Wnt-5a ameliorates sepsis-induced downregulation of renal AQP2 via the calcineurin signaling pathway.

BACKGROUND

Aquaporin 2 (AQP2), a vasopressin-sensitive water channel in the renal collecting ducts, maintains body water homeostasis. Sepsis reduces AQP2 and vasopressin receptor 2 (V2R) levels, contributing to acute kidney injury. In a heritable nephrogenic diabetes insipidus mouse model with V2R mutation, Wnt-5a, a ligand for frizzled receptors (Fzds), enhances AQP2 expression and translocation through calcium/calmodulin/calcineurin signaling. However, the mechanism by which Wnt-5a reduces sepsis-induced AQP2 inhibition remains unclear. We assessed this mechanism and whether Wnt-5a alleviates sepsis-induced downregulation of renal AQP2.

METHODS

Our study used in vitro and in vivo approaches. To study AQP2 trafficking, lipopolysaccharide (LPS) was applied to mouse inner medullary collecting duct 3 (mIMCD3) cells in vitro; subsequently, phosphorylated AQP2 and apical AQP2 expression as well as calcineurin activity and its upstream regulators (endogenous Wnt-5a, Fzds, and intracellular calcium intensity) were examined. In vivo, cecal ligation and puncture (CLP) mice were used to assess AQP2 levels and urine osmolality as indicators of urinary concentration.

RESULTS

In mIMCD3 cells, LPS application was associated with reduced V2R expression, a vasopressin-irreversible reduction in AQP2, and increased Fzds turnover and Wnt-5a-stimulated intracellular calcium, enhancing calcineurin signaling. Subsequent application of Wnt-5a to LPS-exposed mIMCD3 cells prevented AQP2 reduction. Moreover, it increased phosphorylated AQP2 at residue Ser269 (Ser269-pAQP2) and decreased at Ser261-pAQP2 without affecting Ser256-pAQP2. These effects were reversed by the calcineurin inhibitor cyclosporin A. In CLP mice, Wnt-5a injection was associated with increased renal AQP2 and urine osmolality.

CONCLUSION

Wnt-5a attenuates sepsis-induced AQP2 downregulation through the calcineurin signaling pathway.