Abstract 1650: ApolipoproteinCIII induces THP-1 Cell Adhesion to Endothelial Cells via Pertussis Toxin-Sensitive G-Protein- and Protein Kinase Cα-Mediated Nuclear Factor-κB Activation
Background Plasma apoCIII independently predicts risk for coronary heart disease (CHD) despite its relatively low plasma concentration. We examined the direct effect of apoCIII on monocyte-endothelial interaction, and found that apoCIII directly activated human peripheral monocytes and induced their adhesion to vascular endothelial cells through activation of protein kinase C (PKC) α and nuclear factor-κB (NF-κB).
Methods and Results ApoCIII-rich VLDL (VLDL CIII+) were isolated from the fasting plasma of normolipidemic volunteers by immunoaffinity chromatography and sequential ultracentrifugation. Endotoxin levels in apoCIII and VLDL CIII+ were < 0.03 EU/mL. Incubation of THP-1 cells with VLDL CIII+ (10 mg apoB/dL, 8 hours) increased their adhesion to human saphenous vein endothelial cells by 2.4-fold, and increased total and active form of β1-integrin on THP-1 cells via PKC+. ApoCIII alone (10mg /dL, 8 hours) also activated PKCα, and increased THP-1 cell adhesion by 2.1-fold. Anti-apoCIII antibody treatment of VLDL CIII+ abolished THP-1 cell adhesion and PKCα activation. We further found that apoCIII activates phosphatidylcholine-specific phospholipase C (PC-PLC) in THP-1 cells, resulting in PKCα activation. A PC-PLC inhibitor (D609) inhibited apoCIII-induced PKCα activation. PLC activation by apoCIII was inhibited by pertussis toxin (PTX), a Gi protein inhibitor. D609 and PTX inhibited apoCIII-induced THP-1 cell adhesion to ECs by 60% and 65%, respectively. ApoCIII further activated NF-κB in THP-1 cells through PKCΑ and augmented β1-integrin expression. The NF-κB inhibitor peptide SN50 inhibited apoCIII-induced β1-integrin expression and THP-1 cell adhesion. VLDL CIII+ had similar effects to apoCIII itself.
Conclusion ApoCIII as well as VLDL CIII+ increased THP-1 cell adhesion to endothelial cells in a PKCα-dependent manner. A PTX-sensitive G-protein pathway participates critically in PKCα activation by apoCIII, activating NF-κB and increasing β1-integrin. These results suggest that apoCIII activates monocytes, independently of lipids, resulting in their increased adhesion to endothelium. Our observations provide novel insights into a role for apoCIII as a distinct contributor to inflammation and atherosclerosis.