2196-P: HB-EGF Signaling Is Required for Glucose-Induced Pancreatic ß-Cell Proliferation in Rats

Abstract

Background: Glucose is a major β-cell mitogen. Despite recent progress, the underlying mechanisms remain unclear. In a rat model of nutrient excess we previously showed that nutrient-induced β-cell proliferation is blocked when either EGF receptor (EGFR) or mTOR signaling is inhibited. Parallel transcriptomic analyses identified the EGFR ligand, HB-EGF as a potential mediator of nutrient-induced β-cell proliferation. Objective: To determine the role of HB-EGF in glucose-induced β-cell proliferation. Methods: HB-EGF mRNA levels were assessed by real-time PCR in isolated rat islets following a 24-h exposure to 2.8 or 16.7 mM glucose. The Carbohydrate-Responsive Element-Binding Protein (ChREBP) transcription factor was down-regulated by siRNA in dispersed rat islets. For β-cell proliferation studies islets were exposed to 16.7 mM glucose or HB-EGF (100 ng/ml) in the presence of 2.8 mM glucose for 72 h. Islets were co-cultured with the EGFR inhibitor AG1478 (300 nM) or the HB-EGF inhibitor CRM197 (10 ug/ml). shRNA was used to knockdown HB-EGF in isolated islets and either cultured ex vivo or transplanted under the kidney capsule of glucose-infused rats. β-cell proliferation was assessed by immunohistochemistry for Ki67 and insulin. Results: Glucose increased HB-EGF mRNA levels and this was prevented by ChREBP knockdown. HB-EGF potently stimulated β-cell proliferation. Inhibition of the EGFR or HB-EGF completely blocked not only the proliferative response to HB-EGF but also the response to 16.7 mM glucose. Knockdown of HB-EGF blocked the β-cell proliferative response to glucose in isolated rat islets as well as in transplanted islets. Conclusion: HB-EGF is a potent β-cell mitogen in rat islets. Glucose increases HB-EGF gene expression via ChREBP. The proliferative response to glucose requires an intact HB-EGF - EGFR pathway. Our findings identify a novel player in the complex mechanisms controlling β-cell proliferation in response to glucose. Disclosure H. Maachi: None. D. Scott: None. J. Ghislain: None. V. Poitout: None. Funding National Institutes of Health; Fonds de recherche du Québec-Santé