Renal Transcriptional Profiles of Hyperuricemic Mouse Models Reveal Urate Dependent Alternations in Metabolic Pathways.

Increased serum urate (hyperuricemia, HUA) contributes to the development of kidney stones, chronic kidney disease, cardiovascular disease, metabolic syndrome, and gout. HUA is caused by an underexcretion or an overproduction of urate. These two mechanisms result in similar serum urate levels, but critically important differences in how urate is handled in the kidney and resulting tubular urate levels. To better understand altered gene expression by divergent renal handling of urate in each subtype of HUA, we compared transcriptional profiles of kidneys of two functionally different mouse models of HUA. The underexcretion model is our well established ABCG2-Q140K knock-in mouse, which inserts the human pathological variant Q141K into the orthologous position of the mouse Abcg2 gene. This causes decreased secretion of urate, leading to an increase in serum urate in male mice only. The overproduction model is a novel inducible knock-out of the urate metabolizing gene uricase (UOX-iKO), which renders both male (M) and female (F) mice unable to metabolize urate, which increases circulating levels to a similar degree seen in HUA humans. Here, UOX-iKO mice of both sexes were induced at 9 weeks of age, and 2 weeks later, UOX-iKO mice had serum urate levels similar to age matched ABCG2-Q140K M mice. These UOX-iKO mice had increased overall urinary urate excretion (UUE), as well as increased fractional excretion of urate (FEUA) in both M and F, implying higher tubular urate, consistent with urate overproduction. In contrast, ABCG2-Q140K mice demonstrated no change in overall UUE, with a decrease in FEUA seen in M only, implying lower tubular urate, consistent with urate underexcretion. Next, we harvested kidneys from M and F mice of both HUA models and appropriate controls, followed by RNA-Seq. To determine pathways altered by HUA, we utilized pathway analysis (DAVID Bioinformatics Resource 6.8) on all significant differentially expressed genes (DESeq2, p < 0.05, FDR < 0.1). Both models showed similar alterations in gene expression, with approximately 10% of all differentially expressed genes from all 3 groups of HUA mice clustered into metabolic pathways, including genes involved in steroid and amino acid metabolism. M HUA mice of both models also shared differential expression of genes involved in glutathione and fatty acid metabolism. We hypothesize that although luminal urate differs between the two models, the intracellular urate values in the proximal tubule cells will be similarly elevated. This elevation must be influencing the observed changes in metabolism related gene expression. To begin to elucidate urate dependent metabolic regulators, we next explored which transcription factors (TFs) may be driving this differential expression (Enrichr enrichment analysis) and found 2 TFs shared by all 3 HUA groups: Gata2 and Tcf3, with 2 more TFs, Sox2 and Nanog, in both M HUA mice. In conclusion, we found that models of both classical types of HUA alter renal metabolic pathways. We have also identified 2 candidate TFs that may be directly affected by urate, which could drive transcriptional changes in response to HUA. Additional experiments are required to determine the effect of urate itself on the activity of these TFs, as well as mechanistic studies to explore the effects of altered intracellular urate levels. Further elucidation these interactions may lead to improved understanding of urate homeostasis and new insights into HUA treatment.