Alveolar Macrophage Phenotype and Compartmentalization Drive Different Pulmonary Changes in Mouse Strains Exposed to Cigarette Smoke

Immunoregulatory role of platelet derivatives in the macrophage-mediated immune response

Background

Macrophages are innate immune cells that display remarkable phenotypic heterogeneity and functional plasticity. Due to their involvement in the pathogenesis of several human conditions, macrophages are considered to be an attractive therapeutic target. In line with this, platelet derivatives have been successfully applied in many medical fields and as active participants in innate immunity, cooperation between platelets and macrophages is essential. In this context, the aim of this review is to compile the current evidence regarding the effects of platelet derivatives on the phenotype and functions of macrophages to identify the advantages and shortcomings for feasible future clinical applications.

Methods

A total of 669 articles were identified during the systematic literature search performed in PubMed and Web of Science databases.

Results

A total of 27 articles met the inclusion criteria. Based on published findings, platelet derivatives may play an important role in inducing a dynamic M1/M2 balance and promoting a timely M1-M2 shift. However, the differences in procedures regarding platelet derivatives and macrophages polarization and the occasional lack of information, makes reproducibility and comparison of results extremely challenging. Furthermore, understanding the differences between human macrophages and those derived from animal models, and taking into account the peculiarities of tissue resident macrophages and their ontogeny seem essential for the design of new therapeutic strategies.

Conclusion

Research on the combination of macrophages and platelet derivatives provides relevant information on the function and mechanisms of the immune response.

Cigarette Smoke Constituents and Nicotine Differentially Affect Cytokine Production by Human Macrophages Stimulated by TLR Ligands In Vitro: Considerations for a Standardised Protocol

Chronic obstructive pulmonary disease (COPD) is an inflammatory lung condition associated with cigarette (tobacco) smoking. Numerous in vivo animal studies have been conducted to investigate the links between cigarette smoke, nicotine and infection in lung pathology. As an alternative to animal experiments, we used an in vitro system to investigate the effects of cigarette smoke extract (CSE) or nicotine on TNF-α and IL-10 production by monocyte-derived human macrophages. The macrophages were simultaneously stimulated with either poly-IC (as a chemical surrogate for viral infection) or lipopolysaccharide (as a chemical surrogate for Gram-negative bacterial infection). CSE enhanced TNF-α production, whereas nicotine inhibited IL-10 production by the macrophages, particularly when co-stimulated with the microbial chemical surrogates. A system of this type may help to further our understanding of the immunological and inflammatory effects of smoking, without recourse to in vivo studies. Requirements for the optimisation and standardisation of such an in vitro system are also discussed.

Immunohistochemical Study of Airways Fibrous Remodeling in Smoking Mice

The fibrotic remodeling in chronic obstructive pulmonary disease (COPD) is held responsible for narrowing of small airways and thus for disease progression. Oxidant damage and cell senescence factors are recently involved in airways fibrotic remodeling. Unfortunately, we have no indications on their sequential expression at anatomical sites in which fibrotic remodeling develops in smoking subjects. Using immunohistochemical techniques, we investigated in two strains of mice after cigarette smoke (CS) exposure what happens at various times in airway areas where fibrotic remodeling occurs, and if there also exists correspondence among DNA damage induced by oxidants, cellular senescence, the presence of senescence-secreted factors involved in processes that affect transcription, metabolism as well as apoptosis, and the onset of fibrous remodeling that appears at later times in mice exposed to CS. A clear positivity for fibrogenic cytokines TGF-β, PDGF-B, and CTGF, and for proliferation marker PCNA around airways that will be remodeled is observed in both strains. Increased expression of p16ink4A senescence marker and MyoD is also seen in the same areas. p16ink4A and MyoD can promote cell cycle arrest, terminal differentiation of myofibroblasts, and can oppose their dedifferentiation. Of interest, an early progressive attenuation of SIRT-1 is observed after CS exposure. This intracellular regulatory protein can reduce premature cell senescence. These findings suggest that novel agents, which promote myofibroblast dedifferentiation and/or the apoptosis of senescent cells, may dampen progression of airway changes in smoking COPD subjects.

Macrophages in immunoregulation and therapeutics

Macrophages exist in various tissues, several body cavities, and around mucosal surfaces and are a vital part of the innate immune system for host defense against many pathogens and cancers. Macrophages possess binary M1/M2 macrophage polarization settings, which perform a central role in an array of immune tasks via intrinsic signal cascades and, therefore, must be precisely regulated. Many crucial questions about macrophage signaling and immune modulation are yet to be uncovered. In addition, the clinical importance of tumor-associated macrophages is becoming more widely recognized as significant progress has been made in understanding their biology. Moreover, they are an integral part of the tumor microenvironment, playing a part in the regulation of a wide variety of processes including angiogenesis, extracellular matrix transformation, cancer cell proliferation, metastasis, immunosuppression, and resistance to chemotherapeutic and checkpoint blockade immunotherapies. Herein, we discuss immune regulation in macrophage polarization and signaling, mechanical stresses and modulation, metabolic signaling pathways, mitochondrial and transcriptional, and epigenetic regulation. Furthermore, we have broadly extended the understanding of macrophages in extracellular traps and the essential roles of autophagy and aging in regulating macrophage functions. Moreover, we discussed recent advances in macrophages-mediated immune regulation of autoimmune diseases and tumorigenesis. Lastly, we discussed targeted macrophage therapy to portray prospective targets for therapeutic strategies in health and diseases.

Smoking Cessation in Mice Does Not Switch off Persistent Lung Inflammation and Does Not Restore the Expression of HDAC2 and SIRT1

Once COPD is established, pulmonary lesions can only progress and smoking cessation by itself is not sufficient to switch off persistent lung inflammation. Similarly, in former-smoker mice, neutrophil inflammation persists and lung lesions undergo progressive deterioration. The molecular mechanisms underlying disease progression and the inefficiency of smoking cessation in quenching neutrophilic inflammation were studied in male C57 Bl/6 mice after 6 months of rest from smoking cessation. As compared with the mice that continued to smoke, the former-smoker mice showed reduced expression of histone deacetylases HDAC2 and SIRT1 and marked expression of p-p38 MAPK and p-Ser10. All these factors are involved in corticosteroid insensitivity and in perpetuating inflammation. Former-smoker mice do show persistent lung neutrophilic influx and a high number of macrophages which account for the intense staining in the alveolar structures of neutrophil elastase and MMP-9 (capable of destroying lung scaffolding) and 8-OHdG (marker of oxidative stress). “Alarmins” released from necrotic cells together with these factors can sustain and perpetuate inflammation after smoking cessation. Several factors and mechanisms all together are involved in sustaining and perpetuating inflammation in former-smoker mice. This study suggests that a better control of COPD in humans may be achieved by precise targeting of the various molecular mechanisms associated with different phenotypes of disease by using a cocktail of drug active toward specific molecules.

Extracellular Vesicles as Central Mediators of COPD Pathophysiology

Chronic obstructive pulmonary disease (COPD) is a complex, heterogeneous, smoking-related disease of significant global impact. The complex biology of COPD is ultimately driven by a few interrelated processes, including proteolytic tissue remodeling, innate immune inflammation, derangements of the host-pathogen response, aberrant cellular phenotype switching, and cellular senescence, among others. Each of these processes are engendered and perpetuated by cells modulating their environment or each other. Extracellular vesicles (EVs) are powerful effectors that allow cells to perform a diverse array of functions on both adjacent and distant tissues, and their pleiotropic nature is only beginning to be appreciated. As such, EVs are candidates to play major roles in these fundamental mechanisms of disease behind COPD. Furthermore, some such roles for EVs are already established, and EVs are implicated in significant aspects of COPD pathogenesis. Here, we discuss known and potential ways that EVs modulate the environment of their originating cells to contribute to the processes that underlie COPD.

Leukocyte Function in COPD: Clinical Relevance and Potential for Drug Therapy

Chronic obstructive pulmonary disease (COPD) is a progressive lung condition affecting 10% of the global population over 45 years. Currently, there are no disease-modifying treatments, with current therapies treating only the symptoms of the disease. COPD is an inflammatory disease, with a high infiltration of leukocytes being found within the lung of COPD patients. These leukocytes, if not kept in check, damage the lung, leading to the pathophysiology associated with the disease. In this review, we focus on the main leukocytes found within the COPD lung, describing how the release of chemokines from the damaged epithelial lining recruits these cells into the lung. Once present, these cells become active and may be driven towards a more pro-inflammatory phenotype. These cells release their own subtypes of inflammatory mediators, growth factors and proteases which can all lead to airway remodeling, mucus hypersecretion and emphysema. Finally, we describe some of the current therapies and potential new targets that could be utilized to target aberrant leukocyte function in the COPD lung. Here, we focus on old therapies such as statins and corticosteroids, but also look at the emerging field of biologics describing those which have been tested in COPD already and potential new monoclonal antibodies which are under review.

Cigarette smoke extract-treated airway epithelial cells-derived exosomes promote M1 macrophage polarization in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a persistent respiratory disorder that is primarily caused by exposure to cigarette smoke (CS). Exosomes have emerged as crucial mediators of intercellular communication, but their role in CS-induced COPD is not fully understood. Here, we investigated whether exosomes derived from cigarette smoke extract (CSE)-treated mouse airway epithelial cells (MAECs) promote M1 macrophage polarization by upregulating triggering receptor expressed on myeloid cells-1 (TREM-1) expression during COPD pathogenesis. The exosomes isolated from PBS- or CSE-treated MAECs were named as Exo^PBS or Exo^CSE, respectively. Macrophages were transfected with si-TREM-1 to explore the role of TREM-1 in Exo^CSE-induced M1 macrophage polarization. The lentivirus expressing shTREM-1 was injected into COPD model mice by intranasal instillation, which was carried out to explore the in vivo role of TREM-1 in Exo^CSE-induced M1 macrophage polarization and CS-induced lung injury. We isolated Exo^PBS and Exo^CSE successfully, and found that Exo^CSE promoted M1 macrophage polarization. Furthermore, we found that the promotion of Exo^CSE to M1 macrophage polarization was partly reversed by TREM-1 knockdown. The results of animal experiments showed that Exo^CSE administration aggravated CS-induced impairment in pulmonary function, lung injury and M1 macrophage polarization, which were partly rescued by TREM-1 silencing. Overall, Exo^CSE promoted M1 macrophage polarization by upregulating TREM-1 expression, thereby aggravating the development of COPD.

Knockout of Formyl Peptide Receptor-1 Attenuates Cigarette Smoke-Induced Airway Inflammation in Mice

Objective: The formyl peptide receptor-1 (FPR-1) has been reported to be implicated in the regulation of inflammatory disorders, while its role in cigarette smoke (CS)-induced airway inflammation has not been fully explained. In this study, we investigated the role of FPR-1 in CS-induced airway inflammation and the possible mechanism through gene knockout (KO) technology and transcriptional study. Methods: FPR-1 KO or wild-type C57BL/6 mice were exposed to mainstream CS to establish an airway inflammation model. Cell counts and pro-inflammatory cytokines were measured in bronchoalveolar lavage fluid (BALF). Lung tissues were collected for histological examination, polymerase chain reaction, Western blot, transcriptomic gene study, and related bioinformatics analysis. Results: CS exposure induced significant histological inflammatory changes, increased neutrophils, and pro-inflammatory cytokines in the BALF of wild-type mice, which were all attenuated by KO of FPR-1. The transcriptomic gene study showed a total of 198 up-regulated genes and 282 down-regulated genes in mouse lungs. Bioinformatics analysis including Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) suggested these differentiated expressed genes were significantly related to the immune, chemotaxis responses, and cross-talked with a complicated network of signaling pathways including NF-κB. Western blot validated that KO of FPR-1 inhibited CS-induced NF-κB activation. Conclusion: Knockout of FPR-1 significantly ameliorates CS-induced airway inflammation in mice, possibly via its related immune-chemotaxis responses and inhibition of NF-κB activation.