scholarly journals Dynamic changes in β-cell electrical activity and [Ca2+] regulates NFATc3 activation and downstream gene transcription

2020 ◽  
Author(s):  
Jose G. Miranda ◽  
Wolfgang E Schleicher ◽  
David G. Ramirez ◽  
Samantha P Landgrave ◽  
Richard KP Benninger
Keyword(s):  
Electrical Activity ◽  
Gene Transcription ◽  
Cell Activity ◽  
Human Islets ◽  
Membrane Depolarization ◽  
Β Cell ◽  
Dynamic Changes ◽  
Type2 Diabetes ◽  
Nfat Activation ◽  
Elevated Glucose

AbstractDiabetes results from insufficient insulin secretion as a result of dysfunction to β-cells within the islet of Langerhans. Elevated glucose causes β-cell membrane depolarization and action potential generation, voltage gated Ca2+ channel activation and oscillations in free-Ca2+ activity ([Ca2+]), triggering insulin release. Nuclear Factor of Activated T-cell (NFAT) is a transcription factor that is regulated by increases in [Ca2+] and calceineurin (CaN) activation. NFAT regulation links cell activity with gene transcription in many systems, and within the β-cell regulates proliferation and insulin granule biogenesis. However the link between the regulation of β-cell electrical activity and oscillatory [Ca2+], with NFAT activation and downstream transcription is poorly understood. In this study we tested whether dynamic changes to β-cell electrical activity and [Ca2+] regulates NFAT activation and downstream transcription. In cell lines, mouse islets and human islets, including those from donors with type2 diabetes, we applied both agonists/antagonists of ion channels together with optogenetics to modulate β-cell electrical activity. Both glucose-induced membrane depolarization and optogenetic-stimulation triggered NFAT activation, and increased transcription of NFAT targets and intermediate early genes (IEGs). Importantly only conditions in which slow sustained [Ca2+] oscillations were generated led to NFAT activation and downstream transcription. In contrast in human islets from donors with type2 diabetes NFAT activation by glucose was diminished, but rescued upon pharmacological stimulation of electrical activity. Thus, we gain insight into the specific patterns of electrical activity that regulate NFAT activation and gene transcription and how this is disrupted in diabetes.

scholarly journals Dynamic changes in β-cell [Ca2+] regulates NFAT activation, gene transcription and islet gap junction communication

2021 ◽  
pp. 101430
Author(s):  
Jose G. Miranda ◽  
Wolfgang E. Schleicher ◽  
Kristen L. Wells ◽  
David G. Ramirez ◽  
Samantha P. Landgrave ◽  
...  
Keyword(s):  
Gap Junction ◽  
Gene Transcription ◽  
Β Cell ◽  
Dynamic Changes ◽  
Gap Junction Communication ◽  
Nfat Activation

Delayed-rectifier (KV2.1) regulation of pancreatic β-cell calcium responses to glucose: inhibitor specificity and modeling

2005 ◽  
Vol 289 (4) ◽  
pp. E578-E585 ◽  
Author(s):  
Natalia A. Tamarina ◽  
Andrey Kuznetsov ◽  
Leonid E. Fridlyand ◽  
Louis H. Philipson
Keyword(s):  
Plasma Membrane ◽  
Outward Current ◽  
Human Islets ◽  
Delayed Rectifier ◽  
Pancreatic Β Cell ◽  
Β Cells ◽  
Β Cell ◽  
Ionic Flux ◽  
Intracellular Ca ◽  
Elevated Glucose

The delayed-rectifier (voltage-activated) K+ conductance (KV) in pancreatic islet β-cells has been proposed to regulate plasma membrane repolarization during responses to glucose, thereby determining bursting and Ca2+ oscillations. Here, we verified the expression of KV2.1 channel protein in mouse and human islets of Langerhans. We then probed the function of KV2.1 channels in islet glucose responses by comparing the effect of hanatoxin (HaTx), a specific blocker of KV2.1 channels, with a nonspecific K+ channel blocker, tetraethylammonium (TEA). Application of HaTx (1 μM) blocked delayed-rectifier currents in mouse β-cells, resulting in a 40-mV rightward shift in threshold of activation of the voltage-dependent outward current. In the presence of HaTx, there was negligible voltage-activated outward current below 0 mV, suggesting that KV2.1 channels form the predominant part of this current in the physiologically relevant range. We then employed HaTx to study the role of KV2.1 in the β-cell Ca2+ responses to elevated glucose in comparison with TEA. Only HaTx was able to induce slow intracellular Ca2+ concentration ([Ca2+]i) oscillations in cells stimulated with 20 mM glucose, whereas TEA induced an immediate rise in [Ca2+]i followed by rapid oscillations. In human islets, HaTx acted in a similar fashion. The data were analyzed using a detailed mathematical model of ionic flux and Ca2+ regulation in β-cells. The results can be explained by a specific HaTx effect on the KV current, whereas TEA affects multiple K+ conductances. The results underscore the importance of KV2.1 channel in repolarization of the pancreatic β-cell plasma membrane and its role in regulating insulin secretion.

scholarly journals Processing of proglucagon to GLP-1 in pancreatic α-cells: is this a paracrine mechanism enabling GLP-1 to act on β-cells?

2011 ◽  
Vol 211 (1) ◽  
pp. 99-106 ◽  
Author(s):  
N M Whalley ◽  
L E Pritchard ◽  
D M Smith ◽  
A White
Keyword(s):  
Insulin Secretion ◽  
High Glucose ◽  
Culture Media ◽  
Cell Mass ◽  
Glucagon Secretion ◽  
Human Islets ◽  
Β Cell ◽  
Rat Islets ◽  
L Cells ◽  
Elevated Glucose

Proglucagon is cleaved to glucagon by prohormone convertase 2 (PC2) in pancreatic α-cells, but is cleaved to glucagon-like peptide-1 (GLP-1) by PC1 in intestinal L-cells. The aim of this study was to identify mechanisms which switch processing of proglucagon to generate GLP-1 in the pancreas, given that GLP-1 can increase insulin secretion and β-cell mass. The α-cell line, αTC1-6, expressed PC1 at low levels and GLP-1 was detected in cells and in culture media. GLP-1 was also found in isolated human islets and in rat islets cultured for 7 days. High glucose concentrations increasedPc1gene expression and PC1 protein in rat islets. High glucose (25 mM) also increased GLP-1 but decreased glucagon secretion from αTC1-6 cells suggesting a switch in processing to favour GLP-1. Three G protein-coupled receptors, GPR120, TGR5 and GPR119, implicated in the release of GLP-1 from L-cells are expressed in αTC1-6 cells. Incubation of these cells with an agonist of TGR5 increased PC1 promoter activity and GLP-1 secretion suggesting that this is a mechanism for switching processing to GLP-1 in the pancreas. Treatment of isolated rat islets with streptozotocin caused β-cell toxicity as evidenced by decreased glucose-stimulated insulin secretion. This increased GLP-1 but not glucagon in the islets. In summary, proglucagon can be processed to GLP-1 in pancreatic cells. This process is upregulated by elevated glucose, activation of TGR5 and β-cell destruction. Understanding this phenomenon may lead to advances in therapies to protect β-cell mass, and thereby slow progression from insulin resistance to type 2 diabetes.

scholarly journals PDX1LOW MAFALOW β-cells contribute to islet function and insulin release

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Daniela Nasteska ◽  
Nicholas H. F. Fine ◽  
Fiona B. Ashford ◽  
Federica Cuozzo ◽  
Katrina Viloria ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Metabolic Stress ◽  
Human Islets ◽  
Islet Function ◽  
Β Cells ◽  
Β Cell ◽  
Ionic Fluxes ◽  
Transcriptomic Level ◽  
Adult Islet

AbstractTranscriptionally mature and immature β-cells co-exist within the adult islet. How such diversity contributes to insulin release remains poorly understood. Here we show that subtle differences in β-cell maturity, defined using PDX1 and MAFA expression, contribute to islet operation. Functional mapping of rodent and human islets containing proportionally more PDX1HIGH and MAFAHIGH β-cells reveals defects in metabolism, ionic fluxes and insulin secretion. At the transcriptomic level, the presence of increased numbers of PDX1HIGH and MAFAHIGH β-cells leads to dysregulation of gene pathways involved in metabolic processes. Using a chemogenetic disruption strategy, differences in PDX1 and MAFA expression are shown to depend on islet Ca2+ signaling patterns. During metabolic stress, islet function can be restored by redressing the balance between PDX1 and MAFA levels across the β-cell population. Thus, preserving heterogeneity in PDX1 and MAFA expression, and more widely in β-cell maturity, might be important for the maintenance of islet function.

scholarly journals The Islet β Cell-enriched MafA Activator Is a Key Regulator of Insulin Gene Transcription

2005 ◽  
Vol 280 (12) ◽  
pp. 11887-11894 ◽  
Author(s):  
Li Zhao ◽  
Min Guo ◽  
Taka-aki Matsuoka ◽  
Derek K. Hagman ◽  
Susan D. Parazzoli ◽  
...  
Keyword(s):  
Gene Transcription ◽  
Insulin Gene ◽  
Β Cell ◽  
Insulin Gene Transcription

Differential activation of ER stress and apoptosis in response to chronically elevated free fatty acids in pancreatic β-cells

2008 ◽  
Vol 294 (3) ◽  
pp. E540-E550 ◽  
Author(s):  
Elida Lai ◽  
George Bikopoulos ◽  
Michael B. Wheeler ◽  
Maria Rozakis-Adcock ◽  
Allen Volchuk
Keyword(s):  
Er Stress ◽  
Cell Lines ◽  
Cell Apoptosis ◽  
Human Islets ◽  
Pancreatic Β Cell ◽  
Β Cell ◽  
Min6 Cells ◽  
Relative Contribution ◽  
Induced Apoptosis

Chronic exposure to elevated saturated free fatty acid (FFA) levels has been shown to induce endoplasmic reticulum (ER) stress that may contribute to promoting pancreatic β-cell apoptosis. Here, we compared the effects of FFAs on apoptosis and ER stress in human islets and two pancreatic β-cell lines, rat INS-1 and mouse MIN6 cells. Isolated human islets cultured in vitro underwent apoptosis, and markers of ER stress pathways were elevated by chronic palmitate exposure. Palmitate also induced apoptosis in MIN6 and INS-1 cells, although the former were more resistant to both apoptosis and ER stress. MIN6 cells were found to express significantly higher levels of ER chaperone proteins than INS-1 cells, which likely accounts for the ER stress resistance. We attempted to determine the relative contribution that ER stress plays in palmitate-induced β-cell apoptosis. Although overexpressing GRP78 in INS-1 cells partially reduced susceptibility to thapsigargin, this failed to reduce palmitate-induced ER stress or apoptosis. In INS-1 cells, palmitate induced apoptosis at concentrations that did not result in significant ER stress. Finally, MIN6 cells depleted of GRP78 were more susceptible to tunicamycin-induced apoptosis but not to palmitate-induced apoptosis compared with control cells. These results suggest that ER stress is likely not the main mechanism involved in palmitate-induced apoptosis in β-cell lines. Human islets and MIN6 cells were found to express high levels of stearoyl-CoA desaturase-1 compared with INS-1 cells, which may account for the decreased susceptibility of these cells to the cytotoxic effects of palmitate.

Effects of glucose and d-3-hydroxybutyrate on human pancreatic islet cell function

1985 ◽  
Vol 68 (5) ◽  
pp. 567-572 ◽  
Author(s):  
C. J. Rhodes ◽  
I. L. Campbell ◽  
T. M. Szopa ◽  
T. J. Biden ◽  
P. D. Reynolds ◽  
...  
Keyword(s):  
Insulin Release ◽  
Human Tissue ◽  
Islet Cell ◽  
Cell Function ◽  
Human Islets ◽  
Β Cell ◽  
Pancreatic Islet Cell ◽  
Sigmoidal Curve ◽  
Β Cell Function ◽  
Islet Cell Function

1. β-Cell function in human islets derived from a number of kidney donors was investigated by using various types of islet preparations. 2. With fresh islets, both insulin release and biosynthesis were increased by raising glucose concentrations, although the response was a variable one. 3. In fresh islets, the effects of 5 mmol of glucose/l on release were potentiated by 10 mmol of d-3-hydroxybutyrate/l. 4. Insulin release at 20 mmol of glucose/l was inhibited by adrenaline (0.1 mmol/l), and potentiated by theophylline (10 mmol/l) in the presence of 5 mmol of glucose/l, in islets cultured for 4 days. 5. After culture for 8 days, islets still showed an increase in insulin release and biosynthesis in response to glucose. 6. Pancreas slices derived from fresh human tissue also responded to increasing concentrations of glucose with a sigmoidal curve for insulin release.

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