Salt-sensitive hypertension and cardiac hypertrophy in mice deficient in the ubiquitin ligase Nedd4-2

Departments of 1 Obstetrics and Gynecology, 2 Internal Medicine, and 3 Pathology, Carver College of Medicine, University of Iowa, Iowa City; 4 Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland; and 5 Veterans Affairs Medical Center, Iowa City, Iowa Submitted 9 May 2008 ; accepted in final form 3 June 2008 Nedd4-2 has been proposed to play a critical role in regulating epithelial Na + channel (ENaC) activity. Biochemical and overexpression experiments suggest that Nedd4-2 binds to the PY motifs of ENaC subunits via its WW domains, ubiquitinates them, and decreases their expression on the apical membrane. Phosphorylation of Nedd4-2 (for example by Sgk1) may regulate its binding to ENaC, and thus ENaC ubiquitination. These results suggest that the interaction between Nedd4-2 and ENaC may play a crucial role in Na + homeostasis and blood pressure (BP) regulation. To test these predictions in vivo, we generated Nedd4-2 null mice. The knockout mice had higher BP on a normal diet and a further increase in BP when on a high-salt diet. The hypertension was probably mediated by ENaC overactivity because 1 ) Nedd4-2 null mice had higher expression levels of all three ENaC subunits in kidney, but not of other Na + transporters; 2 ) the downregulation of ENaC function in colon was impaired; and 3 ) NaCl-sensitive hypertension was substantially reduced in the presence of amiloride, a specific inhibitor of ENaC. Nedd4-2 null mice on a chronic high-salt diet showed cardiac hypertrophy and markedly depressed cardiac function. Overall, our results demonstrate that in vivo Nedd4-2 is a critical regulator of ENaC activity and BP. The absence of this gene is sufficient to produce salt-sensitive hypertension. This model provides an opportunity to further investigate mechanisms and consequences of this common disorder. ion channels; kidney; sodium channels Address for reprint requests and other correspondence: B. Yang, Dept. of Obstetrics and Gynecology, 463 MRF, Univ. of Iowa, 200 Hawkins Dr., Iowa City, IA 52242 (e-mail: baoli-yang{at}uiowa.edu )