Down-regulation of aquaporin 9 gene transcription by 10-hydroxy-2-decenoic acid: A major fatty acid in royal jelly.

10-Hydroxy--2-decenoic acid (10H2DA) is a unique lipid component of royal jelly produced by worker honeybees that exerts insulin-like effects. We herein investigated the effects of 10H2DA on the gene expression of aquaporin 9 (AQP9), which functions as a glycerol transporter in the liver, to clarify whether 10H2DA modulates energy metabolism. 10H2DA suppressed AQP9 gene expression in HepG2 cells by promoting the phosphorylation of Akt and AMP-activated protein kinase (AMPK). This suppression was partially recovered by the treatment of cells with inhibitors for Akt and AMPK. Based on the result showing that leptomycin B partially recovered the suppression of AQP9 gene expression, 10H2DA inhibited the expression of Foxa2, a transcription factor for the AQP9 gene, and also induced its nuclear exclusion. Although 10H2DA up-regulated phosphoenolpyruvate carboxykinase and glucose-6-phosphatase gene expression, this was suppressed through the modulation of Foxa2 by insulin. These results suggest that 10H2DA suppresses AQP9 gene expression through the phosphorylation of Akt and AMPK and down-regulation of Foxa2 expression.