| 1. |
- Andersson, Sofia A, et al.
(författare)
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Reduced insulin secretion correlates with decreased expression of exocytotic genes in pancreatic islets from patients with type 2 diabetes.
- 2012
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Ingår i: Molecular and Cellular Endocrinology. - : Elsevier BV. - 1872-8057 .- 0303-7207. ; 364:1-2, s. 36-45
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Tidskriftsartikel (refereegranskat)abstract
- Reduced insulin release has been linked to defect exocytosis in β-cells. However, whether expression of genes suggested to be involved in the exocytotic process (exocytotic genes) is altered in pancreatic islets from patients with type 2 diabetes (T2D), and correlate to insulin secretion, needs to be further investigated. Analysing expression levels of 23 exocytotic genes using microarray revealed reduced expression of five genes in human T2D islets (χ(2)=13.25; p<0.001). Gene expression of STX1A, SYT4, SYT7, SYT11, SYT13, SNAP25 and STXBP1 correlated negatively to in vivo measurements of HbA1c levels and positively to glucose stimulated insulin secretion (GSIS) in vitro in human islets. STX1A, SYT4 and SYT11 protein levels correspondingly decreased in human T2D islets. Moreover, silencing of SYT4 and SYT13 reduced GSIS in INS1-832/13 cells. Our data support that reduced expression of exocytotic genes contributes to impaired insulin secretion, and suggest decreased expression of these genes as part of T2D pathogenesis.
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| 2. |
- De Marinis, Yang, et al.
(författare)
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Enhancement of glucagon secretion in mouse and human pancreatic alpha cells by protein kinase C (PKC) involves intracellular trafficking of PKCalpha and PKCdelta.
- 2010
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Ingår i: Diabetologia. - : Springer Science and Business Media LLC. - 1432-0428 .- 0012-186X. ; 53:4, s. 717-729
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Tidskriftsartikel (refereegranskat)abstract
- AIMS/HYPOTHESIS: Protein kinase C (PKC) regulates exocytosis in various secretory cells. Here we studied intracellular translocation of the PKC isoenzymes PKCalpha and PKCdelta, and investigated how activation of PKC influences glucagon secretion in mouse and human pancreatic alpha cells. METHODS: Glucagon release from intact islets was measured in static incubations, and the amounts released were determined by RIA. Exocytosis was monitored as increases in membrane capacitance using the patch-clamp technique. The expression of genes encoding PKC isoforms was analysed by real-time PCR. Intracellular PKC distribution was assessed by confocal microscopy. RESULTS: The PKC activator phorbol 12-myristate 13-acetate (PMA) stimulated glucagon secretion from mouse and human islets about fivefold (p < 0.01). This stimulation was abolished by the PKC inhibitor bisindolylmaleimide (BIM). Whereas PMA potentiated exocytosis more than threefold (p < 0.001), BIM inhibited alpha cell exocytosis by 60% (p < 0.05). In mouse islets, the PKC isoenzymes, PKCalpha and PKCbeta1, were highly abundant, while in human islets PKCeta, PKCepsilon and PKCzeta were the dominant variants. PMA stimulation of human alpha cells correlated with the translocation of PKCalpha and PKCdelta from the cytosol to the cell periphery. In the mouse alpha cells, PKCdelta was similarly affected by PMA, whereas PKCalpha was already present at the cell membrane in the absence of PMA. This association of PKCalpha in alpha cells was principally dependent on Ca(2+) influx through the L-type Ca(2+) channel. CONCLUSIONS/INTERPRETATION: PKC activation augments glucagon secretion in mouse and human alpha cells. This effect involves translocation of PKCalpha and PKCdelta to the plasma membrane, culminating in increased Ca(2+)-dependent exocytosis. In addition, we demonstrated that PKCalpha translocation and exocytosis exhibit differential Ca(2+) channel dependence.
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| 3. |
- Fadista, Joao, et al.
(författare)
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Global genomic and transcriptomic analysis of human pancreatic islets reveals novel genes influencing glucose metabolism.
- 2014
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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
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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.
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| 4. |
- Lyssenko, Valeriya, et al.
(författare)
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Pleiotropic Effects of GIP on Islet Function Involve Osteopontin
- 2011
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Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 60:9, s. 2424-2433
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE-The incretin hormone GIP (glucose-dependent insulinotropic polypeptide) promotes pancreatic beta-cell function by potentiating insulin secretion and beta-cell proliferation. Recently, a combined analysis of several genome-wide association studies (Meta-analysis of Glucose and Insulin-Related Traits Consortium [MAGIC]) showed association to postprandial insulin at the GIP receptor (GIPR) locus. Here we explored mechanisms that could explain the protective effects of GIP on islet function. RESEARCH DESIGN AND METHODS-Associations of GIPR rs10423928 with metabolic and anthropometric phenotypes in both nondiabetic (N = 53,730) and type 2 diabetic individuals (N = 2,731) were explored by combining data from 11 studies.Insulin secretion was measured both in vivo in nondiabetic subjects and in vitro in islets from cadaver donors. Insulin secretion was also measured in response to exogenous GIP. The in vitro measurements included protein and gene expression as well as measurements of beta-cell viability and proliferation. RESULTS-The A allele of GIPR rs10423928 was associated with impaired glucose- and GIP-stimulated insulin secretion and a decrease in BMI, lean body mass, and waist circumference. The decrease in BMI almost completely neutralized the effect of impaired insulin secretion on risk of type 2 diabetes. Expression of GIPR mRNA was decreased in human islets from carriers of the A allele or patients with type 2 diabetes. GIP stimulated osteopontin (OPN) mRNA and protein expression. OPN expression was lower in carriers of the A allele. Both GIP and OPN prevented cytokine-induced reduction in cell viability (apoptosis). In addition, OPN stimulated cell proliferation in insulin-secreting cells. CONCLUSIONS-These findings support beta-cell proliferative and antiapoptotic roles for GIP in addition to its action as an incretin hormone. Identification of a link between GIP and OPN may shed new light on the role of GIP in preservation of functional beta-cell mass in humans. Diabetes 60:2424-2433, 2011
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| 5. |
- Mahdi, Taman, et al.
(författare)
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Secreted frizzled-related protein 4 reduces insulin secretion and is overexpressed in type 2 diabetes.
- 2012
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Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131. ; 16:5, s. 625-633
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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.
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