Pulmonary macrophages and their different roles in health and disease

Exosomes: efficient macrophage-related immunomodulators in chronic lung diseases

Macrophages, the predominant immune cells in the lungs, play a pivotal role in maintaining the delicate balance of the pulmonary immune microenvironment. However, in chronic inflammatory lung diseases and lung cancer, macrophage phenotypes undergo distinct transitions, with M1-predominant macrophages promoting inflammatory damage and M2-predominant macrophages fostering cancer progression. Exosomes, as critical mediators of intercellular signaling and substance exchange, participate in pathological reshaping of macrophages during development of pulmonary inflammatory diseases and lung cancer. Specifically, in inflammatory lung diseases, exosomes promote the pro-inflammatory phenotype of macrophages, suppress the anti-inflammatory phenotype, and subsequently, exosomes released by reshaped macrophages further exacerbate inflammatory damage. In cancer, exosomes promote pro-tumor tumor-associated macrophages (TAMs); inhibit anti-tumor TAMs; and exosomes released by TAMs further enhance tumor proliferation, metastasis, and resistance to chemotherapy. Simultaneously, exosomes exhibit a dual role, holding the potential to transmit immune-modulating molecules and load therapeutic agents and offering prospects for restoring immune dysregulation in macrophages during chronic inflammatory lung diseases and lung cancer. In chronic inflammatory lung diseases, this is manifested by exosomes reshaping anti-inflammatory macrophages, inhibiting pro-inflammatory macrophages, and alleviating inflammatory damage post-reshaping. In lung cancer, exosomes reshape anti-tumor macrophages, inhibit pro-tumor macrophages, and reshaped macrophages secrete exosomes that suppress lung cancer development. Looking ahead, efficient and targeted exosome-based therapies may emerge as a promising direction for treatment of pulmonary diseases.

The Nutritional Intervention of Ingredients from Food Medicine Homology Regulating Macrophage Polarization on Atherosclerosis

The polarization of macrophages plays a crucial regulatory role in a range of physiological and pathological processes involving macrophages. There are numerous concerns with macrophage polarization in atherosclerosis; however, most focus on modulating macrophage polarization to improve the microenvironment, and the mechanism of action remains unknown. In recent years, the advantages of natural and low-toxicity side effects of food medicine homology-derived substances have been widely explored. Few reports have started from ingredients from food medicine homology to regulate the polarization of macrophages so that early intervention can reduce or delay the process of atherosclerosis. This review summarizes the classification of macrophage polarization and related markers in the process of atherosclerosis. It summarizes the regulatory role of ingredients from food medicine homology in macrophage polarization and their possible mechanisms to provide ideas and inspiration for the nutritional intervention in vascular health.

Ubiquitin Ligases Siah1a/2 Control Alveolar Macrophage Functions to Limit Carcinogen-Induced Lung Adenocarcinoma

Cellular components of the tumor microenvironment, including myeloid cells, play important roles in the progression of lung adenocarcinoma (LUAD) and its response to therapy. Here, we characterize the function of the ubiquitin ligases Siah1a/2 in regulating the differentiation and activity of alveolar macrophages (AM) and assess the implication of Siah1a/2 control of AMs for carcinogen-induced LUAD. Macrophage-specific genetic ablation of Siah1a/2 promoted accumulation of AMs with an immature phenotype and increased expression of protumorigenic and pro-inflammatory Stat3 and β-catenin gene signatures. Administration of urethane to wild-type mice promoted enrichment of immature-like AMs and lung tumor development, which was enhanced by macrophage-specific Siah1a/2 ablation. The profibrotic gene signature seen in Siah1a/2-ablated immature-like macrophages was associated with increased tumor infiltration of CD14+ myeloid cells and poorer survival of patients with LUAD. Single-cell RNA-seq confirmed the presence of a cluster of immature-like AMs expressing a profibrotic signature in lungs of patients with LUAD, a signature enhanced in smokers. These findings identify Siah1a/2 in AMs as gatekeepers of lung cancer development.

SIGNIFICANCE

The ubiquitin ligases Siah1a/2 control proinflammatory signaling, differentiation, and profibrotic phenotypes of alveolar macrophages to suppress lung carcinogenesis.

Irisin drives macrophage anti-inflammatory differentiation via JAK2-STAT6-dependent activation of PPARγ and Nrf2 signaling

Irisin is an exercise-induced myokine that alleviates inflammation and obesity. The induction of anti-inflammatory (M2) macrophage is facilitated for treatment of sepsis and associated lung damage. However, whether irisin drives macrophage M2 polarization remains unclear. Here, we found that irisin induced-macrophage anti-inflammatory differentiation in vivo using an LPS-induced septic mice model and in vitro using RAW64.7 cells and bone marrow-derived macrophages (BMDMs). Irisin also promoted the expression, phosphorylation, and nuclear translocation of peroxisome proliferator-activated receptor gamma (PPAR-γ) and nuclear factor-erythroid 2-related factor 2 (Nrf2). Inhibition or knockdown of PPAR-γ and Nrf2 abolished irisin-induced accumulation of M2 macrophage markers, such as interleukin (IL)-10 and Arginase 1. Furthermore, dual-luciferase reporter and chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) assays confirmed that STAT6 boosts PPAR-γ and Nrf2 transcription by binding to their DNA promoters in irisin-stimulated macrophages. In contrast, STAT6 shRNA blocked the irisin-induced activation of Pparγ, Nrf2, and related downstream genes. Moreover, the interaction of irisin with its ligand integrin αVβ5 remarkably promoted Janus kinase 2 (JAK2) phosphorylation, while inhibition or knockdown of integrin αVβ5 and JAK2 attenuated the activation of STAT6, PPAR-γ, and Nrf2 signaling. Interestingly, co-immunoprecipitation (Co-IP) assay also revealed that the binding between JAK2 and integrin αVβ5 is critical for irisin-induced macrophage anti-inflammatory differentiation by enhancing the activation of the JAK2-STAT6 pathway. In conclusion, irisin boosted M2 macrophage differentiation by inducing JAK2-STAT6-dependent transcriptional activation of the PPAR-γ-related anti-inflammatory system and Nrf2-related antioxidant genes. The findings of this study suggest that the administration of irisin is a novel and promising therapeutic strategy for infectious and inflammatory diseases.

On-Off Phagocytosis and Switchable Macrophage Activation Stimulated with NIR for Infected Percutaneous Tissue Repair of Polypyrrole-Coated Sulfonated PEEK

Intelligent control of the immune response is essential for obtaining percutaneous implants with good sterilization and tissue repair abilities. In this study, polypyrrole (Ppy) nanoparticles enveloping a 3D frame of sulfonated polyether ether ketone (SP) surface are constructed, which enhance the surface modulus and hardness of the sulfonated layer by forming a cooperative structure of simulated reinforced concrete and exhibit a superior photothermal effect. Ppy-coated SP could quickly accumulate heat on the surface by responding to 808 nm near-infrared (NIR) light, thereby killing bacteria, and destroying biofilms. Under NIR stimulation, the phagocytosis and M1 activation of macrophages cultured on Ppy-coated SP are enhanced by activating complement 3 and its receptor, CD11b. Phagocytosis and M1 activation are impaired along with abolishment of NIR stimulation in the Ppy-coated SP group, which is favorable for tissue repair. Ppy-coated SP promotes Collagen-I, vascular endothelial growth factor, connective tissue growth factor, and α-actin (Acta2) expression by inducing M2 polarization owing to its higher surface modulus. Overall, Ppy-coated SP with enhanced mechanical properties could be a good candidate for clinical percutaneous implants through on-off phagocytosis and switchable macrophage activation stimulated with NIR.

The crosstalk between parenchymal cells and macrophages: A keeper of tissue homeostasis

Non-parenchymal cells (NPCs) and parenchymal cells (PCs) collectively perform tissue-specific functions. PCs play significant roles and continuously adjust the intrinsic functions and metabolism of organs. Tissue-resident macrophages (TRMs) are crucial members of native NPCs in tissues and are essential for immune defense, tissue repair and development, and homeostasis maintenance. As a plastic-phenotypic and prevalent cluster of NPCs, TRMs dynamically assist PCs in functioning by producing cytokines, inflammatory and anti-inflammatory signals, growth factors, and proteolytic enzymes. Furthermore, the PCs of tissues modulate the functional activity and polarization of TRMs. Dysregulation of the PC-TRM crosstalk axis profoundly impacts many essential physiological functions, including synaptogenesis, gastrointestinal motility and secretion, cardiac pulsation, gas exchange, blood filtration, and metabolic homeostasis. This review focuses on the PC-TRM crosstalk in mammalian vital tissues, along with their interactions with tissue homeostasis maintenance and disorders. Thus, this review highlights the fundamental biological significance of the regulatory network of PC-TRM in tissue homeostasis.

A novel therapeutic approach for IPF: Based on the "Autophagy - Apoptosis" balance regulation of Zukamu Granules in alveolar macrophages

ETHNOPHARMACOLOGICAL RELEVANCE

Zukamu Granules (ZKMG) is one of the representative Uygur patent drugs widely used in China, which is included in the National Essential Drugs List (2018 edition). As the first choice for common cold treatment in Uygur medicine theory, it has unique anti-inflammatory and antitussive efficacy.

AIM OF THE STUDY

According to the recent inflammatory hypothesis, the abnormal proliferation, autophagy and apoptosis process of lung cells especially alveolar macrophages (AMs) may play an important role in the progress of idiopathic pulmonary fibrosis (IPF). Therefore, we came up with a novel treatment approach for IPF by regulating the balance of AMs "autophagy - apoptosis", and took ZKMG as the sample drug for our research.

MATERIALS AND METHODS

Network pharmacology approach was conducted to predict the active components and intersected targets between ZKMG and inflammation. PPI network, GO and KEGG enrichment analysis were screened and analyzed to predict the anti-inflammatory mechanism of ZKMG. Biological experiment adopted from 128 rats, and hematoxylin-eosin staining, flow cytometry and RT-PCR were performed to examine the pathological morphology, HYP contents in lung tissue, AMs counting, AMs apoptosis, AMs phagocytosis rate, mRNA relative quantity determination of 3 key factors associated with AMs "autophagy - apoptosis" and mRNA relative quantity determination of AMs surface receptor signaling pathway.

RESULTS

The predicted results showed that the mechanism of ZKMG in anti-inflammatory was related to the response and elimination of inflammatory stimuli, the intervention of apoptosis and surface receptor signaling pathways of cells. The verification experiments showed that excessive apoptosis and insufficient autophagy of AMs always existed in the progression of IPF. ZKMG could inhibit AMs proliferation, significantly reduce AMs apoptosis rate, intervene the binding of the Bcl-2 to Beclin 1, inhibit the Caspase 3 activation, stimulate the enhancement of AMs phagocytosis, and inhibit the high expression of TLR4/MyD88/NF-κB surface receptor signaling pathway, which may partly retard the fibrosis process.

CONCLUSION

By inhibiting proliferation, enhancing phagocytosis, inhibiting the formation of Bcl-2 complex, and inhibiting the high expression of MYD88-dependent TLR4 signaling pathway, ZKMG can regulate the balance of AMs "autophagy - apoptosis" in the alveolitis stage to retard the fibrosis process partly. With a comprehensive strategy of "target prediction - experimental verification", we have demonstrated that inhibiting the apoptosis and promoting autophagy activity of AMs may suggest a new perspective for IPF treatment, which would provide reference for the subsequent development.

Absence of CCR2 Promotes Proliferation of Alveolar Macrophages That Control Lung Inflammation in Acute Respiratory Distress Syndrome in Mice

Acute respiratory distress syndrome (ARDS) consists of uncontrolled inflammation that causes hypoxemia and reduced lung compliance. Since it is a complex process, not all details have been elucidated yet. In a well-controlled experimental murine model of lipopolysaccharide (LPS)-induced ARDS, the activity and viability of macrophages and neutrophils dictate the beginning and end phases of lung inflammation. C-C chemokine receptor type 2 (CCR2) is a critical chemokine receptor that mediates monocyte/macrophage activation and recruitment to the tissues. Here, we used CCR2-deficient mice to explore mechanisms that control lung inflammation in LPS-induced ARDS. CCR2−/− mice presented higher total numbers of pulmonary leukocytes at the peak of inflammation as compared to CCR2+/+ mice, mainly by enhanced influx of neutrophils, whereas we observed two to six-fold lower monocyte or interstitial macrophage numbers in the CCR2−/−. Nevertheless, the time needed to control the inflammation was comparable between CCR2+/+ and CCR2−/−. Interestingly, CCR2−/− mice presented higher numbers and increased proliferative rates of alveolar macrophages from day 3, with a more pronounced M2 profile, associated with transforming growth factor (TGF)-β and C-C chemokine ligand (CCL)22 production, decreased inducible nitric oxide synthase (Nos2), interleukin (IL)-1β and IL-12b mRNA expression and increased mannose receptor type 1 (Mrc1) mRNA and CD206 protein expression. Depletion of alveolar macrophages significantly delayed recovery from the inflammatory insult. Thus, our work shows that the lower number of infiltrating monocytes in CCR2−/− is partially compensated by increased proliferation of resident alveolar macrophages during the inflammation control of experimental ARDS.

Preexisting Heterogeneity of Inducible Nitric Oxide Synthase Expression Drives Differential Growth of Mycobacterium tuberculosis in Macrophages

Mycobacterium tuberculosis infection is initiated by the inhalation and implantation of bacteria in the lung alveoli, where they are phagocytosed by macrophages. Even a single bacterium may be sufficient to initiate infection. Thereafter, the clinical outcome is highly variable between individuals, ranging from sterilization to active disease, for reasons that are not well understood. Here, we show that the rate of intracellular bacterial growth varies markedly between individual macrophages, and this heterogeneity is driven by cell-to-cell variation of inducible nitric oxide synthase (iNOS) activity. At the single-cell level, iNOS expression fluctuates over time, independent of infection or activation with gamma interferon. We conclude that chance encounters between individual bacteria and host cells randomly expressing different levels of an antibacterial gene can determine the outcome of single-cell infections, which may explain why some exposed individuals clear the bacteria while others develop progressive disease. IMPORTANCE In this report, we demonstrate that fluctuations in the expression of antimicrobial genes can define how single host cells control bacterial infections. We show that preexisting cell-to-cell variation in the expression of a single gene, that for inducible nitric oxide synthase, is sufficient to explain why some macrophages kill intracellular M. tuberculosis while others fail to control bacterial replication, possibly leading to disease progression. We introduce the concept that chance encounters between heterogeneous bacteria and host cells can determine the outcome of a host-pathogen interaction. This concept is particularly relevant for all the infectious diseases in which the number of interacting pathogens and host cells is small at some point during the infection.

In Vitro Immunomodulatory Effects of Inonotus obliquus Extracts on Resting M0 Macrophages and LPS-Induced M1 Macrophages

Background

Inonotus obliquus (Chaga) is a parasitic fungus that is distributed mainly in northeast China. Our literature research showed chaga polysaccharides have bilateral effects on tumor necrosis factor (TNF)-α and interleukin (IL)-1β levels when they exert antitumor and antidiabetic activities. The current research tried to explore the influence of chaga extracts on inflammatory factors via macrophage polarization which has bilateral immune-regulation not only on healthy tissue homeostasis but also on pathologies.

Methods

Chaga was extracted with 100°C water and precipitated with 80% ethanol. The extracts were studied on RAW264.7 macrophage at resting condition (M0) and lipopolysaccharide (LPS)-activated subtype (classic activated macrophage, M1). The IL-1β, TNF-α, nitric oxide (NO) level, and the protein expressions of M1 and alternative activated macrophage (M2) markers including IL-1β, inducible NO synthase (iNOS), mannose receptor (CD206), and arginase (Arg)-1 were compared.

Results

The 100 g extracts contained 13.7 g polysaccharides and 1.9 g polyphenols. Compared with M0, the 50 μg/mL extracts increased NO level (P < 0.05) and decreased CD206 and Arg-1 expression significantly (P < 0.05). The extracts at 100–200 μg/mL increased NO and TNF-α level (P < 0.05), but increased iNOS and IL-1β expression significantly (P < 0.05). Compared with M1, the extracts decreased NO level at 25, 50, 100, and 200 μg/mL and decreased IL-1β and TNF-α level at 100–200 μg/mL significantly (P < 0.05). At 25–200 μg/mL, the extracts significantly increased CD206 and Arg-1 expression and decreased IL-1β and iNOS expression separately (P < 0.05).

Conclusions

Our research suggested that the bilateral effects of the chaga extracts on iNOS, IL-1β, and NO level on M0/M1 macrophages might be related with chaga polysaccharides and chaga polyphenols. Some in vivo anticancer and antidiabetic research of purified chaga polysaccharides related to macrophage differentiation should be conducted further.

Could Interleukin-33 (IL-33) Govern the Outcome of an Equine Influenza Virus Infection? Learning from Other Species

Influenza A viruses (IAVs) are important respiratory pathogens of horses and humans. Infected individuals develop typical respiratory disorders associated with the death of airway epithelial cells (AECs) in infected areas. Virulence and risk of secondary bacterial infections vary among IAV strains. The IAV non-structural proteins, NS1, PB1-F2, and PA-X are important virulence factors controlling AEC death and host immune responses to viral and bacterial infection. Polymorphism in these proteins impacts their function. Evidence from human and mouse studies indicates that upon IAV infection, the manner of AEC death impacts disease severity. Indeed, while apoptosis is considered anti-inflammatory, necrosis is thought to cause pulmonary damage with the release of damage-associated molecular patterns (DAMPs), such as interleukin-33 (IL-33). IL-33 is a potent inflammatory mediator released by necrotic cells, playing a crucial role in anti-viral and anti-bacterial immunity. Here, we discuss studies in human and murine models which investigate how viral determinants and host immune responses control AEC death and subsequent lung IL-33 release, impacting IAV disease severity. Confirming such data in horses and improving our understanding of early immunologic responses initiated by AEC death during IAV infection will better inform the development of novel therapeutic or vaccine strategies designed to protect life-long lung health in horses and humans, following a One Health approach.