Gas6 Ameliorates Inflammatory Response and Apoptosis in Bleomycin-Induced Acute Lung Injury

Human fetal lung mesenchymal stem cells ameliorate lung injury in an animal model

Acute lung injury (ALI) is a critical condition with limited treatment options. This study evaluates the therapeutic potential of human fetal lung-derived mesenchymal stem cells (hFL-MSCs) in an experimental model of ALI. Our proof-of-concept findings suggest a paradigm shift in the approach to cell sourcing for lung diseases, proposing that fetal lung cells may be potential targets for stem cell differentiation studies when the derived cells are intended to be used for lung cell therapy. After characterizing hFL-MSCs, 18-week fetal lung cells were intratracheally instilled into rats with bleomycin-induced ALI. All the animals were evaluated on days 3 - 28 post-injury for cell count and the cytokines in bronchoalveolar lavage fluid (BALF), lung wet/dry weight ratio, lung tissue histological staining and expression of an extracellular matrix component, inflammatory and fibrotic genes. The findings confirm mesenchymal stem cell identity of the isolated cells and stability in their cell cycle distribution. Analysis of BALF showed that immune cell response to acute inflammation and adaptive immunity was significantly ameliorated by cell therapy with hFL-MSCs. Same results were confirmed by the levels of IL-6, TNF-α, IL-10 and NO in BALF, the lung wet/dry weight ratio and histopathological analysis of lung tissues after H&E and Masson's trichrome staining. Effective modulation of key pro-inflammatory (Il6, Tnf, Il1b), pro-fibrotic (Tgfb1) and Col1a1 genes were also confirmed after therapy with hFL-MSCs. Our findings suggest that fetal lung tissue-specific stem cells are viable options for lung cell therapy and could be considered as targets for engineering of regenerative cells for lung diseases.

Gas6 induces AIM to suppress acute lung injury in mice by inhibiting NLRP3 inflammasome activation and inducing autophagy

Introduction

Growth arrest-specific 6 (Gas6) protein signaling plays a critical role in maintaining immune homeostasis and regulating inflammation. However, novel mechanisms for modulating macrophage activity through the Gas6 axis are being identified. Gas6 enhances the production of apoptosis inhibitor of macrophages (AIM), a protein with potent anti-inflammatory properties. This study investigates whether Gas6-induced AIM suppresses acute lung injury (ALI) in mice by modulating key inflammatory pathways, including inflammasome activation, autophagy, reactive oxygen species (ROS) generation, and efferocytosis.

Methods

ALI was induced in wild-type (WT) and AIM-/- mice via intratracheal administration of LPS. To evaluate the effects of the Gas6-AIM axis on lung inflammation, recombinant Gas6 (rGas6) was treated intraperitoneally. Inflammatory responses were evaluated using enzyme-linked immunosorbent assay, a cell-sizing analyzer, and Bicinchoninic acid assays. Lung pathology was assessed using hematoxylin-eosin staining. NLRP3 inflammasome activation and autophagy were evaluated using western blot, quantitative real-time PCR, and immunofluorescence. Reactive oxygen species (ROS) levels in alveolar macrophages were measured via fluorescence microscopy, while efferocytosis was assessed in cytospin-stained BAL cells and cultured alveolar macrophages co-cultured with apoptotic Jurkat cells. Additionally, rGas6-mediated effects on NLRP3 inflammasome activation and autophagy were validated in mouse bone marrow-derived macrophages (BMDMs) using siRNAs targeting AIM, Axl, LXRα, or LXRβ.

Results

Proinflammatory cytokine production, neutrophil infiltration, and protein levels in BALF were significantly reduced by rGas6 administration in WT mice but not in AIM-/- mice. Specifically, rGas6 reduced IL-1β and IL-18 levels, caspase-1 activity, and the production of apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC) in alveolar macrophages. Additionally, rGas6 promoted autophagy and efferocytosis in alveolar macrophages while reducing ROS levels through AIM production. These protective effects were absent in AIM-/- mice. Furthermore, siRNA-mediated silencing of Axl, LXRα, LXRβ, or AIM reversed the inhibitory effects of rGas6 on NLRP3 inflammasome activation in BMDMs, and AIM was essential for rGas6-induced autophagy.

Conclusion

Gas6-induced AIM production protects against LPS-induced ALI by inhibiting NLRP3 inflammasome activation, enhancing autophagy and efferocytosis, and reducing oxidative stress. These findings highlight the Gas6-AIM axis as a potential therapeutic target for mitigating inflammatory lung diseases.

Immunomodulatory effect of efferocytosis at the maternal-fetal interface

Efferocytosis is a mechanism by which phagocytes efficiently clear apoptotic cells, averting their secondary necrosis and the subsequent release of potentially immunogenic or cytotoxic substances that can trigger strong immune and inflammatory responses. During efferocytosis, the metabolic pathways of phagocytes are transformed, which, along with the catabolism of apoptotic cargo, can affect their function and inflammatory state. Extensive apoptosis occurs during placental development, and some studies reported the immunomodulatory effects of efferocytosis at the maternal-fetal interface. The dysregulation of efferocytosis is strongly linked to pregnancy complications such as preeclampsia and recurrent spontaneous abortion. In this review, we discuss the mechanisms of efferocytosis and its relationships with metabolism and inflammation. We also highlight the roles of professional and non-professional phagocytes in efferocytosis at the maternal-fetal interface and their impact on pregnancy outcomes and explore relevant regulatory factors. These insights are expected to guide future basic research and clinical strategies for identifying efferocytosis-related molecules as potential predictors or therapeutic targets in obstetric diseases.

Therapeutic implication of targeting mitochondrial drugs designed for efferocytosis dysfunction

Efferocytosis refers to the process by which phagocytes remove apoptotic cells and related apoptotic products. It is essential for the growth and development of the body, the repair of damaged or inflamed tissues, and the balance of the immune system. Damaged efferocytosis will cause a variety of chronic inflammation and immune system diseases. Many studies show that efferocytosis is a process mediated by mitochondria. Mitochondrial metabolism, mitochondrial dynamics, and communication between mitochondria and other organelles can all affect phagocytes' clearance of apoptotic cells. Therefore, targeting mitochondria to modulate phagocyte efferocytosis is an anticipated strategy to prevent and treat chronic inflammatory diseases and autoimmune diseases. In this review, we introduced the mechanism of efferocytosis and the pivoted role of mitochondria in efferocytosis. In addition, we focused on the therapeutic implication of drugs targeting mitochondria in diseases related to efferocytosis dysfunction.

Administration of Gas6 attenuates lung fibrosis via inhibition of the epithelial-mesenchymal transition and fibroblast activation

The epithelial-mesenchymal transition (EMT) and fibroblast activation are major events in idiopathic pulmonary fibrosis pathogenesis. Here, we investigated whether growth arrest-specific protein 6 (Gas6) plays a protective role in lung fibrosis via suppression of the EMT and fibroblast activation. rGas6 administration inhibited the EMT in isolated mouse ATII cells 14 days post-BLM treatment based on morphologic cellular alterations, changes in mRNA and protein expression profiles of EMT markers, and induction of EMT-activating transcription factors. BLM-induced increases in gene expression of fibroblast activation-related markers and the invasive capacity of primary lung fibroblasts in primary lung fibroblasts were reversed by rGas6 administration. Furthermore, the hydroxyproline content and collagen accumulation in interstitial areas with damaged alveolar structures in lung tissue were reduced by rGas6 administration. Targeting Gas6/Axl signaling events with specific inhibitors of Axl (BGB324), COX-2 (NS-398), EP1/EP2 receptor (AH-6809), or PGD2 DP2 receptor (BAY-u3405) reversed the inhibitory effects of rGas6 on EMT and fibroblast activation. Finally, we confirmed the antifibrotic effects of Gas6 using Gas6-/- mice. Therefore, Gas6/Axl signaling events play a potential role in inhibition of EMT process and fibroblast activation via COX-2-derived PGE2 and PGD2 production, ultimately preventing the development of pulmonary fibrosis.

N-Acetylglucosamine mitigates lung injury and pulmonary fibrosis induced by bleomycin

Lung injury and pulmonary fibrosis contribute to morbidity and mortality, and, in particular, are characterized as leading cause on confirmed COVID-19 death. To date, efficient therapeutic approach for such lung diseases is lacking. N-Acetylglucosamine (NAG), an acetylated derivative of glucosamine, has been proposed as a potential protector of lung function in several types of lung diseases. The mechanism by which NAG protects against lung injury, however, remains unclear. Here, we show that NAG treatment improves pulmonary function in bleomycin (BLM)-induced lung injury model measured by flexiVent system. At early phase of lung injury, NAG treatment results in silenced immune response by targeting ARG1+ macrophages activation, and, consequently, blocks KRT8+ transitional stem cell in the alveolar region to stimulate PDGF Rβ+ fibroblasts hyperproliferation, thereby attenuating the pulmonary fibrosis. This combinational depression of immune response and extracellular matrix deposition within the lung mitigates lung injury and pulmonary fibrosis induced by BLM. Our findings provide novel insight into the protective role of NAG in lung injury.

Ficolin B secreted by alveolar macrophage exosomes exacerbates bleomycin-induced lung injury via ferroptosis through the cGAS-STING signaling pathway

Pathogenesis exploration and timely intervention of lung injury is quite necessary as it has harmed human health worldwide for years. Ficolin B (Fcn B) is a recognition molecule that can recognize a variety of ligands and play an important role in mediating the cell cycle, immune response, and tissue homeostasis in the lung. However, the role of Fcn B in bleomycin (BLM)-induced lung injury is obscure. This study aims to investigate the sources of Fcn B and its mechanism in BLM-induced lung injury. WT, Fcna-/-, and Fcnb-/- mice were selected to construct the BLM-induced lung injury model. Lung epithelial cells were utilized to construct the BLM-induced cell model. Exosomes that were secreted from alveolar macrophages (AMs) were applied for intervention by transporting Fcn B. Clinical data suggested M-ficolin (homologous of Fcn B) was raised in plasma of interstitial lung disease (ILD) patients. In the mouse model, macrophage-derived Fcn B aggravated BLM-induced lung injury and fibrosis. Fcn B further promoted the development of autophagy and ferroptosis. Remarkably, cell experiment results revealed that Fcn B transported by BLM-induced AMs exosomes accelerated autophagy and ferroptosis in lung epithelial cells through the activation of the cGAS-STING pathway. In contrast, the application of 3-Methyladenine (3-MA) reversed the promotion effect of Fcn B from BLM-induced AMs exosomes on lung epithelial cell damage by inhibiting autophagy-dependent ferroptosis. Meanwhile, in the BLM-induced mice model, the intervention of Fcn B secreted from BLM-induced AMs exosomes facilitated lung injury and fibrosis via ferroptosis. In summary, this study demonstrated that Fcn B transported by exosomes from AMs exacerbated BLM-induced lung injury by promoting lung epithelial cells ferroptosis through the cGAS-STING signaling pathway.

Potential protective effect of 3,3'-methylenebis(1-ethyl-4-hydroxyquinolin-2(1H)-one) against bleomycin-induced lung injury in male albino rat via modulation of Nrf2 pathway: biochemical, histological, and immunohistochemical study

Acute lung injury is a serious condition accounting for the majority of acute respiratory failure. Bleomycin (BLM) is an antibiotic that was first described as a chemotherapeutic agent. 3,3'-methylenebis(1-ethyl-4-hydroxyquinolin-2(1H)-one) was reported to have anti-inflammatory, anti-apoptotic, and anti-oxidative properties. The current work aimed to assess the possible protective effects and the mechanism of protection of 3,3'-methylenebis-(1-ethyl-4-hydroxyquinolin-2(1H)-one) on BLM-induced lung injury in addition to the effect and underlying mechanisms of nuclear factor-erythroid-related factor 2 pathway against this injury. Rats were equally divided into four groups: control group, BLM group, 1-ethyl-4-hydroxyquinolin-2(1H)-one-treated group, and BLM with 1-ethyl-4-hydroxyquinolin-2(1H)-one-treated group. At the end of the work, the blood samples were proceeded for biochemical study. Lung specimens were obtained for biochemical, histological, and immunohistochemical study. The results exhibited a significant increase in both malondialdehyde and tumor necrotic factor-α with a significant decrease in glutathione, superoxide dismutase, IL 10, surfactant protein A, and nuclear factor erythroid 2-related factor 2 in BLM group. The lung histological results showed various morphological changes in the form of disturbed architecture, inflammatory cell infiltration, and intraluminal debris. This group also displayed a significant increase in the mean surface area fraction of anti-cleaved caspase 3, while group IV exhibited amelioration in the previously mentioned parameters and histological alternations that were induced by BLM. It could be concluded that 3,3'-methylenebis(1-ethyl-4-hydroxyquinolin-2(1H)-one) has anti-oxidative, anti-inflammatory, and anti-apoptotic protective effects against BLM-induced lung injury.

Mechanisms of efferocytosis in determining inflammation resolution: Therapeutic potential and the association with cardiovascular disease

Efferocytosis is defined as the clearance of apoptotic cells (ACs) in physiological and pathological states and is performed by efferocytes, such as macrophages. Efferocytosis can lead to the resolution of inflammation and restore tissue homoeostasis; however, the mechanisms of efferocytosis in determining inflammation resolution are still not completely understood, and the effects of efferocytosis on other proresolving properties need to be explored and explained. In this review, the process of efferocytosis will be summarized briefly, and then these mechanisms and effects will be thoroughly discussed. In addition, the association between the mechanisms of efferocytosis in determining inflammation resolution and cardiovascular diseases will also be reviewed, as an understanding of this association may provide information on novel treatment targets.

Inhibition of STAT6 Activation by AS1517499 Inhibits Expression and Activity of PPARγ in Macrophages to Resolve Acute Inflammation in Mice

Signal transducer and activator of transcription 6 (STAT6) promotes an anti-inflammatory process by inducing the development of M2 macrophages. We investigated whether modulating STAT6 activity in macrophages using AS1517499, the specific STAT6 inhibitor, affects the restoration of homeostasis after an inflammatory insult by regulating PPARγ expression and activity. Administration of AS1517499 suppressed the enhanced STAT6 phosphorylation and nuclear translocation observed in peritoneal macrophages after zymosan injection. In addition, AS1517499 delayed resolution of acute inflammation as evidenced by enhanced secretion of pro-inflammatory cytokines, reduced secretion of anti-inflammatory cytokines in PLF and supernatants from peritoneal macrophages, and exaggerated neutrophil numbers and total protein levels in PLF. We demonstrate temporal increases in annexin A1 (AnxA1) protein and mRNA levels in peritoneal lavage fluid (PLF), peritoneal macrophages, and spleen in a murine model of zymosan-induced acute peritonitis. In vitro priming of mouse bone marrow-derived macrophages (BMDM) and peritoneal macrophages with AnxA1 induced STAT6 activation with enhanced PPARγ expression and activity. Using AS1517499, we demonstrate that inhibition of STAT6 activation delayed recovery of PPARγ expression and activity, as well as impaired efferocytosis. Taken together, these results suggest that activation of the STAT6 signaling pathway mediates PPARγ expression and activation in macrophages to resolve acute inflammation.