Regulation of the renal epithelial sodium channel (ENaC) by the vascular endothelial growth factor (VEGF) and the pathogenetic role of renal ENaC for VEGF receptor inhibitor-induced hypertension.

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Vascular endothelial growth factor receptor (VEGFR) inhibitors are used in tumor therapy. One therapy-limiting side effect is arterial hypertension. The role of renal mechanisms in VEGFR inhibitor-induced hypertension is currently unclear. In experimental studies in rats, we showed that the VEGFR inhibitor, sunitinib, significantly decreases fractional Na+ excretion while having little effects on vascular function. Fractional Li+ excretion, as a marker for proximal Na+ reabsorption, was unchanged suggesting that Na+ transport was affected at more distal sites. Experiments in murine cortical CD (M1) cells further revealed that VEGF (VEGF-A) significantly decreases epithelial Na+ channel (ENaC) subunit mRNA abundances and that this effect is inhibited by sunitinib. VEGF also significantly reduced alpha-ENaC subunit protein abundance in M1 cells. Again, sunitinib diminished this effect.Our findings suggest that VEGF may be a negative physiological regulator of ENaC in the kidney and that increased ENaC-dependent Na+ reabsorption may contribute to sunitinib-induced hypertension. The first objective of our proposed project is to examine whether VEGF down-regulates ENaC in M1 cells. We will test the hypotheses that VEGF reduces ENaC protein abundances and proteolytic cleavage of gamma-ENaC, activates the VEGFR-2, induces internalization of ENaC and decreases ENaC activity (patch clamp). In addition, we will investigate if the extracellular signal-regulated kinase (ERK1/2)- and the nitric oxide synthase (NOS)-dependent pathways are involved in the VEGF-induced ENaC down-regulation.The second objective is to investigate if the VEGFR inhibitor, sunitinib, increases renal ENaC activity in rats. We will test the hypotheses that sunitinib treatment for 4 days increases renal ENaC expression, enhances proteolytic cleavage of the gamma-ENaC subunit, decreases phosphorylation of beta- and gamma-ENaC subunits or stimulates the insertion of ENaC subunits from the cytoplasm into the apical plasma membrane, leading to enhanced ENaC activity. The third objective is to test if sunitinib reduces renal NO formation in rats. We will test the hypotheses that sunitinib treatment for 4 days decreases renal NOS expression, decreases renal NOS activity and alters the localization of renal NOS isoenzymes. Furthermore, we will treat rats with a combination of sunitinib and the NO donor, nitrate, to test the hypotheses that NO reduces the sunitinib-induced increases in arterial blood pressure and renal sodium reabsorption and reduces the sunitinib-induced increases in renal ENaC expression. Finally, we will perform experiments in CD-specific NOS1 knockout mice to test the hypothesis that sunitinib causes greater elevations in arterial pressure and renal sodium reabsorption in knockout mice than in controls.