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Abstract: PO1090

Mechanistic Importance of Reduced KLHL3 and CUL3 Expression in CUL3-Δ9-Mediated Familial Hyperkalemic Hypertension

Session Information

Category: Fluid, Electrolyte, and Acid-Base Disorders

  • 901 Fluid, Electrolyte, and Acid-Base Disorders: Basic

Authors

  • Maeoka, Yujiro, Oregon Health & Science University, Portland, Oregon, United States
  • Ferdaus, Mohammed Zubaerul, Oregon Health & Science University, Portland, Oregon, United States
  • Sharma, Avika, Oregon Health & Science University, Portland, Oregon, United States
  • Cornelius, Ryan J., Oregon Health & Science University, Portland, Oregon, United States
  • Su, Xiao-Tong, Oregon Health & Science University, Portland, Oregon, United States
  • Robertson, Joshua A., Oregon Health & Science University, Portland, Oregon, United States
  • Gurley, Susan B., Oregon Health & Science University, Portland, Oregon, United States
  • Ellison, David H., Oregon Health & Science University, Portland, Oregon, United States
  • McCormick, James A., Oregon Health & Science University, Portland, Oregon, United States
Background

Mutations in the ubiquitin ligase scaffold protein Cullin 3 (CUL3) cause the disease familial hyperkalemic hypertension (FHHt). In the kidney, mutant CUL3 (CUL3-Δ9) cannot interact with COP9 signalosome subunit JAB1 that negatively regulates CUL3 activity. This leads to CUL3-Δ9 autodegradation, and increased abundance of With-No-Lysine [K] Kinase 4 (WNK4), which inappropriately activates the downstream kinase SPAK, which then phosphorylates and hyperactivates the Na+-Cl cotransporter (NCC). We showed lower that CUL3 alone does not increase WNK4, so the precise mechanism by which CUL3-Δ9 causes FHHt is unclear. We hypothesized CUL3-Δ9 degrades Kelch-like 3 (KLHL3), the CUL3 substrate adaptor for WNK4; thus reduced abundance of KLHL3 combined with reduced CUL3 are mechanistically important in CUL3-Δ9-mediated FHHt.

Methods

We studied Cul3 KO (Cul3–/–) mice, Cul3 KO mice expressing CUL3-Δ9 (Cul3–/–/Δ9), Cul3 heterozygotes expressing CUL3-Δ9 (Cul3+/–/Δ9), compound Cul3 and Klhl3 heterozygotes (Cul3+/–Klhl3+/–), and Jab1 KO (Jab1–/–) mice. All mouse lines were inducible and renal tubule-specific.

Results

CUL3-Δ9 did not promote degradation of CUL3 targets that accumulate in Cul3–/– kidney: WNK4, cyclin E, or NQO1 (a surrogate for the CUL3 substrate Nrf2). In Cul3–/–/Δ9 mice, CUL3-Δ9 prevented KLHL3 accumulation seen in Cul3–/– kidney and promoted KLHL3 degradation in Cul3+/–/Δ9 mice. Higher NQO1 and lower cyclin E abundances were observed in Cul3+/–/Δ9 mice compared to control mice. Cul3+/–Klhl3+/– mice displayed increased WNK4-SPAK activation and phospho-NCC abundance, and FHHt-like phenotype with increased plasma [K+] and salt-sensitive blood pressure. Similarly, reduced CUL3 and KLHL3 abundances and increased abundances of WNK4 and phsopho-NCC were observed in Jab1–/– mice.

Conclusion

Together, these data provide evidence for a mechanism of reduced KLHL3 and reduced CUL3 in CUL3-Δ9-mediated FHHt. CUL3-Δ9 potently degrades KLHL3, but also exerts modest effects on other CUL3 targets, raising the possibility of unidentified renal phenotypes in the human disease.

Funding

  • NIDDK Support