Research Fellow, University of South Australia
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.
Abstract: Cross-linkage of the high-affinity immunoglobulin E (IgE) receptor (FcɛRI) on mast cells by antigen ligation has a critical role in the pathology of IgE-dependent allergic disorders, such as anaphylaxis and asthma. Restraint of intracellular signal transduction pathways that promote release of mast cell-derived pro-inflammatory mediators is necessary to dampen activation and restore homoeostasis. Here we show that the ligase Nedd4-2 and the adaptor Ndfip1 (Nedd4 family interacting protein 1) limit the intensity and duration of IgE-FcɛRI-induced positive signal transduction by ubiquitinating phosphorylated Syk, a tyrosine kinase that is indispensable for downstream FcɛRI signalosome activity. Importantly, loss of Nedd4-2 or Ndfip1 in mast cells results in exacerbated and prolonged IgE-mediated cutaneous anaphylaxis in vivo. Our findings reveal an important negative regulatory function for Nedd4-2 and Ndfip1 in IgE-dependent mast cell activity.
Pub.: 28 Oct '16, Pinned: 27 Jun '18
Abstract: Hypertension is characterized by increased peripheral vascular resistance which is related with elevated myogenic response. Recent findings have indicated that epithelial sodium channel (ENaC) is involved in mechanotransduction of the myogenic response. The purpose of this study was to investigate the involvement of ENaC in the elevated myogenic response of posterior cerebral arteries (PCAs) from spontaneously hypertensive rats (SHRs). Sixteen to eighteen weeks old male wistar kyoto rats (WKYs) and SHRs were used in this study. We found that wall to lumen (W/L) ratio was increased in the PCAs from SHRs compared with WKYs at the resting state. Interestingly, amiloride significantly inhibited myogenic response in the PCAs from SHRs and WKYs, however, the magnitude of the blockade was greater in SHRs. The transfection of γENaC-siRNA significantly reduced the expression of γENaC protein and inhibited myogenic response in the PCAs from SHRs. Furthermore, these data were supported by the findings that serum/glucocorticoid-induced kinase (Sgk1) and neural precursor cell-expressed developmentally downregulated gene 4-2 (Nedd4-2) were increased in SHRs compared with WKYs. Our results suggest that γENaC may play an important role in the elevated myogenic response in PCAs from SHRs.
Pub.: 07 Apr '17, Pinned: 27 Jun '18
Abstract: The epithelial sodium channel (ENaC) plays critical roles in maintaining fluid and electrolyte homeostasis and is located in the aldosterone-sensitive distal nephron (ASDN). We previously found that Nedd4-2 C2 knockout (KO) mice showed salt-sensitive hypertension with paradoxically enhanced ENaC gene expression in ASDN under high oral salt intake. Eplerenone (EPL), a selective aldosterone blocker, is a promising therapeutic option for resistant or/and salt-sensitive hypertension. We examined the effect of EPL on Nedd4-2 C2 KO mice with respect to blood pressure, metabolic parameters, and molecular level changes in ASDN under high oral salt intake. We found that EPL failed to reduce blood pressure in KO mice with high oral salt intake and upregulated ENaC expression in ASDN. Thus, salt-sensitive hypertension in Nedd4-2 C2 KO was EPL-resistant. Gene expression analyses of laser-captured specimens in ASDN suggested the presence of non-aldosterone-dependent activation of ENaC transcription in ASDN of Nedd4-2 C2 KO mice, which was abolished by amiloride treatment. Our results from Nedd4-2 C2 KO mice suggest that enhanced ENaC gene expression is critically involved in salt-sensitive hypertension under certain conditions of specific enzyme isoforms for their ubiquitination.
Pub.: 13 Jun '17, Pinned: 27 Jun '18
Abstract: Authors: Jantina A. Manning, Tanya L. Henshall, Sharad Kumar Article URL: http://www.tandfonline.com/doi/full/10.1080/15384101.2017.1386514?ai=1gnkc&mi=6b657i&af=R Citation: Cell Cycle Publication Date: 2017-11-07T06:29:21Z Journal: Cell Cycle
Pub.: 07 Nov '17, Pinned: 27 Jun '18
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
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