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Type 1 Diabetes (T1D) is a ­cell­targeted autoimmune disease, leading to a reduction in pancreatic ­cell mass that renders patients insulin­dependent for life. In early stages of the disease, cells from the immune system infiltrate pancreatic islets in a process called insulitis. During this stage, a cross­talk is established between cells in the pancreatic islets and the infiltrating immune cells, mediated by the release of cytokines and chemokines. Studying the gene regulatory networks driving cell responses during insulitis, will allow us to pinpoint key gene pathways leading to ­cell loss­of­function and apoptosis, and also to understand the role cells have in their own demise. In the present thesis, we used two different cytokine cocktails, IFN­ and IFN­ + IL­1, to model early and late insulitis, respectively. After exposing cells and pancreatic islets to such proinflammatory cytokines, we characterized the changes in their chromatin landscape, gene networks and protein profiles. Using both models, we observed dramatic chromatin remodeling in terms of accessibility and/or H3K27ac histone modification enrichment, coupled with up­regulation of the nearby genes and increased abundance of the corresponding protein. Mining gene regulatory networks of ­cells exposed to IFN­ revealed two potential therapeutic interventions which were able to reduce interferon signature in cells: 1) Inhibition of bromodomain proteins, which resulted in a down­regulation of IFN­­induced HLA­I and CXCL10 expression; 2) Baricitnib, a JAK1/2 inhibitor, which was able to reduce both IFN­­induced HLA­I and CXCL10 expression levels and cell apoptosis. In cells exposed to IFN­ + IL­1, we were able to identify a subset of novel regulatory elements uncovered upon the exposure, which we named Induced Regulatory Elements (IREs). Such regions were enriched for T1D­associated risk variants, suggesting that cells might carry a portion of T1D genetic risk. Interestingly, we identified two T1D lead variants overlapping IREs, in which the risk allele modulated the IRE enhancer activity, exposing a potential T1D mechanism acting through cells. To facilitate the access to these genomic data, together with other datasets relevant for the pancreatic islet community, we developed the Islet Regulome Browser (http://www.isletregulome.org/), a free web application that allows exploration and integration of pancreatic islet genomic data.

Genetic studies promise to provide insight into the molecular mechanisms underlying type 2 diabetes (T2D). Variants associated with T2D are often located in tissue-specific enhancer clusters or super-enhancers. So far, such domains have been defined through clustering of enhancers in linear genome maps rather than in three-dimensional (3D) space. Furthermore, their target genes are often unknown. We have created promoter capture Hi-C maps in human pancreatic islets. This linked diabetes-associated enhancers to their target genes, often located hundreds of kilobases away. It also revealed1,300 groups of islet enhancers, super-enhancers and active promoters that form 3D hubs, some of which show coordinated glucose-dependent activity. We demonstrate that genetic variation in hubs impacts insulin secretion heritability, and show that hub annotations can be used for polygenic scores that predict T2D risk driven by islet regulatory variants. Human islet 3D chromatin architecture, therefore, provides a framework for interpretation of T2D genome-wide association study (GWAS) signals.

Genetic studies promise to provide insight into the molecular mechanisms underlying type 2 diabetes (T2D). Variants associated with T2D are often located in tissue-specific enhancer clusters or super-enhancers. So far, such domains have been defined through clustering of enhancers in linear genome maps rather than in three-dimensional (3D) space. Furthermore, their target genes are often unknown. We have created promoter capture Hi-C maps in human pancreatic islets. This linked diabetes-associated enhancers to their target genes, often located hundreds of kilobases away. It also revealed >1,300 groups of islet enhancers, super-enhancers and active promoters that form 3D hubs, some of which show coordinated glucose-dependent activity. We demonstrate that genetic variation in hubs impacts insulin secretion heritability, and show that hub annotations can be used for polygenic scores that predict T2D risk driven by islet regulatory variants. Human islet 3D chromatin architecture, therefore, provides a framework for interpretation of T2D genome-wide association study (GWAS) signals. This research was supported by the National Institute for Health Research Imperial Biomedical Research Centre. Work was funded by grants from the Wellcome Trust (nos. WT101033 to J.F. and WT205915 to I.P.), Horizon 2020 (Research and Innovation Programme nos. 667191, to J.F., 633595, to I.P., and 676556, to M.A.M.-R.; Marie Sklodowska-Curie 658145, to I.M.-E., and 43062 ZENCODE, to G.A.), European Research Council (nos. 789055, to J.F., and 609989, to M.A.M.-R.). Marató TV3 (no. 201611, to J.F. and M.A.M.-R.), Ministerio de Ciencia Innovación y Universidades (nos. BFU2014-54284-R, RTI2018-095666, to J.F., BFU2017-85926-P, to M.A.M.-R., IJCI-2015-23352, to I.F.), AGAUR (to M.A.M.-R.). UK Medical Research Council (no. MR/L007150/1, to P.F., MR/L02036X/1 to J.F.), World Cancer Research Fund (WCRF UK, to I.P.) and World Cancer Research Fund International (no. 2017/1641 to I.P.), Biobanking and Biomolecular Resources Research Infrastructure (nos. BBMRI-NL, NWO 184.021.007, to I.O.F.). Work in IDIBAPS, CRG and CNAG was supported by the CERCA Programme, Generalitat de Catalunya and Centros de Excelencia Severo Ochoa (no. SEV-2012-0208). Human islets were provided through the European islet distribution program for basic research supported by JDRF (no. 3-RSC-2016-160-I-X). We thank N. Ruiz-Gomez for technical assistance; R. L. Fernandes, T. Thorne (University of Reading) and A. Perdones-Montero (Imperial College London) for helpful discussions regarding Machine Learning approaches; B. Lenhard and M. Merkenschlager (London Institute of Medical Sciences, Imperial College London), F. Müller (University of Birmingham) and J. L. Gómez-Skarmeta (Centro Andaluz de Biología del Desarrollo) for critical comments on the draft; the CRG Genomics Unit; and the Imperial College High Performance Computing Service.

The early stages of type 1 diabetes (T1D) are characterized by local autoimmune inflammation and progressive loss of insulin-producing pancreatic β cells. Here we show that exposure to proinflammatory cytokines reveals a marked plasticity of the β-cell regulatory landscape. We expand the repertoire of human islet regulatory elements by mapping stimulus-responsive enhancers linked to changes in the β-cell transcriptome, proteome and three-dimensional chromatin structure. Our data indicate that the β-cell response to cytokines is mediated by the induction of new regulatory regions as well as the activation of primed regulatory elements prebound by islet-specific transcription factors. We find that T1D-associated loci are enriched with newly mapped cis-regulatory regions and identify T1D-associated variants disrupting cytokine-responsive enhancer activity in human β cells. Our study illustrates how β cells respond to a proinflammatory environment and implicate a role for stimulus response islet enhancers in T1D. L.Pasquali was supported by grants from the Spanish Ministry of Economy and Competitiveness (nos. BFU2014-58150-R and SAF2017-86242-R), Marató TV3 (no. 201624.10) and a young investigator award from the Spanish Society of Diabetes (Ayuda SED a Proyectos de Investigación, no. 2017-SED). L.Pasquali is a recipient of a Ramon y Cajal contract from the Spanish Ministry of Economy and Competitiveness (no. RYC-2013-12864). The Pasquali lab is further supported by Instituto de Salud Carlos III (no. PIE16/00011). M.R. is supported by an FI Agència de Gestió d’Ajuts Universitaris i de Recerca PhD fellowship (no. 2019FI_B100203). J.J. was supported by a Marie Skłodowska-Curie Actions fellowship grant from the Horizons 2020 European Union (EU) Programme (project no. 660449). M.I.A. was supported by a FRIA fellowship from the Fonds de la Recherche Scientifique (FNRS) (no. 26410496). Human islets were provided through the European Consortium for Islet Transplantation distribution program for basic research supported by JDRF (no. 31-2008-416). D.L.E. was supported by the Walloon Region through the FRFS-WELBIO Fund for Strategic Fundamental research (no. CR-2015A-06s and CR-2019C-04) and by grants from the Fonds National de la Recherche Scientifique (no. T003613F), the Horizon 2020 Programme (project T2Dsystems, no. GA667191), Brussels Capital Region Innoviris (project DiaType, no. 2017-PFS-24), Dutch Diabetes Research Fundation (project Innovate2CureType1, DDRF; no. 2018.10.002) and the Innovative Medicines Initiative 2 Joint Undertaking (project INNODIA, no. 115797). This Innovative Medicines Initiative 2 Joint Undertaking receives support from the EU’s Horizon 2020 Research and Innovation Programme and European Federation of Pharmaceutical Industries and Associations, JDRF and the Leona M. and Harry B. Helmsley Charitable Trust (project INNODIA, no. 115797). T.O.M. and D.L.E. were supported by a grant from the National Institutes of Health-National Institute of Diabetes and Digestive and Kidney Diseases-Human Islet Research Network Consortium (no. 1UC4DK104166-01). Part of the work was performed at the Environmental Molecular Sciences Laboratory, a US Department of Energy national scientific user facility located at Pacific Northwest National Laboratory. Battelle operates the Pacific Northwest National Laboratory for the Department of Energy (contract no. DE-AC05-76RLO01830).