β-Cell pre-mir-21 induces dysfunction and loss of cellular identity by targeting transforming growth factor beta 2 (Tgfb2) and Smad family member 2 (Smad2) mRNAs

Objective: beta-cell microRNA-21 (miR-21) is increased by islet inflammatory stress but it decreases glucose-stimulated insulin secretion (GSIS). Thus, we sought to define the effects of miR-21 on beta-cell function using in vitro and in vivo systems. Methods: We developed a tetracycline-on system of pre-miR-21 induction in clonal beta-cells and human islets, along with transgenic zebrafish and mouse models of beta-cell-specific pre-miR-21 overexpression. Results: beta-cell miR-21 induction markedly reduced GSIS and led to reductions in transcription factors associated with beta-cell identity and increased markers of dedifferentiation, which led us to hypothesize that miR-21 induces beta-cell dysfunction by loss of cell identity. In silico analysis identified transforming growth factor-beta 2 (Tgfb2) and Smad family member 2 (Smad2) mRNAs as predicted miR-21 targets associated with the maintenance of beta-cell identity. Tgfb2 and Smad2 were confirmed as direct miR-21 targets through RT-PCR, immunoblot, pulldown, and luciferase assays. In vivo zebrafish and mouse models exhibited glucose intolerance, decreased peak GSIS, decreased expression of beta-cell identity markers, increased insulin and glucagon co-staining cells, and reduced Tgfb2 and Smad2 expression. Conclusions: These findings implicate miR-21-mediated reduction of mRNAs specifying beta-cell identity as a contributor to beta-cell dysfunction by the loss of cellular differentiation. (C) 2021 The Authors. Published by Elsevier GmbH.