Interleukin-11 drives fibroblast metabolic reprogramming in crystalline silica-induced lung fibrosis.

Environmental exposure to crystalline silica (CS) particles is common and occurs during natural, industrial, and agricultural activities. Prolonged inhalation of CS particles can cause silicosis, a serious and incurable pulmonary fibrosis disease. However, the underlying mechanisms remain veiled. Herein, we aim to elucidate the novel mechanisms of interleukin-11 (IL-11) driving fibroblast metabolic reprogramming during the development of silicosis. We observed that CS exposure induced lung fibrosis in mice and activated fibroblasts, accompanied by increased IL-11 expression and metabolic reprogramming switched from mitochondrial respiration to glycolysis. Besides, we innovatively uncovered that elevated IL-11 promoted the glycolysis process, thereby facilitating the fibroblast-myofibroblast transition (FMT). Mechanistically, CS-stimulated IL-11 activated the extracellular signal-regulated kinase (ERK) pathway and the latter increased the expression of hypoxia inducible factor-1α (HIF-1α) via promoting the translation and delaying the degradation of the protein. HIF-1α further facilitated glycolysis, driving the FMT process and ultimately the formation of silicosis. Moreover, either silence or neutralization of IL-11 inhibited glycolysis augmentation and attenuated CS-induced lung myofibroblast generation and fibrosis. Overall, our findings elucidate the role of IL-11 in promoting fibroblast metabolic reprogramming through the ERK-HIF-1α axis during CS-induced lung fibrosis, providing novel insights into the molecular mechanisms and potential therapeutic targets of silicosis.

Neutralization of interleukin-11 attenuates silica particles-induced pulmonary inflammation and fibrosis in vivo.

Environmental exposure to crystalline silica particles can lead to silicosis, which is one of the most serious pulmonary interstitial fibrosis around the world. Unfortunately, the exact mechanism on silicosis is unclear, and the effective treatments are lacking to date. In this study, we aim to explore the molecular mechanism by which interleukin-11 (IL-11) affects silica particles-induced lung inflammation and fibrosis. We observed that IL-11 expressions in mouse lungs were significantly increased after silica exposure, and maintained at high levels across both inflammation and fibrosis phase. Immunofluorescent dual staining further revealed that the overexpression of IL-11 mainly located in mouse lung epithelial cells and fibroblasts. Using neutralizing anti-IL-11 antibody could effectively alleviate the overexpression of pro-inflammatory cytokines (i.e., interleukin-6 and tumor necrosis factor-α) and fibrotic proteins (i.e., collagen type I and matrix metalloproteinase-2) induced by silica particles. Most importantly, the expressions of IL-11 receptor subunit α (IL-11Rα), Glycoprotein 130 (GP130), and phosphorylated extracellular signal-regulated kinase (p-ERK) were significantly increased in response to silica, whereas blocking of IL-11 markedly reduced their levels. All findings suggested that the overexpression of IL-11 was involved in the pathological of silicosis, while neutralizing IL-11 antibody could effectively alleviate the silica-induced lung inflammation and fibrosis by inhibiting the IL-11Rα/GP130/ERK signaling pathway. IL-11 might be a promising therapeutic target for lung inflammation and fibrosis caused by silica particles exposure.

Gas6 or Mer deficiency ameliorates silica-induced autophagosomes accumulation in mice lung.

Published evidences have shown that autophagy plays an important role in silica-induced lung inflammation and collagen deposition. Our previous study found that the level of growth arrest-specific protein 6 (Gas6) in bronchoalveolar lavage fluid was increased after silica exposure. However, it is unclear whether Gas6 is involved in the regulation of silica-induced autophagy dysfunction. In this study, we observed an autophagosomes accumulation in wild-type C57BL/6 (WT) mice lung after silica intratracheal instillation and then investigated whether genetic loss of Gas6 (Gas6-/-) could ameliorate it. Our data showed that Gas6-/- mice exhibited a limited autophagosomes accumulation from days 7-84 after silica exposure, revealed by reduced induction and increased degradation of autophagosomes in mice lung tissue. Interestingly, silica particles could elevate the expression of Mer receptor, which was significantly decreased in Gas6-/- mice (P < 0.05). Furthermore, we found that Mer deficiency (Mer-/-) could also reduce the formation of autophagosomes and restore the function of impaired lysosomes in silica-treated mice. Taken together, our results indicate that genetic loss of Gas6 attenuates silica-induced autophagosomes accumulation partly through down-regulating the expression of Mer receptor. Targeting Gas6/Mer-mediated autophagy pathway may provide a novel insight into the prevention and therapy of silica-induced pulmonary fibrosis.

Associations between essential metals exposure and metabolic syndrome (MetS): Exploring the mediating role of systemic inflammation in a general Chinese population.

BACKGROUND: Essential metals have been reported to be associated with metabolic diseases. However, the relationships between essential metals exposure and Metabolic Syndrome (MetS) is still uncertain, and the underlying mechanisms of the association remain unclear. OBJECTIVES: To investigate the associations of urinary essential metals with MetS prevalence; and further to explore potential role of systemic inflammation biomarker, C-reactive protein (CRP), in relationships between essential metals exposure and MetS prevalence in a cross-sectional study. METHODS: Concentrations of 8 urinary essential metals and plasma C-reactive protein (CRP) were quantified in 3272 adults from Wuhan-Zhuhai cohort. Urinary essential metals were adjusted by the corresponding urinary creatinine concentrations and reported as µg/mmol creatinine. Multivariable logistic regression and linear regression models were used to evaluate dose-response relationships between essential metals, plasma CRP, and MetS prevalence. Mediation analysis was performed to investigate the role of plasma CRP in the associations between urinary essential metals and MetS prevalence. RESULTS: In the single-metal models, we observed positive dose-dependent relationships of urinary copper and zinc with MetS prevalence. Compared with the lowest quartiles of urinary metals, the ORs (95% CI) of MetS in the highest quartiles were 1.40 (1.03, 1.91) for urinary copper and 2.07 (1.51, 2.84) for zinc, respectively. The dose-dependent relationships of zinc and copper with MetS remained significant in the multiple-metal models and Bayesian kernel machine regression (BKMR) models. No significant associations were observed between others essential metals (e.g. manganese, iron, cobalt, selenium, chromium, molybdenum) and MetS in this general population (all P value > 0.05). In addition, urinary copper and zinc increased monotonically with plasma CRP elevation, and plasma CRP was positively associated with the MetS prevalence. Mediation analysis indicated that plasma CRP mediated 5.2% and 3.2% in the associations of urinary copper and zinc with MetS prevalence, respectively. CONCLUSIONS: Elevated concentrations of urinary copper and zinc were associated with increased prevalence of MetS. Systemic inflammation may play an important role in the associations of copper and zinc exposure with MetS.

High-mobility group box 1 promotes epithelial-to-mesenchymal transition in crystalline silica induced pulmonary inflammation and fibrosis.

Silicosis is an inflammatory and fibrotic lung disease caused by prolonged inhalation of silica. The potential role of high-mobility group box-1 (HMGB-1) and its underlying mechanisms in silicosis remain unclear. In this study, intratracheal instillation of a silica suspension was used to establish silicosis in male C57BL/6 mice. To elucidate the effects of HMGB-1 on the pathogenesis of silicosis, we used HMGB-1 neutralizing antibody (anti-HMGB-1) and recombinant HMGB-1 (rmHMGB-1) to abrogate or increase the HMGB-1 levels, respectively. At days 7, 28, and 84, the accumulation of macrophages and neutrophils decreased by anti-HMGB-1 treatment. The expression levels of interleukin-6 and tumor necrosis factor-α in lung increased in response to silica exposure across three time points; anti-HMGB-1 could alleviate those expressions at day 28 and 84. In contrast, rmHMGB-1 aggravated this process. At days 28 and 84, the protein expression of fibronectin and col1a1 decreased in the silica + anti-HMGB-1 groups but increased in silica + rmHMGB-1 groups compared to mice with silica alone. Further study suggested that HMGB-1-mediated epithelial-mesenchymal transition participated in the development of silicosis. In conclusion, the findings demonstrate that HMGB-1 participates in the pathogenesis of silicosis and may represent a potential therapeutic target for the treatment of silicosis.

Triiodothyronine Attenuates Silica-Induced Oxidative Stress, Inflammation, and Apoptosis via Thyroid Hormone Receptor α in Differentiated THP-1 Macrophages.

Alveolar macrophage (AM) injury and inflammatory response are key processes in pathological damage caused by silica. However, the role of triiodothyronine (T3) in silica-induced AM oxidative stress, inflammation, and mitochondrial apoptosis remained unknown. To investigate the possible effects and underlying mechanism of T3 in silica-induced macrophage damage, differentiated human acute monocytic leukemia cells (THP-1) were exposed to different silica concentrations (0, 50, 100, 200, and 400 µg/mL) for 24 h. Additionally, silica-activated THP-1 macrophages were treated with gradient-dose T3 (0, 5, 10, 20, and 40 nM) for 24 h. To illuminate the potential mechanism, we used short hairpin RNA to knock down the thyroid hormone receptor α (TRα) in the differentiated THP-1 macrophages. The results showed that T3 decreased lactate dehydrogenase and reactive oxygen species levels, while increasing cell viability and superoxide dismutase in silica-induced THP-1 macrophages. In addition, silica increased the expression of interleukin 1 beta (IL-1ß), interleukin 6 (IL-6), and tumor necrosis factor-α (TNF-α), and T3 treatment reduced those pro-inflammatory cytokines secretion. Compared with silica-alone treated groups, cells treated with silica and T3 restored the mitochondrial membrane potential loss and had reduced levels of cytochrome c and cleaved caspase-3 expressions. Lastly, we observed that TRα-knockdown inhibited the protective effects of T3 silica-induced THP-1 macrophages. Together, these findings revealed that T3 could serve as a potential therapeutic target for protection against silica-induced oxidative stress, inflammatory response, and mitochondrial apoptosis, which are mediated by the activation of the T3/TRα signal pathway.

Genetic loss of Gas6/Mer pathway attenuates silica-induced lung inflammation and fibrosis in mice.

Long-term inhalation of crystalline silica particles leads to silicosis characterized by pulmonary inflammation and interstitial fibrosis. The growth arrest-specific protein 6 (Gas6) and its tyrosine receptor Mer have been implicated to involve in the regulation of inflammation, innate immunity and tissue repair. However, the role of Gas6 or Mer in silica-induced lung inflammation and fibrosis has not been investigated previously. In this study, we observed a remarkable increase of Gas6 in bronchoalveolar lavage fluid (BALF) from wild-type C57BL/6 mice after silica intratracheal administration. Then, we investigated whether genetic loss of Gas6 or Mer could attenuate silica-induced lung inflammation and fibrosis. Our results showed that Gas6-/- and Mer-/- mice exhibited reduced lung inflammation response from days 7 to 84 after silica exposure. We also uncovered an overexpression of the suppressor of cytokine signaling protein 1 in silica-treated deficient mice. Moreover, Gas6 or Mer deficiency attenuated silica-induced collagen deposition by inhibiting the expression of transforming growth factor-ß. We conclude that gene absence of Gas6 or Mer is protective against silica-induced lung inflammation and fibrosis in mice. Targeting Gas6/Mer pathway may be a potential therapeutic approach to treat pulmonary fibrosis in patients with silicosis.

Association between Plasma HMGB-1 and Silicosis: A Case-Control Study.

High-mobility group box-1 (HMGB-1) has been associated with fibrotic diseases. However, the role of HMGB-1 in silicosis is still uncertain. In this study, we conducted a case-control study involving 74 patients with silicosis and 107 age/gender-matched healthy controls in China. An Enzyme-linked immunosorbent assay (ELISA) was used to examine the concentrations of plasma HMGB-1 among all subjects. A logistic regression model and receiver operating characteristic curve (ROC) analysis were performed to assess the relationships between HMGB-1 and silicosis. We observed that plasma HMGB-1 concentrations were significantly increased in silicosis patients when compared with healthy controls (p < 0.05). Each 1 ng/mL increase in plasma HMGB-1 was positively associated with increased odds of silicosis, and the odds ratio (OR) (95% confidence interval) was 1.86 (1.52, 2.27). Additionally, compared with subjects with lower HMGB-1 concentrations, increased odds of silicosis were observed in those with higher HMGB-1 concentrations, and the OR was 15.33 (6.70, 35.10). Nonlinear models including a natural cubic spline function of continuous HMGB-1 yielded similar results. In ROC analyses, we found that plasma HMGB-1 >7.419 ng/mL had 81.6% sensitivity and 80.4% specificity for silicosis, and the area under the curve (AUC) was 0.84. Our results demonstrated that elevated plasma HMGB-1 was positivity associated with increased OR of silicosis.