Novel role of urinary urate in renal cystogenesis and water regulation

PROJECT SUMMARY/ABSTRACT Autosomal Dominant Polycystic Kidney Disease (ADPKD), a genetic disorder leading to progressive renal cyst growth, affects 12 million people globally. Arginine vasopressin (AVP) is a key driver of cystogenesis, and in rodent PKD models, the absence of AVP completely prevents cyst formation. Although V2 receptor (V2R) antagonists effectively inhibit cyst growth, their use is limited by significant polyuria (>6 Liters/day). An alternative strategy involves enhancing renal water reabsorption to suppress central AVP release. Promising approaches include regulating the water channel aquaporin-2 (AQP2) through pathways independent of V2R. The urate transporters GLUT9b and ABCG2, located in the collecting duct, may play roles in water homeostasis. Notably, hyperuricosuria is associated with hyponatremia and Glut9 deletion in mice lead to severe polyuria. Additionally, ABCG2 inhibitors might be associated with improved kidney function in ADPKD. Our preliminary findings suggest that intracellular urate accumulation promotes aquaporin-2 (AQP2) exocytosis via AMP-activated protein kinase (AMPK) phosphorylation, independent of V2R/PKA pathways. The overarching hypothesis posits that elevating intracellular urate in collecting ducts promotes AQP2 exocytosis and water reabsorption, suppressing central AVP release and reducing renal cystogenesis in ADPKD. Aim 1 investigates the impact and mechanisms by which urate controls AQP2 trafficking, evaluating the impact of ABCG2 inhibition by Ko143 analog and probenecid on urinary concentration in V2R knockout mice, assessing the impact of ABCG2 deletion on urinary concentration capacity and AQP2 phosphorylation, and exploring mechanisms by which increased intracellular urate, due to GLUT9b overexpression and ABCG2 inhibition, controls AQP2, cyclic AMP levels, Protein Kinase A (PKA), and AMPK activities in V2R-knockdown cell lines. Aim 2 determines the impact and underlying mechanisms of ABCG2 inhibition and genetic deletion in reducing renal cyst growth and mitigating tolvaptan-induced aquaresis in ADPKD, assessing the impact of ABCG2 inhibition and deletion on PKD amelioration in Pkd1RC/RC mice, investigating the long-term impact of ABCG2 inhibition and genetic deletion on the anti-cystogenic and aquaretic effects of tolvaptan, and exploring effects of elevated intracellular urate, ABCG2 inhibition, and AMPK inhibitor on in vitro cystogenesis, cAMP levels, PKA, AMPK, and PDE activities in WT and Pkd1 mice and human collecting duct cells. These investigations aim to elucidate the novel interplay between intracellular urate and AQP2-mediated water transport regulation in ADPKD, potentially leading to innovative treatments to slow cystogenesis.