Hyperinsulinemia and insulin receptor signaling in pancreatic cancer development

Pancreatic ductal adenocarcinoma (PDAC) is the 3rd leading cause of cancer death in Canada and its incidence is increasing, largely driven by the expanding epidemics of PDAC risk factors including obesity and type 2 diabetes (T2D). Hyperinsulinemia is a cardinal feature of obesity and T2D, and is associated with increased PDAC incidence and mortality. Despite epidemiological data linking hyperinsulinemia to PDAC, there was no direct in vivo evidence of a causal role for endogenous insulin in any cancer type before this work. We studied how reduced insulin production or local insulin action affected the development of pancreatic intraepithelial neoplasia (PanIN) precursor lesions in Ptf1aCreER;KrasLSL-G12D mice. We first generated Ptf1aCreER;KrasLSL-G12D;Ins1+/+;Ins2-/- control and Ptf1aCreER;KrasLSL-G12D;Ins1+/-;Ins2-/- experimental mice. We found high fat diet (HFD)-induced hyperinsulinemia was modestly reduced in experimental mice without affecting glucose homeostasis. Genetically reduced insulin production resulted in ~50% suppression of PanIN. However, in this study, only female mice remained normoglycemic and only the gene dosage of rodent-specific Ins1 alleles was tested. Therefore, we then generated Ptf1aCreER;KrasLSL-G12D;Ins1-/-;Ins2+/+ control and Ptf1aCreER;KrasLSL-G12D;Ins1-/-;Ins2+/- experimental mice. Mice with reduced insulin production tended to develop fewer PanIN and acinar-to-ductal metaplasia (ADM) lesions. Using single-cell transcriptomics, we found hyperinsulinemia modulated pathways associated with protein translation, MAPK/ERK signaling and PI3K/AKT/mTOR signaling, which were changed in epithelial cells and subsets of immune cells. Finally, we examined whether hyperinsulinemia contributed to PDAC development directly through insulin receptor (INSR) signaling in KrasG12D carrying pancreatic acinar cells. We generated Ptf1aCreER;LSL-KrasG12D;nTnG mice with an Insrwt/wt, Insrwt/f, or Insrf/f genotype to reduce insulin receptor mRNA by 0%, 50%, or 100% in acinar cells. Loss of insulin receptors from acinar cells did not significantly influence body weight, fasting glucose, or insulin levels. Compared to mice with wild-type INSR expression in acinar cells, mice lacking INSR had a 2.7-fold and 5.3-fold significant reduction in PanIN plus tumor area in males and females, respectively. Collectively, these results indicate that hyperinsulinemia and INSR signaling in acinar cells are important for the early stages of pancreatic cancer. Insulin-lowering interventions such as lifestyle management and therapies targeting insulin receptor signaling may be beneficial in preventing and/or treating pancreatic cancer.Science, Faculty ofGraduat