DOI: 10.5061/dryad.9s4mw6mc5
title: LncRNA-Malat1 is involved in lipotoxicity-induced β-cell dysfunction and the therapeutic effect of exendin-4 via Ptbp1

description: Increasing evidence indicates that long noncoding RNAs (lncRNAs) have
 crucial roles in various biological processes. However, the contribution
 of lncRNAs to β-cell dysfunction and their roles in diabetes therapeutics
 remain poorly understood. The aim of this study was to identify the
 lncRNAs dysregulated in diabetic islets and to explore the lncRNAs
 involved in β-cell function as potential therapeutic targets. By using
 RNA-sequencing and real-time PCR, we identified thousands of lncRNAs in
 the islets of db/db mice and db/m littermate mice. Among the
 differentially expressed lncRNAs, lncRNA-Malat1 (metastasis associated
 lung adenocarcinoma transcript 1) was reduced in the islets of db/db mice
 and palmitate-treated MIN6 cells. The results of TUNEL, western blot and
 flow cytometric analyses and GSIS assays revealed that Malat1 knockdown
 significantly induced β-cell apoptosis and inhibited insulin secretion.
 Mechanistically, RNA-immunoprecipitation showed that Malat1 enhanced Ptbp1
 (polypyrimidine tract-binding protein 1) protein stability by direct
 interaction, thereby adjusting the ratio of PKM (pyruvate kinase muscle)
 isoforms 1 and 2 (PKM1/PKM2). Moreover, luciferase assay and chromatin
 immunoprecipitation indicated that Malat1 was transcriptionally activated
 by Pdx1, through which exendin-4 alleviated lipotoxicity-induced β-cell
 damage. In summary, our findings suggested the involvement of Malat1 in
 β-cell dysfunction under diabetic conditions via the Malat1/Ptbp1/PKM2
 pathway. In addition, exendin-4 ameliorated β-cell impairment by
 Pdx1-mediated Malat1 upregulation. Hence, Malat1 may serve as a
 therapeutic target for the treatment of type 2 diabetes.
description: Six-week-old
 male C57BL/KsJ <i>db</i>/<i>db</i> mice (n=40) and
 their age-matched <i>db</i>/m littermate controls (n=20) were
 purchased from the Model Animal Research Center of Nanjing University
 (Nanjing, China). Random blood glucose levels were monitored once a week.
 At 8 weeks old, C57BL/KsJ <i>db</i>/<i>db</i> mice
 were randomly subdivided to receive either exendin-4 (0.1 mg/kg/d;
 Sigma-Aldrich, St. Louis, MO) or PBS, to serve as controls, by
 intraperitoneal injection during the light cycle for 2 weeks. Glucose
 tolerance tests (GTTs) and insulin tolerance tests (ITTs) were performed
 after 2-week intervention. For the IPGTTs, mice were fasted overnight and
 injected intraperitoneally with glucose at a dose of 2 g/kg body weight.
 For the IPITTs, the animals were intraperitoneally administered with
 insulin (1U/kg body weight, Novolin R, Novo Nordisk INC, Denmark) after
 6-h fasting. Blood samples were collected from the tail vein at 0, 30, 60,
 90 and 120 min after the injection of glucose or insulin, and the blood
 glucose levels were measured with an ACCU-CHEK Performa glucometer (Roche
 Diabetes Care GmbH, Germany). At the end of intervention, the mice were
 sacrificed under anesthesia after fasting overnight, blood samples were
 collected for serum collection, and the islets were isolated. The level of
 serum insulin was measured by a mouse insulin ELISA kit (Mercodia, catalog
 no. 10-1247-01) (17) according to
 manufacturer’s protocols. Triglyceride, low-density lipoprotein
 cholesterol and total cholesterol contents in the serum were quantified
 with a triglyceride GPO-POD assay kit, low-density lipoprotein cholesterol
 assay kit and total cholesterol assay kit, respectively, with a Beckman
 Coulter biochemical analysis system. Pancreas specimens were excised and
 fixed with 4% paraformaldehyde for histological evaluation. Ten-week-old
 female C57BL/6 mice (n=20) were also purchased from the Model Animal
 Research Center of Nanjing University for islet isolation. All animal care
 and experimental procedures were approved by the Institutional Animal Care
 and Use Committee of Sun Yat-sen University.