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Updated: Feb 24, 2026
Investigation of Macrophage Polarization Using Bone Marrow Derived Macrophages
Published on: June 23, 2013
PAI-1 (Plasminogen Activator Inhibitor-1) Expression Renders Alternatively Activated Human Macrophages
Philipp J Hohensinner1, Johanna Baumgartner1, Julia B Kral-Pointner1
1From the Department of Internal Medicine II, Division of Cardiology (P.J.H., J.B., B.E., B.T., K.D., S.S., S.D., W.S.S., J.W.), Center for Physiology and Pharmacology, Institute of Vascular Biology and Thrombosis Research (J.B.K.-P., P.U., G.S.), Department of Laboratory Medicine (S.D.), Clinic for Blood Group Serology and Transfusion Medicine (M.B.F.), and Core Facilities (J.W.), Medical University of Vienna, Austria; Department for Health Science and Biomedicine, Danube University Krems, Austria (M.B.F.); 3rd Medical Department, Wilhelminenspital, Vienna, Austria (K.H.); and Ludwig Boltzmann Cluster for Cardiovascular Research, Vienna, Austria (K.H., J.W.).
Objective:
Macrophages are versatile immune cells capable of polarizing into functional subsets depending on environmental stimulation. In atherosclerotic lesions, proinflammatory polarized macrophages are associated with symptomatic plaques, whereas Th2 (T-helper cell type 2) cytokine-polarized macrophages are inversely related with disease progression. To establish a functional cause for these observations, we analyzed extracellular matrix degradation phenotypes in polarized macrophages.
Approach And Results:
We provide evidence that proinflammatory polarized macrophages rely on membrane-bound proteases including MMP-14 (matrix metalloproteinase-14) and the serine protease uPA (urokinase plasminogen activator) together with its receptor uPAR for extracellular matrix degradation. In contrast, Th2 cytokine alternatively primed macrophages do not show different proteolytic activity in comparison to unpolarized macrophages and lack increased localization of MMP-14 and uPA receptor to the cell membrane. Nonetheless, they express the highest amount of the serine protease uPA. However, uPA activity is blocked by similarly increased expression of its inhibitor PAI-1 (plasminogen activator inhibitor 1). When inhibiting PAI-1 or when analyzing macrophages deficient in PAI-1, Th2 cytokine-polarized macrophages display the same matrix degradation capability as proinflammatory-primed macrophages. Within atherosclerotic lesions, macrophages positive for the alternative activation marker CD206 express high levels of PAI-1. In addition, to test changed tissue remodeling capacities of alternatively activated macrophages, we used a bleomycin lung injury model in mice reconstituted with PAI-1-/- bone marrow. These results supported an enhanced remodeling phenotype displayed by increased fibrosis and elevated MMP activity in the lung after PAI-1 loss.
Conclusions:
We were able to demonstrate matrix degradation dependent on membrane-bound proteases in proinflammatory stimulated macrophages and a forced proteolytical quiescence in alternatively polarized macrophages by the expression of PAI-1.
