Regulation of Inflammation and Angiogenesis in Giant Cell Arteritis by Acute-Phase Serum Amyloid A

Arthritis Rheumatol. 2015 Sep;67(9):2447-56. doi: 10.1002/art.39217.

Abstract

Objective: Giant cell arteritis (GCA) is pathologically characterized by dysfunctional angiogenesis and inflammatory cell infiltration. Acute-phase serum amyloid A (A-SAA) is an acute-phase reactant, but is also produced at sites of inflammation and may contribute to vascular inflammation in atherosclerosis. This study was undertaken to examine the effect of A-SAA on proinflammatory pathways and angiogenesis in GCA, using a novel ex vivo temporal artery tissue explant model.

Methods: Serum A-SAA levels were measured by enzyme-linked immunosorbent assay (ELISA). Temporal artery explants and peripheral blood mononuclear cell (PBMC) cultures were established from patients with GCA. Temporal artery explant morphology, viability, and spontaneous release of proinflammatory mediators following 24-hour culture were assessed by hematoxylin and eosin, calcein viability staining, and ELISA. Temporal artery explants and PBMC cultures were stimulated with A-SAA (10 μg/ml), and interleukin-6 (IL-6), IL-8, vascular endothelial growth factor, Ang2, and matrix metalloproteinase 2 (MMP-2)/MMP-9 were quantified by ELISA and gelatin zymography. The effect of conditioned medium from temporal artery explants on angiogenesis was assessed using endothelial cell Matrigel tube-formation assays. Temporal artery explants were also embedded in Matrigel, and myofibroblast outgrowth was assessed.

Results: Serum A-SAA levels were significantly higher in GCA patients versus healthy controls (P < 0.0001). Intact tissue morphology, cell viability, and spontaneous cytokine secretion were demonstrated in temporal artery explants. A-SAA treatment induced a significant increase in the levels of IL-6 and IL-8 from temporal artery explants (P < 0.05) and IL-8 from PBMCs (P < 0.05) compared to basal conditions. Conditioned medium from A-SAA-treated explants significantly induced angiogenic tube formation (P < 0.05 versus basal controls). Finally, A-SAA induced myofibroblast outgrowth and MMP-9 activation.

Conclusion: Our findings demonstrate a functional role for A-SAA in regulating temporal artery inflammation, angiogenesis, and invasion, all key processes in the pathogenesis of GCA.

MeSH terms

  • Acute-Phase Proteins / immunology
  • Acute-Phase Proteins / pharmacology
  • Aged
  • Aged, 80 and over
  • Cells, Cultured
  • Female
  • Giant Cell Arteritis / immunology*
  • Giant Cell Arteritis / metabolism
  • Humans
  • In Vitro Techniques
  • Inflammation / immunology
  • Interleukin-6 / immunology
  • Interleukin-8 / drug effects
  • Interleukin-8 / immunology
  • Leukocytes, Mononuclear
  • Male
  • Matrix Metalloproteinase 2 / drug effects
  • Matrix Metalloproteinase 2 / immunology
  • Matrix Metalloproteinase 9 / drug effects
  • Matrix Metalloproteinase 9 / immunology
  • Middle Aged
  • Myofibroblasts / drug effects*
  • Neovascularization, Pathologic / immunology*
  • Serum Amyloid A Protein / immunology
  • Serum Amyloid A Protein / pharmacology*
  • Temporal Arteries / drug effects*
  • Temporal Arteries / immunology
  • Vascular Endothelial Growth Factor A / drug effects
  • Vascular Endothelial Growth Factor A / immunology
  • Vesicular Transport Proteins / drug effects
  • Vesicular Transport Proteins / immunology

Substances

  • Acute-Phase Proteins
  • CXCL8 protein, human
  • IL6 protein, human
  • Interleukin-6
  • Interleukin-8
  • Serum Amyloid A Protein
  • VEGFA protein, human
  • VPS51 protein, human
  • Vascular Endothelial Growth Factor A
  • Vesicular Transport Proteins
  • MMP2 protein, human
  • Matrix Metalloproteinase 2
  • MMP9 protein, human
  • Matrix Metalloproteinase 9