The Role of Endothelin-1 in Tubular Injury in Sickle Cell Disease

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1  Project Summary/Abstract 2  Mentored Phase: Sickle cell disease (SCD), the most common hemoglobinopathy in US, is associated with 3  high prevalence of end-stage kidney failure at the median 23 years of age. Due to the lack of kidney-targeted 4  treatment the mean survival is less than 3 years. SCD milieu induces endothelin-1 (ET-1) and elevated ET-1 5  levels in SCD patients correlate with microalbuminuria. I recently demonstrated that both ET receptor A (ETA) 6  and dual ET receptor A and B (ETA+B) antagonists prevented the increase in glomerular permeability to albumin 7  in a mouse model of SCD, but only the ETA receptor antagonist prevented albuminuria. These findings led me 8  to the hypothesis that ET-1 via ETA receptor activation contributes to renal injury in SCD mice, while the ETB 9  receptor provides tubular protection. Thus, the central hypothesis of the mentored phase is that in the SCD 10  milieu, elevated ET-1 and increased ETA receptor activity mediate tubular dysfunction leading to the 11  tubular injury in SCD mice, which is opposed by the ETB activity. The specific aim 1 of the mentored 12  phase will determine if increased ET-1 and the ETA receptor activity mediate tubular injury by decreased 13  tubular albumin uptake mechanism in SCD mice and if ETB receptor antagonism exacerbates ET-1 effects on 14  tubular albumin handling. With the use of new training in in vivo imaging techniques, I will track fluorescent- 15  labeled albumin to assess tubular albumin reabsorption in vehicle- or ET receptor antagonists treated SCD and 16  genetic control mice. We will also determine the direct effect of ET-1 and ET receptors on proximal tubule 17  albumin transporters in ex vivo and in vivo settings. Independent Phase: This phase will focus on an 18  independent line of investigation exploring mechanisms of renal iron handling that builds on previous training. 19  Evidence suggests that increased iron deposition in SCD is associated with albuminuria, both of which can be 20  attenuated by ETA receptor blockade. Although, ET-1 contributes to glomerulopathy in SCD, the relevance of 21  iron-induced toxicity and resultant tubular injury is unclear. Therefore, the overall hypothesis of the 22  independent phase is that elevated ET-1 leads to dysfunctional tubular iron handling, iron overload, and 23  tubular injury in SCD. This will be tested through in vitro experiments on cultured proximal tubules cells and 24  in vivo in SCD mice. The specific aim 2 will determine if impaired tubular iron handling in SCD leads to iron 25  overload via ET-1 induced increase in proximal tubule iron uptake and/or decrease in proximal tubule iron 26  removal. The specific aim 3 will determine mechanisms of iron toxicity that lead to tubular injury in SCD. This 27  will be tested by determining if renal iron-overload leads to tubular injury via oxidative stress and/or 28  mitochondrial dysfunction in SCD nephropathy. The goals of the proposed studies will undoubtedly shed light 29  on novel mechanistic pathways involved in the development and progression of tubular injury, a crucial 30  contributor in chronic kidney disease.