Functional characteristics of neonatal rat ß cells with distinct markers.

Neonatal ß cells are considered developmentally immature and hence less glucose responsive. To study the acquisition of mature glucose responsiveness, we compared glucose-regulated redox state, insulin synthesis, and secretion of ß cells purified from neonatal or 10-week-old rats with their transcriptomes and proteomes measured by oligonucleotide and LC-MS/MS profiling. Lower glucose responsiveness of neonatal ß cells was explained by two distinct properties: higher activity at low glucose and lower activity at high glucose. Basal hyperactivity was associated with higher NAD(P)H, a higher fraction of neonatal ß cells actively incorporating (3)H-tyrosine, and persistently increased insulin secretion below 5 mM glucose. Neonatal ß cells lacked the steep glucose-responsive NAD(P)H rise between 5 and 10 mM glucose characteristic for adult ß cells and accumulated less NAD(P)H at high glucose. They had twofold lower expression of malate/aspartate-NADH shuttle and most glycolytic enzymes. Genome-wide profiling situated neonatal ß cells at a developmental crossroad: they showed advanced endocrine differentiation when specifically analyzed for their mRNA/protein level of classical neuroendocrine markers. On the other hand, discrete neonatal ß cell subpopulations still expressed mRNAs/proteins typical for developing/proliferating tissues. One example, delta-like 1 homolog (DLK1) was used to investigate whether neonatal ß cells with basal hyperactivity corresponded to a more immature subset with high DLK1, but no association was found. In conclusion, the current study supports the importance of glycolytic NADH-shuttling in stimulus function coupling, presents basal hyperactivity as novel property of neonatal ß cells, and provides potential markers to recognize intercellular developmental differences in the endocrine pancreas.

Growth arrest specific protein (GAS) 6: a role in the regulation of proliferation and functional capacity of the perinatal rat beta cell.

AIMS/HYPOTHESIS: Maternal low-protein (LP) diet during gestation results in a reduced beta cell mass in the offspring at birth and this may hamper the ability to adapt to high-energy food and sedentary lifestyle later in life. To investigate the biology behind the LP-offspring phenotype, this study aimed to identify differentially expressed genes in the pancreas and their potential role in the fetal programming. METHODS: Wistar rats were given either an LP diet or normal-chow (NC) diet during gestation and differentially expressed genes in the offspring around the time of birth were identified using RNA microarray and quantitative PCR. The role of a differentially expressed gene, growth arrest specific protein 6 (GAS6), was evaluated in vitro using neonatal rat islets. RESULTS: The mRNA level of Gas6, known to be mitogenic in other tissues, was reduced in LP offspring. The mRNA content of Mafa was increased in LP offspring suggesting an early maturation of beta cells. When applied in vitro, GAS6 increased proliferation of neonatal pancreatic beta cells, while reducing glucose-stimulated insulin secretion without changing the total insulin content of the islets. In addition, GAS6 decreased the mRNA content of Mafa. CONCLUSIONS/INTERPRETATION: We propose a role for GAS6 in the regulation of pancreatic beta cells in the critical period around the time of birth. Our results support the hypothesis that the reduced beta cell mass seen in LP offspring is caused by a change in the intra-uterine environment that favours premature maturation of the beta cells.