1804-P: Beta-Cell Loss with Severe Hyperglycemia Is Responsible for Augmented Notch 1 Expression in the Pancreatic Exocrine Ductal Cells

Abstract

Introduction and Objective: Functional crosstalk between pancreatic islets and exocrine pancreatic tissue may be a determining factor in the progression of type 1 diabetes (T1D). Supporting this premise, we found that inhibition of serpinB13, an inhibitor of cathepsin L (catL) proteinase expressed in the exocrine pancreatic ductal cells, has positive outcomes in T1D. We also found that cleavage of Notch1 (a gatekeeper of β-cell development) following inhibition of serpinB13 with a monoclonal antibody (mAb), is a key molecular event that connects endocrine and exocrine tissue in the pancreas. Based on our observations, we hypothesized that the Notch1 receptor is expressed in the pancreatic ductal tree. Methods: To examine this, we induced β-cell-specific ablation with diphtheria toxin (DT) in InsCre/Rosa26iDTR transgenic mice, which were treated with a wild-type islet transplant or left untreated and sacrificed for pancreatic examination 2 weeks after diabetes induction. To assess Notch1 in the pancreas we used Western blot and IF microscopy with the Visiopharm software. Results: Both methods revealed that severe insulin-dependent diabetes results in marked augmentation of Notch1 expression (p<0.0001 and p=0.0054, respectively). The marked increase in the Notch1 protein level was specific, as expression of presenilins (which are required for processing of Notch1) was intact. We also found that islet transplantation preventing hyperglycemia in DT-treated animals completely blocked Notch1 upregulation. Finally, histological analysis revealed that Notch1 expression is confined to the cytokeratin-19+ epithelial cells in the exocrine ducts. Conclusion: We conclude that high Notch1 expression in the exocrine pancreas may explain its regulation by serpinB13. Moreover, our results demonstarte that hyperglycemia, rather than direct sensing of β-cell loss by the exocrine pancreas, is responsible for Notch upregulation in ductal epithelium. Disclosure Y. Kryvalap: None. R. Habte: None. S.Z. Meng: None. J. Czyzyk: None.