Diesel exhaust exposure in mice induces pulmonary fibrosis by TGF-β/Smad3 signaling pathway

NLRP3/GSDMD mediated pyroptosis induces lung inflammation susceptibility in diesel exhaust exposed mouse strains

BACKGROUND

Genetic diversity among species influences the disease severity outcomes linked to air pollution. However, the mechanism responsible for this variability remain elusive and needs further investigation.

OBJECTIVE

To investigate the genetic factors and pathways linked with differential susceptibility in mouse strains associated with diesel exhaust exposure.

METHODS

C57BL/6 and Balb/c mice were exposed to diesel exhaust (DE) for 5 days/week for 30 min/day for 8 weeks. Body weight of mice was recorded every week and airway hyperresponsiveness towards DE exposure was recorded after 24 h of last exposure. Mice were euthanised to collect BALF, blood, lung tissues for immunobiochemical assays, structural integrity and genetic studies.

RESULTS

C57BL/6 mice showed significantly decreased body weight in comparison to Balb/c mice (p < 0.05). Both mouse strains showed lung resistance and damage to elastance upon DE exposure compared to respective controls (p < 0.05) with more pronounced effects in C57BL/6 mice. Lung histology showed increase in bronchiolar infiltration and damage to the wall in C57BL/6 mice (p < 0.05). DE exposure upregulated pro-inflammatory and Th2 cytokine levels in C57BL/6 in comparison to Balb/c mice. C57BL/6 mice showed increase in Caspase-1 and ASC expression confirming activation of downstream pathway. This showed significant activation of inflammasome pathway in C57BL/6 mice with ∼2-fold increase in NLRP3 and elevated IL-1β expression. Gasdermin-D levels were increased in C57BL/6 mice demonstrating induction of pyroptosis that corroborated with IL-1β secretion (p < 0.05). Genetic variability among both species was confirmed with sanger's sequencing suggesting presence of SNPs in 3'UTRs of IL-1β gene influencing expression between mouse strains.

CONCLUSIONS

C57BL/6 mice exhibited increased susceptibility to diesel exhaust in contrast to Balb/c mice via activation of NLRP3-related pyroptosis. Differential susceptibility between strains may be attributed via SNPs in the 3'UTRs of the IL-1β gene.

Competitive-like binding between carbon black and CTNNB1 to ΔNp63 interpreting the abnormal respiratory epithelial repair after injury

Airway epithelium is extraordinary vulnerable to damage owning to continuous environment exposure. Subsequent repair is therefore essential to restore the homeostasis of respiratory system. Disruptions in respiratory epithelial repair caused by nanoparticles exposure have been linked to various human diseases, yet implications in repair process remain incompletely elucidated. This study aims to elucidate the key stage in epithelial repair disturbed by carbon black (CB) nanoparticles, highlighting the pivotal role of ΔNp63 in mediating the epithelium repair. A competitive-like binding between CB and beta-catenin 1 (CTNNB1) to ΔNp63 is proposed to elaborate the underlying toxicity mechanism. Specifically, CB exhibits a remarkable inhibitory effect on cell proliferation, leading to aberrant airway epithelial repair, as validated in air-liquid culture. ΔNp63 drives efficient epithelial proliferation during CB exposure, and CTNNB1 was identified as a target of ΔNp63 by bioinformatics analysis. Further molecular dynamics simulation reveals that oxygen-containing functional groups on CB disrupt the native interaction of CTNNB1 with ΔNp63 through competitive-like binding pattern. This process modulates CTNNB1 expression, ultimately restraining proliferation during respiratory epithelial repair. Overall, the current study elucidates that the diminished interaction between CTNNB1 and ΔNp63 impedes respiratory epithelial repair in response to CB exposure, thereby enriching the public health risk assessment on CB-related respiratory diseases.

Hypobaric hypoxia drives selection of altitude-associated adaptative alleles in the Himalayan population

Genetic variants play a crucial role in shaping the adaptive phenotypes associated with high-altitude populations. Nevertheless, a comprehensive understanding of the specific impacts of different environments associated with increasing altitudes on the natural selection of these genetic variants remains undetermined. Hence, this study aimed to identify genetic markers responsible for high-altitude adaptation with specific reference to different altitudes, majorly focussing on an altitude elevation range of ∼1500 m and a corresponding decrease of ≥5 % in ambient oxygen availability. We conducted a comprehensive genome-wide investigation (n = 192) followed by a validation study (n = 514) in low-altitude and three high-altitude populations (>2400 m) of Nubra village (NU) (3048 m), Sakti village (SKT) (3812 m), and Tso Moriri village (TK) (4522 m). Extensive genetic analysis identified 86 SNPs that showed significant associations with high-altitude adaptation. Frequency mapping of these SNPs revealed 38 adaptive alleles and specific haplotypes that exhibited a strong linear correlation with increasing altitude. Notably, these SNPs spanned crucial genes, such as ADH6 and NAPG along with the vastly studied genes like EGLN1 and EPAS1, involved in oxygen sensing, metabolism, and vascular homeostasis. Correlation analyses between these adaptive alleles and relevant clinical and biochemical markers provided evidence of their functional relevance in physiological adaptation to hypobaric hypoxia. High-altitude population showed a significant increase in plasma 8-isoPGF2α levels as compared to low-altitude population. Similar observation showcased increased blood pressure in NU as compared to TK (P < 0.0001). In silico analyses further confirmed that these alleles regulate gene expression of EGLN1, EPAS1, COQ7, NAPG, ADH6, DUOXA1 etc. This study provides genetic insights into the effects of hypobaric-hypoxia on the clinico-physiological characteristics of natives living in increasing high-altitude regions. Overall, our findings highlight the synergistic relationship between environment and evolutionary processes, showcasing physiological implications of genetic variants in oxygen sensing and metabolic pathway genes in increasing high-altitude environments.

Fine particulate matter contributes to COPD-like pathophysiology: experimental evidence from rats exposed to diesel exhaust particles

BACKGROUND

Ambient fine particulate matter (PM2.5) is considered a plausible contributor to the onset of chronic obstructive pulmonary disease (COPD). Mechanistic studies are needed to augment the causality of epidemiologic findings. In this study, we aimed to test the hypothesis that repeated exposure to diesel exhaust particles (DEP), a model PM2.5, causes COPD-like pathophysiologic alterations, consequently leading to the development of specific disease phenotypes. Sprague Dawley rats, representing healthy lungs, were randomly assigned to inhale filtered clean air or DEP at a steady-state concentration of 1.03 mg/m3 (mass concentration), 4 h per day, consecutively for 2, 4, and 8 weeks, respectively. Pulmonary inflammation, morphologies and function were examined.

RESULTS

Black carbon (a component of DEP) loading in bronchoalveolar lavage macrophages demonstrated a dose-dependent increase in rats following DEP exposures of different durations, indicating that DEP deposited and accumulated in the peripheral lung. Total wall areas (WAt) of small airways, but not of large airways, were significantly increased following DEP exposures, compared to those following filtered air exposures. Consistently, the expression of α-smooth muscle actin (α-SMA) in peripheral lung was elevated following DEP exposures. Fibrosis areas surrounding the small airways and content of hydroxyproline in lung tissue increased significantly following 4-week and 8-week DEP exposure as compared to the filtered air controls. In addition, goblet cell hyperplasia and mucus hypersecretions were evident in small airways following 4-week and 8-week DEP exposures. Lung resistance and total lung capacity were significantly increased following DEP exposures. Serum levels of two oxidative stress biomarkers (MDA and 8-OHdG) were significantly increased. A dramatical recruitment of eosinophils (14.0-fold increase over the control) and macrophages (3.2-fold increase) to the submucosa area of small airways was observed following DEP exposures.

CONCLUSIONS

DEP exposures over the courses of 2 to 8 weeks induced COPD-like pathophysiology in rats, with characteristic small airway remodeling, mucus hypersecretion, and eosinophilic inflammation. The results provide insights on the pathophysiologic mechanisms by which PM2.5 exposures cause COPD especially the eosinophilic phenotype.

TGF-β Regulates m6A RNA Methylation after PM2.5 Exposure

PM2.5 exposure leads to a variety of respiratory diseases, including pulmonary fibrosis, metastatic lung cancer, etc. Exposure to PM2.5 results in the alteration of epigenetic modification. M6A RNA methylation is an essential epigenetic modification that regulates gene expression at the post-transcriptional level. Our previous study found that PM2.5 exposure up-regulated m6A RNA methylation and TGF-β expression level in the lung, but the mechanisms and pathways of PM2.5 regulation of m6A RNA methylation are still unclear. Moreover, a previous study reported that the TGF-β signal pathway could regulate m6A RNA methylation. Based on this evidence, we investigate the role of the TGF-β signaling pathway in PM2.5-induced m6A RNA methylation with the A549 cell line. Our results showed that PM2.5 could induce upregulation of m6A RNA methylation, accompanied by increased expression of TGF-β, Smad3, methyltransferase-like 3 (METTL3), methyltransferase-like 14 (METTL14). Furthermore, these alterations induced by PM2.5 exposure could be reversed by treatment with TGF-β inhibitor. Therefore, we speculated that the TGF-β signal pathway plays an indispensable role in regulating m6A RNA methylation after PM2.5 exposure. Our study demonstrates that PM2.5 exposure influences m6A RNA methylation by inducing the alteration of the TGF-β signal pathway, which could be an essential mechanism for lung-related diseases induced by PM2.5 exposure.

Resveratrol mitigates miR-212-3p mediated progression of diesel exhaust-induced pulmonary fibrosis by regulating SIRT1/FoxO3

BACKGROUND

Diesel exhaust (DE) exposure contributes to the progression of chronic respiratory diseases and is associated with dysregulation of microRNA expression. The present study aims to investigate the involvement of miRNAs and target genes in DE-induced lung fibrosis.

METHODS

C57BL/6 mice were divided into three groups. Group 1 mice were exposed to filtered air (Control). Group 2 mice were exposed to DE for 30 min per day, 5 days per week, for 8 weeks (DE). Group 3 mice received DE exposure along with resveratrol on alternate days for the last 2 weeks (DE + RES). Mice were sacrificed to isolate RNA from lung tissue for miRNA microarray profiling. Bronchoalveolar lavage fluid and lung tissues were collected for cell count and biochemical analysis.

RESULTS

DE exposure resulted in differential expression of 28 miRNAs with fold change >2 (p < 0.05). The upregulated miR-212-3p was selected for further analysis. Consensus analysis revealed enrichment of SIRT1 in the FoxO pathway, along with a co-annotation of reduced body weight (p < 0.05). A549 cells transfected with a miR-212-3p inhibitor showed a dose-dependent increase in SIRT1 expression, indicating SIRT1 as a direct target. Treatment with resveratrol restored SIRT1 and miR-212-3p expression and led to a reduction in inflammatory cytokines (p < 0.05). The modulation of SIRT1 correlated negatively with macrophage infiltration, confirming its role in regulating cellular infiltration and lung inflammation. Fibronectin, alpha-SMA, and collagen levels were significantly decreased in DE + RES compared to DE group suggesting modulation of cellular functions and resolution of lung fibrosis. Furthermore, a significant decrease in FoxO3a and TGF-β gene expressions was observed upon resveratrol administration thereby downregulating pro-fibrotic pathway.

CONCLUSIONS

The present study demonstrates resveratrol treatment stabilizes SIRT1 gene expression by attenuating miR-212-3p in DE-exposed mice, leading to downregulation of TGF-β and FoxO3a expressions. The study highlights the therapeutic role of resveratrol in the treatment of DE-induced pulmonary fibrosis.

CXCL17 Attenuates Diesel Exhaust Emissions Exposure-Induced Lung Damage by Regulating Macrophage Function

Exposure to diesel exhaust emissions (DEE) is strongly linked to innate immune injury and lung injury, but the role of macrophage chemoattractant CXCL17 in the lung damage caused by DEE exposure remains unclear. In this study, whole-body plethysmography (WBP), inflammatory cell differential count, and histopathological analysis were performed to assess respiratory parameters, airway inflammation, and airway injury in C57BL/6 male mice exposed to DEE for 3 months. qRT-PCR, IHC (immunohistochemistry), and ELISA were performed to measure the CXCL17 expression in airway epithelium or BALF (bronchoalveolar lavage fluid) following DEE/Diesel exhaust particle (DEP) exposure. Respiratory parameters, airway inflammation, and airway injury were assessed in CXCL17-overexpressing mice through adeno-associated virus vector Type 5 (AAV5) infection. Additionally, an in vitro THP-1 and HBE co-culture system was constructed. Transwell assay was carried out to evaluate the effect of rh-CXCL17 (recombinant human protein-CXCL17) on THP-1 cell migration. Flow cytometry and qRT-PCR were conducted to assess the impacts of rh-CXCL17 on apoptosis and inflammation/remodeling of HBE cells. We found that the mice exposed to DEE showed abnormal respiratory parameters, accompanied by airway injury and remodeling (ciliary injury in airway epithelium, airway smooth muscle hyperplasia, and increased collagen deposition). Carbon content in airway macrophages (CCAM), but not the number of macrophages in BALF, increased significantly. CXCL17 expression significantly decreased in mice airways and HBE after DEE/DEP exposure. AAV5-CXCL17 enhanced macrophage recruitment and clearance of DEE in the lungs of mice, and it improved respiratory parameters, airway injury, and airway remodeling. In the THP-1/HBE co-culture system, rh-CXCL17 increased THP-1 cell migration while attenuating HBE cell apoptosis and inflammation/remodeling. Therefore, CXCL17 might attenuate DEE-induced lung damage by recruiting and activating pulmonary macrophages, which is expected to be a novel therapeutic target for DEE-associated lung diseases.

Diesel exhaust exposure impairs recovery of lung epithelial and cellular damage in murine model

Studies have investigated the relationship between diesel exhaust (DE) exposure and lung health, highlighting the potential for DE to induce pulmonary inflammation and oxidative stress. However, the resolution of inflammation upon withdrawal of DE exposure needs further investigation. Therefore, resolution of diesel exhaust-induced lung damage was studied in the murine model. Mice (6 weeks) were divided into three groups. Group 1 (control) mice were exposed to filtered air, Group 2 (DE) mice were exposed to DE (5.1 ± 0.7 mg/m³) & Group 3 (DE-FA) mice were exposed to DE followed by filtered air exposure. Airway hyper-responsiveness was recorded after 24 h of the last exposure. BALF and lung samples were collected for cytokine estimation, immunobiological assays, and western blot analysis. DE exposure showed an increase in lung resistance thereby causing alteration in lung function parameters (p < 0.05) which was restored in the DE-FA group. BALF analysis showed a significant increase in total cell count and protein content in DE with no resolution in DE-FA groups (p < 0.05). Lung histology showed no reduction in the bronchiolar thickness and damage in the DE-FA group suggesting irreversible lung damage (p < 0.05). The significant increase in inflammatory cytokine levels, and collagen deposition showed persistent inflammatory phase and lung damage in the DE-FA group(p < 0.05). ZO-1 was significantly decreased in both test groups indicating disintegrated lung epithelium where in claudin-5 expression showed increased lung permeability. A significant increase in neutrophil elastase activity and decreased expression of, Elafin, resulted in lung epithelial damage in the DE-FA group. Lung injury marker alpha1-antitrypsin was increased in DE-FA groups indicating an immune defense mechanism against neutrophil elastase. The study showed that DE exposure causes persistent lung damage via neutrophil elastase-associated disruption of the epithelial barrier integrity and membrane dysfunction.

Role of Human Aldo-Keto Reductases and Nuclear Factor Erythroid 2-Related Factor 2 in the Metabolic Activation of 1-Nitropyrene via Nitroreduction in Human Lung Cells

1-Nitropyrene (1-NP) is a constituent of diesel exhaust and classified as a group 2A probable human carcinogen. The metabolic activation of 1-NP by nitroreduction generates electrophiles that can covalently bind DNA to form mutations to contribute to cancer causation. NADPH-dependent P450 oxidoreductase (POR), xanthine oxidase (XO), aldehyde oxidase (AOX), and NAD(P)H/quinone oxidoreductase 1 (NQO1) may catalyze 1-NP nitroreduction. We recently found that human recombinant aldo-keto reductases (AKRs) 1C1-1C3 catalyze 1-NP nitroreduction. NQO1 and AKR1C1-1C3 are genes induced by nuclear factor erythroid 2-related factor 2 (NRF2). Despite this knowledge, the relative importance of these enzymes and NRF2 to 1-NP nitroreduction is unknown. We used a combination of pharmacological and genetic approaches to assess the relative importance of these enzymes and NRF2 in the aerobic nitroreduction of 1-NP in human bronchial epithelial cells, A549 and HBEC3-KT. 1-NP nitroreduction was assessed by the measurement of 1-aminopyrene (1-AP), the six-electron reduced metabolite of 1-NP, based on its intrinsic fluorescence properties (λex and λem). We found that co-treatment of 1-NP with salicylic acid, an AKR1C1 inhibitor, or ursodeoxycholate, an AKR1C2 inhibitor, for 48 h decreased 1-AP production relative to 1-NP treatment alone (control) in both cell lines. R-Sulforaphane or 1-(2-cyano-3,12,28-trioxooleana-1,9(11)-dien-28-yl)-1H-imidazole (CDDO-Im), two NRF2 activators, each increased 1-AP production relative to control only in HBEC3-KT cells, which have inducible NRF2. Inhibitors of POR, NQO1, and XO failed to modify 1-AP production relative to control in both cell lines. Importantly, A549 wild-type cells with constitutively active NRF2 produced more 1-AP than A549 cells with heterozygous expression of NFE2L2/NRF2, which were able to produce more 1-AP than A549 cells with homozygous knockout of NFE2L2/NRF2. Together, these data show dependence of 1-NP metabolic activation on AKR1Cs and NRF2 in human lung cells. This is the second example whereby NFE2L2/NRF2 is implicated in the carcinogenicity of diesel exhaust constituents.

3,3'-Diindolylmethane attenuates inflammation and fibrosis in radiation-induced lung injury by regulating NF-κB/TGF-β/Smad signaling pathways

OBJECTIVE

This study aims to investigate the protective effect of 3,3'-diindolylmethane (DIM) on the radiation-induced lung injury (RILI) model and to explore its possible mechanism. Methods: A mouse model of RILI was established by thoracic irradiation, and dexamethasone was used as a positive drug to investigate the effect of DIM on RILI mice. Lung histopathology was analyzed by HE staining and Masson staining. Then the levels of inflammatory cytokines (TGF-β, TNF-α, IL-1β, and IL-6), inflammatory cell counts, and activity of MPO were detected. The expression of TGFβ1/Smad signaling pathway-related proteins was determined by immunohistochemistry. qPCR was used to analyze the mRNA expression levels of inflammatory factors, α‑SMA and COL1A1. The expression of COX-2, NF-κB, IκBα, PI3K, and Akt proteins was assessed by Western blot. Results: Histopathological staining of lung tissues showed that DIM administration alleviated the pulmonary inflammation and fibrosis caused by RILI. Moreover, the content of inflammatory factors such as IL-1β and IL-6, the expression of NF-κB pathway-related proteins, and the counts of inflammatory cells were inhibited in lung tissue, indicating that DIM can inhibit the NF-κB pathway to reduce inflammation. In addition, DIM could down-regulate the mRNA levels of α-SMA, COL1A1, and downregulate TGFβ1, Smad3, and p-Smad2/3 in lung tissues. Conclusion: Our study confirms that DIM has the potential to treat RILI in vivo by inhibiting fibrotic and inflammatory responses in lung tissue through the TGFβ/Smad and NF-κB dual pathways, respectively.