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Puginier E, Leal-Fischer K, Gaitan J, Lallouet M, Scotti PA, Raoux M, Lang J. Extracellular electrophysiology on clonal human β-cell spheroids. Front Endocrinol (Lausanne) 2024; 15:1402880. [PMID: 38883608 PMCID: PMC11176477 DOI: 10.3389/fendo.2024.1402880] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/18/2024] [Accepted: 05/06/2024] [Indexed: 06/18/2024] Open
Abstract
Background Pancreatic islets are important in nutrient homeostasis and improved cellular models of clonal origin may very useful especially in view of relatively scarce primary material. Close 3D contact and coupling between β-cells are a hallmark of physiological function improving signal/noise ratios. Extracellular electrophysiology using micro-electrode arrays (MEA) is technically far more accessible than single cell patch clamp, enables dynamic monitoring of electrical activity in 3D organoids and recorded multicellular slow potentials (SP) provide unbiased insight in cell-cell coupling. Objective We have therefore asked whether 3D spheroids enhance clonal β-cell function such as electrical activity and hormone secretion using human EndoC-βH1, EndoC-βH5 and rodent INS-1 832/13 cells. Methods Spheroids were formed either by hanging drop or proprietary devices. Extracellular electrophysiology was conducted using multi-electrode arrays with appropriate signal extraction and hormone secretion measured by ELISA. Results EndoC-βH1 spheroids exhibited increased signals in terms of SP frequency and especially amplitude as compared to monolayers and even single cell action potentials (AP) were quantifiable. Enhanced electrical signature in spheroids was accompanied by an increase in the glucose stimulated insulin secretion index. EndoC-βH5 monolayers and spheroids gave electrophysiological profiles similar to EndoC-βH1, except for a higher electrical activity at 3 mM glucose, and exhibited moreover a biphasic profile. Again, physiological concentrations of GLP-1 increased AP frequency. Spheroids also exhibited a higher secretion index. INS-1 cells did not form stable spheroids, but overexpression of connexin 36, required for cell-cell coupling, increased glucose responsiveness, dampened basal activity and consequently augmented the stimulation index. Conclusion In conclusion, spheroid formation enhances physiological function of the human clonal β-cell lines and these models may provide surrogates for primary islets in extracellular electrophysiology.
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Affiliation(s)
- Emilie Puginier
- Univiversity of Bordeaux, CNRS, Bordeaux INP, Laboratoire de Chimie et Biologie des Membranes CBMN, UMR 5248, Pessac, Bordeaux, France
| | - Karen Leal-Fischer
- Univiversity of Bordeaux, CNRS, Bordeaux INP, Laboratoire de Chimie et Biologie des Membranes CBMN, UMR 5248, Pessac, Bordeaux, France
| | - Julien Gaitan
- Univiversity of Bordeaux, CNRS, Bordeaux INP, Laboratoire de Chimie et Biologie des Membranes CBMN, UMR 5248, Pessac, Bordeaux, France
| | - Marie Lallouet
- Univiversity of Bordeaux, CNRS, Bordeaux INP, Laboratoire de Chimie et Biologie des Membranes CBMN, UMR 5248, Pessac, Bordeaux, France
| | - Pier-Arnaldo Scotti
- Univiversity of Bordeaux, CNRS, Bordeaux INP, Laboratoire de Chimie et Biologie des Membranes CBMN, UMR 5248, Pessac, Bordeaux, France
| | - Matthieu Raoux
- Univiversity of Bordeaux, CNRS, Bordeaux INP, Laboratoire de Chimie et Biologie des Membranes CBMN, UMR 5248, Pessac, Bordeaux, France
| | - Jochen Lang
- Univiversity of Bordeaux, CNRS, Bordeaux INP, Laboratoire de Chimie et Biologie des Membranes CBMN, UMR 5248, Pessac, Bordeaux, France
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Hali M, Wadzinski BE, Kowluru A. Alpha4 contributes to the dysfunction of the pancreatic beta cell under metabolic stress. Mol Cell Endocrinol 2022; 557:111754. [PMID: 35987388 PMCID: PMC9620510 DOI: 10.1016/j.mce.2022.111754] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Revised: 08/10/2022] [Accepted: 08/12/2022] [Indexed: 11/30/2022]
Abstract
The current study examined the roles of Alpha4, a non-canonical subunit of protein phosphatase 2A, in the regulation of acute (insulin secretion) and chronic (cell dysfunction) effects of glucose in pancreatic beta cells. Alpha4 is expressed in human islets, rat islets and INS-1832/13 cells. Incubation of INS-1832/13 cells and rat islets with high glucose (HG) significantly increased the expression of Alpha4. C2-Ceramide, a biologically active sphingolipid, also increased the expression of Alpha4 in INS-1832/13 cells and rat islets. Subcellular distribution studies of Alpha4 in low glucose (LG) and HG exposed INS-1832/13 cells revealed that it is predominantly cytosolic, and its expression is significantly increased in the non-nuclear/cytosolic fractions in cells exposed to HG. siRNA-mediated knockdown of Alpha4 exerted minimal effects on glucose- or KCl-induced insulin secretion. siRNA-mediated deletion of Alpha4 significantly increased p38MAPK and JNK1/2 phosphorylation under LG conditions, comparable to the degree seen under HG conditions. Paradoxically, a significant potentiation of HG-induced p38MAPK and JNK2 phosphorylation was noted following Alpha4 deletion. HG-induced CHOP expression (ER stress marker) and caspase-3 activation were markedly attenuated in cells following Alpha4 knockdown. Deletion of Alpha4 in INS-1832/13 cells prevented HG-induced loss in the expression of Connexin36, a gap junction channel protein, which has been implicated in normal beta cell function. Lastly, depletion of endogenous Alpha4 significantly reduced HG-induced cell death in INS-1832/13 cells. Based on these findings we conclude that Alpha4 contributes to HG-induced metabolic dysfunction of the islet beta cell.
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Affiliation(s)
- Mirabela Hali
- Biomedical Research Service, John D. Dingell VA Medical Center, Detroit, MI, USA; Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI, USA
| | - Brian E Wadzinski
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA
| | - Anjaneyulu Kowluru
- Biomedical Research Service, John D. Dingell VA Medical Center, Detroit, MI, USA; Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI, USA.
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The Connexin 43 Regulator Rotigaptide Reduces Cytokine-Induced Cell Death in Human Islets. Int J Mol Sci 2020; 21:ijms21124311. [PMID: 32560352 PMCID: PMC7352593 DOI: 10.3390/ijms21124311] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 06/11/2020] [Accepted: 06/15/2020] [Indexed: 01/23/2023] Open
Abstract
Background: Intercellular communication mediated by cationic fluxes through the Connexin family of gap junctions regulates glucose-stimulated insulin secretion and beta cell defense against inflammatory stress. Rotigaptide (RG, ZP123) is a peptide analog that increases intercellular conductance in cardiac muscle cells by the prevention of dephosphorylation and thereby uncoupling of Connexin-43 (Cx43), possibly via action on unidentified protein phosphatases. For this reason, it is being studied in human arrhythmias. It is unknown if RG protects islet cell function and viability against inflammatory or metabolic stress, a question of considerable translational interest for the treatment of diabetes. Methods: Apoptosis was measured in human islets shown to express Cx43, treated with RG or the control peptide ZP119 and exposed to glucolipotoxicity or IL-1β + IFNɣ. INS-1 cells shown to lack Cx43 were used to examine if RG protected human islet cells via Cx43 coupling. To study the mechanisms of action of Cx43-independent effects of RG, NO, IkBα degradation, mitochondrial activity, ROS, and insulin mRNA levels were determined. Results: RG reduced cytokine-induced apoptosis ~40% in human islets. In Cx43-deficient INS-1 cells, this protective effect was markedly blunted as expected, but unexpectedly, RG still modestly reduced apoptosis, and improved mitochondrial function, insulin-2 gene levels, and accumulated insulin release. RG reduced NO production in Cx43-deficient INS-1 cells associated with reduced iNOS expression, suggesting that RG blunts cytokine-induced NF-κB signaling in insulin-producing cells in a Cx43-independent manner. Conclusion: RG reduces cytokine-induced cell death in human islets. The protective action in Cx43-deficient INS-1 cells suggests a novel inhibitory mechanism of action of RG on NF-κB signaling.
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Ek Vitorín JF, Pontifex TK, Burt JM. Determinants of Cx43 Channel Gating and Permeation: The Amino Terminus. Biophys J 2016; 110:127-40. [PMID: 26745416 DOI: 10.1016/j.bpj.2015.10.054] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Revised: 10/11/2015] [Accepted: 10/30/2015] [Indexed: 11/30/2022] Open
Abstract
Separate connexin domains partake in proposed gating mechanisms of gap junction channels. The amino-terminus (NT) domains, which contribute to voltage sensing, may line the channel's cytoplasmic-facing funnel surface, stabilize the channel's overall structure through interactions with the transmembrane domains and each other, and integrate to form a compound particle to gate the channel closed. Interactions of the carboxyl-terminus (CT) and cytoplasmic loop (CL) domains underlie voltage- and low pH-triggered channel closure. To elucidate potential cooperation of these gating mechanisms, we replaced the Cx43NT with the Cx37NT (chimera Cx43(∗)NT37), leaving the remainder of the Cx43 sequence, including the CT and CL, unchanged. Compared to wild-type Cx43 (Cx43WT), Cx43(∗)NT37 junctions exhibited several functional alterations: extreme resistance to halothane- and acidification-induced uncoupling, absence of voltage-dependent fast inactivation, longer channel open times, larger unitary channel conductances, low junctional dye permeability/permselectivity, and an overall cation selectivity more typical of Cx37WT than Cx43WT junctions. Together, these results suggest a cohesive model of channel function wherein: 1) channel conductance and size selectivity are largely determined by pore diameter, whereas charge selectivity results from the NT domains, and 2) transition between fully open and (multiple) closed states involves global changes in structure of the pore-forming domains transduced by interactions of the pore-forming domains with either the NT, CT, or both, with the NT domains forming the gate of the completely closed channel.
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Affiliation(s)
| | - Tasha K Pontifex
- Department of Physiology, University of Arizona, Tucson, Arizona
| | - Janis M Burt
- Department of Physiology, University of Arizona, Tucson, Arizona
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Abstract
OBJECTIVES Mechanisms of toxicity and cell damage were investigated in novel clonal human pancreatic beta cell line, 1.1B4, after exposure to streptozotocin, alloxan, ninhydrin, and hydrogen peroxide. METHODS Viability, DNA damage, insulin secretion/content, [Ca]i, and glucokinase/hexokinase, mRNA expression were measured by MTT assay, comet assay, radioimmunoassay, fluorometric imaging plate reader, enzyme-coupled photometry, and real-time polymerase chain reaction, respectively. RESULTS Chemicals significantly reduced 1.1B4 cell viability in a time/concentration-dependent manner. Chronic 18-hour exposure decreased cellular insulin, glucokinase, and hexokinase activities. Chemicals decreased transcription of INS, GCK, PCSK1, PCSK2, and GJA1 (involved in secretory function). Insulin release and [Ca]i responses to nutrients and membrane-depolarizing agents were impaired. Streptozotocin and alloxan up-regulated transcription of genes, SOD1 and SOD2 (antioxidant enzymes). Ninhydrin and hydrogen peroxide up-regulated SOD2 transcription, whereas alloxan and hydrogen peroxide increased CAT transcription. Chemicals induced DNA damage, apoptosis, and increased caspase 3/7 activity. Streptozotocin and alloxan decreased transcription of BCL2 while increasing transcription of BAX. Chemicals did not affect transcription of HSPA4 and HSPA5 and nitrite production. CONCLUSIONS 1.1B4 cells represent a useful model of human beta cells. Chemicals impaired 1.1B4 cell secretory function and activated antioxidant defense and apoptotic pathways without activating endoplasmic reticulum stress response/nitrosative stress.
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Abstract
The pancreas produces enzymes with a digestive function and hormones with a metabolic function, which are produced by distinct cell types of acini and islets, respectively. Within these units, secretory cells coordinate their functioning by exchanging information via signals that flow in the intercellular spaces and are generated either at distance (several neural and hormonal inputs) or nearby the pancreatic cells themselves (inputs mediated by membrane ionic-specific channels and by ionic- and metabolite-permeant pannexin channels and connexin "hemichannels"). Pancreatic secretory cells further interact via the extracellular matrix of the pancreas (inputs mediated by integrins) and directly with neighboring cells, by mechanisms that do not require extracellular mediators (inputs mediated by gap and tight junction channels). Here, we review the expression and function of the connexins and pannexins that are expressed by the main secretory cells of the exocrine and endocrine pancreatic cells. Available data show that the patterns of expression of these proteins differ in acini and islets, supporting distinct functions in the physiological secretion of pancreatic enzymes and hormones. Circumstantial evidence further suggests that alterations in the signaling provided by these proteins are involved in pancreatic diseases.
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Cherubini C, Filippi S, Gizzi A, Loppini A. Role of topology in complex functional networks of beta cells. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 92:042702. [PMID: 26565267 DOI: 10.1103/physreve.92.042702] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Indexed: 06/05/2023]
Abstract
The activity of pancreatic β cells can be described by biological networks of coupled nonlinear oscillators that, via electrochemical synchronization, release insulin in response to augmented glucose levels. In this work, we analyze the emergent behavior of regular and percolated β-cells clusters through a stochastic mathematical model where "functional" networks arise. We show that the emergence and robustness of the synchronized dynamics depend both on intrinsic and extrinsic parameters. In particular, cellular noise level, glucose concentration, network spatial architecture, and cell-to-cell coupling strength are the key factors for the generation of a rhythmic and robust activity. Their role in the functional network topology associated with β-cells clusters is analyzed and discussed.
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Affiliation(s)
- Christian Cherubini
- Nonlinear Physics and Mathematical Modeling Laboratory, University Campus Bio-Medico of Rome, I-00128, Rome, Italy
- International Center for Relativistic Astrophysics Network-I.C.R.A.Net, University Campus Bio-Medico of Rome, I-00128, Rome, Italy
| | - Simonetta Filippi
- Nonlinear Physics and Mathematical Modeling Laboratory, University Campus Bio-Medico of Rome, I-00128, Rome, Italy
- International Center for Relativistic Astrophysics Network-I.C.R.A.Net, University Campus Bio-Medico of Rome, I-00128, Rome, Italy
| | - Alessio Gizzi
- Nonlinear Physics and Mathematical Modeling Laboratory, University Campus Bio-Medico of Rome, I-00128, Rome, Italy
| | - Alessandro Loppini
- Nonlinear Physics and Mathematical Modeling Laboratory, University Campus Bio-Medico of Rome, I-00128, Rome, Italy
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Yesildag B, Bock T, Herrmanns K, Wollscheid B, Stoffel M. Kin of IRRE-like Protein 2 Is a Phosphorylated Glycoprotein That Regulates Basal Insulin Secretion. J Biol Chem 2015; 290:25891-906. [PMID: 26324709 DOI: 10.1074/jbc.m115.684704] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Indexed: 12/17/2022] Open
Abstract
Direct interactions among pancreatic β-cells via cell surface proteins inhibit basal and enhance stimulated insulin secretion. Here, we functionally and biochemically characterized Kirrel2, an immunoglobulin superfamily protein with β-cell-specific expression in the pancreas. Our results show that Kirrel2 is a phosphorylated glycoprotein that co-localizes and interacts with the adherens junction proteins E-cadherin and β-catenin in MIN6 cells. We further demonstrate that the phosphosites Tyr(595-596) are functionally relevant for the regulation of Kirrel2 stability and localization. Analysis of the extracellular and intracellular domains of Kirrel2 revealed that it is cleaved and shed from MIN6 cells and that the remaining membrane spanning cytoplasmic domain is processed by γ-secretase complex. Kirrel2 knockdown with RNA interference in MIN6 cells and ablation of Kirrel2 from mice with genetic deletion resulted in increased basal insulin secretion from β-cells, with no immediate influence on stimulated insulin secretion, total insulin content, or whole body glucose metabolism. Our results show that in pancreatic β-cells Kirrel2 localizes to adherens junctions, is regulated by multiple post-translational events, including glycosylation, extracellular cleavage, and phosphorylation, and engages in the regulation of basal insulin secretion.
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Affiliation(s)
- Burcak Yesildag
- From the Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology (ETH) Zurich, Otto-Stern-Weg 7, 8093 Zurich
| | - Thomas Bock
- the Department of Health Sciences and Technology, Institute of Molecular Systems Biology, Swiss Federal Institute of Technology Zurich, Auguste-Piccard-Hof 1, 8093 Zurich, and
| | - Karolin Herrmanns
- From the Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology (ETH) Zurich, Otto-Stern-Weg 7, 8093 Zurich
| | - Bernd Wollscheid
- the Department of Health Sciences and Technology, Institute of Molecular Systems Biology, Swiss Federal Institute of Technology Zurich, Auguste-Piccard-Hof 1, 8093 Zurich, and
| | - Markus Stoffel
- From the Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology (ETH) Zurich, Otto-Stern-Weg 7, 8093 Zurich, the Department of Health Sciences and Technology, Institute of Molecular Systems Biology, Swiss Federal Institute of Technology Zurich, Auguste-Piccard-Hof 1, 8093 Zurich, and the Faculty of Medicine, University of Zurich, 8091 Zurich, Switzerland
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Irles E, Ñeco P, Lluesma M, Villar-Pazos S, Santos-Silva JC, Vettorazzi JF, Alonso-Magdalena P, Carneiro EM, Boschero AC, Nadal Á, Quesada I. Enhanced glucose-induced intracellular signaling promotes insulin hypersecretion: pancreatic beta-cell functional adaptations in a model of genetic obesity and prediabetes. Mol Cell Endocrinol 2015; 404:46-55. [PMID: 25633666 DOI: 10.1016/j.mce.2015.01.033] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Revised: 01/20/2015] [Accepted: 01/21/2015] [Indexed: 12/13/2022]
Abstract
Obesity is associated with insulin resistance and is known to be a risk factor for type-2 diabetes. In obese individuals, pancreatic beta-cells try to compensate for the increased insulin demand in order to maintain euglycemia. Most studies have reported that this adaptation is due to morphological changes. However, the involvement of beta-cell functional adaptations in this process needs to be clarified. For this purpose, we evaluated different key steps in the glucose-stimulated insulin secretion (GSIS) in intact islets from female ob/ob obese mice and lean controls. Obese mice showed increased body weight, insulin resistance, hyperinsulinemia, glucose intolerance and fed hyperglycemia. Islets from ob/ob mice exhibited increased glucose-induced mitochondrial activity, reflected by enhanced NAD(P)H production and mitochondrial membrane potential hyperpolarization. Perforated patch-clamp examination of beta-cells within intact islets revealed several alterations in the electrical activity such as increased firing frequency and higher sensitivity to low glucose concentrations. A higher intracellular Ca(2+) mobilization in response to glucose was also found in ob/ob islets. Additionally, they displayed a change in the oscillatory pattern and Ca(2+) signals at low glucose levels. Capacitance experiments in intact islets revealed increased exocytosis in individual ob/ob beta-cells. All these up-regulated processes led to increased GSIS. In contrast, we found a lack of beta-cell Ca(2+) signal coupling, which could be a manifestation of early defects that lead to beta-cell malfunction in the progression to diabetes. These findings indicate that beta-cell functional adaptations are an important process in the compensatory response to obesity.
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Affiliation(s)
- Esperanza Irles
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Patricia Ñeco
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Mónica Lluesma
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Sabrina Villar-Pazos
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Junia Carolina Santos-Silva
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; Department of Structural and Functional Biology, Institute of Biology, State University of Campinas (UNICAMP), Campinas, Brazil
| | - Jean F Vettorazzi
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; Department of Structural and Functional Biology, Institute of Biology, State University of Campinas (UNICAMP), Campinas, Brazil
| | - Paloma Alonso-Magdalena
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Everardo M Carneiro
- Department of Structural and Functional Biology, Institute of Biology, State University of Campinas (UNICAMP), Campinas, Brazil
| | - Antonio C Boschero
- Department of Structural and Functional Biology, Institute of Biology, State University of Campinas (UNICAMP), Campinas, Brazil
| | - Ángel Nadal
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Ivan Quesada
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain.
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Grek CL, Rhett JM, Ghatnekar GS. Cardiac to cancer: connecting connexins to clinical opportunity. FEBS Lett 2014; 588:1349-64. [PMID: 24607540 DOI: 10.1016/j.febslet.2014.02.047] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Revised: 02/25/2014] [Accepted: 02/26/2014] [Indexed: 12/26/2022]
Abstract
Gap junctions and their connexin components are indispensable in mediating the cellular coordination required for tissue and organ homeostasis. The critical nature of their existence mandates a connection to disease while at the same time offering therapeutic potential. Therapeutic intervention may be offered through the pharmacological and molecular disruption of the pathways involved in connexin biosynthesis, gap junction assembly, stabilization, or degradation. Chemical inhibitors aimed at closing connexin channels, peptide mimetics corresponding to short connexin sequences, and gene therapy approaches have been incredibly useful molecular tools in deciphering the complexities associated with connexin biology. Recently, therapeutic potential in targeting connexins has evolved from basic research in cell-based models to clinical opportunity in the form of human trials. Clinical promise is particularly evident with regards to targeting connexin43 in the context of wound healing. The following review is aimed at highlighting novel advances where the pharmacological manipulation of connexin biology has proven beneficial in animals or humans.
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Affiliation(s)
- Christina L Grek
- FirstString Research, Inc., 300 W. Coleman Blvd., Suite 203, Mount Pleasant, SC, United States
| | - J Matthew Rhett
- Department of Surgery, Division of General Surgery, Medical University of South Carolina, Charleston, SC, United States
| | - Gautam S Ghatnekar
- FirstString Research, Inc., 300 W. Coleman Blvd., Suite 203, Mount Pleasant, SC, United States.
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Vasu S, McClenaghan NH, McCluskey JT, Flatt PR. Cellular responses of novel human pancreatic β-cell line, 1.1B4 to hyperglycemia. Islets 2013; 5:170-7. [PMID: 23985558 DOI: 10.4161/isl.26184] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The novel human-derived pancreatic β-cell line, 1.1B4 exhibits insulin secretion and β-cell enriched gene expression. Recent investigations of the cellular responses of this novel cell line to lipotoxicity and cytokine toxicity revealed similarities to primary human β cells. The current study has investigated the responses of 1.1B4 cells to chronic 48 and 72 h exposure to hyperglycemia to probe mechanisms of human β-cell dysfunction and cell death. Exposure to 25 mM glucose significantly reduced insulin content (p<0.05) and glucokinase activity (p<0.01) after 72 h. Basal insulin release was unaffected but acute secretory response to 16.7 mM glucose was impaired (p<0.05). Insulin release stimulated by alanine, GLP-1, KCl, elevated Ca (2+) and forskolin was also markedly reduced after exposure to hyperglycemia (p<0.001). In addition, PDX1 protein expression was reduced by 58% by high glucose (p<0.05). Effects of hyperglycemia on secretory function were accompanied by decreased mRNA expression of INS, GCK, PCSK1, PCSK2, PPP3CB, GJA1, ABCC8, and KCNJ11. In contrast, exposure to hyperglycemia upregulated the transcription of GPX1, an antioxidant enzyme involved in detoxification of hydrogen peroxide and HSPA4, a molecular chaperone involved in ER stress response. Hyperglycemia-induced DNA damage was demonstrated by increased % tail DNA and olive tail moment, assessed by comet assay. Hyperglycemia-induced apoptosis was evident from increased activity of caspase 3/7 and decreased BCL2 protein. These observations reveal significant changes in cellular responses and gene expression in novel human pancreatic 1.1B4 β cells exposed to hyperglycemia, illustrating the usefulness of this novel human-derived cell line for studying human β-cell biology and diabetes.
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Affiliation(s)
- Srividya Vasu
- SAAD Centre for Pharmacy and Diabetes; University of Ulster; Coleraine, Northern Ireland, UK
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Treatment of diabetes mellitus with microencapsulated fetal human liver (FH-B-TPN) engineered cells. Biomaterials 2013; 34:4002-4012. [DOI: 10.1016/j.biomaterials.2013.02.026] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Accepted: 02/10/2013] [Indexed: 12/20/2022]
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Guo-Parke H, McCluskey JT, Kelly C, Hamid M, McClenaghan NH, Flatt PR. Configuration of electrofusion-derived human insulin-secreting cell line as pseudoislets enhances functionality and therapeutic utility. J Endocrinol 2012; 214:257-65. [PMID: 22685334 DOI: 10.1530/joe-12-0188] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Formation of pseudoislets from rodent cell lines has provided a particularly useful model to study homotypic islet cell interactions and insulin secretion. This study aimed to extend this research to generate and characterize, for the first time, functional human pseudoislets comprising the recently described electrofusion-derived insulin-secreting 1.1B4 human β-cell line. Structural pseudoislets formed readily over 3-7 days in culture using ultra-low-attachment plastic, attaining a static size of 100-200 μm in diameter, corresponding to ~6000 β cells. This was achieved by decreases in cell proliferation and integrity as assessed by BrdU ELISA, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, and lactate dehydrogenase assays. Insulin content was comparable between monolayers and pseudoislets. However, pseudoislet formation enhanced insulin secretion by 1·7- to 12·5-fold in response to acute stimulation with glucose, amino acids, incretin hormones, or drugs compared with equivalent cell monolayers. Western blot and RT-PCR showed expression of key genes involved in cell communication and the stimulus-secretion pathway. Expression of E-Cadherin and connexin 36 and 43 was greatly enhanced in pseudoislets with no appreciable connexin 43 protein expression in monolayers. Comparable levels of insulin, glucokinase, and GLUT1 were found in both cell populations. The improved secretory function of human 1.1B4 cell pseudoislets over monolayers results from improved cellular interactions mediated through gap junction communication. Pseudoislets comprising engineered electrofusion-derived human β cells provide an attractive model for islet research and drug testing as well as offering novel therapeutic application through transplantation.
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Affiliation(s)
- Hong Guo-Parke
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
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Abstract
Type 2 diabetes is historically associated with older adults, and glucose tolerance is known to decline with advancing age. During the course of natural ageing, changes in many peripheral tissues contribute to this deterioration of glucose homeostasis. Included in this process are changes to the structure and function of the pancreatic islets, which undergo deviation in endocrine responses to glycaemic challenge. Current knowledge about the changes seen in the ageing pancreas is reviewed here.
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Affiliation(s)
- James E Brown
- Aston Research Centre for Healthy Ageing, School of Life and Health Sciences, Aston University, Birmingham, UK
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Matsumoto T, Sakurai K, Tanaka A, Ishibashi T, Tachibana K, Ishikawa K, Yokote K. The anti-ulcer agent, irsogladine, increases insulin secretion by MIN6 cells. Eur J Pharmacol 2012; 685:213-7. [PMID: 22542662 DOI: 10.1016/j.ejphar.2012.04.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Revised: 03/28/2012] [Accepted: 04/05/2012] [Indexed: 10/28/2022]
Abstract
Insulin secretion by pancreatic islets is a multicellular process. In addition to other essential systems, gap junctions are an important component of cell-to-cell communication in pancreatic islets. It is well known that dysfunction of gap junctions causes inappropriate insulin secretion. The anti-ulcer agent, irsogladine, increases gap junctions in some cell types. To examine the effect of irsogladine on insulin secretion, we investigated insulin secretion by MIN6 cells treated with or without irsogladine. The expression of connexin 36 proteins and intracellular cAMP levels were also determined using immunoblotting and ELISA assays, respectively. Irsogladine had no effect on insulin secretion under 5.6mM glucose conditions. However, under 16.7 mM glucose conditions, irsogladine (1.0 × 10(-5)M) induced a 1.7 ± 0.20 fold increase in insulin secretion compared to the control (P<0.05). This effect of irsogladine on insulin secretion was inhibited by the addition of the gap junction inhibitor 18-beta-glycyrrhetinic acid. Irsogladine treatment increased the protein level of connexin 36 in the plasma membrane fraction. The intracellular cAMP level in MIN6 cells was significantly, but mildly, increased by irsogladine treatment. Furthermore, Rp-cAMP and H89 inhibited the effects of irsogladine on insulin secretion under high glucose conditions. Irsogladine increases insulin secretion under high glucose conditions. The up-regulation of gap junction channels and the increased level of intracellular cAMP induced by irsogladine treatment suggest that these phenomena are involved in irsogladine-induced increased insulin secretion.
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Affiliation(s)
- Tsuyoshi Matsumoto
- Department of Clinical Cell Biology and Medicine, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan.
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16
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Potolicchio I, Cigliola V, Velazquez-Garcia S, Klee P, Valjevac A, Kapic D, Cosovic E, Lepara O, Hadzovic-Dzuvo A, Mornjacovic Z, Meda P. Connexin-dependent signaling in neuro-hormonal systems. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:1919-36. [PMID: 22001400 DOI: 10.1016/j.bbamem.2011.09.022] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2011] [Revised: 09/14/2011] [Accepted: 09/23/2011] [Indexed: 01/04/2023]
Abstract
The advent of multicellular organisms was accompanied by the development of short- and long-range chemical signalling systems, including those provided by the nervous and endocrine systems. In turn, the cells of these two systems have developed mechanisms for interacting with both adjacent and distant cells. With evolution, such mechanisms have diversified to become integrated in a complex regulatory network, whereby individual endocrine and neuro-endocrine cells sense the state of activity of their neighbors and, accordingly, regulate their own level of functioning. A consistent feature of this network is the expression of connexin-made channels between the (neuro)hormone-producing cells of all endocrine glands and secretory regions of the central nervous system so far investigated in vertebrates. This review summarizes the distribution of connexins in the mammalian (neuro)endocrine systems, and what we know about the participation of these proteins on hormone secretion, the life of the producing cells, and the action of (neuro)hormones on specific targets. The data gathered since the last reviews on the topic are summarized, with particular emphasis on the roles of Cx36 in the function of the insulin-producing beta cells of the endocrine pancreas, and of Cx40 in that of the renin-producing juxta-glomerular epithelioid cells of the kidney cortex. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.
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Affiliation(s)
- Ilaria Potolicchio
- Department of Cell Physiology and Metabolism, University of Geneva Medical School, Switzerland
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17
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Abstract
The appearance of multicellular organisms imposed the development of several mechanisms for cell-to-cell communication, whereby different types of cells coordinate their function. Some of these mechanisms depend on the intercellular diffusion of signal molecules in the extracellular spaces, whereas others require cell-to-cell contact. Among the latter mechanisms, those provided by the proteins of the connexin family are widespread in most tissues. Connexin signaling is achieved via direct exchanges of cytosolic molecules between adjacent cells at gap junctions, for cell-to-cell coupling, and possibly also involves the formation of membrane "hemi-channels," for the extracellular release of cytosolic signals, direct interactions between connexins and other cell proteins, and coordinated influence on the expression of multiple genes. Connexin signaling appears to be an obligatory attribute of all multicellular exocrine and endocrine glands. Specifically, the experimental evidence we review here points to a direct participation of the Cx36 isoform in the function of the insulin-producing β-cells of the endocrine pancreas, and of the Cx40 isoform in the function of the renin-producing juxtaglomerular epithelioid cells of the kidney cortex.
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Affiliation(s)
- Domenico Bosco
- Department of Surgery, University of Geneva Medical School, Geneva, Switzerland
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18
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Carvalho CPF, Barbosa HCL, Britan A, Santos-Silva JCR, Boschero AC, Meda P, Collares-Buzato CB. Beta cell coupling and connexin expression change during the functional maturation of rat pancreatic islets. Diabetologia 2010; 53:1428-37. [PMID: 20361177 DOI: 10.1007/s00125-010-1726-8] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/29/2009] [Accepted: 01/22/2010] [Indexed: 12/01/2022]
Abstract
AIMS/HYPOTHESIS Cell-cell coupling mediated by gap junctions formed from connexin (CX) contributes to the control of insulin secretion in the endocrine pancreas. We investigated the cellular production and localisation of CX36 and CX43, and gap junction-mediated beta cell coupling in pancreatic islets from rats of different ages, displaying different degrees of maturation of insulin secretion. METHODS The presence and distribution of islet connexins were assessed by immunoblotting and immunofluorescence. The expression of connexin genes was evaluated by RT-PCR and quantitative real-time PCR. The ultrastructure of gap junctions and the function of connexin channels were assessed by freeze-fracture electron microscopy and tracer microinjection, respectively. RESULTS Young and adult beta cells, which respond to glucose, expressed significantly higher levels of Cx36 (also known as Gjd2) than fetal and newborn beta cells, which respond poorly to the sugar. Accordingly, adult beta cells also showed a significantly higher membrane density of gap junctions and greater intercellular exchange of ethidium bromide than newborn beta cells. Cx43 (also known as Gja1) was not expressed by beta cells, but was located in various cell types at the periphery of fetal and newborn islets. CONCLUSIONS/INTERPRETATION These findings show that the pattern of connexins, gap junction membrane density and coupling changes in islets during the functional maturation of beta cells.
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Affiliation(s)
- C P F Carvalho
- Department of Histology and Embryology, Institute of Biology, University of Campinas (UNICAMP), Campinas, São Paulo, CEP 13083-970, Brazil
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19
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Soria B, Tudurí E, González A, Hmadcha A, Martin F, Nadal A, Quesada I. Pancreatic islet cells: a model for calcium-dependent peptide release. HFSP JOURNAL 2010; 4:52-60. [PMID: 20885773 DOI: 10.2976/1.3364560] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2010] [Accepted: 02/25/2010] [Indexed: 11/19/2022]
Abstract
In mammals the concentration of blood glucose is kept close to 5 mmol∕l. Different cell types in the islet of Langerhans participate in the control of glucose homeostasis. β-cells, the most frequent type in pancreatic islets, are responsible for the synthesis, storage, and release of insulin. Insulin, released with increases in blood glucose promotes glucose uptake into the cells. In response to glucose changes, pancreatic α-, β-, and δ-cells regulate their electrical activity and Ca(2+) signals to release glucagon, insulin, and somatostatin, respectively. While all these signaling steps are stimulated in hypoglycemic conditions in α-cells, the activation of these events require higher glucose concentrations in β and also in δ-cells. The stimulus-secretion coupling process and intracellular Ca(2+) ([Ca(2+)](i)) dynamics that allow β-cells to secrete is well-accepted. Conversely, the mechanisms that regulate α- and δ-cell secretion are still under study. Here, we will consider the glucose-induced signaling mechanisms in each cell type and the mathematical models that explain Ca(2+) dynamics.
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Abstract
Cell-cell communication within any given tissue is an important aspect of correct organ function. The islets of Langerhans forming the endocrine pancreas are composed of alpha-, beta-, delta-, epsilon- and PP-cells, and interactions between these cells are required for fine-tuning glucose homeostasis of the body. The endocrine cells communicate through homotypic or heterotypic cell-cell adhesion, or in a paracrine fashion, and this communication is involved in the regulated secretion of islet hormones. This review discusses how islet hormones, secreted molecules and ions influence the endocrine cells and how cell adhesion molecules such as neural cell adhesion molecule, cadherins, connexin-36, Eph receptors and ephrin ligands, as well as extracellular matrix proteins, modulate pancreatic islet function.
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Affiliation(s)
- R Jain
- Institute of Metabolic Physiology, Heinrich-Heine-University, Düsseldorf, Germany
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21
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del Castillo FJ, Cohen-Salmon M, Charollais A, Caille D, Lampe PD, Chavrier P, Meda P, Petit C. Consortin, a trans-Golgi network cargo receptor for the plasma membrane targeting and recycling of connexins. Hum Mol Genet 2009; 19:262-75. [PMID: 19864490 DOI: 10.1093/hmg/ddp490] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Targeting of numerous transmembrane proteins to the cell surface is thought to depend on their recognition by cargo receptors that interact with the adaptor machinery for anterograde traffic at the distal end of the Golgi complex. We report here on consortin, a novel integral membrane protein that is predicted to be intrinsically disordered, i.e. that contains large segments whose native state is unstructured. We identified consortin as a binding partner of connexins, the building blocks of gap junctions. Consortin is located at the trans-Golgi network (TGN), in tubulovesicular transport organelles, and at the plasma membrane. It directly interacts with the TGN clathrin adaptors GGA1 and GGA2, and disruption of this interaction by expression of a consortin mutant lacking the acidic cluster-dileucine (DXXLL) GGA interaction motif causes an intracellular accumulation of several connexins. RNA interference-mediated silencing of consortin expression in HeLa cells blocks the cell surface targeting of these connexins, which accumulate intracellularly, whereas partial depletion and redistribution of the consortin pool slows down the intracellular degradation of gap junction plaques. Altogether, our results show that, by studying connexin trafficking, we have identified the first TGN cargo receptor for the targeting of transmembrane proteins to the plasma membrane. The identification of consortin provides in addition a potential target for therapies aimed at diseases in which connexin traffic is altered, including cardiac ischemia, peripheral neuropathies, cataracts and hearing impairment. Sequence accession numbers. GenBank: Human CNST cDNA, NM_152609; mouse Cnst cDNA, NM_146105.
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Holmes A, Brown R, Shakesheff K. Engineering tissue alternatives to animals: applying tissue engineering to basic research and safety testing. Regen Med 2009; 4:579-92. [PMID: 19580406 DOI: 10.2217/rme.09.26] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The focus for the rapid progress in the field of tissue engineering has been the clinical potential of the technology to repair, replace, maintain or enhance the function of a particular tissue or organ. However, tissue engineering has much wider applicability in basic research and safety testing, which is often not recognized owing to the clinical focus of tissue engineers. Using examples from a recent National Centre for the Replacement, Refinement and Reduction of Animals in Research/Biotechnology and Biological Sciences Research Council symposium, which brought together tissue engineers and scientists from other research communities, this review highlights the potential of tissue engineering to provide scientifically robust alternatives to animals to address basic research questions and improve drug and chemical development in the pharmaceutical and chemical industries.
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Affiliation(s)
- Anthony Holmes
- National Centre for the Replacement, Refinement & Reduction of Animals in Research, 20 Park Crescent, London, W1B 1AL, UK.
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23
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Heyman NS, Kurjiaka DT, Ek Vitorin JF, Burt JM. Regulation of gap junctional charge selectivity in cells coexpressing connexin 40 and connexin 43. Am J Physiol Heart Circ Physiol 2009; 297:H450-9. [PMID: 19465552 PMCID: PMC2711728 DOI: 10.1152/ajpheart.00287.2009] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/24/2009] [Accepted: 05/20/2009] [Indexed: 11/22/2022]
Abstract
Expression of connexin 40 (Cx40) and Cx43 in cardiovascular tissues varies as a function of age, injury, and development with unknown consequences on the selectivity of junctional communication and its acute regulation. We investigated the PKC-dependent regulation of charge selectivity in junctions composed of Cx43, Cx40, or both by simultaneous assessment of junctional permeance rate constants (B(dye)) for dyes of similar size but opposite charge, N,N,N-trimethyl-2-[methyl-(7-nitro-2,1,3-benzoxadiol-4-yl)amino]ethanaminium (NBD-M-TMA; +1) and Alexa 350 (-1). The ratio of dye rate constants (B(NBD-M-TMA)/B(Alexa 350)) indicated that Cx40 junctions are cation selective (10.7 +/- 0.5), whereas Cx43 junction are nonselective (1.22 +/- 0.14). In coexpressing cells, a broad range of junctional selectivities was observed with mean cation selectivity increasing as the Cx40 to Cx43 expression ratio increased. PKC activation reduced or eliminated dye permeability of Cx43 junctions without altering their charge selectivity, had no effect on either permeability or charge selectivity of Cx40 junctions, and significantly increased the cation selectivity of junctions formed by coexpressing cells (approaching charge selectivity of Cx40 junctions). Junctions composed of Cx43 truncated at residue 257 (Cx43tr) were also not charge selective, but when Cx43tr was coexpressed with Cx40, a broad range of junctional selectivities that was unaffected by PKC activation was observed. Thus, whereas the charge selectivities of homomeric/homotypic Cx43 and Cx40 junctions appear invariant, the selectivities of junctions formed by cells coexpressing Cx40 and Cx43 vary considerably, reflecting both their relative expression levels and phosphorylation-dependent regulation. Such regulation could represent a mechanism by which coexpressing cells such as vascular endothelium and atrial cells regulate acutely the selective intercellular communication mediated by their gap junctions.
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24
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Serre-Beinier V, Bosco D, Zulianello L, Charollais A, Caille D, Charpantier E, Gauthier BR, Diaferia GR, Giepmans BN, Lupi R, Marchetti P, Deng S, Buhler L, Berney T, Cirulli V, Meda P. Cx36 makes channels coupling human pancreatic beta-cells, and correlates with insulin expression. Hum Mol Genet 2009; 18:428-39. [PMID: 19000992 PMCID: PMC2638800 DOI: 10.1093/hmg/ddn370] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Previous studies have documented that the insulin-producing beta-cells of laboratory rodents are coupled by gap junction channels made solely of the connexin36 (Cx36) protein, and have shown that loss of this protein desynchronizes beta-cells, leading to secretory defects reminiscent of those observed in type 2 diabetes. Since human islets differ in several respects from those of laboratory rodents, we have now screened human pancreas, and islets isolated thereof, for expression of a variety of connexin genes, tested whether the cognate proteins form functional channels for islet cell exchanges, and assessed whether this expression changes with beta-cell function in islets of control and type 2 diabetics. Here, we show that (i) different connexin isoforms are differentially distributed in the exocrine and endocrine parts of the human pancreas; (ii) human islets express at the transcript level different connexin isoforms; (iii) the membrane of beta-cells harbors detectable levels of gap junctions made of Cx36; (iv) this protein is concentrated in lipid raft domains of the beta-cell membrane where it forms gap junctions; (v) Cx36 channels allow for the preferential exchange of cationic molecules between human beta-cells; (vi) the levels of Cx36 mRNA correlated with the expression of the insulin gene in the islets of both control and type 2 diabetics. The data show that Cx36 is a native protein of human pancreatic islets, which mediates the coupling of the insulin-producing beta-cells, and contributes to control beta-cell function by modulating gene expression.
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Affiliation(s)
| | - Domenico Bosco
- Cell Isolation and Transplantation Center, Department of Surgery, Geneva University Hospitals, Geneva, Switzerland
| | - Laurence Zulianello
- Department of Cell Physiology and Metabolism, University of Geneva School of Medicine, CMU 1, rue Michel-Servet, 1211 Geneva 4, CH, Switzerland
| | - Anne Charollais
- Department of Cell Physiology and Metabolism, University of Geneva School of Medicine, CMU 1, rue Michel-Servet, 1211 Geneva 4, CH, Switzerland
| | - Dorothée Caille
- Department of Cell Physiology and Metabolism, University of Geneva School of Medicine, CMU 1, rue Michel-Servet, 1211 Geneva 4, CH, Switzerland
| | - Eric Charpantier
- Department of Cell Physiology and Metabolism, University of Geneva School of Medicine, CMU 1, rue Michel-Servet, 1211 Geneva 4, CH, Switzerland
| | - Benoit R. Gauthier
- Department of Cell Physiology and Metabolism, University of Geneva School of Medicine, CMU 1, rue Michel-Servet, 1211 Geneva 4, CH, Switzerland
| | - Giuseppe R. Diaferia
- Islet Research Laboratory, The Whittier Institute for Diabetes, University of California San Diego, La Jolla, CA, USA
| | - Ben N. Giepmans
- Department of Cell Biology, University of Groningen, Groningen, The Netherlands
| | - Roberto Lupi
- Department of Endocrinology and Metabolism, University of Pisa, Pisa, Italy
| | - Piero Marchetti
- Department of Endocrinology and Metabolism, University of Pisa, Pisa, Italy
| | - Shaoping Deng
- Department of Surgery, University of Pennsylvania, Philadelphia, PA, USA
| | - Léo Buhler
- Surgical Research Unit, Department of Surgery
| | - Thierry Berney
- Cell Isolation and Transplantation Center, Department of Surgery, Geneva University Hospitals, Geneva, Switzerland
| | - Vincenzo Cirulli
- Islet Research Laboratory, The Whittier Institute for Diabetes, University of California San Diego, La Jolla, CA, USA
| | - Paolo Meda
- Department of Cell Physiology and Metabolism, University of Geneva School of Medicine, CMU 1, rue Michel-Servet, 1211 Geneva 4, CH, Switzerland
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25
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Li G, Luo R, Zhang J, Yeo KS, Lian Q, Xie F, Tan EKW, Caille D, Kon OL, Salto-Tellez M, Meda P, Lim SK. Generating mESC-derived insulin-producing cell lines through an intermediate lineage-restricted progenitor line. Stem Cell Res 2009; 2:41-55. [DOI: 10.1016/j.scr.2008.07.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/05/2008] [Revised: 07/25/2008] [Accepted: 07/26/2008] [Indexed: 10/21/2022] Open
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26
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Nittala A, Wang X. The hyperbolic effect of density and strength of inter beta-cell coupling on islet bursting: a theoretical investigation. Theor Biol Med Model 2008; 5:17. [PMID: 18673579 PMCID: PMC2538510 DOI: 10.1186/1742-4682-5-17] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2008] [Accepted: 08/03/2008] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Insulin, the principal regulating hormone of blood glucose, is released through the bursting of the pancreatic islets. Increasing evidence indicates the importance of islet morphostructure in its function, and the need of a quantitative investigation. Recently we have studied this problem from the perspective of islet bursting of insulin, utilizing a new 3D hexagonal closest packing (HCP) model of islet structure that we have developed. Quantitative non-linear dependence of islet function on its structure was found. In this study, we further investigate two key structural measures: the number of neighboring cells that each beta-cell is coupled to, nc, and the coupling strength, gc. RESULTS BETA-cell clusters of different sizes with number of beta-cells nbeta ranging from 1-343, nc from 0-12, and gc from 0-1000 pS, were simulated. Three functional measures of islet bursting characteristics--fraction of bursting beta-cells fb, synchronization index lambda, and bursting period Tb, were quantified. The results revealed a hyperbolic dependence on the combined effect of nc and gc. From this we propose to define a dimensionless cluster coupling index or CCI, as a composite measure for islet morphostructural integrity. We show that the robustness of islet oscillatory bursting depends on CCI, with all three functional measures fb, lambda and Tb increasing monotonically with CCI when it is small, and plateau around CCI = 1. CONCLUSION CCI is a good islet function predictor. It has the potential of linking islet structure and function, and providing insight to identify therapeutic targets for the preservation and restoration of islet beta-cell mass and function.
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Affiliation(s)
- Aparna Nittala
- Max McGee National Research Center for Juvenile Diabetes & Human and Molecular Genetics Center, Medical College of Wisconsin and Children's Research Institute of the Children's Hospital of Wisconsin, Milwaukee, WI 53226, USA.
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27
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Jaques F, Jousset H, Tomas A, Prost AL, Wollheim CB, Irminger JC, Demaurex N, Halban PA. Dual effect of cell-cell contact disruption on cytosolic calcium and insulin secretion. Endocrinology 2008; 149:2494-505. [PMID: 18218692 DOI: 10.1210/en.2007-0974] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Cell-to-cell interactions play an important role in insulin secretion. Compared with intact islets, dispersed pancreatic beta-cells show increased basal and decreased glucose-stimulated insulin secretion. In this study, we used mouse MIN6B1 cells to investigate the mechanisms that control insulin secretion when cells are in contact with each other or not. RNAi-mediated silencing of the adhesion molecule E-cadherin in confluent cells reduced glucose-stimulated secretion to the levels observed in isolated cells but had no impact on basal secretion. Dispersed cells presented high cytosolic Ca(2+) activity, depolymerized cytoskeleton and ERK1/2 activation in low glucose conditions. Both the increased basal secretion and the spontaneous Ca(2+) activity were corrected by transient removal of Ca(2+) or prolonged incubation of cells in low glucose, a procedure that restored the ability of dispersed cells to respond to glucose (11-fold stimulation). In conclusion, we show that dispersed pancreatic beta-cells can respond robustly to glucose once their elevated basal secretion has been corrected. The increased basal insulin secretion of dispersed cells is due to spontaneous Ca(2+) transients that activate downstream Ca(2+) effectors, whereas engagement of cell adhesion molecules including E-cadherin contributes to the greater secretory response to glucose seen in cells with normal intercellular contacts.
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Affiliation(s)
- Fabienne Jaques
- Department of Genetic Medicine and Development, University of Geneva Medical Center, 1211 Geneva-4, Switzerland.
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28
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Bellei B, Mastrofrancesco A, Briganti S, Aspite N, Ale-Agha N, Sies H, Picardo M. Ultraviolet A induced modulation of gap junctional intercellular communication by P38 MAPK activation in human keratinocytes. Exp Dermatol 2008; 17:115-24. [DOI: 10.1111/j.1600-0625.2007.00662.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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29
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Bavamian S, Klee P, Britan A, Populaire C, Caille D, Cancela J, Charollais A, Meda P. Islet-cell-to-cell communication as basis for normal insulin secretion. Diabetes Obes Metab 2007; 9 Suppl 2:118-32. [PMID: 17919186 DOI: 10.1111/j.1463-1326.2007.00780.x] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The emergence of pancreatic islets has necessitated the development of a signalling system for the intra- and inter-islet coordination of beta cells. With evolution, this system has evolved into a complex regulatory network of partially cross-talking pathways, whereby individual cells sense the state of activity of their neighbours and, accordingly, regulate their own level of functioning. A consistent feature of this network in vertebrates is the expression of connexin (Cx)-36-made cell-to-cell channels, which cluster at gap junction domains of the cell membrane, and which adjacent beta cells use to share cytoplasmic ions and small metabolites within individual islets. This chapter reviews what is known about Cx36, and the mechanism whereby this beta-cell connexin significantly regulates insulin secretion. It further outlines other less established functions of the protein and evaluates its potential relevance for the development of novel therapeutic approaches to diabetes.
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Affiliation(s)
- S Bavamian
- Department of Cell Physiology and Metabolism, University of Geneva, Medical School, Genève, Switzerland
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30
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Talhouk RS, Zeinieh MP, Mikati MA, El-Sabban ME. Gap junctional intercellular communication in hypoxia-ischemia-induced neuronal injury. Prog Neurobiol 2007; 84:57-76. [PMID: 18006137 DOI: 10.1016/j.pneurobio.2007.10.001] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2006] [Revised: 08/29/2007] [Accepted: 10/04/2007] [Indexed: 01/07/2023]
Abstract
Brain hypoxia-ischemia is a relatively common and serious problem in neonates and in adults. Its consequences include long-term histological and behavioral changes and reduction in seizure threshold. Gap junction intercellular communication is pivotal in the spread of hypoxia-ischemia related injury and in mediating its long-term effects. This review provides a comprehensive and critical review of hypoxia-ischemia and hypoxia in the brain and the potential role of gap junctions in the spread of the neuronal injury induced by these insults. It also presents the effects of hypoxia-ischemia and of hypoxia on the state of gap junctions in vitro and in vivo. Understanding the mechanisms involved in gap junction-mediated neuronal injury due to hypoxia will lead to the development of novel therapeutic strategies.
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Affiliation(s)
- Rabih S Talhouk
- Department of Biology, American University of Beirut, Beirut, Lebanon
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31
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Hindered diffusion through an aqueous pore describes invariant dye selectivity of Cx43 junctions. Biophys J 2007; 94:840-54. [PMID: 17921206 DOI: 10.1529/biophysj.107.115634] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The permselectivity (permeance/conductance) of Cx43-comprised gap junctions is a variable parameter of junctional function. To ascertain whether this variability in junctional permselectivity is explained by heterogeneous charge or size selectivity of the comprising channels, the permeance of individual Cx43 gap junctions to combinations of two dyes differing in either size or charge was determined in four cell types: Rin43, NRKe, HeLa43, and cardiac myocytes. The results show that Cx43 junctions are size- but not charge-selective and that both selectivities are constant parameters of junctional function. The consistency of dye selectivities indicates that the large continuum of measured junctional permselectivities cannot be ascribed to an equivalent continuum of individual channel selectivities. Further, the relative dye permeance sequence of NBD-M-TMA approximately Alexa 350 > Lucifer yellow > Alexa 488 >> Alexa 594 (Stokes radii of 4.3 A, 4.4 A, 4.9 A, 5.8 A, and 7.4 A, respectively) and the conductance sequence of KCl > TEACl approximately Kglutamate are well described by hindered diffusion through an aqueous pore with radius approximately 10 A and length 160 A. The permselectivity and dye selectivity data suggest the variable presence in Cx43-comprised junctions of conductive channels that are either dye-impermeable or dye-permeable.
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Quesada I, Todorova MG, Alonso-Magdalena P, Beltrá M, Carneiro EM, Martin F, Nadal A, Soria B. Glucose induces opposite intracellular Ca2+ concentration oscillatory patterns in identified alpha- and beta-cells within intact human islets of Langerhans. Diabetes 2006; 55:2463-9. [PMID: 16936194 DOI: 10.2337/db06-0272] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Homeostasis of blood glucose is mainly regulated by the coordinated secretion of glucagon and insulin from alpha- and beta-cells within the islets of Langerhans. The release of both hormones is Ca(2+) dependent. In the current study, we used confocal microscopy and immunocytochemistry to unequivocally characterize the glucose-induced Ca(2+) signals in alpha- and beta-cells within intact human islets. Extracellular glucose stimulation induced an opposite response in these two cell types. Although the intracellular Ca(2+) concentration ([Ca(2+)](i)) in beta-cells remained stable at low glucose concentrations, alpha-cells exhibited an oscillatory [Ca(2+)](i) response. Conversely, the elevation of extracellular glucose elicited an oscillatory [Ca(2+)](i) pattern in beta-cells but inhibited low-glucose-induced [Ca(2+)](i) signals in alpha-cells. These Ca(2+) signals were synchronic among beta-cells grouped in clusters within the islet, although they were not coordinated among the whole beta-cell population. The response of alpha-cells was totally asynchronic. Therefore, both the alpha- and beta-cell populations within human islets did not work as a syncitium in response to glucose. A deeper knowledge of alpha- and beta-cell behavior within intact human islets is important to better understand the physiology of the human endocrine pancreas and may be useful to select high-quality islets for transplantation.
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Affiliation(s)
- Ivan Quesada
- Institute of Bioengineering, Miguel Hernandez University, Ctra. N-332, Km. 87, 03550 Sant Joan d'Alacant, Spain.
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33
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Ek-Vitorin JF, King TJ, Heyman NS, Lampe PD, Burt JM. Selectivity of connexin 43 channels is regulated through protein kinase C-dependent phosphorylation. Circ Res 2006; 98:1498-505. [PMID: 16709897 PMCID: PMC1783838 DOI: 10.1161/01.res.0000227572.45891.2c] [Citation(s) in RCA: 181] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Coordinated contractile activation of the heart and resistance to ischemic injury depend, in part, on the intercellular communication mediated by Cx43-composed gap junctions. The function of these junctions is regulated at multiple levels (assembly to degradation) through phosphorylation at specific sites in the carboxyl terminus (CT) of the Cx43 protein. We show here that the selective permeability of Cx43 junctions is regulated through protein kinase C (PKC)-dependent phosphorylation at serine 368 (S368). Selective permeability was measured in several Cx43-expressing cell lines as the rate constant for intercellular dye diffusion relative to junctional conductance. The selective permeability of Cx43 junctions under control conditions was quite variable, as was the open-state behavior of the comprising channels. Coexpression of the CT of Cx43 as a distinct protein, treatment with a PKC inhibitor, or mutation of S368 to alanine, all reduced (or eliminated) phosphorylation at S368, reduced the incidence of 55- to 70-pS channels, and reduced by 10-fold the selective permeability of the junctions for a small cationic dye. Because PKC activation during preischemic conditioning is cardioprotective during subsequent ischemic episodes, we examined no-flow, ischemic hearts for Cx43 phosphorylated at S368 (pS368). Consistent with early activation of PKC, pS368-Cx43 was increased in ischemic hearts; despite extensive lateralization of total Cx43, pS368-Cx43 remained predominantly at intercalated disks. Our data suggest that the selectivity of gap junction channels at intercalated disks is increased early in ischemia.
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34
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Nlend RN, Michon L, Bavamian S, Boucard N, Caille D, Cancela J, Charollais A, Charpantier E, Klee P, Peyrou M, Populaire C, Zulianello L, Meda P. Connexin36 and pancreatic beta-cell functions. Arch Physiol Biochem 2006; 112:74-81. [PMID: 16931449 DOI: 10.1080/13813450600712019] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Most cell types are functionally coupled by connexin (Cx) channels, i.e. exchange cytoplasmic ions and small metabolites through gap junction domains of their membrane. This form of direct cell-to-cell communication occurs in all existing animals, whatever their position in the phylogenetic scale, and up to humans. Pancreatic beta-cells are no exception, and normally cross-talk with their neighbors via channels made of Cx36. These exchanges importantly contribute to coordinate and synchronize the function of individual cells within pancreatic islets, particularly in the context of glucose-induced insulin secretion. Compelling evidence now indicates that Cx36-mediated coupling, and/or the Cx36 protein per se, play significant regulatory roles in various beta-cell functions, ranging from the biosynthesis, storage and release of insulin. Recent preliminary data further suggest that the protein may also be implicated in the balance of beta-cell growth versus necrosis and apoptosis, and in the regulated expression of specific genes. Here, we review this evidence, discuss the possible involvement of Cx36 in the pathophysiology of diabetes, and evaluate the relevance of this connexin in the therapeutic approaches to the disease.
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Affiliation(s)
- Rachel Nlend Nlend
- Department of Cell Physiology and Metabolism, University of Geneva, Medical School, 1211 Genève 4, Switzerland
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35
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Luther MJ, Hauge-Evans A, Souza KLA, Jörns A, Lenzen S, Persaud SJ, Jones PM. MIN6 beta-cell-beta-cell interactions influence insulin secretory responses to nutrients and non-nutrients. Biochem Biophys Res Commun 2006; 343:99-104. [PMID: 16529716 DOI: 10.1016/j.bbrc.2006.02.003] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Accepted: 02/02/2006] [Indexed: 11/17/2022]
Abstract
Insulin-secreting MIN6 cells show greatly enhanced secretory responsiveness to nutrients when grown as islet-like structures (pseudoislets). Since beta-cells use different mechanisms to respond to nutrient and non-nutrient stimuli, we have now investigated the role of homotypic beta-cell interactions in secretory responses to pharmacological or receptor-operated non-nutrient stimuli in MIN6 pseudoislets. In addition to an enhanced secretory responsiveness to glucose, insulin secretion from MIN6 pseudoislets was also enhanced by non-nutrients, including carbachol, tolbutamide, PMA, and forskolin. The improved secretory responsiveness was dependent on the cells being configured as pseudoislets and was lost on dispersal of the pseudoislets into single cells and regained on the re-formation of pseudoislet structures. These observations emphasise the importance of islet anatomy on secretory responsiveness, and demonstrate that homotypic beta-cell interactions play an important role in generating physiologically appropriate insulin secretory responses to both nutrient and non-nutrient stimuli.
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Affiliation(s)
- Melanie J Luther
- Beta Cell Development and Function Group, King's College London, London, UK.
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36
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Villalobos C, Nadal A, Núñez L, Quesada I, Chamero P, Alonso MT, García-Sancho J. Bioluminescence imaging of nuclear calcium oscillations in intact pancreatic islets of Langerhans from the mouse. Cell Calcium 2005; 38:131-9. [PMID: 16095687 DOI: 10.1016/j.ceca.2005.06.029] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2005] [Revised: 05/30/2005] [Accepted: 06/06/2005] [Indexed: 11/17/2022]
Abstract
The stimulus-secretion coupling for insulin secretion by pancreatic beta cells in response to high glucose involves synchronic cytosolic calcium oscillations driven by bursting electrical activity. Calcium inside organelles can regulate additional functions, but analysis of subcellular calcium signals, specially at the single cell level, has been hampered for technical constrains. Here we have monitored nuclear calcium oscillations by bioluminescence imaging of targeted aequorin in individual cells within intact islets of Langerhans as well as in the whole islet. We find that glucose generates a pattern of nuclear calcium oscillations resembling those found in the cytosol. Some cells showed synchronous nuclear calcium oscillations suggesting that the islet of Langerhans may also regulate the activation of Ca(2+)-responsive nuclear processes, such as gene transcription, in a coordinated, synchronic manner. The nuclear Ca(2+) oscillations are due to bursting electrical activity and activation of plasma membrane voltage-gated Ca(2+) channels with little or no contribution of calcium release from the intracellular Ca(2+) stores. Irregularities in consumption of aequorins suggests that depolarization may generate formation of steep Ca(2+) gradients in both the cytosol and the nucleus, but further research is required to investigate the role of such high [Ca(2+)] microdomains.
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Affiliation(s)
- Carlos Villalobos
- Instituto de Biología y Genética Molecular (IBGM), Facultad de Medicina, Universidad de Valladolid and CSIC, Facultad de Medicina, Spain
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37
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Stains JP, Civitelli R. Gap junctions in skeletal development and function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1719:69-81. [PMID: 16359941 DOI: 10.1016/j.bbamem.2005.10.012] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2005] [Revised: 10/26/2005] [Accepted: 10/28/2005] [Indexed: 11/29/2022]
Abstract
Gap junctions play a critical role in the coordinated function and activity of nearly all of the skeletal cells. This is not surprising, given the elaborate orchestration of skeletal patterning, bone modeling and subsequent remodeling, as well as the mechanical stresses, strains and adaptive responses that the skeleton must accommodate. Much remains to be learned regarding the role of gap junctions and hemichannels in these processes. A common theme is that without connexins none of the cells of bone function properly. Thus, connexins play an important role in skeletal form and function.
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Affiliation(s)
- Joseph P Stains
- University of Maryland School of Medicine, Department of Orthopaedics, Baltimore, MD 21201, USA
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38
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Michon L, Nlend Nlend R, Bavamian S, Bischoff L, Boucard N, Caille D, Cancela J, Charollais A, Charpantier E, Klee P, Peyrou M, Populaire C, Zulianello L, Meda P. Involvement of gap junctional communication in secretion. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1719:82-101. [PMID: 16359942 DOI: 10.1016/j.bbamem.2005.11.003] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2005] [Revised: 10/31/2005] [Accepted: 11/07/2005] [Indexed: 11/26/2022]
Abstract
Glands were the first type of tissues in which the permissive role of gap junctions in the cell-to-cell transfer of membrane-impermeant molecules was shown. During the 40 years that have followed this seminal finding, gap junctions have been documented in all types of multicellular secretory systems, whether of the exocrine, endocrine or pheromonal nature. Also, compelling evidence now indicates that gap junction-mediated coupling, and/or the connexin proteins per se, play significant regulatory roles in various aspects of gland functions, ranging from the biosynthesis, storage and release of a variety of secretory products, to the control of the growth and differentiation of secretory cells, and to the regulation of gland morphogenesis. This review summarizes this evidence in the light of recent reports.
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Affiliation(s)
- Laetitia Michon
- Department of Cell Physiology and Metabolism, University of Geneva, C.M.U., 1 rue Michel Servet, 1211 Geneva 4, Switzerland
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39
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Ullrich S, Su J, Ranta F, Wittekindt OH, Ris F, Rösler M, Gerlach U, Heitzmann D, Warth R, Lang F. Effects of I(Ks) channel inhibitors in insulin-secreting INS-1 cells. Pflugers Arch 2005; 451:428-36. [PMID: 16133261 DOI: 10.1007/s00424-005-1479-2] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2005] [Accepted: 06/06/2005] [Indexed: 12/18/2022]
Abstract
Potassium channels regulate insulin secretion. The closure of K(ATP) channels leads to membrane depolarisation, which triggers Ca(2+) influx and stimulates insulin secretion. The subsequent activation of K(+) channels terminates secretion. We examined whether KCNQ1 channels are expressed in pancreatic beta-cells and analysed their functional role. Using RT/PCR cellular mRNA of KCNQ1 but not of KCNE1 channels was detected in INS-1 cells. Effects of two sulfonamide analogues, 293B and HMR1556, inhibitors of KCNQ1 channels, were examined on voltage-activated outwardly rectifying K(+) currents using the patch-clamp method. It was found that 293B inhibited 60% of whole-cell outward currents induced by voltage pulses from -70 to +50 mV with a concentration for half-maximal inhibition (IC(50)) of 37 microM. The other sulfonamide analogue HMR1556 inhibited 48% of the outward current with an IC(50) of 7 microM. The chromanol 293B had no effect on tolbutamide-sensitive K(ATP) channels. Action potentials induced by current injections were broadened and after-repolarisation was attenuated by 293B. Insulin secretion in the presence but not in the absence of tolbutamide was significantly increased by 293B. These results suggest that 293B- and HMR1556-sensitive channels, probably in concert with other voltage-activated K(+) channels, influence action potential duration and frequency and thus insulin secretion.
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Affiliation(s)
- Susanne Ullrich
- Institute of Neurophysiology, University of Köln, Robert Koch Strasse 39, 50931 Cologne, Germany.
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40
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Abstract
Gap junctions, which are essential for functional coordination and homeostasis within tissues, permit the direct intercellular exchange of small molecules. The abundance and diversity of this exchange depends on the number and selectivity of the comprising channels and on the transjunctional gradient for and chemical character of the permeant molecules. Limited knowledge of functionally significant permeants and poor detectability of those few that are known have made it difficult to define channel selectivity. Presented herein is a multifaceted approach to the quantification of gap junction selectivity that includes determination of the rate constant for intercellular diffusion of a fluorescent probe (k2-DYE) and junctional conductance (gj) for each junction studied, such that the selective permeability (k2-DYE/gj) for dyes with differing chemical characteristics or junctions with differing connexin (Cx) compositions (or treatment conditions) can be compared. In addition, selective permeability can be correlated using single-channel conductance when this parameter is also measured. Our measurement strategy is capable of detecting 1) rate constants and selective permeabilities that differ across three orders of magnitude and 2) acute changes in that rate constant. Using this strategy, we have shown that 1) the selective permeability of Cx43 junctions to a small cationic dye varied across two orders of magnitude, consistent with the hypothesis that the various channel configurations adopted by Cx43 display different selective permeabilities; and 2) the selective permeability of Cx37 vs. Cx43 junctions was consistently and significantly lower.
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Affiliation(s)
- Jose F Ek-Vitorín
- Dept. of Physiology, Univ. of Arizona, PO Box 245051, Tucson, AZ 85724-5051, USA
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41
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Stains JP, Civitelli R. Cell-cell interactions in regulating osteogenesis and osteoblast function. ACTA ACUST UNITED AC 2005; 75:72-80. [PMID: 15838921 DOI: 10.1002/bdrc.20034] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Endochondral bone formation requires an elaborate interplay among autocrine, paracrine, and endocrine signals, positional cues, and cell-cell contacts to mediate the complex three-dimensional architecture and function of the skeleton. Embryonic bone development occurs by migration, aggregation, and condensation of immature mesenchymal progenitor cells to form the cartilaginous anlage. Upon vascular invasion, the cartilaginous scaffold is colonized and subsequently mineralized by osteoblasts. Likewise, bone remodeling in the adult skeleton is a dynamic process that requires coordinated cellular activities among osteoblasts, osteocytes, and osteoclasts to maintain bone homeostasis. This review examines the role of cell-cell interactions mediated by adherens junctions formed by cadherins and communicative gap junctions formed by connexins in regulating bone development and osteogenic function.
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Affiliation(s)
- Joseph P Stains
- Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, Maryland, USA
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42
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Abstract
Bone development (modeling) occurs by migration, aggregation, and condensation of immature osteo/chondroprogenitor cells to form the cartilaginous anlage. This process requires precisely controlled cell-cell interactions. Likewise, bone remodeling in the adult skeleton is a dynamic process that requires coordinated cellular activities among osteoblasts, osteocytes, and osteoclasts to maintain bone homeostasis. The cooperative nature of both bone modeling and remodeling requires tightly regulated mechanisms of intercellular recognition and communication that permit the cells to sort and migrate, synchronize activity, equalize hormonal responses, and diffuse locally generated signals. Osteoblasts and osteocytes achieve these interactions through cadherin-based adherens junctions as well as by formation of communicating junctions, gap junctions. This review examines the current knowledge of how direct cell-to-cell interactions modulate osteoblast function.
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Affiliation(s)
- Joseph P Stains
- Division of Bone and Mineral Diseases, Washington University School of Medicine, Barnes-Jewish Hospital, St. Louis, MO, USA
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43
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Leite AR, Carvalho CPF, Furtado AG, Barbosa HCL, Boschero AC, Collares-Buzato CB. Co-expression and regulation of connexins 36 and 43 in cultured neonatal rat pancreatic islets. Can J Physiol Pharmacol 2005; 83:142-51. [PMID: 15791287 DOI: 10.1139/y04-133] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Fetal and neonatal pancreatic islets present a lower insulin secretory response as compared with adult islets. Prolonged culturing leads to an improvement of the glucose-induced insulin secretion response in neonatal pancreatic islets that may involve regulation of gap junction mediated cell communication. In this study, we investigated the effect of culturing neonatal islet cells for varying periods of time and with different glucose medium concentrations on the cellular expression of the endocrine pancreatic gap junction associated connexin (Cx) 36 and Cx43. We report here that the 7-d culture induced upregulation of the expression of these junctional proteins in neonatal islets in a time-dependent manner. A correlation was observed between the increased mRNA and protein expression of Cx36 and Cx43 and the increased insulin secretion following islet culturing. In addition, increasing glucose concentration within the culture medium induced a concentration-dependent enhancement of Cx36 islet expression, but not of Cx43 expression in cultured neonatal islets. In conclusion, we suggest that the regulation of gap junctional proteins by culture medium containing factors and glucose may be an important event for the maturation process of beta cells observed at in vitro conditions.
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Affiliation(s)
- A R Leite
- Department of Physiology and Biophysics, Universidade Estadual de Campinas, Brasil
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44
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Stains JP, Civitelli R. Gap junctions regulate extracellular signal-regulated kinase signaling to affect gene transcription. Mol Biol Cell 2004; 16:64-72. [PMID: 15525679 PMCID: PMC539152 DOI: 10.1091/mbc.e04-04-0339] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Osteoblasts are highly coupled by gap junctions formed by connexin43. Overexpression of connexin45 in osteoblasts results in decreased chemical and electrical coupling and reduces gene transcription from connexin response elements (CxREs) in the osteocalcin and collagen Ialpha1 promoters. Here, we demonstrate that transcription from the gap junction-dependent osteocalcin CxRE is regulated by extracellular signal-regulated protein kinase (ERK) and phosphatidylinositol 3-kinase (PI3K) cascades. Overexpression of a constitutively active mitogen-activated protein kinase kinase (MEK), Raf, or Ras can increase transcription more than twofold of the CxRE, whereas inhibition of MEK or PI3K can decrease transcription threefold from the osteocalcin CxRE. Importantly, disruption of gap junctional communication by overexpression of connexin45 or treatment with pharmacological inhibitors of gap junctions results in reduced Raf, ERK, and Akt activation. The consequence of attenuated gap junction-dependent signal cascade activation is a decrease in Sp1 phosphorylation by ERK, resulting in decreased Sp1 recruitment to the CxRE and inhibited gene transcription. These data establish that ERK/PI3K signaling is required for the optimal elaboration of transcription from the osteocalcin CxRE, and that disruption of gap junctional communication attenuates the ability of cells to respond to an extracellular cue, presumably by limiting the propagation of second messengers among adjacent cells by connexin43-gap junctions.
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Affiliation(s)
- Joseph P Stains
- Division of Bone and Mineral Diseases, Washington University School of Medicine and Barnes-Jewish Hospital, St. Louis, MO 63110, USA
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45
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Calabrese A, Caton D, Meda P. Differentiating the effects of Cx36 and E-cadherin for proper insulin secretion of MIN6 cells. Exp Cell Res 2004; 294:379-91. [PMID: 15023528 DOI: 10.1016/j.yexcr.2003.12.007] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2003] [Indexed: 11/29/2022]
Abstract
Connexins have been implicated in many cell functions, even though in most cases it is still unclear whether these functions may actually be mediated by other proteins that are secondarily affected by connexin changes. Secretory systems provide useful models in which to tackle this central question. Primary pancreatic beta-cells and insulin-producing lines are connected by gap junction channels made of Cx36. Using stable transfection of an antisense Cx36 cDNA, we have previously obtained clones of MIN6 cells that featured a markedly reduced expression of Cx36 and impaired insulin secretion. Here, we first show that this change also resulted in loss of E-cadherin and occludin expression, thus preventing the attribution of the secretory defects to a specific type of membrane protein. To investigate this question, we have now restored the expression of either Cx36 or E-cadherin in the Cx36 antisense-transfected cells. We show that a lentivirus-mediated transduction efficiently restored Cx36 expression in MIN6 cells and allowed for expression of variable levels of this protein. We further document that adequate but not excessive levels of Cx36 allowed for recover of normal insulin secretion in response to various secretagogues. Finally, we demonstrate that restoration of normal E-cadherin expression was not able to achieve the same secretory correction. The data demonstrate that Cx36, but not E-cadherin, is necessary to control specific steps of beta-cell secretion.
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Affiliation(s)
- Alessandra Calabrese
- Department of Morphology, University of Geneva Medical School, Geneva, Switzerland.
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46
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Theis M, Mas C, Döring B, Degen J, Brink C, Caille D, Charollais A, Krüger O, Plum A, Nepote V, Herrera P, Meda P, Willecke K. Replacement by a lacZ reporter gene assigns mouse connexin36, 45 and 43 to distinct cell types in pancreatic islets. Exp Cell Res 2004; 294:18-29. [PMID: 14980497 DOI: 10.1016/j.yexcr.2003.09.031] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2003] [Revised: 09/24/2003] [Indexed: 12/13/2022]
Abstract
Transcripts of three connexin isoforms (Cx36, Cx43 and Cx45) have been reported in rodent pancreatic islets, but the precise distribution of the cognate proteins is still unknown. We determined expression of Cx36 in a cell-autonomous manner using mice with a targeted replacement of the Cx36 coding region by a lacZ reporter gene. For cell-autonomous monitoring of Cx43 expression, we used the Cre/loxP system: Mice carrying the Cx43 coding region flanked by loxP sites (floxed) also carried an embedded lacZ gene that is activated after Cre-mediated recombination in cells with transcriptional activity of the Cx43 gene. Deletion of the Cx43 coding region in beta-cells did not result in the activation of the embedded lacZ reporter gene. Instead, Cx43 expression was found in endothelial cells of the islets of Langerhans in mice with endothelium-specific deletion. Ubiquitous deletion of Cx43 led to a similar endothelial lacZ expression, but again, activity of the reporter gene was not detected in beta-cells. Mice with targeted replacement of the Cx45 coding region by lacZ showed a vascular expression similar to Cx43. The data show that native insulin-producing cells express a connexin isoform (Cx36) which differs from those (Cx43 and Cx45) expressed by vascular islet cells.
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Affiliation(s)
- Martin Theis
- Institut für Genetik, Abteilung Molekulargenetik, Universität Bonn, D-53117 Bonn, Germany
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47
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Martin D, Tawadros T, Meylan L, Abderrahmani A, Condorelli DF, Waeber G, Haefliger JA. Critical role of the transcriptional repressor neuron-restrictive silencer factor in the specific control of connexin36 in insulin-producing cell lines. J Biol Chem 2003; 278:53082-9. [PMID: 14565956 DOI: 10.1074/jbc.m306861200] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Connexin36 (Cx36) is specifically expressed in neurons and in pancreatic beta-cells. Cx36 functions as a critical regulator of insulin secretion and content in beta-cells. In order to identify the molecular mechanisms that control the beta-cell expression of Cx36, we initiated the characterization of the human 5' regulatory region of the CX36 gene. A 2043-bp fragment of the human CX36 promoter was identified from a human BAC library and fused to a luciferase reporter gene. This promoter region was sufficient to confer specific expression to the reporter gene in insulin-secreting cell lines. Within this 5' regulatory region, a putative neuron-restrictive silencer element conserved between rodent and human species was recognized and binds the neuron-restrictive silencing factor (NRSF/REST). This factor is not expressed in insulin-secreting cells and neurons; it functions as a potent repressor through the recruitment of histone deacetylase to the promoter of neuronal genes. The NRSF-mediated repression of Cx36 in HeLa cells was abolished by trichostatin A, confirming the functional importance of histone deacetylase activity. Ectopic expression, by viral gene transfer, of NRSF/REST in different insulin-secreting beta-cell lines induced a marked reduction in Cx36 mRNA and protein content. Moreover, mutations in the Cx36 neuron-restrictive silencer element relieved the low transcriptional activity of the human CX36 promoter observed in HeLa cells and in INS-1 cells expressing NRSF/REST. The data showed that cx36 gene expression in insulin-producing beta-cell lines is strictly controlled by the transcriptional repressor NRSF/REST indicating that Cx36 participates to the neuronal phenotype of the pancreatic beta-cells.
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Affiliation(s)
- David Martin
- Department of Internal Medicine, University Hospital, CHUV-1011 Lausanne, Switzerland
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48
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Hamaguchi K, Utsunomiya N, Takaki R, Yoshimatsu H, Sakata T. Cellular interaction between mouse pancreatic alpha-cell and beta-cell lines: possible contact-dependent inhibition of insulin secretion. Exp Biol Med (Maywood) 2003; 228:1227-33. [PMID: 14610265 DOI: 10.1177/153537020322801020] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The endocrine cells in the pancreatic islet have cellular communication between the heterotypic cells as well as the homotypic cells. The present study was conducted to elucidate the cellular interaction between pancreatic alpha cells and beta cells utilizing differentiated mouse cell lines (i.e., alphaTC clone 6 and betaTC cells). Co-culture of these two cell lines on a gyratory shaker generated numerous cellular aggregates of homogenous size within 48 h. Immunohistochemical staining for insulin and glucagon demonstrated that betaTC cells were located in the central core of each aggregate, while alphaTC cells formed a mantle layer surrounding the betaTC cells. This segregation was observed regardless of the ratios of the two cell types employed. Although glucagon at concentrations of 10(-8) M or higher stimulated insulin secretion from betaTC cells in both monolayer and aggregates, an increase in the ratio of alphaTC/betaTC cells in aggregate cultures was accompanied by a decrease in secreted insulin and a rise in intracellular insulin content of the betaTC component. The inhibitory effect of alphaTC cells on betaTC insulin secretion was not limited to aggregate culture, since insulin secretion from betaTC cells was also suppressed, and intracellular insulin content increased, by co-culture of alphaTC with betaTC cells in monolayer. On the other hand, the secreted and intracellular insulin of betaTC cells was not affected by alphaTC cells in a Transwell co-culture system in which direct cell-to-cell contacts were prevented by a semipermeable membrane that permitted chemical communication via medium metabolites. These data suggest that the insulin secretion from betaTC cells may be inhibited possibly as a result of the contact with alphaTC cells.
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Affiliation(s)
- Kazuyuki Hamaguchi
- Department of Anatomy, Biology and Medicine, Oita Medical University School of Medicine, Oita, Japan.
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Saez JC, Berthoud VM, Branes MC, Martinez AD, Beyer EC. Plasma membrane channels formed by connexins: their regulation and functions. Physiol Rev 2003; 83:1359-400. [PMID: 14506308 DOI: 10.1152/physrev.00007.2003] [Citation(s) in RCA: 876] [Impact Index Per Article: 41.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Members of the connexin gene family are integral membrane proteins that form hexamers called connexons. Most cells express two or more connexins. Open connexons found at the nonjunctional plasma membrane connect the cell interior with the extracellular milieu. They have been implicated in physiological functions including paracrine intercellular signaling and in induction of cell death under pathological conditions. Gap junction channels are formed by docking of two connexons and are found at cell-cell appositions. Gap junction channels are responsible for direct intercellular transfer of ions and small molecules including propagation of inositol trisphosphate-dependent calcium waves. They are involved in coordinating the electrical and metabolic responses of heterogeneous cells. New approaches have expanded our knowledge of channel structure and connexin biochemistry (e.g., protein trafficking/assembly, phosphorylation, and interactions with other connexins or other proteins). The physiological role of gap junctions in several tissues has been elucidated by the discovery of mutant connexins associated with genetic diseases and by the generation of mice with targeted ablation of specific connexin genes. The observed phenotypes range from specific tissue dysfunction to embryonic lethality.
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Affiliation(s)
- Juan C Saez
- Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile.
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Lundquist I, Alm P, Salehi A, Henningsson R, Grapengiesser E, Hellman B. Carbon monoxide stimulates insulin release and propagates Ca2+ signals between pancreatic beta-cells. Am J Physiol Endocrinol Metab 2003; 285:E1055-63. [PMID: 14534076 DOI: 10.1152/ajpendo.00498.2002] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A key question for understanding the mechanisms of pulsatile insulin release is how the underlying beta-cell oscillations of the cytoplasmic Ca2+ concentration ([Ca2+]i) are synchronized within and among the islets in the pancreas. Nitric oxide has been proposed to coordinate the activity of the beta-cells by precipitating transients of [Ca2+]i. Comparing ob/ob mice and lean controls, we have now studied the action of carbon monoxide (CO), another neurotransmitter with stimulatory effects on cGMP production. A strong immunoreactivity for the CO-producing constitutive heme oxygenase (HO-2) was found in ganglionic cells located in the periphery of the islets and in almost all islet endocrine cells. Islets from ob/ob mice had sixfold higher generation of CO (1 nmol.min-1.mg protein-1) than the lean controls. This is 100-fold the rate for their constitutive production of NO. Moreover, islets from ob/ob mice showed a threefold increase in HO-2 expression and expressed inducible HO (HO-1). The presence of an excessive islet production of CO in the ob/ob mouse had its counterpart in a pronounced suppression of the glucose-stimulated insulin release from islets exposed to the HO inhibitor Zn-protoporhyrin (10 microM) and in a 16 times higher frequency of [Ca2+]i transients in their beta-cells. Hemin (0.1 and 1.0 microM), the natural substrate for HO, promoted the appearance of [Ca2+]i transients, and 10 microM of the HO inhibitors Zn-protoporphyrin and Cr-mesoporphyrin had a suppressive action both on the firing of transients and their synchronization. It is concluded that the increased islet production of CO contributes to the hyperinsulinemia in ob/ob mice. In addition to serving as a positive modulator of glucose-stimulated insulin release, CO acts as a messenger propagating Ca2+ signals with coordinating effects on the beta-cell rhythmicity.
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Affiliation(s)
- Ingmar Lundquist
- Department of Pharmacology, Institute of Physiological Sciences, University of Lund, BMC F13, S-221 84 Lund, Sweden.
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