Constitutively Active SPAK Causes Hyperkalemia by Activating NCC and Remodeling Distal Tubules

Abstract

Aberrant activation of with no lysine (WNK) kinases causes familial hyperkalemic hypertension (FHHt). Thiazide diuretics treat the disease, fostering the view that hyperactivation of the thiazide-sensitive sodium-chloride cotransporter (NCC) in the distal convoluted tubule (DCT) is solely responsible. However, aberrant signaling in the aldosterone-sensitive distal nephron (ASDN) and inhibition of the potassium-excretory renal outer medullary potassium (ROMK) channel have also been implicated. To test these ideas, we introduced kinase-activating mutations after Lox-P sites in the mouse gene, which encodes the terminal kinase in the WNK signaling pathway, Ste20-related proline-alanine-rich kinase (SPAK). Renal expression of the constitutively active (CA)-SPAK mutant was specifically targeted to the early DCT using a DCT-driven Cre recombinase. CA-SPAK mice displayed thiazide-treatable hypertension and hyperkalemia, concurrent with NCC hyperphosphorylation. However, thiazide-mediated inhibition of NCC and consequent restoration of sodium excretion did not immediately restore urinary potassium excretion in CA-SPAK mice. Notably, CA-SPAK mice exhibited ASDN remodeling, involving a reduction in connecting tubule mass and attenuation of epithelial sodium channel (ENaC) and ROMK expression and apical localization. Blocking hyperactive NCC in the DCT gradually restored ASDN structure and ENaC and ROMK expression, concurrent with the restoration of urinary potassium excretion. These findings verify that NCC hyperactivity underlies FHHt but also reveal that NCC-dependent changes in the driving force for potassium secretion are not sufficient to explain hyperkalemia. Instead, a DCT-ASDN coupling process controls potassium balance in health and becomes aberrantly activated in FHHt.

Mutant Cullin 3 causes familial hyperkalemic hypertension via dominant effects

“…rothiazide in the Welling model (47), chronic remodeling effects of amiloride may be required to diminish antikaliuresis in CUL3-Het/Δ9 mice (note that, while blunted, amiloride still exerts a natriuretic effect in these mice). The precise mechanisms involved are beyond the scope of this study but will be the subject of future studies.…”

“…Emerging evidence supports a role for the DCT as the key renal sensor of plasma [K + ] (44), with increased NCC activity as plasma [K + ] drops serving to reduce kaliuresis, and vice versa (see above for discussion of the Na + delivery versus remodeling mechanisms of kaliuresis) (47). Redistribution of WNK1, WNK4, and SPAK to larger intracellular puncta has been reported in several mouse models with lower plasma [K + ], including SPAK KOs (42,51,52), and mice fed low K + diets (43,44,51).…”

Lovastatin attenuates hypertension induced by renal tubule‐specific knockout of ATP‐binding cassette transporter A1, by inhibiting epithelial sodium channels

“…Freshly isolated kidney cortex were minced and washed once with PBS and then homogenized using an Omni TH homogenizer (Warrenton, VA) with HEENG buffer (Grimm, Coleman, Delpire, & Welling, ) containing protease and phosphatase inhibitors (Cat. No., 1861280; Thermo Scientific).…”

DNPEP is not the only peptidase that produces SPAK fragments in kidney

“…In contrast, constitutively active SPAK mice show characteristics of Gordon's syndrome (Grimm et al. ). Similarly, WNK4 knockout mice exhibited a mild Gitelman‐like phenotype (Castañeda‐Bueno et al.…”