Extracellular Substrate Stiffness Alters Macrophage Morphology and Function

Abstract

Macrophages participate in immunity, tissue repair, and tissue homeostasis, and also mediate pathologic conditions including atherosclerosis and cancer. Depending on microenvironmental cues, macrophages may adopt a pro‐inflammatory or anti‐inflammatory phenotype. Tissue stiffness influences the behavior and differentiation of cells, yet little is known about how the physical extracellular environment influences macrophage function. To study the role of substrate stiffness in determining macrophage phenotype, we cultured murine macrophages on tunable polyacrylamide gels that approximate different tissue stiffnesses. Macrophages on rigid surfaces had larger surface area and reduced circularity compared to macrophages on compliant gels. On rigid surfaces, phagocytosis was increased, but lipid uptake was decreased. Cytokine secretion differed in macrophages grown on compliant versus rigid surfaces. Differences in response to the toll‐like receptor ligands CpG oligonucleotide and lipopolysaccharide were also noted. The distribution of vinculin, a component of mature focal adhesions that mediate mechanosensing, was punctate in macrophages grown on glass and diffuse in macrophages grown on compliant gels, suggesting a fundamental difference in the quantity and/or character of the focal adhesions. Together, our studies demonstrate that the mechanical properties of the extracellular environment have a direct impact on macrophage behavior and function. Furthermore, these findings have important implications for a variety of pathologic conditions that involve both macrophages and altered tissue stiffness such as fibrosis, atherosclerosis, and neoplasia.The studies were supported by NIH T32 Comparative Medicine Training Grant.