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Suckert C, Zosel C, Schaefer M. Simultaneous TIRF imaging of subplasmalemmal Ca 2+ dynamics and granule fusions in insulin-secreting INS-1 cells reveals coexistent synchronized and asynchronous release. Cell Calcium 2024; 120:102883. [PMID: 38643716 DOI: 10.1016/j.ceca.2024.102883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Revised: 03/21/2024] [Accepted: 03/29/2024] [Indexed: 04/23/2024]
Abstract
The basal and glucose-induced insulin secretion from pancreatic beta cells is a tightly regulated process that is triggered in a Ca2+-dependent fashion and further positively modulated by substances that raise intracellular levels of adenosine 3',5'-cyclic monophosphate (cAMP) or by certain antidiabetic drugs. In a previous study, we have temporally resolved the subplasmalemmal [Ca2+]i dynamics in beta cells that are characterized by trains of sharply delimited spikes, reaching peak values up to 5 µM. Applying total internal reflection fluorescence (TIRF) microscopy and synaptopHluorin to visualize fusion events of individual granules, we found that several fusion events can coincide within 50 to 150 ms. To test whether subplasmalemmal [Ca2+]i microdomains around single or clustered Ca2+ channels may cause a synchronized release of insulin-containing vesicles, we applied simultaneous dual-color TIRF microscopy and monitored Ca2+ fluctuations and exocytotic events in INS-1 cells at high frame rates. The results indicate that fusions can be triggered by subplasmalemmal Ca2+ spiking. This, however, does account for a minority of fusion events. About 90 %-95 % of fusion events either happen between Ca2+ spikes or incidentally overlap with subplasmalemmal Ca2+ spikes. We conclude that only a fraction of exocytotic events in glucose-induced and tolbutamide- or forskolin-enhanced insulin release from INS-1 cells is tightly coupled to Ca2+ microdomains around voltage-gated Ca2+ channels.
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Affiliation(s)
- Charlotte Suckert
- Leipzig University, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Härtelstraße 16-18, Leipzig 04107, Germany
| | - Carolin Zosel
- Leipzig University, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Härtelstraße 16-18, Leipzig 04107, Germany
| | - Michael Schaefer
- Leipzig University, Rudolf-Boehm-Institute of Pharmacology and Toxicology, Härtelstraße 16-18, Leipzig 04107, Germany.
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Jevon D, Cottle L, Hallahan N, Harwood R, Samra JS, Gill AJ, Loudovaris T, Thomas HE, Thorn P. Capillary contact points determine beta cell polarity, control secretion and are disrupted in the db/db mouse model of diabetes. Diabetologia 2024:10.1007/s00125-024-06180-x. [PMID: 38814445 DOI: 10.1007/s00125-024-06180-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/11/2024] [Accepted: 03/26/2024] [Indexed: 05/31/2024]
Abstract
AIMS/HYPOTHESIS Almost all beta cells contact one capillary and insulin granule fusion is targeted to this region. However, there are reports of beta cells contacting more than one capillary. We therefore set out to determine the proportion of beta cells with multiple contacts and the impact of this on cell structure and function. METHODS We used pancreatic slices in mice and humans to better maintain cell and islet structure than in isolated islets. Cell structure was assayed using immunofluorescence and 3D confocal microscopy. Live-cell two-photon microscopy was used to map granule fusion events in response to glucose stimulation. RESULTS We found that 36% and 22% of beta cells in islets from mice and humans, respectively, have separate contact with two capillaries. These contacts establish a distinct form of cell polarity with multiple basal regions. Both capillary contact points are enriched in presynaptic scaffold proteins, and both are a target for insulin granule fusion. Cells with two capillary contact points have a greater capillary contact area and secrete more, with analysis showing that, independent of the number of contact points, increased contact area is correlated with increased granule fusion. Using db/db mice as a model for type 2 diabetes, we observed changes in islet capillary organisation that significantly reduced total islet capillary surface area, and reduced area of capillary contact in single beta cells. CONCLUSIONS/INTERPRETATION Beta cells that contact two capillaries are a significant subpopulation of beta cells within the islet. They have a distinct form of cell polarity and both contact points are specialised for secretion. The larger capillary contact area of cells with two contact points is correlated with increased secretion. In the db/db mouse, changes in capillary structure impact beta cell capillary contact, implying that this is a new factor contributing to disease progression.
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Affiliation(s)
- Dillon Jevon
- Charles Perkins Centre, School of Medical Sciences, University of Sydney, Camperdown, NSW, Australia
| | - Louise Cottle
- Charles Perkins Centre, School of Medical Sciences, University of Sydney, Camperdown, NSW, Australia
| | - Nicole Hallahan
- Charles Perkins Centre, School of Medical Sciences, University of Sydney, Camperdown, NSW, Australia
| | - Richard Harwood
- Charles Perkins Centre, Sydney Microscopy and Microanalysis, University of Sydney, Camperdown, NSW, Australia
| | - Jaswinder S Samra
- The University of Sydney Northern Clinical School, Sydney, NSW, Australia
- Upper Gastrointestinal Surgical Unit, Royal North Shore Hospital, St Leonards, NSW, Australia
| | - Anthony J Gill
- The University of Sydney Northern Clinical School, Sydney, NSW, Australia
- Department of Anatomical Pathology, Royal North Shore Hospital, St Leonards, NSW, Australia
- Cancer Diagnosis and Pathology Research Group, Kolling Institute of Medical Research, St Leonards, NSW, Australia
| | | | - Helen E Thomas
- St Vincent's Institute, Fitzroy, VIC, Australia
- Department of Medicine, St Vincent's Hospital, University of Melbourne, Fitzroy, VIC, Australia
| | - Peter Thorn
- Charles Perkins Centre, School of Medical Sciences, University of Sydney, Camperdown, NSW, Australia.
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Polino AJ, Wen Ng X, Rooks R, Piston DW. Disrupting actin filaments enhances glucose-stimulated insulin secretion independent of the cortical actin cytoskeleton. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.15.549141. [PMID: 37502863 PMCID: PMC10369950 DOI: 10.1101/2023.07.15.549141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Just under the plasma membrane of most animal cells lies a dense meshwork of actin filaments called the cortical cytoskeleton. In insulin-secreting pancreatic β cells, a longstanding model posits that the cortical actin layer primarily acts to restrict access of insulin granules to the plasma membrane. Here we test this model and find that stimulating β cells with pro-secretory stimuli (glucose and/or KCl) has little impact on the cortical actin layer. Chemical perturbations of actin polymerization, by either disrupting or enhancing filamentation, dramatically enhances glucose-stimulated insulin secretion. We find that this enhancement does not correlate with the state of the cortical actin layer, suggesting filament disruptors act on insulin secretion independently of the cortical cytoskeleton.
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Affiliation(s)
| | | | | | - David W. Piston
- Department of Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
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Fye MA, Kaverina I. Insulin secretion hot spots in pancreatic β cells as secreting adhesions. Front Cell Dev Biol 2023; 11:1211482. [PMID: 37305687 PMCID: PMC10250740 DOI: 10.3389/fcell.2023.1211482] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Accepted: 05/18/2023] [Indexed: 06/13/2023] Open
Abstract
Pancreatic β cell secretion of insulin is crucial to the maintenance of glucose homeostasis and prevention of diseases related to glucose regulation, including diabetes. Pancreatic β cells accomplish efficient insulin secretion by clustering secretion events at the cell membrane facing the vasculature. Regions at the cell periphery characterized by clustered secretion are currently termed insulin secretion hot spots. Several proteins, many associated with the microtubule and actin cytoskeletons, are known to localize to and serve specific functions at hot spots. Among these proteins are the scaffolding protein ELKS, the membrane-associated proteins LL5β and liprins, the focal adhesion-associated protein KANK1, and other factors typically associated with the presynaptic active zone in neurons. These hot spot proteins have been shown to contribute to insulin secretion, but many questions remain regarding their organization and dynamics at hot spots. Current studies suggest microtubule- and F-actin are involved in regulation of hot spot proteins and their function in secretion. The hot spot protein association with the cytoskeleton networks also suggests a potential role for mechanical regulation of these proteins and hot spots in general. This perspective summarizes the existing knowledge of known hot spot proteins, their cytoskeletal-mediated regulation, and discuss questions remaining regarding mechanical regulation of pancreatic beta cell hot spots.
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Affiliation(s)
| | - Irina Kaverina
- Kaverina Lab, Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN, United States
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Amin ML, Deng K, Tran HA, Singh R, Rnjak-Kovacina J, Thorn P. Glucose-Dependent Insulin Secretion from β Cell Spheroids Is Enhanced by Embedding into Softer Alginate Hydrogels Functionalised with RGD Peptide. BIOENGINEERING (BASEL, SWITZERLAND) 2022; 9:bioengineering9120722. [PMID: 36550929 PMCID: PMC9774350 DOI: 10.3390/bioengineering9120722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 11/14/2022] [Accepted: 11/20/2022] [Indexed: 11/24/2022]
Abstract
Type 1 diabetes results from the loss of pancreatic β cells, reduced insulin secretion and dysregulated blood glucose levels. Replacement of these lost β cells with stem cell-derived β cells, and protecting these cells within macro-device implants is a promising approach to restore glucose homeostasis. However, to achieve this goal of restoration of glucose balance requires work to optimise β cell function within implants. We know that native β cell function is enhanced by cell-cell and cell-extracellular matrix interactions within the islets of Langerhans. Reproducing these interactions in 2D, such as culture on matrix proteins, does enhance insulin secretion. However, the impact of matrix proteins on the 3D organoids that would be in implants has not been widely studied. Here, we use native β cells that are dispersed from islets and reaggregated into small spheroids. We show these β cell spheroids have enhanced glucose-dependent insulin secretion when embedded into softer alginate hydrogels conjugated with RGD peptide (a common motif in extracellular matrix proteins). Embedding into alginate-RGD causes activation of integrin responses and repositioning of liprin, a protein that controls insulin secretion. We conclude that insulin secretion from β cell spheroids can be enhanced through manipulation of the surrounding environment.
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Affiliation(s)
- Md Lutful Amin
- School of Medical Sciences, Charles Perkins Centre, University of Sydney, Camperdown, NSW 2006, Australia
| | - Kylie Deng
- School of Medical Sciences, Charles Perkins Centre, University of Sydney, Camperdown, NSW 2006, Australia
| | - Hien A. Tran
- Graduate School of Biomedical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia
| | - Reena Singh
- School of Medical Sciences, Charles Perkins Centre, University of Sydney, Camperdown, NSW 2006, Australia
| | - Jelena Rnjak-Kovacina
- Graduate School of Biomedical Engineering, The University of New South Wales, Sydney, NSW 2052, Australia
| | - Peter Thorn
- School of Medical Sciences, Charles Perkins Centre, University of Sydney, Camperdown, NSW 2006, Australia
- Correspondence:
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Barillaro M, Schuurman M, Wang R. β1-Integrin-A Key Player in Controlling Pancreatic Beta-Cell Insulin Secretion via Interplay With SNARE Proteins. Endocrinology 2022; 164:6772824. [PMID: 36282882 DOI: 10.1210/endocr/bqac179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Indexed: 01/16/2023]
Abstract
Shortcomings in cell-based therapies for patients with diabetes have been revealed to be, in part, a result of an improper extracellular matrix (ECM) environment. In vivo, pancreatic islets are emersed in a diverse ECM that provides physical support and is crucial for healthy function. β1-Integrin receptors have been determined to be responsible for modulation of beneficial interactions with ECM proteins influencing beta-cell development, proliferation, maturation, and function. β1-Integrin signaling has been demonstrated to augment insulin secretion by impacting the actin cytoskeleton via activation of focal adhesion kinase and downstream signaling pathways. In other secretory cells, evidence of a bidirectional relationship between integrins and exocytotic machinery has been demonstrated, and, thus, this relationship could be present in pancreatic beta cells. In this review, we will discuss the role of ECM-β1-integrin interplay with exocytotic proteins in controlling pancreatic beta-cell insulin secretion through their dynamic and unique signaling pathway.
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Affiliation(s)
- Malina Barillaro
- Children's Health Research Institute, University of Western Ontario, London, ON N6C 2V5, Canada
- Department of Physiology & Pharmacology, University of Western Ontario, London, ON N6C 2V5, Canada
| | - Meg Schuurman
- Children's Health Research Institute, University of Western Ontario, London, ON N6C 2V5, Canada
- Department of Physiology & Pharmacology, University of Western Ontario, London, ON N6C 2V5, Canada
| | - Rennian Wang
- Children's Health Research Institute, University of Western Ontario, London, ON N6C 2V5, Canada
- Department of Physiology & Pharmacology, University of Western Ontario, London, ON N6C 2V5, Canada
- Department of Medicine, University of Western Ontario, London, ON N6C 2V5, Canada
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Yang L, Fye MA, Yang B, Tang Z, Zhang Y, Haigh S, Covington BA, Bracey K, Taraska JW, Kaverina I, Qu S, Chen W. Genome-wide CRISPR screen identified a role for commander complex mediated ITGB1 recycling in basal insulin secretion. Mol Metab 2022; 63:101541. [PMID: 35835371 PMCID: PMC9304790 DOI: 10.1016/j.molmet.2022.101541] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Revised: 06/30/2022] [Accepted: 07/01/2022] [Indexed: 01/28/2023] Open
Abstract
OBJECTIVES Pancreatic beta cells secrete insulin postprandially and during fasting to maintain glucose homeostasis. Although glucose-stimulated insulin secretion (GSIS) has been extensively studied, much less is known about basal insulin secretion. Here, we performed a genome-wide CRISPR/Cas9 knockout screen to identify novel regulators of insulin secretion. METHODS To identify genes that cell autonomously regulate insulin secretion, we engineered a Cas9-expressing MIN6 subclone that permits irreversible fluorescence labeling of exocytic insulin granules. Using a fluorescence-activated cell sorting assay of exocytosis in low glucose and high glucose conditions in individual cells, we performed a genome-wide CRISPR/Cas9 knockout screen. RESULTS We identified several members of the COMMD family, a conserved family of proteins with central roles in intracellular membrane trafficking, as positive regulators of basal insulin secretion, but not GSIS. Mechanistically, we show that the Commander complex promotes insulin granules docking in basal state. This is mediated, at least in part, by its function in ITGB1 recycling. Defective ITGB1 recycling reduces its membrane distribution, the number of focal adhesions and cortical ELKS-containing complexes. CONCLUSIONS We demonstrated a previously unknown function of the Commander complex in basal insulin secretion. We showed that by ITGB1 recycling, Commander complex increases cortical adhesions, which enhances the assembly of the ELKS-containing complexes. The resulting increase in the number of insulin granules near the plasma membrane strengthens basal insulin secretion.
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Affiliation(s)
- Liu Yang
- Department of Endocrinology and Metabolism, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai 200072, China; Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Margret A Fye
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Bingyuan Yang
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Zihan Tang
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Yue Zhang
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Sander Haigh
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Brittney A Covington
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Kai Bracey
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Justin W Taraska
- Biochemistry and Biophysics Center, NHLBI, NIH, Bethesda, MD 20892, USA
| | - Irina Kaverina
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Shen Qu
- Department of Endocrinology and Metabolism, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai 200072, China.
| | - Wenbiao Chen
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
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