Kidney Week

Abstract: FR-OR064

A Pivotal Role of WNK1/OSR1 Pathway in Regulation of Renal Proximal Sodium Transport

Session Information

• Fluids and Electrolytes: New Insights on Balance
  October 26, 2018 | Location: 8, San Diego Convention Center
  Abstract Time: 05:42 PM - 05:54 PM

Category: Fluid and Electrolytes

• 901 Fluid and Electrolytes: Basic

Authors

• Nakamura, Motonobu, The University of Tokyo, Tokyo, Japan

Motonobu Nakamura, MD, PhD

• Horita, Shoko, The University of Tokyo, Tokyo, Japan

Shoko Horita,

• Satoh, Nobuhiko, The University of Tokyo, Tokyo, Japan

Nobuhiko Satoh,

• Seki, George, Yaizu City Hospital, Yaizu, Japan

George Seki,

• Mizuno, Tomohito, The University of Tokyo, Tokyo, Japan

Tomohito Mizuno,

• Tsukada, Hiroyuki, The University of Tokyo, Tokyo, Japan

Hiroyuki Tsukada,

• Sato, Yusuke, The University of Tokyo Hospital, Tokyo, Japan

Yusuke Sato,

• Kume, Haruki, The University of Tokyo Hospital, Tokyo, Japan

Haruki Kume,

• Nangaku, Masaomi, The University of Tokyo, Tokyo, Japan

Masaomi Nangaku,

• Suzuki, Masashi, Tokyo Gakugei University, Koganei, Tokyo, TOKYO, Japan

Masashi Suzuki,

Background

In renal proximal tubules (PTs) we and others have shown that insulin stimulates both apical Na⁺/H⁺ exchanger (NHE)3 and basolateral Na⁺/HCO₃^- co-transporter (NBCe1) via PI3K/Akt signaling. Pioglitazone (Pio) also stimulates both NHE3 and NBCe1 via non-genomic PPARg/ERK signaling (Cell Metab 2011). In human PTs, angiotensin (Ang)II stimulates both transporters via NO/ERK signaling (JASN 2014). However, the mechanism underlying this coordinate regulation in apical and basolateral PT sodium transport is poorly understood. In this study, we investigated the role of WNK1/OSR1 pathway in regulation of PT sodium transport.

Methods

By using a pH-sensitive dye BCECF we measured the basolateral NBCe1 activity and apical NHE3 activity in freshly-isolated rat PTs as well as human PTs, the latter obtained during surgery for renal cell carcinoma. We also measured the NBCe1 activity in rat PTs incubated overnight with siRNA against WNK1, WNK3, OSR1 or SPAK. Protein phosphorylation was analyzed by Western blotting in rat and human kidney cortex tissue.

Results

In freshly-isolated rat and human PTs, insulin and Pio markedly stimulated both NHE3 and NBCe1 activities, and an OSR1/SPAK inhibitor, Closantel (10mM) completely suppressed these stimulatory effects. Closantel also completely suppressed the AngII-stimulated NBCe1 and NHE3 activities in human PTs. Immunostaining analysis confirmed the expression of OSR1 protein in rat and human PTs. In rat and human kidney cortex, Closantel suppressed the insulin-induced OSR1/SPAK phosphorylation without affecting the Akt phosphorylation. Similarly, Closantel suppressed the OSR1/SPAK phosphorylation by Pio and AngII without affecting the ERK phosphorylation. In overnight incubated rat PTs, siRNA against WNK1 but not WNK3 abolished the stimulatory effects of Pio and insulin on NBCe1. Moreover, siRNA against OSR1 but not SPAK abolished the stimulatory effects of Pio and insulin.

Conclusion

These results indicate, for the first time to our knowledge, that diverse stimuli depending on the distinct signaling cascades converge into WNK1/OSR1 pathway, which may work as a master regulator of PT sodium transport and hence represent a novel therapeutic target in hypertension and/or volume expansion.

Funding

• Government Support - Non-U.S.