Renal tubular epithelial cell (RTC) apoptosis causes tubular atrophy, a hallmark of chronic renal disease. The original term for apoptosis was """"""""shrinkage necrosis"""""""", based upon descriptions of reduced cytoplasmic volume. Apoptotic cells also develop cytosolic acidification, which promotes caspase activation. Preliminary data demonstrate that the plasma membrane Na+/H+ transporter, NHE1, promotes RTC survival by defending cell volume and pHi through Na+/H+ exchange. In addition, apoptotic or osmotic stress activates a signaling cascade that links the NHE1 cytosolic domain to ezrin, radixin, moesin (ERM) proteins, which tether NHE1 to cortical actin, followed by downstream activation of the cell survival kinases, PIS kinase and Akt. Published reports and preliminary data also implicate Rho-dependent kinase (ROCK) and phosphatidylinositol 4,5-bisphosphate (PIP2) in the pathway. Furthermore, a robust death stimulus is associated with caspase-3 degradation of NHE1, cell shrinkage and cytosol acidification. In vivo, NHE1- deficient mice demonstrate increased RTC apoptosis following renal disease induction with adriamycin or streptozotocin. The hypothesis is that NHE1 activation stimulates ROCK activity and ERM recruitment to the NHE1 cytoplasmic domain, to form a cell survival signalplex within a PIP2-rich plasma membrane microenvironment. Tubular atrophy and renal disease progression require NHE1 inactivation due to caspase cleavage of the NHE1 cytoplasmic tail. The hypothesis will be pursued with the following specific aims: (1) To characterize assembly of the NHE1-regulated cell survival signalplex, which is activated by osmotic/apoptotic stress, using biochemical and immunolocalization techniques, (2) To determine the role of NHE1 as a caspase substrate, by identification of the caspase(s) that cleave NHE1, by mapping the NHE1 caspase cleavage sites, and by testing the effect of cleavage-resistant NHE1 mutant expression on cell survival, and (3) To test the role of NHE1 in RTC survival in vivo, kidney phenotypes will be determined in NHE1-deficient vs. control mice following induction of progressive renal diseases. The proposed experiments will prove that NHE1 is a critical cell survival factor and caspase target. Establishing NHE1 as an arbiter of cell survival or death would warrant the design of therapeutic strategies to stabilize the NHE1- regulated survival signalplex and/or inhibit caspase cleavage of NHE1.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK067528-02
Application #
7096016
Study Section
Cellular and Molecular Biology of the Kidney Study Section (CMBK)
Program Officer
Ketchum, Christian J
Project Start
2005-08-01
Project End
2010-07-31
Budget Start
2006-08-01
Budget End
2007-07-31
Support Year
2
Fiscal Year
2006
Total Cost
$315,593
Indirect Cost
Name
Case Western Reserve University
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
077758407
City
Cleveland
State
OH
Country
United States
Zip Code
44106
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Schelling, Jeffrey R (2016) Tubular atrophy in the pathogenesis of chronic kidney disease progression. Pediatr Nephrol 31:693-706
Parker, Mark D; Myers, Evan J; Schelling, Jeffrey R (2015) Na+-H+ exchanger-1 (NHE1) regulation in kidney proximal tubule. Cell Mol Life Sci 72:2061-74
Lakhe-Reddy, Sujata; Li, Vincent; Arnold, Thomas D et al. (2014) Mesangial cell ?v?8-integrin regulates glomerular capillary integrity and repair. Am J Physiol Renal Physiol 306:F1400-9
Khan, Shenaz; Abu Jawdeh, Bassam G; Goel, Monu et al. (2014) Lipotoxic disruption of NHE1 interaction with PI(4,5)P2 expedites proximal tubule apoptosis. J Clin Invest 124:1057-68
Abu Jawdeh, Bassam G; Khan, Shenaz; DeschĂȘnes, Isabelle et al. (2011) Phosphoinositide binding differentially regulates NHE1 Na+/H+ exchanger-dependent proximal tubule cell survival. J Biol Chem 286:42435-45
Khan, Shenaz; Lakhe-Reddy, Sujata; McCarty, Joseph H et al. (2011) Mesangial cell integrin ?v?8 provides glomerular endothelial cell cytoprotection by sequestering TGF-? and regulating PECAM-1. Am J Pathol 178:609-20
Kim, Jane H; Konieczkowski, Martha; Mukherjee, Amitava et al. (2010) Podocyte injury induces nuclear translocation of WTIP via microtubule-dependent transport. J Biol Chem 285:9995-10004
Holthouser, Kristine A; Mandal, Amritlal; Merchant, Michael L et al. (2010) Ouabain stimulates Na-K-ATPase through a sodium/hydrogen exchanger-1 (NHE-1)-dependent mechanism in human kidney proximal tubule cells. Am J Physiol Renal Physiol 299:F77-90
Abu Jawdeh, Bassam G; Kanso, Abbas A; Schelling, Jeffrey R (2009) Evidence-based approach for prevention of radiocontrast-induced nephropathy. J Hosp Med 4:500-6

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