Tooth eruption molecules enhance MCP-1 gene expression in the dental follicle of the rat

Tooth eruption is a localized developmental event that requires the presence of the dental follicle, a loose connective tissue sac that surrounds each tooth. Early postnatally in the first mandibular molar of the rat there is an influx into the follicle of mononuclear cells (monocytes) which, in turn, fuse to form osteoclasts that resorb the bone to form an eruption pathway. The chemoattractant that may attract the mononuclear cells to the follicle to initiate the cellular events of eruption is monocyte chemotactic protein-one (MCP-1). MCP-1 is secreted by the dental follicle cells and its gene is expressed maximally at an early postnatal age, correlating with the monocyte influx into the follicle. In this study, we show that other potential tooth eruption molecules--EGF, IL-1alpha, TGF-beta1 and CSF-1--all enhance the expression of the MCP-1 gene in the cultured dental follicle cells. In vivo, injections of IL-1alpha or EGF also enhance the gene expression of MCP-1 in the follicle with maximal enhancement occurring in the early postnatal days. Thus, there appears to be a redundant function of the different tooth eruption genes to ensure that the MCP-1 gene is expressed. In turn, expression of MCP-1 may be critical for recruiting the monocytes to the dental follicle to initiate the cellular events of tooth eruption.