Reduction of connexin36 content by ICER-1 contributes to insulin-secreting cells apoptosis induced by oxidized LDL particles

PLoS One. 2013;8(1):e55198. doi: 10.1371/journal.pone.0055198. Epub 2013 Jan 30.

Abstract

Connexin36 (Cx36), a trans-membrane protein that forms gap junctions between insulin-secreting beta-cells in the Langerhans islets, contributes to the proper control of insulin secretion and beta-cell survival. Hypercholesterolemia and pro-atherogenic low density lipoproteins (LDL) contribute to beta-cell dysfunction and apoptosis in the context of Type 2 diabetes. We investigated the impact of LDL-cholesterol on Cx36 levels in beta-cells. As compared to WT mice, the Cx36 content was reduced in islets from hypercholesterolemic ApoE-/- mice. Prolonged exposure to human native (nLDL) or oxidized LDL (oxLDL) particles decreased the expression of Cx36 in insulin secreting cell-lines and isolated rodent islets. Cx36 down-regulation was associated with overexpression of the inducible cAMP early repressor (ICER-1) and the selective disruption of ICER-1 prevented the effects of oxLDL on Cx36 expression. Oil red O staining and Plin1 expression levels suggested that oxLDL were less stored as neutral lipid droplets than nLDL in INS-1E cells. The lipid beta-oxidation inhibitor etomoxir enhanced oxLDL-induced apoptosis whereas the ceramide synthesis inhibitor myriocin partially protected INS-1E cells, suggesting that oxLDL toxicity was due to impaired metabolism of the lipids. ICER-1 and Cx36 expressions were closely correlated with oxLDL toxicity. Cx36 knock-down in INS-1E cells or knock-out in primary islets sensitized beta-cells to oxLDL-induced apoptosis. In contrast, overexpression of Cx36 partially protected INS-1E cells against apoptosis. These data demonstrate that the reduction of Cx36 content in beta-cells by oxLDL particles is mediated by ICER-1 and contributes to oxLDL-induced beta-cell apoptosis.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analysis of Variance
  • Animals
  • Apolipoproteins E / genetics
  • Apoptosis / drug effects*
  • Azo Compounds
  • Blotting, Western
  • Carrier Proteins
  • Cell Line
  • Connexins / metabolism*
  • Cyclic AMP Response Element Modulator / metabolism
  • DNA Primers / genetics
  • Gap Junction delta-2 Protein
  • Gene Expression Regulation / drug effects*
  • Humans
  • Hypercholesterolemia / physiopathology*
  • Insulin-Secreting Cells / drug effects
  • Insulin-Secreting Cells / physiology*
  • Lipoproteins, LDL / pharmacology*
  • Luciferases
  • Mice
  • Mice, Knockout
  • Perilipin-1
  • Phosphoproteins
  • Rats
  • Real-Time Polymerase Chain Reaction

Substances

  • Apolipoproteins E
  • Azo Compounds
  • Carrier Proteins
  • Connexins
  • Crem protein, mouse
  • DNA Primers
  • Lipoproteins, LDL
  • PLIN1 protein, human
  • Perilipin-1
  • Phosphoproteins
  • Plin1 protein, mouse
  • Plin1 protein, rat
  • oxidized low density lipoprotein
  • Cyclic AMP Response Element Modulator
  • Luciferases
  • oil red O

Grants and funding

Supported by grants from The Swiss National Science Foundation [31003A_138528/1], the Novartis Foundation; the Octav and Marcella Botnar Foundation. AA was supported by the Chair of Excellence from the French National Agency for Research N°ANR-10-CEXC-005-01, the Regional Council Nord Pas de Calais and the European Regional Development Fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.