A genetic screen in fetal liver-derived alveolar-like macrophages (FLAMs) identifies new regulators of Siglec-F surface expression
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ABSTRACT: Alveolar macrophages (AMs) are tissue resident cells in the lungs derived from the fetal liver that maintain lung homeostasis and respond to inhaled stimuli. While the importance of AMs is undisputed, they remain refractory to standard experimental approaches and high-throughput functional genetics as they are challenging to isolate and rapidly lose AM properties in standard culture. This limitation hinders our understanding of key regulatory mechanisms that control AM maintenance and function. Here, we describe the development of a new model, fetal liver-derived alveolar-like macrophages (FLAMs), which maintains cellular morphologies, expression profiles, and functional mechanisms similar to murine AMs. FLAMs combine treatment with two key cytokines for AM maintenance, GM-CSF and TGFβ. We leveraged the long-term stability of FLAMs to develop functional genetic tools using CRISPR-Cas9-mediated gene editing. Targeted editing confirmed the role of AM-specific gene Marco and the IL-1 receptor Il1r1 in modulating the AM response to crystalline silica. Furthermore, a genome-wide knockout library using FLAMs identified novel genes required for surface expression of the AM marker Siglec-F, most notably those related to the peroxisome. Taken together, our results suggest that FLAMs are a stable, self-replicating model of AM function that enables previously impossible global genetic approaches to define the underlying mechanisms of AM maintenance and function.
Project description:Alveolar macrophages (AMs) are lung resident phagocytes. They derive from fetal liver monocytes, which colonize the lung during embryonic development and give rise to fully mature AMs perinatally. We have identified TGF- signaling as an indispensible regulator during this process. To analyze the impact of TGF- on the entire transcriptome of AMs, we performed RNA-seq on AMs deficient of Tgfbr2 in CD11cCre/+ Tgfbr2fl/fl mice at P3 with Tgfbr2fl/fl littermates as a control.
Project description:Alveolar macrophages (AMs) are key mediators of lung function and are potential targets for therapies during respiratory infections. TGFb is an important regulator of AM differentiation and maintenance but, how TGFb directly modulates the innate immune responses of AMs remains unclear. This shortcoming prevents effective targeting of AMs to improve lung function in health and disease. Here we leveraged an optimized ex vivo AM model system, fetal-liver derived alveolar-like macrophages (FLAMs), to dissect the role of TGFb in AMs. Using transcriptional analysis, we first globally defined how TGFb regulates gene expression of resting FLAMs. We found that TGFb maintains the baseline metabolic state of AMs by driving lipid metabolism through oxidative phosphorylation and restricting inflammation. To better understand inflammatory regulation in FLAMs, we next directly tested how TGFb alters the response to TLR2 agonists. While both TGFb (+) and TGFb (-) FLAMs robustly responded to TLR2 agonists, we found an unexpected activation of type I interferon (IFN) responses in FLAMs and primary AMs in a TGFb-dependent manner. Surprisingly, mitochondrial antiviral signaling protein and the interferon regulator factors 3 and 7 were required for IFN production by TLR2 agonists. Together, these data suggest that TGFb modulates AM metabolic networks and innate immune signaling cascades to control inflammatory pathways in AMs.
Project description:Transcriptional profiling of primary human alveolar macrophages (AMs) comparing control untreated AMs with AMs exposed with Serotype 14 Streptococcus pneumoniae (NCTC11902) strain (MOI 10) for 4 hours) Two-condition experiment, control AMs vs. infected AMs. Biological replicates: 3 control replicates, 3 infected replicates MOI 10.
Project description:Pulmonary alveolar proteinosis (PAP) results from a dysfunction of alveolar macrophages (AMs), chiefly due to disruptions in the signaling of granulocyte macrophage colony-stimulating factor (GM-CSF). We found that mice deficient for the B lymphoid transcription repressor BTB and CNC homology 2 (Bach2) developed PAP-like accumulation of surfactant proteins in the lungs. Bach2 was expressed in AMs, and Bach2-deficient AMs showed alterations in lipid handling in comparison with wild-type (WT) cells. Although Bach2-deficient AMs showed a normal expression of the genes involved in the GM-CSF signaling, they showed an altered expression of the genes involved in chemotaxis, lipid metabolism, and alternative M2 macrophage activation with increased expression of Ym1 and arginase-1, and the M2 regulator Irf4. Peritoneal Bach2-deficient macrophages showed increased Ym1 expression when stimulated with interleukin-4. More eosinophils were present in the lung and peritoneal cavity of Bach2-deficient mice compared with WT mice. The PAP-like lesions in Bach2-deficient mice were relieved by WT bone marrow transplantation even after their development, confirming the hematopoietic origin of the lesions. These results indicate that Bach2 is required for the functional maturation of AMs and pulmonary homeostasis, independently of the GM-CSF signaling. WT (n=8) and Bach2KO (n=3) AMs. One expreriment was performed.
Project description:Background: Degenerative disc disease (DDD) is a primary contributor to low back pain, a leading cause of disability. Progression of DDD is aided by inflammatory cytokines in the intervertebral disc (IVD), particularly TNF-α and IL-1β, but current treatments fail to effectively target this mechanism. The objective of this study was to explore the feasibility of CRISPR epigenome editing based therapy for DDD, by modulation of TNFR1/IL1R1 signaling in pathological human IVD cells. Methods: Human IVD cells from the nucleus pulposus of patients receiving surgery for back pain were obtained and the regulation of TNFR1/IL1R1 signaling by a lentiviral CRISPR epigenome editing system was tested. These cells were tested for successful lentiviral transduction/expression of dCas9-KRAB system and regulation of TNFR1/IL1R1 expression. TNFR1/IL1R1 signaling disruption was investigated via measurement of NF-κB activity, apoptosis, and anabolic/catabolic changes in gene expression post inflammatory challenge. Results: CRISPR epigenome editing systems were effectively introduced into pathological human IVD cells and significantly downregulated TNFR1 and IL1R1. This downregulation significantly attenuated deleterious TNFR1 signaling but not IL1R1 signaling. This is attributed to less robust IL1R1 expression downregulation, and IL-1β driven reversal of IL1R1 expression downregulation in a portion of patient IVD cells. Additionally, RNAseq data indicated a novel transcription factor targets, IRF1 and TFAP2C, as being a primary regulators of inflammatory signaling in IVD cells. Discussion: These results demonstrate the feasibility of CRISPR epigenome editing of inflammatory receptors in pathological IVD cells, but highlight a limitation in epigenome targeting of IL1R1. This method has potential application as a novel gene therapy for DDD, to attenuate the deleterious effect of inflammatory cytokines present in the degenerative IVD.
Project description:Tissue-resident macrophages (TRMs) play central roles in local tissue development and immunity. However, how to control TRM ontogeny and maintenance remains unclear. We performed transcriptional and histone modification analyses of alveolar macrophages in mice with myeloid-specific (Csf1rCre) deletion of HDAC3 using bulk RNA-seq, single-cell RNA-seq and ChIP-seq. We report that HDAC3 deficiency results in metabolic disorders and increased cell death of the fetal lung TRMs, which is partially regulated through directly targeting PPAR-γ. Although the loss of AMs in the absence of HDAC3 is not AM subset specific, the transcriptome changes in HDAC3 deficient AM subsets are different. We propose that HDAC3 serves a key epigenetic regulator that controls embryonic TRM ontogeny and maintenance.
Project description:Tissue-resident macrophages (TRMs) play central roles in local tissue development and immunity. However, how to control TRM ontogeny and maintenance remains unclear. We performed transcriptional and histone modification analyses of alveolar macrophages in mice with myeloid-specific (Csf1rCre) deletion of HDAC3 using bulk RNA-seq, single-cell RNA-seq and ChIP-seq. We report that HDAC3 deficiency results in metabolic disorders and increased cell death of the fetal lung TRMs, which is partially regulated through directly targeting PPAR-γ. Although the loss of AMs in the absence of HDAC3 is not AM subset specific, the transcriptome changes in HDAC3 deficient AM subsets are different. We propose that HDAC3 serves a key epigenetic regulator that controls embryonic TRM ontogeny and maintenance.
Project description:Tissue-resident macrophages (TRMs) play central roles in local tissue development and immunity. However, how to control TRM ontogeny and maintenance remains unclear. We performed transcriptional and histone modification analyses of alveolar macrophages in mice with myeloid-specific (Csf1rCre) deletion of HDAC3 using bulk RNA-seq, single-cell RNA-seq and ChIP-seq. We report that HDAC3 deficiency results in metabolic disorders and increased cell death of the fetal lung TRMs, which is partially regulated through directly targeting PPAR-γ. Although the loss of AMs in the absence of HDAC3 is not AM subset specific, the transcriptome changes in HDAC3 deficient AM subsets are different. We propose that HDAC3 serves a key epigenetic regulator that controls embryonic TRM ontogeny and maintenance.
Project description:The lung is inhabited by resident alveolar and interstitial macrophages as well as monocytic cells that survey the lung. Each cell type plays distinct functional roles under homeostatic and inflammatory conditions, but mechanisms establishing their molecular identities and functional potential remain poorly understood. Here, systematic evaluation of transcriptomes and open chromatin of alveolar macrophages (AMs), interstitial macrophages (IMs) and lung monocytes from two mouse strains enabled inference of common and cell-specific transcriptional regulators. We provide evidence that these factors drive selection of regulatory landscapes that specify distinct phenotypes of AMs and IMs and entrain qualitatively different responses to TLR4 signaling in vivo. These studies reveal a striking divergence in a fundamental innate immune response pathway in AMs and establish a framework for further understanding macrophage diversity in the lung.
Project description:The lung is inhabited by resident alveolar and interstitial macrophages as well as monocytic cells that survey the lung. Each cell type plays distinct functional roles under homeostatic and inflammatory conditions, but mechanisms establishing their molecular identities and functional potential remain poorly understood. Here, systematic evaluation of transcriptomes and open chromatin of alveolar macrophages (AMs), interstitial macrophages (IMs) and lung monocytes from two mouse strains enabled inference of common and cell-specific transcriptional regulators. We provide evidence that these factors drive selection of regulatory landscapes that specify distinct phenotypes of AMs and IMs and entrain qualitatively different responses to TLR4 signaling in vivo. These studies reveal a striking divergence in a fundamental innate immune response pathway in AMs and establish a framework for further understanding macrophage diversity in the lung.