C/EBPβ-XOR Axis Confers Genetic Predisposition to Diabetic Kidney Disease

Background: Diabetes-induced chronic kidney disease (CKD) is the leading cause of renal failure globally and in the United States of America. Interestingly, only about 30% of patients with diabetes develop diabetic kidney disease (DKD), underscoring the role of genetics in the pathophysiology of DKD. Despite this observation, the underlying molecular mechanisms that confer genetic predisposition to DKD remain unclear. Glomerular injury, characterized by podocyte depletion and glomerular hypertrophy are a major feature of progressive DKD. Previously, we reported that mitochondrial dysfunction-induced oxidative damage in glomerular endothelial cells (GECs) drives podocyte loss via GEC-podocyte crosstalk in DKD-susceptible DBA/2J (D2) versus DKD-resistant C57BL/6J (B6) mice. Methods: We mapped potential quantitative trait loci (QTL) that are associated with podocyte depletion in DKD-susceptible DBA/2J (D2) and DKD-resistant C57BL/6J (B6) mice, and in a panel of recombinant BXD mouse strains. Through this, we identified a significant cis-acting variant in the promoter region of xanthine oxidoreductase (Xor). XOR catalyzes the metabolism of purines to uric acid, generating reactive oxygen species (ROS) in the process. Via CRISPR/Cas9, we knocked-in the identified Xor risk variant into DKD-resistant B6 mice to generate mutant B6-Xorem1 mice that displayed markedly higher XOR activity versus wild-type B6 mice. We also determined the effect of this Xor risk variant on susceptibility to DKD in B6-Xorem1mice. Results: The identified Xor promoter risk variant is a transcription factor binding site for C/EBPβ. We detected higher expression of C/EBPβ in GECs from diabetic B6-Xorem1 mice. Diabetic B6-Xorem1 mice exhibited increased mitochondrial ROS in GECs, and this was associated with podocyte depletion, glomerular basement membrane thickening, glomerulosclerosis, and albuminuria. More importantly, these pathophysiologic changes were prevented by the XOR inhibitor, febuxostat. B6-Xorem1 mice also displayed age-related glomerulosclerosis and insulin resistance. Furthermore, In vitro studies in GECs support a possible Xor-mitochondrial ROS interplay in endothelial cells that resulted in GEC dysfunction. Conclusion: High-risk variants in the promoter region of Xor confer genetic susceptibility to DKD and may predispose to other complications of diabetes, and aging-related renal disease. Funding: NIDDK Support, Other U.S. Government Support