Macrophage ferroportin serves as a therapeutic target against bacteria-induced acute lung injury by promoting barrier restoration

Sputum SLC40A1 as a Novel Biomarker is Increased in Patients with Acute Exacerbation of Chronic Obstructive Pulmonary Disease

Background

Solute carrier family 40 member 1 (SLC40A1 or Ferroportin) is a cell surface glycoprotein that participates in the efflux of cellular iron and disease pathogenesis. Induced sputum is a non-invasive method for lung sample collection. However, it remains unknown whether SLC40A1 is a potential diagnostic biomarker in induced sputum cells of patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). We in this study aimed to investigate the expression and the anti-inflammatory role of SLC40A1 in the induced-sputum cells of AECOPD patients.

Methods

A total of 35 induced sputum samples were collected from patients with AECOPD. Flow cytometry analysis was used to determine inflammatory cell phenotypes and SLC40A1 expression. Murine RAW 264.7 cell lines were treated with cigarette smoke extract (CSE) and SLC40A1-shRNA for SLC40A1 expression in vitro. ELISA was used for measurement of pro-inflammatory cytokine expression in vitro.

Results

Flow cytometry analysis showed that sputum neutrophils were increased in AECOPD patients with 3-5 exacerbations per year compared to 1 exacerbation per year, accompanied by elevated expression of CD40 and SLC40A1 in macrophages. The lung function (FEV1%pred) was reduced with a higher COPD exacerbation rate. There was a negative correlation between the FEV1% predicted and sputum neutrophil count. Patients expressing high levels of SLC40A1 exhibited higher exacerbation rates. SLC40A1 expression levels positively correlated with sputum neutrophils and negatively correlated with predicted FEV1%. In addition, mechanical ventilation reduces sputum neutrophils and SLC40A1 expression, particularly in patients with a high exacerbation rate. Further analysis in RAW 264.7 macrophage cell lines showed that cigarette smoke extract (CSE) increased the expression of SLC40A1, TNF-α, IL-6 and IL-10 at a concentration-dependent manner. SLC40A1 knockdown increased the expression of TNF-α and IL-6 and reduced the expression of IL-10 in CSE-treated macrophages.

Conclusion

SLC40A1 in sputum macrophages is increased and closely related to AECOPD severity, it would be a potential anti-inflammatory biomarker of patients with AECOPD.

Inducible antibacterial responses in macrophages

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

The Hydroxypyridinone Iron Chelator DIBI Reduces Bacterial Load and Inflammation in Experimental Lung Infection

Iron plays a critical role in lung infections due to its function in the inflammatory immune response but also as an important factor for bacterial growth. Iron chelation represents a potential therapeutic approach to inhibit bacterial growth and pathologically increased pro-inflammatory mediator production. The present study was designed to investigate the impact of the iron chelator DIBI in murine lung infection induced by intratracheal Pseudomonas aeruginosa (strain PA14) administration. DIBI is a polymer with a polyvinylpyrrolidone backbone containing nine 3-hydroxy-1-(methacrylamidoethyl)-2-methyl-4(1H) pyridinone (MAHMP) residues per molecule and was given by intraperitoneal injection either as a single dose (80 mg/kg) immediately after PA14 administration or a double dose (second dose 4 h after PA14 administration). The results showed that lung NF-κBp65 levels, as well as levels of various inflammatory cytokines (TNFα, IL-1β, IL-6) both in lung tissue and bronchoalveolar lavage fluid (BALF), were significantly increased 24 h after PA14 administration. Single-dose DIBI did not affect the bacterial load or inflammatory response in the lungs or BALF. However, two doses of DIBI significantly decreased bacterial load, attenuated NF-κBp65 upregulation, reduced inflammatory cytokines production, and relieved lung tissue damage. Our findings support the conclusion that the iron chelator, DIBI, can reduce lung injury induced by P. aeruginosa, via its anti-bacterial and anti-inflammatory effects.

Hydralazine represses Fpn ubiquitination to rescue injured neurons via competitive binding to UBA52

A major impedance to neuronal regeneration after peripheral nerve injury (PNI) is the activation of various programmed cell death mechanisms in the dorsal root ganglion. Ferroptosis is a form of programmed cell death distinguished by imbalance in iron and thiol metabolism, leading to lethal lipid peroxidation. However, the molecular mechanisms of ferroptosis in the context of PNI and nerve regeneration remain unclear. Ferroportin (Fpn), the only known mammalian nonheme iron export protein, plays a pivotal part in inhibiting ferroptosis by maintaining intracellular iron homeostasis. Here, we explored in vitro and in vivo the involvement of Fpn in neuronal ferroptosis. We first delineated that reactive oxygen species at the injury site induces neuronal ferroptosis by increasing intracellular iron via accelerated UBA52-driven ubiquitination and degradation of Fpn, and stimulation of lipid peroxidation. Early administration of the potent arterial vasodilator, hydralazine (HYD), decreases the ubiquitination of Fpn after PNI by binding to UBA52, leading to suppression of neuronal cell death and significant acceleration of axon regeneration and motor function recovery. HYD targeting of ferroptosis is a promising strategy for clinical management of PNI.

Iron Chelation as a Potential Therapeutic Approach in Acute Lung Injury

Acute lung injury (ALI) has been challenging health care systems since before the COVID-19 pandemic due to its morbidity, mortality, and length of hospital stay. In view of the complex pathogenesis of ALI, effective strategies for its prevention and treatment are still lacking. A growing body of evidence suggests that iron dysregulation is a common characteristic in many subtypes of ALI. On the one hand, iron is needed to produce reactive oxygen species (ROS) as part of the immune response to an infection; on the other hand, iron can accelerate the occurrence of ferroptosis and extend host cell damage. Iron chelation represents a novel therapeutic strategy for alleviating lung injury and improving the survival of patients with ALI. This article reviews the current knowledge of iron homeostasis, the role of iron in ALI development, and potential therapeutic targets.