Pro- and antiapoptotic proteins regulate apoptosis but do not protect against cytokine-mediated cytotoxicity in rat islets and beta-cell lines

Diabetes. 2006 May;55(5):1398-406. doi: 10.2337/db05-1000.

Abstract

Type 1 diabetes results from islet beta-cell death and dysfunction induced by an autoimmune mechanism. Proinflammatory cytokines such as interleukin-1beta and gamma-interferon are mediators of this beta-cell cytotoxicity, but the mechanism by which damage occurs is not well understood. In the current study, we present multiple lines of evidence supporting the conclusion that cytokine-induced killing of rat beta-cells occurs predominantly by a nonapoptotic mechanism, including the following: 1) A rat beta-cell line selected for resistance to cytokine-induced cytotoxicity (833/15) is equally sensitive to killing by the apoptosis-inducing agents camptothecin and etoposide as a cytokine-sensitive cell line (832/13). 2) Overexpression of a constitutively active form of the antiapoptotic protein kinase Akt1 in 832/13 cells provides significant protection against cell killing induced by camptothecin and etoposide but no protection against cytokine-mediated damage. 3) Small interfering RNA-mediated suppression of the proapoptotic protein Bax enhances viability of 832/13 cells upon exposure to the known apoptosis-inducing drugs but not the inflammatory cytokines. 4) Exposure of primary rat islets or 832/13 cells to the inflammatory cytokines causes cell death as evidenced by the release of adenylate kinase activity into the cell medium, with no attendant increase in caspase 3 activation or annexin V staining. In contrast, camptothecin- and etoposide-induced killing is associated with robust increases in caspase 3 activation and annexin V staining. 5) Camptothecin increases cellular ATP levels, whereas inflammatory cytokines lower ATP levels in both beta-cell lines and primary islets. We conclude that proinflammatory cytokines cause beta-cell cytotoxicity primarily through a nonapoptotic mechanism linked to a decline in ATP levels.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / physiology*
  • Cell Line
  • Cell Survival / drug effects
  • Cells, Cultured
  • Cytokines / pharmacology*
  • Gene Expression Regulation / drug effects
  • Interferon-gamma / pharmacology
  • Interleukin-1 / pharmacology
  • Islets of Langerhans / cytology*
  • Islets of Langerhans / drug effects
  • Islets of Langerhans / physiology
  • Proto-Oncogene Proteins c-akt / genetics
  • Proto-Oncogene Proteins c-akt / metabolism
  • RNA, Small Interfering / genetics
  • Rats
  • Transfection
  • bcl-2 Homologous Antagonist-Killer Protein / genetics
  • bcl-2-Associated X Protein / genetics

Substances

  • Bak1 protein, rat
  • Cytokines
  • Interleukin-1
  • RNA, Small Interfering
  • bcl-2 Homologous Antagonist-Killer Protein
  • bcl-2-Associated X Protein
  • Interferon-gamma
  • Proto-Oncogene Proteins c-akt