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Background: Idiopathic pulmonary fibrosis (IPF) is a progressive and deadly lung disease with limited therapeutic options. Bone morphogenetic protein 4 (BMP4), a multifunctional growth factor that belongs to the transforming growth factor-ß superfamily, is able to relieve pulmonary fibrosis in mice; nevertheless, the potential mechanism of action remains largely unknown. Growing evidence supports the notion that reiterant damage to the alveolar epithelial cells (AECs) is usually the "prime mover" for pulmonary fibrosis. Here, we examined the effect and mechanisms of BMP4 on bleomycin (BLM)-induced activation of NLR family pyrin domain containing 3 (NLRP3) inflammasome and epithelial-mesenchymal transition (EMT) in vivo and in vitro. Methods: The in vivo impact of BMP4 was investigated in a BLM mouse model. Histopathologic changes were analyzed by hematoxylin-eosin (H&E) and Masson's trichrome staining. The NLRP3 inflammasome activation was determined by quantitative real time polymerase chain reaction (qRT-PCR) and immunofluorescence staining. Biomarkers of EMT were measured by qRT-PCR, Western blot and immunofluorescence staining. The in vitro impact of BMP4 on BLM-induced NLRP3 inflammasome activation and EMT was explored in A549 AECs. We also evaluated whether BMP4 inhibited BLM-activated ERK1/2 signaling to address the possible molecular mechanisms. Results: BMP4 was significantly downregulated in the mouse lungs from BLM-induced pulmonary fibrosis. BMP4+/- mice presented with more severe lung fibrosis in response to BLM, and accelerated NLRP3 inflammasome activation and EMT process compared with that in BMP4+/+ mice. Whereas overexpression of BMP4 by injecting adeno-associated virus (AAV) 9 into mice attenuated BLM-induced fibrotic changes, NLRP3 inflammasome activation, and EMT in the mouse lungs, thus exerting protective efficacy against lung fibrosis. In vitro, BMP4 significantly reduced BLM-induced activation of NLRP3 inflammasome and EMT in human alveolar epithelial A549 cells. Mechanically, BMP4 repressed BLM-induced activation of ERK1/2 signaling in vivo and in vitro, suggesting that ERK1/2 inactivation contributes to BMP4-induced effects on BLM-induced activation of NLRP3 inflammasome and EMT. Conclusions: Our findings suggest that BMP4 can suppress NLRP3 inflammasome activation and EMT in AECs via inhibition of ERK1/2 signaling pathway, thus has a potential for the treatment of pulmonary fibrosis.
RESUMO
BACKGROUND: Inflammatory mediators play an important role in the occurrence, development, and metastasis of tumors. The aim of the present study was to elucidate the effect of apurinic/apyrimidinic endonuclease 1/reduction-oxidation effector factor-1 (APE1) on inflammatory mediator secretion, which is dependent on the APE1-mediated NLR family pyrin domain containing 3 (NLRP3) regulatory mechanism. METHODS: The human myeloid leukemia mononuclear cell line (THP-1) cells were cultured and polarized to M2 subset macrophages. Enzyme-linked immunosorbent assay was used for determining tumor necrosis factor-α (TNF-α), interleukin (IL)-1ß, IL-18, IL-10, and IL-33 levels. Reverse transcription-polymerase chain reaction and western blot were used for evaluating TNF-α, NLR family pyrin domain containing 1 (NLRP1), NLRP3, caspase-1, and apoptosis-associated speck-like protein containing a card expression. Plasmid silencing APE1 gene (APE1shRNA) was synthesized and packaged into lentiviral. For activating inflammasomes, M2-type THP-1 cells were transfected with lentiviral vector APE1shRNA incubated with lipopolysaccharide (LPS) (100 ng/mL)/APE1 inhibitor (E3330, 20 µM) and ATP. Electrophoretic mobility shift assay and dual-luciferase reporter assay were used for determining the interaction between NLRP3 and nuclear factor-κB (NF-κB) molecule. RESULTS: APE1 significantly induced LPS-induced pro-inflammatory cytokine production, including TNF-α, IL-1ß, and IL18, compared with THP-1 cells without APE1 treatment (P<0.05). APE1 promoted LPS-induced NLRP3 inflammasome activation by modulating the gene transcription of NLRP3-associated molecules. APE1 enhanced LPS-induced NLRP3 inflammasome activation by regulating NLRP3 and caspase-1 protein expression. APE1 improved NLRP3 activity by modulating the interaction between NLRP3 and NF-κB, and the modulation of NF-κB. APE1 promoted LPS-induced NLRP3 inflammasome activation through an NF-κB-dependent pathway. CONCLUSIONS: APE1 regulates the expression of NLRP3 by modulating transcription factor NF-κB and further promoting the secretion of inflammatory mediators IL-1ß and IL-18 in macrophages. The findings of the present study provide theoretical and experimental bases for the design of tumor-associated macrophage (TAM)-targeted therapy, with APE1 as the target molecule.
RESUMO
Ketosis is an important metabolic disease that can negatively affect the production efficiency of dairy cows. Earlier studies have revealed metabolic and inflammatory alterations in the blood associated with ketosis; however, a link between ketosis and hepatic inflammation has not been well documented. The objective of this study was to investigate whether the nuclear factor kappa B (NF-κB) signaling pathway and NLR family pyrin domain containing 3 (NLRP3) inflammasome were activated in the liver of ketotic cows. Liver and blood samples were collected from healthy (n = 15, control group) and ketotic (n = 15, ketosis group) cows that had a similar number of lactations (median = 3, range = 2 to 4) and days in milk (median = 6 d, range = 3 to 9 d). Results showed that serum levels of fatty acids, ß-hydroxybutyrate (BHB), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) were higher and glucose was lower in ketotic cows. Concentrations of serum proinflammatory cytokines IL18, tumor necrosis factor (TNF)-α, and IL1B were greater and the anti-inflammatory cytokine IL10 was lower in the ketosis group. Cows with ketosis had triacylglycerol accumulation in the liver. Upregulation of phosphorylated (p)-NF-κB and p-inhibitor of κB (IκB)α protein abundance in cows with ketosis indicated that the hepatic NF-κB signaling pathway was overactivated. The mRNA abundance of TNFA, inducible nitric oxide synthase (NOS2), IL18, and IL1B were greater and IL10 was lower in ketotic cows. More importantly, the mRNA and protein abundance of NLRP3 and caspase-1 (CASP1) along with CASP1 activity were greater in the liver of cows with ketosis. Overall, the data indicate that the onset of ketosis is accompanied by activation of the NF-κB signaling pathway and NLRP3 inflammasome, resulting in a state of inflammation.