Search

Objective Metformin is an antidiabetic drug that is widely used to treat patients with diabetes mellitus. Recent studies have reported that treatment with metformin not only improved blood glucose levels but also reduced blood pressure. However, it remains unclear how metformin reduces blood pressure. We hypothesized that metformin affects sodium reabsorption in the kidneys. Methods Urinary sodium excretion and expression of renal sodium transporters were examined in 8-week-old male C57BL/6 mice with acute and chronic treatment of metformin. In addition, we examined metformin effects using ex vivo preparations of mice kidney slices. Results In this study, we demonstrated that metformin increased urinary sodium excretion by reducing phosphorylation of the thiazide-sensitive Na-Cl cotransporter (NCC) in acute and chronic metformin administration. We also confirmed reduction of phosphorylated NCC in an ex vivo study. The activity of other renal sodium transporters, such as NKCC2, ENaC, and NHE3 did not show significant changes. WNK-OSR1/SPAK kinase signals were not involved in this inactivation effect of metformin on NCC. Conclusion Metformin increased urinary sodium excretion by reducing phosphorylation of NCC, suggesting its role in improving hypertension. [ABSTRACT FROM AUTHOR]

Abstract: 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 5min. Conclusion: The regulated AQP5 translocation may contribute to sweat secretion by increasing the water permeability of apical plasma membranes of sweat glands. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Summary: WNK1 and WNK4 mutations have been reported to cause pseudohypoaldosteronism type II (PHAII), an autosomal-dominant disorder characterized by hyperkalemia and hypertension. To elucidate the molecular pathophysiology of PHAII, we generated Wnk4D561A/+ knockin mice presenting the phenotypes of PHAII. The knockin mice showed increased apical expression of phosphorylated Na-Cl cotransporter (NCC) in the distal convoluted tubules. Increased phosphorylation of the kinases OSR1 and SPAK was also observed in the knockin mice. Apical localization of the ROMK potassium channel and transepithelial Cl− permeability in the cortical collecting ducts were not affected in the knockin mice, whereas activity of epithelial Na+ channels (ENaC) was increased. This increase, however, was not evident after hydrochlorothiazide treatment, suggesting that the regulation of ENaC was not a genetic but a secondary effect. Thus, the pathogenesis of PHAII caused by a missense mutation of WNK4 was identified to be increased function of NCC through activation of the OSR1/SPAK-NCC phosphorylation cascade. [Copyright &y& Elsevier]

Objective: To investigate the functional and morphologic role of Aquaporin 7 (AQP7) in testis and sperm. Design: Experimental laboratory study. Setting: University and research institute units. Animal(s): AQP7 knockout mice (C57BL/6J background). Intervention(s): None. Main Outcome Measure(s): Morphologic analysis of testis and epididymis, daily sperm production, sperm motility, in vitro fertilization. Result(s): There was no difference in the morphology of the testes and epididymis between AQP7 knockout and wild-type mice. The AQP7 knockout male mice and wild-type male mice had similar numbers of offspring. Analysis of the daily sperm production and motility of AQP7 knockout mice did not show any abnormalities. Similarly, the rate of in vitro fertilization using sperm from AQP7 knockout mice was not different from wild-type mice. Conclusion(s): Male AQP7 knockout mice were not sterile, and their sperm did not show any morphologic and functional abnormalities. [Copyright &y& Elsevier]

Abstract: The aquaporin7 (AQP7) water channel is known to be a member of the aquaglyceroporins, which allow the rapid transport of glycerol and water. AQP7 is abundantly present at the apical membrane of the proximal straight tubules in the kidney. In this paper, we review the physiological functions of AQP7 in the kidney. To investigate this, we generated AQP7 knockout mice. The water permeability of the proximal straight tubule brush border membrane measured by the stopped flow method was reduced in AQP7 knockout mice compared to wild-type mice (AQP7, 18.0±0.4×10−3 cm/s vs. wild-type, 20.0±0.3×10−3 cm/s). Although AQP7 solo knockout mice did not show a urinary concentrating defect, AQP1/AQP7 double knockout mice showed reduced urinary concentrating ability compared to AQP1 solo knockout mice, indicating that the contribution of AQP7 to water reabsorption in the proximal straight tubules is physiologically substantial. On the other hand, AQP7 knockout mice showed marked glycerol in their urine (AQP7, 1.7±0.34 mg/ml vs. wild-type, 0.005±0.002 mg/ml). This finding identified a novel pathway of glycerol reabsorption that occurs in the proximal straight tubules. In two mouse models of proximal straight tubule injury, the cisplatin-induced acute renal failure (ARF) model and the ischemic–reperfusion ARF model, an increase of urine glycerol was observed (pre-treatment, 0.007±0.005 mg/ml; cisplatin, 0.063±0.043 mg/ml; ischemia, 0.076±0.02 mg/ml), suggesting that urine glycerol could be used as a new biomarker for detecting proximal straight tubule injury. [Copyright &y& Elsevier]

Aquaporin-7 (AQP7) is a water/glycerol transporting protein expressed in adipocyte plasma membranes. We report here remarkable age-dependent hypertrophy in adipocytes in AQP7-deficient mice. Wild type and AQP7 null mice had similar growth at 0-16 weeks as assessed by body weight; however, by 16 weeks AQP7 null mice had 3.7-fold increased body fat mass. Adipocytes from AQP7 null mice of age 16 weeks were greatly enlarged (diameter 118 µm) compared with wild type mice (39 µm). Adipocytes from AQP7 null mice also accumulated excess glycerol (251 versus 86 nmol/mg of protein) and triglycerides (3.4 versus 1.7 µmol/mg of protein). In contrast, at age 4 weeks, adipocyte volume and body fat mass were comparable in wild type and AQP7 null mice. To investigate the mechanism(s) responsible for the progressive adipocyte hypertrophy, glycerol permeability and fat metabolism were studied in adipocytes isolated from the younger mice. Plasma membrane glycerol permeability measured by [14C]glycerol uptake was 3-fold reduced in AQP7-deficient adipocytes. However, adipocyte lipolysis, measured by free fatty acid release and hormone-sensitive lipase activity, and lipogenesis, measured by [14C]glucose incorporation into triglycerides, were not affected by AQP7 deletion. These data suggest that adipocyte hypertrophy in AQP7 deficiency results from defective glycerol exit and consequent accumulation of glycerol and triglycerides. Increasing AQP7 expression/function in adipocytes may reduce adipocyte volume and fat mass in obesity. [ABSTRACT FROM AUTHOR]

Chronic kidney disease (CKD) causes a progressive loss of muscle and bone mass, which frequently overlap with and affect clinical outcomes. However, the impact of sarcopenia, low bone mineral density (BMD; osteopenia or osteoporosis), and osteosarcopenia (sarcopenia and low BMD) on CKD progression is yet to be determined. We aimed to address these issues in patients with CKD without kidney replacement therapy (KRT). This prospective cohort study included 251 outpatients aged ≥65 years with CKD without KRT enrolled in our hospital between June 2016 and March 2017. Sarcopenia was defined according to the 2014 criteria of the Asian Working Group for Sarcopenia (AWGS), and low BMD was defined as a T-score of ≤−1.0. The patients were divided into four groups: normal (no sarcopenia/normal BMD), only low BMD (no sarcopenia/low BMD), only sarcopenia (sarcopenia/normal BMD), and osteosarcopenia (sarcopenia/low BMD). The primary outcome was a composite of all-cause deaths, initiating KRT, and admissions owing to major adverse cardiovascular and cerebrovascular events (MACEs). The secondary outcome was a kidney composite outcome that included a 30 % reduction in creatinine-based estimated glomerular filtration rate (eGFR) and initiating KRT. The outcome risk was determined using the Cox regression models adjusted for potential confounders. Median age (25th–75th percentile) and eGFR of the outpatients (35 % women) were 76 (69–81) years and 32.1 (20.8–41.7) ml/min/1.73 m2, respectively. During a median follow-up period of 5.2 years, there were 22 deaths, 117 30 % eGFR reductions, 48 KRTs, and 18 admissions owing to MACEs. The osteosarcopenia group rather than the only low BMD or only sarcopenia groups exhibited a higher risk of the primary (hazard ratio [HR]: 3.28, 95 % confidence interval [CI]: 1.52–7.08) and kidney composite (HR: 2.07, 95 % CI: 1.10–3.89) outcomes. Among the osteosarcopenia-related body compositions and physical functions, low handgrip strength (HGS) was strongly associated with a high risk of primary and kidney composite outcomes (HR: 2.44, 95 % CI: 1.46–4.08; HR: 1.48, 95 % CI: 0.97–2.24, respectively). The increase in HGS but not the body mass index, skeletal muscle mass index, or BMD was associated with lower risks of primary and kidney composite outcomes (HR: 0.93, 95 % CI: 0.89–0.98; HR: 0.96, 95 % CI: 0.92–0.99 per 1 kg, respectively). Osteosarcopenia was associated with poor survival and kidney outcomes in older patients with CKD. Low HGS, which is common in patients with osteosarcopenia and CKD, was associated with increased mortality risk and kidney function decline. These findings can help the risk prediction and pathogenesis of the kidney–bone–muscle axis and improving muscle strength can help mitigate CKD progression. • This study showed the effect of BMD, muscle mass, and physical functions on outcomes in older adults. • Osteosarcopenia was linked to risks of death, ESKD, and admissions owing to MACEs. • Low HGS common in osteosarcopenia was strongly related to mortality and CKD progression. • Integrating muscle and bone information helps the risk prediction in older CKD adults. • Improving muscle strength can help mitigate CKD progression. [ABSTRACT FROM AUTHOR]

Abstract: Recently, two novel mammalian aquaporins (AQPs), AQPs 11 and 12, have been identified and classified as members of a new AQP subfamily, the “subcellular AQPs”. In members of this subfamily one of the two asparagine–proline–alanine (NPA) motifs, which play a crucial role in selective water conduction, are not completely conserved. Mouse AQP11 (mAQP11) was expressed in Sf9 cells and purified using the detergent Fos-choline 10. The protein was reconstituted into liposomes, which were used for water conduction studies with a stopped-flow device. Single water permeability (pf) of AQP11 was measured to be 1.72±0.03×10−13 cm3/s, suggesting that other members of the subfamily with incompletely conserved NPA motifs may also function as water channels. [Copyright &y& Elsevier]

• This nationwide study investigated overall and site-specific mortality after fractures in hemodialysis patients and the general population. • ESKD patients on hemodialysis experienced a 4.8-fold higher mortality rate after overall fractures than the general population. • Mortality after upper arm fracture was markedly high in hemodialysis patients, oppositely to the lower risk in the general population. • Upper arm fracture was specifically associated with risk of vascular access failure in hemodialysis patients. • There is a need for clinical awareness of upper arm fracture as a fatal fracture in ESKD patients on hemodialysis. End-stage kidney disease (ESKD) is associated with increased risk of fracture and subsequent morbidity and mortality. However, fracture site-specific mortality in ESKD patients have yet to be elucidated in comparison with the general population. In this population-based cohort derived from the Diagnosis Procedure Combination database of Japan from 2012 to 2014, we included 9320 ESKD patients undergoing hemodialysis and 547,726 patients without ESKD who were hospitalized for five major fractures, including hip (proximal femur), spine, forearm, upper arm, and leg (distal femur and proximal tibia). Overall and site-specific risks of in-hospital death were determined by logistic regression models. The age- and sex-adjusted mortality rates were 4.91% (95% confidence interval [CI], 4.46–5.37) and 1.02% (95% CI, 0.99–1.06) in the hemodialysis and general population groups, respectively. The multivariate odds ratio (OR) of death in hemodialysis patients versus the general population was 2.48 (95% CI, 2.25–2.74) for overall fractures, and was particularly high for a subgroup of upper arm fracture (OR 4.82, 95% CI, 3.19–7.28). The site-specific odds of death (95% CI) among hip, spine, forearm, upper arm, and leg (reference) fractures were 1.77 (0.98–3.18), 1.48 (0.79–2.75), 0.19 (0.04–0.86), and 2.01 (1.01–4.01) in hemodialysis patients, and 1.28 (1.13–1.45), 1.00 (0.88–1.14), 0.13 (0.10–0.17), and 0.83 (0.70–0.97) in the general population, respectively. Hemodialysis patients experienced a 4.8-fold higher mortality rate after fractures than the general population. Mortality after upper arm fracture was specifically high in patients on hemodialysis, likely due to the involvement of vascular access located on the fractured arm. [ABSTRACT FROM AUTHOR]