Lack of TXNIP Protects Against Mitochondria-Mediated Apoptosis but Not Against Fatty Acid–Induced ER Stress–Mediated β-Cell Death

  1. Junqin Chen1,
  2. Ghislaine Fontes2,
  3. Geetu Saxena1,
  4. Vincent Poitout2 and
  5. Anath Shalev1
  1. 1Department of Medicine, University of Wisconsin and William F. Middleton Veterans Administration Hospital, Madison, Wisconsin;
  2. 2Montreal Diabetes Research Center, CRCHUM, and Department of Medicine, University of Montreal, Quebec, Canada.
  1. Corresponding author: Anath Shalev, as7{at}medicine.wisc.edu.

Abstract

OBJECTIVE We have previously shown that lack of thioredoxin-interacting protein (TXNIP) protects against diabetes and glucotoxicity-induced β-cell apoptosis. Because the role of TXNIP in lipotoxicity is unknown, the goal of the present study was to determine whether TXNIP expression is regulated by fatty acids and whether TXNIP deficiency also protects β-cells against lipoapoptosis.

RESARCH DESIGN AND METHODS To determine the effects of fatty acids on β-cell TXNIP expression, INS-1 cells and isolated islets were incubated with/without palmitate and rats underwent cyclic infusions of glucose and/or Intralipid prior to islet isolation and analysis by quantitative real-time RT-PCR and immunoblotting. Using primary wild-type and TXNIP-deficient islets, we then assessed the effects of palmitate on apoptosis (transferase-mediated dUTP nick-end labeling [TUNEL]), mitochondrial death pathway (cytochrome c release), and endoplasmic reticulum (ER) stress (binding protein [BiP], C/EBP homologous protein [CHOP]). Effects of TXNIP deficiency were also tested in the context of staurosporine (mitochondrial damage) or thapsigargin (ER stress).

RESULTS Glucose elicited a dramatic increase in islet TXNIP expression both in vitro and in vivo, whereas fatty acids had no such effect and, when combined with glucose, even abolished the glucose effect. We also found that TXNIP deficiency does not effectively protect against palmitate or thapsigargin-induced β-cell apoptosis, but specifically prevents staurosporine- or glucose-induced toxicity.

CONCLUSIONS Our results demonstrate that unlike glucose, fatty acids do not induce β-cell expression of proapoptotic TXNIP. They further reveal that TXNIP deficiency specifically inhibits the mitochondrial death pathway underlying β-cell glucotoxicity, whereas it has very few protective effects against ER stress–mediated lipoapoptosis.

Footnotes

  • The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

    • Received June 29, 2009.
    • Accepted October 22, 2009.
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  1. Diabetes vol. 59 no. 2 440-447
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