Dysregulation of the Pdx1/Ovol2/Zeb2 axis in dedifferentiated β-cells triggers the induction of genes associated with epithelial-mesenchymal transition in diabetes

Abstract

Objective:b-cell dedifferentiation has been revealed as a pathological mechanism underlying pancreatic dysfunction in diabetes. We previouslyshowed that increased miR-7 levels triggerb-cell dedifferentiation and diabetes. We usedb-cell-specific miR-7 overexpressing mice (Tg7) to testthe hypothesis that loss ofb-cell identity triggered by miR-7 overexpression alters islet gene expression and islet microenvironment in diabetes.Methods:We performed bulk and single-cell RNA sequencing (RNA-seq) in islets obtained fromb-cell-specific miR-7 overexpressing mice(Tg7). We carried out loss- and gain-of-function experiments in MIN6 and EndoC-bH1 cell lines. We analysed previously published mouse andhuman T2D data sets.Results:Bulk RNA-seq revealed thatb-cell dedifferentiation is associated with the induction of genes associated with epithelial-to-mesenchymal transition (EMT) in prediabetic (2-week-old) and diabetic (12-week-old) Tg7 mice. Single-cell RNA-seq (scRNA-seq) indicatedthat this EMT signature is enriched specifically inb-cells. These molecular changes are associated with a weakening ofb-cell:b-cell contacts,increased extracellular matrix (ECM) deposition, and TGFb-dependent isletfibrosis. We found that the mesenchymal reprogramming ofb-cells isexplained in part by the downregulation ofPdx1and its inability to regulate a myriad of epithelial-specific genes expressed inb-cells. Notableamong genes transactivated byPdx1isOvol2, which encodes a transcriptional repressor of the EMT transcription factorZeb2. Followingcompromisedb-cell identity, the reduction inPdx1gene expression causes a decrease inOvol2protein, triggering mesenchymal reprogrammingofb-cells through the induction ofZeb2. We provided evidence that EMT signalling associated with the upregulation ofZeb2expression is amolecular feature of islets in T2D subjects.Conclusions:Our study indicates that miR-7-mediatedb-cell dedifferentiation induces EMT signalling and a chronic response to tissue injury,which alters the islet microenvironment and predisposes tofibrosis. This research suggests that regulators of EMT signalling may represent noveltherapeutic targets for treatingb-cell dysfunction andfibrosis in T2D. ; Published version ; This study was supported by core support from the Medical Research Council UK to the London Institute of Medical Sciences grant MC-A654-5QC20. G.A.R. was supported by a Wellcome Trust Senior Investigator Award (WT098424AIA) and Investigator Award (212625/Z/18/Z), MRC Programme grants (MR/R022259/1, MR/J0003042/1, and MR/L020149/1), Experimental Challenge Grant (DIVA MR/L02036X/1), MRC (MR/N00275X/1), Diabetes UK (BDA/11/0004210, BDA/15/0005275, and BDA 16/0005485), Imperial Confidence in Concept (ICiC) grants, and a Royal Society Wolfson Research Merit Award. This study was also supported by the European Union's Innovative Medicines Initiative 2 Joint Undertaking under grant agreement no. 115881 (RHAPSODY) to G.A.R. and M.S. This Joint Undertaking receives support from the European Union's Horizon 2020 research and innovation programme and EFPIA. A.T. was supported by Medical Research Council Grant MR/R010676/1.