Genome-wide mRNA expression profiles of FACS-enriched rat beta cells freshly isolated from neonatal (postnatal day 2-3) and adult (10 weeks-old) Wistar rats

The lower glucose-responsiveness of neonatal beta cells is generally considered a sign of endocrine immaturity. We compared mRNA profiles of neonatal and 10-weeks old rat beta cells to see how their gene expression changes with functional maturation. Neonatal beta cells showed a lower glucose-inducible increment in insulin production than adult cells. This was in part explained by basal protein synthetic hyperactivity of neonatal cells: while at 2.5mM glucose 80% of neonatal beta cells were recruited into active protein synthesis, 10 mM glucose was required to achieve a similar fraction of active adult beta cells. Besides this progressive recruitment, glucose exerted in both age groups an additional amplifying effect in the recruited cells, but clearly more so in adult beta cells that showed a higher maximal synthetic capacity/cell. Neonatal beta cells balanced an advanced endocrine differentiation as judged by their mRNA expression of conserved beta cell marker genes, with higher expression of genes involved in cell cycle and development. One example, Delta-like 1 homolog (DLK1) was used to investigate if neonatal beta cells with basal hyperactivity corresponded to a more immature subset, as marked by high DLK1. Neonatal pancreas contained distinct subsets of DLK1high and DLK1low insulin-expressing cells, but both showed equal hyperactivity. We conclude that neonatal beta cells combine advanced endocrine maturation with traits of residual developmental immaturity. If DLK1 is used as marker for the latter, the basal hyperactivity which proved to be a cardinal feature of neonatal beta cells is not a direct reflection of their residual immaturity.

11

Martens GA, Motté E, Kramer G, Stangé G, Gaarn LW, Hellemans K, Nielsen JH, Aerts JM, Ling Z, Pipeleers D