DEXI, a candidate gene for type 1 diabetes, modulates rat and human pancreatic beta cell inflammation via regulation of the type I IFN/STAT signalling pathway
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The initial stages of type 1 diabetes are characterised by an aberrant islet inflammation that is in part regulated by the interaction between type 1 diabetes susceptibility genes and environmental factors. Chromosome 16p13 is associated with type 1 diabetes and CLEC16A is thought to be the aetiological gene in the region. Recent gene expression analysis has, however, indicated that SNPs in CLEC16A modulate the expression of a neighbouring gene with unknown function named DEXI, encoding dexamethasone-induced protein (DEXI). We therefore evaluated the role of DEXI in beta cell responses to ‘danger signals’ and determined the mechanisms involved.
Functional studies based on silencing or overexpression of DEXI were performed in rat and human pancreatic beta cells. Beta cell inflammation and apoptosis, driven by a synthetic viral double-stranded RNA, were evaluated by real-time PCR, western blotting and luciferase assays.
DEXI-silenced beta cells exposed to a synthetic double-stranded RNA (polyinosinic:polycytidylic acid [PIC], a by-product of viral replication) showed reduced activation of signal transducer and activator of transcription (STAT) 1 and lower production of proinflammatory chemokines that was preceded by a reduction in IFNβ levels. Exposure to PIC increased chromatin-bound DEXI and IFNβ promoter activity. This effect on IFNβ promoter was inhibited in DEXI-silenced beta cells, suggesting that DEXI is implicated in the regulation of IFNβ transcription. In a mirror image of knockdown experiments, DEXI overexpression led to increased levels of STAT1 and proinflammatory chemokines.
These observations support DEXI as the aetiological gene in the type 1 diabetes-associated 16p13 genomic region, and provide the first indication of a link between this candidate gene and the regulation of local antiviral immune responses in beta cells. Moreover, our results provide initial information on the function of DEXI.
KeywordsDEXI Inflammation Pancreatic beta cell Susceptibility gene Type 1 diabetes Type I IFNs Viral infection
Chemokine (C-C motif) ligand 5
Expression quantitative trait locus
Interferon-stimulated response element
Small interfering RNA
Signal transducer and activator of transcription
The authors are grateful to M. Pangerl, A. M. Musuaya, N. Pachera, Y. Cai and I. Millard of the ULB Center for Diabetes Research, Université Libre de Bruxelles, Belgium, for excellent technical support; J.-V. Turantzine of the ULB Center for Diabetes Research, Université Libre de Bruxelles, Belgium, for his help in the analysis of DEXI expression in human islet and Illumina samples; and the Flow Cytometry Facility of the Erasmus campus, Université Libre de Bruxelles, and C. Dubois for the cell sorting. They also thank P. Marchetti and L. Marselli from the Department of Clinical and Experimental Medicine at the University of Pisa (Pisa, Italy) for providing human pancreatic islets, I. Irastorza from the Pediatric Gastroenterology Service at the Cruces University Hospital (Barakaldo, Spain) for intestinal biopsy collection and the Immunogenetics Research Laboratory from the University of the Basque Country (Leioa, Spain) for sample processing.
RSS, LM, TV, AOG, AJM and ACR researched data, and revised and edited the manuscript. DLE contributed to the design and interpretation of the experiments, and to discussion, and wrote, revised and edited the manuscript. LC contributed to interpretation of the experiments and discussion, and revised and edited the manuscript. IS contributed to the original idea, design and interpretation of experiments, researched data, contributed to discussion, and wrote, revised and edited the manuscript. All authors have read and approved the manuscript and given informed consent. IS the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
This work was supported by a Research Project Grant from the Basque Department of Health (2015111068), a Research Grant from Fundación de la Sociedad Española de Diabetes (FSED), the Horizon 2020 Program T2Dsystems (GA667191) and the National Institute of Health–National Institute of Diabetes and Digestive and Kidney Diseases–Human Islet Research Network Consortium 1UC4DK104166-01, USA. TV and AJM were supported by Predoctoral Fellowship grants from the UPV/EHU and the Basque Department of Education, respectively. AOG is supported by a Predoctoral Fellowship Grant from the Basque Department of Education. ACR is supported by an Ikerbasque Research Fellow grant. LM was supported by a Fonds National de la Recherche Scientifique postdoctoral fellowship. DLE has received funding from the Innovative Medicines Initiative 2 Joint Undertaking under grant agreement No 115797 (INNODIA). This Joint Undertaking receives support from the Union’s Horizon 2020 research and innovation programme and European Federation of Pharmaceutical Industries and Association (EFPIA), JDRF and Leona M. and Harry B. Helmsley Charitable Trust.
Duality of interest
The authors declare that there is no duality of interest associated with this manuscript.
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