Selective depletion of CD11b-positive monocytes/macrophages potently suppresses bleomycin-induced pulmonary fibrosis

Role of sex as a biological variable in neonatal alveolar macrophages

The lung macrophages play a crucial role in health and disease. Sexual dimorphism significantly impacts the phenotype and function of tissue-resident macrophages. The primary mechanisms responsible for sexually dimorphic outcomes in bronchopulmonary dysplasia (BPD) remain unidentified. We tested the hypothesis that biological sex plays a crucial role in the transcriptional state of alveolar macrophages, using neonatal murine hyperoxia-induced lung injury as a relevant model for human BPD. The effects of neonatal hyperoxia exposure (95 % FiO2, PND1-5: saccular stage) on the lung myeloid cells acutely after injury and during normoxic recovery were measured. Alveolar macrophages (AM) from room air- and hyperoxia exposed from male and female neonatal murine lungs were subjected to bulk-RNA Sequencing. AMs are significantly depleted in the hyperoxia-exposed lung acutely after injury, with subsequent recovery in both sexes. The transcriptome of the alveolar macrophages is impacted by neonatal hyperoxia exposure and by sex as a biological variable. Pathways related to DNA damage and interferon-signaling were positively enriched in female AMs. Metabolic pathways related to glucose and carbohydrate metabolism were positively enriched in the male AMs, while oxidative phosphorylation was negatively enriched. These pathways were shared with monocytes and airway macrophages from intubated male and female human premature neonates.

Therapeutic effects of MEL-dKLA by targeting M2 macrophages in pulmonary fibrosis

Idiopathic pulmonary fibrosis is a progressive lung disease characterized by excessive extracellular matrix accumulation and myofibroblast proliferation with limited treatment options available. M2 macrophages are pivotal in pulmonary fibrosis, where they induce the epithelial-to-mesenchymal and fibroblast-to-myofibroblast transitions. In this study, we evaluated whether MEL-dKLA, a hybrid peptide that can eliminate M2 macrophages, could attenuate pulmonary fibrosis in a cell co-culture system and in a bleomycin-induced mouse model. Our findings demonstrated that the removal of M2 macrophages using MEL-dKLA stimulated reprogramming to an antifibrotic environment, which effectively suppressed epithelial-to-mesenchymal and fibroblast-to-myofibroblast transition responses in lung epithelial and fibroblast cells and reduced extracellular matrix accumulation both in vivo and in vitro. Moreover, MEL-dKLA exhibited antifibrotic efficacy without damaging tissue-resident macrophages in the bleomycin-induced mouse model. Collectively, our findings suggest that MEL-dKLA may be a new therapeutic option for the treatment of idiopathic pulmonary fibrosis.

The interplay of Cxcl10+/Mmp14+ monocytes and Ccl3+ neutrophils proactively mediates silica-induced pulmonary fibrosis

As a fatal occupational disease with limited therapeutic options, molecular mechanisms underpinning silicosis are still undefined. Herein, single-cell RNA sequencing of the lung tissue of silicosis mice identified two monocyte subsets, which were characterized by Cxcl10 and Mmp14 and enriched in fibrotic mouse lungs. Both Cxcl10+ and Mmp14+ monocyte subsets exhibited activation of inflammatory marker genes and positive regulation of cytokine production. Another fibrosis-unique neutrophil population characterized by Ccl3 appeared to be related to the pro-fibrotic process, specifically the "inflammatory response". Meanwhile, the proportion of monocytes and neutrophils was significantly higher in the serum of silicosis patients and slices of lung tissue from patients with silicosis further validated the over-expression of Cxcl10 and Mmp14 in monocytes, also Ccl3 in neutrophils, respectively. Mechanically, receptor-ligand interaction analysis identified the crosstalk of Cxcl10+/Mmp14+ monocytes with Ccl3+ neutrophils promoting fibrogenesis via coupling of HBEGF-CD44 and CSF1-CSF1R. In vivo, administration of clodronate liposomes, Cxcl10 or Mmp14 siRNA-loaded liposomes, Ccl3 receptor antagonist BX471, CD44 or CSF1R neutralizing antibodies significantly alleviated silica-induced lung fibrosis. Collectively, these results demonstrate that the newly defined Cxcl10+/Mmp14+ monocytes and Ccl3+ neutrophils participate in the silicosis process and highlight anti-receptor-ligand pair treatment as a potentially effective therapeutic strategy in managing silicosis.

GCRV-II invades monocytes/macrophages and induces macrophage polarization and apoptosis in tissues to facilitate viral replication and dissemination

Grass carp reovirus (GCRV), particularly the highly prevalent type II GCRV (GCRV-II), causes huge losses in the aquaculture industry. However, little is known about the mechanisms by which GCRV-II invades grass carp and further disseminates among tissues. In the present study, monocytes/macrophages (Mo/Mφs) were isolated from the peripheral blood of grass carp and infected with GCRV-II. The results of indirect immunofluorescent microscopy, transmission electron microscopy, real-time quantitative RT-PCR (qRT-PCR), western blot (WB), and flow cytometry analysis collectively demonstrated that GCRV-II invaded Mo/Mφs and replicated in them. Additionally, we observed that GCRV-II induced different types (M1 and M2) of polarization of Mo/Mφs in multiple tissues, especially in the brain, head kidney, and intestine. To assess the impact of different types of polarization on GCRV-II replication, we recombinantly expressed and purified the intact cytokines CiIFN-γ2, CiIL-4/13A, and CiIL-4/13B and successfully induced M1 and M2 type polarization of macrophages using these cytokines through in vitro experiments. qRT-PCR, WB, and flow cytometry analyses showed that M2 macrophages had higher susceptibility to GCRV-II infection than other types of Mo/Mφs. In addition, we found GCRV-II induced apoptosis of Mo/Mφs to facilitate virus replication and dissemination and also detected the presence of GCRV-II virus in plasma. Collectively, our findings indicated that GCRV-II could invade immune cells Mo/Mφs and induce apoptosis and polarization of Mo/Mφs for efficient infection and dissemination, emphasizing the crucial role of Mo/Mφs as a vector for GCRV-II infection.IMPORTANCEType II grass carp reovirus (GCRV) is a prevalent viral strain and causes huge losses in aquaculture. However, the related dissemination pathway and mechanism remain largely unclear. Here, our study focused on phagocytic immune cells, monocytes/macrophages (Mo/Mφs) in blood and tissues, and explored whether GCRV-II can invade Mo/Mφs and replicate and disseminate via Mo/Mφs with their differentiated type M1 and M2 macrophages. Our findings demonstrated that GCRV-II infected Mo/Mφs and replicated in them. Furthermore, GCRV-II infection induces an increased number of M1 and M2 macrophages in grass carp tissues and a higher viral load in M2 macrophages. Furthermore, GCRV-II induced Mo/Mφs apoptosis to release viruses, eventually infecting more cells. Our study identified Mo/Mφs as crucial components in the pathway of GCRV-II dissemination and provides a solid foundation for the development of treatment strategies for GCRV-II infection.

Monocytes and macrophages: emerging mechanisms and novel therapeutic targets in pulmonary fibrosis

Pulmonary fibrosis results from a plethora of abnormal pathogenetic events. In idiopathic pulmonary fibrosis (IPF), inhalational, environmental, or occupational exposures in genetically and epigenetically predisposed individuals trigger recurrent cycles of alveolar epithelial cell injury, activation of coagulation pathways, chemoattraction, and differentiation of monocytes into monocyte-derived alveolar macrophages (Mo-AMs). When these events happen intermittently and repeatedly throughout the individual's life cycle, the wound repair process becomes aberrant leading to bronchiolization of distal air spaces, fibroblast accumulation, extracellular matrix deposition, and loss of the alveolar-capillary architecture. The role of immune dysregulation in IPF pathogenesis and progression has been underscored in the past mainly after the disappointing results of immunosuppressant use in IPF patients; however, recent reports highlighting the prognostic and mechanistic roles of monocytes and Mo-AMs revived the interest in immune dysregulation in IPF. In this review, we will discuss the role of these cells in the onset and progression of IPF, as well as potential targeted therapies.

Macrophage Implication in IPF: Updates on Immune, Epigenetic, and Metabolic Pathways

Idiopathic pulmonary fibrosis (IPF) is a lethal interstitial lung disease of unknown etiology with a poor prognosis. It is a chronic and progressive disease that has a distinct radiological and pathological pattern from common interstitial pneumonia. The use of immunosuppressive medication was shown to be completely ineffective in clinical trials, resulting in years of neglect of the immune component. However, recent developments in fundamental and translational science demonstrate that immune cells play a significant regulatory role in IPF, and macrophages appear to be among the most crucial. These highly plastic cells generate multiple growth factors and mediators that highly affect the initiation and progression of IPF. In this review, we will provide an update on the role of macrophages in IPF through a systemic discussion of various regulatory mechanisms involving immune receptors, cytokines, metabolism, and epigenetics.