Epigenetic regulation of Thy-1 gene expression by histone modification is involved in lipopolysaccharide-induced lung fibroblast proliferation

Vimentin regulation of autophagy activation in lung fibroblasts in response to lipopolysaccharide exposure in vitro

Background

The activation and assembly of the NLRP3 inflammasome is dependent on the interaction between NLRP3 and the intermediate filament protein vimentin in an acute respiratory distress syndrome (ARDS) model. We investigated the role of vimentin in this process using human fetal lung (HFL-1) fibroblasts with vimentin transfer genes or gene knockdown and lipopolysaccharide (LPS) intervention.

Methods

HFL-1 cells [con-vector + LPS, vimentin-pCMV3 (VIM-pCMV3), con-siRNA, and vimentin siRNA (VIM-siRNA)] were treated with LPS. An oxidative stress damage assessment, apoptosis analysis, and quantification of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, and IL-10 by enzyme linked immunosorbent assay (ELISA) were performed. Immunoblotting was used to reveal the autophagy pathway.

Results

We demonstrated that in response to LPS vimentin expression was lower in the HFL-1 cells with the vimentin gene knocked down. Specifically, an increase in oxidative stress, a decrease in mitochondrial membrane potential, or an increase in calcium ion permeability resulted in an increase in the fibroblast apoptosis rate. In addition, the inflammatory response after vimentin gene knockout was upregulated, as indicated by higher levels of TNF-a, IL-1β, IL-6, and IL-10. Importantly, the mechanism of suppression of vimentin in the lung fibroblasts was caused by a decrease in autophagy, an increase in mitochondrial membrane protein, and a decrease in mitochondrial function, which may contribute to the augmented cellular injury generated during the response to LPS.

Conclusions

This study provides insights into whether vimentin may interfere with the inflammatory cascade by activating the autophagy pathway of mitochondrial lung fibroblasts in the early stage of acute lung injury (ALI).

More than a Genetic Code: Epigenetics of Lung Fibrosis

At the end of the last century, genetic studies reported that genetic information is not transmitted solely by DNA, but is also transmitted by other mechanisms, named as epigenetics. The well-described epigenetic mechanisms include DNA methylation, biochemical modifications of histones, and microRNAs. The role of altered epigenetics in the biology of various fibrotic diseases is well-established, and recent advances demonstrate its importance in the pathogenesis of pulmonary fibrosis-predominantly referring to idiopathic pulmonary fibrosis, the most lethal of the interstitial lung diseases. The deficiency in effective medications suggests an urgent need to better understand the underlying pathobiology. This review summarizes the current knowledge concerning epigenetic changes in pulmonary fibrosis and associations of these changes with several cellular pathways of known significance in its pathogenesis. It also designates the most promising substances for further research that may bring us closer to new therapeutic options.

Lipopolysaccharide promotes lung fibroblast proliferation through autophagy inhibition via activation of the PI3K-Akt-mTOR pathway

Pulmonary fibrosis is a major cause of death in patients with acute respiratory distress syndrome (ARDS). Our previous study revealed that lipopolysaccharide (LPS) challenge could lead to mouse lung fibroblast proliferation. Additionally, inhibition of autophagy in lung fibroblasts was also reported to be crucial during the process of pulmonary fibrosis. However, the correlation between proliferation and inhibition of autophagy of lung fibroblasts and the underlying mechanism remain unknown. In this study, we report that autophagy was inhibited in mouse lung fibroblasts after LPS challenge, and was accompanied by activation of the PI3K-Akt-mTOR signaling pathway. Treating mouse lung fibroblasts with LPS resulted in mTOR and Akt phosphorylation, p62 up-regulation, and significant down-regulation of autophagosomes, which could be reversed by PI3K-Akt inhibitors (Ly294002) or mTOR inhibitors (rapamycin, RAPA). Furthermore, either LPS or hydroxychloroquine (HCQ), an autophagy inhibitor, could promote mouse lung fibroblast proliferation, which could be reversed by RAPA application. The present research therefore reveals that LPS promotes lung fibroblast proliferation through autophagy inhibition via activation of the PI3K-Akt-mTOR pathway.

Thy-1 depletion and integrin β3 upregulation-mediated PI3K-Akt-mTOR pathway activation inhibits lung fibroblast autophagy in lipopolysaccharide-induced pulmonary fibrosis

Lipopolysaccharide (LPS)-induced autophagy inhibition in lung fibroblasts is closely associated with the activation of the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K-Akt-mTOR) pathway. However, the underlying mechanism remains unknown. In this study, we demonstrated that LPS activated the PI3K-Akt-mTOR pathway and inhibited lung fibroblast autophagy by depleting thymocyte differentiation antigen-1 (Thy-1) and upregulating integrin β3 (Itgb3). Challenge of the human lung fibroblast MRC-5 cell line with LPS resulted in significant upregulation of integrin β3, activation of the PI3K-Akt-mTOR pathway and inhibition of autophagy, which could be abolished by integrin β3 silencing by specific shRNA or treatment with the integrin β3 inhibitor cilengitide. Meanwhile, LPS could inhibit Thy-1 expression accompanied with PI3K-Akt-mTOR pathway activation and lung fibroblast autophagy inhibition; these effects could be prevented by Thy-1 overexpression. Meanwhile, Thy-1 downregulation with Thy-1 shRNA could mimic the effects of LPS, inducing the activation of PI3K-Akt-mTOR pathway and inhibiting lung fibroblast autophagy. Furthermore, protein immunoprecipitation analysis demonstrated that LPS reduced the binding of Thy-1 to integrin β3. Thy-1 downregulation, integrin β3 upregulation and autophagy inhibition were also detected in a mouse model of LPS-induced pulmonary fibrosis, which could be prohibited by intratracheal injection of Thy-1 overexpressing adeno-associated virus (AAV) or intraperitoneal injection of the integrin β3 inhibitor cilengitide. In conclusion, this study demonstrated that Thy-1 depletion and integrin β3 upregulation are involved in LPS-induced pulmonary fibrosis, and may serve as potential therapeutic targets for pulmonary fibrosis.

Thrombin Induces CCL2 Expression in Human Lung Fibroblasts via p300 Mediated Histone Acetylation and NF-KappaB Activation

Thrombin has been shown to play a key role in lung diseases such as pulmonary fibrosis via the induction of fibrotic cytokine- chemokine (CC motif) ligand-2 (CCL2) expression. We previously reported that transcription factor nuclear factor-κB (NF-κB) is responsible for thrombin-induced CCL2 expression in human lung fibroblasts (HLFs). Here, we extended our study to investigate the epigenetic regulation mechanism for thrombin-induced CCL2 expression in HLFs. HLFs were cultured in F-12 medium. CCL2 protein and mRNA levels were detected by ELISA and quantitative real-time PCR, respectively. Histone, histone acetyltransferases, and NF-κB binding to CCL2 promoter were detected by ChIP assay. NF-κB activation was detected by Western blotting. We revealed that increased binding of histone acetyltransferase p300 and acetylated histone H3 and H4 to CCL2 promoter are responsible for thrombin induced CCL2 expression in HLF cells. In addition, p300 inhibition attenuates both thrombin induced-CCL2 expression and histone H3 and H4 acetylation in HLFs, suggesting that p300 is involved in thrombin-induced CCL2 expression via hyperacetylating histone H3 and H4. Our data further showed that p300 also regulates CCL2 expression via interaction with NF-κB p65, as depletion of p300 inhibits both NF-κB p65 activation and its binding to CCL2 promoter. The findings strongly suggest that epigenetic dysregulation and the interaction between histone acetyltransferase and transcription factor may be responsible for thrombin induced-CCL2 expression in HLFs. Increased understanding of the epigenetic mechanisms of CCL2 regulation may provide opportunities for identifying novel molecular targets for therapeutic purposes. J. Cell. Biochem. 118: 4012-4019, 2017. © 2017 Wiley Periodicals, Inc.

Effects of dynamic changes in histone acetylation and deacetylase activity on pulmonary fibrosis

OBJECTIVE

Histone deacetylases (HDACs) play an important role in dysregulation of histone acetylation/deacetylation, which is the main driving force of the progression of pulmonary fibrosis. Here we investigated the changes in histone acetylation/deacetylation, and the contribution of specific class I and class II HDACs in the progression of pulmonary fibrosis.

METHODS

Male C57BL/6J mice received a single dose of tracheal administration of bleomycin to establish the pulmonary fibrosis model. The changes in acetylation rate of histone 3 (H3) and histone 4 (H4), and the activity of HDAC2 and HDAC4 in the lung tissue during the progression from alveolitis to pulmonary fibrosis were measured.

RESULTS

The acetylation rate of H3/H4 significantly decreased during alveolitis and the early and middle stages of fibrosis, but restored in the late stage of fibrosis. Correlation analysis showed that H4 deacetylation affected both alveolitis and pulmonary fibrosis. H3 deacetylation only affected alveolitis. HDAC2 activity significantly increased in the middle and late stages of pulmonary fibrosis. There was no significant difference in HDAC4 activity between bleomycin and saline groups. However, HDAC4 activity changed significantly with the progression of the disease in bleomycin group. The changes in HDAC2 and HDAC4 activity were different. HDAC2 had long-lasting effects, while HDAC4 had transient effects. Correlation analysis showed that HDAC2 and HDAC4 activity was positively correlated with alveolitis score and fibrosis score.

CONCLUSIONS

The changes in histone acetylation may directly regulate the gene expression of inflammatory cytokines/fibronectin and thus affect the progression of pulmonary fibrosis. The injury-induced histone deacetylation switched into acetylation at the late stage of pulmonary fibrosis, which may be involved in the repair process. HDAC2 is mainly involved in the chronic progression of pulmonary fibrosis, and HDAC4 is mainly involved in early stress response to pulmonary fibrosis.

Noggin inactivation affects the number and differentiation potential of muscle progenitor cells in vivo

Inactivation of Noggin, a secreted antagonist of Bone Morphogenetic Proteins (BMPs), in mice leads, among others, to severe malformations of the appendicular skeleton and defective skeletal muscle fibers. To determine the molecular basis of the phenotype, we carried out a histomorphological and molecular analysis of developing muscles Noggin(-/-) mice. We show that in 18.5 dpc embryos there is a marked reduction in muscle fiber size and a failure of nuclei migration towards the cell membrane. Molecularly, the absence of Noggin results in an increased BMP signaling in muscle tissue as shown by the increase in SMAD1/5/8 phosphorylation, concomitant with the induction of BMP target genes such as Id1, 2, 3 as well as Msx1. Finally, upon removal of Noggin, the number of mesenchymal Pax7(+) muscle precursor cells is reduced and they are more prone to differentiate into adipocytes in vitro. Thus, our results highlight the importance of Noggin/BMP balance for myogenic commitment of early fetal progenitor cells.

The biology and function of fibroblasts in cancer

Among all cells, fibroblasts could be considered the cockroaches of the human body. They survive severe stress that is usually lethal to all other cells, and they are the only normal cell type that can be live-cultured from post-mortem and decaying tissue. Their resilient adaptation may reside in their intrinsic survival programmes and cellular plasticity. Cancer is associated with fibroblasts at all stages of disease progression, including metastasis, and they are a considerable component of the general host response to tissue damage caused by cancer cells. Cancer-associated fibroblasts (CAFs) become synthetic machines that produce many different tumour components. CAFs have a role in creating extracellular matrix (ECM) structure and metabolic and immune reprogramming of the tumour microenvironment with an impact on adaptive resistance to chemotherapy. The pleiotropic actions of CAFs on tumour cells are probably reflective of them being a heterogeneous and plastic population with context-dependent influence on cancer.

The biology and function of fibroblasts in cancer

Among all cells, fibroblasts could be considered the cockroaches of the human body. They survive severe stress that is usually lethal to all other cells, and they are the only normal cell type that can be live-cultured from post-mortem and decaying tissue. Their resilient adaptation may reside in their intrinsic survival programmes and cellular plasticity. Cancer is associated with fibroblasts at all stages of disease progression, including metastasis, and they are a considerable component of the general host response to tissue damage caused by cancer cells. Cancer-associated fibroblasts (CAFs) become synthetic machines that produce many different tumour components. CAFs have a role in creating extracellular matrix (ECM) structure and metabolic and immune reprogramming of the tumour microenvironment with an impact on adaptive resistance to chemotherapy. The pleiotropic actions of CAFs on tumour cells are probably reflective of them being a heterogeneous and plastic population with context-dependent influence on cancer.

Epigenetic Alterations Induced by Bacterial Lipopolysaccharides

Lipopolysaccharide (LPS) is one of the principal bacterial products known to elicit inflammation. Cells of myeloid lineage such as monocytes and macrophages, but also epithelial cells give rise to an inflammatory response upon LPS stimulation. This phenomenon implies reprogramming of cell specific gene expression that can occur through different mechanisms including epigenetic modifications. Given their intrinsic nature, epigenetic modifications may be involved both in the acute response to LPS and in the establishment of a preconditioned genomic state (epigenomic memory) that may potentially influence the host response to further contacts with microorganisms. Information has accumulated during the last years aimed at elucidating the epigenetic mechanisms which underlie the cellular LPS response. These findings, summarized in this chapter, will hopefully be a good basis for a definition of the complete cascade of LPS-induced epigenetic events and their biological significance in different cell types.

HDAC is essential for epigenetic regulation of Thy-1 gene expression during LPS/TLR4-mediated proliferation of lung fibroblasts

Lipopolysaccharide (LPS)-induced proliferation of lung fibroblasts is closely correlated with loss of gene expression of thymocyte differentiation antigen-1 (Thy-1), accompanied with deacetylation of histones H3 and H4 at the Thy-1 gene promoter region; however, the mechanism remains enigmatic. We report here that LPS downregulates Thy-1 gene expression by activating histone deacetylases (HDACs) via Toll-like receptor 4 (TLR4) signaling. Treatment of primary cultured mouse lung fibroblasts with LPS resulted in significant upregulation of TLR4 and enhanced cell proliferation that was abolished by silencing TLR4 with lentivirus-delivered TLR4 shRNA. Interestingly, LPS increased the mRNA and protein levels of HDAC-4, -5, and -7, an effect that was abrogated by HDAC inhibitor trichostatin A (TSA) or TLR4-shRNA-lentivirus. Consistent with these findings, Ace-H3 and Ace-H4 were decreased by LPS that was prevented by TSA. Most importantly, chromosome immunoprecipitation (ChIP) analysis demonstrated that LPS decreased the association of Ace-H4 at the Thy-1 promoter region that was efficiently restored by pretreatment with TSA. Accordingly, LPS decreased the mRNA and protein levels of Thy-1 that was inhibited by TSA. Furthermore, silencing the Thy-1 gene by lentivirus-delivered Thy-1 shRNA could promote lung fibroblast proliferation, even in the absence of LPS. Conversely, overexpressing Thy-1 gene could inhibit lung fibroblast proliferation and reduce LPS-induced lung fibroblast proliferation. Our data suggest that LPS upregulates and activates HDACs through TLR4, resulting in deacetylation of histones H3 and H4 at the Thy-1 gene promoter that may contribute to Thy-1 gene silencing and lung fibroblast proliferation.

High-mobility group box 1 accelerates lipopolysaccharide-induced lung fibroblast proliferation in vitro: involvement of the NF-κB signaling pathway

The mechanism underlying lipopolysaccharide (LPS)-induced aberrant proliferation of lung fibroblasts in Gram-negative bacilli-associated pulmonary fibrosis is unknown. High-mobility group box 1 (HMGB1) is a ubiquitous nuclear protein that is released from the nuclei of lung fibroblasts after LPS stimulation. It can exasperate LPS-induced inflammation and hasten cell proliferation. Thus, this study investigated the effects of LPS- and/or HMGB1-stimulating murine lung fibroblasts on gene expression using various assays in vitro. Thiazolyl-diphenyl-tetrazolium bromide (MTT) assay data showed that either LPS or HMGB1 could induce lung fibroblast proliferation. Endogenous HMGB1 secreted from lung fibroblasts was detected by enzyme-linked immunosorbent assay (ELISA) 48 h after LPS stimulation. Pretreatment with an anti-HMGB1 antibody inhibited the proliferative effects of LPS on lung fibroblasts. DNA microarray data showed that the NF-κB signaling genes were upregulated in cells after stimulated with LPS, HMGB1, or both. Secretion of matrix metalloproteinase (MMP)-2 and MMP-9, and tissue inhibitor of metalloproteinase 2 (TIMP-2) was significantly upregulated after treatment with LPS, HMGB1, or their combination. However, an NF-κB inhibitor was able to downregulate levels of these proteins. In addition, levels of Toll-like receptor 4 (TLR4), Toll-like receptor 2 (TLR2), and receptors for advanced glycation end products (RAGE) mRNA and proteins were also upregulated in these cells after LPS treatment and further upregulated by LPS plus HMGB1. In conclusion, the data from the current study demonstrate that LPS-induced lung fibroblast secretion of endogenous HMGB1 can augment the proproliferative effects of LPS and, therefore, may play a key role in exacerbation of pulmonary fibrosis. The underlying molecular mechanisms are related to the activation of the TLR4/NF-κB signaling pathway and its downstream targets.