Aim/hypothesis Neonatal beta cells lack glucose-stimulated insulin secretion and are thus functionally immature. We hypothesised that this lack of glucose responsiveness results from a generalised low expression of genes characteristic of mature functional beta cells. Important glucose-responsive transcription factors, Mafa and Pdx1, regulate genes involved in insulin synthesis and secretion, and have been implicated in late beta cell development. The aim of this study was to assess whether Mafa and/or Pdx1 regulates the postnatal functional maturation of beta cells. Methods By quantitative PCR we evaluated expression of these and other beta cell genes over the first month compared with adult. After infection with adenovirus expressing MAFA, Pdx1 or green fluorescent protein (Gfp), P2 rat islets were evaluated by RT-PCR and insulin secretion with static incubation and reverse haemolytic plaque assay (RHPA). Results At P2 most beta cell genes were expressed at about 10% of adult, but by P7 Pdx1 and Neurod1 no longer differ from adult; by contrast, Mafa expression remained significantly lower than adult through P21. Overexpression of Pdx1 increased Mafa, Neurod1, glucokinase (Gck) mRNA and insulin content but failed to enhance glucose responsiveness. Similar overexpression of MAFA resulted in increased Neurod1, Nkx6-1, Gck and Glp1r mRNAs and no change in insulin content but, importantly, acquisition of glucose-responsive insulin secretion. Both the percentage of secreting beta cells and the amount of insulin secreted per beta cell increased, approaching that of adult beta cells. Conclusions/interpretation In the process of functional maturation acquiring glucose-responsive insulin secretion, neonatal beta cells undergo a coordinated gene expression programme in which Mafa plays a crucial role.

Aims/hypothesis Fetal and neonatal beta cells have poor glucose-induced insulin secretion and only gain robust glucose responsiveness several weeks after birth. We hypothesise that this unresponsiveness is due to a generalised immaturity of the metabolic pathways normally found in beta cells rather than to a specific defect. Methods Using laser-capture microdissection we excised beta cell-enriched cores of pancreatic islets from day 1 (P1) neonatal and young adult Sprague-Dawley rats in order to compare their gene-expression profiles using Affymetrix U34A microarrays (neonatal, n=4; adult, n=3). Results Using dChip software for analysis, 217 probe sets for genes/38 expressed sequence tags (ESTs) were significantly higher and 345 probe sets for genes/33 ESTs significantly lower in beta cell-enriched cores of neonatal islets compared with those of adult islets. Among the genes lower in the neonatal beta cells were key metabolic genes including mitochondrial shuttles (malate dehydrogenase, glycerol-3-phosphate dehydrogenase and glutamate oxalacetate transaminase), pyruvate carboxylase and carnitine palmitoyl transferase 2. Differential expression of these enzyme genes was confirmed by quantitative PCR on RNA from isolated neonatal (P2 until P28) and adult islets and with immunostaining of pancreas. Even by 28 days of age some of these genes were still expressed at lower levels than in adults. Conclusions/interpretation The lack of glucose responsiveness in neonatal islets is likely to be due to a generalised immaturity of the metabolic specialisation of pancreatic beta cells.

Exendin-4 (Ex4), a 39-amino acid polypeptide secreted by the lizard Heloderma suspectrum, shares common bioactivity with the human incretin glucagon-like peptide-1 (GLP-1).1 Both Ex4 and GLP-1 bind to the GLP-1 receptor (GLP-1R) and potentiate the secretion of insulin from pancreatic β-cells.2,3 Because of its high binding affinity and extended in vivo half-life, Ex4 and its analogues have been a focus for the treatment of type2 diabetes.4−7The structure of Ex4 has been determined by both 1H NMR spectroscopy and X-ray crystallography.8,9 Because the solubility of Ex4 inH2Ois limited, its NMR spectra have been acquired in a 30% trifluoroethanol (TFE)/70% H2O mixture8 while the X-ray structure of a truncated Ex4 [Ex4(9−39)] has been determined in a GLP-1R-bound state.9 Ex4 displays significant helicity from residue 7 to 28 with greater fraying at the Nterminus and is stabilized by a Trp cage (TC) tertiary fold at the C-terminal part of the helix. The comparison of the NMR and X-ray structures reveals that the TFE/H2O medium can mimic the receptor bound state as the two types of Ex4 conformers superimpose well.The N-terminal segment of Ex4 is 82% homologous with human GLP-1(7−36); conserved residues include His1, Glu3, Thr5, and Phe6, all of which are crucial for receptor activation ( Figure 1).10−12 The affinity of Ex4 for the GLP-1 receptor's N-terminal domain (nGLP-1R) is governed by the central helical part of the molecule.13 Both hydrophobic and hydrophilic side chains are involved in the binding as revealed by the crystal structure of the complex [Protein Data Bank (PDB) entry 3C5T].9 The binding surface of Ex4 consists of Glu15, Val19, Arg20, Phe22, Ile23, Leu26, Lys27, and Ser32, whereas that of nGLP-1R involves Leu32, Thr35, Val36, Trp39, Tyr69, Tyr88, Leu89, Pro90, Trp91, Leu123, Glu127, and Glu128.9On the basis of recent structure−activity studies, it is known that all peptidic ligands targeting class B G-protein-coupled receptors (GPCRs) bind in a predominantly α-helical manner, and for most ligands, the α-helix forms upon binding of the extracellular N-terminal domain of the GPCR.15 These ligands, including glucagon,16 GLP-1,8,17 GLP-2,18 Ex4,8 glucose dependent insulinotropic polypeptide (GIP),19 pituitary adenylate cyclase activating polypeptide (PACAP),20 and corticotropin-releasing factor (CRF),21 show moderately ordered structure in aqueous solution but adopt a continuous or kinked α-helix in the presence of organic solvents (e.g., in a TFE/water mixed solvent) or in protein crystals. The major structural difference between Ex4 and GLP-1 is the continuity of the α-helix: Ex4 forms a single amphipathic α-helix both in the TFE/water mixed solvent and in the receptor-bound state, while GLP-1 is composed of two adjacent subhelices joined by the flexible Gly22. Binding studies demonstrated that the isolated N-terminal extracellular domain of GLP-1R has a low affinity for endogenous GLP-1 but a high affinity for Ex4.22 The superior affinity of Ex4 stems from the more favorable alignment of the oppositel...

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There has been great interest in the extent of β-cell regeneration after pancreatic duct ligation (PDL) and whether α- to β-cell conversion might account for β-cell regeneration after near-complete β-cell loss. To assess these questions, we established a PDL-model in adult male rats after almost complete beta-cell depletion achieved by giving a single high dose of streptozocin (STZ) in the fasted state. Because of the resultant severe diabetes, rats were given islet cell transplants to allow long-term follow-up. Although animals were followed up to 10 months, there was no meaningful β-cell regeneration, be it through replication, neogenesis, or α- to β-cell conversion. In contrast, the acinar cell compartment underwent massive changes with first severe acinar degeneration upon PDL injury followed by the appearance of pancreatic adipocytes, and finally near-complete reappearance of acini. We conclude that β-cells and acinar cells, although originating from the same precursors during development, have very distinct regenerative potentials in our PDL model in adult rats.

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Preeclampsia is a multifactorial disorder with genetic and environmental components. As Toll-like receptor 4 (TLR4) has an essential role in innate immune response, which is exaggeratedly activated in preeclampsia, our aim was to investigate whether two single nucleotide polymorphisms (SNPs) of the TLR4 gene-

Aims/hypothesis Reprogramming of pancreatic exocrine to insulin-producing cells by viral delivery of the genes encoding transcription factors neurogenin-3 (Ngn3), pancreas/duodenum homeobox protein 1 (Pdx1) and MafA is an efficient method for reversing diabetes in murine models. The variables that modulate reprogramming success are currently ill-defined. Methods Here, we assess the impact of glycaemia on in vivo reprogramming in a mouse model of streptozotocin-induced beta cell ablation, using subsequent islet transplantation or insulin pellet implantation for creation of groups with differing levels of glycaemia before viral delivery of transcription factors. Results We observed that hyperglycaemia significantly impaired reprogramming of exocrine to insulin-producing cells in their quantity, differentiation status and function. With hyperglycaemia, the reprogramming of acinar towards beta cells was less complete. Moreover, inflammatory tissue changes within the exocrine pancreas including macrophage accumulation were found, which may represent the tissue’s response to clear the pancreas from insufficiently reprogrammed cells. Conclusions/interpretation Our findings shed light on normoglycaemia as a prerequisite for optimal reprogramming success in a diabetes model, which might be important in other tissue engineering approaches and disease models, potentially facilitating their translational applications.