Association of Aquaporin 7 and 9 with Obesity and Fatty Liver in db/db Mice

Aquaporin (AQP) 7 and AQP9 are membrane channel proteins called aquaglyceroporins and are related to glucose and lipid metabolism. AQP7 is mainly expressed in white adipose tissue (WAT) and is involved in releasing glycerol into the bloodstream. AQP9 is the glycerol channel in the liver that supplies glycerol to the hepatic cells. In this study, we investigated the relationship between the expression of aquaglyceroporins and lifestyle-related diseases, such as obesity and fatty liver, using 22-week-old db/db mice. Body weight, WAT, and liver weight showed increases in db/db mice. The levels of liver lipids, plasma lipids, insulin, and leptin were also increased in db/db mice. Gene expression related to fatty acid and triglyceride synthesis in the liver was enhanced in db/db mice. In addition, gene and protein expression of gluconeogenesis-related enzymes was increased. Conversely, lipolysis-related gene expression in WAT was reduced. In the db/db mice, AQP9 expression in the liver was raised; however, AQP7 expression in WAT was reduced. These results suggest that in db/db mice, enhanced hepatic AQP9 expression increased the supply of glycerol to the liver and induced fatty liver and hyperglycemia. Additionally, reduced AQP7 expression in WAT is associated with excessive lipid accumulation in adipocytes. Aquaglyceroporins are essential molecules for glucose and lipid metabolism, and may be potential target molecules for the treatment of obesity and lifestyle-related diseases.