SEARCH · PubMed Health

Results for “Endosomal Sorting Complexes Required for Transport”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources

PubMed2001

A novel mouse Nedd4 protein suppresses the activity of the epithelial Na+ channel.

Liddle's syndrome is a form of inherited hypertension linked to mutations in the genes encoding the epithelial Na+ channel (ENaC). These mutations alter or delete PY motifs involved in protein-protein interactions with a ubiquitin-protein ligase, Nedd4. Here we show that Na+ transporting cells, derived from mouse cortical collecting duct, express two Nedd4 proteins with different structural organization and characteristics of ENaC regulation: 1) the classical Nedd4 (herein referred to as Nedd4-1) containing one amino-terminal C2, three WW, and one HECT-ubiquitin protein ligase domain and 2) a novel Nedd4 protein (Nedd4-2), homologous to Xenopus Nedd4 and comprising four WW, one HECT, yet lacking a C2 domain. Nedd4-2, but not Nedd4-1, inhibits ENaC activity when coexpressed in Xenopus oocytes and this property correlates with the ability to bind to ENaC, as only Nedd4-2 coimmunoprecipitates with ENaC. Furthermore, this interaction depends on the presence of at least one PY motif in the ENaC complex and on WW domains 3 and 4 in Nedd4-2. Thus, these results suggest that the novel suppressor protein Nedd4-2 is the regulator of ENaC and hence a potential susceptibility gene for arterial hypertension.

Amino Acid Motifs↗

PubMed2005

Structure and ESCRT-III protein interactions of the MIT domain of human VPS4A.

The VPS4 AAA ATPases function both in endosomal vesicle formation and in the budding of many enveloped RNA viruses, including HIV-1. VPS4 proteins act by binding and catalyzing release of the membrane-associated ESCRT-III protein lattice, thereby allowing multiple rounds of protein sorting and vesicle formation. Here, we report the solution structure of the N-terminal VPS4A microtubule interacting and transport (MIT) domain and demonstrate that the VPS4A MIT domain binds the C-terminal half of the ESCRT-III protein, CHMP1B (Kd = 20 +/- 13 microM). The MIT domain forms an asymmetric three-helix bundle that resembles the first three helices in a tetratricopeptide repeat (TPR) motif. Unusual interhelical interactions are mediated by a series of conserved aromatic residues that form coiled-coil interactions between the second two helices and also pack against the conserved alanines that interdigitate between the first two helices. Mutational analyses revealed that a conserved leucine residue (Leu-64) on the third helix that would normally bind the fourth helix in an extended TPR is used to bind CHMP1B, raising the possibility that ESCRT-III proteins may bind by completing the TPR motif.

ATPases Associated with Diverse Cellular Activitie↗

PubMed2002

An HRD/DER-independent ER quality control mechanism involves Rsp5p-dependent ubiquitination and ER-Golgi transport.

We have identified a new pathway of ER-associated degradation in Saccharomyces cerevisiae that functions separately from the HRD/DER pathway comprised of Hrd1p, Hrd3p, Der1p, and Ubc7p. This pathway, termed Hrd1p independent-proteolysis (HIP), is capable of recognizing and degrading both lumenal (CPY* and PrA*), and integral membrane proteins (Sec61-2p) that misfold in the ER. CPY* overexpression likely saturates the HRD/DER pathway and activates the HIP pathway, so the slowed degradation kinetics of CPY* in a hrd1 Delta strain is restored to a wild-type rate when CPY* is overexpressed. Substrates of HIP require vesicular trafficking between the ER and Golgi apparatus before degradation by the ubiquitin-proteasome system. Ubiquitination of HIP substrates does not involve the HRD/DER pathway ubiquitin ligase Hrd1p, but instead uses another ubiquitin ligase, Rsp5p. HIP is regulated by the unfolded protein response as Ire1p is necessary for the degradation of CPY* when overexpressed, but not when CPY* is expressed at normal levels. Both the HIP and HRD/DER pathways contribute to the degradation of CPY*, and only by eliminating both is CPY* degradation completely blocked.

Cytosol↗

PubMed1997

Ubiquitin lys63 is involved in ubiquitination of a yeast plasma membrane protein.

We have recently reported that the yeast plasma membrane uracil permease undergoes cell-surface ubiquitination, which is dependent on the Npi1/Rsp5 ubiquitin-protein ligase. Ubiquitination of this permease, like that of some other transporters and receptors, signals endocytosis of the protein, leading to its subsequent vacuolar degradation. This process does not involve the proteasome, which binds and degrades ubiquitin-protein conjugates carrying Lys48-linked ubiquitin chains. The data presented here show that ubiquitination and endocytosis of uracil permease are impaired in yeast cells lacking the Doa4p ubiquitin-isopeptidase. Both processes were rescued by overexpression of wild-type ubiquitin. Mutant ubiquitins carrying Lys-->Arg mutations at Lys29 and Lys48 restored normal permease ubiquitination. In contrast, a ubiquitin mutated at Lys63 did not restore permease polyubiquitination. Ubiquitin-permease conjugates are therefore extended through the Lys63 of ubiquitin. When polyubiquitination through Lys63 is blocked, the permease still undergoes endocytosis, but at a reduced rate. We have thus identified a natural target of Lys63-linked ubiquitin chains. We have also shown that monoubiquitination is sufficient to induce permease endocytosis, but that Lys63-linked ubiquitin chains appear to stimulate this process.

Arginine↗

PubMed2005

Acute rejection after rat renal transplantation leads to downregulation of NA+ and water channels in the collecting duct.

Renal transplantation is associated with alterations of tubular functions and of the renin-angiotensin-aldosterone system. The underlying cellular and molecular mechanisms are unclear. We used an allogeneic rat renal transplantation model of acute rejection with and without immunosuppression by cyclosporine A (CsA) and a syngeneic model as control. Uninephrectomized Lewis or Lewis-Brown-Norway (LBN) rats received a kidney from LBN-rats. Renal transporters and receptors were analyzed by immunohistochemistry, semiquantitative RT-PCR and Western-blot analysis. Intracellular Na(+) was analyzed microfluorimetrically in isolated cortical collecting ducts. mRNA expression and function of the epithelial Na(+)-channel (ENaC) and mRNA and protein expression of the water-channel AQP2 were downregulated in transplanted kidneys undergoing rejection. Expression of the serum- and glucocorticoid-kinase (Sgk1) was decreased and that of the ubiquitin-protein ligase Nedd4-2 was increased. These changes were absent under CsA-therapy and in syngeneic model. Expression and function of the Na(+)-K(+)-ATPase, expression of the secretory K(+)-channel and of the mineralocorticoid receptor remained unchanged. Reduced ENaC function is likely due to decreased Sgk1- and increased Nedd4-2 mRNA expression leading to reduced ENaC expression in the membrane. These acute downregulations of ENaC and AQP2 may be triggered to reduce energy consumption in the distal nephron to protect the kidney immediately after transplantation.

Acute Disease↗

PubMed2006

Stimulation of the epithelial sodium channel (ENaC) by the serum- and glucocorticoid-inducible kinase (Sgk) involves the PY motifs of the channel but is independent of sodium feedback inhibition.

The epithelial sodium channel (ENaC) is the major mediator of sodium transport across the apical membranes of the distal nephron, the distal colon, the respiratory tract and the ducts of exocrine glands. It is subject to feedback inhibition by increased intracellular Na+, a regulatory system wherein the ubiquitin protein ligases, Nedd4 and Nedd4-2, bind to conserved PY motifs in the C-termini of ENaC and inactivate the channel. It has been proposed recently that the kinase Sgk activates the channel as a consequence of phosphorylating Nedd4-2, thus preventing it from inhibiting the channels. This proposal predicts that Sgk should interfere with Na+ feedback regulation of ENaC. We have tested this prediction in Xenopus laevis oocytes and in mouse salivary duct cells and found that in neither system did increased activity of Sgk interrupt Na+ feedback inhibition of ENaC. We found, however, that Sgk stimulation was largely abolished in oocytes expressing ENaC channels with C-terminal truncations or mutated PY motifs. We were also unable to confirm that Sgk directly interacts with Nedd4-2 in vitro. We conclude that the stimulatory effect of Sgk on ENaC requires the presence of the channel's PY motifs, but it is not due to the interruption of Na+ feedback regulation.

Amino Acid Motifs↗

PubMed2005

14-3-3 proteins modulate the expression of epithelial Na+ channels by phosphorylation-dependent interaction with Nedd4-2 ubiquitin ligase.

The ubiquitin E3 protein ligase Nedd4-2 is a physiological regulator of the epithelial sodium channel ENaC, which is essential for transepithelial Na+ transport and is linked to Liddle's syndrome, an autosomal dominant disorder of human salt-sensitive hypertension. Nedd4-2 function is negatively regulated by phosphorylation via a serum- and glucocorticoid-inducible protein kinase (Sgk1), which serves as a mechanism to inhibit the ubiquitination-dependent degradation of ENaC. We report here that 14-3-3 proteins participate in this regulatory process through a direct interaction with a phosphorylated form of human Nedd4-2 (a human gene product of KIAA0439, termed hNedd4-2). The interaction is dependent on Sgk1-catalyzed phosphorylation of hNedd4-2 at Ser-468. We found that this interaction preserved the activity of the Sgk1-stimulated ENaC-dependent Na+ current while disrupting the interaction decreased ENaC density on the Xenopus laevis oocytes surface possibly by enhancing Nedd4-2-mediated ubiquitination that leads to ENaC degradation. Our findings suggest that 14-3-3 proteins modulate the cell surface density of ENaC cooperatively with Sgk1 kinase by maintaining hNedd4-2 in an inactive phosphorylated state.

14-3-3 Proteins↗

PubMed2005

Regulation of epithelial sodium channel in puromycin aminonucleoside-induced unilateral experimental nephrotic syndrome in normal and analbuminemic Nagase rats.

BACKGROUND: Nephrotic syndrome (NS) is characterized by renal sodium retention and edema formation. In nephrotic rats the site of enhanced sodium retention has been localized in the cortical collecting duct (CCD). The epithelial sodium channel (ENaC) is the rate-limiting constituent of sodium transport in CCD. Amiloride, an ENaC-blocking drug, corrects the abnormal rate of sodium transport in isolated perfused CCD from puromycin aminonucleoside (PAN)-treated rats. Therefore, we hypothesized that ENaC functional expression is increased in NS. METHODS: Unilateral NS was induced by PAN in Wistar rats and analbuminemic Nagase rats (NAR). Urinary protein excretion, renal abundance of mRNA and protein of ENaC subunits, as well as the ENaC regulatory serum glucocorticoid-inducible kinase (Sgk1) and Nedd4-2, were assessed. RESULTS: Proteinuria appeared at day 2 in the Wistar rats and NAR. Surprisingly a downregulation rather than the expected upregulation of alpha-, beta- and gamma-ENaC mRNA abundance was observed in both Wistar rats and NAR, when the treated kidney was compared with the untreated kidney. The amount of protein of alpha-, beta- and gamma-ENaC was not affected by the NS. Sgk1 mRNA expression did not change and Nedd4-2 protein expression was only decreased at days 1 and 2 in Wistar rats. CONCLUSION: ENaC mRNA and protein expression are not increased in the early phase of unilateral PAN-induced NS. Sgk1, Nedd4-2 and analbuminemia are not important regulatory factors of ENaC protein expression in experimental NS.

Acetylglucosaminidase↗

PubMed2006

The Ca2+-binding protein ALG-2 is recruited to endoplasmic reticulum exit sites by Sec31A and stabilizes the localization of Sec31A.

The formation of transport vesicles that bud from endoplasmic reticulum (ER) exit sites is dependent on the COPII coat made up of three components: the small GTPase Sar1, the Sec23/24 complex, and the Sec13/31 complex. Here, we provide evidence that apoptosis-linked gene 2 (ALG-2), a Ca(2+)-binding protein of unknown function, regulates the COPII function at ER exit sites in mammalian cells. ALG-2 bound to the Pro-rich region of Sec31A, a ubiquitously expressed mammalian orthologue of yeast Sec31, in a Ca(2+)-dependent manner and colocalized with Sec31A at ER exit sites. A Ca(2+) binding-deficient ALG-2 mutant, which did not bind Sec31A, lost the ability to localize to ER exit sites. Overexpression of the Pro-rich region of Sec31A or RNA interference-mediated Sec31A depletion also abolished the ALG-2 localization at these sites. In contrast, depletion of ALG-2 substantially reduced the level of Sec31A associated with the membrane at ER exit sites. Finally, treatment with a cell-permeable Ca(2+) chelator caused the mislocalization of ALG-2, which was accompanied by a reduced level of Sec31A at ER exit sites. We conclude that ALG-2 is recruited to ER exit sites via Ca(2+)-dependent interaction with Sec31A and in turn stabilizes the localization of Sec31A at these sites.

Apoptosis Regulatory Proteins↗

PubMed2000

Ubiquitination and endocytosis of plasma membrane proteins: role of Nedd4/Rsp5p family of ubiquitin-protein ligases.

In addition to its well-known role in recognition by the proteasome, ubiquitin-conjugation is also involved in downregulation of membrane receptors, transporters and channels. In most cases, ubiquitination of these plasma membrane proteins leads to their internalization followed by targeting to the lysosome/vacuole for degradation. A crucial role in ubiquitination of many plasma membrane proteins appears to be played by ubiquitin-protein ligases of the Nedd4/Rsp5p family. All family members carry an N-terminal Ca2+-dependent lipid/protein binding (C2) domain, two to four WW domains and a C-terminal catalytic Hect-domain. Nedd4 is involved in downregulation of the epithelial Na+ channel, by binding of its WW domains to specific PY motifs of the channel. Rsp5p, the unique family member in S. cerevisiae, is involved in ubiquitin-dependent endocytosis of a great number of yeast plasma membrane proteins. These proteins lack apparent PY motifs, but carry acidic sequences, and/or phosphorylated-based sequences that might be important, directly or indirectly, for their recognition by Rsp5p. In contrast to polyubiquitination leading to proteasomal recognition, a number of Rsp5p targets carry few ubiquitins per protein, and moreover with a different ubiquitin linkage. Accumulating evidence suggests that, at least in yeast, ubiquitin itself may constitute an internalization signal, recognized by a hypothetical receptor. Recent data also suggest that Nedd4/Rsp5p might play a role in the endocytic process possibly involving its C2 domain, in addition to its role in ubiquitinating endocytosed proteins.

Animals↗

PubMed2004

Nedd4-2 phosphorylation induces serum and glucocorticoid-regulated kinase (SGK) ubiquitination and degradation.

Serum and glucocorticoid-regulated kinase (SGK) plays a key role in the regulation of epithelial Na+ transport. SGK phosphorylates Nedd4-2, an E3 ubiquitin-protein ligase that targets the epithelial Na+ channel (ENaC) for degradation. Phosphorylation increases Na+ transport by reducing Nedd4-2 binding to ENaC, which increases ENaC expression at the cell surface. Thus, SGK expression must be tightly controlled to maintain Na+ homeostasis. This occurs in part by regulation of SGK transcription; a variety of signals including steroid hormones (aldosterone and glucocorticoids) increase SGK levels by inducing transcription of SGK. However, SGK has a short half-life, suggesting that SGK levels might also be controlled by regulation of SGK degradation. Here we found that SGK degradation is mediated in part by Nedd4-2. Consistent with this model, overexpression of Nedd4-2 decreased steady-state levels of SGK in a dose-dependent manner by increasing SGK ubiquitination and degradation in the 26S proteasome. Conversely, silencing of Nedd4-2 by RNA interference stabilized SGK. Nedd4-2 phosphorylation potentiates SGK degradation; degradation was reduced by Nedd4-2 and SGK mutations that disrupt phosphorylation or by inhibition of SGK kinase activity. Together with previous work, the data support a model in which SGK and Nedd4-2 regulate one another in a reciprocal manner. SGK phosphorylates Nedd4-2, which reduces Nedd4-2 binding and inhibition of ENaC. Conversely, phosphorylation increases Nedd4-2-mediated degradation of SGK. Thus, by phosphorylating Nedd4-2, SGK induces its own degradation. This feedback inhibition may fine-tune the regulation of epithelial Na+ absorption.

Animals↗

PubMed2005

Role of Nedd4-2 and polyubiquitination in epithelial sodium channel degradation in untransfected renal A6 cells expressing endogenous ENaC subunits.

Amiloride-sensitive epithelial sodium channels (ENaC) are responsible for transepithelial Na(+) transport in the kidney, lung, and colon. The channel consists of three subunits (alpha, beta, and gamma). In Madin-Darby canine kidney (MDCK) cells and Xenopus laevis oocytes transfected with all three ENaC subunits, neural precursor cell-expressed developmentally downregulated protein (Nedd4-2) promotes ubiquitin conjugation of ENaC. For native proteins in some cells, ubiquitin conjugation is a signal for their degradation by the ubiquitin-proteasome pathway, whereas in other cell types ubiquitin conjugation is a signal for endocytosis and lysosomal protein degradation. When ENaC are transfected into MDCK cells, ubiquitin conjugation leads to lysosomal degradation. In this paper, we characterize the involvement of the ubiquitin-proteasome proteolytic pathway in the regulation of functional ENaC in untransfected renal A6 cells expressing native ENaC subunits. In contrast to transfected cells, we show that total cellular alpha-, beta-, and gamma-ENaC subunits are polyubiquitinated and that ubiquitin conjugation of subunits increases when the cells are treated with a proteasome inhibitor. We show that Nedd4-2 is associated with alpha- and beta-subunits and is associated with the apical membrane. We also show the Nedd4-2 can regulate the number of functional ENaC subunits in the apical membrane. The results reported here suggest that the ubiquitin-proteasome proteolytic pathway is an important determinant of ENaC function in untransfected renal cells expressing endogenous ENaC.

Animals↗

PubMed2004

Regulation of neuronal voltage-gated sodium channels by the ubiquitin-protein ligases Nedd4 and Nedd4-2.

Nedd4 and Nedd4-2 are ubiquitin-protein ligases known to regulate a number of membrane proteins including receptors and ion transporters. Regulation of the epithelial Na(+) channel by Nedd4 and Nedd4-2 is mediated via interactions between the PY motifs of the epithelial sodium channel subunits and the Nedd4/Nedd4-2 WW domains. This example serves as a model for the regulation of other PY motif-containing ion channels by Nedd4 and Nedd4-2. We found that the carboxyl termini of the six voltage-gated Na(+) (Na(v)) channels contain typical PY motifs (PPXY), and a further Na(v) contains a PY motif variant (LPXY). Not only did we demonstrate by Far-Western analysis that Nedd4 and Nedd4-2 interact with the PY motif-containing Na(v) channels, but we also showed that these channels have conserved WW domain binding specificity. We further showed that the carboxyl termini fusion proteins of one central nervous system and one peripheral nervous system-derived Na(+) channel (Na(v)1.2 and Na(v)1.7, respectively) are readily ubiquitinated by Nedd4-2. In Xenopus oocytes, Nedd4-2 strongly inhibited the activities of all three Na(v)s (Na(v)1.2, Na(v)1.7, and Na(v)1.8) tested. Interestingly, Nedd4 suppressed the activity of Na(v)1.2 and Na(v)1.7 but was a poor inhibitor of Na(v)1.8. Our results provide evidence that Nedd4 and Nedd4-2 are likely to be key regulators of specific neuronal Na(v) channels in vivo.

Amino Acid Sequence↗

PubMed2006

Scoring of predicted GRK2 phosphorylation sites in Nedd4-2.

MOTIVATION: Epithelial Na(+) channels (ENaC) mediate the transport of sodium (Na) across epithelia in the kidney, gut and lungs and are required for blood pressure regulation. They are inhibited by ubiquitin protein ligases, such as Nedd4-2. These ligases bind to proline-rich motifs (PY motifs) present in the C-termini of ENaC subunits. Loss of this inhibition leads to hypertension. We have previously reported that ENaC channels are maintained in the active state by the G protein coupled receptor kinase, GRK2. The enzyme has been implicated in the development of essential hypertension [R. D. Feldman (2002) Mol. Pharmacol., 61, 707-709]. Additional findings in our lab pointed towards a possible role for GRK2 in the phosphorylation and inactivation of Nedd4-2. RESULTS: We have predicted GRK2 phosphorylation sites on Nedd4-2 by combining sequence analysis, homology modeling and surface accessibility calculations. A total of 24 potential phosphorylation sites were predicted by sequence analysis. Of these, 16 could be modeled using homology modeling and 6 of these were found to have sufficient surface exposure to be accessible to the GRK2 enzyme responsible for the phosphorylation of Nedd4-2. The method provides an ordered list of the most probable GRK2 phosphorylation sites on Nedd4-2 providing invaluable guidance to future experimental studies aimed at mutating certain Nedd4-2 residues in order to prevent phosphorylation by GRK2. The method developed could be applied in a wide variety of biological applications involving the binding of one molecule to a protein. The relative effectiveness of the technique is determined mainly by the quality of the homology model built for the protein of interest. CONTACT: jarthur@med.usyd.edu.au

Algorithms↗

PubMed2003

Relative contribution of Nedd4 and Nedd4-2 to ENaC regulation in epithelia determined by RNA interference.

Epithelial Na+ transport is regulated in large part by mechanisms that control expression of the epithelial Na+ channel (ENaC) at the cell surface. Nedd4 and Nedd4-2 are candidates to control ENaC surface expression, but it is not known which of these proteins contributes to ENaC regulation in epithelia. To address this question, we used RNA interference to selectively reduce expression of Nedd4 or Nedd4-2. We found that endogenous Nedd4-2, but not Nedd4, negatively regulates ENaC in two epithelial cell lines (Fischer rat thyroid and H441); small interfering RNA (siRNA) against Nedd4-2 increased amiloride-sensitive Na+ current (compared with control siRNA), but Nedd4 siRNA did not. A mutation associated with Liddle's syndrome (betaR566X) abolished the effect of Nedd4-2 siRNA, suggesting that a defect in ENaC regulation by Nedd4-2 contributes to the pathogenesis of this inherited form of hypertension. Previous work found that Nedd4-2 is phosphorylated by serum and glucocorticoid-regulated kinase, a Ser/Thr kinase induced by steroid hormones. Here we found that Nedd4-2 phosphorylation contributes to ENaC regulation by steroid hormones. Consistent with this model, ENaC stimulation by dexamethasone was reduced by Nedd4-2 siRNA and by overexpression of a mutant Nedd4-2 lacking serum and glucocorticoid-regulated kinase phosphorylation sites. Thus, endogenous Nedd4-2 negatively regulates ENaC in epithelia and is a component of a signaling pathway by which steroid hormones regulate ENaC. Defects in this regulation may contribute to the pathogenesis of hypertension.

Animals↗

PubMed1996

WW domains of Nedd4 bind to the proline-rich PY motifs in the epithelial Na+ channel deleted in Liddle's syndrome.

The amiloride-sensitive epithelial sodium channel (ENaC) plays a major role in sodium transport in kidney and other epithelia, and in regulating blood pressure. The channel is composed of three subunits (alphabetagamma) each containing two proline-rich sequences (P1 and P2) at its C-terminus. The P2 regions in human beta and gammaENaC, identical to the rat betagammarENaC, were recently shown to be deleted in patients with Liddle's syndrome (a hereditary form of hypertension), leading to hyperactivation of the channel. Using a yeast two-hybrid screen, we have now identified the rat homologue of Nedd4 (rNedd4) as the binding partner for the P2 regions of beta and gammarENaC. rNedd4 contains a Ca2+ lipid binding (CaLB or C2) domain, three WW domains and a ubiquitin ligase (Hect) domain. Our yeast two-hybrid and in vitro binding studies revealed that the rNedd4-WW domains mediate this association by binding to the P2 regions, which include the PY motifs (XPPXY) of either betarENaC (PPPNY) or gammarENaC (PPPRY). SH3 domains were unable to bind these sequences. Moreover, mutations to Ala of Pro616 or Tyr618 within the betarENaC P2 sequence (to PPANY or PPPNA, respectively), recently described in Liddle's patients, led to abrogation of rNedd4-WW binding. Nedd4-WW domains also bound to the proline-rich C-terminus (containing the sequence PPPAY) of alpharENaC, and endogenous Nedd4 co-immunoprecipitated with alpharENaC expressed in MDCK cells. These results demonstrate that the WW domains of rNedd4 bind to the PY motifs deleted from beta or gammaENaC in Liddle's syndrome patients, and suggest that Nedd4 may be a regulator (suppressor) of the epithelial Na+ channel.

Amino Acid Sequence↗

PubMed2006

Metabolic acidosis has dual effects on sodium handling by rat kidney.

Chronic metabolic acidosis (CMA) is associated with decreased NaCl reabsorption in the proximal tubule (PT). However, the effect of CMA on Na(+) transport in the distal tubule (DT) and collecting duct (CD) is poorly understood. Rats were placed in metabolic cages and had access to water (control), 0.28 M NH(4)Cl, or 0.28 M KCl solutions in a pair-feeding protocol for 5 days (5d). Metabolic acidosis developed within 24 h in NH(4)Cl-, but not in KCl-loaded rats. Interestingly, NH(4)Cl- but not KCl-loaded rats exhibited a significant natriuresis after 24 h of treatment. Urinary Na(+) excretion increased from 1.94 to 2.97 meq/24 h (P < 0.001) and returned to below baseline level (1.67 meq/l) after 5d of CMA. The protein abundance of the cortical Na-Cl cotransporter (NCC) remained unchanged at 24 h, but increased significantly (P < 0.01) after 5d of CMA. The protein abundance of alpha-, beta-, and gamma-subunits of the epithelial Na(+) channel (ENaC) in the cortex decreased sharply during the first 24 h and then returned to baseline levels after 5d of CMA. Interestingly, Sgk1 expression decreased after 24 h (-31%, P < 0.05) and then returned to baseline after 5d of CMA. Nedd4-2 expression was not altered during CMA. CMA enhanced serum aldosterone levels by 54% and increased the expression of aldosterone synthase in the adrenal gland by 134% after 5d of CMA. In conclusion, metabolic acidosis has dual effects on urinary Na(+) excretion. The early natriuresis results from decreased Na(+) reabsorption in the PT and Sgk1-related decreased ENaC activity in the DT and CD. Aldosterone-induced upregulation of NCC, Sgk1, and ENaC likely contributes to the antinatriuretic phase of metabolic acidosis. This adaptation prevents Na(+) wasting and volume depletion during chronic acid insult.

Acidosis, Renal Tubular↗

PubMed2006

CHMP2B mutations are not a cause of dementia in Dutch patients with familial and sporadic frontotemporal dementia.

Mutations in the CHMP2B gene have been recently identified in a large Danish pedigree with autosomal dominant frontotemporal dementia (FTD) linked to chromosome 3 (FTD3). We report the frequency of CHMP2B mutations in 162 FTD patients recruited from a large population-based study of FTD carried out in The Netherlands. Our results suggest that mutations in CHMP2B are a rare cause of FTD as compared to MAPT mutations.

DNA Mutational Analysis↗