2059-P: Gene Repression during Maturation of Pancreatic ß-Cells Mirrors Those Upregulated in Islets of Diabetic db/db Mice

Pancreatic β-cells are specialized to properly regulate glucose metabolism. Loss of individual transcription factors that are critical for endocrine differentiation embryonically causes a deep loss of cell identity and upregulation of genes normally repressed in mature β-cells. We hypothesized that the factors important for maintenance of mature β-cell homeostasis are those that are lost in the identity loss or dedifferentiation. To identify genes critical for acquisition and loss of β-cell identity, we examined islets and β-cells by comprehensive gene expression analyses. Islets isolated from 8 wk (mature) and 4 wk (immature) old C57BL/6J mice were analyzed by microarray, and FACS-sorted mature β-cells (Mafa+7AAD-) and other islet cells including Mafa negative β-cells (Mafa-7AAD-) purified from Mafa reporter mice by RNAseq. We found that the maturation process involved genome-wide downregulated gene expression. Mature islets and Mafa+ β-cells had suppression of many genes including “β-cell disallowed genes” such as Igfbp4 and Nfib, but little to noupregulation of genes critical for β-cell function such as Ins1, Slc2a2, Ucn3 and Sytl4 from 4 wk to 8 wk. In contrast, most of the suppressed genes were significantly upregulated (by RNAseq) in islets from 21 wk old diabetic BKS-db/db mice compared with BKS-db/+ (misty). Comprehensive methylation screening (MeDIP-seq) of DNA from islets of 4 and 8 wk old C57BL/6J mice specifically identified highly methylated regulatory regions in some “repressed” genes in 8 wk old islets.

In conclusion, the gain of identity during maturation phase of β-cells mirrors that of the dedifferentiation during diabetes.