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

Abstract

Skeletal growth, taking place in the cartilaginous growth plates of long bones, consumes high levels of glucose for both metabolic and anabolic purposes. We previously showed that Glut4 is present in growing bone and is decreased in diabetes. In the present study, we examined the hypothesis that in bone, GLUT4 gene expression and function are regulated via the IGF-I receptor (IGF-IR) and that Glut4 plays an important role in bone growth. Insulin and IGF-I actions on skeletal growth and glucose uptake were determined using mandibular condyle (MC) organ cultures and MC-derived primary cell cultures (MCDC). Chondrogenesis was determined by following proliferation and differentiation activities using immunohistochemical (IHC) analysis of proliferating cell nuclear antigen and type II collagen expression, respectively. Overall condylar growth was assessed morphometrically. GLUT4 mRNA and protein levels were determined using in situ hybridization and IHC, respectively. Glut4 translocation to the cell membrane was assessed using confocal microscopy analysis of GFP-Glut4 fusion-transfected cells and immunogold and electron microscopy on MC sections; glucose uptake was assayed by 2-deoxyglucose (2-DOG) uptake. Both IGF-I and insulin-stimulated glucose uptake in MCDC, with IGF-I being tenfold more potent than insulin. Blockage of IGF-IR abrogated both IGF-I- and insulin-induced chondrogenesis and glucose metabolism. IGF-I, but not insulin, induced Glut4 translocation to the plasma membrane. Additionally, insulin induced both GLUT4 and IGF-IR gene expression and improved condylar growth in insulin receptor knockout mice-derived MC. Moreover, silencing of GLUT4 gene in MCDC culture abolished both IGF-I-induced glucose uptake and chondrocytic proliferation and differentiation. In growing bone, the IGF-IR pathway stimulates Glut4 translocation and enhances glucose uptake. Moreover, intact Glut4 cellular levels and translocation machinery are essential for early skeletal growth.

Morquio a Syndrome: Identification of Differential Patterns of Molecular Pathway Interac-Tions in Bone Lesions

“…We observed altered expression of proteins involved in energygenerating pathways, including glycolysis, the Krebs cycle, and OXPHOS, which produce high oxidative stress. Furthermore, we detected altered expression of proteins such as Rtn2 and Sorl1 that facilitate glucose entry into cells via GLUT-4 [26,27]. Similar alterations in osteoarthritis in humans are described, in which GLUT-1 receptor expression is augmented, thereby increasing cellular glucose levels [28].…”

Inhibition of GDF8 (Myostatin) accelerates bone regeneration in diabetes mellitus type 2

“…Myostatin inhibition re-evaluates the role of muscle metabolism in diabetic disease. The underrated potential of bone and muscle as organs in treating diabetes systemically must be re-evaluated; several glucose transporter types are described to be expressed in different bone cells implicating an important role in glucose-metabolism 47 , 48 . Our work emphasizes the underestimated role of Myostatin in bone metabolism and therefore the potential implication in treating systemic diabetic disease.…”

Morquio A Syndrome: Identification of Differential Patterns of Molecular Pathway Interactions in Bone Lesions

“…We observed altered expression of proteins involved in energy-generating pathways, including glycolysis, the Krebs cycle, and OXPHOS, which produce high oxidative stress. Furthermore, we detected altered expression of proteins such as Rtn2 and Sorl1 that facilitate glucose entry into cells via GLUT-4 [ 26 , 27 ]. Similar alterations in osteoarthritis in humans are described, in which GLUT-1 receptor expression is augmented, thereby increasing cellular glucose levels [ 28 ].…”