Extracellular matrix (ECM) bioscaffolds are widely used to facilitate constructive tissue remodeling[1]-[4], a process that relies upon the infiltration and polarization of host macrophages toward an immunomodulatory, M2 phenotype. While a clear temporal association exists between an M2 macrophage response and downstream remodeling[5]-[8], the ability of ECM bioscaffolds to directly affect macrophage phenotype has not been clearly established. The objective of the present study was to investigate the influence of ECM bioscaffolds on macrophage phenotype. Phenotype was established by surface markers, gene expression, participation in progenitor cell cross talk, and phagocytic capacity.
Primary bone marrow derived macrophages from C57bl/6 mice were exposed to 200 ug/ml of pepsin-digested ECM. Control M1 and M2 polarized macrophages were derived by exposure to IFN-y/LPS and IL-4, respectively. Cells were fixed and immunolabeled for indicators of M1 (iNOS) vs M2 (Fizz1) macrophages. Western blotting, flow cytometry, and qPCR were performed to corroborate immunolabeling results. Macrophage secreted products were used to determine chemotaxis, proliferation, and differentiation of progenitor cells via a Boyden chamber, BrdU incorporation, and differentiation marker expression, respectively. Secreted products from macrophages or ECM bioscaffold degradation products produced by pepsin-digestion were used to examine antimicrobial activity. Phagocytosis was examined using fluorophore-conjugated bioparticles. Macrophage metabolism was analyzed using an MTT assay. The present study shows that degradation products of ECM derived from a variety of tissues (e.g. small intestinal submucosa, urinary bladder, esophagus, brain, and spinal cord) promote a Fizz1+, M2-like macrophage phenotype. Preliminary results suggest ECM-treated macrophages acquire a phenotype unique from the IL-4 induced, M2 phenotype with respect to gene expression and phagocytic function. Together, these results indicate ECM degradation products directly promote constructive macrophage phenotypes, which recruit and promote differentiation of progenitor cells, suggesting a possible mechanism for ECM-mediated remodeling.
References:
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