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CURATOR
A pinboard by
Jantina Manning

Research Fellow, University of South Australia

PINBOARD SUMMARY

We have recently discovered and are characterising a new gene linked to chronic kidney disease

Worldwide, 1 in 10 people currently have chronic kidney disease (defined as a change in structure or function of the kidney over a long period of time) and many are unaware they are living with it. Research in our laboratory has revealed that a protein known to be involved in controlling blood pressure also prevents salt-induced kidney disease, similar to chronic kidney disease. This discovery could improve outcomes for many people living with this disease in the future.

Some kidney diseases (e.g. polycystic kidney disease) are associated with specific genetic mutations. However, the mechanisms that connect underlying genetic defects, as well as environmental factors such as dietary salt intake, to chronic kidney disease are poorly understood. Recently, we have identified the gene Nedd4-2 as a new player that normally protects mice against kidney damage.

There is some evidence that increased salt can initiate or exacerbate kidney damage and it has been predicted that genes that regulate salt (sodium) absorption are likely to be key players in disease progression. Our recent data suggests that kidney disease caused by dysfunction of the Nedd4-2 gene is influenced by dietary sodium intake. High salt consumption is common in a modern diet, and we predict that this contributes to kidney disease in some patients, particularly those with aberrations in sodium transport genes. In human populations, variants in NEDD4-2 are known to be associated with developmental disorders, hypertension and end stage renal disease. This research will highlight the importance of assessing NEDD4L variants in patients with chronic kidney disease-like pathologies, as well as informing clinicians and patients of the risk of high salt consumption to kidney disease. The only current treatment options for patients with chronic kidney disease are dialysis or transplant. This innovative research could direct new treatment strategies for this disease, by targeting the genes that regulate sodium absorption in the kidney.

6 ITEMS PINNED

β1Pix exchange factor stabilizes the ubiquitin ligase Nedd4-2 and plays a critical role in ENaC regulation by AMPK in kidney epithelial cells

Abstract: Our previous work has established that the metabolic sensor AMP-activated protein kinase (AMPK) inhibits the epithelial Na+ channel (ENaC) by promoting its binding to neural precursor cell-expressed, developmentally down-regulated 4-2, E3 ubiquitin protein ligase (Nedd4-2). Here, using MS analysis and in vitro phosphorylation, we show that AMPK phosphorylates Nedd4-2 at the Ser-444 (Xenopus Nedd4-2) site critical for Nedd4-2 stability. We further demonstrate that the Pak-interacting exchange factor β1Pix is required for AMPK-mediated inhibition of ENaC-dependent currents in both CHO and murine kidney cortical collecting duct (CCD) cells. shRNA-mediated knockdown of β1Pix expression in CCD cells attenuated the inhibitory effect of AMPK activators on ENaC currents. Moreover, overexpression of a β1Pix dimerization–deficient mutant unable to bind 14-3-3 proteins (Δ602–611) increased ENaC currents in the CCD cells, whereas overexpression of wild-type (WT) β1Pix had the opposite effect. Using additional immunoblotting and co-immunoprecipitation experiments, we found that treatment with AMPK activators promoted the binding of β1Pix to 14-3-3 proteins in CCD cells. However, the association between Nedd4-2 and 14-3-3 proteins was not consistently affected by AMPK activation, β1Pix knockdown, or overexpression of WT β1Pix or the β1Pix-Δ602–611 mutant. Moreover, we found that β1Pix is important for phosphorylation of the aforementioned Nedd4-2 site critical for its stability. Overall, these findings elucidate novel molecular mechanisms by which AMPK regulates ENaC. Specifically, they indicate that AMPK promotes the assembly of β1Pix, 14-3-3 proteins, and Nedd4-2 into a complex that inhibits ENaC by enhancing Nedd4-2 binding to ENaC and its degradation.

Pub.: 01 Jun '18, Pinned: 27 Jun '18

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.Cell Death and Differentiation advance online publication, 1 September 2017; doi:10.1038/cdd.2017.137.

Pub.: 02 Sep '17, Pinned: 27 Jun '18