Whereas it is believed that the pancreatic duct contains endocrine precursors, the presence of insulin progenitor cells residing in islets remain controversial. We tested whether pancreatic islets of ...adult mice contain precursor β-cells that initiate insulin synthesis during aging and after islet injury. We used bigenic mice in which the activation of an inducible form of Cre recombinase by a one-time pulse of tamoxifen results in the permanent expression of a floxed human placental alkaline phosphatase (PLAP) gene in 30% of pancreatic β-cells. If islets contain PLAP− precursor cells that differentiate into β-cells (PLAP−IN+), a decrease in the percentage of PLAP+IN+ cells per total number of IN+ cells would occur. Conversely, if islets contain PLAP+IN− precursors that initiate synthesis of insulin, the percentage of PLAP+IN+ cells would increase. Confocal microscope analysis revealed that the percentage of PLAP+IN+ cells in islets increased from 30 to 45% at 6 months and to 60% at 12 months. The augmentation in the level of PLAP in islets with time was confirmed by real-time PCR. Our studies also demonstrate that the percentage of PLAP+IN+ cells in islets increased after islet injury and identified putative precursors in islets. We postulate that PLAP+IN− precursors differentiate into insulin-positive cells that participate in a slow renewal of the β-cell mass during aging and replenish β-cells eliminated by injury.
Cell lineage analysis reveals that progenitor cells in mouse islets generate new insulin cells in vivo during aging and following islet injury.
The XlHbox 8 homeodomain protein of Xenopus and STF-1, its mammalian homolog, are selectively expressed by beta cells of adult mouse pancreatic islets, where they are likely to regulate insulin ...expression. We sought to determine whether the expression of the homeobox protein/s during mouse embryonic development was specific to beta cells or, alternatively, whether XlHbox 8/STF-1 protein/s were initially expressed by multipotential precursors and only later became restricted to the insulin-containing cells. With two antibodies, we studied the localization of STF-1 during murine pancreatic development. In embryos, as in adults, STF-1 was expressed by most beta cells, by subsets of the other islet cell types and by mucosal epithelial cells of the duodenum. In addition, most epithelial cells of the pancreatic duct and exocrine cells of the pancreas transiently contained STF-1. We conclude that in mouse, STF-1 not only labels a domain of intestinal epithelial cells but also provides a spatial and temporal marker of endodermal commitment to a pancreatic and subsequently, to an endocrine beta cell fate. We propose a model of pancreatic cell development that suggests that exocrine and endocrine (alpha, beta, delta and PP) cells arise from a common precursor pool of STF-1+ cells and that progression towards a defined monospecific non-beta cell type is correlated with loss of STF-1 expression.
ABSTRACT
Whereas it is believed that the pancreatic duct contains endocrine precursors, the presence insulin progenitor cells residing in islets remain controversial. We tested whether pancreatic ...islets of adult mice contain precursor β-cells that initiate insulin synthesis during aging and after islet injury. We used bigenic mice in which the activation of an inducible form of cAMP response element recombinase by a one-time pulse of tamoxifen results in the permanent expression of a floxed human placental alkaline phosphatase (PLAP) gene in 30% of pancreatic β-cells. If islets contain PLAP− precursor cells that differentiate into β-cells (PLAP−IN+), a decrease in the percentage of PLAP+IN+ cells per total number of IN+ cells would occur. Conversely, if islets contain PLAP+IN− precursors that initiate synthesis of insulin, the percentage of PLAP+IN+ cells would increase. Confocal microscope analysis revealed that the percentage of PLAP+IN+ cells in islets increased from 30 to 45% at 6 months and to 60% at 12 months. The augmentation in the level of PLAP in islets with time was confirmed by real time-PCR. Our studies also demonstrate that the percentage of PLAP+IN+ cells in islets increased after islet injury and identified putative precursors in islets. We postulate that PLAP+IN− precursors differentiate into insulin-positive cells that participate in a slow renewal of the β-cell mass during aging and replenish β-cells eliminated by injury.
To date, the role of pancreatic hormones in pancreatic islet growth and differentiation is poorly understood. To address this issue, we examined mice with a disruption in the gene encoding prohormone ...convertase 2 (PC2). These mice are unable to process proglucagon, prosomatostatin, and other neuroendocrine precursors into mature hormones. Initiation of insulin (IN) expression during development was delayed in PC2 mutant mice. Cells containing IN were first detected in knockout embryos on d 15 of development, 5 d later than in wild-type littermates. However, the IN+ cells of d 15 PC2 mutant mice coexpressed glucagon, as did the first appearing β-cells of controls. In addition, lack of PC2 perturbed the pattern of expression of transcription factors presumed to be involved in the determination of the mature α-cell phenotype. Thus, in contrast to controls, α-cells of mutant mice had protracted expression of Nkx 6.1 and Pdx-1, but did not express Brn-4. Islets of adult mutant mice also contained cells coexpressing insulin and somatostatin, an immature cell type found only in islets of the wild-type strain during development. In addition to the effects on islet cell differentiation, the absence of PC2 activity resulted in a 3-fold increase in the rate of proliferation of proglucagon cells during the perinatal period. This increase contributed to the development of α-cell hyperplasia during postnatal life. Furthermore, the total β-cell volume was increased 2-fold in adult mutants compared with controls. This increase was due to islet neogenesis, as the number of islets per section was significantly higher in knockout mice compared with wild-type mice, whereas both strains had similar rates of IN cell proliferation. These results indicate that hormones processed by PC2 affected processes that regulate islet cell differentiation and maturation in embryos and adults.
A spaghetti calorimeter (SPACAL) prototype with scintillating crystal fibres was assembled and tested with electron beams of energy from 1 to 5 GeV. The prototype comprised radiation-hard ...Cerium-doped Gd3Al2Ga3O12 (GAGG:Ce) and Y3Al5O12 (YAG:Ce) embedded in a pure tungsten absorber. The energy resolution was studied as a function of the incidence angle of the beam and found to be of the order of 10%/E⊕1%, in line with the LHCb Shashlik technology. The time resolution was measured with metal channel dynode photomultipliers placed in contact with the fibres or coupled via a light guide, additionally testing an optical tape to glue the components. Time resolution of a few tens of picosecond was achieved for all the energies reaching down to (18.5 ± 0.2) ps at 5 GeV.
Previous studies have shown that new beta cells differentiate from intra-islet precursors in pancreatic islets of mice in which diabetes is induced by injecting a high dose of the beta-cell toxin ...streptozotocin. Moreover, the re-establishment of euglycaemia by insulin therapy 1 day after streptozotocin treatment improved the process of regeneration. We sought to assess whether a 1-week delay in the restoration of euglycaemia would affect beta-cell regeneration.
Adult CD-1 mice were injected with 200 mg/kg of streptozotocin. One group of mice remained hyperglycaemic throughout the experiment while a second group became normoglycaemic following the administration of insulin therapy 1 week after the injection of streptozotocin. Pancreata removed at different times after treatment were processed for visualization ofbeta precursor-cell markers and insulin by confocal microscopy.
New beta cells appeared in islets of streptozotocin-treated mice after restoration of normoglycaemia. Like islets of streptozotocin mice in which blood glucose concentrations were rapidly restored, islets of mice that became normoglycaemic 1 week after streptozotocin treatment also had two potential insulin precursor cell types. Protracted hyperglycaemia however, had several harmful effects on insulin cell neogenesis, such as a reduction in the number of euglycaemic mice with successful beta-cell regeneration and a decrease in the number and survival of the newly differentiated insulin-containing cells.
These results indicate that islets gradually lose their regenerative potential when they are exposed to high circulating glucose concentrations for an extended period of time.
We previously reported that new β cells differentiated in
pancreatic islets of mice in which diabetes was produced by injection
of a high dose of the β cell toxin streptozotocin (SZ), which
produces ...hyperglycemia due to rapid and massive β cell death. After
SZ-mediated elimination of existing β cells, a population of insulin
containing cells reappeared in islets. However, the number of new β
cells was small, and the animals remained severely hyperglycemic. In
the present study, we tested whether restoration of normoglycemia by
exogenous administered insulin would enhance β cell differentiation
and maturation. We found that β cell regeneration improved in
SZ-treated mice animals that rapidly attained normoglycemia following
insulin administration because the number of β cells per islet
reached near 40% of control values during the first week after
restoration of normoglycemia. Two presumptive precursor cell types
appeared in regenerating islets. One expressed the glucose
transporter-2 (Glut-2), and the other cell type coexpressed insulin and
somatostatin. These cells probably generated the monospecific cells
containing insulin that repopulated the islets. We conclude that β
cell neogenesis occurred in adult islets and that the outcome of this
process was regulated by the insulin-mediated normalization of
circulating blood glucose levels.
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