Polarization affects viscoelasticity and podosome distribution of primary human macrophages

Macrophages are essential cells of the innate immune system that regulate wound healing and tissue homeostasis. They exert diverse functions, depending on their polarization state, which can lead to either functional healing of the tissue or fibrosis. Macrophage polarization state is affected by both the local biochemical and mechanical microenvironment within the tissue, suggesting a possible dependence of macrophage function on cell mechanical state, which has been poorly explored to date. In this study, we provide a systematic and quantitative characterization of the viscoelastic properties of unstimulated, pro-inflammatory, and anti-inflammatory monocyte-derived primary human macrophages at the single-cell level using atomic force microscopy. Pro-inflammatory macrophages exhibited a lower elastic modulus (E = 458.8 ± 179.9 Pa) and a more dissipative response (low frequency exponent α= 0.22 ± 0.03) than anti-inflammatory macrophages (E = 716 ± 345.6 Pa and α = 0.15 ± 0.04). These differences in mechanical properties were independent of cell morphology but correlated with differences in podosome distribution with pro-inflammatory macrophages exhibiting a dispersed distribution, and anti-inflammatory macrophages a more clustered distribution. This study identifies polarization-dependent mechanical differences in human primary macrophages and provides a quantitative experimental framework for future work in macrophage mechanobiology.