Compensatory Aldosterone Elevation and NEDD4-2 Activation in mTORC2 Knockout Mice

Background: Hypertension is a leading risk factor for cardiovascular and renal disease. Its pathophysiology is tightly linked to renal sodium and potassium handling, as well as dietary potassium intake. The epithelial sodium channel (ENaC), regulated by aldosterone, plays a central role in modulating blood pressure via sodium reabsorption and concomitant potassium excretion in the distal nephron. mTORC2, a kinase complex regulated by both potassium and angiotensin II, augments aldosterone activity by promoting stabilization of ENaC in the apical membrane through SGK1- and NEDD4-2–mediated phosphorylation. In mTORC2 knockout mice, acute increases in oral potassium lead to hyperkalemia and hypotension within hours. We hypothesized that a gradual increase in dietary potassium would allow knockout mice time to adapt, revealing new insights into the interplay between mTORC2 and aldosterone signaling. Methods: We used a transgenic mouse line with nephron-specific, inducible deletion of Rictor (TRKO), a critical subunit of mTORC2. Male WT and TRKO mice were fed a series of potassium-enriched diets (0.5% to 3%) over several weeks. Blood pressure was monitored by tail cuff plethysmography. Serum electrolytes, renin, and aldosterone levels were quantified at sacrifice. Following nephrectomy, kidney tissue was used for immunoblotting proteins involved in mTORC2 and aldosterone signaling. Results: Unlike the response to acute potassium loading, TRKO mice on a chronic high-potassium diet paradoxically developed elevated systolic blood pressure beginning at 1.5% dietary potassium, whereas WT controls exhibited decreased systolic blood pressure. Electrolyte analysis revealed higher serum potassium (5.8 vs. 4.2 mmol/L) and BUN (32 vs. 21 mg/dL) in TRKO mice. Serum aldosterone was markedly elevated in TRKO mice (69 nM vs. 1 nM), despite suppressed renin expression, indicating a renin-independent mechanism. Immunoblot analysis showed increased phosphorylation of NEDD4-2 in TRKO mice. Conclusion: Chronic dietary potassium loading induces hypertension in mTORC2-deficient mice via hyperkalemia-triggered aldosterone excess. Despite the absence of mTORC2, the canonical activator of NEDD4-2, phosphorylation of NEDD4-2 persists, suggesting an alternative pathway of activation. These findings point to a compensatory mechanism for ENaC activation in the distal nephron, independent of mTORC2. Funding: NIDDK Support