Role of the CX3CL1-CX3CR1 signaling axis in IPMN - SUMMARY Intraductal papillary mucinous neoplasm (IPMN) is one of the two most common precursor lesions leading to the development of pancreatic ductal adenocarcinoma (PDA). IPMNs comprise a heterogeneous group of tumors with a wide range of grades and histotypes, and the emergence of single-cell RNA sequencing (RNA- seq) and multiplex digital spatial profiling have characterized unique cell populations, including dysplastic epithelial and immune cells, within the heterogeneous tumor microenvironment that carry signature gene expressions, which could be used as markers for disease progression. However, further studies are needed to delineate the biological interaction between epithelial subtypes and immune cells that drive IPMN lesion development. Genetically engineered mouse models (GEMMs) for IPMN have been established using oncogenic mutations and disruption of tumor suppressors found in human IPMN samples. Analyses of these IPMN GEMMs have provided important mechanistic insight into the underlying progression of these precancerous lesions to invasive PDA. Our group has developed a novel KNGC model (KRasG12D, nuclear GSK-3β, PDX1-Cre) resulting in the development of IPMN through the retention of a ductal progenitor pool defined by being AGR2+/AQP5+/DBA-, which are also detected in the IPMN KGC (KRasG12D, GNASR201C, Cre) model and patient samples with IPMN. Additionally, KNGC animals show progressive desmoplasia beginning as early as 4 weeks of age with increased immune cell infiltration, which we hypothesize is due to the high expression of CX3CL1 (fractalkine), a chemokine involved in the recruitment of CX3CR1-expressing monocytes, which are known to promote fibrosis in various disease models upon differentiation into type 2 macrophages. Indeed, our preliminary data from CX3CR1 heterozygous (CX3CR1GFP/+) and homozygous (CX3CR1GFP/GFP) knockout in the KNGC model shows an enrichment of GFP signal in M2-like macrophages in the IPMN lesions of the KNGCXGFP/+ model, whereas KNGCXGFP/GFP animals had a paucity of M2-like macrophages, substantially reduced desmoplasia and impaired development of IPMN. It is our central hypothesis that the ductal expression of CX3CL1 results in the accumulation of M2-like macrophages, which facilitate the development and progression of IPMN in KNGC mice. We will address our hypothesis through the following specific aims: (1) Determine the role of CX3CL1 in promoting IPMN development and desmoplasia in KNGC mice, and (2) Determine the role of CX3CR1 in promoting immune suppressive environment in KNGC mice. Altogether, this project will provide a mechanistic understanding of the CX3CL1- CX3CR1 axis in the generation of an immune/stroma microenvironment facilitating IPMN development. The information obtained in pursuit of the aims might lead to the identification of novel biomarkers that could be used to monitor or treat patients with IPMN.
