The brain depends on glucose as the main source of energy, being GLUT1 (in astrocytes) and GLUT3 (in neurons) the most relevant glucose transporters. One of the latest members of the facilitative glucose transporter family (SLC2A) identified is GLUT12. GLUT12 is expressed in small intestine, adipose tissue, muscle, kidney and brain. Stimulus such as insulin, glucose and TNF-α induce GLUT12 expression and translocation to the membrane. However, expression and function of GLUT12 in the brain is an unexplored topic. Our group has demonstrated GLUT12 expression in different brain areas in mice, but its function has not been established yet. More interesting, we have reported upregulation of GLUT12 in the brain of mouse models of Alzheimer’s disease (AD), in aged mice and senescence accelerated mice models, and in the frontal cortex of AD disease patients. Other authors have shown, among brain cells, the highest expression of GLUT12 mRNA in oligodendrocyte progenitor cells and astrocytes. Since the astrocytes are the main energy providers for the neurons, we decided to investigate GLUT12 expression and regulation by glucose and insulin in the astrocytic human glioblastoma cell line A171, to advance in the knowledge of GLUT12 function in the brain. We also studied GLUT1 expression for comparison.

Cells were incubated in the absence and presence of 50 nM insulin or 25 mM glucose for 1 and 24 h, and expression of the transporters was determined by RT-PCR and Western blot. The ANOVA test and Tukey's Post-Hoc analysis were applied.The number of samples per condition was 3-5. After 24 h incubation, glucose decreased GLUT12 mRNA by 50% (p<0.05), whereas insulin did not modify it. Interestingly, neither glucose nor insulin changed GLUT12 protein expression, which appeared as a dimer with a molecular weight of 140 kDa. Differently, GLUT1 mRNA was not affected by glucose or insulin, while glucose decreased GLUT1 protein expression by 50% (p<0.05). After 1 h incubation, both glucose an insulin reduced GLUT12 mRNA by 50% (p<0.05) and 70% (p<0.01) respectively. Surprisingly, GLUT12 protein increased 5-fold in the presence of glucose (p<0.05), while insulin only induced a trend to increase the transporter expression. Finally, GLUT1 mRNA and protein were reduced by 50 % (p<0.05) by glucose but were not affected by insulin.

Overall, in this work we have demonstrated the expression of GLUT12 in the A172 astroglioma cell line. Of note, mRNA and protein expression were not correlated.  Importantly, we found an increase in GLUT12 protein expression after high glucose incubation, while a decrease in GLUT1 expression was observed. These results will help to understand GLUT12 function in the astrocytes, who are important regulators of brain glucose metabolism.