Upregulation of renal Na-K-2Cl cotransporter 2 in obese diabetes mellitus via a vasopressin receptor 2-dependent pathway

Protein Quality Control of NKCC2 in Bartter Syndrome and Blood Pressure Regulation

Mutations in NKCC2 generate antenatal Bartter syndrome type 1 (type 1 BS), a life-threatening salt-losing nephropathy characterized by arterial hypotension, as well as electrolyte abnormalities. In contrast to the genetic inactivation of NKCC2, inappropriate increased NKCC2 activity has been associated with salt-sensitive hypertension. Given the importance of NKCC2 in salt-sensitive hypertension and the pathophysiology of prenatal BS, studying the molecular regulation of this Na-K-2Cl cotransporter has attracted great interest. Therefore, several studies have addressed various aspects of NKCC2 regulation, such as phosphorylation and post-Golgi trafficking. However, the regulation of this cotransporter at the pre-Golgi level remained unknown for years. Similar to several transmembrane proteins, export from the ER appears to be the rate-limiting step in the cotransporter's maturation and trafficking to the plasma membrane. The most compelling evidence comes from patients with type 5 BS, the most severe form of prenatal BS, in whom NKCC2 is not detectable in the apical membrane of thick ascending limb (TAL) cells due to ER retention and ER-associated degradation (ERAD) mechanisms. In addition, type 1 BS is one of the diseases linked to ERAD pathways. In recent years, several molecular determinants of NKCC2 export from the ER and protein quality control have been identified. The aim of this review is therefore to summarize recent data regarding the protein quality control of NKCC2 and to discuss their potential implications in BS and blood pressure regulation.

Natural phenylethanoid glycosides diuretics derived from Lagopsis supina: Biological activity, mechanism, molecular docking, and structure-activity relationship

Aquaporins (AQPs) and vasopressin type 2 receptor (V2R) play a crucial role in urine excretion and are widely used to explore novel diuretics. In this study, three phenylpropanoids including stachysoside A (L1), acteoside (L2), and glucopyranosyl (1 → 6) martynoside (L3) were isolated from Lagopsis supina (Steph. ex Willd.) lk. -Gal. ex Knorr. Their diuretic activity, mechanism, molecular docking, and structure-activity relationships were explored. The results suggest that L1, L2, and L3 exhibit acute (6 h) and prolonged (6 d) activities including increased urinary excretion volume, diuretic action, and diuretic activity, without affecting the urinary pH and minor altering the electrolyte balance in saline-loaded rats. Further, L1, L2, and L3 significantly reduced the levels of angiotensin II (Ang II), anti-diuretic hormone (ADH), and aldosterone (ALD), AQPs 1-4 and 7, and V2R, and remarkably elevated the atriopeptin (ANP) level. Besides, L1, L2, and L3 obviously suppressed mRNA and protein levels of AQPs 1-4 and 7, and V2R. The hypothetical binding modes of L1, L2, and L3 with these proteins were determined by molecular docking, and a tight structure-activity relationship was also proposed. Collectively, L1, L2, and L3 represent three natively novel phenylethanoid glycoside diuretics, which inhibit AQP and V2R-mediated molecular mechanisms. They are superior to furosemide as long-term diuretics.

Potential effect of tolvaptan on polycystic liver disease for patients with ADPKD meeting the Japanese criteria of tolvaptan use

Polycystic liver disease (PLD) is a common extrarenal complication of autosomal dominant polycystic kidney disease (ADPKD), which causes compression-related syndrome and ultimately leads to liver dysfunction. Tolvaptan, a V2 receptor antagonist, is widely used to protect kidney function in ADPKD but its effect on PLD remains unknown. An observational cohort study was conducted to evaluate tolvaptan’s effect on patients with PLD due to ADPKD. After screening 902 patients, we found the 107 ADPKD patients with PLD who met the criteria of tolvaptan use in Japan. Among them, tolvaptan was prescribed for 62 patients (tolvaptan group), while the other was defined as the non-tolvaptan group. Compared with the non-tolvaptan group, the tolvaptan group had larger height-adjusted total kidney volume (median 994(range 450–4152) mL/m, 513 (405–1928) mL/m, p = 0.01), lower albumin level (mean 3.9±SD 0.4 g/dL, 4.3±0.4g/dL, p<0.01), and higher serum creatinine level (1.2±0.4 mg/dL, 0.9±0.2 mg/dL, p<0.01). Although the median change in annual growth rate of total liver volume (TLV) was not statistically different between the tolvaptan group (-0.8 (-15.9, 16.7) %/year) and the non-tolvaptan group (1.7 (-15.6–18.7) %/year)(p = 0.52), 20 (43.5%) patients in the tolvaptan group experienced a decrease in the growth rate of TLV (responders). A multivariable logistic regression model adjusting for related variables showed that older age (odds ratio 1.15 [95% CI 1.01–1.32]) and a higher growth rate of TLV in the non-tolvaptan period (odds 1.45 95% CI 1.10–1.90) were significantly associated with responders. In conclusion, the change in annual growth rate of TLV in ADPKD patients taking tolvaptan was not statistically different compared with that in ADPKD patients without taking tolvaptan. However, tolvaptan may have the potential to suppress the growth rate of TLV in some PLD patients due to ADPKD, especially in older patients or those that are rapid progressors of PLD. Several limitations were included in this study, therefore well-designed prospective studies were required to confirm the effect of tolvaptan on PLD.

Renal NKCC2 Is Dual Regulated by the Synergy of 20-HETE and High-Fat Diet in CYP4F2 Transgenic Mice

INTRODUCTION

20-Hydroxyeicosatetraenoic acid (20-HETE) is the metabolite of cytochrome P450, which modulates blood pressure by inhibiting renal sodium transport. However, the molecular mechanisms underlying the role of 20-HETE in the development of obesity-related hypertension remain unclear, necessitating this study.

METHODS

Cytochrome P450 4F2 (CYP4F2) transgenic mice fed high-fat diet (HFD) were used as research animal models. The expression of renal ion transport molecules targeted by 20-HETE was evaluated by real-time PCR and Western blot (WB). The regulatory effect of 20-HETE and HFD on renal Na+-K+-2Cl- cotransporter, isoform 2 (NKCC2) was explored by immunoprecipitation, WB, and luciferase assay.

RESULTS

A 2-week HFD feeding dramatically decreased protein abundance but increased renal NKCC2 mRNA expression in CYP4F2 transgenic mice. The decrease in NKCC2 protein was demonstrated to be due to ubiquitination induced by the synergy between 20-HETE and HFD. The increased PPAR-γ protein in CYP4F2 transgenic mice fed HFD and the activation of rosiglitazone on the luciferase reporter construct of the NKCC2 promoter demonstrated that the increase in NKCC2 mRNA in CYP4F2 transgenic mice fed HFD was a consequence of elevated PPAR-γ protein induced by the synergy between 20-HETE and HFD.

CONCLUSIONS

Our data demonstrated that the synergy between 20-HETE and HFD could decrease NKCC2 protein via posttranslational ubiquitination, which was thought to be the main mechanism underlying the short-term effect in response to HFD and might be responsible for the adaptive modulation of renal NKCC2 to resist sodium retention. Moreover, the increased NKCC2 mRNA expression via PPAR-γ-induced transcriptional regulation was thought to be the main mechanism underlying the long-term effect in response to HFD and plays a pivotal role in the development of obesity-related hypertension.