Biology of lung macrophages in health and disease

Targeting ferroptosis offers therapy choice in sepsis-associated acute lung injury

Sepsis-associated acute lung injury (SALI) is a common complication of sepsis, consisting of a dysfunctional host response to infection-mediated heterogenous complexes. SALI is reported in up to 50 % of patients with sepsis and causes poor outcomes. Despite high incidence, there is a lack of understanding in its pathogenesis and optimal treatment. A better understanding of the molecular mechanisms underlying SALI may help produce better therapeutics. The effects of altered cell-death mechanisms, such as non-apoptotic regulated cell death (RCD) (i.e., ferroptosis), on the development of SALI are beginning to be discovered, while targeting ferroptosis as a meaningful target in SALI is increasingly being recognized. Here, we outline how a susceptible lung alveoli may develop SALI. Then we discuss the general mechanisms underlying ferroptosis, and how it contributes to SALI. We then outline the chemical structures of the emerging agents or compounds that can protect against SALI by inhibiting ferroptosis, summarizing their potential pharmacological effects. Finally, we highlight key limitations and possible strategies to overcome them. This review suggests that a detailed mechanistic and biological understanding of ferroptosis can foster the development of pharmacological antagonists in the treatment of SALI.

Synthesis, evaluation and mechanism study of novel pyrazole enamides to alleviate lung injury

Particulate matter with diameter ≤2.5 μm particles (PM2.5) can trigger pulmonary inflammation and lung injury. However, there is still no specific and effective treatment. Lansiumamide B (LB) is a natural cis-enamide compound isolated from wampee seeds, and has potential anti-inflammatory effect. Herein, two series of pyrazole enamide analogues were designed and synthesized based on the scaffold hopping strategy. The inhibition rates of inflammatory cytokines on compound 11a were superior to other compounds and exhibited good dose-dependent manner and safety. Mechanism studies shown that 11a activated the Keap1/Nrf2/HO-1 signaling pathway and promoted Nrf2 entering into nucleus. Further, 11a alleviated pulmonary inflammation, collagen formation and mucus secretion in PM2.5 induced lung injury mice. Besides, 11a administration inhibited M1 macrophage polarization and neutrophil infiltration. Overall, 11a is an effective anti-inflammatory agent which might be a potent candidate to treat lung injury.

Leukocyte kinetics and bacterial clearance during Streptococcus pneumoniae pneumonia and contributions of ICAM-1

Streptococcus pneumoniae is a leading cause of community-acquired pneumonia. Intercellular adhesion molecule-1 (ICAM-1) is an adhesion molecule that is highly expressed on the pulmonary capillary endothelium, alveolar epithelium, and other cell types within the lung. ICAM-1 plays important roles in leukocyte adhesion, migration, and motility. To determine the contributions of ICAM-1 to bacterial clearance and leukocyte kinetics during pneumonia, mice were inoculated with S. pneumoniae and evaluated 1, 4, and 7 days later. Our results show that Icam1-/- mice have a greater number of viable bacteria within the lung at each time point. The impaired clearance observed in Icam1-/- mice was not due to an impediment in leukocyte recruitment. In fact, Icam1-/- mice had a greater number of neutrophils and recruited inflammatory macrophages in the lung tissue and the alveoli/airways on day 7. In contrast, fewer alveolar macrophages were present in the bronchoalveolar lavage (BAL) of Icam1-/- mice. The loss of body weight and the concentrations of inflammatory mediators in the BAL were also significantly greater in Icam1-/- mice. Mechanistic studies to understand the defect in clearance show that neutrophils and macrophage subpopulations had no defect in phagocytosis or acidification of phagosomes. RNA sequencing reveals many differences in gene expression but no suggestion of a defect in phagocytosis or killing. Thus, ICAM-1 is necessary for the clearance of S. pneumoniae and for the resolution of pneumonia but is not required for the recruitment of neutrophils or inflammatory macrophages into the pneumonic lung parenchyma or the alveoli/airways during S. pneumoniae-induced pneumonia.NEW & NOTEWORTHY Streptococcus pneumoniae is the leading cause of community-acquired pneumonia. Our study examined ICAM-1, an adhesion molecule that is expressed on most cell types and plays important roles in leukocyte adhesion, migration, and motility. The data demonstrate that ICAM-1 is necessary for the clearance of S. pneumoniae and for the resolution of pneumonia but is not required for the recruitment of neutrophils or inflammatory macrophages into the pneumonic lung parenchyma or the alveoli/airways.

Dexmedetomidine Regulates Macrophage Phenotype Remodeling Through AMPK/SIRT1 to Alleviate Inflammatory Mediators and Lung Injury

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is associated with high morbidity and mortality in the intensive care unit (ICU) and can cause excessive inflammation. Dexmedetomidine (DEX) is a drug that exerts anti-inflammatory effects. Identifying the anti-inflammatory mechanism of DEX in the context of ALI/ARDS possesses potential significance for the prevention and treatment of ARDS. In this study, DEX was used to treat mouse models of cecal ligation and puncture (CLP) and lipopolysaccharide (LPS)-stimulated cells. Immunofluorescence, western blot analysis, and flow cytometry were used to detect macrophage phenotypic markers in mice, and western blot analysis, real-time qPCR (RT-qPCR), ELISA, and immunofluorescence were used to detect macrophage phenotype markers in RAW264.7 cells. Flow cytometry was used to detect phenotypic markers of bone marrow-derived macrophages (BMDM). Culture medium collected from macrophages was used to cultivate human non-small cell adenocarcinoma epithelial cells (A549) to detect their aquaporins 1 (AQP1) expression and apoptosis status. Western blot analysis was used to detect the activation of the AMP-activated protein kinase (AMPK)/sirtuin 1(SIRT1) signaling pathway both in vivo and in vitro. The regulatory effect of DEX on macrophage phenotype remodeling was detected by knocking down AMPK expression in cells using AMPK shRNA. The results showed that in both in vivo and in vitro experiments, DEX downregulated the expression of M1 markers (tumor necrosis factor-α [TNF-α], nitric oxide synthase [iNOS], and cluster of differentiation [CD]-86) and upregulated the expression of M2 markers (arginase-1 [ARG-1], interleukin [IL]-10, and CD206) in macrophages. The culture medium of macrophages treated with DEX alleviated the edema and apoptosis of A549 cells. DEX activates the AMPK/SIRT1 signaling pathway in macrophages. After AMPK knockdown, the ability of DEX to regulate macrophage phenotype remodeling decreased. Together, this study suggests that DEX regulates macrophage phenotype remodeling by activating the AMPK/SIRT1 pathway, thereby reducing ALI/ARDS.

Tripartite motif-containing 32 regulated by miR-6236-p5 inhibited silica-induced apoptosis of alveolar macrophages

Apoptosis of alveolar macrophages (AMs) induced by silica is one of the crucial driving factors of silicosis inflammation and fibrosis. However, the mechanism of silica-induced AMs apoptosis remains unclear. In this study, transcriptome sequencing identified 11 differentially expressed (DE)-mRNAs enriched in the regulation of apoptotic signaling pathways in AMs treated with 250μg/mL silica for 24h, of which tripartite motif-containing 32 (Trim32) was the most significant and down-regulated. The decreased Trim32 promoted AMs apoptosis, while Trim32 overexpression inhibited the apoptosis of AMs induced by silica at 250μg/mL for 24h. MiR-6236-p5 was then identified by MiRNA sequencing as the most significant DE-miRNA potentially regulating Trim32 expression, and the interaction between miR-6236-p5 and Trim32 3'-UTR was confirmed by dual luciferase reporter gene assay. Treated with 100nM miR-6236-p5 inhibitor increased the expression of Trim32 and inhibited the apoptosis of AMs induced by silica at 250μg/mL for 24h, while miR-6236-p5 mimic promoted the apoptosis of silica-induced AMs. In conclusion, this study identified Trim32 regulated by miR-6236-p5 played an important role in silica-induced AMs apoptosis based on RNA sequencing, which provided a novel clue for exploring the mechanism of silica-induced AMs apoptosis.

ADSCs-derived exosomes suppress macrophage ferroptosis via the SIRT1/NRF2 signaling axis to alleviate acute lung injury in sepsis

Acute lung injury being one of the earliest and most severe complications during sepsis and macrophages play a key role in this process. To investigate the regulatory effects and potential mechanisms of adipose mesenchymal stem cell derived-exosomes (ADSC-exo) on macrophages and septic mice, ADSCs-exo was administrated to both LPS-induced macrophage and cecal ligation and puncture (CLP) induced sepsis mice. ADSCs-exo was confirmed to inhibit M1 polarization of macrophages and to reduce excessive inflammation. The use of ADSCs-exo in CLP mice and in LPS-induced macrophages relieved oxidative stress, cellular damage, and acute lung injury. During this process, ADSCs-exo increased the nuclear translocation of Nrf2, significantly upregulating the activation of the antioxidant pathway Nrf2/HO-1. Concurrently, they enhanced the expression of SIRT1 in macrophages. Further SIRT1 interference experiments demonstrated that ADSCs-exo mitigated macrophage inflammatory responses and LPS-induced ferroptosis by upregulating SIRT1. In the LPS-induced macrophage model, after SIRT1 was interfered with, ADSCs-exo failed to upregulate the Nrf2/HO-1 signaling pathway, leading to enhanced ferroptosis. Finally, in a CLP sepsis mouse model with myeloid-specific SIRT1 knockout, ADSCs-exo was observed to reduce lung tissue injury, oxidative stress damage, and ferroptosis. Still, these beneficial effects were reversed due to the myeloid-specific knockout of SIRT1, while co-administration of a ferroptosis inhibitor rescued this situation, alleviating lung injury and significantly reducing tissue levels of oxidative stress. In conclusion, this study elucidated a novel potential therapeutic mechanism wherein ADSCs-exo upregulates the levels of SIRT1 in macrophages through a non-delivery approach.

Advancements in research and clinical management of interstitial lung injury associated with ADC drugs administration in breast cancer

Antibody-drug conjugates (ADCs) represent a novel class of targeted anti-tumor medications that utilize the covalent linkage between monoclonal antibodies and cytotoxic agents. This unique mechanism combines the cytotoxic potency of drugs with the targeting specificity conferred by antigen recognition. However, it is essential to recognize that many ADCs still face challenges related to off-target toxicity akin to cytotoxic payloads, as well as targeted toxicity and other potential life-threatening adverse effects, such as treatment-induced interstitial lung injury. Currently, of the four approved ADC drugs for breast cancer, several reports have documented post-treatment lung injury-related fatalities. As a result, treatment-induced interstitial lung injury due to ADC drugs has become a clinical concern. In this review article, we delve into the factors associated with ADC-induced interstitial lung injury in patients with advanced-stage breast cancer and highlight strategies expected to decrease the incidence of ADC-related interstitial lung injury in the years ahead. These efforts are directed at enhancing treatment outcomes in both advanced and early-stage cancer patients while also providing insights into the development and innovation of ADC drugs and bolstering clinicians' understanding of the diagnosis and management of ADC-associated interstitial lung injury.

Regulated Cell Death of Alveolar Macrophages in Acute Lung Inflammation: Current Knowledge and Perspectives

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a common and serious clinical lung disease characterized by extensive alveolar damage and inflammation leading to impaired gas exchange. Alveolar macrophages (AMs) maintain homeostatic properties and immune defenses in lung tissues. Several studies have reported that AMs are involved in and regulate ALI/ARDS onset and progression via different regulated cell death (RCD) programs, such as pyroptosis, apoptosis, autophagic cell death, and necroptosis. Notably, the effects of RCD in AMs in disease are complex and variable depending on the environment and stimuli. In this review, we provide a comprehensive perspective on how regulated AMs death impacts on ALI/ARDS and assess its potential in new therapeutic development. Additionally, we describe the crosstalk between different RCD types in ALI, and provide new perspectives for the treatment of ALI/ARDS and other severe lung diseases.

Oxidative stress promotes lipid-laden macrophage formation via CYP1B1

Emerging evidence suggests that lipid-laden macrophages (LLM) participate in lung damage in various clinical conditions. However, the mechanisms involved in LLM formation are not fully understood. In this study, we aimed to investigate the link between reactive oxygen species (ROS) and LLM formation. We found that ROS triggered by cigarette smoke extract (CSE) or H2O2 significantly promoted LLM formation. Given the key role of ROS in LLM formation, we further demonstrated that LLM formation is induced by various ROS-producing stimuli, including bacteria, oxidized low-density lipoprotein (OxLDL), hyperoxia, and E-cigarette vapor extract (EVE). Meanwhile, cytochrome P450 family-1 subfamily B member 1 (CYP1B1) was highly upregulated in lung macrophages from chronic obstructive pulmonary disease (COPD) patients and CSE-treated macrophages. Functionally, CYP1B1 contributes to the CSE-induced lipid accumulation and LLM formation. CYP1B1 expression and LLM formation were effectively suppressed by antioxidant N-acetylcysteine (NAC) and carvedilol. The formation of LLM was also associated with classically activated M1 but not the M2 state. CSE-induced LLM showed time-dependent alterations in inflammatory response and phagocytic ability. In summary, our study highlights the role of oxidative stress in LLM formation. CYP1B1 contributes to ROS-induced LLM formation and may serve as a therapeutic target for reducing LLM-induced lung damage.

Immune dysregulation as a driver of bronchiolitis obliterans

Bronchiolitis obliterans (BO) is a disease characterized by airway obstruction and fibrosis that can occur in all age groups. Bronchiolitis obliterans syndrome (BOS) is a clinical manifestation of BO in patients who have undergone lung transplantation or hematopoietic stem cell transplantation. Persistent inflammation and fibrosis of small airways make the disease irreversible, eventually leading to lung failure. The pathogenesis of BO is not entirely clear, but immune disorders are commonly involved, with various immune cells playing complex roles in different BO subtypes. Accordingly, the US Food and Drug Administration (FDA) has recently approved several new drugs that can alleviate chronic graft-versus-host disease (cGVHD) by regulating the function of immune cells, some of which have efficacy specifically with cGVHD-BOS. In this review, we will discuss the roles of different immune cells in BO/BOS, and introduce the latest drugs targeting various immune cells as the main target. This study emphasizes that immune dysfunction is an important driving factor in its pathophysiology. A better understanding of the role of the immune system in BO will enable the development of targeted immunotherapies to effectively delay or even reverse this condition.

The immune mechanisms of acute exacerbations of idiopathic pulmonary fibrosis

Acute exacerbations of idiopathic pulmonary fibrosis (AE-IPF) are the leading cause of mortality among patients with IPF. There is still a lack of effective treatments for AE-IPF, resulting in a hospitalization mortality rate as high as 70%-80%. To reveal the complicated mechanism of AE-IPF, more attention has been paid to its disturbed immune environment, as patients with IPF exhibit deficiencies in pathogen defense due to local immune dysregulation. During the development of AE-IPF, the classical stimulatory signals in adaptive immunity are inhibited, while the nonclassical immune reactions (Th17) are activated, attracting numerous neutrophils and monocytes to lung tissues. However, there is limited information about the specific changes in the immune response of AE-IPF. We summarized the immune mechanisms of AE-IPF in this review.

Metformin improves Mycobacterium avium infection by strengthening macrophage antimicrobial functions

Introduction

The incidence and prevalence of infections with non-tuberculous mycobacteria such as Mycobacterium avium (Mav) are increasing. Prolonged drug regimens, inherent antibiotic resistance, and low cure rates underscore the need for improved treatment, which may be achieved by combining standard chemotherapy with drugs targeting the host immune system. Here, we examined if the diabetes type 2 drug metformin could improve Mav-infection.

Methods

Metformin was administered to C57BL/6 mice infected intranasally with Mav and C57BL/6 mice were infected intranasally with Mav and treated with metformin over 3 weeks. Organ bacterial loads and lung pathology, inflammatory cytokines and immune cell profiles were assessed. For mechanistic insight, macrophages infected with Mav were treated with metformin alone or in combination with inhibitors for mitochondrial ROS or AMPK and assessed for bacterial burden and phagosome maturation.

Results and discussion

Three weeks of metformin treatment significantly reduced the lung mycobacterial burden in mice infected with Mav without major changes in the overall lung pathology or immune cell composition. Metformin treatment had no significant impact on tissue inflammation except for a tendency of increased lung IFNγ and infiltration of Mav-specific IFNγ-secreting T cells. Metformin did, however, boost the antimicrobial capacity of infected macrophages directly by modulating metabolism/activating AMPK, increasing mitochondrial ROS and phagosome maturation, and indirectly by bolstering type I immunity. Taken together, our data show that metformin improved the control of Mav-infection in mice, mainly by strengthening antimicrobial defenses in macrophages, and suggest that metformin has potential as an adjunct treatment of Mav infections.

Cholesterol restriction primes antiviral innate immunity via SREBP1-driven noncanonical type I IFNs

Cholesterol metabolism is associated with innate immune responses; however, the underlying mechanism remains unclear. Here, we perform chemical screening to isolate small molecules influencing RIG-I activity, a cytoplasmic viral RNA sensor. We find that statins, which inhibit cholesterol synthesis, dramatically enhance RIG-I-dependent antiviral responses in specific cell types. Since statins exhibit pleiotropic effects on type I interferon (IFN) responses, we further focus on their effects on RIG-I signaling. The restriction of cholesterol synthesis induces expression of noncanonical type I IFNs, such as IFN-ω, in an SREBP1 transcription factor-dependent manner. This pathway subsequently enhances RIG-I-mediated signaling following viral infection. Administration of statins augments RIG-I-dependent cytokine expression in the lungs of mice. Conversely, a mouse obesity model shows a diminished RIG-I response. Single-cell transcriptome analyses reveal a subset of alveolar macrophages that increase RIG-I expression in response to inhibited cholesterol synthesis in vivo. This study reveals SREBP1-mediated noncanonical type I IFN expression, linking cholesterol metabolism and RIG-I signaling.

The role of RNA modifications in disease-associated macrophages

In recent years, the field of epitranscriptomics has witnessed significant breakthroughs with the identification of more than 150 different chemical modifications in different RNA species. It has become increasingly clear that these chemical modifications play an important role in the regulation of fundamental processes linked to cell fate and development. Further interest was sparked by the ability of the epitranscriptome to regulate pathogenesis. However, despite the involvement of macrophages in a multitude of diseases, a clear knowledge gap exists in the understanding of how RNA modifications regulate the phenotype of these cells. Here, we provide a comprehensive overview of the known roles of macrophage RNA modifications in the context of different diseases.

Development of anti-cancer drugs for tumor-associated macrophages: a comprehensive review and mechanistic insights

This review provides an in-depth summary of the development of anti-cancer drugs for tumor-associated macrophages (TAMs), with a particular focus on the development and tissue specialization of macrophages, and factors influencing the polarization of M1 and M2 macrophages, and mechanistic insights underlying the targeting therapeutic approaches. TAMs, pivotal in the tumor microenvironment, exhibit notable plasticity and diverse functional roles. Influenced by the complex milieu, TAMs polarize into M1-type, which suppresses tumors, and M2-type, which promotes metastasis. Notably, targeting M2-TAMs is a promising strategy for tumor therapy. By emphasizing the importance of macrophages as a therapeutic target of anti-cancer drugs, this review aims to provide valuable insights and research directions for clinicians and researchers.

Ambient PM2.5 orchestrates M1 polarization of alveolar macrophages via activating glutaminase 1-mediated glutaminolysis in acute lung injury

The temporary explosive growth events of atmospheric fine particulate matter (PM2.5) pollution during late autumn and winter seasons still frequently occur in China. High-concentration exposure to PM2.5 aggravates lung inflammation, leading to acute lung injury (ALI). Alveolar macrophages (AMs) participate in PM2.5-induced pulmonary inflammation and injury. The polarization of AMs is dependent on metabolic reprogramming. However, the mechanism underlying the PM2.5-induced glutaminase-mediated glutaminolysis in AM polarization is still largely obscure. In this study, we found that PM2.5-treated mice exhibited pulmonary dysfunction and inflammation. The concentrations of glutamate and succinate were increased in PM2.5-treated lungs and AMs compared with the controls, whereas glutamine and α-ketoglutarate (α-KG) levels were decreased, indicating that glutaminolysis in AMs was aberrantly activated as evidenced by increased mRNA and protein levels of GLS1 after PM2.5 exposure. Moreover, we determined that the GLS1/nuclear factor kappa-B (NF-κB)/hypoxia-inducible factor-1α (HIF-1α) pathway regulated M1 polarization of AMs upon PM2.5 exposure. Inhibition of glutaminolysis by GLS1 specific inhibitor CB-839 and GLS1 siRNA significantly decreased PM2.5-induced M1 macrophage polarization and attenuated pulmonary damage. Taken together, our findings reveal a novel mechanism by which a metabolic program regulates M1 polarization of AMs and suggest that GLS1-mediated glutaminolysis is a potential therapeutic target for treating PM2.5-induced ALI.

Application of Macrophage Subtype Analysis in Acute Lung Injury/Acute Respiratory Distress Syndrome

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a common critical illness. Supportive therapy is still the main strategy for ALI/ARDS. Macrophages are the predominant immune cells in the lungs and play a pivotal role in maintaining homeostasis, regulating metabolism, and facilitating tissue repair. During ALI/ARDS, these versatile cells undergo polarization into distinct subtypes with significant variations in transcriptional profiles, developmental trajectory, phenotype, and functionality. This review discusses developments in the analysis of alveolar macrophage subtypes in the study of ALI/ARDS, and the potential value of targeting new macrophage subtypes in the diagnosis, prognostic evaluation, and treatment of ALI/ARDS.

Impact of Artificial Sunlight Aging on the Respiratory Effects of Polyethylene Terephthalate Microplastics through Degradation-Mediated Terephthalic Acid Release in Male Mice

Microplastics are ubiquitous in the atmosphere, leading to human exposure through inhalation. Airborne microplastics undergo degradation due to sunlight irradiation, yet the respiratory risks associated with degraded microplastics remain poorly understood. In this study, we investigated the respiratory effects of polyethylene terephthalate (PET) degraded by artificial sunlight and created a transport and degradation model of PET for risk assessment. PET fibers were cut and subjected to artificial sunlight irradiation. Mice exposed to aged PET showed increased airway resistance induced by methacholine inhalation, along with lung inflammation and neutrophil infiltration. Terephthalic acid (TPA) was continuously released from PET aged by artificial sunlight. Exposure to TPA also caused lung inflammation and enhanced airway resistance induced by methacholine (MCh) in mice. These findings indicate that aged PET can cause respiratory impairment via TPA release. A simple transport and degradation model was developed to quantitatively relate the abundance of aged PET produced in this study (ie, 4,000 × 96 W m-2 h) and aged fractions of PET that can be generated in the atmosphere. Our results suggested 10-60% of PET was degraded as that produced in this study over sunny regions in summer, whereas only lower than 1% in high-latitude cities in Europe in winter. This study demonstrates the importance of considering the abundance of aged PET and further development of a transport and degradation model of PET to assess the risk of degraded PET in the atmosphere.

Macrophages in organ fibrosis: from pathogenesis to therapeutic targets

Fibrosis, an excessive self-repair response, is an age-related pathological process that universally affects various major organs such as the heart, liver, kidney, and lungs. Continuous accumulation of pathological tissue fibrosis destroys structural integrity and causes loss of function, with consequent organ failure and increased mortality. Although some differences exist in the triggering mechanisms and pathophysiologic manifestations of organ-specific fibrosis, they usually share similar cascading responses and features, including chronic inflammatory stimulation, parenchymal cell injury, and macrophage recruitment. Macrophages, due to their high plasticity, can polarize into different phenotypes in response to varied microenvironments and play a crucial role in the development of organ fibrosis. This review examined the relationship between macrophages and the pathogenesis of organ fibrosis. Moreover, it analyzed how fibrosis can be modulated by targeting macrophages, which may become a novel and promising therapeutic strategy for fibrosis.

Cancer-induced systemic pre-conditioning of distant organs: building a niche for metastatic cells

From their early genesis, tumour cells integrate with the surrounding normal cells to form an abnormal structure that is tightly integrated with the host organism via blood and lymphatic vessels and even neural associations. Using these connections, emerging cancers send a plethora of mediators that efficiently perturb the entire organism and induce changes in distant tissues. These perturbations serendipitously favour early metastatic establishment by promoting a more favourable tissue environment (niche) that supports the persistence of disseminated tumour cells within a foreign tissue. Because the establishment of early metastatic niches represents a key limiting step for metastasis, the creation of a more suitable pre-conditioned tissue strongly enhances metastatic success. In this Review, we provide an updated view of the mechanisms and mediators of primary tumours described so far that induce a pro-metastatic conditioning of distant organs, which favours early metastatic niche formation. We reflect on the nature of cancer-induced systemic conditioning, considering that non-cancer-dependent perturbations of tissue homeostasis are also able to trigger pro-metastatic conditioning. We argue that a more holistic view of the processes catalysing metastatic progression is needed to identify preventive or therapeutic opportunities.

Cancer treatments as paradoxical catalysts of tumor awakening in the lung

Much of the fatality of tumors is linked to the growth of metastases, which can emerge months to years after apparently successful treatment of primary tumors. Metastases arise from disseminated tumor cells (DTCs), which disperse through the body in a dormant state to seed distant sites. While some DTCs lodge in pre-metastatic niches (PMNs) and rapidly develop into metastases, other DTCs settle in distinct microenvironments that maintain them in a dormant state. Subsequent awakening, induced by changes in the microenvironment of the DTC, causes outgrowth of metastases. Hence, there has been extensive investigation of the factors causing survival and subsequent awakening of DTCs, with the goal of disrupting these processes to decrease cancer lethality. We here provide a detailed overview of recent developments in understanding of the factors controlling dormancy and awakening in the lung, a common site of metastasis for many solid tumors. These factors include dynamic interactions between DTCs and diverse epithelial, mesenchymal, and immune cell populations resident in the lung. Paradoxically, among key triggers for metastatic outgrowth, lung tissue remodeling arising from damage induced by the treatment of primary tumors play a significant role. In addition, growing evidence emphasizes roles for inflammation and aging in opposing the factors that maintain dormancy. Finally, we discuss strategies being developed or employed to reduce the risk of metastatic recurrence.

Innate players in Th2 and non-Th2 asthma: emerging roles for the epithelial cell, mast cell, and monocyte/macrophage network

Asthma is one of the most common chronic respiratory diseases and is characterized by airway inflammation, increased mucus production, and structural changes in the airways. Recently, there is increasing evidence that the disease is much more heterogeneous than expected, with several distinct asthma endotypes. Based on the specificity of T cells as the best-known driving force in airway inflammation, bronchial asthma is categorized into T helper cell 2 (Th2) and non-Th2 asthma. The most studied effector cells in Th2 asthma include T cells and eosinophils. In contrast to Th2 asthma, much less is known about the pathophysiology of non-Th2 asthma, which is often associated with treatment resistance. Besides T cells, the interaction of myeloid cells such as monocytes/macrophages and mast cells with the airway epithelium significantly contributes to the pathogenesis of asthma. However, the underlying molecular regulation and particularly the specific relevance of this cellular network in certain asthma endotypes remain to be understood. In this review, we summarize recent findings on the regulation of and complex interplay between epithelial cells and the "nonclassical" innate effector cells mast cells and monocytes/macrophages in Th2 and non-Th2 asthma with the ultimate goal of providing the rationale for future research into targeted therapy regimens.

Optimized full-spectrum flow cytometry panel for deep immunophenotyping of murine lungs

The lung immune system consists of both resident and circulating immune cells that communicate intricately. The immune system is activated by exposure to bacteria and viruses, when cancer initiates in the lung (primary lung cancer), or when metastases of other cancer types, including breast cancer, spread to and develop in the lung (secondary lung cancer). Thus, in these pathological situations, a comprehensive and quantitative assessment of changes in the lung immune system is of paramount importance for understanding mechanisms of infectious diseases, lung cancer, and metastasis but also for developing efficacious treatments. Unfortunately, lung tissue exhibits high autofluorescence, and this high background signal makes high-parameter flow cytometry analysis complicated. Here, we provide an optimized 30-parameter antibody panel for the analysis of all major immune cell types and states in normal and metastatic murine lungs using spectral flow cytometry.

Fth1-mScarlet Reports Monocyte State during Lipopolysaccharide-induced Lung Inflammation

Monocytes and macrophages are central to host defense but also contribute to inflammation-associated pathology. Efforts to manipulate monocyte and macrophage function are limited by our ability to effectively quantify the functional programs of these cells. We identified the gene Fth1, which encodes the ferritin H chain, as highly predictive of alveolar macrophage transcriptomic states during LPS-induced lung inflammation and developed an Fth1-mScarlet reporter mouse. In the steady-state lung, high Fth1-mScarlet expression is restricted to alveolar macrophages. In response to LPS-induced lung inflammation, Fth1 reporter activity is robustly increased in monocytes, with its expression reporting genes that are differentially expressed in monocytes versus macrophages. Consistent with this reporter-associated gene profile, within the Lyz2-GFP+CD11b+Ly6C+ gate, the highest Fth1 reporter expression was observed in CD11c+ cells, indicative of monocyte-to-macrophage differentiation. Although Fth1-mScarlet was induced in monocytes responding to either TLR4 ligation or M-CSF-induced macrophage differentiation in vitro, TLR4-dependent expression occurred with greater speed and magnitude. Considering this, we suggest that Fth1-mScarlet expression reports monocyte-to-macrophage differentiation, with increased expression in proinflammatory states. Dissecting macrophage differentiation from inflammatory programs will be enhanced when combining Fth1-mScarlet with other reporter systems. Thus, the Fth1-mScarlet model addresses an important lack of tools to report the diverse spectrum of monocyte and macrophage states in vivo.

Antiviral innate immune memory in alveolar macrophages following SARS-CoV-2 infection ameliorates secondary influenza A virus disease

Pathogen encounter can result in epigenetic remodeling that shapes disease caused by heterologous pathogens. Here, we examined innate immune memory in the context of commonly circulating respiratory viruses. Single-cell analyses of airway-resident immune cells in a disease-relevant murine model of SARS-CoV-2 recovery revealed epigenetic reprogramming in alveolar macrophages following infection. Post-COVID-19 human monocytes exhibited similar epigenetic signatures. In airway-resident macrophages, past SARS-CoV-2 infection increased activity of type I interferon (IFN-I)-related transcription factors and epigenetic poising of antiviral genes. Viral pattern recognition and canonical IFN-I signaling were required for the establishment of this innate immune memory and augmented secondary antiviral responses. Antiviral innate immune memory mounted by airway-resident macrophages post-SARS-CoV-2 was necessary and sufficient to ameliorate secondary disease caused by influenza A virus and curtailed hyperinflammatory dysregulation and mortality. Our findings provide insights into antiviral innate immune memory in the airway that may facilitate the development of broadly effective therapeutic strategies.

Epigenetic mechanisms of alveolar macrophage activation in chemical-induced acute lung injury

Airways, alveoli and the pulmonary tissues are the most vulnerable to the external environment including occasional deliberate or accidental exposure to highly toxic chemical gases. However, there are many effective protective mechanisms that maintain the integrity of the pulmonary tissues and preserve lung function. Alveolar macrophages form the first line of defense against any pathogen or chemical/reactant that crosses the airway mucociliary barrier and reaches the alveolar region. Resident alveolar macrophages are activated or circulating monocytes infiltrate the airspace to contribute towards inflammatory or reparative responses. Studies on response of alveolar macrophages to noxious stimuli are rapidly emerging and alveolar macrophage are also being sought as therapeutic target. Here such studies have been reviewed and put together for a better understanding of the role pulmonary macrophages in general and alveolar macrophage in particular play in the pathogenesis of disease caused by chemical induced acute lung injury.

Targeting the PI3K/AKT signaling pathway with PNU120596 protects against LPS-induced acute lung injury

OBJECTIVES

This study investigated the potential therapeutic benefits of PNU120596, a positive allosteric modulator of the α7 nicotinic acetylcholine receptor (α7nAChR), in mitigating acute lung injury (ALI) induced by lipopolysaccharide (LPS) in a mouse model. Specifically, we sought to examine the impact of PNU120596 on the PI3K/AKT signaling pathway in the context of ALI.

METHODS

ALI was induced in mice by LPS administration, and the protective effects of PNU120596 were assessed. Lung injury, lung function, and the inflammatory response were evaluated. Additionally, the activation of the PI3K/AKT signaling pathway was examined, along with the levels of inflammatory factors and oxidative stress markers.

KEY FINDINGS

PNU120596 significantly ameliorated LPS-induced lung injury, improved lung function, and reduced the inflammatory response in the mouse model of ALI. Furthermore, we observed that PNU120596 inhibited the activation of the PI3K/AKT signaling pathway, which was associated with decreased levels of inflammatory factors and oxidative stress markers.

CONCLUSIONS

PNU120596 exhibits promising therapeutic potential for the treatment of acute lung injury, potentially by targeting the PI3K/AKT signaling pathway. These findings suggest that modulation of the α7 nicotinic acetylcholine receptor with PNU120596 may offer a viable strategy for the management of ALI, warranting further investigation and potential clinical applications.

Synthetic vitreous fibers (SVFs): adverse outcome pathways (AOPs) and considerations for next generation new approach methods (NAMs)

Fiber dimension, durability/dissolution, and biopersistence are critical factors for the risk of fibrogenesis and carcinogenesis. In the modern era, to reduce, refine, and replace animals in toxicology research, the application of in vitro test methods is paramount for hazard evaluation and designing synthetic vitreous fibers (SVFs) for safe use. The objectives of this review are to: (1) summarize the international frameworks and acceptability criteria for implementation of new approach methods (NAMs), (2) evaluate the adverse outcome pathways (AOPs), key events (KEs), and key event relationships (KERs) for fiber-induced fibrogenesis and carcinogenesis in accordance with Organization for Economic Co-operation and Development (OECD) guidelines, (3) consider existing and emerging technologies for in silico and in vitro toxicity testing for the respiratory system and the ability to predict effects in vivo, (4) outline a recommended testing strategy for evaluating the hazard and safety of novel SVFs, and (5) reflect on methods needs for in vitro in vivo correlation (IVIVC) and predictive approaches for safety assessment of new SVFs. AOP frameworks following the conceptual model of the OECD were developed through an evaluation of available molecular and cellular initiating events, which lead to KEs and KERs in the development of fiber-induced fibrogenesis and carcinogenesis. AOP framework development included consideration of fiber physicochemical properties, respiratory deposition and clearance patterns, biosolubility, and biopersistence, as well as cellular, organ, and organism responses. Available data support that fiber AOPs begin with fiber physicochemical characteristics which influence fiber exposure and biosolubility and subsequent key initiating events are dependent on fiber biopersistence and reactivity. Key cellular events of pathogenic fibers include oxidative stress, chronic inflammation, and epithelial/fibroblast proliferation and differentiation, which ultimately lead to hyperplasia, metaplasia, and fibrosis/tumor formation. Available in vitro models (e.g. single-, multi-cellular, organ system) provide promising NAMs tools to evaluate these intermediate KEs. However, data on SVFs demonstrate that in vitro biosolubility is a reasonable predictor for downstream events of in vivo biopersistence and biological effects. In vitro SVF fiber dissolution rates >100 ng/cm2/hr (glass fibers in pH 7 and stone fibers in pH 4.5) and in vivo SVF fiber clearance half-life less than 40 or 50 days were not associated with fibrosis or tumors in animals. Long (fiber lengths >20 µm) biodurable and biopersistent fibers exceeding these fiber dissolution and clearance thresholds may pose a risk of fibrosis and cancer. In vitro fiber dissolution assays provide a promising avenue and potentially powerful tool to predict in vivo SVF fiber biopersistence, hazard, and health risk. NAMs for fibers (including SVFs) may involve a multi-factor in vitro approach leveraging in vitro dissolution data in complement with cellular- and tissue- based in vitro assays to predict health risk.

Combined targeting of senescent cells and senescent macrophages: A new idea for integrated treatment of lung cancer

Lung cancer is one of the most common cancers worldwide and a leading cause of cancer-related deaths. Macrophages play a key role in the immune response and the tumour microenvironment. As an important member of the immune system, macrophages have multiple functions, including phagocytosis and clearance of pathogens, modulation of inflammatory responses, and participation in tissue repair and regeneration. In lung cancer, macrophages are considered to be the major cellular component of the tumor-associated inflammatory response and are closely associated with tumorigenesis, progression and metastasis. However, macrophages gradually undergo a senescence process with age and changes in pathological states. Macrophage senescence is an important change in the functional and metabolic state of macrophages and may have a significant impact on lung cancer development. In lung cancer, senescent macrophages interact with other cells in the tumor microenvironment (TME) by secreting senescence-associated secretory phenotype (SASP) factors, which can either promote the proliferation, invasion and metastasis of tumor cells or exert anti-tumor effects through reprogramming or clearance under specific conditions. Therefore, senescent macrophages are considered important potential targets for lung cancer therapy. In this paper, a systematic review of macrophages and their senescence process, and their role in tumors is presented. A variety of inhibitory strategies against senescent macrophages, including enhancing autophagy, inhibiting SASP, reducing DNA damage, and modulating metabolic pathways, were also explored. These strategies are expected to improve lung cancer treatment outcomes by restoring the anti-tumor function of macrophages.

Lung infection with classical Klebsiella pneumoniae strains establishes robust macrophage-dependent protection against heterologous reinfection

At present, there is no approved vaccine for prevention of infection by the opportunistic bacterium Klebsiella pneumoniae (Kp); success in treating these infections is increasingly challenged by the spread of antibiotic resistance. Preclinical investigation of adaptive immunity elicited by lung infection with live classical Kp may reveal host mechanisms of protection against this pathogen. Here, we utilize multiple virulent classical Kp strains to demonstrate that following lung infection, surviving wild-type mice develop protective immunity against both homologous and heterologous (heterotypic) reinfection. For Kp strains with low capacity to disseminate from the lung, this immunity is B-cell-independent. We further demonstrate that this immune protection is also effective against subsequent challenge with hypervirulent Kp if the strains share the same capsule type. Systemic inoculation fails to elicit the same protective effect as lung inoculation, revealing a lung-specific immune effector function is responsible for this protection. We therefore utilized clodronate-loaded liposomes to substantially deplete both alveolar macrophages and lung interstitial macrophages, finding that simultaneous depletion of both subsets entirely ablates protection. These findings indicate that following initial lung infection with Kp, lung macrophages mediate protection against ensuing Kp challenge.

Mycobacterium tuberculosis virulence lipid PDIM inhibits autophagy in mice

Mycobacterium tuberculosis (Mtb) infects several lung macrophage populations, which have distinct abilities to restrict Mtb. What enables Mtb survival in certain macrophage populations is not well understood. Here we used transposon sequencing analysis of Mtb in wild-type and autophagy-deficient mouse macrophages lacking ATG5 or ATG7, and found that Mtb genes involved in phthiocerol dimycocerosate (PDIM) virulence lipid synthesis confer resistance to autophagy. Using ppsD mutant Mtb, we found that PDIM inhibits LC3-associated phagocytosis (LAP) by inhibiting phagosome recruitment of NADPH oxidase. In mice, PDIM protected Mtb from LAP and classical autophagy. During acute infection, PDIM was dispensable for Mtb survival in alveolar macrophages but required for survival in non-alveolar macrophages in an autophagy-dependent manner. During chronic infection, autophagy-deficient mice succumbed to infection with PDIM-deficient Mtb, with impairments in B-cell accumulation in lymphoid follicles. These findings demonstrate that PDIM contributes to Mtb virulence and immune evasion, revealing a contributory role for autophagy in B-cell responses.

Myeloperoxidase-ANCA IgG induces different forms of small vessel vasculitis based on type of synergistic immune stimuli

Anti-neutrophil cytoplasmic autoantibody (ANCA) vasculitis has diverse patterns of injury including microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Necrotizing and crescentic glomerulonephritis (NCGN) occurs in all syndromes and as renal limited vasculitis (RLV). Single-dose intravenous ANCA IgG-specific for mouse myeloperoxidase (MPO) causes RLV in mice. Although multiple mouse models have elucidated ANCA-IgG induced necrotizing and crescentic glomerulonephritis (NCGN), pathogenesis of ANCA-induced granulomatosis and vasculitis outside the kidney has not been clarified. To investigate this, we used intravenous MPO-ANCA IgG in the same strain of mice to induce different patterns of lung disease mirroring patients with granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Repeated intravenous MPO-ANCA IgG induced GPA with NCGN, lung capillaritis, arteritis and granulomatosis. Lung leukocyte phenotypes were evaluated by immunohistochemical image analysis and by flow cytometry. ANCA lung capillaritis and microabscesses began within one day and evolved into granulomas in under seven days. Influenza plus single-dose MPO-ANCA IgG induced MPA with NCGN, lung capillaritis and arteritis, but no granulomatosis. Allergic airway disease caused by house dust mites or ovalbumin plus single-dose intravenous MPO-ANCA IgG induced EGPA with eosinophilic bronchiolitis, NCGN, capillaritis, arteritis, and granulomatosis. Thus, our study shows that the occurrence and pattern of lung lesions are determined by the same ANCA IgG accompanied by different synergistic immune factors.

Opposite effects of systemic and local conditional CD11c+ myeloid cell depletion during bleomycin-induced inflammation and fibrosis in mice

RATIONALE

Elevated levels of CD11c+ myeloid cells are observed in various pulmonary disorders, including Idiopathic Pulmonary Fibrosis (IPF). Dendritic cells (DCs) and macrophages (MΦ) are critical antigen-presenting cells (APCs) that direct adaptive immunity. However, the role of CD11c+ myeloid cells in lung extracellular matrix (ECM) accumulation and pulmonary fibrosis is poorly understood.

OBJECTIVE

We aimed to investigate the impact of depleting CD11c+ myeloid cells, including DCs and macrophages, during bleomycin-induced pulmonary fibrosis in mice.

METHODS

We used a diphtheria toxin (DTx) receptor (DTR) transgenic mouse model (CD11c-DTR-Tg) to deplete CD11c+ myeloid cells through two methods: Systemic Depletion (SD) via intraperitoneal injection (i.p.) and local depletion (LD) via intranasal instillation (i.n.). We then assessed the effects of CD11c+ cell depletion during bleomycin-induced lung inflammation and fibrosis.

RESULTS

Fourteen days after bleomycin instillation, there was a progressive accumulation of myeloid cells, specifically F4/80-MHCII+CD11c+ DCs and F4/80 + MHCII+CD11c+ MΦ, preceding mortality and pulmonary fibrosis. Systemic depletion of CD11c+ DCs and MΦ via i.p. DTx administration in CD11c-DTR-Tg mice protected against bleomycin-induced mortality and pulmonary fibrosis compared to wild-type (WT) mice. Systemic depletion reduced myeloid cells, airway inflammation (total leukocytes, neutrophils, and CD4+ lymphocytes in bronchoalveolar lavage (BAL), inflammatory and fibrogenic mediators, and fibrosis-related mRNAs (Collagen-1α1 and α-SMA). Increased anti-inflammatory cytokine IL-10 and CXCL9 levels were observed, resulting in lower lung hydroxyproline content and Ashcroft fibrosis score. Conversely, local depletion of CD11c+ cells increased mortality by acute leukocyte influx (predominantly neutrophils, DCs, and MΦ in BAL) correlated to IL-1β, with lung hyper-inflammation and early fibrosis development.

CONCLUSION

Systemic depletion of CD11c+ cells confers protection against inflammation and fibrosis induced by Bleomycin, underscoring the significance of myeloid cells expressing F4/80-MHCII+CD11c+ DCs and F4/80 + MHCII+CD11c+ MΦ orchestrating the inflammatory milieu within the lungs, potentially as a source of cytokines sustaining pulmonary chronic inflammation leading to progressive fibrosis and mortality.

TRPM2 channels are essential for regulation of cytokine production in lung interstitial macrophages

Interstitial macrophages (IMs) are essential for organ homeostasis, inflammation, and autonomous immune response in lung tissues, which are achieved through polarization to a pro-inflammatory M1 and an M2 state for tissue repair. Their remote parenchymal localization and low counts, however, are limiting factors for their isolation and molecular characterization of their specific role during tissue inflammation. We isolated viable murine IMs in sufficient quantities by coculturing them with stromal cells and analyzed mRNA expression patterns of transient receptor potential (TRP) channels in naïve and M1 polarized IMs after application of lipopolysaccharide (LPS) and interferon γ. M-RNAs for the second member of the melastatin family of TRP channels, TRPM2, were upregulated in the M1 state and functional channels were identified by their characteristic currents induced by ADP-ribose, its specific activator. Most interestingly, cytokine production and secretion of interleukin-1α (IL-1α), IL-6 and tumor necrosis factor-α in M1 polarized but TRPM2-deficient IMs was significantly enhanced compared to WT cells. Activation of TRPM2 channels by ADP-ribose (ADPR) released from mitochondria by ROS-produced H2O2 significantly increases plasma membrane depolarization, which inhibits production of reactive oxygen species by NADPH oxidases and reduces cytokine production and secretion in a negative feedback loop. Therefore, TRPM2 channels are essential for the regulation of cytokine production in M1-polarized murine IMs. Specific activation of these channels may promote an anti-inflammatory phenotype and prevent a harmful cytokine storm often observed in COVID-19 patients.

Periodontal conditions and salivary microbiota are potential indicators to distinguish silicosis: an exploratory study

BACKGROUND

Silicosis has always been a serious global occupational health problem. Oral microbiota plays important roles in the development of lung disease. However, few studies have investigated the relationship between periodontal conditions, oral bacteria and silicosis disease.

METHOD

A single-center and cross-sectional study was conducted in 2019 in Sichuan Province, China, including a small sample of silicosis patient group and healthy control group. Demographic data and periodontal examinations measured by clinical attachment loss (CAL), bleeding on probing (BOP) and periodontal pocket (PD) were collected from each participant. Phenotypic changes were detected by histopathological staining. Next-generation sequencing targeting 16S ribosomal RNA was targeted to decipher the salivary microbiome of the two groups. Random forest, Least Absolute Shrinkage and Selection Operator (LASSO) logistic regression and multivariable logistic regression analysis were conducted to find potential indicators to distinguish silicosis.

RESULTS

In general, 29 male healthy controls and 24 male silicosis patients were included. The proportion of CAL ≥ 3 mm in silicosis group was greater than control group, while the proportion of BOP (+) and PD ≥ 4 mm was reduced in silicosis group. The α-smooth muscle actin and fibronectin expression increased in gingiva of patients. The composition of salivary microbiota exhibited significant differences between the two groups, with silicosis patients demonstrating a lower diversity of salivary microbiota. Genus of Aggregatibacter [odds ratio (OR) = 0.000, p = 0.003] and Catonella (OR = 0.000, p = 0.049) were identified as biomarkers to distinguish silicosis.

CONCLUSIONS

The silicosis group exhibited worse CAL, improved BOP and PD, which may be related to the gingival fibrosis found in this study. The composition of the oral microbiota underwent significant changes, accompanied by a decrease in diversity, in patients with silicosis. Our study indicates that respirable crystalline silica exposure affects oral health, and alterations of oral microbiota might be implicated in silicosis. We primarily identified Aggregatibacter and Catonella as the potential indicators to distinguish silicosis patients from healthy controls.

Progesterone promotes CXCl2-dependent vaginal neutrophil killing by activating cervical resident macrophage-neutrophil crosstalk

Vaginal infections in women of reproductive age represent a clinical dilemma with significant socioeconomic implications. The current understanding of mucosal immunity failure during early pathogenic invasions that allows the pathogen to grow and thrive is far from complete. Neutrophils infiltrate most tissues following circadian patterns as part of normal repair, regulation of microbiota, or immune surveillance and become more numerous after infection. Neutrophils are responsible for maintaining vaginal immunity. Specific to the vagina, neutrophils continuously infiltrate at high levels, although during ovulation, they retreat to avoid sperm damage and permit reproduction. Here we show that, after ovulation, progesterone promotes resident vaginal macrophage-neutrophil crosstalk by upregulating Yolk sac early fetal organs (FOLR2+) macrophage CXCl2 expression, in a TNFA-patrolling monocyte-derived macrophage-mediated (CX3CR1hiMHCIIhi-mediated) manner, to activate the neutrophils' capacity to eliminate sex-transmitted and opportunistic microorganisms. Indeed, progesterone plays an essential role in conciliating the balance between the commensal microbiota, sperm, and the threat of pathogens because progesterone not only promotes a flurry of neutrophils but also increases neutrophilic fury to restore immunity after ovulation to thwart pathogenic invasion after intercourse. Therefore, modest progesterone dysregulations could lead to a suboptimal neutrophilic response, resulting in insufficient mucosal defense and recurrent unresolved infections.

Role of cuproptosis in mediating the severity of experimental malaria-associated acute lung injury/acute respiratory distress syndrome

BACKGROUND

Malaria-associated acute lung injury/acute respiratory distress syndrome (MA-ALI/ARDS) is a fatal complication of Plasmodium falciparum infection that is partially triggered by macrophage recruitment and polarization. As reported, copper exposure increases the risk of malaria infection, and copper accumulation-induced cuproptosis triggers M1 macrophage polarization. It is thus hypothesized that cuproptosis could act as a critical mediator in the pathogenesis of MA-ALI/ARDS, but its underlying mechanism remains unclear. The present study aimed to explore the role of cuproptosis in the severity of murine MA-ALI/ARDS.

METHODS

We utilized an experimental model of MA-ALI/ARDS using female C57BL/6 mice with P. berghei ANKA infection, and treated these animals with the potent copper ion carrier disulfiram (DSF) or copper ion chelator tetrathiomolybdate (TTM). The RAW 264.7 macrophages, which were stimulated with infected red blood cells (iRBCs) in vitro, were also targeted with DSF-CuCl2 or TTM-CuCl2 to further investigate the underlying mechanism.

RESULTS

Our findings showed a dramatic elevation in the amount of copper and the expression of SLC31A1 (a copper influx transporter) and FDX1 (a key positive regulator of cuproptosis) but displayed a notable reduction in the expression of ATP7A (a copper efflux transporter) in the lung tissue of experimental MA-ALI/ARDS mice. Compared to the P. berghei ANKA-infected control group, mice that were administered DSF exhibited a remarkable increase in parasitemia/lung parasite burden, total protein concentrations in bronchoalveolar lavage fluid (BALF), lung wet/dry weight ratio, vascular leakage, and pathological changes in lung tissue. Strikingly, the experimental MA-ALI/ARDS mice with DSF treatment also demonstrated dramatically elevated copper levels, expression of SLC31A1 and FDX1, numbers of CD86+, CD68+, SLC31A1+-CD68+, and FDX1+-CD68+ macrophages, and messenger RNA (mRNA) levels of pro-inflammatory cytokines (tumor necrosis factor [TNF-α] and inducible nitric oxide synthase [iNOS]) in lung tissue, but showed a remarkable decrease in body weight, survival time, expression of ATP7A, number of CD206+ macrophages, and mRNA levels of anti-inflammatory cytokines (transforming growth factor beta [TGF-β] and interleukin 10 [IL-10]). In contrast, TTM treatment reversed these changes in the infected mice. Similarly, the in vitro experiment showed a notable elevation in the mRNA levels of SLC31A1, FDX1, CD86, TNF-α, and iNOS in iRBC-stimulated RAW 264.7 cells targeted with DSF-CuCl2, but triggered a remarkable decline in the mRNA levels of ATP7A, CD206, TGF-β, and IL-10. In contrast, TTM-CuCl2 treatment also reversed these trends in the iRBC-stimulated RAW 264.7 cells.

CONCLUSIONS

Our data demonstrate that the activation of cuproptosis with DSF aggravated the severity of MA-ALI/ARDS by partially inducing M1 polarization of pulmonary macrophages, while inhibition of cuproptosis with TTM contrarily ameliorated the severity of MA-ALI/ARDS by promoting macrophage M2 polarization. Our findings suggest that blockage of cuproptosis could be a potential therapeutic strategy for treatment of MA-ALI/ARDS.

Atractylodin modulates ASAH3L to improve galactose metabolism and inflammation to alleviate acute lung injury

Acute lung injury (ALI) is a lung disease characterized by an excessive inflammatory response and damage to lung epithelial cells. Atractylodin (ATL) has good anti-inflammatory activity and protects the integrity of the epithelial cell barrier. However, the efficacy of ATL in the treatment of ALI and its mechanism is unclear. We investigated the efficacy of ATL in treating ALI and explored its targets and mechanisms. The results showed that ATL significantly reduced the wet-dry ratio of lungs of rats with ALI, improved the pathological changes, and lowered the expression of the inflammatory factors. Combined metabolomic and transcriptomic analyses showed that ATL can reduce inflammation by inhibiting and activating the HIF-1 signaling pathway and modulating ASAH3L to improve galactose metabolism, thereby alleviating ALI. In conclusion, ATL may be a potential drug for the treatment of acute lung injury.

Dietary Aflatoxin G1 exposure causes an imbalance between pulmonary tissue-resident alveolar macrophages and monocyte-derived macrophages in both mother and offspring mice

Aflatoxin G1 (AFG1) is a mycotoxin commonly found in agricultural products, including dried fruits, meat, and milk products. Oral AFG1 administration induced tumor necrosis factor (TNF)-α-dependent chronic pulmonary inflammation, promoting AFG1-induced damage in alveolar epithelial cell, which is associated with lung adenocarcinoma. Pulmonary macrophages may be divided into tissue-resident alveolar macrophages (TRAMs) and monocyte-derived macrophages (MoMs), which involve in chronic lung inflammation. However, whether these macrophages contribute to AFG1-induced chronic pulmonary inflammation remains unknown. In this study, we found oral AFG1 administration disrupted the balance between TRAMs and MoMs, increasing MoMs infiltration and decreasing the number of TRAMs. AFG1 upregulated TNF-α expression in MoMs, but downregulated sialic acid binding Ig-like lectin F (Siglec-F) expression in TRAMs. Inhibition of TNF-α-dependent inflammation rescued the imbalance between TRAMs and MoMs in AFG1-treated lung tissues. Additionally, AFG1 stimulated MoMs differentiation to the proinflammatory M1 phenotype in vitro. Using a specific in vitro TRAM model, AFG1 downregulated Siglec-F and the M2 phenotypic markers arginase 1 and YM1, and upregulated the M1 phenotypic markers IL-6, iNOS and TNF-α, altering the TRAMs phenotype to the pro-inflammatory M1 phenotype in vitro. Additionally, mouse maternal dietary exposure to AFG1 caused an imbalance in pulmonary macrophages, decreasing TRAMs and increasing MoMs population in offspring, which was associated with proliferative lesions in the alveolar septa. Thus, dietary AFG1 exposure triggered an imbalance in pulmonary macrophages in both mother and offspring mice, and induced pro-inflammatory phenotypic alterations, which contributed to AFG1-induced chronic lung inflammation. These results provide clues to how AFG1-induced immunotoxicity and genotoxicity in humans might be prevented.

Crystalline silica-induced endoplasmic reticulum stress promotes the pathogenesis of silicosis by augmenting proinflammatory interstitial pulmonary macrophages

Crystalline silica (CS) particles are ubiquitously present in the environment, particularly in occupational settings, and exposure to respirable CS causes silicosis, imposing a significant disease burden. However, the pathogenesis of silicosis remains unclear. Exposure to external stimuli, such as CS, leads to the accumulation of unfolded proteins and triggers endoplasmic reticulum (ER) stress, disrupting tissue immune homeostasis and accelerating pathological progression. While pulmonary macrophages phagocytose CS particles to initiate the immune response, the role of ER stress in this process is unknown. Herein, we used a murine model of silicosis to simulate the pathological progression from acute inflammation to fibrosis in silicosis and conducted in vivo pharmacological inhibition of ER stress to explore the underlying mechanism. Using flow cytometry, we further classified pulmonary macrophages into monocyte-like macrophages (monocytes), interstitial macrophages (IMs), and alveolar macrophages (AMs). Our results showed that CS-induced ER stress primarily contributed to the augmentation of IMs and thereby exerted a significant impact on pulmonary macrophages. Despite coexpressing M1- and M2-like markers, IMs predominantly exhibited an M1-like polarization state and played a proinflammatory role by expressing the cytokines pro-IL-1β and TNF-α during the pathological progression of silicosis. Additionally, IMs recruited by CS-induced ER stress also exhibited high expression of MHCII and exerted active immunomodulatory effects. Overall, our study demonstrates that ER stress induced by CS particles triggers a proinflammatory immune microenvironment dominated by IMs and reveals novel insights into the pulmonary toxicological effects of CS particles.

Inhaled GM-CSF administered during ongoing pneumovirus infection alters myeloid and CD8 T cell immunity without affecting disease outcome

Granulocyte-macrophage colony stimulating factor (GM-CSF) is a pleiotropic cytokine, able to promote both myelopoiesis and activation of immune cells. Particularly in the lung, GM-CSF plays an important homeostatic role in the development and maintenance of alveolar macrophages, and is therefore considered to play a role in respiratory virus infections such as influenza and SARS-CoV-2, although the benefits of GM-CSF treatment in clinical studies remain inconclusive. To address this, we tested inhaled GM-CSF treatment in the Pneumonia Virus of Mice (PVM) mouse model. Our findings show that local GM-CSF therapy during PVM disease increased local neutrophilia and monocyte-derived cell influx, but diminished CD8+ T cells responses. Despite this, the observed effects on T cells and myeloid cells did not result in an altered clinical outcome during PVM infection. We conclude that inhaled GM-CSF therapy cannot be considered as a universal protective therapy in respiratory virus infections.

Sustained innate interferon is an essential inducer of tertiary lymphoid structures

Tertiary lymphoid structures (TLS) resemble follicles of secondary lymphoid organs and develop in nonlymphoid tissues during inflammation and cancer. Which cell types and signals drive the development of TLS is largely unknown. To investigate early events of TLS development in the lungs, we repeatedly instilled p(I:C) plus ovalbumin (Ova) intranasally. This induced TLS ranging from lymphocytic aggregates to organized and functional structures containing germinal centers. We found that TLS development is independent of FAP+ fibroblasts, alveolar macrophages, or CCL19 but crucially depends on type I interferon (IFN-I). Mechanistically, IFN-I initiates two synergistic pathways that culminate in the development of TLS. On the one hand, IFN-I induces lymphotoxin (LT)α in lymphoid cells, which stimulate stromal cells to produce the B-cell-attracting chemokine CXCL13 through LTβR-signaling. On the other hand, IFN-I is sensed by stromal cells that produce the T-cell-attracting chemokines CXCL9, CXCL10 as well as CCL19 and CCL21 independently of LTβR. Consequently, B-cell aggregates develop within a week, whereas follicular dendritic cells and germinal centers appear after 3 weeks. Thus, sustained production of IFN-I together with an antigen is essential for the induction of functional TLS in the lungs.

The deadly dance of alveolar macrophages and influenza virus

Influenza A virus (IAV) is one of the leading causes of respiratory infections. The lack of efficient anti-influenza therapeutics requires a better understanding of how IAV interacts with host cells. Alveolar macrophages are tissue-specific macrophages that play a critical role in lung innate immunity and homeostasis, yet their role during influenza infection remains unclear. First, our review highlights an active IAV replication within alveolar macrophages, despite an abortive viral cycle. Such infection leads to persistent alveolar macrophage inflammation and diminished phagocytic function, alongside direct mitochondrial damage and indirect metabolic shifts in the alveolar micro-environment. We also discuss the "macrophage disappearance reaction", which is a drastic reduction of the alveolar macrophage population observed after influenza infection in mice but debated in humans, with unclear underlying mechanisms. Furthermore, we explore the dual nature of alveolar macrophage responses to IAV infection, questioning whether they are deleterious or protective for the host. While IAV may exploit immuno-evasion strategies and induce alveolar macrophage alteration or depletion, this could potentially reduce excessive inflammation and allow for the replacement of more effective cells. Despite these insights, the pathophysiological role of alveolar macrophages during IAV infection in humans remains understudied, urging further exploration to unravel their precise contributions to disease progression and resolution.

Crosstalk between macrophages and immunometabolism and their potential roles in tissue repair and regeneration

Immune metabolism is a result of many specific metabolic reactions, such as glycolysis, the tricarboxylic acid (TCA) pathway, the pentose phosphate pathway (PPP), mitochondrial oxidative phosphorylation (OXPHOS), fatty acid oxidation (FAO), fatty acid biosynthesis (FAs) and amino acid pathways, which promote cell proliferation and maintenance with structural and pathological energy to regulate cellular signaling. The metabolism of macrophages produces many metabolic intermediates that play important regulatory roles in tissue repair and regeneration. The metabolic activity of proinflammatory macrophages (M1) mainly depends on glycolysis and the TCA cycle system, but anti-inflammatory macrophages (M2) have intact functions of the TCA cycle, which enhances FAO and is dependent on OXPHOS. However, the metabolic mechanisms of macrophages in tissue repair and regeneration have not been well investigated. Thus, we review how three main metabolic mechanisms of macrophages, glucose metabolism, lipid metabolism, and amino acid metabolism, regulate tissue repair and regeneration.

Pulmonary and Systemic Immune Profiles Following Lung Volume Reduction Surgery and Allogeneic Mesenchymal Stromal Cell Treatment in Emphysema

Emphysema in patients with chronic obstructive pulmonary disease (COPD) is characterized by progressive inflammation. Preclinical studies suggest that lung volume reduction surgery (LVRS) and mesenchymal stromal cell (MSC) treatment dampen inflammation. We investigated the effects of bone marrow-derived MSC (BM-MSC) and LVRS on circulating and pulmonary immune cell profiles in emphysema patients using mass cytometry. Blood and resected lung tissue were collected at the first LVRS (L1). Following 6-10 weeks of recovery, patients received a placebo or intravenous administration of 2 × 106 cells/kg bodyweight BM-MSC (n = 5 and n = 9, resp.) in week 3 and 4 before the second LVRS (L2), where blood and lung tissue were collected. Irrespective of BM-MSC or placebo treatment, proportions of circulating lymphocytes including central memory CD4 regulatory, effector memory CD8 and γδ T cells were higher, whereas myeloid cell percentages were lower in L2 compared to L1. In resected lung tissue, proportions of Treg (p = 0.0067) and anti-inflammatory CD163- macrophages (p = 0.0001) were increased in L2 compared to L1, while proportions of pro-inflammatory CD163+ macrophages were decreased (p = 0.0004). There were no effects of BM-MSC treatment on immune profiles in emphysema patients. However, we observed alterations in the circulating and pulmonary immune cells upon LVRS, suggesting the induction of anti-inflammatory responses potentially needed for repair processes.

Inflammatory and Immune Mechanisms in COPD: Current Status and Therapeutic Prospects

Background

Chronic obstructive pulmonary disease (COPD) currently ranks among the top three causes of mortality worldwide, presenting as a prevalent and complex respiratory ailment. Ongoing research has underscored the pivotal role of immune function in the onset and progression of COPD. The immune response in COPD patients exhibits abnormalities, characterized by diminished anti-infection capacity due to immune senescence, heightened activation of neutrophils and macrophages, T cell infiltration, and aberrant B cell activity, collectively contributing to airway inflammation and lung injury in COPD.

Objective

This review aimed to explore the pivotal role of the immune system in COPD and its therapeutic potential.

Methods

We conducted a review of immunity and COPD published within the past decade in the Web of Science and PubMed databases, sorting through and summarizing relevant literature.

Results

This article examines the pivotal roles of the immune system in COPD. Understanding the specific functions and interactions of these immune cells could facilitate the development of novel therapeutic strategies and interventions aimed at controlling inflammation, enhancing immune function, and mitigating the impact of respiratory infections in COPD patients.

RAMP1 Signaling Mitigates Acute Lung Injury by Distinctively Regulating Alveolar and Monocyte-Derived Macrophages

Acute respiratory distress syndrome (ARDS) is a life-threatening lung injury that induces cytokine hypersecretion. Receptor activity-modifying protein (RAMP) 1, a subunit of the calcitonin gene-related peptide (CGRP) receptor, regulates the production of cytokines. This study examined the role of RAMP1 signaling during lipopolysaccharide (LPS)-induced acute lung injury (ALI). LPS administration to wild-type (WT) mice depleted alveolar macrophages (AMs) and recruited monocyte-derived macrophages (MDMs) and neutrophils. RAMP1-deficient (RAMP1-/-) mice exhibited higher lung injury scores, cytokine levels, and cytokine-producing neutrophil infiltration. RAMP1-deficient AMs produced more cytokines in response to LPS than WT AMs. Adoptive transfer of RAMP1-deficient AMs to RAMP1-/- mice increased cytokine levels and neutrophil accumulation compared to the transfer of WT AMs. RAMP1-/- mice had reduced MDM recruitment and lower pro-inflammatory and reparative macrophage profiles. Cultured bone marrow (BM)-derived RAMP1-deficient macrophages stimulated with LPS showed decreased expression of pro-inflammatory and pro-repairing genes. CGRP administration to WT mice reduced cytokine production and neutrophil accumulation. These findings indicate that RAMP1 signaling mitigates LPS-induced ALI by inactivating AMs and promoting inflammatory and repair activities of MDMs. Targeting RAMP1 signaling presents a potential therapeutic approach for the treatment of ARDS.

Inducible antibacterial responses in macrophages

Macrophages destroy bacteria and other microorganisms through phagocytosis-coupled antimicrobial responses, such as the generation of reactive oxygen species and the delivery of hydrolytic enzymes from lysosomes to the phagosome. However, many intracellular bacteria subvert these responses, escaping to other cellular compartments to survive and/or replicate. Such bacterial subversion strategies are countered by a range of additional direct antibacterial responses that are switched on by pattern-recognition receptors and/or host-derived cytokines and other factors, often through inducible gene expression and/or metabolic reprogramming. Our understanding of these inducible antibacterial defence strategies in macrophages is rapidly evolving. In this Review, we provide an overview of the broad repertoire of antibacterial responses that can be engaged in macrophages, including LC3-associated phagocytosis, metabolic reprogramming and antimicrobial metabolites, lipid droplets, guanylate-binding proteins, antimicrobial peptides, metal ion toxicity, nutrient depletion, autophagy and nitric oxide production. We also highlight key inducers, signalling pathways and transcription factors involved in driving these different antibacterial responses. Finally, we discuss how a detailed understanding of the molecular mechanisms of antibacterial responses in macrophages might be exploited for developing host-directed therapies to combat antibiotic-resistant bacterial infections.

Evidence of Alveolar Macrophage Metabolic Shift Following Stereotactic Body Radiation Therapy -Induced Lung Fibrosis in Mice

PURPOSE

Radiation-induced pneumopathy is the main dose-limiting factor in cases of chest radiation therapy. Macrophage infiltration is frequently observed in irradiated lung tissues and may participate in lung damage development. Radiation-induced lung fibrosis can be reproduced in rodent models using whole thorax irradiation but suffers from limits concerning the role played by unexposed lung volumes in damage development.

METHODS AND MATERIALS

Here, we used an accurate stereotactic body radiation therapy preclinical model irradiating 4% of the mouse lung. Tissue damage development and macrophage populations were followed by histology, flow cytometry, and single-cell RNA sequencing. Wild-type and CCR2 KO mice, in which monocyte recruitment is abrogated, were exposed to single doses of radiation, inducing progressive (60 Gy) or rapid (80 Gy) lung fibrosis.

RESULTS

Numerous clusters of macrophages were observed around the injured area, during progressive as well as rapid fibrosis. The results indicate that probably CCR2-independent recruitment and/or in situ proliferation may be responsible for macrophage invasion. Alveolar macrophages experience a metabolic shift from fatty acid metabolism to cholesterol biosynthesis, directing them through a possible profibrotic phenotype. Depicted data revealed that the origin and phenotype of macrophages present in the injured area may differ from what has been previously described in preclinical models exposing large lung volumes, representing a potentially interesting trail in the deciphering of radiation-induced lung damage processes.

CONCLUSIONS

Our study brings new possible clues to the understanding of macrophage implications in radiation-induced lung damage, representing an interesting area for exploration in future studies.

Antibiotic use during influenza infection augments lung eosinophils that impair immunity against secondary bacterial pneumonia

A leading cause of mortality after influenza infection is the development of a secondary bacterial pneumonia. In the absence of a bacterial superinfection, prescribing antibacterial therapies is not indicated but has become a common clinical practice for those presenting with a respiratory viral illness. In a murine model, we found that antibiotic use during influenza infection impaired the lung innate immunologic defenses toward a secondary challenge with methicillin-resistant Staphylococcus aureus (MRSA). Antibiotics augment lung eosinophils, which have inhibitory effects on macrophage function through the release of major basic protein. Moreover, we demonstrated that antibiotic treatment during influenza infection caused a fungal dysbiosis that drove lung eosinophilia and impaired MRSA clearance. Finally, we evaluated 3 cohorts of hospitalized patients and found that eosinophils positively correlated with antibiotic use, systemic inflammation, and worsened outcomes. Altogether, our work demonstrates a detrimental effect of antibiotic treatment during influenza infection that has harmful immunologic consequences via recruitment of eosinophils to the lungs, thereby increasing the risk of developing a secondary bacterial infection.