Fig. 4: Serine biosynthesis and folate metabolism were significantly increased in DKD kidneys.

We collected urine samples from T2DM patients without or with DKD, and analyzed the urinary metabolites by nontargeted metabolomics. a Heatmap of nontargeted urinary metabolomics showing the differentially abundant metabolites between non-DKD patients (n = 11) and patients with DKD (n = 40). b Enriched bar plots of KEGG pathways showing 20 pathways that differed between the non-DKD (n = 11) and DKD (n = 40) groups. The red dashed boxes indicate the folate metabolism pathway and glycine, serine, and threonine metabolism pathways. c Enrichment factor analysis showed that folate metabolism was the most-enriched pathway between the non-DKD and DKD groups according to the p value. d Enriched cnet plots of KEGG pathways showing that the abundances of 7 metabolites from the folate metabolism pathway were significantly different between the non-DKD (n = 11) and DKD (n = 40) groups. e, f Two metabolites of serine biosynthesis (2-oxobutanoate and L-serine) showed significantly upregulated in the DKD group, Male: n = 6 for non DKD, n = 28 for DKD group; Female: n = 5 for non DKD, n = 12 for DKD group. g, h Six intermediate metabolites from folate metabolism were measured in the DKD group, Male: n = 6 for non DKD, n = 28 for DKD group; Female: n = 5 for non DKD, n = 12 for DKD group. i–k Representative images of double staining of MTHFD2, SHMT2 or PSPH with that of WT-1 and measurement of MTHFD2, SHMT2, and PSPH expression in glomerular sections. A total of 70 glomeruli from n = 6 mice per group. Arrow and white box indicate the localization of WT1 with MTHFD2, SHMT2, or PSPH. The data were presented as mean ± SD, and analyzed by unpaired two-tailed Student’s t test.