Mitochondrial OGG1 protects against PM2.5-induced oxidative DNA damage in BEAS-2B cells

8-Oxoguanine DNA glycosylase protects cells from senescence via the p53-p21 pathway

Cellular senescence is an important factor leading to pulmonary fibrosis. Deficiency of 8-oxoguanine DNA glycosylase (OGG1) in mice leads to alleviation of bleomycin (BLM)-induced mouse pulmonary fibrosis, and inhibition of the OGG1 enzyme reduces the epithelial mesenchymal transition (EMT) in lung cells. In the present study, we find decreased expression of OGG1 in aged mice and BLM-induced cell senescence. In addition, a decrease in OGG1 expression results in cell senescence, such as increases in the percentage of SA-β-gal-positive cells, and in the p21 and p-H2AX protein levels in response to BLM in lung cells. Furthermore, OGG1 promotes cell transformation in A549 cells in the presence of BLM. We also find that OGG1 siRNA impedes cell cycle progression and inhibits the levels of telomerase reverse transcriptase (TERT) and LaminB1 in BLM-treated lung cells. The increase in OGG1 expression results in the opposite phenomenon. The mRNA levels of senescence-associated secretory phenotype (SASP) components, including IL-1α, IL-1β, IL-6, IL-8, CXCL1/CXCL2, and MMP-3, in the absence of OGG1 are obviously increased in A549 cells treated with BLM. Interestingly, we demonstrate that OGG1 binds to p53 to inhibit the activation of p53 and that silencing of p53 reverses the inhibition of OGG1 on senescence in lung cells. Additionally, the augmented cell senescence is shown in vivo in OGG1-deficient mice. Overall, we provide direct evidence in vivo and in vitro that OGG1 plays an important role in protecting tissue cells against aging associated with the p53 pathway.

Oxidative stress is the pivot for PM2.5-induced lung injury

Fine particulate matter (PM2.5) is a primary air pollutant recognized worldwide as a serious threat to public health. PM2.5, which has a diameter of less than 2.5 μm, is known to cause various diseases, including cardiovascular, respiratory, metabolic, and neurological diseases. Studies have shown that the respiratory system is particularly susceptible to PM2.5 as it is the first line of defense against external pollutants. PM2.5 can cause oxidative stress, which is triggered by the catalyzation of biochemical reactions, the activation of oxidases and metabolic enzymes, and mitochondrial dysfunction, all of which can lead to lung injury and aggravate various respiratory diseases including chronic obstructive pulmonary disease (COPD), asthma, pulmonary fibrosis, and cancer. Oxidative stress plays a crucial role in the harmful effects and mechanisms of PM2.5 on the respiratory system by activating several detrimental pathways related to inflammation and cellular damage. However, experimental studies have shown that antioxidative therapy methods can effectively cure PM2.5-induced lung injury. This review aims to clarify how PM2.5 induces oxidative stress and the mechanisms by which it is involved in the aggravation of various lung diseases. Additionally, we have listed antioxidant treatments to protect against PM2.5-induced lung injury.

PM2.5-derived exosomal long noncoding RNA PAET participates in childhood asthma by enhancing DNA damage via m6A-dependent OXPHOS regulation

Fine particulate matter (PM2.5) is known to enhance DNA damage levels and is involved in respiratory diseases. Exosomes can carry noncoding RNAs, especially long noncoding RNAs (lncRNAs), as regulators of DNA damage, which participate in diseases. However, their role in PM2.5-induced childhood asthma remains unclear. We performed RNA-seq to profile aberrantly expressed exosomal lncRNAs derived from PM2.5-treated human bronchial epithelial (HBE) cell models. The role of exosomal lncRNAs in childhood asthma was determined in a case-control study. The intercellular communication mechanisms of exosomal lncRNA on DNA damage were determined in vitro. Exosomes secreted by PM2.5-treated HBE cells (PM2.5-Exos) could increase the DNA damage levels of recipient HBE cells and promote the expression levels of airway remodeling-related markers in sensitive human bronchial smooth muscle cells (HBSMCs). LncRNA PM2.5-associated exosomal transcript (PAET) was highly expressed in PM2.5-Exos and was associated with PM2.5 exposure in childhood asthma. Mechanistically, exosomal lncRNA PAET promoted methyltransferase-like 3 (METTL3) accumulation by increasing its stability, which stimulated N6-methyladenosine (m6A) modification of cytochrome c oxidase subunit 4I1 (COX4I1), and COX4I1 levels were decreased in a mechanism dependent on the m6A "reader" YTH domain family 3 (YTHDF3). COX4I1 deficiency subsequently disrupted oxidative phosphorylation (OXPHOS), resulting in attenuated adenosine triphosphate (ATP) production and accumulation of reactive oxygen species (ROS), which increased DNA damage levels. This comprehensive study extends the understanding of PM2.5-induced childhood asthma via DNA damage and identifies exosomal lncRNA PAET as a potential target for childhood asthma.

Biological Impact of Organic Extracts from Urban-Air Particulate Matter: An In Vitro Study of Cytotoxic and Metabolic Effects in Lung Cells

Atmospheric particulate matter (PM) with diameters below 10 µm (PM10) may enter the lungs through inhalation and are linked to various negative health consequences. Emergent evidence emphasizes the significance of cell metabolism as a sensitive target of PM exposure. However, the current understanding of the relationship between PM composition, conventional toxicity measures, and the rewiring of intracellular metabolic processes remains limited. In this work, PM10 sampled at a residential area (urban background, UB) and a traffic-impacted location (roadside, RS) of a Portuguese city was comprehensively characterized in terms of polycyclic aromatic hydrocarbons and plasticizers. Epithelial lung cells (A549) were then exposed for 72 h to PM10 organic extracts and different biological outcomes were assessed. UB and RS PM10 extracts dose-dependently decreased cell viability, induced reactive oxygen species (ROS), decreased mitochondrial membrane potential, caused cell cycle arrest at the G0/G1 phase, and modulated the intracellular metabolic profile. Interestingly, the RS sample, richer in particularly toxic PAHs and plasticizers, had a greater metabolic impact than the UB extract. Changes comprised significant increases in glutathione, reflecting activation of antioxidant defences to counterbalance ROS production, together with increases in lactate, NAD+, and ATP, which suggest stimulation of glycolytic energy production, possibly to compensate for reduced mitochondrial activity. Furthermore, a number of other metabolic variations hinted at changes in membrane turnover and TCA cycle dynamics, which represent novel clues on potential PM10 biological effects.

The Effects and Pathogenesis of PM2.5 and Its Components on Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD), a heterogeneous disease, is the leading cause of death worldwide. In recent years, air pollution, especially particulate matter (PM), has been widely studied as a contributing factor to COPD. As an essential component of PM, PM2.5 is associated with COPD prevalence, morbidity, and acute exacerbations. However, the specific pathogenic mechanisms were still unclear and deserve further research. The diversity and complexity of PM2.5 components make it challenging to get its accurate effects and mechanisms for COPD. It has been determined that the most toxic PM2.5 components are metals, polycyclic aromatic hydrocarbons (PAHs), carbonaceous particles (CPs), and other organic compounds. PM2.5-induced cytokine release and oxidative stress are the main mechanisms reported leading to COPD. Nonnegligibly, the microorganism in PM 2.5 may directly cause mononuclear inflammation or break the microorganism balance contributing to the development and exacerbation of COPD. This review focuses on the pathophysiology and consequences of PM2.5 and its components on COPD.

Effect of Ethyl Acetate Fraction from Eucommia ulmoides Leaves on PM2.5-Induced Inflammation and Cognitive Dysfunction

This study aimed to evaluate the protective effect of the ethyl acetate from Eucommia ulmoides leaves (EFEL) on PM2.5-induced cognitive impairment in BALB/c mice. EFEL improved PM2.5-induced cognitive decline by improving spontaneous alternative behavioral and long-term memory ability. EFEL increased ferric reducing activity power (FRAP) in serum. In addition, EFEL increased superoxide dismutase (SOD) and reduced glutathione (GSH) contents and inhibited the production of malondialdehyde (MDA) in lung and brain tissues. EFEL also restored the mitochondrial function by regulating reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP) level, and ATP level in lung and brain tissues. EFEL ameliorated the cholinergic system by regulating the acetylcholine (ACh) content and acetylcholinesterase (AChE) activity in the brain tissue and the expression of AChE and choline acetyltransferase (ChAT) in the whole brain and hippocampal tissues. EFEL reduced PM2.5-induced excessive expression of inflammatory protein related to the lung, whole brain, olfactory bulb, and hippocampus. Physiological compounds of EFEL were identified as 5-O-caffeolyquinic acid, rutin, quercetin, and quercetin glycosides. As a result, EFEL has anti-inflammation and anti-amnesic effect on PM2.5-induced cognitive impairment by regulating the inflammation and inhibiting the lung and brain tissue dysfunction, and its effect is considered to be due to the physiological compounds of EFEL.

Study on Lung Injury Caused by Fine Particulate Matter and Intervention Effect of Rhodiola wallichiana

Objective

The objective of this study was to observe the protective effect of Rhodiola wallichiana drops in a rat model of fine particulate matter (PM2.5) lung injury.

Methods

Forty male Wistar rats were randomly divided into blank control (NC), normal saline (NS), PM2.5-infected (PM), and Rhodiola wallichiana (RW) groups. Rats in the NC group were not provided any interventions, whereas those in the NS and PM groups were administered normal saline and PM2.5 suspension by trachea drip once a week for four weeks. Rats in the RW group were intraperitoneally administered Rhodiola wallichiana for 14 days and then administered PM2.5 suspension by trachea drip 7 days after drug delivery. The levels of inflammatory factors such as interleukin-6, interleukin-1β, and tumor necrosis factor-alpha and oxidative stress biomarkers such as 8-hydroxy-2′-deoxyguanosine, 4-hydroxynonenal, and protein carbonyl content were determined in the serum and bronchoalveolar lavage fluid by ELISA. The level of 4-hydroxynonenal in the lung was also determined using Western blotting and immunohistochemical staining.

Results

Levels of inflammatory factors and oxidative stress biomarkers were all increased in the PM group but decreased in the RW group. Western blotting revealed increased 4-hydroxynonenal levels in the PM group but decreased levels in the RW group. Immunohistochemical staining also provided similar results.

Conclusion

Rhodiola wallichiana could protect rats from inflammation and oxidative stress injury caused by PM2.5.

Real-world PM2.5 exposure induces pathological injury and DNA damage associated with miRNAs and DNA methylation alteration in rat lungs

Fine particulate matter (PM_2.5) has been demonstrated to threaten public health and increase lung cancer risk. DNA damage is involved in the pathogenesis of lung cancer. However, the mechanisms of epigenetic modification of lung DNA damage are still unclear. This study developed a real-world air PM_2.5 inhalation system and exposed rats for 1 and 2 months, respectively, and investigated rat lungs pathological changes, inflammation, oxidative stress, and DNA damage effects. OGG1 and MTH1 expression was measured, along with their DNA methylation status and related miRNAs expression. The results showed that PM_2.5 exposure led to pathological injury, influenced levels of inflammatory cytokines and oxidative stress factors in rat lungs. Of note, 2-month PM_2.5 exposure aggravated pathological injury. Besides, PM_2.5 significantly elevated OGG1 expression and suppressed MTH1 expression, which was correlated to oxidative stress and partially mediated by reducing OGG1 DNA methylation status and increasing miRNAs expression related to MTH1 in DNA damage with increases of γ-H2AX, 8-OHdG and GADD153. PM_2.5 also activated c-fos and c-jun levels and inactivated PTEN levels in rat lungs. These suggested that epigenetic modification was probably a potential mechanism by which PM_2.5-induced genotoxicity in rat lungs.

The pathogenic effects of particulate matter on neurodegeneration: a review

The increasing amount of particulate matter (PM) in the ambient air is a pressing public health issue globally. Epidemiological studies involving data from millions of patients or volunteers have associated PM with increased risk of dementia and Alzheimer’s disease in the elderly and cognitive dysfunction and neurodegenerative pathology across all age groups, suggesting that PM may be a risk factor for neurodegenerative diseases. Neurodegenerative diseases affect an increasing population in this aging society, putting a heavy burden on economics and family. Therefore, understanding the mechanism by which PM contributes to neurodegeneration is essential to develop effective interventions. Evidence in human and animal studies suggested that PM induced neurodenegerative-like pathology including neurotoxicity, neuroinflammation, oxidative stress, and damage in blood–brain barrier and neurovascular units, which may contribute to the increased risk of neurodegeneration. Interestingly, antagonizing oxidative stress alleviated the neurotoxicity of PM, which may underlie the essential role of oxidative stress in PM’s potential effect in neurodegeneration. This review summarized up-to-date epidemiological and experimental studies on the pathogenic role of PM in neurodegenerative diseases and discussed the possible underlying mechanisms.

Targeting mitochondrial permeability transition pore ameliorates PM2.5-induced mitochondrial dysfunction in airway epithelial cells

Particulate matter with aerodynamic diameter not larger than 2.5 μm (PM_2.5) escalated the risk of respiratory diseases. Mitochondrial dysfunction may play a pivotal role in PM_2.5-induced airway injury. However, the potential effect of PM_2.5 on mitochondrial permeability transition pore (mPTP)-related airway injury is still unknown. This study aimed to investigate the role of mPTP in PM_2.5-induced mitochondrial dysfunction in airway epithelial cells in vitro. PM_2.5 significantly reduced cell viability and caused apoptosis in BEAS-2B cells. We also found PM_2.5 caused cellular and mitochondrial morphological alterations, evidenced by the disappearance of mitochondrial cristae, mitochondrial swelling, and the rupture of the outer mitochondrial membrane. PM_2.5 induced mPTP opening via upregulation of voltage-dependent anion-selective channel (VDAC), leading to deprivation of mitochondrial membrane potential, increased mitochondrial reactive oxygen species (ROS) generation and intracellular calcium level. PM_2.5 suppressed mitochondrial respiratory function by reducing basal and maximal respiration, and ATP production. The mPTP targeting compounds cyclosporin A [CsA; a potent inhibitor of cyclophilin D (CypD)] and VBIT-12 (a selective VDAC1 inhibitor) significantly inhibited PM_2.5-induced mPTP opening and apoptosis, and preserved mitochondrial function by restoring mitochondrial membrane potential, reducing mitochondrial ROS generation and intracellular calcium content, and maintaining mitochondrial respiration function. Our data further demonstrated that PM_2.5 caused reduction in nuclear expressions of PPARγ and PGC-1α, which were reversed in the presence of CsA. These findings suggest that mPTP might be a potential therapeutic target in the treatment of PM_2.5-induced airway injury.

Biomarkers for the adverse effects on respiratory system health associated with atmospheric particulate matter exposure

Large amounts of epidemiological evidence have confirmed the atmospheric particulate matter (PM_2.5) exposure was positively correlated with the morbidity and mortality of respiratory diseases. Nevertheless, its pathogenesis remains incompletely understood, probably resulting from the activation of oxidative stress, inflammation, altered genetic and epigenetic modifications in the lung upon PM_2.5 exposure. Currently, biomarker investigations have been widely used in epidemiological and toxicological studies, which may help in understanding the biologic mechanisms underlying PM_2.5-elicited adverse health outcomes. Here, the emerging biomarkers to indicate PM_2.5-respiratory system interactions were summarized, primarily related to oxidative stress (ROS, MDA, GSH, etc.), inflammation (Interleukins, FE_NO, CC16, etc.), DNA damage (8-OHdG, γH2AX, OGG1) and also epigenetic modulation (DNA methylation, histone modification, microRNAs). The identified biomarkers shed light on PM_2.5-elicited inflammation, fibrogenesis and carcinogenesis, thus may favor more precise interventions in public health. It is worth noting that some inconsistent findings may possibly relate to the inter-study differentials in the airborne PM_2.5 sample, exposure mode and targeted subjects, as well as methodological issues. Further research, particularly by -omics technique to identify novel, specific biomarkers, is warranted to illuminate the causal relationship between PM_2.5 pollution and deleterious lung outcomes.

Real-world particulate matters induce lung toxicity in rats fed with a high-fat diet: Evidence of histone modifications

Exposure to ambient particulate matters (PMs) has been associated with a variety of lung diseases, and high-fat diet (HFD) was reported to exacerbate PM-induced lung dysfunction. However, the underlying mechanisms for the combined effects of HFD and PM on lung functions remain poorly unraveled. By performing a comparative proteomic analysis, the current study investigated the global changes of histone post-translational modifications (PTMs) in rat lung exposed to long-term, real-world PMs. In result, after PM exposure the abundance of four individual histone PTMs (1 down-regulated and 3 up-regulated) and six combinatorial PTMs (1 down-regulated and 5 up-regulated) were significantly altered in HFD-fed rats while only one individual PTM was changed in rats with normal diet (ND) feeding. Histones H3K18ac, H4K8ac and H4K12ac were reported to be associated with DNA damage response, and we found that these PTMs were enhanced by PM in HFD-fed rats. Together with the elevated DNA damage levels in rat lungs following PM and HFD co-exposure, we demonstrate that PM exposure combined with HFD could induce lung injury through altering more histone modifications accompanied by DNA damage. Overall, these findings will augment our knowledge of the epigenetic mechanisms for pulmonary toxicity caused by ambient PM and HFD exposure.

Toxicity of Water- and Organic-Soluble Wood Tar Fractions from Biomass Burning in Lung Epithelial Cells

Widespread smoke from wildfires and biomass burning contributes to air pollution and the deterioration of air quality and human health. A common and major emission of biomass burning, often found in collected smoke particles, is spherical wood tar particles, also known as "tar balls". However, the toxicity of wood tar particles and the mechanisms that govern their health impacts and the impact of their complicated chemical matrix are not fully elucidated. To address these questions, we generated wood tar material from wood pyrolysis and isolated two main subfractions: water-soluble and organic-soluble fractions. The chemical characteristics as well as the cytotoxicity, oxidative damage, and DNA damage mechanisms were investigated after exposure of A549 and BEAS-2B lung epithelial cells to wood tar. Our results suggest that both wood tar subfractions reduce cell viability in exposed lung cells; however, these fractions have different modes of action that are related to their physicochemical properties. Exposure to the water-soluble wood tar fraction increased total reactive oxygen species production in the cells, decreased mitochondrial membrane potential (MMP), and induced oxidative damage and cell death, probably through apoptosis. Exposure to the organic-soluble fraction increased superoxide anion production, with a sharp decrease in MMP. DNA damage is a significant process that may explain the course of toxicity of the organic-soluble fraction. For both subfractions, exposure caused cell cycle alterations in the G2/M phase that were induced by upregulation of p21 and p16. Collectively, both subfractions of wood tar are toxic. The water-soluble fraction contains chemicals (such as phenolic compounds) that induce a strong oxidative stress response and penetrate living cells more easily. The organic-soluble fraction contained more polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs and induced genotoxic processes, such as DNA damage.

REDD1 (regulated in development and DNA damage-1)/autophagy inhibition ameliorates fine particulate matter (PM2.5) -induced inflammation and apoptosis in BEAS-2B cells

This study aimed to investigate the implication of REDD1 on airborne particle matter-induced lung injury and whether it is mediated through autophagy. Cell viability in BEAS-2B cells induced by PM2.5 was measured by CCK-8. RT-qPCR and Western blot were performed to determine mRNA and protein levels of REDD1 as well as inflammatory cytokines, respectively. Cell apoptosis was observed with TUNEL staining. The expression of autophagy-related genes was detected by Western blot. Autophagy level was observed with GFP-LC3 staining. PM2.5 induced the expression of REDD1 in BEAS-2B cells. The inhibition by silencing REDD1 ameliorated the viability damage, blocked the inflammatory response and reduced the number of apoptotic BEAS-2B cells all induced by PM2.5. It was also found that PM2.5 induced autophagy in BEAS-2B cells, which was reversed by interference with REDD1. Furthermore, interference with REDD1 alleviated PM2.5-induced cell damage, inflammatory response and apoptosis in BEAS-2B cells through inhibiting autophagy. REDD1/autophagy inhibition ameliorates PM2.5-induced viability damage, inflammation and apoptosis in BEAS-2B cells.

Expression patterns of peroxiredoxin genes in bronchial epithelial cells exposed to diesel exhaust particles

Several mechanisms have been suggested to explain the adverse effects of air pollutants on airway cells. One such explanation is the presence of high concentrations of oxidants and pro-oxidants in environmental pollutants. All animal and plant cells have developed several mechanisms to prevent damage by oxidative molecules. Among these, the peroxiredoxins (PRDXs) are of interest due to a high reactivity with reactive oxygen species (ROS) through the functioning of the thioredoxin/thioredoxin reductase system. This study aimed to verify the gene expression patterns of the PRDX family in bronchial epithelial airway cells (BEAS-2B) cells exposed to diesel exhaust particles (DEPs) at a concentration of 15 μg/mL for 1 or 2 h because this it is a major component of particulate matter in the atmosphere. There was a significant decrease in mRNA fold changes of PRDX2 (0.43 ± 0.34; *p = 0.0220), PRDX5 (0.43 ± 0.34; *p = 0.0220), and PRDX6 (0.33 ± 0.25; *p = 0.0069) after 1 h of exposure to DEPs. The reduction in mRNA levels may consequently lead to a decrease in the levels of PRDX proteins, increasing oxidative stress in bronchial epithelial cells BEAS-2B and thus, negatively affecting cellular functions.

DNA repair enzyme OGG1 promotes alveolar progenitor cell renewal and relieves PM2.5-induced lung injury and fibrosis

Fine particulate matter (PM2.5) airborne pollution increases the risk of chronic respiratory diseases, such as idiopathic pulmonary fibrosis (IPF), which is characterized by non-specific inflammation of the interstitial lung and extensive deposition of collagen fibers. Type 2 alveolar epithelial cells (AEC2s) are alveolar stem cells in the adult lung that contribute to the lung repair process through complex signaling. Our previous studies demonstrated that OGG1, a kind of DNA repair enzyme, have a critical role in protecting cells from oxidative damage and apoptosis induced by PM2.5, but the contribution of OGG1 in proliferation and self-renewal of AEC2s is not known. Here, we constructed OGG1^-/-mice to test the effect and mechanism of OGG1 on PM2.5-induced pulmonary fibrosis and injury in vivo. We detected proliferation and self-renewal of OGG1 overexpression or OGG1 knockout AEC2s after PM2.5 injury by flow cytometry and clone formation. We observed that knockout of OGG1 aggravated pulmonary fibrosis, oxidative stress, and AEC2 cell death in PM2.5-injured mice. In addition, OGG1 is required for the proliferation and renewal of AEC2s after PM2.5 injury. Overexpression of OGG1 promotes the proliferation and self-renewal of AEC2s by inhibiting PM2.5-mediated oxidative stress and NF-κB signaling hyperactivation in vitro. Furthermore, NF-κB inhibitors promoted proliferation and self-renewal of OGG1-deficient AEC2s cells after PM2.5 injury, and attenuated PM2.5-induced pulmonary fibrosis and injury in mice. These data establish OGG1 as a regulator of NF-κB signal that serves to regulate AEC2 cell proliferation and self-renewal, and suggest a mechanism that inhibition of the NF-κB signaling pathway may represent a potential therapeutic strategy for IPF patients with low-expression of OGG1.

PM2.5 triggered apoptosis in lung epithelial cells through the mitochondrial apoptotic way mediated by a ROS-DRP1-mitochondrial fission axis

Epidemiological studies revealed a sharp increase in respiratory diseases attributed to PM_2.5. However, the underlying mechanisms remain unclear. Evidence suggested mitochondrion as a sensitive target upon the stimulus of PM_2.5, and the centrality in the pathological processes and clinical characterization of lung diseases. To investigate cell fate and related mechanisms caused by PM_2.5, we exposed human lung epithelial cells (BEAS-2B) to PM_2.5 (0-100 μg/mL). Consequently, PM_2.5 components were found in cytoplasm, and morphological and functional alterations in mitochondria occurred, as evidenced by loss of cristae, vacuolization and even the outer mitochondrial membrane rupture, mitochondrial membrane potential collapse, enhanced reactive oxygen species (ROS)/mtROS level, calcium overload, suppressed cellular respiration and ATP production in PM_2.5-treated cells. Further, disturbed dynamics toward fission was clearly observed in PM_2.5-treated mitochondria, associated with DRP1 mitochondrial translocation and phosphorylation. Besides, PM_2.5 induced mitochondria-mediated apoptosis. More importantly, mechanistic results revealed ROS- and DRP1-mediated mitochondrial fission in a reciprocal way, and DRP1 inhibitor (Mdivi-1) significantly alleviated the pro-apoptotic effect of PM_2.5 through reversing the activated mitochondrial apoptotic pathway. In summary, our results firstly revealed PM_2.5 induced apoptosis in lung epithelial cells through a ROS-DRP1-mitochodrial fission axis-mediated mitochondrial apoptotic pathway, ultimately contributing to the onset and development of pulmonary diseases.

Small GTPase RAB6 deficiency promotes alveolar progenitor cell renewal and attenuates PM2.5-induced lung injury and fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease characterized by chronic non-specific inflammation of the interstitial lung and extensive deposition of collagen fibers leading to destruction of lung function. Studies have demonstrated that exposure to fine particulate matter (PM2.5) increases the risk of IPF. In order to recover from PM2.5-induced lung injury, alveolar epithelial cells need to be repaired and regenerated to maintain lung function. Type 2 alveolar epithelial cells (AEC2) are stem cells in the adult lung that contribute to the lung repair process through complex signaling. Our previous studies demonstrated that RAB6, a RAS family member lowly expressed in lung cancer, inhibited lung cancer stem cell self-renewal, but it is unclear whether or not and how RAB6 may regulate AEC2 cell proliferation and self-renewal in PM2.5-induced pulmonary fibrosis. Here, we demonstrated that knockout of RAB6 inhibited pulmonary fibrosis, oxidative stress, and AEC2 cell death in PM2.5-injured mice. In addition, knockout of RAB6 decreased Dickkopf 1(DKK1) autocrine and activated proliferation, self-renewal, and wnt/β-catenin signaling of PM2.5-injured AEC2 cells. RAB6 overexpression increased DKK1 autocrine and inhibited proliferation, self-renewal and wnt/β-catenin signaling in AEC2 cells in vitro. Furthermore, DKK1 inhibitors promoted proliferation, self-renewal and wnt/β-catenin signaling of RAB6 overexpressing AEC2 cells, and attenuated PM2.5-induced pulmonary fibrosis in mice. These data establish RAB6 as a regulator of DKK1 autocrine and wnt/β-catenin signal that serves to regulate AEC2 cell proliferation and self-renewal, and suggest a mechanism that RAB6 disruption may promote AEC2 cell proliferation and self-renewal to enhance lung repair following PM2.5 injury.

Amelioration of PM2.5-induced lung toxicity in rats by nutritional supplementation with biochanin A

Epidemiological studies have shown that particulate matter with an aerodynamic diameter less than 2.5 μm (PM_2.5) is closely associated with human health issues, especially pulmonary diseases such as chronic obstructive pulmonary disease (COPD), asthma and lung cancer. In this study, particles were characterized by scanning electron microscopy (SEM), microbeam energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography (HPLC). A rat model of PM_2.5 exposure was established by nonsurgical intratracheal instillation, and the effects of biochanin A (BCA) treatment were examined. BCA showed a protective effect; it reduced PM_2.5-induced apoptosis and the production of proinflammatory factors, such as tumor necrosis factor-α (TNF-α), interleukin-2 (IL-2), interleukin-6 (IL-6), and the chemokine interleukin-8 (IL-8), as measured using ELISA. These effects were accompanied by increases in the levels of antioxidant enzymes and decreases in the levels of malondialdehyde (MDA), lactate dehydrogenase (LDH) and alkaline phosphatase (AKP). Furthermore, isobaric tag for relative and absolute quantitation (iTRAQ)-based analytical techniques and bioinformatics tools were used to identify putative biomarkers, including XRCC1, MP2K5, IGJ, and F1LQ12, and the results were verified by Western blot analysis. In conclusion, our findings have scientific significance for the application of flavonoids in preventive and therapeutic strategies for PM_2.5-associated pulmonary diseases and for the promotion of human health.

Urban particulate matter disturbs the equilibrium of mitochondrial dynamics and biogenesis in human vascular endothelial cells

Since ambient particulate matter (APM) is closely related to cardiovascular damage with mitochondria being its potential targets, this study was designed to explore the impact of APM on mitochondrial homeostasis, especially on mitochondrial dynamics and biogenesis in human vascular endothelial cells, using a kind of standard material, PM SRM1648a. As a result, internalized particles lead to mitochondrial dysfunction in EA.hy926 human endothelial cells, including mitochondrial reactive oxygen species (mtROS) overproduction, mitochondrial membrane potential (MMP) reduction and adenosine triphosphate (ATP) inhibition, coupled with additional release of mitochondrial DNA (mtDNA) into the cytosol. Moreover, morphological and structural changes in mitochondria are observed in response to PM SRM1648a. In that aspect, according to the evidence of shorter fragmented mitochondria dispersed throughout the cytoplasm, along with aberrant upregulation of fission-related mRNAs/proteins, the mitochondria exhibit a fission phenotype shifting from intact reticular network to fragmentized punctate shapes. Mechanistically, PM SRM1648a facilitates phosphorylation of DRP1 at Ser616 in HUVECs, and triggers its dephosphorylation at Ser637 residue in both EA.hy926 and HUVECs, which are supportive events for mitochondrial fission during particle exposure. Additionally, suppression of a master energy modulator, PGC-1α, reveals that PM SRM1648a has the ability to impair mitochondrial biogenesis. Collectively, it could be well concluded that PM SRM1648a interferes with the equilibrium of mitochondrial dynamics and biogenesis, which is likely to play a pivotal role in mitochondrial dysfunction driven by particles, eventually contributing to endothelial cell damage. Of note, it is more reasonable to conduct risk assessment from both cellular level and subcellular structures, among which mitochondria-targeted toxicity supplements more comprehensive understanding of APM inducible vascular toxicity.

8-Oxoguanine DNA glycosylase modulates the cell transformation process in pulmonary fibrosis by inhibiting Smad2/3 and interacting with Smad7

The DNA repair enzyme 8-oxoguanine DNA glycosylase-1 (OGG1) is involved in early embryonic development, as well as in multiple conditions, including cardiac fibrosis, diabetes, and neurodegenerative diseases. But, function of OGG1 in pulmonary fibrosis was not entirely clear. In this study, we identified a novel function of OGG1 in the cell transformation process in pulmonary fibrosis. We demonstrated that OGG1 and Smad7 co-localize and interact in A549 cells. Bleomycin-induced pulmonary fibrosis was established in wild-type (WT) and Ogg1^-/- mice. Upon treatment with transforming growth factor (TGF)-β1, increased OGG1 expression was observed in WT mice with pulmonary fibrosis as well as in A549 cells, MRC-5 cells, and primary rat type II alveolar epithelial cells. The increased expression of OGG1 promoted cell migration, while OGG1 depletion decreased migration ability. Expression of the transformation-associated markers vimentin and alpha-smooth muscle actin were also affected by OGG1. We also observed that OGG1 promoted TGF-β1-induced cell transformation and activated Smad2/3 by interacting with Smad7. The interaction between OGG1 and the TGF-β/Smad axis modulates the cell transformation process in lung epithelial cells and fibroblasts. Moreover, we demonstrated that Ogg1 deficiency relieved pulmonary fibrosis in bleomycin-treated mice. Ogg1 knockout decreased the bleomycin-induced expression of Smad7 and phosphorylation of Smad2/3 in mice. These findings suggest that OGG1 has multiple biological functions in the pathogenesis of pulmonary fibrosis.

Oxidative stress activates the TRPM2-Ca2+-NLRP3 axis to promote PM2.5-induced lung injury of mice

PM_2.5, a main particulate air pollutant, poses a serious hazard to human health. The exposure to PM_2.5 increases mortality and morbidity of many respiratory diseases such as asthma, chronic obstructive pulmonary diseases and even lung cancer. The contribution of reactive oxygen species (ROS) in the PM_2.5-induced acute lung injury process was confirmed in our previous research, but the molecular mechanism based for it remains unclarified. In this research, ROS-induced lung injury after exposure to PM_2.5 was explored in vivo and in vitro. The in vivo study indicated that N-acetyl-L-cysteine (NAC) could attenuate the accumulation of inflammatory cells, the thickening of alveolar wall and the degree of lung injury. Furthermore, we found ROS could regulate the intracellular Ca²⁺ level, expression of the Transient Receptor Potential Melastatin 2 (TRPM2), NLRP3 and its downstream inflammatory factors in vivo. In vitro experiments with A549 cells and primary type II alveolar epithelium cells (SD cells) showed that ROS induced by PM_2.5 exposure could mediate intracellular Ca²⁺ mobilization via TRPM2, with a subsequent activation of NLRP3. In our present study, we demonstrated the contribution of the ROS-TRPM2-Ca²⁺-NLRP3 pathway in PM_2.5-induced acute lung injury and offered a potential therapeutical target valid for related pathology.

Effects of DNA Damage and Oxidative Stress in Human Bronchial Epithelial Cells Exposed to PM2.5 from Beijing, China, in Winter

Epidemiological studies have corroborated that respiratory diseases, including lung cancer, are related to fine particulate matter (<2.5 μm) (PM_2.5) exposure. The toxic responses of PM_2.5 are greatly influenced by the source of PM_2.5. However, the effects of PM_2.5 from Beijing on bronchial genotoxicity are scarce. In the present study, PM_2.5 from Beijing was sampled and applied in vitro to investigate its genotoxicity and the mechanisms behind it. Human bronchial epithelial cells 16HBE were used as a model for exposure. Low (67.5 μg/mL), medium (116.9 μg/mL), and high (202.5 μg/mL) doses of PM_2.5 were used for cell exposure. After PM_2.5 exposure, cell viability, oxidative stress markers, DNA (deoxyribonucleic acid) strand breaks, 8-OH-dG levels, micronuclei formation, and DNA repair gene expression were measured. The results showed that PM_2.5 significantly induced cytotoxicity in 16HBE. Moreover, the levels of reactive oxygen species (ROS), malondialdehyde (MDA), and cellular heme oxygenase (HO-1) were increased, and the level of glutathione (GSH) was decreased, which represented the occurrence of severe oxidative stress in 16HBE. The micronucleus rate was elevated, and DNA damage occurred as indicators of the comet assay, γ-H2AX and 8-OH-dG, were markedly enhanced by PM_2.5, accompanied by the influence of 8-oxoguanine DNA glycosylase (OGG1), X-ray repair cross-complementing gene 1 (XRCC1), and poly (ADP-ribose) polymerase-1 (PARP1) expression. These results support the significant role of PM_2.5 genotoxicity in 16HBE cells, which may occur through the combined effect on oxidative stress and the influence of DNA repair genes.

Screening of X-ray responsive substances for the next generation of radiosensitizers

X-ray responsivity resulting in the generation of reactive oxygen species (ROS) was investigated in 9600 organic compounds that were selected by considering their structural diversity. We focused on superoxides that were primarily detected using dihydroethidium (DHE) and hydroxyl radicals, that were identified fluorometrically using 3'-(p-aminophenyl) Fluorescein (APF). Many organic compounds were discovered that responded to the DHE and/or APF assay using X-ray irradiation. These results suggest that some of these organic compounds emit either superoxides or hydroxyl radicals whereas others emit both under the influence of X-ray irradiation. The response of the derivatives of a hit compound with a partial change in the structure was also investigated. The products produced from DHE by X-ray irradiation were identified by HPLC to confirm the integrity of the process. Although, the reactions were suppressed by the superoxide dismutase (SOD), not only 2-hydroxyethidium (2-OH-E⁺), but also ethidium (E⁺) were detected. The results suggest that apart from a direct reaction, an indirect reaction may occur between DHE and the superoxides. Although X-ray responsiveness could not be inferred due to the molecular complexity of the investigated compounds, delineation of these reactions will facilitate the development of the next generation of radiosensitizers.

Enhanced Mitochondrial DNA Repair Resuscitates Transplantable Lungs Donated After Circulatory Death

BACKGROUND

Transplantation of lungs procured after donation after circulatory death (DCD) is challenging because postmortem metabolic degradation may engender susceptibility to ischemia-reperfusion (IR) injury. Because oxidative mitochondrial DNA (mtDNA) damage has been linked to endothelial barrier disruption in other models of IR injury, here we used a fusion protein construct targeting the DNA repair 8-oxoguanine DNA glycosylase-1 (OGG1) to mitochondria (mtOGG1) to determine if enhanced repair of mtDNA damage attenuates endothelial barrier dysfunction after IR injury in a rat model of lung procurement after DCD.

MATERIALS AND METHODS

Lungs excised from donor rats 1 h after cardiac death were cold stored for 2 h after which they were perfused ex vivo in the absence and presence of mt-OGG1 or an inactive mt-OGG1 mutant. Lung endothelial barrier function and mtDNA integrity were determined during and at the end of perfusion, respectively.

RESULTS AND CONCLUSIONS

Mitochondria-targeted OGG1 attenuated indices of lung endothelial dysfunction incurred after a 1h post-mortem period. Oxidative lung tissue mtDNA damage as well as accumulation of proinflammatory mtDNA fragments in lung perfusate, but not nuclear DNA fragments, also were reduced by mitochondria-targeted OGG1. A repair-deficient mt-OGG1 mutant failed to protect lungs from the adverse effects of DCD procurement.

CONCLUSIONS

These findings suggest that endothelial barrier dysfunction in lungs procured after DCD is driven by mtDNA damage and point to strategies to enhance mtDNA repair in concert with EVLP as a means of alleviating DCD-related lung IR injury.

Nrf2 protects against diverse PM2.5 components-induced mitochondrial oxidative damage in lung cells

Nrf2 is an important transcription factor implicated in the oxidative stress response, which has been reported to play an important role in the way by which air pollution particulate matter (PM_2.5) induces adverse health effects. This study investigates the mechanism by which Nrf2 exerts its protective effect in PM_2.5 induced toxicity in lung cells. Lung cells silenced for Nrf2 (shNrf2) demonstrated diverse susceptibility to various PM extracts; water extracts containing high levels of dissolved metals exhibited higher capacity to generate mitochondrial reactive oxygen species (ROS) and hence increased oxidative stress levels. Organic extracts containing high levels of polycyclic aromatic hydrocarbons (PAHs) increased mortality and reduced ROS production in the silenced cells. shNrf2 cells exhibited a higher basal mitochondrial respiration rate compared to the control cells. Following exposure to water extracts, the mitochondrial respiration increased, which was not observed with the organic extracts. shNrf2 cells exposed to the organic extracts showed lower mitochondrial membrane potential and lower mtDNA copy number. Nrf2 may act as a signaling mediator for the mitochondria function following PM_2.5 exposure.

Ambient PM2.5 causes lung injuries and coupled energy metabolic disorder

Ambient fine particulate matter (PM_2.5) is a challenge to public health worldwide. Although increasing numbers of recent epidemiological studies have emphasized the critical role of PM_2.5 in promoting respiratory diseases, the precise mechanism behind PM_2.5-mediated lung obstruction remains obscure. In the present study, we analyzed lung structure and function and further investigated mitochondrial morphology and transcription-modulated energy metabolism in mice following PM_2.5 aspiration. The results showed that PM_2.5 exposure reduced pulmonary function and induced severe pathological alterations, including alveolar endothelial disruption and airway obstruction. Based on ultrastructural observations, we also found mitochondrial vacuolation and mitochondrial membrane rupture in alveolar type II epithelial cells. Importantly, the abnormality of mitochondrial structure was coupled with energy metabolism disorders, as evidenced by the decrease in ATP levels, the accumulation of pyruvate and lactate content, and the altered transcription of related genes. Moreover, the reduction in mitochondrial markers, including PGC-1α, NRF-1, and TFAM, were involved in mitochondrial dysfunction. These findings suggest that energy metabolic disorders and mitochondrial dysfunction may be the important contributors to pulmonary injuries in response to PM_2.5 exposure, indicating possible targets for protection and therapy in polluted areas.

Fine particulate matter induces mitochondrial dysfunction and oxidative stress in human SH-SY5Y cells

Exposure to ambient fine particulate matter (PM_2.5) is associated with neurodegenerative diseases. Mitochondrion is key to brain degeneration. However, the underlying mechanism of PM_2.5-induced brain injury, especially mitochondrial damage, is still unclear. In this study, changes in mitochondrial dynamics, mitochondrial permeability transition pore (mPTP), mitochondrial DNA (mtDNA) and oxidative stress in human SH-SY5Y cells exposed to PM_2.5 at different concentrations (0, 25, 100, and 250 μg mL^-1) were investigated. The results showed that PM_2.5 caused more mitochondrial swell, accompanied by the opening of mPTP and the decrease of ATP levels, mitochondrial membrane potential and mtDNA copy number in SH-SY5Y cells. PM_2.5 significantly enhanced the expression of mitochondrial fission/fusion genes (Drp1 and OPA1) and affected the gene expression of CypD, SIRT3, and COX Ⅳ in SH-SY5Y cells. Besides, PM_2.5 triggered the increase of cellular ROS, Ca²⁺ and Aβ-42 levels, inhibition of manganese-superoxide dismutase (SOD₂) activities, reduction of GSH levels GSH/GSSG ratio, and elevation of mitochondrial malondialdehyde contents. It suggests that mitochondrial dysfunction and oxidative stress are the potential mechanisms underlying PM_2.5-induced brain nerve cell injury, which may be related to neurological diseases. Additionally, our study elucidated that PM_2.5 components trigger different cytotoxicity.

Role and underlying mechanism of SPATA12 in oxidative damage

Spermatogenesis-associated gene 12 (SPATA12) functions as an inhibitor in spermatogenesis and tumorigenesis. Our previous study demonstrated that SPATA12 may be induced in tumor cells by ultraviolet (UV) C-mediated DNA damage, suggesting its importance in maintaining genomic integrity. In order to understand whether and how SPATA12 responds to oxidative damage, the present study established a cellular model of oxidative stress by detecting the effect of H₂O₂ on cell viability and intracellular superoxide dismutase activity, and the levels of glutathione and malondialdehyde (MDA). Quantitative polymerase chain reaction results demonstrated that H₂O₂ upregulated the expression of SPATA12, and a dual luciferase reporter gene assay indicated that transcription factor activator protein-1 (AP-1) was involved in the response of SPATA12 to oxidative stress. Through the exogenous expression of SPATA12, it was identified that SPATA12 decreased the level of reactive oxygen species and MDA, and also may reduce the degree of cellular oxidative damage and apoptosis induced by H₂O₂. In addition, resveratrol was demonstrated to increase the expression of SPATA12 by activating AP-1, and it may be used as a nontoxic activator of the SPATA12 gene. In conclusion, these results suggest that SPATA12 is upregulated by oxidative stress via AP-1, and that the exogenous expression of SPATA12 protects against H₂O₂-induced oxidative damage and apoptosis.

Flavone protects HBE cells from DNA double-strand breaks caused by PM2.5

Ambient air particulate matter 2.5 (PM2.5) contains many harmful components that can enter the circulatory system and produce reactive oxygen species (ROS) in body. Oxidative stress and DNA damage induced by ROS may affect any cellular macromolecule and lead to DNA double-strand breaks (DSBs). Flavonoids, widely distributed in some herbs and berries, have been proved having anti-oxidative or anti-cancer efficacy. In this study, we investigated whether Flavone, a kind of flavonoids, can protect human bronchial epithelial cells (HBE) from DSBs caused by PM2.5 and how this function is probably implemented. We found that cells exposed to PM2.5 obviously induced viability inhibition, DNA damage and part of apoptosis. However, Flavone treatment prior to PM2.5 apparently improved cell viability, and mitigated the formation of 8-hydroxy-2-deoxyguanosine, the expression of DNA damage-relative protein and cell apoptosis. Our studies demonstrated that PM2.5 induced oxidative DSBs while Flavone ameliorated the DNA damage and increased cell viability probably through influencing DNA repair mechanism of cells.

Effects of ambient PM2.5 and 9-nitroanthracene on DNA damage and repair, oxidative stress and metabolic enzymes in the lungs of rats

Ambient fine particulate matter (PM2.5) is a complex mixture associated with lung cancer risk. PM2.5-bound nitro-polycyclic aromatic hydrocarbons (NPAHs) have been demonstrated to possess mutagenicity and carcinogenicity. Previous studies showed that PM2.5 induced DNA damage, whereas there is little knowledge of whether 9-nitroanthracene (9-NA), a typical compound of NPAHs in PM2.5, causes DNA damage. Also, the regulating mechanisms of PM2.5 and 9-NA in DNA damage and repair are not yet fully established. Here we sought to investigate the molecular mechanisms of DNA damage and repair in the lungs of male Wistar rats exposed to PM2.5 (1.5 mg per kg body weight) or three different dosages of 9-NA. And then DNA strand breaks, 8-OH-dG formation, DNA-protein crosslink and DNA repair gene expressions in rat lungs were analyzed. In addition, alteration in oxidative stress factors and metabolic enzymes were detected. The results showed that (1) PM2.5 and higher dosage 9-NA (4.0 × 10-5 and 1.2 × 10-4 mg per kg body weight) significantly caused lung DNA damage, accompanied by increasing OGG1 expression while inhibiting MTH1 and XRCC1 expression, elevating the levels of GADD153, hemeoxygenase-1 and malondialdehyde, and promoting the activities of CYP450 isozymes and glutathione S-transferase. (2) 1.3 × 10-5 mg kg-1 9-NA exposure couldn't cause DNA damage and oxidative stress. (3) At the approximately equivalent dose level, PM2.5-induced DNA damage effects were more obvious than 9-NA with positive correlation. It suggests that DNA damage caused by PM2.5 and 9-NA may be mediated partially through influencing the DNA repair capacity and enhancing oxidative stress and biotransformation, and this negative effect of 9-NA might be related to the PM2.5-induced lung genotoxicity.

Analysis of the miRNA-mRNA networks in malignant transformation BEAS-2B cells induced by alpha-particles

The aim of this study was to determine the toxicity induced by irradiation with alpha-particles on malignant transformation of immortalized human bronchial epithelial cells (BEAS-2B) using miRNA-mRNA networks. The expression of BEAS-2B cells was determined by measuring colony formation, mtDNA, mitochondrial membrane potential (MMP), and ROS levels. Changes in BEAS-2B cell gene expression were observed and quantified using microarrays that included an increase in 157 mRNA and 20 miRNA expression and a decrease in 77 mRNA and 48 miRNA. Bioinformatic software was used to analyze these different mRNA and miRNA, which indicated that miR-107 and miR-494 play an important role in alpha-particles-mediated cellular malignant transformation processes. The pathways related to systemic lupus erythematosus, cytokine-cytokine receptor interaction, MAPK signaling pathway, regulation of actin cytoskeleton, and cell adhesion molecules (CAMs) were stimulated, while those of ribosome, transforming growth factor (TGF)-beta signaling pathway, and metabolic pathways were inhibited. Data suggest that miRNA and mRNA play a crucial role in alpha-particles-mediated malignant transformation processes. It is worth noting that three target genes associated with lung cancer were identified and upregulated PEG 10 (paternally expressed gene 10), ARHGAP26, and IRS1.