Figure 4. L-Lactate Impairs Glucose-Derived Serine Production.

Tconvs were co-stimulated with CD3ε/CD28 mAb-coated beads for 20 h and were then labeled with [¹³C₆] D-glucose in serine and glycine free media for 3 h with either 20 mM of NaCl or Na L-lactate (L-lac) and 1 mM NaCl or Na oxalate (Ox). Metabolites were extracted and analyzed for derivative analysis, with M+1−10 indicating the number of [¹³C] labeling per molecule.

(A–E) Prior to GAPDH, L-lactate and oxalate lead to an accumulation of M+6 glucose and M+3 triose-P. Oxalate and lactate also lead to some reverse glycolysis (M+3 tracing in hexose 6P and fructose 1,6-BP).

(F–J) Post-GAPDH glycolytic intermediates: oxalate inhibits pyruvate kinase reaction. Both L-lactate and oxalate diminish the amount of pyruvate made from glucose.

(K–M) L-lactate decreases and oxalate increases glucose-derived serine.

(N) The pentose phosphate pathway is not diminished by L-lactate, if anything augmented by L-lactate/oxalate.

(O) Heatmap of total ion counts of ATP shows equal M+5 but diminished M+7 to M+9 with L-lactate treatment. Data are derived from three independent samples per condition (one-way ANOVA or Student’s t test of the highest enriched isotopologue).