397-P: The C/EBPß-XOR Axis and Genetic Risk for Diabetic Kidney Disease

Introduction & Objective: Diabetic kidney disease (DKD) is the leading single cause of end-stage renal disease in the United States. Approximately 30% of diabetics develop DKD with comparable blood glucose levels, indicating a significant genetic predisposition. However, the underlying mechanisms that contribute to differential susceptibility are unclear. The glomerulus is the primary site of injury with hypertrophy and podocyte depletion being the hallmarks for progressive DKD. We have demonstrated that mitochondrial oxidative damage in glomerular endothelial cells (GECs), leads to podocyte loss via GEC-to-podocyte crosstalk in DKD susceptible DBA/2J (D2) mice compared to DKD resistant C57BL/6J (B6) mice.

Methods: We mapped potential genetic loci associated with podocyte depletion after long-term diabetes (6mth using 39 strains of BXD, parental B6 and D2 mice). We identified a significant cis-acting variant in the promoter of xanthine oxidoreductase (Xor). XOR catalyze the oxidation of purine substrates to uric acid and reactive oxygen species (ROS). Using CRISPR/Cas9 to knock-in the Xor risk variant into DKD-resistant B6 mice, we generated mutant B6-Xor^em1 mice with significantly higher XOR activity than B6.

Results: This risk variant is a transcription factor binding site to C/EBPβ. We observed higher C/EBPβ expression in GECs from diabetic B6-Xor^em1 mice. B6-Xor^em1 mice had increased mitochondrial oxidative stress in GECs, podocyte depletion, basement membrane thickening, albuminuria, glomerulosclerosis and tubular injury. These changes were prevented with XOR inhibition. Interestingly B6-Xor^em1 mice developed age-associated glomerulosclerosis. In vitro studies support a Xor and mitochondrial ROS interplay in endothelial cells that resulted in GEC dysfunction.

Conclusion: Xor promoter variants are causal for DKD susceptibility and may predispose to aging and other diabetic complications.