Conditional Tissue-Specific Foxa2 Ablation in Mouse Pancreas Causes Hyperinsulinemic Hypoglycemia

The forkhead/winged helix transcription factor Foxa2 is a major upstream regulator of Pdx1, a transcription factor necessary for pancreatic development. In the present study, we conditionally knocked out Foxa2 in Pdx1-expressing domain and further analyzed the contribution of Foxa2 to α- and β-cell development and the effect of Foxa2 deletion on plasma insulin, glucagon, and glucose levels. Homozygous pdx1 Foxa2 mice and heterozygous pdx1 Foxa2 mice were generated by homologous recombination using a Foxa2 gene-targeting vector. α- and β-cell mass was examined by immunofluorescence microscopy. Plasma glucose, insulin, and plasma were measured at postnatal day 10. For pdx1 lineage tracing studies, heterozygous pdx1 Foxa2 EYFP and homozygous pdx1 Foxa2 EYFP mice were used. Our immunofluorescence analysis revealed that in the pancreas sections of the homozygous mutant mice, Foxa2 was virtually absent from non-β cells and its expression almost exclusively coincided with remnant β cells. The density of both α and β cells apparently decreased in the pancreas of the heterozygous mutant mice and in the pancreas of the homozygous mutant mice, α cells lost its predominance and β cells increased proportionally. Direct Pdx1 cell lineage tracing revealed that, on embryonic day 18.5, in the homozygous mutant mice, Pdx1 expression coincided almost exclusively with that of insulin-secreting β cells. Chemiluminescence assays revealed that heterozygous pdx1 Foxa2 mice had significantly lower insulin levels than control mice (P < 0.01). However, no apparent difference was observed between homozygous pdx1 Foxa2 mice and control mice (P > 0.05). Chemiluminescence assays also showed that Foxa2 deletion significantly depressed plasma glucagon levels in both homozygous pdx1 Foxa2 mice and heterozygous pdx1 Foxa2 mice (P < 0.01 vs. controls). Plasma glucose on postnatal day 10 was significantly lower in homozygous pdx1 Foxa2 mice compared with control mice (P < 0.01). Our study demonstrates that homozygous Foxa2 ablation leads to an imbalance in β/α ratio, profound hypoglucagonemia, inappropriate hyperinsulinemia, and hypoglycemia in mice. Our conditional tissue-specific Foxa2 ablation mouse model will be useful in elucidating regulation of normal and abnormal α- and β-cell differentiation and pinpointing novel targets for diabetes control.