Increased Expression of AQP7 in the Skeletal Muscles of Diet Induced Obesity Mice

Aquaporin (AQP) 7 and AQP9 are membrane proteins and are the members of aquaglyceroporin which transports glycerol in addition to water molecule. Glycerol is a direct source of glycerol-3 phosphate for the synthesis of triglyceride which is a main substance of lipid droplet seen in skeletal myofibers. We thought that the expression of AQP7 and AQP9 would be altered in the skeletal myofibers in diet-induced obese (DIO) mice as compared with that of control chaw-fed mice. Both RNA and protein levels of AQP7 and AQP9 were studied in the quadriceps femoris muscles of DIO mice and normal control mice. Real time quantitative RT-PCR analysis showed that mouse AQP7 mRNA levels in skeletal muscles were significantly higher in DIO mice compared with normal control mice (P < 0.01); whereas mouse AQP9 mRNA levels were not different between the two groups (P > 0.05). Histochemically the myofibers of DIO mice contained numerous lipid droplets in oil red O stain samples. Immunohistochemical study of DIO mouse muscles showed enhanced expression of AQP7 at the myofiber surface membranes; while expression of AQP9 appeared to be similar to that of normal control mice. These findings imply that the up-regulated expression of AQP7 in DIO mouse muscles facilitates the secretion of glycerol from myocytes.