The glucose transporter GLUT12, a new actor in obesity and cancer.

Obesity constitutes a global health epidemic which worsens the main leading death causes such as type 2 diabetes, cardiovascular diseases, and cancer. Changes in the metabolism in patients with obesity frequently lead to insulin resistance, along with hyperglycemia, dyslipidemia and low-grade inflammation, favoring a more aggressive tumor microenvironment. One of the hallmarks of cancer is the reprogramming of the energy metabolism, in which tumor cells change oxidative phosphorylation to aerobic glycolysis or "Warburg effect". Aerobic glycolysis is faster than oxidative phosphorylation, but less efficient in terms of ATP production. To obtain sufficient ATP, tumor cells increase glucose uptake by the glucose transporters of the GLUT/SLC2 family. The human glucose transporter GLUT12 was isolated from the breast cancer cell line MCF7. It is expressed in adipose tissue, skeletal muscle and small intestine, where insulin promotes its translocation to the plasma membrane. Moreover, GLUT12 over-expression in mice increases the whole-body insulin sensitivity. Thus, GLUT12 has been proposed as a second insulin-responsive glucose transporter. In obesity, GLUT12 is downregulated and does not respond to insulin. In contrast, GLUT12 is overexpressed in human solid tumors such as breast, prostate, gastric, liver and colon. High glucose concentration, insulin, and hypoxia upregulate GLUT12 both in adipocytes and tumor cells. Inhibition of GLUT12 mediated Warburg effect suppresses proliferation, migration, and invasion of cancer cells and xenografted tumors. This review summarizes the up-to-date information about GLUT12 physiological role and its implication in obesity and cancer, opening new perspectives to consider this transporter as a therapeutic target.

Differential remodeling of subcutaneous white and interscapular brown adipose tissue by long-term exercise training in aged obese female mice

Obesity exacerbates aging-induced adipose tissue dysfunction. This study aimed to investigate the effects of long-term exercise on inguinal white adipose tissue (iWAT) and interscapular brown adipose tissue (iBAT) of aged obese mice. Two-month-old female mice received a high-fat diet for 4 months. Then, six-month-old diet-induced obese animals were allocated to sedentarism (DIO) or to a long-term treadmill training (DIOEX) up to 18 months of age. In exercised mice, iWAT depot revealed more adaptability, with an increase in the expression of fatty acid oxidation genes (Cpt1a, Acox1), and an amelioration of the inflammatory status, with a favorable modulation of pro/antiinflammatory genes and lower macrophage infiltration. Additionally, iWAT of trained animals showed an increment in the expression of mitochondrial biogenesis (Pgc1a, Tfam, Nrf1), thermogenesis (Ucp1), and beige adipocytes genes (Cd137, Tbx1). In contrast, iBAT of aged obese mice was less responsive to exercise. Indeed, although an increase in functional brown adipocytes genes and proteins (Pgc1a, Prdm16 and UCP1) was observed, few changes were found on inflammation-related and fatty acid metabolism genes. The remodeling of iWAT and iBAT depots occurred along with an improvement in the HOMA index for insulin resistance and in glucose tolerance. In conclusion, long-term exercise effectively prevented the loss of iWAT and iBAT thermogenic properties during aging and obesity. In iWAT, the long-term exercise program also reduced the inflammatory status and stimulated a fat-oxidative gene profile. These exercise-induced adipose tissue adaptations could contribute to the beneficial effects on glucose homeostasis in aged obese mice. (AU)