More than 30 million Americans have pre- or existing diabetes. An innovative approach to treat diabetes is to generate functional beta cells, which originate from a multipotent progenitor population in the early pancreas bud. This approach is currently in clinical trials, but a recognized problem is suboptimal progenitor generation. While mechanisms regulating later pancreas development have been well defined, how pancreas progenitor specification is regulated remains unclear. This proposal will examine genetic pathways downstream of the Hippo signaling pathway using transgenic mouse models, as well as tissue culture techniques that include organ explants and pancreatic organoids. Bioinformatic approaches will be used to (1) determine if Hippo signaling regulates pancreatic progenitor specification, morphogenesis, or cell differentiation, and (2) determine crosstalk mechanisms between Yap1/Taz and NF?B that regulate progenitor specification and beta cell differentiation in the pancreas. We have found that deleting the Lats kinases dysregulates epithelial cell proliferation, leading to aberrant morphogenesis and cell differentiation, supporting the idea that pancreatic morphogenesis is closely tied to cell differentiation. Using transcriptional profiling, we have found that Yap1/Taz promote NF?B activator genes and here we will define the mechanisms involved. In this proposal, we propose the unique idea that Hippo pathway components act as a rheostat to control levels of NF?B activity during this process, sculpting the epithelial niche that generates beta cells. This niche is a specialized and transient epithelial plexus at the core of the embryonic pancreas. We hypothesize that Lats1/2 activity is required homeostatically to inactivate Yap1/Taz and thereby suppress aberrant NF?B signaling in the normal pancreas. Elevated NF?B activity in pancreatic epithelium results in dysregulated EMT initiation and loss of ?-cell fate, due to disruption of the epithelial plexus niche. We hypothesize that elevated Yap1 activity stimulates NF?B signaling at least in part via the pantetheinase Vanin1 (Vnn1).
Our aims will use in vivo and in vitro models to investigate these observations. Our hypotheses will be tested via: 1) an examination of how loss of Lats1 and Lats2 affects epithelial integrity and initiation of epithelial-to-mesenchymal transitions (EMTs); 2) an examination of whether overexpression of Yap1 mimics the Lats1/2 double deletion (1/2DKO) in single or clusters of epithelial cells, as well as an assessment of downstream targets known to be affected in 1/2DKO; and 3) an evaluation of the role of the NFkB pathway in pancreatic epithelial homeostasis and an examination of the role of Vnn1 in this process. We hope this work will enhance translational impact of downstream targets in pancreas progenitors and beta cells, with the goal of therapeutic beta cell replacement and regeneration to treat diabetes.
Progenitor, or stem cells, that give rise to insulin-producing islet cells emerge from embryonic endodermal epithelium within the early pancreatic bud. This work focuses on the basic molecular mechanisms that shape the cellular microenvironment and 3D epithelial architecture where pancreatic endocrine cells are born, via regulation of intrinsic signaling pathways that control cell proliferation. We use mouse models and cultured cells to ablate critical regulators of epithelial development, as well as pharmacological approaches, to disrupt epithelial architecture of the pancreatic bud and to ask how cell fate is affected. Understanding these basic processes will lead to novel insights into regenerative and replacement therapies for diabetes mellitus.