely, an influx of monocytes into the follicle early post-natally to form the osteocl asts needed to resorb bone for the eruption pathway. Because CSF-1 lev els are at a peak at day 3 post-natally, and because CSF-1 has an auto crine effect on its own gene expression, the question remains as to wh at causes the subsequent decline in CSF-1 protein and mRNA after day 3 post-natally. To determine if the autocrine effect is inhibited throu gh the CSF-1 receptor, analysis of the CSF-1 receptor mRNA levels in c ultured dental follicle cells reveals that high concentrations of CSF- 1 reduce the gene expression of the CSF-1 receptor. Interleukin 1 alph a, a molecule that enhances CSF-1 gene expression, has no effect on CS F-1 receptor mRNA levels. Immunostaining for the CSF-1 receptor protei n shows that it is present in the dental follicle early post-natally a nd is either absent or greatly reduced by day 10 post-natally. Earlier studies showed that the mRNA levels of the CSF-1 receptor also parall el this time course. Thus, the above results suggest that the feedback inhibition of the autocrine effect of CSF-1 on its own expression is through the effect of CSF-1 inhibiting the translation and transcripti on of its receptor. In turn, these molecular interactions possibly reg ulate the cellular events that occur in the follicle prior to and duri ng eruption.