The role of NFAT in podocyte damage and proteinuric kidney disease

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DESCRIPTION (provided by applicant): Chronic kidney disease (CKD) is a growing worldwide public health concern. Over 11% of adults living in the US are estimated to suffer from CKD, which leads to a diminished quality of life, financial health burden and premature death. Aberrant calcium signaling has been implicated in many scenarios of kidney disease and glomerular damage. Gain of function mutations in TRCP6 calcium channels can lead to alterations in proper podocyte morphology and the loss of the glomerular filter leading to loss of proteins into the urine (proteinura). Additionally, increases in intracellular calcium in the podocyte occur under other non-genetic insults such as increases in blood pressure, bacterial infection, and trauma. The calcium sensitive phosphatase calcineurin is activated in the presence of calcium, and our group has demostrated that constitutive activation of calcineurin leads to proteinuria. However, to date calcineurins canonical downstream target, the transcription factor nuclear factor of activated T-cells (NFAT), has not been well characterized for its role in changes that lead to disease phenotypes in the kidney. We have developed an animal model where the transcription factor, NFAT, is constitutively active in the podocyte in the presence of doxycycline. These animals develop profound proteinuria within fours days of doxycycline exposure and display foot process effacement upon analysis with electron microscopy. Our preliminary data also show that animals on prolonged doxycycline exposure (2 months) are unable to revert to normal podocyte morphology and glomerular filter function once the doxycycline is removed and normal animal chow is re-introduced. Interestingly, the glomerulus appears normal under histological techniques such as hematoxylin and eosin (H+E) staining and periodic acid Schiff staining (PAS). The proteinuric phenotype and podocyte foot process effacement of our animals coupled with the lack of observed pathology on H+E and PAS is reminiscent of the pathology of patients with Minimal Change Disease (MCD). The goals of the proposed study are two-fold. One, we intend to identify the NFAT target genes in our animal model that are responsible for the acute induction of proteinuria and recapitulate expression of those genes in vitro to assess possible changes in the podocyte. Two, we aim to completely characterize our animal model, both histologically and genetically, over several time courses of doxycycline exposure in comparison to MCD patient profiles. It is the hope that downstream targets of NFAT can be identified for the proteinuric phenotype of our animals and to provide the scientific community with an animal model for a debilitating disease. PUBLIC HEALTH RELEVANCE: Chronic kidney disease (CKD) affects over 11% of the US population, and accounts for nearly $60 billion in healthcare spending annually. Aberrant calcium signaling has been implicated in many scenarios of kidney disease and glomerular damage. Nuclear factor of activated T-cells (NFAT), a transcription factor, is activated upon increases in intracellular calcium. However, NFAT target genes remain un-characterized for their role in disease phenotypes in the kidney. Our research aims to identify NFAT target genes associated with disease phenotypes in the hope that new drug targets can be identified to ameliorate proteinuria in CKD patients.