Segmental sclerosis is a characteristic lesion defining both primary and secondary glomerulosclerosis. In most diseases causing glomerulosclerosis, Tgfb expression in podocytes is a stress response signal associated with sclerosis lesions. To define precisely how activation of Tgfb type I receptor (TbrI) signaling in podocytes affects glomerular cells in vivo, we generated a transgenic mouse model (PodTbrI(AAD) that enables conditional (Doxycycline-inducible) expression of a constitutively-active TbrI mutant (TbrI(AAD). When TbrI(AAD) signaling is activated in podocytes, mice eventually develop albuminuria and subsequently progressive glomerulosclerosis associated with podocyte depletion. However, podocyte morphology remains normal while podocytes initially release endothelin 1 (Edn1) to cause endothelial cell mitochondrial oxidative stress (ENDO mtStress) and endothelial dysfunction (ED). Furthermore, treatment with an inhibitor of endothelin 1 type A receptor (Ednra) or mitochondrial-targeted superoxide scavenger, eliminated ENDO mtStress and prevented albuminuria and segmental sclerosis. These results suggest a novel podocyte-to-endothelial-to- podocyte crosstalk, where Edn1/Ednra meditated ENDO mtStress and ED is essential for manifestation of podocyte damage/loss in progressive sclerosis. Using in vitro co-culture system of PodTbrI(AAD) podocytes and mouse glomerular endothelial cells (mGECs), we confirmed that Dox-activated PodTbrI(AAD) conditioned medium or Edn1 treatment of mGEC was sufficient to initiate ED, and subsequent mGEC supernatant was sufficient to induce podocyte apoptosis. Finally, we timed Dox withdrawal and found that 100-fold increase of urine albumin/creatinine ratio and at least 40% loss of podocytes were phenotypic markers for irreversible progression of sclerosis even in the absence of Dox. HYPOTHESIS: Perturbation of podocyte homeostasis can be associated with Edn1 release to initiate Edn1/Ednra-mediated mtStress and dysfunction of adjacent endothelial cells, which in response release soluble signal(s) that mediate progressive damage and depletion of adjacent podocytes characteristic of progressive segmental sclerosis.
SPECIFIC AIMS : 1) Identify soluble molecular signal(s) produced by endothelial cells, subject to Edn1-activated dysfunction, that is required for manifestation of podocyte apoptosis in vitro. 2) Refine and pinpoint the phenotypic markers (thresholds) and the underlying molecular mechanisms that demarcate precisely the onset of irreversible progression of glomerulosclerosis in PodTbrI(AAD) mice. 3) Delineate whether segmental sclerosis and podocyte lesions in human primary and secondary podocytopathies are correlated with underlying podocyte-endothelial crosstalk in human kidney biopsy cases. LONGTERM: the proposed studies should elucidate the requirements and mechanisms for interdependent signaling crosstalk between dysregulated podocytes and endocapillary cells that determine irreversible segmental sclerosis characteristic of glomerular disease progression.
This research aims to identify novel glomerular lesion-specific therapeutic targets.

Public Health Relevance

Chronic kidney disease (CKD) affects one in ten Americans and is a major public health problem in the U.S., both in terms of disease burden and health expenditure. We developed a unique new animal model for studies proposed in this application to define cell-type specific characteristic cellular responses and signals of glomerular disease progression in CKD. In the longterm, these studies should lead to a better understanding of the cell damage mechanisms that promote progression of CKD in humans.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK097253-02
Application #
8650823
Study Section
Pathobiology of Kidney Disease Study Section (PBKD)
Program Officer
Rys-Sikora, Krystyna E
Project Start
2013-04-15
Project End
2018-02-28
Budget Start
2014-03-01
Budget End
2015-02-28
Support Year
2
Fiscal Year
2014
Total Cost
$368,663
Indirect Cost
$151,163
Name
Icahn School of Medicine at Mount Sinai
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
078861598
City
New York
State
NY
Country
United States
Zip Code
10029
Daehn, Ilse; Casalena, Gabriella; Zhang, Taoran et al. (2014) Endothelial mitochondrial oxidative stress determines podocyte depletion in segmental glomerulosclerosis. J Clin Invest 124:1608-21