TLR4 Activity Is Required in the Resolution of Pulmonary Inflammation and Fibrosis after Acute and Chronic Lung Injury

Identification of oxidative stress-related diagnostic markers and immune infiltration features for idiopathic pulmonary fibrosis by bibliometrics and bioinformatics

Idiopathic pulmonary fibrosis (IPF) garners considerable attention due to its high fatality rate and profound impact on quality of life. Our study conducts a comprehensive literature review on IPF using bibliometric analysis to explore existing hot research topics, and identifies novel diagnostic and therapeutic targets for IPF using bioinformatics analysis. Publications related to IPF from 2013 to 2023 were searched on the Web of Science Core Collection (WoSCC) database. Data analysis and visualization were conducted using CiteSpace and VOSviewer software primarily. The gene expression profiles GSE24206 and GSE53845 were employed as the training dataset. The GSE110147 dataset was employed as the validation dataset. We identified differentially expressed genes (DEGs) and differentially expressed genes related to oxidative stress (DEOSGs) between IPF and normal samples. Then, we conducted Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. The hub genes were screened by protein-protein interaction (PPI) networks and machine learning algorithms. The CIBERSORT was used to analyze the immune infiltration of 22 kinds of immune cells. Finally, we conducted the expression and validation of hub genes. The diagnostic efficacy of hub genes was evaluated by employing Receiver Operating Characteristic (ROC) curves and the associations between hub genes and immune cells were analyzed. A total of 6,500 articles were identified, and the annual number of articles exhibited an upward trend. The United States emerged as the leading contributor in terms of publication count, institutional affiliations, highly cited articles, and prolific authorship. According to co-occurrence analysis, oxidative stress and inflammation are hot topics in IPF research. A total of 1,140 DEGs were identified, and 72 genes were classified as DEOSGs. By employing PPI network analysis and machine learning algorithms, PON2 and TLR4 were identified as hub genes. A total of 10 immune cells exhibited significant differences between IPF and normal samples. PON2 and TLR4, as oxidative stress-related genes, not only exhibit high diagnostic efficacy but also show close associations with immune cells. In summary, our study highlights oxidative stress and inflammation are hot topics in IPF research. Oxidative stress and immune cells play a vital role in the pathogenesis of IPF. Our findings suggest the potential of PON2 and TLR4 as novel diagnostic and therapeutic targets for IPF.

The current landscape of antifibrotic therapy across different organs: A systematic approach

Fibrosis is a common pathological process that can affect virtually all the organs, but there are hardly any effective therapeutic options. This has led to an intense search for antifibrotic therapies over the last decades, with a great number of clinical assays currently underway. We have systematically reviewed all current and recently finished clinical trials involved in the development of new antifibrotic drugs, and the preclinical studies analyzing the relevance of each of these pharmacological strategies in fibrotic processes affecting tissues beyond those being clinically studied. We analyze and discuss this information with the aim of determining the most promising options and the feasibility of extending their therapeutic value as antifibrotic agents to other fibrotic conditions.

Sinomenine attenuates bleomycin-induced pulmonary fibrosis, inflammation, and oxidative stress by inhibiting TLR4/NLRP3/TGFβ signaling

OBJECTIVE

The present work concentrated on validating whether sinomenine alleviates bleomycin (BLM)-induced pulmonary fibrosis, inflammation, and oxidative stress.

METHODS

A rat model of pulmonary fibrosis was constructed through intratracheal injection with 5 mg/kg BLM, and the effects of 30 mg/kg sinomenine on pulmonary inflammation, fibrosis, apoptosis, and 4-hydroxynonenal density were evaluated by hematoxylin and eosin staining, Masson's trichrome staining, TUNEL staining, and immunohistochemistry. Hydroxyproline content and concentrations of inflammatory cytokines and oxidative stress markers were detected using corresponding kits. MRC-5 cells were treated with 10 ng/ml PDGF, and the effects of 1 mM sinomenine on cell proliferation were assessed by EdU assays. The mRNA expression of inflammatory cytokines and the protein levels of collagens, fibrosis markers, and key markers involved in the TLR4/NLRP3/TGFβ signaling were tested with RT-qPCR and immunoblotting analysis.

RESULTS

Sinomenine attenuated pulmonary fibrosis and inflammation while reducing hydroxyproline content and the protein expression of collagens and fibrosis markers in BLM-induced pulmonary fibrosis rats. Sinomenine reduced apoptosis in lung samples of BLM-challenged rats by increasing Bcl-2 and reducing Bax and cleaved caspase-3 protein expression. In addition, sinomenine alleviated inflammatory response and oxidative stress in rats with pulmonary fibrosis induced by BLM. Moreover, sinomenine inhibited the TLR4/NLRP3/TGFβ signaling pathway in lung tissues of BLM-stimulated rats. Furthermore, TLR4 inhibitor, TAK-242, attenuated PDGF-induced fibroblast proliferation and collagen synthesis in MRC-5 cells.

CONCLUSION

Sinomenine attenuates BLM-caused pulmonary fibrosis, inflammation, and oxidative stress by inhibiting the TLR4/NLRP3/TGFβ signaling, indicating that sinomenine might become a therapeutic candidate to treat pulmonary fibrosis.

Design and synthesis of forsythin derivatives as anti-inflammatory agents for acute lung injury

Acute lung injury (ALI) is a clinically high mortality disease, which has not yet been effectively treated. The development of anti-ALI drugs is imminent. ALI can be effectively treated by inhibiting the inflammatory cascade and reducing the inflammatory response in the lung. Forsythia suspense is a common Chinese herbal medicine with significant anti-inflammatory activity. Using forsythin as the parent, 27 Forsythin derivatives were designed and synthesized, and the anti-AIL activity of these compounds was evaluated. Among them, compound B5 has the best activity to inhibit the release of IL-6, and the inhibition rate reaches 91.79% at 25 μM, which was 7.5 times that of the parent forsythin. In addition, most of the compounds have no significant cytotoxicity in vitro. Further studies showed that compound B5 had a concentration-dependent inhibitory effect on NO, IL-6 and TNF-α. And the IC50 values of compound B5 for NO and IL-6 are 10.88 μM and 4.93 μM, respectively. We also found that B5 could significantly inhibit the expression of some immune-related cytotoxic factors, including inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). In addition, B5 inhibits NF-κB/MAPK signaling pathway. In vivo experiments showed that B5 could alleviate lung inflammation in LPS-induced ALI mice and inhibit IL-6, TNF-α, COX-2 and iNOS. In summary, B5 has anti-inflammatory effects and alleviates ALI by regulating inflammatory mediators and inhibiting MAPK and NF-κB signaling pathways.

Anti-Inflammatory and Cytotoxic Compounds Isolated from Plants of Euphorbia Genus

Euphorbia is a large genus of the Euphorbiaceae family. Around 250 species of the Euphorbia genus have been studied chemically and pharmacologically; different compounds have been isolated from these species, especially diterpenes and triterpenes. Several reports show that several species have anti-inflammatory activity, which can be attributed to the presence of diterpenes, such as abietanes, ingenanes, and lathyranes. In addition, it was found that some diterpenes isolated from different Euphorbia species have anti-cancer activity. In this review, we included compounds isolated from species of the Euphorbia genus with anti-inflammatory or cytotoxic effects published from 2018 to September 2023. The databases used for this review were Science Direct, Scopus, PubMed, Springer, and Google Scholar, using the keywords Euphorbia with anti-inflammatory or cytotoxic activity. In this review, 68 studies were collected and analyzed regarding the anti-inflammatory and anti-cancer activities of 264 compounds obtained from 36 species of the Euphorbia genus. The compounds included in this review are terpenes (95%), of which 68% are diterpenes, especially of the types ingenanes, abietanes, and triterpenes (approximately 15%).

Cell-free hemoglobin triggers macrophage cytokine production via TLR4 and MyD88

Cell-free hemoglobin (CFH) is elevated in the airspace of patients with acute respiratory distress syndrome (ARDS) and is sufficient to cause acute lung injury in a murine model. However, the pathways through which CFH causes lung injury are not well understood. Toll-like receptor 4 (TLR4) is a mediator of inflammation after detection of damage- and pathogen-associated molecular patterns. We hypothesized that TLR4 signaling mediates the proinflammatory effects of CFH in the airspace. After intratracheal CFH, BALBc mice deficient in TLR4 had reduced inflammatory cell influx into the airspace [bronchoalveolar lavage (BAL) cell counts, median TLR4 knockout (KO): 0.8 × 104/mL [IQR 0.4-1.2 × 104/mL], wild-type (WT): 3.0 × 104/mL [2.2-4.0 × 104/mL], P < 0.001] and attenuated lung permeability (BAL protein, TLR4KO: 289 µg/mL [236-320], WT: 488 µg/mL [422-536], P < 0.001). These mice also had attenuated production of interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α in the airspace. C57Bl/6 mice lacking TLR4 on myeloid cells only (LysM.Cre+/-TLR4fl/fl) had reduced cytokine production in the airspace after CFH, without attenuation of lung permeability. In vitro studies confirm that WT primary murine alveolar macrophages exposed to CFH (0.01-1 mg/mL) had dose-dependent increases in IL-6, IL-1 β, CXC motif chemokine ligand 1 (CXCL-1), TNF-α, and IL-10 (P < 0.001). Murine MH-S alveolar-like macrophages show TLR4-dependent expression of IL-1β, IL-6, and CXCL-1 in response to CFH. Primary alveolar macrophages from mice lacking TLR4 adaptor proteins myeloid differentiation primary response 88 (MyD88) or TIR-domain-containing adapter-inducing interferon-β (TRIF) revealed that MyD88KO macrophages had 71-96% reduction in CFH-dependent proinflammatory cytokine production (P < 0.001), whereas macrophages from TRIFKO mice had variable changes in cytokine responses. These data demonstrate that myeloid TLR4 signaling through MyD88 is a key regulator of airspace inflammation in response to CFH.NEW & NOTEWORTHY Cell-free hemoglobin (CFH) is elevated in the airspace of most patients with acute respiratory distress syndrome and causes severe inflammation. Here, we identify that CFH contributes to macrophage-induced cytokine production via Toll-like receptor 4 (TLR4) and myeloid differentiation primary response 88 (MyD88) signaling. These data increase our knowledge of the mechanisms through which CFH contributes to lung injury and may inform development of targeted therapeutics to attenuate inflammation.

Anthelmintic nitazoxanide protects against experimental pulmonary fibrosis

BACKGROUND AND PURPOSE

Nitazoxanide is a therapeutic anthelmintic drug. Our previous studies found that nitazoxanide and its metabolite tizoxanide activated adenosine 5'-monophosphate-activated protein kinase (AMPK) and inhibited signal transducer and activator of transcription 3 (STAT3) signals. As AMPK activation and/or STAT3 inhibition are targets for treating pulmonary fibrosis, we hypothesized that nitazoxanide would be effective in experimental pulmonary fibrosis.

EXPERIMENTAL APPROACH

The mitochondrial oxygen consumption rate of cells was measured by using the high-resolution respirometry system Oxygraph-2K. The mitochondrial membrane potential of cells was evaluated by tetramethyl rhodamine methyl ester (TMRM) staining. The target protein levels were measured by using western blotting. The mice pulmonary fibrosis model was established through intratracheal instillation of bleomycin. The examination of the lung tissues changes were carried out using haematoxylin and eosin (H&E), and Masson staining.

KEY RESULTS

Nitazoxanide and tizoxanide activated AMPK and inhibited STAT3 signalling in human lung fibroblast cells (MRC-5 cells). Nitazoxanide and tizoxanide inhibited transforming growth factor-β1 (TGF-β1)-induced proliferation and migration of MRC-5 cells, collagen-I and α-smooth muscle cell actin (α-SMA) expression, and collagen-I secretion from MRC-5 cells. Nitazoxanide and tizoxanide inhibited epithelial-mesenchymal transition (EMT) and inhibited TGF-β1-induced Smad2/3 activation in mouse lung epithelial cells (MLE-12 cells). Oral administration of nitazoxanide reduced the bleomycin-induced mice pulmonary fibrosis and, in the established bleomycin-induced mice, pulmonary fibrosis. Delayed nitazoxanide treatment attenuated the fibrosis progression.

CONCLUSIONS AND IMPLICATIONS

Nitazoxanide improves the bleomycin-induced pulmonary fibrosis in mice, suggesting a potential application of nitazoxanide for pulmonary fibrosis treatment in the clinic.

An important call: Suggestion of using IL-10 as therapeutic agent for COVID-19 with ARDS and other complications

The global coronavirus disease 2019 (COVID-19) pandemic has a detrimental impact on public health. COVID-19 usually manifests as pneumonia, which can progress into acute respiratory distress syndrome (ARDS) related to uncontrolled TH17 immune reaction. Currently, there is no effective therapeutic agent to manage COVID-19 with complications. The currently available anti-viral drug remdesivir has an effectiveness of 30% in SARS-CoV-2-induced severe complications. Thus, there is a need to identify effective agents to treat COVID-19 and the associated acute lung injury and other complications. The host immunological pathway against this virus typically involves the THαβ immune response. THαβ immunity is triggered by type 1 interferon and interleukin-27 (IL-27), and the main effector cells of the THαβ immune response are IL10-CD4 T cells, CD8 T cells, NK cells, and IgG1-producing B cells. In particular, IL-10 exerts a potent immunomodulatory or anti-inflammatory effect and is an anti-fibrotic agent for pulmonary fibrosis. Concurrently, IL-10 can ameliorate acute lung injury or ARDS, especially those caused by viruses. Owing to its anti-viral activity and anti-pro-inflammatory effects, in this review, IL-10 is suggested as a possible treatment agent for COVID-19.

Jinzhen Oral Liquid alleviates lipopolysaccharide-induced acute lung injury through modulating TLR4/MyD88/NF-κB pathway

BACKGROUND

Acute lung injury (ALI) has the attribution of excessive inflammation of the lung. Jinzhen oral liquid (JO), a famous Chinese recipe used to treat ALI, has a favorable therapeutic effect on ALI. However, its anti-inflammatory mechanism has not been extensively studied.

PURPOSE

This study was to elucidate the effects of JO on lipopolysaccharide (LPS)-induced ALI and its molecular mechanism.

METHODS

An ALI model was established by intratracheal instillation of LPS (2 mg/50 μl). The open field experiment was carried out to explore the spontaneous movement and exploratory behavior of ALI mice. Cytokines levels concentrations (IL-6, IL-10 and TNF-α) were determined by enzyme-linked immunosorbent assay (ELISA). Network pharmacology was used to predict the mechanism of JO against ALI. Immunofluorescence, co-immunoprecipitation, fluorescence resonance energy transfer (FRET), Western blot and RT-PCR were used to verify the molecular mechanisms of JO.

RESULTS

The in vivo results suggested that JO (1, 2, 4 g/kg) dose-dependently improved the exercise performance of mice and reduced the lung W/D weight ratio as well as the production of IL-6 and TNF-α, but increased the release of IL-10 in the ALI group. The network pharmacological analysis demonstrated that the Toll-like receptor (TLR) pathway might be the fundamental action mechanisms of JO against ALI. Immunofluorescence staining and co-immunoprecipitation analysis showed that JO decreased the expression levels of TLR4 and MyD88 and reduced their interaction in the lung tissue of ALI mice. Meanwhile, JO decreased nuclear translocation and phosphorylation of NF-κB P65. The results from cellular experiments were in line with those in vivo. The FRET experiment also confirmed that JO disturbed the interaction of TLR4 and MyD88. Subsequently, we also found that the six indicative components of JO have the similar therapeutic effect as JO.

CONCLUSIONS

In summary, we suggested that JO suppressed the TLR4/MyD88/NF-κB signaling pathway, thus inhibiting LPS-induced ALI in vitro and in vivo. The clarified mechanism provided an important theoretical basis and a novel treatment strategy for the ALI treatment of JO.

Silencing of Long Non-coding RNA H19 Alleviates Lipopolysaccharide (LPS)-induced Apoptosis and Inflammation Injury by Regulating miR-140-5p/TLR4 Axis in Cell Models of Pneumonia

OBJECTIVE

Mounting studies have clarified the link between long non-coding RNAs (lncRNAs) and pneumonia. This research aims to probe the function and regulatory mechanism of lncRNA H19 in lipopolysaccharide (LPS)-induced cell models of pneumonia.

METHODS

WI-38 cells were exposed to LPS for 12 h to mimic cell models of pneumonia. The relative expression of H19, miR-140-5p, and toll-like receptor 4 (TLR4) were detected by quantitative real-time polymerase chain reaction (qRT-PCR). The cell viability was detected by MTT assay. The protein expression of apoptosis-associated proteins (Bax and Bcl-2) and TLR4 were determined by western blot. Moreover, the content of interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-α were measured by enzyme-linked immunosorbent assay (ELISA). The target relationship between miR- 140-5p and H19/ TLR4 was confirmed by Dual luciferase reporter (DLR) assay.

RESULTS

LncRNA H19 and TLR4 were up-regulated, while miR-140-5p was downregulated in peripheral blood of patients with pneumonia and LPS-treated WI-38 cells compared with their controls. Silencing of H19 or miR-140-5p mimics facilitated cell viability, whereas repressed apoptosis and reduced content of TNF-α, IL-6, and IL-1β in LPS-induced WI-38 cells. H19 targeted miR-140-5p and it inversely regulated miR-140- 5p expression. MiR-140-5p targeted TLR4 and it inversely regulated TLR4 expression. H19 positively regulated TLR4 expression. Moreover, inhibition of miR-140-5p or overexpression of TLR4 reversed the effects of H19 silencing on cell viability, inflammation, and apoptosis in LPS-induced WI-38 cells.

CONCLUSION

Silencing of H19 inhibited apoptosis and inflammation by miR-140- 5p/TLR4 pathway in LPS-induced WI-38 cells.

Arachidonate 15-lipoxygenase type B: Regulation, function, and its role in pathophysiology

As a lipoxygenase (LOX), arachidonate 15-lipoxygenase type B (ALOX15B) peroxidizes polyenoic fatty acids (PUFAs) including arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and linoleic acid (LA) to their corresponding fatty acid hydroperoxides. Distinctive to ALOX15B, fatty acid oxygenation occurs with positional specificity, catalyzed by the non-heme iron containing active site, and in addition to free PUFAs, membrane-esterified fatty acids serve as substrates for ALOX15B. Like other LOX enzymes, ALOX15B is linked to the formation of specialized pro-resolving lipid mediators (SPMs), and altered expression is apparent in various inflammatory diseases such as asthma, psoriasis, and atherosclerosis. In primary human macrophages, ALOX15B expression is associated with cellular cholesterol homeostasis and is induced by hypoxia. Like in inflammation, the role of ALOX15B in cancer is inconclusive. In prostate and breast carcinomas, ALOX15B is attributed a tumor-suppressive role, whereas in colorectal cancer, ALOX15B expression is associated with a poorer prognosis. As the biological function of ALOX15B remains an open question, this review aims to provide a comprehensive overview of the current state of research related to ALOX15B.

Prevention of bleomycin-induced pulmonary fibrosis by a RANKL peptide in mice

Despite the recent therapeutic developments for the treatment of pulmonary fibrosis, its prognosis is still not well controlled, and a novel therapeutic agent is needed. Recently, the critical role of Toll-like receptors (TLRs) in the pathophysiology of pulmonary fibrosis has been reported; however, the effects of multiple TLR signaling inhibition are still unknown. Here, we examined how the inhibition of multiple TLRs affects pulmonary fibrosis using a novel synthetic receptor activator of nuclear factor κB ligand (RANKL) partial peptide, MHP1-AcN, which could suppress TLR2, 3, 4, 7, and 9 signaling through CD14 and RANK. When MHP1-AcN was administered in the bleomycin-induced lung fibrosis model, reduced collagen deposition was observed, with suppressed fibrosis-related gene expression including Col1a1, Col1a2, Acta2, Tgfb1 and Tgfbr2. MHP1-AcN also decreased proinflammatory M1 and profibrotic M2 macrophage marker expression. Furthermore, MHP1-AcN treatment inhibited transforming growth factor (TGF-β)-induced Smad2/3 phosphorylation and myofibroblast differentiation in human fetal lung fibroblast (MRC-5) cells. This effect was associated with decreased TGF-β receptor levels and the upregulated Bmp7 and Smad7 expression. These findings suggest that MHP1-AcN protects mice against bleomycin-induced pulmonary fibrosis. MHP1-AcN might provide a novel therapeutic strategy for the pulmonary fibrosis.

The Impact of Inflammatory Stimuli on Xylosyltransferase-I Regulation in Primary Human Dermal Fibroblasts

Inflammation plays a vital role in regulating fibrotic processes. Beside their classical role in extracellular matrix synthesis and remodeling, fibroblasts act as immune sentinel cells participating in regulating immune responses. The human xylosyltransferase-I (XT-I) catalyzes the initial step in proteoglycan biosynthesis and was shown to be upregulated in normal human dermal fibroblasts (NHDF) under fibrotic conditions. Regarding inflammation, the regulation of XT-I remains elusive. This study aims to investigate the effect of lipopolysaccharide (LPS), a prototypical pathogen-associated molecular pattern, and the damage-associated molecular pattern adenosine triphosphate (ATP) on the expression of XYLT1 and XT-I activity of NHDF. We used an in vitro cell culture model and mimicked the inflammatory tissue environment by exogenous LPS and ATP supplementation. Combining gene expression analyses, enzyme activity assays, and targeted gene silencing, we found a hitherto unknown mechanism involving the inflammasome pathway components cathepsin B (CTSB) and caspase-1 in XT-I regulation. The suppressive role of CTSB on the expression of XYLT1 was further validated by the quantification of CTSB expression in fibroblasts from patients with the inflammation-associated disease Pseudoxanthoma elasticum. Altogether, this study further improves the mechanistic understanding of inflammatory XT-I regulation and provides evidence for fibroblast-targeted therapies in inflammatory diseases.

Artemisinin Attenuates Amyloid-Induced Brain Inflammation and Memory Impairments by Modulating TLR4/NF-κB Signaling

The abnormal immune response is an early change in the pathogenesis of Alzheimer’s disease (AD). Microglial activation is a crucial regulator of the immune response, which contributes to progressive neuronal injury by releasing neurotoxic products. Therefore, finding effective drugs to regulate microglial homeostasis and neuroinflammation has become a new AD treatment strategy. Artemisinin has potent anti-inflammatory and immune activities. However, it is unclear whether Artemisinin contributes to the regulation of microglial activation, thereby improving AD pathology. This study found that Artemisinin significantly reduced amyloid beta-peptide 1–42 (Aβ_1–42)-induced increases in nitric oxide and reactive oxygen species and inflammatory factors in BV2 cells. In addition, Artemisinin inhibited the migration of microglia and prevented the expansion of the inflammatory cascade. The mechanical studies showed Artemisinin inhibited neuroinflammation and exerted neuroprotective effects by regulating the Toll-like receptor 4 (TLR4)/Nuclear factor-kappa B (NF-κB) signaling pathway. Similar results were obtained in AD model mice, in which Artemisinin administration attenuated Aβ_1–42-induced neuroinflammation and neuronal injury, reversing spatial learning and memory deficits. The anti-inflammatory effect of Artemisinin is also accompanied by the activation of the TLR4/NF-κB signaling pathway in the animal model. Our results indicate that Artemisinin attenuated Aβ_1–42-induced neuroinflammation and neuronal injury by stimulating the TLR4/NF-κB signaling pathway. These findings suggest that Artemisinin is a potential therapeutic agent for AD.

Paraquat Induces Lung Injury via miR-199-Mediated SET in a Mouse Model

Objective: To explore the molecular mechanism of lung injury caused by paraquat (PQ) poisoning by investigating miR-199-mediated SET.

Methods: A paraquat poisoning model was established in C57BL/6 male mice via intraperitoneal injection of paraquat. The mice were transfected with miR-199 siRNA and or mimic. After 14 days of treatment, pathophysiological changes of the lung were observed and lung tissue was analyzed via Hematoxylin-Eosin staining. The levels of miR-199, SETs, surfactant protein SP-A and SP-B, and inflammatory and oxidative factors were analyzed by qPCR, Western Blot, and ELISA kits.

Results: A acute lung-injury (ALI) model was established using PQ treatment and confirmed with edema of pulmonary endothelium with low electronic density of endothelial cytoplasm, presence of protein-rich fluid, and numerous erythrocytes in alveolar space, concentric figures of damaged tubular myelin, alveolar destruction, and increase in inflammatory cell numbers. Compared with the control group, miR-199 and SET levels were reduced in the PQ-treated group. miR-199 siRNA increased the SET level, inflammatory and oxidative levels, and reduced the levels of SP-A and SP-B, and miR-199 mimic reduced the SET level, inflammatory and oxidative levels, and increased the levels of SP-A and SP-B. PQ treatment reduced miR-199 level.

Conclusion: Paraquat induces ALI by affecting miR-199-mediated SET.

Protective Effects of the Wenfei Buqi Tongluo Formula on the Inflammation in Idiopathic Pulmonary Fibrosis through Inhibiting the TLR4/MyD88/NF-κB Pathway

Background. Idiopathic pulmonary fibrosis (IPF) is a progressive disease with high mortality and poor prognosis. The prognostic signatures related to conventional therapy response remain limited. The Wenfei Buqi Tongluo (WBT) formula, a traditional Chinese medicine (TCM) formula, has been widely utilized to treat respiratory diseases in China, which is particularly effective in promoting inflammatory absorption. In this study, we aim to explore the mechanism of the WBT formula in the inhibition of inflammatory response during IPF, based on network pharmacology and in vivo experiments. Methods. Network pharmacology was applied to predict the changes of biological processes and potential pathways for the WBT formula against IPF. Histopathological changes, inflammatory factors (IL-6, IL-1β, and TNF-α), and the proteins of the TLR4/MyD88/NF-κB pathway in bleomycin- (BLM-) induced mice model were examined by hematoxylin-eosin (H&E), Masson or immunohistochemistry staining, Western blot, and enzyme-linked immunosorbent assay analysis. Results. A total of 163 possible components and 167 potential targets between the WBT formula and IPF were obtained. The enrichments of network pharmacology showed that inflammation response, TNF, and NF-κB pathways were involved in the treatment of WBT against IPF. The in vivo experiments indicated that the WBT formula could ameliorate inflammatory exudation and collagen deposition at a histopathology level in the BLM-induced mice model. The levels of IL-6, IL-1β, and TNF-α were reduced after the WBT formula treatment. Moreover, the expressions of phosphorylated-NF-κB p65, TLR4, and MyD88 were significantly downregulated by the WBT formula, compared with the BLM-induced group. Conclusion. These results indicated that the WBT formula can suppress BLM-induced IPF in a mouse model by inhibiting the inflammation via the TLR4/MyD88/NF-κB pathway. This study provides a new insight into the molecular mechanisms of the WBT formula in the application at the clinic.

Oxymatrine promotes hypertrophic scar repair through reduced human scar fibroblast viability, collagen and induced apoptosis via autophagy inhibition

Scars are common complications of burns and trauma, resulting in mental trauma, physical pain, and a heavy financial burden for patients. Specific and effective anti‐scarring drugs are lacking in clinical practice. Phytochemicals are easily accessible, low in toxicity, and have various biological and pharmacological properties. Oxymatrine is a phytochemical that regulates autophagy networks. Autophagy is closely related to the maintenance, activity, differentiation, and life‐death of skin fibroblasts during wound repair, which results in pathological scars. We hypothesised that oxymatrine may promote hypertrophic scar repair by inhibiting fibroblast autophagy. In vitro studies showed that inhibition of autophagy by oxymatrine decreased viability and collagen metabolism, and increased apoptosis of human scar fibroblasts (HSFs). In vivo studies showed that inhibition of autophagy by oxymatrine promoted scar repair, resulting in a significantly improved final outcome of the hypertrophic scars, a smaller scar area, decreased epidermal and dermal thickness, and a significant downregulation of CK10, P63, collagen I, α‐SMA, and TGF‐β1. In summary, oxymatrine promoted hypertrophic scar repair by decreasing HSF viability and collagen, and inducing apoptosis via autophagy inhibition. This study provides a new perspective on the mechanism of hypertrophic burn scar formation, as well as key scientific data for the application of the phytochemical oxymatrine as a new method for the prevention and treatment of hypertrophic scars.

Interrelation Between Fibroblasts and T Cells in Fibrosing Interstitial Lung Diseases

Interstitial lung diseases (ILDs) are a heterogeneous group of diseases characterized by varying degrees of inflammation and fibrosis of the pulmonary interstitium. The interrelations between multiple immune cells and stromal cells participate in the pathogenesis of ILDs. While fibroblasts contribute to the development of ILDs through secreting extracellular matrix and proinflammatory cytokines upon activation, T cells are major mediators of adaptive immunity, as well as inflammation and autoimmune tissue destruction in the lung of ILDs patients. Fibroblasts play important roles in modulating T cell recruitment, differentiation and function and conversely, T cells can balance fibrotic sequelae with protective immunity in the lung. A more precise understanding of the interrelation between fibroblasts and T cells will enable a better future therapeutic design by targeting this interrelationship. Here we highlight recent work on the interactions between fibroblasts and T cells in ILDs, and consider the implications of these interactions in the future development of therapies for ILDs.

Scorpion bradykinin potentiating factor mitigates lung damage induced by γ-irradiation in rats: Insights on AngII/ACE/Ang(1-7) axis

The goal of this research is to study the mitigating impact of bradykinin potentiating factor (BPF) found in scorpion Androctonus bicolor venom on irradiation-induced lung damage as a new functional target for angiotensin-converting enzyme inhibitors (ACEIs). Male rats were exposed to 7 Gy of γ-radiation as a single dose, with a biweekly intraperitoneal injection of 1 μg/g BPF. Gamma irradiation not only boosted the ACE activity and angiotensin II (Ang II) level, in lung tissue but also significantly depressed the angiotensin (1-7) (Ang (1-7)) that, lead to lung toxicity through a significant elevation of pulmonary levels of CXC-chemokine receptor 4 (CXCR4), toll-like receptor 4 (TLR4), nitric oxide (NO) and lactate dehydrogenase (LDH) activity with a marked disruption in oxidative stress markers, via a reduction in the level of total thiol (tSH) and superoxide dismutase (SOD) activity associated with an elevation in protein carbonyl (PCO) contents. In addition, apoptotic consequences of gamma irradiation were evidenced by raising the levels of mitogen-activated protein kinase (MAPK), C-Jun N-Terminal Kinases (JNK), and cleaved caspase-3. BPF administration leads to ACE inhibition, consequently sustaining decreased Ang II alongside increased Ang (1-7) production. Those sensitive molecules reduce irradiated lung issues. In conclusion, BPF significantly diminished the biochemical and histopathological consequences of radiation through renin-angiotensin system (RAS) control and ACE suppression in the lung.

TLR4 is required for macrophage efferocytosis during resolution of ventilator-induced lung injury

Mechanical ventilation is a life-sustaining therapy for patients with respiratory failure but can cause further lung damage known as ventilator-induced lung injury (VILI). However, the intrinsic molecular mechanisms underlying recovery of VILI remain unknown. Phagocytosis of apoptotic cells (also known as efferocytosis) is a key mechanism orchestrating successful resolution of inflammation. Here we show the positive regulation of macrophage Toll-like receptor (TLR) 4 in efferocytosis and resolution of VILI. Mice were depleted of alveolar macrophages and then subjected to injurious ventilation (tidal volume, 20 mL/kg) for 4 h. On day 1 after mechanical ventilation, Tlr4^+/+ or Tlr4^-/- bone marrow-derived macrophages (BMDMs) were intratracheally administered to alveolar macrophage-depleted mice. We observed that mice depleted of alveolar macrophages exhibited defective resolution of neutrophilic inflammation, exuded protein, lung edema, and lung tissue injury after ventilation, whereas these delayed responses were reversed by administration of Tlr4^+/+ BMDMs. Importantly, these proresolving effects by Tlr4^+/+ BMDMs were abolished in mice receiving Tlr4^-/- BMDMs. The number of macrophages containing apoptotic cells or bodies in bronchoalveolar lavage fluid was much less in mice receiving Tlr4^-/- BMDMs than that in those receiving Tlr4^+/+ BMDMs. Macrophage TLR4 deletion facilitated a disintegrin and metalloprotease 17 maturation and enhanced Mer cleavage in response to mechanical ventilation. Heat shock protein 70 dramatically increased Mer tyrosine kinase surface expression, phagocytosis of apoptotic neutrophils, and rescued the inflammatory phenotype in alveolar macrophage-depleted mice receiving Tlr4^+/+ BMDMs, but not Tlr4^-/- BMDMs. Our results suggest that macrophage TLR4 promotes resolution of VILI via modulation of Mer-mediated efferocytosis.

Autophagy in pulmonary fibrosis: friend or foe?

Autophagy is an evolutionarily conserved process where long-lived and damaged organelles are degraded. Autophagy has been widely associated with several ageing-process as well in diseases such as neurodegeneration, cancer and fibrosis, and is now being utilised as a target in these diseases. Idiopathic pulmonary fibrosis (IPF) is a progressive, interstitial lung disease with limited treatment options available. It is characterised by abnormal extracellular matrix (ECM) deposition by activated myofibroblasts. It is understood that repetitive micro-injuries to aged-alveolar epithelium combined with genetic factors drive the disease. Several groups have demonstrated that autophagy is altered in IPF although whether autophagy has a protective effect or not is yet to be determined. Autophagy has also been shown to influence many other processes including epithelial-mesenchymal transition (EMT) and endothelial-mesenchymal transition (EndMT) which are known to be key in the pathogenesis of IPF. In this review, we summarise the findings of evidence of altered autophagy in IPF lungs, as well as examine its roles within lung fibrosis. Given these findings, together with the growing use of autophagy manipulation in a clinical setting, this is an exciting area for further research in the study of lung fibrosis.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

Discovery of Novel Pterostilbene Derivatives That Might Treat Sepsis by Attenuating Oxidative Stress and Inflammation through Modulation of MAPKs/NF-κB Signaling Pathways

Sepsis remains one of the most common life-threatening illnesses that is characterized by a systemic inflammatory response syndrome (SIRS) and usually arises following severe trauma and various septic infections. It is still in urgent need of new effective therapeutic agents, and chances are great that some candidates can be identified that can attenuate oxidative stress and inflammatory responses. Pterostilbene, which exerts attractive anti-oxidative and anti-inflammatory activities, is a homologue of natural polyphenolic derivative of resveratrol. Starting from it, we have made several rounds of rational optimizations. Firstly, based on the strategy of pharmacophore combination, indanone moiety was introduced onto the pterostilbene skeleton to generate a novel series of pterostilbene derivatives (PIF_1–PIF_16) which could possess both anti-oxidative and anti-inflammatory activities for sepsis treatment. Then, all target compounds were subjected to their structure–activity relationships (SAR) screening of anti-inflammatory activity in mouse mononuclear macrophage RAW264.7 cell line, and their cytotoxicities were determined after. Finally, an optimal compound, PIF_9, was identified. It decreased the mRNA levels of lipopolysaccharide (LPS)-induced interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS), and cyclooxygenase 2 (COX2). We also found that the anti-inflammatory effects might be contributed by its suppression on the nuclear factor-κB (NF-κB) and MAPKs signaling pathway. Moreover, PIF_9 also demonstrated potent anti-oxidative activity in RAW264.7 macrophages and the sepsis mouse model. Not surprisingly, with the benefits mentioned above, it ameliorated LPS-induced sepsis in C57BL/6J mice and reduced multi-organ toxicity. Taken together, PIF_9 was identified as a potential sepsis solution, targeting inflammation and oxidative stress through modulating MAPKs/NF-κB.

Association of rs3750920 polymorphism in TOLLIP with clinical characteristics of fibrosing interstitial lung diseases in Japanese

TOLLIP polymorphism has been implicated in the development and prognosis of idiopathic pulmonary fibrosis (IPF), mainly in whites. However, ethnic differences in the characteristics of other interstitial pneumonia (non-IPF) subtypes are unclear. We evaluated the association between the rs3750920 genotype and the clinical characteristics of Japanese patients with fibrosing interstitial lung diseases (ILD). We genotyped 102 patients with fibrosing ILD (75 IPF and 27 non-IPF patients) and analyzed the interaction between the rs3750920 genotype distribution and their clinical characteristics. The overall frequencies of the C/C, C/T, and T/T genotypes were 69%, 25%, and 6%, respectively. The proportion of minor T allele carriers was larger in IPF patients than in non-IPF patients (37% vs. 15%, P = 0.031). In addition, survival at 3 years was significantly better for carriers than for non-carriers of the T allele. There was no significant association between genotype distribution and change in pulmonary function after introduction of antifibrotic agents. The frequency of the minor T allele of rs3750920 was low in Japanese patients with fibrosing ILD, particularly in non-IPF patients. Carriers of the minor T allele had better survival than non-carriers. Presence of the T allele might thus be an indicator of better outcomes for fibrosing ILD.

Danggui Buxue Tang Ameliorates Bleomycin-Induced Pulmonary Fibrosis by Suppressing the TLR4/NLRP3 Signaling Pathway in Rats

Objective

To investigate the effects of Danggui Buxue Tang (DBT) on rats with pulmonary fibrosis (PF) and the underlying mechanism.

Methods

Sixty specific pathogen-free (SPF) male Sprague-Dawley (SD) rats were randomly divided into 4 groups: control, PF, prednisone treatment, and DBT treatment. Intratracheal instillation of bleomycin (BLM) was performed to establish a PF rat model. DBT was administered to PF rats concurrently for 2 weeks. Lung samples were then collected for HE and Masson staining after pulmonary function testing, and semiquantitative analysis for the degree of alveolitis and fibrosis was performed using the Szapiel and Ashcroft score systems. Myeloperoxidase (MPO) activity, hydroxyproline (HYP), hyaluronic acid (HA), and inflammatory cytokine content were measured. Western blotting was performed to detect fibrotic marker and TLR4/NLRP3 signaling pathway changes.

Results

Oral administration of DBT attenuated weight loss, survival rate, and pulmonary index. Lung histopathologic lesions were also reduced. DBT inhibited PF by decreasing the secretion of inflammatory cytokines and collagen deposition. Specifically, DBT reduced tumor necrosis factor-alpha (TNF-α), interleukin 1 beta (IL-1β), IL-6, HYP, alpha-smooth muscle actin (α-SMA), collagen I, and collagen III levels. Corollary experiments identified a potential mechanism involving suppression of TLR4/MyD88/NF-κB signaling pathway activation and the NLRP3/ASC/caspase-1 axis, the downstream regulatory pathway.

Conclusion

DBT exhibited a potent effect on BLM-induced PF rats by inhibiting the TLR4/NLRP3 signaling pathway. Thus, DBT alleviates pulmonary inflammation to inhibit fibrotic pathology and should be considered as a candidate for the clinical treatment of PF.

Overexpression of TOLLIP Protects against Acute Kidney Injury after Paraquat Intoxication through Inhibiting NLRP3 Inflammasome Activation Modulated by Toll-Like Receptor 2/4 Signaling

Paraquat (PQ) can cause multiorgan failure including acute kidney injury (AKI). Our prior study showed that Toll-interacting protein (TOLLIP) protected against PQ-induced acute lung injury. However, the role of TOLLIP in PQ-induced AKI remains undefined. This study was aimed at understanding the role and mechanism of TOLLIP in AKI. Six-eight-week-old male Wistar rats were intraperitoneally injected with 25 mg/kg PQ to induce AKI for 24 h in vivo. HK-2 cells were treated with 300 μM PQ for 24 h to induce cellular injury in vitro or 300 μM PQ and 5 μM nuclear factor-κB (NF-κB) inhibitor BAY11-7082 for 24 h. Rats were infected with adenovirus carrying TOLLIP shRNA via tail vein injection and HK-2 cells with adenovirus carrying TOLLIP shRNA or TOLLIP 48 h before PQ exposure. Results showed that TOLLIP and Toll-like receptor 2/4 (TLR2/4) expressions were boosted in the kidney after PQ intoxication. The toxic effect of PQ on the kidney and HK-2 cells was exacerbated by TOLLIP knockdown, as evidenced by aggravated glomerulus and tubule injury, inflammatory infiltration, and cell apoptosis in the kidney and increased loss of cell viability and apoptotic cells in HK-2 cells. TOLLIP knockdown also enhanced PQ-induced NLR family pyrin domain-containing 3 (NLRP3) inflammasome activation in vivo and in vitro and TLR2/4-NF-κB signaling in vitro, reflected by increased contents of proinflammatory cytokines and expressions of NLRP3 inflammasome-related proteins in the kidney and HK-2 cells and expressions of TLR2, TLR4, and nuclear NF-κB p65 in HK-2 cells. However, TOLLIP overexpression inhibited PQ-induced loss of cell viability, cell apoptosis, NLRP3 inflammasome activation, and TLR2/4-NF-κB signaling in vitro. Additionally, BAY11-7082 abolished TOLLIP knockdown-induced NLRP3 inflammasome activation in vitro, indicating that TOLLIP protected against NLRP3 inflammasome activation in PQ-induced AKI through inhibiting TLR2/4-NF-κB signaling. This study highlights the importance of TOLLIP in AKI after PQ intoxication.

The interplay of DAMPs, TLR4, and proinflammatory cytokines in pulmonary fibrosis

Pulmonary fibrosis is a chronic debilitating condition characterized by progressive deposition of connective tissue, leading to a steady restriction of lung elasticity, a decline in lung function, and a median survival of 4.5 years. The leading causes of pulmonary fibrosis are inhalation of foreign particles (such as silicosis and pneumoconiosis), infections (such as post COVID-19), autoimmune diseases (such as systemic autoimmune diseases of the connective tissue), and idiopathic pulmonary fibrosis. The therapeutics currently available for pulmonary fibrosis only modestly slow the progression of the disease. This review is centered on the interplay of damage-associated molecular pattern (DAMP) molecules, Toll-like receptor 4 (TLR4), and inflammatory cytokines (such as TNF-α, IL-1β, and IL-17) as they contribute to the pathogenesis of pulmonary fibrosis, and the possible avenues to develop effective therapeutics that disrupt this interplay.

Macrophage-stroma interactions in fibrosis: biochemical, biophysical, and cellular perspectives

Fibrosis results from aberrant wound healing and is characterized by an accumulation of extracellular matrix, impairing the function of an affected organ. Increased deposition of extracellular matrix proteins, disruption of matrix degradation, but also abnormal post-translational modifications alter the biochemical composition and biophysical properties of the tissue microenvironment - the stroma. Macrophages are known to play an important role in wound healing and tissue repair, but the direct influence of fibrotic stroma on macrophage behaviour is still an under-investigated element in the pathogenesis of fibrosis. In this review, the current knowledge on interactions between macrophages and (fibrotic) stroma will be discussed from biochemical, biophysical, and cellular perspectives. Furthermore, we provide future perspectives with regard to how macrophage-stroma interactions can be examined further to ultimately facilitate more specific targeting of these interactions in the treatment of fibrosis. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Genistein Attenuates Isoflurane-Induced Neuroinflammation by Inhibiting TLR4-Mediated Microglial-Polarization in vivo and in vitro

Background

Isoflurane, a widely used anesthetic in surgery, has been found to induce neurotoxicity. In parallel, genistein is thought to attenuate isoflurane-induced neurotoxicity, although underlying molecular mechanisms are still unclear. In this study, we studied the protective effects of genistein on isoflurane-induced neuroinflammation in rats and BV2 cells.

Methods

Sprague-Dawley rat pups were exposed to 0.75% isoflurane for 6 hours at postnatal day 7 (P7), and genistein (20, 40, or 80 mg/kg/day) or saline administered from P3 to P15. Hippocampal single-cell suspensions were prepared and apoptosis analyzed by flow cytometry. mRNA expression was determined by RT-qPCR, while protein expression was assessed using Western blot, immunochemistry and immunofluorescence. TLR4 was knocked-out in BV2 cells through CRISPR-Cas9.

Results

Genistein treatment reduced isoflurane-induced apoptosis and inflammation in rat hippocampus. Importantly, genistein promoted M2 and suppressed M1 microglia polarization in rat hippocampus after stimulation with isoflurane. In addition, genistein reduced isoflurane-induced protein expression levels of TLR4, MyD88, TRAF6, p-TAK1, p-p38, p-ERK, p-IκBα and p-NF-κB in rat hippocampus. In BV2 cells exposed to isoflurane, genistein treatment decreased IL-1β, TNF-α, IL-6 and IL-8 mRNA expressions, promoted M2 and suppressed M1 microglia polarization. Similarly, genistein also decreased TLR4 protein levels in isoflurane-induced BV2 cells. However, genistein did not affect CD16, iNOS, CD206 and Arg1 protein levels in TLR4-KO BV2 cells exposed to isoflurane.

Conclusion

Genistein attenuates isoflurane-induced neurotoxicity by inhibiting TLR4-mediated microglial inflammation in vivo and in vitro.

Role and mechanisms of autophagy in lung metabolism and repair

Mammalian lungs are metabolically active organs that frequently encounter environmental insults. Stress responses elicit protective autophagy in epithelial barrier cells and the supportive niche. Autophagy promotes the recycling of damaged intracellular organelles, denatured proteins, and other biological macromolecules for reuse as components required for lung cell survival. Autophagy, usually induced by metabolic defects, regulates cellular metabolism. Autophagy is a major adaptive response that protects cells and organisms from injury. Endogenous region-specific stem/progenitor cell populations are found in lung tissue, which are responsible for epithelial repair after lung damage. Additionally, glucose and fatty acid metabolism is altered in lung stem/progenitor cells in response to injury-related lung fibrosis. Autophagy deregulation has been observed to be involved in the development and progression of other respiratory diseases. This review explores the role and mechanisms of autophagy in regulating lung metabolism and epithelial repair.

Dynamic role of LMW-hyaluronan fragments and Toll-like receptors 2,4 in progression of bleomycin induced lung parenchymal injury to fibrosis

Background

Pulmonary fibrosis (PF) is a progressive and lethal lung disease of elderly whose incidence has been increasing following the Covid-19 pandemic caused by severe acute respiratory syndrome corona virus 2 (SARS-CoV-2). PF immunopathogenesis involves progressive alveolar epithelial cell damage, release of damage-associated molecular patterns (DAMPs), and extracellular matrix (ECM) injury. We assessed the dynamic role of LMW-hyaluronan (LMW-HA) as DAMP in initiation of host immune TLR-2,4 responses and as determinant in progression of ECM injury to fibrosis. Male Wistar rats were divided into Group I (saline control, n = 24) and Group II (intratracheal bleomycin, 7 U/kg/animal, n = 24). Animals were euthanized on 0, 7, 14, and 28 days. The time course of release of LMW-HA, TLR-2,4 mRNA and protein levels, and NF-κB-p65 levels after bleomycin injury were correlated with the development of parenchymal inflammation, remodelling, and fibrosis.

Results

Acute lung injury caused by bleomycin significantly increases the pro-inflammatory LMW-HA levels and elevates TLR-2,4 levels on day 7. Subsequently, TLR-2 upregulation, TLR-4 downregulation, and NF-κB signalling follow on days 14 and 28. This results in progressive tissue inflammation, alveolar and interstitial macrophage accumulation, and fibrosis.

Conclusions

LMW-HA significantly increases in PF caused by non-infectious and infectious (Covid-19) etiologies. The accumulating HA fragments function as endogenous DAMPs and trigger inflammatory responses, through differential TLR2 and TLR4 signalling, thus promoting inflammation and macrophage influx. LMW-HA are reflective of the state of ongoing tissue inflammation and may be considered as a natural biosensor for fibrotic lung diseases and as potential therapeutic targets.

The Epithelial-Immune Crosstalk in Pulmonary Fibrosis

Interactions between the lung epithelium and the immune system involve a tight regulation to prevent inappropriate reactions and have been connected to several pulmonary diseases. Although the distal lung epithelium and local immunity have been implicated in the pathogenesis and disease course of idiopathic pulmonary fibrosis (IPF), consequences of their abnormal interplay remain less well known. Recent data suggests a two-way process, as illustrated by the influence of epithelial-derived periplakin on the immune landscape or the effect of macrophage-derived IL-17B on epithelial cells. Additionally, damage associated molecular patterns (DAMPs), released by damaged or dying (epithelial) cells, are augmented in IPF. Next to “sterile inflammation”, pathogen-associated molecular patterns (PAMPs) are increased in IPF and have been linked with lung fibrosis, while outer membrane vesicles from bacteria are able to influence epithelial-macrophage crosstalk. Finally, the advent of high-throughput technologies such as microbiome-sequencing has allowed for the identification of a disease-specific microbial environment. In this review, we propose to discuss how the interplays between the altered distal airway and alveolar epithelium, the lung microbiome and immune cells may shape a pro-fibrotic environment. More specifically, it will highlight DAMPs-PAMPs pathways and the specificities of the IPF lung microbiome while discussing recent elements suggesting abnormal mucosal immunity in pulmonary fibrosis.

Ac-SDKP Attenuates Activation of Lung Macrophages and Bone Osteoclasts in Rats Exposed to Silica by Inhibition of TLR4 and RANKL Signaling Pathways

Background

Silica-induced inflammatory activation is associated with silicosis and various non-respiratory conditions. The present study was designed to examine the anti-inflammatory effects of N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) on lung macrophages and bone osteoclasts after silica inhalation in rats.

Methods

Wistar rats and NR8383 and RAW 264.7 cell lines were used in the present study. The receptor activator of nuclear factor kappa-B ligand (RANKL) and toll-like receptor 4 (TLR4) signaling pathways was measured in the lung tissue of rats or NR8383/RAW 264.7 cells exposed to silica. The microarchitecture of the trabecular bone in the tibia and femur was evaluated in silicotic rats. Furthermore, the roles of Ac-SDKP on silicotic rats, silica-treated NR8383/RAW 264.7 cells, and RANKL-induced osteoclast differentiation were studied.

Results

The data indicated that silica inhalation might activate the RANKL and TLR4 signaling pathways in lung macrophages, thus inducing the lung inflammatory and proteolytic phenotype of macrophages and osteoclasts in lung and bone. Ac-SDKP maintained the lung elastin level by inhibiting lung inflammation and macrophage activation via the RANKL and TLR4 signaling pathways. Ac-SDKP also attenuated the reduction in femoral bone mineral density in silicotic rats by inhibiting osteoclast differentiation via the RANKL signaling pathway.

Conclusion

Our findings support the hypothesis that inhalation of crystalline silica induces activation of lung macrophages and bone osteoclasts via the RANKL and TLR4 signaling pathways. Ac-SDKP has the potential to stabilize lung homeostasis and bone metabolism.

Hyaluronan, Transforming Growth Factor β, and Extra Domain A-Fibronectin: A Fibrotic Triad

Significance: Inflammation is a critical aspect of injury repair. Nonresolving inflammation, however, is perpetuated by the local generation of extracellular matrix-derived damage-associated molecular pattern molecules (DAMPs), such as the extra domain A (EDA) isoform of fibronectin and hyaluronic acid (HA) that promote the eventual acquisition of a fibrotic response. DAMPs contribute to the inflammatory environment by engaging Toll-like, integrin, and CD44 receptors while stimulating transforming growth factor (TGF)-β signaling to activate a fibroinflammatory genomic program leading to the development of chronic disease. Recent Advances: Signaling through TLR4, CD44, and the TGF-β pathways impact the amplitude and duration of the innate immune response to endogenous DAMPs synthesized in the context of tissue injury. New evidence indicates that crosstalk among these three networks regulates phase transitions as well as the repertoire of expressed genes in the wound healing program determining, thereby, repair outcomes. Clarifying the molecular mechanisms underlying pathway integration is necessary for the development of novel therapeutics to address the spectrum of fibroproliferative diseases that result from maladaptive tissue repair. Critical Issues: There is an increasing appreciation for the role of DAMPs as causative factors in human fibroinflammatory disease regardless of organ site. Defining the involved intermediates essential for the development of targeted therapies is a daunting effort, however, since various classes of DAMPs activate different direct and indirect signaling pathways. Cooperation between two matrix-derived DAMPs, HA, and the EDA isoform of fibronectin, is discussed in this review as is their synergy with the TGF-β network. This information may identify nodes of signal intersection amenable to therapeutic intervention. Future Directions: Clarifying mechanisms underlying the DAMP/growth factor signaling nexus may provide opportunities to engineer the fibroinflammatory response to injury and, thereby, wound healing outcomes. The identification of shared and unique DAMP/growth factor-activated pathways is critical to the design of optimized tissue repair therapies while preserving the host response to bacterial pathogens.

Hirsutella sinensis mycelium regulates autophagy of alveolar macrophages via TLR4/NF-κB signaling pathway

Background: Hirsutella sinensis mycelium (HSM) has potent anti-pulmonary fibrotic activities and has been proposed as an effective treatment for idiopathic pulmonary fibrosis. Macrophages are the main innate immune cells in the lung tissue, playing key roles in pulmonary fibrosis repair and homeostasis. Excessive macrophage autophagy plays a vital role in pulmonary fibrosis. The protective effect of HSM on macrophages of bleomycin (BLM)-induced pulmonary fibrotic mice remain unclear. Methods: In this study, we collected lung tissue and bronchoalveolar lavage fluid (BALF) samples from pulmonary fibrotic mice. Meanwhile, alveolar macrophages were isolated and murine macrophage RAW264.7 cell line was cultured for further study of HSM autophagy. Results: First, we found that HSM decreased the number of autophagosomes, as well as the levels of LC3B and ATG5, and increased the protein level of P62 during the development of pulmonary fibrosis. Meanwhile, HSM reduced alveolar macrophages infiltration into the BALF and inhibited their accumulation in the fibrotic lung tissue. Flow cytometry analysis showed that HSM administration inhibited the autophagy marker LC3B expression in CD11bloCD11chi alveolar macrophages in BLM-induced lung fibrosis without affecting CD11bhiCD11clo interstitial macrophages. Transmission electron microscopy and JC-1 staining for mitochondrial membrane potential of alveolar macrophages also verified that the HSM significantly decreased autophagy in the alveolar macrophages of BLM-treated mice. In vitro, autophagosomes-lysosome fusion inhibitor chloroquine (CQ) was pre-incubated with RAW264.7 cells, and HSM reduced CQ-induced autophagosomes accumulation. TLR4 signaling inhibitor CLI095 reversed the above effects, suggesting HSM could reduce the cumulation of autophagosomes dependent on TLR4. Furthermore, lipopolysaccharide (LPS)-stimulated TLR4-related autophagy was significantly inhibited by HSM treatment. In addition, the protein expressions of TLR4 and phospho-NF-κB p65 were markedly inhibited in cells treated with HSM. Conclusions: These results indicated that HSM could inhibit the autophagy of alveolar macrophages through TLR4/NF-κB signaling pathway to achieve anti-fibrotic effect.

Macrophage Autophagy and Silicosis: Current Perspective and Latest Insights

Silicosis is an urgent public health problem in many countries. Alveolar macrophage (AM) plays an important role in silicosis progression. Autophagy is a balanced mechanism for regulating the cycle of synthesis and degradation of cellular components. Our previous study has shown that silica engulfment results in lysosomal rupture, which may lead to the accumulation of autophagosomes in AMs of human silicosis. The excessive accumulation of autophagosomes may lead to apoptosis in AMs. Herein, we addressed some assumptions concerning the complex function of autophagy-related proteins on the silicosis pathogenesis. We also recapped the molecular mechanism of several critical proteins targeting macrophage autophagy in the process of silicosis fibrosis. Furthermore, we summarized several exogenous chemicals that may cause an aggravation or alleviation for silica-induced pulmonary fibrosis by regulating AM autophagy. For example, lipopolysaccharides or nicotine may have a detrimental effect combined together with silica dust via exacerbating the blockade of AM autophagic degradation. Simultaneously, some natural product ingredients such as atractylenolide III, dioscin, or trehalose may be the potential AM autophagy regulators, protecting against silicosis fibrosis. In conclusion, the deeper molecular mechanism of these autophagy targets should be explored in order to provide feasible clues for silicosis therapy in the clinical setting.

LncRNA UCA1 remits LPS-engendered inflammatory damage through deactivation of miR-499b-5p/TLR4 axis

Neonatal pneumonia is a high neonatal mortality disease. The current research was designed to elucidate the modulatory function and feasible molecular mechanism of UCA1 in LPS-induced injury in pneumonia. Herein, LPS was applied to induce WI-38 cell inflammatory damage. We displayed that UCA1 was elevated in LPS-injured WI-38 cells. In the functional aspect, intervention of UCA1 evidently aggrandized cell viability in LPS-triggered WI-38 cells. In the meanwhile, elimination of UCA1 distinctly assuaged cell apoptosis concomitant with declined levels of proapoptotic proteins Bax and C-caspase-3, and ascended the expression of antiapoptotic protein Bcl-2. Subsequently, disruption of UCA1 manifestly restrained inflammatory damage as characterized by declination of multiple pro-inflammatory factors IL-1β, IL-6, and TNF-α in WI-38 cells under LPS circumstance. More importantly, we predicted and verified that UCA1 functioned as a ceRNA by efficaciously binding to miR-499b-5p thereby inversely adjusting miR-499b-5p expression. Interesting, TLR4 was identified as direct target of miR-499b-5p, and positively regulated by UCA1 through sponging miR-499b-5p. Mechanistically, absence of miR-499b-5p or restoration of TLR4 impeded the beneficial effects of UCA1 ablation on LPS-stimulated apoptosis and inflammatory response. Collectively, these observations illuminated that UCA1 inhibition protected WI-38 cells against LPS-managed inflammatory injury and apoptosis process via miR-499b-5p/TLR4 crosstalk, which ultimately influencing the development of pneumonia.

Comparison of reversal of rat pulmonary fibrosis of nintedanib, pirfenidone, and human umbilical mesenchymal stem cells from Wharton's jelly

Background

The present study compared the effects of antifibrotic medications, pirfenidone, and nintedanib, with transplantation of human umbilical mesenchymal stem cells (HUMSCs) in restoring rat pulmonary fibrosis (PF).

Methods

A stable animal model was established via an intratracheal injection of 5 mg bleomycin (BLM). One single transplantation of 2.5× 10⁷ HUMSCs or initiation of daily oral nintedanib/pirfenidone administration was performed on day 21 following BLM damage.

Results

Pulmonary function examination revealed that BLM rats exhibited a significant decrease in blood oxygen saturation and an increase in respiratory rates. While no significant improvements were found in BLM rats receiving nintedanib or pirfenidone, those who transplanted with HUMSCs showed a statistical amelioration in blood oxygen saturation and significant alleviation in respiratory rates. Quantification results revealed that a significant reduction in alveolar space and marked increases in substantial cell infiltration and collagen deposition in the left lungs of BLM rats. No significant alteration was observed in BLM rats administered nintedanib or pirfenidone. However, BLM rats transplanted with HUMSCs had a significant recovery in alveolar space and noticeable decreases in cell infiltration and collagen deposition. The inflammatory cell numbers in the bronchoalveolar lavage was increased in the BLM group. While the rats treated with nintedanib or pirfenidone had a lower cell number than the BLM group, a higher cell number was found as compared with the Normal group. In rats transplanted with HUMSCs, the cell number did not differ from the Normal group.

Conclusions

Transplantation of HUMSCs could effectively treat PF as opposed to the administration of anti-fibrotic drugs with nintedanib or pirfenidone with a significant better result in lung volume, pathological changes, lung function, and blood oxygen saturation.

Phytochemicals: Potential Therapeutic Interventions Against Coronavirus-Associated Lung Injury

Since the outbreak of coronavirus disease 2019 (COVID-19) in December 2019, millions of people have been infected and died worldwide. However, no drug has been approved for the treatment of this disease and its complications, which urges the need for finding novel therapeutic agents to combat. Among the complications due to COVID-19, lung injury has attained special attention. Besides, phytochemicals have shown prominent anti-inflammatory effects and thus possess significant effects in reducing lung injury caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Also, the prevailing evidence reveales the antiviral effects of those phytochemicals, including anti-SARS-CoV activity, which could pave the road in providing suitable lead compounds in the treatment of COVID-19. In the present study, candidate phytochemicals and related mechanisms of action have been shown in the treatment/protection of lung injuries induced by various methods. In terms of pharmacological mechanism, phytochemicals have shown potential inhibitory effects on inflammatory and oxidative pathways/mediators, involved in the pathogenesis of lung injury during COVID-19 infection. Also, a brief overview of phytochemicals with anti-SARS-CoV-2 compounds has been presented.

Hyperinflammation and Fibrosis in Severe COVID-19 Patients: Galectin-3, a Target Molecule to Consider

COVID-19 disease have become so far the most important sanitary crisis in the XXI century. In light of the events, any clinical resource should be considered to alleviate this crisis. Severe COVID-19 cases present a so-called cytokine storm as the most life-threatening symptom accompanied by lung fibrosis. Galectin-3 has been widely described as regulator of both processes. Hereby, we present compelling evidences on the potential role of galectin-3 in COVID-19 in the regulation of the inflammatory response, fibrosis and infection progression. Moreover, we provide a strong rationale of the utility of measuring plasma galectin-3 as a prognosis biomarker for COVID-19 patients and propose that inhibition of galectin-3 represents a feasible and promising new therapeutical approach.

Polygonatum sibiricum polysaccharides prevent LPS-induced acute lung injury by inhibiting inflammation via the TLR4/Myd88/NF-κB pathway

Inflammation plays an important role in cases of acute lung injury (ALI), and the Toll-like receptor 4/nuclear factor-κB (TLR4/NF-κB) pathway, which can be regulated by Polygonatum sibiricum polysaccharides (PSPs), is closely related to the dynamics of lipopolysaccharide (LPS)-induced inflammation. Thus, we sought to evaluate whether or not PSPs prevent LPS-induced ALI by way of inhibiting inflammation via the TLR4/NF-κB pathway in rats. We established an ALI rat model by tracheal instillation of LPS, and by pre-injection of PSPs into rats to examine PSPs in the ALI rat model. We found that PSPs attenuated LPS-induced lung pathological changes in ALI rats, decreased LPS-induced myeloperoxidase (MOP) activity, and elevated malondialdehyde (MDA) levels in lung tissue. However, PSPs also decreased the LPS-induced increase in the neutrophil ratio, and decreased inflammatory factor levels in bronchoalveolar lavage fluid (BALF). Moreover, PSPs decreased LPS-induced increases in inflammatory factors measured by mRNA expression, and altered the levels of expression of TLR4, medullary differentiation protein 88 (Myd88), p-IKB-α/IKB-α and p-p65/p65 proteins in lung tissue. In vitro, PSPs also reduced apoptosis induced by LPS in BEAS-2B cells by suppressing inflammation through its effect of inhibiting the TLR4/NF-κB pathway. In conclusion, our results suggest that PSPs may be a potential drug for effective treatment of LPS-induced ALI, due to the ability to inhibit inflammation through effects exerted on the TLR4/Myd88/NF-κB pathway.

Pathogenesis and treatment of idiopathic and rheumatoid arthritis-related interstitial pneumonia. The possible lesson from COVID-19 pneumonia

INTRODUCTION

Main clinical manifestations of SARS-CoV-2 infection are characterized by fever, dyspnea, and interstitial pneumonia, frequently evolving in acute respiratory distress syndrome (ARDS).

AREAS COVERED

Features of coronavirus disease 2019 (COVID-19) presents some common points with interstitial lung disease (ILD) both idiopathic and related to rheumatoid arthritis (RA), typically characterized by a chronic progression over time and possibly complicated by acute exacerbation (AE). The study of common pathogenetic mechanisms, such as the involvement of toll-like receptor 4, could contribute to the knowledge and treatment of idiopathic and RA-ILD. Moreover, hyperinflammation, mainly characterized by increase of effector T-cells and inflammatory cytokines, and activation of coagulation cascade, observed in COVID-19 related ARDS have been already shown in patients with AE of idiopathic and RA-ILD. A literature search was performed in PubMed, Embase, Scopus, and Web of Science, together with a manual search in COVID-resource centers of the main journals.

EXPERT OPINION

Despite the uncertainty about pathogenetic aspects about COVID-19- pneumonia, it could be a possible model for other forms of ILD and AE. The great amount of data from studies on COVID-19 could be helpful in proposing safe therapeutic approaches for RA-ILD, in understanding pathogenesis of usual interstitial pneumonia and to develop new therapeutic strategies for AE.

Role of Alarmins in the Pathogenesis of Systemic Sclerosis

Systemic sclerosis (SSc) is a rare chronic autoimmune disease associated with significant morbidity and mortality. Two main subsets of SSc are recognized: (i) diffuse cutaneous SSc with rapidly progressive fibrosis of the skin, lungs, and other internal organs; and (ii) limited cutaneous SSc, which is dominated by vascular manifestations, with skin and organ fibrosis generally limited and slowly progressing. In spite of intense investigation, both etiology and pathogenesis of SSc are still unknown. Genetic and environmental factors, as well as abnormalities of immune functions, are strongly suggested for etiology, while microvascular abnormalities, immune system activation, and oxidative stress are suggested for the pathogenesis. Recently, it has been found that a multitude of mediators and cytokines are implicated in the fibrotic processes observed in SSc. Among these, a central role could be exerted by “alarmins”, endogenous and constitutively expressed proteins/peptides that function as an intercellular signal defense. This review describes, in a detailed manner, the role of alarmins in the pathogenesis of scleroderma.

Curcumin attenuates endothelial cell fibrosis through inhibiting endothelial-interstitial transformation

Curcumin (Cur) has various pharmacological activities, including anti-inflammatory, antiapoptotic and anticancer effects. However, there is no report on the effect of Cur on endothelial cell fibrosis. This study was designed to investigate the effect and mechanism of Cur on endothelial cell fibrosis. An endothelial cell fibrosis model was established by using transforming growth factor (TGF) induction. Proliferation assays, qRT-PCR, western blotting and immunostaining were performed to investigate the effects and mechanism of Cur on endothelial cell fibrosis. We found that in human umbilical vein endothelial cells (HUVECs), TGF-β1 treatment significantly decreased the expression of nuclear factor erythroid-2-related factor 2 (NRF-2), dimethylarginine dimethylaminohydrolase-1 (DDAH1), and VE-cadherin, the secretion of cellular nitric oxide (NO) and the activity of nitrous oxide synthase (NOS), while asymmetric dimethylarginine (ADMA) and the release of inflammatory factors were elevated. Immunofluorescence showed decreased CD31 and increased α-smooth muscle actin (α-SMA). Overexpression of NRF-2 significantly attenuated the effects of TGF-β1, while downregulation of DDAH1 potently counteracted the effect of NRF-2. In addition, ADMA treatment resulted in similar results to those of TGF-β1, and Cur significantly attenuated the effect of TGF-β1, accompanied by increased VE-cadherin, DDAH1 and NRF-2 and decreased matrix metalloproteinase-9 (MMP-9) and extracellular regulated protein kinases 1/2 (ERK1/2) phosphorylation. The NRF-2 inhibitor ML385 had the opposite effect as that of Cur. These results demonstrated that Cur inhibits TGF-β1-induced endothelial-to-mesenchymal transition (EndMT) by stimulating DDAH1 expression via the NRF-2 pathway, thus attenuating endothelial cell fibrosis.

Self-eating: friend or foe? The emerging role of autophagy in fibrotic diseases

Fibrosis occurs in most human organs including the liver, lung, heart and kidney, and is crucial for the progression of most chronic diseases. As an indispensable catabolic process for intracellular quality control and homeostasis, autophagy occurs in most mammalian cells and is implicated in many biological processes including fibrogenesis. Although advances have been made in understanding autophagy process, the potential role of autophagy in fibrotic diseases remains controversial and has recently attracted a great deal of attention. In the current review, we summarize the commonalities of autophagy affecting different types of fibrosis in different organs, including the liver, lung, heart, and kidney as well as in cystic fibrosis, systematically outline the contradictory results and highlight the distinct role of autophagy during the various stages of fibrosis. In summary, the exact role autophagy plays in fibrogenesis depends on specific cell types and different stimuli, and identifying and evaluating the pathogenic contribution of autophagy in fibrogenesis will promote the discovery of novel therapeutic strategies for the clinical management of these fibrotic diseases.

Cardiac Damage in Anthracyclines Therapy: Focus on Oxidative Stress and Inflammation

Significance: Despite their serious side effects, anthracyclines (ANTs) are the most prescribed chemotherapeutic drugs because of their strong efficacy in both solid and hematological tumors. A major limitation to ANTs clinical application is the severe cardiotoxicity observed both acutely and chronically. The mechanism underlying cardiac dysfunction under chemotherapy is mainly dependent on the generation of oxidative stress and systemic inflammation, both of which lead to progressive cardiomyopathy and heart failure. Recent Advances: Over the years, the iatrogenic ANTs-induced cardiotoxicity was believed to be simply given by iron metabolism and reactive oxygen species production; however, several experimental data indicate that ANTs may use alternative damaging mechanisms, such as topoisomerase 2β inhibition, inflammation, pyroptosis, immunometabolism, and autophagy. Critical Issues: In this review, we aimed at discussing ANTs-induced cardiac injury from different points of view, updating and focusing on oxidative stress and inflammation, since these pathways are not exclusive or independent from each other but they together importantly contribute to the complexity of ANTs-induced multifactorial cardiotoxicity. Future Directions: A deeper understanding of the mechanistic signaling leading to ANTs side effects could reveal crucial targeting molecules, thus representing strategic knowledge to promote better therapeutic efficacy and lower cardiotoxicity during clinical application.

Autophagy is involved in the sclerotic phase of systemic sclerosis

Autophagy is an essential intracellular self-degradation system, and is known to maintain the homeostatic balance between the synthesis, degradation, and recycling of cellular proteins and organelles. Recent studies have suggested a possible role of autophagy in systemic sclerosis (SSc);however, differences in autophagy among pathological phases of SSc have not yet been examined. Therefore, in the current study we investigated the expression pattern of an autophagosome marker protein, microtubule-associated protein 1 light chain 3 (LC3) in the lesional skin of a murine model and human SSc. In bleomycin-induced mouse scleroderma skin, the number of LC3-positive puncta was significantly higher than that in phosphate buffered salts-injected control skin after 4 weeks of treatment. Such an increase, however, was not observed in the skin after 2 weeks of bleomycin treatment, in which few myofibroblasts were detected. In the sclerotic phase of SSc patients, the number of LC3-positive puncta in the lower dermis was significantly higher than in the upper dermis. It was also significantly higher than in the lower dermis of the control patients. No increase in LC3-positive puncta was observed in the skin from SSc patients in edematous phase, in which myofibroblasts were hardly detected. These results suggest that changes in the autophagic degradation system reflect a skin remodeling process that leads to fibrosis.

Long-term stimulation of toll-like receptor-2 and -4 upregulates 5-LO and 15-LO-2 expression thereby inducing a lipid mediator shift in human monocyte-derived macrophages

Macrophage polarization switches during the course of inflammation along with the lipid mediators released. We investigated the lipid mediator formation in human monocyte-derived macrophages during in vitro differentiation and pathogen stimulation. For this, peripheral blood monocytes were differentiated into M1 (CSF-2/IFNγ) or M2 (CSF-1/IL-4) macrophages followed by stimulation with the toll-like receptor (TLR) ligands zymosan (TLR-2), Poly(I:C) (TLR-3) or bacterial lipopolysaccharides (TLR-4) mimicking fungal, viral and bacterial infection, respectively. Expression of enzymes involved in lipid mediator formation such as 5- and 15-lipoxygenases (LO), the 5-LO activating protein and cyclooxygenase-2 (COX-2) was monitored on mRNA and protein level and lipid mediator formation was assessed. In addition, cytokine release was measured. In vitro differentiation of human peripheral blood monocytes to M1 and M2 macrophages considerably attenuated 5-LO activity. Furthermore, while TLR-2 and -4 stimulation of M1 macrophages primarily triggered pro-inflammatory cytokines and lipid mediators, persistent stimulation (16 h) of human M2 macrophages induced a coordinated upregulation of 5- and 15-LO-2 expression. This was accompanied by a marked increase in IL-10 and monohydroxylated 15-LO products in the conditioned media of the cells. After additional stimulation with Ca²⁺ ionophore combined with supplementation of arachidonic, eicosapentaenoic and docosahexaenoic acid these cells also released small amounts of SPM such as lipoxins and resolvins. From this we conclude that activation of TLR-2 or -4 triggers the biosynthesis of pro-inflammatory 5-LO and COX-2 derived lipid mediators in human monocyte-derived M1 macrophages while persistent stimulation of M2 macrophages induces a shift towards pro-resolving 15-LO derived oxylipins.

TLR4 Stimulation Promotes Human AVIC Fibrogenic Activity through Upregulation of Neurotrophin 3 Production

BACKGROUND

Calcific aortic valve disease (CAVD) is a chronic inflammatory disease that manifests as progressive valvular fibrosis and calcification. An inflammatory milieu in valvular tissue promotes fibrosis and calcification. Aortic valve interstitial cell (AVIC) proliferation and the over-production of the extracellular matrix (ECM) proteins contribute to valvular thickening. However, the mechanism underlying elevated AVIC fibrogenic activity remains unclear. Recently, we observed that AVICs from diseased aortic valves express higher levels of neurotrophin 3 (NT3) and that NT3 exerts pro-osteogenic and pro-fibrogenic effects on human AVICs.

HYPOTHESIS

Pro-inflammatory stimuli upregulate NT3 production in AVICs to promote fibrogenic activity in human aortic valves.

METHODS AND RESULTS

AVICs were isolated from normal human aortic valves and were treated with lipopolysaccharide (LPS, 0.20 µg/mL). LPS induced TLR4-dependent NT3 production. This effect of LPS was abolished by inhibition of the Akt and extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) pathways. The stimulation of TLR4 in human AVICs with LPS resulted in a greater proliferation rate and an upregulated production of matrix metallopeptidases-9 (MMP-9) and collagen III, as well as augmented collagen deposition. Recombinant NT3 promoted AVIC proliferation in a tropomyosin receptor kinase (Trk)-dependent fashion. The neutralization of NT3 or the inhibition of Trk suppressed LPS-induced AVIC fibrogenic activity.

CONCLUSIONS

The stimulation of TLR4 in human AVICs upregulates NT3 expression and promotes cell proliferation and collagen deposition. The NT3-Trk cascade plays a critical role in the TLR4-mediated elevation of fibrogenic activity in human AVICs. Upregulated NT3 production by endogenous TLR4 activators may contribute to aortic valve fibrosis associated with CAVD progression.