Metaplasia‐induced Epithelial Heterogeneity Directs Pancreatic Injury and Tumorigenesis

Abstract

Background and AimsDespite years of research, mechanisms of pancreatic injury and healing remain poorly understood. Acute pancreatitis is a painful and debilitating condition; chronic pancreatitis may be asymptomatic, but greatly enhances the risk of pancreatic ductal adenocarcinoma (PDAC). Acinar to ductal metaplasia (ADM), or the transdifferentiation of digestive enzyme producing acinar cells to ductal cells, is an early event in both conditions. While ADM is thought to function in healing and regeneration, it also represents a first step in tumorigenesis, demonstrating the duplicitous nature of this inherent plasticity. The goal of these studies was to define the populations arising in ADM, associated transcriptional changes, and their role in disease progression.MethodsAcinar cells were lineage traced to follow their fate upon injury. Transcripts of more than 13,000 EYFP+ cells were determined using single cell RNA sequencing (scRNA‐seq). Developmental trajectories were generated using several computational biology approaches that rely on non‐overlapping assumptions. Data were compared to scRNA‐seq studies of gastric metaplasia, oncogenic KrasG12D‐induced ADM, and human pancreatitis. Results were confirmed using immunostaining and electron microscopy. Tuft and enteroendocrine cell (EEC) populations were quantified throughout tumorigenesis. KrasG12D was expressed in injury‐induced ADM populations using several inducible Cre drivers.ResultsscRNA‐seq of ADM from chronically injured pancreata revealed emergence of a mucin/ductal population that resembles gastric pyloric metaplasia. Developmental trajectories suggest that some pyloric metaplasia cells generate tuft or EEC populations as distinct lineages. Comparison to KrasG12D‐induced ADM reveals populations associated with disease progression. Immunostaining demonstrates that tuft and EEC formation is an early event in tumorigenesis. Activation of KrasG12D in ADM populations results in neoplastic transformation and the formation of MUC5AC+ pit cells. Human pancreatitis samples reflect a pyloric metaplasia phenotype as well as the formation of tuft and EEC populations.ConclusionsADM under conditions of chronic injury results in the formation of a pyloric‐type metaplasia which seeds disparate tuft and EEC lineages. This carefully orchestrated plasticity generates myriad epithelial cell types which likely mitigate injury, providing protection from the formation of pancreatitis and PDAC. KrasG12D expression is sufficient to drive neoplasia when targeted to injury‐induced ADM populations offering an alternative origin for tumorigenesis. This program is conserved in human pancreatitis and provides insight into early events in pancreas diseases.