High glucose and hydrogen peroxide increase c-Myc and haeme-oxygenase 1 mRNA levels in rat pancreatic islets without activating NFkappaB.
OBJECTIVE
Hyperglycaemia and the pro-inflammatory cytokine IL-1beta induce similar alterations of beta cell gene expression, including up-regulation of c-Myc and haeme-oxygenase 1. These effects of hyperglycaemia may result from nuclear factor-kappa B (NFkappaB) activation by oxidative stress. To test this hypothesis, we compared the effects of IL-1beta, high glucose, and hydrogen peroxide, on NFkappaB DNA binding activity and target gene mRNA levels in cultured rat islets.


METHODS
Rat islets were pre-cultured for 1 week in serum-free RPMI medium containing 10 mmol/l glucose, and further cultured in glucose concentrations of 5-30 mmol/l plus various test substances. Islet NFkappaB activity was measured by ELISA and gene mRNA expression was measured by RT-PCR.


RESULTS
IL-1beta consistently increased islet NFkappaB activity and c-Myc, haeme-oxygenase 1, inducible nitric oxide synthase (iNOS), Fas, and inhibitor of NFkappaB alpha (IkappaBalpha) mRNA levels. In comparison, 1- to 7-day culture in 30 mmol/l instead of 10 mmol/l glucose stimulated islet c-Myc and haeme-oxygenase 1 expression without affecting NFkappaB activity or iNOS and IkappaBalpha mRNA levels. Fas mRNA levels only increased after 1 week in 30 mmol/l glucose. Overnight exposure to hydrogen peroxide mimicked the effects of 30 mmol/l glucose on haeme-oxygenase 1 and c-Myc mRNA levels without activating NFkappaB. On the other hand, the antioxidant N-acetyl-L-cysteine inhibited the stimulation of haeme-oxygenase 1 and c-Myc expression by 30 mmol/l glucose and/or hydrogen peroxide.


CONCLUSIONS
In contrast to IL-1beta, high glucose and hydrogen peroxide do not activate NFkappaB in cultured rat islets. It is suggested that the stimulation of islet c-Myc and haeme-oxygenase 1 expression by 30 mmol/l glucose results from activation of a distinct, probably oxidative-stress-dependent signalling pathway.
Elouil
H
H
Endocrinology and Metabolism, Université Catholique de Louvain (UCL), 55.30, Avenue Hippocrate, 55, 1200, Brussels, Belgium.
Cardozo
A K
AK
Eizirik
D L
DL
Henquin
J C
JC
Jonas
J C
JC
D000818:Animals; D005947:Glucose / Q000494:pharmacology*; D006419:Heme Oxygenase (Decyclizing) / Q000235:genetics*; D051547:Heme Oxygenase-1; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D016328:NF-kappa B / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics*; D051381:Rats; D014158:Transcription, Genetic / Q000187:drug effects*
D016328:NF-kappa B; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D006861:Hydrogen Peroxide; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; D005947:Glucose
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