Surface association of pregnancy-associated plasma protein-A accounts for its colocalization with activated macrophages.

Abstract

Intense immunostaining for pregnancy-associated plasma protein-A (PAPP-A), a newly characterized metalloproteinase in the insulin-like growth factor system, colocalizes with activated macrophages in human atherosclerotic plaque. To determine macrophage regulation of PAPP-A expression, we developed two models of human macrophages with basal and activated phenotypes. THP-1 cells and peripheral blood monocytes could be differentiated into macrophages and activated upon specific treatment regimens with phorbol myristate acetate, macrophage colony-stimulating factor, and interleukin-1beta. Activation was assessed by cell secretion of tumor necrosis factor-alpha, which increased 30- to 100-fold with activation. Activated macrophages also secreted matrix metalloproteinase-9. However, no PAPP-A mRNA or PAPP-A antigen could be detected in these cells under any condition. Upon incubation with recombinant PAPP-A, we found that activated macrophages bound and internalized more PAPP-A than unactivated macrophages or monocytes. Internalization accounted for at least 50% of macrophage-associated PAPP-A, as assessed in studies with cytochalasin B. Membrane-bound PAPP-A retained protease activity, whereas internalized PAPP-A had little or no activity. Similar experiments carried out with a mutated variant of PAPP-A, which retains functionality as a protease but is unable to bind surface-associated glycosaminoglycan, showed no macrophage association or internalization. Absence of PAPP-A expression was confirmed in activated macrophages isolated from a hypercholesterolemic rabbit model of atherosclerosis. We therefore conclude that PAPP-A is not synthesized in, but rather is bound and internalized by, macrophages. Our findings likely account for the observed intense immunostaining for PAPP-A colocalizing with activated macrophages and may have physiological significance in the development of vulnerable plaque.

• Authors: Cheryl A Conover, Sean C Harrington, Laurie K Bale, Claus Oxvig
• Journal: American journal of physiology. Heart and circulatory physiology (Am J Physiol Heart Circ Physiol) Vol. 292 Issue 2 Pg. H994-H1000 (Feb 2007) ISSN: 0363-6135 [Print] United States
• PMID: 17040968 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Insulin-Like Growth Factor Binding Protein 4
• Interleukin-1beta
• Recombinant Proteins
• Tumor Necrosis Factor-alpha
• Macrophage Colony-Stimulating Factor
• Pregnancy-Associated Plasma Protein-A
• Matrix Metalloproteinase 9
• Tetradecanoylphorbol Acetate

Topics

• Animals
• Atherosclerosis (etiology, metabolism)
• Cell Differentiation (drug effects)
• Cell Line
• Disease Models, Animal
• Endocytosis (drug effects)
• Humans
• Hypercholesterolemia (complications)
• Insulin-Like Growth Factor Binding Protein 4 (metabolism)
• Interleukin-1beta (pharmacology)
• Macrophage Activation (drug effects)
• Macrophage Colony-Stimulating Factor (metabolism)
• Macrophages (cytology, drug effects, metabolism)
• Matrix Metalloproteinase 9 (metabolism)
• Mutation
• Pregnancy-Associated Plasma Protein-A (genetics, metabolism)
• Rabbits
• Recombinant Proteins (pharmacology)
• Tetradecanoylphorbol Acetate (pharmacology)
• Tumor Necrosis Factor-alpha (metabolism)