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

Abstract

Articular chondrocytes exist in an environment lacking in oxygen and nutrients due to the avascular nature of cartilage. The main source of metabolic energy is glucose, which is taken up by glucose transporters (GLUTs). In diseased joints, oxygen tensions and glucose availability alter as a result of inflammation and changes in vascularisation. Accordingly, in this study we examined the effects of hypoxia and the hypoxia mimetic cobalt chloride (CoCl 2 ) on glucose transport in equine chondrocytes and compared expression of the hypoxia responsive GLUT1 gene in normal and diseased cartilage. Monolayers of equine chondrocytes were exposed to 20% O 2 , 1% O 2 , CoCl 2 (75 mM), or a combination of 1% O 2 and CoCl 2 . Glucose uptake was measured using 2-deoxy-D-[2,6-3 H] glucose. GLUT1 protein and mRNA expression were determined by FACS analysis and qPCR, respectively. GLUT1 mRNA expression in normal and diseased cartilage was analyzed using explants derived from normal, OA, and OCD cartilage. Chondrocytes under hypoxic conditions exhibited a significantly increased glucose uptake as well as upregulated GLUT1 protein expression. GLUT1 mRNA expression significantly increased in combined hypoxia-CoCl 2 treatment. Analysis of clinical samples indicated a significant reduction in GLUT1 mRNA in OA samples. In OCD samples GLUT1 expression also decreased but did not reach statistical significance. The increase in glucose uptake and GLUT1 expression under hypoxic conditions confirms that hypoxia alters the metabolic requirements of chondrocytes. The altered GLUT1 mRNA expression in diseased cartilage with significance in OA suggests that reduced GLUT1 may contribute to the failure of OA cartilage repair. ß

HIF1α is a central regulator of collagen hydroxylation and secretion under hypoxia during bone development

“…It was previously reported that interference with proteoglycan glycosylation in the Golgi inhibits their secretion (Hameetman et al, 2007;Ratcliffe et al, 1985). HIF1 is known to regulate uptake and consumption of glucose, which is necessary for proteoglycan glycosylation (Mobasheri et al, 2002;Peansukmanee et al, 2009;Ren et al, 2008). This suggests that HIF1 may regulate not only collagen hydroxylation, but also proteoglycan glycosylation.…”

Expression of Hypoxia-Inducible Factor 1α in Invasive Breast Cancer with Metastasis to Lymph Nodes: Correlation with Steroid Receptors, HER2 and EPO-R

“…The expression of HIF-1α and EPO-R were most often found in cancers with PR-/ER-/ /HER2+/ immunohistochemical profile (42.85%). opment of the existing vessels that are unable to supply oxygen to the intensely proliferating neoplastic tissue [9]. In solid tumors hypoxia is a result of growing metabolic activity and oxygen consumption by rapidly proliferating tumor cells and a drop in pH of surrounding environment [10].…”

“…EPO and its receptor (EPO-R) have recently been found to be expressed on several normal non-hematopoietic cells as well as in cancer tissues. Specifically, high expression of EPO-R has been found on the surface of endothelial cells and various solid tumors [9][10][11].…”

Hypoxia in breast cancer

“…Increased expression of GLUT 1 was demonstrated as a response to hypoxia in stem cells, adipocytes, neurons, astrocytes and chondrocytes [19]. Increased expression of GLUT 4 was observed in skeletal muscle cells and cardiomyocytes [20,21].…”