d-Serine Mediates Cellular Proliferation for Kidney Remodeling

d-serine, a long-term undetected enantiomer of serine, is a biomarker that reflects kidney function and disease activity. The physiologic functions of d-serine are unclear. The dynamics of d-serine were assessed by measuring d-serine in human samples of living kidney donors using two-dimensional high-performance liquid chromatography, and by autoradiographic studies in mice. The effects of d-serine on the kidney were examined by gene expression profiling and metabolic studies using unilateral nephrectomy mice, and genetically modified cells. Unilateral nephrectomy in human living kidney donors decreases urinary excretion and thus increases the blood level of d-serine. d-serine is quickly and dominantly distributed to the kidney on injection in mice, suggesting the kidney is a main target organ. Treatment of d-serine at a low dose promotes the enlargement of remnant kidney in mouse model. Mechanistically, d-serine activates the cell cycle for tissue remodeling through an mTOR-related pathway. d-serine is a physiologic molecule that promotes kidney remodeling. Besides its function as a biomarker, d-serine has a physiologic activity that influences kidney function.