Project Summary/Abstract Early mucosal restitution is an important primary repair modality in the gastrointestinal (GI) tract and its defective regulation underlies various critical pathological states such as mucosal bleeding and acute injury, disruption of GI epithelial integrity, and barrier dysfunction. Since the exact mechanisms underlying acute mucosal injury and early rapid mucosal reepithelialization after superficial wounds are still obscure, effective therapies to preserve GI epithelial integrity in clinic are limited, especially in patients with critical surgical illnesses. During previous funding period, we have established the importance of canonical transient receptor potential-1 (TRPC1)-mediated Ca2+ signaling in regulating intestinal epithelial restitution after mucosal injury. However, the exact upstream signals initiating TRPC1 channel activation after mucosal injury remain elusive and are the focus of this competitive renewal application. Recently, stromal interaction molecule 1 (STIM1) was identified in screens for molecules that are essential for the activation of store-operated Ca2+ channels (SOCs), whereas inhibition of STIM1 expression reduces store-operated Ca2+ entry (SOCE) after store depletion. Our preliminary results indicate that a) levels of levels of STIM1 at the plasma membrane increase significantly after wounding, b) overexpression of the constitutively active STIM1 EF-hand mutant increases SOCE and enhances epithelial restitution after wounding, and c) STIM1 silencing decreases SOCE and represses epithelial restitution in cells overexpressing TRPC1. Based on these exciting observations, we HYPOTHESIZE that STIM1 plays an important role in promoting GI epithelial restitution after mucosal injury by activating TRPC1 channel activity. Three specific aims are proposed to test the hypothesis. 1) To determine the pattern and role of STIM1 in gut epithelial restitution after mucosal injury in vitro as well as in vivo. 2) To characterize functional and physical interactions of STIM1 with TRPC1 in regulating SOCE during intestinal epithelial restitution. 3) To define the cellular signaling pathways regulating STIM1 subcellular redistribution and its expression after mucosal injury. Completion of these aims will identify the up stream signals initially activating TRPC1 channels after mucosal injury and also yield a novel model in which STIM1 subcellular trafficking and expression are regulated during restitution. It is hoped that our findings will provide supportive data to strengthen our long-term goal that is to develop therapeutic approaches for GI mucosal injury-related diseases and for maintaining epithelial integrity under various clinical conditions.