Camk2n1 deficiency reduces the NaCl cotransporter activity through the CUL3/KLHL3/WNK4 complex in the kidney

Calcium/calmodulin dependent protein kinase II inhibitor 1 (Camk2n1) is closely associated with a peak logarithm of odds score in quantitative trait loci for systolic blood pressure. Increased Camk2n1 mRNA expression has been specifically observed in the kidneys of hypertension mouse models. However, the precise role of Camk2n1 in the kidney remains unclear. We generated Camk2n1-/- mice using the CRISPR/Cas9 system. Compared to controls, Camk2n1-/- mice exhibited consistently lower systolic blood pressure across all measured time points. Deletion of Camk2n1 resulted in decreased apical labeling of phosphorylated and total thiazide-sensitive NaCl cotransporter (NCC) in the distal convoluted tubule. NCC phosphorylation is regulated by activated SPAK/OSR1 kinases, which act downstream of With-No-lysine (K) kinase (WNK). In Camk2n1-/- mice, the elevated abundances of key components of the Cullin 3 (CUL3) RING ubiquitin ligase, including neddylated CUL3 and the adaptor Kelch-like protein 3, promoted proteasomal degradation of WNK4. In renal tissues, Camk2n1 deletion led to increased mRNA and protein levels of ubiquitin-like modifier-activating enzyme 3 (UBA3) and ubiquitin-conjugating enzyme E2 (UBE2M). Conversely, Camk2n1 overexpression in HEK293 cells resulted in decreased levels of UBA3 and UBE2M, along with reduced CUL3 neddylation. Treatment with MLN4924 effectively suppressed CUL3 hyperneddylation and restored WNK4 levels in the kidneys of Camk2n1-/- mice. In summary, Camk2n1 deletion lowers blood pressure, likely by promoting WNK4 degradation through dysregulated CUL3 RING ubiquitin ligase activity, which leads to decreased NCC activity.