UC Irvine

Type one diabetes is an autoimmune condition characterized by the loss of insulin producing beta cells of the pancreas. A loss of beta cells leads to a dysregulation in glucose homeostasis and results in prolonged hyperglycemia. If left untreated, numerous secondary complications can result such as neuropathy, nephropathy, retinopathy, limb amputation, and eventually death. Current treatments for type one diabetes rely on the administration of exogenous insulin or cell transplantation methods which have a variety of problems such as donor scarcity, a high cost, and requires immunosuppressants to be taken. Our lab is interested in inducing the body to produce its own beta cells endogenously via neogenesis. Since the mammalian pancreas is limited in its capacity to regenerate beta cells, zebrafish function as an excellent model to study neogenesis because they have a beta-cell progenitor called a centroacinar cell. Zebrafish centroacinar cells are like mammalian Ngn3+ progenitor cells of the developing pancreas. However, zebrafish centroacinar cells retain their progenitor capacity in adult fish. From mammalian models, centroacinar cells have also been suggested as a potential origin of pancreatic cancer. This is because centroacinar cells express similar pathways utilized by pancreatic cancer. These pathways are also conserved in zebrafish centroacinar cells. In this thesis, I am interested in further understanding the biology of centroacinar cells in order to elucidate (1) how zebrafish centroacinar cells can function as an in vivo model to better study the pathways involved in pancreatic cancer and (2) how the pathways utilized by zebrafish centroacinar cells allow them to behave as a beta-cell progenitor compared to mammalian centroacinar cells. In Chapter 1 I focused on the importance of the SOX9 pathway in pancreatic cancer and related this pathway back to zebrafish centroacinar cells. Previous work in our lab used RNA-seq and ChIP-seq in PANC-1 cells to identify the targets of SOX9. One of these targets was EPCAM. Using zebrafish, I demonstrated that epcam is expressed in centroacinar cells and is regulated by levels of sox9b. In Chapter 2 I focused on improving our lab’s nitroreductase/metronidazole transgenic zebrafish line to facilitate beta-cell regeneration. Using this line, I have shown that a lower dose of prodrug is required to ablate beta cells. As a result of this lower dose, it reduces the toxic side effects experienced by both larvae and adult fish. Unlike our old nitroreductase transgenic line, adult fish expressing this improved nitroreductase can achieve complete beta-cell loss by simply immersing them in prodrug. Additionally, my improved nitroreductase model can also be used to study chronic hyperglycemia which could not be done using our old nitroreductase model. In Chapter 3, I took advantage of using single-cell RNA sequencing to uncover centroacinar cell heterogeneity. Uncovering heterogeneity is important because it has allowed us to further uncover the role of centroacinar cells as a beta-cell progenitor but also as a potential origin for pancreatic cancer. From my genomics study, I have identified various subpopulations of centroacinar cells including a potential transitioning subpopulation of acinar cells toward a centroacinar cell fate, an immune-like cell population of centroacinar cells, and a potential endocrine precursor cell population. Additionally, I used both an in silico and in vivo approach to uncover new marker genes of centroacinar cells that may have an important role in their progenitor and cancerous behavior.