Overexpression of the Aldose Reductase Gene Induces Apoptosis in Pancreatic .BETA.-Cells by Causing a Redox Imbalance.

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To determine the role of the polyol metabolizing pathway under hyperglycemic conditions, the effects of aldose reductase (AR) on the cellular functions of pancreatic β-cells were examined. Stable transfectants of rat AR cDNA were obtained with a pancreatic β-cell line, HIT, in which a negligible amount of AR was originally expressed. Overproduction of AR triggered DNA fragmentation, as judged with the TUNEL method and agarose gel electrophoresis. Morphological analysis by electron microscopy also clearly showed apoptosis of the AR-overexpressing HIT cells. Induction by interleukin-1 β of gene expression such as those of an inducible form of nitric oxide synthase (NOS-II) and Mn-superoxide dismutase (Mn-SOD), was much lower in the transfectants than in the control cells, while the expression of constitutively expressed genes such as those for Cu, Zn-superoxide dismutase and insulin was not changed. The susceptibility to interleukin-1 β stimulation of the expression of the NOS II and Mn-SOD genes was due to suppressed NF-κB activity, which is essential for the expression of these genes. In addition, the intracellular NADPH/NADP+ ratio was considerably lower in the AR-transfected cells than in control cells. Thus, the overexpression of AR in pancreatic β-cells induced apoptosis that may be caused by a redox imbalance.
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