Systems level identification of a matrisome-associated macrophage polarization state in multi-organ fibrosis.

Tissue fibrosis affects multiple organs and involves a master-regulatory role of macrophages which respond to an initial inflammatory insult common in all forms of fibrosis. The recently unravelled multi-organ heterogeneity of macrophages in healthy and fibrotic human disease suggests that macrophages expressing osteopontin (SPP1), associate with lung and liver fibrosis. However, the conservation of this SPP1 + macrophage population across different tissues, and its specificity to fibrotic diseases with different etiologies remain unclear. Integrating 15 single cell RNA-sequencing datasets to profile 235,930 tissue macrophages from healthy and fibrotic heart, lung, liver, kidney, skin and endometrium, we extended the association of SPP1 + macrophages with fibrosis to all these tissues. We also identified a subpopulation expressing matrisome-associated genes (e.g., matrix metalloproteinases and their tissue inhibitors), functionally enriched for ECM remodelling and cell metabolism, representative of a matrisome-associated macrophage (MAM) polarization state within SPP1 + macrophages. Importantly, the MAM polarization state follows a differentiation trajectory from SPP1 + macrophages and is associated with a core set of regulon activity. SPP1 + macrophages without the MAM polarization state (SPP1 + MAM - ) show a positive association with ageing lung in mice and humans. These results suggest an advanced and conserved polarization state of SPP1 + macrophages in fibrotic tissues resulting from prolonged inflammatory cues within each tissue microenvironment.