Muscle wasting or sarcopenia contributes to morbidity and mortality in patients with cancer, renal failure, or heart failure, and in elderly individuals. Na+-K+-2Cl− cotransporter 1 (NKCC1) is highly expressed in mammalian skeletal muscle, where it contributes to the generation of membrane ion currents and potential. However, the physiologic function of NKCC1 in myogenesis is unclear. We investigated this issue using the NKCC1 inhibitors bumetanide and furosemide, which are commonly used loop diuretics. NKCC1 protein levels increased during C2C12 murine skeletal myoblast differentiation, similarly to those of the myogenic markers myogenin and myosin heavy chain (MHC). NKCC1 inhibitors markedly suppressed myoblast fusion into myotubes and the expression of myogenin and MHC. Furthermore, phosphorylated and total NKCC1 levels were elevated in mouse skeletal muscles after 6 weeks’ voluntary wheel running. Immunofluorescence analyses of myofiber cross-sections revealed more large myofibers after exercise, but this was impaired by daily intraperitoneal bumetanide injections (0.2 or 10 mg/kg/day). NKCC1 plays an essential role in myogenesis and exercise-induced skeletal muscle hypertrophy, and sarcopenia in patients with renal or heart failure may be attributable to treatment with loop diuretics.

Mutations in the with-no-lysine kinase 1 (WNK1), WNK4, kelch-like 3 (KLHL3), and cullin3 (CUL3) genes are known to cause the hereditary disease pseudohypoaldosteronism type II (PHAII). It was recently demonstrated that this results from the defective degradation of WNK1 and WNK4 by the KLHL3/CUL3 ubiquitin ligase complex. However, the other physiological in vivo roles of KLHL3 remain unclear. Therefore, here we generated KLHL3 Ϫ/Ϫ mice that expressed ␤-galactosidase (␤-Gal) under the control of the endogenous KLHL3 promoter. Immunoblots of ␤-Gal and LacZ staining revealed that KLHL3 was expressed in some organs, such as brain. However, the expression levels of WNK kinases were not increased in any of these organs other than the kidney, where WNK1 and WNK4 increased in KLHL3 Ϫ/Ϫ mice but not in KLHL3 ϩ/Ϫ mice. KLHL3 Ϫ/Ϫ mice also showed PHAII-like phenotypes, whereas KLHL3 ϩ/Ϫ mice did not. This clearly demonstrates that the heterozygous deletion of KLHL3 was not sufficient to cause PHAII, indicating that autosomal dominant type PHAII is caused by the dominant negative effect of mutant KLHL3. We further demonstrated that the dimerization of KLHL3 can explain this dominant negative effect. These findings could help us to further understand the physiological roles of KLHL3 and the pathophysiology of PHAII caused by mutant KLHL3.KEYWORDS kelch-like 3 (KLHL3), distal convoluted tubule, hypertension, kidney, NaCl cotransporter, with-no-lysine kinase (WNK) P seudohypoaldosteronism type II (PHAII) is a hereditary disease that is characterized by salt-sensitive hypertension, hyperkalemia, metabolic acidosis, and thiazide sensitivity (1). Mutations in the with-no-lysine kinase 1 (WNK1) and WNK4 genes are known to cause PHAII (2). Furthermore, it has generally been considered that overactivation of the thiazide-sensitive Na-Cl cotransporter (NCC) is the main cause of PHAII (3).Many studies have demonstrated that WNK kinases are at the top of the signaling cascade, along with oxidative stress-responsive gene 1 (OSR1), Ste20-related prolinealanine-rich kinase (SPAK), and the solute carrier family 12a (SLC12a) transporter family, which includes the NCC and Na-K-Cl cotransporter (NKCC). WNK phosphorylates and activates OSR1/SPAK, which in turn phosphorylate and activate the SLC12a transporters (4-6). The regulation of NCC by WNK-OSR1/SPAK signaling was confirmed in vivo using various genetically engineered mouse models (7-14) and overactivation of this WNK-OSR1/SPAK-NCC phosphorylation signal in the kidney causes PHAII (5, 6, 15, 16).

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.

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.

BackgroundHyponatremia is associated with increased mortality in chronic kidney disease with and without end-stage renal disease (ESRD). Increasing evidence suggests that hyponatremia is not only a marker of severe underlying disease, but also a direct contributor to mortality. However, specific pathogenesis or diseases contributing to mortality in the hyponatremic population are unknown. This study aimed to clarify the relationship between serum sodium level (sNa) and infection risk in ESRD patients.MethodsThis observational cohort study included 332 patients on maintenance hemodialysis in our dialysis unit in May 2009. The mean of 3 monthly measurements of glucose-corrected sNa before each dialysis session in May, June, and July 2009 was applied as baseline sNa. The primary endpoint was first infection-related hospitalization (IRH), and the secondary endpoint was death of any cause. Data were analyzed using Cox hazards modeling, adjusted for baseline demographics and characteristics, or laboratory data. Patients were followed until transfer, kidney transplantation, death, or study end on January 31, 2013.ResultsMean sNa was 138.9 mEq/L (1st tertile: <138.0, n = 104; 2nd tertile: 138.0–140.0, n = 116; 3rd tertile: >140.0, n = 112). During 39.5 months’ mean follow-up, 57 patients experienced IRH (56.4/1,000 patient-years overall; 89.7/1,000 in 1st tertile; 57.9/1,000 in 2nd tertile; 28.0/1,000 in 3rd tertile), and 68 patients died. The hazard ratio (HR) for IRH was higher for the 1st and 2nd tertiles than the 3rd tertile (unadjusted HR, 3.20; 95% confidence interval (CI), 1.54–6.64; p = 0.002; adjusted HR, 2.36; 95% CI, 1.10–5.04; p = 0.027; and unadjusted HR, 2.07; 95% CI, 0.98–4.40; p = 0.058; adjusted HR, 2.11; 95% CI, 0.99–4.51; p = 0.054 respectively). In a continuous model, higher sNa was associated with lower risk of IRH (adjusted HR, 0.90; 95% CI, 0.81–0.99; p = 0.040), and lower all-cause mortality (adjusted HR, 0.91; 95% CI, 0.83–1.00; p = 0.049).ConclusionsLower sNa is an independent predictor of higher risk for infection-related hospitalization in maintenance hemodialysis patients. Infectious disease may partially account for the increased mortality observed in the hyponatremic population with ESRD.