| 1. |
- Fred, Rikard G.
(författare)
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The Role of RNA Binding Proteins in Insulin Messenger Stability and Translation
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although the reason for insufficient release of insulin in diabetes mellitus may vary depending on the type and stage of the disease, it is of vital importance that an amplified insulin biosynthesis can meet the increased need during periods of hyperglycemia. The insulin mRNA is highly abundant in beta cells and changes in insulin mRNA levels are, at least in part, controlled by altered rates of mRNA degradation. Since the mechanisms behind the control of insulin messenger stability and translation are still largely obscure, the work presented in this thesis therefore aimed to further investigate the role of insulin mRNA binding proteins in the control of insulin mRNA break-down and utilization for insulin biosynthesis. To clarify how glucose regulates insulin mRNA stability and translation we studied the correlation between polypyrimidine tract binding protein (PTB) gene expression and insulin mRNA levels. It was found that an increase in PTB mRNA and protein levels is paralleled by an increase in insulin mRNA levels. It was also found that PTB binds to the 5’-untranslated region of the insulin mRNA and that insulin mRNA can be translated through a cap-independent mechanism in human islets of Langerhans, possibly due to the interaction with PTB. Further it was discovered that the suppressed insulin biosynthesis in human islets during glucotoxicity is partly due to an induction of the microRNA miR-133a. This induction leads to decreased levels of PTB and insulin biosynthesis rates in human islets. Finally, we were able to identify two proteins, hnRNP U and TIAR, that bind specifically to the insulin mRNA in vitro, and show that the stability and translation of insulin mRNA is oppositely affected by these proteins. In conclusion, insulin producing cells seem to be able to regulate insulin messenger stability and translation by a control mechanism in which the binding of specific proteins to the insulin messenger dictates the outcome. A better understanding of the events leading to insulin production may in the future aid in optimal diagnosis and treatment of type 2 diabetes.
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| 2. |
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| 3. |
- 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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| 4. |
- Pugliese, Alberto, et al.
(författare)
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Sequence analysis of the diabetes-protective human leukocyte antigen-DQB1*0602 allele in unaffected, islet cell antibody-positive first degree relatives and in rare patients with type 1 diabetes
- 1999
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Ingår i: Journal of Clinical Endocrinology and Metabolism. - : The Endocrine Society. - 0021-972X .- 1945-7197. ; 84:5, s. 1722-1728
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Tidskriftsartikel (refereegranskat)abstract
- The human leukocyte antigen (HLA)-DQA1*0102/DQB1*0602/DRB1*1501 (DR2) haplotype confers strong protection from type 1 diabetes. Growing evidence suggests that such protection may be mostly encoded by the DQB1*0602 allele, and we reported that even first degree relatives with islet cell antibodies (ICA) have an extremely low diabetes risk if they carry DQB1*0602. Recently, novel variants of the DQB1*0602 and *0603 alleles were reported in four patients with type 1 diabetes originally typed as DQB1*0602 with conventional techniques. One inference from this observation is that DQB1*0602 may confer absolute protection and may never occur in type 1 diabetes. By this hypothesis, all patients typed as DQB1*0602 positive with conventional techniques should carry one of the above diabetes-permissive variants instead of the protective DQB1*0602. Such variants could also occur in ICA/DQB1*0602-positive relatives, with the implication that their diabetes risk could be significantly higher than previously estimated. We therefore sequenced the DQB1*0602 and DQA1*0102 alleles in all ICA/DQB1*0602-positive relatives (n = 8) previously described and in six rare patients with type 1 diabetes and DQB1*0602. We found that all relatives and patients carry the known DQB1*0602 and DQA1*0102 sequences, and none of them has the mtDNA A3243G mutation associated with late-onset diabetes in ICA-positive individuals. These findings suggest that diabetes-permissive DQB1*0602/3 variants may be very rare. Thus, although the protective effect associated with DQB1*0602 is extremely powerful, it is not absolute. Nonetheless, the development of diabetes in individuals with DQB1*0602 remains extremely unlikely, even in the presence of ICA, as confirmed by our further evaluation of ICA/DQB1*0602-positive relatives, none of whom has yet developed diabetes.
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| 5. |
- Seiron, Peter, 1990-
(författare)
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Studies of the Pancreas: Implications for Type 1 Diabetes Aetiology
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Type 1 diabetes (T1D) is a disease of severe insulin deficiency through loss of β cells in the endocrine pancreas. The T1D dogma maintains that a precipitating event unleashes autoimmunity in at-risk individuals, often measured through autoantibodies against β cell antigens. This is followed by the death of β cells at the hands of autoreactive cytotoxic T cells. However, several findings have not found their place within this dogma; first, the immune cell infiltrate in islets is usually located outside the islets, and second, there is a pronounced impact on the exocrine pancreas with lower pancreatic weight and fibrosis surrounding the ducts. In this thesis, pancreata from human subjects without diabetes (ND) as well as with T1D or type 2 diabetes (T2D) have been examined in an attempt to clarify the aetiology of T1D.The consensus definition of insulitis (≥15 CD45+ cells per islet in ≥3 islets) was validated against ND pancreata. In paper I we show that this definition cannot sufficiently discriminate between the findings in T1D and T2D pancreata, due to an increase in exocrine infiltration in T2D, predominantly made up by macrophages. As exocrine infiltration is also a common finding in T1D, we propose a new definition. In paper II we found tissue resident memory T (TRM) cells in association to islets in both ND and T1D pancreata, and they made up a significant proportion of the insulitic lesion in T1D. Islets contain on average 60% β cells. In paper III we found that despite the seeming loss of this predominant cell type in the T1D islets, islet size remained the same. Instead, islet density was markedly reduced. The islets contained mainly α cells, some of which expressed PDX1, a transcription factor marker of β cells. In paper IV we examined pancreata from ND organ donors aged 1-81 years. For the first time, the islet transcriptome was analysed without prior enzymatic digestion of the tissue. We corroborate earlier findings of reduced cell cycle activity and increased senescence with increasing age, as well as present a hypothesis of how islet age might affect T1D.The findings in this thesis sprout an alternative hypothesis that disturbed establishment of β cells in early life, due to lower islet density and lower pancreatic weight, would lead to β cell stress as insulin demand increases with physical growth. However, as islets do not decrease in size, we suggest that the disappearance of β cells could be explained by transdifferentiation into glucagon-producing cells.
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| 6. |
- Slieker, Roderick C, et al.
(författare)
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Identification of biomarkers for glycaemic deterioration in type 2 diabetes
- 2023
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Ingår i: Nature Communications. - 2041-1723. ; 14, s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- We identify biomarkers for disease progression in three type 2 diabetes cohorts encompassing 2,973 individuals across three molecular classes, metabolites, lipids and proteins. Homocitrulline, isoleucine and 2-aminoadipic acid, eight triacylglycerol species, and lowered sphingomyelin 42:2;2 levels are predictive of faster progression towards insulin requirement. Of ~1,300 proteins examined in two cohorts, levels of GDF15/MIC-1, IL-18Ra, CRELD1, NogoR, FAS, and ENPP7 are associated with faster progression, whilst SMAC/DIABLO, SPOCK1 and HEMK2 predict lower progression rates. In an external replication, proteins and lipids are associated with diabetes incidence and prevalence. NogoR/RTN4R injection improved glucose tolerance in high fat-fed male mice but impaired it in male db/db mice. High NogoR levels led to islet cell apoptosis, and IL-18R antagonised inflammatory IL-18 signalling towards nuclear factor kappa-B in vitro. This comprehensive, multi-disciplinary approach thus identifies biomarkers with potential prognostic utility, provides evidence for possible disease mechanisms, and identifies potential therapeutic avenues to slow diabetes progression.
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