Figure 4.

Role of AMPK in hypoxia-induced HNF4α down-regulation. A and B, MIN6 cells expressing the pMX empty vector or pMX-KD-AMPKα2 vector were cultured at either 5% O₂ or 20% O₂ for 20 h, and HNF4α protein levels were examined (n = 3). C and D, an insulin secretion assay was performed (n = 6–9), and insulin concentration was determined by an insulin ELISA. Fold-change in glucose-stimulated insulin secretion (insulin level at 22 mm glucose divided by that at 2.2 mm glucose) is shown (n = 6–9). E, mouse isolated islets expressing either LacZ or KD-AMPKα2 were treated with 5% O₂ for 20 h, and HNF4α protein levels were examined by Western blot analysis. F and G, islet insulin secretion was examined, and insulin levels are expressed as absolute values or as fold-change (n = 5–10). Data are presented as mean ± S.E. (error bars). N.S., not significant; *, p < 0.05; **, p < 0.01; ***, p < 0.001.