Transcriptomic Analysis of Monocyte-Derived Non-Phagocytic Macrophages Favors a Role in Limiting Tissue Repair and Fibrosis

Abstract

Monocyte-derived macrophages are readily differentiating cells that adapt their gene expression profile to environmental cues and functional needs. During the resolution of inflammation, monocytes initially differentiate to reparative phagocytic macrophages and later to pro-resolving non-phagocytic macrophages that produce high levels of IFNβ to boost resolutive events. Here, we performed in-depth analysis of phagocytic and non-phagocytic myeloid cells to reveal their distinct features. Unexpectedly, our analysis revealed that the non-phagocytic compartment of resolution phase myeloid cells is composed of Ly6C med F4/80 − and Ly6C hi F4/80 lo monocytic cells in addition to the previously described Ly6C − F4/80 + satiated macrophages. In addition, we found that both Ly6C + monocytic cells differentiate to Ly6C − F4/80 + macrophages, and their migration to the peritoneum is CCR2 dependent. Notably, satiated macrophages expressed high levels of IFNβ, whereas non-phagocytic monocytes of either phenotype did not. A transcriptomic comparison of phagocytic and non-phagocytic resolution phase F4/80 + macrophages showed that both subtypes express similar gene signatures that make them distinct from other myeloid cells. Moreover, we confirmed that these macrophages express closer transcriptomes to monocytes than to resident peritoneal macrophages (RPM) and resemble resolutive Ly6C lo macrophages and monocyte-derived macrophages more than their precursors, inflammatory Ly6C hi monocytes, recovered following liver injury and healing, and thioglycolate-induced peritonitis, respectively. A direct comparison of these subsets indicated that the non-phagocytic transcriptome is dominated by satiated macrophages and downregulate gene clusters associated with excessive tissue repair and fibrosis, ROS and NO synthesis, glycolysis, and blood vessel morphogenesis. On the other hand, non-phagocytic macrophages enhance the expression of genes associated with migration, oxidative phosphorylation, and mitochondrial fission as well as anti-viral responses when compared to phagocytic macrophages. Notably, conversion from phagocytic to satiated macrophages is associated with a reduction in the expression of extracellular matrix constituents that Butenko et al. Non-Phagocytic Macrophages Express an Anti-Fibrotic Transcriptomewere demonstrated to be associated with idiopathic pulmonary fibrosis (IPF). Thus, macrophage satiation during the resolution of inflammation seems to bring about a transcriptomic transition that resists tissue fibrosis and oxidative damage while promoting the restoration of tissue homeostasis to complete the resolution of inflammation.

Multi-Modal Characterization of Monocytes in Idiopathic Pulmonary Fibrosis Reveals a Primed Type I Interferon Immune Phenotype

“…Interestingly, this satiated macrophage state appears to be associated with increased IFN-β although not IFN-α production ( 33 , 34 ). A recent study suggests that these IFN-β producing satiated macrophages are associated with an anti- fibrotic phenotype ( 45 ). This calls into possibility the differential contribution of the type 1 IFN subtypes to fibrosis and further studies in this area.…”

Macrophage-Regulatory T Cell Interactions Promote Type 2 Immune Homeostasis Through Resistin-Like Molecule α

“…As sentinels, they are rapid responders to microbial invasion resulting from injury of the serous organs, such as the spleen, liver and intestinal tract, and can be mobilized to traffic to the injured organ and mediate tissue repair (2). Peritoneal macrophages also perform homeostatic functions to support innate B1 cells (3), clear debris and apoptotic cells (4,5), and dampen inflammation (6)(7)(8). On the other hand, dysregulated peritoneal macrophage responses are associated with diseases including peritonitis, bacterial dissemination, and cancer metastases (9)(10)(11)(12).…”

Inhibition of mPGES-1 attenuates efficient resolution of acute inflammation by enhancing CX3CL1 expression

“…1D ). Importantly, two subsets of Mϕ are found in the peritoneum, F4/80 lo , MerTK lo Mϕ, which are considered as infiltrating Mϕ of monocytic origin, and F4/80 hi , MerTK hi Mϕ, which represent the resident Mϕ population, either of mesodermal descent or differentiated from infiltrating Mϕ 27 , 28 . In control animals, F4/80 lo Mϕ number behaved similarly to MO although their increase was less pronounced at day 1, returning to baseline levels at day 6 (Fig.…”