Patrolling Alveolar Macrophages Conceal Bacteria from the Immune System to Maintain Homeostasis.

During respiration, humans breathe in more than 10,000 liters of non-sterile air daily, allowing some pathogens access to alveoli. Interestingly, alveoli outnumber alveolar macrophages (AMs), which favors alveoli devoid of AMs. If AMs, like most tissue macrophages, are sessile, then this numerical advantage would be exploited by pathogens unless neutrophils from the blood stream intervened. However, this would translate to omnipresent persistent inflammation. Developing in vivo real-time intravital imaging of alveoli revealed AMs crawling in and between alveoli using the pores of Kohn. Importantly, these macrophages sensed, chemotaxed, and, with high efficiency, phagocytosed inhaled bacterial pathogens such as P. aeruginosa and S. aureus, cloaking the bacteria from neutrophils. Impairing AM chemotaxis toward bacteria induced superfluous neutrophil recruitment, leading to inappropriate inflammation and injury. In a disease context, influenza A virus infection impaired AM crawling via the type II interferon signaling pathway, and this greatly increased secondary bacterial co-infection.

Lung Single-Cell Signaling Interaction Map Reveals Basophil Role in Macrophage Imprinting.

Lung development and function arises from the interactions between diverse cell types and lineages. Using single-cell RNA sequencing (RNA-seq), we characterize the cellular composition of the lung during development and identify vast dynamics in cell composition and their molecular characteristics. Analyzing 818 ligand-receptor interaction pairs within and between cell lineages, we identify broadly interacting cells, including AT2, innate lymphocytes (ILCs), and basophils. Using interleukin (IL)-33 receptor knockout mice and in vitro experiments, we show that basophils establish a lung-specific function imprinted by IL-33 and granulocyte-macrophage colony-stimulating factor (GM-CSF), characterized by unique signaling of cytokines and growth factors important for stromal, epithelial, and myeloid cell fates. Antibody-depletion strategies, diphtheria toxin-mediated selective depletion of basophils, and co-culture studies show that lung resident basophils are important regulators of alveolar macrophage development and function. Together, our study demonstrates how whole-tissue signaling interaction map on the single-cell level can broaden our understanding of cellular networks in health and disease.

Induction of Autonomous Memory Alveolar Macrophages Requires T Cell Help and Is Critical to Trained Immunity.

Innate immune memory is an emerging area of research. However, innate immune memory at major mucosal sites remains poorly understood. Here, we show that respiratory viral infection induces long-lasting memory alveolar macrophages (AMs). Memory AMs are programed to express high MHC II, a defense-ready gene signature, and increased glycolytic metabolism, and produce, upon re-stimulation, neutrophil chemokines. Using a multitude of approaches, we reveal that the priming, but not maintenance, of memory AMs requires the help from effector CD8 T cells. T cells jump-start this process via IFN-γ production. We further find that formation and maintenance of memory AMs are independent of monocytes or bone marrow progenitors. Finally, we demonstrate that memory AMs are poised for robust trained immunity against bacterial infection in the lung via rapid induction of chemokines and neutrophilia. Our study thus establishes a new paradigm of immunological memory formation whereby adaptive T-lymphocytes render innate memory of mucosal-associated macrophages.

Biology of lung macrophages in health and disease.

Tissue-resident alveolar and interstitial macrophages and recruited macrophages are critical players in innate immunity and maintenance of lung homeostasis. Until recently, assessing the differential functional contributions of tissue-resident versus recruited macrophages has been challenging because they share overlapping cell surface markers, making it difficult to separate them using conventional methods. This review describes how scRNA-seq and spatial transcriptomics can separate these subpopulations and help unravel the complexity of macrophage biology in homeostasis and disease. First, we provide a guide to identifying and distinguishing lung macrophages from other mononuclear phagocytes in humans and mice. Second, we outline emerging concepts related to the development and function of the various lung macrophages in the alveolar, perivascular, and interstitial niches. Finally, we describe how different tissue states profoundly alter their functions, including acute and chronic lung disease, cancer, and aging.

Uncoupling of macrophage inflammation from self-renewal modulates host recovery from respiratory viral infection.

Tissue macrophages self-renew during homeostasis and produce inflammatory mediators upon microbial infection. We examined the relationship between proliferative and inflammatory properties of tissue macrophages by defining the impact of the Wnt/ß-catenin pathway, a central regulator of self-renewal, in alveolar macrophages (AMs). Activation of ß-catenin by Wnt ligand inhibited AM proliferation and stemness, but promoted inflammatory activity. In a murine influenza viral pneumonia model, ß-catenin-mediated AM inflammatory activity promoted acute host morbidity; in contrast, AM proliferation enabled repopulation of reparative AMs and tissue recovery following viral clearance. Mechanistically, Wnt treatment promoted ß-catenin-HIF-1α interaction and glycolysis-dependent inflammation while suppressing mitochondrial metabolism and thereby, AM proliferation. Differential HIF-1α activities distinguished proliferative and inflammatory AMs in vivo. This ß-catenin-HIF-1α axis was conserved in human AMs and enhanced HIF-1α expression associated with macrophage inflammation in COVID-19 patients. Thus, inflammatory and reparative activities of lung macrophages are regulated by ß-catenin-HIF-1α signaling, with implications for the treatment of severe respiratory diseases.

The Cytokine TGF-ß Promotes the Development and Homeostasis of Alveolar Macrophages.

Alveolar macrophages (AMs) derive from fetal liver monocytes, which colonize the lung during embryonic development and give rise to fully mature AMs perinatally. AM differentiation requires granulocyte macrophage colony-stimulating factor (GM-CSF), but whether additional factors are involved in AM regulation is not known. Here we report that AMs, in contrast to most other tissue macrophages, were also dependent on transforming growth factor-ß receptor (TGF-ßR) signaling. Conditional deletion of TGF-ßR in mice at different time points halted the development and differentiation of AMs. In adult mice, TGF-ß was also critical for AM homeostasis. The source of TGF-ß was AMs themselves, indicative of an autocrine loop that promotes AM self-maintenance. Mechanistically, TGF-ßR signaling resulted in upregulation of PPAR-γ, a signature transcription factor essential for the development of AMs. These findings reveal an additional layer of complexity regarding the guidance cues, which govern the genesis, maturation, and survival of AMs.

Identification of immune-related gene signatures for chronic obstructive pulmonary disease with metabolic syndrome: evidence from integrated bulk and single-cell RNA sequencing data.

Chronic obstructive pulmonary disease (COPD) is closely related to innate and adaptive inflammatory immune responses. It is increasingly becoming evident that metabolic syndrome (MetS) affects a significant portion of COPD patients. Through this investigation, we identify shared immune-related candidate biological markers. The Weighted Gene Co-Expression Network Analysis (WGCNA) was utilized to reveal the co-expression modules linked to COPD and MetS. The commonly expressed genes in the COPD and MetS were utilized to conduct an enrichment analysis. We adopted machine-learning to screen and validate hub genes. We also assessed the relationship between hub genes and immune cell infiltration in COPD and MetS, respectively. Moreover, associations across hub genes and metabolic pathways were also explored. Finally, we chose a single-cell RNA sequencing (scRNA-seq) dataset to investigate the hub genes and shared mechanisms at the level of the cells. We also applied cell trajectory analysis and cell-cell communication analysis to focus on the vital immune cell we were interested in. As a result, we selected and validated 13 shared hub genes for COPD and MetS. The enrichment analysis and immune infiltration analysis illustrated strong associations between hub genes and immunology. Additionally, we applied metabolic pathway enrichment analysis, indicating the significant role of reactive oxygen species (ROS) in COPD with MetS. Through scRNA-seq analysis, we found that ROS might accumulate the most in the alveolar macrophages. In conclusion, the 13 hub genes related to the immune response and metabolism may serve as diagnostic biomarkers and treatment targets of COPD with MetS.

Inhaled Fine Particles Induce Alveolar Macrophage Death and Interleukin-1α Release to Promote Inducible Bronchus-Associated Lymphoid Tissue Formation.

Particulate pollution is thought to function as an adjuvant that can induce allergic responses. However, the exact cell types and immunological factors that initiate the lung-specific immune responses are unclear. We found that upon intratracheal instillation, particulates such as aluminum salts and silica killed alveolar macrophages (AMs), which then released interleukin-1α (IL-1α) and caused inducible bronchus-associated lymphoid tissue (iBALT) formation in the lung. IL-1α release continued for up to 2 weeks after particulate exposure, and type-2 allergic immune responses were induced by the inhalation of antigen during IL-1α release and iBALT formation, even long after particulate instillation. Recombinant IL-1α was sufficient to induce iBALTs, which coincided with subsequent immunoglobulin E responses, and IL-1-receptor-deficient mice failed to induce iBALT formation. Therefore, the AM-IL-1α-iBALT axis might be a therapeutic target for particulate-induced allergic inflammation.

ISM1 protects lung homeostasis via cell-surface GRP78-mediated alveolar macrophage apoptosis.

Alveolar macrophages (AMs) are critical for lung immune defense and homeostasis. They are orchestrators of chronic obstructive pulmonary disease (COPD), with their number significantly increased and functions altered in COPD. However, it is unclear how AM number and function are controlled in a healthy lung and if changes in AMs without environmental assault are sufficient to trigger lung inflammation and COPD. We report here that absence of isthmin 1 (ISM1) in mice (Ism1-/- ) leads to increase in both AM number and functional heterogeneity, with enduring lung inflammation, progressive emphysema, and significant lung function decline, phenotypes similar to human COPD. We reveal that ISM1 is a lung resident anti-inflammatory protein that selectively triggers the apoptosis of AMs that harbor high levels of its receptor cell-surface GRP78 (csGRP78). csGRP78 is present at a heterogeneous level in the AMs of a healthy lung, but csGRP78high AMs are expanded in Ism1-/- mice, cigarette smoke (CS)-induced COPD mice, and human COPD lung, making these cells the prime targets of ISM1-mediated apoptosis. We show that csGRP78high AMs mostly express MMP-12, hence proinflammatory. Intratracheal delivery of recombinant ISM1 (rISM1) depleted csGRP78high AMs in both Ism1-/- and CS-induced COPD mice, blocked emphysema development, and preserved lung function. Consistently, ISM1 expression in human lungs positively correlates with AM apoptosis, suggesting similar function of ISM1-csGRP78 in human lungs. Our findings reveal that AM apoptosis regulation is an important physiological mechanism for maintaining lung homeostasis and demonstrate the potential of pulmonary-delivered rISM1 to target csGRP78 as a therapeutic strategy for COPD.

Mast-cell expressed membrane protein-1 is expressed in classical monocytes and alveolar macrophages in idiopathic pulmonary fibrosis and regulates cell chemotaxis, adhesion, and migration in a TGFß-dependent manner.

Mast-cell expressed membrane protein-1 (MCEMP1) is higher in patients with idiopathic pulmonary fibrosis (IPF) with an increased risk of death. Here we aimed to establish the mechanistic role of MCEMP1 in pulmonary fibrosis. We identified increased MCEMP1 expression in classical monocytes and alveolar macrophages in IPF compared with controls. MCEMP1 is upregulated by transforming growth factor beta (TGFß) at the mRNA and protein levels in monocytic leukemia THP-1 cells. TGFß-mediated MCEMP1 upregulation results from the cooperation of SMAD3 and SP1 via concomitant binding to SMAD3/SP1 cis-regulatory elements within the MCEMP1 promoter. We also found that MCEMP1 regulates TGFß-mediated monocyte chemotaxis, adhesion, and migration. Our results suggest that MCEMP1 may regulate the migration and transition of monocytes to monocyte-derived alveolar macrophages during pulmonary fibrosis development and progression.NEW & NOTEWORTHY MCEMP1 is highly expressed in circulating classical monocytes and alveolar macrophages in IPF, is regulated by TGFß, and participates in the chemotaxis, adhesion, and migration of circulating monocytes by modulating the effect of TGFß in RHO activity.

Alveolar macrophage lipid burden correlates with clinical improvement in patients with pulmonary alveolar proteinosis.

Pulmonary alveolar proteinosis (PAP) is a life-threatening, rare lung syndrome for which there is no cure and no approved therapies. PAP is a disease of lipid accumulation characterized by alveolar macrophage foam cell formation. While much is known about the clinical presentation, there is a paucity of information regarding temporal changes in lipids throughout the course of disease. Our objectives were to define the detailed lipid composition of alveolar macrophages in PAP patients at the time of diagnosis and during treatment. We performed comprehensive mass spectrometry to profile the lipid signature of alveolar macrophages obtained from three independent mouse models of PAP and from PAP and non-PAP patients. Additionally, we quantified changes in macrophage-associated lipids during clinical treatment of PAP patients. We found remarkable variations in lipid composition in PAP patients, which were consistent with data from three independent mouse models. Detailed lipidomic analysis revealed that the overall alveolar macrophage lipid burden inversely correlated with clinical improvement and response to therapy in PAP patients. Specifically, as PAP patients experienced clinical improvement, there was a notable decrease in the total lipid content of alveolar macrophages. This crucial observation suggests that the levels of these macrophage-associated lipids can be utilized to assess the efficacy of treatment. These findings provide valuable insights into the dysregulated lipid metabolism associated with PAP, offering the potential for lipid profiling to serve as a means of monitoring therapeutic interventions in PAP patients.

Identification of Siglec-1-negative alveolar macrophages with proinflammatory phenotypes in chronic obstructive pulmonary disease.

Alveolar macrophages (AMs) in patients with chronic obstructive pulmonary disease (COPD) orchestrate persistent inflammation in the airway. However, subpopulations of AMs participating in chronic inflammation have been poorly characterized. We previously reported that Siglec-1 expression on AMs, which is important for bacteria engulfment, was decreased in COPD. Here, we show that Siglec-1-negative AMs isolated from COPD lung tissues exhibit a proinflammatory phenotype and are associated with poor clinical outcomes in patients with COPD. Using flow cytometry, we segregated three subsets of AMs based on the expression of Siglec-1 and their side scattergram (SSC) and forward scattergram (FSC) properties: Siglec-1+SSChiFSChi, Siglec-1-SSChiFSChi, and Siglec-1-SSCloFSClo subsets. The Siglec-1-SSCloFSClo subset number was increased in COPD. RNA sequencing revealed upregulation of multiple proinflammatory signaling pathways and emphysema-associated matrix metalloproteases in the Siglec-1-SSCloFSClo subset. Gene set enrichment analysis indicated that the Siglec-1-SSCloFSClo subset adopted intermediate phenotypes between monocytes and mature alveolar macrophages. Functionally, these cells produced TNF-α, IL-6, and IL-8 at baseline, and these cytokines were significantly increased in response to viral RNA. The increase in Siglec-1-negative AMs in induced sputum is associated with future exacerbation risk and lung function decline in patients with COPD. Collectively, the novel Siglec-1-SSCloFSClo subset of AMs displays proinflammatory properties, and their emergence in COPD airways may be associated with poor clinical outcomes.NEW & NOTEWORTHY Alveolar macrophages (AMs) in patients with chronic obstructive pulmonary disease (COPD) orchestrate persistent inflammation in the airway. We find that Siglec-1-negative alveolar macrophages have a wide range of proinflammatory landscapes and a protease-expressing phenotype. Moreover, this subset is associated with the pathogenesis of COPD and responds to viral stimuli.

Transplantation of alveolar macrophages improves the efficacy of endothelial progenitor cell therapy in mouse model of bronchopulmonary dysplasia.

Bronchopulmonary dysplasia (BPD) is a severe complication of preterm births, which develops due to exposure to supplemental oxygen and mechanical ventilation. Published studies demonstrated that the number of endothelial progenitor cells (EPC) is decreased in mouse and human BPD lungs and that adoptive transfer of EPC is an effective approach in reversing the hyperoxia-induced lung damage in mouse model of BPD. Recent advancements in macrophage biology identified the specific subtypes of circulating and resident macrophages mediating the developmental and regenerative functions in the lungs. Several studies reported the successful application of macrophage therapy in accelerating the regenerative capacity of damaged tissues and enhancing the therapeutic efficacy of other transplantable progenitor cells. In the present study, we explored the efficacy of combined cell therapy with EPC and resident alveolar macrophages (rAM) in hyperoxia-induced BPD mouse model. rAM and EPC were purified from neonatal mouse lungs and were used for adoptive transfer to the recipient neonatal mice exposed to hyperoxia. Adoptive transfer of rAM alone did not result in engraftment of donor rAM into the lung tissue but increased the mRNA level and protein concentration of proangiogenic CXCL12 chemokine in recipient mouse lungs. Depletion of rAM by chlodronate-liposomes decreased the retention of donor EPC after their transplantation into hyperoxia-injured lungs. Adoptive transfer of rAM in combination with EPC enhanced the therapeutic efficacy of EPC as evidenced by increased retention of EPC, increased capillary density, improved arterial oxygenation, and alveolarization in hyperoxia-injured lungs. Dual therapy with EPC and rAM has promise in human BPD.NEW & NOTEWORTHY Recent studies demonstrated that transplantation of lung-resident endothelial progenitor cells (EPC) is an effective therapy in mouse model of bronchopulmonary dysplasia (BPD). However, key factors regulating the efficacy of EPC are unknown. Herein, we demonstrate that transplantation of tissue-resident alveolar macrophages (rAM) increases CXCL12 expression in neonatal mouse lungs. rAM are required for retention of donor EPC in hyperoxia-injured lungs. Co-transplantation of rAM and EPC improves the efficacy of EPC therapy in mouse BPD model.

Fetal monocytes possess increased metabolic capacity and replace primitive macrophages in tissue macrophage development.

Tissue-resident macrophages (MΦTR ) originate from at least two distinct waves of erythro-myeloid progenitors (EMP) arising in the yolk sac (YS) at E7.5 and E8.5 with the latter going through a liver monocyte intermediate. The relative potential of these precursors in determining development and functional capacity of MΦTR remains unclear. Here, we studied development of alveolar macrophages (AM) after single and competitive transplantation of different precursors from YS, fetal liver, and fetal lung into neonatal Csf2ra-/- mice, which lack endogenous AM. Fetal monocytes, promoted by Myb, outcompeted primitive MΦ (pMΦ) in empty AM niches and preferentially developed to mature AM, which is associated with enhanced mitochondrial respiratory and glycolytic capacity and repression of the transcription factors c-Maf and MafB. Interestingly, AM derived from pMΦ failed to efficiently clear alveolar proteinosis and protect from fatal lung failure following influenza virus infection. Thus, our data demonstrate superior developmental and functional capacity of fetal monocytes over pMΦ in AM development and underlying mechanisms explaining replacement of pMΦ in fetal tissues.

Th2-dependent disappearance and phenotypic conversion of mouse alveolar macrophages.

Alveolar macrophages (alvMs) play an important role for maintenance of lung function by constant removal of cellular debris in the alveolar space. They further contribute to defense against microbial or viral infections and limit tissue damage during acute lung injury. alvMs arise from embryonic progenitor cells, seed the alveoli before birth, and have life-long self-renewing capacity. However, recruited monocytes may also help to restore the alvM population after depletion caused by toxins or influenza virus infection. At present, the population dynamics and cellular plasticity of alvMs during allergic lung inflammation is poorly defined. To address this point, we used a mouse model of Aspergillus fumigatus-induced allergic lung inflammation and observed that Th2-derived IL-4 and IL-13 caused almost complete disappearance of alvMs. This effect required STAT6 expression in alvMs and also occurred in various other settings of type 2 immunity-mediated lung inflammation or administration of IL-4 complexes to the lung. In addition, Th2 cells promoted conversion of alvMs to alternatively activated macrophages and multinucleated giant cells. Given the well-established role of alvMs for maintenance of lung function, this process may have implications for resolution of inflammation and tissue homeostasis in allergic asthma.

Multiomic analysis of monocyte-derived alveolar macrophages in idiopathic pulmonary fibrosis.

BACKGROUND: Monocyte-derived alveolar macrophages (Mo_AMs) are increasingly recognised as potential pathogenic factors for idiopathic pulmonary fibrosis (IPF). While scRNAseq analysis has proven valuable in the transcriptome profiling of Mo_AMs, the integration analysis of multi-omics may provide additional dimensions of understanding of these cellular populations. METHODS: We performed multi-omics analysis on 116 scRNAseq, 119 bulkseq and five scATACseq lung tissue samples from IPF. We built a large-scale IPF scRNAseq atlas and conducted the Monocle 2/3 as well as the Cellchat to explore the developmental path and intercellular communication on Mo_AMs. We also reported the difference in metabolisms, tissue repair and phagocytosis between Mo_AMs and tissue-resident alveolar macrophages (TRMs). To determine whether Mo_AMs affected pulmonary function, we projected clinical phenotypes (FVC%pred) from the bulkseq dataset onto the scRNAseq atlas. Finally, we used scATATCseq to uncover the upstream regulatory mechanisms and determine key drivers in Mo_AMs. RESULTS: We identified three Mo_AMs clusters and the trajectory analysis further validated the origin of these clusters. Moreover, via the Cellchat analysis, the CXCL12/CXCR4 axis was found to be involved in the molecular basis of reciprocal interactions between Mo_AMs and fibroblasts through the activation of the ERK pathway in Mo_AMs. SPP1_RecMacs (RecMacs, recruited macrophages) were higher in the low-FVC group than in the high-FVC group. Specifically, compared with TRMs, the functions of lipid and energetic metabolism as well as tissue repair were higher in Mo_AMs than TRMs. But, TRMs may have higher level of phagocytosis than TRMs. SPIB (PU.1), JUNB, JUND, BACH2, FOSL2, and SMARCC1 showed stronger association with open chromatin of Mo_AMs than TRMs. Significant upregulated expression and deep chromatin accessibility of APOE were observed in both SPP1_RecMacs and TRMs. CONCLUSION: Through trajectory analysis, it was confirmed that SPP1_RecMacs derived from Monocytes. Besides, Mo_AMs may influence FVC% pred and aggravate pulmonary fibrosis through the communication with fibroblasts. Furthermore, distinctive transcriptional regulators between Mo_AMs and TRMs implied that they may depend on different upstream regulatory mechanisms. Overall, this work provides a global overview of how Mo_AMs govern IPF and also helps determine better approaches and intervention therapies.

Modulation of alveolar macrophage and mitochondrial fitness by medicinal plant-derived nanovesicles to mitigate acute lung injury and viral pneumonia.

Acute lung injury (ALI) is generally caused by severe respiratory infection and characterized by overexuberant inflammatory responses and inefficient pathogens-containing, the two major processes wherein alveolar macrophages (AMs) play a central role. Dysfunctional mitochondria have been linked with distorted macrophages and hence lung disorders, but few treatments are currently available to correct these defects. Plant-derive nanovesicles have gained significant attention because of their therapeutic potential, but the targeting cells and the underlying mechanism remain elusive. We herein prepared the nanovesicles from Artemisia annua, a well-known medicinal plant with multiple attributes involving anti-inflammatory, anti-infection, and metabolism-regulating properties. By applying three mice models of acute lung injury caused by bacterial endotoxin, influenza A virus (IAV) and SARS-CoV-2 pseudovirus respectively, we showed that Artemisia-derived nanovesicles (ADNVs) substantially alleviated lung immunopathology and raised the survival rate of challenged mice. Macrophage depletion and adoptive transfer studies confirmed the requirement of AMs for ADNVs effects. We identified that gamma-aminobutyric acid (GABA) enclosed in the vesicles is a major molecular effector mediating the regulatory roles of ADNVs. Specifically, GABA acts on macrophages through GABA receptors, promoting mitochondrial gene programming and bioenergy generation, reducing oxidative stress and inflammatory signals, thereby enhancing the adaptability of AMs to inflammation resolution. Collectively, this study identifies a promising nanotherapeutics for alleviating lung pathology, and elucidates a mechanism whereby the canonical neurotransmitter modifies AMs and mitochondria to resume tissue homeostasis, which may have broader implications for treating critical pulmonary diseases such as COVID-19.

2-Deoxy-D-glucose ameliorates inflammation and fibrosis in a silicosis mouse model by inhibiting hypoxia-inducible factor-1α in alveolar macrophages.

Inhaling silica causes the occupational illness silicosis, which mostly results in the gradual fibrosis of lung tissue. Previous research has demonstrated that hypoxia-inducible factor-1α (HIF-1α) and glycolysis-related genes are up-regulated in silicosis. The role of 2-deoxy-D-glucose (2-DG) as an inhibitor of glycolysis in silicosis mouse models and its molecular mechanisms remain unclear. Therefore, we used 2-DG to observe its effect on pulmonary inflammation and fibrosis in a silicosis mouse model. Furthermore, in vitro cell experiments were conducted to explore the specific mechanisms of HIF-1α. Our study found that 2-DG down-regulated HIF-1α levels in alveolar macrophages induced by silica exposure and reduced the interleukin-1ß (IL-1ß) level in pulmonary inflammation. Additionally, 2-DG reduced silica-induced pulmonary fibrosis. From these findings, we hypothesize that 2-DG reduced glucose transporter 1 (GLUT1) expression by inhibiting glycolysis, which inhibits the expression of HIF-1α and ultimately reduces transcription of the inflammatory cytokine, IL-1ß, thus alleviating lung damage. Therefore, we elucidated the important regulatory role of HIF-1α in an experimental silicosis model and the potential defense mechanisms of 2-DG. These results provide a possible effective strategy for 2-DG in the treatment of silicosis.

Polyhexamethylene guanidine accelerates the macrophage foamy formation mediated pulmonary fibrosis.

Polyhexamethylene guanidine (PHMG) is manufactured and applied extensively due to its superior disinfectant capabilities. However, the inhalatory exposure to PHMG aerosols is increasingly recognized as a potential instigator of pulmonary fibrosis, prompting an urgent call for elucidation of the underlying pathophysiological mechanisms. Within this context, alveolar macrophages play a pivotal role in the primary immune defense in the respiratory tract. Dysregulated lipid metabolism within alveolar macrophages leads to the accumulation of foam cells, a process that is intimately linked with the pathogenesis of pulmonary fibrosis. Therefore, this study examines PHMG's effects on alveolar macrophage foaminess and its underlying mechanisms. We conducted a 3-week inhalation exposure followed by a 3-week recovery period in C57BL/6 J mice using a whole-body exposure system equipped with a disinfection aerosol generator (WESDAG). The presence of lipid-laden alveolar macrophages and downregulation of pulmonary tissue lipid transport proteins ABCA1 and ABCG1 were observed in mice. In cell culture models involving lipid-loaded macrophages, we demonstrated that PHMG promotes foam cell formation by inhibiting lipid efflux in mouse alveolar macrophages. Furthermore, PHMG-induced foam cells were found to promote an increase in the release of TGF-ß1, fibronectin deposition, and collagen remodeling. In vivo interventions were subsequently implemented on mice exposed to PHMG aerosols, aiming to restore macrophage lipid efflux function. Remarkably, this intervention demonstrated the potential to retard the progression of pulmonary fibrosis. In conclusion, this study underscores the pivotal role of macrophage foaming in the pathogenesis of PHMG disinfectants-induced pulmonary fibrosis. Moreover, it provides compelling evidence to suggest that the regulation of macrophage efflux function holds promise for mitigating the progression of pulmonary fibrosis, thereby offering novel insights into the mechanisms underlying inhaled PHMG disinfectants-induced pulmonary fibrosis.

Alveolar Macrophages-Mediated Translocation of Intratracheally Delivered Perfluorocarbon Nanoparticles to Achieve Lung Cancer 19F-MR Imaging.

Recent advances in intratracheal delivery strategies have sparked considerable biomedical interest in developing this promising approach for lung cancer diagnosis and treatment. However, there are very few relevant studies on the behavior and mechanism of imaging nanoparticles (NPs) after intratracheal delivery. Here, we found that nanosized perfluoro-15-crown-5-ether (PFCE NPs, ∼200 nm) exhibite significant 19F-MRI signal-to-noise ratio (SNR) enhancement than perfluorooctyl bromide (PFOB NPs) up to day 7 after intratracheal delivery. Alveolar macrophages (AMs) engulf PFCE NPs, become PFCE NPs-laden AMs, and then migrate into the tumor margin, resulting in increased tumor PFCE concentration and 19F-MRI signals. AMs-mediated translocation of PFCE NPs to lung draning lymph nodes (dLNs) decreases the background PFCE concentration. Our results shed light on the dynamic AMs-mediated translocation of intratracheally delivered PFC NPs for effective lung tumor visualization and reveal a pathway to develop and promote the clinical translation of an intratracheal delivery-based imaging strategy.