Fig. 1: Sources and sinks of altered serine metabolism in diabetes.

a, Levels of glycine, serine and methionine in the liver of wild-type and BKS-db/db mice after a 6-h fast (n = 6 per group). b, Schematic of serine and glycine biosynthetic and catabolic pathways. Upregulated hepatic genes in BKS-db/db mice are in purple, and downregulated are genes are in blue. 10-formylTHF, 10-formyltetrahydrofolate; 3-PG, 3-phosphoglycerate; 5,10-meTHF, 5,10-methylenetetrahydrofolate; dTMP, deoxythymidine monophosphate; f-Met, N-formylmethionine; PEP, phosphoenol pyruvate; TCA, tricarboxylic acid; THF, tetrahydrofolate. c, mRNA expression of liver enzyme genes regulating SGOC metabolism in wild-type and BKS-db/db mice (n = 6 per group). d, Plasma serine, glucose, glycine and methionine-labelling fraction (1 − M₀) in wild-type mice administered [U-¹³C₃]serine via oral gavage after an overnight fast (n = 4 per time point). e, Tissue glycine labelling fraction in wild-type mice 15 min after [U-¹³C₃]serine administration via oral gavage (n = 4 per tissue) following an overnight fast. f, Tissue pyruvate labelling fraction in wild-type mice 15 min after [U-¹³C₃]serine administration via oral gavage (n = 4 per tissue) after an overnight fast. g, Combined OGTT and STT in wild-type and BKS-db/db mice (n = 6 per group) after an overnight fast. h, STT AUC in wild-type and BKS-db/db mice (n = 6 per group). i, Combined OGTT and STT in vehicle- (n = 7) and STZ-treated (n = 6) C57BL/6J mice after an overnight fast. j, STT AUC in vehicle- (n = 7) and STZ-treated (n = 6) C57BL/6J mice. Data are mean ± s.e.m., and were analysed using two-sided independent t-test (a,c,h,j) and two-way ANOVA with Fisher’s least significant difference post hoc test (g,i). The schematic in Fig. 1b was prepared in BioRender.