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Abstract

Profibrotic and prohomeostatic macrophage phenotypes remain ill-defined, both in vivo and in vitro, impeding the successful development of drugs that reprogram macrophages as an attractive therapeutic approach to manage fibrotic disease. The goal of this study was to reveal profibrotic and prohomeostatic macrophage phenotypes that could guide the design of new therapeutic approaches targeting macrophages to treat fibrotic disease. This study used nintedanib, a broad kinase inhibitor approved for idiopathic pulmonary fibrosis, to dissect lung macrophage phenotypes during fibrosis-linked inflammation by combining in vivo and in vitro bulk and single-cell RNA-sequencing approaches. In the bleomycin model, nintedanib drove the expression of IL-4/IL-13-associated genes important for tissue regeneration and repair at early and late time points in lung macrophages. These findings were replicated in vitro in mouse primary bone marrow-derived macrophages exposed to IL-4/IL-13 and nintedanib. In addition, nintedanib promoted the expression of IL-4/IL-13 pathway genes in human macrophages in vitro. The molecular mechanism was connected to inhibition of the colony stimulating factor 1 (CSF1) receptor in both human and mouse macrophages. Moreover, nintedanib counterbalanced the effects of TNF on IL-4/IL-13 in macrophages to promote expression of IL-4/IL-13-regulated tissue repair genes in fibrotic contexts in vivo and in vitro. This study demonstrates that one of nintedanib's antifibrotic mechanisms is to increase IL-4 signaling in macrophages through inhibition of the CSF1 receptor, resulting in the promotion of tissue repair phenotypes.