Immunocytochemical demonstration of glucose transporters in epiphyseal growth plate chondrocytes of young rats in correlation with autoradiographic distribution of 2-deoxyglucose in chondrocytes of mice

The epiphyseal growth plate, where chondrocytes proliferate and differentiate, is the major site for longitudinal bone growth, matrix synthesis and mineralization. Glucose is an important energy source for the metabolism and growth of chondrocytes. The family of facilitative glucose transporters (GLUTs) mediates glucose transport across the plasma membrane in mammalian cells. We used immunocytochemical methods with anti-GLUT antibodies to investigate the localization of GLUTs in chondrocytes of the epiphyseal growth plate in 3 age groups of rats (3, 7, and 28 days after birth). Intense immunoreactivity of GLUT isoforms 1-5 was detected in chondrocytes of 3-day and 7-day old rats, and all GLUTs were localized in the maturation zone of the hypertrophic zone. On postnatal day 28, chondrocytes in the maturation zone showed intense GLUT 1, 4 and 5 immunoreactivity, and weak GLUT2 and 3 immunoreactivity. In addition to chondrocytes in the maturation zone, those in the degenerative zone and in the zone of provisional caicification showed strong GLUT4 and 5 immunoreactivity. Autoradiography of bone sections from 4-week old mice injected with 14C-2-deoxyglucose showed high silver grain density within matrix tissue in the reserve and proliferative zones but not around chondrocytes. However, in the hypertrophic zone, silver grain density was high in matrix and chondrocytes. These data indicate that chondrocytes in the hypertrophic zones use glucose as energy source. High levels of GLUT4 expression imply that glucose use in chondrocytes is regulated by insulin. Expression of GLUT5 in chondrocytes suggests that fructose is also used as an energy source.