Search

Abstract: Blood glucose regulation has likely evolved during early vertebrate evolution to allow and secure the concurrent evolution of complex brains and nervous systems: an inner milieu of constant blood glucose levels through millions of years has provided an extra degree of freedom for the brain to evolve without having to think of getting energy supply. Key regulators of blood glucose, insulin, and glucagon are produced by the dominating cell types of the pancreatic islet of Langerhans: the insulin producing beta cells and the glucagon producing alpha cells. Interestingly, it appears that the beta cell pioneered the formation or the foundation of the pancreatic organ according to current phylogenetic insights. Such phylogenetic aspects of a pancreatic stem cell are at the end discussed in relation to directed differentiation of embryonic stem cells/ES cells towards therapeutic beta cells. To cite this article: O.D. Madsen, C. R. Biologies 330 (2007). [Copyright &y& Elsevier]

Focuses on the possibility that islet and stem cell transplantation may one day be a viable treatment for diabetes. Obstacles to such techniques including a lack of donor organs and a lack of control over the side effects associated with immunosuppression; Different methods of treatment for diabetes; Outlook for technological breakthroughs.

The article examines the usage of embryonic stem cells as potential sources of pancreatic beta cells for the transplantation therapy involving diabetic patients. A five step medical protocol based on pancreatic development that converts embryonic stem cells into insulin producing cells is discussed. The article includes suggestions on improving the protocol to produce therapeutic beta cells that resemble human pancreatic beta cells.

It has been reported that endogenous retroviruses can contaminate human cell lines that have been passaged as xenotransplants in immunocompromised mice. We previously developed and described 2 human pancreatic β cell lines (EndoC-βH1 and EndoC-βH2) that were generated in this way. Here, we have shown that B10 xenotropic virus 1 (Bxv1), a xenotropic endogenous murine leukemia virus (MuLV), is present in these 2 recently described cell lines. We determined that Bxv1 was also present in SCID mice that were used for in vivo propagation of EndoC-βH1/2 cells, suggesting that contamination occurred during xenotransplantation. EndoC-βH1/2 cells released Bxv1 particles that propagated to human 293T and Mus dunni cells. Mobilization assays demonstrated that Bxv1 transcomplements defective MuLV-based retrovectors. In contrast, common rodent β cell lines, rat INS-1E and RIN-5F cells and mouse MIN6 and βTC3 cells, displayed either no or extremely weak xenotropic helper activity toward MuLV-based retrovectors, although xenotropic retrovirus sequences and transcripts were detected in both mouse cell lines. Bxv1 propagation from EndoC-βH1/2 to 293T cells occurred only under optimized conditions and was overall poorly efficient. Thus, although our data imply that MuLV-based retrovectors should be cautiously used in EndoC-βH1/2 cells, our results indicate that an involuntary propagation of Bxv1 from these cells can be easily avoided with good laboratory practices. [ABSTRACT FROM AUTHOR]

Insulin-like growth factor 2 (IGF2), produced and secreted by adult β-cells, functions as an autocrine activator of the β-cell insulin-like growth factor 1 receptor signaling pathway. Whether this autocrine activity of IGF2 plays a physiological role in β-cell and whole-body physiology is not known. Here, we studied mice with β-cell-specific inactivation of Igf2 (βIGF2KO mice) and assessed β-cell mass and function in aging, pregnancy, and acute induction of insulin resistance. We showed that glucose-stimulated insulin secretion (GSIS) was markedly reduced in old female βIGF2KO mice; glucose tolerance was, however, normal because of increased insulin sensitivity. While on a high-fat diet, both male and female βIGF2KO mice displayed lower GSIS compared with control mice, but reduced β-cell mass was observed only in female βIGF2KO mice. During pregnancy, there was no increase in β-cell proliferation and mass in βIGF2KO mice. Finally, β-cell mass expansion in response to acute induction of insulin resistance was lower in βIGF2KO mice than in control mice. Thus, the autocrine action of IGF2 regulates adult β-cell mass and function to preserve in vivo GSIS in aging and to adapt β-cell mass in response to metabolic stress, pregnancy hormones, and acute induction of insulin resistance. [ABSTRACT FROM AUTHOR]

Summary: We have previously reported that the loss of Arx and/or Pax4 gene activity leads to a shift in the fate of the different endocrine cell subtypes in the mouse pancreas, without affecting the total endocrine cell numbers. Here, we conditionally and ectopically express Pax4 using different cell-specific promoters and demonstrate that Pax4 forces endocrine precursor cells, as well as mature α cells, to adopt a β cell destiny. This results in a glucagon deficiency that provokes a compensatory and continuous glucagon+ cell neogenesis requiring the re-expression of the proendocrine gene Ngn3. However, the newly formed α cells fail to correct the hypoglucagonemia since they subsequently acquire a β cell phenotype upon Pax4 ectopic expression. Notably, this cycle of neogenesis and redifferentiation caused by ectopic expression of Pax4 in α cells is capable of restoring a functional β cell mass and curing diabetes in animals that have been chemically depleted of β cells. [ABSTRACT FROM AUTHOR]

Abstract: The Meriones Jirds belong to the genus of Gerbillinae (Rodentia: Muridae). We and others have previously reported the lack of the pancreatic β-cell transcription factor, Pdx-1 in the fat sand rat, Psammomys obesus. The aim of the study was to investigate the expression and localization of Pdx-1 in phylogenetically related members of the Gerbillinae subfamily. In addition, we characterized by IHC the expression pattern of islet hormones and additional important pancreatic transcription factors in order to evaluate overall endocrine pancreas appearance. PCR showed that Pdx-1 was easily amplified from a wide range of phylogenetically distant species but not from 13 different gerbilline species. Identical to P. obesus the important β-cell transcription factor Pdx-1 was absent from all five jirds. However, expression of other critical islet transcription factors and islet hormones was generally normal. Insulin was localized in the center of the islets with glucagon, somatostatin and pancreatic polypeptide (PP) found in the islet mantle. PYY cells were also observed and colocalized with PP cells. The NKX family of transcription factors were localized to the same cell types as seen in other rodents. MafA was nuclear localized in some of the insulin immunoreactive but not in other cell types, while MafB was found not only in the glucagon cells but also in many of the insulin cells. In conclusion, Pdx-1 appears to be lacking in all gerbils and despite the lack of Pdx-1, the Meriones Jirds have islets that are morphologically similar to other rodents and express hormones and transcription factors in the expected pattern except for MafA and MafB. [Copyright &y& Elsevier]

Abstract: Recently, the expression of the peptide hormone ghrelin was detected in α-cells of the islets of Langerhans as well as in ε-cells, a newly discovered endocrine cell type, but it remains unclear how the latter is related in lineage to the four classical islet cell types, α-, β-, δ-, and PP-cells. Here, we provide further evidence that ghrelin is predominantly produced in the α-cells of mouse islets but also in single hormone ghrelin-secreting ε-cells. We additionally demonstrate that pancreatic ε-cells derive from Neurogenin3-expressing precursor cells and their genesis depends on Neurogenin3 activity. Furthermore, our data indicate that the number of ghrelin-producing cells is differentially regulated during pancreas morphogenesis by the homeodomain-containing transcription factors Arx, Pax4, and Pax6. Arx mutants lack ghrelin+ glucagon+ α-cells whereas Pax4 mutants develop an excess of these cells. Importantly, the ghrelin+ glucagon− ε-cell population is not affected following Arx or Pax4 disruption. In contrast, the loss of Pax6 provokes an unexpected increase of the ghrelin+ glucagon− ε-cell number which is not due to increased proliferation. Thus, we demonstrate that the development of ghrelin-producing cells is differentially dependent on Neurogenin3 in different domains of the gastrointestinal tract and that, in the endocrine pancreas, ε-cell genesis does not require Arx or Pax4 activities but is antagonized by Pax6. [Copyright &y& Elsevier]

We tested the hypothesis that variants in the gene encoding the prepropeptide YY (PYY) associate with type 2 diabetes and/or obesity. Mutation analyses of DNA from 84 patients with obesity and familial type 2 diabetes identified two polymorphisms, IVS3 + 68C>T and Arg72Thr, and one rare variant, +151C>A of PYY. The common allele of the Arg72Thr variant associated with type 2 diabetes with an allele frequency of the Arg allele of 0.667 (95% CI 0.658-0.677) among 4,639 glucose-tolerant subjects and 0.692 (0.674-0.710) among 1,326 patients with type 2 diabetes (P = 0.005, odds ratio 1.19 [95% CI 1.05-1.35]). The same polymorphism associated with overweight (25 ≤ BMI < 30 kg/m²) (P = 0.018, 1.15 [1.02-1.28]). In quantitative trait analyses of a population-based sample of 6,022 subjects, the Arg allele was associated with an increased plasma glucose level 2 h after an oral glucose tolerance test (OGTT) (P = 0.03), an increased area under the curve for the post-OGTT plasma glucose level (P = 0.03), and a lower insulinogenic index (P = 0.01). In conclusion, the common Arg allele of the PYY Arg72Thr variant modestly associates with type 2 diabetes and with type 2 diabetes-related quantitative traits. [ABSTRACT FROM AUTHOR]

Brain 4 (Brn4/Pou3f4) and Pax6 are POU-homeodomain and paired-homeodomain transcription factors, respectively, that are expressed in the brain and the glucagon-expressing cells in the pancreas. Brn4 expression begins at embryonic day 10 in the pancreas, just before pax6 and both appear in the glucagon immunoreactive cells. At a later time point, E19, no Brn4 co-localization is observed with insulin or somatostatin but a rare pancreatic polypeptide (PP)-producing cell can be found, while Pax6 is found in all endocrine cells. These data suggest that brn4 is the only α-cell specific transcription factor yet identified; therefore, we sought to analyze α-cell development and function in mice with a targeted disruption of the brn4 gene. In homozygous brn4−/− mice, pancreatic bud formation, glucagon cell numbers and physiological measurements all appear normal. Examination of other transcription factors found in the glucagon cells showed normal Pax6 and Nkx2.2 immunoreactivity, suggesting that Brn4 does not regulate these transcription factors. Pax6 mutant mice (pax6Sey/Sey), with a natural inactivating mutation in pax6, have few endocrine cells but normal numbers of Brn4 and Nkx2.2 cells. The pancreatic phenotype of the pax6 mutants can be rescued with a YAC clone containing the human Pax6 gene. [Copyright &y& Elsevier]

Mice carrying loss-of-function mutations in certain Notch pathway genes display increased and accelerated pancreatic endocrine development, leading to depletion of precursor cells followed by pancreatic hypoplasia. Here, we have investigated the effect of expressing a constitutively active form of the Notch1 receptor (Notch1ICD) in the developing pancreas using the pdx1 promoter. At e10.5 to e12.5, we observe a disorganized pancreatic epithelium with reduced numbers of endocrine cells, confirming a repressive activity of Notch1 upon the early differentiation program. Subsequent branching morphogenesis is impaired and the pancreatic epithelium forms cyst-like structures with ductal phenotype containing a few endocrine cells but completely devoid of acinar cells. The endocrine cells that do form show abnormal expression of cell type-specific markers. Our observations show that sustained Notch1 signaling not only significantly represses endocrine development, but also fully prevents pancreatic exocrine development, suggesting that a possible role of Notch1 is to maintain the undifferentiated state of common pancreatic precursor cells. [Copyright &y& Elsevier]

Identifies a subset of the pancreatic duodenal homeobox factor-1 (PDX1) epithelial cells. Expression of neurogenin3 (Ngn3); Nature and identity of the pancreatic beta-cell precursor; Ngn3 cells as fulfilling the criteria for an endocrine precursor cell; Temporal sequence of gene activation and inactivation for developing alpha and beta cells.

Development of endocrine cells in the endoderm involves Atonal and Achaete/Scute-related basic helix-loop-helix (bHLH) proteins. These proteins also serve as neuronal determination and differentiation factors, and are antagonized by the Notch pathway partly acting through Hairy and Enhancer-of-split (HES)-type proteins. Here we show that mice deficient in Hes1 (encoding Hes-1) display severe pancreatic hypoplasia caused by depletion of pancreatic epithelial precursors due to accelerated differentiation of post-mitotic endocrine cells expressing glucagon. Moreover, upregulation of several bHLH components is associated with precocious and excessive differentiation of multiple endocrine cell types in the developing stomach and gut, showing that Hes-1 operates as a general negative regulator of endodermal endocrine differentiation. [ABSTRACT FROM AUTHOR]

Pancreatic beta-cells are more sensitive to several toxins (e.g., streptozotocin, alloxan, cytokines) than the other three endocrine cell types in the islets of Langerhans. Cytokine-induced free radicals in beta-cells may be involved in beta-cell-specific destruction in type 1 diabetes. To investigate if this sensitivity represents an acquired trait during beta-cell maturation, we used two in vitro cultured cell systems: 1) a pluripotent glucagon-positive pre-beta-cell phenotype (NHI-glu) that, after in vivo passage, matures into an insulin-producing beta-cell phenotype (NHI-ins) and 2) a glucagonoma cell-type (AN-glu) that, after stable transfection with pancreatic duodenal homeobox factor-1 (PDX-1), acquires the ability to produce insulin (AN-ins). After exposure to interleukin (IL)-1beta, both of the insulin-producing phenotypes were significantly more susceptible to toxic effects than their glucagon-producing counterparts. Nitric oxide (NO) production was induced in both NHI phenotypes, and inhibition with 0.5 mmol/l N(G)-monomethyl-L-arginine (NMMA) fully protected the cells. In addition, maturation into the NHI-ins phenotype was associated with an acquired dose-dependent sensitivity to the toxic effect of streptozotocin. Our results support the hypothesis that the exquisite sensitivity of beta-cells to IL-1beta and streptozotocin is an acquired trait during beta-cell maturation. These two cell systems will be useful tools for identification of molecular mechanisms involved in beta-cell maturation and sensitivity to toxins in relation to type 1 diabetes. [ABSTRACT FROM AUTHOR]

Reports on experiments which show that cocaine- and amphetamine-regulated transcript (CART), a brain-located peptide is a satiety factor and is closely associated with the actions of two important regulators of food intake, leptin and nueropeptide Y. Effects of CART, which was intracerebroventricularly injected into mice; Results; Methods.

Neurog3-induced Dll1 expression in pancreatic endocrine progenitors ostensibly activates Hes1 expression via Notch and thereby represses Neurog3 and endocrine differentiation in neighboring cells by lateral inhibition. Here we show in mouse that Dll1 and Hes1 expression deviate during regionalization of early endoderm, and later during early pancreas morphogenesis. At that time, Ptf1a activates Dll1 in multipotent pancreatic progenitor cells (MPCs), and Hes1 expression becomes Dll1 dependent over a brief time window. Moreover, Dll1, Hes1 and Dll1/Hes1 mutant phenotypes diverge during organ regionalization, become congruent at early bud stages, and then diverge again at late bud stages. Persistent pancreatic hypoplasia in Dll1 mutants after eliminating Neurog3 expression and endocrine development, together with reduced proliferation of MPCs in both Dll1 and Hes1 mutants, reveals that the hypoplasia is caused by a growth defect rather than by progenitor depletion. Unexpectedly, we find that Hes1 is required to sustain Ptf1a expression, and in turn Dll1 expression in early MPCs. Our results show that Ptf1a-induced Dll1 expression stimulates MPC proliferation and pancreatic growth by maintaining Hes1 expression and Ptf1a protein levels. [ABSTRACT FROM AUTHOR]