Phenotyping of macrophages derived from TpMos and Mature Ly6Chi monocytes
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ABSTRACT: Monocytes are integral cells of the innate immune system that play important roles in host defence and tissue repair. It is well established that monocytes are derived from the common monocyte progenitor (cMoP) in the bone marrow (BM) before giving rise to Ly6Chi mature monocytes that enter the circulation. However, our lab has discovered that BM Ly6Chi monocytes are not homogenous, and consist of two subpopulations (CXCR4hi and CXCR4lo) in both mice and humans. In particular, the CXCR4hi subset (termed transitional pre-monocyte (TpMo) population) actively proliferates in the BM and matures into the CXCR4lo subset, which represents mature Ly6Chi monocytes. Nevertheless, how this TpMo population may behave beyond their precursor role in the BM remains undefined. While TpMos have been shown to be strictly immobilized in the BM in the steady state, our preliminary data revealed the mobilization of TpMos into the circulation during sepsis. Furthermore, TpMos were found to give rise to more macrophages than mature Ly6Chi monocytes. Our data hence suggests a critical peripheral role for TpMos that may implicate the outcome of sepsis and possible potential implications in future therapies associated with monocytes. Based on our preliminary findings, we aim to have a better understanding of these monocyte subsets and how they are transcriptionally distinct when they have become macrophages. In particular, we would like to determine if TpMo-derived macrophages are less inflammatory compared to mature monocyte-derived macrophages.
Project description:Monocytes are circulating myeloid immune precursor cells that are generated in the bone marrow (BM). Upon their release into the circulation, monocytes are recruited to inflammatory sites, where they differentiate into monocyte-derived effector cells. In absence of overt inflammation, monocytes also extravasate into selected tissues, where they complement tissue-resident macrophage compartments. Recent studies have uncovered binary developmental trajectories of monocytes in the BM with Neutrophil-like (NeuMo) and dendritic cell (DC)-like (DCMo) monocytes differentiating downstream of granulocyte-macrophage progenitors (GMP) and macrophage-dendritic cell progenitors (MDP), respectively (Weinreb et al., 2020; Yanez et al., 2017). Yet, the molecular cues that dictate BM monocyte differentiation remain incompletely understood. The COMMD (copper metabolism MURR1 domain) family includes 10 evolutionarily conserved proteins. Functions of COMMD proteins are still being defined, but they seem to play non-redundant roles in regulating transcription and protein trafficking. Utilizing conditional COMMD10 knockout mice we uncovered a role for COMMD10 in limiting inflammasome activation in Ly6Chi monocytes during experimental sepsis and colitis (Mouhadeb et al., 2018), and in supporting phagolysosomal biogenesis and maturation in KCs and BM-derived macrophages infected with Staphylococcus aureus (Ben Shlomo et al., 2019). Hence, these studies mark COMMD10 as a candidate mediator of monocyte and macrophage fate and immune responses. Here we studied the effect of COMMD10-deficiency on Ly6Chi monocyte differentiation. We show that COMMD10-deficiency in steady state Ly6Chi monocytes promotes a differentiation bias towards NeuMo fate.
Project description:Hepatic macrophages play a central role in the initiation, progression and resolution of various liver diseases. Specifically, infiltrating Ly6Chi monocytes and their-derived macrophage (MoMFs) descendants prevail in acute or chronic liver injury, display marked transcriptional variance and provide crucial functional plasticity. A specific example of MoMFs are lipid associated macrophages (LAMs) involved in progression of metabolic liver disease (Remmerie et al., 2020). Recent studies have uncovered binary developmental trajectories of monocytes in the BM with Neutrophil-like (NeuMo) and dendritic cell (DC)-like (DCMo) monocytes (Weinreb et al., 2020; Yanez et al., 2017), hence further challenging our current comprehension of macrophage heterogeneity in the diseased liver. Yet, the molecular factors regulating their inflammatory versus restorative activity remains enigmatic. The COMMD (copper metabolism MURR1 domain) family includes 10 evolutionarily conserved proteins. Functions of COMMD proteins are still being defined, but they seem to play non-redundant roles in regulating transcription and protein trafficking. Utilizing conditional COMMD10 knockout mice we uncovered a role for COMMD10 in limiting inflammasome activation in Ly6Chi monocytes during experimental sepsis and colitis (Mouhadeb et al., 2018), and in supporting phagolysosomal biogenesis and maturation in KCs and BM-derived macrophages infected with Staphylococcus aureus (Ben Shlomo et al., 2019). Hence, these studies mark COMMD10 as a candidate mediator of monocyte and macrophage fate and immune responses. Here we studeid the effect of COMMD10-deficiency on Ly6Chi monocyte differentiation and inflammatory behaviour in the injured liver, using an acute model of acetaminophen-induced liver injury (AILI). Bulk RNAseq analysis of sorted Ly6Chi monocytes, comparing between COMMD10+ and COMMD10-deficient cells, revealed an increased differentiation bias of Ly6Chi monocytes towards NeuMo and LAM differentiation fates. Collectively, COMMD10 appears as an important regulator of Ly6Chi monocyte fate decisions and reparative behavior in the diseased liver.
Project description:Hepatic macrophages play a central role in the initiation, progression and resolution of various liver diseases. Specifically, infiltrating Ly6Chi monocytes and their-derived macrophage (MoMFs) descendants prevail in acute or chronic liver injury, display marked transcriptional variance and provide crucial functional plasticity. A specific example of MoMFs are lipid associated macrophages (LAMs) involved in progression of metabolic liver disease (Remmerie et al., 2020). Recent studies have uncovered binary developmental trajectories of monocytes in the BM with Neutrophil-like (NeuMo) and dendritic cell (DC)-like (DCMo) monocytes (Weinreb et al., 2020; Yanez et al., 2017), hence further challenging our current comprehension of macrophage heterogeneity in the diseased liver. Yet, the molecular factors regulating their inflammatory versus restorative activity remains enigmatic. The COMMD (copper metabolism MURR1 domain) family includes 10 evolutionarily conserved proteins. Functions of COMMD proteins are still being defined, but they seem to play non-redundant roles in regulating transcription and protein trafficking. Utilizing conditional COMMD10 knockout mice we uncovered a role for COMMD10 in limiting inflammasome activation in Ly6Chi monocytes during experimental sepsis and colitis (Mouhadeb et al., 2018), and in supporting phagolysosomal biogenesis and maturation in KCs and BM-derived macrophages infected with Staphylococcus aureus (Ben Shlomo et al., 2019). Hence, these studies mark COMMD10 as a candidate mediator of monocyte and macrophage fate and immune responses. Here we studeis the effect of COMMD10-deficiency on Ly6Chi monocyte differentiation and inflammatory behaviour in the injured liver, using an acute model of acetaminophen-induced liver injury (AILI). Single cell RNAseq analysis of sorted Ly6Chi monocytes, comparing between COMMD10+ and COMMD10-deficient cells, revealed increased differentiation bias of Ly6Chi monocytes towards NeuMo and LAM differentiation fates. Collectively, COMMD10 appears as an important regulator of Ly6Chi monocyte fate decisions and reparative behavior in the diseased liver.
Project description:Purpose: In our study, we identified a heterogeneity among bone marrow (BM) Ly6Chi monocytes, which can be subdivided the expression of CXCR4. In order to understand the development of BM monocytes, the goal of this experiment is to compare the transcriptome of these 2 BM Ly6Chi monocyte subsets to those of the common monocyte progenitor (cMoP) and Ly6Clo monocytes.
Project description:We performed a single-cell transcriptomic analysis of monocyte and monocyte progenitors by single-cell mRNA sequencing (scRNA-seq) using the C1 Fluidigm platform. We sorted BM cMoPs (Lin−CD117+CD115+CD135−Ly6C+), BM Ly6C+ monocytes (Lin−CD117-CD115+CD135−Ly6C+) and blood Ly6Chi monocytes (CD115+CD11b+Ly6Chi) from wild-type (WT) C57BL/6 mice by fluorescence-activated cell sorting (FACS) and generated transcriptional profiles for each individual cell (n = 38 for blood Ly6Chi monocytes, n = 66 for BM cMoPs, n = 57 for BM Ly6C+ monocytes).
Project description:Circulating monocytes are crucial for tissue resident macrophage (TRM) replenishment. While a temporary loss of TRMs does not impose immediate danger to the host in sterile conditions, the niche comprising of dying macrophages in the presence of pathogenic bacteria predisposes the host to increased morbidity if these cells are not effectively replaced. Importantly, monocytes have been shown to be susceptible to cell death after executing effector functions such as phagocytosis. Hence, the demands and contribution of monocytes in pathogen clearance and macrophage differentiation is perplexing. Interestingly, we show that proliferating transitional pre-monocytes (TpMos), an immediate precursor of mature Ly6Chi monocytes (MatMos), were mobilized into the periphery in response to acute bacterial infection and sepsis. Since TpMos are absent in the circulation in the steady state, we aim to understand how TpMo recruitment into the periphery may result in differing functions from MatMos during sepsis.
Project description:Monocytes comprise two major subsets, Ly6Chi classical monocytes and Ly6Clo non-classical monocytes. Notch2 signaling in Ly6Chi monocytes triggers transition to Ly6Clo monocytes, which require Nr4a1, Bcl6, Irf2 and Cebpb. By comparison, less is known about transcriptional requirements for Ly6Chi monocytes. We find transcription factor CCAAT/enhancer-binding protein alpha (C/EBPα) is highly expressed in Ly6Chi monocytes, but down-regulated in Ly6Clo monocytes. A few previous studies described the requirement of C/EBPα in the development of neutrophils and eosinophils. However, role of C/EBPα for in vivo monocyte development has not been understood. We deleted the Cebpa +37 kb enhancer in mice, eliminating hematopoietic expression of C/EBPα, reproducing the expected neutrophil defect. Surprisingly, we also discovered a severe and selective loss of Ly6Chi monocytes, while preserving Ly6Clo monocytes. We find that BM progenitors from Cebpa +37–/– mice rapidly progress through the cMoP stage to develop directly into Ly6Clo monocytes even in the absence of Notch2 signaling. These results identify a previously unrecognized role for C/EBPα in maintaining Ly6Chi monocyte identity.
Project description:We studied the role of Notch2 signaling in Ly6Chi monocyte cell fate during TLR7-induced acute inflammation. To characterize the gene expression changes involved in monocyte differentiation, we subjected monocyte subsets from peripheral blood of wt and myeloid Notch2 mutant mice after Sham or IMQ treatment to RNA-sequencing and gene expression analysis. We found that Cell-intrinsic Notch2 and TLR7-Myd88 pathways independently and synergistically promote Ly6Clo patrolling monocyte development from Ly6Chi monocytes under inflammatory conditions. At the same time TLR7 stimulation in the absence of functional Notch2 signaling promotes resident tissue macrophage gene expression signatures in monocytes and ectopic differentiation of Ly6Chi monocytes into macrophages and dendritic cells. Thus, Notch2 is a master regulator of Ly6Chi monocyte cell fate and inflammation in response to TLR signaling.
Project description:Although most tissue macrophages are embryonically derived it is evident that circulating monocytes can compete for virtually any macrophage niche. Monocytes can thus become long-lived replacements of tissue macrophages that are indistinguishable from their embryonic counterparts, but the factors regulating this process are incompletely understood. To study niche competition in the CNS we depleted microglia with >95% efficiency using CX3CR1CreER/+R26DTA/+ mice and monitored long-term repopulation. The microglial niche was repopulated within weeks by a combination of local microglia proliferation giving rise to CX3CR1+F4/80lowClec12a– microglia, as well as infiltration of CX3CR1+F4/80hiClec12a+ macrophages. Adoptive transfer experiments demonstrated that peripherally-derived macrophages arose directly from Ly6Chi monocytes without contribution from hematopoietic progenitors and was independent of BBB breakdown. After repopulation we sorted microglia and monocyte-derived macrophages and performed transcriptional, epigenetic (DNA methylation) and ex vivo functional profiling. This revealed that Ly6Chi monocytes upregulated microglia gene expression and adopted microglia DNA methylation signatures. However, in contrast to proliferating microglia, which rapidly regained their homeostatic gene signature, monocyte-derived macrophages retained a distinct gene signature associated with antigen presentation, interferon signaling and chemotaxis. This translated into functional changes in monocyte-derived macrophages, as demonstrated by differences in surface marker expression, phagocytosis and cytokine production. Our results demonstrate that monocytes are imprinted by the CNS microenvironment but remain transcriptionally, epigenetically and functionally distinct. This may have implications for neuroinflammatory disease states and direct design of novel therapies.