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Protein kinase A (PKA) directly phosphorylates aquaporin-2 (AQP2) water channels in renal collecting ducts to reabsorb water from urine for the maintenance of systemic water homeostasis. More than 50 functionally distinct PKA-anchoring proteins (AKAPs) respectively create compartmentalized PKA signaling to determine the substrate specificity of PKA. Identification of an AKAP responsible for AQP2 phosphorylation is an essential step toward elucidating the molecular mechanisms of urinary concentration. PKA activation by several compounds is a novel screening strategy to uncover PKA substrates whose phosphorylation levels were nearly perfectly correlated with that of AQP2. The leading candidate in this assay proved to be an AKAP termed lipopolysaccharide-responsive and beige-like anchor protein (LRBA). We found that LRBA colocalized with AQP2 in vivo, and Lrba knockout mice displayed a polyuric phenotype with severely impaired AQP2 phosphorylation. Most of the PKA substrates other than AQP2 were adequately phosphorylated by PKA in the absence of LRBA, demonstrating that LRBA-anchored PKA preferentially phosphorylated AQP2 in renal collecting ducts. Furthermore, the LRBA–PKA interaction, rather than other AKAP–PKA interactions, was robustly dissociated by PKA activation. AKAP–PKA interaction inhibitors have attracted attention for their ability to directly phosphorylate AQP2. Therefore, the LRBA–PKA interaction is a promising drug target for the development of anti-aquaretics.

Sorafenib is one of the multi-targeted tyrosine kinase inhibitors (TKI), mainly used for treating advanced renal cell carcinoma. Accumulated evidence indicates a minority of patients develop nephrotic syndrome (NS) as a high-grade nephrotoxic injury; however, evidence of NS after long-term use of sorafenib remains unclear. A 64-year-old man developed NS following 2-year use of sorafenib and his NS persisted even after sorafenib use was discontinued. Renal biopsy disclosed minimal change disease (MCD) concurrent with acute tubulointerstitial nephritis, indicating secondary MCD with which sorafenib may be involved. To prevent permanent renal insufficiency, we administered glucocorticoid and succeeded in achieving complete remission from NS. Nephrotoxic injuries could occur at any time with variable onset after sorafenib. Renal biopsy should be pursued in the case of NS associated with TKI therapy. To facilitate recovery of renal dysfunction, administration of prednisolone should be considered, particularly when NS does not disappear after cessation of TKIs.

AQP2 water channel is critical for urinary concentration in the kidney. Interestingly, AQP2 is abundantly excreted in the urine as extracellular vesicles (EVs), which is known to be a useful biomarker for water-balance disorders although the character of AQP2-enriched EVs is poorly understood including water channel function. Human urine EVs were obtained by a differential centrifugation method. AQP2-bearing EVs were isolated by immunoprecipitation with an AQP2-specific antibody, and the proteins in the EVs were analyzed by LC–MS/MS proteomic analysis. Osmotic water permeability (Pf) of the AQP2-rich EVs was measured by a stopped-flow method monitoring scattered light intensity in response to outwardly directed osmotic gradient. Sequential centrifugation of human urine showed that AQP2 was present predominantly (80%) in low-density EVs (160,000 g), whereas negligible amount in high-density EVs (17,000 g). Proteomic analysis of the AQP2-bearing EVs identified 137 proteins, mostly in the endosome pathway, including the components of ESCRT (endosomal sorting complex required transporter)-I, II, III. Pf value of the 160,000 g EVs was 4.75 ± 0.38 × 10−4 cm s−1 (mean ± SE) with the activation energy of 3.51 kcal mol−1 which was inhibited with 0.3 mM HgCl2 by 63%, suggesting a channel-mediated water transport. Moreover, Pf value showed a significant correlation with the abundance of AQP2 protein in EVs. Taken together, AQP2 is localized predominantly to urinary exosomes with preserved water channel activities.

Objective An arteriovenous bridging graft is a viable option for patients with compromised arteries or veins because of advanced age or diabetes. Arteriovenous graft with graft insertion anastomosis (AVGI) is the novel technique for graft-vein anastomosis where the prosthesis is inserted into the vein, and the anastomosis is performed on the surface of the prosthesis. This study assessed the short-term and long-term results of AVGI to clarify the efficacy of this technique. Methods Between 2010 and 2015, AVGI was performed in graft-vein anastomosis of prosthetic forearm loop access. Characteristics and level of complications were assessed. To evaluate the long-term results, functional graft patency and frequency of percutaneous transluminal angioplasty were examined. Results The study comprised 58 patients. There were no deaths related to the surgery. The time of hemostasis after AVGI was recorded at 0 seconds because no bleeding from the suture holes was seen. At 1, 2, and 3 years, primary patency were 45.1% ± 7.5%, 23.1% ± 7.5%, and 23.1% ± 7.5%, respectively, and assisted primary patency rates were 59.4% ± 7.2%, 50.8% ± 7.6%, and 50.8% ± 7.6%, respectively. Secondary patency rates at 4 and 5 years were 100% ± 0% and 94.1% ± 5.7%, respectively. The frequency of percutaneous balloon angioplasty to maintain the patency was 1.61 ± 0.53 times per year. Graft infection occurred in four patients (6.9%). Conclusions AVGI is an advantageous technique for graft vein anastomosis in an arteriovenous bridging graft in both the short-term and long-term.

Vasopressin catalyzes aquaporin-2 phosphorylation at several serine sites in the C-terminal region. Compared with Ser-256 and Ser-269 phosphorylation, the role of Ser-261 phospho-regulation on vasopressin-regulated AQP2 apical translocation is largely unknown. In addition, recent discovery of transcytotic apical delivery of AQP2 made the concept of its intracellular trafficking even more complicated. In this study, we evaluated how intact phospho-AQP2 signals fit with the transcytosis trafficking model in Madin-Darby canine kidney cells. PS256 and pS269 signals were intracellularly detectable in wild-type AQP2 at the beginning of forskolin stimulation (1 min). These phospho-signals were detectable in basolateral membranes even after 10 min of stimulation. AQP2 stably inserted in the apical membrane increased pS269 and decreased pS261 signals. In an NDI-causing mutant P262L-AQP2, in which Ser-261 phospho-regulation is impaired, the pS256 and pS269 signals were detectable in the basolateral membranes with increased pS261 signals after forskolin stimulation. These results suggest that Ser-261 phospho-regulation is involved in pS256- and pS269-mediated AQP2 apical translocation.

Systemic lupus erythematosus is an autoimmune disease associated with mild valvular regurgitation. However, there have been no detailed reports of infective endocarditis in patients with systemic lupus erythematosus. Here, we describe a case of a 55-year-old woman without any cardiac abnormalities who was diagnosed with lupus nephritis by renal biopsy; she contracted infective endocarditis while receiving immunosuppressive therapy. Our case emphasizes that special consideration of the occurrence of infective endocarditis, and its early diagnosis and treatment are mandatory for patient survival. We propose that echocardiography should be performed before treating patients with systemic lupus erythematosus who have an uncertain cardiac status.

Aquaporin-2 (AQP2) is a water channel in collecting duct principal cells in the kidney. Vasopressin catalyzes AQP2 phosphorylation at several serine sites in its C-terminus: Ser-256, Ser-261, and Ser-269. Upon stimulation by vasopressin, Ser-269 phosphorylation increases and Ser-261 phosphorylation decreases. Ser-256 phosphorylation is relatively constant. However, whether these types of phospho-regulation occur independently in distinct AQP2 populations or sequentially in the same AQP2 population is unclear. Especially, the manner of vasopressin-mediated Ser-261 phospho-regulation has been in controversy. In this study, we established phospho-specific AQP2 immunoprecipitation assays and investigated how pS256-positive AQP2 and pS269-positive AQP2 are catalyzed by forskolin or vasopressin, focusing on their Ser-261 phosphorylation status in polarized Madin-Darby canine kidney (MDCK) cells and in mice. In forskolin-treated MDCK cells, Ser-269 phosphorylation preceded Ser-261 dephosphorylation and Ser-256 phosphorylation was constant. In both MDCK cells and mouse kidney, phospho-specific immunoprecipitation revealed that the regulated Ser-269 phosphorylation occurred in the pS256-positive AQP2 population. Importantly, basal-state Ser-261 phosphorylation and its regulated dephosphorylation occurred in the pS256- and pS269-positive AQP2 population. These results provide the direct evidence that the Ser-261 dephosphorylation is involved in the pS256- and pS269-related AQP2 regulation.

Gene identification of hereditary kidney diseases by DNA sequencing is important for precise diagnosis, treatment, and genetic consultations. However, the conventional Sanger sequencing is now practically powerless in the face of ever increasing numbers of reported causative genes of various hereditary diseases. The advent of next-generation sequencing technology has enabled large-scale, genome-wide, simultaneous sequence analyses of multiple candidate genes. We designed and verified a comprehensive diagnosis panel for approximately 100 major inherited kidney diseases, including 127 known genes. The panel was named Simple, sPEedy and Efficient Diagnosis of Inherited KIdney Diseases (SPEEDI-KID). We applied the panel to 73 individuals, clinically diagnosed with an inherited kidney disease, from 56 families. The panel efficiently covered the candidate genes and allowed a prompt and accurate genetic diagnosis. Moreover, 18 unreported mutations suspected as the disease causes were detected. All these mutations were validated by Sanger sequencing, with 100 % concordance. In conclusion, we developed a powerful diagnostic method, focusing on inherited kidney diseases, using a custom panel, SPEEDI-KID, allowing a fast, easy, and comprehensive diagnosis regardless of the disease type.

The relationship between protein–energy wasting and chronic kidney disease (CKD) progression is unknown. In the present prospective cohort study, we evaluated the hypothesis that a combination of low body mass index (BMI) and serum albumin level is associated with rapid CKD progression. The study cohort comprised 728 predialysis Japanese patients with CKD (stages 2–5) enrolled from 2010 to 2011. Patients were categorized into four groups according to their serum albumin levels and BMI: group 1, low serum albumin level (

Congenital nephrogenic diabetes insipidus (NDI) is characterized by the inability of the kidney to concentrate urine. Congenital NDI is mainly caused by loss-of-function mutations in the vasopressin type 2 receptor (V2R), leading to impaired aquaporin-2 (AQP2) water channel activity. So far, treatment options of congenital NDI either by rescuing mutant V2R with chemical chaperones or by elevating cyclic adenosine monophosphate (cAMP) levels have failed to yield effective therapies. Here we show that inhibition of A-kinase anchoring proteins (AKAPs) binding to PKA increases PKA activity and activates AQP2 channels in cortical collecting duct cells. In vivo, the low molecular weight compound 3,3′-diamino-4,4′-dihydroxydiphenylmethane (FMP-API-1) and its derivatives increase AQP2 activity to the same extent as vasopressin, and increase urine osmolality in the context of V2R inhibition. We therefore suggest that FMP-API-1 may constitute a promising lead compound for the treatment of congenital NDI caused by V2R mutations., Patients suffering from congenital nephrogenic diabetes insipidus (NDI) fail to concentrate urine due to mutations in vasopressin type 2 receptor (V2R). Here Ando et al. show that agents disrupting the interaction between PKA and AKAPs restore aquaporin-2 activity downstream of V2R, offering a therapeutic approach for the treatment of NDI.

Recently, the kelch-like protein 3 (KLHL3)–Cullin3 complex was identified as an E3 ubiquitin ligase for with no lysine (WNK) kinases, and the impaired ubiquitination of WNK4 causes pseudohypoaldosteronism type II (PHAII), a hereditary hypertensive disease. However, the involvement of WNK kinase regulation by ubiquitination in situations other than PHAII has not been identified. Previously, we identified the WNK3–STE20/SPS1-related proline/alanine-rich kinase–Na/K/Cl cotransporter isoform 1 phosphorylation cascade in vascular smooth muscle cells and found that it constitutes an important mechanism of vascular constriction by angiotensin II (AngII). In this study, we investigated the involvement of KLHL proteins in AngII-induced WNK3 activation of vascular smooth muscle cells. In the mouse aorta and mouse vascular smooth muscle (MOVAS) cells, KLHL3 was not expressed, but KLHL2, the closest homolog of KLHL3, was expressed. Salt depletion and acute infusion of AngII decreased KLHL2 and increased WNK3 levels in the mouse aorta. Notably, the AngII-induced changes in KLHL2 and WNK3 expression occurred within minutes in MOVAS cells. Results of KLHL2 overexpression and knockdown experiments in MOVAS cells confirmed that KLHL2 is the major regulator of WNK3 protein abundance. The AngII-induced decrease in KLHL2 was not caused by decreased transcription but increased autophagy-mediated degradation. Furthermore, knockdown of sequestosome 1/p62 prevented the decrease in KLHL2, suggesting that the mechanism of KLHL2 autophagy could be selective autophagy mediated by sequestosome 1/p62. Thus, we identified a novel component of signal transduction in AngII-induced vascular contraction that could be a promising drug target.

Aim To investigate the association between iron deficiency anaemia and mortality risk and assess the changes in anaemia and iron status after primary management by a nephrologist. Methods In this prospective cohort study, we stratified 951 non-dialysis chronic kidney disease (CKD) G2–G5 patients newly visiting 16 nephrology centres into four groups according to the presence of anaemia with or without iron deficiency. All-cause mortality, cardiovascular (CV)-related mortality, and a change in anaemia and iron status after specialized primary care were the endpoints evaluated. Results During a median follow-up time of 19 months, the number of all-cause deaths and CV-related deaths were 56 and 26, respectively. Compared with the control group, the groups with isolated anaemia and iron deficiency anaemia had significantly higher all-cause mortalities (isolated anaemia: hazard ratio (HR), 3.37; 95% confidence intervals (CI), 1.76–6.44; iron deficiency anaemia: HR, 3.11; 95% CI, 1.21–8.01) and CV-related mortalities (isolated anaemia: HR, 3.64; 95% CI, 1.36–9.73; iron deficiency anaemia: HR, 3.86; 95% CI, 1.11–13.41). In the isolated anaemia group, erythropoietin-stimulating agent (ESA) prescriptions significantly increased to approximately 70%. However, in patients with both anaemia and iron deficiency, iron prescriptions only increased to 48.1%. Conclusions Iron deficiency anaemia and isolated anaemia were associated with all-cause and CV-related mortality. The absence of relative increase in iron prescriptions suggests that iron deficiency should be accurately assessed and iron supplementation should be appropriately used to manage anaemia in non-dialysis patients with CKD.

Upon activation by with-no-lysine kinases, STE20/SPS1-related proline-alanine-rich protein kinase (SPAK) phosphorylates and activates SLC12A transporters such as the Na(+)-Cl(-) cotransporter (NCC) and Na(+)-K(+)-2Cl(-) cotransporter type 1 (NKCC1) and type 2 (NKCC2); these transporters have important roles in regulating BP through NaCl reabsorption and vasoconstriction. SPAK knockout mice are viable and display hypotension with decreased activity (phosphorylation) of NCC and NKCC1 in the kidneys and aorta, respectively. Therefore, agents that inhibit SPAK activity could be a new class of antihypertensive drugs with dual actions (i.e., NaCl diuresis and vasodilation). In this study, we developed a new ELISA-based screening system to find novel SPAK inhibitors and screened >20,000 small-molecule compounds. Furthermore, we used a drug repositioning strategy to identify existing drugs that inhibit SPAK activity. As a result, we discovered one small-molecule compound (Stock 1S-14279) and an antiparasitic agent (Closantel) that inhibited SPAK-regulated phosphorylation and activation of NCC and NKCC1 in vitro and in mice. Notably, these compounds had structural similarity and inhibited SPAK in an ATP-insensitive manner. We propose that the two compounds found in this study may have great potential as novel antihypertensive drugs.

We previously reported that disruption of the aquaporin-11 (AQP11) gene in mice resulted in cystogenesis in the kidney. In this study, we aimed to clarify the mechanism of cystogenesis in AQP11(-/-) mice. To enable the analyses of AQP11 at the protein level in vivo, AQP11 BAC transgenic mice (Tg(AQP11)) that express 3×HA-tagged AQP11 protein were generated. This AQP11 localized to the endoplasmic reticulum (ER) of proximal tubule cells in Tg(AQP11) mice and rescued renal cystogenesis in AQP11(-/-) mice. Therefore, we hypothesized that the absence of AQP11 in the ER could result in impaired quality control and aberrant trafficking of polycystin-1 (PC-1) and polycystin-2 (PC-2). Compared with kidneys of wild-type mice, AQP11(-/-) kidneys exhibited increased protein expression levels of PC-1 and decreased protein expression levels of PC-2. Moreover, PC-1 isolated from AQP11(-/-) mice displayed an altered electrophoretic mobility caused by impaired N-glycosylation processing, and density gradient centrifugation of kidney homogenate and in vivo protein biotinylation revealed impaired membrane trafficking of PC-1 in these mice. Finally, we showed that the Pkd1(+/-) background increased the severity of cystogenesis in AQP11(-/-) mouse kidneys, indicating that PC-1 is involved in the mechanism of cystogenesis in AQP11(-/-) mice. Additionally, the primary cilia of proximal tubules were elongated in AQP11(-/-) mice. Taken together, these data show that impaired glycosylation processing and aberrant membrane trafficking of PC-1 in AQP11(-/-) mice could be a key mechanism of cystogenesis in AQP11(-/-) mice.

Aim Estimating fluid balance in haemodialysis patients is essential when determining dry weight, but limited methods are currently available. B-type natriuretic peptide (BNP) is a useful surrogate marker in patients with congestive heart failure (CHF), but whether its validity could be generalized to haemodialysis patients has not been studied well. Methods A total of 457 haemodialysis patients at a dialysis centre were analyzed. Determinants of BNP were assessed in connection with ultrasound cardiography (UCG) records, Kt/V, ultrafiltration rate (UFR), and demographic factors. All-cause death and cardiovascular (CV) events were recorded as the main outcome. Results Among the UCG records, left atrial diameter (LAD), left ventricular ejection fraction (LVEF), were determinants of log-transformed (ln) BNP; UFR, age and sex were also significant. There was a positive correlation between BNP and LAD (r = 0.285, P

AQP2 water channel is critical for urinary concentration in the kidney. Interestingly, AQP2 is abundantly excreted in the urine as extracellular vesicles (EVs), which is known to be a useful biomarker for water-balance disorders although the character of AQP2-enriched EVs is poorly understood including water channel function.Human urine EVs were obtained by a differential centrifugation method. AQP2-bearing EVs were isolated by immunoprecipitation with an AQP2-specific antibody, and the proteins in the EVs were analyzed by LC-MS/MS proteomic analysis. Osmotic water permeability (Pf) of the AQP2-rich EVs was measured by a stopped-flow method monitoring scattered light intensity in response to outwardly directed osmotic gradient.Sequential centrifugation of human urine showed that AQP2 was present predominantly (80%) in low-density EVs (160,000 g), whereas negligible amount in high-density EVs (17,000 g). Proteomic analysis of the AQP2-bearing EVs identified 137 proteins, mostly in the endosome pathway, including the components of ESCRT (endosomal sorting complex required transporter)-I, II, III. Pf value of the 160,000 g EVs was 4.75 ± 0.38 × 10Taken together, AQP2 is localized predominantly to urinary exosomes with preserved water channel activities.

Pseudohypoaldosteronism type II (PHAII) is a hereditary disease characterized by salt-sensitive hypertension, hyperkalemia and metabolic acidosis, and genes encoding with-no-lysine kinase 1 (WNK1) and WNK4 kinases are known to be responsible. Recently, Kelch-like 3 (KLHL3) and Cullin3, components of KLHL3-Cullin3 E3 ligase, were newly identified as responsible for PHAII. We have reported that WNK4 is the substrate of KLHL3-Cullin3 E3 ligase-mediated ubiquitination. However, WNK1 and Na-Cl cotransporter (NCC) were also reported to be a substrate of KLHL3-Cullin3 E3 ligase by other groups. Therefore, it remains unclear which molecule is the target(s) of KLHL3. To investigate the pathogenesis of PHAII caused by KLHL3 mutation, we generated and analyzed KLHL3(R528H/+) knock-in mice. KLHL3(R528H/+) knock-in mice exhibited salt-sensitive hypertension, hyperkalemia and metabolic acidosis. Moreover, the phosphorylation of NCC was increased in the KLHL3(R528H/+) mouse kidney, indicating that the KLHL3(R528H/+) knock-in mouse is an ideal mouse model of PHAII. Interestingly, the protein expression of both WNK1 and WNK4 was significantly increased in the KLHL3(R528H/+) mouse kidney, confirming that increases in these WNK kinases activated the WNK-OSR1/SPAK-NCC phosphorylation cascade in KLHL3(R528H/+) knock-in mice. To examine whether mutant KLHL3 R528H can interact with WNK kinases, we measured the binding of TAMRA-labeled WNK1 and WNK4 peptides to full-length KLHL3 using fluorescence correlation spectroscopy, and found that neither WNK1 nor WNK4 bound to mutant KLHL3 R528H. Thus, we found that increased protein expression levels of WNK1 and WNK4 kinases cause PHAII by KLHL3 R528H mutation due to impaired KLHL3-Cullin3-mediated ubiquitination.

Aim Impaired mobility at the onset of dialysis is considered one of the most important risk factors for short-term mortality after initiation of dialysis in elderly patients. However, whether a decline in mobility after starting dialysis also affects mortality is unclear. Methods A total of 202 patients (age, >75 years; mean, 80.4 ± 4.3) were enrolled in this retrospective cohort study in Yokosuka, Japan. They were divided into three subgroups by mobility: independent mobility at onset of dialysis and preservation of mobility after starting dialysis (group 1, n = 104); independent mobility at onset of dialysis and decline in mobility after starting dialysis (group 2, n = 48); and impaired mobility at onset of dialysis (group 3, n = 50). They were followed for 6 months after starting dialysis. A Cox proportional hazards model was used to evaluate the association between mobility and mortality. Results A total of 24.8% of patients had impaired mobility at the start of dialysis, and 68.9% declined in mobility after starting dialysis. In multivariate Cox proportional hazards analysis, the adjusted hazard ratios of groups 2 and 3 compared with group 1 were 3.80 (95% confidence interval, 1.02–14.10) and 4.94 (95% confidence interval, 1.42–17.10), respectively. Conclusion Not only impaired mobility at the start of dialysis but also a decline in mobility after starting dialysis is associated with short-term mortality after initiation of dialysis.

In 2001, with-no-lysine (WNK) kinases were identified as the genes responsible for the human hereditary hypertensive disease pseudohypoaldosteronism type II (PHAII). It took a further 6 years to clarify that WNK kinases participate in a signaling cascade with oxidative stress-responsive gene 1 (OSR1), Ste20-related proline-alanine-rich kinase (SPAK), and thiazide-sensitive NaCl cotransporter (NCC) in the kidney and the constitutive activation of this signaling cascade is the molecular basis of PHAII. Since this discovery, the WNK-OSR1/SPAK-NCC signaling cascade has been shown to be involved not only in PHAII but also in the regulation of blood pressure under normal and pathogenic conditions, such as hyperinsulinemia. However, the molecular mechanisms of WNK kinase regulation by dietary and hormonal factors and by PHAII-causing mutations remain poorly understood. In 2012, two additional genes responsible for PHAII, Kelch-like 3 (KLHL3) and Cullin3, were identified. At the time of their discovery, the molecular mechanisms underlying the interaction between these genes and their involvement in PHAII were unknown. Here we review the pathophysiological roles of the WNK signaling cascade clarified to date and introduce a new mechanism of WNK kinase regulation by KLHL3 and Cullin3, which provides insight on previously unknown mechanisms of WNK kinase regulation.

Heritable nephrogenic diabetes insipidus (NDI) is characterized by defective urine concentration mechanisms in the kidney, which are mainly caused by loss-of-function mutations in the vasopressin type 2 receptor. For the treatment of heritable NDI, novel strategies that bypass the defective vasopressin type 2 receptor are required to activate the aquaporin-2 (AQP2) water channel. Here we show that Wnt5a regulates AQP2 protein expression, phosphorylation and trafficking, suggesting that Wnt5a is an endogenous ligand that can regulate AQP2 without the activation of the classic vasopressin/cAMP signalling pathway. Wnt5a successfully increases the apical membrane localization of AQP2 and urine osmolality in an NDI mouse model. We also demonstrate that calcineurin is a key regulator of Wnt5a-induced AQP2 activation without affecting intracellular cAMP level and PKA activity. The importance of calcineurin is further confirmed with its activator, arachidonic acid, which shows vasopressin-like effects underlining that calcineurin activators may be potential therapeutic targets for heritable NDI., The water channel AQP2 mediates the concentration of urine in the kidney. Here Ando et al. show that Wnt5 promotes collecting duct permeability by regulating AQP2 expression and localization through activation of the calmodulin/calcineurin signalling pathway.

Elevated white blood cell (WBC) count is a well-known predictor of chronic kidney disease (CKD) progression. However, elderly patients commonly fail to develop a high WBC count in response to several diseased states and may instead present a low WBC count. Therefore, we hypothesized that low WBC count, in addition to high WBC count, is associated with CKD progression in the elderly. We conducted a prospective cohort study using 3-year follow-up data from the CKD Research of Outcomes in Treatment and Epidemiology study. In the present study, participants aged over 60 years with pre-dialysis CKD stages G2–G5 were eligible. Patients were stratified into three groups according to WBC count using tertiles (T). The primary outcome was a composite of end-stage renal disease and a 50% reduction in estimated glomerular filtration rate. Data were analyzed using Cox proportional hazard models with adjustments for covariates. We enrolled 697 patients (males, 69%). The median WBC count was 6100 cells/µl (T1

Erythropoiesis-stimulating agents (ESAs) are standard therapy for chronic kidney disease (CKD) patients with renal anemia. However, few studies have compared the effects of different ESAs on anemia in identical pre-dialysis CKD patients.Seventy-nine patients who switched from epoetin beta to darbepoetin alfa (Group 1), and 82 patients who switched from darbepoetin alfa to epoetin beta pegol (Group 2) were enrolled in this study. Clinical and laboratory parameters were assessed for 6 months before and after switching ESAs. The prevalence of adverse events, the dose conversion ratio of ESAs, and the frequency of ESA administration were also analyzed.Analysis of variance showed that switching ESAs did not significantly change hemoglobin levels for the study duration in both groups (mean hemoglobin 10.3-10.5 g/dL in Group 1 and 10.4-10.7 g/dL in Group 2). Estimated glomerular filtration rate, blood pressure, transferrin saturation, ferritin, and albumin remained constant in both groups. The prevalence of adverse effects was quite low (0-3.8 %) during both 6-month study periods. The mean dose conversion ratio for epoetin beta:darbepoetin alfa was 163.7 units:1 μg and for darbepoetin alfa:epoetin beta pegol was 1.08 μg:1 μg. The intervals of ESA administration significantly differed (epoetin beta pegoldarbepoetin alfaepoetin beta).Epoetin beta, darbepoetin alfa, and epoetin beta pegol are effective and well-tolerated agents for managing anemia in Japanese pre-dialysis CKD patients. The intervals of ESA administration to maintain a patient's target hemoglobin were longer in the order of epoetin beta pegoldarbepoetin alfaepoetin beta.

Summary It has been reported that chloride–proton exchanger ClC-5 and vacuolar-type H+-ATPase are essential for endosomal acidification in the renal proximal cells. Here, we found that ClC-5 is expressed in the gastric parietal cells which secrete actively hydrochloric acid at the luminal region of the gland, and that it is partially localized in the intracellular tubulovesicles in which gastric H+,K+-ATPase is abundantly expressed. ClC-5 was co-immunoprecipitated with H+,K+-ATPase in the lysate of tubulovesicles. The ATP-dependent uptake of 36Cl− into the vesicles was abolished by 2-methyl-8-(phenylmethoxy)imidazo[1,2-a]pyridine-3-acetonitrile (SCH28080), an inhibitor of H+,K+-ATPase, suggesting functional expression of ClC-5. In the tetracycline-regulated expression system of ClC-5 in the HEK293 cells stably expressing gastric H+,K+-ATPase, ClC-5 was co-immunoprecipitated with H+,K+-ATPase, but not with endogenous Na+,K+-ATPase. The SCH28080-sensitive 36Cl− transporting activity was observed in the ClC-5-expressing cells, but not in the ClC-5-non-expressing cells. The mutant (E211A-ClC-5), which has no H+ transport activity, did not show the SCH28080-sensitive 36Cl− transport. On the other hand, both ClC-5 and its mutant (E211A) significantly increased the activity of H+,K+-ATPase. Our results suggest that ClC-5 and H+,K+-ATPase are functionally associated and that they may contribute to gastric acid secretion.

The Na-Cl cotransporter (NCC) in the distal convoluted tubules in kidney is known to be excreted in urine. However, its clinical significance has not been established because of the lack of quantitative data on urinary NCC. We developed highly sensitive enzyme-linked immunosorbent assays (ELISAs) for urinary total NCC (tNCC) and its active form, phosphorylated NCC (pNCC). We first measured the excretion of tNCC and pT55-NCC in urinary exosomes in pseudohypoaldosteronism type II (PHAII) patients since PHAII is caused by NCC activation. Highly increased excretion of tNCC and pNCC was observed in PHAII patients. In contrast, the levels of tNCC and pNCC in the urine of patients with Gitelman's syndrome were not detectable or very low, indicating that both assays could specifically detect the changes in urinary NCC excretion caused by the changes of NCC activity in the kidney. Then, to test whether these assays could be feasible for a more general patient population, we measured tNCC and pNCC in the urine of outpatients with different clinical backgrounds. Although urinary protein levels >30 mg/dl interfered with our ELISA, we could measure urinary pNCC in all patients without proteinuria. Thus we established highly sensitive and quantitative assays for urinary NCC, which could be valuable tools for estimating NCC activity in vivo.

Na–K–Cl cotransporter isoform 1 (NKCC1) is involved in the regulation of vascular smooth muscle cell contraction. Recently, the with-no-lysine kinase (WNK)–STE20/SPS1-related proline/alanine-rich kinase (SPAK)–NKCC1 phosphorylation cascade in vascular smooth muscle cells was found to be important in the regulation of vascular tone. In this study, we investigated whether the WNK–SPAK–NKCC1 cascade in mouse aortic tissue is regulated by dietary salt intake and the mechanisms responsible. Phosphorylation of SPAK and NKCC1 was significantly reduced in the aorta in high-salt–fed mice and was increased in the aorta in low-salt–fed mice, indicating that the WNK–SPAK–NKCC1 phosphorylation cascade in the aorta was indeed regulated by dietary salt intake. Acute and chronic angiotensin II infusion increased phosphorylation of SPAK and NKCC1 in the mouse aorta. In addition, valsartan, an antagonist of angiotensin II type 1 receptor, inhibited low-salt diet–induced phosphorylation of SPAK and NKCC1, demonstrating that angiotensin II activates the WNK–SPAK–NKCC1 phosphorylation cascade through the angiotensin II type 1 receptor. However, a low-salt diet and angiotensin II together did not increase phosphorylation of SPAK and NKCC1 in the aorta in WNK3 knockout mice, indicating that activation of the WNK–SPAK–NKCC1 phosphorylation cascade induced by a low-salt diet and angiotensin II is dependent on WNK3. Indeed, angiotensin II–induced increases in blood pressure were diminished in WNK3 knockout mice. In addition, decreased response to angiotensin II in the mesenteric arteries was observed in WNK3 knockout mice. Our data also clarified a novel mechanism for regulation of vascular tonus by angiotensin II. Inhibition of this cascade could, therefore, be a novel therapeutic target in hypertension.

Chronic kidney disease is a risk factor for cardiovascular mortality and morbidity of cardiovascular events (CVEs). We obtained baseline data regarding blood biochemistry, ankle-brachial index (ABI), brachial-ankle pulse wave velocity (baPWV) and echocardiographic parameters from 300 patients on hemodialysis in 2005. We also measured ABI and baPWV annually from June 2005 until June 2012 and calculated rates of changes in ABI and baPWV to identify factors associated with CVEs. Seventy-three patients died of cardiovascular disease and 199 CVEs occurred in 164 patients during the study period. Cardiac, cerebrovascular and peripheral artery disease (PAD) events occurred in 124, 43 and 32 patients, respectively, and 30 patients had more than two types of CVEs. Analysis using the Cox proportional hazards model showed that a higher rate of decline in ABI (hazard ratio [HR], 4.034; P < 0.001) was the most significant risk factor for decreased patient survival. Multivariate Cox analysis revealed that a higher rate of ABI decline (HR, 2.342; P < 0.001) was a significant risk factor for cardiac events, and that a lower baseline ABI was a risk factor for cerebrovascular (HR, 0.793; P = 0.03) and PAD (HR, 0.595; P < 0.0001) events. Our findings suggested that the rate of a decline in ABI and the baseline ABI value are potent correlation factors for survival and CVE morbidity among patients on hemodialysis in Japan.

Background Aquaporin-5 (AQP5) is a member of the water channel protein family. Although AQP5 was shown to be present in sweat glands, the presence or absence of regulated intracellular translocation of AQP5 in sweat glands remained to be determined. Objective We investigated whether AQP5 in sweat glands translocated during sweating, and also sought to determine the intracellular signal that triggers this translocation. Methods Immunofluorescent analyses of AQP5 in mouse and human sweat glands were performed. Madin-Darby Canine kidney (MDCK) cell lines stably expressing human AQP5 were generated, and the regulated translocation of AQP5 in the polarized cells was assessed by immunofluorescent analysis and biotinylation assays. Results AQP5 showed rapid translocation to the apical membranes during sweating. In human eccrine sweat glands, immunoreactive AQP5 was detected in the apical membranes and the intercellular canaliculi of secretory coils, and in the basolateral membranes of the clear cells. Treatment of human AQP5-expressing MDCK cells with calcium ionophore A23187 resulted in a twofold increase of AQP5 in the apical membranes within 5 min. Conclusion The regulated AQP5 translocation may contribute to sweat secretion by increasing the water permeability of apical plasma membranes of sweat glands.

Summary Mutations in WNK kinases cause the human hypertensive disease pseudohypoaldosteronism type II (PHAII), but the regulatory mechanisms of the WNK kinases are not well understood. Mutations in kelch-like 3 ( KLHL3 ) and Cullin3 were also recently identified as causing PHAII. Therefore, new insights into the mechanisms of human hypertension can be gained by determining how these components interact and how they are involved in the pathogenesis of PHAII. Here, we found that KLHL3 interacted with Cullin3 and WNK4, induced WNK4 ubiquitination, and reduced the WNK4 protein level. The reduced interaction of KLHL3 and WNK4 by PHAII-causing mutations in either protein reduced the ubiquitination of WNK4, resulting in an increased level of WNK4 protein. Transgenic mice overexpressing WNK4 showed PHAII phenotypes, and WNK4 protein was indeed increased in Wnk4 D561A/+ PHAII model mice. Thus, WNK4 is a target for KLHL3-mediated ubiquitination, and the impaired ubiquitination of WNK4 is a common mechanism of human hereditary hypertension.

Acetylated wood meals of Sugi (Cryptomeria japonica D.Don) wood were prepared by mechanochemical processing using a high-speed vibration rod mill. Weight percent gain (WPG) of the acetylated wood meals ranged from 7.0 to 35.5 %. Wood–plastic composites (WPCs) containing 50 % acetylated woods were produced by an injection molding technique. The polymer matrix used was polypropylene homopolymer. Maleic anhydride-grafted polypropylene (MAPP) was also used as a compatibilizing agent. The mechanical properties of WPCs in bending and tensile tests were independent of WPG of acetylated wood meals, and the test values for WPCs containing acetylated wood meals were lower than that of unmodified wood meal. The use of MAPP increased bending and tensile strength, but no effect on bending modulus was found. An increase in WPG significantly decreased water absorbability and thickness swelling of WPCs as measured by dimensional stability tests. These results demonstrated that mechanochemical processing is a promising technique for preparing WPC material with improved dimensional stability. The future challenge is to inhibit the decreases in mechanical properties of WPCs containing acetylated wood meals.

Wood meals of Sugi (Cryptomeria japonica D.Don) passing 2.0 mm and retained on 1.0 mm mesh screens were milled along with acetic anhydride (AA) and pyridine as a catalyst in a high-speed vibration rod mill at ambient temperature. The weight percent gain (WPG) of the chemically modified wood was calculated based on the yield after washing with deionized water. The effects of amounts of AA and catalyst added, pulverization time, and saponification of the acetylated wood on WPG were examined. In addition, FT-IR analysis, and water vapor adsorption and desorption tests were performed as functions of the WPG. Increases in WPG, the acetyl contents of the acetylated wood after saponification, changes in the FT-IR spectra after pulverization, and the water vapor sorption isotherms showed that the one-step acetylation systematically modified the hydroxyl groups of the wood into acetyl groups. Up to 38 % WPG was obtained at 100 phr AA and 15 phr catalyst, and 120 min pulverization. Pulverization time and the amounts of AA and catalyst added to the wood meals could be adjusted to obtain acetylated wood meal with the desired WPG. These demonstrated that the mechanochemical acetylation is a method to prepare acetylated wood meals with high WPG at less reaction time and required AA addition.

Anti-centromere antibody (ACA), a typical autoantibody of systemic sclerosis, is also detected in primary biliary cirrhosis (PBC). However, its pathogenic role is not fully understood. The aim of this study was to determine the association between ACA and kidney function in PBC.A cohort of 37 patients diagnosed as having PBC from July 2001 to November 2011 at Yokosuka Kyosai Hospital was retrospectively analyzed for a follow-up period of 12 months. The annual rate of estimated glomerular filtration rate (eGFR) decline within 1 year after the diagnosis was evaluated. The factors associated with eGFR decline were evaluated by linear regression analysis and logistic regression analysis.Overall, 37 PBC patients were included, of whom 12 (32%) had ACA. The patients with ACA had a lower eGFR (65.9 ± 19.9 vs. 80.3 ± 12.1 mL/min/1.73 m(2), P = 0.01), a higher likelihood of chronic kidney disease (CKD) (58 vs. 4%, P = 0.0005), and a higher rate of annual eGFR decline (-4.3 ± 5.1 vs. 0.2 ± 4.6 mL/min/year, P = 0.01) than those without ACA. Univariate regression analysis and multivariate regression analysis adjusted for potential cofounders including age, eGFR, sex, diabetes mellitus, and hypertension showed that ACA was associated with eGFR decline (P = 0.011 and 0.017, respectively). Multivariate logistic regression analysis adjusted for these cofounders showed that ACA was associated with eGFR decline less than -4 mL/min/year (odds ratio 7.21, 95% confidence interval 0.93-56.1, P = 0.059).ACA is an independent risk factor for CKD in PBC. Evaluation of ACA and kidney function is necessary to prevent CKD progression in PBC patients.

Familial form of nephrogenic diabetes insipidus (NDI) is a rare hereditary disease caused by arginine vasopressin type 2 receptor (AVPR2) or water channel aquaporin 2 (AQP2) gene mutations. It is speculated that 90% of NDI families carry disease-causing mutations in AVPR2 and 10% carry the mutations in AQP2; however, these percentages have not been supported by actual data. It is also unknown whether these percentages vary in different ethnic groups.Gene mutation analyses were performed for 78 Japanese NDI families. All exons and intron-exon boundaries of the AVPR2 and AQP2 genes were directly sequenced.A total of 62 families (79%) carried disease-causing mutations in AVPR2, while nine families (12%) carried mutations in AQP2. We identified 22 novel putatively disease-causing mutations (19 in AVPR2 and 3 in AQP2). Regarding AVPR2, 52 disease-causing mutations were identified. Among them, missense mutations were most common (54%), followed by deletion mutations. In the 64 women who had monoallelic disease-causing AVPR2 mutations, 16 (25%) had NDI symptoms, including 4 complete NDI subjects. Regarding AQP2, 9 disease-causing mutations were identified in nine families. Two missense mutations and one deletion mutation showed a recessive inheritance, while one missense mutation and five small deletion mutations in the C-terminus of AQP2 showed a dominant inheritance.Most Japanese NDI families carry disease-causing mutations in AVPR2 and 12% carry mutations in AQP2. A total of 22 novel putatively disease-causing mutations were identified. The relatively high occurrence of symptomatic carriers of AVPR2 mutations needs attention.

Chronic kidney disease (CKD) increases the risk of developing cardiovascular diseases such as heart failure (HF) and ischemic heart disease (IHD). The characteristics of patients with CKD complicated with HF at the time of starting hemodialysis have not yet been evaluated. We enrolled 347 patients in this study and compared gender, age, body mass index, laboratory data, causative disease, complications, and echocardiographic findings between groups with (n = 105) and without (n = 242) HF. Type II diabetic nephropathy and estimated glomerular filtration rate (eGFR; mL/min/1.73 m2) were the independent factors for HF (OR: 3.004, 95% CI: 1.754 to 5.146 and OR: 1.215, 95% CI: 1.101 to 1.330, [per 1 mL/min/1.73 m2 increase], respectively). The higher GFR appeared to be not a risk factor for HF, probably because the HF group included patients who required periodic dialysis to prevent fatal HF, even if their renal function was not extremely deteriorated. The prevalence of hypertension, IHD and values of body mass index, triglycerides, and LDL-cholesterol did not differ between these two groups. Echocardiographic data showed that left ventricular mass index was an independent risk factor for HF (OR: 1.006, 95% CI: 1.001 to 1.012, per 1 g/m2 increase) and more than half of the patients appeared to have left ventricular diastolic dysfunction. Our findings suggest that not only CKD, but also type II DM, is a potent risk for left ventricular dysfunction, which causes HF and IHD in pre-dialysis patients with CKD.

Na-Cl cotransporter (NCC) is phosphorylated in its amino terminus based on salt intake under the regulation of the WNK-OSR1/SPAK kinase cascade. We have observed that total protein abundance of NCC and its apical membrane expression varies in the kidney based on the phosphorylation status. To clarify the mechanism, we examined NCC ubiquitination status in mice fed low, normal and high salt diets, as well as in a model mouse of pseudohypoaldosteronism type II (PHAII) where NCC phosphorylation is constitutively elevated. Low-salt diet decreased NCC ubiquitination, while high-salt diet increased NCC ubiquitination in the kidney, and this was inversely correlated with total and phosphorylated NCC abundance. In the PHAII model, the ubiquitination of NCC in kidney was also lower when compared to that in wild-type littermates. To evaluate the relationship between phosphorylation and ubiquitination of NCC, we expressed wild-type, phospho-deficient and -mimicking NCC in COS7 cells, and the ubiquitination of immunoprecipitated total and biotinylated surface NCC was evaluated. NCC ubiquitination was increased in the phospho-deficient NCC and decreased in phospho-mimicking NCC in both total and surface NCC. Thus, we demonstrated that NCC phosphorylation decreased NCC ubiquitination, which may contribute to the increase of NCC abundance mostly on plasma membranes.

Cause-and-effect associations between sevelamer hydrochloride (HCl) and mortality have yet to be clarified. The effects of sevelamer HCl on mortality, lipid abnormality and arterial stiffness were examined in patients with chronic kidney disease stage 5D.The effects of sevelamer HCl were studied by a single-center cohort study that was conducted from January 1, 2005 to December 31, 2008 (n = 483). By the end of the study, 172 patients (Sevelamer group) had succeeded in continuing sevelamer HCl for6 months (median 37 months), and 300 patients (Control group) had received calcium carbonate (n = 264) or no phosphate binder (n = 36). The mortality and other outcomes were compared between these two groups after matching by a propensity score calculated using age, gender, diabetes prevalence, and dialysis vintage.All-cause [hazard ratio (HR) 0.4, P = 0.02] and cardiovascular (CV)-cause [HR 0.29, P = 0.03] cumulative mortality were significantly lower in the matched Sevelamer group than in the matched Control group. The matched Sevelamer group showed increased high-density lipoprotein cholesterol (P = 0.003) and no change in pulse wave velocity (PWV) and ankle-brachial index (ABI), whereas the matched Control group showed increased serum low-density lipoprotein (LDL) cholesterol (P = 0.003), increased PWV (P = 0.03), and decreased ABI (P = 0.0009). Change in serum LDL cholesterol level correlated inversely with sevelamer HCl dosage (P = 0.02).Reduced mortality in patients with sevelamer HCl may, at least in part, be explained by an improvement in dyslipidemia and arterial stiffness by sevelamer HCl.

We found that a mechanism of hypertension in pseudohypoaldosteronism type II (PHAII) caused by a WNK4 missense mutation (D561A) was activation of the WNK-OSR1/SPAK-NCC signal cascade. However, the pathogenic effect of intronic deletions in WNK1 genes also observed in PHAII patients remains unclear. To understand the pathophysiological roles of WNK1 in vivo, WNK1(+/-)mice have been analyzed, because homozygous WNK1 knockout is embryonic lethal. Although WNK1(+/-) mice have been reported to have hypotension, detailed analyses of the WNK signal cascade in the kidney and other organs of WNK1(+/-) mice have not been performed.We assess the effect of heterozygous deletion of WNK1 on the WNK-OSR1/SPAK-NCC/NKCC1/NKCC2 signal cascade in the kidney and blood vessels.Contrary to the previous report, the blood pressure of WNK1(+/-) mice was not decreased, even under a low-salt diet. Under a WNK4(D561A/+) background, the heterozygous deletion of the WNK1 gene did not reduce the high blood pressure either. We then evaluated the phosphorylation status of OSR1, SPAK, NCC, NKCC1, and NKCC2 in the kidney, but no significant decrease in the phosphorylation was observed in WNK1(+/-) mice or WNK1(+/-)WNK4(D561A/+) mice. In contrast, a significant decrease in NKCC1 phosphorylation in the aorta and a decreased pressure-induced myogenic response in the mesenteric arteries were observed in WNK1(+/-) mice.The contribution of WNK1 to total WNK kinase activity in the kidney may be small, but that WNK1 may play a substantial role in the regulation of blood pressure in the arteries.

Two patients with anti-centromere antibody (ACA), hypertensive emergency, and acute renal failure, mimicking scleroderma renal crisis, without Raynaud's phenomenon and typical skin manifestations of systemic sclerosis (SSc), are reported. A review of 26 ACA-positive patients between March 2003 and March 2011 in Yokosuka Kyosai Hospital identified four additional patients with similar manifestations. All patients were Japanese women between 41 and 84 years of age at presentation. Human leukocyte antigen (HLA) genotyping tests revealed the absence of the HLA-DQB1*0501 and DRB1*0101 alleles, which are associated with disease susceptibility to ACA-positive SSc among Japanese. These subjects' manifestations may represent a novel entity.

Electrolyte abnormalities, particularly dysnatremia, are independent predictors of adverse outcome in individuals with and without renal failure. However, the association of serum chloride level (Cl−) with mortality or risk of cardiovascular (CV) events in chronic kidney disease (CKD) remains unclear. This prospective cohort study included 923 pre-dialysis CKD G2–G5 patients among the participants of the CKD Research of Outcomes in Treatment and Epidemiology (CKD-ROUTE) study, who newly visited 16 nephrology centers. The primary outcome was a composite of overall death and CV events, and the secondary outcome was overall death. Data were analyzed using the Cox hazards model with adjustment for potential confounders. Median Cl− was 106.0 mEq/L at enrollment [quartile (Q) 1: ≤103.9, n = 207; Q2: 104.0–105.9, n = 207; Q3: 106.0–108.0, n = 289; Q4: ≥108.1, n = 220]. During a median follow-up of 33 months, there were 98 CV events, 66 deaths, and 154 composite outcomes. The hazard ratio (HR) for the composite outcome was higher for Q1 than Q3 [HR 1.72; 95 % confidence interval (CI) 1.08–2.72; P = 0.022]. As a continuous variable in a subset of patients whose Cl− was ≤106.0 mEq/L, higher Cl− was associated with lower risk of the composite outcome (HR 0.93; 95 % CI 0.87–0.99; P = 0.023). HR for all-cause mortality was also higher for Q1 than Q3 (HR 2.48; 95 % CI 1.22–5.03; P = 0.012). Low Cl− was associated with increased mortality and risk of CV events in pre-dialysis CKD patients. Cl− may be an additional prognostic indicator in CKD.

Urinary excretion of aquaporin 2 (AQP2) is a useful marker of kidney collecting duct function. A specific and convenient method to measure AQP2 in human urine would help to treat water balance disorders. It is unknown whether urinary excretion of AQP2 shows any daily variance.A sandwich enzyme-linked immunosorbent assay (ELISA) method for AQP2 was established using two different kinds of antibodies, and its sensitivity and specificity were examined. Daily variance of urinary excretion of AQP2 and responses to acute water load were examined.The established ELISA specifically detected urine AQP2 with high sensitivity (detected as low as 0.34 pmol/mL). Urinary excretion of AQP2 did not show daily variance between 9 a.m. and 9 p.m. in healthy subjects.The developed ELISA method using two different antibodies is convenient and highly sensitive, and could be useful in clinical practice. Urinary excretion of AQP2 is relatively constant from morning to night, and spot urine sampling at any time during this time period does not affect the results.

Na + -K + -2Cl − cotransporters (NKCCs), including NKCC1 and renal-specific NKCC2, and the Na + -Cl − cotransporter (NCC) play pivotal roles in the regulation of blood pressure (BP) and renal NaCl reabsorption. Oxidative stress-responsive kinase-1 (OSR1) is a known upstream regulator of N(K)CCs. We generated and analyzed global and kidney tubule-specific (KSP) OSR1 KO mice to elucidate the physiological role of OSR1 in vivo, particularly on BP and kidney function. Although global OSR1 −/− mice were embryonically lethal, OSR1 +/− mice had low BP associated with reduced phosphorylated (p) STE20 (sterile 20)/SPS1-related proline/alanine-rich kinase (SPAK) and p-NKCC1 abundance in aortic tissue and attenuated p-NKCC2 abundance with increased total and p-NCC expression in the kidney. KSP-OSR1 −/− mice had normal BP and hypercalciuria and maintained significant hypokalemia on a low-K + diet. KSP-OSR1 −/− mice exhibited impaired Na + reabsorption in the thick ascending loop on a low-Na + diet accompanied by remarkably decreased expression of p-NKCC2 and a blunted response to furosemide, an NKCC2 inhibitor. The expression of total SPAK and p-SPAK was significantly increased in parallel to that of total NCC and p-NCC despite unchanged total NKCC2 expression. These results suggest that, globally, OSR1 is involved in the regulation of BP and renal tubular Na + reabsorption mainly via the activation of NKCC1 and NKCC2. In the kidneys, NKCC2 but not NCC is the main target of OSR1 and the reduced p-NKCC2 in KSP-OSR1 −/− mice may lead to a Bartter-like syndrome.

Dendritic cells (DCs) have the ability to present antigen and play a critical role in the induction of the acquired immune response. Skin DCs uptake antigen and subsequently migrate to regional draining lymph nodes (LNs), where they activate naive T cells. Here we show that the water/glycerol channel protein aquaporin 7 (AQP7) is expressed on epidermal and dermal DCs and involved in the initiation of primary immune responses. AQP7-deficient DCs showed a decreased cellular uptake of low-molecular-mass compounds (fluorescein isothiocyanate and Lucifer yellow) and high-molecular-mass substances (ovalbumin and dextran), suggesting that AQP7 is involved in antigen uptake. AQP7-deficient DCs also exhibited reduced chemokine-dependent cell migration in comparison to wild-type DCs. Consistent with these in vitro results, AQP7-deficient mice demonstrated a reduced accumulation of antigen-retaining DCs in the LNs after antigen application to the skin, which could be attributed to decreased antigen uptake and migration. Coincidentally, AQP7-deficient mice had impaired antigen-induced sensitization in a contact hypersensitivity model. These observations suggested that AQP7 in skin DCs is primarily involved in antigen uptake and in the subsequent migration of DCs and is responsible for antigen presentation and the promotion of downstream immune responses.

We reported that nephrin is phosphorylated at Y1204 and Y1228 under normal conditions and that the phosphorylation is decreased in puromycin nephrosis and in human minimal change nephrosis. These results indicate that the phosphorylation of nephrin is important for maintaining normal podocyte function. However, little is known about the regulation of nephrin phosphorylation. Here, we investigated whether glucocorticoid, a drug used to treat glomerular diseases with proteinuria, might affect the phosphorylation of nephrin. Human cultured podocytes transiently expressing human nephrin were treated with dexamethasone (Dex), and the phosphorylation of nephrin was determined by immunoblot with the anti-pY1228 antibody. Dex treatment for 24 h increased the phosphorylation of nephrin; this increased phosphorylation was inhibited by the glucocorticoid receptor antagonist but not by the mineral corticoid receptor antagonist. A shorter incubation time (30 min) did not increase the phosphorylation, and actinomycin D and cycloheximide treatments abolished the increased phosphorylation. The activation of Src-family kinases was correlated with nephrin phosphorylation, both of which were abolished by small interfering RNA (siRNA) treatment for serum/glucocorticoid-induced kinase 1 (SGK1). These results clarify a novel action of glucocorticoid on nephrin phosphorylation through SGK1. Glucocorticoid treatment for human glomerulonephritis may exert its function by regulating the phosphorylation of nephrin.