POLARIZATION OF ALVEOLAR MACROPHAGE IN MODEL OF DIET INDUCED OBESE MICE WITH VENTILATOR INDUCED LUNG INJURY

In patients requiring mechanical ventilation for acute lung injury or acute respiratory distress syndrome (ARDS), tidal volume reduction decreases mortality, but the mechanisms of the protective effect have not been fully explored. To test the hypothesis that alveolar macrophage activation is an early and critical event in the initiation of ventilator-induced lung injury (VILI), rats were ventilated with high tidal volume (HVT) for 10 min to 4 h. Alveolar macrophage counts in bronchoalveolar lavage (BAL) fluid decreased 45% by 20 min of HVT( P < 0.05) consistent with activation-associated adhesion. Depletion of alveolar macrophages in vivo with liposomal clodronate significantly decreased permeability and pulmonary edema following 4 h of HVT( P < 0.05). BAL fluid from rats exposed to 20 min of HVTincreased nitric oxide synthase activity nearly threefold in naïve primary alveolar macrophages ( P < 0.05) indicating that soluble factors present in the air spaces contribute to macrophage activation in VILI. Media from cocultures of alveolar epithelial cell monolayers and alveolar macrophages exposed to 30 min of stretch in vitro also significantly increased nitrite production in naïve macrophages ( P < 0.05), but media from stretched alveolar epithelial cells or primary alveolar macrophages alone did not, suggesting alveolar epithelial cell-macrophage interaction was required for the subsequent macrophage activation observed. These data demonstrate that injurious mechanical ventilation rapidly activates alveolar macrophages and that alveolar macrophages play an important role in the initial pathogenesis of VILI.

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Obesity Attenuates Ventilator-Induced Lung Injury by Modulating the STAT3–SOCS3 Pathway

Frontiers in Immunology ◽

10.3389/fimmu.2021.720844 ◽

2021 ◽

Vol 12 ◽

Author(s):

Shih-Wei Wu ◽

Chung-Kan Peng ◽

Shu-Yu Wu ◽

Yu Wang ◽

Sung-Sen Yang ◽

...

Keyword(s):

Lung Injury ◽

Lung Injury Score ◽

Protective Mechanism ◽

Free Access ◽

Obese Mice ◽

Wild Type ◽

Barrier Dysfunction ◽

Ventilator Induced Lung Injury ◽

Nfκb Pathway ◽

Set Up

BackgroundVentilator-induced lung injury (VILI) is characterized by vascular barrier dysfunction and suppression of alveolar fluid clearance (AFC). Obesity itself leads to chronic inflammation, which may initiate an injurious cascade to the lungs and simultaneously induce a protective feedback. In this study, we investigated the protective mechanism of obesity on VILI in a mouse model.MethodsThe VILI model was set up via 6-h mechanical ventilation with a high tidal volume. Parameters including lung injury score, STAT3/NFκB pathway, and AFC were assessed. Mice with diet-induced obesity were obtained by allowing free access to a high-fat diet since the age of 3 weeks. After a 9-week diet intervention, these mice were sacrificed at the age of 12 weeks. The manipulation of SOCS3 protein was achieved by siRNA knockdown and pharmaceutical stimulation using hesperetin. WNK4 knockin and knockout obese mice were used to clarify the pathway of AFC modulation.ResultsObesity itself attenuated VILI. Knockdown of SOCS3 in obese mice offset the protection against VILI afforded by obesity. Hesperetin stimulated SOCS3 upregulation in nonobese mice and provided protection against VILI. In obese mice, the WNK4 axis was upregulated at the baseline, but was significantly attenuated after VILI compared with nonobese mice. At the baseline, the manipulation of SOCS3 by siRNA and hesperetin also led to the corresponding alteration of WNK4, albeit to a lesser extent. After VILI, WNK4 expression correlated with STAT3/NFκB activation, regardless of SOCS3 status. Obese mice carrying WNK4 knockout had VILI with a severity similar to that of wild-type obese mice. The severity of VILI in WNK4-knockin obese mice was counteracted by obesity, similar to that of wild-type nonobese mice only.ConclusionsObesity protects lungs from VILI by upregulating SOCS3, thus suppressing the STAT3/NFκB inflammatory pathway and enhancing WNK4-related AFC. However, WNK4 activation is mainly from direct NFκB downstreaming, and less from SOCS3 upregulation. Moreover, JAK2–STAT3/NFκB signaling predominates the pathogenesis of VILI. Nevertheless, the interaction between SOCS3 and WNK4 in modulating VILI in obesity warrants further investigation.

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TLR4 is required for macrophage efferocytosis during resolution of ventilator-induced lung injury

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00226.2021 ◽

2021 ◽

Vol 321 (4) ◽

pp. L787-L801

Author(s):

Kai Su ◽

Lulong Bo ◽

Chunling Jiang ◽

Xiaoming Deng ◽

You-Yang Zhao ◽

...

Keyword(s):

Mechanical Ventilation ◽

Lung Injury ◽

Alveolar Macrophage ◽

Alveolar Macrophages ◽

Molecular Mechanisms ◽

Tissue Injury ◽

Lung Damage ◽

Lung Edema ◽

Apoptotic Cells ◽

Ventilator Induced Lung Injury

Mechanical ventilation is a life-sustaining therapy for patients with respiratory failure but can cause further lung damage known as ventilator-induced lung injury (VILI). However, the intrinsic molecular mechanisms underlying recovery of VILI remain unknown. Phagocytosis of apoptotic cells (also known as efferocytosis) is a key mechanism orchestrating successful resolution of inflammation. Here we show the positive regulation of macrophage Toll-like receptor (TLR) 4 in efferocytosis and resolution of VILI. Mice were depleted of alveolar macrophages and then subjected to injurious ventilation (tidal volume, 20 mL/kg) for 4 h. On day 1 after mechanical ventilation, Tlr4+/+ or Tlr4−/− bone marrow-derived macrophages (BMDMs) were intratracheally administered to alveolar macrophage-depleted mice. We observed that mice depleted of alveolar macrophages exhibited defective resolution of neutrophilic inflammation, exuded protein, lung edema, and lung tissue injury after ventilation, whereas these delayed responses were reversed by administration of Tlr4+/+ BMDMs. Importantly, these proresolving effects by Tlr4+/+ BMDMs were abolished in mice receiving Tlr4−/− BMDMs. The number of macrophages containing apoptotic cells or bodies in bronchoalveolar lavage fluid was much less in mice receiving Tlr4−/− BMDMs than that in those receiving Tlr4+/+ BMDMs. Macrophage TLR4 deletion facilitated a disintegrin and metalloprotease 17 maturation and enhanced Mer cleavage in response to mechanical ventilation. Heat shock protein 70 dramatically increased Mer tyrosine kinase surface expression, phagocytosis of apoptotic neutrophils, and rescued the inflammatory phenotype in alveolar macrophage-depleted mice receiving Tlr4+/+ BMDMs, but not Tlr4−/− BMDMs. Our results suggest that macrophage TLR4 promotes resolution of VILI via modulation of Mer-mediated efferocytosis.

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