DNA methylation Dependent Restriction of Tyrosine Hydroxylase Contributes to Pancreatic β-cell Heterogeneity

The molecular and functional heterogeneity of pancreatic β -cells is well recognized. Pancreatic islets harbor a small subset of β -cells that co-express Tyrosine Hydroxylase (TH), an enzyme involved in synthesis of catecholamines that repress insulin secretion. Restriction of this sub-population within islets is essential for appropriate insulin secretion. However, the distinguishing characteristics of this subpopulation and the mechanisms that restrict TH expression in β -cells are not known. Here, we define the specific molecular and metabolic characteristics of the TH+ β -cells and show that TH expression in β -cells is restricted by DNA methylation patterning during β -cell lineage specification. Ablation of de novo DNA methyltransferase Dnmt3a in the pancreatic- and endocrine-progenitor lineages results in a dramatic increase in the proportion of TH+ β -cells, while β -cell specific ablation of Dnmt3a has no effect on this sub-population. We demonstrate that maintenance of Th promoter DNA methylation patterns is essential for its continued restriction in postnatal β -cells, and that loss of DNA methylation dysregulates TH expression in β -cells in response to chronic overnutrition, contributing to impairment of β -cell identity. These data highlight the essential requirement of DNA methylation patterning in regulating endocrine cell fates, and reveal a novel role of DNA methylation in β -cell heterogeneity.