Vers une meilleure compréhension de l’implication de WNK1, Cullin-3 et SPAK dans l’hypertension hyperkaliémique familiale

Abstract : Familial Hyperkalemic Hypertension (FHHt) is a rare form of hypertension associated with hyperkalemia and hyperchloremic metabolic acidosis. These disorders are all corrected by thiazide diuretics that inhibit the Na+-Cl- NCC cotransporter expressed in the distal nephron. The sensitivity of FHHt patients to thiazide diuretics strongly suggested that FHHt is caused by NCC activation. In 2001, gain-of function-mutations were identified in the genes encoding the serine-threonine kinases WNK1 and WNK4 [With No (K) lysine] in a subst of FHHt patients. In vitro studies demonstrate that WNK1 and WNK4 indirectly stimulate NCC, through the phosphorylation and activation of SPAK (Ste20 like Proline-Alanine rich Kinase). In vivo, SPAK activation plays a central role in the pathogenesis of FHHt caused by WNK4 mutations. However, the implication of SPAK has never been shown for the WNK1 mutations. Thus, we crossed WNK1+/FHHt mice, bearing the WNK1-FHHt mutation, with SPAK243A/243A mice bearing a mutation abolishing SPAK activation by the WNKs. All FHHt phenotypes observed in WNK1+/FHHt were corrected in WNK1+/FHHt:SPAK243A/243A mice demonstrating the central role of SPAK in FHHt caused by WNK1 mutations. In 2012, new mutations have been identified in CUL3 and KLHL3 genes. The products of these genes are both part of a ubiquitin ligase complex. As WNK1 and WNK4 mutations, these mutations lead to an increased expression of L-WNK1 and/or WNK4. Surprisingly, patients with CUL3 mutations display a more severe phenotype. Previous studies have suggested that CUL3 could be involved not only in the regulation of ion transport in the distal nephron but also in the regulation of vascular tone. To verify this hypothesis, we generated and compared two mouse models: pgk-Cul3Δ9 mouse model bearing, as patients, an ubiquitous Cul3 mutation, and sm22-Cul3Δ9 mouse model that express the Cul3 mutation only in vascular smooth muscle cells. Both models are hypertensive, but pgk-Cul3Δ9 mice display a more severe hypertension than sm22-Cul3Δ9 mice. It demonstrates that the hypertension caused by Cul3 mutations results from both renal and vascular disorders. Recently, new missense mutations have been identified in WNK1 acidic motif in a small number of FHHt patients. This acidic motif is necessary for the liaison to KLHL3 and therefore for WNK ubiquitination. Our study shows that, in vitro, these mutations lead to the accumulation of only one isoform of WNK1. In mice, the mutation of WNK1 acidic motif leads to an increased phosphorylation of SPAK and NCC. Therefore, it demonstrates the essential role of the acidic motif in the regulation of WNK1 abundance in vivo in the distal nephron. This work contributes to a better comprehension of the role played by SPAK, WNK1 and CUL3 in FHHt and more generally in the regulation of blood pressure and Na+/K+ homeostasis.
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Chloé Rafael. Vers une meilleure compréhension de l’implication de WNK1, Cullin-3 et SPAK dans l’hypertension hyperkaliémique familiale. Cardiologie et système cardiovasculaire. Université Sorbonne Paris Cité, 2017. Français. ⟨NNT : 2017USPCB068⟩. ⟨tel-02129289⟩

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