| 1. |
- Idevall Hagren, Olof, 1980-, et al.
(författare)
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Keeping pace : the primary cilium as the conducting baton of the islet
- 2024
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Ingår i: Diabetologia. - : Springer. - 0012-186X .- 1432-0428. ; 67, s. 773-782
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Forskningsöversikt (refereegranskat)abstract
- Primary cilia are rod-like sensory organelles that protrude from the surface of most mammalian cells, including the cells of the islet, and mounting evidence supports important roles of these structures in the regulation of beta cell function and insulin secretion. The sensory abilities of the cilium arise from local receptor activation that is coupled to intrinsic signal transduction, and ciliary signals can propagate into the cell and influence cell function. Here, we review recent advances and studies that provide insights into intra-islet cues that trigger primary cilia signalling; how second messenger signals are generated and propagated within cilia; and how ciliary signalling affects beta cell function. We also discuss the potential involvement of primary cilia and ciliary signalling in the development and progression of type 2 diabetes, identify gaps in our current understanding of islet cell cilia function and provide suggestions on how to further our understanding of this intriguing structure.
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| 2. |
- Idevall Hagren, Olof, 1980-, et al.
(författare)
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Metabolic regulation of calcium signaling in beta cells
- 2020
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Ingår i: Seminars in Cell and Developmental Biology. - : ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD. - 1084-9521 .- 1096-3634. ; 103, s. 20-30
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Forskningsöversikt (refereegranskat)abstract
- The cytoplasmic Ca2+ concentration ([Ca2+](cyt)) regulates a vast number of cellular functions, including insulin secretion from beta cells. The major physiological insulin secretagogue, glucose, triggers [Ca2+](cyt) oscillations in beta cells. Synchronization of the oscillations among the beta cells within an islet underlies the generation of pulsatile insulin secretion. This review describes the mechanisms generating [Ca2+](cyt) oscillations, the interactions between [Ca2+](cyt) and cell metabolism, as well as the contribution of various organelles to the shaping of [Ca2+](cyt) signals and insulin secretion. It also discusses how Ca2+ signals are coordinated and spread throughout the islets and data indicating that altered Ca2+ signaling is associated with beta cell dysfunction and development of type 2 diabetes.
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| 3. |
- Li, Hanbing, et al.
(författare)
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Dual Function of PI(4,5)P2 in Insulin-Regulated Exocytic Trafficking of GLUT4 in Adipocytes
- 2020
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Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 432:16, s. 4341-4357
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Tidskriftsartikel (refereegranskat)abstract
- Phosphoinositides are important signaling molecules involved in the regulation of vesicular trafficking. It has been implicated that phosphatidylinositol 4,5-bisphosphate [PI(4,5)P-2] is involved in insulin-regulated GLUT4 translocation in adipocytes. However, it remains unclear where and how PI(4,5)P-2 regulates discrete steps of GLUT4 vesicle translocation in adipocytes, especially on the exocytic arm of regulation. Here, we employed optogenetic tools to acutely control the PI(4,5)P-2 metabolism in living cells. By combination of TIRFM imaging, we were able to monitor the temporal-spatial-dependent PI(4,5)P-2 regulation on discrete steps of GLUT4 translocation in adipocytes. We found that the plasma membrane localized PI(4,5)P-2 is crucial for proper insulin signaling propagation and for insulin-stimulated GLUT4 vesicle translocation in 3T3-L1 adipocytes. Global depletion of PI(4,5)P-2 on the cell surface blunted insulin-stimulated Akt phosphorylation and abolished insulin effects in promotion of the docking and fusion of GLUT4 vesicle with the plasma membrane. Furthermore, by development of a novel optogenetic module to selectively modulate PI(4,5)P-2 levels on the GLUT4 vesicle docking site, we identified an important regulatory role of PI(4,5)P-2 in controlling of vesicle docking process. Local depletion of PI(4,5)P-2 at the vesicle docking site promoted GLUT4 vesicle undocking, diminished insulin-stimulated GLUT4 vesicle docking and fusion, but without perturbation of insulin signaling propagation in adipocytes. Our results provide strong evidence that cell surface PI(4,5)P-2 plays two distinct functions on regulation of the exocytic trafficking of GLUT4 in adipocytes. PI(4,5)P-2 not only regulates the proper activation of insulin signaling in general but also controls GLUT4 vesicle docking process at the vesicle-membrane contact sites.
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| 4. |
- Mousavy Gharavy, S. Neda, et al.
(författare)
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Sexually dimorphic roles for the type 2 diabetes-associated C2cd4b gene in murine glucose homeostasis
- 2021
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Ingår i: Diabetologia. - : Springer Nature. - 0012-186X .- 1432-0428. ; 64:4, s. 850-864
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Tidskriftsartikel (refereegranskat)abstract
- Aims/hypothesis Variants close to the VPS13C/C2CD4A/C2CD4B locus are associated with altered risk of type 2 diabetes in genome-wide association studies. While previous functional work has suggested roles for VPS13C and C2CD4A in disease development, none has explored the role of C2CD4B. Methods CRISPR/Cas9-induced global C2cd4b-knockout mice and zebrafish larvae with c2cd4a deletion were used to study the role of this gene in glucose homeostasis. C2 calcium dependent domain containing protein (C2CD)4A and C2CD4B constructs tagged with FLAG or green fluorescent protein were generated to investigate subcellular dynamics using confocal or near-field microscopy and to identify interacting partners by mass spectrometry. Results Systemic inactivation of C2cd4b in mice led to marked, but highly sexually dimorphic changes in body weight and glucose homeostasis. Female C2cd4b mice displayed unchanged body weight compared with control littermates, but abnormal glucose tolerance (AUC, p = 0.01) and defective in vivo, but not in vitro, insulin secretion (p = 0.02). This was associated with a marked decrease in follicle-stimulating hormone levels as compared with wild-type (WT) littermates (p = 0.003). In sharp contrast, male C2cd4b null mice displayed essentially normal glucose tolerance but an increase in body weight (p < 0.001) and fasting blood glucose (p = 0.003) after maintenance on a high-fat and -sucrose diet vs WT littermates. No metabolic disturbances were observed after global inactivation of C2cd4a in mice, or in pancreatic beta cell function at larval stages in C2cd4a null zebrafish. Fasting blood glucose levels were also unaltered in adult C2cd4a-null fish. C2CD4B and C2CD4A were partially localised to the plasma membrane, with the latter under the control of intracellular Ca2+. Binding partners for both included secretory-granule-localised PTPRN2/phogrin. Conclusions/interpretation Our studies suggest that C2cd4b may act centrally in the pituitary to influence sex-dependent circuits that control pancreatic beta cell function and glucose tolerance in rodents. However, the absence of sexual dimorphism in the impact of diabetes risk variants argues for additional roles for C2CD4A or VPS13C in the control of glucose homeostasis in humans. Data availability The datasets generated and/or analysed during the current study are available in the Biorxiv repository (www. biorxiv.org/content/10.1101/2020.05.18.099200v1). RNA-Seq (GSE152576) and proteomics (PXD021597) data have been deposited to GEO (www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE152576) and ProteomeXchange (www.ebi.ac.uk/pride/ archive/projects/PXD021597) repositories, respectively.
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| 5. |
- Ngamjariyawat, Anongnad, 1976-, et al.
(författare)
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Metabolic stress-induced human beta-cell death is mediated by increased intracellular levels of adenosine
- 2023
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Ingår i: Frontiers in Endocrinology. - : Frontiers Media S.A.. - 1664-2392. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: High intracellular concentrations of adenosine and 2'-deoxyadenosine have been suggested to be an important mediator of cell death. The aim of the present study was to characterize adenosine-induced death in insulin-producing beta-cells, at control and high glucose + palmitate-induced stress conditions.Methods: Human insulin-producing EndoC-betaH1 cells were treated with adenosine, 2'-deoxyadenosine, inosine and high glucose + sodium palmitate, and death rates using flow cytometry were studied.Results: We observed that adenosine and the non-receptor-activating analogue 2-deoxyadenosine, but not the adenosine deamination product inosine, promoted beta-cell apoptosis at concentrations exceeding maximal adenosine-receptor stimulating concentrations. Both adenosine and inosine were efficiently taken up by EndoC-betaH1 cells, and inosine counteracted the cell death promoting effect of adenosine by competing with adenosine for uptake. Both adenosine and 2'-deoxyadenosine promptly reduced insulin-stimulated production of plasma membrane PI(3,4,5)P-3, an effect that was reversed upon wash out of adenosine. In line with this, adenosine, but not inosine, rapidly diminished Akt phosphorylation. Both pharmacological Bax inhibition and Akt activation blocked adenosine-induced beta-cell apoptosis, indicating that adenosine/2'-deoxyadenosine inhibits the PI3K/Akt/BAD anti-apoptotic pathway. High glucose + palmitate-induced cell death was paralleled by increased intracellular adenosine and inosine levels. Overexpression of adenosine deaminase-1 (ADA1) in EndoC-betaH1 cells, which increased Akt phosphorylation, prevented both adenosine-induced apoptosis and high glucose + palmitate-induced necrosis. ADA2 overexpression not only failed to protect against adenosine and high glucose + palmitate-activated cell death, but instead potentiated the apoptosis-stimulating effect of adenosine. In line with this, ADA1 overexpression increased inosine production from adenosine-exposed cells, whereas ADA2 did not. Knockdown of ADA1 resulted in increased cell death rates in response to both adenosine and high glucose + palmitate. Inhibition of miR-30e-3p binding to the ADA1 mRNA 3'-UTR promoted the opposite effects on cell death rates and reduced intracellular adenosine contents.Discussion: It is concluded that intracellular adenosine/2'-deoxyadenosine regulates negatively the PI3K pathway and is therefore an important mediator of beta-cell apoptosis. Adenosine levels are controlled, at least in part, by ADA1, and strategies to upregulate ADA1 activity, during conditions of metabolic stress, could be useful in attempts to preserve beta-cell mass in diabetes.
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| 6. |
- O'Callaghan, Paul, et al.
(författare)
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Piezo1 activation attenuates thrombin-induced blebbing in breast cancer cells
- 2022
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Ingår i: Journal of Cell Science. - : The Company of Biologists. - 0021-9533 .- 1477-9137. ; 135:7
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Tidskriftsartikel (refereegranskat)abstract
- Cancer cells exploit a variety of migration modes to leave primary tumors and establish metastases, including amoeboid cell migration, which is typically reliant on bleb formation. Here we demonstrate that thrombin induces dynamic blabbing in the MDA-MB-231 breast cancer cell line and confirm that protease-activated receptor 1 (PAR1) activation is sufficient to induce this effect. Cell confinement has been implicated as a driving force in bleb-based migration. Unexpectedly, we found that gentle contact compression, exerted using a custom built 'cell press' to mechanically stimulate cells, reduced thrombin-induced blebbing. Thrombin-induced blebbing was similarly attenuated using the small molecule Yoda1, an agonist of the mechanosensitive Ca2+ channel Piezo1, and this attenuation was impaired in Piezo1-depleted cells. Additionally, Piezo1 activation suppressed thrombin-induced phosphorylation of ezrin, radixin and moesin (ERM) proteins, which are implicated in the blabbing process. Our results provide mechanistic insights into Piezo1 activation as a suppressor of dynamic blebbing, specifically that which is induced by thrombin.
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| 7. |
- Omar-Hmeadi, Muhmmad, et al.
(författare)
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Insulin granule biogenesis and exocytosis
- 2021
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Ingår i: Cellular and Molecular Life Sciences (CMLS). - : Springer. - 1420-682X .- 1420-9071. ; 78:5, s. 1957-1970
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Forskningsöversikt (refereegranskat)abstract
- Insulin is produced by pancreatic beta-cells, and once released to the blood, the hormone stimulates glucose uptake and suppresses glucose production. Defects in both the availability and action of insulin lead to elevated plasma glucose levels and are major hallmarks of type-2 diabetes. Insulin is stored in secretory granules that form at the trans-Golgi network. The granules undergo extensive modifications en route to their release sites at the plasma membrane, including changes in both protein and lipid composition of the granule membrane and lumen. In parallel, the insulin molecules also undergo extensive modifications that render the hormone biologically active. In this review, we summarize current understanding of insulin secretory granule biogenesis, maturation, transport, docking, priming and eventual fusion with the plasma membrane. We discuss how different pools of granules form and how these pools contribute to insulin secretion under different conditions. We also highlight the role of the beta-cell in the development of type-2 diabetes and discuss how dysregulation of one or several steps in the insulin granule life cycle may contribute to disease development or progression.
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| 8. |
- Panagiotou, Styliani, et al.
(författare)
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OSBP-mediated PI(4)P-cholesterol exchange at endoplasmic reticulum-secretory granule contact sites controls insulin secretion
- 2024
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Ingår i: Cell Reports. - : Cell Press. - 2211-1247. ; 43:4
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Tidskriftsartikel (refereegranskat)abstract
- Insulin is packaged into secretory granules that depart the Golgi and undergo a maturation process that involves changes in the protein and lipid composition of the granules. Here, we show that insulin secretory granules form physical contacts with the endoplasmic reticulum and that the lipid exchange protein oxysterol-binding protein (OSBP) is recruited to these sites in a Ca2+-dependent manner. OSBP binding to insulin granules is positively regulated by phosphatidylinositol-4 (PI4)-kinases and negatively regulated by the PI4 phosphate (PI(4)P) phosphatase Sac2. Loss of Sac2 results in excess accumulation of cholesterol on insulin granules that is normalized when OSBP expression is reduced, and both acute inhibition and small interfering RNA (siRNA)-mediated knockdown of OSBP suppress glucose-stimulated insulin secretion without affecting insulin production or intracellular Ca2+ signaling. In conclusion, we show that lipid exchange at endoplasmic reticulum (ER)-granule contact sites is involved in the exocytic process and propose that these contacts act as reaction centers with multimodal functions during insulin granule maturation.
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| 9. |
- Sanchez, Gonzalo, et al.
(författare)
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The β-cell primary cilium is an autonomous Ca2+ compartment for paracrine GABA signaling
- 2023
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Ingår i: Journal of Cell Biology. - : Rockefeller University Press. - 0021-9525 .- 1540-8140. ; 222:1
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Tidskriftsartikel (refereegranskat)abstract
- The primary cilium is an organelle present in most adult mammalian cells that is considered as an antenna for sensing the local microenvironment. Here, we use intact mouse pancreatic islets of Langerhans to investigate signaling properties of the primary cilium in insulin-secreting β-cells. We find that GABAB1 receptors are strongly enriched at the base of the cilium, but are mobilized to more distal locations upon agonist binding. Using cilia-targeted Ca2+ indicators, we find that activation of GABAB1 receptors induces selective Ca2+ influx into primary cilia through a mechanism that requires voltage-dependent Ca2+ channel activation. Islet β-cells utilize cytosolic Ca2+ increases as the main trigger for insulin secretion, yet we find that increases in cytosolic Ca2+ fail to propagate into the cilium, and that this isolation is largely due to enhanced Ca2+ extrusion in the cilium. Our work reveals local GABA action on primary cilia that involves Ca2+ influx and depends on restricted Ca2+ diffusion between the cilium and cytosol.
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| 10. |
- Xie, Beichen, et al.
(författare)
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The endoplasmic reticulum-plasma membrane tethering protein TMEM24 is a regulator of cellular Ca2+ homeostasis
- 2022
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Ingår i: Journal of Cell Science. - : The Company of Biologists. - 0021-9533 .- 1477-9137. ; 135:5
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Tidskriftsartikel (refereegranskat)abstract
- Endoplasmic reticulum (ER)-plasma membrane (PM) contacts are sites of lipid exchange and Ca2+ transport, and both lipid transport proteins and Ca2+ channels specifically accumulate at these locations. In pancreatic beta-cells, both lipid and Ca2+ signaling are essential for insulin secretion. The recently characterized lipid transfer protein TMEM24 (also known as C2CD2L) dynamically localizes to ER-PM contact sites and provides phosphatidylinositol, a precursor of phosphatidylinositol-4-phosphate [PI(4)P] and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P-2], to the PM. beta-cells lacking TMEM24 exhibit markedly suppressed glucose-induced Ca2+ oscillations and insulin secretion, but the underlying mechanism is not known. We now show that TMEM24 onlyweakly interacts with the PM, and dissociates in response to both diacylglycerol and nanomolar elevations of cytosolic Ca2+. Loss of TMEM24 results in hyper-accumulation of Ca2+ in the ER and in excess Ca2+ entry into mitochondria, with resulting impairment in glucose-stimulated ATP production.
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