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 0.05). 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.