CaMKIIδ/ZO-2-Mediated Phosphorylation of AQP9 at Ser292 Drives Hepatic Steatosis and Oxidative Stress in MASLD.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a prevalent chronic liver disorder with limited treatment options. Aquaporin 9 (AQP9) is the main glycerol channel in hepatocytes, but its regulatory mechanisms in MASLD remain unclear. Here, we identified Ser292 as a key phosphorylation site on AQP9. We demonstrate that CaMKIIδ, scaffolded by ZO-2, phosphorylates AQP9 at Ser292. This modification increases the plasma-membrane localization of AQP9 and thereby enhances glycerol uptake, leading to increased hepatic lipid accumulation and, notably, exacerbates oxidative stress. Both pharmacological inhibition of CaMKIIδ and genetic disruption of this pathway (via TJP2 knockdown or an AQP9-S292A mutant) effectively reduced lipid deposition and oxidative damage in vitro and in mouse models of MASLD. Our findings reveal the CaMKIIδ/ZO-2/AQP9-Ser292 axis as a critical driver that integrates metabolic and oxidative stress pathways in MASLD. Targeting this axis, particularly via hepatocyte-specific CaMKIIδ inhibition, represents a promising therapeutic strategy to simultaneously ameliorate steatosis and oxidative injury.