329-LB: Exocrine Pancreas Proteases Are Drivers of ß-Cell Proliferation

The clinical link between loss of β-cell mass and diabetes susceptibility provides a promising avenue of research for novel therapeutics targeting the proliferative axis. To identify potential new pathways involved we utilized two zebrafish genetic models Alström Syndrome (AS) and Bardet-Biedl Syndrome (BBS) that exhibit strikingly different diabetes rates, ∼75% in AS and ∼4% in BBS. We have previously shown β-cell loss in AS and increase in BBS, corresponding to their diabetes rates. RNA-Sequencing of these models identified several exocrine pancreas proteases that were differentially expressed between AS and BBS. Thus, we hypothesized that the exocrine pancreas proteases affect endocrine pancreas function. To test our hypothesis, we overexpressed each enzyme in transgenic zebrafish embryos in which β-cells can be visualized. In control animals, overexpression of exocrine pancreas proteases significantly increased the β-cell number. Overexpression rescued the loss of β-cells observed in animals depleted of alms1. We found ctrb1 overexpression led to increased β-cell proliferation in transgenic larvae and rescued the AS model reduction in proliferation. To test for endogenous protease uptake, we generated a transgenic GFP-tagged CTRB1 and found that 10% of β-cells were GFP+, suggesting a direct interaction between the exocrine and endocrine pancreas. We also found that the inactive, zymogen, form of these enzymes are taken up by β-cells in vitro and induce proliferation in cultured MIN6 β-cells and freshly isolated ex vivo islet cultures, suggesting this effect is conserved in mammalian systems. These data support an important role for exocrine pancreatic enzymes in the modulation of β-cells in diabetes.