| 1. |
- Fadista, Joao, et al.
(författare)
-
Global genomic and transcriptomic analysis of human pancreatic islets reveals novel genes influencing glucose metabolism.
- 2014
-
Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 111:38, s. 13924-13929
-
Tidskriftsartikel (refereegranskat)abstract
- Genetic variation can modulate gene expression, and thereby phenotypic variation and susceptibility to complex diseases such as type 2 diabetes (T2D). Here we harnessed the potential of DNA and RNA sequencing in human pancreatic islets from 89 deceased donors to identify genes of potential importance in the pathogenesis of T2D. We present a catalog of genetic variants regulating gene expression (eQTL) and exon use (sQTL), including many long noncoding RNAs, which are enriched in known T2D-associated loci. Of 35 eQTL genes, whose expression differed between normoglycemic and hyperglycemic individuals, siRNA of tetraspanin 33 (TSPAN33), 5'-nucleotidase, ecto (NT5E), transmembrane emp24 protein transport domain containing 6 (TMED6), and p21 protein activated kinase 7 (PAK7) in INS1 cells resulted in reduced glucose-stimulated insulin secretion. In addition, we provide a genome-wide catalog of allelic expression imbalance, which is also enriched in known T2D-associated loci. Notably, allelic imbalance in paternally expressed gene 3 (PEG3) was associated with its promoter methylation and T2D status. Finally, RNA editing events were less common in islets than previously suggested in other tissues. Taken together, this study provides new insights into the complexity of gene regulation in human pancreatic islets and better understanding of how genetic variation can influence glucose metabolism.
|
|
| 2. |
- Prasad, Rashmi B., et al.
(författare)
-
Excess maternal transmission of variants in the THADA gene to offspring with type 2 diabetes
- 2016
-
Ingår i: Diabetologia. - : Springer Science and Business Media LLC. - 0012-186X .- 1432-0428. ; 59:8, s. 1702-1713
-
Tidskriftsartikel (refereegranskat)abstract
- Aims/hypothesis: Genome-wide association studies (GWAS) have identified more than 65 genetic loci associated with risk of type 2 diabetes. However, the contribution of distorted parental transmission of alleles to risk of type 2 diabetes has been mostly unexplored. Our goal was therefore to search for parent-of-origin effects (POE) among type 2 diabetes loci in families. Methods: Families from the Botnia study (n = 4,211, 1,083 families) were genotyped for 72 single-nucleotide polymorphisms (SNPs) associated with type 2 diabetes and assessed for POE on type 2 diabetes. The family-based Hungarian Transdanubian Biobank (HTB) (n = 1,463, >135 families) was used to replicate SNPs showing POE. Association of type 2 diabetes loci within families was also tested. Results: Three loci showed nominal POE, including the previously reported variants in KCNQ1, for type 2 diabetes in families from Botnia (rs2237895: pPOE = 0.037), which can be considered positive controls. The strongest POE was seen for rs7578597 SNP in the THADA gene, showing excess transmission of the maternal risk allele T to diabetic offspring (Botnia: pPOE = 0.01; HTB pPOE = 0.045). These data are consistent with previous evidence of allelic imbalance for expression in islets, suggesting that the THADA gene can be imprinted in a POE-specific fashion. Five CpG sites, including those flanking rs7578597, showed differential methylation between diabetic and non-diabetic donor islets. Conclusions/interpretation: Taken together, the data emphasise the need for genetic studies to consider from which parent an offspring has inherited a susceptibility allele.
|
|
| 3. |
- Scheja, Agneta, et al.
(författare)
-
Von Willebrand factor propeptide as a marker of disease activity in systemic sclerosis (scleroderma)
- 2001
-
Ingår i: Arthritis Research & Therapy. - : Springer Science and Business Media LLC. - 1465-9913 .- 1465-9905. ; 3:3, s. 178-182
-
Tidskriftsartikel (refereegranskat)abstract
- In 44 consecutive patients with systemic sclerosis (SSc), plasma concentrations of von Willebrand factor (vWf) were higher than those of the vWf propeptide, but the propeptide showed less variability within patient subgroups. Higher values of the propeptide were observed in patients with early pulmonary involvement. A closer correlation of the propeptide than of vWf to biochemical markers of activity was also evident. Our results suggest that the propeptide, despite a shorter circulating half-time and lower plasma concentrations than vWf, is more useful in the assessment of disease activity in SSc.
|
|
| 4. |
- Abels, Mia, et al.
(författare)
-
CART is overexpressed in human type 2 diabetic islets and inhibits glucagon secretion and increases insulin secretion
- 2016
-
Ingår i: Diabetologia. - : Springer Science and Business Media LLC. - 0012-186X .- 1432-0428. ; 59:9, s. 1928-1937
-
Tidskriftsartikel (refereegranskat)abstract
- Aims/hypothesis Insufficient insulin release and hyperglucagonaemia are culprits in type 2 diabetes. Cocaine- and amphetamine-regulated transcript (CART, encoded by Cartpt) affects islet hormone secretion and beta cell survival in vitro in rats, and Cart(-/-) mice have diminished insulin secretion. We aimed to test if CART is differentially regulated in human type 2 diabetic islets and if CART affects insulin and glucagon secretion in vitro in humans and in vivo in mice. Methods CART expression was assessed in human type 2 diabetic and non-diabetic control pancreases and rodent models of diabetes. Insulin and glucagon secretion was examined in isolated islets and in vivo in mice. Ca2+ oscillation patterns and exocytosis were studied in mouse islets. Results We report an important role of CART in human islet function and glucose homeostasis in mice. CART was found to be expressed in human alpha and beta cells and in a subpopulation of mouse beta cells. Notably, CART expression was several fold higher in islets of type 2 diabetic humans and rodents. CART increased insulin secretion in vivo in mice and in human and mouse islets. Furthermore, CART increased beta cell exocytosis, altered the glucose-induced Ca2+ signalling pattern in mouse islets from fast to slow oscillations and improved synchronisation of the oscillations between different islet regions. Finally, CART reduced glucagon secretion in human and mouse islets, as well as in vivo in mice via diminished alpha cell exocytosis. Conclusions/interpretation We conclude that CART is a regulator of glucose homeostasis and could play an important role in the pathophysiology of type 2 diabetes. Based on the ability of CART to increase insulin secretion and reduce glucagon secretion, CART-based agents could be a therapeutic modality in type 2 diabetes.
|
|
| 5. |
- Andersson, Lotta E., et al.
(författare)
-
Glutamine-elicited secretion of glucagon-like peptide 1 is governed by an activated glutamate dehydrogenase
- 2018
-
Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 67:3, s. 372-384
-
Tidskriftsartikel (refereegranskat)abstract
- Glucagon-like peptide 1 (GLP-1), secreted from intestinal L cells, glucose dependently stimulates insulin secretion from β-cells. This glucose dependence prevents hypoglycemia, rendering GLP-1 analogs a useful and safe treatment modality in type 2 diabetes. Although the amino acid glutamine is a potent elicitor of GLP-1 secretion, the responsible mechanism remains unclear. We investigated how GLP-1 secretion is metabolically coupled in L cells (GLUTag) and in vivo inmice using the insulin-secreting cell line INS-1 832/13 as reference. A membrane-permeable glutamate analog (dimethylglutamate [DMG]), acting downstream of electrogenic transporters, elicited similar alterations in metabolism as glutamine in both cell lines. Both DMG and glutamine alone elicited GLP-1 secretion in GLUTag cells and in vivo, whereas activation of glutamate dehydrogenase (GDH) was required to stimulate insulin secretion from INS-1 832/13 cells. Pharmacological inhibition in vivo of GDH blocked secretion of GLP-1 in response to DMG. In conclusion, our results suggest that nonelectrogenic nutrient uptake and metabolism play an important role in L cell stimulus-secretion coupling. Metabolism of glutamine and related analogs by GDH in the L cell may explain why GLP-1 secretion, but not that of insulin, is activated by these secretagogues in vivo.
|
|
| 6. |
- Asplund, Olof, et al.
(författare)
-
Islet Gene View-a tool to facilitate islet research
- 2022
-
Ingår i: Life Science Alliance. - : Life Science Alliance, LLC. - 2575-1077. ; 5:12
-
Tidskriftsartikel (refereegranskat)abstract
- Characterization of gene expression in pancreatic islets and its alteration in type 2 diabetes (T2D) are vital in understanding islet function and T2D pathogenesis. We leveraged RNA sequencing and genome-wide genotyping in islets from 188 donors to create the Islet Gene View (IGW) platform to make this information easily accessible to the scientific community. Expression data were related to islet phenotypes, diabetes status, other islet-expressed genes, islet hormone-encoding genes and for expression in insulin target tissues. The IGW web application produces output graphs for a particular gene of interest. In IGW, 284 differentially expressed genes (DEGs) were identified in T2D donor islets compared with controls. Forty percent of DEGs showed cell-type enrichment and a large proportion significantly co-expressed with islet hormone-encoding genes; glucagon (GCG, 56%), amylin (IAPP, 52%), insulin (INS, 44%), and somatostatin (SST, 24%). Inhibition of two DEGs, UNC5D and SERPINE2, impaired glucose-stimulated insulin secretion and impacted cell survival in a human beta-cell model. The exploratory use of IGW could help designing more comprehensive functional follow-up studies and serve to identify therapeutic targets in T2D.
|
|
| 7. |
- Axelsson, Annika S., et al.
(författare)
-
Sulforaphane reduces hepatic glucose production and improves glucose control in patients with type 2 diabetes
- 2017
-
Ingår i: Science Translational Medicine. - : American Association for the Advancement of Science (AAAS). - 1946-6234 .- 1946-6242. ; 9:394
-
Tidskriftsartikel (refereegranskat)abstract
- A potentially useful approach for drug discovery is to connect gene expression profiles of disease-affected tissues ("disease signatures") to drug signatures, but it remains to be shown whether it can be used to identify clinically relevant treatment options. We analyzed coexpression networks and genetic data to identify a disease signature for type 2 diabetes in liver tissue. By interrogating a library of 3800 drug signatures, we identified sulforaphane as a compound that may reverse the disease signature. Sulforaphane suppressed glucose production from hepatic cells by nuclear translocation of nuclear factor erythroid 2-related factor 2 (NRF2) and decreased expression of key enzymes in gluconeogenesis. Moreover, sulforaphane reversed the disease signature in the livers from diabetic animals and attenuated exaggerated glucose production and glucose intolerance by a magnitude similar to that of metformin. Finally, sulforaphane, provided as concentrated broccoli sprout extract, reduced fasting blood glucose and glycated hemoglobin (HbA1c) in obese patients with dysregulated type 2 diabetes.
|
|
| 8. |
- Barghouth, Mohammad, et al.
(författare)
-
The structure of insulin granule core determines secretory capacity being reduced in type-2 diabetes
- 2022
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Exocytosis in excitable cells is essential for their physiological functions. Although the exocytotic machinery controlling cellular secretion has been well investigated, the function of the vesicular cargo, i.e. secretory granular content remains obscure. Here we combine dSTORM imaging and single-domain insulin antibody, to dissect the in situ structure of insulin granule cores (IGCs) at nano level. We demonstrate that the size and shape of the IGCs can be regulated by the juxta-granular molecules Nucleobindin-2 and Enolase-1, that further contribute to the stimulated insulin secretion. IGCs located at the plasma membrane are larger than those in the cytosol. The IGCs size is decreased by ∼20% after glucose stimulation due to the release of the peripheral part of IGCs through incomplete granule fusion. Importantly, the reduction of the IGCs size is also observed in non-stimulatory pancreatic β-cells from diabetic db/db mice, Akita (Ins2+/-) mice and human Type-2 diabetic donors, in accordance with impaired secretion. These findings overall highlight the structure of exocytotic insulin cores as a novel modality amenable to targeting in the stimulated exocytosis in β-cells with impaired insulin secretion.Competing Interest StatementThe authors have declared no competing interest.
|
|
| 9. |
- Dayeh, Tasnim, et al.
(författare)
-
Genome-wide DNA methylation analysis of human pancreatic islets from type 2 diabetic and non-diabetic donors identifies candidate genes that influence insulin secretion.
- 2014
-
Ingår i: PLoS Genetics. - : Public Library of Science (PLoS). - 1553-7404. ; 10:3
-
Tidskriftsartikel (refereegranskat)abstract
- Impaired insulin secretion is a hallmark of type 2 diabetes (T2D). Epigenetics may affect disease susceptibility. To describe the human methylome in pancreatic islets and determine the epigenetic basis of T2D, we analyzed DNA methylation of 479,927 CpG sites and the transcriptome in pancreatic islets from T2D and non-diabetic donors. We provide a detailed map of the global DNA methylation pattern in human islets, β- and α-cells. Genomic regions close to the transcription start site showed low degrees of methylation and regions further away from the transcription start site such as the gene body, 3'UTR and intergenic regions showed a higher degree of methylation. While CpG islands were hypomethylated, the surrounding 2 kb shores showed an intermediate degree of methylation, whereas regions further away (shelves and open sea) were hypermethylated in human islets, β- and α-cells. We identified 1,649 CpG sites and 853 genes, including TCF7L2, FTO and KCNQ1, with differential DNA methylation in T2D islets after correction for multiple testing. The majority of the differentially methylated CpG sites had an intermediate degree of methylation and were underrepresented in CpG islands (∼7%) and overrepresented in the open sea (∼60%). 102 of the differentially methylated genes, including CDKN1A, PDE7B, SEPT9 and EXOC3L2, were differentially expressed in T2D islets. Methylation of CDKN1A and PDE7B promoters in vitro suppressed their transcriptional activity. Functional analyses demonstrated that identified candidate genes affect pancreatic β- and α-cells as Exoc3l silencing reduced exocytosis and overexpression of Cdkn1a, Pde7b and Sept9 perturbed insulin and glucagon secretion in clonal β- and α-cells, respectively. Together, our data can serve as a reference methylome in human islets. We provide new target genes with altered DNA methylation and expression in human T2D islets that contribute to perturbed insulin and glucagon secretion. These results highlight the importance of epigenetics in the pathogenesis of T2D.
|
|
| 10. |
- Fällman, Maria
(författare)
-
Complement receptor-mediated signal transduction in human neutrophils : A role for protein kinase C in the phagocytic process
- 1992
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The neutrophil granulocyte comprises the first line of human defense against invading microorganisms. A versatile motile machinery enables the cell to migrate to the inflammatory site and there engulf and destroy the pathogens by phagocytosis. Engulfment is facilitated by opsonization of the microbes with C3b or C3bi complement fragments or with immunoglobulins, proteins which respectively bind to complement receptors (CRs) and Fe receptors on the neutrophil surface. The aim of the present thesis was to investigate the transmembrane signaling events involved in receptor-mediated engulfment. Experimentially induced inhibition of the phagocytic capacity of human neutrophils could be reversed by pretrcating the cells with protein kinase C (PKC)-activating agents such as PMA and a synthetic diglyceride. This indirectly suggests an important role for PKC in the process of engulfment. Presentation of opsonized yeast particles to neutrophils stimulated the phosphoinositide signaling pathway, resulting in an accumulation of Ins(1,4,5)P3 (IP3) and diglyceride (DG; the endogenous activator of PKC) with a time kinetic correlating that of the cellular uptake of the particles. However, in calcium-depleted neutrophils, formation of IP3 was totally abolished during phagocytosis of complement-opsonized yeast particles, thereby excluding this signal as a regulator of the engulfment process. DG, on the other hand, was still produced in these cells, suggesting a source other than phosphatidylinositols for the generation of this second messenger. Further studies revealed that a major part of CR-mediated DG formation originated from phospholipase D (PLD)-mediated hydrolysis of phosphatidylcholine (PC). The presence of DG suggested a subsequent activation of PKC, which was confirmed by the demonstration of CR-mediated phosphorylation of a well-known PKC substrate, myristoylated alanine-rich C kinase substrate (MARCKS). Moreover, the activity of PLD was shown to be regulated by PKC, which stimulated the production of its own activator by enhancing the activity of the lipase: PKC should thereby be able to maintain its own activity.Furthermore, we could also show that both CRI and CR3 can mediate PLO activation and that the degree of this activation is potentiated by PMA pretreatment and dependent on the fonn of ligand presentation. In conclusion, CR-mediated phagocytosis is associated with PLDmediated hydrolysis of PC and stimulation of PKC, the activity of the latter enzyme appears to be an important regulatory event in the engulfment process.
|
|
| 11. |
- Hall, Elin, et al.
(författare)
-
DNA methylation of the glucagon-like peptide 1 receptor (GLP1R) in human pancreatic islets.
- 2013
-
Ingår i: BMC Medical Genetics. - : Springer Science and Business Media LLC. - 1471-2350. ; 14:Jul,23
-
Tidskriftsartikel (refereegranskat)abstract
- Insulin secretion is enhanced upon the binding of Glucagon-like peptide-1 (GLP-1) to its receptor (GLP1R) in pancreatic β cells. Although a reduced expression of GLP1R in pancreatic islets from type 2 diabetic patients and hyperglycaemic rats has been established, it is still unknown if this is caused by differential DNA methylation of GLP1R in pancreatic islets of type 2 diabetic patients.
|
|
| 12. |
- Hänzelmann, Sonja, et al.
(författare)
-
Thrombin stimulates insulin secretion via protease-activated receptor-3.
- 2015
-
Ingår i: Islets. - : Informa UK Limited. - 1938-2022 .- 1938-2014. ; 7:4, s. 1118195-1118195
-
Tidskriftsartikel (refereegranskat)abstract
- The disease mechanisms underlying type 2 diabetes (T2D) remain poorly defined. Here we aimed to explore the pathophysiology of T2D by analyzing gene co-expression networks in human islets. Using partial correlation networks we identified a group of co-expressed genes ('module') including F2RL2 that was associated with glycated hemoglobin. F2Rl2 is a G-protein-coupled receptor (GPCR) that encodes protease-activated receptor-3 (PAR3). PAR3 is cleaved by thrombin, which exposes a 6-amino acid sequence that acts as a 'tethered ligand' to regulate cellular signaling. We have characterized the effect of PAR3 activation on insulin secretion by static insulin secretion measurements, capacitance measurements, studies of diabetic animal models and patient samples. We demonstrate that thrombin stimulates insulin secretion, an effect that was prevented by an antibody that blocks the thrombin cleavage site of PAR3. Treatment with a peptide corresponding to the PAR3 tethered ligand stimulated islet insulin secretion and single β-cell exocytosis by a mechanism that involves activation of phospholipase C and Ca(2+) release from intracellular stores. Moreover, we observed that the expression of tissue factor, which regulates thrombin generation, was increased in human islets from T2D donors and associated with enhanced β-cell exocytosis. Finally, we demonstrate that thrombin generation potential in patients with T2D was associated with increased fasting insulin and insulinogenic index. The findings provide a previously unrecognized link between hypercoagulability and hyperinsulinemia and suggest that reducing thrombin activity or blocking PAR3 cleavage could potentially counteract the exaggerated insulin secretion that drives insulin resistance and β-cell exhaustion in T2D.
|
|
| 13. |
- Mahdi, Taman, et al.
(författare)
-
Secreted frizzled-related protein 4 reduces insulin secretion and is overexpressed in type 2 diabetes.
- 2012
-
Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131. ; 16:5, s. 625-633
-
Tidskriftsartikel (refereegranskat)abstract
- A plethora of candidate genes have been identified for complex polygenic disorders, but the underlying disease mechanisms remain largely unknown. We explored the pathophysiology of type 2 diabetes (T2D) by analyzing global gene expression in human pancreatic islets. A group of coexpressed genes (module), enriched for interleukin-1-related genes, was associated with T2D and reduced insulin secretion. One of the module genes that was highly overexpressed in islets from T2D patients is SFRP4, which encodes secreted frizzled-related protein 4. SFRP4 expression correlated with inflammatory markers, and its release from islets was stimulated by interleukin-1β. Elevated systemic SFRP4 caused reduced glucose tolerance through decreased islet expression of Ca(2+) channels and suppressed insulin exocytosis. SFRP4 thus provides a link between islet inflammation and impaired insulin secretion. Moreover, the protein was increased in serum from T2D patients several years before the diagnosis, suggesting that SFRP4 could be a potential biomarker for islet dysfunction in T2D.
|
|
| 14. |
- Mohammad Al-Amily, Israa, et al.
(författare)
-
Ablation of GPR56 Causes β-Cell Dysfunction by ATP Loss through Mistargeting of Mitochondrial VDAC1 to the Plasma Membrane
- 2023
-
Ingår i: Biomolecules. - : MDPI AG. - 2218-273X. ; 13:3
-
Tidskriftsartikel (refereegranskat)abstract
- The activation of G Protein-Coupled Receptor 56 (GPR56), also referred to as Adhesion G-Protein-Coupled Ceceptor G1 (ADGRG1), by Collagen Type III (Coll III) prompts cell growth, proliferation, and survival, among other attributes. We investigated the signaling cascades mediating this functional effect in relation to the mitochondrial outer membrane voltage-dependent anion Channel-1 (VDAC1) expression in pancreatic β-cells. GPR56KD attenuated the Coll III-induced suppression of P70S6K, JNK, AKT, NFκB, STAT3, and STAT5 phosphorylation/activity in INS-1 cells cultured at 20 mM glucose (glucotoxicity) for 72 h. GPR56-KD also increased Chrebp, Txnip, and Vdac1 while decreasing Vdac2 mRNA expression. In GPR56-KD islet β-cells, Vdac1 was co-localized with SNAP-25, demonstrating its plasma membrane translocation. This resulted in ATP loss, reduced cAMP production and impaired glucose-stimulated insulin secretion (GSIS) in INS-1 and human EndoC βH1 cells. The latter defects were reversed by an acute inhibition of VDAC1 with an antibody or the VDAC1 inhibitor VBIT-4. We demonstrate that Coll III potentiates GSIS by increasing cAMP and preserving β-cell functionality under glucotoxic conditions in a GPR56-dependent manner by attenuating the inflammatory response. These results emphasize GPR56 and VDAC1 as drug targets in conditions with impaired β-cell function.
|
|
| 15. |
- Moore, Benjamin D, et al.
(författare)
-
Transcriptional Regulation of X-Box-Binding Protein One (XBP1) by Hepatocyte Nuclear Factor 4α (HNF4α) is Vital to Beta-Cell Function.
- 2016
-
Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 291:12, s. 6146-6157
-
Tidskriftsartikel (refereegranskat)abstract
- The transcription factor, X-box Binding Protein-One (XBP1), controls the development and maintenance of the endoplasmic reticulum (ER) in multiple secretory cell lineages. We show here that Hepatocyte Nuclear Factor 4-alpha (HNF4α) directly induces XBP1 expression. Mutations in HNF4α cause Mature-Onset Diabetes of the Young I (MODYI), a subset of diabetes characterized by diminished GSIS. In mouse models, cell lines, and ex vivo islets, using dominant negative and human-disease-allele point mutants or knockout and knockdown models, we show that disruption of HNF4α caused decreased expression of XBP1 and reduced cellular ER networks. GSIS depends on ER Ca2+ signaling; we show that diminished XBP1 and/or HNF4α in β-cells led to impaired ER Ca2+ homeostasis. Restoring XBP1 expression was sufficient to completely rescue GSIS in HNF4α-deficient β-cells. Our findings uncover a transcriptional relationship between HNF4α and Xbp1 with potentially broader implications about MODYI and the importance of transcription factor signaling in the regulation of secretion.
|
|
| 16. |
- Nagao, Mototsugu, et al.
(författare)
-
Potential Protection Against Type 2 Diabetes in Obesity Through Lower CD36 Expression and Improved Exocytosis in β-Cells
- 2020
-
Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 69:6, s. 1193-1205
-
Tidskriftsartikel (refereegranskat)abstract
- Obesity is a risk factor for type 2 diabetes (T2D); however, not all obese individuals develop the disease. In this study, we aimed to investigate the cause of differential insulin secretion capacity of pancreatic islets from donors with T2D and non-T2D (ND), especially obese donors (BMI ≥30 kg/m2). Islets from obese donors with T2D had reduced insulin secretion, decreased β-cell exocytosis, and higher expression of fatty acid translocase CD36. We tested the hypothesis that CD36 is a key molecule in the reduced insulin secretion capacity. Indeed, CD36 overexpression led to decreased insulin secretion, impaired exocytosis, and reduced granule docking. This was accompanied by reduced expression of the exocytotic proteins SNAP25, STXBP1, and VAMP2, likely because CD36 induced downregulation of the insulin receptor substrate (IRS) proteins, suppressed the insulin-signaling phosphatidylinositol 3-kinase/AKT pathway, and increased nuclear localization of the transcription factor FoxO1. CD36 antibody treatment of the human β-cell line EndoC-βH1 increased IRS1 and exocytotic protein levels, improved granule docking, and enhanced insulin secretion. Our results demonstrate that β-cells from obese donors with T2D have dysfunctional exocytosis likely due to an abnormal lipid handling represented by differential CD36 expression. Hence, CD36 could be a key molecule to limit β-cell function in T2D associated with obesity.
|
|
| 17. |
- Nguyen, Ha Thu, et al.
(författare)
-
CDN1163, an activator of sarco/endoplasmic reticulum Ca2+ ATPase, up-regulates mitochondrial functions and protects against lipotoxicity in pancreatic β-cells
- 2023
-
Ingår i: British Journal of Pharmacology. - 0007-1188. ; 180:21, s. 2762-2776
-
Tidskriftsartikel (refereegranskat)abstract
- Background and Purpose: High levels of Ca2+ in the endoplasmic reticulum (ER), established by the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA), are required for protein folding and cell signalling. Excessive ER Ca2+ release or decreased SERCA activity induces unfolded protein accumulation and ER stress in pancreatic β-cells, leading to defective insulin secretion and diabetes. Here we have investigated the consequences of enhancing ER Ca2+ uptake on β-cell survival and function. Experimental Approach: The effects of SERCA activator, CDN1163, on Ca2+ homeostasis, protein expression, mitochondrial activities, insulin secretion, and lipotoxicity have been studied in mouse pancreatic β-cells and MIN6 cells. Key Results: CDN1163, increased insulin synthesis and exocytosis from islets. CDN1163 also increased the sensitivity of the cytosolic Ca2+ oscillation response to glucose and potentiated it in dispersed and sorted β-cells. CDN1163 augmented the ER and mitochondrial Ca2+ content, the mitochondrial membrane potential, respiration, and ATP synthesis. CDN1163 up-regulated expression of inositol 1,4,5-trisphosphate receptors and antioxidant enzymes, and mitochondrial biogenesis, including peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α). Overexpression of SERCA2a or 2b replicated the effects of CDN1163, while knockdown of SERCA2 abolished the stimulatory actions of CDN1163. In palmitate-treated β-cells, CDN1163 prevented ER Ca2+ depletion, mitochondrial dysfunction, cytosolic and mitochondrial oxidative stress, defective insulin secretion, and apoptotic cell death. Conclusions and Implications: Activation of SERCA enhanced mitochondrial bioenergetics and antioxidant capability, suppressing the cytotoxic effects of palmitate. Our results suggest that targeting SERCA could be a novel therapeutic strategy to protect β-cells from lipotoxicity and the development of Type 2 diabetes.
|
|
| 18. |
- Nguyen, Ha Thu, et al.
(författare)
-
Regulation of autophagy by perilysosomal calcium : a new player in β-cell lipotoxicity
-
Ingår i: Experimental and Molecular Medicine. - 1226-3613.
-
Forskningsöversikt (refereegranskat)abstract
- Autophagy is an essential quality control mechanism for maintaining organellar functions in eukaryotic cells. Defective autophagy in pancreatic beta cells has been shown to be involved in the progression of diabetes through impaired insulin secretion under glucolipotoxic stress. The underlying mechanism reveals the pathologic role of the hyperactivation of mechanistic target of rapamycin (mTOR), which inhibits lysosomal biogenesis and autophagic processes. Moreover, accumulating evidence suggests that oxidative stress induces Ca2+ depletion in the endoplasmic reticulum (ER) and cytosolic Ca2+ overload, which may contribute to mTOR activation in perilysosomal microdomains, leading to autophagic defects and β-cell failure due to lipotoxicity. This review delineates the antagonistic regulation of autophagic flux by mTOR and AMP-dependent protein kinase (AMPK) at the lysosomal membrane, and both of these molecules could be activated by perilysosomal calcium signaling. However, aberrant and persistent Ca2+ elevation upon lipotoxic stress increases mTOR activity and suppresses autophagy. Therefore, normalization of autophagy is an attractive therapeutic strategy for patients with β-cell failure and diabetes.
|
|
| 19. |
- Ofori, Jones K., et al.
(författare)
-
Elevated miR-130a/miR130b/miR-152 expression reduces intracellular ATP levels in the pancreatic beta cell
- 2017
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- MicroRNAs have emerged as important players of gene regulation with significant impact in diverse disease processes. In type-2 diabetes, in which impaired insulin secretion is a major factor in disease progression, dysregulated microRNA expression in the insulin-secreting pancreatic beta cell has been widely-implicated. Here, we show that miR-130a-3p, miR-130b-3p, and miR-152-3p levels are elevated in the pancreatic islets of hyperglycaemic donors, corroborating previous findings about their upregulation in the islets of type-2 diabetes model Goto-Kakizaki rats. We demonstrated negative regulatory effects of the three microRNAs on pyruvate dehydrogenase E1 alpha (PDHA1) and on glucokinase (GCK) proteins, which are both involved in ATP production. Consequently, we found both proteins to be downregulated in the Goto-Kakizaki rat islets, while GCK mRNA expression showed reduced trend in the islets of type-2 diabetes donors. Overexpression of any of the three microRNAs in the insulin-secreting INS-1 832/13 cell line resulted in altered dynamics of intracellular ATP/ADP ratio ultimately perturbing fundamental ATP-requiring beta cell processes such as glucose-stimulated insulin secretion, insulin biosynthesis and processing. The data further strengthen the wide-ranging influence of microRNAs in pancreatic beta cell function, and hence their potential as therapeutic targets in type-2 diabetes.
|
|
| 20. |
- Sanches, Jose Marcos, et al.
(författare)
-
Pathophysiology of type 2 diabetes and the impact of altered metabolic interorgan crosstalk
- 2023
-
Ingår i: The FEBS Journal. - : Wiley. - 1742-464X .- 1742-4658. ; 290:3, s. 620-648
-
Forskningsöversikt (refereegranskat)abstract
- Diabetes is a complex and multifactorial disease that affects millions of people worldwide, reducing the quality of life significantly, and results in grave consequences for our health care system. In type 2 diabetes (T2D), the lack of β-cell compensatory mechanisms overcoming peripherally developed insulin resistance is a paramount factor leading to disturbed blood glucose levels and lipid metabolism. Impaired β-cell functions and insulin resistance have been studied extensively resulting in a good understanding of these pathways but much less is known about interorgan crosstalk, which we define as signaling between tissues by secreted factors. Besides hormones and organokines, dysregulated blood glucose and long-lasting hyperglycemia in T2D is associated with changes in metabolism with metabolites from different tissues contributing to the development of this disease. Recent data suggest that metabolites, such as lipids including free fatty acids and amino acids, play important roles in the interorgan crosstalk during the development of T2D. In general, metabolic remodeling affects physiological homeostasis and impacts the development of T2D. Hence, we highlight the importance of metabolic interorgan crosstalk in this review to gain enhanced knowledge of the pathophysiology of T2D, which may lead to new therapeutic approaches to treat this disease.
|
|
| 21. |
|
|
| 22. |
- Spégel, Peter, et al.
(författare)
-
Time-resolved metabolomics analysis of beta-cells implicates the pentose phosphate pathway in the control of insulin release
- 2013
-
Ingår i: Biochemical Journal. - 0264-6021. ; 450, s. 595-605
-
Tidskriftsartikel (refereegranskat)abstract
- Insulin secretion is coupled with changes in beta-cell metabolism. To define this process, 195 putative metabolites, mitochondrial respiration, NADP(+), NADPH and insulin secretion were measured within 15 mm of stimulation of clonal INS-1 832/13 beta-cells with glucose. Rapid responses in the major metabolic pathways of glucose occurred, involving several previously suggested metabolic coupling factors. The complexity of metabolite changes observed disagreed with the concept of one single metabolite controlling insulin secretion. The complex alterations in metabolite levels suggest that a coupling signal should reflect large parts of the beta-cell metabolic response. This was fulfilled by the NADPH/NADP(+) ratio, which was elevated (8-fold; P < 0.01) at 6 min after glucose stimulation. The NADPH/NADP+ ratio paralleled an increase in ribose 5-phosphate (>2.5-fold; P < 0.001). Inhibition of the pentose phosphate pathway by trans-dehydroepiandrosterone (DHEA) suppressed ribose 5-phosphate levels and production of reduced glutathione, as well as insulin secretion in INS-1 832/13 beta-cells and rat islets without affecting ATP production. Metabolite profiling of rat islets confirmed the glucose-induced rise in ribose 5-phosphate, which was prevented by DHEA. These findings implicate the pentose phosphate pathway, and support a role for NADPH and glutathione, in beta-cell stimulus-secretion coupling.
|
|
| 23. |
- Stamenkovic, Jelena, et al.
(författare)
-
Inhibition of the malate-aspartate shuttle in mouse pancreatic islets abolishes glucagon secretion without affecting insulin secretion
- 2015
-
Ingår i: Biochemical Journal. - 0264-6021. ; 468, s. 49-63
-
Tidskriftsartikel (refereegranskat)abstract
- Altered secretion of insulin as well as glucagon has been implicated in the pathogenesis of Type 2 diabetes (T2D), but the mechanisms controlling glucagon secretion from alpha-cells largely remain unresolved. Therefore, we studied the regulation of glucagon secretion from alpha TC1-6 (alpha TC1 clone 6) cells and compared it with insulin release from INS-1 832/13 cells. We found that INS-1 832/13 and alpha TC1-6 cells respectively secreted insulin and glucagon concentration-dependently in response to glucose. In contrast, tight coupling of glycolytic and mitochondrial metabolism was observed only in INS-1 832/13 cells. Although glycolytic metabolism was similar in the two cell lines, TCA (tricarboxylic acid) cycle metabolism, respiration and ATP levels were less glucose-responsive in alpha TC1-6 cells. Inhibition of the malate-aspartate shuttle, using phenyl succinate (PhS), abolished glucose-provoked ATP production and hormone secretion from alpha TC1-6 but not INS-1 832/13 cells. Blocking the malate-aspartate shuttle increased levels of glycerol 3-phosphate only in INS-1 832/13 cells. Accordingly, relative expression of constituents in the glycerol phosphate shuttle compared with malate-aspartate shuttle was lower in alpha TC1-6 cells. Our data suggest that the glycerol phosphate shuttle augments the malate-aspartate shuttle in INS-1 832/13 but not alpha TC1-6 cells. These results were confirmed in mouse islets, where PhS abrogated secretion of glucagon but not insulin. Furthermore, expression of the rate-limiting enzyme of the glycerol phosphate shuttle was higher in sorted primary beta-than in alpha-cells. Thus, suppressed glycerol phosphate shuttle activity in the alpha-cell may prevent a high rate of glycolysis and consequently glucagon secretion in response to glucose. Accordingly, pyruvate-and lactate-elicited glucagon secretion remains unaffected since their signalling is independent of mitochondrial shuttles.
|
|
| 24. |
- Sörhede Winzell, Maria, et al.
(författare)
-
Beta-Cell-Targeted Expression of a Dominant-Negative Mutant of Hepatocyte Nuclear Factor-1{alpha} in Mice: Diabetes Model with {beta}-Cell Dysfunction Partially Rescued by Nonglucose Secretagogues.
- 2004
-
Ingår i: Diabetes. - 1939-327X. ; 53:suppl_3, s. 92-96
-
Tidskriftsartikel (refereegranskat)abstract
- We studied islet function in mice with beta-cell-targeted expression of a dominant-negative mutant of hepatocyte nuclear factor (HNF)-1alpha. At age 2-3 months, anesthetized transgenic and wild-type male mice underwent an intravenous glucose (1 g/kg) tolerance test (IVGTT). It was found that transgenic mice had an abolished insulin response in association with severe glucose intolerance. In other tests, the 5-min insulin response to intravenous arginine was impaired by 79% (P=0.032) and the 15-min insulin response to gastric glucose was suppressed by 97% (P=0.006). In islets incubated for 60 min, the insulin response to glucose (3.3-22.2 mmol/l) was impaired by >80% in transgenic mice. In contrast, insulin responses to nonglucose secretagogues were only partially suppressed (to GLP-1 [100 nmol/l] by 40%, to carbachol [1 micromol/l] by 20%, and to palmitate [0.5 mmol/l] by 15%), whereas the response to depolarization by KCl (50 mmol/l) was not reduced. Finally, the IVGTT data insulin sensitivity in transgenic mice was not significantly different from that of wild-type mice. Thus, mice with targeted suppression of beta-cell HNF-1alpha represent a good diabetes model exhibiting severely impaired insulin secretion after glucose with marked glucose intolerance. In contrast, the insulin responses to nonglucose stimuli are not suppressed when the islet insulin content is taken into account.
|
|
| 25. |
- Taneera, Jalal, et al.
(författare)
-
A Systems Genetics Approach Identifies Genes and Pathways for Type 2 Diabetes in Human Islets
- 2012
-
Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131 .- 1932-7420. ; 16:1, s. 122-134
-
Tidskriftsartikel (refereegranskat)abstract
- Close to 50 genetic loci have been associated with type 2 diabetes (T2D), but they explain only 15% of the heritability. In an attempt to identify additional T2D genes, we analyzed global gene expression in human islets from 63 donors. Using 48 genes located near T2D risk variants, we identified gene coexpression and protein-protein interaction networks that were strongly associated with islet insulin secretion and HbA(1c). We integrated our data to form a rank list of putative T2D genes, of which CHL1, LRFN2, RASGRP1, and PPM1K were validated in INS-1 cells to influence insulin secretion, whereas GPR120 affected apoptosis in islets. Expression variation of the top 20 genes explained 24% of the variance in HbA(1c) with no claim of the direction. The data present a global map of genes associated with islet dysfunction and demonstrate the value of systems genetics for the identification of genes potentially involved in T2D.
|
|
| 26. |
- Taneera, Jalal, et al.
(författare)
-
Identification of novel genes for glucose metabolism based upon expression pattern in human islets and effect on insulin secretion and glycemia.
- 2015
-
Ingår i: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 24:7, s. 1945-1955
-
Tidskriftsartikel (refereegranskat)abstract
- Normal glucose homeostasis is characterized by appropriate insulin secretion and low HbA1c. Gene expression signatures associated with these two phenotypes could be essential for islet function and patho-physiology of type 2 diabetes (T2D). Herein, we employed a novel approach to identify candidate genes involved in T2D by correlating islet microarray gene expression data (78 donors) with insulin secretion and HbA1c level. Expression of 649 genes (p<0.05) was correlated with insulin secretion and HbA1c. Of them, 5 genes (GLR1A, PPP1R1A, PLCDXD3, FAM105A and ENO2) correlated positively with insulin secretion/negatively with HbA1c and one gene (GNG5) correlated negatively with insulin secretion/positively with HbA1c were followed up. The 5 positively correlated genes have lower expression levels in diabetic islets, whereas, GNG5 expression is higher. Exposure of human islets to high glucose for 24 hrs resulted in up-regulation of GNG5 and PPP1R1A expression, while expression of ENO2 and GLRA1 was down-regulated. No effect was seen on the expression of FAM105A and PLCXD3. siRNA silencing in INS-1 832/13 cells showed reduction in insulin secretion for PPP1R1A, PLXCD3, ENO2, FAM105A and GNG5 but not GLRA1. Although, no SNP in these gene loci passed the genome-wide significance for association with T2D in DIAGRAM+ database, four SNPs influenced gene expression in cis in human islets. In conclusion, we identified and confirmed PPP1R1A, FAM105A, ENO2, PLCDX3 and GNG5 as potential regulators of islet function. We provide a list of candidate genes as a resource for exploring their role in the pathogenesis of T2D.
|
|
| 27. |
- Taneera, Jalal, et al.
(författare)
-
Silencing of the FTO gene inhibits insulin secretion : An in vitro study using GRINCH cells
- 2018
-
Ingår i: Molecular and Cellular Endocrinology. - : Elsevier BV. - 0303-7207. ; 472, s. 10-17
-
Tidskriftsartikel (refereegranskat)abstract
- Expression of fat mass and obesity-associated gene (FTO) and ADP-ribosylation factor-like 15 (ARL15) in human islets is inversely correlated with HbA1c. However, their impact on insulin secretion is still ambiguous. Here in, we investigated the role of FTO and ARL15 using GRINCH (Glucose-Responsive Insulin-secreting C-peptide-modified Human proinsulin) clonal rat β-cells. GRINCH cells have inserted GFP into the human C-peptide insulin gene. Hence, secreted CpepGFP served to monitor insulin secretion. mRNA silencing of FTO in GRINCH cells showed a significant reduction in glucose but not depolarization-stimulated insulin secretion, whereas ARL15 silencing had no effect. A significant down-regulation of insulin mRNA was observed in FTO knockdown cells. Type-2 Diabetic islets revealed a reduced expression of FTO mRNA. In conclusion, our data suggest that fluorescent CpepGFP released from GRINCH cells may serve as a convenient marker for insulin secretion. Silencing of FTO expression, but not ARL15, inhibits insulin secretion by affecting metabolic signaling.
|
|
| 28. |
- Thörn, Kristofer, 1981-
(författare)
-
Palmitate-induced Apoptosis in Insulin-producing β-cells
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Type 2 diabetes is a disease characterized by the inability of pancreatic β-cells to secrete sufficient amounts of insulin to maintain normoglycemia. Increased levels of saturated fatty acids such as palmitate are believed to contribute to β-cell failure and the development of the disease. In the present thesis, mechanisms behind palmitate-induced β-cell apoptosis were explored. Palmitate augmented insulin secretion after short exposure to the fatty acid, but attenuated the secretory response after longer exposure. Elevated levels of palmitate increased endoplasmic reticulum (ER) stress and induced apoptosis. When insulin secretion was inhibited by diazoxide, palmitate-induced ER stress and apoptosis were reduced. In comparison to palmitate, the mono-unsaturated fatty acid oleate increased neither ER stress nor apoptosis. Furthermore, shuttling of fatty acids into triglycerides and β-oxidation was favored in cells exposed to oleate compared to palmitate. When the levels of stearoyl-CoA desaturase 1 (SCD1), the enzyme responsible for conversion of saturated to mono-unsaturated fatty acids, were reduced, up-regulation of ER chaperones and components of the proteasome was observed. Cells with reduced levels of SCD1 showed increased sensitivity to palmitate, as exposure to the fatty acid increased levels of ER stress and apoptosis. Palmitate-induced apoptosis of the β-cell has been linked to alterations in sphingolipid metabolism. In cells with reduced levels of sphingosine kinase (SphK) 2, palmitate failed to induce apoptosis, and ER stress was reduced. Furthermore, SphK2 was required for the palmitate-induced activation of c-Jun N-terminal kinase (JNK). In contrast, knockdown of SphK1 sensitized the cell to palmitate-induced apoptosis independently of ER stress. In summary, palmitate induces β-cell apoptosis, which is partly dependent on the induction of ER stress. The mechanisms investigated support the notion that increased protein load on the ER, low degree of triglyceride formation and β-oxidation, and perturbations in sphingolipid metabolism contribute to palmitate-induced apoptosis in insulin-producing β-cells.
|
|
| 29. |
- Tubbs, Emily, et al.
(författare)
-
Sulforaphane improves disrupted ER-mitochondria interactions and suppresses exaggerated hepatic glucose production
- 2018
-
Ingår i: Molecular and Cellular Endocrinology. - : Elsevier BV. - 0303-7207. ; 461:C, s. 205-214
-
Tidskriftsartikel (refereegranskat)abstract
- Aims: Exaggerated hepatic glucose production is one of the hallmarks of type 2 diabetes. Sulforaphane (SFN) has been suggested as a new potential anti-diabetic compound. However, the effects of SFN in hepatocytes are yet unclear. Accumulating evidence points to the close structural contacts between the ER and mitochondria, known as mitochondria-associated ER membranes (MAMs), as important hubs for hepatic metabolism. We wanted to investigate whether SFN could affect hepatic glucose production and MAMs. Materials and methods: We used proximity ligation assays, analysis of ER stress markers and glucose production assays in hepatoma cell lines, primary mouse hepatocytes and diabetic animal models. Results: SFN counteracted the increase of glucose production in palmitate-treated mouse hepatocytes. SFN also counteracted palmitate-induced MAM disruptions. Moreover, SFN decreased the ER stress markers CHOP and Grp78. In ob/ob mice, SFN improved glucose tolerance and reduced exaggerated glucose production. In livers of these mice, SFN increased MAM protein content, restored impaired VDAC1-IP3R1 interactions and reduced ER stress markers. In mice on HFHSD, SFN improved glucose tolerance, MAM protein content and ER-mitochondria interactions to a similar extent to that of metformin. Conclusions: The present findings show that MAMs are severely reduced in animal models of glucose intolerance, which reinforces the role of MAMs as a hub for insulin signaling in the liver. We also show that SFN restores MAMs and improves glucose tolerance by a similar magnitude to that of metformin. These data highlight SFN as a new potential anti-diabetic compound. (C) 2017 Elsevier B.V. All rights reserved.
|
|
| 30. |
- Wu, Chuanyan, et al.
(författare)
-
Elevated circulating follistatin associates with an increased risk of type 2 diabetes
- 2021
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12, s. 1-10
-
Tidskriftsartikel (refereegranskat)abstract
- The hepatokine follistatin is elevated in patients with type 2 diabetes (T2D) and promotes hyperglycemia in mice. Here we explore the relationship of plasma follistatin levels with incident T2D and mechanisms involved. Adjusted hazard ratio (HR) per standard deviation (SD) increase in follistatin levels for T2D is 1.24 (CI: 1.04-1.47, p < 0.05) during 19-year follow-up (n = 4060, Sweden); and 1.31 (CI: 1.09-1.58, p < 0.01) during 4-year follow-up (n = 883, Finland). High circulating follistatin associates with adipose tissue insulin resistance and non-alcoholic fatty liver disease (n = 210, Germany). In human adipocytes, follistatin dose-dependently increases free fatty acid release. In genome-wide association study (GWAS), variation in the glucokinase regulatory protein gene (GCKR) associates with plasma follistatin levels (n = 4239, Sweden; n = 885, UK, Italy and Sweden) and GCKR regulates follistatin secretion in hepatocytes in vitro. Our findings suggest that GCKR regulates follistatin secretion and that elevated circulating follistatin associates with an increased risk of T2D by inducing adipose tissue insulin resistance.
|
|
| 31. |
- Yang, Beatrice, et al.
(författare)
-
Increased DNA Methylation and Decreased Expression of PDX-1 in Pancreatic Islets from Patients with Type 2 Diabetes.
- 2012
-
Ingår i: Molecular Endocrinology. - : The Endocrine Society. - 0888-8809 .- 1944-9917. ; 26:7, s. 1203-1212
-
Tidskriftsartikel (refereegranskat)abstract
- Mutations in pancreatic duodenal homeobox 1 (PDX-1) can cause a monogenic form of diabetes (maturity onset diabetes of the young 4) in humans, and silencing Pdx-1 in pancreatic β-cells of mice causes diabetes. However, it is not established whether epigenetic alterations of PDX-1 influence type 2 diabetes (T2D) in humans. Here we analyzed mRNA expression and DNA methylation of PDX-1 in human pancreatic islets from 55 nondiabetic donors and nine patients with T2D. We further studied epigenetic regulation of PDX-1 in clonal β-cells. PDX-1 expression was decreased in pancreatic islets from patients with T2D compared with nondiabetic donors (P = 0.0002) and correlated positively with insulin expression (rho = 0.59, P = 0.000001) and glucose-stimulated insulin secretion (rho = 0.41, P = 0.005) in the human islets. Ten CpG sites in the distal PDX-1 promoter and enhancer regions exhibited significantly increased DNA methylation in islets from patients with T2D compared with nondiabetic donors. DNA methylation of PDX-1 correlated negatively with its gene expression in the human islets (rho = -0.64, P = 0.0000029). Moreover, methylation of the human PDX-1 promoter and enhancer regions suppressed reporter gene expression in clonal β-cells (P = 0.04). Our data further indicate that hyperglycemia decreases gene expression and increases DNA methylation of PDX-1 because glycosylated hemoglobin (HbA1c) correlates negatively with mRNA expression (rho = -0.50, P = 0.0004) and positively with DNA methylation (rho = 0.54, P = 0.00024) of PDX-1 in the human islets. Furthermore, while Pdx-1 expression decreased, Pdx-1 methylation and Dnmt1 expression increased in clonal β-cells exposed to high glucose. Overall, epigenetic modifications of PDX-1 may play a role in the development of T2D, given that pancreatic islets from patients with T2D and β-cells exposed to hyperglycemia exhibited increased DNA methylation and decreased expression of PDX-1. The expression levels of PDX-1 were further associated with insulin secretion in the human islets.
|
|
| 32. |
- Yang, Beatrice, et al.
(författare)
-
Insulin promoter DNA methylation correlates negatively with insulin gene expression and positively with HbA(1c) levels in human pancreatic islets.
- 2011
-
Ingår i: Diabetologia. - : Springer Science and Business Media LLC. - 1432-0428 .- 0012-186X. ; Dec, s. 360-367
-
Tidskriftsartikel (refereegranskat)abstract
- AIMS/HYPOTHESIS: Although recent studies propose that epigenetic factors influence insulin expression, the regulation of the insulin gene in type 2 diabetic islets is still not fully understood. Here, we examined DNA methylation of the insulin gene promoter in pancreatic islets from patients with type 2 diabetes and non-diabetic human donors and related it to insulin expression, HbA(1c) levels, BMI and age. METHODS: DNA methylation was analysed in 25 CpG sites of the insulin promoter and insulin mRNA expression was analysed using quantitative RT-PCR in pancreatic islets from nine donors with type 2 diabetes and 48 non-diabetic donors. RESULTS: Insulin mRNA expression (p = 0.002), insulin content (p = 0.004) and glucose-stimulated insulin secretion (p = 0.04) were reduced in pancreatic islets from patients with type 2 diabetes compared with non-diabetic donors. Moreover, four CpG sites located 234 bp, 180 and 102 bp upstream and 63 bp downstream of the transcription start site (CpG -234, -180, -102 and +63, respectively), showed increased DNA methylation in type 2 diabetic compared with non-diabetic islets (7.8%, p = 0.03; 7.1%, p = 0.02; 4.4%, p = 0.03 and 9.3%, p = 0.03, respectively). While insulin mRNA expression correlated negatively (p < 1 × 10(-6)), the level of HbA(1c) correlated positively (p ≤ 0.01) with the degree of DNA methylation for CpG -234, -180 and +63. Furthermore, DNA methylation for nine additional CpG sites correlated negatively with insulin mRNA expression (p ≤ 0.01). Also, exposure to hyperglycaemia for 72 h increased insulin promoter DNA methylation in clonal rat beta cells (p = 0.005). CONCLUSIONS/INTERPRETATIONS: This study demonstrates that DNA methylation of the insulin promoter is increased in patients with type 2 diabetes and correlates negatively with insulin gene expression in human pancreatic islets.
|
|
| 33. |
|
|
| 34. |
- Zhou, Yuedan, et al.
(författare)
-
TCF7L2 is a master regulator of insulin production and processing
- 2014
-
Ingår i: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 23:24, s. 6419-6431
-
Tidskriftsartikel (refereegranskat)abstract
- Genome-wide association studies have revealed > 60 loci associated with type 2 diabetes ( T2D), but the underlying causal variants and functional mechanisms remain largely elusive. Although variants in TCF7L2 confer the strongest risk of T2D among common variants by presumed effects on islet function, the molecular mechanisms are not yet well understood. Using RNA-sequencing, we have identified a TCF7L2-regulated transcriptional network responsible for its effect on insulin secretion in rodent and human pancreatic islets. ISL1 is a primary target of TCF7L2 and regulates proinsulin production and processing via MAFA, PDX1, NKX6.1, PCSK1, PCSK2 and SLC30A8, thereby providing evidence for a coordinated regulation of insulin production and processing. The risk T-allele of rs7903146 was associated with increased TCF7L2 expression, and decreased insulin content and secretion. Using gene expression profiles of 66 human pancreatic islets donors', we also show that the identified TCF7L2-ISL1 transcriptional network is regulated in a genotype-dependent manner. Taken together, these results demonstrate that not only synthesis of proinsulin is regulated by TCF7L2 but also processing and possibly clearance of proinsulin and insulin. These multiple targets in key pathways may explain why TCF7L2 has emerged as the gene showing one of the strongest associations with T2D.
|
|
