OR36 - Hypoxia-induced Heat Shock Proteins in the Dental Pulp: Possible Endogenous Activators of the Innate Immune Response

Abstract: Purpose: Dental trauma may disrupt periradicular vasculature resulting in dental pulp hypoxia, inflammation and potentially subsequent pulpal necrosis. Heat shock proteins (HSP) are known to be up-regulated and released upon tissue injury. To date, the mechanisms of hypoxia-induced pulpal inflammation and subsequent necrosis are largely unknown. We hypothesized that HSPs released under conditions of hypoxia interact with TLRs contributing to pulpitis and necrosis. Methods: Tooth slices of freshly extracted teeth were cultured for 3 days in normoxia or hypoxia conditions in the presence or absence of HSP or TLR inhibitors. After 3 days, the expression of HSP27, HSP 60, HSP 70, and HSP 90, cytokines and chemokine gene expressions were evaluated using qRT-PCR arrays as well as multiplex analysis of cytokines/chemokine levels. Data were analyzed with a paired Student’s t-test (p< 0.05). Results: There was a significant up-regulation in the expression of inflammatory mediators such as IL1-β in dental pulp due to hypoxia. In addition, there was a robust up-regulation of HSP 70 and HSP27, whereas HSP90 was down regulated. The increased expression of IL1- α and IL-β was blocked by a TRL2 inhibitor. Further, our interim data demonstrates that HSPs are involved in this TLR-mediated response Conclusions: This is the first study to use a human tooth ex vivo model to evaluate the mechanisms of hypoxia-induced pulpal inflammation. This study highlights the roles of TLRs and HSP in this response. Future interventions at these pathways may preserve pulpal homeostasis following trauma.