Figure 2. SDH deficiency commits cells to consume extracellular pyruvate to maintain maximal glycolytic flux and cell growth.

(a) Number of cells cultured in presence (+) or absence (−) of pyruvate measured at the indicated time points. Data are presented as mean±s.e.m of one representative experiment (n=4 wells), independently replicated three times. (b) Schematic representation of effects of pyruvate consumption on maintenance of NAD⁺/NADH redox state and glycolytic flux. Red and white circles indicate ¹³C and ¹²C carbon unit, respectively. (c) Secretion rate of exogenous pyruvate-derived lactate (¹³C₃-lactate) of Sdhb^fl/fl and Sdhb^Δ/Δ cells cultured for 48h with U-¹³C-Pyruvate. Data are presented as mean±s.e.m of n=6 wells pooled from two independent experiments. (d) Measurement of NAD⁺/NADH ratio expressed as fold change compared to pyruvate-fed Sdhb^fl/fl cells (e) Pentose phosphate pathway and glycolytic intermediates in cells cultured for 24h in presence (+) or absence (−) of pyruvate. Data in d, e are presented as mean±s.e.m of one representative experiment (n=3 wells), independently replicated twice. (f) Exchange rates of the indicated labeled metabolites upon 48h of incubation of Sdhb^fl/fl and Sdhb^Δ/Δ cells with U-¹³C-glucose in presence (+) or absence (−) of pyruvate. Data are presented as mean±s.e.m of n=18 wells pooled from three independent experiments. Raw data of independently repeated experiments are provided in Supplementary Table 3.