Polycystic kidney disease (PKD) is a ciliopathic disorder that results in multiple kidney cysts and hypertension (HTN), which eventually leads to kidney failure. A hallmark of PKD is the early development of HTN, which is inadequately controlled by conventional therapies including angiotensin converting enzyme (ACE) inhibitors. In this regard, there is evidence for the activation of the intrarenal renin-angiotensin system (RAS) in PKD. In PKD only 2 to 3% of nephrons become cystic and the development of hypertension should be dependent upon inappropriate reabsorption of salt and water by non-cystic nephrons; the most likely site would be at the collecting duct. Indeed we have previously shown, in an immortalized collecting duct cell line from a cilia deficient PKD mouse model, increased expression of aquaporin (AQP2) and mislocalized apical vasopressin receptor (V2R) leading to increased transepithelial salt and water absorption compared to a control. Therefore, we hypothesize that increased salt and water reabsorption by the collecting duct, which leads to HTN in PKD, may be due to mislocalization/altered activity and regulation by intrarenal RAS of critical transport proteins. Thus the first Specific Aim (SA1) is to determine if there is increase salt and water transport in the collecting duct from Ift88 and Pkd1 conditional knockout mice compared to control. This will be accomplished by: assessing salt and water transport rates in isolated perfused tubules; measuring channel activity by patch clamp of micro-dissected split open collecting ducts; and testing expression and/or mislocalization of transport proteins utilizing in vivo biotinylation. In preliminary experiments we found that renal angiotensinogen (AGT) is up-regulated in both Ift88 and Pkd1 knockout mice and hypothesized that AGT may be an effective target for blockade of intrarenal RAS. Therefore, we recently tested a novel antisense oligonucleotide (ASO) targeting AGT and compared to conventional lisinopril therapy or no treatment in Pkd1 knockout mice and found that there was a significant reduction in the rate of renal cystic growth. AGT-ASO was not as effective as lisinopril in lowering blood pressure perhaps due to an AGT-ASO induced increase in renin levels. Therefore, (SA2) will determine the effect of inhibiting AGT or renin, or both, on hypertension and the rate of cystogenesis in Ift88 and Pkd1 models. This will be accomplished by determining whether AGT-ASO in combination with a renin inhibition (aliskiren) in Pkd1 and Ift88 conditional knockout mice leads to increased suppression of intrarenal renin, AGT, and angiotensin II levels, and whether this leads to better control of BP and a significant reduction in kidney cyst expansion compared to AGT-ASO treatment or lisinopril plus losartan. These proposed studies should lead to fundamentally new insights into the mechanism for PKD induced hypertension as well as test the therapeutic potential of a novel intrarenal RAS inhibitor for the treatment of HTN and renal cyst progression in PKD.
Currently, there is no cure for Polycystic Kidney Disease (PKD) and once kidney dysfunction occurs there is a universal rapid decline in kidney function leading to end stage kidney disease. Therefore early treatment is critical. Hypertension is one early manifestation of PKD and these studies are designed to determine if cilia and /or polycystin1 dysfunction results in altered protein localization in the kidney increased intrarenal renin angiotensin system and thus lead to increased salt and water absorption and hypertension. This would have important implications in early stages of human PKD and may help in design of therapeutic agents to slow the progression of PKD.
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