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.
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/EBPβ signaling pathway may participate in it.
Xiang-Zhu
XZ
Xie
Xin
X
Huang
Shui-Ping
SP
Zhao
Bi-Lian
BL
Yu
Qiao-Qing
QQ
Zhong
Department of Geriatric Cardiology, Chinese PLA General Hospital, Beijing 100853, China.
Jian
J
Cao
D041721:3T3-L1 Cells; D000818:Animals; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000032:analysis / Q000502:physiology*; D018932:Chemokine CCL2 / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D006801:Humans; D008077:Lipoproteins, LDL / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D051379:Mice; D010455:Peptides / Q000494:pharmacology*; D015398:Signal Transduction / Q000502:physiology*
D022782:CCAAT-Enhancer-Binding Protein-beta; C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; C472885:L-4F peptide; D008077:Lipoproteins, LDL; D010455:Peptides; C099252:oxidized low density lipoprotein; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases