Role of hypoxia in fibroblast reprogramming in pancreatic cancer

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PROJECT SUMMARY Pancreatic ductal adenocarcinoma (PDAC) is a prevalent form of pancreatic cancer, accounting for about 90% of all cases of this disease. PDAC is highly fatal, where mortality closely parallels incidence, primarily due to the inability to diagnose PDAC at early stages and resistance to all existing treatments. Besides genetic changes in tumor cells, the tumor microenvironment plays a key role in tumor initiation, progression, and therapeutic resistance. PDAC is notable for its dense desmoplastic stroma, consisting of extracellular matrix, cancer- associated fibroblasts (CAFs), and immune cells. Another notable feature of the PDAC microenvironment is hypoxia, a condition of insufficient oxygen availability. Although hypoxia leads to adaptive responses in both cancer cells and stromal cells, the effects of hypoxia and hypoxia-inducible factor 1ɑ (HIF1ɑ), a master regulator of hypoxic adaptation, on the PDAC stroma and tumor-stroma interactions are not fully understood. We have recently found that inflammatory CAFs (iCAFs), a CAF subset producing high levels of inflammatory cytokines, are linked to the hypoxia-related gene signature and the HIF1 signaling pathway in human and mouse PDAC. By exposing 3D cocultures of pancreatic tumor cells and fibroblasts to either hypoxia or normoxia, we demonstrated that hypoxia promotes iCAF formation via IL1ɑ secreted from tumor cells. Importantly, the presence of hypoxic fibroblasts further elevated IL1ɑ levels in tumor cells, implicating hypoxia as a modulator of bidirectional interactions between tumor cells and fibroblasts. Based on these data, I hypothesize that hypoxia promotes iCAF formation by modulating bidirectional interactions between tumor cells and fibroblasts in PDAC. In Specific Aim 1, I will determine how hypoxia induces IL1ɑ expression in tumor cells via fibroblasts by using a three-dimensional (3D) coculture system of pancreatic tumor cells and fibroblasts and exposing the coculture to either hypoxia or normoxia. In Specific Aim 2, I will determine whether and how fibroblast HIF1ɑ regulates tumor cell-fibroblast interactions and pancreatic tumorigenesis by using 3D cocultures of tumor cells and fibroblasts deficient of HIF1ɑ, and using mouse models lacking fibroblast expression of HIF1ɑ. My work will identify the molecular mechanisms underlying hypoxic regulation of cancer cell-CAF crosstalk. In addition, my studies will determine how activation of HIF1ɑ within CAFs regulates the tumor stroma and PDAC progression, which will inform targeting fibroblast HIF1ɑ as a potential therapeutic avenue to treat PDAC patients.