Symptomatic kidney stones can be a significant source of severe pain, infection, and morbidity, affecting up to 12% of Americans and generating more than $2 billion in healthcare costs annually. The process of kidney stone formation remains poorly understood and there has been limited progress in developing medical or dietary interventions to prevent the occurrence or recurrence of stones due to paucity of good models for kidney stone formation. In Drosophila melanogaster (D. melanogaster), the Malpighian tubule is the functional equivalent of the human convoluted tubule and transports ions and other solutes from the fly circulatory system into the excretory system. Furthermore, a number of genes found in the fly excretory system play a conserved role in the human excretory system. The fly tubule produces crystalline concretions containing calcium, phosphorus, and other ions combined with an organic matrix. These concretions appear to be formed from small spherical structures that bear a striking resemblance to the nanoparticles (spherites) seen in Randall plaques, the nidus of early stone formation in human kidneys. We show that these fly stones contain xanthine and a bisphosphonate-binding substance, presumably hydroxyapatite and calcium, the primary component of early human stones. We have also found that inhibition of xanthine dehydrogenase (XDH) in D. melanogaster leads to increased accumulation of concretions on a high protein diet which can be rescued by inhibition of a Vitamin D receptor ortholog. Notably these genes and a high protein diet have been implicated in human stone disease. Given the similarities in tubule physiology, conservation of genes in the excretory system, and characteristics of stone formation between D. melanogaster and humans, and the availability of powerful genetic tools in the fly, we hypothesize that D. melanogaster can be utilized as a meaningful model to improve understanding of kidney stone disease and to identify novel therapeutics.
The aims of the proposed study are: (1) Characterization of early stone formation and tubule physiology in the XDH knockdown fly;and (2) identification of genetic and pharmacologic manipulations that modulate early fly stone formation, The significance of developing D. melanogaster as a translational model for studying nephrolithiasis is that it would provide an opportunity to better understand the mechanism of human kidney stone formation and to discover novel therapeutics for kidney stone disease. This proposal is innovative because of the application of an invertebrate translational model characterized by a short lifespan and relatively low cost of maintenance, to achieve large scale screening of genetic and pharmacological manipulations for developing therapeutics for nephrolithiasis.
While kidney stone disease is a significant source of medical cost and morbidity in the United States, minimal advancement in the areas of medical treatment and prevention has been made in the last several decades. Given the similarity in various aspects of stone formation and renal physiology between flies and humans, this proposal aims to develop a novel animal model for kidney stone disease using D. melanogaster. Such a model holds significant promise for better understanding of the pathophysiologic mechanisms underlying early stone formation as well as for the discovery of novel therapeutics for renal stone disease.
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