NLRP3 inflammasome activation is associated with PM2.5 -induced cardiac functional and pathological injury in mice

Fine particulate matter‑induced cardiac developmental toxicity (Review)

Fine particulate matter (PM2.5) has become an important risk factor threatening human health. Epidemiological and toxicological investigations have revealed that PM2.5 not only leads to cardiovascular dysfunction, but it also gives rise to various adverse health effects on the human body, such as cardiovascular and cerebrovascular diseases, cancers, neurodevelopmental disorders, depression and autism. PM2.5 is able to penetrate both respiratory and placental barriers, thereby resulting in negative effects on fetal development. A large body of epidemiological evidences has suggested that gestational exposure to PM2.5 increases the incidence of congenital diseases in offspring, including congenital heart defects. In addition, animal model studies have revealed that gestational exposure to PM2.5 can disrupt normal heart development in offspring, although the potential molecular mechanisms have yet to be fully elucidated. The aim of the present review was to provide a brief overview of what is currently known regarding the molecular mechanisms underlying cardiac developmental toxicity in offspring induced by gestational exposure to PM2.5.

Carbonaceous cores serve as surrogates for environmental particulate matter inducing vascular endothelial inflammation via inflammasome activation

Ambient particulate matter (PM) exposure is a known risk factor for cardiovascular diseases. Epidemiological studies have shown the association between PM exposure and vascular complications, including vasculitis, embolism, hypertension, stroke, and atherosclerosis. However, the exact mechanisms underlying its vascular toxicity, especially in relation to short-term exposures, remain incompletely understood. This study investigates the role of PM and its carbonaceous cores in driving vascular endothelial inflammation via inflammasome activation. We hypothesized that PM SRM1648a exposure induces vascular endothelial inflammation through oxidative stress and inflammasome activation. Short-term exposure to PM SRM1648a was assessed in BALB/c mice for systemic inflammation and oxidative stress biomarkers, alongside in vitro studies in HUVECs and EA.hy926 endothelial cells to elucidate inflammasome activation pathways. PM SRM1648a exposure significantly altered redox balance and cytokine profiles in mice and upregulated NLRP3/NLRC4 inflammasomes in vascular endothelial cells, leading to caspase-1/IL-1β activation. Intriguingly, pyroptosis was not the primary mode of cell death. In vitro studies demonstrated that antioxidants glutathione monoethyl ester effectively mitigated oxidative stress and inflammasome activation in endothelial cells. This study highlights the critical role of ROS-mediated inflammasome activation in vascular inflammation induced by PM SRM1648a, with carbon-based cores as key contributors.

Ambient fine particulate matter provokes multiple modalities of cell death via perturbation of subcellular structures

Fine particulate matter (PM2.5) is increasingly recognized for its detrimental effects on human health, with substantial evidence linking exposure to various forms of cell death and dysfunction across multiple organ systems. This review examines key cell death mechanisms triggered by PM2.5, including PANoptosis, necroptosis, autophagy, and ferroptosis, while other forms such as oncosis, paraptosis, and cuprotosis remain unreported in relation to PM2.5 exposure. Mitochondria, endoplasmic reticulum, and lysosomes emerge as pivotal organelles in the disruption of cellular homeostasis, with mitochondrial dysfunction particularly implicated in metabolic dysregulation and the activation of pro-apoptotic pathways. Although PM2.5 primarily affects the nucleus, cytoskeleton, mitochondria, endoplasmic reticulum, and lysosomes, other organelles like ribosomes, Golgi apparatus, and peroxisomes have received limited attention. Interactions between these organelles, such as endoplasmic reticulum-associated mitochondrial membranes, lysosome-associated mitophagy, and mitochondria-nuclei retro-signaling may significantly contribute to the cytotoxic effects of PM2.5. The mechanisms of PM2.5 toxicity, encompassing oxidative stress, inflammatory responses, and metabolic imbalances, are described in detail. Notably, PM2.5 activates the NLRP3 inflammasome, amplifying inflammatory responses and contributing to chronic diseases. Furthermore, PM2.5 exposure disrupts genetic and epigenetic regulation, often resulting in cell cycle arrest and exacerbating cellular damage. The composition, concentration, and seasonal variability of PM2.5 modulate these effects, underscoring the complexity of PM2.5-induced cellular dysfunction. Despite significant advances in understanding these pathways, further research is required to elucidate the long-term effects of chronic PM2.5 exposure, the role of epigenetic regulation, and potential strategies to mitigate its harmful impact on human health.

PM2.5-mediated cardiovascular disease in aging: Cardiometabolic risks, molecular mechanisms and potential interventions

Air pollution, particularly fine particulate matter (PM2.5) with <2.5 μm in diameter, is a major public health concern. Studies have consistently linked PM2.5 exposure to a heightened risk of cardiovascular diseases (CVDs) such as ischemic heart disease (IHD), heart failure (HF), and cardiac arrhythmias. Notably, individuals with pre-existing age-related cardiometabolic conditions appear more susceptible. However, the specific impact of PM2.5 on CVDs susceptibility in older adults remains unclear. Therefore, this review addresses this gap by discussing the factors that make the elderly more vulnerable to PM2.5-induced CVDs. Accordingly, we focused on physiological aging, increased susceptibility, cardiometabolic risk factors, CVDs, and biological mechanisms. This review concludes by examining potential interventions to reduce exposure and the adverse health effects of PM2.5 in the elderly population. The latter includes dietary modifications, medications, and exploration of the potential benefits of supplements. By comprehensively analyzing these factors, this review aims to provide a deeper understanding of the detrimental effects of PM2.5 on cardiovascular health in older adults. This knowledge can inform future research and guide strategies to protect vulnerable populations from the adverse effects of air pollution.

TBHQ Alleviates Particulate Matter-Induced Pyroptosis in Human Nasal Epithelial Cells

Pyroptosis represents a type of cell death mechanism notable for its cell membrane disruption and the subsequent release of proinflammatory cytokines. The Nod-like receptor family pyrin domain containing inflammasome 3 (NLRP3) plays a critical role in the pyroptosis mechanism associated with various diseases resulting from particulate matter (PM) exposure. Tert-butylhydroquinone (tBHQ) is a synthetic antioxidant commonly used in a variety of foods and products. The aim of this study is to examine the potential of tBHQ as a therapeutic agent for managing sinonasal diseases induced by PM exposure. The occurrence of NLRP3 inflammasome-dependent pyroptosis in RPMI 2650 cells treated with PM < 4 µm in size was confirmed using Western blot analysis and enzyme-linked immunosorbent assay results for the pyroptosis metabolites IL-1β and IL-18. In addition, the inhibitory effect of tBHQ on PM-induced pyroptosis was confirmed using Western blot and immunofluorescence techniques. The inhibition of tBHQ-mediated pyroptosis was abolished upon nuclear factor erythroid 2-related factor 2 (Nrf2) knockdown, indicating its involvement in the antioxidant mechanism. tBHQ showed potential as a therapeutic agent for sinonasal diseases induced by PM because NLRP3 inflammasome activation was effectively suppressed via the Nrf2 pathway.

Chronic exposure to PM10 induces anxiety-like behavior via exacerbating hippocampal oxidative stress

As one of the most environmental concerns, inhaled particulate matter (PM10) causes numerous health problems. However, the associations between anxiety behavior and toxicity caused by PM10 have rarely been reported so far. To investigate the changes of behavior after PM10 exposure and to identify the potential mechanisms of toxicity, PM10 samples (with doses of 15 mg/kg and 30 mg/kg) were intratracheally instilled into rats to simulate inhalation of polluted air by the lungs. After instillation for eight weeks, anxiety-like behavior was evaluated, levels of oxidative stress and morphological changes of hippocampus were measured. The behavioral results indicated that PM10 exposure induced obvious anxiety-like behavior in the open field and elevated plus maze tests. Both PM10 concentrations tested could increase whole blood viscosity and trigger hippocampal neuronal damage and oxidative stress by increasing superoxide dismutase (SOD) activities and malondialdehyde levels, and decreasing the expressions of antioxidant-related proteins (e.g., nuclear factor erythroid 2-related factor 2 (Nrf2), SOD1 and heme oxygenase 1). Furthermore, through collecting and analyzing questionnaires, the data showed that the participants experienced obvious anxiety-related emotions and negative somatic responses under heavily polluted environments, especially PM10 being the main pollutant. These results show that PM10 exposure induces anxiety-like behavior, which may be related to suppressing the Nrf2/Keap1-SOD1 pathway.

The mechanism underlying correlation of particulate matter-induced ferroptosis with inflammasome activation and iron accumulation in macrophages

Particulate matter (PM) is a global environmental hazard, which affects human health through free radical production, cell death induction, and immune responses. PM activates inflammasomes leading to excessive inflammatory responses and induces ferroptosis, a type of cell death. Despite ongoing research on the correlation among PM-induced ferroptosis, immune response, and inflammasomes, the underlying mechanism of this relationship has not been elucidated. In this study, we demonstrated the levels of PM-induced cell death and immune responses in murine macrophages, J774A.1 and RAW264.7, depending on the size and composition of particulate matter. PM2.5, with extraction ions, induced significant levels of cell death and immune responses; it induces lipid peroxidation, iron accumulation, and reactive oxygen species (ROS) production, which characterize ferroptosis. In addition, inflammasome-mediated cell death occurred owing to the excessive activation of inflammatory responses. PM-induced iron accumulation activates ferroptosis and inflammasome formation through ROS production; similar results were observed in vivo. These results suggest that the link between ferroptosis and inflammasome formation induced by PM, especially PM2.5 with extraction ions, is established through the iron-ROS axis. Moreover, this study can effectively facilitate the development of a new therapeutic strategy for PM-induced immune and respiratory diseases.

Molecular mechanisms underlying NLRP3 inflammasome activation and IL-1β production in air pollution fine particulate matter (PM2.5)-primed macrophages

Exposure to air pollution fine particulate matter (PM2.5) aggravates respiratory and cardiovascular diseases. It has been proposed that PM2.5 uptake by alveolar macrophages promotes local inflammation that ignites a systemic response, but precise underlying mechanisms remain unclear. Here, we demonstrate that PM2.5 phagocytosis leads to NLRP3 inflammasome activation and subsequent release of the pro-inflammatory master cytokine IL-1β. Inflammasome priming and assembly was time- and dose-dependent in inflammasome-reporter THP-1-ASC-GFP cells, and consistent across PM2.5 samples of variable chemical composition. While inflammasome activation was promoted by different PM2.5 surrogates, significant IL-1β release could only be observed after stimulation with transition-metal rich Residual Oil Fly Ash (ROFA) particles. This effect was confirmed in primary human monocyte-derived macrophages and murine bone marrow-derived macrophages (BMDMs), and by confocal imaging of inflammasome-reporter ASC-Citrine BMDMs. IL-1β release by ROFA was dependent on the NLRP3 inflammasome, as indicated by lack of IL-1β production in ROFA-exposed NLRP3-deficient (Nlrp3-/-) BMDMs, and by specific NLRP3 inhibition with the pharmacological compound MCC950. In addition, while ROFA promoted the upregulation of pro-inflammatory gene expression and cytokines release, MCC950 reduced TNF-α, IL-6, and CCL2 production. Furthermore, inhibition of TNF-α with a neutralizing antibody decreased IL-1β release in ROFA-exposed BMDMs. Using electron tomography, ROFA particles were observed inside intracellular vesicles and mitochondria, which showed signs of ultrastructural damage. Mechanistically, we identified lysosomal rupture, K+ efflux, and impaired mitochondrial function as important prerequisites for ROFA-mediated IL-1β release. Interestingly, specific inhibition of superoxide anion production (O2•-) from mitochondrial respiratory Complex I, but not III, blunted IL-1β release in ROFA-exposed BMDMs. Our findings unravel the mechanism by which PM2.5 promotes IL-1β release in macrophages and provide a novel link between innate immune response and exposure to air pollution PM2.5.

Redox and inflammatory mechanisms linking air pollution particulate matter with cardiometabolic derangements

Air pollution is the largest environmental risk factor for disease and premature death. Among the different components that are present in polluted air, fine particulate matter below 2.5 μm in diameter (PM2.5) has been identified as the main hazardous constituent. PM2.5 mainly arises from fossil fuel combustion during power generation, industrial processes, and transportation. Exposure to PM2.5 correlates with enhanced mortality risk from cardiovascular diseases (CVD), such as myocardial infarction and stroke. Over the last decade, it has been increasingly suggested that PM2.5 affects CVD already at the stage of risk factor development. Among the multiple biological mechanisms that have been described, the interplay between oxidative stress and inflammation has been consistently highlighted as one of the main drivers of pulmonary, systemic, and cardiovascular effects of PM2.5 exposure. In this context, PM2.5 uptake by tissue-resident immune cells in the lung promotes oxidative and inflammatory mediators release that alter tissue homeostasis at remote locations. This pathway is central for PM2.5 pathogenesis and might account for the accelerated development of risk factors for CVD, including obesity and diabetes. However, transmission and end-organ mechanisms that explain PM2.5-induced impaired function in metabolic active organs are not completely understood. In this review, the main features of PM2.5 physicochemical characteristics related to PM2.5 ability to induce oxidative stress and inflammation will be presented. Hallmark and recent epidemiological and interventional studies will be summarized and discussed in the context of current air quality guidelines and legislation, knowledge gaps, and inequities. Lastly, mechanistic studies at the intersection between redox metabolism, inflammation, and function will be discussed, with focus on heart and adipose tissue alterations. By offering an integrated analysis of PM2.5-induced effects on cardiometabolic derangements, this review aims to contribute to a better understanding of the pathogenesis and potential interventions of air pollution-related CVD.

The Cellular Accumulation of Vehicle Exhaust Particulates Changes the Acidic pH Environment of Lysosomes in BEAS-2B Airway Epithelial Cells

Many people are exposed every day to vehicle exhaust particulates (VEPs), which are thought to be taken up by epithelial cells that are the first barrier in our biological defense. The study aim was to investigate how VEPs are processed in the lysosomal degradation system. BEAS-2B airway epithelial cells easily ingest VEPs and have been shown to accumulate in cells for several days, but no elevated cytotoxicity was observed over that time period. An analysis of 3D images confirmed the presence of VEPs in or near lysosomes, and an accumulation of VEPs resulted in an increase in the normal acidic pH in lysosomes and the extracellular release of the lysosomal enzyme β-hexosaminidase. Epithelial cells were thought to activate the lysosome-mediated secretion of extracellular vesicles to avoid damage caused by non-degradable foreign substances, such as VEPs, and as a side reaction, the acidic pH environment of the lysosomes could not be maintained.

PM2.5 induces the inflammatory response in rat spleen lymphocytes through autophagy activation of NLRP3 inflammasome

Recent evidence has suggested that fine particulate matter (PM2.5) can induce inflammatory injury in spleen. However, the underlying mechanisms of injury remain enigmatic. In this study, we aim to clarify the inflammatory injury mechanisms of PM2.5 through investigating the crosstalk between autophagy and nod-like receptor protein 3 (NLRP3) inflammasome. The spleen lymphocytes were extracted from SD rats and subjected to PM2.5 and its water-soluble components. The CCK-8 assay was utilized to explore the effects of PM2.5 and its water-soluble components on lymphocytes. Then, the effects of PM2.5 and its water-soluble components exposure on autophagy and NLRP3 inflammasome were detected by qRT-PCR, western blotting, and immunofluorescence staining. The autophagosome production was observed under the transmission electron microscope. The autophagy inhibitor 3-methyladenine (3MA) following PM2.5 water-soluble components was used to investigate the regulation of NLRP3 inflammasome by autophagy. We found that PM2.5 and its water-soluble components decreased the viability of spleen lymphocytes in a dose-dependent manner. PM2.5 exposure and its water-soluble components exposure activated the autophagy and NlRP3 inflammasome, as indicated by an increased expression of LC3, P62, NLRP3, Caspase-1 p10, and increased release of IL-1β. Furthermore, the treatment with autophagy inhibitor 3MA attenuated the production of autophagosome and NLRP3 inflammasome induced by PM2.5 water-soluble components with decreased expression of NLRP3, Caspase-1 p10, and diminished production of IL-1β. These results suggested that PM2.5 and its water-soluble components could induce autophagy and inflammatory response through NLRP3 inflammasome in spleen lymphocytes, while the NLRP3 inflammasome induced by PM2.5 could be significantly alleviated by inhibition of autophagy, further providing new insights for the understanding of spleen injury caused by PM2.5.

Particulate air pollution exaggerates diet-induced insulin resistance through NLRP3 inflammasome in mice

Air particulate matter 2.5 (PM2.5) has been demonstrated to exaggerate insulin resistance in both human and animal studies. However, the exact molecular mechanisms remain elusive. This study sought to assess the role of NLRP3 inflammasome in PM2.5 exposure-induced insulin resistance and explore the underlying mechanisms. Wild-type (WT), Nlrp3-/-, Tlr4Lps-d, or Nrf2-/- mice, on a normal diet or high-fat diet (HFD), were exposed to PM2.5 or filtered air (FA) in a whole-body exposure facility. Priming (first signal) and assembly (second signal) of NLRP3 inflammasome activation were assessed by measuring the transcription of Nlrp3/Il-1β and detecting the activity of caspase-1 and secretion of IL-1β. We found PM2.5 exposure exaggerated insulin resistance and increased IL-1β production in the HFD-fed WT mice, but not Nlrp3-/- mice. Gene expressions of Nlrp3 and Il-1β in the lungs and peritoneal macrophages were upregulated in WT mice exposed to PM2.5. When stimulated with LPS (first signal) or monosodium urate (second signal), PM2.5 exposure was able to enhance the activity of caspase-1 and IL-1β secretion, suggesting that PM2.5 may serve as a stimulus of either the first or second signal for NLRP3 inflammasome activation. Effects of PM2.5 on caspase-1 activation and IL-1β secretion were partially blocked in Tlr4Lps-d mice. Reactive oxygen species (ROS), co-localization of NLRP3 and mitochondria, and secondary lysosomes in macrophages were increased after PM2.5 exposure, while deficiency of antioxidant gene Nrf2 in mice significantly enhanced PM2.5-induced secretion of IL-1β. Imaging flow cytometry and transmission electron microscopy demonstrated an engulfment of PM2.5 particles by macrophages, while suppression of phagocytosis by cytochalasin D abolished PM2.5-induced transcription of Nlrp3/Il-1β. Our results demonstrated a critical role of NLRP3 inflammasome in PM2.5 exaggerated insulin resistance, and multiple pathways in the first and second signals of NLRP3 inflammasome activation may be involved.

3-Bromo-4,5-dihydroxybenzaldehyde Protects Keratinocytes from Particulate Matter 2.5-Induced Damages

Cellular senescence can be activated by several stimuli, including ultraviolet radiation and air pollutants. This study aimed to evaluate the protective effect of marine algae compound 3-bromo-4,5-dihydroxybenzaldehyde (3-BDB) on particulate matter 2.5 (PM_2.5)-induced skin cell damage in vitro and in vivo. The human HaCaT keratinocyte was pre-treated with 3-BDB and then with PM_2.5. PM_2.5-induced reactive oxygen species (ROS) generation, lipid peroxidation, mitochondrial dysfunction, DNA damage, cell cycle arrest, apoptotic protein expression, and cellular senescence were measured using confocal microscopy, flow cytometry, and Western blot. The present study exhibited PM_2.5-generated ROS, DNA damage, inflammation, and senescence. However, 3-BDB ameliorated PM_2.5-induced ROS generation, mitochondria dysfunction, and DNA damage. Furthermore, 3-BDB reversed the PM_2.5-induced cell cycle arrest and apoptosis, reduced cellular inflammation, and mitigated cellular senescence in vitro and in vivo. Moreover, the mitogen-activated protein kinase signaling pathway and activator protein 1 activated by PM_2.5 were inhibited by 3-BDB. Thus, 3-BDB suppressed skin damage induced by PM_2.5.

Sema3A alleviates viral myocarditis by modulating SIRT1 to regulate cardiomyocyte mitophagy

Viral myocarditis (VMC) is a common myocardial inflammatory disease characterized by inflammatory cell infiltration and cardiomyocyte necrosis. Sema3A was reported to reduce cardiac inflammation and improve cardiac function after myocardial infarction, but its role in VMC remains to be explored. Here, a VMC mouse model was established by infection with CVB3, and Sema3A was overexpressed in vivo by intraventricular injection of an adenovirus-mediated Sema3A expression vector (Ad-Sema3A). We found that Sema3A overexpression attenuated CVB3-induced cardiac dysfunction and tissue inflammation. And Sema3A also reduced macrophage accumulation and NLRP3 inflammasome activation in the myocardium of VMC mice. In vitro, LPS was used to stimulate primary splenic macrophages to mimic the macrophage activation state in vivo. Activated macrophages were co-cultured with primary mouse cardiomyocytes to evaluate macrophage infiltration-induced cardiomyocyte damage. Ectopic expression of Sema3A in cardiomyocytes effectively protected cardiomyocytes from activated macrophage-induced inflammation, apoptosis, and ROS accumulation. Mechanistically, cardiomyocyte-expressed Sema3A mitigated macrophage infiltration-caused cardiomyocyte dysfunction by promoting cardiomyocyte mitophagy and hindering NLRP3 inflammasome activation. Furthermore, NAM (a SIRT1 inhibitor) reversed the protective effect of Sema3A against activated macrophage-induced cardiomyocyte dysfunction by suppressing cardiomyocyte mitophagy. In conclusion, Sema3A promoted cardiomyocyte mitophagy and suppressed inflammasome activation by regulating SIRT1, thereby attenuating macrophage infiltration-induced cardiomyocyte injury in VMC.

Cell Death Pathways: The Variable Mechanisms Underlying Fine Particulate Matter-Induced Cytotoxicity

Recently, the advent of health risks due to the cytotoxicity of fine particulate matter (FPM) is concerning. Numerous studies have reported abundant data elucidating the FPM-induced cell death pathways. However, several challenges and knowledge gaps are still confronted nowadays. On one hand, the undefined components of FPM (such as heavy metals, polycyclic aromatic hydrocarbons, and pathogens) are all responsible for detrimental effects, thus rendering it difficult to delineate the specific roles of these copollutants. On the other hand, owing to the crosstalk and interplay among different cell death signaling pathways, precisely determining the threats and risks posed by FPM is difficult. Herein, we recapitulate the current knowledge gaps present in the recent studies regarding FPM-induced cell death, and propose future research directions for policy-making to prevent FPM-induced diseases and improve knowledge concerning the adverse outcome pathways and public health risks of FPM.

PM2.5 induce myocardial injury in hyperlipidemic mice through ROS-pyroptosis signaling pathway

Exposure to particulate matters with diameters below 2.5 µm (PM_2.5) is considered a major risk factor for cardiovascular diseases (CVDs). The closest associations between PM_2.5 and CVDs have been observed in hyperbetalipoproteinemia cases, although the detailed underpinning mechanism remains undefined. In this work, hyperlipidemic mice and H9C2 cells were used to examine the effects of PM_2.5 on myocardial injury and their underlying mechanisms. The results revealed that PM_2.5 exposure caused severe myocardial damage in the high-fat mouse model. Oxidative stress and pyroptosis were also observed along with myocardial injury. After inhibiting pyroptosis with disulfiram (DSF), the level of pyroptosis was effectively reduced as well as myocardial injury, suggesting that PM_2.5 induced the pyroptosis pathway and further caused myocardial injury and cell death. Afterwards, by suppressing PM_2.5-induced oxidative stress with N-acetyl-L-cysteine (NAC), myocardial injury was markedly ameliorated, and the upregulation of pyroptosis markers was reversed, which indicated that PM_2.5-pyroptosis was also improved. Taken together, this study revealed that PM_2.5 induce myocardial injury through the ROS-pyroptosis signaling pathway in hyperlipidemia mice models, providing a potential approach for clinical interventions.

On the Need for Human Studies of PM Exposure Activation of the NLRP3 Inflammasome

Particulate matter air pollution is associated with blood inflammatory biomarkers, however, the biological pathways from exposure to periferal inflammation are not well understood. We propose that the NLRP3 inflammasome is likely stimulated by ambient particulate matter, as it is by some other particles and call for more research into this pathway.

The pathophysiological and molecular mechanisms of atmospheric PM2.5 affecting cardiovascular health: A review

BACKGROUND

Exposure to ambient fine particulate matter (PM2.5, with aerodynamic diameter less than 2.5 µm) is a leading environmental risk factor for global cardiovascular health concern.

OBJECTIVE

To provide a roadmap for those new to this field, we reviewed the new insights into the pathophysiological and cellular/molecular mechanisms of PM2.5 responsible for cardiovascular health.

MAIN FINDINGS

PM2.5 is able to disrupt multiple physiological barriers integrity and translocate into the systemic circulation and get access to a range of secondary target organs. An ever-growing body of epidemiological and controlled exposure studies has evidenced a causal relationship between PM2.5 exposure and cardiovascular morbidity and mortality. A variety of cellular and molecular biology mechanisms responsible for the detrimental cardiovascular outcomes attributable to PM2.5 exposure have been described, including metabolic activation, oxidative stress, genotoxicity, inflammation, dysregulation of Ca2+ signaling, disturbance of autophagy, and induction of apoptosis, by which PM2.5 exposure impacts the functions and fates of multiple target cells in cardiovascular system or related organs and further alters a series of pathophysiological processes, such as cardiac autonomic nervous system imbalance, increasing blood pressure, metabolic disorder, accelerated atherosclerosis and plaque vulnerability, platelet aggregation and thrombosis, and disruption in cardiac structure and function, ultimately leading to cardiovascular events and death. Therein, oxidative stress and inflammation were suggested to play pivotal roles in those pathophysiological processes.

CONCLUSION

Those biology mechanisms have deepen insights into the etiology, course, prevention and treatment of this public health concern, although the underlying mechanisms have not yet been entirely clarified.

Inhibiting EGFR/HER-2 ameliorates neuroinflammatory responses and the early stage of tau pathology through DYRK1A

The FDA-approved EGFR/HER2 inhibitor varlitinib inhibits tumor growth and is used in cancer treatment. However, the neuroinflammatory response associated with EGFR/HER2 and its underlying mechanism have not been elucidated. This study evaluates the impact of varlitinib on LPS- and tau-mediated neuroinflammatory responses for the first time. In BV2 microglial cells, varlitinib reduced LPS-stimulated il-1β and/or inos mRNA levels and downstream AKT/FAK/NF-kB signaling. Importantly, varlitinib significantly diminished LPS-mediated microglial nlrp3 inflammasome activation in BV2 microglial cells. In primary astrocytes, varlitinib downregulated LPS-evoked astroglial il-1β mRNA levels, AKT signaling, and nlrp3 inflammasome activation. In LPS-treated wild-type mice, varlitinib significantly reduced LPS-stimulated glial activation and IL-1β/NLRP3 inflammasome formation. Moreover, varlitinib significantly reduced micro- and astroglial activation and tau hyperphosphorylation in 3-month-old tau-overexpressing PS19 mice by downregulating tau kinase DYRK1A levels. However, in 6-month-old tau-overexpressing PS19 mice, varlitinib only significantly diminished astroglial activation and tau phosphorylation at Thr212/Ser214. Taken together, our findings suggest that varlitinib has therapeutic potential for LPS- and tau-induced neuroinflammatory responses and the early stages of tau pathology.

Ubiquitination as a key regulatory mechanism for O3-induced cutaneous redox inflammasome activation

NLRP1 is one of the major inflammasomes modulating the cutaneous inflammatory responses and therefore linked to a variety of cutaneous conditions. Although NLRP1 has been the first inflammasome to be discovered, only in the past years a significant progress was achieved in understanding the molecular mechanism and the stimuli behind its activation. In the past decades a crescent number of studies have highlighted the role of air pollutants as Particulate Matter (PM), Cigarette Smoke (CS) and Ozone (O3) as trigger stimuli for inflammasomes activation, especially via Reactive Oxygen Species (ROS) mediators. However, whether NLRP1 can be modulated by air pollutants via oxidative stress and the mechanism behind its activation is still poorly understood. Here we report for the first time that O3, one of the most toxic pollutants, activates the NLRP1 inflammasome in human keratinocytes via oxidative stress mediators as hydrogen peroxide (H2O2) and 4-hydroxy-nonenal (4HNE). Our data suggest that NLRP1 represents a target protein for 4HNE adduction that possibly leads to its proteasomal degradation and activation via the possible involvement of E3 ubiquitin ligase UBR2. Of note, Catalase (Cat) treatment prevented inflammasome assemble and inflammatory cytokines release as well as NLRP1 ubiquitination in human keratinocytes upon O3 exposure. The present work is a mechanistic study that follows our previous work where we have showed the ability of O3 to induce cutaneous inflammasome activation in humans exposed to this pollutant. In conclusion, our results suggest that O3 triggers the cutaneous NLRP1 inflammasome activation by ubiquitination and redox mechanism.

TGF-β-Containing Small Extracellular Vesicles From PM2.5-Activated Macrophages Induces Cardiotoxicity

Numerous epidemiological and experimental studies have demonstrated that the exposure to fine particulate matter (aerodynamic diameter <2.5 μm, PM_2.5) was closely associated with cardiovascular morbidity and mortality. Our previous studies revealed that PM_2.5 exposure induced cardiac dysfunction and fibrosis. However, the corresponding underlying mechanism remains largely unaddressed. Here, PM_2.5-induced cardiotoxicity is presented to directly promote collagen deposition in cardiomyocytes through the transforming growth factor-β (TGF-β)-containing small extracellular vesicles (sEV). The sEV transition may play an important role in PM_2.5-induced cardiac fibrosis. Firstly, long-term PM_2.5 exposure can directly induce cardiac fibrosis and increase the level of serum sEV. Secondly, PM_2.5 can directly activate macrophages and increase the release of tumor necrosis factor α (TNF-α), interleukin-6 (IL-6), and TGF-β-containing sEV. Thirdly, TGF-β-containing sEV increases the expression of α-smooth muscle actin (α-SMA), collagen I, and collagen III in mouse cardiac muscle HL-1 cells. Finally, TGF-β-containing sEV released from PM_2.5-treated macrophages can increase collagen through the activation of the TGF-β-Smad2/3 signaling pathway in HL-1 cells from which some fibroblasts involved in cardiac fibrosis are thought to originate. These findings suggest that TGF-β-containing sEV from PM_2.5-activated macrophages play a critical role in the process of increasing cardiac collagen content via activating the TGF-β-Smad2/3 signaling pathway.

Fine particulate matter exposure aggravates ischemic injury via NLRP3 inflammasome activation and pyroptosis

Aims

Accumulating evidence has suggested that airborne fine particulate matter (PM2.5) exposure is associated with an increased risk of ischemic stroke. However, the underlying mechanisms have not been fully elucidated. In this study, we aim to investigate the role and mechanisms of NLRP3 inflammasome and pyroptosis in ischemic stroke after PM2.5 exposure.

Methods

The BV‐2 and HMC‐3 microglial cell lines were established and subjected to oxygen–glucose deprivation and reoxygenation (OGD/R) with or without PM2.5 exposure. We used the CCK‐8 assay to explore the effects of PM2.5 on cell viability of BV‐2 and HMC‐3 cells. Then, the effects of PM2.5 exposure on NLRP3 inflammasome and pyroptosis following OGD/R were detected by western blotting, ELISA, and the confocal immunofluorescence staining. Afterwards, NLRP3 was knocked down to further validate the effects of PM2.5 on cell viability, NLRP3 inflammasome activation, and pyroptosis after OGD/R in HMC‐3 cells. Finally, the intracellular reactive oxygen species (ROS) was measured and the ROS inhibitor N‐acetyl‐L‐cysteine (NAC) was used to investigate whether ROS was required for PM2.5‐induced NLRP3 inflammasome activation and pyroptosis under ischemic conditions.

Results

We found that PM2.5 exposure decreased the viability of BV‐2 and HMC‐3 cells in a dose‐ and time‐dependent manner under ischemic conditions. Furthermore, PM2.5 exposure aggravated NLRP3 inflammasome activation and pyroptosis after OGD/R, as indicated by an increased expression of NLRP3, ASC, pro‐caspase‐1, Caspase‐1, GSDMD, and GSDMD‐N; increased production of IL‐1β and IL‐18; and enhanced Caspase‐1 activity and SYTOX green uptake. However, shRNA NLRP3 treatment attenuated the effects of PM2.5 on cell viability, NLRP3 inflammasome activation, and pyroptosis. Moreover, we observed that PM2.5 exposure increased the production of intracellular ROS following OGD/R, while inhibiting ROS production with NAC partially attenuated PM2.5‐induced NLRP3 inflammasome activation and pyroptosis under ischemic conditions.

Conclusion

These results suggested that PM2.5 exposure triggered the activation of NLRP3 inflammasome and pyroptosis under ischemic conditions, which may be mediated by increased ROS production after ischemic stroke. These findings may provide a more enhanced understanding of the interplay between PM2.5 and neuroinflammation and cell death, and reveal a novel mechanism of PM2.5‐mediated toxic effects after ischemic stroke.

Adverse outcome pathway of fine particulate matter leading to increased cardiovascular morbidity and mortality: An integrated perspective from toxicology and epidemiology

Fine particulate matter (PM_2.5) exposure is a major threat to public health, and is listed as one of the leading factors associated with global premature mortality. Among the adverse health effects on multiple organs or tissues, the influence of PM_2.5 exposure on cardiovascular system has drawn more and more attention. Although numerous studies have investigated the mechanisms responsible for the cardiovascular toxicity of PM_2.5, the various mechanisms have not been integrated due to the variety of the study models, different levels of toxicity assessment endpoints, etc. Adverse Outcome Pathway (AOP) framework is a useful tool to achieve this goal so as to facilitate comprehensive understanding of toxicity assessment of PM_2.5 on cardiovascular system. This review aims to illustrate the causal mechanistic relationships of PM_2.5-triggered cardiovascular toxicity from different levels (from molecular/cellular/organ to individual/population) by using AOP framework. Based on the AOP Wiki and published literature, we propose an AOP framework focusing on the cardiovascular toxicity induced by PM_2.5 exposure. The molecular initiating event (MIE) is identified as reactive oxygen species generation, followed by the key events (KEs) of oxidative damage and mitochondria dysfunction, which induces vascular endothelial dysfunction via vascular endothelial cell autophagy dysfunction, vascular fibrosis via vascular smooth muscle cell activation, cardiac dysregulation via myocardial apoptosis, and cardiac fibrosis via fibroblast proliferation and myofibroblast differentiation, respectively; all of the above cardiovascular injuries ultimately elevate cardiovascular morbidity and mortality in the general population. As far as we know, this is the first work on PM_2.5-related cardiovascular AOP construction. In the future, more work needs to be done to explore new markers in the safety assessment of cardiovascular toxicity induced by PM_2.5.

Quantum dots bind nanosheet to promote nanomaterial stability and resist endotoxin-induced fibrosis and PM2.5-induced pneumonia

Endotoxin lipopolysaccharide (LPS) is a harmful substance commonly found in various environments that causes lung fibrosis. Exposure to PM2.5 also increases the risk of respiratory diseases. Through sulfur-carbon bonds and the edge S effect, GOQDs were used to bind in single-layer molybdenum disulfide (SLMoS2) nanosheets to synthesize SLMoS2@GOQDs heterojunction structures. GOQDs doping greatly increased the water solubility and stabilized of SLMoS2. SLMoS2@GOQDs with catalase-like activity protected cells from ultrastructural and cytomembrane damage and apoptosis induced by LPS. Moreover, the doping of GOQDs enhanced the escape of SLMoS2@GOQDs from cellular uptake and suppressed the release of Mo ions. Nanosheet-cell interface interactions that were regulated by quantum dots supported these positive effects. Immunofluorescence analysis and cell imaging confirmed that the nanomaterial protected against cell injury by regulating the canonical Wnt/β-catenin pathway and the secretion of relevant cytokines, such as interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). Moreover, SLMoS2@GOQDs also mitigated pneumonia caused by PM2.5 in vivo. Collectively, our findings not only provide a simple and effective approach to control lung diseases (caused by LPS or PM2.5), but also reveal the potential value of heterojunction materials in the fields of toxicology and human health, boosting the application of nanotechnology in the fields of ecotoxicology and environmental safety.

PM2.5 exposure inducing ATP alteration links with NLRP3 inflammasome activation

Fine particulate matter (PM_2.5) has been the primary air pollutant and the fourth leading risk factor for disease and death in the world. Exposure to PM_2.5 is related to activation of the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, but the mechanism of PM_2.5 affecting the NLRP3 inflammasome is still unclear. Previous studies have shown that PM_2.5 can cause alterations in adenosine triphosphate (ATP), and an increase in extracellular ATP and a decrease in intracellular ATP can trigger the activation process of the NLRP3 inflammasome. Therefore, we emphasize that ATP changes may be the central link and key mechanism of PM_2.5 exposure that activates the NLRP3 inflammasome. This review briefly elucidates and summarizes how PM_2.5 acts on ATP and subsequently further impacts the NLRP3 inflammasome. Investigation of ATP changes due to exposure to PM_2.5 may be essential to regulate NLRP3 inflammasome activation and treat inflammation-related diseases such as coronavirus disease 2019 (COVID-19).

PM2.5 activated NLRP3 inflammasome and IL-1β release in MH-S cells by facilitating autophagy via activating Wnt5a

Particulate matter 2.5 (PM2.5)-induced pulmonary inflammation is an important issue worldwide. NLRP3 inflammasome activation has been found to be involved in pulmonary inflammation development. However, whether PM2.5 induces pulmonary inflammation by activating the NLRP3 inflammasome has not yet been fully elucidated. This study researched whether PM2.5 induces the NLRP3 inflammasomes activation to trigger pulmonary inflammation.

Mice and MH-S cells were exposed to PM2.5, BOX5, and Rapamycin. Hematoxylin and eosin staining was performed on the lung tissues of mice. M1 macrophage marker CD80 expression in the lung tissues of mice and LC3B expression in MH-S cells was detected by immunofluorescence. IL-1β level in the lavage fluid and MH-S cells were detected by enzyme-linked immunosorbent assay. Protein expression was detected by Western blot. Autophagy assay in MH-S cells was performed by LC3B-GFP punctae experiment.PM2.5 exposure induced the lung injury of mice and increased NLRP3, P62, Wnt5a, LC3BII/I, and CD80 expression and IL-1β release in the lung tissues. PM2.5 treatment increased NLRP3, pro-caspase-1, cleaved caspase-1, Pro-IL-1β, Pro-IL-18, P62, LC3BII/I, and Wnt5a expression, IL-1β release, and LC3B-GFP punctae in MH-S cells. However, BOX5 treatment counteracted this effect of PM2.5 on lung tissues of mice and MH-S cells. Rapamycin reversed the effect of BOX5 on PM2.5-induced lung tissues of mice and MH-S cells.PM2.5 activated the NLRP3 inflammasome and IL-1β release in MH-S cells by facilitating the autophagy via activating Wnt5a. The findings of this study provided a new clue for the treatment of pulmonary inflammation caused by PM2.5.

NLRP3 inflammasome activation determines the fibrogenic potential of PM2.5 air pollution particles in the lung

Airborne fine particulate matter (PM_2.5) is known to cause respiratory inflammation such as chronic obstructive pulmonary disease and lung fibrosis. NLRP3 inflammasome activation has been implicated in these diseases; however, due to the complexity in PM_2.5 compositions, it is difficult to differentiate the roles of the components in triggering this pathway. We collected eight real-life PM_2.5 samples for a comparative analysis of their effects on NLRP3 inflammasome activation and lung fibrosis. In vitro assays showed that although the PM_2.5 particles did not induce significant cytotoxicity at the dose range of 12.5 to 100 µg/mL, they induced potent TNF-α and IL-1β production in PMA differentiated THP-1 human macrophages and TGF-β1 production in BEAS-2B human bronchial epithelial cells. At the dose of 100 µg/mL, PM_2.5 induced NLRP3 inflammasome activation by inducing lysosomal damage and cathepsin B release, leading to IL-1β production. This was confirmed by using NLRP3- and ASC-deficient cells as well as a cathepsin B inhibitor, ca-074 ME. Administration of PM_2.5 via oropharyngeal aspiration at 2 mg/kg induced significant TGF-β1 production in the bronchoalveolar lavage fluid and collagen deposition in the lung at 21 days post-exposure, suggesting PM_2.5 has the potential to induce pulmonary fibrosis. The ranking of in vitro IL-1β production correlates well with the in vivo total cell count, TGF-β1 production, and collagen deposition. In summary, we demonstrate that the PM_2.5 is capable of inducing NLRP3 inflammasome activation, which triggers a series of cellular responses in the lung to induce fibrosis.

Property-activity relationship between physicochemical properties of PM2.5 and their activation of NLRP3 inflammasome

Air pollution is becoming severe environment factor affecting human health. More and more research has indicated that fine particulate matter (PM_2.5) plays a critical role in causing pulmonary inflammation or fibrosis, which potentially is ascribed to the activation of nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3) inflammasome. However, the underlying property-activity relationship between the physicochemical properties of PM_2.5 and their activation of NLRP3 inflammasome remains unclear. Herein, various ways, such as metal chelation, organic extraction, ROS consumption, charge neutralization and particle dispersion, were applied to interfere with the effects of metal ion, polycyclic aromatic hydrocarbons (PAHs), reactive oxygen species (ROS), charge and size. It was found that aggregated size and PAHs could activate the NLRP3 inflammasome through lysosome rupture and potassium efflux, respectively. Metal ion, PAHs and surface ROS could also activate the NLRP3 inflammasome through mitochondrial ROS production. However, neutralization of PM_2.5 with the negative surface charge could not relieve the activation of NLRP3 inflammasome. Furthermore, oropharyngeal aspiration of various modified PM_2.5 were adopted to explore their effects on lung fibrosis, which showed the consistent results with those in cellular levels. Removal of metal ion, PAHs and ROS as well as reduction of size of PM_2.5 could reduce collagen deposition in the lung tissue of mice, while the charge neutralization of PM_2.5 increased this collagen deposition. This study provides great insights to clarify the property-activity relationship of PM_2.5.

The involvement of DRP1-mediated caspase-1 activation in inflammatory response by urban particulate matter in EA.hy926 human vascular endothelial cells

Atmospheric particulate matter (PM) has been reported to be closely related to cardiovascular adverse events. However, the underlying mode of action remains to be elucidated. Previous studies have documented that PM induces mitochondrial damage and inflammation, the relation between these two biological outcomes is still unclear though. In this study, we used EA.hy926 human vascular endothelial cells and a standard PM, PM SRM1648a to study the potential effects of mitochondrial dysfunction on endothelial inflammatory responses. As a result, PM SRM1648a changes mitochondrial morphology and interrupts mitochondrial dynamics with a persistent tendency of fission in a dose-dependent manner. Additionally, the caspase-1/IL-1β axis is involved in inflammatory responses but not cell pyroptosis in EA.hy926 cells following the exposure to PM SRM1648a. The activation of caspase-1 has implications in inflammation but not pyroptosis, because caspase-1-dependent pyroptosis is not the main modality of cell death in PM SRM1648a-treated EA.hy926 cells. With regard to the association between mitochondrial damage and inflammation in the case of particle stimulation, DRP1-mediated mitochondrial fission is responsible for inflammatory responses as a result of caspase-1 activation. The current study showed that PM SRM1648a has the ability to disturb mitochondrial dynamics, and trigger endothelial inflammation via DRP1/caspase-1/IL-1β regulatory pathway. In a conclusion, mitochondrial fission enables EA.hy926 cells to facilitate caspase-1 activation in response to PM SRM1648a, which is a crucial step for inflammatory reaction in vascular endothelial cells.

NLRP3 inflammasome is involved in ambient PM2.5-related metabolic disorders in diabetic model mice but not in wild-type mice

AIMS

To explore the role of nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3) inflammasome in ambient fine particulate matter (PM_2.5)-related metabolic disorders.

METHODS

In this study, the C57BL/6 and db/db mice were exposed to concentrated PM_2.5 or filtered air (FA) using Shanghai Meteorological and Environmental Animal Exposure System (Shanghai-METAS) for 12 weeks. Indices of lipid metabolism, glucose metabolism, insulin sensitivity, and protein expression of NLRP3 inflammasome in visceral adipose tissue (VAT) were measured, respectively.

RESULTS

The results showed that PM_2.5 exposure increased circulatory insulin, triglycerides (TG), and total cholesterol (TC), and decreased high-density lipoprotein (HDL) in both C57BL/6 and db/db mice. The levels of NLRP3-related circulatory inflammatory cytokines including both interleukin (IL)-18 and IL-1β in serum were increased in the PM_2.5-exposed mice and accompanied by the elevation in fasting blood glucose and insulin. The results also showed that exposure to PM_2.5 promoted the activation of NLRP3, pro-caspase-1, caspase-1, and apoptosis-associated speck-like protein containing CARD (ASC), simultaneously accompanied by the increase of IL-18 and IL-1β expression in VAT, but the statistically significant difference only found in the db/db mice, not in C57BL/6 mice.

CONCLUSION

The activation of NLRP3 inflammasome might be not the main mechanism of PM_2.5-related metabolic disorders in wide type mice but it partly mediated the exacerbation of metabolic disorders in diabetic model mice.

PM2.5 induces endothelial dysfunction via activating NLRP3 inflammasome

PM2.5 (particulate matter <2.5 μm in diameter) is proven to contribute to the development of atherosclerosis. Endothelial cell dysfunction is the initial step of atherosclerosis. The underlying mechanisms of endothelial cell damage exposed to PM2.5 are still obscure. In our study, PM2.5 was administrated to C57BL/6 male mice by intranasal instillation for 2 weeks. Human umbilical vein endothelial cells (HUVECs) were also treated with PM2.5 to evaluate the adverse effect in vitro. The immunohistochemical staining of aortas showed that the expressions of proinflammatory cytokines and endothelial adhesion markers were significantly increased in PM2.5-exposed mice than that in saline-exposed mice. In vitro, PM2.5 could inhibit HUVECs viability and impair cell migration in a concentration-dependent manner. Besides, PM2.5 exposure downregulated eNOS expression while upregulated reactive oxygen species (ROS) levels. Mechanistically, PM2.5 activated the NLRP3 inflammasome in HUVECs while knockdown of NLRP3 could effectively reverse the downregulation of eNOS expression and production of ROS after PM2.5 exposure. In summary, our data showed that PM2.5 could cause endothelial dysfunction, and probably via NLRP3 inflammasome activation.

Taurine reduction associated with heart dysfunction after real-world PM2.5 exposure in aged mice

Ambient PM_2.5 has been proved to be an independent risk factor for cardiovascular diseases; however, little information is available on the age-dependent effects of PM_2.5 on the cardiovascular system and the underlying mechanisms following chronic exposure. In this study, multi-aged mice were exposed to PM_2.5 via the newly developed real-ambient PM_2.5 exposure system to investigate age-related effects on the heart after long-term exposure. First, the chemical and physical properties of PM_2.5 used in the exposure system were analyzed. The heart rate of conscious mice was recorded, and results showed that exposure of aged mice to PM_2.5 for 26 weeks significantly increased heart rate. Histological analysis and ELISA assays indicated that aged mice were more sensitive to PM_2.5 exposure in terms of inducing cardiac oxidative stress and inflammation. Furthermore, untargeted metabolomics revealed that taurine was involved with the PM_2.5-induced cardiac dysfunction. The reduced taurine concentration in the heart was examined by LC-MS and imaging mass spectrometry; it may be due to the increased p53 expression level, ROS and inflammatory cytokines. These results emphasize the age-dependent effects of PM_2.5 on the cardiovascular system and suggest that taurine may be the novel cardiac effect target for PM_2.5-induced heart dysfunction in the aged.

Ambient air PM2.5 exposure induces heart injury and cardiac hypertrophy in rats through regulation of miR-208a/b, α/β-MHC, and GATA4

Ambient air fine particulate matter (PM2.5) may increase cardiovascular disease risks. In this study, we investigated the miR-208/GATA4/myosin heavy chain (MHC) regulation mechanisms on cardiac injury in rats after PM2.5 exposure via an animal inhalation device. The results showed that PM2.5 exposure for 2 months caused pathological heart injury, reduced nucleus-cytoplasm ratio, and increased the levels of CK-MB and cTnI, showing cardiac hypertrophy. Oxidative stress and inflammatory responses were also observed in rats' hearts exposed to PM2.5. Of note, PM2.5 exposure for 2-month significantly elevated GATA4 and β-MHC mRNA and protein expression compared with the corresponding controls, along with the high-expression of miR-208b. The ratios of β-MHC/α-MHC expression induced by PM2.5 were remarkably raised in comparison to their controls. It suggested that the up-regulation of miR-208b/β-MHC and GATA4 and the conversion from α-MHC to β-MHC may be the important causes of cardiac hypertrophy in rats incurred by PM2.5.

Inflammasome Activation in Pollution-Induced Skin Conditions

SUMMARY

Exposure to air pollutants has been now associated with detrimental effects on a variety of organs, including the heart, lungs, GI tract, and brain. However, recently it has become clear that pollutant exposure can also promote the development/exacerbation of a variety of skin conditions, including premature aging, psoriasis, acne, and atopic dermatitis. Although the molecular mechanisms by which pollutant exposure results in these cutaneous pathological manifestations, it has been noticed that an inflammatory status is a common denominator of all those skin conditions. For this reason, recently, the activation of a cytosolic multiprotein complex involved in inflammatory responses (the inflammasome) that could promote the maturation of proinflammatory cytokines interleukin-1β and interleukin-18 has been hypothesized to play a key role in pollution-induced skin damage. In this review, we summarize and propose the cutaneous inflammasome as a novel target of pollutant exposure and the eventual usage of inflammasome inhibitor as new technologies to counteract pollution-induced skin damage. Possibly, the ability to inhibit the inflammasome activation could prevent cutaneous inflammaging and ameliorate the health and appearance of the skin.

Airborne particulate matter (PM2.5) triggers ocular hypertension and glaucoma through pyroptosis

Background

Particulate matter (PM) is strongly linked to human health and has detrimental effects on the eye. Studies have, however, focused on the ocular surface, with limited research on the impact of PM_2.5 on intraocular pressure (IOP).

Methods

To investigate the impact of PM_2.5 on IOP and the associated mechanism, C57BL/6 mouse eyes were topically exposed to a PM_2.5 suspension for 3 months, and human trabecular meshwork (HTM) cells were subjected to various PM_2.5 concentrations in vitro. Cell viability, NLRP3/caspase-1, IL-1β, and GSDMD expression, reactive oxygen species (ROS) production and cell contractility were measured by western blot, ELISA, cell counting kit-8, ROS assay kit or a cell contractility assay. ROS scavenger N-acetyl-L-cysteine (NAC) and caspase-1 inhibitor VX-765 were used to intervene in PM_2.5-induced damages.

Results

The results revealed that the IOP increased gradually after PM_2.5 exposure, and upregulations of the NLRP3 inflammasome, caspase-1, IL-1β, and GSDMD protein levels were observed in outflow tissues. PM_2.5 exposure decreased HTM cell viability and affected contraction. Furthermore, elevated ROS levels were observed as well as an activation of the NLRP3 inflammasome and downstream inflammatory factors caspase-1 and IL-1β. NAC improved HTM cell viability, inhibited the activation of the NLRP3 inflammasome axis, and HTM cell contraction by scavenging ROS. VX-765 showed similar protection against the PM_2.5 induced adverse effects.

Conclusion

This study provides novel evidence that PM_2.5 has a direct toxic effect on intraocular tissues and may contribute to the initiation and development of ocular hypertension and glaucoma. This occurs as a result of increased oxidative stress and the subsequent induction of NLRP3 inflammasome mediated pyroptosis in trabecular meshwork cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00403-4.

PM2.5-related cell death patterns

With the increasingly serious problem of environmental pollution, the health problems caused by PM2.5 are gradually coming into our line of sight. Previous researches have indicated that air pollution is nearly related to various diseases, but few studies have focused on the exact function mediated by particulate matter less than 2.5 (PM2.5) in these diseases. PM2.5 is known to induce multiple ways of cell death, including autophagy, necrosis, apoptosis, pyroptosis and ferroptosis. Therefore, it is of much importance to understand the different ways of cell death caused by PM2.5 in the pathogenesis and treatment of PM2.5-related diseases. This present review is an insight of multiple ways of PM2.5‑induced cell death in different diseases.

Airborne particulate matter (PM2.5) triggers cornea inflammation and pyroptosis via NLRP3 activation

Although studies have demonstrated that fine particulate matter (PM_2.5) induces ocular surface damage, PM2.5 exposure causes cornea toxicity is not entirely clear. The aim of this study is to investigate the role of the nod-like receptor family pyrin domain containing three (NLRP3) inflammasome-mediated pyroptosis in PM_2.5-related corneal toxicity. Human corneal epithelial cells (HCECs) were exposed to different concentrations of PM_2.5, and the cell viability, expressions of NLRP3 inflammasome mediated pyroptosis axis molecules and intracellular reactive oxygen species (ROS) formation were measured in HCECs. Animal experiments were undertaken to topically apply PM_2.5 suspension to mouse eyes for three months and the pyroptosis related molecules in the mouse corneas were measured. RESULTS: Our results showed a dose-dependent decrease of HCEC viability in the PM_2.5-treated cells. NLRP3 inflammasome-mediated pyroptosis axis (NLRP3, ASC, GSDMD, caspase-1, IL-1β, and IL-18) were activated in the PM_2.5-treated HCECs, accompanied by increased ROS formation. Further in vivo study confirmed the activation of this pathway in the mouse corneas exposed to PM_2.5. In conclusion, this study provids novel evidence that PM_2.5 induces corneal toxicity by triggering cell pyroptosis.

Particulate matter (PM10) as a newly identified environmental risk factor for acute gout flares: A time-series study

OBJECTIVES

This study aimed to investigate the effect of short-term exposure to ambient particulate matter less than 10μm in diameter (PM₁₀) on occurrence of acute gout flares in the general population and identify susceptible groups accordingly.

METHODS

The data of emergency department (ED) cases with acute gout flare in Incheon city, Korea between January 1st 2008 and December 31st 2015 were collected from the National Health Insurance Service claims data. The levels of PM₁₀ and meterological measurements were provided by the Ministry of Environment and the National Meterological Office, respectively. To estimate the risk of daily ED visits due to acute gout flare, these time-series data set were analyzed using generalized additive models with Poisson distribution, including daily average PM₁₀ level, temperature, relative humidity, day of the week, national holiday, season, and date.

RESULTS

The risk of daily ED visits for acute gout flares per interquartile range increment of the average daily PM₁₀ levels significantly increased in the cumulative lag 0-7 model (relative risk, 1.018; 95% confidence interval, 1.008-1.027, P<0.001). In particular, men aged≥40 years and those with a history of diabetes mellitus or gout were significantly at a high risk of acute gout flares by subgroup analysis.

CONCLUSIONS

Our time-series study demonstrated a modest, but significant effect of short-term exposure to PM₁₀ on ED visits for acute gout flares. Ambient PM₁₀ may be a newly identified environmental risk factor for acute gout flares.

Fine Particulate Matter (PM2.5) upregulates expression of Inflammasome NLRP1 via ROS/NF-κB signaling in HaCaT Cells

Skin, as the major organ of a human body, is constantly exposed to PM2.5 stimulation, which may exert specific toxic influences on the physiology of skin. This study aims to investigate the effect of PM2.5 on the formation of inflammasomes in skin cells and to explore the potential mechanism linking PM2.5 and skin inflammation. Changes in mRNA and protein levels of inflammasome-related genes were detected by real-time PCR and western blot in human immortalized epidermal cells (HaCaT) treated with PM2.5 at multiple concentrations for 24 hours. The expression of NLRP1 was increased significantly both in mRNA and protein levels after PM2.5 exposure while the elevated secretory protein level of IL-1β in cell culture was detected by ELISA, which is one of the main downstream factors of NLRP1. In addition, the upregulation of NLRP1 and IL-1β could be reversed by NF-κB inhibitor indicating that PM2.5 may promote NLRP1 expression through activating NF-κB pathway. Furthermore, high ROS level was also found in cells treated with PM2.5 and inhibition of ROS could also reverse NK-κB production stimulated by PM2.5 that means ROS is involved in this skin inflammation process.

NLRP3 Inflammasome: A Potential Therapeutic Target in Fine Particulate Matter-Induced Neuroinflammation in Alzheimer's Disease

As one of the most harmful air pollutants, fine particulate matter (PM2.5) has been implicated as a risk factor for multiple diseases, which has generated widespread public concern. Accordingly, a growing literature links PM2.5 exposure with Alzheimer's disease (AD). A critical gap in our understanding of the adverse effects of PM2.5 on AD is the mechanism triggered by PM2.5 that contributes to disease progression. Recent evidence has demonstrated that PM2.5 can activate NLRP3 inflammasome-mediated neuroinflammation. In this review, we highlight the novel evidence between PM2.5 exposure and AD incidence, which is collected and summarized from neuropathological, epidemiological, and neuroimaging studies to in-depth deciphering molecular mechanisms. First, neuropathological, epidemiological, and neuroimaging studies will be summarized. Then, the transport pathway for central nervous system delivery of PM2.5 will be presented. Finally, the role of NLRP3 inflammasome-mediated neuroinflammation in PM2.5 induced-effects on AD will be recapitulated.

Oxidative stress pathways of air pollution mediated toxicity: Recent insights

Ambient air pollution is a leading environmental cause of morbidity and mortality globally with most of the outcomes of cardiovascular origin. While numerous mechanisms are proposed to explain the link between air pollutants and cardiovascular events, the evidence supports a role for oxidative stress as a critical intermediary pathway in the transduction of systemic responses in the cardiovascular system. Indeed, alterations in vascular function are a critical step in the development of cardiometabolic disorders such as hypertension, diabetes, and atherosclerosis. This review will provide an overview of the impact of particulate and gaseous pollutants on oxidative stress from human and animal studies published in the last five years. We discuss current gaps in knowledge and evidence to date implicating the role of oxidative stress with an emphasis on inhalational exposures. We conclude with the identification of gaps, and an exhortation for further studies to elucidate the impact of oxidative stress in air pollution mediated effects.

•

Particulate matter air pollution is the leading risk factor for cardiovascular morbidity and mortality globally.

•

Mechanisms of oxidative stress mediated pathways.

•

How does lung inflammation crucial to inhalational exposure mediate systemic toxicity?

•

Review of recent animal and human exposure studies providing insights into oxidative stress pathways.