Fig. 6.

Activation of STAT3 contributes to high-glucose-induced ER stress in TR-iBRB cells. (a–d) TR-iBRB cells were pretreated with cucurbitacin I (Cu I) for 1 h, followed by treatment with high glucose (HG) for 8 h. (a,b) Levels of phosphorylated (p) and total (t) PERK and eIF2α proteins were determined by western blot analysis. Levels of p-eIF2α (black bar) and t-eIF2α (white bar) were quantified by densitometry (mean±SD, n=3). *p<0.05, **p<0.01 vs control. (c) Immunostaining showing increased GRP78 level in HG-treated cells, but not in those treated with HG+Cu I compared with control cells. GRP78 (red) and DAPI (blue). (d) Immunofluorescence showing nuclear translocation of ATF4 in HG-treated cells, but not in cells exposed to HG+Cu I. ATF4 (red) and DAPI (blue). (e–g) STAT3 was knocked down using siRNA (Stat3i), followed by treatment with HG for 8 h in TR-iBRB cells. Ctrli: scrambled/control siRNA. Levels of STAT3, GRP78 and p-eIF2α were determined by western blot analysis and quantified by densitometry (mean±SD, n=3). **p<0.01 vs Ctrli; ^††p<0.01 vs Ctrli+HG