Objective: To examine the role of the acute-phase protein serum amyloid A (A-SAA) in regulating cell adhesion molecule expression, leukocyte recruitment, and angiogenesis in rheumatoid arthritis (RA).
Methods: Intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and matrix metalloproteinase 1 (MMP-1) expression was examined in RA fibroblast-like synoviocytes (FLS) and human microvascular endothelial cells (HMVECs) using flow cytometry and enzyme-linked immunosorbent assay techniques. Peripheral blood mononuclear cell (PBMC) adhesion to FLS/HMVECs was determined by flow cytometry. Angiogenesis was examined using a Boyden chemotaxis chamber and Matrigel tubule formation. NF-kappaB/IkappaBalpha mediation of the effects of A-SAA was investigated using a specific NF-kappaB inhibitor and Western blotting.
Results: A-SAA significantly enhanced the time- and dose-dependent expression of ICAM-1 and VCAM-1 as effectively as interleukin-1beta/tumor necrosis factor alpha. A-SAA promoted the adhesion of PBMCs to FLS and HMVECs. In addition, A-SAA at 10 mug/ml and 50 mug/ml significantly increased endothelial cell tube formation by 69% and 207%, respectively. At 50 mug/ml and 100 mug/ml, A-SAA increased HMVEC migration by 188 +/- 54% and 296 +/- 71%, respectively (mean +/- SEM). A-SAA-induced expression of VCAM-1, ICAM-1, and MMP-1 was down-regulated by NF-kappaB inhibition. Furthermore, A-SAA induced IkappaBalpha degradation and NF-kappaB translocation, suggesting that its proinflammatory effects are mediated in part by NF-kappaB signaling.
Conclusion: Our findings demonstrate the ability of A-SAA to induce adhesion molecule expression, angiogenesis, and matrix degradation, mechanisms that are mediated by NF-kappaB. Targeting A-SAA and its signaling pathways may represent a new therapeutic approach in the treatment of RA.