Intracellular morphogenesis of diatom silica is guided by local variations in membrane curvature.

Silica cell-wall formation in diatoms is a showcase for the ability of organisms to control inorganic mineralization. The process of silicification by these unicellular algae is tightly regulated within a membrane-bound organelle, the silica deposition vesicle (SDV). Two opposing scenarios were proposed to explain the tight regulation of this intracellular process: a template-mediated process that relies on preformed scaffolds, or a template-independent self-assembly process. The present work points to a third scenario, where the SDV membrane is a dynamic mold that shapes the forming silica. We use in-cell cryo-electron tomography to visualize the silicification process in situ, in its native-state, and with a nanometer-scale resolution. This reveals that the plasma membrane interacts with the SDV membrane via physical tethering at membrane contact sites, where the curvature of the tethered side of the SDV membrane mirrors the intricate silica topography. We propose that silica growth and morphogenesis result from the biophysical properties of the SDV and plasma membranes.

Nanoparticle-assisted tubulin assembly is environment dependent.

Nanomaterials acquire a biomolecular corona upon introduction to biological media, leading to biological transformations such as changes in protein function, unmasking of epitopes, and protein fibrilization. Ex vivo studies to investigate the effect of nanoparticles on protein-protein interactions are typically performed in buffer and are rarely measured quantitatively in live cells. Here, we measure the differential effect of silica nanoparticles on protein association in vitro vs. in mammalian cells. BtubA and BtubB are a pair of bacterial tubulin proteins identified in Prosthecobacter strains that self-assemble like eukaryotic tubulin, first into dimers and then into microtubules in vitro or in vivo. Förster resonance energy transfer labeling of each of the Btub monomers with a donor (mEGFP) and acceptor (mRuby3) fluorescent protein provides a quantitative tool to measure their binding interactions in the presence of unfunctionalized silica nanoparticles in buffer and in cells using fluorescence spectroscopy and microscopy. We show that silica nanoparticles enhance BtubAB dimerization in buffer due to protein corona formation. However, these nanoparticles have little effect on bacterial tubulin self-assembly in the complex mammalian cellular environment. Thus, the effect of nanomaterials on protein-protein interactions may not be readily translated from the test tube to the cell in the absence of particle surface functionalization that can enable targeted protein-nanoparticle interactions to withstand competitive binding in the nanoparticle corona from other biomolecules.

Comparative CO2 and SiO2 hydratase activity of an enzyme from the siliceous demosponge Suberitesdomuncula.

Silicase, an enzyme that catalyzes the hydrolysis of silicon-oxygen bonds, is a crucial player in breaking down silicates into silicic acid, particularly in organisms like aquatic sponges with siliceous skeletons. Despite its significance, our understanding of silicase remains limited. This study comprehensively examines silicase from the demosponge Suberites domuncula, focusing on its kinetics toward CO2 as a substrate, as well as its silicase and esterase activity. It investigates inhibition and activation profiles with a range of inhibitors and activators belonging to various classes. By comparing its esterase activity to human carbonic anhydrase II, we gain insights into its enzymatic properties. Moreover, we investigate silicase's inhibition and activation profiles, providing valuable information for potential applications. We explore the evolutionary relationship of silicase with related enzymes, revealing potential functional roles in biological systems. Additionally, we propose a biochemical mechanism through three-dimensional modeling, shedding light on its catalytic mechanisms and structural features for both silicase activity and CO2 hydration. We highlight nature's utilization of enzymatic expertise in silica metabolism. This study enhances our understanding of silicase and contributes to broader insights into ecosystem functioning and Earth's geochemical cycles, emphasizing the intricate interplay between biology and the environment.

Nanoparticles Dysregulate the Human Placental Secretome with Consequences on Angiogenesis and Vascularization.

Exposure to nanoparticles (NPs) in pregnancy is increasingly linked to adverse effects on embryo-fetal development and health later in life. However, the developmental toxicity mechanisms of NPs are largely unknown, in particular potential effects on the placental secretome, which orchestrates many developmental processes pivotal for pregnancy success. This study demonstrates extensive material- and pregnancy stage-specific deregulation of placental signaling from a single exposure of human placental explants to physiologically relevant concentrations of engineered (silica (SiO2) and titanium dioxide (TiO2) NPs) and environmental NPs (diesel exhaust particles, DEPs). This includes a multitude of secreted inflammatory, vascular, and endocrine placental factors as well as extracellular vesicle (EV)-associated proteins. Moreover, conditioned media (CM) from NP-exposed explants induce pronounced anti-angiogenic and anti-vasculogenic effects, while early neurodevelopmental processes are only marginally affected. These findings underscore the potential of metal oxide NPs and DEPs for widespread interference with the placental secretome and identify vascular morphogenesis as a sensitive outcome for the indirect developmental toxicity of different NPs. Overall, this work has profound implications for the future safety assessment of NPs for industrial, commercial, or medical applications in pregnancy, which should consider placenta-mediated toxicity by holistic secretomics approaches to ensure the development of safe nanotechnologies.

Ferroptosis contributing to cardiomyocyte injury induced by silica nanoparticles via miR-125b-2-3p/HO-1 signaling.

BACKGROUND: Amorphous silica nanoparticles (SiNPs) have been gradually proven to threaten cardiac health, but pathogenesis has not been fully elucidated. Ferroptosis is a newly defined form of programmed cell death that is implicated in myocardial diseases. Nevertheless, its role in the adverse cardiac effects of SiNPs has not been described. RESULTS: We first reported the induction of cardiomyocyte ferroptosis by SiNPs in both in vivo and in vitro. The sub-chronic exposure to SiNPs through intratracheal instillation aroused myocardial injury, characterized by significant inflammatory infiltration and collagen hyperplasia, accompanied by elevated CK-MB and cTnT activities in serum. Meanwhile, the activation of myocardial ferroptosis by SiNPs was certified by the extensive iron overload, declined FTH1 and FTL, and lipid peroxidation. The correlation analysis among detected indexes hinted ferroptosis was responsible for the SiNPs-aroused myocardial injury. Further, in vitro tests, SiNPs triggered iron overload and lipid peroxidation in cardiomyocytes. Concomitantly, altered expressions of TfR, DMT1, FTH1, and FTL indicated dysregulated iron metabolism of cardiomyocytes upon SiNP stimuli. Also, shrinking mitochondria with ridge fracture and ruptured outer membrane were noticed. To note, the ferroptosis inhibitor Ferrostatin-1 could effectively alleviate SiNPs-induced iron overload, lipid peroxidation, and myocardial cytotoxicity. More importantly, the mechanistic investigations revealed miR-125b-2-3p-targeted HO-1 as a key player in the induction of ferroptosis by SiNPs, probably through regulating the intracellular iron metabolism to mediate iron overload and ensuing lipid peroxidation. CONCLUSIONS: Our findings firstly underscored the fact that ferroptosis mediated by miR-125b-2-3p/HO-1 signaling was a contributor to SiNPs-induced myocardial injury, which could be of importance to elucidate the toxicity and provide new insights into the future safety applications of SiNPs-related nano products.

Equisetum arvense as a silica fertilizer.

The aim was to use the agricultural weed and silica (Si) hyperaccumulator Equisetum arvense as Si fertilizer in plant cultivation. We investigated (1) the Si uptake in various Equisetum species, (2) where Si accumulates in the Equisetum plant, (3) processing methods to release as much Si as possible from dried, ground E. arvense plants and (4) which treatment yields gives the highest uptake of Si in young wheat plants cultivated in soil containing ground E. arvense. The results showed that E. arvense containes 22% Si and was among the best Si accumulators. Equisetum arvense accumulates Si as both soluble and firmly bound fractions. Amorphous silica (SiO2) accumulates in the outer cell walls of epidermis of the entire plant. Regarding the processing method, a longer treatment time, greater concentration of Equisetum, boiling, and the addition of sodium bicarbonate increased the Si availability in ground, dried E. arvense. The addition of untreated, ground, dried E. arvense to the soil, corresponding to 160 kg Si ha-1, increased the available Si in the soil and the Si uptake in wheat plants by five-fold, compared with the control. Boiling the ground E. arvense increased the Si uptake by 10 times, and the of sodium bicarbonate increased the availability and uptake by 40 times, compared with the control. In conclusion, dried, ground E. arvense can be used as a Si fertilizer as is, after boiling for a slightly better effect, or with sodium bicarbonate (up to a similar amount as the ground material) for best effect.

Increased endocytosis rate and enhanced lysosomal pathway of silica-coated superparamagnetic nanoparticles into M-HeLa cells compared with cultured primary motor neurons.

The unique properties of superparamagnetic iron oxide nanoparticles (SPIONs) enable their use as magnetic biosensors, targeted drug delivery, magnetothermia, magnetic resonance imaging, etc. Today, SPIONs are the only type of metal oxide nanoparticles approved for biomedical application. In this work, we analyzed the cellular response to the previously reported luminescent silica coated SPIONs of the two cell types: M-HeLa cells and primary motor neuron culture. Both internalization pathways and intracellular fate of SPIONs have been compared for these cell lines using fluorescence and transmission electron microscopy. We also applied a pharmacological approach to analyze the endocytosis pathways of SPIONs into the investigated cell lines. The penetration of SPIONs into M-HeLa cells is already noticeable within 30 s of incubation through both caveolin-dependent endocytosis and micropinocytosis. However, incubation for a longer time (1 h at least) is required for the internalization of SPIONs into motor neuron culture cells provided by dynamin-dependent endocytosis and macropinocytosis. The intracellular colocalization assay reveals that the lysosomal internalization pathway of SPIONs is also dependent on the cell type. The lysosomal pathway is much more pronounced for M-HeLa cells compared with motor neurons. The emphasized differences in cellular responses of the two cell lines open up new opportunities in the application of SPIONs in the diagnostics and therapy of cancer cells.

Macrophage-derived exosomal HMGB3 regulates silica-induced pulmonary inflammation by promoting M1 macrophage polarization and recruitment.

BACKGROUND: Chronic inflammation and fibrosis are characteristics of silicosis, and the inflammatory mediators involved in silicosis have not been fully elucidated. Recently, macrophage-derived exosomes have been reported to be inflammatory modulators, but their role in silicosis has not been explored. The purpose of the present study was to investigate the role of macrophage-derived exosomal high mobility group box 3 (HMGB3) in silica-induced pulmonary inflammation. METHODS: The induction of the inflammatory response and the recruitment of monocytes/macrophages were evaluated by immunofluorescence, flow cytometry and transwell assays. The expression of inflammatory cytokines was examined by RT-PCR and ELISA, and the signalling pathways involved were examined by western blot analysis. RESULTS: HMGB3 expression was increased in exosomes derived from silica-exposed macrophages. Exosomal HMGB3 significantly upregulated the expression of inflammatory cytokines, activated the STAT3/MAPK (ERK1/2 and p38)/NF-κB pathways in monocytes/macrophages, and promoted the migration of these cells by CCR2. CONCLUSIONS: Exosomal HMGB3 is a proinflammatory modulator of silica-induced inflammation that promotes the inflammatory response and recruitment of monocytes/macrophages by regulating the activation of the STAT3/MAPK/NF-κB/CCR2 pathways.

Genome-wide forward genetic screening to identify receptors and proteins mediating nanoparticle uptake and intracellular processing.

Understanding how cells process nanoparticles is crucial to optimize nanomedicine efficacy. However, characterizing cellular pathways is challenging, especially if non-canonical mechanisms are involved. In this Article a genome-wide forward genetic screening based on insertional mutagenesis is applied to discover receptors and proteins involved in the intracellular accumulation (uptake and intracellular processing) of silica nanoparticles. The nanoparticles are covered by a human serum corona known to target the low-density lipoprotein receptor (LDLR). By sorting cells with reduced nanoparticle accumulation and deep sequencing after each sorting, 80 enriched genes are identified. We find that, as well as LDLR, the scavenger receptor SCARB1 also mediates nanoparticle accumulation. Additionally, heparan sulfate acts as a specific nanoparticle receptor, and its role varies depending on cell and nanoparticle type. Furthermore, some of the identified targets affect nanoparticle trafficking to the lysosomes. These results show the potential of genetic screening to characterize nanoparticle pathways. Additionally, they indicate that corona-coated nanoparticles are internalized via multiple receptors.

Lethal puncturing of planktonic Gram-positive and Gram-negative bacteria by magnetically-rotated silica hexapods.

Planktonic bacterial presence in many industrial and environmental applications and personal health-care products is generally countered using antimicrobials. However, antimicrobial chemicals present an environmental threat, while emerging resistance reduces their efficacy. Suspended bacteria have no defense against mechanical attack. Therefore, we synthesized silica hexapods on an α-Fe2O3 core that can be magnetically-rotated to inflict lethal cell-wall-damage to planktonic Gram-negative and Gram-positive bacteria. Hexapods possessed 600 nm long nano-spikes, composed of SiO2, as shown by FTIR and XPS. Fluorescence staining revealed cell wall damage caused by rotating hexapods. This damage was accompanied by DNA/protein release and bacterial death that increased with increasing rotational frequency up to 500 rpm. Lethal puncturing was more extensive on Gram-negative bacteria than on Gram-positive bacteria, which have a thicker peptidoglycan layer with a higher Young's modulus. Simulations confirmed that cell-wall-puncturing occurs at lower nano-spike penetration levels in the cell walls of Gram-negative bacteria. This approach offers a new way to kill bacteria in suspension, not based on antimicrobial chemicals.

Transcriptional responses to salinity-induced changes in cell wall morphology of the euryhaline diatom Pleurosira laevis.

Diatoms are unicellular algae with morphologically diverse silica cell walls, which are called frustules. The mechanism of frustule morphogenesis has attracted attention in biology and nanomaterials engineering. However, the genetic regulation of the morphology remains unclear. We therefore used transcriptome sequencing to search for genes involved in frustule morphology in the centric diatom Pleurosira laevis, which exhibits morphological plasticity between flat and domed valve faces in salinity 2 and 7, respectively. We observed differential expression of transposable elements (TEs) and transporters, likely due to osmotic response. Up-regulation of mechanosensitive ion channels and down-regulation of Ca2+-ATPases in cells with flat valves suggested that cytosolic Ca2+ levels were changed between the morphologies. Calcium signaling could be a mechanism for detecting osmotic pressure changes and triggering morphological shifts. We also observed an up-regulation of ARPC1 and annexin, involved in the regulation of actin filament dynamics known to affect frustule morphology, as well as the up-regulation of genes encoding frustule-related proteins such as BacSETs and frustulin. Taken together, we propose a model in which salinity-induced morphogenetic changes are driven by upstream responses, such as the regulation of cytosolic Ca2+ levels, and downstream responses, such as Ca2+-dependent regulation of actin dynamics and frustule-related proteins. This study highlights the sensitivity of euryhaline diatoms to environmental salinity and the role of active cellular processes in controlling gross valve morphology under different osmotic pressures.

Transcriptomic and biochemical insights into fall armyworm (Spodoptera frugiperda) responses on silicon-treated maize.

Background: The fall armyworm, Spodoptera frugiperda, is an agricultural pest of significant economic concern globally, known for its adaptability, pesticide resistance, and damage to key crops such as maize. Conventional chemical pesticides pose challenges, including the development of resistance and environmental pollution. The study aims to investigate an alternative solution: the application of soluble silicon (Si) sources to enhance plant resistance against the fall armyworm. Methods: Silicon dioxide (SiO2) and potassium silicate (K2SiO3) were applied to maize plants via foliar spray. Transcriptomic and biochemical analyses were performed to study the gene expression changes in the fall armyworm feeding on Si-treated maize. Results: Results indicated a significant impact on gene expression, with a large number of differentially expressed genes (DEGs) identified in both SiO2 and K2SiO3 treatments. Furthermore, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis identified critical DEGs involved in specific pathways, including amino acid, carbohydrate, lipid, energy, xenobiotics metabolisms, signal transduction, and posttranslational modification, significantly altered at both Si sources. Biochemical analyses further revealed that Si treatments inhibited several enzyme activities (glutamate dehydrogenase, trehalase, glucose-6-phosphate dehydrogenase, chitinase, juvenile hormone esterase, and cyclooxygenase while simultaneously inducing others (total protein, lipopolysaccharide, fatty acid synthase, ATPase, and cytochrome P450), thus suggesting a toxic effect on the fall armyworm. In conclusion, Si applications on maize influence the gene expression and biochemical activities of the fall armyworm, potentially offering a sustainable pest management strategy.

Porous Se@SiO2 nanospheres alleviate diabetic retinopathy by inhibiting excess lipid peroxidation and inflammation.

BACKGROUND: Lipid peroxidation is a characteristic metabolic manifestation of diabetic retinopathy (DR) that causes inflammation, eventually leading to severe retinal vascular abnormalities. Selenium (Se) can directly or indirectly scavenge intracellular free radicals. Due to the narrow distinction between Se's effective and toxic doses, porous Se@SiO2 nanospheres have been developed to control the release of Se. They exert strong antioxidant and anti-inflammatory effects. METHODS: The effect of anti-lipid peroxidation and anti-inflammatory effects of porous Se@SiO2 nanospheres on diabetic mice were assessed by detecting the level of Malondialdehyde (MDA), glutathione peroxidase 4 (GPX4), decreased reduced/oxidized glutathione (GSH/GSSG) ratio, tumor necrosis factor (TNF)-α, interferon (IFN)-γ, and interleukin (IL) -1ß of the retina. To further examine the protective effect of porous Se@SiO2 nanospheres on the retinal vasculopathy of diabetic mice, retinal acellular capillary, the expression of tight junction proteins, and blood-retinal barrier destruction was observed. Finally, we validated the GPX4 as the target of porous Se@SiO2 nanospheres via decreased expression of GPX4 and detected the level of MDA, GSH/GSSG, TNF-α, IFN-γ, IL -1ß, wound healing assay, and tube formation in high glucose (HG) cultured Human retinal microvascular endothelial cells (HRMECs). RESULTS: The porous Se@SiO2 nanospheres reduced the level of MDA, TNF-α, IFN-γ, and IL -1ß, while increasing the level of GPX4 and GSH/GSSG in diabetic mice. Therefore, porous Se@SiO2 nanospheres reduced the number of retinal acellular capillaries, depletion of tight junction proteins, and vascular leakage in diabetic mice. Further, we identified GPX4 as the target of porous Se@SiO2 nanospheres as GPX4 inhibition reduced the repression effect of anti-lipid peroxidation, anti-inflammatory, and protective effects of endothelial cell dysfunction of porous Se@SiO2 nanospheres in HG-cultured HRMECs. CONCLUSION: Porous Se@SiO2 nanospheres effectively attenuated retinal vasculopathy in diabetic mice via inhibiting excess lipid peroxidation and inflammation by target GPX4, suggesting their potential as therapeutic agents for DR.

Differential Expression of Stress Adaptation Genes in a Diatom Ulnaria acus under Different Culture Conditions.

Diatoms are a group of unicellular eukaryotes that are essential primary producers in aquatic ecosystems. The dynamic nature of their habitat necessitates a quick and specific response to various stresses. However, the molecular mechanisms of their physiological adaptations are still underexplored. In this work, we study the response of the cosmopolitan freshwater diatom Ulnaria acus (Bacillariophyceae, Fragilariophycidae, Licmophorales, Ulnariaceae, Ulnaria) in relation to a range of stress factors, namely silica deficiency, prolonged cultivation, and interaction with an algicidal bacterium. Fluorescent staining and light microscopy were used to determine the physiological state of cells under these stresses. To explore molecular reactions, we studied the genes involved in the stress response-type III metacaspase (MC), metacaspase-like proteases (MCP), death-specific protein (DSP), delta-1-pyrroline-5-carboxylate dehydrogenase (ALDH12), and glutathione synthetase (GSHS). We have described the structure of these genes, analyzed the predicted amino acid sequences, and measured their expression dynamics in vitro using qRT-PCR. We demonstrated that the expression of UaMC1, UaMC3, and UaDSP increased during the first five days of silicon starvation. On the seventh day, it was replaced with the expression of UaMC2, UaGSHS, and UaALDH. After 45 days of culture, cells stopped growing, and the expression of UaMC1, UaMC2, UaGSHS, and UaDSP increased. Exposure to an algicidal bacterial filtrate induced a higher expression of UaMC1 and UaGSHS. Thus, we can conclude that these proteins are involved in diatoms' adaptions to environmental changes. Further, these data show that the molecular adaptation mechanisms in diatoms depend on the nature and exposure duration of a stress factor.

Silica nanoparticles enhance the cyto- and hemocompatibility of a multilayered extracellular matrix scaffold for vascular tissue regeneration.

PURPOSE: The limited availability of autologous vessels for vascular bypass surgeries is a major roadblock to treating severe cardiovascular diseases. Based on this clinical priority, our group has developed a novel engineered vascular graft by rolling human amniotic membranes into multilayered extracellular matrixes (ECM). When treated with silica nanoparticles (SiNP), these rolled scaffolds showed a significant improvement in their structural and mechanical properties, matching those from gold standard autologous grafts. However, it remained to be determined how cells respond to SiNP-treated materials. As a first step toward understanding the biocompatibility of SiNP-dosed biomaterials, we aimed to assess how endothelial cells and blood components interact with SiNP-treated ECM scaffolds. METHODS: To test this, we used established in vitro assays to study SiNP and SiNP-treated scaffolds' cyto and hemocompatibility. RESULTS: Our results showed that SiNP effects on cells were concentration-dependent with no adverse effects observed up to 10 µg/ml of SiNP, with higher concentrations inducing cytotoxic and hemolytic responses. The SiNP also enhanced the scaffold's hydrophobicity state, a feature known to inhibit platelet and immune cell adhesion. Accordingly, SiNP-treated scaffolds were also shown to support endothelial cell growth while preventing platelet and leukocyte adhesion. CONCLUSION: Our findings suggest that the addition of SiNP to human amniotic membrane extracellular matrixes improves the cyto- and hemocompatibility of rolled scaffolds and highlights this strategy as a robust mechanism to stabilize layered collagen scaffolds for vascular tissue regeneration.

Silica nanoparticles inhibit cadmium uptake by the protozoan Tetrahymena thermophila without the need for adsorption.

The simultaneous presence of nanoparticles (NPs) and heavy metals in the environment may affect their mutual biological uptake. Although previous studies showed that NPs could alter the cellular uptake of heavy metals by their adsorption of heavy metals, whether they could affect metal uptake without the need for adsorption is unknown. This study examined the effects of silica (SiO2) NPs on the uptake of Cd ion by the protozoan Tetrahymena thermophila. We found that, even with negligible levels of adsorption, SiO2 NPs at concentrations of 3 to 100 mg/L inhibited Cd uptake. This inhibitory effect decreased as the ambient Cd concentration increased from 1 to 100 µg/L, suggesting the involvement of at least two transporters with different affinities for Cd. The transporters were subsequently identified by the specific protein inhibitors amiloride and tariquidar as NCX and ABCB1, which are responsible for the uptake of Cd at low and high Cd levels, respectively. RT-qPCR and molecular dynamics simulation further showed that the inhibitory effects of SiO2 NPs were attributable to the down-regulated expression of the genes Ncx and Abcb1, steric hindrance of Cd uptake by NCX and ABCB1, and the shrinkage of the central channel pore of the transporters in the presence of SiO2 NPs. SiO2 NPs more strongly inhibited Cd transport by NCX than by ABCB1, due to the higher binding affinity of SiO2 NPs with NCX. Overall, our study sheds new light on a previously overlooked influence of NPs on metal uptake and the responsible mechanism.

Lysosomal BK channels facilitate silica-induced inflammation in macrophages.

BACKGROUND: Lysosomal ion channels are proposed therapeutic targets for a number of diseases, including those driven by NLRP3 inflammasome-mediated inflammation. Here, the specific role of the lysosomal big conductance Ca2+-activated K+ (BK) channel was evaluated in a silica model of inflammation in murine macrophages. A specific-inhibitor of BK channel function, paxilline (PAX), and activators NS11021 and NS1619 were utilized to evaluate the role of lysosomal BK channel activity in silica-induced lysosomal membrane permeabilization (LMP) and NLRP3 inflammasome activation resulting in IL-1ß release. METHODS: Murine macrophages were exposed in vitro to crystalline silica following pretreatment with BK channel inhibitors or activators and LMP, cell death, and IL-1ß release were assessed. In addition, the effect of PAX treatment on silica-induced cytosolic K+ decrease was measured. Finally, the effects of BK channel modifiers on lysosomal pH, proteolytic activity, and cholesterol transport were also evaluated. RESULTS: PAX pretreatment significantly attenuated silica-induced cell death and IL-1ß release. PAX caused an increase in lysosomal pH and decrease in lysosomal proteolytic activity. PAX also caused a significant accumulation of lysosomal cholesterol. BK channel activators NS11021 and NS1619 increased silica-induced cell death and IL-1ß release. BK channel activation also caused a decrease in lysosomal pH and increase in lysosomal proteolytic function as well as a decrease in cholesterol accumulation. CONCLUSION: Taken together, these results demonstrate that inhibiting lysosomal BK channel activity with PAX effectively reduced silica-induced cell death and IL-1ß release. Blocking cytosolic K+ entry into the lysosome prevented LMP through the decrease of lysosomal acidification and proteolytic function and increase in lysosomal cholesterol.

Lipid characteristics of lung tissue in silicosis rat model were studied based on lipid metabolomics.

Silicosis is a common occupational disease caused by the long-term inhalation of large amounts of silica dust. Lipid metabolism plays an important role in the progression of silicosis, but its contributing mechanism remains unclear. The aim of this study was to investigate the differential lipid metabolites and active metabolic pathways in silicosis rat lung tissue. We first constructed a silicosis rat model, and randomly divided 24 male SD rats into control group (C), silicosis group for 1 week (S1W), silicosis group for 2 weeks (S2W) and silicosis group for 4 weeks (S4W) with 6 rats in each group. 1 mL SiO2 suspension (50 mg/mL) or normal saline were injected into the trachea, and the rats were killed at 1 week, 2 weeks and 4 weeks, respectively. The lung tissue pathology of the rats was observed by HE staining and VG staining, and the plasma TC and FC levels were detected by the kit. Western blot was used to detect the expression of lipid-related factors CD36, PGC1α and LXR. In addition, lipidomics analysis of lung tissue samples was performed using UPLC-IMS-QTOF mass spectrometer to screen out potential differential metabolites in silicosis models and analyze lipid enrichment, and verified the expression of differential gene CHPT1 in the metabolic pathway. HE and VG staining showed that the number of nodules and fibrosis increased in a time-dependent manner in the silicosis model group, and the levels of TC, FC and CE in silicosis plasma increased. Western blot results showed that PGC1α and LXR decreased in the silicosis model group, while CD36 expression increased. In addition, metabolomics screened out 28 differential metabolites in the S1W group, 32 in the S2W group, and 22 in the S4W group, and found that the differential metabolites were mainly enriched in metabolic pathways such as glycerophospholipid metabolism and ether lipid metabolism, and the expression of differential gene CHPT1 in the metabolic pathway was decreased in the silicosis model group. These results suggest that there are significant changes in lipid metabolites in lung tissue in silicosis rat models, and glycerophospholipid metabolism was significantly enriched, suggesting that glycerophospholipids play an important role in the progression of silicosis. The differential metabolites and pathways reported in this study may provide new ideas for the pathogenesis of silicosis.

IRF4 Participates in Pulmonary Fibrosis Induced by Silica Particles through Regulating Macrophage Polarization and Fibroblast Activation.

Long-term exposure to silica dust can cause silicosis, which is characterized by chronic progressive inflammatory injury, fibroblast activation, and the deposition of extracellular matrix. IRF4 is involved in immune response. However, the potential regulation of IRF4 in silicosis and pulmonary fibrosis remains largely unexplored. In this study, RNA-seq analysis identified the upregulated expression of IRF4 in fibrotic lung tissues of mice exposed to silica particles. And we verified the increased expression of IRF4 in SiO2-treated macrophages and TGF-ß1-treated fibroblasts. We further found that the down-regulation of IRF4 impeded the macrophage polarization and the release of pro-fibrotic factors. Moreover, the down-regulation of IRF4 alleviated the migration, invasion, and the expression of fibrotic molecules in fibroblasts. Using ChIP-qPCR assay, we confirmed that IRF4 regulated the transcriptional activity of the IL-17A promoter, thus stimulated fibroblast activation, migration and invasion. In vivo experiment, the AAV-siIRF4 was designed to interfere with the expression of IRF4 in lung tissues of mice exposed to silica particles. Whole blood, bronchoalveolar lavage fluid and lung tissues were obtained from mice at 7, 14, 28 and 56 days after silica exposure. The results showed that the leukocyte content and inflammatory factors reached a peak at day 14 and remained peak for a long time after IRF4 knockdown. Furthermore, the fibrotic responses of mouse lung tissues were alleviated after IRF4 knockdown. Our study explored the important roles of IRF4 in inflammatory and fibrotic responses, which provided a new target for the treatment of silicosis and pulmonary fibrosis.

The role of mitochondrial dysfunction in macrophages on SiO2 -induced pulmonary fibrosis: A review.

Several epidemiologic and toxicological studies have widely regarded that mitochondrial dysfunction is a popular molecular event in the process of silicosis from different perspectives, but the details have not been systematically summarized yet. Thus, it is necessary to investigate how silica dust leads to pulmonary fibrosis by damaging the mitochondria of macrophages. In this review, we first introduce the molecular mechanisms that silica dust induce mitochondrial morphological and functional abnormalities and then introduce the main molecular mechanisms that silica-damaged mitochondria induce pulmonary fibrosis. Finally, we conclude that the mitochondrial abnormalities of alveolar macrophages caused by silica dust are involved deeply in the pathogenesis of silicosis through these two sequential mechanisms. Therefore, reducing the silica-damaged mitochondria will prevent the potential occurrence and fatality of the disease in the future.