Aquaporin-9 facilitates liver regeneration following hepatectomy

Aquaporin-9 (AQP9) is an aquaglyceroporin strongly expressed in the basolateral membrane of hepatocytes facing the sinusoids. AQP9 is permeable to hydrogen peroxide (H₂O₂) and glycerol as well as to water. Here, we report impaired liver regeneration in AQP9^-/- mice which involves altered steady-state H₂O₂ concentration and glucose metabolism in hepatocytes. AQP9^-/- mice showed remarkably delayed liver regeneration and increased mortality following 70% or 90% partial hepatectomy. Compared to AQP9^+/+ littermates, AQP9^-/- mice showed significantly greater hepatic H₂O₂ concentration and more severe liver injury. Fluorescence measurements indicated impaired H₂O₂ transport across plasma membrane of primary cultured hepatocytes from AQP9^-/- mice, supporting the hypothesis that AQP9 deficiency results in H₂O₂ accumulation and oxidative injury in regenerating liver because of reduced export of intracellular H₂O₂ from hepatocytes. The H₂O₂ overload in AQP9^-/- hepatocytes reduced PI3K-Akt and insulin signaling, inhibited autophagy and promoted apoptosis, resulting in impaired proliferation and increased cell death. In addition, hepatocytes from AQP9^-/- mice had low liver glycerol and high blood glycerol levels, suggesting decreased glycerol uptake and gluconeogenesis in AQP9^-/- hepatocytes. Adeno-associated virus (AAV)-mediated expression of hepatic expression of aquaglyceroporins AQP9 and AQP3 in AQP9^-/- mice, but not water-selective channel AQP4, fully rescued the impaired liver regeneration phenotype as well as the oxidative injury and abnormal glucose metabolism. Our data revealed a pivotal role of AQP9 in liver regeneration by regulating hepatocyte H₂O₂ homeostasis and glucose metabolism, suggesting AQP9 as a novel target to enhance liver regeneration following injury, surgical resection or transplantation.