High-Mobility Group Box 1 Mediates Epithelial-to-Mesenchymal Transition in Pulmonary Fibrosis Involving Transforming Growth Factor-β1/Smad2/3 Signaling

Abstract

Epithelial-to-mesenchymal transition (EMT) is a crucial event in the cellular origin of myofibroblasts that secrete extracellular matrix in the progression of pulmonary fibrosis (PF). Highmobility group box 1 (HMGB1) is a novel mediator of EMT. However, whether this process involves the recognized transforming growth factor-b1 (TGF-b1)/Smad signaling that also contributes to EMT in PF has not yet been elucidated. Here, we developed a model of PF induced by bleomycin (BLM) in rats and conducted several simulation experiments in A549 (human) and RLE-6TN (rat) alveolar epithelial cell (AEC) lines to unravel the role of TGF-b1/Smad2/3 signaling in HMGB1-mediated EMT. We found that the levels of serum HMGB1 and lung hydroxyproline were severely elevated after BLM administration. Moreover, the protein expression of HMGB1, TGF-b1, phosphorylated Smad2/3 (p-Smad2/3), and mesenchymal markers including a-smooth muscle actin, vimentin, and type I collagen were significantly increased with the reduced protein expression of an epithelial marker (E-cadherin) in the rat model by Western blot or immunohistochemical analysis. In addition, the uptake of both exogenous TGF-b1 and HMGB1 by AECs could induce EMT; meanwhile, HMGB1 dramatically enhanced TGF-b1 expression and triggered Smad2/3 phosphorylation. In contrast, TGF-b1 deficiency evidently ameliorated HMGB1-mediated EMT with reduced p-Smad2/3 in A549 cells. It provides new insights that HMGB1 release from injured lungs promotes AEC damage through induction of the EMT process, in which TGF-b1/Smad2/3 signaling is activated and contributes to PF. These results suggest that HMGB1 may constitute a therapeutic target for developing antifibrotic agents for abnormal lung remodeling.

HMGB1 induces lung fibroblast to myofibroblast differentiation through NF-κB-mediated TGF-β1 release

“…Previous studies have revealed that fibroblast to myofibroblast differentiation is pathologically altered during lung fibrosis. Furthermore, it has been suggested that HMGB1 may be associated with lung fibrosis (24–28); however, the role of HMGB1 in lung fibroblast activation and differentiation is unclear. The present study revealed that HMGB1 increased α-SMA and collagen I expression in human lung fibroblasts, indicating that HMGB1 may induce fibroblast to myofibroblast differentiation of lung fibroblasts.…”

“…Entezari et al (27) demonstrated that inhibition of HMGB1 may enhance bacterial clearance and protect against Pseudomonas aeruginosa pneumonia in cystic fibrosis. Li et al (28) revealed that HMGB1 mediates the epithelial-to-mesenchymal transition in pulmonary fibrosis, which involves the transforming growth factor (TGF)-β1/Smad2/3 signaling pathway. However, the role of HMGB1 in lung fibroblast to myofibroblast differentiation remains unclear.…”

Traditional Chinese medicine for pulmonary fibrosis therapy: Progress and future prospects

“…In the early period of PF, the affected lungs are mainly inflammatory cell infiltration, edema and congestion, and then converted to the injury of alveolar epithelial cells (AEC), abnormal proliferation of ECM-producing cells (mesenchymal cells including fibroblasts (FB) and myofibroblasts (MFb)), the overproduction of ECM (collagens, laminin, tenascin-C, etc. ), resulting in progressive scarring and loss of lung function (Rajasekaran et al, 2015;Li et al, 2015a;Craig et al, 2015). Up to now, lots of studies have shown that the molecular mechanisms of PF is involved in the superabundant inflammation such as cytokines release and inflammasome activation (Hosseinian et al, 2015), macrophages activation , FB to MFb transformation (Wollin et al, 2014), epithelial-mesenchymal transition (EMT, converting from epithelial phenotype to fibroblastic phenotype) , matrix metalloproteinase (MMP)/(tissue inhibitor of metalloproteinase (TIMP)) balance , oxidative stress (Brass et al, 2016) and several signaling pathways activation (Chaudhary et al, 2007;Chen et al, 2016b) (Fig.…”

High‐mobility group box‐B1 (HMGB1) mediates the hypoxia‐induced mesenchymal transition of osteoblast cells via activating ERK/JNK signaling

“…HMGB1 downregulated E‐cadherin expression, increased α‐SMA expression, and enhanced cell migration in human tubular epithelial cells (Lynch et al, ). Such mediation involves the recognition of transforming growth factor‐β1 (TGF‐β1)/Smad signaling in pulmonary fibrosis (Li et al, ). The HMGB1‐induced EMT was also confirmed in colorectal carcinoma (CRC), via activating the receptor for advanced glycation end‐products (RAGE)/Snail/NF‐κB pathways (Zhu et al, ).…”