T. Matsuoka et al., GLYCATION-DEPENDENT, REACTIVE OXYGEN SPECIES-MEDIATED SUPPRESSION OF THE INSULIN GENE PROMOTER ACTIVITY IN HIT CELLS, The Journal of clinical investigation, 99(1), 1997, pp. 144-150
Prolonged poor glycemic control in non-insulin-dependent diabetes mell
itus patients often leads to a decline in insulin secretion from pancr
eatic beta cells, accompanied by a decrease in the insulin content of
the cells, As a step toward elucidating the pathophysiological backgro
und of the so-called glucose toxicity to pancreatic beta cells, we ind
uced glycation in HIT-TIS cells using a sugar with strong deoxidizing
activity, D-ribose, and examined the effects on insulin gene transcrip
tion. The results of reporter gene analyses revealed that the insulin
gene promoter is more sensitive to glycation than the control p-actin
gene promoter; similar to 50 and 80% of the insulin gene promoter acti
vity was lost when the cells were kept for 3 d in the presence of 40 a
nd 60 mM D-ribose, respectively. In agreement with this, decrease in t
he insulin mRNA and insulin content was observed in the glycation-indu
ced cells, Also, gel mobility shift analyses using specific antiserum
revealed decrease in the DNA-binding activity of an insulin gene trans
cription factor, PDX-1/IPF1/STF-1. These effects of D-ribose seemed al
most irreversible but could be prevented by addition of 1 mM aminoguan
idine or 10 mM N-acetylcysteine, thus suggesting that glycation and re
active oxygen species, generated through the glycation reaction, serve
as mediators of the phenomena, These observations suggest that protei
n glycation in pancreatic beta cells, which occurs in vivo under chron
ic hyperglycemia, suppresses insulin gene transcription and thus can e
xplain part of the beta cell glucose toxicity.