Abstract A005: Deciphering the Hierarchy of Notch Signaling in Pancreatic Ductal Adenocarcinoma

Abstract

Notch is a contact-dependent signaling pathway that plays critical roles in spatiotemporal patterning during embryogenesis. Beyond its role in development, Notch signaling regulates tissue patterning in adult organs in response to tissue injury or cancer. In the context of cancer, the role of Notch signaling has been extensively characterized in cancer cells, T cells, and endothelial cells. However, the role of Notch signaling in other cell types, such as fibroblasts and myeloid cells, in the pancreatic tumor microenvironment (TME) have remained understudied. Our previous work has implicated Notch signaling in the myeloid cells and fibroblasts of the pancreatic tumor TME. In our current work we used genetically engineered mouse models to inhibit canonical Notch activation in fibroblasts (Pdgfra CreERT2/+, LSL-DNMAML) and myeloid cells (LysM Cre/+, LSL-DNMAML) separately. In both an orthotopic and genetic model (Ptf1a FlpO/+;FSF-Kras G12D/+) of pancreatic cancer progression, inhibition of fibroblast-specific Notch activation had limited effects on disease progression and the transcriptional profile of the fibroblasts themselves. In contrast, inhibition of myeloid-specific Notch activation resulted in smaller orthotopic tumors and slowed progression in a genetic model of pancreatic neoplasia. These samples had reduced overall macrophage infiltration and a secondary alteration of the fibroblast phenotypes was also seen. Furthermore, co-culture of bone-marrow derived macrophages with ligand-expressing fibroblasts revealed Notch-dependent changes in chemokine production and expression of tumor-associated macrophage markers. Collectively, these results suggest that pancreatic cancer-associated fibroblasts have a primary role in providing Notch ligand (JAG1) to neighboring cells. In addition to fibroblasts, epithelial and endothelial cells express ligands that likely activate Notch signaling in the myeloid compartment—reprogramming myeloid cells, potentially regulating chemokine responses, and ultimately supporting disease progression. Future studies will further interrogate how myeloid-specific Notch activation promotes disease progression and affects Notch signaling activation in adjacent compartments.