Dysregulation of the sensory and regulatory pathways controlling cellular iron metabolism in unilateral obstructive nephropathy

Abstract

Chronic kidney disease (CKD) involves disturbances in iron metabolism including anemia caused by insufficient erythropoietin (EPO) production. However, underlying mechanisms responsible for the dysregulation of cellular iron metabolism are incompletely defined. Using the unilateral ureteral obstruction (UUO) model in Irp1+/+ and Irp1-/- mice we asked if iron regulatory proteins (IRP), the central regulators of cellular iron metabolism and also suppressors of EPO production, contribute to the etiology of anemia in kidney failure. We identified a significant reduction in IRP protein level and RNA binding activity that associated with a loss of the iron uptake protein transferrin receptor 1, increased expression of the iron storage protein subunits H- and L-ferritin, and a low but overall variable level of stainable iron in the obstructed kidney. This reduction in IRP RNA binding activity and ferritin RNA levels suggests the concomitant rise in ferritin expression and iron content in kidney failure is IRP-dependent. In contrast, the reduction in Epo mRNA level in the obstructed kidney was not rescued by genetic ablation of IRP1 suggesting disruption of normal HIF-2a regulation. Furthermore, reduced expression of some HIFa target genes in UUO occurred in the face of increased expression of HIFa proteins and the prolyl hydroxylases (PHD) 2 and PHD1, the latter of which is not known to be HIFa mediated. Our results suggest that the IRP system drives changes in cellular iron metabolism that are associated with kidney failure in UUO but that the impact of IRP on EPO production is overridden by disrupted hypoxia signaling.