Downregulation of EGF Receptor Signaling in Pancreatic Islets Causes Diabetes Due to Impaired Postnatal β-Cell Growth

Abstract

Epidermal growth factor receptor (EGF-R) signaling is essential for proper fetal development and growth of pancreatic islets, and there is also evidence for its involvement in beta-cell signal transduction in the adult. To study the functional roles of EGF-R in beta-cell physiology in postnatal life, we have generated transgenic mice that carry a mutated EGF-R under the pancreatic duodenal homeobox-1 promoter (E1-DN mice). The transgene was expressed in islet beta- and delta-cells but not in alpha-cells, as expected, and it resulted in an approximately 40% reduction in pancreatic EGF-R, extracellular signal-related kinase, and Akt phosphorylation. Homozygous E1-DN mice were overtly diabetic after the age of 2 weeks. The hyperglycemia was more pronounced in male than in female mice. The relative beta-cell surface area of E1-DN mice was highly reduced at the age of 2 months, while alpha-cell surface area was not changed. This defect was essentially postnatal, since the differences in beta-cell area of newborn mice were much smaller. An apparent explanation for this is impaired postnatal beta-cell proliferation; the normal surge of beta-cell proliferation during 2 weeks after birth was totally abolished in the transgenic mice. Heterozygous E1-DN mice were glucose intolerant in intraperitoneal glucose tests. This was associated with a reduced insulin response. However, downregulation of EGF-R signaling had no influence on the insulinotropic effect of glucagon-like peptide-1 analog exendin-4. In summary, our results show that even a modest attenuation of EGF-R signaling leads to a severe defect in postnatal growth of the beta-cells, which leads to the development of diabetes.