DNA Methylation-Dependent Restriction of Tyrosine Hydroxylase Contributes to Pancreatic -Cell Heterogeneity

The molecular and functional heterogeneity of pancreatic beta-cells is well recognized, but the underlying mechanisms remain unclear. Pancreatic islets harbor a subset of beta-cells that co-express tyrosine hydroxylase (TH), an enzyme involved in synthesis of catecholamines that repress insulin secretion. Restriction of the TH+ beta-cells within islets is essential for appropriate function in mice, such that a higher proportion of these cells corresponds to reduced insulin secretion. Here, we use these cells as a model to dissect the developmental control of beta-cell heterogeneity. We define the specific molecular and metabolic characteristics of TH+ beta-cells and show differences in their developmental restriction in mice and humans. We show that TH expression in beta-cells is restricted by DNA methylation during beta-cell differentiation. Ablation of de novo DNA methyltransferase Dnmt3a in the embryonic progenitors results in a dramatic increase in the proportion of TH+ beta-cells, whereas beta-cell-specific ablation of Dnmt3a does not. We demonstrate that maintenance of Th promoter methylation is essential for its continued restriction in postnatal beta-cells. Loss of Th promoter methylation in response to chronic overnutrition increases the number of TH+ beta-cells, corresponding to impaired beta-cell function. These results reveal a regulatory role of DNA methylation in determining beta-cell heterogeneity.