Enhanced expression of PDX-1 and Ngn3 by exendin-4 during beta cell regeneration in STZ-treated mice

Progenitor cells exist in the adult pancreas and transform to endocrine cells in pathological conditions. To address the mechanism of beta cell regeneration, mice were treated with streptozotocin (STZ group) or streptozotocin and exendin-4 (STZ + Ex-4 group), and the expression of PDX-1, Ngn3, insulin, IRS-2, and Foxo1 was investigated. PDX-1 mRNA was upregulated biphasically and induction of Ngn3 mRNA occurred shortly after the first increase of PDX-1 expression, a pattern similar to that observed during embryogenesis. PDX-1-positive cells appeared only in islet-like cell clusters (ICCs) in STZ group, but they appeared both in ducts and ICCs in STZ + Ex-4 group. Ngn3-positive cells emerged in ICCs but not in ducts. Therefore, regeneration seemed to occur mainly from intra-islet stem/progenitor cells. Exendin-4 upregulated PDX-1 expression which paralleled increased IRS-2 expression and translocation of Foxo1 from nucleus to cytoplasm. Further analysis of beta cell regeneration should help in the design of novel therapy for diabetes.