Abstract
2-deoxy-D-glucose (2DG) is known as a synthetic inhibitor of glucose. 2DG regulates various cellular responses including proliferation, apoptosis and differentiation by regulation of glucose metabolism in cancer cells. However, the effects of 2DG in normal cells, including chondrocytes, are not clear yet. We examined the effects of 2DG on dedifferentiation with a focus on the beta-catenin pathway in rabbit articular chondrocytes. The rabbit articular chondrocytes were treated with 5 mM 2DG for the indicated time periods or with various concentrations of 2DG for 24 h, and the expression of type II collagen, c-jun and beta-catenin was determined by Western blot, RT-PCR, immunofluorescence staining and immunohistochemical staining and reduction of sulfated proteoglycan synthesis detected by Alcain blue staining. Luciferase assay using a TCF (T cell factor)/LEF (lymphoid enhancer factor) reporter construct was used to demonstrate the transcriptional activity of beta-catenin. We found that 2DG treatment caused a decrease of type II collagen expression. 2DG induced dedifferentiation was dependent on activation of beta-catenin, as the 2DG stimulated accumulation of beta-catenin, which is characterized by translocation of beta-catenin into the nucleus determined by immunofluorescence staining and luciferase assay. Inhibition of beta-catenin degradation by inhibition of glycogen synthase kinase 3-beta with lithium chloride (LiCl) or inhibition of proteasome with z-Leu-Leu-Leu-CHO (MG132) accelerated the decrease of type II collagen expression in the chondrocytes. 2DG regulated the post-translational level of beta-catenin whereas the transcriptional level of beta-catenin was not altered. These results collectively showed that 2DG regulates dedifferentiation via beta-catenin pathway in rabbit articular chondrocytes.
Highlights
Chondrocytes of articular cartilage develop through differentiation of mesenchymal cells during embryonic development (Barth et al, 1997; Sandell and Adler, 1999; DeLise et al, 2000)
Because glucose serves as a precursor of glycosaminoglycan in chondrocytes, the supply of glucose is important for the formation of cartilage
The differentiated phenotype of chondrocytes is determined by the expression levels of the extracellular matrix, such as glucosaminoglycan and type II collagen
Summary
Chondrocytes of articular cartilage develop through differentiation of mesenchymal cells during embryonic development (Barth et al, 1997; Sandell and Adler, 1999; DeLise et al, 2000). Chondrocytes are composed of a dense extracellular matrix (ECM), such as collagen, fibronectin and sulfated proteoglycan (Eyre, 2002). The phenotype of the differentiated chondrocyte is distinguished by type II collagen expression and synthesis of sulfated proteoglycan including aggrecan. Destruction of cartilage-specific matrix molecules such as type II collagen and proteoglycan leads to arthritis by biochemical changes in chondrocytes (Charni-Ben Tabassi and Garnero, 2007; Rousseau and Delmas, 2007; Dayer et al, 2007; Henrotin et al, 2007). Synthesis and maintenance of type II collagen and proteoglycan are important for proper function of articular chondrocytes
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