N-Acetyl-Seryl-Asparyl-Lysyl-Proline regulates lung renin angiotensin system to inhibit epithelial-mesenchymal transition in silicotic mice

Exercise training inhibits macrophage-derived IL-17A-CXCL5-CXCR2 inflammatory axis to attenuate pulmonary fibrosis in mice exposed to silica

Exposure to crystalline silica leads to health effects beyond occupational silicosis. Exercise training's potential benefits on pulmonary diseases yield inconsistent outcomes. In this study, we utilized experimental silicotic mice subjected to exercise training and pharmacological interventions, including interleukin-17A (IL-17A) neutralizing antibody or clodronate liposome for macrophage depletion. Findings reveal exercise training's ability to mitigate silicosis progression in mice by suppressing scavenger receptor B (SRB)/NOD-like receptor thermal protein domain associated protein 3 (NLRP3) and Toll-like receptor 4 (TLR4) pathways. Macrophage-derived IL-17A emerges as primary source and trigger for silica-induced pulmonary inflammation and fibrosis. Exercise training effectively inhibits IL-17A-CXC motif chemokine ligand 5 (CXCL5)-Chemokine (C-X-C motif) Receptor 2 (CXCR2) axis in silicotic mice. Our study evidences exercise training's potential to reduce collagen deposition, preserve elastic fibers, slow pulmonary fibrosis advancement, and enhance pulmonary function post silica exposure by impeding macrophage-derived IL-17A-CXCL5-CXCR2 axis.

ISRIB inhibits the senescence of type II pulmonary epithelial cells to alleviate pulmonary fibrosis induced by silica in mice

The role and mechanisms of integrated stress response inhibitor (ISRIB) on silicosis are still not well defined. In the present study, the effects of ISRIB on cellular senescence and pulmonary fibrosis in silicosis were evaluated by RNA sequencing, micro-computed tomography, pulmonary function assessment, histological examination, and Western blot analysis. The results showed that ISRIB significantly reduced the degree of pulmonary fibrosis in mice with silicosis and reduced the expression of type I collagen, fibronectin, α-smooth muscle actin, and transforming growth factor-β1. Both in vivo and in vitro results showed that ISRIB reversed the expression of senescence-related factors β-galactosidase, phosphor-ataxia telangiectasia mutated, phosphor-ataxia telangiectasia and Rad3-related protein, p-p53, p21, p16, and plasminogen activator inhibitor type 1. The aforementioned results were consistent with the sequencing results. These findings implied that ISRIB might reduce the degree of pulmonary fibrosis in mice with silicosis by inhibiting the cellular senescence of alveolar epithelial cell type II.

Ac-SDKP promotes KIF3A-mediated β-catenin suppression through a ciliary mechanism to constrain silica-induced epithelial-myofibroblast transition

Kinesin family member 3 A (KIF3A) decrease have been reported in silicotic patients and rats. However, the detailed mechanisms of KIF3A in silicosis remain unknown. In this study, we demonstrated that KIF3A effectively blocked the expression of β-catenin and downstream myocardin-related transcription factor (MRTF)-A/serum response factor (SRF) signaling, thus inhibiting silica-induced epithelial-myofibroblast transition (EMyT). Moreover, KIF3A was identified as a downstream mediator of an antifibrotic tetrapeptide N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP). Knockdown of KIF3A expression reactivated β-catenin/myocardin-related transcription factor (MRTF)-A/serum response factor (SRF) signaling that was attenuated by Ac-SDKP in vitro. Collectively, our findings suggest that Ac-SDKP plays its anti-fibrosis role via KIF3A-mediated β-catenin suppression, at least in part, in both in vivo model of silicosis and in vitro model of EMyT.

The Role of Tβ4-POP-Ac-SDKP Axis in Organ Fibrosis

Fibrosis is a pathological process in which parenchymal cells are necrotic and excess extracellular matrix (ECM) is accumulated due to dysregulation of tissue injury repair. Thymosin β4 (Tβ4) is a 43 amino acid multifunctional polypeptide that is involved in wound healing. Prolyl oligopeptidase (POP) is the main enzyme that hydrolyzes Tβ4 to produce its derivative N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) which is found to play a role in the regulation of fibrosis. Accumulating evidence suggests that the Tβ4-POP-Ac-SDKP axis widely exists in various tissues and organs including the liver, kidney, heart, and lung, and participates in the process of fibrogenesis. Herein, we aim to elucidate the role of Tβ4-POP-Ac-SDKP axis in hepatic fibrosis, renal fibrosis, cardiac fibrosis, and pulmonary fibrosis, as well as the underlying mechanisms. Based on this, we attempted to provide novel therapeutic strategies for the regulation of tissue damage repair and anti-fibrosis therapy. The Tβ4-POP-Ac-SDKP axis exerts protective effects against organ fibrosis. It is promising that appropriate dosing regimens that rely on this axis could serve as a new therapeutic strategy for alleviating organ fibrosis in the early and late stages.

Thalidomide Alleviates Pulmonary Fibrosis Induced by Silica in Mice by Inhibiting ER Stress and the TLR4-NF-κB Pathway

Silicosis is the most prevalent occupational disease in China. It is a form of pulmonary fibrosis caused by the inhalation of silicon particles. As there is no cure for the potentially lethal and progressive condition, the treatment of silicotic fibrosis is an important and difficult problem to address. Thalidomide, a drug with anti-inflammatory and immunoregulatory properties, has been reported to have lung-protective effects. The purpose of this study was to observe the therapeutic effect of thalidomide on silicotic mice and to determine the protective mechanism. By using silicotic mice models and MH-S cells, we found the expression of endoplasmic reticulum stress (ER stress) and Toll-like receptor 4 (TLR4)-nuclear factor kappa-B (NF-κB) pathway as well as inflammation-related factors were upregulated in the macrophages of silicotic mice. The same indexes were detected in silica-stimulated MH-S cells, and the results were consistent with those in vivo. That is, silica activated ER stress and the TLR4-NF-κB pathway as well as the inflammatory response in vitro. Treating both silicotic mice and silica-stimulated MH-S cells with thalidomide inhibited ER stress and the TLR4-NF-κB pathway as well as the inflammatory response. The present study demonstrates thalidomide as a potential therapeutic agent against silicosis.

Early Identification, Accurate Diagnosis, and Treatment of Silicosis

Silicosis is a global problem, and it has brought about great burdens to society and patients' families. The etiology of silicosis is clear, preventable, and controllable, but the onset is hidden and the duration is long. Thus, it is difficult to diagnose it early and treat it effectively, leaving workers unaware of the consequences of dust exposure. As such, a lack of details in the work history and a slow progression of lung disease contribute to the deterioration of patients until silicosis has advanced to fibrosis. These issues are the key factors impeding the diagnosis and the treatment of silicosis. This article reviews the literature on the early identification, diagnosis, and treatment of silicosis as well as analyzes the difficulties in the diagnosis and the treatment of silicosis and discusses its direction of future development.

Tidal Volume-Dependent Activation of the Renin-Angiotensin System in Experimental Ventilator-Induced Lung Injury

OBJECTIVES

Ventilator-induced lung injury (VILI) is a major contributor to morbidity and mortality in critically ill patients. Mechanical damage to the lungs is potentially aggravated by the activation of the renin-angiotensin system (RAS). This article describes RAS activation profiles in VILI and discusses the effects of angiotensin (Ang) 1-7 supplementation or angiotensin-converting enzyme (ACE) inhibition with captopril as protective strategies.

DESIGN

Animal study.

SETTING

University research laboratory.

SUBJECTS

C57BL/6 mice.

INTERVENTIONS

Anesthetized mice (n = 12-18 per group) were mechanically ventilated with low tidal volume (LVT, 6 mL/kg), high tidal volume (HVT, 15 mL/kg), or very high tidal volume (VHVT, 30 mL/kg) for 4 hours, or killed after 3 minutes (sham). Additional VHVT groups received infusions of 60 μg/kg/hr Ang 1-7 or a single dose of 100 mg/kg captopril.

MEASUREMENTS AND MAIN RESULTS

VILI was characterized by increased bronchoalveolar lavage fluid levels of interleukin (IL)-6, keratinocyte-derived cytokine, and macrophage inflammatory protein-2 (MIP2). The Ang metabolites in plasma measured with liquid chromatography tandem mass spectrometry showed a strong activation of the classical (Ang I, Ang II) and alternative RAS (Ang 1-7, Ang 1-5), with highest concentrations found in the HVT group. Although the lung-tissue ACE messenger RNA expression was unchanged, its protein expression showed a dose-dependent increase under mechanical ventilation. The ACE2 messenger RNA expression decreased in all ventilated groups, whereas ACE2 protein levels remained unchanged. Both captopril and Ang 1-7 led to markedly increased Ang 1-7 plasma levels, decreased Ang II levels, and ACE activity (Ang II/Ang I ratio), and effectively prevented VILI.

CONCLUSIONS

VILI is accompanied by a strong activation of the RAS. Based on circulating Ang metabolite levels and tissue expression of RAS enzymes, classical ACE-dependent and alternative RAS cascades were activated in the HVT group, whereas classical RAS activation prevailed with VHVT ventilation. Ang 1-7 or captopril protected from VILI primarily by modifying the systemic RAS profile.

Silica Induction of Diverse Inflammatory Proteome in Lungs of Lupus-Prone Mice Quelled by Dietary Docosahexaenoic Acid Supplementation

Repeated short-term intranasal instillation of lupus-prone mice with crystalline silica (cSiO2) induces inflammatory gene expression and ectopic lymphoid neogenesis in the lung, leading to early onset of systemic autoimmunity and rapid progression to glomerulonephritis. These responses are suppressed by dietary supplementation with the ω-3 polyunsaturated fatty acid docosahexaenoic acid (DHA). Here, we tested the hypothesis that dietary DHA supplementation suppresses cSiO2-induced inflammatory proteins in bronchoalveolar alveolar lavage fluid (BALF) and plasma of lupus-prone mice. Archived tissue fluid samples were used from a prior investigation in which 6 wk-old lupus-prone female NZBWF1 mice were fed isocaloric diets containing 0 or 10 g/kg DHA for 2 wks and then intranasally instilled with 1 mg cSiO2 or vehicle once weekly for 4 wks. Cohorts were terminated at 1, 5, 9 or 13 wk post-instillation (PI). BALF and plasma from each cohort were analyzed by high density multiplex array profiling of 200 inflammatory proteins. cSiO2 time-dependently induced increases in the BALF protein signatures that were highly reflective of unresolved lung inflammation, although responses in the plasma were much less robust. Induced proteins in BALF included chemokines (e.g., MIP-2, MCP-5), enzymes (e.g., MMP-10, granzyme B), adhesion molecules (e.g., sE-selectin, sVCAM-1), co-stimulatory molecules (e.g., sCD40L, sCD48), TNF superfamily proteins (e.g., sTNFRI, sBAFF-R), growth factors (e.g., IGF-1, IGFBP-3), and signal transduction proteins (e.g., MFG-E8, FcgRIIB), many of which were blocked or delayed by DHA supplementation. The BALF inflammatory proteome correlated positively with prior measurements of gene expression, pulmonary ectopic lymphoid tissue neogenesis, and induction of autoantibodies in the lungs of the control and treatment groups. Ingenuity Pathway Analysis (IPA) revealed that IL-1β, TNF-α, and IL-6 were among the top upstream regulators of the cSiO2-induced protein response. Furthermore, DHA's effects were associated with downregulation of cSiO2-induced pathways involving i) inhibition of ARE-mediated mRNA decay, ii) bacterial and viral pattern recognition receptor activation, or iii) TREM1, STAT3, NF-κB, and VEGF signaling and with upregulation of PPAR, LXR/RXR and PPARα/RXRα signaling. Altogether, these preclinical findings further support the contention that dietary DHA supplementation could be applicable as an intervention against inflammation-driven autoimmune triggering by cSiO2 or potentially other environmental agents.

Glycolytic Reprogramming in Silica-Induced Lung Macrophages and Silicosis Reversed by Ac-SDKP Treatment

Glycolytic reprogramming is an important metabolic feature in the development of pulmonary fibrosis. However, the specific mechanism of glycolysis in silicosis is still not clear. In this study, silicotic models and silica-induced macrophage were used to elucidate the mechanism of glycolysis induced by silica. Expression levels of the key enzymes in glycolysis and macrophage activation indicators were analyzed by Western blot, qRT-PCR, IHC, and IF analyses, and by using a lactate assay kit. We found that silica promotes the expression of the key glycolysis enzymes HK2, PKM2, LDHA, and macrophage activation factors iNOS, TNF-α, Arg-1, IL-10, and MCP1 in silicotic rats and silica-induced NR8383 macrophages. The enhancement of glycolysis and macrophage activation induced by silica was reduced by Ac-SDKP or siRNA-Ldha treatment. This study suggests that Ac-SDKP treatment can inhibit glycolytic reprogramming in silica-induced lung macrophages and silicosis.