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.