Immunohistolocalization of HGF and c-Met in human dental pulp

Objectives: Hepatocyte Growth Factor (HGF) and c-Met participate in the epithelial-mesenchymal interactions during tooth development. HGF is recognized as a broad-spectrum and multifunctional cytokine that exhibits mitogenic, motogenic and morphogenic activities on epithelial and endothelial cells and it is produced by cells of mesenchymal origin such as fibroblasts. Its pleiotropic actions are mediated via a single receptor c-Met, the product of the c-Met proto-oncogene, encoding an intracellular tyrosine-kinase domain which is expressed on both epithelial and endothelial cells. The aim of this study was to examine the immunoreactivity for HGF and c-Met in dental pulp of human third molars. Methods: All teeth used in the experiments were extracted for orthodontic or therapeutic reasons. After extraction, the apical part of the teeth was removed with a scalpel and the dental pulps were removed with a forceps. 25 dental pulps were prepared for immunohistochemistry using routine fixation (Unifix®) and embedding (paraffine sections) techniques. Immunostaining for HGF and c-Met was carried out using the DAB envision® kit. Results: Immunoreactivity for both HGF and c-Met was seen in the odontoblast layer of the dental pulps. The cell bodies of the odontoblasts exhibited the strongest staining for both antibodies. The odontoblast-processes were stained to a lesser degree. The pulpal fibroblasts stained weakly for HGF but strongly for c-Met. Furthermore, c-Met staining was also observed on endothelial cells and nerve fibers. Conclusions: As it is already described that HGF has the ability to attract sensory nerve fibers, our results lead to the hypothesis that odontoblasts could use HGF to establish and to support the neuro-odontoblast interactions seen in dental pulp. The presence of c-Met on the odontoblasts could point to a possible feed-back mechanism for HGF-production.