Deletion of Nedd4-2 results in progressive kidney disease in mice

Abstract

NEDD4-2 (NEDD4L), a ubiquitin protein ligase of the Nedd4 family, is a key regulator of cell surface expression and activity of the amiloride-sensitive epithelial Na+ channel (ENaC). While hypomorphic alleles of Nedd4-2 in mice show salt-sensitive hypertension, complete knockout results in pulmonary distress and perinatal lethality due to increased cell surface levels of ENaC. We now show that Nedd4-2 deficiency in mice also results in an unexpected progressive kidney injury phenotype associated with elevated ENaC and Na+Cl− cotransporter expression, increased Na+ reabsorption, hypertension and markedly reduced levels of aldosterone. The observed nephropathy is characterized by fibrosis, tubule epithelial cell apoptosis, dilated/cystic tubules, elevated expression of kidney injury markers and immune cell infiltration, characteristics reminiscent of human chronic kidney disease. Importantly, we demonstrate that the extent of kidney injury can be partially therapeutically ameliorated in mice with nephron-specific deletions of Nedd4-2 by blocking ENaC with amiloride. These results suggest that increased Na+ reabsorption via ENaC causes kidney injury and establish a novel role of NEDD4-2 in preventing Na+-induced nephropathy. Contrary to some recent reports, our data also indicate that ENaC is the primary in vivo target of NEDD4-2 and that Nedd4-2 deletion is associated with hypertension on a normal Na+ diet. These findings provide further insight into the critical function of NEDD4-2 in renal pathophysiology.

NEDD4-2-dependent control of Na+ homeostasis and renal disease

“…Importantly, the administration of amiloride to these mice reduces the renal damage, suggesting that the elevated levels of active ENaC are, at least in part, responsible for the observed kidney disease. In contrast, although we also observe an increase in the levels of the Na C Cl ¡ cotransporter (NCC) protein, treatment of mice with an inhibitor of NCC (hydrochlorothiazide) does not ameliorate the kidney disease, suggesting that ENaC, and not NCC, is the major contributor to the pathology 6 .…”

“…Our data suggest that in addition to hypertension caused by an upregulation of mature membrane-localized ENaC (and also elevated NCC expression 7 ), the increased Na C reabsorption via ENaC in mice lacking Nedd4-2 also causes progressive kidney injury 6 . However, the mechanism by which this elevated Na C reabsorption in renal tubules causes cell death and kidney damage remains to be fully understood.…”

“…Our recent results show that both global and kidney-tubule specific Nedd4-2 KO in mice cause progressive kidney disease, largely due to increased retention of functional ENaC at the apical membrane in the tubular epithelia 6 . In global Nedd4-2 knockout mice that survive birth, kidney damage characterised by cortical cysts, cellular debris, mesenchymal infiltration and fibrosis becomes apparent within a few days after birth, and progresses with time until the animals die from respiratory distress at three weeks of age.…”

“…In Nedd4-2 Ksp1.3 animals the expression of the mature, active forms of all three ENaC subunits is increased 6 . Importantly, the administration of amiloride to these mice reduces the renal damage, suggesting that the elevated levels of active ENaC are, at least in part, responsible for the observed kidney disease.…”

Ubiquitin Ligases Involved in the Regulation of Wnt, TGF-β, and Notch Signaling Pathways and Their Roles in Mouse Development and Homeostasis

“…The kidney-specific knockout mice suffer from a progressive kidney injury phenotype associated with increased sodium ion reabsorption, hypertension, and reduced levels of aldosterone. The phenotype is manifested by fibrosis, higher apoptosis, and cystic tubules [146]. In the mast cell-specific knockout, NEDD4L limits the intensity and duration of immunoglobulin E (IgE)-Fc ε RI-induced positive signal transduction.…”