Spatial confinement downsizes the inflammatory response of macrophages

Macrophages respond to chemical/metabolic and physical stimuli, but their effects cannot be readily decoupled in vivo during pro-inflammatory activation. Here, we show that preventing macrophage spreading by spatial confinement, as imposed by micropatterning, microporous substrates or cell crowding, suppresses late lipopolysaccharide (LPS)-activated transcriptional programs (biomarkers IL-6, CXCL9, IL-1 beta, and iNOS) by mechanomodulating chromatin compaction and epigenetic alterations (HDAC3 levels and H3K36-dimethylation). Mechanistically, confinement reduces actin polymerization, thereby lowers the LPS-stimulated nuclear translocation of MRTF-A. This lowers the activity of the MRTF-A-SRF complex and subsequently downregulates the inflammatory response, as confirmed by chromatin immunoprecipitation coupled with quantitative PCR and RNA sequencing analysis. Confinement thus downregulates pro-inflammatory cytokine secretion and, well before any activation processes, the phagocytic potential of macrophages. Contrarily, early events, including activation of the LPS receptor TLR4, and downstream NF-kappa B and IRF3 signalling and hence the expression of early LPS-responsive genes were marginally affected by confinement. These findings have broad implications in the context of mechanobiology, inflammation and immunology, as well as in tissue engineering and regenerative medicine.