Distal convoluted tubule-specific disruption of the COP9 signalosome but not its regulatory target Cullin 3 causes tubular injury.

Abstract

The disease Familial Hyperkalemic Hypertension (FHHt; also known as Gordon Syndrome) is caused by aberrant accumulation of WNK4 activating the NaCl cotransporter (NCC) in the distal convoluted tubule (DCT) of the kidney. Mutations in cullin 3 (CUL3) cause FHHt by disrupting interaction with the deneddylase COP9 signalosome (CSN). Deletion of Cul3 or Jab1 (the catalytically active CSN subunit) along the entire nephron causes a partial FHHt phenotype with activation of the WNK4-SPAK-NCC pathway. However, progressive kidney injury likely prevents hypertension, hyperkalemia, and hyperchloremic metabolic acidosis associated with FHHt. We hypothesized that DCT-specific deletion would more closely model the disease. We utilized Slc12a3-Cre-ERT2 mice to delete Cul3 (DCT-Cul3^-/-) or Jab1 (DCT-Jab1^-/-) only in DCT and examined the mice after short- and long-term deletion. Short-term, DCT-specific knockout of both Cul3 and Jab1 mice caused elevated WNK4, SPAK, and pNCC abundance. However, neither model demonstrated changes in plasma K⁺, Cl^-, or TCO₂, even though no injury was present. Long-term DCT-Jab1^-/- mice showed significantly lower NCC and parvalbumin abundance, and higher abundance of kidney injury molecule 1 (KIM-1), a marker of proximal tubule injury. No injury, or reduction in NCC or parvalbumin were observed in long-term DCT-Cul3^-/- mice. In summary, the prevention of injury outside the DCT did not lead to a complete FHHt phenotype despite activation of the WNK4-SPAK-NCC pathway, possibly due to insufficient NCC activation. Chronically, only DCT-Jab1^-/- mice developed tubule injury and atrophy of the DCT, suggesting a direct JAB1 effect or dysregulation of other cullins as mechanisms for injury.