GLUT12 and adipose tissue: Expression, regulation and its relation with obesity in mice
AimThe facilitative glucose transporter GLUT12 was isolated from the breast cancer cell line MCF-7 by its homology with GLUT4. GLUT12 is expressed in insulin-sensitive tissues such as adipose tissue. The aim of this work was to investigate GLUT12 expression and hormonal regulation in 3T3-L1 adipocytes and in adipose tissue of lean and diet-induced obese mice. MethodsUptake studies were performed using radio-labelled sugars; alpha-methyl-d-glucose (alpha MG) was used as specific substrate of GLUT12. Expression and localization of GLUT12 in adipocytes were investigated by western blot and immunohistochemical methods. ResultsGLUT12 is expressed in the peri-nuclear region of mouse adipocytes. Insulin, by AKT activation, and TNF-alpha, by AMPK activation, increase alpha MG uptake by inducing GLUT12 translocation to the membrane. In contrast, leptin and adiponectin decrease GLUT12 activity through its internalization. Under hypoxia conditions GLUT12 expression is upregulated. The response of GLUT12 to TNF-alpha, leptin, adiponectin and hypoxia is the opposite to that of GLUT4. In diet-induced obese mice and obese subjects, GLUT12 protein is decreased. Intraperitoneal injection of insulin increases AKT phosphorylation and GLUT12 expression, but this effect is lost in obese animals. ConclusionWe hypothesize that GLUT12 would contribute to modulate sugar absorption in physiological and pathophysiological situations such as obesity.