Evasion of myofibroblasts from immune surveillance: a mechanism for tissue fibrosis

S-Glutathionylation-Controlled Apoptosis of Lung Epithelial Cells; Potential Implications for Lung Fibrosis

Glutathione (GSH), a major antioxidant in mammalian cells, regulates several vital cellular processes, such as nutrient metabolism, protein synthesis, and immune responses. In addition to its role in antioxidant defense, GSH controls biological processes through its conjugation to reactive protein cysteines in a post-translational modification known as protein S-glutathionylation (PSSG). PSSG has recently been implicated in the pathogenesis of multiple diseases including idiopathic pulmonary fibrosis (IPF). Hallmarks of IPF include repeated injury to the alveolar epithelium with aberrant tissue repair, epithelial cell apoptosis and fibroblast resistance to apoptosis, and the accumulation of extracellular matrix and distortion of normal lung architecture. Several studies have linked oxidative stress and PSSG to the development and progression of IPF. Additionally, it has been suggested that the loss of epithelial cell homeostasis and increased apoptosis, accompanied by the release of various metabolites, creates a vicious cycle that aggravates disease progression. In this short review, we highlight some recent studies that link PSSG to epithelial cell apoptosis and highlight the potential implication of metabolites secreted by apoptotic cells.

Fibroblasts From Idiopathic Pulmonary Fibrosis Induce Apoptosis and Reduce the Migration Capacity of T Lymphocytes

Idiopathic pulmonary fibrosis (IPF) is a progressive and irreversible lung disease of unknown etiology. Myofibroblasts are organized in peculiar subepithelial fibroblasts foci (FF), where they abnormally persist and exclude lymphocytes by unclear mechanisms. FF are the source of an excessive extracellular matrix, which results in progressive stiffening and destruction of the lung architecture. We hypothesized that the absence of T cells inside the FF could be related, at least partially, to an inefficient function of lymphocytes induced by IPF fibroblasts. Here, we evaluated the effect of a supernatant from IPF fibroblasts on T-cell apoptosis and migration capacity. Data showed that IPF fibroblasts secrete pro-apoptotic molecules (both from extrinsic and intrinsic pathways), generating a microenvironment that induces apoptosis of T cells at 3 h of culture, despite a weak anti-apoptotic profile exhibited by these T cells. At 24 h of culture, the supernatants from both IPF and control fibroblasts provoked T-cell death. However, at this time of culture, IPF fibroblasts caused a marked decrease in T-cell migration; in contrast, control lung fibroblasts induced an increase of T-cell migration. The reduction of T-cell migratory capacity provoked by IPF fibroblasts was associated with a negative regulation of RHOA and ROCK, two essential GTPases for migration, and was independent of the expression of chemokine receptors. In conclusion, our findings demonstrate that IPF fibroblasts/myofibroblasts induce apoptosis and affect T-cell migration, revealing a mechanism involved in the virtual absence of T lymphocytes inside the FF.

ELF3 mediates IL-1α induced differentiation of mesenchymal stem cells to inflammatory iCAFs

Stromal cells in the tumor microenvironment regulate the immune landscape and tumor progression. Yet, the ontogeny and heterogeneity of reactive stromal cells within tumors is not well understood. Carcinoma-associated fibroblasts exhibiting an inflammatory phenotype (iCAFs) have been identified within multiple cancers; however, mechanisms that lead to their recruitment and differentiation also remain undefined. Targeting these mechanisms therapeutically may be important in managing cancer progression. Here, we identify the ELF3 transcription factor as the canonical mediator of IL-1α-induced differentiation of prostate mesenchymal stem cells to an iCAF phenotype, typical of the tumor microenvironment. Furthermore, IL-1α-induced iCAFs were subsequently refractive to TGF-β1 induced trans-differentiation to a myofibroblast phenotype (myCAF), another key carcinoma-associated fibroblast subtype typical of reactive stroma in cancer. Restricted trans-differentiation was associated with phosphorylation of the YAP protein, indicating that interplay between ELF3 action and activation of the Hippo pathway are critical for restricting trans-differentiation of iCAFs. Together, these data show that the IL-1α/ELF3/YAP pathways are coordinate for regulating inflammatory carcinoma-associated fibroblast differentiation.

The emerging role of metabolism in fibrosis

The metabolic shift that cancer cells undergo towards aerobic glycolysis was identified as a defining feature in tumours almost 100 years ago; however, it has only recently become apparent that similar metabolic reprogramming is a key feature in other diseases - with fibrosis now entering the fray. In this perspective, an overview of the recent evidence implicating increased glycolysis and glutaminolysis as mediators of fibrosis is presented, with a particular emphasis on the novel therapeutic possibilities this introduces. Furthermore, the impact that metabolic reprogramming has on redox homeostasis is discussed, providing an insight into how this often-overlooked mechanism may drive the pathogenesis.

sFasL-The Key to a Riddle: Immune Responses in Aging Lung and Disease

By dint of the aging population and further deepened with the Covid-19 pandemic, lung disease has turned out to be a major cause of worldwide morbidity and mortality. The condition is exacerbated when the immune system further attacks the healthy, rather than the diseased, tissue within the lung. Governed by unremittingly proliferating mesenchymal cells and increased collagen deposition, if inflammation persists, as frequently occurs in aging lungs, the tissue develops tumors and/or turns into scars (fibrosis), with limited regenerative capacity and organ failure. Fas ligand (FasL, a ligand of the Fas cell death receptor) is a key factor in the regulation of these processes. FasL is primarily found in two forms: full length (membrane, or mFasL) and cleaved (soluble, or sFasL). We and others found that T-cells expressing the mFasL retain autoimmune surveillance that controls mesenchymal, as well as tumor cell accumulation following an inflammatory response. However, mesenchymal cells from fibrotic lungs, tumor cells, or cells from immune-privileged sites, resist FasL⁺ T-cell-induced cell death. The mechanisms involved are a counterattack of immune cells by FasL, by releasing a soluble form of FasL that competes with the membrane version, and inhibits their cell death, promoting cell survival. This review focuses on understanding the previously unrecognized role of FasL, and in particular its soluble form, sFasL, in the serum of aged subjects, and its association with the evolution of lung disease, paving the way to new methods of diagnosis and treatment.

You Say You Want a Resolution (of Fibrosis)

In pathological fibrosis, aberrant tissue remodeling with excess extracellular matrix leads to organ dysfunction and eventual morbidity. Diseases of fibrosis create significant global health and economic burdens and are often deadly. Although fibrosis has traditionally been thought of as an irreversible process, a growing body of evidence demonstrates that organ fibrosis can reverse in certain circumstances, especially if an underlying cause of injury can be removed. This body of evidence has uncovered more and more contributors to persistent and nonresolving tissue fibrosis. Here, we review the present knowledge on resolution of organ fibrosis and restoration of near-normal tissue architecture. We emphasize three critical areas of tissue homeostasis that are necessary for fibrosis resolution, namely, the elimination of matrix-producing cells, the clearance of excess matrix, and the regeneration of normal tissue constituents. In so doing, we also highlight how profibrotic pathways interact with one another and where there may be therapeutic opportunities to intervene and remediate pathological persistent fibrosis.

CMH-Small Molecule Docks into SIRT1, Elicits Human IPF-Lung Fibroblast Cell Death, Inhibits Ku70-deacetylation, FLIP and Experimental Pulmonary Fibrosis

Regenerative capacity in vital organs is limited by fibrosis propensity. Idiopathic pulmonary fibrosis (IPF), a progressive lung disease linked with aging, is a classic example. In this study, we show that in flow cytometry, immunoblots (IB) and in lung sections, FLIP levels can be regulated, in vivo and in vitro, through SIRT1 activity inhibition by CMH (4-(4-Chloro-2-methylphenoxy)-N-hydroxybutanamide), a small molecule that, as we determined here by structural biology calculations, docked into its nonhistone substrate Ku70-binding site. Ku70 immunoprecipitations and immunoblots confirmed our theory that Ku70-deacetylation, Ku70/FLIP complex, myofibroblast resistance to apoptosis, cell survival, and lung fibrosis in bleomycin-treated mice, are reduced and regulated by CMH. Thus, small molecules associated with SIRT1-mediated regulation of Ku70 deacetylation, affecting FLIP stabilization in fibrotic-lung myofibroblasts, may be a useful strategy, enabling tissue regeneration.

SIRT1 Deficiency, Specifically in Fibroblasts, Decreases Apoptosis Resistance and Is Associated with Resolution of Lung-Fibrosis

In contrast to normal regenerating tissue, resistance to Fas- and FasL-positive T cell-induced apoptosis were detected in myofibroblasts from fibrotic-lungs of humans and mice following bleomycin (BLM) exposure. In this study we show, decreased FLIP expression in lung-tissues with resolution of BLM-induced fibrosis and in isolated-lung fibroblasts, with decreased resistance to apoptosis. Using a FLIP-expression vector or a shFLIP-RNA, we further confirmed the critical need for FLIP to regain/lose susceptibility of fibrotic-lung myofibroblast to Fas-induced apoptosis. Our study further show that FLIP is regulated by SIRT1 (Sirtuin 1) deacetylase. Chimeric mice, with SIRT1-deficiency in deacetylase domain (H355Y-Sirt1^y/y), specifically in mesenchymal cells, were not only protected from BLM-induced lung fibrosis but, as assessed following Ku70 immunoprecipitation, had also decreased Ku70-deacetylation, decreasedKu70/FLIP complex, and decreased FLIP levels in their lung myofibroblasts. In addition, myofibroblasts isolated from lungs of BLM-treated miR34a-knockout mice, exposed to a miR34a mimic, which we found here to downregulate SIRT1 in the luciferase assay, had a decreased Ku70-deacetylation indicating decrease in SIRT1 activity. Thus, SIRT1 may mediate, miR34a-regulated, persistent FLIP levels by deacetylation of Ku70 in lung myofibroblasts, promoting resistance to cell-death and lung fibrosis.

Comprehensive analysis of lncRNA-associated competing endogenous RNA network and immune infiltration in idiopathic pulmonary fibrosis

Background

Idiopathic pulmonary fibrosis (IPF) is a life-threatening lung disorder with an unknown aetiology. The roles of long non-coding RNAs (lncRNAs) and its related competing endogenous RNAs (ceRNA) network in IPF remains poorly understood. In this study, we aimed to build a lncRNA-miRNA-mRNA network and explore the pathogenesis of IPF.

Methods

We screened differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs) between IPF and control lung tissues from two datasets. The ceRNA network was built according to the interactions between DElncRNA, miRNA, and DEmRNA. Functional enrichment analysis of DemRNAs was performed using Metascape. CIBERSORT (Cell type Identification by Estimating Relative Subsets Of known RNA Transcripts) was applied to estimate the fraction of 22 immune cells in IPF and controls lung tissue samples. Then we investigated the correlation between immune cells and clinical traits.

Results

We constructed a lncRNA-miRNA-mRNA network, which was composed of two DElncRNAs, 18 miRNAs, 66 DemRNAs. Functional enrichment analysis showed that the DEmRNAs mainly participated in MicroRNAs in cancer. By applying CIBERSORT, we found that IPF tissue samples had a higher proportion of plasma cells, resting mast cells and a lower proportion of resting NK cells, monocytes, neutrophils compared with control tissue samples. Also, our results indicated that immune cells were associated with the severity of IPF.

Conclusions

In summary, this is the first study to build lncRNA-miRNA-mRNA ceRNA network of IPF, which may improve our understanding of IPF pathogenesis. Our study indicates that immune cells in lung tissues may predict disease severity and participate in the development of IPF. Future prospective studies are required to confirm the findings of the current study.

Forefront: MiR-34a-Knockout Mice with Wild Type Hematopoietic Cells, Retain Persistent Fibrosis Following Lung Injury

MicroRNAs (miRs) are known to limit gene expression at the post-transcriptional level and have important roles in the pathogenesis of various conditions, including acute lung injury (ALI) and fibrotic diseases such as idiopathic pulmonary fibrosis (IPF). In this study, we found increased levels of miR-34 at times of fibrosis resolution following injury, in myofibroblasts from Bleomycin-treated mouse lungs, which correlates with susceptibility to cell death induced by immune cells. On the contrary, a substantial downregulation of miR-34 was detected at stages of evolution, when fibroblasts resist cell death. Concomitantly, we found an inverse correlation between miR-34 levels with that of the survival molecule FLICE-like inhibitory protein (FLIP) in lung myofibroblasts from humans with IPF and the experimental model. Forced upregulation of miR-34 with miR-34 mimic in human IPF fibrotic-lung myofibroblasts led to decreased cell survival through downregulation of FLIP. Using chimeric miR-34 knock-out (KO)-C57BL/6 mice with miR34KO myofibroblasts but wild-type (WT) hematopoietic cells, we found, in contrast to WT mice, increased and persistent FLIP levels with a more severe fibrosis and with no signs of resolution as detected in pathology and collagen accumulation. Moreover, a mimic of miR-34a decreased FLIP expression and susceptibility to cell death was regained in miR-34KO fibroblasts. Through this study, we show for the first time an inverse correlation between miR-34a and FLIP expression in myofibroblasts, which affects survival, and accumulation in lung fibrosis. Reprogramming fibrotic-lung myofibroblasts to regain susceptibility to cell-death by specifically increasing their miR34a and downregulating FLIP, may be a useful strategy, enabling tissue regeneration following lung injury.

Matrix Metalloproteinases Retain Soluble FasL-mediated Resistance to Cell Death in Fibrotic-Lung Myofibroblasts

A prominent feature of obstructed tissue regeneration following injury in general, and fibrotic lung tissue in particular, is fibroblast proliferation and accumulation. The Fas/FasL apoptotic pathway has been shown to be involved in human idiopathic pulmonary fibrosis (IPF) and bleomycin-induced lung fibrosis in rodents. We previously showed that in normal injury repair, myofibroblasts' accumulation is followed by their decline by FasL⁺ T cell-induced cell death. In pathological lung fibrosis, myofibroblasts resist cell death and accumulate. Like other members of the tumor necrosis factor (TNF) family, membrane-bound FasL can be cleaved from the cell surface to generate a soluble form (sFasL). Metalloproteinases (MMPs) are known to convert the membrane-bound form of FasL to sFasL. MMP-7 knockout (KO) mice were shown to be protected from bleomycin (BLM)-induced lung fibrosis. In this study, we detected increased levels of sFasL in their blood serum, as in the lungs of patients with IPF, and IPF-lung myofibroblast culture medium. In this study, using an MMP-inhibitor, we showed that sFasL is decreased in cultures of IPF-lung myofibroblasts and BLM-treated lung myofibroblasts, and in the blood serum of MMP-7KO mice. Moreover, resistant fibrotic-lung myofibroblasts, from the lungs of humans with IPF and of BLM-treated mice, became susceptible to T-cell induced cell death in a co-culture following MMP-inhibition- vs. control-treatment or BLM-treated MMP-7KO vs. wild-type mice, respectively. sFasL may be an unrecognized mechanism for MMP-7-mediated decreased tissue regeneration following injury and the evolution of lung fibrosis.

Increased Regeneration Following Stress-Induced Lung Injury in Bleomycin-Treated Chimeric Mice with CD44 Knockout Mesenchymal Cells

CD44, an adhesion-molecule promoting cell-migration, is shown here to increase in stress conditions following bleomycin-induced apoptosis in alveolar epithelial cells (AECs), a main target of lung injury. In vivo, it inhibits tissue regeneration and leads to fibrosis. We show that some AECs survive by the ataxia-telangiectasia mutated kinase/ATM pathway, and undergo a CD44-mediated epithelial-mesenchymal transdifferentiation (EMT) with migratory capacities in vitro, and in vivo. We assessed apoptosis vs. proliferation of AECs following bleomycin, ATM/P53 signaling pathway in AECs, and CD44 involvement in EMT, cell motility and tissue regeneration in vitro and in vivo. Expression of survival genes, CD44, and ATM/p53 pathway was elevated in AECs surviving bleomycin injury, as were the markers of EMT (downregulation of E-cadherin, upregulation of N-cadherin and vimentin, nuclear translocation of β-catenin). Inhibition of CD44 decreased AECs transdifferentiation. Bleomycin-treated chimeric CD44^KO-mice had decreased EMT markers, ATM, and mesenchymal cells (α-SMA⁺) accumulation in lung, increased surfactant-b, diminished lung mesenchymal cell motility, and increased lung tissue regenerative capacity following bleomycin injury, as indicated by lung collagen content and semiquantitave morphological index scoring. Thus, AECs surviving lung injury are plastic and undergo ATM-mediated, CD44-dependent transdifferentiation, preventing tissue regeneration and promoting fibrosis. Synthetic or natural compounds that downregulate CD44 may improve tissue regeneration following injury.

Functional heterogeneity of resident fibroblasts in the kidney

Chronic kidney disease (CKD) is a global public health problem, affecting over 10% of the world's population and more than half of the population aged over 70 years, imposing major costs on healthcare systems. Although the primary causes of CKD include various diseases such as diabetes, glomerulonephritis, and acute kidney injury (AKI), the progression of CKD is mediated by a common pathological pathway, which is mainly characterized by fibrosis and chronic inflammation. In this process, resident fibroblasts in the kidney play crucial roles. Accumulating evidence highlights the existence of functional heterogeneity and plasticity of fibroblasts and their diverse roles in kidney disease progression and resolution. In addition to renal fibrosis, renal anemia and peritubular capillary loss, two major complications of progressive CKD, are also caused by dysfunction of resident fibroblasts. Furthermore, age-dependent alterations in fibroblast behavior also contribute to age-dependent unique pathological conditions. In this article, we describe the current understanding regarding the behaviors of fibroblasts in the kidney in health, disease, and aging.

Notch signaling regulates cell density-dependent apoptosis of NIH 3T3 through an IL-6/STAT3 dependent mechanism

Apoptosis is a physiological process that plays a critical maintenance role in cellular homeostasis. Previous reports have demonstrated that cells undergo apoptosis in a cell density-dependent manner, which is regulated, in part, by signal transducers and activators of transcription (STAT) 3. The molecular mechanisms regulating cell density-dependent apoptosis, however, has not been thoroughly investigated to date. Since Notch signaling is activated via direct cell-to-cell contact and plays a pivotal role in cell fate decisions, we examined the role of Notch signaling in cell density-dependent apoptosis of mouse embryonic fibroblasts NIH 3T3 cells. With the increase in cell density, IL-6 expression was induced, which was necessary for STAT3 activation as well as apoptosis regulation. Notch signaling was also activated in a cell-density dependent manner. Blocking Notch signaling either through siRNA-mediated targeting of Jagged1 expression or γ-secretase inhibitor treatment demonstrated that Notch signaling activation was necessary for IL-6 induction. Constitutive activation of Notch signaling via the overexpression of Notch1 intracellular domain was sufficient for the induction of IL-6, which was mediated via direct transcriptional activation. Taken together, our study indicates that Notch signaling regulates cell density-dependent apoptosis through IL-6/STAT3-dependent mechanism. Consequently, Notch signaling might represent a novel therapeutic target in diseases characterized by dysregulated apoptosis.

A Profibrotic Phenotype in Naïve and in Fibrotic Lung Myofibroblasts Is Governed by Modulations in Thy-1 Expression and Activation

Lung fibrosis is characterized by abnormal accumulation of Thy-deficient fibroblasts in the interstitium of the alveolar space. We have previously shown in bleomycin-treated chimeric Thy1-deficient mice with wild-type lymphocytes that Thy1-deficient fibroblasts accumulate and promote fibrosis and an “inflammation-free” environment. Here, we aimed to identify the critical effects of Thy1, or the absence of Thy1, in lung myofibroblast profibrotic functions, particularly proliferation and collagen deposition. Using specific Thy1 siRNA in Thy1-positive cells, Thy1 knockout cells, Thy1 cDNA expression vector in Thy1-deficient cells, and Thy1 cross-linking, we evaluated cell proliferation (assessed by cell mass and BrdU uptake), differentiation (using immunofluorescence), and collagen deposition (using Sircol assay). We found that myofibroblast Thy1 cross-linking and genetic manipulation modulate cell proliferation and expression of Fgf (fibroblast growth factor) and Angtl (angiotensin) receptors (using qPCR) that are involved in myofibroblast proliferation, differentiation, and collagen deposition. In conclusion, lung myofibroblast downregulation of Thy1 expression is critical to increase proliferation, differentiation, and collagen deposition.

Regulation of fibroblast Fas expression by soluble and mechanical pro-fibrotic stimuli

Background

Fibroblast apoptosis is a critical component of normal repair and the acquisition of an apoptosis-resistant phenotype contributes to the pathogenesis of fibrotic repair. Fibroblasts from fibrotic lungs of humans and mice demonstrate resistance to apoptosis induced by Fas-ligand and prior studies have shown that susceptibility to apoptosis is enhanced when Fas (CD95) expression is increased in these cells. Moreover, prior work shows that Fas expression in fibrotic lung fibroblasts is reduced by epigenetic silencing of the Fas promoter. However, the mechanisms by which microenvironmental stimuli such as TGF-β1 and substrate stiffness affect fibroblast Fas expression are not well understood.

Methods

Primary normal human lung fibroblasts (IMR-90) were cultured on tissue culture plastic or on polyacrylamide hydrogels with Young’s moduli to recapitulate the compliance of normal (400 Pa) or fibrotic (6400 Pa) lung tissue and treated with or without TGF-β1 (10 ng/mL) in the presence or absence of protein kinase inhibitors and/or inflammatory cytokines. Expression of Fas was assessed by quantitative real time RT-PCR, ELISA and Western blotting. Soluble Fas (sFas) was measured in conditioned media by ELISA. Apoptosis was assessed using the Cell Death Detection Kit and by Western blotting for cleaved PARP.

Results

Fas expression and susceptibility to apoptosis was diminished in fibroblasts cultured on 6400 Pa substrates compared to 400 Pa substrates. TGF-β1 reduced Fas mRNA and protein in a time- and dose-dependent manner dependent on focal adhesion kinase (FAK). Surprisingly, TGF-β1 did not significantly alter cell-surface Fas expression, but did stimulate secretion of sFas. Finally, enhanced Fas expression and increased susceptibility to apoptosis was induced by combined treatment with TNF-α/IFN-γ and was not inhibited by TGF-β1.

Conclusions

Soluble and matrix-mediated pro-fibrotic stimuli promote fibroblast resistance to apoptosis by decreasing Fas transcription while stimulating soluble Fas secretion. These findings suggest that distinct mechanisms regulating Fas expression in fibroblasts may serve different functions in the complex temporal and spatial evolution of normal and fibrotic wound-repair responses.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0801-4) contains supplementary material, which is available to authorized users.

Lung carcinogenesis and fibrosis taken together: just coincidence?

PURPOSE OF REVIEW

The pathogenesis of lung cancer and pulmonary fibrotic disorders partially overlaps. This review focuses on the common features of the two disease categories, aimed at advancing our translational understanding of their pathobiology and at fostering the development of new therapies.

RECENT FINDINGS

Both malignant and collagen-producing lung cells display enhanced cellular proliferation, increased resistance to apoptosis, a propensity for invading and distorting the lung parenchyma, as well as stemness potential. These characteristics are reinforced by the tissue microenvironment and inflammation seems to play an important adjuvant role in both types of disorders.

SUMMARY

Unraveling the thread of the common and distinct characteristics of lung fibrosis and cancer might contribute to a more comprehensive approach of the pathobiology of both diseases and to a pathfinder for novel and personalized therapeutic strategies.

Immunohistochemical analysis of stromal fibrocytes and myofibroblasts to envision the invasion and lymph node metastasis in oral squamous cell carcinoma

Background:

Tumor cells work in close coordination with stromal elements from its stage of emergence to metastasis. The study was designed to assess the presence and distribution pattern of stromal fibrocytes and myofibroblasts in oral squamous cell carcinoma (OSCC). Possibility of using these stromal cells as a marker for invasion and lymphnode metastasis was evaluated.

Materials and Methods:

A total of 40 cases of OSCC consisting twenty cases of each lymph node positive (pN+) and lymph node negative (pN0) samples and ten normal oral mucosa (NOM) tissues were subjected to double immunostaining using CD34 and alpha-smooth muscle actin (α-SMA) antibodies. Stained sections were evaluated semiquantitatively.

Results:

CD34 fibrocytes were seen in 70% of NOM and none of OSCC samples. α-SMA myofibroblasts were seen in 80% of OSCC and none of NOM samples. A statistically significant difference was found in fibrocyte values (P < 0.001) and myofibroblast values (P < 0.001) between NOM and OSCC study samples. No statistical significance in myofibroblast values between pN0 and pN+ study groups; however, their distribution pattern appreciably varied.

Conclusions:

This study suggested that fibrocytes could be used as one of the markers for early invasion. Abrupt loss of fibrocytes at the transition zone toward carcinoma and statistical significance in their values supported this inference. Heterogeneity in the distribution pattern of myofibroblasts in tumor stroma indicates that this variability may predict the tumor behavior toward nodal metastasis rather than their mere presence or absence.

"Scar-cinoma": viewing the fibrotic lung mesenchymal cell in the context of cancer biology

Lung cancer and pulmonary fibrosis are common, yet distinct, pathological processes that represent urgent unmet medical needs. Striking clinical and mechanistic parallels exist between these distinct disease entities. The goal of this article is to examine lung fibrosis from the perspective of cancer-associated phenotypic hallmarks, to discuss areas of mechanistic overlap and distinction, and to highlight profibrotic mechanisms that contribute to carcinogenesis. Ultimately, we speculate that such comparisons might identify opportunities to leverage our current understanding of the pathobiology of each disease process in order to advance novel therapeutic approaches for both. We anticipate that such "outside the box" concepts could be translated to a more precise and individualised approach to fibrotic diseases of the lung.

Contribution of Human Fibroblasts and Endothelial Cells to the Hallmarks of Inflammation as Determined by Proteome Profiling

In order to systematically analyze proteins fulfilling effector functionalities during inflammation, here we present a comprehensive proteome study of inflammatory activated primary human endothelial cells and fibroblasts. Cells were stimulated with interleukin 1-β and fractionated in order to obtain secreted, cytoplasmic and nuclear protein fractions. Proteins were submitted to a data-dependent bottom up analytical platform using a QExactive orbitrap and the MaxQuant software for protein identification and label-free quantification. Results were further combined with similarly generated data previously obtained from the analysis of inflammatory activated peripheral blood mononuclear cells. Applying a false discovery rate of less than 0.01 at both, peptide and protein level, a total of 8370 protein groups assembled from 117,599 peptides was identified; mass spectrometry data have been made fully accessible via ProteomeXchange with identifier PXD003406 to PXD003417.Comparative proteome analysis allowed us to determine common and cell type-specific inflammation signatures comprising novel candidate marker molecules and related expression patterns of transcription factors. Cardinal features of inflammation such as interleukin 1-β processing and the interferon response differed substantially between the investigated cells. Furthermore, cells also exerted similar inflammation-related tasks; however, by making use of different sets of proteins. Hallmarks of inflammation thus emerged, including angiogenesis, extracellular matrix reorganization, adaptive and innate immune responses, oxidative stress response, cell proliferation and differentiation, cell adhesion and migration in addition to monosaccharide metabolic processes, representing both, common and cell type-specific responsibilities of cells during inflammation.

Mechanisms of Lung Fibrosis Resolution

Fibrogenesis involves a dynamic interplay between factors that promote the biosynthesis and deposition of extracellular matrix along with pathways that degrade the extracellular matrix and eliminate the primary effector cells. Opposing the often held perception that fibrotic tissue is permanent, animal studies and clinical data now demonstrate the highly plastic nature of organ fibrosis that can, under certain circumstances, regress. This review describes the current understanding of the mechanisms whereby the lung is known to resolve fibrosis focusing on degradation of the extracellular matrix, removal of myofibroblasts, and the role of inflammatory cells. Although there are significant gaps in understanding lung fibrosis resolution, accelerated improvements in biotechnology and bioinformatics are expected to improve the understanding of these mechanisms and have high potential to lead to novel and effective restorative therapies in the treatment not only of pulmonary fibrosis, but also of a wide-ranging spectrum of chronic disorders.

Myofibroblast persistence with real-time changes in boundary stiffness

Myofibroblasts are critical for connective tissue remodeling and wound healing since they can close wound beds and shape tissues rapidly by generating high traction forces and secreting abundant extracellular matrix proteins and matrix metalloproteinases. However, their presence in excessive numbers is associated with fibrotic and calcific diseases and tissue thickening in engineered tissues. While activation of the myofibroblast phenotype has been studied extensively, whether myofibroblasts are "cleared" by phenotypic reversal or by apoptosis remains controversial. The goal of this work is to test the hypothesis that mechanical inhibition of myofibroblast force generation leads to de-differentiation or apoptosis depending upon the magnitude of the decrease in tension. To test this hypothesis, we cultured valvular interstitial cells (VICs) in fibrin micro-tissues suspended between flexible posts and dynamically altered the ability of the cells to generate tension by altering boundary stiffness via magnetic forces applied to posts. The flexible posts capped with magnetic beads enable the measurement and modulation of tension generated by the cells within the tissue. As expected, the cell-generated forces were elevated with dynamically increased boundary (post) stiffness, yet surprisingly, the forces continued to increase following dynamic reduction of boundary stiffness back to baseline levels. Increased apoptosis and reduced α-SMA staining were observed with complete freeing of the tissues from the posts but not upon removal of the magnet, resulting in a twofold decrease in post stiffness. Together, these data indicate that an increase in myofibroblast force generation, even if modest and temporary (1 day), can have lasting effects on myofibroblast persistence in tissues, and that a significant reduction in the ability of the cells to generate tension is required to trigger dedifferentiation and/or apoptosis. The ability to dedifferentiate myofibroblasts to a quiescent phenotype and to control the percentage of apoptosis would be of great benefit for therapeutic and tissue engineering applications.

STATEMENT OF SIGNIFICANCE

Myofibroblasts play an important role in tissue remodeling and wound healing. However, excessive activation of this phenotype is associated with fibrotic diseases and scar formation. Being able to dedifferentiate these cells or controlling their clearance with apoptosis (programmed cell death) would be beneficial. It is known that releasing rigid tissue boundaries trigger apoptosis, while reducing the substrate stiffness can cause myofibroblast dedifferentiation. However, the mechanical tension was not quantified in any of the studies. Here we used micro-cantilever posts at tissue boundaries to measure tension and to regulate boundary stiffness in real time by pulling posts with magnets. We show that temporary stiffening of boundary causes irreversible myofibroblast activation and the magnitude of tension drop controls apoptosis.

Bleomycin-Treated Chimeric Thy1-Deficient Mice with Thy1-Deficient Myofibroblasts and Thy-Positive Lymphocytes Resolve Inflammation without Affecting the Fibrotic Response

Lung fibrosis is characterized by abnormal accumulation of fibroblasts in the interstitium of the alveolar space. Two populations of myofibroblasts, distinguished by Thy1 expression, are detected in human and murine lungs. Accumulation of Thy1-negative (Thy1(-)) myofibroblasts was shown in the lungs of humans with idiopathic pulmonary fibrosis (IPF) and of bleomycin-treated mice. We aimed to identify genetic changes in lung myofibroblasts following Thy1 crosslinking and assess the impact of specific lung myofibroblast Thy1-deficiency, in vivo, in bleomycin-injured mouse lungs. Thy1 increased in mouse lung lymphocytes following bleomycin injury but decreased in myofibroblasts when fibrosis was at the highest point (14 days), as assessed by immunohistochemistry. Using gene chip analysis, we detected that myofibroblast Thy1 crosslinking mediates downregulation of genes promoting cell proliferation, survival, and differentiation, and reduces production of extracellular matrix (ECM) components, while concurrently mediating the upregulation of genes known to foster inflammation and immunological functions. Chimeric Thy1-deficient mice with Thy1(+) lymphocytes and Thy1(-) myofibroblasts showed fibrosis similar to wild-type mice and an increased number of CD4/CD25 regulatory T cells, with a concomitant decrease in inflammation. Lung myofibroblasts downregulate Thy1 expression to increase their proliferation but to diminish the in vivo inflammatory milieu. Inflammation is not essential for evolution of fibrosis as was previously stated.

Overexpression of Telomerase Protects Human and Murine Lung Epithelial Cells from Fas- and Bleomycin-Induced Apoptosis via FLIP Upregulation

High doses of bleomycin administered to patients with lymphomas and other tumors lead to significant lung toxicity in general, and to apoptosis of epithelial cells, in particular. Apoptosis of alveolar epithelium is an important step in the pathogenesis of bleomycin-induced pulmonary fibrosis. The Fas-FasL pathway is one of the main apoptotic pathways involved. Telomerase is a ribonucleoprotein RNA-dependent DNA polymerase complex consisting of an RNA template and a catalytic protein, telomerase reverse transcriptase (TERT). Telomerase also possess extra-telomeric roles, including modulation of transcription of anti-apoptotic genes, differentiation signals, and more. We hypothesized that telomerase overexpression affects Fas-induced epithelial cell apoptosis by an extra-telomeric role such as regulation of anti-apoptotic genes, specifically FLICE-like inhibitory protein (FLIP). Telomerase in mouse (MLE) and human (A549) lung epithelial cell lines was upregulated by transient transfection using cDNA hTERT expression vector. Telomerase activity was detected using a real-time PCR-based system. Bleomycin, and bleomycin-induced Fas-mediated apoptosis following treatment with anti-Fas activating mAb or control IgG, were assessed by Annexin V staining, FACS analysis, and confocal microscopy; caspase cleavage by Western blot; FLIP or Fas molecule detection by Western blot and flow cytometry. hTERT transfection of lung epithelial cells resulted in a 100% increase in their telomerase activity. Fas-induced lung epithelial cell apoptosis was significantly reduced in hTERT-transfected cells compared to controls in all experiments. Lung epithelial cells with increased telomerase activity had higher levels of FLIP expression but membrane Fas expression was unchanged. Upregulation of hTERT+ in human lung epithelial cells and subsequent downregulation of FLIP by shFLIP-RNA annulled hTERT-mediated resistance to apoptosis. Telomerase-mediated FLIP overexpression may be a novel mechanism to confer protection from apoptosis in bleomycin-exposed human lung epithelial cells.

Cutting edge: FasL(+) immune cells promote resolution of fibrosis

Immune cells, particularly those expressing the ligand of the Fas-death receptor (FasL), e.g. cytotoxic T cells, induce apoptosis in 'undesirable' self- and non-self-cells, including lung fibroblasts, thus providing a means of immune surveillance. We aimed to validate this mechanism in resolution of lung fibrosis. In particular, we elucidated whether FasL(+) immune cells possess antifibrotic capabilities by induction of FasL-dependent myofibroblast apoptosis and whether antagonists of membrane (m) and soluble (s) FasL can inhibit these capabilities. Myofibroblast interaction with immune cells and its FasL-dependency, were investigated in vitro in coculture with T cells and in vivo, following transplantation into lungs of immune-deficient syngeneic Rag-/- as well as allogeneic SCID mice, and into lungs and air pouches of FasL-deficient (gld) mice, before and after reconstitution of the mice with wild-type (wt), FasL(+) immune cells. We found that myofibroblasts from lungs resolving fibrosis undergo FasL-dependent T cell-induced apoptosis in vitro and demonstrate susceptibility to in vivo immune surveillance in lungs of reconstituted, immune- and FasL-deficient, mice. However, immune-deficient Rag-/- and SCID mice, and gld-mice with FasL-deficiency, endure the accumulation of transplanted myofibroblasts in their lungs with subsequent development of fibrosis. Concomitantly, gld mice, in contrast to chimeric FasL-deficient mice with wt immune cells, accumulated transplanted myofibroblasts in the air pouch model. In humans we found that myofibroblasts from fibrotic lungs secrete sFasL and resist T cell-induced apoptosis, whereas normal lung myofibroblasts are susceptible to apoptosis but acquire resistance upon addition of anti-s/mFasL to the coculture. Immune surveillance, particularly functional FasL(+) immune cells, may represent an important extrinsic component in myofibroblast apoptosis and serve as a barrier to fibrosis. Factors interfering with Fas/FasL-immune cell-myofibroblast interaction such as sFasL secreted by fibrotic-lung myofibroblasts, may abrogate immune surveillance during fibrosis. Annulling these factors may pave a new direction to control human lung fibrosis.

IPF fibroblasts are desensitized to type I collagen matrix-induced cell death by suppressing low autophagy via aberrant Akt/mTOR kinases

Idiopathic pulmonary fibrosis (IPF) is a chronic, lethal interstitial lung disease in which the aberrant PTEN/Akt axis plays a major role in conferring a survival phenotype in response to the cell death inducing properties of type I collagen matrix. The underlying mechanism by which IPF fibroblasts become desensitized to polymerized collagen, thereby eluding collagen matrix-induced cell death has not been fully elucidated. We hypothesized that the pathologically altered PTEN/Akt axis suppresses autophagy via high mTOR kinase activity, which subsequently desensitizes IPF fibroblasts to collagen matrix induced cell death. We found that the autophagosome marker LC3-2 expression is suppressed, while mTOR activity remains high when IPF fibroblasts are cultured on collagen. However, LC3-2 expression increased in response to IPF fibroblast attachment to collagen in the presence of rapamycin. In addition, PTEN over-expression or Akt inhibition suppressed mTOR activity, thereby increasing LC3-2 expression in IPF fibroblasts. Furthermore, the treatment of IPF fibroblasts over-expressing PTEN or dominant negative Akt with autophagy inhibitors increased IPF fibroblast cell death. Enhanced p-mTOR expression along with low LC3-2 expression was also found in myofibroblasts within the fibroblastic foci from IPF patients. Our data show that the aberrant PTEN/Akt/mTOR axis desensitizes IPF fibroblasts from polymerized collagen driven stress by suppressing autophagic activity, which produces a viable IPF fibroblast phenotype on collagen. This suggests that the aberrantly regulated autophagic pathway may play an important role in maintaining a pathological IPF fibroblast phenotype in response to collagen rich environment.

The wound healing, chronic fibrosis, and cancer progression triad

For decades tumors have been recognized as "wounds that do not heal." Besides the commonalities that tumors and wounded tissues share, the process of wound healing also portrays similar characteristics with chronic fibrosis. In this review, we suggest a tight interrelationship, which is governed as a concurrence of cellular and microenvironmental reactivity among wound healing, chronic fibrosis, and cancer development/progression (i.e., the WHFC triad). It is clear that the same cell types, as well as soluble and matrix elements that drive wound healing (including regeneration) via distinct signaling pathways, also fuel chronic fibrosis and tumor progression. Hence, here we review the relationship between fibrosis and cancer through the lens of wound healing.

Neutrophils recruit regulatory T-cells into tumors via secretion of CCL17--a new mechanism of impaired antitumor immunity

The mechanisms by which tumor-associated neutrophils (TANs) affect tumor growth are to a large extent unknown. Regulatory T-cells (T-regs) are functionally immune-suppressive subsets of T-cells. Depletion or inhibition of T-regs can enhance antitumor immunity. We demonstrated both by RT-PCR and by ELISA that murine TANs secrete significant amounts of the T-regs chemoattractant, CCL17, much more than circulating or splenic neutrophils, and at a level progressively increasing during tumor development. Migration assays, both in vitro and in vivo, showed recruitment of T-regs by TANs, which was inhibited with anti-CCL17 monoclonal antibodies. Systemic neutrophil depletion in tumor-bearing mice using anti-Ly6G monoclonal antibodies reduced the migration of T-regs into the tumors. We further showed, using flow cytometry, that CCL17 secretion by TANs is not limited to mouse models of cancer but is also relevant to human TANs. Our results suggest a new indirect mechanism by which TANs may inhibit antitumor immune activity, thus promoting tumor growth. We further describe, for the first time, a clear link between TANs and T-regs acting together to impair antitumor immunity.

Histone modifications are responsible for decreased Fas expression and apoptosis resistance in fibrotic lung fibroblasts

Although the recruitment of fibroblasts to areas of injury is critical for wound healing, their subsequent apoptosis is necessary in order to prevent excessive scarring. Fibroproliferative diseases, such as pulmonary fibrosis, are often characterized by fibroblast resistance to apoptosis, but the mechanism(s) for this resistance remains elusive. Here, we employed a murine model of pulmonary fibrosis and cells from patients with idiopathic pulmonary fibrosis (IPF) to explore epigenetic mechanisms that may be responsible for the decreased expression of Fas, a cell surface death receptor whose expression has been observed to be decreased in pulmonary fibrosis. Murine pulmonary fibrosis was elicited by intratracheal injection of bleomycin. Fibroblasts cultured from bleomycin-treated mice exhibited decreased Fas expression and resistance to Fas-mediated apoptosis compared with cells from saline-treated control mice. Although there were no differences in DNA methylation, the Fas promoter in fibroblasts from bleomycin-treated mice exhibited decreased histone acetylation and increased histone 3 lysine 9 trimethylation (H3K9Me3). This was associated with increased histone deacetylase (HDAC)-2 and HDAC4 expression. Treatment with HDAC inhibitors increased Fas expression and restored susceptibility to Fas-mediated apoptosis. Fibroblasts from patients with IPF likewise exhibited decreased histone acetylation and increased H3K9Me3 at the Fas promoter and increased their expression of Fas in the presence of an HDAC inhibitor. These findings demonstrate the critical role of histone modifications in the development of fibroblast resistance to apoptosis in both a murine model and in patients with pulmonary fibrosis and suggest novel approaches to therapy for progressive fibroproliferative disorders.

The splicing factor SRSF6 is amplified and is an oncoprotein in lung and colon cancers

An increasing body of evidence connects alterations in the process of alternative splicing with cancer development and progression. However, a direct role of splicing factors as drivers of cancer development is mostly unknown. We analysed the gene copy number of several splicing factors in colon and lung tumours, and found that the gene encoding for the splicing factor SRSF6 is amplified and over-expressed in these cancers. Moreover, over-expression of SRSF6 in immortal lung epithelial cells enhanced proliferation, protected them from chemotherapy-induced cell death and converted them to be tumourigenic in mice. In contrast, knock-down of SRSF6 in lung and colon cancer cell lines inhibited their tumourigenic abilities. SRSF6 up- or down-regulation altered the splicing of several tumour suppressors and oncogenes to generate the oncogenic isoforms and reduce the tumour-suppressive isoforms. Our data suggest that the splicing factor SRSF6 is an oncoprotein that regulates the proliferation and survival of lung and colon cancer cells.

Carp head kidney leukocytes display different patterns of oxygen radical production after stimulation with PAMPs and DAMPs

Wound healing and tissue regeneration are essential mechanisms to ensure the survival and health of any organism. Despite this, only a few studies have been devoted to study tissue regeneration during wound healing in fish. Reactive oxygen species (ROS), in particular hydrogen peroxide, play an important dual role both for promoting tissue repair, but also for eradication of pathogens. This study aims at dissecting the contribution of PAMPs (using β-glucan) and DAMPs in the respiratory burst response of carp head kidney-derived leukocytes, and address their contribution to wound healing processes. Consistent with a pathogen eradication strategy, ROS responses to PAMP stimulation (β-glucan) was fast, vigorous and highly dominated by production of superoxide anion. In contrast, stimulation with DAMPs led to a slow, subtle but long-lasting production of oxygen radicals dominated by hydrogen peroxide. Using an in vitro model of scratch-wounded CCB fibroblast cell cultures and a novel PhotoID proliferation assay, stimulation with low and continuous levels of hydrogen peroxide (5 μM) led to a slight increase in the percentage of wound recovery and thus promoted wound closure. In contrast, high doses of hydrogen peroxide (300 μM) impaired fibroblast scratch-wound recovery and caused cell death. These results elucidate the capacity of hydrogen peroxide to influence the fate of tissue regeneration through the establishment of environments suitable for promoting either tissue regeneration or oxidative stress and thereby potential tissue damage. Direct in vitro stimulation with β-glucans did not impact fibroblast scratch-wound recovery, which further suggests that interaction with tissue-resident leukocytes or other components of the fish immune system are required to induce fibroblast proliferation and thus for the accelerated wound healing promoted by β-glucan stimulation.

The role of stromal cells in the persistence of chronic inflammation

Inflammation is an unstable state; it either resolves or persists. Inflammatory reactions often have a propensity for specific anatomical sites. Why inflammation persists with specific tissue tropism remains obscure. Increasing evidence suggests that stromal cells which define tissue architecture are the key cells involved, and therefore make attractive therapeutic targets. Research on stromal cells in general and fibroblasts in particular has so far been hampered by a lack of fibroblast-specific cell markers. This review highlights our increasing understanding of the role of fibroblasts in inflammation, and suggests that these cells provide the cellular basis for site specific chronic inflammation.

Host responses in tissue repair and fibrosis

Myofibroblasts accumulate in the spaces between organ structures and produce extracellular matrix (ECM) proteins, including collagen I. They are the primary "effector" cells in tissue remodeling and fibrosis. Previously, leukocyte progenitors termed fibrocytes and myofibroblasts generated from epithelial cells through epithelial-to-mesenchymal transition (EMT) were considered the primary sources of ECM-producing myofibroblasts in injured tissues. However, genetic fate mapping experiments suggest that mesenchyme-derived cells, known as resident fibroblasts, and pericytes are the primary precursors of scar-forming myofibroblasts, whereas epithelial cells, endothelial cells, and myeloid leukocytes contribute to fibrogenesis predominantly by producing key fibrogenic cytokines and by promoting cell-to-cell communication. Numerous cytokines derived from T cells, macrophages, and other myeloid cell populations are important drivers of myofibroblast differentiation. Monocyte-derived cell populations are key regulators of the fibrotic process: They act as a brake on the processes driving fibrogenesis, and they dismantle and degrade established fibrosis. We discuss the origins, modes of activation, and fate of myofibroblasts in various important fibrotic diseases and describe how manipulation of macrophage activation could help ameliorate fibrosis.

Redirecting valvular myofibroblasts into dormant fibroblasts through light-mediated reduction in substrate modulus

Fibroblasts residing in connective tissues throughout the body are responsible for extracellular matrix (ECM) homeostasis and repair. In response to tissue damage, they activate to become myofibroblasts, which have organized contractile cytoskeletons and produce a myriad of proteins for ECM remodeling. However, persistence of myofibroblasts can lead to fibrosis with excessive collagen deposition and tissue stiffening. Thus, understanding which signals regulate de-activation of myofibroblasts during normal tissue repair is critical. Substrate modulus has recently been shown to regulate fibrogenic properties, proliferation and apoptosis of fibroblasts isolated from different organs. However, few studies track the cellular responses of fibroblasts to dynamic changes in the microenvironmental modulus. Here, we utilized a light-responsive hydrogel system to probe the fate of valvular myofibroblasts when the Young’s modulus of the substrate was reduced from ∼32 kPa, mimicking pre-calcified diseased tissue, to ∼7 kPa, mimicking healthy cardiac valve fibrosa. After softening the substrata, valvular myofibroblasts de-activated with decreases in α-smooth muscle actin (α-SMA) stress fibers and proliferation, indicating a dormant fibroblast state. Gene signatures of myofibroblasts (including α-SMA and connective tissue growth factor (CTGF)) were significantly down-regulated to fibroblast levels within 6 hours of in situ substrate elasticity reduction while a general fibroblast gene vimentin was not changed. Additionally, the de-activated fibroblasts were in a reversible state and could be re-activated to enter cell cycle by growth stimulation and to express fibrogenic genes, such as CTGF, collagen 1A1 and fibronectin 1, in response to TGF-β1. Our data suggest that lowering substrate modulus can serve as a cue to down-regulate the valvular myofibroblast phenotype resulting in a predominantly quiescent fibroblast population. These results provide insight in designing hydrogel substrates with physiologically relevant stiffness to dynamically redirect cell fate in vitro.

Myofibroblasts and their resistance to apoptosis: a possible mechanism of osteoradionecrosis

Osteoradionecrosis (ORN) in the head and neck area is the most devastating long-term complication of radiotherapy, with slow progression and inability to heal spontaneously. ORN can lead to intolerable pain, fractures, and sequestration of devitalized bone and fistulae, making oral feeding impossible and causing facial deformation. In spite of its notorious reputation over at least 90 years, the precise pathogenesis of ORN has not been fully clarified, which has led to obstacles in the management of the disease. Several theories about its pathogenesis have been formulated, and radiation-induced fibrosis is the newest one. According to this theory, ORN is essentially a type of fibrosis induced by radiotherapy, and antifibrosis therapy has been shown to be effective in its treatment. We assumed that ORN, like fibrosis in other organs, is the result of a process of fibrogenesis in which myofibroblasts are the key effector cells. The uninterrupted accumulation of myofibroblasts and consequent persistent excess production of collagenous extracellular matrix and tensile force result in loss of normal function and ultimately radiation-induced fibrosis. During this process, myofibroblasts may be protected from apoptosis by acquiring an immune-privileged capacity, which allows continuous matrix synthesis. If this hypothesis proves to be correct, it would enable better understanding of the cellular and molecular mechanisms underlying the pathogenesis and progression of ORN, and would help improve our ability to prevent occurrence of ORN, give an earlier diagnosis, and treat it more effectively.

Oxidative processing of latent Fas in the endoplasmic reticulum controls the strength of apoptosis

We recently demonstrated that S-glutathionylation of the death receptor Fas (Fas-SSG) amplifies apoptosis (V. Anathy et al., J. Cell Biol. 184:241-252, 2009). In the present study, we demonstrate that distinct pools of Fas exist in cells. Upon ligation of surface Fas, a separate pool of latent Fas in the endoplasmic reticulum (ER) underwent rapid oxidative processing characterized by the loss of free sulfhydryl content (Fas-SH) and resultant increases in S-glutathionylation of Cys294, leading to increases of surface Fas. Stimulation with FasL rapidly induced associations of Fas with ERp57 and glutathione S-transferase π (GSTP), a protein disulfide isomerase and catalyst of S-glutathionylation, respectively, in the ER. Knockdown or inhibition of ERp57 and GSTP1 substantially decreased FasL-induced oxidative processing and S-glutathionylation of Fas, resulting in decreased death-inducing signaling complex formation and caspase activity and enhanced survival. Bleomycin-induced pulmonary fibrosis was accompanied by increased interactions between Fas-ERp57-GSTP1 and S-glutathionylation of Fas. Importantly, fibrosis was largely prevented following short interfering RNA-mediated ablation of ERp57 and GSTP. Collectively, these findings illuminate a regulatory switch, a ligand-initiated oxidative processing of latent Fas, that controls the strength of apoptosis.

Cellular FLICE-like inhibitory protein deviates myofibroblast fas-induced apoptosis toward proliferation during lung fibrosis

A prominent feature of fibrotic tissue in general and of lungs in particular is fibroblast proliferation and accumulation. In patients overcoming fibrosis, apoptosis limits this excessive cell growth. We have previously shown resistance to Fas-induced apoptosis of primary lung fibroblasts from mice with bleomycin-induced lung fibrosis, their escape from immune surveillance, and continued accumulation in spite of overexpression of the Fas death receptor. Cellular FLICE-like inhibitory protein (c-FLIP) is a regulator of cell death receptor-induced apoptosis in many cell types. We aimed to determine c-FLIP levels in myofibroblasts from fibrotic lungs and to directly assess c-FLIP's role in apoptosis and proliferation of primary lung myofibroblasts. c-FLIP levels were determined by apoptosis gene array, flow cytometry, Western blot, and immunofluorescence before and after down-regulation with a specific small interfering RNA. Apoptosis was assessed by caspase cleavage in Western blot and by Annexin V affinity labeling after FACS and tissue immunofluorescence. Proliferation was assessed by BrdU uptake, also using FACS and immunofluorescence. We show that myofibroblasts from lungs of humans with idiopathic pulmonary fibrosis and from bleomycin-treated versus normal saline-treated mice up-regulate c-FLIP levels. Using the animal model, we show that fibrotic lung myofibroblasts divert Fas signaling from apoptosis to proliferation and that this requires signaling by TNF receptor-associated factor (TRAF) and NF-κB. c-FLIP down-regulation reverses the effect of Fas activation, causing increased apoptosis, decreased proliferation, and diminished recruitment of TRAF to the DISC complex. This indicates that c-FLIP is essential for myofibroblast accumulation and may serve as a potential target to manipulate tissue fibrosis.

Increased cell surface Fas expression is necessary and sufficient to sensitize lung fibroblasts to Fas ligation-induced apoptosis: implications for fibroblast accumulation in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is associated with the accumulation of collagen-secreting fibroblasts and myofibroblasts in the lung parenchyma. Many mechanisms contribute to their accumulation, including resistance to apoptosis. In previous work, we showed that exposure to the proinflammatory cytokines TNF-α and IFN-γ reverses the resistance of lung fibroblasts to apoptosis. In this study, we investigate the underlying mechanisms. Based on an interrogation of the transcriptomes of unstimulated and TNF-α- and IFN-γ-stimulated primary lung fibroblasts and the lung fibroblast cell line MRC5, we show that among Fas-signaling pathway molecules, Fas expression was increased ∼6-fold in an NF-κB- and p38(mapk)-dependent fashion. Prevention of the increase in Fas expression using Fas small interfering RNAs blocked the ability of TNF-α and IFN-γ to sensitize fibroblasts to Fas ligation-induced apoptosis, whereas enforced adenovirus-mediated Fas overexpression was sufficient to overcome basal resistance to Fas-induced apoptosis. Examination of lung tissues from IPF patients revealed low to absent staining of Fas in fibroblastic cells of fibroblast foci. Collectively, these findings suggest that increased expression of Fas is necessary and sufficient to overcome the resistance of lung fibroblasts to Fas-induced apoptosis. Our findings also suggest that approaches aimed at increasing Fas expression by lung fibroblasts and myofibroblasts may be therapeutically relevant in IPF.

Evaluation of myofibroblasts in oral submucous fibrosis: correlation with disease severity

BACKGROUND

Oral submucous fibrosis (OSMF) is a chronic debilitating disease and a premalignant condition of the oral cavity characterized by generalized submucosal fibrosis. Myofibroblasts are contractile cells expressing α-smooth muscle actin (α-SMA) and are considered primary producers of extracellular matrix after injury. Their accumulation has been established as a marker of progressive fibrosis in organs like lungs, liver, kidney and skin. This study aims to evaluate the presence of myofibroblasts in various histological stages of OSMF.

MATERIALS AND METHOD

Seventy cases of OSMF, which were further categorized histologically into early (35 cases) and advanced (35 cases), were subjected to immunohistochemistry using α-SMA antibody for detection of myofibroblasts. Fifteen normal oral mucosa specimens were also stained as controls.

RESULTS

The number of α-SMA-stained myofibroblasts in OSMF was significantly increased when compared to that of the normal controls (P<0.001). Additionally, a statistically significant increase in the myofibroblasts population between early and advanced stages was observed (P=0.000).

CONCLUSIONS

Our results corroborate the possibility that OSMF actually represents an abnormal healing process in response to chronic mechanical and chemical irritation because of areca nut chewing as demonstrated by the increased incidence of myofibroblasts in this disease. Furthermore, the progressive increase in myofibroblasts from early to advanced stages suggests their potential use as markers for evaluating the severity of OSMF.

Regulation of apoptosis through cysteine oxidation: implications for fibrotic lung disease

Tissue fibrosis is believed to be a manifestation of dysregulated repair following injury, in association with impaired reepithelialization, and aberrant myofibroblast activation and proliferation. Numerous pathways have been linked to the pathogenesis of fibrotic lung disease, including the death receptor Fas, which contributes to apoptosis of lung epithelial cells. A redox imbalance also has been implicated in disease pathogenesis, although mechanistic details whereby oxidative changes intersect with profibrotic signaling pathways remain elusive. Oxidation of cysteines in proteins, such as S-glutathionylation (PSSG), is known to act as a regulatory event that affects protein function. This manuscript will discuss evidence that S-glutathionylation regulates death receptor induced apoptosis, and the potential implications for cysteine oxidations in the pathogenesis of in fibrotic lung disease.

Interstitial lung diseases in children

Interstitial lung disease (ILD) in infants and children comprises a large spectrum of rare respiratory disorders that are mostly chronic and associated with high morbidity and mortality. These disorders are characterized by inflammatory and fibrotic changes that affect alveolar walls. Typical features of ILD include dyspnea, diffuse infiltrates on chest radiographs, and abnormal pulmonary function tests with restrictive ventilatory defect and/or impaired gas exchange. Many pathological situations can impair gas exchange and, therefore, may contribute to progressive lung damage and ILD. Consequently, diagnosis approach needs to be structured with a clinical evaluation requiring a careful history paying attention to exposures and systemic diseases. Several classifications for ILD have been proposed but none is entirely satisfactory especially in children. The present article reviews current concepts of pathophysiological mechanisms, etiology and diagnostic approaches, as well as therapeutic strategies. The following diagnostic grouping is used to discuss the various causes of pediatric ILD: 1) exposure-related ILD; 2) systemic disease-associated ILD; 3) alveolar structure disorder-associated ILD; and 4) ILD specific to infancy. Therapeutic options include mainly anti-inflammatory, immunosuppressive, and/or anti-fibrotic drugs. The outcome is highly variable with a mortality rate around 15%. An overall favorable response to corticosteroid therapy is observed in around 50% of cases, often associated with sequelae such as limited exercise tolerance or the need for long-term oxygen therapy.

Pathogenesis of tubulointerstitial fibrosis in chronic allograft dysfunction

The term chronic allograft nephropathy (CAN) was originally coined in 1991 to replace chronic rejection which was used too generalized. However, the revised Banff classification, published in 2007, eliminated the term CAN again because it was felt that the term was used too broadly and prevented the search for the underlying cause. Interstitial fibrosis and tubular atrophy are integral parts of chronic allograft dysfunction and represent in the new classification a separate entity with or without the identification of a specific etiology. Myofibroblasts are the key, albeit not exclusive, effector cells in renal fibrogenesis resulting in upregulated extracellular matrix synthesis and eventually in interstitial fibrosis. These cells are formed mainly by stimulation of resident interstitial fibroblasts but also by differentiation processes of periadventitial cells, bone marrow derived cells and by a process entitled epithelial mesenchymal transition (EMT) of tubular epithelial cells. EMT has been described by many groups to be of high prevalence in renal allograft dysfunction contributing to matrix accumulation and renal function deterioration. This is of particular interest because immunosuppressive therapy has differential effects on EMT with calcineurin inhibitors in particular inducing the process. Moreover, specific therapies inhibiting EMT have been applied in experimental studies although the effects of their application in chronic allograft dysfunction remain to be studied. At the same time, immunosuppression may interfere with physiologic clearance of myofibroblasts by apoptosis, explaining in part the high prevalence of interstitial fibrosis in allograft biopsies. The Fas system has been identified to be mainly responsible for this physiologic apoptosis in non-renal scarring models; however, its relevance for renal fibrosis and particular fibrosis in renal allograft dysfunction remains to be determined. These findings point to a cautious and individualized use of immunosuppressive therapy in patients with allografts and particular those with chronic allograft dysfunction not because of rejection processes. Protocols using CNI-free immunosuppression are interesting options to prevent fibrosis in chronic allograft dysfunction.

Injection of plasmin in local area: a new treatment option for nasal polypsis

Nasal polypsis(NP), is one of the most difficult challenges in otorhinolaryngology, as the aetiology and pathophysiology are largely unknown unfortunately, medical treatment is unsatisfactory, and, because of frequent recurrences, repeated surgical interventions are often necessary. Now in clinic, the therapy for NP involves a combination of observation, medical, and surgical treatments. But with both treatments of medical and surgical, recurrences are still common. In nasal polypsis, although fibrotic changes do not dominate, myofibroblasts are significantly more abundant in the pedicle where the polyps can be thought to "grow" than in the central or tip areas. But in the "health" nasal mucosa, myofibroblasts can not been observed. Under normal conditions, when the injury is recovery, myofibroblats subsequent disappear from the injured site due to apoptosis. It is very interesting that myofibroblasts can survival in nasal polyps. We hypothesize here that, in nasal polyps, myofibroblasts adopt strategies to avoid apoptosis and consequent clearance by the immune system. In the "grow" area where the conditions are unchecked, deranged or repeated tissue repair, myofibroblasts, as the key factors, push about the formation or growth of the nasal polyps. So we try injecting plasmin in the pedicle of nasal polypsis to promote myofibroblast apoptosis, which may lead to a new treatment option for this incapacitating disease.

Naringenin: a potential immunomodulator for inhibiting lung fibrosis and metastasis

Patients with idiopathic pulmonary fibrosis have a high incidence of lung cancer and a worse prognosis for clinical treatment. A few molecules with antifibrosis properties have been shown promoting cancer progression in clinical trials. The objective of this study was to determine whether there is a similar tendency in mice as in human beings and whether these mice models may be used to find new therapeutic agents with antifibrotic properties but not cancer-promoting properties. We used bleomycin to induce pulmonary fibrosis in mice with or without naringenin treatment and measured the immune-associated lymphocytes and their secreted cytokines using flow cytometry and ELISA from lung tissue. Both passive and spontaneous metastatic models in bleomycin-treated C57BL/6 and BALB/c mice were used to test the hypothesis that mice with pulmonary fibrosis could have an increased risk of lung cancer and associated cancer progression. Here, we show that mice with lung fibrosis challenged using tumors show an increased incidence of lung metastasis and shorter life spans compared with the mice without lung fibrosis. A fibrotic environment in the lung results in increased abundance of transforming growth factor-beta1 and CD4(+)CD25(+)Foxp3(+) regulatory T cells and a decreased proportion of activated effector T cells. This grave immunosuppressive environment favors tumor localization and growth. Naringenin significantly reduces lung metastases in mice with pulmonary fibrosis and increases their survival by improving the immunosuppressive environment through down-regulating transforming growth factor-beta1 and reducing regulatory T cells. Naringenin could be an ideal therapeutic agent in the treatment of both cancer and fibrosis.

Osteopontin induces airway remodeling and lung fibroblast activation in a murine model of asthma

Airway remodeling is a central feature of asthma; however, the mechanisms underlying its development have not been fully elucidated. We have demonstrated that osteopontin, an inflammatory cytokine and an extracellular matrix glycoprotein with profibrotic properties, is up-regulated in a murine model of allergen-induced airway remodeling. In the present study, we determined whether osteopontin plays a functional role in airway remodeling. Osteopontin (OPN)-deficient (OPN(-/-)) and wild-type mice were sensitized and exposed to inhaled ovalbumin (OVA) or saline for 5 weeks. Collagen production, peribronchial smooth muscle area, mucus-producing cell number, and bronchoalveolar cell counts were assessed. The functional behavior and phenotype of lung fibroblasts from OVA-treated OPN(-/-) and from wild-type mice were studied using ex vivo cultures. OVA-treated OPN(-/-) mice exhibited reduced lung collagen content, smooth muscle area, mucus-producing cells, and inflammatory cell accumulation as compared with wild-type mice. Reduced matrix metalloproteinase-2 activity and expression of transforming growth factor-beta1 and vascular endothelial growth factor were observed in OVA-treated OPN(-/-) mice. Lung fibroblasts from OVA-treated OPN(-/-) mice showed reduced proliferation, migration, collagen deposition, and alpha-smooth muscle actin expression in comparison with OVA-treated wild-type lung fibroblasts. Thus, OPN is key for the development of allergen-induced airway remodeling in mice. In response to allergen, OPN induces the switching of lung fibroblasts to a pro-fibrogenic myofibroblast phenotype.