Project Summary/Abstract: Loss of salivary gland function severely affects patient’s oral health and overall quality of life. Restoration of secretory units and gland function through promoting endogenous healing and regeneration of acinar cells may offer an effective and non-invasive treatment option for patient with salivary dysfunction. By combining genetic lineage tracing approaches with a classic model of severe and reversible glandular injury in the adult mouse submandibular gland, we have interrogated the capacity of diverse parenchymal cell populations to undergo lineage reprogramming toward secretory acinar cells. Our data revealed that following substantial loss of acinar cells, not only ductal stem cells but differentiated cell populations including myoepithelial and ductal cells serve as reserve acinar progenitors and contribute to more than 90% of regenerated acini. We found that plasticity of myoepithelial and cKit+ duct cells that involves reversion into a bipotent progenitor-like state before re-differentiation to proacinar/acinar cells is the major mechanism of acinar regeneration in this model of injury. These novel findings provide the first direct evidence for plasticity of diverse epithelial cells toward saliva-secreting acinar cells; and build the foundation for a clear operational understanding of the molecular mechanisms that could be harnessed to induce endogenous regeneration of acini in the degenerative salivary glands. What triggers this broad lineage plasticity in epithelial cells and how these cells reprogram their fate and acquire proliferative and bi-lineage differentiation capacity is currently unknown. We hypothesize that cues from the wound environment provoke lineage plasticity in diverse epithelial cell populations toward acinar cells. To test this hypothesis we will use our established transgenic mouse models and two models of mild and severe obstruction-induced injury to characterize inflammatory and stromal components that are specific to a pro-plastic microenvironment and then functionally assess the role of these components on promoting de novo formation of acini (Aim 1). We then take a systematic approach to decipher the unique and common molecular signature of myoepithelial cells and ductal cells as they undergo lineage reversion, and gain valuable insights into reprogramming of these two relatively abundant cell populations into acinar cells (Aim 2). This exploratory/developmental R21 proposal will yield important information that can be used as a foundation for developing effective targeted strategies for endogenous regeneration of acinar cells in damaged, degenerative or aging salivary glands, an important therapy for a large patient population suffering from hyposalivation and may also identify gatekeepers of epithelial differentiation that inhibit progenitor-like traits under normal condition.