Expression of the GLUT1 and GLUT9 facilitative glucose transporters in embryonic chondroblasts and mature chondrocytes in ovine articular cartilage

Abstract

Glucose transport across the chondrocyte membrane is essential for chondrogenesis and the development of the skeletal system. We have previously used RT-PCR to show that fully developed human articular chondrocytes express transcripts for the GLUT1 and GLUT9 glucose transporters. In this study we report on the expression and immunohistochemical localization of the GLUT1 and GLUT9 proteins in embryonic and mature ovine cartilage. We also provide Western blot evidence for GLUT1 and GLUT9 expression in mature ovine chondrocytes. Ovine embryos (developmental stages E32 to E36 and E42 to E45) were obtained from pregnant ewes humanely killed by injection with sodium pentobarbitone. Embryos were fixed and processed for immunohistochemistry. Polyclonal antibodies to GLUT1 and GLUT9 revealed that both transporters are expressed in developing chondrocytes in ovine embryos and in the superficial, middle and deep layers of ovine cartilage from mature animals. GLUT1 expression was observed in erythrocytes and organs including heart, liver, and kidney. GLUT9 was also found in heart, kidney and liver. Western blotting confirmed the presence of the GLUT1 protein which migrated between the 50 and 64 kDa markers and two specific GLUT9 bands migrating under the 50 and 60 kDa markers, respectively. The presence of GLUT1 and GLUT9 in developing joints of ovine embryos suggests that these proteins may be important in glucose delivery to developing chondroblasts. Expression of these GLUT isoforms may be an important bioenergetic adaptation for chondrocytes in the extracellular matrix of developing cartilage.

GLUT4 in murine bone growth: from uptake and translocation to proliferation and differentiation

“…The close relationship between energy metabolism and skeletal growth is supported by the well-established growthregulatory role of insulin during early postnatal life (20,65) as well as chondrogenesis in prenatal life and in postnatal development of articular cartilage (32). However, the definite relationship between energy controlling mechanisms and growth in skeletal tissues still remains to be elucidated.…”

Uric acid transport and disease

“…Human GLUT9a has 540 amino acids and is encoded by 12 exons, whereas GLUT9b is 512 amino acids long and encoded by 13 exons, spread over an approximately 250-kb genomic region. In both humans and mice, GLUT9b expression is restricted to liver and kidney, whereas GLUT9a has a broad tissue distribution including liver, kidney, intestine, leukocytes, and chondrocytes (85), where its expression is upregulated by inflammatory cytokines (86) (Figure 4). In polarized epithelial cells, human GLUT9a is expressed in the basolateral membrane, whereas GLUT9b is targeted to the apical pole (84), and in human kidney, GLUT9 is present in the proximal tubule (84).…”

Effects of hypoxia on glucose transport in primary equine chondrocytes in vitro and evidence of reduced GLUT1 gene expression in pathologic cartilage in vivo

“…We have previously confirmed that this GLUT1 antibody recognizes GLUT1 across a diverse number of mammalian species including rats, humans, dogs, sheep, and horses. 23,24 In this study we used this GLUT1 antibody in Western blots of equine chondrocyte lysates to confirm positive immunoreactivity with a band migrating at 45-50 kDa (the expected molecular weight for GLUT1 25 ) (data not shown).…”