Defining the role of tissue-resident macrophages during salivary gland morphogenesis

PROJECT SUMMARY Salivary glands (SGs) are complex structures composed of heterogenous epithelial populations, each possessing unique and crucial functions that contribute to the production and secretion of saliva. Hyposalivation, caused by irreversible damage to SG epithelium in conditions such as Sjögren’s Syndrome or irradiation treatment for head and neck cancer, leads to chronic dry mouth and increased risk of dental caries, oral infections, and overall discomfort. The differentiation and organization of epithelial lineages during embryonic SG development relies on the surrounding niche, actively signaling to epithelial cells from the start of SG initiation and continuing into maturity. Developmental roles of tissue-resident macrophages (TRMs) have been defined in the prostate and mammary glands, yet despite prominence in the SG, their functional contribution during SG morphogenesis remains unknown. My preliminary work utilizing transcriptional analysis, transgenic mouse models, and explant cultures has defined a significant upregulation of TRMs to the SG niche during embryonic development. I have further characterized an immune-epithelial crosstalk via ligand-receptor signaling, and aberrant SG morphogenesis induced by a timed TRM-depletion, pointing to the necessity of TRMs in the regulation of SG development. Thus, I hypothesize that processes of SG formation are regulated through diverse TRM functions. In AIM 1, I will determine the functional contribution of TRMs through conditional depletions at multiple timepoints of early development and characterize changes to organization of major niche structures, SG epithelial morphology and differentiation dynamics, and global transcriptomic changes. In AIM 2, I will define the role of a secreted ligand signaling pathway in mediating SG epithelial and niche cell identity and differentiation dynamics through interrogation of single cell transcriptomics generated from transgenic global knockout mouse SGs, and leverage in vitro explant cultures to determine downstream signaling mechanisms in epithelium. Outcomes of this study will define temporal dynamics of immune-epithelial interactions and their contribution to SG development, and further characterize candidate factors as regulators of morphogenic processes with therapeutic potential in regenerating damaged SGs. The proposed project, supported by the Icahn School of Medicine at Mount Sinai, will provide me rigorous training in in vivo transgenics, embryonic tissue preparation, high-resolution imaging, epithelial explant culture, and bulk/single-cell transcriptomics, thereby preparing me for a future career as an independent researcher studying developmental and stem cell biology.