Fig. 3.

PHGDH regulates nucleotide synthesis in chondrocytes. a Purine (AMP, GMP), pyrimidine (UMP) and ribose-5-phosphate (R-5-P) levels in cultured chondrocytes derived from wild-type (Phgdh^chon+) and chondrocyte-specific PHGDH knockout (Phgdh^chon-) mice (n = 3). Schematic of carbon atom (circles) transitions of ¹³C₆-glucose used to detect label incorporation into AMP (b) and UMP (c). Serine (Ser; d) and glycine (Gly; e) labeling from ¹³C₆-glucose in cultured chondrocytes (n = 3). Specific mass distribution vectors (MDVs) for each metabolite are shown. f Intracellular Ser and Gly levels in cultured chondrocytes (n = 3). AMP (g), ribose-5-phosphate (R-5-P; h), UMP (i) and aspartate (Asp; j) labeling from ¹³C₆-glucose in cultured chondrocytes (n = 3). Specific MDVs for each metabolite are shown. k Proliferation of cultured chondrocytes with or without nucleotide (nucl) supplementation (n = 4–5), as determined by BrdU incorporation. The data are presented as the means ± SDs; *P < 0.05 vs. Phgdh^chon+, **P < 0.01 vs. Phgdh^chon+, ***P < 0.001 vs. Phgdh^chon+ (Student’s t test), ^#P < 0.05 (ANOVA)