Vitamin D is involved in the effects of the intestinal flora and its related metabolite TMAO on perirenal fat and kidneys in mice with DKD

BACKGROUND: Vitamin D was shown to directly exert a protective effect on diabetic kidney disease (DKD) in our previous study. However, whether it has an effect on perirenal adipose tissue (PRAT) or the intestinal flora and its metabolites (trimethylamine N-oxide, TMAO) is unclear. METHODS: DKD mice received different concentrations of 1,25-(OH)2D3 for 2 weeks. Serum TNF-α and TMAO were measured. 16S rRNA sequencing profiled gut microbiota. qPCR assessed TLR4, NF-κB, PGC1α, and UCP-1 expression in kidney and adipose tissue. Kidney and PRAT histology was evaluated by HE, PAS, Masson and Oil Red O staining; immunofluorescence and immunohistochemistry detected VDR, PGC1α, podocin, and UCP-1; electron microscopy examined renal ultrastructure. VDR knockout mice were generated to assess gut and adipose changes and renal UCP-1 and collagen IV. RESULTS: 1,25-(OH)2D3 improved intestinal dysbiosis in DKD mice, increased beneficial bacteria and decreased harmful bacteria, reduced renal pathology and fat infiltration, and downregulated renal TLR4 and NF-κB. Serum TMAO was significantly elevated in DKD versus controls and positively correlated with urine ACR. Vitamin D increased PGC1α, UCP-1, and VDR expression in PRAT; TMAO downregulated PRAT and renal VDR. CONCLUSIONS: The protective effect of 1,25-(OH)2D3 in DKD mice may involve modulation of intestinal flora and its metabolite TMAO, influencing PRAT and kidney.