Vitamin B12 Protects Against Early Diabetic Kidney Injury and Alters Clock Gene Expression in Mice

Vitamin B12 (B12) is a strong antioxidant and a cofactor for methionine synthase supporting DNA/RNA/protein methylation. We previously demonstrated that oral high-dose B12 supplement mitigates diabetic cardiomyopathy in Akita diabetic mice expressing twice the normal levels of Elmo1 (Engulfment and cell motility 1). To assess how B12 prevents early kidney damage, we treated <i>Elmo1^HH</i> mice and diabetic <i>Elmo1^HH Ins2^Akita/+</i> mice with or without B12 in drinking water starting at 8 weeks of age. At 16 weeks, markedly reduced mesangial expansion was detected in the B12-treated diabetic kidneys (22% of glomeruli affected vs. 70% in the untreated diabetic kidneys). RNAseq analysis of the kidneys revealed that B12 suppressed expression of genes for adaptive immune response, while it upregulated those for solute carrier transporters and antioxidant genes. Strikingly, B12 treatment suppressed activators of circadian rhythm, <i>Clock</i> and <i>Bmal1</i>, and upregulated repressors like <i>Cry1/2</i>, <i>Per1-3</i> and <i>Dbp</i>, suggesting a shift in their rhythmicity. B12 also upregulated linker histone H1 variants, and enhanced chromatin stability and cell cycle regulation. In BU.MPT proximal tubular cells in culture, B12 shifted forward the circadian expression phase of <i>Bmal1</i> and <i>Per1</i>. Taken together, B12 supplement effectively mitigates early development of diabetic nephropathy in diabetic mice, potentially involving regulation of circadian rhythm.