Figure 3.

Glucose-derived carbon fuels nucleotide synthesis in young but not senescent HMECs. A, purine and pyrimidine metabolites show significantly reduced [U-¹³C]glucose carbon labeling in senescent HMECs. The volcano plot represents the average log₂ -fold change (senescent/proliferating) for fractional contribution (38) of U-¹³C–labeled glucose and FDR-corrected Fisher's combined p value from two independent experiments. B, glucose flux into nucleotide synthesis pathways is globally reduced in senescent HMECs. Shown is the fractional contribution of U-¹³C-labeled glucose for selected pyrimidines. * and **, FDR-corrected Student's t test p values less than 0.01 and 0.0001, respectively. C, [U-¹³C]glucose isotopomer distributions for dCDP but not PRPP are significantly different in senescent HMECs. D, metabolic pathway map depicting the average log₂ -fold change of fractional contribution from [U-¹³C]glucose in senescent/proliferating HMECs on the indicated color scale for metabolites in glycolysis, pentose phosphate pathway, nucleotide synthesis, and the TCA cycle. Metabolites that were not measured are shown as small circles with gray color. Metabolites with isomers that were not resolved on LC-MS are shown as diamonds. E, immunoblot for RRM2 and actin with lysates from proliferating and senescent HMECs. A protein lysate from the 293T cell line was used as a positive control, and actin was used as an equal loading control. The RRM2 antibody was obtained from GeneTex. Error bars, S.D.