Effect of forkhead box O1 (FOXO1) on beta cell development in the human fetal pancreas

Abstract

Aims/hypothesis Recent studies have demonstrated that in adult murine beta cells the forkhead box O1 (FOXO1) transcription factor regulates proliferation and stress resistance. However, the role of FOXO1 during pancreatic development remains largely unknown. The present study aimed to characterise the expression of the FOXO1 transcription factor in the early to mid-gestation human fetal pancreas and to understand its role in islet cell development. Methods Human (8-21 week fetal age) pancreases were examined using immunohistological, quantitative RT-PCR and western blotting. Isolated human (18-21 week) fetal islet epithelial cell clusters were treated with insulin or glucose, or transfected with FOXO1 small interfering RNA (siRNA). Results Nuclear and cytoplasmic FOXO1 were widely produced during human fetal endocrine pancreatic development, co-localising in cells with the transcription factors pancreatic and duodenal homeobox 1 (PDX-1) and neurogenin 3 (NGN3) as well as cytokeratin 19 (CK19), insulin and glucagon. Treatment with exogenous insulin (50 nmol/l) induced the nuclear exclusion of FOXO1 in both cytokeratin 19 (CK19) + (p<0.01) and insulin + cells (p<0.05) in parallel with increased phospho-Akt (p<0.05) production. siRNA knockdown of FOXO1 significantly increased the number of NGN3 + (p<0.01) and NK6 homeobox 1 (NKX6-1) + (p<0.05) cells in parallel with increases in insulin gene expression (p<0.03) and C-peptide + cells (p<0.05) and reduced levels of hairy and enhancer of split 1 (HES1) (p<0.01). Conclusions/interpretation Our results indicate that FOXO1 may negatively regulate beta cell differentiation in the human fetal pancreas by controlling critical transcription factors, including NGN3 and NKX6-1. These data suggest that the manipulation of FOXO1 levels may be a useful tool for improving cell-based strategies for the treatment of diabetes.Keywords Human fetal pancreas . Human islet epithelial cell clusters . Islet transcription factors . Nuclear FOXO1 . FOXO1 siRNA Electronic supplementary material The online version of this article

FoxO1 Protein Cooperates with ATF4 Protein in Osteoblasts to Control Glucose Homeostasis

“…In the pancreas FoxO1 negatively regulates expression of Pdx1, which regulates ␤-cell development and mass by competing with the transcription factor FoxA2 for binding to the Pdx1 promoter (24). This is one of the main effects that mediates the suppressive effect of pancreatic FoxO1 on ␤-cell differentiation (25). A similar functional and physical interaction of FoxO1 with Notch1 is described in myoblasts, which leads to corepressor clearance from the Notch effector Csl, leading to stabilization of a functional FoxO1-Notch1 complex (12).…”

Targeting Forkhead Box O1 from the Concept to Metabolic Diseases: Lessons from Mouse Models

“…Loss and gain of FOXO1 function has been investigated in the tissues and cells of various genetically modified mice, including hepatocytes (18,19,25,82), brain (95), muscle (20,45,55), adipose (17,88), pancreas (2,3,84), and heart (99) ( Table 1). …”

“…The development and proliferation of b-cells require multiple transcription factors-pancreatic and duodenal homeobox 1 (PDX1), neurogenin 3, and cytokeratin 19-that induce expression of insulin, islet amyloid polypeptide, and Glut2, but suppresses glucagon expression (1,3). In the human fetal pancreas FOXO1 has been found to negatively regulate b-cell differentiation by suppressing PDX1, neurogenin 3, and NKX61 (3).…”

“…Because these 2 forkhead transcription factors share common DNAbinding sites in the Pdx1 promoter, FOXO1 competes with FOXA2 for binding to Pdx1 promoter and inhibits PDX1 transcription (62). Moreover, nuclear translocation of FOXO1 is prone to exclude PDX1 from the nuclei, or vice versa (3,57,62). This serves as a second mechanism that FOXO1 inhibits bcell proliferation (Fig.…”

Peroxisome Proliferator-activated Receptor γ (PPARγ) and Its Target Genes Are Downstream Effectors of FoxO1 Protein in Islet β-Cells

“…FoxO1 is a member of the family of winged-helix/forkhead transcription factors that serve important roles in cellular differentiation, proliferation, apoptosis, and the response to cellular stress in many tissues. FoxO1 is highly expressed in ␤-cells and is a key regulator of ␤-cell development, mass, and function (13)(14)(15)(16). The best described FoxO1 target gene in ␤-cells is Pdx1 (17).…”