PROJECT SUMMARY Deep caries and pulp exposures are normally treated by pulp capping or partial pulp amputation to preserve the vitality of the pulp. Control of dental caries is a major public health program. Discovery of the dental pulp stem cells (DPSCs) have opened up new avenues for regeneration or repair of the pulp-dentin complex. The use of adult stem cells for tissue regeneration and repair is important in regenerative medicine. Another important component for tissue engineering is a bioactive signaling molecule. For the last two decades we have been studying the acidic phosphoproteins of the organic matrix of bone and dentin. Besides their function in the extracellular matrix, many of these proteins are now implicated in stimulating signaling events. One such protein identified in the dentin matrix is dentin phosphophoryn (DPP). Until recently, the function of DPP was thought to be structural; however, recent studies have suggested that DPP may have other functions in cell signaling. Our preliminary data indicate that DPP activates the Wnt signaling pathway to promote odontoblast differentiation of the dental pulp stem cells. Wnt5a was the specific Wnt activated by DPP in DPSCs. The downstream effectors of Wnt5a signaling that we propose to investigate are β-catenin, TAZ and RhoC. We hypothesize that these DPP-mediated activation of these effectors are responsible for differentiation of DPSC's and their migratory properties. To test this hypothesis we propose to use molecular approaches : (a) To investigate the molecular mechanisms by which DPP mediates the activation of Wnt signaling to stabilize β-catenin and TAZ resulting in the differentiation of DPSCs into odontoblasts; (b) To examine the influence of DPP stimulation on RhoC GTPase signaling and its effect on the reorganization of the actin cytoskeleton in DPSCs leading to changes in cell shape and migration; (c ) To evaluate DPP as a therapeutic agent in an ectopic model for dentin- pulp regeneration. Overall, results from these studies would reveal an unprecedented signaling framework modulated by DPP that could be utilized in the future to develop therapies to restore lost damaged or diseased dentin-pulp complex with a vital pulp leading to tooth survival.