Leucine Predicts Progression of Diabetic Kidney Disease and Mediates Metabolic Remodeling in Kidney Tubular Cells of Diabetic Models

Background: Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease and end-stage renal failure; however, the dominant mechanisms remain obscure and few biomarkers are available. We recently performed a targeted metabolomics study to identify leucine as a novel metabolite biomarker of DKD. Here, we evaluated whether leucine could play a role in progression of kidney disease in patients with diabetes. Methods: Urine from participants with diabetes from two independent cohorts determined whether urinary leucine-to-creatinine ratio (ULeuCR) could be a mechanistic biomarker for progression of DKD as demonstrated by composite kidney outcomes, including rapid decline in kidney function, end-stage renal failure, and death from a renal cause. Whether defective leucine degradation causes DKD was assessed by metabolic flux assay and metabolomics analysis in kidney tubular epithelial cells and diabetic mice models. Results: Composite kidney outcomes were associated with the higher ULeuCR quantile in both discovery cohort (HR 4.55, 95% CI 1.40-14.78) and validation cohort (HR 2.93, 95% CI 1.44-5.97). Kidney function decline was associated with the higher ULeuCR quantile in both female (HR 3.78, 95% CI 1.31-10.95) and male (HR 3.35, 95% CI 1.64-6.82) patients with diabetes. Metabolites and enzymes measurement suggested defective leucine degradation in kidney tubular epithelial cells during the progression of DKD. Genetic or pharmacological improvement of leucine degradation by repressing branched-chain ketoacid dehydrogenase kinase (BCKDK) relieved glucose-induced metabolic remodeling in tubular cells and mitigated DKD in diabetic mice models. Hypoxia inducible factor 1α promoted BCKDK expression. In vitro experiment indicated that leucine stimulated metabolic remodeling in tubular cells via mTOR signaling pathway. Restriction of dietary leucine content was found to dramatically reduce albuminuria, kidney hypertrophy and lipid accumulation in diabetic mice models. Conclusion: We reveal defective leucine degradation in kidney tubules from diabetic subjects and propose leucine as a causative factor in DKD, which warrants further exploration as therapeutic targets. Funding: Government Support – Non-U.S.