title: Metabolomics Reveals a Key Role for Fumarate in Mediating the Effects of NADPH Oxidase 4 in Diabetic Kidney Disease.
abstract: The NADPH oxidase (NOX) isoform NOX4 has been linked with diabetic kidney disease (DKD). However, a mechanistic understanding of the downstream effects of NOX4 remains to be established. We report that podocyte-specific induction of NOX4 in vivo was sufficient to recapitulate the characteristic glomerular changes noted with DKD, including glomerular hypertrophy, mesangial matrix accumulation, glomerular basement membrane thickening, albuminuria, and podocyte dropout. Intervention with a NOX1/NOX4 inhibitor reduced albuminuria, glomerular hypertrophy, and mesangial matrix accumulation in the F1 Akita model of DKD. Metabolomic analyses from these mouse studies revealed that tricarboxylic acid (TCA) cycle-related urinary metabolites were increased in DKD, but fumarate levels were uniquely reduced by the NOX1/NOX4 inhibitor. Expression of fumarate hydratase (FH), which regulates urine fumarate accumulation, was reduced in the diabetic kidney (in mouse and human tissue), and administration of the NOX1/NOX4 inhibitor increased glomerular FH levels in diabetic mice. Induction of Nox4 in vitro and in the podocyte-specific NOX4 transgenic mouse led to reduced FH levels. In vitro, fumarate stimulated endoplasmic reticulum stress, matrix gene expression, and expression of hypoxia-inducible factor-1α (HIF-1α) and TGF-β. Similar upregulation of renal HIF-1α and TGF-β expression was observed in NOX4 transgenic mice and diabetic mice and was attenuated by NOX1/NOX4 inhibition in diabetic mice. In conclusion, NOX4 is a major mediator of diabetes-associated glomerular dysfunction through targeting of renal FH, which increases fumarate levels. Fumarate is therefore a key link connecting metabolic pathways to DKD pathogenesis, and measuring urinary fumarate levels may have application for monitoring renal NOX4 activity.
authors.affiliation: Division of Nephrology-Hypertension, Institute of Metabolomic Medicine, Center for Renal Translational Medicine, University of California-San Diego, La Jolla, California;
authors.forename: Young-Hyun
authors.initials: YH
authors.lastname: You
authors.affiliation: Division of Nephrology-Hypertension, Institute of Metabolomic Medicine, Center for Renal Translational Medicine, University of California-San Diego, La Jolla, California;
authors.forename: Tammy
authors.initials: T
authors.lastname: Quach
authors.affiliation: Division of Nephrology-Hypertension, Institute of Metabolomic Medicine, Center for Renal Translational Medicine, University of California-San Diego, La Jolla, California;
authors.forename: Rintaro
authors.initials: R
authors.lastname: Saito
authors.affiliation: Division of Nephrology-Hypertension, Institute of Metabolomic Medicine, Center for Renal Translational Medicine, University of California-San Diego, La Jolla, California;
authors.forename: Jessica
authors.initials: J
authors.lastname: Pham
authors.affiliation: Division of Nephrology-Hypertension, Institute of Metabolomic Medicine, Center for Renal Translational Medicine, University of California-San Diego, La Jolla, California; Division of Medical Genetics, Department of Medicine, University of California-San Diego, La Jolla, California; and Division of Nephrology-Hypertension, Veterans Affairs San Diego Healthcare System, La Jolla, California kumarsharma@ucsd.edu.
authors.forename: Kumar
authors.initials: K
authors.lastname: Sharma
mesh_terms: D000818:Animals; D003928:Diabetic Nephropathies / Q000378:metabolism*; D005649:Fumarate Hydratase / Q000502:physiology*; D008297:Male; D055432:Metabolomics; D051379:Mice; D008810:Mice, Inbred C57BL; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000502:physiology*
chemical_list: D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; C422943:Nox4 protein, mouse; D005649:Fumarate Hydratase
keywords: NADPH oxidase; diabetic nephropathy; fibrosis; mitochondria; podocyte; reactive oxygen species