Figure 5.

HIF1α-dependent elevation of the intracellular NADH/NAD⁺ ratio leads to reduced lactate secretion

(A) The reaction shows the regeneration of NAD⁺ by the conversion of pyruvate or αKB to lactate and α-hydroxybutyrate (αHB), respectively, through LDH activity.

(B) Oxygen consumption rate (OCR) in 786-O-HIF1α cells (n = 9) and 786-O control cells (n = 10) (left), as well as in G55 control cells (n = 5) and those treated with 0.2 mM DMOG (n = 5) or 2 mM metformin (n = 5) (right).

(C) NADH/NAD⁺ ratio in 786-O-HIF1α cells, 786-O-HIF1α-bHLH^∗ cells, and their corresponding control cells in the presence (n = 3) or absence (n = 6) of extracellular pyruvate or αKB (1 mM).

(D) NADH/NAD⁺ ratio in G55 treated with 0.2 mM DMOG and control G55 cells in the presence (n = 3) or absence (n = 6) of extracellular pyruvate or αKB (1 mM).

(E) The relative amount of extracellular lactate released by 786-O-HIF1α cells, 786-O-HIF1α-bHLH^∗ cells, and their corresponding control cells in the presence or absence of extracellular αKB (1 mM) (n = 6).

(F) The relative amount of extracellular lactate released by control G55 cells and G55 treated with 0.2 mM DMOG in the presence or absence of extracellular αKB (1 mM) (n = 9).

(G) NADH/NAD⁺ ratio in G55 treated with 2 mM metformin and control G55 cells in the presence (n = 3–6) or absence (n = 6) of αKB (1 mM).

(H) Relative amount of extracellular lactate released by control G55 cells and G55 treated with 2 mM metformin in the presence (n = 6) or absence (n = 12) of αKB (1 mM).

In the bar graphs, the values represent the mean ± SEM, and statistical analysis was performed using a two-tailed unpaired t test when comparing 2 groups or a one-way (B, right) or two-way (C–H) ANOVA followed by Tukey’s post hoc test: ^∗p < 0.05, ^∗∗p < 0.01, and ^∗∗∗p < 0.001 represent significant p values.