Activation of SHH signaling pathway in response to pulp capping

Objectives: Sonic hedgehog (SHH) signaling pathway plays a critical role in tooth development. The present study was designed to investigate the protein distribution of SHH and its receptor PTC, SMO and transcription factor GLI1 after ordinary pulp capping of adult rat molars.

Methods: The mesio-buccal pulp horn in the first mandibular molars of Wistar rats were perforated and the exposed pulps were directly capped with calcium hydroxide. The animals were sacrificed after 0, 1 , 3 or 7d of pulp treatment respectively. The protein distribution and staining intensity of SHH,PTC, SMO and GLI1 in the pulp tissues were examined by immunohistochemistry.

Results: Immunoreactivity for SHH, PTC, SMO and GLI1 was not observed in rat normal dental pulp on day 0 or in the control group. However, the SHH signaling pathway genes were expressed in the inflammationary dental pulp after pulp injury on day 1, 3 and 7. Each of the genes in the pathway were detected mainly in the cytoplasm. The protein expression of SHH was detected in the pulpal fibroblasts, odontoblasts, monocytes and vascular endothelial cells around the exposed pulp and in the root pulp. PTC, SMO and GLI1 expression were also detected in the inflammationary dental pulpal cells around the exposed site. Immunohistochemistry revealed an increased expression of Shh signailing pathway genes on day 3 , which showed a tendency to decrease on day 7.

Conclusion: These results indicate that SHH signaling pathway is activated in response to pulp injury and might participate in dental pulp repair.

This research was supported by the grants from the National Natural Science Foundation of China (30171011).