PM2.5 induces ferroptosis in human endothelial cells through iron overload and redox imbalance

Ferroptosis: the potential value target in atherosclerosis

In advanced atherosclerosis (AS), defective function-induced cell death leads to the formation of the characteristic necrotic core and vulnerable plaque. The forms and mechanisms of cell death in AS have recently been elucidated. Among them, ferroptosis, an iron-dependent form of necrosis that is characterized by oxidative damage to phospholipids, promotes AS by accelerating endothelial dysfunction in lipid peroxidation. Moreover, disordered intracellular iron causes damage to macrophages, vascular smooth muscle cells (VSMCs), vascular endothelial cells (VECs), and affects many risk factors or pathologic processes of AS such as disturbances in lipid peroxidation, oxidative stress, inflammation, and dyslipidemia. However, the mechanisms through which ferroptosis initiates the development and progression of AS have not been established. This review explains the possible correlations between AS and ferroptosis, and provides a reliable theoretical basis for future studies on its mechanism.

Endothelium-derived Cdk5 deficit aggravates air pollution-induced peripheral vasoconstriction through AT1R upregulation

PM_2.5 infiltrates into circulation and increases the risk of systemic vascular dysfunction. As the first-line barrier against external stimuli, the molecular mechanism of the biological response of vascular endothelial cells to PM_2.5 exposure remains unclear. In this study, 4-week-old mice were exposed to Hangzhou 'real' airborne PM_2.5 for 2 months and were found to display bronchial and alveolar damage. Importantly, in the present study, we have demonstrated that Cdk5 deficit induced peripheral vasoconstriction through angiotensin II type 1 receptor under angiotensin II stimulation in Cdh5-cre;Cdk5^f/n mice. In the brain, Cdk5 deficit increased the myogenic activity in the medullary arterioles under external pressure. On the other hand, no changes in cerebral blood flow and behavior patterns were observed in the Cdh5-cre;Cdk5^f/n mice exposed to PM_2.5. Therefore, our current findings indicate that CDK5 plays an important role in endothelium cell growth, migration, and molecular transduction, which is also a sensor for the response of vascular endothelial cells to PM_2.5.

Ferroptosis and Its Potential Role in Metabolic Diseases: A Curse or Revitalization?

Ferroptosis is classified as an iron-dependent form of regulated cell death (RCD) attributed to the accumulation of lipid hydroperoxides and redox imbalance. In recent years, accumulating researches have suggested that ferroptosis may play a vital role in the development of diverse metabolic diseases, for example, diabetes and its complications (e.g., diabetic nephropathy, diabetic cardiomyopathy, diabetic myocardial ischemia/reperfusion injury and atherosclerosis [AS]), metabolic bone disease and adrenal injury. However, the specific physiopathological mechanism and precise therapeutic effect is still not clear. In this review, we summarized recent advances about the development of ferroptosis, focused on its potential character as the therapeutic target in metabolic diseases, and put forward our insights on this topic, largely to offer some help to forecast further directions.

Cigarette smoke-induced toxicity consequences of intracellular iron dysregulation and ferroptosis

Despite numerous studies on the mechanisms of cigarette smoking toxicity over the past three decades, some aspects remain obscure. Recent developments have drawn attention to some hopeful indicators that allow us to advance our awareness of cigarette-induced cell death. Ferroptosis is considered a type of governed death of cells distinguished by the iron-dependent lipid hydroperoxide deposition to fatal concentrations. Ferroptosis has been linked with pathological settings such as neurodegenerative diseases, cancer, heart attack, hemorrhagic stroke, traumatic brain injury, ischemia-reperfusion injury, and renal dysfunction. This review tries to explain the causal role of ferroptosis cascade in cigarette smoke-mediated toxicity and cell death, highlighting associations on potential action mechanisms and proposing suggestions for its detoxifying and therapeutic interventions.

Endothelial Dysfunction in Atherosclerotic Cardiovascular Diseases and Beyond: From Mechanism to Pharmacotherapies

The endothelium, a cellular monolayer lining the blood vessel wall, plays a critical role in maintaining multiorgan health and homeostasis. Endothelial functions in health include dynamic maintenance of vascular tone, angiogenesis, hemostasis, and the provision of an antioxidant, anti-inflammatory, and antithrombotic interface. Dysfunction of the vascular endothelium presents with impaired endothelium-dependent vasodilation, heightened oxidative stress, chronic inflammation, leukocyte adhesion and hyperpermeability, and endothelial cell senescence. Recent studies have implicated altered endothelial cell metabolism and endothelial-to-mesenchymal transition as new features of endothelial dysfunction. Endothelial dysfunction is regarded as a hallmark of many diverse human panvascular diseases, including atherosclerosis, hypertension, and diabetes. Endothelial dysfunction has also been implicated in severe coronavirus disease 2019. Many clinically used pharmacotherapies, ranging from traditional lipid-lowering drugs, antihypertensive drugs, and antidiabetic drugs to proprotein convertase subtilisin/kexin type 9 inhibitors and interleukin 1β monoclonal antibodies, counter endothelial dysfunction as part of their clinical benefits. The regulation of endothelial dysfunction by noncoding RNAs has provided novel insights into these newly described regulators of endothelial dysfunction, thus yielding potential new therapeutic approaches. Altogether, a better understanding of the versatile (dys)functions of endothelial cells will not only deepen our comprehension of human diseases but also accelerate effective therapeutic drug discovery. In this review, we provide a timely overview of the multiple layers of endothelial function, describe the consequences and mechanisms of endothelial dysfunction, and identify pathways to effective targeted therapies. SIGNIFICANCE STATEMENT: The endothelium was initially considered to be a semipermeable biomechanical barrier and gatekeeper of vascular health. In recent decades, a deepened understanding of the biological functions of the endothelium has led to its recognition as a ubiquitous tissue regulating vascular tone, cell behavior, innate immunity, cell-cell interactions, and cell metabolism in the vessel wall. Endothelial dysfunction is the hallmark of cardiovascular, metabolic, and emerging infectious diseases. Pharmacotherapies targeting endothelial dysfunction have potential for treatment of cardiovascular and many other diseases.

Ferritinophagy and ferroptosis in the management of metabolic diseases

Ferroptosis is a form of regulated cell death modality associated with disturbed iron-homeostasis and unrestricted lipid peroxidation. Ample evidence has depicted an essential role for ferroptosis as either the cause or consequence for human diseases, denoting the likely therapeutic promises for targeting ferroptosis in the preservation of human health. Ferritinophagy, a selective form of autophagy, contributes to the initiation of ferroptosis through degradation of ferritin, which triggers labile iron overload (IO), lipid peroxidation, membrane damage, and cell death. In this review, we will delineate the role of ferritinophagy in ferroptosis, and its underlying regulatory mechanisms, to unveil the therapeutic value of ferritinophagy as a target in the combat of ferroptosis to manage metabolic diseases.

Ferroptotic Cell Death: New Regulatory Mechanisms for Metabolic Diseases

Background:

Cell death is a fundamental biological phenomenon that contributes to the pathogenesis of various diseases. Regulation of iron and iron metabolism has received considerable research interests especially concerning the progression of metabolic diseases.

Discussion:

Emerging evidence shows that ferroptosis, a non-apoptotic programmed cell death induced by iron-dependent lipid peroxidation, contributes to the development of complex diseases such as non-alcoholic steatohepatitis, cardiomyopathy, renal ischemia-reperfusion, and neurodegenerative diseases. Therefore, inhibiting ferroptosis can improve the pathophysiology of associated metabolic diseases. This review describes the vital role of ferroptosis in mediating the development of certain metabolic diseases. Besides, the potential risk of iron and ferroptosis in atherosclerosis and cardiovascular diseases is also described. Iron overload and ferroptosis are potential secondary causes of death in metabolic diseases. Moreover, this review also provides potential novel approaches against ferroptosis based on recent research advances.

Conclusion:

Several controversies exist concerning mechanisms underlying ferroptotic cell death in metabolic diseases, particularly in atherosclerosis. Since ferroptosis participates in the progression of metabolic diseases such as non-alcoholic steatohepatitis (NASH), there is a need to develop new drugs targeting ferroptosis to alleviate such diseases.

WDR45 Mutation Impairs the Autophagic Degradation of Transferrin Receptor and Promotes Ferroptosis

WDR45 is an autophagy-related protein that involves in the formation of autophagosome. Mutations in WDR45 lead to the impairment of autophagy which is associated with the human β-propeller protein-associated neurodegeneration (BPAN). However, the relationship between autophagy and brain iron accumulation in patients with BPAN remains unclear. Here, we demonstrated that transferrin receptor (TfRC) which is critical for the iron import of cells was degraded via autophagy. TfRC was accumulated after the inhibition of autophagy by treatment with autophagic inhibitor chloroquine or knockdown of ATG2A. The intracellular iron content was increased in cells overexpressing TfRC or mutant WDR45, however, ferritin H (FTH) chain was decreased. Increased TfRC and simultaneously decreased FTH consequently resulted in an elevated level of ferrous iron (Fe²⁺) which further promoted cell ferroptosis, demonstrated by the increased lipid peroxidation and reactive oxygen species (ROS) and the decreased glutathione peroxidase 4 (GPX4) and cell viability. Taken together, these findings provide a piece of important evidence that WDR45 deficiency impairs autophagic degradation of TfRC, therefore leading to iron accumulation, and the elevated iron promotes ferroptosis which may contribute to the progression of BPAN.

Natural compounds protect the skin from airborne particulate matter by attenuating oxidative stress

Particulate matter (PM) is a common indirect indicator of air pollution and threatens public health upon prolonged exposure, leading to oxidative stress, increasing the risk of develop respiratory and cardiovascular, as well as several autoimmune diseases and cancer. Nowadays, as a first line defense against PM, skin health attracted much attention. Our review summarized the skin damage mechanism induced by PM, including damage skin barrier directly, reactive oxygen species (ROS) accumulation, autophagy, and two canonical signaling pathways. Furthermore, ROS and oxidative stress have been considered pathogenesis centers, with essential skin damage roles. Extracts from plants and natural compounds which present high antioxidant capacity could be used to treat or protect against air pollution-related skin damage. We conclude the extracts reported in recent studies with protective effects on PM-mediated skin damage. Besides, the mechanism of extracts' positive effects has been revealed partially.

Atmospheric particulate matter impedes autophagic flux by impairing lysosomal milieu and integrity in human umbilical vein endothelial cells (HUVECs)

Autophagy is a dynamic process for waste disposal and cell equilibrium. Previous studies have demonstrated that atmospheric particulate matter (APM) induces autophagy and enhances LC3II expression in human vascular endothelial cells. However, the underlying mechanism of autophagosome accumulation in human vascular endothelial cells under the exposure to APM has not been understood. In principle, the upregulation of LC3II or autophagosomes accumulation is presumably caused by the enhancement of autophagic ability, or alternatively, by the abnormal autophagic degradation. Therefore, in the current study, autophagic ability and autophagic flux are systemically studied to decipher the exact cause of autophagosomes accumulation in human umbilical vein endothelial cells (HUVECs) in response to a standard urban particulate matter, PM SRM1648a. As a result, it was observed that after 24 h of exposure, PM SRM1648a significantly increases LC3II expression with apparent autophagosomes accumulation in HUVECs. Compared with the control group, there is a time-dependent increase in p62, a protein of autophagic substrate that can be preliminarily used to evaluate the autophagic degradation, in the PM SRM1648a-exposed HUVECs, which suggested that normal function of autophagic degradation was probably impaired. Additionally, mRFP-GFP-LC3 assay and LAMP-2/LC3B co-localization suggested that autolysosomes (fusion between autophagosomes and lysosomes) were partially inhibited in PM SRM1648a-treated HUVECs. Furthermore, LC3II turn-over assay hinted that after 24 h, LC3II upregulation is attributed to the blockage of autophagic flux instead of the enhancement of autophagic induction. Mechanistically, the blockade of autophagic flux can be explained by the detrimental effects of PM SRM1648a on lysosomal function, including lysosomal destabilization, lysosomal alkalization and hydrolase inactivation, which are involved in the blockade of fusion between autophagosomes and lysosomes, further disrupting autophagic degradation and waste disposal. These observations provide evidence that PM SRM1648a destroys the equilibrium of lysosomal stability and thus results in the dysfunction of autophagic flux, eventually contributing to endothelial cell damage.

Ferroptosis and its emerging roles in cardiovascular diseases

Ferroptosis is a new form of regulated cell death (RCD) driven by iron-dependent lipid peroxidation, which is morphologically and mechanistically distinct from other forms of RCD including apoptosis, autophagic cell death, pyroptosis and necroptosis. Recently, ferroptosis has been found to participate in the development of various cardiovascular diseases (CVDs) including doxorubicin-induced cardiotoxicity, ischemia/reperfusion-induced cardiomyopathy, heart failure, aortic dissection and stroke. Cardiovascular homeostasis is indulged in delicate equilibrium of assorted cell types composing the heart or vessels, and how ferroptosis contributes to the pathophysiological responses in CVD progression is unclear. Herein, we reviewed recent discoveries on the basis of ferroptosis and its involvement in CVD pathogenesis, together with related therapeutic potentials, aiming to provide insights on fundamental mechanisms of ferroptosis and implications in CVDs and associated disorders.

Acute exposure of di(2-ethylhexyl) phthalate (DEHP) induces immune signal regulation and ferroptosis in oryzias melastigma

The plasticizer di (2-ethylhexyl) phthalate (DEHP) is becoming increasingly abundant throughout the global environment as plastic pollution becomes highly severe, especially in the ocean. The adverse effects of DEHP have garnered increasing concern as they are recognized as endocrine disruptors. However, information on the effects of DEHP in marine organisms remains limited. In this study, acute toxic effects on marine medaka (Oryzias melastigma) following DEHP exposure were investigated. Transcriptome analysis was performed on the livers of medaka exposed to DEHP for 6 and 24 h. Results showed that 1595 genes were affected in all the analyzed specimens, and several genes expressed variably according to sex. Some pathways associated with immunity, metabolism, and endocrine system were significantly enriched, with the complement system appearing to be the most affected immune pathway. Pathway enrichment indicated that, under acute DEHP exposure, the immune response of females tended to be more sensitive than that of males. In addition, ferroptosis occurred in response to DEHP exposure, which resulted in an enrichment of the ferroptosis pathway along with iron overload, an increase in malondialdehyde (MDA) and lipid peroxidation (LPO) content, and a decrease in glutathione (GSH) levels. These results indicate that a form of cell death characterized by iron-dependence occurred following DEHP exposure, but the underlying mechanism requires further analysis. This study implies that DEHP can alter some molecular regulation patterns within a short period and induce cell death through ferroptosis.

SARS-CoV-2 infection, COVID-19 pathogenesis, and exposure to air pollution: What is the connection?

Exposure to air pollutants has been previously associated with respiratory viral infections, including influenza, measles, mumps, rhinovirus, and respiratory syncytial virus. Epidemiological studies have also suggested that air pollution exposure is associated with increased cases of SARS-CoV-2 infection and COVID-19-associated mortality, although the molecular mechanisms by which pollutant exposure affects viral infection and pathogenesis of COVID-19 remain unknown. In this review, we suggest potential molecular mechanisms that could account for this association. We have focused on the potential effect of exposure to nitrogen dioxide (NO2 ), ozone (O3 ), and particulate matter (PM) since there are studies investigating how exposure to these pollutants affects the life cycle of other viruses. We have concluded that pollutant exposure may affect different stages of the viral life cycle, including inhibition of mucociliary clearance, alteration of viral receptors and proteases required for entry, changes to antiviral interferon production and viral replication, changes in viral assembly mediated by autophagy, prevention of uptake by macrophages, and promotion of viral spread by increasing epithelial permeability. We believe that exposure to pollutants skews adaptive immune responses toward bacterial/allergic immune responses, as opposed to antiviral responses. Exposure to air pollutants could also predispose exposed populations toward developing COIVD-19-associated immunopathology, enhancing virus-induced tissue inflammation and damage.

Transcriptomic analysis of key genes and pathways in human bronchial epithelial cells BEAS-2B exposed to urban particulate matter

Urban particulate matter (PM), a great danger to public health, is associated with increasing risk of pulmonary diseases. However, the involved key genes and signaling pathways mediating the cellular responses to urban PM are largely unknown. In this study, human bronchial epithelial cells BEAS-2B was exposed to Standard reference material (SRM) 1649b, followed by RNA-sequencing (RNA-seq) and a combination of different bioinformatics analysis. A total of 201 genes (111 upregulated and 90 downregulated) were identified as the differentially expressed genes (DEGs). Moreover, Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and gene set enrichment analysis (GSEA) unveiled several significant genes and pathways involved in PM-induced lung toxicity. Protein-protein interaction (PPI) network was performed with the Search Tool for the Retrieval of Interacting Genes (STRING), and the hub gene modules were recognized by Molecular Complex Detection (MCODE), a plug-in of Cytoscape. Moreover, Connectivity Map (CMap) analysis found six candidate small molecular compounds to reverse PM-altered gene expression, including aminohippuric acid, captopril, cinoxacin, fasudil, pargyline, and altizide. Finally, the expressions of part vital genes related to inflammation (IL-1β, CXCL2, CXCL5, CXCL8), ferroptosis (HMOX1, GCLM), and autophagy (BECN1, MAPK1LC3B) were in accordance with the RNA-seq data, with a concentration-dependent manner. This study may be helpful in revealing the complex molecular mechanisms underlying PM-induced lung toxicity and provide some new therapeutic targets for PM-related pulmonary diseases.

Analysis by Metabolomics and Transcriptomics for the Energy Metabolism Disorder and the Aryl Hydrocarbon Receptor Activation in Male Reproduction of Mice and GC-2spd Cells Exposed to PM2.5

Fine particulate matter (PM_2.5)-induced male reproductive toxicity arouses global public health concerns. However, the mechanisms of toxicity remain unclear. This study aimed to further investigate toxicity pathways by exposure to PM_2.5in vitro and in vivo through the application of metabolomics and transcriptomics. In vitro, spermatocyte-derived GC-2spd cells were treated with 0, 25, 50, 100 μg/mL PM_2.5 for 48 h. In vivo, the real-world exposure of PM_2.5 for mouse was established. Forty-five male C57BL/6 mice were exposed to filtered air, unfiltered air, and concentrated ambient PM_2.5 in Tangshan of China for 8 weeks, respectively. The results in vitro and in vivo showed that PM_2.5 exposure inhibited GC-2spd cell proliferation and reduced sperm motility. Mitochondrial damage was observed after PM_2.5 treatment. Increased Humanin and MOTS-c levels and decreased mitochondrial respiratory indicated that mitochondrial function was disturbed. Furthermore, nontargeted metabolomics analysis revealed that PM_2.5 exposure could disturb the citrate cycle (TCA cycle) and reduce amino acids and nucleotide synthesis. Mechanically, the aryl hydrocarbon receptor (AhR) pathway was activated after exposure to PM_2.5, with a significant increase in CYP1A1 expression. Further studies showed that PM_2.5 exposure significantly increased both intracellular and mitochondrial reactive oxygen species (ROS) and activated NRF2 antioxidative pathway. With the RNA-sequencing technique, the differentially expressed genes induced by PM_2.5 exposure were mainly enriched in the metabolism of xenobiotics by the cytochrome P450 pathway, of which Cyp1a1 was the most significantly changed gene. Our findings demonstrated that PM_2.5 exposure could induce spermatocyte damage and energy metabolism disorder. The activation of the aryl hydrocarbon receptor might be involved in the mechanism of male reproductive toxicity.

microRNA-146a-5p negatively modulates PM2.5 caused inflammation in THP-1 cells via autophagy process

Ambient fine particulate matter (PM_2.5) can change the expression profile of microRNAs (miRs), which may play important roles in mediating inflammatory responses. The present study attempts to investigate the roles of miR-146a-5p in regulating cytokine expression in a human monocytic leukemia cell line (THP-1). Four types of PM_2.5 extracts obtained from Beijing, China, were subjected to cytotoxic tests in THP-1 cells. These four PM_2.5 extracts included two water extracts collected from non-heating and heating season (WN and WH), and two organic extracts from non-heating and heating season (DN and DH). Firstly, the four PM_2.5 extracts caused cytotoxicity, oxidative stress responses, cytokine gene expressions and interleukin 8 (IL-8) release in THP-1 cells, with WH showing the highest cytotoxicity, WN showing the highest oxidative stress and inflammatory responses. Additionally, we observed expression of miR-146a-5p was significantly increased, with the maximal response of six folds in WN group. Cellular autophagy was initiated by PM_2.5 indicated by related protein and gene expressions. Both RNA interference and autophagy inhibitor were applied to interrupt autophagy process in THP-1 cells. Autophagy dysfunction could alleviate IL-8 expression, suggesting autophagy process regulated cytokine expression and inflammatory response caused by PM_2.5. A chemical inhibitor was applied to inhibit the function of miR-146a-5p, and then the expressions of IL-8 and autophagic genes were significantly aggravated. Meanwhile, two target genes of miR-146a-5p, interleukin-1 associated-kinase-1 (IRAK1) and tumor-necrosis factor receptor-associated factor-6 (TRAF6) were increased dramatically, which also played important roles in regulation of autophagy. These data suggested miR-146a-5p negatively modulated cytokine expression caused by PM_2.5 via autophagy process through the target genes of IRAK1 and TRAF6. Our findings raised the concerns of the changes of miR expression profile and following responses caused by PM_2.5.

The critical role of endothelial function in fine particulate matter-induced atherosclerosis

Ambient and indoor air pollution contributes annually to approximately seven million premature deaths. Air pollution is a complex mixture of gaseous and particulate materials. In particular, fine particulate matter (PM2.5) plays a major mortality risk factor particularly on cardiovascular diseases through mechanisms of atherosclerosis, thrombosis and inflammation. A review on the PM2.5-induced atherosclerosis is needed to better understand the involved mechanisms. In this review, we summarized epidemiology and animal studies of PM2.5-induced atherosclerosis. Vascular endothelial injury is a critical early predictor of atherosclerosis. The evidence of mechanisms of PM2.5-induced atherosclerosis supports effects on vascular function. Thus, we summarized the main mechanisms of PM2.5-triggered vascular endothelial injury, which mainly involved three aspects, including vascular endothelial permeability, vasomotor function and vascular reparative capacity. Then we reviewed the relationship between PM2.5-induced endothelial injury and atherosclerosis. PM2.5-induced endothelial injury associated with inflammation, pro-coagulation and lipid deposition. Although the evidence of PM2.5-induced atherosclerosis is undergoing continual refinement, the mechanisms of PM2.5-triggered atherosclerosis are still limited, especially indoor PM2.5. Subsequent efforts of researchers are needed to improve the understanding of PM2.5 and atherosclerosis. Preventing or avoiding PM2.5-induced endothelial damage may greatly reduce the occurrence and development of atherosclerosis.

Oxidative Damage and Antioxidant Defense in Ferroptosis

Many new types of regulated cell death have been recently implicated in human health and disease. These regulated cell deaths have different morphological, genetic, biochemical, and functional hallmarks. Ferroptosis was originally described as a carcinogenic RAS-dependent non-apoptotic cell death, and is now defined as a type of regulated necrosis characterized by iron accumulation, lipid peroxidation, and the release of damage-associated molecular patterns (DAMPs). Multiple oxidative and antioxidant systems, acting together autophagy machinery, shape the process of lipid peroxidation during ferroptosis. In particular, the production of reactive oxygen species (ROS) that depends on the activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) and the mitochondrial respiratory chain promotes lipid peroxidation by lipoxygenase (ALOX) or cytochrome P450 reductase (POR). In contrast, the glutathione (GSH), coenzyme Q10 (CoQ10), and tetrahydrobiopterin (BH4) system limits oxidative damage during ferroptosis. These antioxidant processes are further transcriptionally regulated by nuclear factor, erythroid 2-like 2 (NFE2L2/NRF2), whereas membrane repair during ferroptotic damage requires the activation of endosomal sorting complexes required for transport (ESCRT)-III. A further understanding of the process and function of ferroptosis may provide precise treatment strategies for disease.

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.

Mitochondrial superoxide mediates PM2.5-induced cytotoxicity in human pulmonary lymphatic endothelial cells

Exposure to airborne fine particulate matter (PM_2.5) is associated with a variety of respiratory health effects and contributes to premature mortality. Lymphatic vessels are instrumental in facilitating the transport of toxic materials away from the lung to maintain alveolar clearance and have been shown to play important roles in lung injury and repair. Despite intense research efforts in delineating the effects of PM_2.5 on blood vascular endothelial cells, the impacts of PM_2.5 on lymphatic endothelial cells (LECs), a specialized subset of endothelial cells that comprise lymphatic vessels, remain enigmatic. Here, we conducted MTT assay and show that treatment of human pulmonary LECs with PM_2.5 suppresses cell viability in a time- and dose-dependent manner. We subsequently performed Annexin V/propidium iodide labeling and demonstrate that PM_2.5 induces LECs apoptosis and necrosis. Furthermore, we found that manganese superoxide dismutase (SOD2) expression and mitochondrial SOD activity were profoundly reduced following PM_2.5 exposure. Mechanistically, we provide compelling evidence that PM_2.5 reduces SOD2 expression through activation of Akt pathway, which leads to a disruption of mitochondrial redox homeostasis characterized by increased accumulation of mitochondrial superoxide. Conversely, mitochondria-targeted SOD mimetic (MitoTEMPO) corrects the disturbed oxidative milieu in PM_2.5-treated LECs. Additionally, MitoTEMPO ameliorates the deleterious impacts of PM_2.5 on mitochondrial DNA integrity and preserves the viability of LECs. Taken together, these novel data support a critical role for mitochondrial superoxide in the pathogenesis of PM_2.5-induced LECs injury and identity mitochondrial-targeted antioxidants as promising therapeutic options to treat environmental lung diseases. Our findings are limited to experimental studies with primary LECs, and future investigations in animal models are warranted to shed light on the precise pathophysiology of lymphatic system in response to PM exposure.

Ambient particulate matter triggers dysfunction of subcellular structures and endothelial cell apoptosis through disruption of redox equilibrium and calcium homeostasis

Ambient particulate matter (APM) is becoming a global environmental problem that seriously jeopardizes public health. Previous evidence hinted that APM correlates to cardiovascular diseases. As a potential target, equilibrium of endothelial cell is a prerequisite for vascular health which could be vulnerably attacked by particles, but the specific mechanisms whereby APM damages endothelial cells have not been fully elucidated. In the current study, based on two classical mechanisms of oxidative stress and intracellular calcium overload, we aimed to explore their roles in APM-induced endothelial cell apoptosis from the perspective of subcellular levels, including endoplasmic reticulum (ER) stress and mitochondrial dysfunction. As a result, PM SRM1648a results in oxidative stress and calcium overload in EA.hy926 cells. Additionally, ERs and mitochondria could be severely disturbed by particles in morphology and function, characterized by swelling ERs, mitochondrial fission and disappearance of cristae, coupled with ER damage, mtROS overproduction and significant reduction in mitochondrial membrane potential (MMP). Adverse effects on these organelles are the prime culprits of following apoptosis in endothelial cells. Fortunately, additional antioxidants and calcium inhibitors could mitigate cellular lesion through improvement of subcellular function. Intriguingly, antioxidants relieve cell stress via both mitochondrial and ER stress-mediated pathways, whereas the role of calcium modulators in cell apoptosis is independent of the mitochondrial pathway but could be explained by amelioration of ER stress. In conclusion, our data basically revealed that internalized PM SRM1648a triggers oxidative stress and calcium influx in EA.hy926 endothelial cells, followed by multiple subcellular damage and eventually contributes to cell death, during which antioxidants and calcium inhibitors confer protective effects.

Study on ferroptosis pathway that operates in hypertensive brain damage

OBJECTIVE

This study aimed to explore the mechanism of hypertensive brain damage from ferroptosis pathway.

METHODS

Ten 22-week-old SHR rats were labeled as hypertension group(HBP), while ten WKY rats of comparable age, weight were used as normal blood pressure group(NBP). After 2 weeks of feeding, hypertensive brain damage was observed by comparing the pathological changes of brain tissue in SHR rats and WKY rats. Furthermore, the expression of GPX4 in the cerebral cortex was detected by immunofluorescence. The content of GSH was determined by spectrophotometer. The content of iron was detected by ferrous chromite colorimetry. And the content of MDA was determined by spectrophotometer. Compare the difference to investigate the role of ferroptosis mechanism in hypertensive brain damage.

RESULTS

Brain damage occurred in 24-week-old SHR rats compared with WKY rats. In the HBP, the GPX4 and GSH were significantly lower than those in the NBP, and the total iron content and MDA were significantly increased.

CONCLUSION

Thses findings suggest ferroptosis is closely related to hypertensive brain damage. Elevated blood pressure leads to iron overload in the brain. Excessive iron increases oxidative stress and lipid peroxidation in the brain, and eventually causes brain damage.

Fine particulate matter increases airway hyperresponsiveness through kallikrein-bradykinin pathway

Epidemiological studies have reported short-term fine particulate matter (PM2.5) exposure to increase incidence of asthma, related to the increase of airway hyperresponsiveness (AHR); however, the underlying mechanism remains unclear. Aim of this study was to elucidate the role of kallikrein in PM2.5-induced airway hyperresponsiveness and understand the underlying mechanism. Nose-only PM2.5 exposure system was used to generate a mouse model of airway hyperresponsiveness. Compared with the control group, PM2.5 exposure could significantly increase airway resistance, lung inflammation, kallikrein expression of bronchi-lung tissue and bradykinin (BK) secretion. However, these changes could be alleviated by kallikrein inhibitor. In addition，PM2.5 could increase the viability of human airway smooth muscle cells (hASMCs), accompanied by increased expression of kallikrein 14 (Klk14), bradykinin 2 receptor (B2R), bradykinin secretion and cytosol calcium level, while kallikrein 14 gene knockdown could significantly amelioratethe above response induced by PM2.5. Taken together, the data suggested kallikrein to play a key role in PM2.5-induced airway hyperresponsiveness, and that it could be a potential therapeutic target in asthma.

Nano-bio interactions: the implication of size-dependent biological effects of nanomaterials

Due to their many advantageous properties, nanomaterials (NMs) have been utilized in diverse consumer goods, industrial products, and for therapeutic purposes. This situation leads to a constant risk of exposure and uptake by the human body, which are highly dependent on nanomaterial size. Consequently, an improved understanding of the interactions between different sizes of nanomaterials and biological systems is needed to design safer and more clinically relevant nano systems. We discuss the sizedependent effects of nanomaterials in living organisms. Upon entry into biological systems, nanomaterials can translocate biological barriers, distribute to various tissues and elicit different toxic effects on organs, based on their size and location. The association of nanomaterial size with physiological structures within organs determines the site of accumulation of nanoparticles. In general, nanomaterials smaller than 20 nm tend to accumulate in the kidney while nanomaterials between 20 and 100 nm preferentially deposit in the liver. After accumulating in organs, nanomaterials can induce inflammation, damage structural integrity and ultimately result in organ dysfunction, which helps better understand the size-dependent dynamic processes and toxicity of nanomaterials in organisms. The enhanced permeability and retention effect of nanomaterials and the utility of this phenomenon in tumor therapy are also highlighted.

Air pollutants disrupt iron homeostasis to impact oxidant generation, biological effects, and tissue injury

Air pollutants cause changes in iron homeostasis through: 1) a capacity of the pollutant, or a metabolite(s), to complex/chelate iron from pivotal sites in the cell or 2) an ability of the pollutant to displace iron from pivotal sites in the cell. Through either pathway of disruption in iron homeostasis, metal previously employed in essential cell processes is sequestered after air pollutant exposure. An absolute or functional cell iron deficiency results. If enough iron is lost or is otherwise not available within the cell, cell death ensues. However, prior to death, exposed cells will attempt to reverse the loss of requisite metal. This response of the cell includes increased expression of metal importers (e.g. divalent metal transporter 1). Oxidant generation after exposure to air pollutants includes superoxide production which functions in ferrireduction necessary for cell iron import. Activation of kinases and phosphatases and transcription factors and increased release of pro-inflammatory mediators also result from a cell iron deficiency, absolute or functional, after exposure to air pollutants. Finally, air pollutant exposure culminates in the development of inflammation and fibrosis which is a tissue response to the iron deficiency challenging cell survival. Following the response of increased expression of importers and ferrireduction, activation of kinases and phosphatases and transcription factors, release of pro-inflammatory mediators, and inflammation and fibrosis, cell iron is altered, and a new metal homeostasis is established. This new metal homeostasis includes increased total iron concentrations in cells with metal now at levels sufficient to meet requirements for continued function.

PM2.5 induces autophagy and apoptosis through endoplasmic reticulum stress in human endothelial cells

Endothelial cells integrally form a crucial interface that maintains homeostasis of the cardiovascular system. As a vulnerable target of PM2.5, the underlying mechanisms of endothelial cell damage have yet to be fully elucidated. In the current study, two types of cell death, including autophagy and apoptosis, and an important organelle of the endoplasmic reticulum (ER) were focalized following PM2.5 exposure. As a result, the internalization of PM2.5 has the ability to induce excess ER stress, which is a crucial step for further autophagy and apoptosis in human endothelial cells, as confirmed by the pre-treatment with the inhibitor of ER stress (4-PBA) which effectively mitigates the apoptosis rate and LC3II expression. Intriguingly, crosstalk between ER stress and autophagy demonstrated that ER stress is probably involved in autophagic events, whereas autophagy has no significant effect on ER stress but confer a protective role against PM2.5-induced endothelial cell apoptosis. Moreover, PM2.5 results in blockage of autophagic flux (failed fusion between autophagosomes and lysosomes), which is detrimental to endothelial cell survival. In conclusion, our findings provide a valuable insight into the relation between autophagy and apoptosis under PM2.5-induced ER stress conditions, where the interplay between them ultimately determines cell fate.

Hemolysis Derived Products Toxicity and Endothelium: Model of the Second Hit

Vascular diseases are multifactorial, often requiring multiple challenges, or ‘hits’, for their initiation. Intra-vascular hemolysis illustrates well the multiple-hit theory where a first event lyses red blood cells, releasing hemolysis-derived products, in particular cell-free heme which is highly toxic for the endothelium. Physiologically, hemolysis derived-products are rapidly neutralized by numerous defense systems, including haptoglobin and hemopexin which scavenge hemoglobin and heme, respectively. Likewise, cellular defense mechanisms are involved, including heme-oxygenase 1 upregulation which metabolizes heme. However, in cases of intra-vascular hemolysis, those systems are overwhelmed. Heme exerts toxic effects by acting as a damage-associated molecular pattern and promoting, together with hemoglobin, nitric oxide scavenging and ROS production. In addition, it activates the complement and the coagulation systems. Together, these processes lead to endothelial cell injury which triggers pro-thrombotic and pro-inflammatory phenotypes. Moreover, among endothelial cells, glomerular ones display a particular susceptibility explained by a weaker capacity to counteract hemolysis injury. In this review, we illustrate the ‘multiple-hit’ theory through the example of intra-vascular hemolysis, with a particular focus on cell-free heme, and we advance hypotheses explaining the glomerular susceptibility observed in hemolytic diseases. Finally, we describe therapeutic options for reducing endothelial injury in hemolytic diseases.