GTS-21 Reduces Inflammation in Acute Lung Injury by Regulating M1 Polarization and Function of Alveolar Macrophages

GTS-21 alleviates sepsis-induced atrial fibrillation susceptibility by modulating macrophage polarization and Neuregulin-1 secretion

OBJECTIVE

Sepsis-induced atrial fibrillation (AF) is driven by systemic inflammation and macrophage-mediated atrial remodeling, with proinflammatory M1 macrophages playing a key role. This study investigates whether GTS-21, an α7nAChR agonist, can reduce AF susceptibility by promoting macrophage polarization towards the anti-inflammatory M2 phenotype.

METHODS

A mouse model of lipopolysaccharide (LPS) (10 mg/kg)-induced sepsis was used to explore the relationship between atrial inflammation and AF. GTS-21 (20 mg/kg) was administered to assess its impact on 48-h survival and AF incidence. Cardiac function was evaluated using echocardiography. Markers of myocardial injury, including CK-MB, LDH, and cTnI, were measured. Macrophage polarization and atrial inflammation were assessed using immunofluorescence, flow cytometry, RT-qPCR, and western blotting. Oxidative stress and mitochondrial function were evaluated using reactive oxygen species (ROS) measurements, electron microscopy, and mitochondrial protein expression analysis. Calcium dynamics were studied using western blotting and confocal microscopy.

RESULTS

In LPS-induced septic mice, GTS-21 improved 48-h survival rates and reduced the induction rate and duration of AF (P < 0.05). Echocardiography showed a preserved left ventricular ejection fraction and enhanced diastolic function. Mechanistically, it promoted M2 macrophage polarization, inhibited the NF-κB P65/NLRP3/C-caspase 1 pathway to reduce IL-1β release, and alleviated oxidative stress. Additionally, mitochondrial structure was restored by reversing fission and promoting fusion, while calcium-handling proteins (NCX-1, RYR2, and SERCA2a) were regulated to prevent intracellular calcium overload, reducing AF susceptibility.

CONCLUSION

GTS-21 mitigated atrial inflammation and reduced the incidence of AF in mice with sepsis by regulating macrophage polarization, reducing oxidative stress, and preserving mitochondrial and calcium dynamics in cardiomyocytes. These findings highlight the therapeutic potential of GTS-21 in treating sepsis-induced AF.

Macrophage Polarization in Lung Diseases: From Mechanisms to Therapeutic Strategies

Macrophages are pivotal immune cells involved in maintaining immune homeostasis and defending against pathogens. They exhibit significant plasticity and heterogeneity, enabling polarization into pro-inflammatory M1 or anti-inflammatory M2 phenotypes in response to distinct microenvironmental cues. The process of macrophage polarization is tightly regulated by complex signaling pathways and transcriptional networks. This review explores the factors influencing macrophage polarization, the associated signaling pathways, and their roles in the pathogenesis of lung diseases, including fibrosis, cancer, and chronic inflammatory conditions. By summarizing recent advances, we aim to provide insights into the immunoregulatory functions of macrophages and their therapeutic potential. Based on our review, it is believed that targeting macrophage polarization emerges as a promising approach for developing effective treatments for lung diseases, balancing inflammation and repair while mitigating disease progression.

GTS-21 modulates rheumatoid arthritis Th17 and Th2 lymphocyte subset differentiation through the ɑ7nAch receptor

Previous research has demonstrated ɑ7nAch receptor (ɑ7nAchR) agonists to provide benefit for rheumatoid arthritis (RA) patients. However, the immunological mechanism of action for these ɑ7nAchR agonists has not been elucidated. Herein, the effect of GTS-21, a selective ɑ7nAchR agonist, on the differentiation of Th17 and Th2 cells was assessed. CD4 + T cells were obtained from the peripheral blood mononuclear cells (PBMCs) of RA patients and healthy donors. CD4 + T cells were separately differentiated into Th2 or Th17 cells with or without GTS-21 and with or without alpha-bungarotoxin (ɑBgt) (a ɑ7nAchR antagonist). The proportions of Th17 and Th2 cells were assessed by flow cytometry. Levels of the T cell cytokines, IL-17A and IL-4, were assessed by ELISA. Specific transcription factors, retinoic orphan receptor c (RORc), and GATA Binding Protein 3 (GATA-3) were detected by western blot. GTS-21 reduced IL-17A and increased IL-4 production by RA PBMCs. GTS-21 reduced the percentage of Th17 cells and increased the percentage of Th2 cells during Th17 and Th2 differentiation, respectively. GTS-21 downregulated RA CD4 + T cells RORc levels and reduced the secretion of IL-17A during Th17 differentiation. GTS-21 upregulated RA CD4 + T cells GATA3 and promoted IL-4 production during Th2 differentiation. ɑ-Bgt blocked the effects of GTS-21 during Th17 and Th2 differentiation. These results demonstrated that GTS-21 suppressed RA Th17 differentiation and promoted Th2 differentiation. As such, the use of GTS-21 may be a new therapeutic approach by which to treat RA patients. Key Points • GTS-21 suppressed RA Th17 differentiation and promoted Th2 differentiation via acting on ɑ7nAchR. • The protective effect of GTS-21 on RA may be related to its regulation of Th cell subsets.

Molecular mechanisms of Sepsis attacking the immune system and solid organs

Remarkable progress has been achieved in sepsis treatment in recent times, the mortality rate of sepsis has experienced a gradual decline as a result of the prompt administration of antibiotics, fluid resuscitation, and the implementation of various therapies aimed at supporting multiple organ functions. However, there is still significant mortality and room for improvement. The mortality rate for septic patients, 22.5%, is still unacceptably high, accounting for 19.7% of all global deaths. Therefore, it is crucial to thoroughly comprehend the pathogenesis of sepsis in order to enhance clinical diagnosis and treatment methods. Here, we summarized classic mechanisms of sepsis progression, activation of signal pathways, mitochondrial quality control, imbalance of pro-and anti- inflammation response, diseminated intravascular coagulation (DIC), cell death, presented the latest research findings for each mechanism and identify potential therapeutic targets within each mechanism.

GTS-21 attenuates ACE/ACE2 ratio and glycocalyx shedding in lipopolysaccharide-induced acute lung injury by targeting macrophage polarization derived ADAM-17

Acute lung injury (ALI) has received considerable attention in intensive care owing to its high mortality rate. It has been demonstrated that the selective alpha7 nicotinic acetylcholine receptor agonist Gainesville Tokushima scientists (GTS)-21 is promising for treating ALI caused by lipopolysaccharides (LPS). However, the precise underlying mechanism remains unknown. This study aimed to investigate the potential efficacy of GTS-21 in the treatment of ALI. We developed mouse models of ALI and alveolar epithelial type II cells (AT2s) injury following treatment with LPS and different polarized macrophage supernatants, respectively. Pathological changes, pulmonary edema, and lung compliance were assessed. Inflammatory cells count, protein content, and pro-inflammatory cytokine levels were analysed in the bronchoalveolar lavage fluid. The expression of angiotensin-converting enzyme (ACE), ACE2, syndecan-1 (SDC-1), heparan sulphate (HS), heparanase (HPA), exostosin (EXT)-1, and NF-κB were tested in lung tissues and cells. GTS-21-induced changes in macrophage polarization were verified in vivo and in vitro. Polarized macrophage supernatants with or without recombination a disintegrin and metalloproteinase-17 (ADAM-17) and small interfering (si)RNA ADAM-17 were used to verify the role of ADAM-17 in AT2 injury. By reducing pathological alterations, lung permeability, inflammatory response, ACE/ACE2 ratio, and glycocalyx shedding, as well as by downregulating the HPA and NF-κB pathways and upregulating EXT1 expression in vivo, GTS-21 significantly diminished LPS-induced ALI compared to that of the LPS group. GTS-21 significantly attenuated macrophage M1 polarization and augmented M2 polarization in vitro and in vivo. The destructive effects of M1 polarization supernatant can be inhibited by GTS-21 and siRNA ADAM-17. GTS-21 exerted a protective effect against LPS-induced ALI, which was reversed by recombinant ADAM-17. Collectively, GTS-21 alleviates LPS-induced ALI by attenuating AT2s ACE/ACE2 ratio and glycocalyx shedding through the inhibition of macrophage M1 polarization derived ADAM-17.

Paralemmin-3 augments lipopolysaccharide-induced acute lung injury with M1 macrophage polarization via the notch signaling pathway

BACKGROUND

Acute lung injury (ALI) involves severe lung damage and respiratory failure, which are accompanied by alveolar macrophage (AM) activation. The aim of this article is to verify the influence of paralemmin-3 (PALM3) on alveolar macrophage (AM) polarization in ALI and the underlying mechanism of action.

METHODS

An ALI rat model was established by successive lipopolysaccharide (LPS) inhalations. The influence of PALM3 on the survival rate, severity of lung injury, and macrophage polarization was analyzed. Furthermore, we explored the underlying mechanism of PALM3 in regulating macrophage polarization.

RESULTS

PALM3 overexpression increased mortality of ALI rats, augmented lung pathological damage, and promoted AM polarization toward M1 cells. Conversely, PALM3 knockdown had the opposite effects. Mechanistically, PALM3 might promote M1 polarization by acting as an adaptor to facilitate transduction of Notch signaling.

CONCLUSION

PALM3 aggravates lung injury and induces macrophage polarization toward M1 cells by activating the Notch signaling pathway in LPS-induced ALI, which may shed light on ALI/ARDS treatments.

Cholinergic signaling via the α7 nicotinic acetylcholine receptor regulates the migration of monocyte-derived macrophages during acute inflammation

BACKGROUND

The involvement of the autonomic nervous system in the regulation of inflammation is an emerging concept with significant potential for clinical applications. Recent studies demonstrate that stimulating the vagus nerve activates the cholinergic anti-inflammatory pathway that inhibits pro-inflammatory cytokines and controls inflammation. The α7 nicotinic acetylcholine receptor (α7nAChR) on macrophages plays a key role in mediating cholinergic anti-inflammatory effects through a downstream intracellular mechanism involving inhibition of NF-κB signaling, which results in suppression of pro-inflammatory cytokine production. However, the role of the α7nAChR in the regulation of other aspects of the immune response, including the recruitment of monocytes/macrophages to the site of inflammation remained poorly understood.

RESULTS

We observed an increased mortality in α7nAChR-deficient mice (compared with wild-type controls) in mice with endotoxemia, which was paralleled with a significant reduction in the number of monocyte-derived macrophages in the lungs. Corroborating these results, fluorescently labeled α7nAChR-deficient monocytes adoptively transferred to WT mice showed significantly diminished recruitment to the inflamed tissue. α7nAChR deficiency did not affect monocyte 2D transmigration across an endothelial monolayer, but it significantly decreased the migration of macrophages in a 3D fibrin matrix. In vitro analysis of major adhesive receptors (L-selectin, β1 and β2 integrins) and chemokine receptors (CCR2 and CCR5) revealed reduced expression of integrin αM and αX on α7nAChR-deficient macrophages. Decreased expression of αMβ2 was confirmed on fluorescently labeled, adoptively transferred α7nAChR-deficient macrophages in the lungs of endotoxemic mice, indicating a potential mechanism for α7nAChR-mediated migration.

CONCLUSIONS

We demonstrate a novel role for the α7nAChR in mediating macrophage recruitment to inflamed tissue, which indicates an important new aspect of the cholinergic regulation of immune responses and inflammation.

Proinflammatory Bone Marrow Mesenchymal Stem Cell-Derived Exosomal miR-150-3p Suppresses Proinflammatory Polarization of Alveolar Macrophages in Sepsis by Targeting Inhibin Subunit Beta A

Bone marrow mesenchymal stem cell (BMSC)-derived exosomes can protect lung tissues against sepsis, but its related mechanism remains elusive. BMSCs were primed with or without lipopolysaccharide (LPS) before extracting exosomes. The isolated exosomes were identified by transmission electron microscopy, nanoparticle tracking analysis, and western blot. LPS-stimulated macrophages were cocultured with exosomes for 24 h, followed by enzyme-linked immunosorbent assay, flow cytometry, and molecular experiments. Bioinformatics and luciferase assay were employed to investigate the interaction between miR-150-3p and inhibin subunit beta A (INHBA). MiR-150-3p expression was increased in exosomes in a proinflammatory environment. Exosomes suppressed proinflammatory polarization by downregulating IL-6, IL-1β, iNOS, and CD86, as well as promoted anti-inflammatory polarization by upregulating IL-10, ARG-1, and CD206 in LPS-stimulated macrophages. Such effects were more pronounced by LPS-primed exosomes, which was reversed in the absence of miR-150-3p. MiR-150-3p targeted INHBA. INHBA silencing decreased CD86 expression and increased CD206 expression in macrophages, but these effects were reversed by exosomal miR-150-3p inhibition. Proinflammatory BMSC-derived exosomal miR-150-3p suppressed proinflammatory polarization and promoted anti-inflammatory polarization of alveolar macrophages to attenuate LPS-induced sepsis by targeting INHBA.

The role of macrophages polarization in sepsis-induced acute lung injury

Sepsis presents as a severe infectious disease frequently documented in clinical settings. Characterized by its systemic inflammatory response syndrome, sepsis has the potential to trigger multi-organ dysfunction and can escalate to becoming life-threatening. A common fallout from sepsis is acute lung injury (ALI), which often progresses to acute respiratory distress syndrome (ARDS). Macrophages, due to their significant role in the immune system, are receiving increased attention in clinical studies. Macrophage polarization is a process that hinges on an intricate regulatory network influenced by a myriad of signaling molecules, transcription factors, epigenetic modifications, and metabolic reprogramming. In this review, our primary focus is on the classically activated macrophages (M1-like) and alternatively activated macrophages (M2-like) as the two paramount phenotypes instrumental in sepsis' host immune response. An imbalance between M1-like and M2-like macrophages can precipitate the onset and exacerbate the progression of sepsis. This review provides a comprehensive understanding of the interplay between macrophage polarization and sepsis-induced acute lung injury (SALI) and elaborates on the intervention strategy that centers around the crucial process of macrophage polarization.

Single-cell analysis reveals dysregulated inflammatory response in peripheral blood immunity in patients with acute respiratory distress syndrome

Introduction: Acute respiratory distress syndrome (ARDS) remains a major clinical challenge for patients in intensive care units. Determining the differential mechanisms underlying ARDS with different etiologies is a key goal to improve the effectiveness of ARDS therapy. Despite growing evidence that different immune cell types are involved in ARDS, the role of altered immune cell subpopulations in disease progression is unelucidated. Methods: In this study, we combined scRNA-seq and bulk-level sequencing to analyze the transcriptomes of peripheral blood mononuclear cells from healthy volunteers and patients with septic ARDS (sep-ARDS) and pneumonic ARDS (PNE-ARDS). Results: Our data revealed differential alterations at the cellular and molecular levels and within biological signaling pathways in ARDS with different etiologies. The dynamics of neutrophils, macrophages (Macs), classical dendritic cells (cDCs), myeloid-derived suppressive cells (MDSCs), and CD8⁺ T cells varied significantly among groups of different samples, with neutrophils and cDCs at higher, and Macs at significantly lower, amounts in the patients with sep-ARDS. Furthermore, MDSCs were highly enriched only in the sep-ARDS patients, whereas a higher abundance of CD8⁺ T cells was observed in patients with PNE-ARDS. In addition, these cell subpopulations were found to be significantly involved in apoptosis, inflammatory, and immune-related pathways. In particular, a significant enhancement of the oxidative stress response was observed in the neutrophil subpopulation. Conclusion: Our study shows that the composition of cells involved in the main peripheral circulation differs in patients with ARDS with different etiologies. Studying the role and mechanism of action of these cells during ARDS will provide new opportunities for the treatment of this condition.

Role of endoplasmic reticulum autophagy in acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), the prime causes of morbidity and mortality in critically ill patients, are usually treated by general supportive treatments. Endoplasmic reticulum autophagy (ER-phagy) maintains cellular homeostasis by degrading damaged endoplasmic reticulum (ER) fragments and misfolded proteins. ER-phagy is crucial for maintaining ER homeostasis and improving the internal environment. ER-phagy has a particular role in some aspects, such as immunity, inflammation, cell death, pathogen infection, and collagen quality. In this review, we summarized the definition, epidemiology, and pathophysiology of ALI/ARDS and described the regulatory mechanisms and functions of ER-phagy as well as discussed the potential role of ER-phagy in ALI/ARDS from the perspectives of immunity, inflammation, apoptosis, pathogen infection, and fibrosis to provide a novel and effective target for improving the prognosis of ALI/ARDS.

Exploring the Modulatory Effect of High-Fat Nutrition on Lipopolysaccharide-Induced Acute Lung Injury in Vagotomized Rats and the Role of the Vagus Nerve

During esophagectomy, the vagus nerve is transected, which may add to the development of postoperative complications. The vagus nerve has been shown to attenuate inflammation and can be activated by a high-fat nutrition via the release of acetylcholine. This binds to α7 nicotinic acetylcholine receptors (α7nAChR) and inhibits α7nAChR-expressing inflammatory cells. This study investigates the role of the vagus nerve and the effect of high-fat nutrition on lipopolysaccharide (LPS)-induced lung injury in rats. Firstly, 48 rats were randomized in 4 groups as follows: sham (sparing vagus nerve), abdominal (selective) vagotomy, cervical vagotomy and cervical vagotomy with an α7nAChR-agonist. Secondly, 24 rats were randomized in 3 groups as follows: sham, sham with an α7nAChR-antagonist and cervical vagotomy with an α7nAChR-antagonist. Finally, 24 rats were randomized in 3 groups as follows: fasting, high-fat nutrition before sham and high-fat nutrition before selective vagotomy. Abdominal (selective) vagotomy did not impact histopathological lung injury (LIS) compared with the control (sham) group (p > 0.999). There was a trend in aggravation of LIS after cervical vagotomy (p = 0.051), even after an α7nAChR-agonist (p = 0.090). Cervical vagotomy with an α7nAChR-antagonist aggravated lung injury (p = 0.004). Furthermore, cervical vagotomy increased macrophages in bronchoalveolar lavage (BAL) fluid and negatively impacted pulmonary function. Other inflammatory cells, TNF-α and IL-6, in the BALF and serum were unaffected. High-fat nutrition reduced LIS after sham (p = 0.012) and selective vagotomy (p = 0.002) compared to fasting. vagotomy. This study underlines the role of the vagus nerve in lung injury and shows that vagus nerve stimulation using high-fat nutrition is effective in reducing lung injury, even after selective vagotomy.

Neutralization of excessive levels of active TGF-β1 reduces MSC recruitment and differentiation to mitigate peritendinous adhesion

Peritendinous adhesion formation (PAF) can substantially limit the range of motion of digits. However, the origin of myofibroblasts in PAF tissues is still unclear. In this study, we found that the concentration of active TGF-β1 and the numbers of macrophages, mesenchymal stromal cells (MSCs), and myofibroblasts in human and mouse adhesion tissues were increased. Furthermore, knockout of TGF-β1 in macrophages or TGF-β1R2 in MSCs inhibited PAF by reducing MSC and myofibroblast infiltration and collagen I and III deposition, respectively. Moreover, we found that MSCs differentiated into myofibroblasts to form adhesion tissues. Systemic injection of the TGF-β-neutralizing antibody 1D11 during the granulation formation stage of PAF significantly reduced the infiltration of MSCs and myofibroblasts and, subsequently, PAF. These results suggest that macrophage-derived TGF-β1 recruits MSCs to form myofibroblasts in peritendinous adhesions. An improved understanding of PAF mechanisms could help identify a potential therapeutic strategy.

Neuroimmune nexus in the pathophysiology and therapy of inflammatory disorders: role of α7 nicotinic acetylcholine receptors

The α7-nicotinic acetylcholine receptor (α7nAChR) is a key protein in the cholinergic anti-inflammatory pathway (CAP) that links the nervous and immune systems. Initially, the pathway was discovered based on the observation that vagal nerve stimulation (VNS) reduced the systemic inflammatory response in septic animals. Subsequent studies form a foundation for the leading hypothesis about the central role of the spleen in CAP activation. VNS evokes noradrenergic stimulation of ACh release from T cells in the spleen, which in turn activates α7nAChRs on the surface of macrophages. α7nAChR-mediated signaling in macrophages reduces inflammatory cytokine secretion and modifies apoptosis, proliferation, and macrophage polarization, eventually reducing the systemic inflammatory response. A protective role of the CAP has been demonstrated in preclinical studies for multiple diseases including sepsis, metabolic disease, cardiovascular diseases, arthritis, Crohn's disease, ulcerative colitis, endometriosis, and potentially COVID-19, sparking interest in using bioelectronic and pharmacological approaches to target α7nAChRs for treating inflammatory conditions in patients. Despite a keen interest, many aspects of the cholinergic pathway are still unknown. α7nAChRs are expressed on many other subsets of immune cells that can affect the development of inflammation differently. There are also other sources of ACh that modify immune cell functions. How the interplay of ACh and α7nAChR on different cells and in various tissues contributes to the anti-inflammatory responses requires additional study. This review provides an update on basic and translational studies of the CAP in inflammatory diseases, the relevant pharmacology of α7nAChR-activated drugs and raises some questions that require further investigation.

The Role of the Acetylcholine System in Common Respiratory Diseases and COVID-19

As an indispensable component in human beings, the acetylcholine system regulates multiple physiological processes not only in neuronal tissues but also in nonneuronal tissues. However, since the concept of the "Nonneuronal cholinergic system (NNCS)" has been proposed, the role of the acetylcholine system in nonneuronal tissues has received increasing attention. A growing body of research shows that the acetylcholine system also participates in modulating inflammatory responses, regulating contraction and mucus secretion of respiratory tracts, and influencing the metastasis and invasion of lung cancer. In addition, the susceptibility and severity of respiratory tract infections caused by pathogens such as Mycobacterium Tuberculosis and the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) can also correlate with the regulation of the acetylcholine system. In this review, we summarized the major roles of the acetylcholine system in respiratory diseases. Despite existing achievements in the field of the acetylcholine system, we hope that more in-depth investigations on this topic will be conducted to unearth more possible pharmaceutical applications for the treatment of diverse respiratory diseases.

GAT107-mediated α7 nicotinic acetylcholine receptor signaling attenuates inflammatory lung injury and mortality in a mouse model of ventilator-associated pneumonia by alleviating macrophage mitochondrial oxidative stress via reducing MnSOD-S-glutathionylation

Supraphysiological concentrations of oxygen (hyperoxia) can compromise host defense and increase susceptibility to bacterial and viral infections, causing ventilator-associated pneumonia (VAP). Compromised host defense and inflammatory lung injury are mediated, in part, by high extracellular concentrations of HMGB1, which can be decreased by GTS-21, a partial agonist of α7 nicotinic acetylcholine receptor (α7nAChR). Here, we report that a novel α7nAChR agonistic positive allosteric modulator (ago-PAM), GAT107, at 3.3 mg/kg, i.p., significantly decreased animal mortality and markers of inflammatory injury in mice exposed to hyperoxia and subsequently infected with Pseudomonas aeruginosa. The incubation of macrophages with 3.3 μM of GAT107 significantly decreased hyperoxia-induced extracellular HMGB1 accumulation and HMGB1-induced macrophage phagocytic dysfunction. Hyperoxia-compromised macrophage function was correlated with impaired mitochondrial membrane integrity, increased superoxide levels, and decreased manganese superoxide dismutase (MnSOD) activity. This compromised MnSOD activity is due to a significant increase in its level of glutathionylation. The incubation of hyperoxic macrophages with 3.3 μM of GAT107 significantly decreases the levels of glutathionylated MnSOD, and restores MnSOD activity and mitochondrial membrane integrity. Thus, GAT107 restored hyperoxia-compromised phagocytic functions by decreasing HMGB1 release, most likely via a mitochondrial-directed pathway. Overall, our results suggest that GAT107 may be a potential treatment to decrease acute inflammatory lung injury by increasing host defense in patients with VAP.

hUC-MSCs exosomal miR-451 alleviated acute lung injury by modulating macrophage M2 polarization via regulating MIF-PI3K-AKT signaling pathway

In the previous study, we have proved that exosomal miR-451 from human umbilical cord mesenchymal stem cells (hUC-MSCs) attenuated burn-induced acute lung injury (ALI). However, the mechanism of exosomal miR-451 in ALI remains unclear. Therefore, this study aimed to study the molecular mechanism of hUC-MSCs-derived exosomal miR-451 on ALI by regulating macrophage polarization. Exosomes were isolated and identified by transmission electron microscope (TEM) and nanoparticle tracking analysis (NTA). The expression of miR-451, macrophage migration inhibitory factor (MIF) and PI3K/AKT signaling pathway proteins were detected by qRT-PCR and western blot. Flow cytometry was used to detect the CD80 and CD206 positive cells. Severe burn rat model was established and HE was used to detect the inflammatory cell infiltration and inflammatory injury. Dual luciferase reporter system was used to detect the regulation of miR-451 to MIF. The contents of cytokines were detected by ELISA. The results showed that hUC-MSCs exosomes promoted macrophage M1 to M2 polarization. Furthermore, hUC-MSCs-derived exosomal miR-451 alleviated ALI development and promoted macrophage M1 to M2 polarization. Moreover, MIF was a direct target of miR-451. Downregulation of MIF regulated by miR-451 alleviated ALI development promoted macrophage M1 to M2 polarization. In addition, we found that MIF and hUC-MSCs-derived exosomal miR-451 participated in ALI by regulating PI3K/AKT signaling pathway. In conclusion, we indicated that hUC-MSCs-derived exosomal miR-451 alleviated ALI by modulating macrophage M2 polarization via regulating MIF-PI3K-AKT signaling pathway, which provided great scientific significance and clinical application value for the treatment of burn-induced ALI.

Nicotinic acetylcholine receptor agonist reduces acute lung injury after renal ischemia-reperfusion injury by acting on splenic macrophages in mice

Acute kidney injury (AKI) contributes to the development of acute lung injury (ALI) via proinflammatory responses. We hypothesized that activation of a nicotinic acetylcholine receptor (nAChR), which exerts cholinergic anti-inflammatory effects on macrophages, could reduce ALI after AKI. We aimed to determine whether nAChR agonists could reduce ALI after AKI and which macrophages in the lung or spleen contribute to the improvement of ALI by nAChR agonists. We induced AKI in male mice by unilateral ischemia-reperfusion injury (IRI) with contralateral nephrectomy and administered nAChR agonists in three experimental settings: 1) splenectomy, 2) deletion of splenic macrophages and systemic mononuclear phagocytes via intravenous administration of clodronate liposomes, and 3) alveolar macrophage deletion via intratracheal administration of clodronate liposomes. Treatment with GTS-21, an α7nAChR-selective agonist, significantly reduced the levels of circulating IL-6, a key proinflammatory cytokine, and lung chemokine (C-X-C motif) ligand (CXCL)1 and CXCL2 and neutrophil infiltration, and Evans blue dye (EBD) vascular leakage increased after renal IRI. In splenectomized mice, GTS-21 did not reduce circulating IL-6 and lung CXCL1 and CXCL2 levels and neutrophil infiltration, and EBD vascular leakage increased after renal IRI. In mice depleted of splenic macrophages and systemic mononuclear phagocytes, GTS-21 treatment did not reduce lung neutrophil infiltration, and EBD vascular leakage increased after renal IRI. In mice depleted of alveolar macrophages, GTS-21 treatment significantly reduced lung neutrophil infiltration, and EBD vascular leakage increased after renal IRI. Our findings show that nAChR agonist reduces circulating IL-6 levels and acute lung injury after renal IRI by acting on splenic macrophages.NEW & NOTEWORTHY Acute lung injury associated with acute kidney injury contributes to high mortality. This study showed, for the first time, that nicotinic acetylcholine receptor agonists reduced circulating IL-6 and ALI after renal ischemia-reperfusion injury in mice. These effects of α7nAChR agonist were eliminated in both splenectomized and splenic macrophage (including systemic mononuclear phagocyte)-depleted mice but not alveolar macrophage-depleted mice. nAChR agonist could reduce ALI after AKI via splenic macrophages and provide a novel strategy in AKI.

Adverse effects of PM2.5 on cardiovascular diseases

As an air pollutant, fine particulate matter with a diameter  ≤ 2.5 μm (PM_2.5) can enter the body through the respiratory tract and cause adverse cardiovascular effects. Here, the effects of PM_2.5 on atherosclerosis, hypertension, arrhythmia, myocardial infarction are summarized from the perspective researches of human epidemiology, animal, cell and molecule. The results of this review should be proved useful as a scientific basis for the prevention and treatment of cardiovascular disease caused by PM_2.5.

The Effect of α7nAChR Signaling on T Cells and Macrophages and Their Clinical Implication in the Treatment of Rheumatic Diseases

Rheumatoid arthritis (RA) is one of the most common autoimmune disease and until now, the etiology and pathogenesis of RA is not fully understood, although dysregulation of immune cells is one of the leading cause of RA-related pathological changes. Based on current understanding, the priority of anti-rheumatic treatments is to restore immune homeostasis. There are several anti-rheumatic drugs with immunomodulatory effects available nowadays, but most of them have obvious safety or efficacy shortcomings. Therefore, the development of novel anti-rheumatic drugs is still in urgently needed. Cholinergic anti-inflammatory pathway (CAP) has been identified as an important aspect of the so-called neuro-immune regulation feedback, and the interaction between acetylcholine and alpha 7 nicotinic acetylcholine receptor (α7nAChR) serves as the foundation for this signaling. Consistent to its immunomodulatory functions, α7nAChR is extensively expressed by immune cells. Accordingly, CAP activation greatly affects the differentiation and function of α7nAChR-expressing immune cells. As a result, targeting α7nAChR will bring profound therapeutic impacts on the treatment of inflammatory diseases like RA. RA is widely recognized as a CD4+ T cells-driven disease. As a major component of innate immunity, macrophages also significantly contribute to RA-related immune abnormalities. Theoretically, manipulation of CAP in immune cells is a feasible way to treat RA. In this review, we summarized the roles of different T cells and macrophages subsets in the occurrence and progression of RA, and highlighted the immune consequences of CAP activation in these cells under RA circumstances. The in-depth discussion is supposed to inspire the development of novel cell-specific CAP-targeting anti-rheumatic regimens.

Differential Lung Protective Capacity of Exosomes Derived from Human Adipose Tissue, Bone Marrow, and Umbilical Cord Mesenchymal Stem Cells in Sepsis-Induced Acute Lung Injury

Exosomes derived from human mesenchymal stem cells (hMSCs) have the capacity to regulate various biological events associated with sepsis-induced acute respiratory distress syndrome (ARDS), including cellular immunometabolism, the production of proinflammatory cytokines, allowing them to exert therapeutic effects. However, little is known about which type of hMSC-derived exosomes (hMSC-exo) is more effective and suitable for the treatment of sepsis-induced ARDS. The purpose of this study is to compare the efficacy of hMSC-derived exosomes from human adipose tissue (hADMSC-exo), human bone marrow (hBMMSC-exo), and human umbilical cord (hUCMSC-exo) in the treatment of sepsis-induced ARDS. We cocultured lipopolysaccharide- (LPS-) stimulated RAW264.7 macrophage cells with the three kinds of hMSCs and found that all hMSCs reduced the glycolysis level and the content of lactic acid in macrophages. Accordingly, the expression of proinflammatory cytokines also decreased. Notably, the protective effects of hMSCs from adipose tissue were more obvious than those of bone marrow and umbilical cord hMSCs. However, this protective effect was eliminated when an exosome inhibitor, GW4869, was added. Subsequently, we extracted and cocultured hMSC-derived exosomes with LPS-stimulated RAW264.7 cells and found that all three kinds of exosomes exerted a similar protective effect as their parental cells, with exosomes from adipose hMSCs showing the strongest protective effect. Finally, an experimental sepsis model in mice was established, and we found that all three types of hMSCs have obvious lung-protective effects, in reducing lung injury scores, lactic acid, and proinflammatory cytokine levels in the lung tissues and decreasing the total protein content and inflammatory cell count in the bronchoalveolar lavage fluid (BALF), and also can attenuate the systemic inflammatory response and improve the survival rate of mice. Intravenous injection of three types of hMSC-exo, in particular those derived from adipose hADMSCs, also showed lung-protective effects in mice. These findings revealed that exosomes derived from different sources of hMSCs can effectively downregulate sepsis-induced glycolysis and inflammation in macrophages, ameliorate the lung pathological damage, and improve the survival rate of mice with sepsis. It is worth noting that the protective effect of hADMSC-exo is better than that of hBMMSC-exo and hUCMSC-exo.

Role of Cholinergic Anti-Inflammatory Pathway in Protecting Sepsis-Induced Acute Lung Injury through Regulation of the Conventional Dendritic Cells

BACKGROUND

The cholinergic anti-inflammatory pathway connects the immune response system and the nervous system via the vagus nerve. The key regulatory receptor is the α7-subtype of the nicotinic acetylcholine receptor (α7nAChR). Cholinergic anti-inflammatory pathway has been proved to be effective in suppressing the inflammation responses in acute lung injury (ALI). Dendritic cells (DCs), the important antigen-presenting cells, also express the α7nAChR. Past studies have indicated that reducing the quantity of mature conventional DCs and inhibiting the maturation of pulmonary DCs may prove effective for the treatment of ALI. However, the effects of cholinergic anti-inflammatory pathway on maturation, function, and quantity of DCs and conventional DCs in ALI remain unclear.

OBJECTIVE

It was hypothesized that cholinergic anti-inflammatory pathway may inhibit the inflammatory response of ALI by regulating maturation, phenotype, and quantity of DCs and conventional DCs.

METHODS

GTS-21 (GTS-21 dihydrochloride), an α7nAchR agonist, was prophylactically administered in sepsis-induced ALI mouse model and LPS-primed bone marrow-derived dendritic cells. The effects of GTS-21 were observed with respect to maturation, phenotype, and quantity of DCs, conventional DCs, and conventional DCs2 (type 2 conventional DCs) and the release of DC-related proinflammatory cytokines in vivo and in vitro.

RESULTS

The results of the present study revealed that GTS-21 treatment decreased the maturation of DCs and the production of DC-related proinflammatory cytokines in vitro and in sepsis-induced ALI mouse model; it reduced the quantity of CD11c+MHCII+ conventional DCs and CD11c+CD11b+ conventional DCs2 in vivo experiment.

CONCLUSIONS

Cholinergic anti-inflammatory pathway contributes to the reduction in the inflammatory response in ALI by regulating maturation, phenotype, and quantity of DCs, conventional DCs, and conventional DCs2.

Gut-Lung Crosstalk in Sepsis-Induced Acute Lung Injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are common acute and severe cases of the respiratory system with complicated pathogenesis and high mortality. Sepsis is the leading indirect cause of ALI/ARDS in the intensive care unit (ICU). The pathogenesis of septic ALI/ARDS is complex and multifactorial. In the development of sepsis, the disruption of the intestinal barrier function, the alteration of gut microbiota, and the translocation of the intestinal microbiome can lead to systemic and local inflammatory responses, which further alter the immune homeostasis in the systemic environment. Disruption of homeostasis may promote and propagate septic ALI/ARDS. In turn, when ALI occurs, elevated levels of inflammatory cytokines and the shift of the lung microbiome may lead to the dysregulation of the intestinal microbiome and the disruption of the intestinal mucosal barrier. Thus, the interaction between the lung and the gut can initiate and potentiate sepsis-induced ALI/ARDS. The gut–lung crosstalk may be a promising potential target for intervention. This article reviews the underlying mechanism of gut-lung crosstalk in septic ALI/ARDS.

Paraquat promotes acute lung injury in rats by regulating alveolar macrophage polarization through glycolysis

The present study investigates whether paraquat (PQ) regulates polarization of alveolar macrophages through glycolysis and promotes the occurrence of acute lung injury in rats. In vivo, the PQ intraperitoneal injection was used to construct a model of acute lung injury in rats. In vitro, the study measured the effect of different concentrations of PQ on the viability of the alveolar macrophages, and explored the polarization and glycolysis metabolism of alveolar macrophages at different time points after PQ intervention. Compared with the normal control (NC) group, the lung pathological damage in rats increased gradually after PQ poisoning, reaching a significant degree at 48 h after poisoning. The PQ-poisoned rat serum showed increased expressions of interleukin-6 (IL-6), tumor necrosis factor- α (TNF-α), and M1 macrophage marker, iNOS, while the expression of interleukin-10 (IL-10) and M2 macrophage marker, Arg1, decreased. The toxic effect of PQ on alveolar macrophages was dose- and time-dependent. Compared with the NC group, IL-6 and TNF-α in the cell supernatant gradually increased after PQ intervention, while the IL-10 content gradually decreased. The PQ intervention in alveolar macrophages increased the expression of intracellular glycolysis rate-limiting enzyme pyruvate kinase isozymes M1/M2 (PKM1/M2), lactate, lactate/pyruvate ratio, and the polarization of alveolar macrophage towards M1. Inhibition of cellular glycolysis significantly reduced the PQ-induced alveolar macrophage polarization to M1 type. Thus, PQ induced increased polarization of lung macrophages toward M1 and decreased polarization toward M2, promoting acute lung injury. Therefore, it can be concluded that PQ regulates the polarization of alveolar macrophages through glycolysis.

Nicotinic Acetylcholine Receptors in the Respiratory Tract

Nicotinic acetylcholine receptors (nAChR) are widely distributed in neuronal and non-neuronal tissues, where they play diverse physiological roles. In this review, we highlight the recent findings regarding the role of nAChR in the respiratory tract with a special focus on the involvement of nAChR in the regulation of multiple processes in health and disease. We discuss the role of nAChR in mucociliary clearance, inflammation, and infection and in airway diseases such as asthma, chronic obstructive pulmonary disease, and cancer. The subtype diversity of nAChR enables differential regulation, making them a suitable pharmaceutical target in many diseases. The stimulation of the α3β4 nAChR could be beneficial in diseases accompanied by impaired mucociliary clearance, and the anti-inflammatory effect due to an α7 nAChR stimulation could alleviate symptoms in diseases with chronic inflammation such as chronic obstructive pulmonary disease and asthma, while the inhibition of the α5 nAChR could potentially be applied in non-small cell lung cancer treatment. However, while clinical studies targeting nAChR in the airways are still lacking, we suggest that more detailed research into this topic and possible pharmaceutical applications could represent a valuable tool to alleviate the symptoms of diverse airway diseases.

The Cholinergic Anti-Inflammatory Pathway Attenuates the Development of Atherosclerosis in Apoe-/- Mice through Modulating Macrophage Functions

(1) Background: The cholinergic anti-inflammatory pathway (CAP) has been implicated in the regulation of various diseases, including chronic inflammatory cardiovascular disorders such as atherosclerosis (AS). This study aims to explore the underlying regulatory mechanisms of CAP activity in the progression of AS. (2) Methods: The Apoe^-/- mice were subjected to sham, bilateral cervical vagotomy surgery (VGX), and VGX supplemented with Gainesville Tokushima scientists (GTS)-21 (4 mg/kg/d) and then fed with a high-fat diet for 10 weeks. Atherosclerotic lesion size and inflammation levels were investigated by histology and inflammatory cytokines analysis. The blood M1/M2 macrophages were analyzed by flow cytometry. Primary mouse bone marrow-derived macrophages (BMDM), peritoneal macrophages, and RAW264.7 cells were treated with CAP agonists acetylcholine (Ach) and GTS-21 to study their effects on macrophage functions. (3) Results: Compared with the sham group, inhibition of CAP by the VGX resulted in growing aortic lipid plaque area, deteriorated inflammatory levels, and aberrant quantity of M1/M2 macrophages in Apoe^-/- mice. However, these detrimental effects of VGX were significantly ameliorated by the reactivation of CAP through GTS-21 treatment. The in vitro study using macrophages revealed that stimulation with CAP agonists suppressed M1, but promoted M2 macrophage polarization through the upregulation of TNFAIP3 and phosphorylation STAT3 levels, respectively. Moreover, the activation of CAP inhibited the formation of macrophage foam cells in the peritoneal cavity by regulating genes related to cholesterol metabolism. (4) Conclusions: This study provides novel evidence and mechanisms that the CAP plays an important role in the regulation of AS development by controlling macrophage functions, implying a potential use of CAP activation as a therapeutic strategy for AS treatment.

Therapeutic Targeting of α7 Nicotinic Acetylcholine Receptors

The α7-type nicotinic acetylcholine receptor is one of the most unique and interesting of all the members of the cys-loop superfamily of ligand-gated ion channels. Since it was first identified initially as a binding site for α-bungarotoxin in mammalian brain and later as a functional homomeric receptor with relatively high calcium permeability, it has been pursued as a potential therapeutic target for numerous indications, from Alzheimer disease to asthma. In this review, we discuss the history and state of the art for targeting α7 receptors, beginning with subtype-selective agonists and the basic pharmacophore for the selective activation of α7 receptors. A key feature of α7 receptors is their rapid desensitization by standard "orthosteric" agonist, and we discuss insights into the conformational landscape of α7 receptors that has been gained by the development of ligands binding to allosteric sites. Some of these sites are targeted by positive allosteric modulators that have a wide range of effects on the activation profile of the receptors. Other sites are targeted by direct allosteric agonist or antagonists. We include a perspective on the potential importance of α7 receptors for metabotropic as well as ionotropic signaling. We outline the challenges that exist for future development of drugs to target this important receptor and approaches that may be considered to address those challenges. SIGNIFICANCE STATEMENT: The α7-type nicotinic acetylcholine receptor (nAChR) is acknowledged as a potentially important therapeutic target with functional properties associated with both ionotropic and metabotropic signaling. The functional properties of α7 nAChR can be regulated in diverse ways with the variety of orthosteric and allosteric ligands described in this review.

The Role of Macrophages in the Pathogenesis of SARS-CoV-2-Associated Acute Respiratory Distress Syndrome

Macrophages are cells that mediate both innate and adaptive immunity reactions, playing a major role in both physiological and pathological processes. Systemic SARS-CoV-2-associated complications include acute respiratory distress syndrome (ARDS), disseminated intravascular coagulation syndrome, edema, and pneumonia. These are predominantly effects of massive macrophage activation that collectively can be defined as macrophage activation syndrome. In this review we focus on the role of macrophages in COVID-19, as pathogenesis of the new coronavirus infection, especially in cases complicated by ARDS, largely depends on macrophage phenotypes and functionalities. We describe participation of monocytes, monocyte-derived and resident lung macrophages in SARS-CoV-2-associated ARDS and discuss possible utility of cell therapies for its treatment, notably the use of reprogrammed macrophages with stable pro- or anti-inflammatory phenotypes.

Cholinergic modulation of the immune system - A novel therapeutic target for myocardial inflammation

The immune system and the nervous system depend on each other for their fine tuning and working, thus cooperating to maintain physiological homeostasis and prevent infections. The cholinergic system regulates the mobilization, differentiation, secretion, and antigen presentation of adaptive and innate immune cells mainly through α7 nicotinic acetylcholine receptors (α7nAChRs). The neuro-immune interactions are established and maintained by the following mechanisms: colocalization of immune and neuronal cells at defined anatomical sites, expression of the non-neuronal cholinergic system by immune cells, and the acetylcholine receptor-mediated activation of intracellular signaling pathways. Based on these immunological mechanisms, the protective effects of cholinergic system in animal models of diseases were summarized in this paper, such as myocardial infarction/ischemia-reperfusion, viral myocarditis, and endotoxin-induced myocardial damage. In addition to maintaining hemodynamic stability and improving the energy metabolism of the heart, both non-neuronal acetylcholine and neuronal acetylcholine in the heart can alleviate myocardial inflammation and remodeling to exert a significant cardioprotective effect. The new findings on the role of cholinergic agonists and vagus nerve stimulation in immune regulation are updated, so as to develop improved approaches to treat inflammatory heart disease.

The Role of α7nAChR-Mediated Cholinergic Anti-inflammatory Pathway in Immune Cells

Alpha 7 nicotinic acetylcholine receptor (α7nAChR) is widely distributed in the nervous and non-cholinergic immune systems. It is necessary for the cholinergic transmitter to participate in the regulation of inflammatory response and is the key element of cholinergic anti-inflammatory pathway (CAP). Because of the profound impact of CAP on the immune system, α7nAChR is considered as a potential therapeutic target for the treatment of inflammatory diseases. Available evidences confirmed that manipulation of CAP by activating α7nAChR with either endogenous acetylcholine (ACh) or cholinergic agonists can substantially alleviate inflammatory responses both in vivo and in vitro. However, the mechanism through which CAP curbs the excessive pro-inflammatory responses and maintains immune homeostasis is not fully understood. Obtained clues suggest that the crosstalk between CAP and classical inflammatory pathways is the key to elucidate the anti-inflammatory mechanism, and the impacts of CAP activation in α7nAChR-expressing immune cells are the foundation of the immunoregulatory property. In this article, we review and update the knowledge concerning the progresses of α7nAChR-based CAP, including α7nAChR properties, signal transductions, interactions with classic immune pathways, and immunoregulatory functions in different immune cells. Certain critical issues to be addressed are also highlighted. By providing a panoramic view of α7nAChR, the summarized evidences will pave the way for the development of novel anti-inflammatory reagents and strategy and inspire further researches.

The Role of Pancreatic Infiltrating Innate Immune Cells in Acute Pancreatitis

Acute pancreatitis (AP) is a leading cause of gastrointestinal-related hospital admissions with significant morbidity and mortality. Although the underlying pathophysiology of AP is rather complex, which greatly limits the treatment options, more and more studies have revealed that infiltrating immune cells play a critical role in the pathogenesis of AP and determine disease severity. Thus, immunomodulatory therapy targeting immune cells and related inflammatory mediators is expected to be a novel treatment modality for AP which may improve the prognosis of patients. Cells of the innate immune system, including macrophages, neutrophils, dendritic cells, and mast cells, represent the majority of infiltrating cells during AP. In this review, an overview of different populations of innate immune cells and their role during AP will be discussed, with a special focus on neutrophils and macrophages.

Bone Marrow Mesenchymal Stem Cell-Derived Exosomes Attenuate LPS-Induced ARDS by Modulating Macrophage Polarization Through Inhibiting Glycolysis in Macrophages

Macrophages play a key role in the development of sepsis-induced acute respiratory distress syndrome (ARDS). Recent evidence has proved that glycolysis plays an important role in regulating macrophage polarization through metabolic reprogramming. Bone marrow mesenchymal stem cells (BMSCs) can alleviate sepsis-induced lung injury and possess potent immunomodulatory and immunosuppressive properties via secreting exosomes. However, it is unknown whether BMSCs-derived exosomes exert their therapeutic effect against sepsis-induced lung injury by inhibiting glycolysis in macrophages. Therefore, the present study aimed to evaluate the anti-inflammatory effects of exosomes released from BMSCs on acute lung injury induced by lipopolysaccharide (LPS) in mice and explored the possible underlying mechanisms in vitro and in vivo. We found that BMSCs inhibited M1 polarization and promoted M2 polarization in MH-S cells (a murine alveolar macrophage cell line) by releasing exosomes. Further experiments showed that exosomes secreted by BMSCs modulated LPS-treated MH-S cells polarization by inhibiting cellular glycolysis. Moreover, our results showed that BMSCs-derived exosomes down-regulated the expression of several essential proteins of glycolysis via inhibition of hypoxia-inducible factor 1 (HIF-1)α. Finally, a model of LPS-induced ARDS in mice was established, we found that BMSCs-derived exosomes ameliorated the LPS-induced inflammation and lung pathological damage. Meanwhile, we found that intratracheal delivery of BMSCs-derived exosomes effectively down-regulated LPS-induced glycolysis in mice lung tissue. These findings reveal new mechanisms of BMSCs-derived exosomes in regulating macrophage polarization which may provide novel strategies for the prevention and treatment of LPS-induced ARDS.

The role of the cholinergic anti-inflammatory pathway in septic cardiomyopathy

Septic cardiomyopathy (SCM)is common in septic patients and results in cardiovascular failure. The pathogenesis of SCM is complicated, and patients with SCM have high mortality because current treatment methods are limited. The cholinergic anti-inflammatory pathway (CAP) modulates inflammatory responses through vagus nerve stimulation that leads to the release of acetylcholine (ACh), which binds to the alpha7 nicotinic acetylcholine receptor (α7nAChR). Moreover, α7nAChR activation by its agonists at the tissue level inhibits inflammatory mediators and regulates the function of immune cells in sepsis. Therefore, the α7nAChR can maintain balance of the inflammatory-immune response in sepsis. CAP has been elucidated as a critical regulator of anti-inflammation in many diseases, including rheumatoid arthritis, inflammatory boweldisease and SCM. Additionally, some clinical and preclinical trials show therapeutic potential via regulating CAP. There are excellent studies regarding the beneficial role of CAP activation, especially α7nAChR, in experimental SCM. This review aims to discuss the CAP in attenuating inflammation and the potential role of α7nAChR activation in regulating immune and reducing inflammation in SCM.

The α7 nicotinic acetylcholine receptor agonist GTS-21 improves bacterial clearance in mice by restoring hyperoxia-compromised macrophage function

BACKGROUND

Mechanical ventilation, in combination with supraphysiological concentrations of oxygen (i.e., hyperoxia), is routinely used to treat patients with respiratory distress, such as COVID-19. However, prolonged exposure to hyperoxia compromises the clearance of invading pathogens by impairing macrophage phagocytosis. Previously, we have shown that the exposure of mice to hyperoxia induces the release of the nuclear protein high mobility group box-1 (HMGB1) into the pulmonary airways. Furthermore, extracellular HMGB1 impairs macrophage phagocytosis and increases the mortality of mice infected with Pseudomonas aeruginosa (PA). The aim of this study was to determine whether GTS-21 (3-(2,4-dimethoxybenzylidene) anabaseine), an α7 nicotinic acetylcholine receptor (α7nAChR) agonist, could (1) inhibit hyperoxia-induced HMGB1 release into the airways; (2) enhance macrophage phagocytosis and (3) increase bacterial clearance from the lungs in a mouse model of ventilator-associated pneumonia.

METHOD

GTS-21 (0.04, 0.4, and 4 mg/kg) or saline were administered by intraperitoneal injection to mice that were exposed to hyperoxia (≥ 99% O₂) and subsequently challenged with PA.

RESULTS

The systemic administration of 4 mg/kg i.p. of GTS-21 significantly increased bacterial clearance, decreased acute lung injury and decreased accumulation of airway HMGB1 compared to the saline control. To determine the mechanism of action of GTS-21, RAW 264.7 cells, a macrophage-like cell line, were incubated with different concentrations of GTS-21 in the presence of 95% O₂. The phagocytic activity of macrophages was significantly increased by GTS-21 in a dose-dependent manner. In addition, GTS-21 significantly inhibited the cytoplasmic translocation and release of HMGB1 from RAW 264.7 cells and attenuated hyperoxia-induced NF-κB activation in macrophages and mouse lungs exposed to hyperoxia and infected with PA.

CONCLUSIONS

Our results indicate that GTS-21 is efficacious in improving bacterial clearance and reducing acute lung injury via enhancing macrophage function by inhibiting the release of nuclear HMGB1. Therefore, the α7nAChR represents a possible pharmacological target to improve the clinical outcome of patients on ventilators by augmenting host defense against bacterial infections.

Mediation of Cardiac Macrophage Activity via Auricular Vagal Nerve Stimulation Ameliorates Cardiac Ischemia/Reperfusion Injury

Background

Myocardial infarction (MI) reperfusion therapy causes paradoxical cardiac complications. Following restoration of blood flow to infarcted regions, a multitude of inflammatory cells are recruited to the site of injury for tissue repair. Continual progression of cardiac inflammatory responses does, however, lead to adverse cardiac remodeling, inevitably causing heart failure.

Main Body

Increasing evidence of the cardioprotective effects of both invasive and non-invasive vagal nerve stimulation (VNS) suggests that these may be feasible methods to treat myocardial ischemia/reperfusion injury via anti-inflammatory regulation. The mechanisms through which auricular VNS controls inflammation are yet to be explored. In this review, we discuss the potential of autonomic nervous system modulation, particularly via the parasympathetic branch, in ameliorating MI. Novel insights are provided about the activation of the cholinergic anti-inflammatory pathway on cardiac macrophages. Acetylcholine binding to the α7 nicotinic acetylcholine receptor (α7nAChR) expressed on macrophages polarizes the pro-inflammatory into anti-inflammatory subtypes. Activation of the α7nAChR stimulates the signal transducer and activator of transcription 3 (STAT3) signaling pathway. This inhibits the secretion of pro-inflammatory cytokines, limiting ischemic injury in the myocardium and initiating efficient reparative mechanisms. We highlight recent developments in the controversial auricular vagal neuro-circuitry and how they may relate to activation of the cholinergic anti-inflammatory pathway.

Conclusion

Emerging published data suggest that auricular VNS is an inexpensive healthcare modality, mediating the dynamic balance between pro- and anti-inflammatory responses in cardiac macrophages and ameliorating cardiac ischemia/reperfusion injury.

HMGB1 aggravates lipopolysaccharide-induced acute lung injury through suppressing the activity and function of Tregs

BACKGROUND

CD4⁺CD25⁺FoxP3⁺ T helper cells (Tregs), a subgroup of CD4⁺ T helper cells, are critical effectors that protect against acute lung injury (ALI) by contact-dependent suppression or releasing anti-inflammatory cytokines including interleukin-10 (IL-10), and transforming growth factor (TGF-β). HMGB1 (High mobility group box 1 protein) was identified as a nuclear non-histone DNA-binding chromosomal protein, which participates in the regulation of lung inflammatory response and pathological processes in ALI. Previous studies have suggested that Tregs overexpresses the HMGB1-recognizing receptor. However, the interaction of HMGB1 with Tregs in ALI is still unclear.

OBJECTIVE

To investigate whether HMGB1 aggravates ALI by suppressing immunosuppressive function of Tregs.

METHODS

Anti-HMGB1 antibody and recombinant mouse HMGB1 (rHMGB1) were administered in lipopolysaccharide (LPS)-induced ALI mice and polarized LPS-primed Tregs in vitro. The Tregs pre-stimulated with or without rHMGB1 were adoptively transferred to ALI mice and depleted by Diphtheria toxin (DT). For coculture experiment, isolated Tregs were first pre-stimulated with or without rHMGB1 or anti-HMGB1 antibody, then they were cocultured with bone marrow-derived macrophages (BMMs) under LPS stimulation.

RESULTS

Tregs protected against acute lung pathological injury. HMGB1 modulated the suppressive function of Tregs as follows: reduction in the number of the cells and the activity of Tregs, the secretion of anti-inflammatory cytokines (IL-10, TGF-β) from Tregs, the production of IL-2 from CD4⁺ T cells and CD11c⁺ DCs, and the M2 polarization of macrophages, as well as inducing proinflammatory response of macrophages.

CONCLUSIONS

HMGB1 could aggravate LPS induced-ALI through suppressing the activity and function of Tregs.

Macrophage polarization and its role in the pathogenesis of acute lung injury/acute respiratory distress syndrome

PURPOSE

Macrophages are highly plastic cells. Under different stimuli, macrophages can be polarized into several different subsets. Two main macrophage subsets have been suggested: classically activated or inflammatory (M1) macrophages and alternatively activated or anti-inflammatory (M2) macrophages. Macrophage polarization is governed by a highly complex set of regulatory networks. Many recent studies have shown that macrophages are key orchestrators in the pathogenesis of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) and that regulation of macrophage polarization may improve the prognosis of ALI/ARDS. A further understanding of the mechanisms of macrophage polarization is expected to be helpful in the development of novel therapeutic targets to treat ALI/ARDS. Therefore, we performed a literature review to summarize the regulatory mechanisms of macrophage polarization and its role in the pathogenesis of ALI/ARDS.

METHODS

A computer-based online search was performed using the PubMed database and Web of Science database for published articles concerning macrophages, macrophage polarization, and ALI/ARDS.

RESULTS

In this review, we discuss the origin, polarization, and polarization regulation of macrophages as well as the role of macrophage polarization in various stages of ARDS. According to the current literature, regulating the polarized state of macrophages might be a potential therapeutic strategy against ALI/ARDS.

Vagal-α7nAChR signaling promotes lung stem cells regeneration via fibroblast growth factor 10 during lung injury repair

BACKGROUND

Proliferation and transdifferentiation of lung stem cells (LSCs) could promote lung injury repair. The distal airways of the lung are innervated by the vagus nerve. Vagal-alpha7 nicotinic acetylcholine receptor (α7nAChR) signaling plays a key role in regulating lung infection and inflammation; however, whether this pathway could regulate LSCs remains unknown.

METHODS

LSCs (Sca1⁺CD45^-CD31^- cells) were isolated and characterized according to a previously published protocol. α7nAChR knockout mice and wild-type littermates were intratracheally challenged with lipopolysaccharide (LPS) to induce lung injury. A cervical vagotomy was performed to study the regulatory effect of the vagus nerve on LSCs-mediated lung repair. α7nAChR agonist or fibroblast growth factor 10 (FGF10) was intratracheally delivered to mice. A single-cell suspension of lung cells was analyzed by flow cytometry. Lung tissues were collected for histology, quantitative real-time polymerase chain reaction (RT-PCR), and immunohistochemistry.

RESULTS

We found that LSCs maintained multilineage differentiation ability and transdifferentiated into alveolar epithelial type II cells (AEC2) following FGF10 stimulation in vitro. Vagotomy or α7nAChR deficiency reduced lung Ki67⁺ LSCs expansion and hampered the resolution of LPS-induced lung injury. Vagotomy or α7nAChR deficiency decreased lung FGF10 expression and the number of AEC2. The α7nAChR agonist-GTS-21 reversed the reduction of FGF10 expression in the lungs, as well as the number of Ki67⁺ cells, LSCs, Ki67⁺ LSCs, and AEC2 in LPS-challenged vagotomized mice. Supplementation with FGF10 counteracted the loss of Ki67⁺ LSCs and AEC2 in LPS-challenged α7nAChR knockout mice.

CONCLUSIONS

The vagus nerve deploys α7nAChR to enhance LSCs proliferation and transdifferentiation and promote lung repair in an FGF10-dependent manner during LPS-induced lung injury.

GTS-21, an α7nAChR agonist, suppressed the production of key inflammatory mediators by PBMCs that are elevated in COPD patients and associated with impaired lung function

Chronic obstructive pulmonary disease (COPD) is a lung inflammatory disease characterized by progressive airflow limitation, chronic respiratory symptoms and frequent exacerbations. There is an unmet need to identify novel therapeutic alternatives beside bronchodilators that prevent disease progression. Levels of both Nitric Oxide (NO) and IL-6 were significantly increased in the plasma of patients in the exacerbation phase (ECOPD, n = 13) when compared to patients in the stable phase (SCOPD, n = 38). Levels of both NO and IL-6 were also found to inversely correlate with impaired lung function (%FEV1 predicted). In addition, there was a strong positive correlation between levels of IL-6 and NO found in the plasma of patients and those spontaneously produced by their peripheral blood mononuclear cells (PBMCs), identifying these cells as a major source of these key inflammatory mediators in COPD. GTS-21, an agonist for the alpha 7 nicotinic receptors (α7nAChR), was found to exert immune-modulatory actions in PBMCs of COPD patients by suppressing the production of IL-6 and NO. This study provides the first evidence supporting the therapeutic potential of α7nAChR agonists in COPD due to their ability to suppress the production of key inflammatory markers associated with disease severity.

Glycyrrhizin administration ameliorates Streptococcus aureus-induced acute lung injury

Streptococcus aureus (S. aureus)-induced acute lung injury (ALI) has a high incidence of mortality clinically. Glycyrrhizin (GL) is a traditional Chinese medicine for anti-inflammatory. However, the role of GL in S. aureus-induced ALI has not previously been elucidated. GL (25 mg/kg i.p.) administration exerts potent anti-inflammatory effect in this model. GL administration significantly alleviated inflammation via reduction of multiple cytokines (serum and lung tissue IL-6, TNF-α, IL-8, IL-1β and HMGB1) and immune cells (lung tissue neutrophil and macrophage infiltration). Additionally, we measured the signaling pathways (NF-kB and MARKs) and inflammasome dependent pyroptosis. The results suggest that GL inhibits NF-kB, p38/ERK pathways and pyroptosis. Furthermore, we used different inhibitors to treat infected-A549 cells and found that BMS-582949 (a p38 inhibitor) is the most effective inhibitor for inhibiting pro-inflammatory cytokines (IL-6, TNF-α and IL-1β) production, which suggests that p38 signaling pathway might be the main pathway for S. aureus-induced inflammation. Collectively, the data demonstrates that GL could mitigate inflammation after S. aureus infection.

Activation of Nicotinic Acetylcholine α7 Receptor Attenuates Progression of Monocrotaline-Induced Pulmonary Hypertension in Rats by Downregulating the NLRP3 Inflammasome

Background: Inflammation and altered immunity contribute to the development of pulmonary arterial hypertension (PH). The alpha 7 nicotinic acetylcholine receptor (α7nAChR) possesses anti-inflammatory activities. The current study was performed to investigate the effects of a selective α7nAChR agonist, PNU-282987, on controlling a monocrotaline (MCT)-induced rat model of PH and explored the underlying mechanisms.

Methods: Sprague-Dawley rats were injected with MCT and treated with PNU-282987 at the prevention (starting 1 week before MCT) and treatment (starting 2 weeks after MCT) settings. Four weeks after MCT injection, hemodynamic changes, right ventricular structure, and lung morphological features were assessed. Enzyme-linked immunosorbent assay, Western blot and qRT-PCR were performed to assess levels of inflammatory cytokines and NLRP3 (Nod-like receptor family pyrin domain-containing 3) inflammasome pathway in the rat lung tissues. In addition, the lung macrophage line NR8383 was used to confirm the in vivo data.

Results: Monocrotaline injection produced PH in rats and downregulated α7nAChR mRNA and protein expression in rat lung tissues compared to sham controls. Pharmacological activation of α7nAChR by PNU-282987 therapy improved the rat survival rate, attenuated the development of PH as assessed by remodeling of pulmonary arterioles, reduced the right ventricular (RV) systolic pressure, and ameliorated the hypertrophy and fibrosis of the RV in rats with MCT-induced PH. The expression of TNF-α, IL-6, IL-1β, and IL-18 were downregulated in rat lung tissues, which implied that PNU-282987 therapy may help regulate inflammation. These protective effects involved the inhibition of the NLRP3 inflammasome. In vitro assays of cultured rat lung macrophages confirmed that the anti-inflammation effect of PNU-282987 therapy may contribute to the disturbance of NLRP3 inflammasome activation.

Conclusion: Targeting α7nAChR with PNU-282987 could effectively prevent and treat PH with benefits for preventing ongoing inflammation in the lungs of rats with MCT-induced PH by inhibiting NLRP3 inflammasome activation.

The Cholinergic Pathways in Inflammation: A Potential Pharmacotherapeutic Target for COPD

In COPD, the activity of the cholinergic system is increased, which is one of the reasons for the airflow limitation caused by the contraction of airway smooth muscles. Therefore, blocking the contractive actions with anticholinergics is a useful therapeutic intervention to reduce the airflow limitation. In addition to the effects of bronchoconstriction and mucus secretion, accumulating evidence from animal models of COPD suggest acetylcholine has a role in inflammation. Experiments using muscarinic M₃-receptor deficient mice or M₃ selective antagonists revealed that M₃-receptors on parenchymal cells, but not on hematopoietic cells, are involved in the pro-inflammatory effect of acetylcholine. Recently, combinations of long-acting β2 adrenergic agonists (LABAs) and long-acting muscarinic antagonists (LAMAs) have become available for COPD treatment. These dual long-acting bronchodilators may have synergistic anti-inflammatory effects because stimulation of β2 adrenergic receptors induces inhibitory effects in inflammatory cells via a different signaling pathway from that by antagonizing M₃-receptor, though these anti-inflammatory effects have not been clearly demonstrated in COPD patients. In contrast to the pro-inflammatory effects by ACh via muscarinic receptors, it has been demonstrated that the cholinergic anti-inflammatory pathway, which involves the parasympathetic nervous systems, regulates excessive inflammatory responses to protect organs during tissue injury and infection. Stimulation of acetylcholine via the α7 nicotinic acetylcholine receptor (α7nAChR) exerts inhibitory effects on leukocytes including macrophages and type 2 innate lymphoid cells. Although it remains unclear whether the inhibitory effects of acetylcholine via α7nAChR in inflammatory cells can regulate inflammation in COPD, neuroimmune interactions including the cholinergic anti-inflammatory pathway might serve as potential therapeutic targets.