L-4F Inhibits Oxidized Low-density Lipoprotein-induced Inflammatory Adipokine Secretion via Cyclic AMP/Protein Kinase A-CCAAT/Enhancer Binding Protein β Signaling Pathway in 3T3-L1 Adipocytes

摘要

Background:Adipocytes behave like a rich source of pro-inflammatory cytokines including monocyte chemoattractant protein-1 (MCP-1).Oxidized low-density lipoprotein (oxLDL) participates in the local chronic inflammatory response,and high-density lipoprotein could counterbalance the proinflammatory function of oxLDL,but the underlying mechanism is not completely understood.This study aimed to evaluate the effect of apolipoprotein A-I mimetic peptide L-4F on the secretion and expression of MCP-1 in fully differentiated 3T3-L1 adipocytes induced by oxLDL and to elucidate the possible mechanisms.Methods:Fully differentiated 3T3-L1 adipocytes were incubated in the medium containing various concentration of L-4F (0-50 μg/ml) with oxLDL (50 μg/ml) stimulated,with/without protein kinase A (PKA) inhibitor H-89 (10 μmol/L) preincubated.The concentrations of MCP-1 in the supernatant,the mRNA expression of MCP-1,the levels of CCAAT/enhancer binding protein α (C/EBPα),and CCAAT/enhancer binding protein β (C/EBPβ) were evaluated.The monocyte chemotaxis assay was performed by micropore filter method using a modified Boyden chamber.Results:OxLDL stimulation induced a significant increase of MCP-1 expression and secretion in 3T3-L1 adipocytes,which were inhibited by L-4F preincubation in a dose-dependent manner.PKA inhibitor H-89 markedly reduced the oxLDL-induced MCP-1 expression,but no further decrease was observed when H-89 was used in combination with L-4F (50 μg/ml) (P ＞ 0.05).OxLDL stimulation showed no significant effect on C/EBPα protein level but increased C/EBPβ protein level in a time-dependent manner.H-89 and L-4F both attenuated C/EBPβ protein level in oxLDL-induced 3T3-L1 adipocytes.Conclusions:OxLDL induces C/EBPβ protein synthesis in a time-dependent manner and enhances MCP-1 secretion and expression in 3T3-L1 adipocytes.L-4F dose-dependently counterbalances the pro-inflammatory effect of oxLDL,and cyclic AMP/PKA-C/EBPβsignaling pathway may participate in it.