With-No-Lysine Kinase 1 (WNK1) Augments TRPV4 Function in the Aldosterone-Sensitive Distal Nephron

by Selleckchem | Oct 11 2023

Kidneys play a central role in regulation of potassium homeostasis and maintenance of plasma K+ levels within a narrow physiological range. With-no-lysine (WNK) kinases, specifically WNK1 and WNK4, have been recognized to regulate K+ balance, in part, by orchestrating maxi K+ channel (BK)-dependent K+ secretion in the aldosterone-sensitive distal nephron (ASDN), which includes the connecting tubule and collecting duct. We recently demonstrated that the Ca2+-permeable TRPV4 channel is essential for BK activation in the ASDN. Furthermore, high K+ diet increases TRPV4 activity and expression largely in an aldosterone-dependent manner. In the current study, we aimed to test whether WNK kinases contribute to regulation of TRPV4 activity and its stimulation by aldosterone. Systemic inhibition of WNK with WNK463 (1 mg/kgBW for 3 days) markedly decreased TRPV4-dependent Ca2+ influx in freshly isolated split-opened collecting ducts. Aldosterone greatly increased TRPV4 activity and expression in cultured mpkCCDc14 cells and this effect was abolished in the presence of WNK463. Selective inhibition of WNK1 with WNK-in-11 (400 nM, 24 h) recapitulated the effects of WNK463 on TRPV4-dependent Ca2+ influx. Interestingly, WNK-in-11 did not interfere with up-regulation of TRPV4 expression by aldosterone, but prevented translocation of the channel to the apical plasma membrane. Furthermore, co-expression of TRPV4 and WNK1 into Chinese hamster ovary (CHO) cells increased the macroscopic TRPV4-dependent cation currents. In contrast, over-expression of TRPV4 with a dominant negative WNK1 variant (K233M) decreased the whole-cell currents, suggesting both stimulatory and permissive roles of WNK1 in regulation of TRPV4 activity. Overall, we show that WNK1 is essential for setting functional TRPV4 expression in the ASDN at the baseline and in response to aldosterone. We propose that this new mechanism contributes to regulation of K+ secretion and, by extension, urinary K+ levels to maintain systemic potassium homeostasis.

Comments:

The kidneys are vital organs involved in the regulation of potassium levels in the body. They maintain plasma potassium (K+) within a narrow physiological range, and two specific enzymes called with-no-lysine (WNK) kinases, WNK1 and WNK4, have been identified as regulators of potassium balance. These kinases play a role in the activation of maxi K+ channels (BK) and subsequent potassium secretion in the aldosterone-sensitive distal nephron (ASDN), which consists of the connecting tubule and collecting duct.

Recent research has shown that the TRPV4 channel, which allows calcium ions to enter cells, is crucial for the activation of BK channels in the ASDN. Additionally, it has been observed that a high-potassium diet increases both the activity and expression of TRPV4, primarily in response to aldosterone.

The aim of the current study was to investigate the contribution of WNK kinases to the regulation of TRPV4 activity and its stimulation by aldosterone. To achieve this, a WNK inhibitor called WNK463 was administered systemically (1 mg/kgBW for 3 days), resulting in a significant decrease in TRPV4-mediated calcium influx in freshly isolated collecting ducts. In cultured mpkCCDc14 cells, which are commonly used to study the ASDN, aldosterone significantly increased TRPV4 activity and expression. However, in the presence of WNK463, this effect was abolished. Furthermore, selective inhibition of WNK1 using a specific inhibitor called WNK-in-11 (400 nM, 24 h) replicated the effects of WNK463 on TRPV4-mediated calcium influx. Interestingly, WNK-in-11 did not interfere with the up-regulation of TRPV4 expression by aldosterone but prevented the translocation of the channel to the apical plasma membrane.

In additional experiments, the co-expression of TRPV4 and WNK1 in Chinese hamster ovary (CHO) cells resulted in increased TRPV4-dependent cation currents. Conversely, over-expression of a dominant negative variant of WNK1 (K233M) along with TRPV4 decreased the whole-cell currents, suggesting that WNK1 has both stimulatory and permissive roles in the regulation of TRPV4 activity.

Overall, the findings of this study demonstrate that WNK1 is essential for the functional expression of TRPV4 in the ASDN, both at baseline and in response to aldosterone. This newly identified mechanism likely contributes to the regulation of potassium secretion and, consequently, the maintenance of urinary potassium levels to ensure systemic potassium homeostasis.