MafB Is Critical for Glucagon Production and Secretion in Mouse Pancreatic α Cells
                    In Vivo

ABSTRACT The MafB transcription factor is expressed in pancreatic α and β cells during development but becomes exclusive to α cells in adult rodents. Mafb -null ( Mafb −/− ) mice were reported to have reduced α- and β-cell numbers throughout embryonic development. To further analyze the postnatal function of MafB in the pancreas, we generated endocrine cell-specific ( Mafb Δ Endo ) and tamoxifen-dependent ( Mafb Δ TAM ) Mafb knockout mice. Mafb Δ Endo mice exhibited reduced populations of insulin-positive (insulin + ) and glucagon + cells at postnatal day 0, but the insulin + cell population recovered by 8 weeks of age. In contrast, the Arx + glucagon + cell fraction and glucagon expression remained decreased even in adulthood. Mafb Δ TAM mice, with Mafb deleted after pancreas maturation, also demonstrated diminished glucagon + cells and glucagon content without affecting β cells. A decreased Arx + glucagon + cell population in Mafb Δ Endo mice was compensated for by an increased Arx + pancreatic polypeptide + cell population. Furthermore, gene expression analyses from both Mafb Δ Endo and Mafb Δ TAM islets revealed that MafB is a key regulator of glucagon expression in α cells. Finally, both mutants failed to respond to arginine, likely due to impaired arginine transporter gene expression and glucagon production ability. Taken together, our findings reveal that MafB is critical for the functional maintenance of mouse α cells in vivo , including glucagon production and secretion, as well as in development.

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The pancreatic islet β-cell-enriched transcription factor Pdx-1 regulates Slc30a8 gene transcription through an intronic enhancer

Biochemical Journal ◽

10.1042/bj20101488 ◽

2010 ◽

Vol 433 (1) ◽

pp. 95-105 ◽

Cited By ~ 19

Author(s):

Lynley D. Pound ◽

Yan Hang ◽

Suparna A. Sarkar ◽

Yingda Wang ◽

Laurel A. Milam ◽

...

Keyword(s):

Gene Expression ◽

Transcription Factor ◽

Pancreatic Islet ◽

Fusion Gene ◽

Association Studies ◽

Genome Wide Association Studies ◽

Β Cells ◽

Β Cell ◽

Specific Expression

The SLC30A8 gene encodes the zinc transporter ZnT-8, which provides zinc for insulin-hexamer formation. Genome-wide association studies have shown that a polymorphic variant in SLC30A8 is associated with altered susceptibility to Type 2 diabetes and we recently reported that glucose-stimulated insulin secretion is decreased in islets isolated from Slc30a8-knockout mice. The present study examines the molecular basis for the islet-specific expression of Slc30a8. VISTA analyses identified two conserved regions in Slc30a8 introns 2 and 3, designated enhancers A and B respectively. Transfection experiments demonstrated that enhancer B confers elevated fusion gene expression in both βTC-3 cells and αTC-6 cells. In contrast, enhancer A confers elevated fusion gene expression selectively in βTC-3 and not αTC-6 cells. These data suggest that enhancer A is an islet β-cell-specific enhancer and that the mechanisms controlling Slc30a8 expression in α- and β-cells are overlapping, but distinct. Gel retardation and ChIP (chromatin immunoprecipitation) assays revealed that the islet-enriched transcription factor Pdx-1 binds enhancer A in vitro and in situ respectively. Mutation of two Pdx-1-binding sites in enhancer A markedly reduces fusion gene expression suggesting that this factor contributes to Slc30a8 expression in β-cells, a conclusion consistent with developmental studies showing that restriction of Pdx-1 to pancreatic islet β-cells correlates with the induction of Slc30a8 gene expression and ZnT-8 protein expression in vivo.

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The Many Lives of Myc in the Pancreatic β-Cell

Journal of Biological Chemistry ◽

10.1074/jbc.rev120.011149 ◽

2020 ◽

pp. jbc.REV120.011149

Author(s):

Carolina Rosselot ◽

Sharon Baumel-Alterzon ◽

Yansui Li ◽

Gabriel Brill ◽

Luca Lambertini ◽

...

Keyword(s):

Cell Death ◽

Transcription Factor ◽

Therapeutic Potential ◽

Ex Vivo ◽

Diabetic Patients ◽

Cell Regeneration ◽

Diabetes Research ◽

Β Cells ◽

Β Cell

Diabetes results from insufficient numbers of functional pancreatic β-cells. Thus, increasing the number of available functional β-cells ex vivo for transplantation, or regenerating them in situ in diabetic patients, is a major focus of diabetes research. The transcription factor, Myc, discovered decades ago, lies at the nexus of most, if not all, known proliferative pathways. Based on this, many studies in the 1990’s and early 2000’s explored the potential of harnessing Myc expression to expand β-cells for diabetes treatment. Nearly all these studies in β-cells used pathophysiological or supraphysiological levels of Myc and reported enhanced β-cell death, de-differentiation or the formation of insulinomas if co-overexpressed with Bcl-xL, an inhibitor of apoptosis. This obviously reduced the enthusiasm for Myc as a therapeutic target for β-cell regeneration. However, recent studies indicate that “gentle” induction of Myc expression enhances β-cell replication without induction of cell death or loss of insulin secretion, suggesting that appropriate levels of Myc could have therapeutic potential for β-cell regeneration. Furthermore, although it has been known for decades that Myc is induced by glucose in β-cells very little is known about how this essential anabolic transcription factor perceives and responds to nutrients and increased insulin demand in vivo. Here we summarize the previous and recent knowledge of Myc in the β-cell, its potential for β-cell regeneration and its physiological importance for neonatal and adaptive β-cell expansion.

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Naringin (4′,5,7-Trihydroxyflavanone 7-Rhamnoglucoside) Attenuates β-Cell Dysfunction in Diabetic Rats through Upregulation of PDX-1

Cells Tissues Organs ◽

10.1159/000496506 ◽

2018 ◽

Vol 206 (3) ◽

pp. 133-143 ◽

Cited By ~ 2

Author(s):

Manickam Subramanian ◽

Balaji Thotakura ◽

Swathi Priyadarshini Chandra Sekaran ◽

Ashok kumar Jyothi ◽

Indumathi Sundaramurthi

Keyword(s):

Gene Expression ◽

Transcription Factor ◽

Insulin Secretion ◽

Protein Expression ◽

Serum Insulin ◽

Diabetic Rats ◽

Insulin Gene ◽

Β Cells ◽

Β Cell ◽

Insulin Gene Expression

Background: Pancreatic duodenal homeobox-1 (PDX-1) is a key transcription factor which regulates Insulin gene expression and insulin secretion in adult β-cells and helps to maintain β-cells mass. Naringin, a flavanone, owing to its antioxidant property, is reported to have antidiabetic effects. Objectives: The present study tries to evaluate the role of naringin on the β-cell-specific transcription factor PDX-1 in diabetic rats. Methods: Diabetes was induced in male rats using streptozotocin and treated with naringin (100 mg/kg) orally for 4 and 8 weeks. Serum insulin level, Pdx-1 and Insulin gene expression, and PDX-1 protein expression were assessed in the rat pancreas. Histopathological and ultrastructural changes in the islet and β-cells were observed. Results: Naringin prevented leukocytic infiltration in the pancreas of diabetic rats and recouped the β-cells with adequate secretory granules. Naringin-treated diabetic rats showed significantly increased mRNA expression of Pdx-1 and Insulin genes, increased expression of transcription factor PDX-1, and higher serum insulin levels than the diabetic control animals. These changes were more pronounced in the 8-week naringin-treated diabetic animals. Conclusions: Naringin was found to be an effective antidiabetic agent which increased Insulin gene expression and insulin secretion by upregulating the PDX-1 gene and protein expression.

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Exocrine pancreas proteases regulate β-cell proliferation in zebrafish ciliopathy models and in murine systems

Biology Open ◽

10.1242/bio.046839 ◽

2021 ◽

Vol 10 (6) ◽

Author(s):

Timothy L. Hostelley ◽

Jessica E. Nesmith ◽

Emily Larkin ◽

Amanda Jones ◽

Daniel Boyes ◽

...

Keyword(s):

Exocrine Pancreas ◽

Ex Vivo ◽

Cell Mass ◽

Transgenic Zebrafish ◽

Genetic Syndromes ◽

Β Cells ◽

Β Cell ◽

Cell Numbers ◽

Pancreatic Proteases

ABSTRACT Pancreatic β-cells are a critical cell type in the pathology of diabetes. Models of genetic syndromes featuring diabetes can provide novel mechanistic insights into regulation of β-cells in the context of disease. We previously examined β-cell mass in models of two ciliopathies, Alström Syndrome (AS) and Bardet-Biedl Syndrome (BBS), which are similar in the presence of metabolic phenotypes, including obesity, but exhibit strikingly different rates of diabetes. Zebrafish models of these disorders show deficient β-cells with diabetes in AS models and an increased β-cells absent diabetes in BBS models, indicating β-cell generation or maintenance that correlates with disease prevalence. Using transcriptome analyses, differential expression of several exocrine pancreas proteases with directionality that was consistent with β-cell numbers were identified. Based on these lines of evidence, we hypothesized that pancreatic proteases directly impact β-cells. In the present study, we examined this possibility and found that pancreatic protease genes contribute to proper maintenance of normal β-cell numbers, proliferation in larval zebrafish, and regulation of AS and BBS β-cell phenotypes. Our data suggest that these proteins can be taken up directly by cultured β-cells and ex vivo murine islets, inducing proliferation in both. Endogenous uptake of pancreatic proteases by β-cells was confirmed in vivo using transgenic zebrafish and in intact murine pancreata. Taken together, these findings support a novel proliferative signaling role for exocrine pancreas proteases through interaction with endocrine β-cells.

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Regulation of islet function and gene expression by prolactin during pregnancy

10.1101/830836 ◽

2019 ◽

Author(s):

Vipul Shrivastava ◽

Megan Lee ◽

Marle Pretorius ◽

Guneet Makkar ◽

Carol Huang

Keyword(s):

Gene Expression ◽

Insulin Secretion ◽

Serum Insulin ◽

Prolactin Receptor ◽

Cell Mass ◽

Insulin Level ◽

Β Cells ◽

Β Cell

AbstractPancreatic islets adapt to insulin resistance of pregnancy by up regulating β-cell proliferation and increase insulin secretion. Previously, we found that prolactin receptor (Prlr) signaling is important for this process, as heterozygous prolactin receptor-null (Prlr+/−) mice are glucose intolerant, had a lower number of β cells and lower serum insulin levels than wild type mice during pregnancy. However, since Prlr expression is ubiquitous, to determine its β-cell specific effects, we generated a transgenic mouse with a floxed Prlr allele under the control of an inducible promoter, allowing conditional deletion of Prlr from β cells in adult mice. In this study, we found that β-cell-specific Prlr reduction resulted in elevated blood glucose during pregnancy. Similar to our previous finding in mouse with global Prlr reduction, β-cell-specific Prlr loss led to a lower β-cell mass and a lower in vivo insulin level during pregnancy. However, these islets do not have an intrinsic insulin secretion defect when tested in vitro. Interestingly, when we compared the islet gene expression profile, using islets isolated from mice with global versus β-cell-specific Prlr reduction, we found some important differences in genes that regulate apoptosis and insulin secretion. This suggests that Prlr has both cell-autonomous and non-cell-autonomous effect on β cells, beyond its regulation of pro-proliferative genes.

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Beta cell adaptation to pregnancy requires prolactin action on both beta and non-beta cells

Scientific Reports ◽

10.1038/s41598-021-89745-9 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Vipul Shrivastava ◽

Megan Lee ◽

Daniel Lee ◽

Marle Pretorius ◽

Bethany Radford ◽

...

Keyword(s):

Gene Expression ◽

Insulin Secretion ◽

Transgenic Mouse ◽

Cell Mass ◽

Differentially Expressed Gene ◽

Specific Effect ◽

Β Cells ◽

Β Cell ◽

Prolactin Signaling

AbstractPancreatic islets adapt to insulin resistance of pregnancy by up regulating β-cell mass and increasing insulin secretion. Previously, using a transgenic mouse with global, heterozygous deletion of prolactin receptor (Prlr+/−), we found Prlr signaling is important for this adaptation. However, since Prlr is expressed in tissues outside of islets as well as within islets and prolactin signaling affects β-cell development, to understand β-cell-specific effect of prolactin signaling in pregnancy, we generated a transgenic mouse with an inducible conditional deletion of Prlr from β-cells. Here, we found that β-cell-specific Prlr reduction in adult mice led to elevated blood glucose, lowed β-cell mass and blunted in vivo glucose-stimulated insulin secretion during pregnancy. When we compared gene expression profile of islets from transgenic mice with global (Prlr+/−) versus β-cell-specific Prlr reduction (βPrlR+/−), we found 95 differentially expressed gene, most of them down regulated in the Prlr+/− mice in comparison to the βPrlR+/− mice, and many of these genes regulate apoptosis, synaptic vesicle function and neuronal development. Importantly, we found that islets from pregnant Prlr+/− mice are more vulnerable to glucolipotoxicity-induced apoptosis than islets from pregnant βPrlR+/− mice. These observations suggest that down regulation of prolactin action during pregnancy in non-β-cells secondarily and negatively affect β-cell gene expression, and increased β-cell susceptibility to external insults.

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Subnuclear compartmentalization of sequence-specific transcription factors and regulation of eukaryotic gene expression

Biochemistry and Cell Biology ◽

10.1139/o05-062 ◽

2005 ◽

Vol 83 (4) ◽

pp. 535-547 ◽

Cited By ~ 7

Author(s):

Gareth N Corry ◽

D Alan Underhill

Keyword(s):

Gene Expression ◽

Transcription Factor ◽

Transcription Factors ◽

Transcriptional Activation ◽

Current Knowledge ◽

Nuclear Architecture ◽

Subnuclear Localization ◽

Modular Structures

To date, the majority of the research regarding eukaryotic transcription factors has focused on characterizing their function primarily through in vitro methods. These studies have revealed that transcription factors are essentially modular structures, containing separate regions that participate in such activities as DNA binding, protein–protein interaction, and transcriptional activation or repression. To fully comprehend the behavior of a given transcription factor, however, these domains must be analyzed in the context of the entire protein, and in certain cases the context of a multiprotein complex. Furthermore, it must be appreciated that transcription factors function in the nucleus, where they must contend with a variety of factors, including the nuclear architecture, chromatin domains, chromosome territories, and cell-cycle-associated processes. Recent examinations of transcription factors in the nucleus have clarified the behavior of these proteins in vivo and have increased our understanding of how gene expression is regulated in eukaryotes. Here, we review the current knowledge regarding sequence-specific transcription factor compartmentalization within the nucleus and discuss its impact on the regulation of such processes as activation or repression of gene expression and interaction with coregulatory factors.Key words: transcription, subnuclear localization, chromatin, gene expression, nuclear architecture.

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Pericytes contribute to the islet basement membranes to promote beta-cell gene expression

Scientific Reports ◽

10.1038/s41598-021-81774-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Lina Sakhneny ◽

Alona Epshtein ◽

Limor Landsman

Keyword(s):

Gene Expression ◽

Cell Function ◽

Basement Membranes ◽

Cell Physiology ◽

Β Cells ◽

Β Cell ◽

Cell Clustering ◽

Β Cell Function ◽

Cell Gene Expression ◽

Glucose Stimulated Insulin Secretion

Abstractβ-Cells depend on the islet basement membrane (BM). While some islet BM components are produced by endothelial cells (ECs), the source of others remains unknown. Pancreatic pericytes directly support β-cells through mostly unidentified secreted factors. Thus, we hypothesized that pericytes regulate β-cells through the production of BM components. Here, we show that pericytes produce multiple components of the mouse pancreatic and islet interstitial and BM matrices. Several of the pericyte-produced ECM components were previously implicated in β-cell physiology, including collagen IV, laminins, proteoglycans, fibronectin, nidogen, and hyaluronan. Compared to ECs, pancreatic pericytes produce significantly higher levels of α2 and α4 laminin chains, which constitute the peri-islet and vascular BM. We further found that the pericytic laminin isoforms differentially regulate mouse β-cells. Whereas α2 laminins promoted islet cell clustering, they did not affect gene expression. In contrast, culturing on Laminin-421 induced the expression of β-cell genes, including Ins1, MafA, and Glut2, and significantly improved glucose-stimulated insulin secretion. Thus, alongside ECs, pericytes are a significant source of the islet BM, which is essential for proper β-cell function.

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NEUROD1 Is Required for the Early α and β Endocrine Differentiation in the Pancreas

International Journal of Molecular Sciences ◽

10.3390/ijms22136713 ◽

2021 ◽

Vol 22 (13) ◽

pp. 6713

Author(s):

Romana Bohuslavova ◽

Ondrej Smolik ◽

Jessica Malfatti ◽

Zuzana Berkova ◽

Zaneta Novakova ◽

...

Keyword(s):

Transcription Factor ◽

Cell Fate ◽

Cell Mass ◽

Neonatal Diabetes ◽

Diabetes Research ◽

Pancreas Development ◽

Β Cells ◽

Β Cell ◽

Pancreatic Islet Cell ◽

Endocrine Differentiation

Diabetes is a metabolic disease that involves the death or dysfunction of the insulin-secreting β cells in the pancreas. Consequently, most diabetes research is aimed at understanding the molecular and cellular bases of pancreatic development, islet formation, β-cell survival, and insulin secretion. Complex interactions of signaling pathways and transcription factor networks regulate the specification, growth, and differentiation of cell types in the developing pancreas. Many of the same regulators continue to modulate gene expression and cell fate of the adult pancreas. The transcription factor NEUROD1 is essential for the maturation of β cells and the expansion of the pancreatic islet cell mass. Mutations of the Neurod1 gene cause diabetes in humans and mice. However, the different aspects of the requirement of NEUROD1 for pancreas development are not fully understood. In this study, we investigated the role of NEUROD1 during the primary and secondary transitions of mouse pancreas development. We determined that the elimination of Neurod1 impairs the expression of key transcription factors for α- and β-cell differentiation, β-cell proliferation, insulin production, and islets of Langerhans formation. These findings demonstrate that the Neurod1 deletion altered the properties of α and β endocrine cells, resulting in severe neonatal diabetes, and thus, NEUROD1 is required for proper activation of the transcriptional network and differentiation of functional α and β cells.

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5-Bromoprotocatechualdehyde Combats against Palmitate Toxicity by Inhibiting Parkin Degradation and Reducing ROS-Induced Mitochondrial Damage in Pancreatic β-Cells

Antioxidants ◽

10.3390/antiox10020264 ◽

2021 ◽

Vol 10 (2) ◽

pp. 264

Author(s):

Seon-Heui Cha ◽

Chunying Zhang ◽

Soo-Jin Heo ◽

Hee-Sook Jun

Keyword(s):

Cell Loss ◽

Cellular Damage ◽

Mitochondrial Morphology ◽

Protective Effects ◽

Β Cells ◽

Β Cell ◽

Zebrafish Model ◽

Cell Dysfunction ◽

Glucose Stimulated Insulin Secretion

Pancreatic β-cell loss is critical in diabetes pathogenesis. Up to now, no effective treatment has become available for β-cell loss. A polyphenol recently isolated from Polysiphonia japonica, 5-Bromoprotocatechualdehyde (BPCA), is considered as a potential compound for the protection of β-cells. In this study, we examined palmitate (PA)-induced lipotoxicity in Ins-1 cells to test the protective effects of BPCA on insulin-secreting β-cells. Our results demonstrated that BPCA can protect β-cells from PA-induced lipotoxicity by reducing cellular damage, preventing reactive oxygen species (ROS) overproduction, and enhancing glucose-stimulated insulin secretion (GSIS). BPCA also improved mitochondrial morphology by preserving parkin protein expression. Moreover, BPCA exhibited a protective effect against PA-induced β-cell dysfunction in vivo in a zebrafish model. Our results provide strong evidence that BPCA could be a potential therapeutic agent for the management of diabetes.

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