LXA4 Inhibits Lipopolysaccharide-Induced Inflammatory Cell Accumulation by Resident Macrophages in Mice

Significance of Pyroptosis in Immunoregulation and Prognosis of Patients with Acute Respiratory Distress Syndrome: Evidence from RNA-Seq of Alveolar Macrophages

Objective

This study aimed to investigate the role of pyroptosis in alveolar macrophages regarding the immune microenvironment of acute respiratory distress syndrome (ARDS) and its prognosis.

Methods

ARDS Microarray data were downloaded from Gene Expression Omnibus (GEO). Support vector machine (SVM) and random forest (RF) models were applied to identify hub pyroptosis-related genes (PRGs) with prognostic significance in ARDS. RT-PCR was used to detect the relative expression of PRGs mRNA in alveolar macrophages of ARDS mice. Consensus clustering analysis was conducted based on the expression of the PRGs to identify pyroptosis modification patterns. Bioinformatic algorithms were used to study the immune traits and biological functions of the pyroptosis patterns. Finally, protein-protein interaction (PPI) networks were established to identify hub regulatory proteins with implications for the pyroptosis patterns.

Results

In our study, a total of 12 PRGs with differential expression were obtained. Four hub PRGs, including GPX4, IL6, IL18 and NLRP3, were identified and proven to be predictive of ventilator-free days (VFDS) in ARDS patients. The AUC values of the 4 PRGs were 0.911 (GPX4), 0.879 (IL18), 0.851 (IL6) and 0.841 (NLRP3), respectively. In ARDS mice, GPX4 mRNA decreased significantly, while IL6, IL18, and NLRP3 mRNA increased. Functional analysis revealed that IL6 had the strongest positive correlation with the CCR pathway, while GPX4 exhibited the strongest negative correlation with the T co-inhibition pathway. Based on the expression of the 4 PRGs, three pyroptosis modification patterns representing different immune states were obtained, and pattern C might represent immune storm.

Conclusion

The results showed that pyroptosis plays an important regulatory role in the immune microenvironment of ARDS. This finding provides new insights into the pathogenesis, diagnosis, and treatment of ARDS.

Lipoxin A4 Ameliorates Imiquimod-Induced Psoriasis-Like Dermatitis via Promoting the Regression of Inflammation

Introduction

As a mediator of inflammation resolution, lipoxin A4 (LXA4) mainly plays an anti-inflammatory role and promotes inflammation resolution. LXA4 plays an inhibiting inflammatory role in a variety of diseases, tissues and cells, including keratinocytes. Psoriasis is a chronic inflammatory skin disease mediated by dysregulation of inflammation of immune cells and keratinocytes. However, the expression and role of LXA4 in psoriasis-like mouse models are still unclear.

Methods

Imiquimod (IMQ) topical treatment of dorsal skin induces psoriasis-like dermatitis in BALB/c mice, pretreated intraperitoneally with or without LXA4 prior to IMQ application. Severity of dorsal lesions is assessed by using a modified human scoring system and histopathology. The concentration of LXA4 and the expression of ALOX15 (a key gene in LXA4 metabolic synthesis) in lesional skins were detected by ELISA and Western blot. Quantitative PCR and ELISA were conducted to detect the mRNA and secretion levels of inflammatory cytokines. The proportion of IL-17A-producing γδT cells in skin and skin draining cervical lymph nodes and helper (Th) 17 cells in spleens was evaluated by flow cytometry. Western blotting was used to analyze the expressions of p-STAT3 and TRAF6.

Results

The concentration of LXA4 and the expression of ALOX15 were decreased in IMQ-induced lesional skin. LXA4 significantly relieved psoriasis-like lesions in IMQ-induced mouse models. Furthermore, LXA4 decreased IMQ-induced systemic inflammation, including reduced the proportion of IL-17A-producing gdT cells in skin and skin draining cervical lymph nodes and Th17 cells in spleens, the secretion and expression of CCL20, IL-17A, IL-1β, and TNF-α in skin and serum. LXA4 markedly inhibited IMQ-induced expression of TRAF6 and p-STAT3.

Conclusion

LXA4 significantly ameliorates IMQ-induced psoriasis-like inflammation, and LXA4 can be used as a target for psoriasis treatment.

Exosomal PGE2 from M2 macrophages inhibits neutrophil recruitment and NET formation through lipid mediator class switching in sepsis

BACKGROUND

Excess polymorphonuclear neutrophil (PMN) recruitment or excessive neutrophil extracellular trap (NET) formation can lead to the development of multiple organ dysfunction during sepsis. M2 macrophage-derived exosomes (M2-Exos) have exhibited anti-inflammatory activities in some inflammatory diseases to mediate organ functional protection, but their role in treating sepsis-related acute lung injury (ALI) remains unclear. In this study, we sought to investigate whether M2-Exos could prevent potentially deleterious inflammatory effects during sepsis-related ALI by modulating abnormal PMN behaviours.

METHODS

C57BL/6 wild-type mice were subjected to a caecal ligation and puncture (CLP) mouse model to mimic sepsis in vivo, and M2-Exos were administered intraperitoneally 1 h after CLP. H&E staining, immunofluorescence and immunohistochemistry were conducted to investigate lung tissue injury, PMN infiltration and NET formation in the lung. We further demonstrated the role of M2-Exos on PMN function and explored the potential mechanisms through an in vitro coculture experiment using PMNs isolated from both healthy volunteers and septic patients.

RESULTS

Here, we report that M2-Exos inhibited PMN migration and NET formation, alleviated lung injury and reduced mortality in a sepsis mouse model. In vitro, M2-Exos significantly decreased PMN migration and NET formation capacity, leading to lipid mediator class switching from proinflammatory leukotriene B4 (LTB4) to anti-inflammatory lipoxin A4 (LXA4) by upregulating 15-lipoxygenase (15-LO) expression in PMNs. Treatment with LXA4 receptor antagonist attenuated the effect of M2-Exos on PMNs and lung injury. Mechanistically, prostaglandin E2 (PGE2) enriched in M2-Exos was necessary to increase 15-LO expression in PMNs by functioning on the EP4 receptor, upregulate LXA4 production to downregulate chemokine (C-X-C motif) receptor 2 (CXCR2) and reactive oxygen species (ROS) expressions, and finally inhibit PMN function.

CONCLUSIONS

Our findings reveal a previously unknown role of M2-Exos in regulating PMN migration and NET formation through lipid mediator class switching, thus highlighting the potential application of M2-Exos in controlling PMN-mediated tissue injury in patients with sepsis.

Formyl peptide receptor 2 activation by mitochondrial formyl peptides stimulates the neutrophil proinflammatory response via the ERK pathway and exacerbates ischemia-reperfusion injury

BACKGROUND

Ischemia-reperfusion injury (IRI) is an inevitable process in renal transplantation that significantly increases the risk of delayed graft function, acute rejection, and even graft loss. Formyl peptide receptor 2 (FPR2) is an important receptor in multiple septic and aseptic injuries, but its functions in kidney IRI are still unclear. This study was designed to reveal the pathological role of FPR2 in kidney IRI and its functional mechanisms.

METHODS

To explore the mechanism of FPR2 in kidney IRI, the model rats were sacrificed after IRI surgery. Immunofluorescence, enzyme-linked immunosorbent assays, and western blotting were used to detect differences in the expression of FPR2 and its ligands between the IRI and control groups. WRW₄ (WRWWWW-NH2), a specific antagonist of FPR2, was administered to kidney IRI rats. Kidney function and pathological damage were detected to assess kidney injury and recovery. Flow cytometry was used to quantitatively compare neutrophil infiltration among the experimental groups. Mitochondrial formyl peptides (mtFPs) were synthesized and administered to primary rat neutrophils together with the specific FPR family antagonist WRW₄ to verify our hypothesis in vitro. Western blotting and cell function assays were used to examine the functions and signaling pathways that FPR2 mediates in neutrophils.

RESULTS

FPR2 was activated mainly by mtFPs during the acute phase of IRI, mediating neutrophil migration and reactive oxygen species production in the rat kidney through the ERK1/2 pathway. FPR2 blockade in the early phase protected rat kidneys from IRI.

CONCLUSIONS

mtFPs activated FPR2 during the acute phase of IRI and mediated rat kidney injury by activating the migration and reactive oxygen species generation of neutrophils through the ERK1/2 pathway.

The protective effects of lipoxin A4 on type 2 diabetes mellitus: A Chinese prospective cohort study

BACKGROUND

Several cellular and animal studies have suggested that lipoxin A4 (LXA4) has a protective effect on type 2 diabetes mellitus (T2DM) development. However, little is known about whether LXA4 influences T2DM development at the population level.

METHODS

We included 2755 non-diabetic participants from a cohort study in China who were followed for about seven years. Cox proportional hazards model was used to estimate hazard ratios (HRs) and 95% confidence intervals (CI) for the association between LXA4 and incident T2DM. Mediation models were used to examine how serum lipids as mediators impact the association between LXA4 and T2DM.

RESULTS

In total, 172 newly diagnosed T2DM cases were identified. Multivariate-adjusted HR for T2DM in the fourth compared with the first quartile of LXA4 was 0.62 (95% CI: 0.40-0.96). When used the optimal cutoff value determined by the receiver operating characteristic curve, the results showed participants with LXA4 > 2.84 ng/mL had a decreased T2DM risk compared to those with LXA4 ≤ 2.84 ng/mL (HR: 0.63, 95% CI: 0.45-0.89). The effect of LXA4 on incident T2DM was significantly modified by gender (P _-interaction = 0.024) and family history of diabetes (P _-interaction = 0.025). Additionally, the association between LXA4 and incident T2DM was partially suppressed by the TyG and TG/HDL-c ratio, with a suppression proportion of 22.2% and 16.0%, respectively.

CONCLUSIONS

Higher LXA4 levels are significantly associated with a lower risk of T2DM development. The present findings would be helpful in understanding the effect of LXA4 on T2DM development at the population level.

The role of lung macrophages in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is an acute and diffuse inflammatory lung injury in a short time, one of the common severe manifestations of the respiratory system that endangers human life and health. As an innate immune cell, macrophages play a key role in the inflammatory response. For a long time, the role of pulmonary macrophages in ARDS has tended to revolve around the polarization of M1/M2. However, with the development of single-cell RNA sequencing, fate mapping, metabolomics, and other new technologies, a deeper understanding of the development process, classification, and function of macrophages in the lung are acquired. Here, we discuss the function of pulmonary macrophages in ARDS from the two dimensions of anatomical location and cell origin and describe the effects of cell metabolism and intercellular interaction on the function of macrophages. Besides, we explore the treatments for targeting macrophages, such as enhancing macrophage phagocytosis, regulating macrophage recruitment, and macrophage death. Considering the differences in responsiveness of different research groups to these treatments and the tremendous dynamic changes in the gene expression of monocyte/macrophage, we discussed the possibility of characterizing the gene expression of monocyte/macrophage as the biomarkers. We hope that this review will provide new insight into pulmonary macrophage function and therapeutic targets of ARDS.

Wnt/β-catenin signaling regulates lipopolysaccharide-altered polarizations of RAW264.7 cells and alveolar macrophages in mouse lungs

Introduction

Macrophages are capable of exerting both proinflammatory and anti-inflammatory functions in response to distinct environmental stimuli, by polarizing into classically inflammatory state (M1) and anti-inflammatory phenotype (M2), respectively. The Wnt/β-catenin signaling plays an important role in the tissue homeostasis and immune regulations, including the macrophage polarizations. However, the molecular mechanism of Wnt/β-catenin signaling in regulating alveolar macrophage polarization in an inflammatory state remains unclear.

Methods

The Wnt/β-catenin signaling-altered phenotypes of murine macrophage-like RAW264.7 cells in vitro and alveolar macrophage in vivo in both of naïve and lipopolysaccharide-induced inflammation states were accessed by immunoblotting and immunostaining assays.

Results

The activation of Wnt/β-catenin signaling inhibited macrophage M1 polarization, but promoted alternative M2 polarization in murine RAW264.7 cells under a naïve state. Interestingly, in an LPS-induced inflammation condition, the enhanced Wnt/β-catenin activity suppressed both M1 and M2 polarizations in RAW264.7 cells in vitro, and primary alveolar macrophages of LPS-challenged mice in vivo. Molecular analysis further demonstrated an involvement of Stat signing in regulating Wnt/β-catenin signaling-altered polarizations in mouse alveolar macrophages.

Conclusion

These results suggest a mechanism by which Wnt/β-catenin signaling modulates macrophage polarization in an inflammation state by regulating the Stat signaling pathway.

Effects of Arachidonic Acid Metabolites on Cardiovascular Health and Disease

Arachidonic acid (AA) is an essential fatty acid that is released by phospholipids in cell membranes and metabolized by cyclooxygenase (COX), cytochrome P450 (CYP) enzymes, and lipid oxygenase (LOX) pathways to regulate complex cardiovascular function under physiological and pathological conditions. Various AA metabolites include prostaglandins, prostacyclin, thromboxanes, hydroxyeicosatetraenoic acids, leukotrienes, lipoxins, and epoxyeicosatrienoic acids. The AA metabolites play important and differential roles in the modulation of vascular tone, and cardiovascular complications including atherosclerosis, hypertension, and myocardial infarction upon actions to different receptors and vascular beds. This article reviews the roles of AA metabolism in cardiovascular health and disease as well as their potential therapeutic implication.

Molecular biochemical aspects of salt (sodium chloride) in inflammation and immune response with reference to hypertension and type 2 diabetes mellitus

Obesity, insulin resistance, type 2 diabetes mellitus (T2DM) and hypertension (HTN) are common that are associated with low-grade systemic inflammation. Diet, genetic factors, inflammation, and immunocytes and their cytokines play a role in their pathobiology. But the exact role of sodium, potassium, magnesium and other minerals, trace elements and vitamins in the pathogenesis of HTN and T2DM is not known. Recent studies showed that sodium and potassium can modulate oxidative stress, inflammation, alter the autonomic nervous system and induce dysfunction of the innate and adaptive immune responses in addition to their action on renin-angiotensin-aldosterone system. These actions of sodium, potassium and magnesium and other minerals, trace elements and vitamins are likely to be secondary to their action on pro-inflammatory cytokines IL-6, TNF-α and IL-17 and metabolism of essential fatty acids that may account for their involvement in the pathobiology of insulin resistance, T2DM, HTN and autoimmune diseases.