The epithelial sodium channel γ-subunit is processed proteolytically in human kidney

Area of Science:

• Nephrology
• Molecular Biology
• Physiology

Background:

• The epithelial sodium channel (ENaC) is crucial for kidney function, regulating extracellular volume and blood pressure.
• ENaC activity is modulated by proteolytic cleavage of its gamma (γ) subunit, releasing an inhibitory tract.
• Aberrant ENaC activation is implicated in various kidney diseases.

Purpose of the Study:

• To investigate whether proteolytic processing of γENaC occurs in the human kidney under physiological conditions.
• To determine if proteinuria contributes to aberrant proteolytic activation of γENaC.
• To characterize the specific cleavage sites and fragments of γENaC in human kidney tissue.

Main Methods:

• Utilized monoclonal antibodies (mAbs) specific to the γENaC inhibitory tract and a neoepitope generated by prostasin/kallikrein cleavage.
• Examined human nephrectomy specimens using immunoblotting techniques.
• Compared γENaC processing in kidney homogenates from patients with and without proteinuria, and those on different medications.

Main Results:

• No significant differences in full-length or furin-cleaved γENaC were observed between patients on no medication, ARBs, or ACE inhibitors.
• Diuretic use was associated with increased abundance of full-length and furin-cleaved γENaC, but not altered cleavage ratios.
• In proteinuric patients, the inhibitory tract was only detected in full-length γENaC, while prostasin/kallikrein-cleaved γENaC was consistently found in collecting ducts.

Conclusions:

• Human kidney γENaC undergoes proteolytic cleavage, consistent with furin activity.
• Proteinuria is associated with cleavage at the prostasin/kallikrein site, leading to the removal of the γENaC inhibitory tract.
• These findings suggest a mechanism for aberrant ENaC activation in proteinuric kidney diseases.