Circadian Clock Disruption in the Pathogenesis and Therapy of Polycystic Kidney Disease

University Of Kansas Medical Center, Kansas City KS

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Abstract

SPECIFIC AIMS: Polycystic Kidney Disease (PKD) is the most common inherited kidney disease that affects over 12.5 million people worldwide 1. Our long-term goal is to find effective therapies for PKD. Autosomal dominant PKD (ADPKD) is caused by mutations of PKD1 and PKD2 genes that encode for polycystin 1 and polycystin 2. The disease features development of fluid-filled cysts in the kidneys and liver, the progressive growth of which is accompanied by inflammation, fibrosis and metabolic defects, often leading to chronic kidney disease (CKD) and end stage renal disease (ESRD). Although we now have an FDA approved drug for PKD, it is critically important to develop better therapies and lifestyle modification strategies for ADPKD patients. The goal of this project is to generate preliminary data on circadian rhythm disruption in ADPKD kidneys, and identify mechanisms to target for therapy. Circadian rhythms are intrinsic cyclical ~24-hour oscillations in behavior and physiology that coordinate the diverse biological processes with the time of day. The mammalian circadian system is built upon a cell-autonomous transcription-translation delayed feedback molecular mechanism by the clock genes. These include the transcription factors, circadian locomotor output cycles kaput (CLOCK) and brain and muscle ARNT-like protein-1 (BMAL1), which drive Cryptochrome (CRY) and Period (PER) genes, whose products inhibit CLOCK and BMAL1. Circadian rhythms regulate fundamental renal functions such as expression of transporters, tubular reabsorption, secretion, plasma flow and glomerular filtration rate. Renal functional circadian rhythms are disrupted in diabetic kidney disease, kidney stone disease and hypertension in humans, and in mouse models of adenine induced CKD and cisplatin induced acute kidney injury. Importantly, gene mutation or deletion of clock genes in mouse kidneys result in uncontrolled blood pressure and unbalanced urinary excretion of salt and water. Circadian rhythm disruption (chronodisruption) is known to drive disease progression in cancer, metabolic syndrome, liver diseases and Alzheimer?s disease. However, it is currently unknown if circadian rhythm disruptions in ADPKD contribute to disease pathology. We made a novel observation that mouse tubular epithelial cells with PKD1 gene deletion show significant disruption in 24h circadian oscillations of core clock genes such as CLOCK, BMAL1, PER2 and CRY1, when compared to control cells. ADPKD mouse kidneys also showed significant diurnal variations in cyst-growth regulating cell signaling factors compared to WT mouse kidneys. Moreover, renal circadian clock gene expression and renal physiological diurnal rhythms were also found to be disrupted in mouse ADPKD kidneys and corresponded to increase in age and renal cyst growth. Importantly, chronotherapy using Nobiletin, a pharmacological enhancer of PER2 significantly reduced cell proliferation and cyst growth by ADPKD cells in in vitro studies. Based on these observations, we hypothesized that circadian rhythms are disrupted and promote disease progression in ADPKD and restoring the circadian rhythm can slow or stop cyst growth. To generate preliminary data, the following aims will be accomplished: Specific Aim 1. To determine pathogenic mechanisms underlying disruption of circadian rhythms in ADPKD kidneys and how such changes contribute to ADPKD progression. Studies will identify differences in periodicity of expression of clock genes between WT and Pkd1RC/RC mouse kidneys. The role of adiponectin-AMPK-mTOR pathway will be examined as a pathogenic cell signaling pathway for circadian disruption in the ADPKD kidney, and possible links to fat metabolism will be examined. To determine if such changes contribute ADPKD progression, selected genes and cell signaling mechanisms will be examined in chronodisruption studies. Specific Aim 2. To determine if chronodisruption contributes to phenotypic change or disease progression in ADPKD. We propose to examine the effect of renal tubule-specific gene knockout of BMAL1, (an important clock gene) in ADPKD mice. PKD1RC/RC-BMAL1f/f-PkhD1cre mouse will be generated by breeding PKD1RC/RC mice with BMAL1f/f mice and PkhD1cre mice. Age dependent changes in disease progression will be characterized to determine the effect of BMAl1 gene deletion (chronodisruption) on ADPKD progression early during cyst growth.