Effects of High Glucose Concentrations on HMGB1 Expression in MG-63 Cells

Diabetes is a metabolic disorder that causes a long-term hyperglycemic state with complications that affect multiple tissues, including bone. HMGB1, a nonhistone chromosomal binding protein, is released from the nucleus of damaged cells and secreted extracellularly, where it mediates inflammatory responses. Hyperglycemia induces HMGB1 expression in cell types associated with diabetic complications. Therefore, we evaluated the effect of a high glucose concentration on HMGB1 production in MG-63 osteoblast-like cells. MG-63 cells were cultured in the presence of glucose at 5.5 mM (control) or 25.0 mM (high glucose). The mRNA levels of HMGB1, HMGB1 receptors (RAGE, TLR2, and TLR4), HSP90AA1, and inflammatory cytokines (IL-6 and TNF-α) were analyzed by quantitative PCR. The protein levels of HMGB1 and TNF-α were evaluated by ELISA, immunofluorescence staining, and Western blotting. The mRNA levels of HMGB1, HSP90AA1, RAGE, TLR2, TLR4, TNF-α, and IL-6 were higher in the high glucose group than in the control group. Also, high glucose upregulated the HMGB1 protein level. Anti-HMGB1 antibodies partially blocked the high glucose-induced increase in the TNF-α, but not IL-6, mRNA level. The TNF-α protein level in the presence of high glucose was also decreased by anti-HMGB1 antibodies. In conclusion, high glucose induced the expression and secretion of HMGB1 in MG-63 cells, suggesting that the extracellular HMGB1 induces TNF-α expression in osteoblasts under high glucose conditions.