Upregulated Matrisomal Proteins and Extracellular Matrix Mechanosignaling Underlie Obesity-Associated Promotion of Pancreatic Ductal Adenocarcinoma.

Simple Summary: Epidemiologic evidence and previous research have established obesity, diabetes and the metabolic syndrome as risk factors for pancreatic cancer in humans, while the precise mechanisms remain incompletely characterized. The concept that these metabolic diseases may be driven by diet implies that many cancers could be prevented or delayed through lifestyle modifications. By design, genetically engineered mouse models expressing oncogenic mutants of KRAS protein within the epithelial cells of the pancreas closely recapitulate the human disease. Research on diet-induced obesity in such mice implies the involvement of diverse factors including elevated insulin/insulin-like growth factors, inflammation, and genetic/epigenetic alterations and has revealed dramatic acceleration of cancer incidence that was more marked in males than females. The present research uses proteomic and phosphoproteomic analysis as a foundation to assess differentially expressed proteins and associated signal transduction pathways, yielding further novel mechanistic insights into the influence of tumor microenvironment on diet-induced obesity-associated pancreatic cancer. Diet-induced obesity (DIO) promotes pancreatic ductal adenocarcinoma (PDAC) in mice expressing KRasG12D in the pancreas (KC mice), but the precise mechanisms remain unclear. Here, we performed multiplex quantitative proteomic and phosphoproteomic analysis by liquid chromatography–tandem mass spectrometry and further bioinformatic and spatial analysis of pancreas tissues from control-fed versus DIO KC mice after 3, 6, and 9 months. Normal pancreatic parenchyma and associated proteins were steadily eliminated and the novel proteins, phosphoproteins, and signaling pathways associated with PDAC tumorigenesis increased until 6 months, when most males exhibited cancer, but females did not. Differentially expressed proteins and phosphoproteins induced by DIO revealed the crucial functional role of matrisomal proteins, which implies the roles of upstream regulation by TGFβ, extracellular matrix-receptor signaling to downstream PI3K-Akt-mTOR-, MAPK-, and Yap/Taz activation, and crucial effects in the tumor microenvironment such as metabolic alterations and signaling crosstalk between immune cells, cancer-associated fibroblasts (CAFs), and tumor cells. Staining tissues from KC mice localized the expression of several prognostic PDAC biomarkers and elucidated tumorigenic features, such as robust macrophage infiltration, acinar–ductal metaplasia, mucinous PanIN, distinct nonmucinous atypical flat lesions (AFLs) surrounded by smooth muscle actin-positive CAFs, invasive tumors with epithelial–mesenchymal transition arising close to AFLs, and expanding deserted areas by 9 months. We next used Nanostring GeoMX to characterize the early spatial distribution of specific immune cell subtypes in distinct normal, stromal, and PanIN areas. Taken together, these data richly contextualize DIO promotion of Kras-driven PDAC tumorigenesis and provide many novel insights into the signaling pathways and processes involved. [ABSTRACT FROM AUTHOR]