1733-P: Foxo3 and Heterogeneity of Dedifferentiating ß-Cells

Type 2 diabetes is associated with β-cell dedifferentiation. This process is linked to a loss of Foxo1 function and can be recapitulated by genetic inactivation of Foxo1. Notably, β-cell dedifferentiation is heterogeneous, with distinct cells in the same islet exhibiting different stages of dedifferentiation. To understand the heterogeneity of β-cell dedifferentiation, we purified islets from β-cell-specific Foxo1 knockout mice and separated them by flow cytometry using an insulin promoter (Rip-Cre)-driven Rosa26 tdTomato reporter to select β-cells. Surprisingly, tdTomato-positive (β-) cells partitioned into two distinct clusters based on signal intensity. Both clusters were Foxo1-deficient. The subpopulation characterized by low levels of tdTomato expression (T^low β-cells), increased from 2 to ~13% of the total β-cell population as animals aged from 3- to 24-months, and was absent in WT controls. Strikingly, this subpopulation was characterized by a compensatory increase of Foxo3 expression. To assess the function of T^low β-cells, we performed glucose-stimulated insulin secretion assays on sorted pseudo-islets. T^low β-cells exhibited enhanced glucose-dependent insulin secretion compared to Foxo1 knockout β-cells that failed to increase Foxo3 expression. Gene Ontology (GO) analyses of RNA-seq data revealed that the main difference between Foxo1 knockout cells without Foxo3 compensation and T^low β-cells was in the oxidative phosphorylation and ATP synthesis-coupled electron transport pathways. This study illuminates β-cell heterogeneity in diabetic islets and suggests a role of Foxo3 compensation in the heterogeneity of β-cell dedifferentiation and in age-dependent changes of β-cell function.