Abstract PO-051: The splanchnic mesenchyme during fetal development is the major source of pancreatic cancer associated fibroblasts

Abstract

Abstract In pancreatic ductal adenocarcinoma (PDAC), cancer associated fibroblasts (CAFs) play critical and complex roles in the tumor microenvironment. CAFs are also a major cell type in the desmoplastic stroma in PDAC and may account for half of the entire tumor tissue. Multiple subtypes of CAFs have been identified based on gene expressions, but the tissue origin(s) of CAF subtypes are unknown and genetic tools to robustly target them in vivo are lacking. Here we aimed to examine three potential tissue sources of CAFs: the pancreatic epithelium (through epithelium-to-mesenchyme transition), the bone marrow (through migration via the circulation), and the pancreatic mesenchyme or tissue resident fibroblasts (TRFs) in the normal pancreas (through proliferation). We utilized a genetically engineered mouse model of PDAC, where Kras and p53 mutations were engineered in the pancreatic epithelium using an Flp-Frt system. To determine whether the pancreatic epithelium gives rise to CAFs, we permanently labeled the pancreatic epithelium with a GFP reporter and traced their cell descendants by GFP expression. Despite robust GFP labeling of the epithelium, GFP expression was rarely identified in CAFs, suggesting little contribution of epithelium to the CAF pool. To determine whether the bone marrow gives rise to CAFs, we transplanted donor bone marrow carrying a ubiquitously expressed GFP reporter allele to GFP-negative recipient mice. We found that only a small proportion of pancreatic CAFs were tagged with GFP, suggesting a small proportion of CAFs have a bone marrow origin. Lastly, to determine whether the splanchnic mesenchyme during fetal development gives rise to CAFs, we used an inducible CreER-Loxp system to activate Tomato expression in the splanchnic mesenchyme during mid-gestation, and lineage traced their cell descendants. Tomato expression was identified in the majority of both pancreatic TRFs and CAFs, suggesting that they originate from the splanchnic mesenchyme. In summary, we found that TRFs are derived from the splanchnic mesenchyme during fetal development and they expand to contribute to the vast majority of CAFs in PDAC. The bone marrow contributes to a small proportion of CAFs, and the pancreatic epithelium contributes even less. This provides approaches to robustly target CAFs in vivo to further investigate their heterogeneity and function in PDAC. Citation Format: Lu Han, Yongxia Wu, Sean Sweeney, Ulyss Roesner, Khushbu Patel, Melodie Parrish, Xuezhong Yu, Cynthia Timmers, Michael Ostrowski, Gustavo Leone. The splanchnic mesenchyme during fetal development is the major source of pancreatic cancer associated fibroblasts [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-051.