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

ABSTRACT Objective β-cell dedifferentiation has been revealed as a pathological mechanism underlying pancreatic dysfunction in diabetes. We have previously shown that increased miR-7 levels trigger β-cell dedifferentiation and diabetes. We used β-cell-specific miR-7 overexpressing mice (Tg7) to test the hypothesis that loss of β-cell identity triggered by miR-7 overexpression alters islet gene expression and islet microenvironment in diabetes. Method We performed bulk and single-cell RNA-Sequencing (RNA-seq) in islets obtained from β-cell-specific miR-7 overexpressing mice (Tg7). We carried out loss- and gain-of-function experiments in MIN6 and EndoC-βH1 cell lines. We analysed previously published mouse and human T2D datasets. Results Βulk RNA-seq revealed that β-cell dedifferentiation is associated with the induction of genes associated with epithelial to mesenchymal transition (EMT) in pre-diabetic (2-week-old) and diabetic (12-week-old) Tg7 mice. Single-cell RNA-seq (scRNA-seq) indicated that this EMT signature is enriched specifically in β-cells. These molecular changes are associated with a weakening of β-cell:β-cell contacts, increased extracellular matrix (ECM) deposition and TGFβ-dependent islet fibrosis. We find that the mesenchymal reprogramming of β-cells is explained in part by the downregulation of Pdx1 and its inability to regulate a myriad of epithelial-specific genes expressed in β-cells. Notable among genes transactivated by Pdx1 is Ovol2, which encodes a transcriptional repressor of the EMT transcription factor ZEB2. Following compromised β-cell identity, the reduction of Pdx1 gene expression causes a decrease of Ovol2 protein, thereby triggering mesenchymal reprogramming of β-cells through the induction of Zeb2. Finally, we provided evidence that EMT signalling associated with the upregulation of Zeb2 expression is a molecular feature of islet of T2D subjects. Conclusions Our study indicates that miR-7-mediated β-cell dedifferentiation induces EMT signalling and a chronic response to tissue injury, which alters the islet microenvironment and predispose to fibrosis. This work suggests that regulators of EMT signalling may represent novel therapeutic targets for the treatment of β-cell dysfunction and fibrosis in T2D.