Although obstructive nephropathy is the leading cause of pediatric renal failure, current management fails to prevent progression. Underlying renal cellular mechanisms will be investigated using a model of reversible variable chronic partial unilateral ureteral obstruction (UUO) in the neonatal mouse, which parallels human fetal urinary tract obstruction. Persistent UUO leads to injury to the glomerulotubular junction, an important but under-recognized pathway that leads to the formation of atubular glomeruli (ATG) and aglomerular tubules. For each aim, the role of oxidant injury will be investigated in this animal model by the administration of MitoQ, a potent antioxidant targeted to mitochondria. In Specific Aim 1, the role of the Notch signaling pathway in the generation of ATG and in the remodeling/regeneration process after release of obstruction will be determined by timed administration of γ-secretase inhibitor (DBZ), an inhibitor of Notch activation. The fate of tubular and stromal cells will be tracked using Cre recombinant mouse lines. In Specific Aim 2, modulation of ATG formation by endothelial nitric oxide synthase (eNOS), whose activity impacts the progression of renal injury, will be examined by comparing wild-type with eNOS knock out mice subjected to UUO. Since progression of obstructive nephropathy is dependent on number of nephrons at birth, in Specific Aim 3, mutant Os/+ mice, which have a 50% reduction in nephron number, will be compared to wild-type mice subjected to UUO. In each model, the fraction of nephrons undergoing proximal tubular injury will be determined. Quantitative immunohistochemical renal tissue analysis will include tracking phenotypic transition of epithelial cells, and tracking the fate of tubular and stromal cells. Cell death will be tracked by markers of apoptosis and autophagy, and these will be correlated with markers of reactive oxygen species. The results of these studies will reveal the role of mitochondrial oxidant injury in the formation of ATG, which may lead to the development of new therapies to allow slowing or reversal of progression that occurs prior to the development of interstitial fibrosis.
Most pediatric renal failure is due to malformations of the kidneys and urinary tract. Using a recently developed mouse model of congenital urinary tract obstruction, this project will investigate a novel and important pathway leading to selective damage to the nephrons, the functioning subunits of each kidney. Understanding mechanisms underlying this pathway may lead to new therapies to prevent progressive nephron loss.