1.
Li, Dai-Qing, et al.
(författare)
Suppression of sulfonylurea- and glucose-induced insulin secretion in vitro and in vivo in mice lacking the chloride transport protein ClC-3.
2009
Ingår i: Cell metabolism. - : Elsevier BV. - 1932-7420 .- 1550-4131. ; 10:4, s. 309-15
Tidskriftsartikel (refereegranskat) abstract
Priming of insulin secretory granules for release requires intragranular acidification and depends on vesicular Cl(-)-fluxes, but the identity of the chloride transporter/ion channel involved is unknown. We tested the hypothesis that the chloride transport protein ClC-3 fulfills these actions in pancreatic beta cells. In ClC-3(-/-) mice, insulin secretion evoked by membrane depolarization (high extracellular K(+), sulfonylureas), or glucose was >60% reduced compared to WT animals. This effect was mirrored by a approximately 80% reduction in depolarization-evoked beta cell exocytosis (monitored as increases in cell capacitance) in single ClC-3(-/-) beta cells, as well as a 44% reduction in proton transport across the granule membrane. ClC-3 expression in the insulin granule was demonstrated by immunoblotting, immunostaining, and negative immuno-EM in a high-purification fraction of large dense-core vesicles (LDCVs) obtained by phogrin-EGFP labeling. The data establish the importance of granular Cl(-) fluxes in granule priming and provide direct evidence for the involvement of ClC-3 in the process.
2.
Salunkhe, Vishal A., et al.
(författare)
MiR-335 overexpression impairs insulin secretion through defective priming of insulin vesicles
2017
Ingår i: Physiological Reports. - : Wiley. - 2051-817X. ; 5:21
Tidskriftsartikel (refereegranskat) abstract
MicroRNAs contribute to the maintenance of optimal cellular functions by fine-tuning protein expression levels. In the pancreatic β-cells, imbalances in the exocytotic machinery components lead to impaired insulin secretion and type 2 diabetes (T2D). We hypothesize that dysregulated miRNA expression exacerbates β-cell dysfunction, and have earlier shown that islets from the diabetic GK-rat model have increased expression of miRNAs, including miR-335- 5p (miR-335). Here, we aim to determine the specific role of miR-335 during development of T2D, and the influence of this miRNA on glucose-stimulated insulin secretion and Ca2+-dependent exocytosis. We found that the expression of miR-335 negatively correlated with secretion index in human islets of individuals with prediabetes. Overexpression of miR-335 in human KndoC- (βH\ and in rat INS-1 832/13 cells (OE335) resulted in decreased glucose-sti- mulated insulin secretion, and OE335 cells showed concomitant reduction in three exocytotic proteins: SNAP25, Syntaxin-binding protein 1 (STXBPl), and synaptotagmin 11 (SYTll). Single-cell capacitance measurements, complemented with TIRF microscopy of the granule marker NPY-mEGFP demonstrated a significant reduction in exocytosis in OE335 cells. The reduction was not associated with defective docking or decreased Ca2+ current More likely, it is a direct consequence of impaired priming of already docked granules. Earlier reports have proposed reduced granular priming as the cause of reduced first-phase insulin secretion during prediabetes. Here, we show a specific role of miR-335 in regulating insulin secretion during this transition period. Moreover, we can conclude that miR-335 has the capacity to modulate insulin secretion and Ca2+-dependent exocytosis through effects on granular priming.
3.
Skoug, Cecilia, et al.
(författare)
Density of Sphingosine-1-Phosphate Receptors Is Altered in Cortical Nerve-Terminals of Insulin-Resistant Goto-Kakizaki Rats and Diet-Induced Obese Mice
2023
Ingår i: Neurochemical Research. - 0364-3190.
Tidskriftsartikel (refereegranskat) abstract
Sphingosine-1-phosphate (S1P) is a phosphosphingolipid with pleiotropic biological functions. S1P acts as an intracellular second messenger, as well as extracellular ligand to five G-protein coupled receptors (S1PR1-5). In the brain, S1P regulates neuronal proliferation, apoptosis, synaptic activity and neuroglia activation. Moreover, S1P metabolism alterations have been reported in neurodegenerative disorders. We have previously reported that S1PRs are present in nerve terminals, exhibiting distinct sub-synaptic localization and neuromodulation actions. Since type 2 diabetes (T2D) causes synaptic dysfunction, we hypothesized that S1P signaling is modified in nerve terminals. In this study, we determined the density of S1PRs in cortical synaptosomes from insulin-resistant Goto-Kakizaki (GK) rats and Wistar controls, and from mice fed a high-fat diet (HFD) and low-fat-fed controls. Relative to their controls, GK rats showed similar cortical S1P concentration despite higher S1P levels in plasma, yet lower density of S1PR1, S1PR2 and S1PR4 in nerve-terminal-enriched membranes. HFD-fed mice exhibited increased plasma and cortical concentrations of S1P, and decreased density of S1PR1 and S1PR4. These findings point towards altered S1P signaling in synapses of insulin resistance and diet-induced obesity models, suggesting a role of S1P signaling in T2D-associated synaptic dysfunction.
4.
Barghouth, Mohammad, et al.
(författare)
The T-type calcium channel CaV3.2 regulates insulin secretion in the pancreatic β-cell
2022
Ingår i: Cell Calcium. - : Elsevier BV. - 0143-4160. ; 108
Tidskriftsartikel (refereegranskat) abstract
Voltage-gated Ca2+ (CaV) channel dysfunction leads to impaired glucose-stimulated insulin secretion in pancreatic β-cells and contributes to the development of type-2 diabetes (T2D). The role of the low-voltage gated T-type CaV channels in β-cells remains obscure. Here we have measured the global expression of T-type CaV3.2 channels in human islets and found that gene expression of CACNA1H, encoding CaV3.2, is negatively correlated with HbA1c in human donors, and positively correlated with islet insulin gene expression as well as secretion capacity in isolated human islets. Silencing or pharmacological blockade of CaV3.2 attenuates glucose-stimulated cytosolic Ca2+ signaling, membrane potential, and insulin release. Moreover, the endoplasmic reticulum (ER) Ca2+ store depletion is also impaired in CaV3.2-silenced β-cells. The linkage between T-type (CaV3.2) and L-type CaV channels is further identified by the finding that the intracellular Ca2+ signaling conducted by CaV3.2 is highly dependent on the activation of L-type CaV channels. In addition, CACNA1H expression is significantly associated with the islet predominant L-type CACNA1C (CaV1.2) and CACNA1D (CaV1.3) genes in human pancreatic islets. In conclusion, our data suggest the essential functions of the T-type CaV3.2 subunit as a mediator of β-cell Ca2+ signaling and membrane potential needed for insulin secretion, and in connection with L-type CaV channels.
5.
Björkqvist, Maria, et al.
(författare)
Somatostatin, misoprostol and galanin inhibit gastrin- and PACAP-stimulated secretion of histamine and pancreastatin from ECL cells by blocking specific Ca(2+) channels.
2005
Ingår i: Regulatory Peptides. - : Elsevier BV. - 1873-1686 .- 0167-0115. ; 130:1-2, s. 81-90
Tidskriftsartikel (refereegranskat) abstract
The oxyntic mucosa is rich in ECL cells. They secrete histamine and chromogranin A-derived peptides, such as pancreastatin, in response to gastrin and pituitary adenylate cyclase-activating peptide (PACAP). Secretion is initiated by Ca2+ entry. While gastrin stimulates secretion by opening L-type and N-type Ca2+ channels, PACAP stimulates secretion by activating L-type and receptor-operated Ca2+ channels. Somatostatin, galanin and prostaglandin E2 (PGE2) inhibit gastrin- and PACAP-stimulated secretion from the ECL cells. In the present study, somatostatin and the PGE2 congener misoprostol inhibited gastrin- and PACAP-stimulated secretion 100%, while galanin inhibited at most 60–65%. Bay K 8644, a specific activator of L-type Ca2+ channels, stimulated ECL-cell secretion, an effect that was inhibited equally effectively by somatostatin, misoprostol and galanin (75–80% inhibition). Pretreatment with pertussis toxin, that inactivates inhibitory G-proteins, prevented all three agents from inhibiting stimulated secretion (regardless of the stimulus). Pretreatment with nifedipine (10 μM), an L-type Ca2+ channel blocker, reduced PACAP-evoked pancreastatin secretion by 50–60%, gastrin-evoked secretion by not, vert, similar 80% and abolished the response to Bay K 8644. The nifedipine-resistant response to PACAP was abolished by somatostatin and misoprostol but not by galanin. Gastrin and PACAP raised the intracellular Ca2+ concentration in a biphasic manner, believed to reflect mobilization of internal Ca2+ followed by Ca2+ entry. Somatostatin and misoprostol blocked Ca2+ entry (and histamine and pancreastatin secretion) but not mobilization of internal Ca2+. The present observations on isolated ECL cells suggest that Ca2+ entry rather than mobilization of internal Ca2+ triggers exocytosis, that gastrin and PACAP activate different (but over-lapping) Ca2+ channels, that somatostatin, misoprostol and galanin interact with inhibitory G-proteins to block Ca2+ entry via L-type Ca2+ channels, and that somatostatin and misoprostol (but not galanin) in addition block N-type and/or receptor-operated Ca2+ channels.
6.
Dalgaard, Louise Torp, et al.
(författare)
An 'alpha-beta' of pancreatic islet microribonucleotides
2017
Ingår i: International Journal of Biochemistry and Cell Biology. - : Elsevier BV. - 1357-2725. ; 88, s. 208-219
Tidskriftsartikel (refereegranskat) abstract
MicroRNAs (miRNAs) are cellular, short, non-coding ribonucleotides acting as endogenous posttranscriptional repressors following incorporation in the RNA-induced silencing complex. Despite being chemically and mechanistically very similar, miRNAs exert a multitude of different cellular effects by acting on mRNA species, whose gene-products partake in a wide array of processes.Here, the aim was to review the knowledge of miRNA expression and action in the islet of Langerhans. We have focused on: 1) physiological consequences of islet or beta cell specific inhibition of miRNA processing, 2) mechanisms regulating processing of miRNAs in islet cells, 3) presence and function of miRNAs in alpha versus beta cells - the two main cell types of islets, and 4) miRNA mediators of beta cell decompensation.It is clear that miRNAs regulate pancreatic islet development, maturation, and function in vivo. Moreover, processing of miRNAs appears to be altered by obesity, diabetes, and aging. A number of miRNAs (such as miR-7, miR-21, miR-29, miR-34a, miR-212/miR-132, miR-184, miR-200 and miR-375) are involved in mediating beta cell dysfunction and/or compensation induced by hyperglycemia, oxidative stress, cytotoxic cytokines, and in rodent models of fetal metabolic programming prediabetes and overt diabetes. Studies of human type 2 diabetic islets underline that these miRNA families could have important roles also in human type 2 diabetes.Furthermore, there is a genuine gap of knowledge regarding miRNA expression and function in pancreatic alpha cells. Progress in this area would be enhanced by improved in vitro alpha cell models and better tools for islet cell sorting.
7.
De Marinis, Yang, et al.
(författare)
GLP-1 inhibits and adrenaline stimulates glucagon release by differential modulation of N- and L-type Ca2+ channel-dependent exocytosis.
2010
Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131. ; 11:6, s. 543-553
Tidskriftsartikel (refereegranskat) abstract
Glucagon secretion is inhibited by glucagon-like peptide-1 (GLP-1) and stimulated by adrenaline. These opposing effects on glucagon secretion are mimicked by low (1-10 nM) and high (10 muM) concentrations of forskolin, respectively. The expression of GLP-1 receptors in alpha cells is <0.2% of that in beta cells. The GLP-1-induced suppression of glucagon secretion is PKA dependent, is glucose independent, and does not involve paracrine effects mediated by insulin or somatostatin. GLP-1 is without much effect on alpha cell electrical activity but selectively inhibits N-type Ca(2+) channels and exocytosis. Adrenaline stimulates alpha cell electrical activity, increases [Ca(2+)](i), enhances L-type Ca(2+) channel activity, and accelerates exocytosis. The stimulatory effect is partially PKA independent and reduced in Epac2-deficient islets. We propose that GLP-1 inhibits glucagon secretion by PKA-dependent inhibition of the N-type Ca(2+) channels via a small increase in intracellular cAMP ([cAMP](i)). Adrenaline stimulates L-type Ca(2+) channel-dependent exocytosis by activation of the low-affinity cAMP sensor Epac2 via a large increase in [cAMP](i).
8.
Eliasson, Lena, et al.
(författare)
Lessons from basic pancreatic beta cell research in type-2 diabetes and vascular complications
2017
Ingår i: Diabetology International. - : Springer Science and Business Media LLC. - 2190-1686 .- 2190-1678. ; 8:2, s. 139-152
Forskningsöversikt (refereegranskat) abstract
The changes in life-style with increased access of food and reduced physical activity have resulted in the global epidemic of obesity. Consequently, individuals with type 2 diabetes and cardiovascular disease have also escalated. A central organ in the development of diabetes is the pancreas, and more specifically the pancreatic beta cells within the islets of Langerhans. Beta cells have been assigned the important task of secreting insulin when blood glucose is increased to lower the glucose level. An early sign of diabetes pathogenesis is lack of first phase insulin response and reduced second phase secretion. In this review, which is based on the foreign investigator award lecture given at the JSDC meeting in Sendai in October 2016, we discuss a possible cellular explanation for the reduced first phase insulin response and how this can be influenced by lipids. Moreover, since patients with cardiovascular disease and high levels of cholesterol are often treated with statins, we summarize recent data regarding effects on statins on glucose homeostasis and insulin secretion. Finally, we suggest microRNAs (miRNAs) as central players in the adjustment of beta cell function during the development of diabetes. We specifically discuss miRNAs regarding their involvement in insulin secretion regulation, differential expression in type 2 diabetes, and potential as biomarkers for prediction of diabetes and cardiovascular complications.
9.
Eliasson, Lena
(författare)
The small RNA miR-375 - a pancreatic islet abundant miRNA with multiple roles in endocrine beta cell function
2017
Ingår i: Molecular and Cellular Endocrinology. - : Elsevier BV. - 0303-7207. ; 456, s. 95-101
Tidskriftsartikel (refereegranskat) abstract
The pathophysiology of diabetes is complex and recent research put focus on the pancreatic islets of Langerhans and the insulin-secreting beta cells as central in the development of the disease. MicroRNAs (miRNAs), the small non-coding RNAs regulating post-transcriptional gene expression, are significant regulators of beta cell function. One of the most abundant miRNAs in the islets is miR-375. This review focus on the role of miR-375 in beta cell function, including effects in development and differentiation, proliferation and regulation of insulin secretion. It also discusses the regulation of miR-375 expression, miR-375 as a potential circulating biomarker in type 1 and type 2 diabetes, and the need for the beta cell to keep expression of miR-375 within optimal levels. The summed picture of miR-375 is a miRNA with multiple functions with importance in the formation of beta cell identity, control of beta cell mass and regulation of insulin secretion.
10.
Esguerra, Jonathan L.S., et al.
(författare)
Glucocorticoid induces human beta cell dysfunction by involving riborepressor GAS5 LincRNA
2020
Ingår i: Molecular Metabolism. - : Elsevier BV. - 2212-8778. ; 32, s. 160-167
Tidskriftsartikel (refereegranskat) abstract
Objective: A widely recognized metabolic side effect of glucocorticoid (GC) therapy is steroid-induced diabetes mellitus (DM). However, studies on the molecular basis of GC-induced pancreatic beta cell dysfunction in human beta cells are lacking. The significance of non-coding RNAs in various cellular processes is emerging. In this study, we aimed to show the direct negative impact of GC on beta cell function and elucidate the role of riborepressor GAS5 lincRNA in the GC signaling pathway in human pancreatic beta cells. Methods: Patients undergoing two weeks of high-dose prednisolone therapy were monitored for C-peptide levels. Human pancreatic islets and the human beta cell line EndoC-βH1 were incubated in pharmacological concentrations of dexamethasone. The GAS5 level was modulated using anti-sense LNA gapmeR or short oligonucleotides with GAS5 HREM (hormone response element motif). Immunoblotting and/or real-time PCR were used to assess changes in protein and RNA expression, respectively. Functional characterization included glucose-stimulated insulin secretion and apoptosis assays. Correlation analysis was performed on RNAseq data of human pancreatic islets. Results: We found reduced C-peptide levels in patients undergoing high-dose GC therapy. Human islets and the human beta cell line EndoC-βH1 exposed to GC exhibited reduced insulin secretion and increased apoptosis. Concomitantly, reduced expression of important beta cell transcription factors, PDX1 and NKX6-1, as well as exocytotic protein SYT13 were observed. The expression of the glucocorticoid receptor was decreased, while that of serum and glucocorticoid-regulated kinase 1 (SGK1) was elevated. The expression of these genes was found to significantly correlate with GAS5 in human islet transcriptomics data. Increasing GAS5 levels using GAS5 HREM alleviated the inhibitory effects of dexamethasone on insulin secretion. Conclusions: The direct adverse effect of glucocorticoid in human beta cell function is mediated via important beta cell proteins and components of the GC signaling pathway in an intricate interplay with GAS5 lincRNA, a potentially novel therapeutic target to counter GC-mediated beta cell dysfunction.
