An In Vitro Model to Probe the Regulation of Adipocyte Differentiation under Hyperglycemia

BACKGROUND: The aim of this study was an in vitro investigation of the effect of high glucose concentration on adipogenesis, as prolonged hyperglycemia alters adipocyte differentiation. METHODS: 3T3-L1 preadipocytes differentiated in the presence of varying concentrations of glucose (25, 45, 65, 85, and 105 mM) were assessed for adipogenesis using AdipoRed (Lonza) assay. Cell viability and proliferation were measured using MTT reduction and [(3)H] thymidine incorporation assay. The extent of glucose uptake and glycogen synthesis were measured using radiolabelled 2-deoxy-D-[1-(3)H] glucose and [(14)C]-UDP-glucose. The gene level expression was evaluated using reverse transcription-polymerase chain reaction and protein expression was studied using Western blot analysis. RESULTS: Glucose at 105 mM concentration was observed to inhibit adipogenesis through inhibition of CCAAT-enhancer-binding proteins, sterol regulatory element-binding protein, peroxisome proliferator-activated receptor and adiponectin. High concentration of glucose induced stress by increasing levels of toll-like receptor 4, nuclear factor κB and tumor necrosis factor α thereby generating activated preadipocytes. These cells entered the state of hyperplasia through inhibition of p27 and proliferation was found to increase through activation of protein kinase B via phosphoinositide 3 kinase dependent pathway. This condition inhibited insulin signaling through decrease in insulin receptor β. Although the glucose transporter 4 (GLUT4) protein remained unaltered with the glycogen synthesis inhibited, the cells were found to exhibit an increase in glucose uptake via GLUT1. CONCLUSION: Adipogenesis in the presence of 105 mM glucose leads to an uncontrolled proliferation of activated preadipocytes providing an insight towards understanding obesity.